Contents Articles Dynamic Vibration Absorber
1
Entertainment engineering
1
Mechanical engineering
5
Vibration
15
AFGROW
27
Agitator (device)
29
Air handler
30
Air preheater
34
Airshaft
38
American Machinists' Handbook
38
Applied mechanics
40
Atmosphere (unit)
43
Automaton clock
45
Backdrive
46
Ball detent
46
Beale number
47
Bearing surface
48
Bellcrank
49
Bimetallic strip
50
Block and bleed manifold
52
Blood viscoelasticity
53
Bolted joint
59
Brake shoe
64
Break-in (mechanical run-in)
65
Brinelling
67
Built-up gun
68
Bullwheel
71
Burmester's theory
72
Burnishing (metal)
74
Bushing (isolator)
77
Calibrated orifice
79
Cam
79
Cam follower
81
Cam plastometer
83
Campbell diagram
84
Central Mechanical Engineering Research Institute
85
Centrifugal-type supercharger
86
Century tower clocks
87
Chilled water
94
Chiller
95
CILAS
101
Circle grid analysis
106
Coefficient of performance
107
Collapse action
109
Combined cycle
110
Compliant mechanism
115
Compound lever
117
Compression (physical)
119
Constant air volume
120
Constrained-layer damping
121
Contact mechanics
121
Frictional contact mechanics
137
Cooling tower
142
Coupling
156
Crank (mechanism)
161
Critical speed
168
Cryogenic engineering
168
d'Alembert–Euler condition
170
D-value (transport)
171
Damper (flow)
171
Damping matrix
174
Demister (vapor)
175
Design and manufacturing of gears
176
Design for manufacturability for CNC machining
182
Dexel
183
Disc coupling
184
Docking sleeve
185
Drive by wire
185
Duality (mechanical engineering)
187
Dunkerley's method
187
Duty cycle
188
Dynamometer
190
Edmund Key
201
Embedment
201
Engineering design process
203
Engineering Equation Solver
205
Engineering fit
206
Envelope (motion)
207
ERF damper
208
Euler–Bernoulli beam equation
208
Fan coil unit
221
Feedwater heater
225
Fillet (mechanics)
226
Flange
227
Float (liquid level)
231
Flow stress
231
Fluid power
232
Formability
233
Fretting Wear
235
Friction loss
235
Galling
236
Gear
240
Gudgeon pin
261
Heat transfer
262
Heisler Chart
273
Mechanical Engineering Heritage (Japan)
278
User:Hg82/Larry Howell
282
Hinge
284
Hydraulics
287
Hydrogen pinch
290
Hydrogen turboexpander-generator
291
Ideal machine
292
Idler
293
Idler-wheel
293
Index of mechanical engineering articles
294
Indexing (motion)
297
Injector
299
Interference fit
304
ITA – Iscar Tool Advisor
306
Jaw coupling
307
JIC fitting
308
Kinematic coupling
308
Kinematic determinacy
309
Kinematic diagram
309
Laboratory for Energy Conversion
310
Lamina emergent mechanisms (LEMs)
312
Larry Howell
313
Light Aid Detachment
315
Limits and fits
315
List of gear nomenclature
316
Machine (mechanical)
337
Machinery's Handbook
343
Maintenance engineering
344
Maintenance, repair, and operations
345
Marks' Standard Handbook for Mechanical Engineers
348
Mass transfer
350
Mating connection
352
McKinley Climatic Laboratory
353
Mechanical advantage device
356
Mechanical efficiency
358
Mechanical engineering technology
358
Mechanical singularity
359
Mechanical system
360
Metallurgical failure analysis
362
Microelectromechanical systems
364
User:Mkoronowski/turbomachinery
372
Modal analysis
378
Motion ratio
380
Multi-function structure
381
Multiphase heat transfer
382
Non-synchronous transmission
383
Nutation
386
Orifice plate
388
Ortman Key
393
Oscillating reciprocation
393
Overspeed (engine)
393
Parallel motion
394
Particle damping
396
Photoelasticity
397
Pinch analysis
401
Piping
402
Piston motion equations
405
Power engineering
409
Precision engineering
415
Pressure exchanger
417
Proactive maintenance
419
Process integration
420
Pulverizer
422
Radiation properties
425
Railworthiness
427
Range of motion
428
Reciprocating compressor
429
Reciprocating motion
430
Recuperator
431
Reel
433
Relief valve
435
Residual stress
438
Reynolds transport theorem
440
Roadworthiness
443
Roark's Formulas for Stress and Strain
444
Rotary feeder
445
Rotor
448
Run-around coil
449
Sacrificial part
450
Screw theory
451
Self-exciting oscillation
457
Shear pin
459
Shear strength
459
Sieving coefficient
460
Sight glass
461
Simple machine
464
Slip joint
467
Slip line field
468
Society of Tribologists and Lubrication Engineers
469
South-pointing chariot
473
Split pin
484
Standard conditions for temperature and pressure
487
Steam rupture
491
Stick-slip phenomenon
492
Strain hardening exponent
493
Streamlines, streaklines, and pathlines
494
Structural load
498
Surface integrity
501
Surface roughness
503
Swivel
506
Systematic Hierarchical Approach for Resilient Process Screening (SHARPS)
507
Tail lift
507
Thermal efficiency
509
Thermal engineering
514
Thermal science
515
Thermo-mechanical fatigue
516
Thermomechanical generator
519
Timken OK Load
521
Tip clearance
522
Tolerance analysis
523
Tooth Interior Fatigue Fracture
524
Torque density
525
Total indicator reading
525
Transmission (mechanics)
526
Treadle
535
Tribology
535
Trunnion
539
Tuned mass damper
543
Turboexpander
548
Turbomachinery
554
Undercut (manufacturing)
556
Units conversion by factor-label
558
Variable air volume
560
Vibration isolation
561
Vibratory stress relief
566
Victaulic
572
Virtual work
573
VOICED
583
Water cascade analysis
584
Water chiller
585
Water pinch analysis
585
Wells turbine
586
West number
587
Work (physics)
588
Zero seek
593
References Article Sources and Contributors
594
Image Sources, Licenses and Contributors
605
Article Licenses License
615
Dynamic Vibration Absorber
Dynamic Vibration Absorber In vibration analysis, a dynamic vibration absorber, or vibration neutralizer, is a tuned spring-mass system which reduces or eliminates the vibration of a harmonically excited system. Rotating machines such as engines, motors, and pumps often incite vibration due to rotational imbalances. A dynamic absorber can be affixed to the rotating machine and tuned to oscillate in such a way that exactly counteracts the force from the rotating imbalance. This reduces the possibility that a resonance condition will occur, which can cause rapid catastrophic failure.[1] Properly implemented, a dynamic absorber will neutralize the undesirable vibration, which would otherwise reduce service life or cause mechanical damage. Dynamic absorbers differ from tuned mass dampers in that dynamic absorbers do not require any damping to function satisfactorily. Damping can, however, be introduced to increase the range of frequencies for which the dynamic absorber is effective.
References [1] "The Dynamic Vibration Absorber" (http:/ / paws. kettering. edu/ ~drussell/ Demos/ absorber/ DynamicAbsorber. html). Acoustics and Vibrations Animations. Retrieved: Dec 12, 2010.
• Rao, S. (2003), Mechanical Vibrations, Upper Saddle River, N.J.: Prentice Hall, ISBN 0130489875.
External links • (http://www.diracdelta.co.uk/science/source/d/y/dynamic vibration absorber/source.html) - Dynamic Vibration Absorber
Entertainment engineering Entertainment engineering is an engineering discipline that involves the application of traditional engineering programs such as mechanical engineering, electrical engineering and structural engineering to create the highly technical designs that the entertainment industry has come to demand. It involves the use of equipment from many industries to create highly specialized devices for the entertainment industry.
Education Currently, the only university offering a degree specifically in Entertainment Engineering and Design (EED) is the University of Nevada, Las Vegas (UNLV). Because UNLV's program is in its infancy, current entertainment engineers come from a wide variety of educational backgrounds, the most prevalent of which are theater and mechanical engineering. Several other institutions of higher education offer similar programs for entertainment related ventures.
License Engineers may seek license by a state, provincial, or national government. The purpose of this process is to ensure that engineers possess the necessary technical knowledge, real-world experience, and knowledge of the local legal system to practice engineering at a professional level. Once certified, the engineer is given the title of Professional Engineer (in the United States, Canada, Japan, South Korea, Bangladesh and South Africa), Chartered Engineer (in the UK, Ireland, India and Zimbabwe), Chartered Professional Engineer (in Australia and New Zealand) or European Engineer (much of the European Union). Not all mechanical engineers choose to become licensed; those
1
Entertainment engineering that do can be distinguished as Chartered or Professional Engineers by the post-nominal title P.E., P. Eng., or C.Eng., as in: John Doe, P.Eng. In the U.S., to become a licensed Professional Engineer, an engineer must pass the comprehensive FE (Fundamentals of Engineering) exam, work a given number of years as an Engineering Intern (EI) or Engineer-in-Training (EIT), and finally pass the "Principles and Practice" or PE (Practicing Engineer or Professional Engineer) exams. In the United States, the requirements and steps of this process are set forth by the National Council of Examiners for Engineering and Surveying (NCEES), a national non-profit representing all states. In the UK, current graduates require a BEng plus an appropriate masters degree or an integrated MEng degree plus a minimum of 4 years post graduate on the job competency development in order to become chartered through the Institution of Mechanical Engineers. In most modern countries, certain engineering tasks, such as the design of bridges, electric power plants, and chemical plants, must be approved by a Professional Engineer or a Chartered Engineer. "Only a licensed engineer, for instance, may prepare, sign, seal and submit engineering plans and drawings to a public authority for approval, or to seal engineering work for public and private clients."[1] This requirement can be written into state and provincial legislation, such as Quebec's Engineer Act.[2] In other countries, such as Australia, no such legislation exists; however, practically all certifying bodies maintain a code of ethics independent of legislation that they expect all members to abide by or risk expulsion.[3] Further information: FE Exam, Professional Engineer, Chartered Engineer, Incorporated Engineer, and Washington Accord
Modern tools Many mechanical engineering companies, especially those in industrialized nations, have begun to incorporate computer-aided engineering (CAE) programs into their existing design and analysis processes, including 2D and 3D solid modeling computer-aided design (CAD). This method has many benefits, including easier and more exhaustive visualization of products, the ability to create virtual assemblies of parts, and the ease of use in designing mating interfaces and tolerances. Other CAE programs commonly used by mechanical engineers include product lifecycle management (PLM) tools and analysis tools used to perform complex simulations. Analysis tools may be used to predict product response to expected loads, including fatigue life and manufacturability. These tools include finite element analysis (FEA), computational fluid dynamics (CFD), and computer-aided manufacturing (CAM). Using CAE programs, a mechanical design team can quickly and cheaply iterate the design process to develop a product that better meets cost, performance, and other constraints. No physical prototype need be created until the design nears completion, allowing hundreds or thousands of designs to be evaluated, instead of a relative few. In addition, CAE analysis programs can model complicated physical phenomena which cannot be solved by hand, such as viscoelasticity, complex contact between mating parts, or non-Newtonian flows As mechanical engineering begins to merge with other disciplines, as seen in mechatronics, multidisciplinary design optimization (MDO) is being used with other CAE programs to automate and improve the iterative design process. MDO tools wrap around existing CAE processes, allowing product evaluation to continue even after the analyst goes home for the day. They also utilize sophisticated optimization algorithms to more intelligently explore possible designs, often finding better, innovative solutions to difficult multidisciplinary design problems.
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Entertainment engineering
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Mechanics Mechanics is, in the most general sense, the study of forces and their effect upon matter. Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both elastic and plastic) of objects under known forces (also called loads) or stresses. Subdisciplines of mechanics include • Statics, the study of non-moving bodies under known loads • Dynamics (or kinetics), the study of how forces affect moving bodies • Mechanics of materials, the study of how different materials deform under various types of stress • Fluid mechanics, the study of how fluids react to forces[4]
Mohr's circle, a common tool to study stresses in a mechanical element
• Continuum mechanics, a method of applying mechanics that assumes that objects are continuous (rather than discrete) Mechanical engineers typically use mechanics in the design or analysis phases of engineering. If the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. Dynamics might be used when designing the car's engine, to evaluate the forces in the pistons and cams as the engine cycles. Mechanics of materials might be used to choose appropriate materials for the frame and engine. Fluid mechanics might be used to design a ventilation system for the vehicle (see HVAC), or to design the intake system for the engine.
Kinematics Kinematics is the study of the motion of bodies (objects) and systems (groups of objects), while ignoring the forces that cause the motion. The movement of a crane and the oscillations of a piston in an engine are both simple kinematic systems. The crane is a type of open kinematic chain, while the piston is part of a closed four-bar linkage. Mechanical engineers typically use kinematics in the design and analysis of mechanisms. Kinematics can be used to find the possible range of motion for a given mechanism, or, working in reverse, can be used to design a mechanism that has a desired range of motion.
Mechatronics and robotics Mechatronics is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid systems. In this way, machines can be automated through the use of electric motors, servo-mechanisms, and other electrical systems in conjunction with special software. A common example of a mechatronics system is a CD-ROM drive. Mechanical systems open and close the drive, spin the CD and move the laser, while an optical system reads the data on the CD and converts it to bits. Integrated software controls the process and communicates the contents of the CD to the computer.
Training FMS with learning robot SCORBOT-ER 4u, workbench CNC Mill and CNC Lathe
Robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. These robots may be of any shape and size, but all are preprogrammed and
Entertainment engineering interact physically with the world. To create a robot, an engineer typically employs kinematics (to determine the robot's range of motion) and mechanics (to determine the stresses within the robot). Robots are used extensively in industrial engineering. They allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to insure better quality. Many companies employ assembly lines of robots, and some factories are so robotized that they can run by themselves. Outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. Robots are also sold for various residential applications.
Structural analysis Structural analysis is the branch of mechanical engineering (and also civil engineering) devoted to examining why and how objects fail. Structural failures occur in two general modes: static failure, and fatigue failure. Static structural failure occurs when, upon being loaded (having a force applied) the object being analyzed either breaks or is deformed plastically, depending on the criterion for failure. Fatigue failure occurs when an object fails after a number of repeated loading and unloading cycles. Fatigue failure occurs because of imperfections in the object: a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle (propagation) until the crack is large enough to cause ultimate failure. Failure is not simply defined as when a part breaks, however; it is defined as when a part does not operate as intended. Some systems, such as the perforated top sections of some plastic bags, are designed to break. If these systems do not break, failure analysis might be employed to determine the cause. Structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure. Engineers often use online documents and books such as those published by ASM[5] to aid them in determining the type of failure and possible causes. Structural analysis may be used in the office when designing parts, in the field to analyze failed parts, or in laboratories where parts might undergo controlled failure tests.
Related fields Like manufacturing engineering and aerospace engineering, entertainment engineering and design are typically grouped with mechanical engineering. A bachelor's degree in these areas will typically have a difference of only a few specialized classes.
References [1] "Why Get Licensed?" (http:/ / www. nspe. org/ Licensure/ WhyGetLicensed/ index. html). National Society of Professional Engineers. . Retrieved May 6, 2008. [2] "Engineers Act" (http:/ / www. canlii. org/ qc/ laws/ sta/ i-9/ 20050616/ whole. html). Quebec Statutes and Regulations (CanLII). . Retrieved July 24, 2005. [3] "Codes of Ethics and Conduct" (http:/ / web. archive. org/ web/ 20050619081942/ http:/ / onlineethics. org/ codes/ ). Online Ethics Center. Archived from the original (http:/ / onlineethics. org/ codes/ ) on June 19, 2005. . Retrieved July 24, 2005. [4] Note: fluid mechanics can be further split into fluid statics and fluid dynamics, and is itself a subdiscipline of continuum mechanics. The application of fluid mechanics in engineering is called hydraulics and pneumatics. [5] [[ASM International (society)|ASM International (http:/ / asmcommunity. asminternational. org/ portal/ site/ asm/ )]'s site containing more than 20,000 searchable documents, including articles from the ASM Handbook series and Advanced Materials & Processes]
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External links http://www.entertainmentengineering.com
Mechanical engineering Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the design, production, and operation of machines and tools.[1] It is one of the oldest and broadest engineering disciplines. The engineering field requires an understanding of core concepts including mechanics, kinematics, thermodynamics, materials science, and structural analysis. Mechanical engineers use these core principles along with tools like computer-aided engineering and product lifecycle management to design and analyze manufacturing plants, industrial equipment and machinery, heating and cooling systems, transport systems, aircraft, watercraft, robotics, medical devices and more.
Mechanical engineers design and build engines and power plants...
Mechanical engineering emerged as a field during the industrial revolution in Europe in the 18th century; however, ...structures and vehicles of all sizes. its development can be traced back several thousand years around the world. Mechanical engineering science emerged in the 19th century as a result of developments in the field of physics. The field has continually evolved to incorporate advancements in technology, and mechanical engineers today are pursuing developments in such fields as composites, mechatronics, and nanotechnology. Mechanical engineering overlaps with aerospace engineering, building services engineering, civil engineering, electrical engineering, petroleum engineering, and chemical engineering to varying amounts.
Development Applications of mechanical engineering are found in the records of many ancient and medieval societies throughout the globe. In ancient Greece, the works of Archimedes (287 BC–212 BC) deeply influenced mechanics in the Western tradition and Heron of Alexandria (c. 10–70 AD) created the first steam engine.[2] In China, Zhang Heng (78–139 AD) improved a water clock and invented a seismometer, and Ma Jun (200–265 AD) invented a chariot with differential gears. The medieval Chinese horologist and engineer Su Song (1020–1101 AD) incorporated an escapement mechanism into his astronomical clock tower two centuries before any escapement can be found in clocks of medieval Europe, as well as the world's first known endless power-transmitting chain drive.[3] During the years from 7th to 15th century, the era called the Islamic Golden Age, there were remarkable contributions from Muslim inventors in the field of mechanical technology. Al-Jazari, who was one of them, wrote his famous Book of Knowledge of Ingenious Mechanical Devices in 1206, and presented many mechanical designs. He is also considered to be the inventor of such mechanical devices which now form the very basic of mechanisms,
Mechanical engineering such as the crankshaft and camshaft.[4] Important breakthroughs in the foundations of mechanical engineering occurred in England during the 17th century when Sir Isaac Newton both formulated the three Newton's Laws of Motion and developed Calculus. Newton was reluctant to publish his methods and laws for years, but he was finally persuaded to do so by his colleagues, such as Sir Edmund Halley, much to the benefit of all mankind. During the early 19th century in England, Germany and Scotland, the development of machine tools led mechanical engineering to develop as a separate field within engineering, providing manufacturing machines and the engines to power them.[5] The first British professional society of mechanical engineers was formed in 1847 Institution of Mechanical Engineers, thirty years after the civil engineers formed the first such professional society Institution of Civil Engineers.[6] On the European continent, Johann Von Zimmermann (1820–1901) founded the first factory for grinding machines in Chemnitz (Germany) in 1848. In the United States, the American Society of Mechanical Engineers (ASME) was formed in 1880, becoming the third such professional engineering society, after the American Society of Civil Engineers (1852) and the American Institute of Mining Engineers (1871).[7] The first schools in the United States to offer an engineering education were the United States Military Academy in 1817, an institution now known as Norwich University in 1819, and Rensselaer Polytechnic Institute in 1825. Education in mechanical engineering has historically been based on a strong foundation in mathematics and science.[8]
Education Degrees in mechanical engineering are offered at universities worldwide. In Brazil, Ireland, Philippines, China, Greece, Turkey, North America, South Asia, India and the United Kingdom, mechanical engineering programs typically take four to five years of study and result in a Bachelor of Science (B.Sc), Bachelor of Science Engineering (B.ScEng), Bachelor of Engineering (B.Eng), Bachelor of Technology (B.Tech), or Bachelor of Applied Science (B.A.Sc) degree, in or with emphasis in mechanical engineering. In Spain, Portugal and most of South America, where neither BSc nor BTech programs have been adopted, the formal name for the degree is "Mechanical Engineer", and the course work is based on five or six years of training. In Italy the course work is based on five years of training, but in order to qualify as an Engineer you have to pass a state exam at the end of the course. In Australia, mechanical engineering degrees are awarded as Bachelor of Engineering (Mechanical) or similar nomenclature[9] although there are an increasing number of specialisations. The degree takes four years of full time study to achieve. To ensure quality in engineering degrees, Engineers Australia accredits engineering degrees awarded by Australian universities in accordance with the global Washington Accord. Before the degree can be awarded, the student must complete at least 3 months of on the job work experience in an engineering firm. Similar systems are also present in South Africa and are overseen by the Engineering Council of South Africa (ECSA). In the United States, most undergraduate mechanical engineering programs are accredited by the Accreditation Board for Engineering and Technology (ABET) to ensure similar course requirements and standards among universities. The ABET web site lists 276 accredited mechanical engineering programs as of June 19, 2006.[10] Mechanical engineering programs in Canada are accredited by the Canadian Engineering Accreditation Board (CEAB),[11] and most other countries offering engineering degrees have similar accreditation societies. Some mechanical engineers go on to pursue a postgraduate degree such as a Master of Engineering, Master of Technology, Master of Science, Master of Engineering Management (MEng.Mgt or MEM), a Doctor of Philosophy in engineering (EngD, PhD) or an engineer's degree. The master's and engineer's degrees may or may not include research. The Doctor of Philosophy includes a significant research component and is often viewed as the entry point to academia.[12] The Engineer's degree exists at a few institutions at an intermediate level between the master's degree and the doctorate.
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Coursework Standards set by each country's accreditation society are intended to provide uniformity in fundamental subject material, promote competence among graduating engineers, and to maintain confidence in the engineering profession as a whole. Engineering programs in the U.S., for example, are required by ABET to show that their students can "work professionally in both thermal and mechanical systems areas."[13] The specific courses required to graduate, however, may differ from program to program. Universities and Institutes of technology will often combine multiple subjects into a single class or split a subject into multiple classes, depending on the faculty available and the university's major area(s) of research. The fundamental subjects of mechanical engineering usually include: • • • • • • • •
Statics and dynamics Strength of materials and solid mechanics Instrumentation and measurement Electrotechnology Electronics Thermodynamics, heat transfer, energy conversion, and HVAC Combustion, automotive engines, fuels Fluid mechanics and fluid dynamics
• • • • • • • • •
Mechanism design (including kinematics and dynamics) Manufacturing engineering, technology, or processes Hydraulics and pneumatics Mathematics - in particular, calculus, differential equations, and linear algebra. Engineering design Product design Mechatronics and control theory Material Engineering Design engineering, Drafting, computer-aided design (CAD) (including solid modeling), and computer-aided manufacturing (CAM)[14] [15]
Mechanical engineers are also expected to understand and be able to apply basic concepts from chemistry, physics, chemical engineering, civil engineering, and electrical engineering. Most mechanical engineering programs include multiple semesters of calculus, as well as advanced mathematical concepts including differential equations, partial differential equations, linear algebra, abstract algebra, and differential geometry, among others. In addition to the core mechanical engineering curriculum, many mechanical engineering programs offer more specialized programs and classes, such as robotics, transport and logistics, cryogenics, fuel technology, automotive engineering, biomechanics, vibration, optics and others, if a separate department does not exist for these subjects.[16] Most mechanical engineering programs also require varying amounts of research or community projects to gain practical problem-solving experience. In the United States it is common for mechanical engineering students to complete one or more internships while studying, though this is not typically mandated by the university. Cooperative education is another option.
License Engineers may seek license by a state, provincial, or national government. The purpose of this process is to ensure that engineers possess the necessary technical knowledge, real-world experience, and knowledge of the local legal system to practice engineering at a professional level. Once certified, the engineer is given the title of Professional Engineer (in the United States, Canada, Japan, South Korea, Bangladesh and South Africa), Chartered Engineer (in the United Kingdom, Ireland, India and Zimbabwe), Chartered Professional Engineer (in Australia and New Zealand) or European Engineer (much of the European Union). Not all mechanical engineers choose to become
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Mechanical engineering licensed; those that do can be distinguished as Chartered or Professional Engineers by the post-nominal title P.E., P.Eng., or C.Eng., as in: Mike Thompson, P.Eng. In the U.S., to become a licensed Professional Engineer, an engineer must pass the comprehensive FE (Fundamentals of Engineering) exam, work a given number of years as an Engineering Intern (EI) or Engineer-in-Training (EIT), and finally pass the "Principles and Practice" or PE (Practicing Engineer or Professional Engineer) exams. In the United States, the requirements and steps of this process are set forth by the National Council of Examiners for Engineering and Surveying (NCEES), a national non-profit representing all states. In the UK, current graduates require a BEng plus an appropriate masters degree or an integrated MEng degree, a minimum of 4 years post graduate on the job competency development, and a peer reviewed project report in the candidates specialty area in order to become chartered through the Institution of Mechanical Engineers. In most modern countries, certain engineering tasks, such as the design of bridges, electric power plants, and chemical plants, must be approved by a Professional Engineer or a Chartered Engineer. "Only a licensed engineer, for instance, may prepare, sign, seal and submit engineering plans and drawings to a public authority for approval, or to seal engineering work for public and private clients."[17] This requirement can be written into state and provincial legislation, such as in the Canadian provinces, for example the Ontario or Quebec's Engineer Act.[18] In other countries, such as Australia, no such legislation exists; however, practically all certifying bodies maintain a code of ethics independent of legislation that they expect all members to abide by or risk expulsion.[19] Further information: FE Exam, Professional Engineer, Incorporated Engineer, and Washington Accord
Salaries and workforce statistics The total number of engineers employed in the U.S. in 2009 was roughly 1.6 million. Of these, 239,000 were mechanical engineers (14.9%), the second largest discipline by size behind civil (278,000). The total number of mechanical engineering jobs in 2009 was projected to grow 6% over the next decade, with average starting salaries being $58,800 with a bachelor's degree.[20] The median annual income of mechanical engineers in the U.S. workforce was roughly $74,900. This number was highest when working for the government ($86,250), and lowest in education ($63,050).[21] In 2007, Canadian engineers made an average of CAD$29.83 per hour with 4% unemployed. The average for all occupations was $18.07 per hour with 7% unemployed. Twelve percent of these engineers were self-employed, and since 1997 the proportion of female engineers had risen to 6%.[22]
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Modern tools Many mechanical engineering companies, especially those in industrialized nations, have begun to incorporate computer-aided engineering (CAE) programs into their existing design and analysis processes, including 2D and 3D solid modeling computer-aided design (CAD). This method has many benefits, including easier and more exhaustive visualization of products, the ability to create virtual assemblies of parts, and the ease of use in designing mating interfaces and tolerances. Other CAE programs commonly used by mechanical engineers include product lifecycle management (PLM) tools and analysis tools used to perform complex simulations. Analysis tools may be used to predict An oblique view of a four-cylinder inline crankshaft with pistons product response to expected loads, including fatigue life and manufacturability. These tools include finite element analysis (FEA), computational fluid dynamics (CFD), and computer-aided manufacturing (CAM). Using CAE programs, a mechanical design team can quickly and cheaply iterate the design process to develop a product that better meets cost, performance, and other constraints. No physical prototype need be created until the design nears completion, allowing hundreds or thousands of designs to be evaluated, instead of a relative few. In addition, CAE analysis programs can model complicated physical phenomena which cannot be solved by hand, such as viscoelasticity, complex contact between mating parts, or non-Newtonian flows. As mechanical engineering begins to merge with other disciplines, as seen in mechatronics, multidisciplinary design optimization (MDO) is being used with other CAE programs to automate and improve the iterative design process. MDO tools wrap around existing CAE processes, allowing product evaluation to continue even after the analyst goes home for the day. They also utilize sophisticated optimization algorithms to more intelligently explore possible designs, often finding better, innovative solutions to difficult multidisciplinary design problems.
Subdisciplines The field of mechanical engineering can be thought of as a collection of many mechanical engineering science disciplines. Several of these subdisciplines which are typically taught at the undergraduate level are listed below, with a brief explanation and the most common application of each. Some of these subdisciplines are unique to mechanical engineering, while others are a combination of mechanical engineering and one or more other disciplines. Most work that a mechanical engineer does uses skills and techniques from several of these subdisciplines, as well as specialized subdisciplines. Specialized subdisciplines, as used in this article, are more likely to be the subject of graduate studies or on-the-job training than undergraduate research. Several specialized subdisciplines are discussed in this section.
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Mechanics Mechanics is, in the most general sense, the study of forces and their effect upon matter. Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both elastic and plastic) of objects under known forces (also called loads) or stresses. Subdisciplines of mechanics include • Statics, the study of non-moving bodies under known loads, how forces affect static bodies • Dynamics (or kinetics), the study of how forces affect moving bodies • Mechanics of materials, the study of how different materials deform under various types of stress • Fluid mechanics, the study of how fluids react to forces[23]
Mohr's circle, a common tool to study stresses in a mechanical element
• Kinematics, the study of the motion of bodies (objects) and systems (groups of objects), while ignoring the forces that cause the motion. Kinematics is often used in the design and analysis of mechanisms. • Continuum mechanics, a method of applying mechanics that assumes that objects are continuous (rather than discrete) Mechanical engineers typically use mechanics in the design or analysis phases of engineering. If the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. Dynamics might be used when designing the car's engine, to evaluate the forces in the pistons and cams as the engine cycles. Mechanics of materials might be used to choose appropriate materials for the frame and engine. Fluid mechanics might be used to design a ventilation system for the vehicle (see HVAC), or to design the intake system for the engine.
Mechatronics and robotics Mechatronics is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid systems. In this way, machines can be automated through the use of electric motors, servo-mechanisms, and other electrical systems in conjunction with special software. A common example of a mechatronics system is a CD-ROM drive. Mechanical systems open and close the drive, spin the CD and move the laser, while an optical system reads the data on the CD and converts it to bits. Integrated software controls the process and communicates the contents of the CD to the computer.
Training FMS with learning robot SCORBOT-ER 4u, workbench CNC Mill and CNC Lathe
Robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. These robots may be of any shape and size, but all are preprogrammed and
Mechanical engineering interact physically with the world. To create a robot, an engineer typically employs kinematics (to determine the robot's range of motion) and mechanics (to determine the stresses within the robot). Robots are used extensively in industrial engineering. They allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to ensure better quality. Many companies employ assembly lines of robots,especially in Automotive Industries and some factories are so robotized that they can run by themselves. Outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. Robots are also sold for various residential applications.
Structural analysis Structural analysis is the branch of mechanical engineering (and also civil engineering) devoted to examining why and how objects fail and to fix the objects and their performance. Structural failures occur in two general modes: static failure, and fatigue failure. Static structural failure occurs when, upon being loaded (having a force applied) the object being analyzed either breaks or is deformed plastically, depending on the criterion for failure. Fatigue failure occurs when an object fails after a number of repeated loading and unloading cycles. Fatigue failure occurs because of imperfections in the object: a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle (propagation) until the crack is large enough to cause ultimate failure. Failure is not simply defined as when a part breaks, however; it is defined as when a part does not operate as intended. Some systems, such as the perforated top sections of some plastic bags, are designed to break. If these systems do not break, failure analysis might be employed to determine the cause. Structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure. Engineers often use online documents and books such as those published by ASM[24] to aid them in determining the type of failure and possible causes. Structural analysis may be used in the office when designing parts, in the field to analyze failed parts, or in laboratories where parts might undergo controlled failure tests.
Thermodynamics and thermo-science Thermodynamics is an applied science used in several branches of engineering, including mechanical and chemical engineering. At its simplest, thermodynamics is the study of energy, its use and transformation through a system. Typically, engineering thermodynamics is concerned with changing energy from one form to another. As an example, automotive engines convert chemical energy (enthalpy) from the fuel into heat, and then into mechanical work that eventually turns the wheels. Thermodynamics principles are used by mechanical engineers in the fields of heat transfer, thermofluids, and energy conversion. Mechanical engineers use thermo-science to design engines and power plants, heating, ventilation, and air-conditioning (HVAC) systems, heat exchangers, heat sinks, radiators, refrigeration, insulation, and others.
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Design and Drafting Drafting or technical drawing is the means by which mechanical engineers design products and create instructions for manufacturing parts. A technical drawing can be a computer model or hand-drawn schematic showing all the dimensions necessary to manufacture a part, as well as assembly notes, a list of required materials, and other pertinent information. A U.S. mechanical engineer or skilled worker who creates technical drawings may be referred to as a drafter or draftsman. Drafting has historically been a two-dimensional process, but computer-aided design (CAD) programs now allow the designer to create in three dimensions. A CAD model of a mechanical double seal
Instructions for manufacturing a part must be fed to the necessary machinery, either manually, through programmed instructions, or through the use of a computer-aided manufacturing (CAM) or combined CAD/CAM program. Optionally, an engineer may also manually manufacture a part using the technical drawings, but this is becoming an increasing rarity, with the advent of computer numerically controlled (CNC) manufacturing. Engineers primarily manually manufacture parts in the areas of applied spray coatings, finishes, and other processes that cannot economically or practically be done by a machine. Drafting is used in nearly every subdiscipline of mechanical engineering, and by many other branches of engineering and architecture. Three-dimensional models created using CAD software are also commonly used in finite element analysis (FEA) and computational fluid dynamics (CFD).
Frontiers of research Mechanical engineers are constantly pushing the boundaries of what is physically possible in order to produce safer, cheaper, and more efficient machines and mechanical systems. Some technologies at the cutting edge of mechanical engineering are listed below (see also exploratory engineering).
Micro electro-mechanical systems (MEMS) Micron-scale mechanical components such as springs, gears, fluidic and heat transfer devices are fabricated from a variety of substrate materials such as silicon, glass and polymers like SU8. Examples of MEMS components are the accelerometers that are used as car airbag sensors, modern cell phones, gyroscopes for precise positioning and microfluidic devices used in biomedical applications.
Friction stir welding (FSW) Friction stir welding, a new type of welding, was discovered in 1991 by The Welding Institute (TWI). This innovative steady state (non-fusion) welding technique joins materials previously un-weldable, including several aluminum alloys. It may play an important role in the future construction of airplanes, potentially replacing rivets. Current uses of this technology to date include welding the seams of the aluminum main Space Shuttle external tank, Orion Crew Vehicle test article, Boeing Delta II and Delta IV Expendable Launch Vehicles and the SpaceX Falcon 1 rocket, armor plating for amphibious assault ships, and welding the wings and fuselage panels of the new Eclipse 500 aircraft from Eclipse Aviation among an increasingly growing pool of uses.[25] [26] [27]
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Composites Composites or composite materials are a combination of materials which provide different physical characteristics than either material separately. Composite material research within mechanical engineering typically focuses on designing (and, subsequently, finding applications for) stronger or more rigid materials while attempting to reduce weight, susceptibility to corrosion, and other undesirable factors. Carbon fiber reinforced composites, for instance, have been used in such diverse applications as spacecraft and fishing rods.
Mechatronics
Composite cloth consisting of woven carbon fiber.
Mechatronics is the synergistic combination of mechanical engineering, Electronic Engineering, and software engineering. The purpose of this interdisciplinary engineering field is the study of automation from an engineering perspective and serves the purposes of controlling advanced hybrid systems.
Nanotechnology At the smallest scales, mechanical engineering becomes nanotechnology —one speculative goal of which is to create a molecular assembler to build molecules and materials via mechanosynthesis. For now that goal remains within exploratory engineering.
Finite element analysis This field is not new, as the basis of Finite Element Analysis (FEA) or Finite Element Method (FEM) dates back to 1941. But evolution of computers has made FEM a viable option for analysis of structural problems. Many commercial codes such as ANSYS, Nastran and ABAQUS are widely used in industry for research and design of components. Other techniques such as finite difference method (FDM) and finite-volume method (FVM) are employed to solve problems relating heat and mass transfer, fluid flows, fluid surface interaction etc.
Biomechanics Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells.[28] Biomechanics is closely related to engineering, because it often uses traditional engineering sciences to analyse biological systems. Some simple applications of Newtonian mechanics and/or materials sciences can supply correct approximations to the mechanics of many biological systems.
Mechanical engineering
Related fields Manufacturing engineering and Aerospace Engineering are sometimes grouped with mechanical engineering. A bachelor's degree in these areas will typically have a difference of a few specialized classes.
Notes and references [1] engineering "mechanical engineering. (n.d.)" (http:/ / dictionary. reference. com/ browse/ mechanical). The American Heritage Dictionary of the English Language, Fourth Edition. Retrieved: May 08, 2010. [2] "Heron of Alexandria" (http:/ / www. britannica. com/ EBchecked/ topic/ 263417/ Heron-of-Alexandria). Encyclopædia Britannica 2010 Encyclopædia Britannica Online. Accessed: 09 May 2010. [3] Needham, Joseph (1986). Science and Civilization in China: Volume 4. Taipei: Caves Books, Ltd. [4] Al-Jazarí. The Book of Knowledge of Ingenious Mechanical Devices: Kitáb fí ma'rifat al-hiyal al-handasiyya. Springer, 1973. ISBN 9027703299. [5] Engineering (http:/ / www. britannica. com/ eb/ article-9105842/ engineering) - Encyclopedia Brittanica, accessed 06 May 2008 [6] R. A. Buchanan. The Economic History Review, New Series, Vol. 38, No. 1 (Feb., 1985), pp. 42–60. [7] ASME history (http:/ / anniversary. asme. org/ history. shtml), accessed 06 May 2008. [8] The Columbia Encyclopedia, Sixth Edition. 2001-07, engineering (http:/ / www. bartleby. com/ 65/ en/ engineer. html), accessed 06 May 2008 [9] "Mechanical Engineering" (http:/ / www. flinders. edu. au/ science_engineering/ csem/ disciplines/ mecheng/ ). . Retrieved 8 December 2011. [10] ABET searchable database of accredited engineering programs (http:/ / www. abet. org/ accrediteac. asp), Accessed June 19, 2006. [11] Accredited engineering programs in Canada by the Canadian Council of Professional Engineers (http:/ / www. engineerscanada. ca/ e/ acc_programs_1. cfm), Accessed April 18, 2007. [12] Types of post-graduate degrees offered at MIT (http:/ / www-me. mit. edu/ GradProgram/ GradDegrees. htm) - Accessed 19 June 2006. [13] 2008-2009 ABET Criteria (http:/ / www. abet. org/ Linked Documents-UPDATE/ Criteria and PP/ E001 08-09 EAC Criteria 11-30-07. pdf), p. 15. [14] University of Tulsa Required ME Courses - Undergraduate Majors and Minors (http:/ / www. me. utulsa. edu/ Undergraduate. html). Department of Mechanical Engineering, University of Tulsa, 2010. Accessed: 17 December 2010. [15] Harvard Mechanical Engineering Page (http:/ / www. deas. harvard. edu/ undergradstudy/ engineeringsciences/ mechanical/ index. html). Harvard.edu. Accessed: 19 June 2006. [16] Mechanical Engineering courses (http:/ / student. mit. edu/ catalog/ m2a. html), MIT. Accessed 14 June 2008. [17] "Why Get Licensed?" (http:/ / www. nspe. org/ Licensure/ WhyGetLicensed/ index. html). National Society of Professional Engineers. . Retrieved May 6, 2008. [18] "Engineers Act" (http:/ / www. canlii. org/ qc/ laws/ sta/ i-9/ 20050616/ whole. html). Quebec Statutes and Regulations (CanLII). . Retrieved July 24, 2005. [19] "Codes of Ethics and Conduct" (http:/ / web. archive. org/ web/ 20050619081942/ http:/ / onlineethics. org/ codes/ ). Online Ethics Center. Archived from the original (http:/ / onlineethics. org/ codes/ ) on June 19, 2005. . Retrieved July 24, 2005. [20] 2010-11 Edition, Engineers (http:/ / www. bls. gov/ oco/ ocos027. htm#earnings) - Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, Accessed: 9 May 2010. [21] Document National Sector NAICS Industry-Specific estimates (xls) (http:/ / www. bls. gov/ oes/ oes_dl. htm) Accessed: 9 May 2010. [22] Mechanical Engineers (http:/ / www. jobfutures. ca/ noc/ 2132p4. shtml) - Jobfutures.ca, Accessed: June 30, 2007. [23] Note: fluid mechanics can be further split into fluid statics and fluid dynamics, and is itself a subdiscipline of continuum mechanics. The application of fluid mechanics in engineering is called hydraulics and pneumatics. [24] [[ASM International (society)|ASM International (http:/ / asmcommunity. asminternational. org/ portal/ site/ asm/ )]'s site containing more than 20,000 searchable documents, including articles from the ASM Handbook series and Advanced Materials & Processes] [25] Advances in Friction Stir Welding for Aerospace Applications (http:/ / www. niar. wichita. edu/ media/ pdf/ nationalpublication/ Nov2-06. pdf) [26] PROPOSAL NUMBER: 08-1 A1.02-9322 (http:/ / sbir. nasa. gov/ SBIR/ abstracts/ 08/ sbir/ phase1/ SBIR-08-1-A1. 02-9322. html?solicitationId=SBIR_08_P1) - NASA 2008 SBIR [27] Nova-Tech LLC (http:/ / www. ntefsw. com/ military_applications. htm) [28] R. McNeill Alexander (2005) Mechanics of animal movement (http:/ / www. sciencedirect. com/ science?_ob=ArticleURL& _udi=B6VRT-4GXV66S-6& _user=10& _coverDate=08/ 23/ 2005& _rdoc=6& _fmt=high& _orig=browse& _srch=doc-info(#toc#6243#2005#999849983#604671#FLA#display#Volume)& _cdi=6243& _sort=d& _docanchor=& view=c& _ct=27& _acct=C000050221& _version=1& _urlVersion=0& _userid=10& md5=a2e1364289e07dd87feb65f9dc4086c0), Current Biology Volume 15, Issue 16, 23 August 2005, Pages R616-R619
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Further reading • Burstall, Aubrey F. (1965). A History of Mechanical Engineering. The MIT Press. ISBN 0-262-52001-X.
External links • Kinematic Models for Design Digital Library (KMODDL) (http://kmoddl.library.cornell.edu/index.php) – Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library (http://kmoddl.library.cornell.edu/e-books.php) of classic texts on mechanical design and engineering. • Mechanical Engineering (http://mechanicalengineerings.com) – Global community and platform connecting all mechanical engineers. • Engineering Motion (http://www.engineeringmotion.com) – Mechanical engineering videos.
Vibration Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road. Vibration is occasionally "desirable". For example the motion of a tuning fork, the reed in a woodwind instrument or harmonica, or the cone of a loudspeaker is desirable vibration, necessary for the correct functioning of the various devices. More often, vibration is undesirable, wasting energy and creating unwanted sound – noise. For example, the vibrational motions of engines, electric motors, or any mechanical device in operation are typically unwanted. Such vibrations can be caused by imbalances in the rotating parts, uneven friction, the meshing of gear teeth, etc. Careful designs usually minimize unwanted vibrations. The study of sound and vibration are closely related. Sound, or "pressure waves", are generated by vibrating structures (e.g. vocal cords); these pressure waves can also induce the vibration of structures (e.g. ear drum). Hence, when trying to reduce noise it is often a problem in trying to reduce vibration.
Types of vibration Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. The mechanical system will then vibrate at one or more of its "natural frequency" and damp down to zero.
One of the possible modes of vibration of a circular drum (see other modes).
Forced vibration is when an alternating force or motion is applied to a mechanical system. Examples of this type of vibration include a shaking washing machine due to an imbalance, transportation vibration (caused by truck engine, springs, road, etc.), or the vibration of a building during an earthquake. In forced vibration the frequency of the vibration is the frequency
Vibration
of the force or motion applied, with order of magnitude being dependent on the actual mechanical system.
Vibration testing Vibration testing is accomplished by introducing a forcing function into a structure, usually with some type of shaker. Alternately, a DUT (device under test) is attached to the "table" of a shaker. For relatively low frequency forcing, servohydraulic (electrohydraulic) One of the possible modes of vibration of a cantilevered I-beam. shakers are used. For higher frequencies, electrodynamic shakers are used. Generally, one or more "input" or "control" points located on the DUT-side of a fixture is kept at a specified acceleration.[1] Other "response" points experience maximum vibration level (resonance) or minimum vibration level (anti-resonance). Two typical types of vibration tests performed are random- and sine test. Sine (one-frequency-at-a-time) tests are performed to survey the structural response of the device under test (DUT). A random (all frequencies at once) test is generally considered to more closely replicate a real world environment, such as road inputs to a moving automobile. Most vibration testing is conducted in a single DUT axis at a time, even though most real-world vibration occurs in various axes simultaneously. MIL-STD-810G, released in late 2008, Test Method 527, calls for multiple exciter testing.
Vibration analysis The fundamentals of vibration analysis can be understood by studying the simple mass–spring–damper model. Indeed, even a complex structure such as an automobile body can be modeled as a "summation" of simple mass–spring–damper models. The mass–spring–damper model is an example of a simple harmonic oscillator. The mathematics used to describe its behavior is identical to other simple harmonic oscillators such as the RLC circuit. Note: In this article the step by step mathematical derivations will not be included, but will focus on the major equations and concepts in vibration analysis. Please refer to the references at the end of the article for detailed derivations.
Free vibration without damping To start the investigation of the mass–spring–damper we will assume the damping is negligible and that there is no external force applied to the mass (i.e. free vibration). The force applied to the mass by the spring is proportional to the amount the spring is stretched "x" (we will assume the spring is already compressed due to the weight of the mass). The proportionality constant, k, is the stiffness of the spring and has units of force/distance (e.g. lbf/in or N/m). The negative sign indicates that the force is always opposing the motion of the mass attached to it.
The force generated by the mass is proportional to the acceleration of the mass as given by Newton’s second law of motion.
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The sum of the forces on the mass then generates this ordinary differential equation:
If we assume that we start the system to vibrate by stretching the spring by the distance of A and letting go, the solution to the above equation that describes the motion of mass is:
Simple harmonic motion of the mass–spring system
This solution says that it will oscillate with simple harmonic motion that has an amplitude of A and a frequency of The number is one of the most important quantities in vibration analysis and is called the undamped natural frequency. For the simple mass–spring system,
Note: Angular frequency
(
is defined as:
) with the units of radians per second is often used in equations because it
simplifies the equations, but is normally converted to “standard” frequency (units of Hz or equivalently cycles per second) when stating the frequency of a system. If you know the mass and stiffness of the system you can determine the frequency at which the system will vibrate once it is set in motion by an initial disturbance using the above stated formula. Every vibrating system has one or more natural frequencies that it will vibrate at once it is disturbed. This simple relation can be used to understand in general what will happen to a more complex system once we add mass or stiffness. For example, the above formula explains why when a car or truck is fully loaded the suspension will feel “softer” than unloaded because the mass has increased and therefore reduced the natural frequency of the system.
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What causes the system to vibrate: from conservation of energy point of view Vibrational motion could be understood in terms of conservation of energy. In the above example we have extended the spring by a value of
and therefore have stored some potential energy (
) in the spring. Once we let go of
the spring, the spring tries to return to its un-stretched state (which is the minimum potential energy state) and in the process accelerates the mass. At the point where the spring has reached its un-stretched state all the potential energy that we supplied by stretching it has been transformed into kinetic energy ( ). The mass then begins to decelerate because it is now compressing the spring and in the process transferring the kinetic energy back to its potential. Thus oscillation of the spring amounts to the transferring back and forth of the kinetic energy into potential energy. In our simple model the mass will continue to oscillate forever at the same magnitude, but in a real system there is always something called damping that dissipates the energy, eventually bringing it to rest.
Free vibration with damping We now add a "viscous" damper to the model that outputs a force that is proportional to the velocity of the mass. The damping is called viscous because it models the effects of an object within a fluid. The proportionality constant c is called the damping coefficient and has units of Force over velocity (lbf s/ in or N s/m).
Mass Spring Damper Model
By summing the forces on the mass we get the following ordinary differential equation:
The solution to this equation depends on the amount of damping. If the damping is small enough the system will still vibrate, but eventually, over time, will stop vibrating. This case is called underdamping – this case is of most interest in vibration analysis. If we increase the damping just to the point where the system no longer oscillates we reach the point of critical damping (if the damping is increased past critical damping the system is called overdamped). The value that the damping coefficient needs to reach for critical damping in the mass spring damper model is:
To characterize the amount of damping in a system a ratio called the damping ratio (also known as damping factor and % critical damping) is used. This damping ratio is just a ratio of the actual damping over the amount of damping required to reach critical damping. The formula for the damping ratio ( ) of the mass spring damper model is:
For example, metal structures (e.g. airplane fuselage, engine crankshaft) will have damping factors less than 0.05 while automotive suspensions in the range of 0.2–0.3. The solution to the underdamped system for the mass spring damper model is the following:
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The value of X, the initial magnitude, and
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phase shift, are determined by the amount the spring is stretched. The formulas for these values can be found in the references. Damped and undamped natural frequencies The major points to note from the solution are the exponential term and the cosine function. The exponential term defines how quickly the system “damps” down – the larger the damping ratio, the quicker it damps to zero. The cosine function is the oscillating portion of the solution, but the frequency of the oscillations is different from the undamped case. The frequency in this case is called the "damped natural frequency", and is related to the undamped natural frequency by the following formula:
The damped natural frequency is less than the undamped natural frequency, but for many practical cases the damping ratio is relatively small and hence the difference is negligible. Therefore the damped and undamped description are often dropped when stating the natural frequency (e.g. with 0.1 damping ratio, the damped natural frequency is only 1% less than the undamped). The plots to the side present how 0.1 and 0.3 damping ratios effect how the system will “ring” down over time. What is often done in practice is to experimentally measure the free vibration after an impact (for example by a hammer) and then determine the natural frequency of the system by measuring the rate of oscillation as well as the damping ratio by measuring the rate of decay. The natural frequency and damping ratio are not only important in free vibration, but also characterize how a system will behave under forced vibration.
Forced vibration with damping In this section we will see the behavior of the spring mass damper model when we add a harmonic force in the form below. A force of this type could, for example, be generated by a rotating imbalance.
If we again sum the forces on the mass we get the following ordinary differential equation:
The steady state solution of this problem can be written as:
The result states that the mass will oscillate at the same frequency, f, of the applied force, but with a phase shift
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The amplitude of the vibration “X” is defined by the following formula.
Where “r” is defined as the ratio of the harmonic force frequency over the undamped natural frequency of the mass–spring–damper model.
The phase shift ,
is defined by the following formula.
The plot of these functions, called "the frequency response of the system", presents one of the most important features in forced vibration. In a lightly damped system when the forcing frequency nears the natural frequency ( ) the amplitude of the vibration can get extremely high. This phenomenon is called resonance (subsequently the natural frequency of a system is often referred to as the resonant frequency). In rotor bearing systems any rotational speed that excites a resonant frequency is referred to as a critical speed. If resonance occurs in a mechanical system it can be very harmful – leading to eventual failure of the system. Consequently, one of the major reasons for vibration analysis is to predict when this type of resonance may occur and then to determine what steps to take to prevent it from occurring. As the amplitude plot shows, adding damping can significantly reduce the magnitude of the vibration. Also, the magnitude can be reduced if the natural frequency can be shifted away from the forcing frequency by changing the stiffness or mass of the system. If the system cannot be changed, perhaps the forcing frequency can be shifted (for example, changing the speed of the machine generating the force). The following are some other points in regards to the forced vibration shown in the frequency response plots. • At a given frequency ratio, the amplitude of the vibration, X, is directly proportional to the amplitude of the force (e.g. if you double the force, the vibration doubles) • With little or no damping, the vibration is in phase with the forcing frequency when the frequency ratio r < 1 and 180 degrees out of phase when the frequency ratio r > 1 • When r ≪ 1 the amplitude is just the deflection of the spring under the static force
This deflection is called
the static deflection Hence, when r ≪ 1 the effects of the damper and the mass are minimal. • When r ≫ 1 the amplitude of the vibration is actually less than the static deflection In this region the force generated by the mass (F = ma) is dominating because the acceleration seen by the mass increases with the frequency. Since the deflection seen in the spring, X, is reduced in this region, the force transmitted by the spring (F = kx) to the base is reduced. Therefore the mass–spring–damper system is isolating the harmonic force from the mounting base – referred to as vibration isolation. Interestingly, more damping actually reduces the effects of
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vibration isolation when r ≫ 1 because the damping force (F = cv) is also transmitted to the base. What causes resonance? Resonance is simple to understand if you view the spring and mass as energy storage elements – with the mass storing kinetic energy and the spring storing potential energy. As discussed earlier, when the mass and spring have no external force acting on them they transfer energy back and forth at a rate equal to the natural frequency. In other words, if energy is to be efficiently pumped into both the mass and spring the energy source needs to feed the energy in at a rate equal to the natural frequency. Applying a force to the mass and spring is similar to pushing a child on swing, you need to push at the correct moment if you want the swing to get higher and higher. As in the case of the swing, the force applied does not necessarily have to be high to get large motions; the pushes just need to keep adding energy into the system. The damper, instead of storing energy, dissipates energy. Since the damping force is proportional to the velocity, the more the motion, the more the damper dissipates the energy. Therefore a point will come when the energy dissipated by the damper will equal the energy being fed in by the force. At this point, the system has reached its maximum amplitude and will continue to vibrate at this level as long as the force applied stays the same. If no damping exists, there is nothing to dissipate the energy and therefore theoretically the motion will continue to grow on into infinity. Applying "complex" forces to the mass–spring–damper model In a previous section only a simple harmonic force was applied to the model, but this can be extended considerably using two powerful mathematical tools. The first is the Fourier transform that takes a signal as a function of time (time domain) and breaks it down into its harmonic components as a function of frequency (frequency domain). For example, let us apply a force to the mass–spring–damper model that repeats the following cycle – a force equal to 1 newton for 0.5 second and then no force for 0.5 second. This type of force has the shape of a 1 Hz square wave. The Fourier transform of the square wave generates a frequency spectrum that presents the magnitude of the harmonics that make up the square wave (the phase is also generated, but is typically of less concern and therefore is often not plotted). The Fourier transform can also be used to analyze non-periodic functions such as transients (e.g. impulses) and random functions. With the advent of the modern computer the Fourier transform is almost always computed using the Fast Fourier Transform (FFT) computer algorithm in combination with a window function. In the case of our square wave force, the first component is actually a constant force of 0.5 newton and is represented by a value at "0" Hz in the frequency spectrum. The next component is a 1 Hz sine wave with an amplitude of 0.64. This is shown by the line at 1 Hz. The remaining components are at
How a 1 Hz square wave can be represented as a summation of sine waves(harmonics) and the corresponding frequency spectrum. Click and go to full resolution for an animation
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odd frequencies and it takes an infinite amount of sine waves to generate the perfect square wave. Hence, the Fourier transform allows you to interpret the force as a sum of sinusoidal forces being applied instead of a more "complex" force (e.g. a square wave). In the previous section, the vibration solution was given for a single harmonic force, but the Fourier transform will in general give multiple harmonic forces. The second mathematical tool, "the principle of superposition", allows you to sum the solutions from multiple forces if the system is linear. In the case of the spring–mass–damper model, the system is linear if the spring force is proportional to the displacement and the damping is proportional to the velocity over the range of motion of interest. Hence, the solution to the problem with a square wave is summing the predicted vibration from each one of the harmonic forces found in the frequency spectrum of the square wave. Frequency response model We can view the solution of a vibration problem as an input/output relation – where the force is the input and the output is the vibration. If we represent the force and vibration in the frequency domain (magnitude and phase) we can write the following relation:
is called the frequency response function (also referred to as the transfer function, but not technically as accurate) and has both a magnitude and phase component (if represented as a complex number, a real and imaginary component). The magnitude of the frequency response function (FRF) was presented earlier for the mass–spring–damper system. where The phase of the FRF was also presented earlier as:
For example, let us calculate the FRF for a mass–spring–damper system with a mass of 1 kg, spring stiffness of 1.93 N/mm and a damping ratio of 0.1. The values of the spring and mass give a natural frequency of 7 Hz for this specific system. If we apply the 1 Hz square wave from earlier we can calculate the predicted vibration of the mass. The figure illustrates the resulting vibration. It happens in this example that the fourth harmonic of the square wave falls at 7 Hz. The frequency response of the mass–spring–damper therefore outputs a high 7 Hz vibration even though the input force had a relatively low 7 Hz harmonic. This example highlights that the resulting vibration is dependent on both the forcing function and the system that the force is applied to. The figure also shows the time domain representation of the resulting vibration. This is done by performing an inverse Fourier Transform that converts frequency domain data to time domain. In practice, this is rarely done because the frequency spectrum provides all the necessary information. The frequency response function (FRF) does not necessarily have to be calculated from the knowledge of the Frequency response model
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23
mass, damping, and stiffness of the system, but can be measured experimentally. For example, if you apply a known force and sweep the frequency and then measure the resulting vibration you can calculate the frequency response function and then characterize the system. This technique is used in the field of experimental modal analysis to determine the vibration characteristics of a structure.
Multiple degrees of freedom systems and mode shapes The simple mass–spring damper model is the foundation of vibration analysis, but what about more complex systems? The mass–spring–damper model described above is called a single degree of freedom (SDOF) model since we have assumed the mass only moves up and down. In the case of more complex systems we need to discretize the system into more masses and allow them to move in more than one direction – adding degrees of freedom. The major concepts of multiple degrees of freedom (MDOF) can be understood by looking at just a 2 degree of freedom model as shown in the figure. The equations of motion of the 2DOF system are found to be:
2 degree of freedom model
We can rewrite this in matrix format:
A more compact form of this matrix equation can be written as:
where
and
are symmetric matrices referred respectively as the mass, damping, and stiffness
matrices. The matrices are NxN square matrices where N is the number of degrees of freedom of the system. In the following analysis we will consider the case where there is no damping and no applied forces (i.e. free vibration). The solution of a viscously damped system is somewhat more complicated.[2]
This differential equation can be solved by assuming the following type of solution:
Note: Using the exponential solution of
is a mathematical trick used to solve linear differential equations.
If we use Euler's formula and take only the real part of the solution it is the same cosine solution for the 1 DOF system. The exponential solution is only used because it easier to manipulate mathematically. The equation then becomes:
Vibration
Since
24
cannot equal zero the equation reduces to the following.
Eigenvalue problem This is referred to an eigenvalue problem in mathematics and can be put in the standard format by pre-multiplying the equation by
and if we let
and
The solution to the problem results in N eigenvalues (i.e.
), where N corresponds to the number of
degrees of freedom. The eigenvalues provide the natural frequencies of the system. When these eigenvalues are substituted back into the original set of equations, the values of that correspond to each eigenvalue are called the eigenvectors. These eigenvectors represent the mode shapes of the system. The solution of an eigenvalue problem can be quite cumbersome (especially for problems with many degrees of freedom), but fortunately most math analysis programs have eigenvalue routines. The eigenvalues and eigenvectors are often written in the following matrix format and describe the modal model of the system:
and A simple example using our 2 DOF model can help illustrate the concepts. Let both masses have a mass of 1 kg and the stiffness of all three springs equal 1000 N/m. The mass and stiffness matrix for this problem are then: and Then The eigenvalues for this problem given by an eigenvalue routine will be:
The natural frequencies in the units of hertz are then (remembering
)
and
.
The two mode shapes for the respective natural frequencies are given as:
Since the system is a 2 DOF system, there are two modes with their respective natural frequencies and shapes. The mode shape vectors are not the absolute motion, but just describe relative motion of the degrees of freedom. In our case the first mode shape vector is saying that the masses are moving together in phase since they have the same value and sign. In the case of the second mode shape vector, each mass is moving in opposite direction at the same rate.
Vibration
25
Illustration of a multiple DOF problem When there are many degrees of freedom, the best method of visualizing the mode shapes is by animating them. An example of animated mode shapes is shown in the figure below for a cantilevered I-beam. In this case, a finite element model was used to generate the mass and stiffness matrices and solve the eigenvalue problem. Even this relatively simple model has over 100 degrees of freedom and hence as many natural frequencies and mode shapes. In general only the first few modes are important. In this table the first and second (top and bottom respectively) horizontal bending (left), torsional (middle), and vertical bending (right) vibrational modes of an
I-beam have been visualized. There also exist other kinds of vibrational modes in which the beam gets compressed/stretched out in the height, width and length directions respectively. The mode shapes of a cantilevered I-beam
Multiple DOF problem converted to a single DOF problem The eigenvectors have very important properties called orthogonality properties. These properties can be used to greatly simplify the solution of multi-degree of freedom models. It can be shown that the eigenvectors have the following properties:
and
are diagonal matrices that contain the modal mass and stiffness values for each one of the
modes. (Note: Since the eigenvectors (mode shapes) can be arbitrarily scaled, the orthogonality properties are often used to scale the eigenvectors so the modal mass value for each mode is equal to 1. The modal mass matrix is therefore an identity matrix) These properties can be used to greatly simplify the solution of multi-degree of freedom models by making the following coordinate transformation.
If we use this coordinate transformation in our original free vibration differential equation we get the following equation.
Vibration
26
We can take advantage of the orthogonality properties by premultiplying this equation by
The orthogonality properties then simplify this equation to:
This equation is the foundation of vibration analysis for multiple degree of freedom systems. A similar type of result can be derived for damped systems.[2] The key is that the modal and stiffness matrices are diagonal matrices and therefore we have "decoupled" the equations. In other words, we have transformed our problem from a large unwieldy multiple degree of freedom problem into many single degree of freedom problems that can be solved using the same methods outlined above. Instead of solving for x we are instead solving for q, referred to as the modal coordinates or modal participation factors. It may be clearer to understand if we write
as:
Written in this form we can see that the vibration at each of the degrees of freedom is just a linear sum of the mode shapes. Furthermore, how much each mode "participates" in the final vibration is defined by q, its modal participation factor.
References [1] Tustin, Wayne. Where to place the control accelerometer: one of the most critical decisions in developing random vibration tests also is the most neglected (http:/ / findarticles. com/ p/ articles/ mi_hb4797/ is_10_45/ ai_n29299213/ ), EE-Evaluation Engineering, 2006 [2] Maia, Silva. Theoretical And Experimental Modal Analysis, Research Studies Press Ltd., 1997, ISBN 0471970670
Further reading • • • • •
Tongue, Benson, Principles of Vibration, Oxford University Press, 2001, ISBN 0-195-142462 Inman, Daniel J., Engineering Vibration, Prentice Hall, 2001, ISBN 013726142X Rao, Singiresu, Mechanical Vibrations, Addison Wesley, 1990, ISBN 0-201-50156-2 Thompson, W.T., Theory of Vibrations, Nelson Thornes Ltd, 1996, ISBN 0-412-783908 Hartog, Den, Mechanical Vibrations, Dover Publications, 1985, ISBN 0-486-647854
External links • Hyperphysics Educational Website, Concepts (http://hyperphysics.phy-astr.gsu.edu/hbase/permot. html#permot''Oscillation/Vibration) • Nelson Publishing, Evaluation Engineering Magazine (http://www.evaulationengineering.com/) • Structural Dynamics and Vibration Laboratory of McGill University (http://structdynviblab.mcgill.ca) • Normal vibration modes of a circular membrane (http://web.mat.bham.ac.uk/C.J.Sangwin/Teaching/ CircWaves/waves.html) • Free Excel sheets to estimate modal parameters (http://www.noisestructure.com/products/MPE_SDOF.php)
AFGROW
AFGROW AFGROW is the Air Force Growth (AFGROW) crack life prediction software tool that allows users to analyze crack initiation, fatigue crack growth, fracture, and assess the life of metallic structures. AFGROW is one of the fastest, most efficient, and user-friendly crack life prediction tools available today. AFGROW is mainly used for aerospace applications; however it can be applied to any type of metallic structure that experiences fatigue cracking.
Software architecture The stress intensity factor library provides models for over 30 different crack geometries (including tension, bending and bearing loading for many cases). In addition, an advanced, multiple crack capability allows AFGROW to analyze two independent cracks in a plate (including hole effects), non-symmetric corner cracked. Finite Element (FE) based solutions are available for two, non-symmetric through cracks at holes as well as cracks growing toward holes. This capability allows AFGROW to handle cases with more than one crack growing from a row of fastener holes. AFGROW implements five different material models (Forman Equation, Walker Equation, Tabular lookup, Harter-T Method and NASGRO Equation) to determine crack growth per applied cyclic loading. Other AFGROW user options include five load interaction (retardation) models (Closure, FASTRAN, Hsu, Wheeler, and Generalized Willenborg), a strain-life based fatigue crack initiation model, and the ability to perform a crack growth analysis with the effect of the bonded repair. AFGROW also includes useful tools such as: user-defined stress intensity solutions, user-defined beta modification factors (ability to estimate stress intensity factors for cases, which may not be an exact match for one of the stress intensity solutions in the AFGROW library), a residual stress analysis capability, cycle counting, and the ability to automatically transfer output data to Microsoft Excel. AFGROW provides COM (Component Object Model) Automation interfaces that allow users to build scripts in other Windows applications to perform repetitive tasks or control AFGROW from their applications. AFGROW also has new plug-in crack geometry interface that allows AFGROW to interface with any structural analysis program capable of calculating stress intensity factors (K) in the Windows environment. Users may create their own stress intensity solutions by writing and compiling dynamic link libraries (DLLs) using relatively simple codes. This includes the ability to animate the crack growth as is done in all other native AFGROW solutions. This interface also makes it possible for FE analysis software (for example, StressCheck) to feed AFGROW three-dimensional based stress intensity information throughout the crack life prediction process, allowing for a tremendous amount of analytical flexibility.
History AFGROW's history traces back to a crack growth life prediction program (ASDGRO) which was written in BASIC for IBM-PCs by Mr. Ed Davidson at ASD/ENSF in the early-mid-1980s. In 1985, ASDGRO was used as the basis for crack growth analysis for the Sikorsky H-53 Helicopter under contract to Warner-Robins ALC. The program was modified to utilize very large load spectra, approximate stress intensity solutions for cracks in arbitrary stress fields, and use a tabular crack growth rate relationship based on the Walker equation on a point-by-point basis (Harter T-Method). The point loaded crack solution from the Tada, Paris, and Irwin Stress Intensity Factor Handbook was originally used to determine K (for arbitrary stress fields) by integration over the crack length using the unflawed stress distribution independently for each crack dimension. After discussions with Dr. Jack Lincoln (ASD/ENSF), a new method was developed by Mr. Frank Grimsley (AFWAL/FIBEC) to determine stress intensity, which used a 2-D Gaussian integration scheme with Richardson Extrapolation which was optimized by Dr. George Sendeckyj (AFWAL/FIBEC). The resulting program was named MODGRO since it was a modified version of ASDGRO.
27
AFGROW
Early years Many upgrades were made during the late 1980s and early 1990s. The primary improvement was modifying the coding language from BASIC to Turbo Pascal and C. Numerous small changes/repairs were made based on errors that were discovered. During this time period, NASA/Dryden implemented MODGRO in the analysis for the flight test program for the X-29.
Recent times In 1993, the Navy was interested in using MODGRO to assist in a program to assess the effect of certain (classified) environments on the damage tolerance of aircraft. Work began at that time to convert the MODGRO, Version 3.X to the C language for UNIX to provide performance and portability to several UNIX Workstations. In 1994, the results of the Navy project were presented to the Navy sponsor and MODGRO was renamed AFGROW, Version 3.X. Since 1996, the Windows based version of AFGROW has replaced the UNIX version since the demand for the UNIX version did not justify the cost to maintain it. There was also an experiment to port AFGROW to the Mac OS. The Mac version had the same problem (lack of demand) as the UNIX version. An automated capability was added to AFGROW in the form of a Microsoft Component Object Model (COM) interface. The AFGROW COM interface allows users to use AFGROW as the crack growth analysis engine for any Windows based software.
Present Day An advanced model feature has been added to allow users to select cases with two, independent cracks (with and without holes). This feature continues to be improved and expanded to cover more combinations of corner and through-the-thickness cracks. A user-defined plug-in stress intensity model capability has also been added to AFGROW. This allows users to create their own stress intensity solutions in the form of a Windows DLL (dynamic link library). Drawing tools have been included in AFGROW to allow the user-defined solution to be animated during the analysis. Interactive stress intensity solutions have been demonstrated using AFGROW to perform life predictions while sending geometric data to an external FEM code, which returns updated stress intensity solutions back to AFGROW. Verification testing is a continuing process to improve AFGROW and expand the available database. There are plans to continue to add new technology and improvements to AFGROW. A Consortium has been started with users in Government and Industry to combine the best fracture mechanics methods available.
External links • Homepage [1] • Version Information [2]
References [1] http:/ / www. afgrow. net/ [2] http:/ / www. afgrow. net/ about/ currentver. aspx
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Agitator (device)
29
Agitator (device) An agitator is a device or mechanism to put something into motion by shaking or stirring.
Manual agitator • Manual dishwashers • A rock can be a device used to agitate dirt and other solids from fabric in washing • A stirring rod
agitating vessel
Washing machine agitator In a top load washing machine the agitator projects from the bottom of the wash basket and creates the wash action by rotating back and forth, rolling garments from the top of the load, down to the bottom, then back up again and due to that it seems so. There are several types of agitators with the most common being the "straight-vane" and "dual-action." The "straight-vane" is a one-part agitator with bottom and side fins that usually turns back and forth. The Dual-action is a two-part agitator that has bottom washer fins that moves back and forth and a spiral top that rotates clockwise to help guide the clothes to the bottom washer fins.
Agitator for a laundromat washing machine.
The modern agitator, which is the dual action, was first made in Kenmore washing machines in the 1980s to present. These agitators are known by Kenmore as dual-rollover and triple-rollover action agitators.
Magnetic agitator This is a device formed by a little metallic bar (called the agitation bar) which is normally covered by a plastic layer, and by a sheet that has underneath it a rotatory magnet or a series of electromagnets arranged in a circular form to create a magnetic rotatory field. It is very common that the sheet has an arrangement of electric resistances that can heat some chemical solutions. Thus, during the operation of a typical magnetic agitator, the magnetic agitator bar is moved inside a container that can be a flask or a glass with some liquid inside that can be agitated. The container must be placed on the sheet, so that the magnetic field influences the agitation bar and makes it rotate. This allows it to mix different substances at high speeds.
Air handler
30
Air handler An air handler, or air handling unit (often abbreviated to AHU), is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the building and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork. Small air handlers, for local use, are called terminal units, and may only include an air filter, coil, and blower; these simple terminal units are called blower coils or fan coil units. A larger air handler that conditions 100% outside air, and no recirculated air, is known as a makeup air unit (MAU). An air handler designed for outdoor use, typically on roofs, is known as a packaged unit (PU) or rooftop unit (RTU).
An air handling unit; air flow is from the right to left in this case. Some AHU components shown are: 1 - Supply duct 2 - Fan compartment 3 - Vibration isolator ('flex joint') 4 - Heating and/or cooling coil 5 - Filter compartment 6 - Mixed (recirculated + outside) air duct
Air handler components Blower/fan Air handlers typically employ a large squirrel cage blower driven by an AC induction electric motor to move the air. The blower may operate at a single speed, offer a variety of set speeds, or be driven by A rooftop packaged unit or RTU a Variable Frequency Drive to allow a wide range of air flow rates. Flow rate may also be controlled by inlet vanes or outlet dampers on the fan. Some residential air handlers (central 'furnaces' or 'air conditioners') use a brushless DC electric motor that has variable speed capabilities. Multiple blowers may be present in large commercial air handling units, typically placed at the end of the AHU and the beginning of the supply ductwork (therefore also called "supply fans"). They are often augmented by fans in the return air duct ("return fans") pushing the air into the AHU.
Air handler
Heating and/or cooling elements Air handlers may need to provide heating, cooling, or both to change the supply air temperature depending on the location and the application. Smaller air handlers may contain a fuel-burning heater or a refrigeration evaporator, placed directly in the air stream. Electric resistance and heat pumps can be used as well. Evaporative cooling is possible in dry climates. Large commercial air handling units contain coils that circulate hot water or steam for heating, and chilled water for cooling. Coils are typically manufactured from copper for the tubes, with copper or aluminium fins to aid heat transfer. Cooling coils will also employ eliminator plates to remove and drain condensate. The hot water or steam is provided by a central boiler, and the chilled water is provided by a central chiller. Downstream temperature sensors are typically used to monitor and control 'off coil' temperatures, in conjunction with an appropriate motorized control valve prior to the coil.
Filters Air filtration is almost always present in order to provide clean dust-free air to the building occupants. It may be via simple low-MERV pleated media, HEPA, electrostatic, or a combination of techniques. Gas-phase and ultraviolet air treatments may be employed as well. It is typically placed first in the AHU in order to keep all its components clean. Depending upon the grade of filtration required, typically filters will be arranged in two (or more) banks with a coarse-grade panel filter provided in front of a fine-grade bag filter, or other 'final' filtration medium. The panel filter is cheaper to replace and maintain, and thus protects the more expensive bag filters. The life of a filter may be assessed by monitoring the pressure drop through the filter medium at design air volume flow rate. This may be done by means of a visual display, using a pressure gauge, or by a pressure switch linked to an alarm point on the building control system. Failure to replace a filter may eventually lead to its collapse, as the forces exerted upon it by the fan overcome its inherent strength, resulting in collapse and thus contamination of the air handler and downstream ductwork.
Humidifier Humidification is often necessary in colder climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity. Various types of humidification may be used: • Evaporative: dry air blown over a reservoir will evaporate some of the water. The rate of evaporation can be increased by spraying the water onto baffles in the air stream. • Vaporizer: steam or vapour from a boiler is blown directly into the air stream. • Spray mist: water is diffused either by a nozzle or other mechanical means into fine droplets and carried by the air. • Ultrasonic: A tray of fresh water in the airstream is excited by an ultrasonic device forming a fog or water mist. • Wetted medium: A fine fibrous medium in the airstream is kept moist with fresh water from a header pipe with a series of small outlets. As the air passes through the medium it entrains the water in fine droplets. This type of humidifier can quickly clog if the primary air filtration is not maintained in good order.
31
Air handler
Mixing chamber In order to maintain indoor air quality, air handlers commonly have provisions to allow the introduction of outside air into, and the exhausting of air from the building. In temperate climates, mixing the right amount of cooler outside air with warmer return air can be used to approach the desired supply air temperature. A mixing chamber is therefore used which has dampers controlling the ratio between the return, outside, and exhaust air.
Heat recovery device A heat recovery device heat exchanger of many types, may be fitted to the air handler between supply and extract airstreams for energy savings and increasing capacity. These types more commonly include for: • Recuperator, or Plate Heat exchanger: A sandwich of plastic or metal plates with interlaced air paths. Heat is transferred between airstreams from one side of the plate to the other. The plates are typically spaced at 4 to 6mm apart. Can also be used to recover coolth. Heat recovery efficiency up to 70%. • Thermal Wheel, or Rotary heat exchanger: A slowly rotating matrix of finely corrugated metal, operating in both opposing airstreams. When the air handling unit is in heating mode, heat is absorbed as air passes through the matrix in the exhaust airstream, during one half rotation, and released during the second half rotation into the supply airstream in a continuous process. When the air handling unit is in cooling mode, heat is released as air passes through the matrix in the exhaust airstream, during one half rotation, and absorbed during the second half rotation into the supply airstream. Heat recovery efficiency up to 85%. Wheels are also available with a hydroscopic coating to provide latent heat transfer and also the drying or humidification of airstreams • Run around coil: Two air to liquid heat exchanger coils, in opposing airstreams, piped together with a circulating pump and using water or a brine as the heat transfer medium. This device, although not very efficient, allows heat recovery between remote and sometimes multiple supply and exhaust airstreams. Heat recovery efficiency up to 50%. • Heat Pipe: Operating in both opposing air paths, using a confined refrigerant as a heat transfer medium. The 'pipe' is multiple sealed pipes mounted in a coil configuration with fins to increase heat transfer. Heat is absorbed on one side of the pipe, by evaporation of the refrigerant, and released at the other side, by condensation of the refrigerant. Condensed refrigerant flows by gravity to the first side of the pipe to repeat the process. Heat recovery efficiency up to 65%.
Controls Controls are necessary to regulate every aspect of an air handler, such as: flow rate of air, supply air temperature, mixed air temperature, humidity, air quality. They may be as simple as an off/on thermostat or as complex as a building automation system using BACnet or LonWorks, for example. Common control components include temperature sensors, humidity sensors, sail switches, actuators, motors, and controllers.
Vibration isolators The blowers in an air handler can create substantial vibration and the large area of the duct system would transmit this noise and vibration to the occupants of the building. To avoid this, vibration isolators (flexible sections) are normally inserted into the duct immediately before and after the air handler and often also between the fan compartment and the rest of the AHU. The rubberized canvas-like material of these sections allow the air handler to vibrate without transmitting much vibration to the attached ducts. The fan compartment can be further isolated by placing it on a spring suspension, which will mitigate the transfer of vibration through the floor.
32
Air handler
33
European Market The European market of air handling units (AHU) is dominated by Germany and the Northern Countries, where are located the main manufacturers, and reaches a total of 1 343.06M€. The number of units sold, by range of capacity, is split as following [1] : • • • • •
≤ 5.000 m3/h : 55% 5.001 - 15.000 m3/h : 31% 15.001-30.000 m3/h : 10% 30.001 - 50.000 m3/h : 3% ≥ 50.001 m3/h : 1%
The market by country is split in 2010 as following: Countries
Sales Volume in M€
Share
Benelux
111.06
8.3%
France
94.34
7.0%
Germany
323.00
24.0%
Italy
76.08
5.7%
Portugal
23.81
1.8%
Russia, Ukraine and CIS countries
130.59
9.7%
Scandinavia and Baltic countries
240.60
17.9%
Spain
49.58
3.7%
Turkey
38.53
2.9%
UK and Ireland
102.88
7.7%
Eastern Europe
152.60
11.4%
Major manufacturers • • • • • • • • •
[2]
GEA Group Carrier Corporation (also makes Bryant and Payne brands) Daikin Industries (also makes McQuay International brands) TANGRA - Heating, Ventilation & Air Conditioning [3] Johnson Controls (also makes York International brand) Lennox International Rheem (also makes Ruud) Trane Air Design
References [1] Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ [2] Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ [3] http:/ / www. tangra. bg
Air preheater
34
Air preheater An air preheater (APH) is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil. In particular, this article describes the combustion air preheaters used in large boilers found in thermal power stations producing electric power from e.g. fossil fuels, biomasses or waste.[1] [2] [3] [4] [5]
Schematic diagram of typical coal-fired power plant steam generator highlighting the air preheater (APH) location. (For simplicity, any radiant section tubing is not shown.)
The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack (to meet emissions regulations, for example).
Types There are two types of air preheaters for use in steam generators in thermal power stations: One is a tubular type built into the boiler flue gas ducting, and the other is a regenerative air preheater.[1] [2] [6] These may be arranged so the gas flows horizontally or vertically across the axis of rotation. Another type of air preheater is the regenerator used in iron or glass manufacture.
Tubular type Construction features Tubular preheaters consist of straight tube bundles which pass through the outlet ducting of the boiler and open at each end outside of the ducting. Inside the ducting, the hot furnace gases pass around the preheater tubes, transferring heat from the exhaust gas to the air inside the preheater. Ambient air is forced by a fan through ducting at one end of the preheater tubes and at other end the heated air from inside of the tubes emerges into another set of ducting, which carries it to the boiler furnace for combustion.
Air preheater Problems The tubular preheater ductings for cold and hot air require more space and structural supports than a rotating preheater design. Further, due to dust-laden abrasive flue gases, the tubes outside the ducting wear out faster on the side facing the gas current. Many advances have been made to eliminate this problem such as the use of ceramic and hardened steel. Many new circulating fluidized bed (CFB) and bubbling fluidized bed (BFB) steam generators are currently incorporating tubular air heaters offering an advantage with regards to the moving parts of a rotary type. Dew point corrosion Dew point corrosion occurs for a variety of reasons.[7] [8] The type of fuel used, its sulfur content and moisture content are contributing factors. However, by far the most significant cause of dew point corrosion is the metal temperature of the tubes. If the metal temperature within the tubes drops below the acid saturation temperature, usually at between 190°F (88°C)and 230°F (110°C), but sometimes at temperatures as high as 260°F (127°C), then the risk of dew point corrosion damage becomes considerable.
Regenerative air preheaters There are two types of regenerative air preheaters: the rotating-plate regenerative air preheaters (RAPH) and the stationary-plate regenerative air preheaters (Rothemuhle).[1] [2] [3] [9] Rotating-plate regenerative air preheater The rotating-plate design (RAPH)[2] consists of a central rotating-plate element installed within a casing that is divided into two (bi-sector type), three (tri-sector type) or four (quad-sector type) sectors containing seals around the element. The seals allow the element to rotate through all the sectors, but keep gas leakage between sectors to a minimum while providing separate gas air and flue gas paths through each sector. Tri-sector types are the most common in modern power generation [11] facilities. In the tri-sector design, the largest sector (usually spanning about half the cross-section of the [10] Typical Rotating-plate Regenerative Air Preheater (Bi-sector type) casing) is connected to the boiler hot gas outlet. The hot exhaust gas flows over the central element, transferring some of its heat to the element, and is then ducted away for further treatment in dust collectors and other equipment before being expelled from the flue gas stack. The second, smaller sector, is fed with ambient air by a fan, which passes over the heated element as it rotates into the sector, and is heated before being carried to the boiler furnace for combustion. The third sector is the smallest one and it heats air which is routed into the pulverizers and used to carry the coal-air mixture to coal boiler burners. Thus, the total air heated in the RAPH provides: heating air to remove the moisture from the pulverised coal dust, carrier air for transporting the pulverised coal to the boiler burners and the primary air for combustion.
35
Air preheater The rotor itself is the medium of heat transfer in this system, and is usually composed of some form of steel and/or ceramic structure. It rotates quite slowly (around 3-5 RPM) to allow optimum heat transfer first from the hot exhaust gases to the element, then as it rotates, from the element to the cooler air in the other sectors. Construction features In this design the whole air preheater casing is supported on the boiler supporting structure itself with necessary expansion joints in the ducting. The vertical rotor is supported on thrust bearings at the lower end and has an oil bath lubrication, cooled by water circulating in coils inside the oil bath. This arrangement is for cooling the lower end of the shaft, as this end of the vertical rotor is on the hot end of the ducting. The top end of the rotor has a simple roller bearing to hold the shaft in a vertical position. The rotor is built up on the vertical shaft with radial supports and cages for holding the baskets in position. Radial and circumferential seal plates are also provided to avoid leakages of gases or air between the sectors or between the duct and the casing while in rotation. For on line cleaning of the deposits from the baskets steam jets are provided such that the blown out dust and ash are collected at the bottom ash hopper of the air preheater. This dust hopper is connected for emptying along with the main dust hoppers of the dust collectors. The rotor is turned by an air driven motor and gearing, and is required to be started before starting the boiler and also to be kept in rotation for some time after the boiler is stopped, to avoid uneven expansion and contraction resulting in warping or cracking of the rotor. The station air is generally totally dry (dry air is required for the instrumentation), so the air used to drive the rotor is injected with oil to lubricate the air motor. Safety protected inspection windows are provided for viewing the preheater's internal operation under all operating conditions. The baskets are in the sector housings provided on the rotor and are renewable. The life of the baskets depend on the ash abrasiveness and corrosiveness of the boiler outlet gases. Problems The boiler flue gas contains many dust particles (due to high ash content) not contributing towards combustion, such as silica, which cause abrasive wear of the baskets, and may also contain corrosive gases depending on the composition of the fuel. For example, Indian coals generally result in high levels of ash, sulfur and silica in the flue gas. The wear of the baskets therefore is generally more than other, cleaner-burning fuels. In this RAPH, the dust laden, corrosive boiler gases have to pass between the elements of air preheater baskets. The elements are made up of zig zag corrugated plates pressed into a steel basket giving sufficient annular space in between for the gas to pass through. These plates are corrugated to give more surface area for the heat to be absorbed and also to give it the rigidity for stacking them into the baskets. Hence frequent replacements are called for and new baskets are always kept ready. In the early days, Cor-ten steel was being used for the elements. Today due to technological advance many manufacturers may use their own patents. Some manufacturers supply different materials for the use of the elements to lengthen the life of the baskets. In certain cases the unburnt deposits may occur on the air preheater elements causing it to catch fire during normal operations of the boiler, giving rise to explosions inside the air preheater. Sometimes mild explosions may be detected in the control room by variations in the inlet and outlet temperatures of the combustion air.
36
Air preheater
Stationary-plate regenerative air preheater The heating plate elements in this type of regenerative air preheater are also installed in a casing, but the heating plate elements are stationary rather than rotating. Instead the air ducts in the preheater are rotated so as to alternatively expose sections of the heating plate elements to the upflowing cool air.[1] [2] [3] As indicated in the adjacent drawing, there are rotating inlet air ducts at the bottom of the stationary plates similar to the rotating outlet air ducts at the top of the stationary plates. Stationary-plate regenerative air preheaters are also known as Rothemuhle preheaters, manufactured for over 25 years by Balke-Dürr GmbH of Ratingen, Germany.
Regenerator A regenerator consists of a brick checkerwork: Schematic of typical stationary-plate regenerative air preheater bricks laid with spaces equivalent to a brick's width between them, so that air can flow relatively easily through the checkerwork. The idea is that as hot exhaust gases flow through the checkerwork, they give up heat to the bricks. The airflow is then reversed, so that the hot bricks heat up the incoming combustion air and fuel. For a glass-melting furnace, a regenerator sits on either side of the furnace, often forming an integral whole. For a blast furnace, the regenerators (commonly called Cowper stoves) sit separate to the furnace. A furnace needs no less than two stoves, but may have three. One of the stoves is 'on gas', receiving hot gases from the furnace top and heating the checkerwork inside, whilst the other is 'on blast', receiving cold air from the blowers, heating it and passing it to the blast furnace.
References [1] Sadik Kakaç and Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd Edition ed.). CRC Press. ISBN 0-8493-0902-6. [2] Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st edition ed.). ISBN 0-9634570-0-4. [3] Sadik Kakaç (Editor) (April, 1991). Boilers. Evaporators and Condensers. Wiley Interscience. ISBN 0-471-62170-6. (See Chapter 8 by Z.H. Lin) [4] British Electricity International (1991). Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-040510-X. [5] Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997). Standard Handbook of Powerplant Engineering (2nd edition ed.). McGraw-Hill Professional. ISBN 0-07-019435-1. [6] Trisector Ljungström Air Preheater (http:/ / www. airpreheatercompany. com/ Products/ Category. aspx?cat=1& subcat=12) [7] Examples of dewpoint corrosion (http:/ / cmsinc. us/ ) [8] More examples of dewpoint corrosion (http:/ / cmsinc. us/ ) [9] Lawrence Drbak, Patrica Boston, Kalya Westra, and R. Bruce Erickson (Editors) (1996). Power Plant Engineering (Black and Veatch). Chapman & Hall. ISBN 0-412-06401-4. [10] Course SI:428A (http:/ / yosemite. epa. gov/ oaqps/ EOGtrain. nsf/ fabbfcfe2fc93dac85256afe00483cc4/ 0747540cee26044285256db900597c4c/ $FILE/ SI 428A_1. pdf) Online publication of the U.S. Environmental Protection Agency's Air Pollution Training Institute, known as APTI (Scroll down to page 23 of 28) [11] Air preheaters: Rotating regenerative heat exchangers (http:/ / bwe. dk/ pdf/ brochure-01 APH_06. pdf)
37
Airshaft
Airshaft In manufacturing, an airshaft is a device used for handling winding reels in the processing of web-fed materials, such as continuous-process printing presses. Airshafts are used in the manufacturing processes for fitting into a core onto which materials such as paper, card and plastic film are wound. An airshaft is designed so that, on fitting into a core, it can be readily expanded, thereby achieving a quick and firm attachment, it may also be easily deflated to facilitate easy withdrawal of the shaft after winding of product is complete. Their efficient design makes them ideal for mounting onto bearing housings to enable the winding or unwinding of rolls of stock material with the minimum of equipment down time. The advantage of using an airshaft is its ability to grip the core, without damage, whilst providing a positive interface to control the web via motors & brakes. Airshafts are available as either lug type (with bladder down the centre) or strip type (bladders on the periphery of the shaft).
American Machinists' Handbook American Machinists' Handbook was a McGraw-Hill reference book similar to Industrial Press's Machinery's Handbook. (The latter title, still in print and regularly revised, is the one that machinists today are usually referring to when they speak imprecisely of "the machinist's handbook" or "the machinists' handbook".) The somewhat generic sound of the title American Machinists' Handbook, and the ambiguity of its apostrophe usage, no doubt contributed to the confounding of the two books' titles and identities. It capitalized on readers' familiarity with American Machinist, McGraw-Hill's popular trade journal. But the usage could have benefited from some branding discipline, because the confusion over whether the title was properly "American Machinist's Handbook" or "American Machinists' Handbook" or "American Machinist 's Handbook" was (and is) considerable. ("American Machinist 's Handbook" would be parallel to the construction of the title "Machinery's Handbook"; perhaps McGraw-Hill's handbook's title was originally conceived as that and later was muddied into "American Machinists' Handbook".) Although McGraw-Hill's American Machinists' Handbook appeared first (1908), it is doubtful that Industrial Press's Machinery's Handbook (1914) was a mere me-too conceived afterwards in response. The eager market for such a reference work had probably been obvious for at least a decade before either work was compiled, and presumably the appearance of the McGraw-Hill title merely prodded Industrial Press to finally get moving on a handbook of its own. American Machinists' Handbook, coedited by Fred H. Colvin and Frank A. Stanley, went through eight editions between 1908 and 1945. In 1955, McGraw-Hill published The new American machinist's handbook. Based upon earlier editions of American machinists' handbook (sic; note the apostrophe usage difference within that title), but presumably the book did not compete well enough with Machinery's Handbook, because no subsequent editions were produced. Meanwhile, Machinery's Handbook has continued to be regularly revised and updated, right up to today, and it is still a "bible of the metalworking industries."
List of the editions of American Machinists' Handbook
38
American Machinists' Handbook
Coeditors
39
Title ± subtitle
Year
Edition number
City, Publisher
Notes
Fred H. 1908 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine shop and drawing room data, methods, and definitions
1st ed
New York and London, Hill
This edition is public-domain (copyright expired) and can be read for [1] free in digitized form via Google Book Search.
Fred H. 1914 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine shop and drawing room data, methods and definitions
2nd ed
New York and London, McGraw-Hill
This edition is public-domain (copyright expired) and can be read for [2] free in digitized form via Google Book Search.
Fred H. 1920 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine shop and drawing room data, methods and definitions
3rd ed
New York and London, McGraw-Hill
This edition is public-domain (copyright expired).
Fred H. 1926 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine-shop and drawing-room data, methods and definitions
4th ed
New York and London, McGraw-Hill
Copyright renewed 1954-01-18
Fred H. 1932 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine shop and drawing room data, methods and definitions
5th ed
New York and London, McGraw-Hill
Copyright renewed 1959-12-07
Fred H. 1935 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms, a reference book of machine shop and drawing room data, methods and definitions
6th ed
New York and London, McGraw-Hill
Copyright renewed 1963-05-06
Fred H. 1940 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms
7th ed
New York and London, McGraw-Hill
Copyright renewed 1967-11-03
Fred H. 1945 Colvin, Frank A. Stanley
American machinists' handbook and dictionary of shop terms: a reference book of machine-shop and drawing-room data, methods, and definitions
8th ed
New York and London, McGraw-Hill
Copyright renewed 1963-05-06
Fred H. 1955 Colvin, Frank A. Stanley
The new American machinist's handbook. Based upon earlier editions of American machinists' handbook
1st ed
New York and London, McGraw-Hill
(1) Note the apostrophe usage in the title. (2) Copyright renewed 1955-07-26
Renewal data from Rutgers [3]. All works after 1923 with renewed copyright are presumably still protected.
References [1] http:/ / books. google. com/ books?id=o9ANAAAAYAAJ& printsec=titlepage#v=onepage& q=& f=false [2] http:/ / books. google. com/ books?id=4Q8LAAAAIAAJ& pg=PA1& dq=Colvin+ %22American+ machinists%27+ handbook%22#PPR3,M1 [3] http:/ / www. scils. rutgers. edu/ ~lesk/ copyrenew. html
Applied mechanics
Applied mechanics Applied mechanics is a branch of the physical sciences and the practical application of mechanics. Applied mechanics examines the response of bodies (solids and fluids) or systems of bodies to external forces. Some examples of mechanical systems include the flow of a liquid under pressure, the fracture of a solid from an applied force, or the vibration of an ear in response to sound. A practitioner of the discipline is known as a mechanician. Applied mechanics, as its name suggests, bridges the gap between physical theory and its application to technology. As such, applied mechanics is used in many fields of engineering, especially mechanical engineering. In this context, it is commonly referred to as engineering mechanics. Much of modern engineering mechanics is based on Isaac Newton's laws of motion while the modern practice of their application can be traced back to Stephen Timoshenko, who is said to be the father of modern engineering mechanics. Within the theoretical sciences, applied mechanics is useful in formulating new ideas and theories, discovering and interpreting phenomena, and developing experimental and computational tools. In the application of the natural sciences, mechanics was said to be complemented by thermodynamics by physical chemists Gilbert N. Lewis and Merle Randall, the study of heat and more generally energy, and electromechanics, the study of electricity and magnetism.[1]
Applied mechanics in practice n Civil Engineering, Mechanical Engineering, Construction Engineering, Materials Science and Engineering, Aerospace Engineering, Chemical Engineering, Electrical Engineering, Nuclear Engineering, Structural engineering and Bioengineering.
Applied mechanics in engineering Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both elastic and plastic) of objects under known forces (also called loads) or stresses. When treated as an area of study within a larger engineering curriculum, engineering mechanics can be subdivided into • Statics, the study of non-moving bodies under known loads • Dynamics (or kinetics), the study of how forces affect moving bodies • Mechanics of materials or strength of materials, the study of how different materials deform under various types of stress • Deformation mechanics, the study of deformations typically in the elastic range • Fluid mechanics, the study of how fluids react to forces. Note that fluid mechanics can be further split into fluid statics and fluid dynamics, and is itself a subdiscipline of continuum mechanics. The application of fluid mechanics in engineering is called hydraulics. • Continuum mechanics is a method of applying mechanics that assumes that all objects are continuous. It is contrasted by discrete mechanics.
40
Applied mechanics
Major topics of applied mechanics • • • • • • • • • • • • • • • •
Acoustics Analytical mechanics Computational mechanics Contact mechanics Continuum mechanics Dynamics (mechanics) Elasticity (physics) Experimental mechanics Fatigue (material) Finite element method Fluid mechanics Fracture mechanics Mechanics of materials Mechanics of structures Rotordynamics Solid mechanics
• Soil mechanics • Stress waves • Viscoelasticity
Examples of applications • Earthquake engineering
Further reading • • • • • • • • • • • • •
J.P. Den Hartog, Strength of Materials, Dover, New York, 1949. F.P. Beer, E.R. Johnston, J.T. DeWolf, Mechanics of Materials, McGraw-Hill, New York, 1981. S.P. Timoshenko, History of Strength of Materials, Dover, New York, 1953. J.E. Gordon, The New Science of Strong Materials, Princeton, 1984. H. Petroski, To Engineer Is Human, St. Martins, 1985. T.A. McMahon and J.T. Bonner, On Size and Life, Scientific American Library, W.H. Freeman, 1983. M. F. Ashby, Materials Selection in Design, Pergamon, 1992. A.H. Cottrell, Mechanical Properties of Matter, Wiley, New York, 1964. S.A. Wainwright, W.D. Biggs, J.D. Currey, J.M. Gosline, Mechanical Design in Organisms, Edward Arnold, 1976. S. Vogel, Comparative Biomechanics, Princeton, 2003. J. Howard, Mechanics of Motor Proteins and the Cytoskeleton, Sinauer Associates, 2001. J.L. Meriam, L.G. Kraige. Engineering Mechanics Volume 2: Dynamics, John Wiley & Sons., New York, 1986. J.L. Meriam, L.G. Kraige. Engineering Mechanics Volume 1: Statics, John Wiley & Sons., New York, 1986.
41
Applied mechanics
References [1] Thermodynamics - and the Free Energy of Chemical Substances. Lewis, G. and M. Randall (1923)
Video Lectures • Applied Mechanics Video Lectures By Prof.SK. Gupta, Department of Applied Mechanics, IIT Delhi (http:// www.nptelvideos.com/applied_mechanics/)
Professional organizations • American Academy of Mechanics (http://coewww.rutgers.edu/aam/) • Applied Mechanics Division, American Society of Mechanical Engineers • Engineering Mechanics Institute of the American Society of Civil Engineers (EMI) (http://www.asce.org/emi/ ) • International Union of Theoretical and Applied Mechanics (http://www.iutam.net/iutam/Organization/) • US National Committee on Theoretical and Applied Mechanics (http://www7.nationalacademies.org/usnctam/ index.html)
Professional publications • Advances in Applied Mechanics (http://www.elsevier.com/wps/find/bookdescription.cws_home/704246/ description#description) • Applied Mechanics Reviews (http://scitation.aip.org/ASMEJournals/AMR/) • International Journal of Solids and Structures (http://www.elsevier.com/wps/find/journaldescription. cws_home/297/description?navopenmenu=-2) • Journal of Engineering Mechanics (http://ascelibrary.org/emo/) • Journal of Nanomechanics and Micromechanics (http://ascelibrary.org/nmo/) • Journal of Fluid Mechanics (http://jfm-www.damtp.cam.ac.uk/) • Journal of Mechanics of Materials and Structures (http://www.jomms.org) • Journal of Applied Mechanics (http://scitation.aip.org/ASMEJournals/AppliedMechanics/) • Journal of the Mechanics and Physics of Solids (http://www.elsevier.com/wps/find/journaldescription. cws_home/220/description#description) • Mechanics of Materials (http://www.elsevier.com/wps/find/journaldescription.cws_home/505659/ description#description) • Mechanics Research Communications (http://www.elsevier.com/wps/find/journaldescription.cws_home/ 374/description#description) • Quarterly Journal of Mechanics and Applied Mathematics (http://qjmam.oxfordjournals.org/) • Nonlinear Dynamics (http://www.springer.com/west/home?SGWID=4-102-70-35759614-0& changeHeader=true&SHORTCUT=www.springer.com/journal/11071) • Journal of Vibration and Control (http://www.sagepub.com/journalsProdEditBoards. nav?prodId=Journal201401)
42
Atmosphere (unit)
43
Atmosphere (unit) The standard atmosphere (symbol: atm) is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure.[1] For practical purposes it has been replaced by the bar which is 105 Pa.[1] The difference of about 1% is not significant for many applications, and is within the error range of common pressure gauges.
History In 1954 the 10th Conférence Générale des Poids et Mesures (CGPM) adopted standard atmosphere for general use and affirmed its definition of being precisely equal to 1,013,250 dynes per square centimeter (101 325 Pa).[2] This value was intended to represent the mean atmospheric pressure at mean sea level at the latitude of Paris, France, and as a practical matter, truly reflects the mean sea level pressure for many of the industrialized nations (those with latitudes similar to Paris). In chemistry, the original definition of “Standard Temperature and Pressure” (STP) was a reference temperature of 0 °C (273.15 K) and pressure of 101.325 kPa (1 atm). However, in 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, “the standard pressure” should be defined as precisely 100 kPa (exactly 1 bar).[3]
Pressure units and equivalencies Pressure units Pascal
Bar
Technical atmosphere Standard atmosphere
Torr
Pound per square inch
Pa
bar
at
atm
torr
psi
1 Pa
≡ 1 N/m2
10−5
1.0197×10−5
9.8692×10−6
7.5006×10−3
145.04×10−6
1 bar
105
≡ 106 dyn/cm2
1.0197
0.98692
750.06
14.5037744
1 at
0.980665 ×105
0.980665
≡ 1 kp/cm2
0.96784
735.56
14.223
1 atm
1.01325 ×105
1.01325
1.0332
≡ p0
760
14.696
1 Torr
133.322
1.3332×10−3
1.3595×10−3
1.3158×10−3
= 1 mmHg
19.337×10−3
1 psi
6.895×103
68.948×10−3
70.307×10−3
68.046×10−3
51.715
≡ 1 lbF/in2
A pressure of 1 atm can also be stated as: ≡1.013 25 bar ≡ 101325 pascal (Pa) ≡ 1013.25 millibars (mbar, also mb) ≡ 760 torr [B] ≈ 760.001 mm-Hg, 0 °C, subject to revision as more precise measurements of mercury’s density become available [B, C] ≈ 29.9213 in-Hg, 0 °C, subject to revision as more precise measurements of mercury’s density become available [C] ≈ 1.033 227 452 799 886 kgf/cm² ≈ 1.033 227 452 799 886 technical atmosphere
Atmosphere (unit) ≈ 1033.227 452 799 886 cm–H2O, 4 °C [A] ≈ 406.782 461 732 2385 in–H2O, 4 °C [A] ≈ 14.695 948 775 5134 pounds-force per square inch (psi) ≈ 2116.216 623 673 94 pounds-force per square foot (psf) Notes: A
This is the customarily-accepted value for cm–H2O, 4 °C. It is precisely the product of 1 kg-force per square centimeter (one technical atmosphere) times 1.013 25 (bar/atmosphere) divided by 0.980 665 (one gram-force). It is not accepted practice to define the value for water column based on a true physical realization of water (which would be 99.997 495% of this value because the true maximum density of Vienna Standard Mean Ocean Water is 0.999 974 95 kg/l at 3.984 °C). Also, this “physical realization” would still ignore the 8.285 cm–H2O reduction that would actually occur in a true physical realization due to the vapor pressure over water at 3.984 °C. B
Torr and mm-Hg, 0°C are often taken to be identical. For most practical purposes (to 5 significant digits), they are interchangeable. C
NIST value of 13.595 078(5) g/ml assumed for the density of Hg at 0 °C
Other applications Scuba divers and others use the word atmosphere and "atm" in relation to pressures that are relative to mean atmospheric pressure at sea level (1.013 bar). For example, a partial pressure of oxygen is calibrated typically using air at sea level, so is expressed in units of atm. The old European unit technical atmosphere (at) is roughly equal to the gauge pressure under 10 m of water; 1 at = 98066.5 Pa.
References [1] British Standard BS 350:2004 Conversion Factors for Units [2] BIPM Definition of the standard atmosphere (http:/ / www. bipm. org/ jsp/ en/ ViewCGPMResolution. jsp?CGPM=10& RES=4) [3] IUPAC.org, Gold Book, Standard Pressure (http:/ / goldbook. iupac. org/ S05921. html)
44
Automaton clock
45
Automaton clock An automaton clock or automata clock is a type of striking clock featuring automatons.[1] Clocks like these were built from the Middle Ages through to Victorian times in Europe. A Cuckoo clock is a simple form of this type of clock. The automatons usually perform on the hour, half-hour or quarter-hour, usually to strike bells. Common figures in older clocks include Death (as a reference to human mortality), Old Father Time, saints and angels. In the Regency and Victorian eras, common figures also included royalty, famous composers or industrialists. More recently constructed automaton clocks are widespread in Japan, where they are known as karakuri-dokei. Notable examples of such clocks include the Nittele Ōdokei, designed by Hayao Miyazaki to be affixed on the Nippon Television headquarters in Tokyo, touted to be the largest animated clock in the world.[2] In the United Kingdom, Kit Williams produced a series of large automaton clocks for a handful of British shopping centres, featuring frogs, ducks and fish.
Automaton clock in Gloucester. The figures striking the quarter hours and the chimes represent the constituent countries of the United Kingdom. They are (L–R) Ireland, England, Scotland and Wales. In the centre is Old Father Time, who strikes the hours.
References [1] "Musical automaton clock" (http:/ / www. vam. ac. uk/ content/ videos/ m/ musical-automaton-clock/ ). Victoria and Albert Museum, London. . Retrieved 2011-09-16. [2] Hayao Miyazaki’s Nittele Nippon Terebi Clock (http:/ / www. lostinjapan. com/ 2009/ 07/ hayao-miyazakis-nittele-nippon-terebi-clock/ ), Lost in Japan (blog). 4 July 2009.
Backdrive
Backdrive Backdriving is when a component is used in reverse to obtain its input from its output. This extends to many concepts and systems from thought based to practical mechanical applications. Not every system can be backdriven. A DC electrical generator can be implemented by backdriving a DC electric motor, however a worm drive works only in one direction. Example: A CNC vertical mill has a vertical lead screw on the Z-axis. A low lead screw pitch (i.e. 5 turns per inch or fewer) means when the driving motor power is removed such as by turning the machine off, the weight of the spindle will cause the lead screw to rotate as the spindle motor falls down. Obviously this is a bad thing. The solution to prevent back-driving is to use a finer (higher) lead screw pitch (i.e. 10tpi or greater) or have a locking mechanism.
Ball detent A ball detent is a simple mechanical arrangement used to hold a moving part in a temporarily fixed position relative to another part. Usually the moving parts slide with respect to each other, or one part rotates within the other. The ball is a single, usually metal sphere, sliding within a bored cylinder, against the pressure of a spring, which pushes the ball against the other part of the mechanism, which carries the detent - which can be as simple as a hole of smaller diameter than the ball. When the hole is in line with the cylinder, the ball falls partially into the hole under spring pressure, holding the parts at that position. Additional force applied to the moving parts will push the ball back into its cylinder, compressing the spring, and allowing the parts to move to another position. Ball detents are commonly found in the selector mechanism of a gearbox, holding the selector rods in the correct position to engage the desired gear. Other applications include clutches that slip at a preset torque, and calibrated ball detent mechanisms are typically found in a torque wrench. Ball detents are one of the mechanisms often used in folding knives to prevent unwanted opening of the blade when carrying it.
Use in Paintball Markers The term "ball detent" is also used when referring to a mechanism in paintball markers designed to prevent the paintball from rolling out of the firing chamber before being fired. Some designs are similar to those outlined above, with a cartridge utilizing a ball bearing in a bore with spring pressure. The cartridge is installed perpendicular to the barrel bore axis, just ahead of where the ball rests before being fired. Other designs use elastic rubber protrusions that block the ball until it is pushed over it by the bolt. Some designs use precisely calibrated rings or "barrel sizers" that are selected to have a slightly smaller inner diameter than the outer diameter of the paintballs being used. They rely on simple constriction of the bore to prevent paintballs from rolling through them from the force of gravity. When the marker is fired, the air pressure pushes the ball through the bore, causing it to compress enough to pass through. Paintballs have varying diameters depending on a number of factors; this type of ball detent must be sized correctly to avoid compressing the paintball too much, causing it to burst. If a too large sizer is selected, balls may roll through it. The cartridge and elastic rubber protrusion type detents are primarily used for open bolt markers, or on closed bolt markers to prevent double feeding (feeding more than one ball when the bolt is open for loading). Closed bolt markers generally use the constriction method to prevent "roll outs". A roll out is a frustrating malfunction where the ball completely rolls out of the barrel, causing no paintball to be fired when the trigger is pulled. A partial roll out is when the ball rolls partially through the barrel, causing reduced velocity.
46
Beale number
Beale number In mechanical engineering, the Beale number is a parameter that characterizes the performance of Stirling engines. It is often used to estimate the power output of a Stirling engine design. For engines operating with a high temperature differential, typical values for the Beale number range from ( 0.11 ) to ( 0.15 ); where a larger number indicates higher performance.
Definition The Beale number can be defined in terms of a Stirling engine's operating parameters:
where: • • • •
Bn is the Beale number Wo is the power output of the engine (watts) P is the mean average gas pressure (Pa) or (MPa, if volume is in cm3) V is swept volume of the expansion space (m3) or (cm3, if pressure is in MPa)
• F is the engine cycle frequency (Hz)
Estimating Stirling power To estimate the power output of an engine, nominal values are assumed for the Beale number, pressure, swept volume and frequency, then the power is calculated as the product of these parameters, as follows:
External links • Stirling Engine Performance Calculator [1]
References [1] http:/ / www. bekkoame. ne. jp/ ~khirata/ academic/ simple/ simplee. htm
47
Bearing surface
Bearing surface A bearing surface is a mechanical engineering term that refers to the area of contact between two objects. It usually is used in reference to bolted joints and bearings, but can be applied to a wide variety of engineering applications. On a screw the bearing area loosely refers to the underside of the head.[1] Strictly speaking, the bearing area refers to the area of the screw head that directly bears on the part being fastened.[2] For a cylindrical bearing it is the projected area perpendicular to the applied force.[3] On a spring the bearing area refers to the amount of area on the top or bottom surface of the spring in contact with the constraining part.[4] The ways of machine tools, such as dovetail slides, box ways, prismatic ways, and other types of machine slide are also bearing surfaces.
References [1] Smith 1990, p. 38. [2] Fastener terms (http:/ / www. canadianstainless. ca/ page9. html), , retrieved 2009-06-29. [3] Low & Bevis 1908, p. 115. [4] Helical Compression Spring Terminology (http:/ / www. masterspring. com/ technical_resources/ helical_compression_spring_terminology/ default. html), , retrieved 2009-06-29.
Bibliography • Low, David Allan; Bevis, Alfred William (1908), Manual of machine drawing and design (http://books.google. com/?id=acYJAAAAIAAJ) (Revised ed.), Longmans, Green, and co. • Smith, Carroll (1990), Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook (http://books.google. com/?id=A81HmmRCN7YC), MotorBooks/MBI Publishing Company, ISBN 0879384069.
48
Bellcrank
49
Bellcrank A bell crank is a type of crank that changes motion through an angle. The angle can be any angle from 0 to 360 degrees, although 90 degrees and 180 degrees are common. The name comes from its first use, changing the vertical pull on a rope to a horizontal pull on the striker of a bell, used for calling staff in large houses or commercial establishments. A typical 90 degree bell crank consists of an "L" shaped crank pivoted where the two arms of the L meet. Moving rods (or cables or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivot point, pulling on the other arm.
An example of a bell crank mechanism modeled using computer aided design.
A typical 180 degree bell crank consists of a straight bar pivoted in the center. When one arm is pulled or pushed, the bar rotates around the pivot point, pulling or pushing on the other arm. Changing the length of the arms changes the mechanical advantage of the system. Many applications do not change the direction of motion, but instead to amplify a force "in line", which a bell crank can do in a limited space. There is a tradeoff between range of motion, linearity of motion, and size. The greater the angle traversed by the crank, the more non-linear the motion becomes (the more the motion ratio changes).
1920s car mechanical braking system, relying on a number of bellcranks to link the pullrods
Bellcranks are often used in aircraft contol systems to connect the pilot's controls to the control surfaces. For example: on light aircraft, the rudder often has a bellcrank whose pivot point is the rudder hinge. A cable connects the pilot's rudder pedal to one side of the bellcrank. When the pilot pushes on the rudder pedal, the rudder rotates on its hinge. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in the opposite direction. Bellcranks are also seen in automotive applications, as part of the linkage connecting the throttle pedal to the carburetor, and connecting the brake pedal to the master brake cylinder.
External links • Bell Crank [1]
References [1] http:/ / linesanddots. net/ mechanisms/ pages/ bellcrank. html
Bimetallic strip
50
Bimetallic strip A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases brass instead of copper. The strips are joined together throughout their length by riveting, brazing or welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.
Diagram of a bimetallic strip showing how the difference in thermal expansion in the two metals leads to a much larger sideways displacement of the strip
The sideways displacement of the strip is much larger than the small lengthways expansion in either of the two metals. This effect is used in a range of mechanical and electrical devices. In some applications the bimetal strip is used in the flat form. In others, it is wrapped into a coil for compactness. The greater length of the coiled version gives improved sensitivity.
A bimetallic coil from a thermometer reacts to the heat from a lighter, by uncoiling and then coiling back up when the lighter is removed.
History The earliest surviving bimetallic strip was made by the eighteenth-century clockmaker John Harrison who is generally credited with its invention. He made it for his third marine chronometer (H3) of 1759 to compensate for temperature-induced changes in the balance spring.[1] It should not be confused with his bimetallic mechanism for correcting for thermal expansion in the gridiron pendulum. His earliest examples had two individual metal strips joined by rivets but he also invented the later technique of directly fusing molten brass onto a steel substrate. A strip of this type was fitted to his last timekeeper, H5. Harrison's invention is recognized in the memorial to him in Westminster Abbey, England.
Applications
John Harrison's Memorial in Westminster Abbey, London
Bimetallic strip
Clocks Mechanical clock mechanisms are sensitive to temperature changes which lead to errors in time keeping. A bimetallic strip is used to compensate for this in some mechanisms. The most common method is to use a bimetallic construction for the circular rim of the balance wheel. As the spring controlling the balance becomes weaker with increasing temperature, so the balance becomes smaller in diameter to keep the period of oscillation (and hence timekeeping) constant.
Thermostats In the regulation of heating and cooling, thermostats that operate over a wide range of temperatures are used. In these, one end of the bimetal strip is mechanically fixed and attached to an electrical power source, while the other (moving) end carries an electrical contact. In adjustable thermostats another contact is positioned with a regulating knob or lever. The position so set controls the regulated temperature, called the set point. Some thermostats use a mercury switch connected to both electrical leads. The angle of the entire mechanism is adjustable to control the set point of the thermostat. Depending upon the application, a higher temperature may open a contact (as in a heater control) or it may close a contact (as in a refrigerator or air conditioner). The electrical contacts may control the power directly (as in a household iron) or indirectly, switching electrical power through a relay or the supply of natural gas or fuel oil through an electrically operated valve. In some natural gas heaters the power may be provided with a thermocouple that is heated by a pilot light (a small, continuously burning, flame). In devices without pilot lights Thermostat with bimetal coil at (2) for ignition (as in most modern gas clothes dryers and some natural gas heaters and decorative fireplaces) the power for the contacts is provided by reduced household electrical power that operates a relay controlling an electronic ignitor, either a resistance heater or an electrically powered spark generating device.
Thermometers A direct indicating dial thermometer (such as a patio thermometer or a meat thermometer) uses a bimetallic strip wrapped into a coil. One end of the coil is fixed to the housing of the device and the other drives an indicating needle. A bimetallic strip is also used in a recording thermometer.
Heat engines Simple toys have been built which demonstrate how the principle can be used to drive a heat engine.
Electrical devices Bimetal strips are used in miniature circuit breakers to protect circuits from excess current. A coil of wire is used to heat a bimetal strip, which bends and operates a linkage that unlatches a spring-operated contact. This interrupts the circuit and can be reset when the bimetal strip has cooled down. Bimetal strips are also used in time-delay relays, lamp flashers, and fluorescent lamp starters. In some devices the current running directly through the bimetal strip is sufficient to heat it and operate contacts directly.
51
Bimetallic strip
52
Calculations Curvature of a Bimetallic Beam:
Where
and
are the Young's Modulus and height of Material One and
and height of Material Two.
and
are the Young's Modulus
is the misfit strain, calculated by:
Where α1 is the Coefficient of Thermal Expansion of Material One and α2 is the Coefficient of Thermal Expansion of Material Two. ΔT is the current temperature minus the reference temperature (the temperature where the beam has no flexure).[2] [3]
External links • Video of a circular bimetalic wire powering a small motor with iced water [4]. Accessed February 2011.
Notes [1] Sobel, Dava (1995). Longitude. London: Fourth Estate. pp. 103. ISBN 0-00-721446-4. "One of the inventions Harrison introduced in H-3... is called... a bi-metallic strip." [2] Clyne, TW. “Residual stresses in surface coatings and their effects on interfacial debonding.” Key Engineering Materials (Switzerland). Vol. 116-117, pp. 307-330. 1996 [3] Timoshenko, J. Opt. Soc. Am. 11, 233 (1925) [4] http:/ / www. youtube. com/ watch?v=-a0u4Lw1YEY& feature=fvst
Block and bleed manifold A block and bleed manifold is a hydraulic manifold that combines one or more block/isolate valves, usually ball valves, and one or more bleed/vent valves, usually ball or needle valves, into one component, for interface with other components (pressure measurement transmitters, gauges, switches, etc.) of a hydraulic (fluid) system. The purpose of the block and bleed manifold is to isolate or block the flow of fluid in the system, so the fluid from upstream of the manifold does not reach other components of the system that are downstream, then bleed off or vent the remaining fluid from the system on the downstream side of the manifold. For example, a block and bleed manifold would be used to stop the flow of fluids to some component, then vent the fluid from that component’s side of the manifold, in order to effect some kind of work (maintenance/repair/replacement) on that component. A block and bleed manifold with one block valve and one bleed valve is also known as an isolation valve or block and bleed valve; a block and bleed manifold with multiple valves is also known as an isolation manifold. Also used in combustionable gas trains in many industrial applications. Double Block and Bleed Valves replace existing traditional techniques employed by pipeline engineers to generate a double block and bleed configuration in the pipeline. Cartridge Type Standard Length Double Block and Bleed Valves have a patented design which incorporates two ball valves and a bleed valve into one compact cartridge type unit with ANSI B16.5 tapped flanged connections. The major benefit of this design configuration is that the valve has the same face-to-face dimension as a single block ball valve (as specified in API 6D and ANSI B16.10), which means the valve can easily be installed into an existing pipeline without the need for any pipeline re-working. Three Piece Non Standard Length Double Block and Bleed Valves (DBB Valves) feature the traditional style of flange-by-flange type valve and is available with ANSI B16.5 flanges, hub connections and welded ends to suit the
Block and bleed manifold pipeline system it is to be installed in. It features all the benefits of the single unit DBB valve, with the added benefit of a bespoke face-to-face dimension if required. The single unit DBB design also has operational advantages, there are significantly fewer potential leak paths within the double block and bleed section of the pipeline. Because the valves are full bore with an uninterrupted flow orifice they have got a negligible pressure drop across the unit. The pipelines where these valves are installed can also be pigged without any problems. There are several advantages in using a Double Block and Bleed Valve. Significantly, because all the valve components are housed in a single unit, the space required for the installation is dramatically reduced thus freeing up room for other pieces of essential equipment. Considering the operations and procedures executed before an operator can intervene, the Double Block and Bleed manifold offers further advantages over the traditional hook up. Due to the volume of the cavity between the two balls being so small, the operator is afforded the opportunity to evacuate this space efficiently thereby quickly establishing a safe working environment.
Blood viscoelasticity Blood Viscoelasticity is a property of human blood that is primarily due to the elastic energy that is stored in the deformation of red blood cells as the heart pumps the blood through the body. The energy transferred to the blood by the heart is partially stored in the elastic structure, another part is dissipated by viscosity, and the remaining energy is stored in the kinetic motion of the blood. When the pulsation of the heart is taken into account, an elastic regime becomes clearly evident. It has been shown that the previous concept of blood as a purely viscous fluid was inadequate since blood is not an ordinary fluid. Blood can more accurately be described as a fluidized suspension of elastic cells.
History In early theoretical work, blood was treated as a non-Newtonian viscous fluid. Initial studies had evaluated blood during steady flow and later, using oscillating flow.[1] Professor George B. Thurston, of the University of Texas, first presented the idea of blood being viscoelastic in 1972. The previous studies that looked at blood in steady flow showed negligible elastic properties because the elastic regime is stored in the blood during flow initiation and so its presence is hidden when a flow reaches steady state. The early studies used the properties found in steady flow to derive properties for unsteady flow situations.[2] [3] Advancements in medical procedures and devices required a better understanding of the mechanical properties of blood.
Viscoelasticity of Blood The red blood cells occupy about half of the volume of blood and possess elastic properties. This elastic property is the largest contributing factor to the viscoelastic behavior of blood. The large volume percentage of red blood cells at a normal hematocrit level leaves little room for cell motion and deformation without interacting with a neighboring cell. Calculations have shown that the maximum volume percentage of red blood cells without deformation is 58% which is in the range of normally occurring levels.[4] Due to the limited space between red blood cells, it is obvious that in order for blood to flow, significant cell to cell interaction will play a key role. This interaction and tendency for cells to aggregate is a major contributor to the viscoelastic behavior of blood. Red blood cell deformation and aggregation is also coupled with flow induced changes in the arrangement and orientation as a third major factor in its viscoelastic behavior.[5] [6] Other factors contributing to the viscoelastic properties of blood is the plasma viscosity, plasma composition, temperature, and the rate of flow or shear rate. Together, these factors make human blood viscoelastic, non-Newtonian, and thixotropic.[7]
53
Blood viscoelasticity
54
When the red cells are at rest or at very small shear rates, they tend to aggregate and stack together in an energetically favorable manner. The attraction is attributed to charged groups on the surface of cells and to the presence of fibrinogen and globulins.[8] This aggregated configuration is an arrangement of cells with the least amount of deformation. With very low shear rates, the viscoelastic property of blood is dominated by the aggregation and cell deformability is relatively insignificant. As the shear rate increases the size of the aggregates begins to decrease. With a further increase in shear rate, the cells will rearrange and orient to provide channels for the plasma to pass through and for the cells to slide. In this low to medium shear rate range, the cells wiggle with respect to the neighboring cells allowing flow. The influence of aggregation properties on the viscoelasticity diminish and the influence of red cell deformability begins to increase. As shear rates become large, red blood cells will stretch or deform and align with the flow. Cell layers are formed, separated by plasma, and flow is now attributed to layers of cells sliding on layers of plasma. The cell layer allows for easier flow of blood and as such there is a reduced viscosity and reduced elasticity. The viscoelasticity of the blood is dominated by the deformability of the red blood cells.
Modeling Viscoelasticity of Blood Maxwell Model If a small cubical volume of blood is considered, with forces being acted upon it by the heart pumping and shear forces from boundaries. The change in shape of the cube will have 2 components: • Elastic deformation which is recoverable and is stored in the structure of the blood. • Slippage which is associated with a continuous input of viscous energy. When the force is removed, the cube would recover partially. The elastic deformation is reversed but the slippage is not. This explains why the elastic portion is only noticeable in unsteady flow. In steady flow, the slippage will continue to increase and the measurements of non time varying force will neglect the contributions of the elasticity. Figure 1 can be used to calculate the following parameters necessary for the evaluation of blood when a force is exerted.
Figure 1 - Displacement due to Elastic and Viscous Effects
Shear Stress: Shear Strain: Shear Rate: A sinusoidal time varying flow is used to simulate the pulsation of a heart. A viscoelastic material subjected to a time varying flow will result in a phase variation between and represented by . If , the material is a
Blood viscoelasticity
55
purely elastic because the stress and strain are in phase, so that the response of one caused by the other is immediate. If = 90°, the material is a purely viscous because strain lags behind stress by 90 degrees. A viscoelastic material will be somewhere in between 0 and 90 degrees. The sinusoidal time variation is proportional to
. Therefore the size and phase relation between the stress,
strain, and shear rate are described using this relationship and a radian frequency,
were
is the
frequency in Hertz. Shear Stress: Shear Strain: Shear Rate: The components of the complex shear stress can be written as:
Where
is the viscous stress and
is the elastic stress. The complex coefficient of viscosity [9]
taking the ratio of the complex shear stress and the complex shear rate
can be found by
:
Similarly, the complex dynamic modulus G can be obtained by taking the ratio of the complex shear stress to the complex shear strain.
Relating the equations to common viscoelastic terms we get the storage modulus,G', and the loss modulus,G".
A viscoelastic Maxwell material model is commonly used to represent the viscoelastic properties of blood. It uses purely viscous damper and a purely elastic spring connected in series. Analysis of this model gives the complex viscosity in terms of the dashpot constant and the spring constant.
Figure 2 - Schematic of Maxwell model using one dash-pot and one spring connected in series
Oldroyd-B model One of the most frequently used constitutive models for the viscoelasticity of blood is the Oldroyd-B model. There are several variations of the Oldroyd-B non-Newtonian model characterizing shear thinning behavior due to red blood cell aggregation and dispersion at low shear rate. Here we consider a three-dimensional Oldroyd-B model coupled with the momentum equation and the total stress tensor.[10] A non Newtonian flow is used which insures that the viscosity of blood is a function of vessel diameter d and hematocrit h. In the Oldroyd-B model, the relation between the shear stress tensor B and the orientation stress tensor A is given by:
where D/Dt is the material derivative, V is the velocity of the fluid, C1, C2, g, as follows:
are constants. S and B are defined
Blood viscoelasticity
56
Viscoelasticity of Red Blood Cells Red blood cells are subjected to intense mechanical stimulation from both blood flow and vessel walls, and their rheological properties are important to their effectiveness in performing their biological functions in the microcirculation.[11] Red blood cells by themselves have been shown to exhibit viscoelastic properties. There are several methods used to explore the mechanical properties of red blood cells such as: • micropipette aspiration[12] • micro indentation • optical tweezers • high frequency electrical deformation tests These methods worked to characterize the deformability of the red blood cell in terms of the shear, bending, area expansion moduli, and relaxation times.[13] However, they were not able to explore the viscoelastic properties. Other techniques have been implemented such as photoacoustic measurements. This technique uses a single-pulse laser beam to generate a photoacoustic signal in tissues and the decay time for the signal is measured. According to the theory of linear viscoelasticity, the decay time is equal to the viscosity-elasticity ratio and therefore the viscoelasticity characteristics of the red blood cells could be obtained.[14] Another experimental technique used to evaluate viscoelasticity consisted of using ferriomagnetic beads bonded to a cells surface. Forces are then applied to the magnetic bead using optical magnetic twisting cytometry which allowed researchers to explore the time dependent responses of red blood cells.[15] is the mechanical torque per unit bead volume (units of stress) and is given by: where H is the applied magnetic twisting field,
is the angle of the bead’s magnetic moment relative to the original
magnetization direction, and c is the bead constant which is found by experiments conducted by placing the bead in a fluid of known viscosity and applying a twisting field. Complex Dynamic modulus G can be used to represent the relations between the oscillating stress and strain:
where
is the storage modulus and
where
and
is the loss modulus:
are the amplitudes of stress and strain and
is the phase shift between them.
Blood viscoelasticity
57
From the above relations, the components of the complex modulus are determined from a loop that is created by comparing the change in torque with the change in time which forms a loop when represented graphically. The limits of - d(t) loop and the area, A, bounded by the
- d(t) loop, which
represents the energy dissipation per cycle, are used in the calculations. The phase angle , storage modulus G', and loss modulus G then become:
Figure 3 - Torque vs. Displacement graph showing viscoelastic behavior
where d is the displacement. The hysteresis shown in figure 3 represents the viscoelasticity present in red blood cells. It is unclear if this is related to membrane molecular fluctuations or metabolic activity controlled by intracellular concentrations of ATP. Further research is needed to fully explore these interaction and to shed light on the underlying viscoelastic deformation characteristics of the red blood cells.
Effects of Blood Vessels When looking at viscoelastic behavior of blood in vivo, it is necessary to also consider the effects of arteries, capillaries, and veins. The viscosity of blood has a primary influence on flow in the larger arteries, while the elasticity, which resides in the elastic deformability of red blood cells, has primary influence in the arterioles and the capillaries.[16] Understanding wave propagation in arterial walls, local hemodynamics, and wall shear stress gradient is important in understanding the mechanisms of cardiovascular function. Arterial walls are anisotropic and heterogeneous, composed of layers with different bio-mechanical characteristics which makes understanding the mechanical influences that arteries contribute to blood flow very difficult.[17]
Blood viscoelasticity
Medical Reasons for Better Understanding From a medical standpoint, the importance of studying the viscoelastic properties of blood becomes evident. With the development of cardiovascular prosthetic devices such as heart valves and blood pumps, the understanding of pulsating blood flow in complex geometries is required. A few specific examples are the effects of viscoelasticity of blood and its implications for the testing of a pulsatile Blood Pumps.[18] Strong correlations between blood viscoelasticity and regional and global cerebral blood flow during cardiopulmonary bypass have been documented.[19] This has also led the way for developing a blood analog in order to study and test prosthetic devices. The classic analog of glycerin and water provides a good representation of viscosity and inertial effects but lacks the elastic properties of real blood. One such blood analog is an aqueous solution of Xanthan gum and glycerin developed to match both the viscous and elastic components of the complex viscosity of blood.[20] Normal red blood cells are deformable but many conditions, such as sickle cell disease, reduce their elasticity which makes them less deformable. Red blood cells with reduced deformability have increasing impedance to flow, leading to an increase in red blood cell aggregation and reduction in oxygen saturation which can lead to further complications. The presence of cells with diminished deformability, as is the case in sickle cell disease, tends to inhibit the formation of plasma layers and by measuring the viscoelasticity, the degree of inhibition can be quantified.[21]
References [1] J. Womersley, Method for Calculation of Velocity, Rate of Flow and Viscous Drag in Arteries when the Pressure Gradient is Known, Amer. Journal Physiol. 1955, 127, 553-563. [2] G. Thurston, Viscoelasticity of human blood, Biophysical Journal, 1972, 12, 1205–1217. [3] G. Thurston, The Viscosity and Viscoelasticity of Blood in Small Diameter Tubes, Microvascular Research, 1975, 11, 133-146. [4] A. Burton, Physiology and Biophysics of Circulation, Year Book Medical Publisher Inc., Chicago, 1965, p. 53. [5] G. Thurston and Nancy M. Henderson, Effects of flow geometry on blood Viscoelasticity, Biorheology 2006, 43, 729–746 [6] G. Thurston, Plasma Release – Cell Layering Theory for Blood Flow, Biorheology 1989, 26, 199–214 [7] G. Thurston, Plasma Rheological Parameters for the Viscosity, Viscoelasticity, and thixotropy of Blood, Biorheology 1979, 16, 149–162 [8] L. Pirkl and T. Bodnar, Numerical Simulation of Blood Flow Using Generalized Oldrroyd-B Model, European Conference on Computational Fluid Dynamics, 2010 [9] T. How, Advances in Hemodynamics and Hemorheology Vol. 1, JAI Press LTD., 1996, 1-32. [10] R. Bird, R. Armstrong, O. Hassager, Dynamics of Polymeric Liquids; Fluid Mechanic, 1987, 2, 493 - 496 [11] M. Mofrad, H. Karcher, and R. Kamm, Cytoskeletal mechanics: models and measurements, 2006, 71-83 [12] V. Lubarda and A. Marzani, Viscoelastic response of thin membranes with application to red blood cells, Acta Mechanica, 2009, 202, 1–16 [13] D. Fedosov, B. Caswell, and G. Karniadakis, Coarse-Grained Red Blood Cell Model with Accurate Mechanical Properties, Rheology and Dynamics, 31st Annual International Conference of the IEEE EMBS, Minneapolis, Minnesota, 2009 [14] J. Li, Z. Tang, Y. Xia, Y. Lou, and G. Li, Cell viscoelastic characterization using photoacoustic measurement, Journal of Applied Physics, 2008, 104 [15] M. Marinkovic, K. Turner, J. Butler, J. Fredberg, and S. Suresh, Viscoelasticity of the Human Red Blood Cell, American Journal of Physiology - Cell Physiology 2007, 293, 597-605. [16] A. Ündar, W. Vaughn, and J. Calhoon, The effects of cardiopulmonary bypass and deep hypothermic circulatory arrest on blood viscoelasticity and cerebral blood flow in a neonatal piglet model, Perfusion 2000, 15, 121–128 [17] S. Canic, J. Tambaca, G. Guidoboni, A. Mikelic, C Hartley, and D Rosenstrauch, Modeling Viscoelastic Behavior of Arterial Walls and their Interaction with Pulsatile Blood Flow, Journal of Applied Mathematics, 2006, 67, 164–193 [18] J. Long, A. Undar, K. Manning, and S. Deutsch, Viscoelasticity of Pediatric Blood and its Implications for the Testing of a Pulsatile Pediatric Blood Pump, American Society of Internal Organs, 2005, 563 - 566 [19] A. Undar and W. Vaughn, Effects of Mild Hypothermic Cardiopulmonary Bypass on Blood Viscoelasticity in Coronary Artery Bypass Grafting Patients, Artificial Organs 26(11), 964–966 [20] K. Brookshier and J. Tarbell, Evaluation of a transparent blood analog fluid: aqueous xanthan gum/glycerin, Biorheology, 1993, 2, 107-16 [21] G. Thurston, N. Henderson, and M. Jeng, Effects of Erythrocytapheresis Transfusion on the Viscoelasticity of Sickle Cell Blood, Clinical Hemorheology and Microcirculation 30 (2004) 61–75
58
Bolted joint
59
Bolted joint
Bolted joint in vertical cutaway
Screw joint
Stud joint
Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads. There are two main types of bolted joint designs. In one method the bolt is tightened to a calculated clamp load, usually by applying a measured torque load. The joint will be designed such that the clamp load is never overcome by the forces acting on the joint (and therefore the joined parts see no relative motion). The other type of bolted joint does not have a designed clamp load but relies on the shear strength of the bolt shaft. This may include clevis linkages, joints that can move, and joints that rely on a locking mechanism (like lock washers, thread adhesives, and lock nuts). This type of joint design provides several properties: • Greater preloads in bolted joints reduce the fatigue loading of the fastener. • For cyclic loads, the fastener is not subjected to the full amplitude of the load; as a result, the fastener's fatigue life can be increased or—if the material exhibits an endurance limit—extended indefinitely.[1] • As long as the external loads on a joint don't exceed the clamp load, the fastener is not subjected to any motion and will not come loose, obviating the need for locking mechanisms.
Theory The clamp load, also called preload, of a fastener is created when a torque is applied, and is generally a percentage of the fastener's proof strength; a fastener is manufactured to various standards that define, among other things, its strength and clamp load. Torque charts are available to identify the required torque for a fastener based on its property class or grade. When a fastener is tightened, it is stretched and the parts being fastened are compressed; this can be modeled as a spring-like assembly that has a non-intuitive distribution of strain. External forces are designed to act on the fastened parts rather than on the fastener, and as long as the forces acting on the fastened parts do not exceed the clamp load, the fastener is not subjected to any increased load.
Bolted joint
However, this is a simplified model that is only valid when the fastened parts are much stiffer than the fastener. In reality, the fastener is subjected to a small fraction of the external load even if that external load does not exceed the clamp load. When the fastened parts are less stiff than the fastener (soft, compressed gaskets for example), this model breaks down; the fastener is subjected to a load that is the sum of the preload and the external load. In some applications, joints are designed so that the fastener eventually fails before more expensive components do. In this case, replacing an existing fastener with a higher strength fastener can result in equipment damage. Thus, it is generally good practice to replace old fasteners with new fasteners of the same grade.
Thread engagement Thread engagement is the length or number of threads that are engaged between the screw and the female threads. Screws are designed so that the shank fails before the threads, but for this to hold true, a minimum thread engagement must be used. The following equation defines this minimum thread engagement:[2]
Where Le is the thread engagement length, At is the tensile stress area, D is the major diameter of the screw, and p is the pitch. This equation only holds true if the screw and female thread materials are the same. If they are not the same, then the following equations can be used to determine the additional thread length that is required:[2]
Where Le2 is the new required thread engagement. While these formulas give absolute minimum thread engagement, many industries specify that bolted connections be at least fully engaged. For instance, the FAA has determined that in general cases, at least one thread must be protruding from any bolted connection. [3]
Setting the torque Engineered joints require the torque to be accurately set. Setting the torque for fasteners is commonly achieved using a torque wrench.[4] The required torque value for a particular fastener application may be quoted in the published standard document or defined by the manufacturer. The clamp load produced during tightening is higher than 75% of the fastener's proof load.[4] To achieve the benefits of the preloading, the clamping force must be higher than the joint separation load. For some joints, multiple fasteners are required to secure the joint; these are all hand tightened before the final torque is applied to ensure an even joint seating.
60
Bolted joint The torque value is dependent on the friction produced by the threads and by the fastened material's contact with both the fastener head and the associated nut. Moreover, this friction can be affected by the application of a lubricant or any plating (e.g. cadmium or zinc) applied to the threads, and the fastener's standard defines whether the torque value is for dry or lubricated threading, as lubrication can reduce the torque value by 15% to 25%; lubricating a fastener designed to be torqued dry could over-tighten it, which may damage threading or stretch the fastener beyond its elastic limit, thereby reducing its clamping ability. Also, if the fastener rather than its associated nut is torqued, then the torque value should be increased[5] to compensate for the additional friction; fasteners should only be torqued if they are fitted in clearance holes. Torque wrenches do not give a direct measurement of the clamping force in the screw, and indeed much of the force applied is lost just to overcoming friction. More accurate methods for setting the clamping force rely on defining or measuring the screw extension; for instance, measurement of the angular rotation of the nut can serve as the basis for defining screw extension on thread pitch.[6] Measuring the screw extension directly allows the clamping force to be very accurately calculated. This can be achieved using a dial test indicator, reading deflection at the fastener tail, using a strain gauge, or ultrasonic length measurement. There is no simple method to measure the tension of a fastener already in place other than to tighten it and identify at which point the fastener starts moving. This is known as re-torqueing. An electronic torque wrench can be used on the fastener in question, so that the torque applied can be constantly measured as it is slowly increased in magnitude; when the fastener starts moving (that is, becoming tightened) the required torque magnitude briefly drops sharply, and this drop-off point is considered the measure of tension. Recent developments enable tensions to be estimated by using ultrasonic testing. Another way to ensure correct tension (mainly in steel erecting) involves the use of crush-washers. These are washers that have been drilled and filled with orange RTV. When the orange rubber strands appear, the tension is correct. Large-volume users (such as auto makers) frequently use computer controlled nut drivers. With such machines, the computer in effect plots a graph of the torque exerted. Once the torque reaches a set maximum torque chosen by the designer, the machine stops. Such machines are often used to fit wheelnuts and normally tighten all the wheel nuts simultaneously.
Failure modes The most common mode of failure is overloading: Operating forces of the application produce loads that exceed the clamp load, causing the joint to loosen over time or fail catastrophically. Over-torquing might cause failure by damaging the threads and deforming the fastener, though this can happen over a very long time. Under-torquing can cause failures by allowing a joint to come loose, and it may also allow the joint to flex and thus fail under fatigue. Brinelling may occur with poor quality washers, leading to a loss of clamp load and subsequent failure of the joint. Other modes of failure include corrosion, embedment, and exceeding the shear stress limit. Bolted joints may be used intentionally as sacrificial parts, which are intended to fail before other parts, as in a shear pin.
61
Bolted joint
62
Locking mechanisms Locking mechanisms keep bolted joints from coming loose. They are required when vibration or joint movement will cause loss of clamp load and joint failure, and in equipment where the security of bolted joints is essential. • Two nuts, tightened on each other. In this application a thinner nut should be placed adjacent to the joint, and a thicker nut tightened onto it. The thicker nut applies more force to the joint, first relieving the force on the threads of the thinner nut and then applying a force in the opposite direction. In this way the thicker nut presses tightly on the side of the threads away from the joint, while the thinner nut presses on the side of the threads nearest the joint, tightly locking the two nuts against the threads in both directions.[7]
Measurement of frictional torque of threads in bolt
Bolted joints in an automobile wheel. Here the outer fasteners are four studs with three of the four nuts that secure the wheel. The central nut (with locking cover and cotter pin) secures the wheel bearing to the spindle.
The torque is applied by means of suspending the weights on one end of the rope and other end is wound around the head of the fastener and tied to the projection. The amount of load is increased gradually until the fastener starts rotating. The applied load is then calculated by adding up the weights. This is the load that is required to overcome the friction between the threads. Similarly, the net applied torque is calculated by multiplying the resultant load by the radius of the fastener's head. In another method, the torque is applied to the nut by an electromagnetic force. A specially designed gripper is used to grip the nut. A bar magnet is mounted on the gripper, and the gripper is then surrounded by a coil of wire through which alternating current is passed. As the magnetic field from the permanent magnet interacts with the field created by the coil, the permanent magnet (and thus the nut) is subjected to a torque. This is quite similar to the construction of an electric motor, and hence a motor can be directly used to provide the torque. A stepper motor can be used so that the torque is provided in steps, each of which causes a small, measurable angular displacement in the nut from which the torque can be calculated. The discrete torques can be added to get the net torque consumed in displacing the nut from one end of the fastener to the desired location. This is the torque that is required to overcome the friction between the threads.
Bolt banging Bolt banging occurs in buildings when bolted joints slip into bearing under load, thus causing a loud and potentially frightening noise resembling a rifle shot that is not, however, of structural significance and does not pose any threat to occupants.[8]
International standards • SA-193 • SA-194 • SA-320
Bolted joint
References Notes [1] Collins, p. 481. [2] Minimum Thread Engagement Formula and Calculation ISO (http:/ / www. engineersedge. com/ thread_strength/ thread_minimum_length_engagement. htm), , retrieved 2010-02-08. [3] http:/ / rgl. faa. gov/ Regulatory_and_Guidance_Library/ rgAdvisoryCircular. nsf/ 0/ 99c827db9baac81b86256b4500596c4e/ $FILE/ Chapter%2007. pdf [4] Oberg et al. 2004, p. 1495. [5] AIPS 01-02-008: "Bolt Torque" [6] Oberg et al. 2004, p. 1499. [7] "The use of two nuts to prevent self loosening" (http:/ / www. boltscience. com/ pages/ twonuts. htm). boltscience.com. . [8] "Steel Interchange: 'Banging Bolts'" (http:/ / www. modernsteel. com/ steelinterchange_details. php?id=516), MSC: Modern Steel Construction.
Bibliography • Collins, Jack A.; Staab, George H.; Busby, Henry R. (2002), Mechanical Design of Machine Elements and Machines, Wiley, ISBN 0471033073. • Oberg, Erik; Jones, Franklin D.; McCauley, Christopher J.; Heald, Ricardo M. (2004), Machinery's Handbook (27th ed.), Industrial Press, ISBN 978-0831127008.
External links • Bolts - AISC | Home (http://www.aisc.org/SearchTaxonomy/TechnicalLibraryResults.aspx?topic=388) • AISC THE BANGING BOLT SYNDROME (http://www.aisc.org/bookstore/itemRedirector.aspx?id=14854) • AISC BANGING BOLTS— ANOTHER PERSPECTIVE (http://www.aisc.org/bookstore/itemRedirector. aspx?id=14858) • Bolt Science - The Jost Effect (http://www.boltscience.com/pages/josteffect.htm) • Threaded Fasteners - Tightening to Proper Tension (http://assist.daps.dla.mil/quicksearch/basic_profile. cfm?ident_number=70455), US Department of Defense document MIL-HDBK-60, 2.6MB pdf. • NASA Reference Publication 1228 Fastener Design Manual (http://gltrs.grc.nasa.gov/reports/1990/RP-1228. pdf) • Mechanics of screws (http://www.mech.uwa.edu.au/DANotes/threads/mechanics/mechanics.html) • FAA Advisory Circular 43.13-1B (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular. nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter 07.pdf), Paragraph 7-37 "Grip Length"
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Brake shoe
64
Brake shoe A brake shoe is the part of a braking system which carries the brake lining in the drum brakes used on automobiles, or the brake block in train brakes and bicycle brakes.
Automobile drum brake The brake shoe carries the brake lining, which is riveted or glued to the shoe. When the brake is applied, the shoe moves and presses the lining against the inside of the drum. The friction between lining and drum provides the braking effort. Energy is dissipated as heat. Modern cars have disc brakes all round, or discs at the front and drums at the rear. An advantage of discs is that they can dissipate heat more quickly than drums so there is less risk of overheating.
Drum brake shoes and linings
The reason for retaining drums at the rear is that a drum is more effective than a disc as a parking brake.
Railway tread brake The brake shoe carries the brake block. The block was originally made of wood but is now usually cast iron. When the brake is applied, the shoe moves and presses the block against the tread of the wheel. As well as providing braking effort this also "scrubs" the wheel and keeps it clean. Tread brakes on passenger trains have now largely been superseded by disc brakes.
Bicycle rim brake This comprises a pair of rectangular open boxes which are mounted on the brake calipers of a bicycle and that hold the brake blocks which rub on the rim of a bicycle wheel to slow the bicycle down or stop it.
Cataloguing There are different systems for the cataloguing of brake shoes. The most frequently used system in Europe is the WVA numbering system.[1]
References [1] WVA numbering system (http:/ / www. vri. de/ 3. html)
Break-in (mechanical run-in)
Break-in (mechanical run-in) Break-in or breaking in, also known as run-in or running in, is the procedure of conditioning a new piece of equipment by giving it an initial period of running, usually under light load, but sometimes under heavy load or normal load. It is generally a process of moving parts wearing against each other to produce the last small bit of size and shape adjustment that will settle them into a stable relationship for the rest of their working life. One of the most common examples of break-in is engine break-in for petrol engines and diesel engines.
Engine break-in A new engine is broken in by following specific driving guidelines during the first few hours of its use. The focus of breaking in an engine is on the contact between the piston rings of the engine and the cylinder wall. There is no universal preparation or set of instructions for breaking in an engine. Most importantly, experts disagree on whether it is better to start engines on high or low power to break them in. While there are still consequences to an unsuccessful break-in, they are harder to quantify on modern engines than on older models. In general, people no longer break in the engines of their own vehicles after purchasing a car or motorcycle, because the process is done in production. It is still common, even today, to find that an owner's manual recommends gentle use at first (often specified as the first 500 or 1000 kilometers or miles). But it is usually only normal use without excessive demands that is specified, as opposed to light/limited use. For example, the manual will specify that the car be driven normally, but not in excess of the highway speed limit.
Goal The goal of modern engine break-ins is the settling of piston rings into an engine's cylinder wall. A cylinder wall is not perfectly smooth but has a deliberate slight roughness to help oil adhesion. As the engine is powered up, the piston rings between the pistons and cylinder wall will begin to seal against the wall's small ridges.[1] If the engine is powered up too quickly or not enough (depending on engine), the rings may grind against the ridges and wear them down. The tighter the piston rings are set in, the longer an engine is expected to last.[2]
Preparation There are important preparations which must be made before the actual process of running the engine. The break-in can take place either in the vehicle or on an engine stand. Each engine has specific preparation needs of its own due to factors such as the many different types of engine models, the vehicles it belongs to, and conflicting expert instructions. For example, each engine should be lubricated and run on oil specified by its designers which can be found in a manual.[3]
Process The main area of controversy among engine break-in instructions is whether to run the engine slowly or quickly to initiate the process. Those who promote raising the power settings steadily will recommend changing the engine setting from low to high powers as to not work the engine too hard and create excessive glazing on the cylinder wall (which would require the pistons to be removed and wall fixed). Other experts disagree and believe that to start the engine at a high power is the best way to effectively set in the pistons. The following are examples of how the two processes can be carried out:
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Break-in (mechanical run-in) Start high power Start with Revolutions per minute (rpm) between 2500 and 4000, and run the engine for about 20 minutes while watching so that the oil pressure does not get too high, which is dangerous. After changing oil and checking that the engine functions, drive using lower power settings.[1] A high power setting is relative to the vehicle type, so half as many rpm may be necessary if a car has a smaller cylinder wall. Start low power Setting will be around 1500 rpm, run for about half an hour while like the other method checking oil pressure and begin again should there be any over-boiling of the engine's coolant, which is a combination of air, oil, and water. Once this initial step is completed, drive in varying speeds on the road (or stand) by accelerating between speeds of 30 and 50 miles per hour.[4]
Consequences The following are consequences of a bad engine break-in:[1] 1. Oil will be allowed to gather in the cylinder wall, and a vehicle will use much more of it than necessary. 2. If a ring does not set into the grooves of the cylinder wall but creates friction against them each time an engine runs, the cylinder wall will be worn out. 3. Unsuccessfully setting piston rings into a cylinder wall will result in the necessity of new engine parts, or the entire engine depending on how extensive the damage is.
Modern versus older break-in regimens For many kinds of equipment (with automotive engines being the prime example), the time it takes to complete break-in procedures has decreased significantly from a number of days to a few hours, for several reasons. The main reason is that the factories in which they are produced are now capable of better machining and assembly. For example, it is easier to hold tighter tolerances now, and the average surface finish of a new cylinder wall has improved. Manufacturers decades ago were capable of such accuracy and precision, but not with as low a unit cost or with as much ease. Therefore, the average engine made today resembles, in some technical respects, the top-end custom work of back then.[5] For some equipment, break-in is now done at the factory, obviating end-user break-in. This is advantageous for several reasons. It is a selling point with customers who don't want to have to worry about break-in and want full performance "right out of the box". And it also aligns with the fact that compliance rates are always uncertain in the hands of end users. As with medical compliance or regulatory compliance, an authority can give all the instructions it wants, but there is no guarantee that the end user will follow them. The other reason for shorter break-in regimens today is that a greater amount of science has been applied to the understanding of break-in, and this has led to the realization that some of the old, long, painstaking break-in regimens were based on specious reasoning. People developed elaborate theories on what was needed and why, and it was hard to sift the empirical evidence in trying to test or confirm the theories. Anecdotal evidence and confirmation bias definitely played at least some part. Today engineers can confidently advise users not to put too much stock in old theories of long, elaborate break-in regimens. Some users will not give credence to the engineers and will stick to their own ideas anyway; but their careful break-in beliefs are still harmless and serve roughly like a placebo in allowing them to assure themselves that they've maximized the equipment's working lifespan through their due diligence.
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Break-in (mechanical run-in)
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Speakers and headphones Some speaker manufacturers recommend a period of break-in, for example by playing white or pink noise.
References [1] Aircooled.Net. "How to Break In a New or Rebuilt Engine - Aircooled.Net, Inc. (n.d.).” (http:/ / www. aircooled. net/ gnrlsite/ resource/ articles/ engnbrkn. htm) (accessed January 21, 2010). [2] NTNOA. "New Engine Break-in Procedure (n.d.)." (http:/ / www. ntnoa. org/ enginebreakin. htm) (accessed January 21, 2010). [3] Road & Track 51, no. 11: 152. "Technical correspondence." (http:/ / search. ebscohost. com/ login. aspx?direct=true& db=a9h& AN=3333174& site=ehost-live)(accessed January 19, 2010). [4] AERA. "BREAK-IN PROCEDURES FOR REMANUFACTURED ENGINES." (http:/ / www. aera. org/ downloads/ BIP. pdf) (accessed January 23, 2010). [5] Zelinski, Peter (14 December 2010), "Machining for Air Quality" (http:/ / www. mmsonline. com/ articles/ machining-for-air-quality), Modern Machine Shop (January 2011), .
Brinelling Brinelling is a material surface failure caused by contact stress that exceeds the material limit. This failure is caused by just one application of a load great enough to exceed the material limit. The result is a permanent dent or "brinell" mark. It is a common cause of roller bearing failures, and loss of preload in bolted joints when a hardened washer is not used. Engineers can use the Brinell hardness of materials in their calculations to avoid this mode of failure. A rolling element bearing's static load rating is defined to avoid this failure type. A similar-looking kind of damage is called false brinelling. This occurs when contacting bodies vibrate against each other in the presence of very small loads, which pushes lubricant out of the contact surface area, and the bearing assembly can not move far enough to redistribute the displaced lubricant. The result is a finely polished surface that resembles a brinell mark, but has not permanently deformed either contacting surface.
Failed steering hub swivel bearing
Built-up gun
Built-up gun The term built-up gun describes a construction technique for artillery barrels. An inner tube of metal which stretches most within its elastic limit enlarges under the pressure of confined powder gases to transmit stress to outer cylinders under tension.[1] Concentric metal cylinders and/or wire windings are assembled to minimize the weight required to resist the pressure of powder gases pushing a projectile out of the barrel. Built-up construction was the norm for guns mounted aboard 20th century Dreadnoughts and contemporary railway guns, coastal artillery, and siege guns through World War II.
Background Velocity and range of artillery vary directly with pressure of gunpowder or smokeless powder gasses pushing the shell out of a gun barrel; but a gun will be deformed or explode if chamber pressures strain a gun barrel beyond the elastic limit of the metal from which the barrel is made.[1] Thickness of homogeneous cast metal gun barrels reached a useful limit at approximately one-half caliber. Additional thickness Diagram illustrating arrangement of components of a built-up gun, in this case the British provided little practical benefit, since BL 6-inch Mark IV naval gun of the 1880s. higher pressures generated cracks from the bore before the outer portion of the cylinder could respond, and those cracks would extend outward during subsequent firings.[2] Claverino's 1876 treatise on the "Resistance of Hollow Cylinders" was published in Giornale d'Artigliera.[3] The concept was to give exterior portions of the gun initial tension, gradually decreasing toward the interior, while giving interior parts a normal state of compression by the outer cylinders and wire windings.[4] Theoretical maximum performance would be achieved if the inner cylinder forming the rifled bore were compressed to its elastic limit by surrounding elements while at rest before firing, and expanded to its elastic limit by internal gas pressure during firing.[5]
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Built-up gun
Nomenclature The innermost cylinder forming the chamber and rifled bore is called a tube or, with certain construction techniques, a liner. A second layer cylinder called the jacket extends rearward past the chamber to house the breechblock. The jacket usually extends forward through the areas of highest pressure, through the recoil slide, and may extend all the way to the muzzle. The forward part of the barrel may be tapered toward the muzzle because less strength is required for reduced pressures as the projectile nears the muzzle. This tapered portion of barrel is called the chase. Very large guns sometimes use shorter outer Abrupt diameter change steps on the tapered cylinders called hoops when manufacturing limitations make full chase indicate the forward extent of external length jackets impractical. Hoops forward of the slide are called chase tensioned cylinders. hoops.[6] The jacket or forward chase hoop may be flared outward in the form of a bell at the muzzle for extra strength to reduce splitting because the metal at that point is not supported on the forward end.[7] As many as four or five layers, or hoop courses, of successively tensioned cylinders have been used.[8] Layers are designated alphabetically as the "A" tube enclosed by the "B" jacket and chase hoops, enclosed by the "C" hoop course, enclosed by the "D" hoop course, etc. Individual hoops within a course are numbered from the breech forward as the B1 jacket, the B2 chase hoop, and then the C1 jacket hoop, the C2 hoop etc.[9] Successive hoop course joints are typically staggered and individual hoop courses use lap joints in preference to butt joints to minimize the weakness of joint locations. Cylinder diameter may be varied by including machined shoulders to prevent forward longitudinal movement of an inner cylinder within an outer cylinder during firing. Shoulder locations are similarly staggered to minimize weakness.[10]
Assembly Procedure After the tube, jacket, and hoops have been machined to appropriate dimensions, the jacket is carefully heated to approximately 400 degrees Celsius (800 degrees Fahrenheit) in a vertical air furnace so thermal expansion allows the cool tube to be lowered into place. When the jacket is in position, it is cooled to form a tensioned shrink fit over the tube. Then the next hoop (either B2 or C1) is similarly heated so the assembled A tube and B1 jacket can be lowered into position for a successive shrink fit. The assembled unit may be machined prior to fitting a new hoop. The process continues as remaining tubes are heated sequentially and cooled onto the built-up unit until all elements have been assembled.[11] When tensioned wire winding is used in place of a hoop course, the wire is typically covered by an outer tensioned cylinder also called a jacket.
Liners Burning powder gasses melt part of the bore each time a gun is fired. This melted metal is oxidized or blown out of the muzzle until the barrel is eroded to the extent shell dispersion becomes unacceptable. After firing several hundred shells, a gun may be reconditioned by boring out the interior and inserting a new liner as the interior cylinder. Exterior cylinders are heated as a unit to approximately 200 degrees Celsius (400 degrees Fahrenheit) to allow insertion of a new liner and the liner is bored and rifled after installation. A new liner may be bored for a different projectile diameter than used in the original gun. Liners may be either cylindrical or conical. Conical liners are tapered toward the muzzle for ease of removal from the breech end while limiting forward creep during firing. Conical liners may be removed by water cooling the liner after re-heating the barrel, but cylindrical liners must be bored out.[12]
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Built-up gun
Monoblock Guns With the obsolescence of very large guns following World War II, metallurgical advances encouraged use of monoblock (one-piece) construction for postwar guns of medium caliber. In a procedure called autofrettage, a bored monoblock tube is filled with hydraulic fluid at pressures higher than the finished gun will experience during firing. Upon release of hydraulic pressure, the internal diameter of the monoblock tube will have been increased by approximately six percent; but the outer portion of the finished monoblock rebounds to approximate its original diameter and exerts compressive forces on the inner portion similar to the separate cylinders of a built-up gun.[13]
Notes [1] [2] [3] [4] [5] [6] [7] [8] [9]
Fairfield (1921) p.161 Fairfield (1921) p.160 Fairfield (1921) p.165 Fairfield (1921) pp.161–2 Fairfield (1921) pp.200–201 Fairfield (1921) p.220 Fairfield (1921) p.229 Fairfield (1921) p.234 Fairfield (1921) p.301
[10] Fairfield (1921) p.235 [11] Fairfield (1921) pp.309–315 [12] Fairfield (1921) pp.323–326 [13] "Gun Barrel Construction" (http:/ / www. eugeneleeslover. com/ USNAVY/ GUN-BARL-CONSTRUCTION-1. html). Slover, Eugene. . Retrieved 2010-08-21.
References • Fairfield, A.P., CDR, USN Naval Ordnance (1921) Lord Baltimore Press
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Bullwheel
Bullwheel A bullwheel is a large wheel on which a rope turns, such as in a chairlift. In that application, the bullwheel that is attached to the prime mover is called the drive bullwheel, with the other known as the return bullwheel. Originally, bullwheel was an oil field term applied to the large wheel that turns the drum upon which the drilling line is wound in percussion drilling. The bullwheel (or bull wheel) began use in farm implements with A chairlift's return bullwheel the reaper. The term was commonly used to describe the traveling wheel, traction wheel, drive wheel, or harvester wheel. The bullwheel powered all the moving parts of these farm machines including the reciprocating knives, reel, rake, and self binder. The bull wheel's outer surface provided traction against the ground and turned when the draft animals or tractor pulled the implement forward.[1] Cyrus McCormick used the bullwheel to power his 1834 reaper and up until the early 1920s when small internal combustion engine gasoline engines like the Cushman Motor[2] began to be favored.
References [1] Reaper Bull Wheel Improvements (http:/ / www. machine-history. com/ Reaper Bull Wheel Improvements) [2] Breaking the Land: The Transformation of Cotton, Tobacco, and Rice Cultures Since 1880
• This article contains public domain text from USNS Bullwheel (http://www.history.navy.mil/danfs/b10/ bullwheel-i.htm) in the Dictionary of American Naval Fighting Ships.
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Burmester's theory
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Burmester's theory Burmester's theory is named after Ludwig Burmester (1840-1927). Burmester introduced geometric techniques for synthesis of linkages in the late 19th century.[1] His approach was to compute the geometric constraints of the linkage directly from the inventor's desired movement for a floating link. From this point of view a four-bar linkage is a floating link that has two points constrained to lie on two circles. Burmester began with a set of locations, often called poses, for the floating link, which are viewed as snapshots of the constrained movement of this floating link in the device that is to be designed. The design of a crank for the linkage now becomes finding a point in the moving floating link that when viewed in each of these specified positions has a trajectory that lies on a circle. The dimension of the crank is the distance from the point in the floating link, called the circling point, to the center of the circle it travels on, called the center point.[2] Two cranks designed in this way form the desired four-bar linkage. This formulation of the mathematical synthesis of a four-bar linkage and the solution to the resulting equations is known as Burmester Theory.[3] [4] [5] The approach has been generalized to the synthesis of spherical and spatial mechanisms.[6]
Finite position synthesis Burmester theory seeks points in a moving body that have trajectories that lie on a circle called circling points. The designer approximates the desired movement with a finite number of task positions; and Burmester showed that circling points exist for as many as five task positions. Finding these circling points requires solving five quadratic equations in five unknowns, which he did using techniques in descriptive geometry. Burmester's graphical constructions still appear in machine theory textbooks to this day. Two positions: As an example consider a task defined by two positions of the coupler link, as shown in the figure. Choose two points A and B in the body, so its two positions define the segments A¹B¹ and A²B². It is easy to see that A is a circling point with a center that is on the perpendicular bisector of the segment A¹A². Similarly, B is a circling point with a center that is any point on the perpendicular bisector of B¹B². A four-bar linkage can be constructed from any point on the two perpendicular bisectors as the fixed pivots and A and B as the moving pivots. The point P is clearly special, because it is a hinge that allows pure rotational movement of A¹B¹ to A²B². It is called the relative displacement pole. P is the pole of the displacement of A¹B¹ to A²B²
Three positions: If the designer specifies three task positions, then points A and B in the moving body are circling points each with a unique center point. The center point for A is the center of the circle that passes through A¹, A² and A³ in the three positions. Similarly, the center point for B is the center of the circle that passes through B¹, B² and B³. Thus for three task positions, a four-bar linkage is obtained for every pair of points A and B chosen as moving pivots. Four positions: Graphical solution to the synthesis problem becomes more interesting in the case of four task positions, because not every point in the body is a circling point. Four task positions yield six relative displacement
Burmester's theory poles, and Burmester selected four to form the opposite pole quadrilateral, which he then used to graphically generate the circling point curve (Kreispunktcurven). Burmester also showed that the circling point curve was a circular cubic curve in the moving body. Five positions: To reach five task positions, Burmester intersects the circling point curve generated by the opposite pole quadrilateral for a set of four of the five task positions, with the circling point curve generated by the opposite pole quadrilateral for different set of four task positions. Five poses imply ten relative displacement poles, which yields four different opposite pole quadrilaterals each having its own circling point curve. Burmester shows that these curves will intersect in as many as four points, called the Burmester points, each of which will trace five points on a circle around a center point. Because, two circling points define a four-bar linkage, these four points can yield as many as six four-bar linkages that guide the coupler link through the five specified task positions.
References [1] Hartenberg, R. S., and J. Denavit. Kinematic Synthesis of Linkages. New York: McGraw-Hill, 1964 on-line through KMODDL (http:/ / ebooks. library. cornell. edu/ k/ kmoddl/ toc_hartenberg1. html) [2] Burmester,L., 'Lehrbuch der Kinematik, Verlag Von Arthur Felix, Leipzig, Germany, 1886. [3] Suh, C. H., and Radcliffe, C. W., Kinematics and Mechanism Design, John Wiley and Sons, New York, 1978. [4] Sandor,G.N.,andErdman,A.G.,1984,AdvancedMechanismDesign:AnalysisandSynthesis, Vol. 2. Prentice-Hall, Englewood Cliffs, NJ. [5] Hunt, K. H., Kinematic Geometry of Mechanisms, Oxford Engineering Science Series, 1979 [6] J. M. McCarthy and G. S. Soh, Geometric Design of Linkages, 2nd Edition, Springer 2010 (http:/ / books. google. co. uk/ books?id=jv9mQyjRIw4C& printsec=frontcover& dq=geometric+ design+ of+ linkages& hl=en& ei=3L_5TcvZGaHV0QG2wMiDAw& sa=X& oi=book_result& ct=result& resnum=1& ved=0CDMQ6AEwAA#v=onepage& q& f=false)
Further reading • Ian R. Porteous (2001) Geometric Differentiation, § 3.5 Burmester Points, page 58, Cambridge University Press ISBN 0-521-00264-8 . • M. Ceccarelli and T. Koetsier, Burmester and Allievi: A Theory and Its Application for Mechanism Design at the End of the 19th Century, ASME 2006 (http://webuser.unicas.it/weblarm/old/file pdf/327-burmester& allieviDETC2006-99165.pdf)
External links • R. E. Kaufman provides links to videos of KINSYN which is the original interactive graphics software implementing Burmester's four position synthesis. (http://www.seas.gwu.edu/~kaufman1/) • The University of Minnesota Lincages software implements Burmester's four position synthesis. (http://www. me.umn.edu/labs/lincages/) • The Synthetica 3.0 software applies Burmester's approach to the synthesis of spatial linkages. (http://www. umbc.edu/engineering/me/vrml/research/software/synthetica/) • Linkage synthesis on mechanicaldesign101.com provides a Mathematica notebook for Burmester's five position synthesis. (http://mechanicaldesign101.com/linkage-synthesis/)
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Burnishing (metal)
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Burnishing (metal) Burnishing is the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a rough surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield strength of the material.
The inner ring of this bearing has been burnished by the bearing's rollers.
Mechanics To understand burnishing, first look at the simple case of a hardened ball on a flat plate. If the ball is pressed directly into the plate, stresses develop in both objects around the area where they contact. As this normal force increases, both the ball and the plate's surface deform. The deformation caused by the hardened ball is different depending on the magnitude of the force pressing against it. If the force on it is small, when the force is released both the ball and plate's surface will return to their original, undeformed shape. In this case, the stresses in the plate are always less than the yield strength of the material, so the deformation is purely elastic. Since it was given that the flat plate is softer A ball plowing a trough through a flat plate. than the ball, the plate's surface will always deform more. (Note 1: this is not necessarily true. For instance: if both items are steel, hardened steel has the same Young's Modulus as soft steel) If a larger force is used, there will also be plastic deformation and the plate's surface will be permanently altered. (Note 2: In this situation, hardness does play a role, as increasing hardness will delay plastic deformation) A bowl-shaped indentation will be left behind, surrounded by a ring of raised material that was displaced by the ball. The stresses between the ball and the plate are described in more detail by Hertzian stress theory. Now consider what happens if the external force on the ball drags it across the plate. In this case, the force on the ball can be decomposed into two component forces: one normal to the plate's surface, pressing it in, and the other tangential, dragging it along. As the tangential component is increased, the ball will start to slide along the plate. At the same time, the normal force will deform both objects, just as with the static situation. If the normal force is low, the ball will rub against the plate but not permanently alter its surface. The rubbing action will create friction and heat, but it will not leave a mark on the plate. However, as the normal force increases, eventually the stresses in the plate's surface will exceed its yield strength. When this happens the ball will plow through the surface and create a trough behind it. The plowing action of the ball is burnishing. Burnishing also occurs when the ball can rotate, as
Burnishing (metal)
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would happen in the above scenario if another flat plate was brought down from above to induce downwards loading, and at the same time to cause rotation and translation of the ball, or in the case of a ball bearing Burnishing also occurs on surfaces that conform to each other, such as between two flat plates, but it happens on a microscopic scale. Even the smoothest of surfaces will have imperfections if viewed at a high enough magnification. The imperfections that extend above the general form of a surface are called asperities, and they can plow material on another surface just like the ball dragging along the plate. The combined effect of many of these asperities produce the smeared texture that is associated with burnishing.
Upon magnification, two flat plates touch only at a few asperities.
Effects on mechanical components Burnishing is normally undesirable in mechanical components for a variety of reasons, sometimes simply because its effects are unpredictable. Even light burnishing will significantly alter the surface finish of a part. Initially the finish will be smoother, but with repetitive sliding action, grooves will develop on the surface along the sliding direction. The plastic deformation associated with burnishing will harden the surface and generate compressive residual stresses. Although these properties are usually advantageous, excessive burnishing leads to sub-surface cracks which cause spalling, a phenomenon where the upper layer of a surface flakes off of the bulk material. Burnishing may also affect the performance of a machine. The plastic deformation associated with burnishing creates greater heat and friction than from rubbing alone. This reduces the efficiency of the machine and limits its speed. Furthermore, plastic deformation alters the form and geometry of the part. This reduces the precision and accuracy of the machine. The combination of higher friction and degraded form often leads to a runaway situation that continually worsens until the component fails. To prevent destructive burnishing, sliding must be avoided, and in rolling situations, loads must be beneath the spalling threshold. In the areas of a machine that slide with respect to each other, roller bearings can be inserted so that the components are in rolling contact instead of sliding. If sliding cannot be avoided, then a lubricant should be added between the components. The purpose of the lubricant in this case is to separate the components with a lubricant film so they cannot contact. The lubricant also distributes the load over a larger area, so that the local contact forces are not as high. If there was already a lubricant, its film thickness must be increased; usually this can be accomplished by increasing the viscosity of the lubricant.
Burnishing in manufacturing Burnishing is not always bad. If it occurs in a controlled manner, it can have desirable effects. Burnishing processes are used in manufacturing to improve the size, shape, surface finish, or surface hardness of a workpiece. It is essentially a forming operation that occurs on a small scale. The benefits of burnishing often include: Combats fatigue failure, prevents corrosion and stress corrosion, textures surfaces to eliminate visual defects, closes porosity, creates surface compressive residual stress. There are several forms of burnishing processes, the most common are roller burnishing and ball burnishing (a subset of which is also referred to as ballizing). In both cases, a burnishing tool runs against the workpiece and plastically deforms its surface. In some instances of the latter case (and always in ballizing), it rubs, in the former it generally rotates and rolls. The workpiece may be at ambient temperature, or heated to reduce the forces and wear on the tool. The tool is usually hardened and coated with special materials to increase its life.
Burnishing (metal) Ball burnishing, or ballizing, is a replacement for other bore finishing operations such as grinding, honing, or polishing. A ballizing tool consists of one or more over-sized balls that are pushed through a hole. The tool is similar to a broach, but instead of cutting away material, it plows it out of the way.[1] Ball burnishing is also used as a deburring operation. It is especially useful for removing the burr in the middle of a through hole that was drilled from both sides.[1] Ball burnishing tools of another type are sometimes used in CNC milling centres to follow a ball-nosed milling operation: the hardened ball is applied along a zig-zag toolpath in a holder similar to a ball-point pen, except that the 'ink' is pressurised, recycled lubricant. This combines the productivity of a machined finish which is achieved by a 'semi-finishing' cut, with a better finish than obtainable with slow and timeconsuming finish cuts. The feedrate for burnishing is that associated with 'rapid traverse' rather than finish machining. Roller burnishing, or surface rolling, is used on cylindrical, conical, or disk shaped workpieces. The tool resembles a roller bearing, but the rollers are generally very slightly tapered so that their envelope diameter can be accurately adjusted. The rollers typically rotate within a cage, as in a roller bearing. Typical applications for roller burnishing include hydraulic system components, shaft fillets, and sealing surfaces.[2] Very close control of size can be exercised. Burnishing also occurs to some extent in machining processes. In turning, burnishing occurs if the cutting tool is not sharp, if a large negative rake angle is used, if a very small depth of cut is used, or if the workpiece material is gummy. As a cutting tool wears, it becomes more blunt and the burnishing effect becomes more pronounced. In grinding, since the abrasive grains are randomly oriented and some are not sharp, there is always some amount of burnishing. This is one reason the grinding is less efficient and generates more heat than turning. In drilling, burnishing occurs with drills that have lands to burnish the material as it drills into it. Regular twist drills or straight fluted drills have 2 lands to guide them through the hole. On burnishing drills there are 4 or more lands, similar to reamers.
References [1] Bakerjian, Ramon; Cubberly, W. H. (1989). Tool and manufacturing engineers handbook. Dearborn, Mich: Society of Manufacturing Engineers. pp. 45–7 to 45-11. ISBN 0-87263-351-9. [2] Kalpakjian, Serope; Steven R. Schmid (2003). Manufacturing Processes for Engineering Materials. Pearson Education. pp. 152. ISBN 8178089904. OCLC 66275970.
External links • Information on Burnishing and Other Surface Enhancement Practices (http://www.lambdatechs.com/ surface-enhancement/surface-enhancement-methods.html) • Metal Burnishing (Cutlery, Pewter, Silver) (http://knolik.com/article0004009.html) Spons' Workshop
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Bushing (isolator)
Bushing (isolator) A bushing or rubber bushing is a type of vibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension systems, where a bushing made of rubber (or, more often, synthetic rubber or polyurethane) separates the faces of two metal objects while allowing a certain amount of movement. This movement allows the suspension parts to move freely, for example, when traveling over a large bump, while minimizing transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as a flexible mounting or antivibration mounting. These bushings often take the form of an annular cylinder of flexible material inside a metallic casing or outer tube. They might also feature an internal crush tube which protects the bushing from being crushed by the fixings which hold it onto a threaded spigot. Many different types of bushing designs exist. An important difference compared with plain bearings is that the relative motion between the two connected parts is accommodated by strain in the rubber, rather than by shear or friction at the interface. Some rubber bushings, such as the D block for a sway bar, do allow sliding at the interface between one part and the rubber.
Advantages and disadvantages The main advantage of a bushing, as compared to a solid connection, is less noise and vibration are transmitted. Another advantage is that they require little to no lubrication. Disadvantages include: • Rubber bushings can deteriorate quickly in the presence of oils (e.g., motor oil, mineral oil) and extreme heat and cold. • The flexibility of rubber also introduces an element of play in the suspension system. This may result in camber, caster, or toe changes in the wheels of the vehicle during high-load conditions (cornering and braking), adversely affecting the vehicle's handling. For this reason, a popular aftermarket performance upgrade is the replacement of rubber suspension bushes with bushes made of more rigid materials, such as polyurethane. Polyurethane bushes are also available for many vehicles with the same characteristics as the manufacturers original bushes, but with greatly increased durability. This is useful on vehicles that have a reputation for wearing out standard rubber bushes, but for which harder bushings with increased harshness of ride are not wanted.
Applications • In vehicles: • Sway bar links and mountings • Shock absorber mountings • Double wishbone suspension assemblies • Norton Commando motorcycle • In skateboards, bushings limit the motion of the trucks. • In fastening, bushings are also used to transfer loads from a fastening to a much larger area in the underlying structure, the object being to reduce the strain on individual fibers within the underlying structure. (See also grommet.) • In crankshaft balancing, certain high-speed inline internal combustion engines are prone to torsional vibration of their crankshafts; the straight six and straight eight engines being particularly prone to this problem due to their long crankshaft length. Although straight eight engines faded from the marketplace in the 1950s, many straight six engines have and still do feature crankshaft vibration damping utilizing rubber bushes. The 3,442 cc Jaguar XK 6-cylinder engine of 1948 and most subsequent versions of the ubiquitous Jaguar XK engine used a proprietary Metalastik vibration damper to protect their crankshafts from potentially damaging torsional
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Bushing (isolator) vibrations. To quote William Heynes,[1] "The Metalastik damper consists of a steel plate to which is bonded, through a thick rubber disk, a malleable iron floating weight. Variations of the weight, rubber volume and mix, give these dampers a very wide field over which they can operate."
History Charles E. Sorensen credits Walter Chrysler as being a leader in encouraging the adoption of rubber vibration-isolating mounts. In his memoir (1956), he says that, on March 10, 1932, Chrysler called at Ford headquarters to show off a new Plymouth model. "The most radical feature of his car was the novel suspension of its six-cylinder engine so as to cut down vibration. The engine was supported on three points and rested on rubber mounts. Noise and vibration were much less. There was still a lot of movement of the engine when idling, but under a load it settled down. Although it was a great success in the Plymouth, Henry Ford did not like it. For no given reason, he just didn't like it, and that was that. I told Walter that I felt it was a step in the right direction, that it would smooth out all noises and would adapt itself to axles and springs and steering-gear mounts, which would stop the transfer of road noises into the body. Today rubber mounts are used on all cars. They are also found on electric-motor mounts, in refrigerators, radios, television sets—wherever mechanical noises are apparent, rubber is used to eliminate them. We can thank Walter Chrysler for a quieter way of life. Mr. Ford could have installed this new mount at once in the V‑8, but he missed the value of it. Later Edsel and I persuaded him. Rubber mounts are now found also in doors, hinges, windshields, fenders, spring hangers, shackles, and lamps—all with the idea of eliminating squeaks and rattles."[2] Chrysler's novel engine-mounting method was marketed as "Floating Power". Its basic idea soon became the conventional method throughout the automotive industry.
References [1] Heynes, WM. The Jaguar Engine, a paper presented to the Institution of Mechanical Engineers on 27 February 1953. [2] Sorensen 1956, pp. 226–227.
Bibliography • Sorensen, Charles E.; with Williamson, Samuel T. (1956), My Forty Years with Ford, New York, New York, USA: Norton, LCCN 56-010854. Various republications, including ISBN 9780814332795.
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Calibrated orifice
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Calibrated orifice A calibrated orifice is a restriction that is deliberately placed into a system of pipes to set the flow rate through the system. The orifice may be designed to produce proportional flow (as in the jet in a carburetor), or choked flow (as in a filtering bypass in a closed industrial cooling system, which might be designed to pass a particular flow rate through a filter assembly to maintain cleanliness of a closed-loop fluid system). Many pressure gauges also use an orifice (also called a restrictor) to limit the flow into a gauge. Since the pressure is even throughout the system, allowing only a small portion of the flow into the actual gauge allows it to be in parallel with the pressure circuit and still measure accurately. It also prevents or minimizes damage to the gauge during pressure surges at start-up, or due to any spikes in the system pressure.
Cam A Cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa.[1] [2] It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating (back and forth) motion in the follower, which is a lever making contact with the cam. Fig. 1 Animation showing rotating cams and cam followers producing reciprocating motion.
Overview The cam can be seen as a device that translates from circular to reciprocating (or sometimes oscillating) motion.[3] A common example is the camshaft of an automobile, which takes the rotary motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders. The opposite operation, translation of reciprocating motion to circular motion, is done by a crank. An example is the crankshaft of a car, which takes the reciprocating motion of the pistons and translates it into the rotary motion necessary to operate the wheels. Cams can also be viewed as information-storing and -transmitting devices. Examples are the cam-drums that direct the notes of a musical box or the movements of a screw machine's various tools and chucks. The information stored and transmitted by the cam is the answer to the question, "What actions should happen, and when?" (Even an automotive camshaft essentially answers that question, although the music box cam is a still-better example in illustrating this concept.)
Cam
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Displacement diagram Certain cams can be characterized by their displacement diagrams, which reflect the changing position a roller follower (a shaft with a rotating wheel at the end) would make as the cam rotates about an axis. These diagrams relate angular position, usually in degrees, to the radial displacement experienced at that position. Displacement diagrams are traditionally presented as graphs with non-negative values. A simple Fig. 2 Basic displacement diagram displacement diagram illustrates the follower motion at a constant velocity rise followed by a similar return with a dwell in between as depicted in figure 2.[4] The rise is the motion of the follower away from the cam center, dwell is the motion where the follower is at rest, and return is the motion of the follower toward the cam center. [5]
Plate cam The most commonly used cam is the plate cam which is cut out of a piece of flat metal or plate.[6] Here, the follower moves in a plane perpendicular to the axis of rotation of the camshaft.[7] Several key terms are relevant in such a construction of plate cams: base circle, prime circle (with radius equal to the sum of the follower radius and the base circle radius), pitch curve which is the radial curve traced out by applying the radial displacements away from the prime circle across all angles, and the lobe separation angle (LSA - the angle between two adjacent intake and exhaust cam lobes).
Fig. 3 Cam Profile
History An early cam was built into Hellenistic water-driven automata from the 3rd century BC.[8] The use of cams was later employed by Al-Jazari who employed them in his own automata.[9] The cam and camshaft appeared in European mechanisms from the 14th century.[10]
References [1] "cam definition" (http:/ / www. merriam-webster. com/ dictionary/ cam). Merriam Webster. . Retrieved 2010-04-05. "a rotating or sliding piece (as an eccentric wheel or a cylinder with an irregular shape) in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa" [2] Pennock, G., Shigley, J., & Uicker, J. (2010). Cam Design. Theory of Machines and Mechanisms (4 ed.). Oxford University Press, USA.. p. 200. [3] Jensen, Preben w. (1965). Cam Design and Manufacture. The Industrial Press, New York.. p. 1. [4] Jensen, Preben w. (1965). Cam Design and Manufacture. The Industrial Press, New York.. p. 8. [5] Introduction to Mechanisms - Cams (http:/ / www. cs. cmu. edu/ ~rapidproto/ mechanisms/ chpt6. html)"rise is the motion of the follower away from the cam center, dwell is the motion where the follower is at rest, and return is the motion of the follower toward the cam center" [6] Jensen, Preben w. (1965). Cam Design and Manufacture. The Industrial Press, New York.. p. 1. [7] Introduction to Mechanisms - Cams (http:/ / www. cs. cmu. edu/ ~rapidproto/ mechanisms/ chpt6. html) "The follower moves in a plane perpendicular to the axis of rotation of the camshaft." [8] Wilson, Andrew (2002): "Machines, Power and the Ancient Economy", The Journal of Roman Studies, Vol. 92, pp. 1–32 (16) [9] Georges Ifrah (2001). The Universal History of Computing: From the Abacus to the Quatum Computer, p. 171, Trans. E.F. Harding, John Wiley & Sons, Inc. (See (http:/ / www. banffcentre. ca/ bnmi/ programs/ archives/ 2005/ refresh/ docs/ conferences/ Gunalan_Nadarajan. pdf)) [10] A. Lehr (1981), De Geschiedenis van het Astronomisch Kunstuurwerk, p. 227, Den Haag. (See (http:/ / odur. let. rug. nl/ ~koster/ musicbox/ musicbox2. htm))
Cam
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External links • Cam design pages (http://www.Saltire.com/CamDesign) Creates animated cams for specified follower motions. • How round is your circle? (http://www.howround.com/) Contains various linkages. • Kinematic Models for Design Digital Library (KMODDL) (http://kmoddl.library.cornell.edu/index.php) Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library (http://kmoddl.library.cornell.edu/e-books.php) of classic texts on mechanical design and engineering. • Introduction to Mechanisms - Cams (http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt6.html) Classification, nomenclature, motion, and design of cams; information for the course, Introduction to Mechanisms, at Carnegie Mellon University.
Cam follower A cam follower, also known as a track follower,[1] is a specialized type of roller or needle bearing designed to follow cams. Cam followers come in a vast array of different configurations, however the most defining characteristic is how the cam follower mounts to its mating part; stud style cam followers use a stud while the yoke style has a hole through the middle.[2] The first cam follower was invented and patented in 1937 by Thomas L. Robinson of the McGill Manufacturing Company.[3] It replaced using just a standard bearing and bolt. The new cam followers were easier to use because the stud was already included and they could also handle higher loads.[2]
Construction While cam and followers appear to be very similar to roller bearings in construction they have quite a few differences. Standard ball and roller bearings are designed to be pressed into a rigid housing, which provides circumferential support. This keeps the outer race from deforming, so the race cross-section is relatively thin. In the case of cam followers the outer race is loaded at a single point, so the outer race needs a thicker cross-section to reduce deformation. However, in order to facilitate this the roller diameter must be decreased, which also decreases the dynamic bearing capacity.[4]
A cross-sectional view of a stud type cam follower
End plates are used to contain the needles or bearing axially. On stud style followers one of the end plates is integrated into the inner race/stud; the other is pressed onto the stud up to a shoulder on the inner race. The inner race is induction hardened so that the stud remains soft if modifications need to be made. On yoke style followers the end plates are peened or pressed onto the inner race or liquid metal injected onto the inner race. The inner race is either induction hardened or through hardened.[2] Another difference is that a lubrication hole is provided to relubricate the follower periodically. A hole is provided at both ends of the stud for lubrication. They also usually they have a black oxide finish to help reduce corrosion.[2]
Cam follower
Types There are many different types of cam followers available.
Anti-friction element The most common anti-friction element employed is a full complement of needle rollers. This design can withstand high radial loads but no thrust loads. A similar design is the caged needle roller design, which also uses needle rollers, but uses a cage to keep them separated. This design allows for higher speeds but decreases the load capacity. The cage also increases internal space so it can hold more lubrication, which increases the time between relubrications. Depending on the exact design sometimes two rollers are put in each pocket of the cage.[2] For heavy-duty applications a roller design can be used. This employs two rows of larger rollers to increase the dynamic load capacity and provide some thrust capabilities. This design can support higher speeds than the full complement design.[2] For light-duty applications a bushing type follower can be used. Instead of using a type of a roller a plastic bushing is used to reduce friction, which provides a maintenance free follower. The disadvantage is that it can only support light loads, slow speeds, no thrust loads, and the temperature limit is 200 °F (93 °C). A bushing type stud follower can only support approximately 25% of the load of a roller type stud follower, while the heavy and yoke followers can handle 50%.[2]
Shape The outer diameter (OD) of the cam follower (stud or yoke) can be the standard cylindrical shape or be crowned. Crowned cam followers are used to keep the load evenly distributed if it deflects or if there is any misalignment between the follower and the followed surface. They are also used in turntable type applications to reduce skidding. Crowned followers can compensate for up to 0.5° of misalignment, while a cylindrical OD can only tolerate 0.06°.[5] The only disadvantage is that they cannot bear as much load because of higher stresses.[2]
Stud Stud style cam followers usually have a standard sized stud, but a heavy stud is available for increased static load capacity.[2] Drives The standard driving system for a stud type cam follower is a slot, for use with a flat head screwdriver. However, hex sockets are available for higher torquing ability, which is especially useful for eccentric cam followers and those used in blind holes. The only problem with hex sockets is that it eliminates relubrication capabilities on that end of the cam follower.[2] Eccentricity Stud type cam followers are available with an eccentric stud. The stud has a bushing pushed onto it that has an eccentric outer diameter. This allows for adjustability during installation to eliminate any backlash. The adjustable range for an eccentric bearing is twice that of the eccentricity.[2]
Yoke Yoke type cam followers are usually used in applications where minimal deflection is required, as they can be support on both sides. They can support the same static load as a heavy stud follower.[2]
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Cam follower
Track followers All cam followers can be track followers, but not all track followers are cam followers. Some track followers have specially shaped outer diameters (OD) to follow tracks. For example, track followers are available with a V-groove for following a V-track, or the OD can have a flange to follow the lip of the track.[6] Specialized track followers are also designed to withstand thrust loads so the anti-friction elements are usually bearing balls or of a tapered roller bearing construction.[6]
References [1] Cam follower selection guide (http:/ / www. rbcbearings. com/ camfollowers/ selguide. htm), , retrieved 2009-07-20 [2] McGill CAMROL Bearings (http:/ / www. alliedbearings. com/ mfg_prod/ bearings/ ept_brgs/ camrolrevised2. pdf), , retrieved 2009-07-20 [3] US 2099660 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=US2099660), Robinson, Thomas L., "Bearing", published 1937-11-16 [4] Difference from standard bearings (http:/ / www. rbcbearings. com/ camfollowers/ difference. htm), , retrieved 2009-07-21 [5] Misalignment (http:/ / www. rbcbearings. com/ camfollowers/ misalignment. htm), , retrieved 2009-07-21 [6] Cam followers (http:/ / www. emerson-ept. com/ eptroot/ public/ prod/ dynamic_frame. asp?strMain=http:/ / www. emerson-ept. com/ EPTroot/ public/ prod/ McGCamFl/ McGCamF. htm), , retrieved 2009-07-21
Cam plastometer The cam plastometer is a physical testing machine. It measures the resistance of non-brittle materials to compressive deformation at constant true-strain rates. In this way, it can be compared a bit to the gleeble. In the early days, the machine operates at relatively low strain rates, but over time it has been enhanced and currently it can operate over a wide range of strain rates[1] The machine is patented under the name of "United States Patent 4109516"[2] . In the machine, deformation compressive forces are applied to a specimen by two flat, opposing platens which impact a flat, rectangular specimen. The deformation forces can be varied during operation, to simulate actual conditions which occur during industrial pressing and forming operations. The plastometer is also capable of torsional testing of specimens"[2] . The cam plastometers are expensive and there are only a few of them in the world[3] .
References [1] J.E. Hockett and N.A. Lindsay, Journal of Physics E: Scientific Instruments 4 (1971), 520-522. [2] Cam plastometer (freepatentsonline.com) (http:/ / www. freepatentsonline. com/ 4109516. html) [3] G.E. Dieter et al., Handbook of Workability and Process Design, ASM International 2003, page 49
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Campbell diagram
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Campbell diagram A Campbell diagram plot represents a system's response spectrum as a function of its oscillation regime. It is named for Wilfred Campbell, who has introduced the concept, see Campbell 1924[1] .
In rotordynamics In rotordynamical systems, the eigenfrequencies often depend on the rotation rates due to the induced gyroscopic effects or variable hydrodynamic conditions in fluid bearings. It might represent the following cases: 1. Analytically computed values of eigenfrequencies as a function of the shaft's rotation speed. This case is also called "whirl speed map", see Logan 2003. Such chart can be used in turbine design as shown in the numerically calculated Campbell Diagram example illustrated by the image: analysis shows that there are well-damped Analytical Campbell Diagram for a Simple Rotor critical speed at lower speed range. Another critical speed at mode 4 is observed at 7810 rpm (130 Hz) in dangerous vicinity of nominal shaft speed, but it has 30% damping - enough to safely ignore it. 2. Experimentally measured vibration response spectrum as a function of the shaft's rotation speed (waterfall plot), the peak locations for each slice usually corresponding to the eigenfrequencies.
In acoustical engineering In acoustical engineering, the Campbell diagram would represent the pressure spectrum waterfall plot vs the machine's shaft rotation speed (sometimes also called 3D noise map).
Notes [1] cited after Meher-Homji 2005
Campbell Diagram of a steam turbine
Campbell diagram
External links • Frederick Nelson, Rotor Dynamics without Equations (http://www.comadem.com/sample copy journal website.pdf)
References • Campbell, Wilfred (1924). "Protection of Steam Turbine Disk Wheels from Axial Vibration". Transactions of the ASME: 31–160. • Logan, Earl Jr (2003-05-01). Handbook of Turbomachinery (Mechanical Engineering, No. 158) (2 ed.). CRC Press. ISBN 0824709950. • Meher-Homji, Cyrus B.; Erik Prisell (2005-04). "Dr. Max Bentele---Pioneer of the Jet Age" (http://link.aip.org/ link/?GTP/127/231/1). Journal of Engineering for Gas Turbines and Power 127 (2): 231–239. doi:10.1115/1.1807412. Retrieved 2010-07-27.
Central Mechanical Engineering Research Institute Central Mechanical Engineering Research Institute CMERI is an engineering research institute based in Durgapur, West Bengal, India. It was established in February 1958 with the specific task of development of mechanical engineering technology and is funded by the Council of Scientific and Industrial Research (CSIR). It is located opposite to National Institute of Technology, Durgapur, a premier engineering institute and among the top 20 in the country for undergraduate courses. It conducts research in varied fields of engineering and technology aimed at providing assistance to mechanical engineering industries in the form of feasibility studies, research, training and consultancy. It conducts several short term courses in emerging and cutting-edge technology.[1]
Research The institute performs research in various fields. The chief areas of research include Robotics & Mechatronics, Embedded Systems & Electronics, Energy & Process Plant, Chemistry & Biomimetics, Mechanical Design & Manufacturing Technology, Rapid Prototyping & Tooling, Farm Machinery & Post Harvest Technology and Life Enhancement Studies (RLA).
MERADO MERADO or Mechanical Engineering Research & Development Organization was developed as an extension center of the Central Mechanical Engineering Research Institute to focus on the development of the small and medium scale industries, especially in the Northern States of India.
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Central Mechanical Engineering Research Institute
References [1] "CMERI bid to promote small, medium-scale industries." (http:/ / www. accessmylibrary. com/ coms2/ summary_0286-13445564_ITM). Business Line via Asia Africa Intelligence Wire. 22 September 2004. . Retrieved 2009-02-09.
External Links Official Website (http://www.cmeri.res.in/)
Centrifugal-type supercharger The centrifugal-type supercharger is an engine-driven compressor used to increase the power output of an internal-combustion engine by increasing the amount of available oxygen by compressing air that is entering the engine. This type of supercharger is practically identical in operation to a turbocharger, with the exception that instead of exhaust gases driving the compressor via a turbine, the compressor is driven from the crankshaft by a belt, gear or chain drive. Like any centrifugal pump, the boost provided by the centrifugal supercharger increases with the square of the speed. This World War II Daimler-Benz DB60X series aircraft engine showing centrifugal means that the centrifugal design provides blower intake at right. This engine is a DB601 model. little boost at low engine speeds, in some cases allowing air to pass back through the supercharger, such as during deceleration. On the other hand, the design is also the most efficient, besting designs like the Roots type supercharger and twin-screw type supercharger, which have the advantage of producing boost at any speed. Many World War II piston aircraft engines, such as the Rolls-Royce Merlin and the Daimler-Benz DB 601, utilized single-speed or multi-speed centrifugal superchargers. Because high-performance aircraft engines were typically mated to constant-speed propellers and did not see a great variation in engine speeds, the poor low-rpm performance of centrifugal superchargers was not an issue. Superchargers have since fallen from use in the aviation world, replaced by turbochargers of ever-improving quality. Due to its design and lack of low-RPM boost it is often employed on near-standard compression engines. This means that it can facilitate airflow at higher engine RPMs, when most motors tend to have poor volumetric efficiency, without substantially increasing cylinder pressures at low- to mid-RPM operation, causing knock. This principle makes this type of supercharger ideally fit for a "bolt-on" type power adder, with no modification of the pistons and/or compression ratio necessary. Since gasoline must mix with air in a fairly narrow ratio to achieve combustion, the fact that centrifugals do not add much air at low and mid-range RPM's means fuel mileage is near-stock in the cruise RPM range. They appear to be most popular with cars that have a sufficiently large engine to provide adequate acceleration from a standing start without boost, while at the same time avoiding wheelspin. Then, the engine encounters breathing limitations in the mid-RPM range, often because it may only use two valves per cylinder. Centrifugals are also popular in places where the power-adder must be removed for frequent government engine inspections, as the exhaust system is unaffected (as it would be with a turbocharger).
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Centrifugal-type supercharger
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Compared to a turbocharger (which uses an almost identical compressor design, but instead is powered by exhaust gasses), a supercharger has the benefit of being able to reach peak boost earlier in the RPM range. A turbocharger will maintain the desired boost pressure by leaking excess gasses using a Wastegate, to keep the boost pressure at the desired level and also allow the engine to continue accelerating. A centrifugal supercharger does not have the ability to do this, so it will always make peak boost at the engine's own peak RPM (provided that the engine's peak RPM isn't beyond the peak efficiency of the compressor). The flaw in this application is that the engine will not have the same torque at lower RPM, using a centrifugal supercharger. All supercharger types benefit from the use of an intercooler to remove heat produced during compression.
Century tower clocks Century tower clocks were tower clocks manufactured by Nels Johnson, designed to last 100 years.[1] They were "clocks built to last a century," hence the name "Century" tower clocks.[1] These tower clocks were mostly produced from 1880 to 1910.[2] Johnson, by himself, made between 50 and 60 of these clocks.[3] Johnson designed and manufactured these tower clocks at his machine shop in Manistee, Michigan. He built the clocks by himself and had no employees. Because of this he had low overhead and was able to underbid his competitors many times and obtain the order. The chief competitors of his in tower clock manufacturing were E. Howard & Co. of Boston and the Seth Thomas Clock Co. of Thomaston, Connecticut. These firms had large tower-clock departments and large department overhead as well. They were usually considerably greater than Johnson's and he was often able to underbid them. The actual bells he used in his striking clocks were from well-known bell founders such as Meneely in Troy, New York or Chaplin-Fulton bell foundry of Pittsburgh.[3]
Century clock bell
One of his tower clocks is that installed in 1906 by Nels Johnson at the Mason County Courthouse in Michigan that is still in use as of 2010. This tower clock he had originally installed in the Congregational Church at Manistee, Michigan, in 1892. The church had the clock removed in 1905 when they received a new clock.[4] He also has one of his clocks at the Lutheran Church in Rochester, N.Y., one at Fond du Lac, Wisconsin, three in Milwaukee, one in Big Rapids, Michigan, and one in Postville, Iowa. One of his finest clocks was in the famed Fort Street Union Depot railroad station of Detroit, Michigan.[4] Johnson made about 50 to 60 tower clocks. Some are: • Los Angeles Times Building (1912) in Los Angeles, • San Jose Post Office (1909), • The Michigan Building at the 1893 Chicago World's Fair, • Detroit Post Office (1891) in Detroit, • A bank in Holland, MI,
Nels Johnson in his clock shop circa 1895
Century tower clocks • • • • • • • • • •
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Lansing City Hall in Lansing MI, Lyman Building (1889) in Muskegon MI, St. Joseph Court House in St. Joseph MI, Faith Church (1905) in Pelican Falls MN, One installed in 1892 at Rochester NY, U. S. Customs House at Memphis TN, Milwaukee City Hall, Emmanuel's Evangelical Lutheran Church (1890) of Milwaukee, Bethlehem Evangelical Lutheran Church (1891) of Milwaukee, Zion Evangelical Lutheran Church (1894) of Milwaukee.
right: Nels Johnson clock shop, circa 1912 left: Amateur Astronomical Observatory of Johnson's with removable window.
In Manistee: • St. Joseph's Polish Catholic Church (1894), • First Methodist Episcopal Church (1893) • Johnson's Machine Shop around 1889. There are two known international installations. One in Chengtu, China, installed in 1914 and another at the Isabella Thoburn College in Lucknow, India in 1910. Johnson did not go to these locations to install these clocks, though he did go and set up his tower clocks himself in every instance when they were installed in the United States.[4]
Nels Johnson at his observatory
Gallery of clock mechanism
second hand
Gallery Century Tower Clocks
clock works
clock mechanism
snail and rack
Century tower clocks
89 City Hall, circa 1915 Lansing, Michigan
U S Custom House 1885, Memphis, Tennessee
Michigan State Building 1893 Columbia Exposition
Detroit Post Office, circa 1900
Century tower clocks
90
San Jose Post Office circa 1900
Cheboygan, Michigan county courthouse, c.1910
Lyman Block & Post Office in 1911 with tower clock
Century tower clocks
91
Los Angeles Times Building 1912 with Nel's tower clock Cheboygan county courthouse building was sold to a paper company and taken down in 1970 for a parking lot.[5] The Lyman Block & Post Office were taken down and replaced in the 1930s.[6] Detroit Post Office was located at Shelby & Fort Streets in downtown Detroit, Michigan, and demolished in 1931. The San Jose Post Office became the San Jose Museum of Art and the tower clock still exists. The U S Custom House of Memphis, Tennessee, built in 1885, is now the Cecil C. Humphreys School of Law and the tower clock still exists.[7] [8]
Nels Johnson tower clocks over 100 years old Century Tower Clocks
Nisbett-Fairman Residences in Big Rapids, Michigan, 2010
Century tower clocks
92 Mason County Courthouse in Ludington, Michigan, 2008
San Jose Art Museum 2009 tower clock inside photos [9]
Milwaukee City Hall 1896 built tower clock in 2010
Faith Lutheran Church 2010 Pelican Rapids, Minnesota
Century tower clocks
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St Joseph county courthouse Centerville, Michigan
References [1] NAWCC Bulletin No. 108, (February 1964), p. 89 Nels Johnson and his Century tower clocks by Dana J. Blackwell; He called his clocks "Century" tower clocks, designed to last one hundred years, and those still serving faithfully are a living testimony to his craftsmanship and integrity. [2] NAWCC Bulletin, August 2006, pp. 391-401, Nels Johnson, Michigan clockmaker by Jack Linahan [3] NAWCC Bulletin No. 108, (February 1964), pages 82-89 Nels Johnson and his Century tower clocks by Dana J. Blackwell [4] Record Publishing Company, pp. 185-87 [5] Fedynsky, p. 36 [6] Lyman Block & Post Office in 1911 (http:/ / www. flickr. com/ photos/ eridony/ 2333171237/ in/ set-72157601059788760/ ) [7] Cecil C. Humphreys School of Law (http:/ / www. memphis. edu/ law/ presskit/ Law_School_Press_Kit. pdf) [8] Dignitaries announce the U of M's purchase of a historic Downtown building for legal education (http:/ / iw. newsbank. com/ iw-search/ we/ InfoWeb?p_action=doc& p_theme=aggdocs& p_topdoc=1& p_docnum=1& p_sort=YMD_date:D& p_product=NewsBank& p_docid=10F20864083983B8& p_text_direct-0=document_id=( 10F20864083983B8 )& p_multi=CMAB& s_lang=en-US& p_nbid=O47I52WFMTI5MTIyMjEwMy42Nzc1MTA6MToxMjoxNjcuMjkuNC4xNTA) [9] http:/ / www. shomler. com/ other/ clocktower/ index. htm
Sources • Record Publishing Company (Chicago), Portrait and biographical record of northern Michigan: containing portraits and biographical sketches of prominent and representative citizens, together with biographies of all the presidents of the United States, 1895 • Fedynsky, John, Michigan's County Courthouses, University of Michigan, 2010, ISBN 978-0-472-11728-4
External links • San Jose Museum of Art Clock Tower (http://www.shomler.com/other/clocktower/clocktower1.htm) • San Jose tower clock background history (http://www.sjclocktower.org/clock) • some Nels Johnson "Century" tower clock locations (http://homepages.sover.net/~donnl/makers. html#johnson1) • The 1908 Nels Johnson Century Clock in the San Jose Museum of Art Clock Tower (http://www.shomler.com/ other/clocktower/clocktower1.htm)
Chilled water
Chilled water Chilled water is a commodity often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel. The chilled water can be supplied by a vendor, such as a public utility or created at the location of the building that will use it, which has been the norm.
Use Chilled water cooling is very different from typical residential air conditioning where a refrigerant is pumped through an air handler to cool the air. Regardless of who provides it, the chilled water (between 4° and 7°C) is pumped through an air handler, which captures the heat from the air, then disperses the air throughout the area to be cooled.[1] [2]
Site generated The condenser water absorbs heat from the refrigerant in the condenser barrel of the water chiller, and is then sent via return lines to a cooling tower, which is a heat exchange device used to transfer waste heat to the atmosphere. The extent to which the cooling tower decreases the temperature depends upon the outside temperature, the relative humidity and the atmospheric pressure. The water in the chilled water circuit will be lowered to the Wet-bulb temperature or dry-bulb temperature before proceeding to the water chiller, where it is cooled to between 4° and 7°C and pumped to the air handler, where the cycle is repeated.[3] The equipment required includes chillers, cooling towers, pumps and electrical control equipment. The initial capital outlay for these is substantial and maintenance costs can fluctuate. Adequate space must be included in building design for the physical plant and access to equipment.
Utility generated The chilled water, which absorbed heat from the air, is sent via return lines back to the utility facility, where the process described in the previous section occurs. Utility generated chilled water eliminates the need for chillers and cooling towers at the property, reduces capital outlays and eliminates ongoing maintenance costs. The physical space saved can also become rentable, increasing revenue.[3] Utility supplied chilled water has been used successfully since the 1960’s in many cities, and technological advances in the equipment, controls and trenchless installation have increased efficiency and lowered costs.[3] The advantage of utility-supplied chilled water is based on economy of scale. A utility can operate one large system more economically than a customer can operate the individual system in one building. The utility's system also has back-up capacity to protect against sudden outages. The cost of such "insurance" is also markedly lower than what it would be for an individual structure. The use of utility supplied chilled water is most cost effective when it is designed into the building’s infrastructure or when chiller/cooling tower equipment must be replaced. Commercial customers often lower their air conditioning costs from 10-20% by purchasing chilled water.[3]
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Chilled water
References [1] How Stuff Works: How Air Conditioners Work-Chilled-water and Cooling-tower AC Units (http:/ / home. howstuffworks. com/ ac4. htm) [2] Air conditioning and refrigeration guide: Chilled Water Air Conditioning (http:/ / www. air-conditioning-and-refrigeration-guide. com/ chilled-water-air-conditioning. html) [3] Jacksonville Business Journal: July 11, 2003-JEA's cool idea can save by Chuck Day (http:/ / www. bizjournals. com/ jacksonville/ stories/ 2003/ 07/ 14/ focus2. html)
External links • Chilled Water Plant Design and Specification Guide (http://www.taylor-engineering.com/downloads/ cooltools/EDR_DesignGuidelines_CoolToolsChilledWater.pdf)
Chiller A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.
Use in air conditioning In air conditioning systems, chilled water is typically distributed to heat exchangers, or coils, in air handling units, or other type of terminal devices which cool the air in its respective space(s), and then the chilled water is re-circulated back to the chiller to be cooled again. York International water-cooled chiller. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus cooling and usually dehumidifying the air stream. A typical chiller for air conditioning applications is rated between 15 to 1500 tons (180,000 to 18,000,000 BTU/h or 53 to 5,300 kW) in cooling capacity, and at least one company has a 2,700 ton chiller for special uses. Chilled water temperatures can range from 35 to 45 degrees Fahrenheit (1.5 to 7 degrees Celsius), depending upon application requirements.[1] [2]
Use in industry In industrial application, chilled water or other liquid from the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. They are often used in the plastic industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum systems, X-ray diffraction, power supplies and power generation stations, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines and lasers, and in hospitals, hotels and campuses. Chillers for industrial applications can be centralized, where each chiller serves multiple cooling needs, or decentralized where each application or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of both centralized and decentralized chillers, especially if the cooling requirements are the same for some applications or points of use, but not all.
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Chiller Decentralized chillers are usually small in size (cooling capacity), usually from 0.2 tons to 10 tons. Centralized chillers generally have capacities ranging from ten tons to hundreds or thousands of tons. Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional (CII) facilities. Water chillers can be water-cooled, air-cooled, or evaporatively cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Evaporatively cooled chillers offer higher efficiencies than air-cooled chillers but lower than water-cooled chillers. Water-cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere. Air-cooled and evaporatively cooled chillers are intended for outdoor installation and operation. Air-cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Evaporatively cooled machines are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air-cooled machine. No remote cooling tower is typically required with either of these types of packaged air-cooled or evaporatively cooled chillers. Where available, cold water readily available in nearby water bodies might be used directly for cooling, place or supplement cooling towers. The Deep Lake Water Cooling System in Toronto, Canada, is an example. It uses cold lake water to cool the chillers, which in turn are used to cool city buildings via a district cooling system. The return water is used to warm the city's drinking water supply, which is desirable in this cold climate. Whenever a chiller's heat rejection can be used for a productive purpose, in addition to the cooling function, very high thermal effectiveness is possible.
Vapor-compression chiller technology There are four basic types of compressors used in vapor compression chillers: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that can be powered by electric motors, steam, or gas turbines. They produce their cooling effect via the "reverse-Rankine" cycle, also known as 'vapor-compression'. With evaporative cooling heat rejection, their coefficients-of-performance (COPs) are very high; typically 4.0 or more. In recent years, application of Variable Speed Drive (VSD) technology has increased efficiencies of vapor compression chillers. The first VSD was applied to centrifugal compressor chillers in the late 1970s and has become the norm as the cost of energy has increased. Now, VSDs are being applied to rotary screw and scroll technology compressors.
How absorption technology works Absorption chillers are driven by hot water. This hot water may come from any number of industrial sources including waste heat from industrial processes, prime heat from solar thermal installations or from the exhaust or water jacket heat of a piston engine or turbine.rts and eliminating the noise associated with those moving parts. The silica gel or zeolite, create an extremely low humidity condition that causes the water refrigerant to evaporate at a low temperature. As water evaporates in the evaporator, it cools the chilled water. After a functioning point, though, the adsorber is saturated - cannot adsorb any more water- and needs regeneration. This regeneration needs high temperature, which comes from hot water. The use of silica gel and zeolites desiccant keeps the maintenance costs and operating costs of adsorption chillers low.
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Chiller
How absorption technology works The thermodynamic cycle of an absorption chiller is driven by a heat source; this heat is usually delivered to the chiller via steam, hot water, or combustion. Compared to electrically powered chillers, an absorption chiller has very low electrical power requirements - very rarely above 15 kW combined consumption for both the solution pump and the refrigerant pump. However, its heat input requirements are large, and its COP is often 0.5 (single-effect) to 1.0 (double-effect). For the same tonnage capacity, an absorption chiller requires a much larger cooling tower than a vapor-compression chiller. However, absorption chillers, from an energy-efficiency point-of-view, excel where cheap, high grade heat or waste heat is readily available. In extremely sunny climates, solar energy has been used to operate absorption chillers. The single effect absorption cycle uses water as the refrigerant and lithium bromide as the absorbent. It is the strong affinity that these two substances have for one another that makes the cycle work. The entire process occurs in almost a complete vacuum. 1. Solution Pump : A dilute lithium bromide solution (63 % concerntration) is collected in the bottom of the absorber shell. From here, a hermetic solution pump moves the solution through a shell and tube heat exchanger for preheating. 2. Generator : After exiting the heat exchanger, the dilute solution moves into the upper shell. The solution surrounds a bundle of tubes which carries either steam or hot water. The steam or hot water transfers heat into the pool of dilute lithium bromide solution. The solution boils, sending refrigerant vapor upward into the condenser and leaving behind concentrated lithium bromide. The concentrated lithium bromide solution moves down to the heat exchanger, where it is cooled by the weak solution being pumped up to the generator. 3. Condenser : The refrigerant vapor migrates through mist eliminators to the condenser tube bundle. The refrigerant vapor condenses on the tubes. The heat is removed by the cooling water which moves through the inside of the tubes. As the refrigerant condenses, it collects in a trough at the bottom of the condenser. 4. Evaporator : The refrigerant liquid moves from the condenser in the upper shell down to the evaporator in the lower shell and is sprayed over the evaporator tube bundle. Due to the extreme vacuum of the lower shell [6 mm Hg (0.8 kPa) absolute pressure], the refrigerant liquid boils at approximately 39°F (3.9°C), creating the refrigerant effect. (This vacuum is created by hygroscopic action - the strong affinity lithium bromide has for water - in the Absorber directly below.) 5. Absorber : As the refrigerant vapor migrates to the absorber from the evaporator, the strong lithium bromide solution from the generator is sprayed over the top of the absorber tube bundle. The strong lithium bromide solution actually pulls the refrigerant vapor into solution, creating the extreme vacuum in the evaporator. The absorption of the refrigerant vapor into the lithium bromide solution also generates heat which is removed by the cooling water. The now dilute lithium bromide solution collects in the bottom of the lower shell, where it flows down to the solution pump. The chilling cycle is now completed and the process begins once again.
Industrial chiller technology Industrial chillers typically come as complete, packaged, closed-loop systems, including the chiller unit, condenser, and pump station with recirculating pump, expansion valve, no-flow shutdown, internal cold water tank, and temperature control. The internal tank helps maintain cold water temperature and prevents temperature spikes from occurring. Closed-loop industrial chillers recirculate a clean coolant or clean water with condition addititives at a constant temperature and pressure to increase the stability and reproducibility of water-cooled machines and instruments. The water flows from the chiller to the application's point of use and back. If the water temperature differentials between inlet and outlet are high, then a large external water tank would be used to store the cold water. In this case the chilled water is not going directly from the chiller to the application, but goes to the external water tank which acts as a sort of "temperature buffer." The cold water tank is much larger than the internal water tank. The cold water goes from the external tank to the application and the return hot water from
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Chiller the application goes back to the external tank, not to the chiller. The less common open loop industrial chillers control the temperature of a liquid in an open tank or sump by constantly recirculating it. The liquid is drawn from the tank, pumped through the chiller and back to the tank. An adjustable thermostat senses the makeup liquid temperature, cycling the chiller to maintain a constant temperature in the tank. One of the newer developments in industrial water chillers is the use of water cooling instead of air cooling. In this case the condenser does not cool the hot refrigerant with ambient air, but uses water that is cooled by a cooling tower. This development allows a reduction in energy requirements by more than 15% and also allows a significant reduction in the size of the chiller, due to the small surface area of the water based condenser and the absence of fans. Additionally, the absence of fans allows for significantly reduced noise levels. Most industrial chillers use refrigeration as the media for cooling, but some rely on simpler techniques such as air or water flowing over coils containing the coolant to regulate temperature. Water is the most commonly used coolant within process chillers, although coolant mixtures (mostly water with a coolant additive to enhance heat dissipation) are frequently employed.
Industrial chiller selection Important specifications to consider when searching for industrial chillers include the total life cycle cost, the power source, chiller IP rating, chiller cooling capacity, evaporator capacity, evaporator material, evaporator type, condenser material, condenser capacity, ambient temperature, motor fan type, noise level, internal piping materials, number of compressors, type of compressor, number of fridge circuits, coolant requirements, fluid discharge temperature, and COP (the ratio between the cooling capacity in RT to the energy consumed by the whole chiller in KW). For medium to large chillers this should range from 3.5-7.0 with higher values meaning higher efficiency. Chiller efficiency is often specified in kilowatts per refrigeration ton (kW/RT). Process pump specifications that are important to consider include the process flow, process pressure, pump material, elastomer and mechanical shaft seal material, motor voltage, motor electrical class, motor IP rating and pump rating. If the cold water temperature is lower than −5°C, then a special pump needs to be used to be able to pump the high concentrations of ethylene glycol. Other important specifications include the internal water tank size and materials and full load current. Control panel features that should be considered when selecting between industrial chillers include the local control panel, remote control panel, fault indicators, temperature indicators, and pressure indicators. Additional features include emergency alarms, hot gas bypass, city water switchover, and casters.
Refrigerants A vapor-compression chiller uses a refrigerant internally as its working fluid. Many refrigerants options are available; when selecting a chiller, the application cooling temperature requirements and refrigerant's cooling characteristics need to be matched. Important parameters to consider are the operating temperatures and pressures. There are several environmental factors that concern refrigerants, and also affect the future availability for chiller applications. This is a key consideration in intermittent applications where a large chiller may last for 25 years or more. Ozone depletion potential (ODP) and global warming potential (GWP) of the refrigerant need to be considered. ODP and GWP data for some of the more common vapor-compression refrigerants:
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Chiller
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Refrigerant
ODP
GWP
R134a
0
1300
R123
0.012
76
R22
0.05
1700
R290 (propane)
0
3
R401a
0.027
970
R404a
0
3260
R407a
0
???
R407c
0
1525
R408a
0.016
3020
R409a
0.039
1290
R410a
0
1725
R500
0.7
???
R502
0.18
5600
R717 (ammonia) 0
0
The refrigerants used in the chillers sold in Europe are mainly R410a (70%), R407c (20%) and R134a (10%).[3]
European Market In Europe, the chiller market is divided in 2 main categories of chillers: • the market of residential reversible chillers under 50 kW, called heat pumps, which is very developed in France, Italy and the Northern countries ; • the market of industrial and commercial chillers often above 50 kW, which is very developed in industrial countries, such as Germany, UK, France, Italy and Benelux. Regarding the chillers above 50 kW, the kW of chillers sold each year are split as following [4] : • 72% air-cooled (almost all non-ducted), 25% water-cooled and 3% condenserless, • 58,5% cooling only, 7,9% reversible and 33,6% heating only. The market by country is split in 2010 as following: Countries
Sales Volume in MkW
[5]
Share
Benelux
1.090
9.8%
France
1.706
15.3%
Germany
1.253
11.2%
Greece
0.176
1.6%
Italy
1.815
16.3%
Poland
0.314
2.8%
Portugal
0.215
1.9%
Russia, Ukraine and CIS countries
0.565
5.1%
Scandinavia and Baltic countries
0.555
5.0%
Spain
0.926
8.3%
Turkey
0.658
5.9%
Chiller
100 UK and Ireland
0.929
8.3%
Eastern Europe
0.955
8.6%
References [1] [2] [3] [4] [5]
American Society of Heating, Refrigerating and Air-Conditioning Engineers http:/ / www. ashrae. org/ publications/ page/ 158 Hydronika supplies 5 ton chiller units http:/ / hydronika. com Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/
External links • Chiller Energy Consumption Calculator (requires Java) (http://www.flowmeterdirectory.com/ energy_consumption_calculator.html) • Adsorption chillers (http://www.eco-maxchillers.com) • Conversion of HCFC chillers to hydrocarbons in the Philippines (http://www.hydrocarbons21.com/content/ articles/2010-06-08-philippines-cdm-project-to-replace-375-inefficient-chillers.php)
CILAS
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CILAS CILAS
Type
S.A. (corporation)
Founded
1966
Headquarters
Orléans, France
Key people
Philippe Lugherini
Revenue
26,7 million € (2009)
Employees
170 (2009)
Website
www.cilas.com
[1]
CILAS is a French company, a subsidiary of EADS Astrium, specialized in laser and optics technology, founded in 1966. This high-technology engineering company was the inventor of the particle size analyzer. Today, it develops, manufactures and produces systems combining laser and precision optics in the field of high technology, accounting. Products for the military represent 80% of turnover against 20% civilian.
History This company was founded in 1966 by two companies : CGE (Compagnie Generale d'Électricité becoming Alcatel-Alsthom) and Saint-Gobain. The aim was to exploit industrially and commercially the work of laboratories working on laser sources and laser equipment. In 1983, it became CILAS-Alcatel. In 1985, it was absorbed by two companies of optics : SORO Electro-Optics and BBT (Barbier Bernard and Turenne). Alcatel withdraws its laser activities in 1989, resulting in a change of ownership. In early 1990, the capital is divided between three companies, CEA Industries (now Areva), SAT and Unilaser Holding (Aerospace Group). CILAS-Alcatel becomes CILAS. Meanwhile, from late 1989, the Unilaser group also acquired the Optronics Division of Alcatel Marcoussis laboratories and named it Laserdot. Unilaser now gather Quantel, LISA, CILAS and Laserdot. From this moment, Laserdot and CILAS collaborate on joint projects. Laserdot is more oriented toward research and development whereas CILAS toward industrialization and production. In 1994, SAT withdraws CILAS' capital and shares of the two remaining shareholders passed to 57% for Unilaser and 43% for CEA Industry. On September 1, 1995, CILAS and Laserdot are merged into a single entity which reteins the name CILAS.
CILAS
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Defence and security Cilas develops and manufactures differents products in the field of defence and security. It offers laser designators, counter-snipers optical sight systems detectors, rangefinders, airborne laser sources ans shipborne helicopters landing aids. Optics detector : The SLD 500 laser surveillance system and sniper detector is a reliable tool for surveillance of sensitive areas and critical infrastructures protection. The system can detect and locate any kind of optical sight systems: optical scopes used by snipers or optronic sight systems. Not only is it capable of accurately localizing a threat, the system can also perform clear target identification using a high definition daylight camera or an infrared camera for night vision. Optics detector
[2]
Laser designator : The DHY 307 ground laser target designator belongs to the Modular Illuminating Range Finders (TIM) family developed by CILAS. Intended for use by small ground units, it provides precision guidance for any missile, bomb or shell fitted with final laser guidance targeting an individual tactical objective. Laser target designator
[3]
Helicopter visual landing aids system : Safecopter is a complete lighting system formed by a Glide Slope Indicator with a lighting deck system. The SAFECOPTER provides day and night, in all weather, perfect safety for pilots during landing of helicopters. SAFECOPTER
[4]
CILAS
103
Particle size analysis Over 30 years ago, CILAS developed the world's first diffraction laser particle size analyzer for industrial applications. Since then, CILAS has been the market leader in product innovation; constantly striving to make their particle size analyzer easier to use, more reliable and flexible. CILAS' state of the art laser particle size analyzer include features such as their patented short optical branch, intuitive software interface and a 2 in 1 design which effortlessly integrates wet and dry modes in the same system. CILAS particle size analyzer works on determination and on control of the particle size in powder matter, in suspension or in emulsion which meet the needs of many and various fields like cement, ceramics, manufacturing industries, pharmaceuticals, cosmetics, biology, food or environmental industries. Particle size analyzer
[5]
Shape anlyzer
[6]
Particle size analysis principles
[7]
Optical coatings CILAS uses a wide range of technologies which allow to target various applications in scientific, industrial, military and space fields : classical evaporation, assisted evaporation, ion beam assisted deposition, magnetron sputtering. The production means are suitable for large quantities of optical components, and automated to ensure the best reproducibility. It produces : • Optical components : lenses, mirrors, optical fibers, optromechanical systems • UV range : anti-reflection coatings, enhanced metallic coatings • Visible and near-IR range : anti-reflection coatings, metallic and dielectric coatings, absorbing coatings, partially-reflective coatings, beam-splitters, filters • IR range : anti-reflection coatings, metallic mirrors, filters Optical components - Thin film coatings
[8]
Large optical coatings
[9]
CILAS
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Adaptive optics Image has become an important tool for communication and scientific knowledge. When passing through distorting and turbulent media, Light waves and therefore images are distorted and blurred. Since several years, the adaptive optic has become an essential component for Wave Front Correction, and has found numerous applications in astronomy, military observation, correction of scientific and industrial laser beams, and in medical imaging, especially in ophthalmology. An Adaptive Optics system is a device which corrects, in real time, perturbed optical wavefronts. It is composed of: An analyzer which measures the wave deformation. A deformable mirror which corrects the wavefront. A computer which drives the mirror with informations coming from the analyzer.
Deformable mirror MONO63 for high power [10] laser
Deformable mirror SAM416 DM 4.5 for [10] Gemini
Prototype of the future M4 deformable mirror for [10] E-ELT
Optical ceramics CILAS develops transparent ceramics that are usable as optical components. These top-quality materials, which have an excellent level of resistance and transparency, are fabricated using new synthesis techniques. CILAS optical ceramics are the fruit of research that has been conducted by the Limoges Ceramic Processes and Surface Treatment Sciences Laboratory (SPCTS), a Joint Research Unit federating the French National Centre for Scientific Research (CNRS) and the local university, for some ten years. The SPCTS has developed a process to fabricate transparent ceramics, known as “YAG” (due to the name of the components: Yttrium and Aluminium Garnet). The feasibility of this operation was proven in cooperation with the Solids Modelling, Properties and Structures laboratory at the prestigious Ecole Centrale in Paris. This transparent ceramic production activity is also the fruit of a partnership between CILAS, Rhodia Electronics & Catalysis and the European Centre of Ceramics within the framework of the Ceramoptic project. This project is backed by the French Minister for Industry, the Limousin region and the City of Limoges.
CILAS
105
Transparent optical ceramic - Sample
[11]
Transparent optical ceramic - Zoom x50
[11]
Release furnace
[11]
Nanotechnology The term nanotechnologies refers to all theories and techniques used to produce and handle minuscule objects equal in size to one billionth of a metre (i.e. a nanometre). This technology requires very high precision tools to visualise, detect and analyse activities on such a small scale. The nanotechnologies sector is flourishing, with nanotechnology company turnover growing 100 times quicker than information technology majors. In this domain, CILAS coordinates the European project Saphir for the safe, integrated and controlled production of nanostructured products. Recently, CILAS has developed a new product : the Nanoparticle aerosol monitor - SafeAir.
References • The M4 adaptive unit for the E-ELT [12], B Crepy, 2009 • Multifunction laser source for ground and airborne applications [13], B Crepy, 4th International Symposium on Optronics in Defence and security in Paris, 2010 • Mechanism of the liquid-phase sintering for Nd:YAG ceramics [14], R. Bouleisteix, A. Maître, J-F. Baumard, C. Sallé, Y. Rabinovitch, 2008 (elsevier) • Five factors to consider when choosing a particle size analyzer [15], Nicolas Marchet, PBE/I, 2010 • Conference ceramics department - Optro 2010 [16], Y. Rabinovitch, 2010 • Progress on the laser source for DIRCM presented for the 4th International Symposium on Optronics in Defence and security in Paris (2010) [17], B, Crépy, 2009 • Stand-off biological detection by lif (laser induced fluorescence) lidar - Optro 2010 [18], O. Meyer, 2010 • Temperature insensitive laser for very compact designation function on small plateforms - Optro 2010 [19], J. Montagne, 2010
CILAS
External links • Official website [1]
References [1] http:/ / www. cilas. com/ index-us. htm [2] http:/ / www. cilas. com/ optics-detector-sld500. htm [3] http:/ / www. cilas. com/ laser-target-designator_dhy307. htm [4] http:/ / www. cilas. com/ glide-slope-indicator-helicopter-visual-landing-aids. htm [5] http:/ / www. cilas. com/ particle_size_analyzer. htm [6] http:/ / www. cilas. com/ shape-analysis. htm [7] http:/ / www. cilas. com/ laser-diffraction-particle-size-analysis-principles. htm [8] http:/ / www. cilas. com/ optical-component. htm [9] http:/ / www. Cilas. com/ large-optical-coating-paca2m. htm [10] http:/ / www. cilas. com/ adaptative-mirrors. htm [11] http:/ / www. cilas. com/ optical-ceramics. htm [12] http:/ / www. cilas. com/ cilas/ the-m4-adaptive-unit-for-the-e-elt. pdf [13] http:/ / www. cilas. com/ cilas/ multifunction-laser-source-for-ground-and-airborne-applications. pdf [14] http:/ / www. cilas. com/ cilas/ mechanism-of-the-liquid-phase-sintering-for-NdYAG-ceramics. pdf [15] http:/ / www. cilas. com/ particle-size-analyser/ five-factors-to-consider-when-choosing-a-particle-size-analyzer. pdf [16] http:/ / www. cilas. com/ cilas/ optro-2010-conference-ceramics-department. pdf [17] http:/ / www. cilas. com/ cilas/ progress-on-the-laser-source-for-dircm-at-cilas. pdf [18] http:/ / www. cilas. com/ defense-securite/ stand-off-biological-detection-by%20lif-lidar. pdf [19] http:/ / www. cilas. com/ defense-securite/ temperature-insensitive-laser-for-very-compact-designation. pdf
Circle grid analysis Circle grid analysis (CGA), also known as circle grid strain analysis, is a method of measuring the strain levels of sheet metal after a part is formed by stamping or drawing. The name itself is a fairly accurate description of the process. Literally, a grid of circles of known diameter is etched to the surface of the sheet metal to be formed. After the part is formed, the circles have been stretched into ellipses. By measuring the longest part of the ellipse (called the “major strain”) and the shortest part of the ellipse (called the “minor strain”), it is possible to determine how close any stamped part is to splitting or fracturing. The goal of using circle grid strain analysis is to predict potential problems before they become problems. Once you have a forming problem, chances are circle grid analysis won’t be able to help you, unless it’s intermittent enough to form a “good” part from time to time.
References • Engineering Quality Solutions [1]
References [1] http:/ / www. eqsgroup. com/ circle-grid-strain-analysis/ introduction-to-circle-grid-strain-analysis. asp
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Coefficient of performance
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Coefficient of performance The coefficient of performance or COP (sometimes CP), of a heat pump is the ratio of the change in heat at the "output" (the heat reservoir of interest) to the supplied work.
Equation The equation is:
where • •
is the heat supplied to the hot reservoir is the work consumed by the heat pump.
The COP for heating and cooling are thus different, because the heat reservoir of interest is different. When one is interested in how well a machine cools, the COP is the ratio of the heat removed from the cold reservoir to input work. However, for heating, the COP is the ratio to input work of the heat removed from the cold reservoir plus the heat added to the hot reservoir by the input work:
where •
is the heat removed from the cold reservoir.
Derivation According to the first law of thermodynamics, in a reversible system we can show that , where
is the heat given off by the hot heat reservoir and
and is the heat taken in
by the cold heat reservoir. Therefore, by substituting for W,
For a heat pump operating at maximum theoretical efficiency (i.e. Carnot efficiency), it can be shown that and
, where
and
are the absolute temperatures of the hot and
cold heat reservoirs respectively. At maximum theoretical efficiency,
Which is equal to the inverse of the ideal Carnot cycle efficiency because a heat pump is a heat engine operating in reverse. Similarly,
It can also be shown that temperature (the Kelvin or Rankine scale.)
. Note that these equations must use the absolute
Coefficient of performance
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applies to heat pumps and
applies to air conditioners or refrigerators. For heat engines,
see Efficiency. Values for actual systems will always be less than these theoretical maximums. In Europe, ground source heat pump units are standard tested at
is 35 °C (95 °F) and
is 0 °C (32 °F). According to the
above formula, the maximum achievable COP would be 8.8. Test results of the best systems are around 4.5. When measuring installed units over a whole season and one also counts the energy needed to pump water through the piping systems, then seasonal COP's are around 3.5 or less. This indicates room for improvement.
Improving COP As the formula shows, to improve the COP of a heat pump system, one needs to reduce the temperature gap minus
at which the system works. For a heating system this would mean two things. One is to reduce output
temperature to around 30 °C (86 °F) which requires piped floor- or wall- or ceiling heating, or oversized water to air heaters. The other is to increase input temperature (by using an oversized ground source). For an air cooler, COP could be improved by using ground water as an input instead of air, and by reducing temperature drop on output side through increasing air flow. For both systems, also increasing the size of pipes and air canals would help to reduce noise and the energy consumption of pumps (and ventilators). Also the heat pump itself can be improved a lot. The two most simple ways to improve heat pump units, is to double the size of the internal heat exchangers relative to the power of the compressor, and to reduce the system's internal temperature gap over the compressor. This last measure however, makes such heat pumps unsuitable to produce output above roughly 40 °C (104 °F) which means that a separate machine is needed for producing hot tap water.
Example A geothermal heat pump operating at
3.5 provides 3.5 units of heat for each unit of energy consumed
(i.e. 1 kWh consumed would provide 3.5 kWh of output heat). The output heat comes from both the heat source and 1 kWh of input energy, so the heat-source is cooled by 2.5 kWh, not 3.5 kWh. A heat pump of
3.5, such as in the example above, could be less expensive to use than even the most
efficient gas furnace except in areas where the electricity cost per unit is higher than 3.5 times the cost of natural gas (i.e. Connecticut or New York City). A heat pump cooler operating at
2.0 removes 2 units of heat for each unit of energy consumed (e.g. an
air conditioner consuming 1 kWh would remove 2 kWh of heat from a building's air). Given the same energy source and operating conditions, a higher COP heat pump will consume less purchased energy than one with a lower COP. The overall environmental impact of a heating or air conditioning installation depends on the source of energy used as well as the COP of the equipment. The operating cost to the consumer depenends on the cost of energy as well as the COP or efficiency of the unit. Some areas provide two or more sources of energy, for example, natural gas and electricity. A high COP of a heat pump may not entirely overcome a relatively high cost for electicity compared with the same heating value from natural gas. For example, the 2009 US average price per therm (100,000 BTU) of electricity was $3.38 while the average price per therm of natural gas was $1.16.[1] Using these prices, a heat pump with a COP of 3.5 in moderate climate would cost $0.97[2] to provide one therm of heat, while a high efficiency gas furnace with 95% efficiency would cost $1.22[3] to provide one therm of heat. With these average prices, the heat pump costs 20% less[4] to provide the same amount of heat. At 0 °F (-18 °C) COP is much lower. Then, the same system costs as much to operate as an efficient gas heater. The yearly savings will depend on the actual cost of electricity and natural gas, which can both vary widely. However, a COP may help make a determination of system choice based on carbon contribution. Although a heat pump may cost more to operate than a conventional natural gas or electric heater, depending on the source of electricity generation in one's area, it may contribute less net carbon dioxide to the environment than burning natural
Coefficient of performance gas or heating fuel. If locally no green electricity is available, then carbon wise the best option would be to drive a heat pump on piped gas or oil, to store excess heat in the ground source for use in winter, while using the same machine also for producing electricity with a built-in Stirling engine.
Conditions of use While the COP is partly a measure of the efficiency of a heat pump, it is also a measure of the conditions under which it is operating: the COP of a given heat pump will rise as the input temperature increases or the output temperature decreases because it is linked to a warm temperature distribution system like underfloor heating.
References [1] Based on average prices of 11.55 cents per kWh for electricity (http:/ / www. eia. doe. gov/ cneaf/ electricity/ epm/ table5_3. html) and $13.68 per thousand cubic feet for natural gas (http:/ / tonto. eia. doe. gov/ dnav/ ng/ hist/ n3010us3a. htm), and conversion factors of 29.308 kWh per therm and 97.2763 cubic feet per therm (http:/ / www. eia. doe. gov/ kids/ energyfacts/ science/ energy_calculator. html). [2] $3.38/3.5~$0.97 [3] $1.16/.95~$1.22 [4] ($1.16-$0.95)/$1.16~20%
External links • Discussion on changes to COP of a heat pump depending on input and output temperatures (http://www.icax. co.uk/gshp.html)
Collapse action Collapse action is a device behaviour that snaps a switch into place, usually using a bistable element. When flipping a light switch, strain on one spring increases until it flips position, pulling down the switch. Collapse action allows you to remove your hand from the switch without risk it falls to the down position, as the force needed to overcome the resistance is too great. The action also does not exert force in the lower position, avoiding the spontaneous rise to the up position that a spring invites.
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Combined cycle
Combined cycle In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators. The principle is that the exhaust of one heat engine is used as the heat source for another, thus extracting more useful energy from the heat, increasing the system's overall efficiency. This works because heat engines are only able to use a portion of the energy their fuel generates (usually less than 50%). The remaining heat (e.g., hot exhaust fumes) from combustion is generally wasted. Combining two or more thermodynamic cycles results in improved overall efficiency, reducing fuel costs. In stationary power plants, a successful, common combination is the Brayton cycle (in the form of a turbine burning natural gas or synthesis gas from coal) and the Rankine cycle (in the form of a steam power plant). Multiple stage turbine or steam cylinders are also common. Historically successful combined cycles have used hot cycles with mercury vapor turbines, magnetohydrodynamic generators or molten carbonate fuel cells, with steam plants for the low temperature bottoming cycle. Bottoming cycles operating from a steam condenser's heat are theoretically possible, but uneconomical because of the very large, expensive equipment needed to extract energy from the small temperature differences between condensing steam and outside air or water. However, it is common in cold climates (such as Finland) to drive community heating systems from a power plant's condenser heat. Such cogeneration systems can yield theoretical efficiencies above 95%. In automotive and aeronautical engines, turbines have been driven from the exhausts of Otto, Diesel, and Crower cycles. These are called turbo-compound engines. Aside from turbochargers, they have failed commercially because their mechanical complexity and weight are less economical than multistage turbines. Stirling engines are also a good theoretical fit for this application. In a combined cycle power plant (CCPP), or combined cycle gas turbine (CCGT) plant, a gas turbine generator generates electricity and heat in the exhaust is used to make steam, which in turn drives a steam turbine to generate additional electricity. This last step enhances the efficiency of electricity generation. Many new gas power plants in North America and Europe are of this type. Such an arrangement used for marine propulsion is called combined gas (turbine) and steam (turbine) (COGAS).
Design principle In a thermal power station water is the working medium. High pressure steam requires strong, bulky components. High temperatures require expensive alloys made from nickel or cobalt, rather than inexpensive steel. These alloys limit practical steam temperatures to 655 °C while the lower temperature of a steam plant is fixed by the boiling point of water. With these limits, a steam plant has a fixed upper efficiency of 35 to 42%. An open circuit gas turbine cycle has a compressor, a combustor and a turbine. For gas turbines the amount of metal that must withstand the Working principle of a combined cycle power high temperatures and pressures is small, and lower quantities of plant (Legend: 1-Electric generators, 2-Steam expensive materials can be used. In this type of cycle, the input turbine, 3-Condenser, 4-Pump, 5-Boiler/heat temperature to the turbine (the firing temperature), is relatively high exchanger, 6-Gas turbine) (900 to 1,400 °C). The output temperature of the flue gas is also high (450 to 650 °C). This is therefore high enough to provide heat for a second cycle which uses steam as the working fluid; (a Rankine cycle).
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Combined cycle In a combined cycle power plant, the heat of the gas turbine's exhaust is used to generate steam by passing it through a heat recovery steam generator (HRSG) with a live steam temperature between 420 and 580 °C. The condenser of the Rankine cycle is usually cooled by water from a lake, river, sea or cooling towers. This temperature can be as low as 15 °C In an automotive powerplant, an Otto, Diesel, Atkinson or similar engine would provide one part of the cycle and the waste heat would power a Rankine cycle steam or Stirling engine, which could either power ancillaries (such as the alternator) or be connected to the crankshaft by a turbo compounding system.
Typical size of CCGT plants For large scale power generation, a typical set would be a 270 MW gas turbine coupled to a 130 MW steam turbine giving 400 MW. A typical power station might consist of between 1 and 6 such sets. Plant size is important in the cost of the plant. The larger plant sizes benefit from economies of scale (lower initial cost per kilowatt) and improved efficiency. A single shaft combined cycle plant comprises a gas turbine and a steam turbine driving a common generator. In a multi-shaft combined cycle plant, each gas turbine and each steam turbine has its own generator. The single shaft design provides slightly less initial cost and slightly better efficiency than if the gas and steam turbines had their own generators. The multi-shaft design enables 2 or more gas turbines to operate in conjunction with a single steam turbine, which can be more economical than a number of single shaft units. The primary disadvantage of multiple stage combined cycle power plants is that the number of steam turbines, condensers and condensate systems - and perhaps the number of cooling towers and circulating water systems increases to match the number of gas turbines. For a multiple shaft combined cycle power plant there is only one steam turbine, condenser and the rest of the heat sink for up to three gas turbines; only their size increases. Having only one large steam turbine and heat sink results in low cost because of economies of scale. A larger steam turbine also allows the use of higher pressures and results in a more efficient steam cycle. Thus the overall plant size and the associated number of gas turbines required have a major impact on whether a single shaft combined cycle power plant or a multiple shaft combined cycle power plant is more economical. Gas turbines of about 150 MW size are already in operation manufactured by at least four separate groups - General Electric and its licensees, Alstom, Siemens, and Westinghouse/Mitsubishi. These groups are also developing, testing and/or marketing gas turbine sizes of about 200 MW. Combined cycle units are made up of one or more such gas turbines, each with a waste heat steam generator arranged to supply steam to a single steam tubine, thus forming a combined cycle block or unit. Typical Combined cycle block sizes offered by three major manufacturers (Alstom, General Electric and Siemens) are roughly in the range of 50 MW to 500 MW and costs are about $600/kW.
Efficiency of CCGT plants To avoid confusion, the efficiency of heat engines and power stations should be stated HHV (aka Gross Heating Value) or LCV (aka Net Heating value), and whether Gross output at the generator terminals or Net Output at the power station fence are being considered. In general in service Combined Cycle efficiencies are over 50 percent on a lower heating value and Gross Output basis. Most combined cycle units, especially the larger units, have peak, steady state efficiencies of 55 to 59%. Research aimed at 1370°C (2500°F) turbine inlet temperature has led to even more efficient combined cycles and 60 percent efficiency has been reached in the combined cycle unit of Baglan Bay, a GE H-technology gas turbine with a NEM 3 pressure reheat boiler, utilising steam from the HRSG to cool the turbine blades. Siemens AG announced in may 2011 to have achieved a 60.75% net efficiency with a 578 megawatts SGT5-8000H gas turbine at the Irsching Power Station.[1]
111
Combined cycle By combining both gas and steam cycles, high input temperatures and low output temperatures can be achieved. The efficiency of the cycles add, because they are powered by the same fuel source. So, a combined cycle plant has a thermodynamic cycle that operates between the gas-turbine's high firing temperature and the waste heat temperature from the condensers of the steam cycle. This large range means that the Carnot efficiency of the cycle is high. The actual efficiency, while lower than this, is still higher than that of either plant on its own.[2] The actual efficiency achievable is a complex area.[3] The electric efficiency of a combined cycle power station, calculated as electric energy produced as a percent of the lower heating value of the fuel consumed, may be as high as 58 percent when operating new, ie unaged, and at continuous output which are ideal conditions. As with single cycle thermal units, combined cycle units may also deliver low temperature heat energy for industrial processes, district heating and other uses. This is called cogeneration and such power plants are often referred to as a Combined Heat and Power (CHP) plant.
Boosting Efficiency The efficiency of CCGT and GT can be boosted by pre-cooling combustion air. This is practised in hot climates and also has the effect of increasing power output. This is achieved by evaporative cooling of water using a moist matrix placed in front of the turbine, or by using Ice storage air conditioning. The latter has the advantage of greater improvements due to the lower temperatures available. Furthermore, ice storage can be used as a means of load control or load shifting since ice can be made during periods of low power demand and, potentially in the future the anticipated high availability of other resources such as renewables during certain periods.
Supplementary firing and blade cooling Supplementary firing may be used in combined cycles (in the HRSG) raising exhaust temperatures from 600°C (GT exhaust) to 800 or even 1000°C. Using supplemental firing will however not raise the combined cycle efficiency for most combined cycles. For single boilers it may raise the efficiency if fired to 700- 750°C - for multiple boilers however, supplemental firing is often used to improve peak power production of the unit, or to enable higher steam production to compensate for failure of a second unit. Maximum supplementary firing refers to the maximum fuel that can be fired with the oxygen available in the gas turbine exhaust. The steam cycle is conventional with reheat and regeneration. Hot gas turbine exhaust is used as the combustion air. Regenerative air preheater is not required. A fresh air fan which makes it possible to operate the steam plant even when the gas turbine is not in operation,increases the availability of the unit. The use of large supplementary firing in Combined Cycle Systems with high gas turbine inlet temperatures causes the efficiency to drop. For this reason the Combined Cycle Plants with maximum supplementary firing are only of minimal importance today, in comparison to simple Combined Cycle installations. However, they have two advantages that is a) coal can be burned in the steam generator as the supplementary fuel, b) has very good part load efficiency. The HRSG can be designed with supplementary firing of fuel after the gas turbine in order to increase the quantity or temperature of the steam generated. Without supplementary firing, the efficiency of the combined cycle power plant is higher, but supplementary firing lets the plant respond to fluctuations of electrical load. Supplementary burners are also called duct burners. More fuel is sometimes added to the turbine's exhaust. This is possible because the turbine exhaust gas (flue gas) still contains some oxygen. Temperature limits at the gas turbine inlet force the turbine to use excess air, above the optimal stoichiometric ratio to burn the fuel. Often in gas turbine designs part of the compressed air flow bypasses the burner and is used to cool the turbine blades. Supplementary firing raises the temperature of the exhaust gas from 800 to 900 degree Celsius. Relatively high flue gas temperature raises the condition of steam (84 bar, 525 degree Celsius) thereby improving the efficiency of steam cycle.
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Combined cycle
Fuel for combined cycle power plants The turbines used in Combined Cycle Plants are commonly fueled with natural gas. However, global natural gas reserves are expected to be fully consumed by 2070.[4] Despite this fact, it is becoming the fuel of choice for an increasing amount of private investors and consumers because it is more versatile than coal or oil and can be used in 90% of energy applications. Chile which once depended on hydropower for 70% of its electricity supply, is now boosting its gas supplies to reduce reliance on its drought afflicted hydro dams. Similarly China is tapping its gas reserves to reduce reliance on coal, which is currently burned to generate 80% of the country’s electric supply. Where the extension of a gas pipeline is impractical or cannot be economically justified, electricity needs in remote areas can be met with small scale Combined Cycle Plants, using renewable fuels. Instead of natural gas, Combined Cycle Plants can be filled with biogas derived from agricultural and forestry waste, which is often readily available in rural areas. Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other fuels can be used. The supplementary fuel may be natural gas, fuel oil, or coal. Biofuels can also be used. Integrated solar combined cycle power stations combine the energy harvested from solar radiation with another fuel to cut fuel costs and environmental impact. The first such system to come online is Yazd power plant, Iran[5] [6] and more are under construction at Hassi R'mel, Algeria and Ain Beni Mathar, Morocco. Next generation nuclear power plants are also on the drawing board which will take advantage of the higher temperature range made available by the Brayton top cycle, as well as the increase in thermal efficiency offered by a Rankine bottoming cycle. Low-Grade Fuel for Turbines: Gas turbines burn mainly natural gas and light oil. Crude oil, residual, and some distillates contain corrosive components and as such require fuel treatment equipment. In addition, ash deposits from these fuels result in gas turbine debating’s of up to 15 percent they may still be economically attractive fuels however, particularly in combined-cycle plants. Sodium and potassium are removed from residual, crude and heavy distillates by a water washing procedure. A simpler and less expensive purification system will do the same job for light crude and light distillates. A magnesium additive system may also be needed to reduce the corrosive effects if vanadium is present. Fuels requiring such treatment must have a separate fuel-treatment plant and a system of accurate fuel monitoring to assure reliable, low-maintenance operation of gas turbines.
Configuration of CCGT plants The combined-cycle system includes single-shaft and multi-shaft configurations. The single-shaft system consists of one gas turbine, one steam turbine, one generator and one Heat Recovery Steam Generator (HRSG), with the gas turbine and steam turbine coupled to the single generator in a tandem arrangement on a single shaft. Key advantages of the single-shaft arrangement are operating simplicity, smaller footprint, and lower startup cost. Single-shaft arrangements, however, will tend to have less flexibility and equivalent reliability than multi-shaft blocks. Additional operational flexibility is provided with a steam turbine which can be disconnected, using an synchro-self-shifting (SSS) Clutch,[7] for start up or for simple cycle operation of the gas turbine. Multi-shaft systems have one or more gas turbine-generators and HRSGs that supply steam through a common header to a separate single steam turbine-generator. In terms of overall investment a multi-shaft system is about 5% higher in costs. Single- and multiple-pressure non-reheat steam cycles are applied to combined-cycle systems equipped with gas turbines having rating point exhaust gas temperatures of approximately 540 °C or less. Selection of a single- or multiple-pressure steam cycle for a specific application is determined by economic evaluation which considers plant installed cost, fuel cost and quality, plant duty cycle, and operating and maintenance cost. Multiple-pressure reheat steam cycles are applied to combined-cycle systems with gas turbines having rating point exhaust gas temperatures of approximately 600 °C.
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Combined cycle
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The most efficient power generation cycles are those with unfired HRSGs with modular pre-engineered components. These unfired steam cycles are also the lowest in cost. Supplementary-fired combined-cycle systems are provided for specific application. The primary regions of interest for cogeneration combined-cycle systems are those with unfired and supplementary fired steam cycles. These systems provide a wide range of thermal energy to electric power ratio and represent the range of thermal energy capability and power generation covered by the product line for thermal energy and power systems. by Engr. Bilal Pervez
Integrated gasification combined cycle (IGCC) An integrated gasification combined cycle, or IGCC, is a power plant using synthesis gas (syngas). Syngas can be produced from a number of sources, including coal and biomass.
Integrated solar combined cycle (ISCC) An integrated solar combined cycle, or ISCC, is a power plant using solar thermal collectors. This is typically in the form of parabolic troughs.
Automotive use Any turbocharged engine is effectively a combined cycle with the turbo charger extracting extra energy from the exhaust gases. Theoretically, this extracted energy could be used to drive the wheels, but it is more practical to use it to force air into the engine which reduces the suction loss and thereby improves the efficiency overall. On large marine diesels turbo-compounding has been employed where the turbocharger physically pushes the engine around via some sort of gearing arrangement. Combined cycles have traditionally only been used in large power plants. BMW, however, has proposed that automobiles use exhaust heat to drive steam turbines.[8] This can even be connected to the car or truck's cooling system to save space and weight, but also to provide a condenser in the same location as the radiator and preheating of the water using heat from the engine block. However, stirling engines can also be used if light weight is a priority (as in a sports car or racing application), because they use a gas such as air rather than water as the working fluid. It may be possible to use the pistons in a reciprocating engine for both combustion and steam expansion like in the Crower six stroke.[9]
Aeromotive use Some versions of the Wright R-3350 were produced as turbo-compound engines. Three turbines driven by exhaust gases, known as power recovery turbines, provided nearly 600 hp at takeoff. These turbines added power to the engine crankshaft through bevel gears and fluid couplings.[10]
References
[1] "Siemens pushes world record in efficiency to over 60 percent while achieving maximum operating flexibility" (http:/ / www. siemens. com/ press/ en/ pressrelease/ ?press=/ en/ pressrelease/ 2011/ fossil_power_generation/ efp201105064. htm). Siemens AG. 19 May 2011. . [2] "Efficiency by the Numbers" (http:/ / memagazine. asme. org/ Web/ Efficiency_by_Numbers. cfm) by Lee S. Langston [3] "The difference between LCV and HCV (or Lower and Higher Heating Value, or Net and Gross) is clearly understood by all energy engineers. There is no ‘right’ or ‘wrong’ definition." (http:/ / www. claverton-energy. com/ the-difference-between-lcv-and-hcv-or-lower-and-higher-heating-value-or-net-and-gross-is-clearly-understood-by-all-energy-engineers-there-is-no-right-or-wrong html). Claverton Energy Research Group. . [4] "Natural Gas reserves" (http:/ / www. bp. com/ sectiongenericarticle800. do?categoryId=9037178& contentId=7068624). BP. . Retrieved 19 September 2011.
Combined cycle [5] "Yazd Solar Energy Power Plant 1st in its kind in world" (http:/ / payvand. com/ news/ 07/ apr/ 1132. html). Payvand Iran news. 13 April 2007. . [6] "CCGT Plants in Iran - other provinces" (http:/ / www. industcards. com/ cc-iran. htm). Power Plants Around the World Photo Gallery. . [7] "SSS Clutch Operating Principle" (http:/ / www. sssclutch. com/ howitworks/ 100-2SSSPrinciples. pdf). SSS Gears Limited. . [8] "BMW Turbosteamer gets hot and goes" (http:/ / www. autoblog. com/ 2005/ 12/ 09/ bmw-turbosteamer-gets-hot-and-goes/ ) by John Neff, AutoBlog, December 9, 2005 [9] "Inside Bruce Crower’s Six-Stroke Engine" (http:/ / www. autoweek. com/ apps/ pbcs. dll/ article?AID=/ 20060227/ FREE/ 302270007/ 1023/ THISWEEKSISSUE) By Pete Lyons, AutoWeek, February 23, 2006 [10] Goleta Air and Space Museum: 2002 Camarillo EAA Fly-in (http:/ / www. air-and-space. com/ 20020811 Camarillo page 1. htm)
External links • Hunstown: Ireland's most efficient power plant (http://www.powergeneration.siemens.com/en/press/ pg200303017e/index.cfm) @ Siemens Power Generation website • ABB Power Generation website (http://www.abb.com/powergeneration) @ ABB_Group • Natural Gas Combined-cycle Gas Turbine Power Plants (http://www.westgov.org/wieb/electric/Transmission Protocol/SSG-WI/pnw_5pp_02.pdf) Northwest Power Planning Council, New Resource Characterization for the Fifth Power Plan, August 2002 • Combined cycle solar power (http://www.ingenia.org.uk/ingenia/articles.aspx?index=244&print=true)
Compliant mechanism In mechanical engineering, compliant mechanisms are flexible mechanisms that transfer an input force or displacement to another point through elastic body deformation. These are usually monolithic (single-piece) or jointless structures with certain advantages over the rigid-body, or jointed, mechanisms. Since the compliant mechanisms are single-piece structures, there is no need of assembly. With no joints, "rubbing" between two parts or friction as seen at the joints of rigid body mechanisms is absent. Compliant mechanisms are elastic. They do not have the backlash common in rigid-body, jointed mechanisms. They are cheaper to make than the jointed variety. Compliant mechanisms are usually designed using two techniques, the first being a pseudo-rigid-body model and the second, the topology optimization. Other techniques are being conceived to design these mechanisms. Compliant mechanisms manufactured in a plane the have motion emerging from that plane are known as lamina emergent mechanisms (LEMs) The flexible drive or resilient drive, often used to couple an electric motor to a machine (for example. a pump), is one example. The drive consists of a rubber "spider" sandwiched between two metal dogs. One dog is fixed to the motor shaft and the other to the pump shaft. The flexibility of the rubber part compensates for any slight misalignment between the motor and the pump. See rag joint and giubo. Compliant mechanisms are found in micro-electromechanical systems. For example, amplifying compliant mechanisms are used in micro-accelerometers and electro-thermal micro-actuators. On Dec 17, 2007, the first International Symposium on Compliant Mechanisms was held at the Indian Institute of Science, Bangalore. The Second International Symposium on Compliant Mechanisms ([1]) was held on May 19-20th 2011 at Delft, The Netherlands.
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Compliant mechanism
Research Labs and Researchers • University of Michigan Compliant Mechanism Design Lab [2] • Prof. Larry Howell at Brigham Young University Compliant Mechanisms research [3] • The Multidisciplinary and Multiscale Device and Design Laboratory (M2D2) at the Indian Institute of Science, Bangalore [4] • Prof. Sridhar Kota's Home Page [5] • Prof. Martin Culpepper at MIT Precision Compliant Systems Laboratory [6] • Prof. Shorya Awtar at University of Michigan [7] • Prof. Just L. Herder at Delft University of Technology [8] • Prof. G. K. Ananthasuresh at IISc, Bangalore [9] • Prof. Stephen L. Canfield at Tennessee Tech University [10] • Prof. Charles Kim at Bucknell University [11] • Prof. Anupam Saxena at IIT Kanpur, India [12] • Prof. Mary Frecker at The Pennsylvania State University, University Park [13]
References For a comprehensive list of references on synthesis of compliant mechanisms check the wiki page from the Interactive Mechanisms Research Group [14]
References [1] http:/ / compliantmechanisms. 3me. tudelft. nl/ mw/ index. php/ CoMe2011'''CoMe2011''' [2] http:/ / www. engin. umich. edu/ labs/ csdl/ index. htm [3] http:/ / cmr. byu. edu/ [4] http:/ / www. mecheng. iisc. ernet. in/ ~m2d2/ [5] http:/ / www-personal. umich. edu/ ~kota/ [6] http:/ / pcsl. mit. edu/ [7] http:/ / www-personal. umich. edu/ ~awtar/ [8] http:/ / compliantmechanisms. 3me. tudelft. nl [9] http:/ / www. mecheng. iisc. ernet. in/ ~suresh/ [10] http:/ / www. tntech. edu/ ME/ Faculty_Bios/ scanfieldbio. html [11] http:/ / www. bucknell. edu/ x16384. xml [12] http:/ / home. iitk. ac. in/ ~anupams/ [13] http:/ / edog. mne. psu. edu/ [14] http:/ / compliantmechanisms. 3me. tudelft. nl/ mw/ index. php/ Compliant_mechanisms
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Compound lever
117
Compound lever The compound lever is a simple machine operating on the premise that the resistance from one lever in a system of levers will act as power for the next, and thus the applied force will be amplified from one lever to the next (as long as the mechanical advantage for each lever is greater than one). Almost all scales use some sort of compound lever to work. Other examples include nail clippers and piano keys.
Nail clippers are a simple form of compound lever
Mechanical advantage A lever arm uses the fulcrum to lift the load using and intensifying an applied force. In practice, conditions may prevent the use of a single lever to accomplish the desired result,[1] e.g., a restricted space, the inconvenient location of the point of delivery of the resultant force, or the prohibitive length of the lever arm needed. In these conditions, combinations of simple levers, called compound levers, are used. Compound levers can be constructed from first, second and/or third-order levers. In all types of compound lever, the rule is that force multiplied by the force arm equals the weight multiplied by the weight arm. The output from one lever becomes the input for the next lever in the system, and so the advantage is magnified. The figure on the left illustrates a compound lever formed from two first-class levers, along with a short derivation of how to compute the mechanical advantage. With the dimensions shown, the mechanical advantage, W/F can be calculated as(9x10)/(3x4)= 7.5 This means that an applied force of 1 pound (or 1 kg) could lift a weight of 7.5 lb (or 7.5 kg). Alternately, if the position of the fulcrum on lever AA' were moved so that A1=4 units and A2=9 units, then the mechanical advantage W/F is calculated as (4x9)/(9x4) = 1 This means that an applied force will lift an equivalent weight and there is no mechanical advantage. This is not usually the goal of a compound lever system, though in rare situations the geometry may suit a specific purpose.
Compound lever
118
Examples A few examples of the compound lever are the scale, train brakes, and a common type of nail clippers. Another example is the elbow-joint press, which is used in printing, molding or handloading bullets, minting coins and medals, and in hole punching. Compound balances are used to weigh heavy items. These all use multiple levers to magnify force to accomplish a specific purpose. The train brake translates the force of pushing back the stick to the levers and they rub against the wheels, using friction to slow and eventually stop the train. These are everyday applications of this mechanism.
A handloading press uses a compound lever to reduce the force the operator must apply and confine the action to a relatively small space.
A piano key is a compound lever of the first-class, since the fulcrum is between the weight to be moved and the power. The purpose of this lever is to translate a small movement (depression of the key) into a larger and fast movement of the hammer on the strings. The quality of the resulting tone depends on whether the final speed is brought about by gradual or sudden movement of the key.[2] A compound lever translates the small movement of a piano key to the fast, hard strike of the hammer on the strings
History
The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. "Give me a place to stand, and I shall move the earth with a lever" is a remark attributed to Archimedes, who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).[3] The idea of the compound lever is attributed to the Birmingham inventor John Wyatt in 1743,[4] when he designed a weighing machine that used four compound levers to transfer a load from a weighing platform to a central lever from which the weight could be measured.[5]
Compound lever
119
References [1] [2] [3] [4]
Popular Mechanics magazine, April, 1924, p. 615-617 Presser T, Cooke JF. The etude. T. Presser, 1916, p. 497 Mackay, Alan Lindsay (1991). "Archimedes ca 287–212 BC". A Dictionary of scientific quotations. London: Taylor and Francis. p. 11. Ceccarelli, Marco (2007). Distinguished Figures in Mechanism and Machine Science: Their Contributions and Legacies (http:/ / books. google. co. uk/ books?id=UmBnVMA5ri4C). Dordrecht: Springer. p. 16. ISBN 1402063652. . Retrieved 2010-01-17. "Then in 1743 John Wyatt (1700–1766) introduced the idea of the compound lever, in which two or more levers work together to further reduce effort." [5] "The History of Weighing" (http:/ / www. averyweigh-tronix. com/ main. aspx?p=1. 1. 3. 4). Avery Weigh-Tronix. . Retrieved 2010-01-17.
Compression (physical) Physical compression is the result of the subjection of a material to compressive stress, which results in reduction of volume as compared to an uncompressed but otherwise identical state. The opposite of compression in a solid is tension. In any medium transmitting waves, the opposite of compression is rarefaction. In simple terms, compression is a pushing force.
Explanation Compression has many implications in materials science, physics and structural engineering, for compression yields noticeable amounts of stress and tension.
Compression test on a universal testing machine
By inducing compression, mechanical properties such as compressive strength or modulus of elasticity, can be measured. Scientists and engineers may utilize compression machines to measure the resistance of materials and structures to compression. Compression machines range from very small table top systems to ones with over 53 MN capacity.[1]
In engines Internal combustion engines In internal combustion engines it is a necessary condition of economy to compress the explosive mixture before it is ignited: in the Otto cycle, for instance, the second stroke of the piston effects the compression of the charge which has been drawn into the cylinder by the first forward stroke.
Steam engines The term is applied to the arrangement by which the exhaust valve of a steam engine is made to close, shutting a portion of the exhaust steam in the cylinder, before the stroke of the piston is quite complete. This steam being compressed as the stroke is completed, a cushion is formed against which the piston does work while its velocity is being rapidly reduced, and thus the stresses in the mechanism due to the inertia of the reciprocating parts are lessened. This compression, moreover, obviates the shock which would otherwise be caused by the admission of the fresh steam for the return stroke.
Compression (physical)
References [1] NIST, Large Scale Structure Testing Facility (http:/ / www. nist. gov/ bfrl/ facilities_instruments/ large_scale_struct_testing_fac. cfm), , retrieved 04-05-2010.
• Beer, Ferdinand Pierre; Elwood Russell Johnston, John T. DeWolf (1992). Mechanics of Materials. McGraw-Hill Professional. ISBN 0071129391.
Constant air volume Constant Air Volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space.[1] Most CAV systems are small, and serve a single thermal zone. However, variations such as CAV with reheat, CAV multizone, and CAV primary-secondary systems can serve multiple zones and larger buildings. In mid to large size buildings, new central CAV systems are somewhat rare. Due to fan energy savings potential, variable air volume systems are more common. However, in small buildings and residences, CAV systems are often the system of choice due to simplicity, low cost, and reliability. Such small CAV systems often have on/off control, rather than supply air temperature modulation, to vary their heating or cooling capacities. There are two types of CAV systems that are commonly in use to modify the supply air temperature: the terminal reheat system and the mixed air system. The terminal reheat system cools the air in the air handling unit down to the lowest possible needed temperature within its zone of spaces. This supplies a comfortable quality to the space, but wastes energy. The mixed air system has two air streams, typically one for the coldest and one for the hottest needed air temperature in the zone. The two air streams are strategically combined to offset the space's load. The mixed air system option is not as proficient at controlling the humidity, yet it does do well at controlling the temperature. (reference: Heating/Piping/Air Conditioning, December 1993 p.53-57)
References [1] Systems and Equipment volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2004
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Constrained-layer damping
121
Constrained-layer damping Constrained-layer damping is a mechanical engineering technique for suppression of vibration. Typically a viscoelastic or other damping material, is sandwiched between two sheets of stiff materials that lack sufficient damping by themselves.
External links Constrained-Layer Systems Provide Weight-Efficient, High-level Damping material
[1]
by a maker of viscoelastic damping
Passive Viscoelastic Constrained Layer Damping Application for a Small Aircraft Landing Gear System engineering Master's thesis
[2]
An
References [1] http:/ / www. earsc. com/ pdfs/ engineering/ CLD. pdf [2] http:/ / scholar. lib. vt. edu/ theses/ available/ etd-10102008-124400/ unrestricted/ Thesis_CraigGallimore_Rev1. pdf
Contact mechanics Contact mechanics is the study of the deformation of solids that touch each other at one or more points.[1] [2] The physical and mathematical formulation of the subject is built upon the mechanics of materials and continuum mechanics and focuses on computations involving elastic, viscoelastic, and plastic bodies in static or dynamic contact. Central aspects in contact mechanics are the pressures and adhesion acting perpendicular to the contacting bodies' surfaces, the normal direction, and the frictional stresses acting tangentially between the surfaces. This page focuses mainly on the normal direction, i.e. on frictionless contact mechanics. Frictional contact mechanics is discussed separately.
Stresses in a contact area loaded simultaneously with a normal and a tangential force. Stresses were made visible using photoelasticity.
Contact mechanics is foundational to the field of mechanical engineering; it provides necessary information for the safe and energy efficient design of technical systems and for the study of tribology and indentation hardness. Principles of contacts mechanics can be applied in areas such as locomotive wheel-rail contact, coupling devices, braking systems, tires, bearings, combustion engines, mechanical linkages, gasket seals, metalworking, metal forming, ultrasonic welding, electrical contacts, and many others. Current challenges faced in the field may include stress analysis of contact and coupling members and the influence of lubrication and material design on friction and wear. Applications of contact mechanics further extend into the micro- and nanotechnological realm. The original work in contact mechanics dates back to 1882 with the publication of the paper "On the contact of elastic solids"[3] ("Ueber die Berührung fester elastischer Körper" [4]) by Heinrich Hertz. Hertz was attempting to understand how the optical properties of multiple, stacked lenses might change with the force holding them together.
Contact mechanics Hertzian contact stress refers to the localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. This amount of deformation is dependent on the modulus of elasticity of the material in contact. It gives the contact stress as a function of the normal contact force, the radii of curvature of both bodies and the modulus of elasticity of both bodies. Hertzian contact stress forms the foundation for the equations for load bearing capabilities and fatigue life in bearings, gears, and any other bodies where two surfaces are in contact.
History Classical contact mechanics is most notably associated with Heinrich Hertz.[5] In 1882 Hertz solved the problem involving contact between two elastic bodies with curved surfaces. This still-relevant classical solution provides a foundation for modern problems in contact mechanics. For example, in mechanical engineering and tribology, Hertzian contact stress, is a description of the stress within mating parts. In general, the Hertzian contact stress usually refers to the stress close to the area of contact between two spheres of different radii. It was not until nearly one hundred years later that Johnson, Kendall, and Roberts found a similar solution for the case of adhesive contact.[6] This theory was rejected by Boris Derjaguin and co-workers[7] who proposed a different theory of adhesion[8] in the 1970s. The Derjaguin model came to be known as the When a sphere is pressed against an elastic material, the contact area increases. DMT (after Derjaguin, Muller and Toporov) [8] model, and the Johnson et al. model came to be known as the JKR (after Johnson, Kendall and Roberts) model for adhesive elastic contact. This rejection proved to be instrumental in the development of the Tabor[9] and later Maugis[7] [10] parameters that quantify which contact model (of the JKR and DMT models) represent adhesive contact better for specific materials. Further advancement in the field of contact mechanics in the mid-twentieth century may be attributed to names such as Bowden and Tabor. Bowden and Tabor were the first to emphasize the importance of surface roughness for bodies in contact.[11] [12] Through investigation of the surface roughness, the true contact area between friction partners is found to be less than the apparent contact area. Such understanding also drastically changed the direction of undertakings in tribology. The works of Bowden and Tabor yielded several theories in contact mechanics of rough surfaces. The contributions of Archard (1957)[13] must also be mentioned in discussion of pioneering works in this field. Archard concluded that, even for rough elastic surfaces, the contact area is approximately proportional to the normal force. Further important insights along these lines were provided by Greenwood and Williamson (1966),[14] Bush (1975),[15] and Persson (2002).[16] The main findings of these works were that the true contact surface in rough materials is generally proportional to the normal force, while the parameters of individual micro-contacts (i.e. pressure, size of the micro-contact) are only weakly dependent upon the load.
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123
Classical solutions for non-adhesive elastic contact The theory of contact between elastic bodies can be used to find contact areas and indentation depths for simple geometries. Some commonly used solutions are listed below. The theory used to compute these solutions is discussed later in the article.
Contact between a sphere and an elastic half-space An elastic sphere of radius
indents an elastic half-space to depth
, and thus creates a contact area of radius force
is related to the displacement
. The applied
by
Contact between a sphere and an elastic half-space
where
and
,
are the elastic moduli and
,
the Poisson's ratios associated with each body.
Contact between two spheres For contact between two spheres of radii
and
, the area of contact is a circle
of radius . The distribution of normal traction in the contact area as a function of distance from the center of the circle is[1]
Contact between two spheres
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124
Contact between two crossed cylinders of equal radius
where
is the maximum contact pressure given by
where the effective radius
is defined as
The area of contact is related to the applied load
The depth of indentation
by the equation
is related to the maximum contact pressure by
The maximum shear stress occurs in the interior at
for
.
Contact between two crossed cylinders of equal radius This is equivalent to contact between a sphere of radius
and a plane (see above).
Contact between a rigid cylinder and an elastic half-space If a rigid cylinder is pressed into an elastic half-space, it creates a pressure distribution described by[17]
Contact between a rigid cylindrical indenter and an elastic half-space
Contact mechanics
where
125
is the radius of the cylinder and
The relationship between the indentation depth and the normal force is given by
Contact between a rigid conical indenter and an elastic half-space In the case of indentation of an elastic half-space using a rigid conical indenter, the indentation depth and contact radius are related by[17]
Contact between a rigid conical indenter and an elastic half-space
with
defined as the angle between the plane and the side surface of the cone. The pressure distribution takes on
the form
The stress has a logarithmic singularity on the tip of the cone. The total force is
Contact mechanics
126
Contact between two cylinders with parallel axes In contact between two cylinders with parallel axes, the force is linearly proportional to the indentation depth:
Contact between two cylinders with parallel axes
The radii of curvature are entirely absent from this relationship. The contact radius is described through the usual relationship
with
as in contact between two spheres. The maximum pressure is equal to
Hertzian theory of non-adhesive elastic contact The classical theory of contact focused primarily on non-adhesive contact where no tension force is allowed to occur within the contact area, i.e., contacting bodies can be separated without adhesion forces. Several analytical and numerical approaches have been used to solve contact problems that satisfy the no-adhesion condition. Complex forces and moments are transmitted between the bodies where they touch, so problems in contact mechanics can become quite sophisticated. In addition, the contact stresses are usually a nonlinear function of the deformation. To simplify the solution procedure, a frame of reference is usually defined in which the objects (possibly in motion relative to one another) are static. They interact through surface tractions (or pressures/stresses) at their interface. As an example, consider two objects which meet at some surface
in the (
,
)-plane with the
-axis
assumed normal to the surface. One of the bodies will experience a normally-directed pressure distribution and in-plane surface traction distributions and over the region
. In terms of a Newtonian force balance, the forces:
must be equal and opposite to the forces established in the other body. The moments corresponding to these forces:
Contact mechanics are also required to cancel between bodies so that they are kinematically immobile.
Assumptions in Hertzian theory The following assumptions are made in determining the solutions of Hertzian contact problems: • the strains are small and within the elastic limit, • each body can be considered an elastic half-space, i.e., the area of contact is much smaller than the characteristic radius of the body, • the surfaces are continuous and non-conforming, and • the surfaces are frictionless. Additional complications arise when some or all these assumptions are violated and such contact problems are usually called non-Hertzian.
Analytical solution techniques Analytical solution methods for non-adhesive contact problem can be classified into two types based on the geometry of the area of contact.[18] A conforming contact is one in which the two bodies touch at multiple points before any deformation takes place (i.e., they just "fit together"). A non-conforming contact is one in which the shapes of the bodies are dissimilar enough that, under zero load, they only touch at a point (or possibly along a line). In the non-conforming case, the contact area is small compared to the sizes of the objects and the stresses are highly concentrated in this area. Such a contact is called concentrated, otherwise it is called diversified. A common approach in linear elasticity is to Contact between two spheres. superpose a number of solutions each of which corresponds to a point load acting over the area of contact. For example, in the case of loading of a half-plane, the Flamant solution is often used as a starting point and then generalized to various shapes of the area of contact. The force and moment balances between the two bodies in contact act as additional constraints to the solution.
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Contact mechanics
128
Point contact on a (2D) half-plane A starting point for solving contact problems is to understand the effect of a "point-load" applied to an isotropic, homogeneous, and linear elastic half-plane, shown in the figure to the right. The problem may be either be plane stress or plane strain. This is a boundary value problem of linear elasticity subject to the traction boundary conditions:
Schematic of the loading on a plane by force P at a point (0,0).
where
is the Dirac delta function. The boundary conditions state that are no shear stresses on the surface
and a singular normal force P is applied at (0,0). Applying these conditions to the governing equations of elasticity produces the result
for some point,
, in the half-plane. The circle shown in the figure indicates a surface on which the maximum
shear stress is constant. From this stress field, the strain components and thus the displacements of all material points may be determined. Line contact on a (2D) half-plane Normal loading over a region Suppose, rather than a point load
, a distributed load
is applied to the surface instead, over the range
. The principle of linear superposition can be applied to determine the resulting stress field as the solution to the integral equations:
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129
Shear loading over a region The same principle applies for loading on the surface in the plane of the surface. These kinds of tractions would tend to arise as a result of friction. The solution is similar the above (for both singular loads and distributed loads ) but altered slightly:
These results may themselves be superposed onto those given above for normal loading to deal with more complex loads. Point contact on a (3D) half-space Analogously to the Flamant solution for the 2D half-plane, fundamental solutions are known for the linearly elastic 3D half-space as well. These were found by Boussinesq for a concentrated normal load and by Cerutti for a tangential load. See the section on this in Linear elasticity.
Numerical solution techniques Distinctions between conforming and non-conforming contact do not have to be made when numerical solution schemes are employed to solve contact problems. These methods do not rely on further assumptions within the solution process since they base solely on the general formulation of the underlying equations [19] [20] [21] [22] .[23] Besides the standard equations describing the deformation and motion of bodies two additional inequalities can be formulated. The first simply restricts the motion and deformation of the bodies by the assumption that no penetration can occur. Hence the gap between two bodies can only be positive or zero
where
denotes contact. The second assumption in contact mechanics is related to the fact, that no tension
force is allowed to occur within the contact area (contacting bodies can be lifted up without adhesion forces). This leads to an inequality which the stresses have to obey at the contact interface. It is formulated for the contact pressure
Since for contact, is open,
, the contact pressure is always negative, , and the contact pressure is zero,
, and further for non contact the gap
, the so called Kuhn–Tucker form of the contact
constraints can be written as These conditions are valid in a general way. The mathematical formulation of the gap depends upon the kinematics of the underlying theory of the solid (e.g., linear or nonlinear solid in two- or three dimensions, beam or shell model).
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130
Non-adhesive contact between rough surfaces When two bodies with rough surfaces are pressed into each other, the true contact area apparent contact area
area is related to the normal force
with
is much smaller than the
. In contact between a "random rough" surface and an elastic half-space, the true contact [1] [24] [25] [26]
by
equal to the root mean square (also known as the quadratic mean) of the surface slope and
. The
median pressure in the true contact surface
can be reasonably estimated as half of the effective elastic modulus surface slope
multiplied with the root mean square of the
.
For the situation where the asperities on the two surfaces have a Gaussian height distribution and the peaks can be assumed to be spherical,[24] the average contact pressure is sufficient to cause yield when where
is the uniaxial yield stress and
dimensionless parameter
is the indentation hardness.[1] Greenwood and Williamson[24] defined a
called the plasticity index that could be used to determine whether contact would be
elastic or plastic. The Greenwood-Williamson model requires knowledge of two statistically dependent quantities; the standard deviation of the surface roughness and the curvature of the asperity peaks. An alternative definition of the plasticity index has been given by Mikic.[25] Yield occurs when the pressure is greater than the uniaxial yield stress. Since the yield stress is proportional to the indentation hardness , Micic defined the plasticity index for elastic-plastic contact to be
In this definition
represents the micro-roughness in a state of complete plasticity and only one statistical quantity,
the rms slope, is needed which can be calculated from surface measurements. For
, the surface behaves
elastically during contact. In both the Greenwood-Williamson and Mikic models the load is assumed to be proportional to the deformed area. Hence, whether the system behaves plastically or elastically is independent of the applied normal force.[1]
Adhesive contact between elastic bodies When two solid surfaces are brought into close proximity to each other they experience attractive van der Waals forces. Bradley's van der Waals model[27] provides a means of calculating the tensile force between two rigid spheres with perfectly smooth surfaces. The Hertzian model of contact does not consider adhesion possible. However, in the late 1960s, several contradictions were observed when the Hertz theory was compared with experiments involving contact between rubber and glass spheres. It was observed[6] that, though Hertz theory applied at large loads, at low loads • the area of contact was larger than that predicted by Hertz theory, • the area of contact had a non-zero value even when the load was removed, and • there was strong adhesion if the contacting surfaces were clean and dry. This indicated that adhesive forces were at work. The Johnson-Kendall-Roberts (JKR) model and the Derjaguin-Muller-Toporov (DMT) models were the first to incorporate adhesion into Hertzian contact.
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131
Bradley model of rigid contact It is commonly assumed that the surface force between two atomic planes at a distance derived from the Lennard-Jones potential. With that assumption we can write
where and
is the force (positive in compression),
from each other can be
is the is the total surface energy of both surfaces per unit area,
is the equilibrium separation of the two atomic planes.
The Bradley model applied the Lennard-Jones potential to find the force of adhesion between two rigid spheres. The total force between the spheres is found to be
where
are the radii of the two spheres.
The two spheres separate completely when the pull-off force is achieved at
at which point
Johnson-Kendall-Roberts (JKR) model of elastic contact To incorporate the effect of adhesion in Hertzian contact, Johnson, Kendall, and Roberts[6] formulated the JKR theory of adhesive contact using a balance between the stored elastic energy and the loss in surface energy. The JKR model considers the effect of contact pressure and adhesion only inside the area of contact. The general solution for the pressure distribution in the contact area in the JKR model is
Schematic of contact area for the JKR model.
Note that in the original Hertz theory, the term containing
was neglected on the ground that tension could not be
sustained in the contact zone. For contact between two spheres
where
is the radius of the area of contact,
per unit contact area,
is the applied force,
is the total surface energy of both surfaces
are the radii, Young's moduli, and Poisson's ratios of the two spheres,
and
The approach distance between the two spheres is given by
Contact mechanics
132
The Hertz equation for the area of contact between two spheres, modified to take into account the surface energy, has the form
When the surface energy is zero,
, the Hertz equation for contact between two spheres is recovered. When
the applied load is zero, the contact radius is
The tensile load at which the spheres are separated, i.e.,
, is predicted to be
This force is also called the pull-off force. Note that this force is independent of the moduli of the two spheres. However, there is another possible solution for the value of at this load. This is the critical contact area , given by
If we define the work of adhesion as
where
are the adhesive energies of the two surfaces and
is an interaction term, we can write the JKR
contact radius as
The tensile load at separation is
and the critical contact radius is given by
The critical depth of penetration is
Derjaguin-Muller-Toporov (DMT) model of elastic contact The Derjaguin-Muller-Toporov (DMT) model[28] [29] is an alternative model for adhesive contact which assumes that the contact profile remains the same as in Hertzian contact but with additional attractive interactions outside the area of contact. The area of contact between two spheres from DMT theory is
and the pull-off force is
Contact mechanics
133
When the pull-off force is achieved the contact area becomes zero and there is no singularity in the contact stresses at the edge of the contact area. In terms of the work of adhesion
and
Tabor coefficient In 1977, Tabor[30] showed that the apparent contradiction between the JKR and DMT theories could be resolved by noting that the two theories were the extreme limits of a single theory parametrized by the Tabor coefficient ( ) defined as
where is the equilibrium separation between the two surfaces in contact. The JKR theory applies to large, compliant spheres for which is large. The DMT theory applies for small, stiff spheres with small values of .
Maugis-Dugdale model of elastic contact Further improvement to the Tabor idea was provided by Maugis[10] who represented the surface force in terms of a Dugdale cohesive zone approximation such that the work of adhesion is given by
Schematic of contact area for the Maugis-Dugdale model.
where
is the maximum force predicted by the Lennard-Jones potential and
is the maximum separation
obtained by matching the areas under the Dugdale and Lennard-Jones curves (see adjacent figure). This means that the attractive force is constant for . There is not further penetration in compression. Perfect contact occurs in an area of radius
and adhesive forces of magnitude
extend to an area of radius
. In
Contact mechanics
134
the region
, the two surfaces are separated by a distance
with
and
. The ratio
. In the Maugis-Dugdale theory,[31] the surface traction distribution is divided into two parts - one due to the Hertz contact pressure and the other from the Dugdale adhesive stress. Hertz contact is assumed in the region . The contribution to the surface traction from the Hertz pressure is given by
where the Hertz contact force
is given by
The penetration due to elastic compression is
The vertical displacement at
is
and the separation between the two surfaces at
is
The surface traction distribution due to the adhesive Dugdale stress is
The total adhesive force is then given by
The compression due to Dugdale adhesion is
and the gap at
is
The net traction on the contact area is then given by . When Non-dimensionalized values of
and the net contact force is
the adhesive traction drops to zero. are introduced at this stage that are defied as
is defined
Contact mechanics
135
In addition, Maugis proposed a parameter
which is equivalent to the Tabor coefficient. This parameter is defined
as
Then the net contact force may be expressed as
and the elastic compression as
The equation for the cohesive gap between the two bodies takes the form
This equation can be solved to obtain values of
for various values of
and the JKR model is obtained. For small values of
and
. For large values of
,
the DMT model is retrieved.
Carpick-Ogletree-Salmeron (COS) model The Maugis-Dugdale model can only be solved iteratively if the value of Carpick-Ogletree-Salmeron approximate solution determine the contact radius :
where
is the contact area at zero load, and
The case cases
[32]
is not known a-priori. The
simplifies the process by using the following relation to
is a transition parameter that is related to
corresponds exactly to JKR theory while
by
corresponds to DMT theory. For intermediate
the COS model corresponds closely to the Maugis-Dugdale solution for
.
References [1] Johnson, K. L, 1985, Contact mechanics, Cambridge University Press. [2] Popov, Valentin L., 2010, Contact Mechanics and Friction. Physical Principles and Applications, Springer-Verlag, 362 p., ISBN 978-3-642-10802-0. [3] H. Hertz, Über die berührung fester elastischer Körper (On the contact of rigid elastic solids). In: Miscellaneous Papers (http:/ / www. archive. org/ details/ cu31924012500306). Jones and Schott, Editors, J. reine und angewandte Mathematik 92, Macmillan, London (1896), p. 156 English translation: Hertz, H. [4] http:/ / gdz. sub. uni-goettingen. de/ no_cache/ dms/ load/ img/ ?IDDOC=251917 [5] Hertz, H. R., 1882, Ueber die Beruehrung elastischer Koerper (On Contact Between Elastic Bodies), in Gesammelte Werke (Collected Works), Vol. 1, Leipzig, Germany, 1895. [6] K. L. Johnson and K. Kendall and A. D. Roberts, Surface energy and the contact of elastic solids, Proc. R. Soc. London A 324 (1971) 301-313 [7] D. Maugis, Contact, Adhesion and Rupture of Elastic Solids, Springer-Verlag, Solid-State Sciences, Berlin 2000, ISBN 3-540-66113-1 [8] B. V. Derjaguin and V. M. Muller and Y. P. Toporov, Effect of contact deformations on the adhesion of particles, J. Colloid Interface Sci. 53 (1975) 314--325 [9] D. Tabor, The hardness of solids, J. Colloid Interface Sci. 58 (1977) 145-179 [10] D. Maugis, Adhesion of spheres: The JKR-DMT transition using a Dugdale model, J. Colloid Interface Sci. 150 (1992) 243--269
Contact mechanics [11] , Bowden, FP and Tabor, D., 1939, The area of contact between stationary and between moving surfaces, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 169(938), pp. 391--413. [12] Bowden, F.P. and Tabor, D., 2001, The friction and lubrication of solids, Oxford University Press. [13] Archard, JF, 1957, Elastic deformation and the laws of friction, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 243(1233), pp.190--205. [14] Greenwood, JA and Williamson, JBP., 1966, Contact of nominally flat surfaces, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, pp. 300-319. [15] Bush, AW and Gibson, RD and Thomas, TR., 1975, The elastic contact of a rough surface, Wear, 35(1), pp. 87-111. [16] Persson, BNJ and Bucher, F. and Chiaia, B., 2002, Elastic contact between randomly rough surfaces: Comparison of theory with numerical results, Physical Review B, 65(18), p. 184106. [17] Sneddon, I. N., 1965, The Relation between Load and Penetration in the Axisymmetric Boussinesq Problem for a Punch of Arbitrary Profile. Int. J. Eng. Sci. v. 3, pp. 47–57. [18] Shigley, J.E., Mischke, C.R., 1989, Mechanical Engineering Design, Fifth Edition, Chapter 2, McGraw-Hill, Inc, 1989, ISBN 0-07-056899-5. [19] Kalker, J.J. 1990, Three-Dimensional Elastic Bodies in Rolling Contact. (Kluwer Academic Publishers: Dordrecht). [20] Wriggers, P. 2006, Computational Contact Mechanics. 2nd ed. (Springer Verlag: Heidelberg). [21] Laursen, T. A., 2002, Computational Contact and Impact Mechanics: Fundamentals of Modeling Interfacial Phenomena in Nonlinear Finite Element Analysis, (Springer Verlag: New York). [22] Acary V. and Brogliato B., 2008,Numerical Methods for Nonsmooth Dynamical Systems. Applications in Mechanics and Electronics. Springer Verlag, LNACM 35, Heidelberg. [23] Popov, Valentin L., 2009, Kontaktmechanik und Reibung. Ein Lehr- und Anwendungsbuch von der Nanotribologie bis zur numerischen Simulation, Springer-Verlag, 328 S., ISBN 978-3-540-88836-9. [24] Greenwood, J. A. and Williamson, J. B. P., (1966), Contact of nominally flat surfaces, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, vol. 295, pp. 300--319. [25] Mikic, B. B., (1974), Thermal contact conductance; theoretical considerations, International Journal of Heat and Mass Transfer, 17(2), pp. 205-214. [26] Hyun, S., and M.O. Robbins, 2007, Elastic contact between rough surfaces: Effect of roughness at large and small wavelengths. Trobology International, v.40, pp. 1413-1422. [27] Bradley, RS., 1932, The cohesive force between solid surfaces and the surface energy of solids, Philosophical Magazine Series 7, 13(86), pp. 853--862. [28] Derjaguin, BV and Muller, VM and Toporov, Y.P., 1975, Effect of contact deformations on the adhesion of particles, Journal of Colloid and Interface Science, 53(2), pp. 314-326. [29] Muller, VM and Derjaguin, BV and Toporov, Y.P., 1983, On two methods of calculation of the force of sticking of an elastic sphere to a rigid plane, Colloids and Surfaces, 7(3), pp. 251-259. [30] Tabor, D., 1977, Surface forces and surface interactions, Journal of Colloid and Interface Science, 58(1), pp. 2-13. [31] Johnson, KL and Greenwood, JA, 1997, An adhesion map for the contact of elastic spheres, Journal of Colloid and Interface Science, 192(2), pp. 326-333. [32] Carpick, R.W. and Ogletree, D.F. and Salmeron, M., 1999, A general equation for fitting contact area and friction vs load measurements, Journal of colloid and interface science, 211(2), pp. 395-400.
External links • (http://gltrs.grc.nasa.gov/reports/1997/TM-107440.pdf): More about contact stresses and the evolution of bearing stress equations can be found in this publication by NASA Glenn Research Center head the NASA Bearing, Gearing and Transmission Section, Erwin Zaretsky.
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Frictional contact mechanics
Frictional contact mechanics Contact mechanics is the study of the deformation of solids that touch each other at one or more points.[1] [2] This can be divided into compressive and adhesive forces in the direction perpendicular to the interface, and frictional forces in the tangential direction. Frictional contact mechanics is the study of the deformation of bodies in the presence of frictional effects, whereas frictionless contact mechanics assumes the absence of such effects. Frictional contact mechanics is concerned with a large range of different scales. • At the macroscopic scale, it is applied for the investigation of the motion of contacting bodies (see Contact dynamics). For instance the bouncing of a rubber ball on a surface depends on the frictional interaction at the contact interface. Here the total force versus indentation and lateral displacement are of main concern. • At the intermediate scale, one is interested in the local stresses, strains and deformations of the contacting bodies in and near the contact area. For instance to derive or validate contact models at the macroscopic scale, or to investigate wear and damage of the contacting bodies’ surfaces. Application areas of this scale are tire-pavement interaction, railway wheel-rail interaction, roller bearing analysis, etc. • Finally, at the microscopic and nano-scales, contact mechanics is used to increase our understanding of tribological systems, e.g. investigate the origin of friction, and for the engineering of advanced devices like atomic force microscopes and MEMS devices. This page is mainly concerned with the second scale: getting basic insight in the stresses and deformations in and near the contact patch, without paying too much attention to the detailed mechanisms by which they come about.
History Several famous scientists and engineers contributed to our understanding of friction.[3] They include Leonardo da Vinci, Guillaume Amontons, John Theophilus Desaguliers, Leonard Euler, and Charles-Augustin de Coulomb. Later, Nikolai Pavlovich Petrov, Osborne Reynolds and Stribeck supplemented this understanding with theories of lubrication. Deformation of solid materials was investigated in the 17th and 18th centuries by Robert Hooke, Joseph Louis Lagrange, and in the 19th and 20th centuries by d’Alembert and Timoshenko. With respect to contact mechanics the classical contribution by Heinrich Hertz[4] stands out. Further the fundamental solutions by Boussinesq and Cerruti are of primary importance for the investigation of frictional contact problems in the (linearly) elastic regime. Classical results for a true frictional contact problem concern the papers by F.W. Carter (1926) and H. Fromm (1927). They independently presented the creep-force relation for two cylinders in steady rolling conditions using Coulomb’s dry friction law.[5] These are applied to railway locomotive traction, and for understanding the hunting oscillation of railway vehicles. With respect to sliding, the classical solutions are due to C. Cattaneo (1938) and R.D. Mindlin (1949), who considered the tangential shifting of a cylinder on a plane (see below).[1] In the 1950s interest in the rolling contact of railway wheels grew. In 1958 K.L. Johnson presented an approximate approach for the 3D frictional problem with Hertzian geometry, with either lateral or spin creepage. Among others he found that spin creepage, which is symmetric about the center of the contact patch, leads to a net lateral force in rolling conditions. This is due to the fore-aft differences in the distribution of tractions in the contact patch. In 1967 Joost Kalker published his milestone PhD thesis on the linear theory for rolling contact.[6] This theory is exact for the situation of an infinite friction coefficient in which case the slip area vanishes, and is approximative for non-vanishing creepages. It does assume Coulomb’s friction law, which more or less requires (scrupulously) clean surfaces. This theory is for massive bodies such as the railway wheel-rail contact. With respect to road-tire interaction, an important contribution concerns the so-called magic tire formula by Hans Pacejka.[7] In the 1970s many numerical models were devised. Particularly variational approaches, such as those relying on Duvaut and Lion’s existence and uniqueness theories. Over time, these grew into finite element approaches for
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138
contact problems with general material models and geometries, and into half-space based approaches for so-called smooth-edged contact problems for linearly elastic materials. Models of the first category were presented by Laursen[8] and by Wriggers.[9] An example of the latter category is Kalker’s CONTACT model.[10] A drawback of the well-founded variational approaches is their large computation times. Therefore many different approximate approaches were devised as well. Several well-known approximate theories for the rolling contact problem are Kalker’s FASTSIM approach, the Shen-Hedrick-Elkins formula, and Polach’s approach. More information on the history of the wheel/rail contact problem is provided in Knothe's paper.[5] Further Johnson collected in his book a tremendous amount of information on contact mechanics and related subjects.[1] With respect to rolling contact mechanics an overview of various theories is presented by Kalker as well.[10] Finally the proceedings of a CISM course are of interest, which provide an introduction to more advanced aspects of rolling contact theory.[11]
Problem formulation Central in the analysis of frictional contact problems is the understanding that the stresses at the surface of each body are spatially varying. Consequently the strains and deformations of the bodies are varying with position too. And the motion of particles of the contacting bodies can be different at different locations: in part of the contact patch particles of the opposing bodies may adhere (stick) to each other, whereas in other parts of the contact patch relative movement occurs. This local relative sliding is called micro-slip. This subdivision of the contact area into stick (adhesion) and slip areas manifests itself a.o. in fretting wear. Note that wear occurs only where power is dissipated, which requires stress and local relative displacement (slip) between the two surfaces. The size and shape of the contact patch itself and of its adhesion and slip areas are generally unknown in advance. If these were known, then the elastic fields in the two bodies could be solved independently from each other and the problem would not be a contact problem anymore. Three different components can be distinguished in a contact problem. 1. First of all, there is the reaction (deformation) of the separate bodies to loads applied on their surfaces. This is the subject of general continuum mechanics. It depends largely on the geometry of the bodies and on their (constitutive) material behavior (e.g. elastic vs. plastic response, homogeneous vs. layered structure etc.). 2. Secondly, there is the overall motion of the bodies relative to each other. For instance the bodies can be at rest (statics) or approaching each other quickly (impact), and can be shifted (sliding) or rotated (rolling) over each other. These overall motions are generally studied in classical mechanics, see for instance multibody dynamics. 3. Finally there are the processes at the contact interface: compression and adhesion in the direction perpendicular to the interface, and friction and micro-slip in the tangential directions. The last aspect is the primary concern of contact mechanics. It is described in terms of so-called “contact conditions”. For the direction perpendicular to the interface, the normal contact problem, adhesion effects are usually small (at larger spatial scales) and the following conditions are typically employed: 1. The gap
between the two surfaces must be zero (contact) or strictly positive (
2. The normal stress
acting on each body is zero (separation) or compressive (
Mathematically:
. Here
, separation); in contact).
are functions that vary with the position along the
bodies' surfaces. In the tangential directions the following conditions are often used: 1. The local (tangential) shear stress
(if the normal direction is parallel to the
exceed a certain position-dependent maximum, the so-called traction bound
;
-axis) cannot
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139
2. Where the magnitude of tangential traction falls below the traction bound
, the opposing surfaces
adhere together and micro-slip vanishes, ; 3. Micro-slip occurs where the tangential tractions are at the traction bound; the direction of the tangential traction is then opposite to the direction of micro-slip . The precise form of the traction bound is the so-called local friction law. For this Coulomb's (global) friction law is often applied locally: , with the friction coefficient. More detailed formulae are also possible, for instance with
depending on temperature
, local sliding velocity
, etc.
Solutions for static cases Rope on a bollard, the capstan equation Consider a rope where equal forces (e.g.
) are
exerted on both sides. By this the rope is stretched a bit and an internal tension is induced ( on every position along the rope). The rope is wrapped around a fixed item such as a bollard; it is bent and makes contact to the item's surface over a contact angle (e.g. ). Normal pressure comes into being between the rope and bollard, but no friction occurs yet. Next the force on one side of the bollard is increased to a higher value (e.g. ). This does cause frictional shear stresses in the contact area. In the final situation the bollard exercises a friction force on the rope such that a static situation occurs. The tension distribution in the rope in this final situation is described by the capstan equation, with solution:
The tension increases from
on the slack side (
) to
Illustration of an elastic rope wrapped around a fixed item such as a bollard. The contact area is divided into stick and slip zones, depending on the loads exerted on both ends and on the loading history.
on the high side
viewed from the high side, the tension drops exponentially, until it reaches the lower load at there on it is constant at this value. The transition point
. When . From
is determined by the ratio of the two loads and the
friction coefficient. Here the tensions are in Newtons and the angles in radians. The tension in the rope in the final situation is increased with respect to the initial state. Therefore the rope is elongated a bit. This means that not all surface particles of the rope can have held their initial position on the bollard surface. During the loading process, the rope slipped a little bit along the bollard surface in the slip area . This slip is precisely large enough to get to the elongation that occurs in the final state. Note that there is no slipping going on in the final state; the term slip area refers to the slippage that occurred during the loading process. Note further that the location of the slip area depends on the initial state and the loading process. If the initial tension is and the tension is reduced to at the slack side, then the slip area occurs at the slack side of the contact area. For initial tensions between with a stick area in between.
and
, there can be slip areas on both sides
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140
Sphere on a plane, the (3D) Cattaneo problem Consider a sphere that is pressed onto a plane (half space) and then shifted over the plane's surface. If the sphere and plane are idealised as rigid bodies, then contact would occur in just a single point, and the sphere would not move until the tangential force that is applied reaches the maximum friction force. Then it starts sliding over the surface until the applied force is reduced again. How different is the situation in reality, if we include elastic effects. If an elastic sphere is pressed onto an elastic plane of the same material then both bodies deform, a circular contact area comes into being, and a (Hertzian) normal pressure distribution arises. Also, the center of the sphere is moved down a bit by a distance that is called the approach, which is also the maximum penetration of the undeformed surfaces.
Now consider that a tangential force is applied that is lower than the Coulomb friction bound. The center of the sphere will then be moved sideways by a small distance that is called the shift. A static equilibrium is obtained in which elastic deformations occur as well as frictional shear stresses in the contact interface. In this case, if the tangential force is reduced then the elastic deformations and shear stresses reduce as well. The sphere largely shifts back to its original position, except for frictional losses that arise due to local slip in the contact patch. This contact problem was solved approximately by Cattaneo using an analytical approach. The stress distribution in the equilibrium state consists of two parts:
In the central, sticking region
, the surface particles of the plane displace over
whereas the surface particles of the sphere displace over whole moves over annulus This shift
to the right
to the left. Even though the sphere as a
relative to the plane, these surface particles did not move relative to each other. In the outer , the surface particles did move relative to each other. Their local shift is obtained as is precisely as large such that a static equilibrium is obtained with shear stresses at the traction
bound in this so-called slip area. During the tangential loading of the sphere, partial sliding occurs. The contact area is thus divided into a slip area where the surfaces move relative to each other and a stick area where they do not. In the equilibrium state no more sliding is going on.
Solutions for dynamic sliding problems The solution of a contact problem, that is, the elastic field in the bodies' interiors together with the state at the interface (division of stick and slip zones, normal and shear stress distributions), depends on the history of the contact. This can be seen by extension of the Cattaneo problem described above. • In the Cattaneo problem, the sphere is first pressed onto the plane and then shifted tangentially. This yields partial slip as described above. • If the sphere is first shifted tangentially and then pressed onto the plane, then there is no tangential displacement difference between the opposing surfaces and consequently there is no tangential stress in the contact interface. • If the approach in normal direction and tangential shift are increased simultaneously then a situation can be achieved with tangential stress but without local slip.[2] This demonstrates that the state in the contact interface is not only dependent on the relative positions of the two bodies, but also on their motion history. Another example of this occurs if the sphere is shifted back to its original
Frictional contact mechanics position. Initially there was no tangential stress in the contact interface. After the initial shift micro-slip has occurred. This micro-slip is not entirely undone by shifting back, such that eventually tangential stresses remain in the interface in what on an overall level looks like the same as the original configuration.
Solution of rolling contact problems Rolling contact problems are dynamic problems in which the contacting bodies are continuously moving with respect to each other. A difference to dynamic sliding contact problems is that there is more variety in the state of different surface particles. Whereas the contact patch in a sliding problem continuously consists of more or less the same particles, in a rolling contact problem particles enter and leave the contact patch incessantly. Moreover, in a sliding problem the surface particles in the contact patch are all subjected to more or less the same tangential shift everywhere, whereas in a rolling problem the surface particles are stressed in rather different ways. They are free of stress when entering the contact patch, then stick to a particle of the opposing surface, are strained by the overall motion difference between the two bodies, until the local traction bound is exceeded and local slip sets in. This process is in different stages for different parts of the contact area. If the overall motion of the bodies is constant, then an overall steady state may be attained. Here the state of each surface particle is varying in time, but the overall distribution can be constant. This is formalised by using a coordinate system that is moving along with the contact patch.
Half-space based approaches When considering contact problems at the intermediate spatial scales, the small-scale material inhomogeneities and surface roughness are ignored. The bodies are considered as consisting of smooth surfaces and homogeneous materials. A continuum approach is taken where the stresses, strains and displacements are described by (piecewise) continuous functions. The half-space approach is an elegant solution strategy for so-called "smooth-edged" or "concentrated" contact problems. 1. If a massive elastic body is loaded on a small section of its surface, then the elastic stresses attenuate proportional to and the elastic displacements by when one moves away from this surface area. 2. If a body has no sharp corners in or near the contact region, then its response to a surface load may be approximated well by the response of an elastic half-space (e.g. all points with ). 3. The elastic half-space problem is solved analytically, see the Boussinesq-Cerruti solution. 4. Due to the linearity of this approach, multiple partial solutions may be super-imposed. Using the fundamental solution for the half-space, the full 3D contact problem is reduced to a 2D problem for the bodies' bounding surfaces. A further simplification occurs if the two bodies are “geometrically and elastically alike”. In general, stress inside a body in one direction induces displacements in perpendicular directions too. Consequently there is an interaction between the normal stress and tangential displacements in the contact problem, and an interaction between the tangential stress and normal displacements. But if the normal stress in the contact interface induces the same tangential displacements in both contacting bodies, then there is no relative tangential displacement of the two surfaces. In that case, the normal and tangential contact problems are decoupled. If this is the case then the two bodies are called quasi-identical. This happens for instance if the bodies are mirror-symmetric with respect to the contact plane and have the same elastic constants. Classical solutions based on the half-space approach are: 1. Hertz solved the contact problem in the absence of friction, for a simple geometry (curved surfaces with constant radii of curvature).
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Frictional contact mechanics 2. Carter and Fromm considered the rolling contact between two cylinders with parallel axes. (Relatively) far away from the ends of the cylinders a situation of plane strain occurs and the problem is 2-dimensional. A complete analytical solution is provided for the tangential traction. 3. Cattaneo considered the compression and shifting of two spheres, as described above. Note that this analytical solution is approximate. In reality small tangential tractions occur which are ignored.
References [1] Johnson, K.L. (1985). Contact Mechanics. Cambridge: Cambridge University Press. [2] Popov, V.L. (2010). Contact Mechanics and Friction. Physical Principles and Applications. Berlin: Springer-Verlag. [3] "Introduction to Tribology – Friction" (http:/ / depts. washington. edu/ nanolab/ ChemE554/ Summaries ChemE 554/ Introduction Tribology. htm). . Retrieved 2008-12-21. [4] Hertz, Heinrich (1882). "Contact between solid elastic bodies". Journ. Für reine und angewandte Math. 92. [5] Knothe, K. (2008). "History of wheel/rail contact mechanics: from Redtenbacher to Kalker". Vehicle System Dynamics 46 (1-2): 9–26. [6] Kalker, Joost J. (1967). On the rolling contact of two elastic bodies in the presence of dry friction. Delft University of Technology. [7] Pacejka, Hans (2002). Tire and Vehicle Dynamics. Oxford: Butterworth-Heinemann. [8] Laursen, T.A., 2002, Computational Contact and Impact Mechanics, Fundamentals of Modeling Interfacial Phenomena in Nonlinear Finite Element Analysis, Springer, Berlin [9] Wriggers, P., 2006, Computational Contact Mechanics, 2nd ed., Springer, Heidelberg [10] Kalker, J.J., 1990, Three-Dimensional Elastic Bodies in Rolling Contact, Kluwer Academic Publishers, Dordrecht [11] B. Jacobsen and J.J. Kalker, ed (2000). Rolling Contact Phenomena. Wien New York: Springer-Verlag.
External links • (http://www.ewi.tudelft.nl/live/pagina.jsp?id=4d033735-89db-4454-91be-d599a17d67fd&lang=en) Biography of Prof.dr.ir. J.J. Kalker (Delft University of Technology). • (http://www.kalkersoftware.org) Kalker's Hertzian/non-Hertzian CONTACT software.
Cooling tower Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and building cooling. The towers vary in size from small roof-top units Natural draft wet cooling hyperboloid towers at Didcot Power Station, UK to very large hyperboloid structures (as in Image 1) that can be up to 200 metres tall and 100 metres in diameter, or rectangular structures (as in Image 2) that can be over 40 metres tall and 80 metres long. Smaller towers are normally factory-built, while larger ones are constructed on site. They are often associated with nuclear power plants in popular culture, although cooling towers are constructed on many types of buildings. A hyperboloid cooling tower was patented by Frederik van Iterson and Gerard Kuypers in 1918.[1] The first hyperboloid cooling towers were built in the last 1920s in Liverpool, England to cool water used at a electrical power station that used coal.[2]
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Cooling tower
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Classification by use HVAC An HVAC (heating, ventilating, and air conditioning) cooling tower is a subcategory rejecting heat from a chiller. Water-cooled chillers are normally more energy efficient than air-cooled chillers due to heat rejection to tower water at or near wet-bulb temperatures. Air-cooled chillers must reject heat at the dry-bulb temperature, and thus have a lower average reverse-Carnot cycle effectiveness. Large office buildings, hospitals, and schools typically use one or more cooling towers as part of their air conditioning systems. Generally, industrial cooling towers are much larger than HVAC towers. HVAC use of a cooling tower pairs the cooling tower with a water-cooled chiller or water-cooled condenser. A ton of air-conditioning is the removal of 12,000 Btu/hour (3500 W). The equivalent ton on the cooling tower side actually rejects about 15,000 Btu/hour (4400 W) due to the heat-equivalent of the energy needed to drive the chiller's compressor. This equivalent ton is defined as the heat rejection in cooling 3 U.S. gallons/minute (1,500 pound/hour) of water 10 °F (6 °C), which amounts to 15,000 Btu/hour, or a chiller coefficient of performance (COP) of 4.0. This COP is equivalent to an energy efficiency ratio (EER) of 14.
An abandoned cooling tower at the derelict Thorpe Marsh Power Station in Yorkshire, England.
A mechanical induced-draft cooling tower
Cooling towers are also used in HVAC systems that have multiple water source heat pumps that share a common piping water loop. In this type of system, the water circulating inside the water loop removes heat from the condenser of the heat pumps whenever the heat pumps are working in the cooling mode, then the cooling tower is used to remove heat from the water loop and reject it to the atmosphere. When the heat pumps are working in heating mode, the condensers draw heat out of the loop water and reject it into the space to be heated.
Industrial cooling towers Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semi-conductor plants, and for other industrial facilities such as in condensers of distillation columns, for cooling liquid in crystallization, etc.[3] The circulation rate of cooling water in Industrial cooling towers for a power plant a typical 700 MW coal-fired power plant with a cooling tower amounts to about 71,600 cubic metres an hour (315,000 U.S. gallons per minute)[4] and the circulating water requires a supply water make-up rate of perhaps 5 percent (i.e., 3,600 cubic metres an hour). If that same plant had no cooling tower and used once-through cooling water, it would require about 100,000 cubic metres an hour[5] and that amount of water would have to be continuously returned to the ocean, lake or river from
Cooling tower
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which it was obtained and continuously re-supplied to the plant. Furthermore, discharging large amounts of hot water may raise the temperature of the receiving river or lake to an unacceptable level for the local ecosystem. Elevated water temperatures can kill fish and other aquatic organisms (see thermal pollution). A cooling tower serves to dissipate the heat into the atmosphere instead and wind and air diffusion spreads the heat over a much larger area than hot water can distribute heat in a body of water. Some coal-fired and nuclear power plants located in coastal areas do make use of once-through ocean water. But even there, the offshore discharge water outlet requires very careful design to avoid environmental problems. Petroleum refineries also have very large cooling tower systems. A typical large refinery processing 40,000 metric tonnes of crude oil per day (300000 barrels (48000 m3) per day) circulates about 80,000 cubic metres of water per hour through its cooling tower system. The world's tallest cooling tower is the 200 metres tall cooling tower of Niederaussem Power Station.
Classification by build Package Type This type of cooling towers are preassembled and can be simply transported on trucks as they are compact machines. The capacity of package type towers is limited and for that reason, they are usually preferred by facilities with low heat rejection requirements such as food processing plants, textile plants, buildings like hospitals, hotels, malls, chemical processing plants, automotive factories etc. Due to intensive use in domestic areas, sound level control is a relatively more important issue for package type cooling towers.
Package type cooling towers
Field Erected Type Such facilities as power plants, steel processing plants, petroleum refineries, petrochemical plants prefer field erected type cooling towers due to their large requirements of heat rejection. These towers are a lot larger in size compared to the package type cooling towers. A typical field erected cooling tower has pultruded FRP structure, FRP cladding, a mechanical unit for air draft, drift eliminator and fill.
Field erected cooling towers
Cooling tower
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Heat transfer methods With respect to the heat transfer mechanism employed, the main types are: • Wet cooling towers or simply open circuit cooling towers operate on the principle of evaporation. The working fluid and the evaporated fluid (usually water) are one and the same. • Dry cooling towers operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a tube to air heat exchanger, utilizing convective heat transfer. They do not use evaporation. • Fluid coolers or closed circuit cooling towers are hybrids that pass Mechanical draft crossflow cooling tower used in the working fluid through a tube bundle, upon which clean water is an HVAC application sprayed and a fan-induced draft applied. The resulting heat transfer performance is much closer to that of a wet cooling tower, with the advantage provided by a dry cooler of protecting the working fluid from environmental exposure and contamination. In a wet cooling tower (or open circuit cooling tower), the warm water can be cooled to a temperature lower than the ambient air dry-bulb temperature, if the air is relatively dry (see dew point and psychrometrics). As ambient air is drawn past a flow of water, a small portion of the water evaporate, the energy required by that portion of the water to evaporate is taken from the remaining mass of water reducing his temperature (approximately by 970 BTU for each pound of evaporated water). Evaporation results in saturated air conditions, lowering the temperature of the water process by the tower to a value close to wet bulb air temperature, which is lower than the ambient dry bulb air temperature, the difference determined by the humidity of the ambient air. To achieve better performance (more cooling), a medium called fill is used to increase the surface area and the time of contact between the air and water flows. Splash fill consists of material placed to interrupt the water flow causing splashing. Film fill is composed of thin sheets of material (usually PVC) upon which the water flows. Both methods create increased surface area and time of contact between the fluid (water) and the gas (air).
Air flow generation methods With respect to drawing air through the tower, there are three types of cooling towers: • Natural draft, which utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due to the density differential to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces a current of air through the tower. • Mechanical draft, which uses power driven fan motors to force or draw air through the tower. • Induced draft: A mechanical draft tower with a fan at the discharge which pulls air through tower. The fan induces hot moist air out the discharge. This produces low entering and high exiting air velocities, reducing the possibility of recirculation in which discharged air flows back into the air intake. This fan/fin arrangement is also known as draw-through. (see Image 3)
A forced draft cooling tower
Cooling tower • Forced draft: A mechanical draft tower with a blower type fan at the intake. The fan forces air into the tower, creating high entering and low exiting air velocities. The low exiting velocity is much more susceptible to recirculation. With the fan on the air intake, the fan is more susceptible to complications due to freezing conditions. Another disadvantage is that a forced draft design typically requires more motor horsepower than an equivalent induced draft design. The forced draft benefit is its ability to work with high static pressure. They can be installed in more confined spaces and even in some indoor situations. This fan/fill geometry is also known as blow-through. (see Image 4)
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Forced draft counter flow package type cooling towers
• Fan assisted natural draft. A hybrid type that appears like a natural draft though airflow is assisted by a fan. Hyperboloid (sometimes incorrectly known as hyperbolic) cooling towers (Image 1) have become the design standard for all natural-draft cooling towers because of their structural strength and minimum usage of material. The hyperboloid shape also aids in accelerating the upward convective air flow, improving cooling efficiency. They are popularly associated with nuclear power plants. However, this association is misleading, as the same kind of cooling towers are often used at large coal-fired power plants as well. Similarly, not all nuclear power plants have cooling towers, instead cooling their heat exchangers with lake, river or ocean water.
Categorization by air-to-water flow Crossflow Crossflow is a design in which the air flow is directed perpendicular to the water flow (see diagram below). Air flow enters one or more vertical faces of the cooling tower to meet the fill material. Water flows (perpendicular to the air) through the fill by gravity. The air continues through the fill and thus past the water flow into an open plenum area. A distribution or hot water basin consisting of a deep pan with holes or nozzles in the bottom is utilized in a crossflow tower. Gravity distributes the water through the nozzles uniformly across the fill material.
Cooling tower
147
Cooling tower
148
Counterflow In a counterflow design the air flow is directly opposite to the water flow (see diagram below). Air flow first enters an open area beneath the fill media and is then drawn up vertically. The water is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air flow.
Common to both designs: • The interaction of the air and water flow allow a partial equalization and evaporation of water. • The air, now saturated with water vapor, is discharged from the cooling tower. • A collection or cold water basin is used to contain the water after its interaction with the air flow. Both crossflow and counterflow designs can be used in natural draft and mechanical draft cooling towers.
Cooling tower as a flue gas stack At some modern power stations, equipped with flue gas purification like the Power Station Staudinger Grosskrotzenburg and the Power Station Rostock, the cooling tower is also used as a flue gas stack (industrial chimney). At plants without flue gas purification, problems with corrosion may occur. 123
Wet cooling tower material balance Quantitatively, the material balance around a wet, evaporative cooling tower system is governed by the operational variables of makeup flow rate, evaporation and windage losses, draw-off rate, and the concentration cycles:[6]
Base of a cooling tower with falling water
Cooling tower
149
M = Make-up water in m³/h C = Circulating water in m³/h D = Draw-off water in m³/h E = Evaporated water in m³/h W = Windage loss of water in m³/h X = Concentration in ppmw (of any completely soluble salts … usually chlorides) XM = Concentration of chlorides in make-up water (M), in ppmw XC = Concentration of chlorides in circulating water (C), in ppmw Cycles = Cycles of concentration = XC / XM (dimensionless) ppmw = parts per million by weight
In the above sketch, water pumped from the tower basin is the cooling water routed through the process coolers and condensers in an industrial facility. The cool water absorbs heat from the hot process streams which need to be cooled or condensed, and the absorbed heat warms the circulating water (C). The warm water returns to the top of the cooling tower and trickles downward over the fill material inside the tower. As it trickles down, it contacts ambient air rising up through the tower either by natural draft or by forced draft using large fans in the tower. That contact causes a small amount of the water to be lost as windage (W) and some of the water (E) to evaporate. The heat required to evaporate the water is derived from the water itself, which cools the water back to the original basin water temperature and the water is then ready to recirculate. The evaporated water leaves its dissolved salts behind in the bulk of the water which has not been evaporated, thus raising the salt concentration in the circulating cooling water. To prevent the salt concentration of the water from becoming too high, a portion of the water is drawn off (D) for disposal. Fresh water makeup (M) is supplied to the tower basin to compensate for the loss of evaporated water, the windage loss water and the draw-off water. A water balance around the entire system is: M=E+D+W Since the evaporated water (E) has no salts, a chloride balance around the system is:
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M (XM) = D (XC) + W (XC) = XC (D + W) and, therefore: XC / XM = Cycles of concentration = M ÷ (D + W) = M ÷ (M – E) = 1 + [E ÷ (D + W)] From a simplified heat balance around the cooling tower: E = C · ΔT · cp ÷ HV where: HV = latent heat of vaporization of water = ca. 2260 kJ / kg ΔT = water temperature difference from tower top to tower bottom, in °C cp = specific heat of water = ca. 4.184 kJ / (kg °C)
Windage (or drift) losses (W) from large-scale industrial cooling towers, in the absence of manufacturer's data, may be assumed to be: W = 0.3 to 1.0 percent of C for a natural draft cooling tower without windage drift eliminators W = 0.1 to 0.3 percent of C for an induced draft cooling tower without windage drift eliminators W = about 0.005 percent of C (or less) if the cooling tower has windage drift eliminators Cycles of concentration represents the accumulation of dissolved minerals in the recirculating cooling water. Draw-off (or blowdown) is used principally to control the buildup of these minerals. The chemistry of the makeup water including the amount of dissolved minerals can vary widely. Makeup waters low in dissolved minerals such as those from surface water supplies (lakes, rivers etc.) tend to be aggressive to metals (corrosive). Makeup waters from ground water supplies (wells) are usually higher in minerals and tend to be scaling (deposit minerals). Increasing the amount of minerals present in the water by cycling can make water less aggressive to piping however excessive levels of minerals can cause scaling problems. As the cycles of concentration increase the water may not be able to hold the minerals in solution. When the solubility of these minerals have been exceeded they can precipitate out as mineral solids and cause fouling and heat exchange problems in the cooling tower or the heat exchangers. The temperatures of the recirculating water, piping and heat exchange surfaces determine if and where minerals will precipitate from the recirculating water. Often a professional water treatment consultant will evaluate the makeup water and the operating conditions of the cooling tower and recommend an appropriate range for the cycles of concentration. The use of water treatment chemicals, pretreatment such as water softening, pH adjustment, and other techniques can affect the acceptable range of cycles of concentration. Concentration cycles in the majority of cooling towers usually range from 3 to 7. In the United States the majority of water supplies are well waters and have significant levels of dissolved solids. On the other hand one of the largest water supplies, New York City, has a surface supply quite low in minerals and cooling towers in that city are often allowed to concentrate to 7 or more cycles of concentration. Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and fouling, the water should be filtered and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water.[6] For closed loop evaporative towers, corrosion inhibitors may be used, but caution should be taken to meet local environmental regulations as some inhibitors use chromates. Ambient conditions dictate the efficiency of any given tower due to the amount of water vapor the air is able to absorb and hold, as can be determined on a psychrometric chart.
Cooling tower
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Cooling towers and Legionnaires' disease Further information: Legionellosis and Legionella Another very important reason for using biocides in cooling towers is to prevent the growth of Legionella, including species that cause legionellosis or Legionnaires' disease, most notably L. pneumophila[7] , or Mycobacterium avium[8] . The various Legionella species are the cause of Legionnaires' disease in humans and transmission is via exposure to aerosols—the inhalation of mist droplets containing the bacteria. Common sources of Legionella include cooling towers used in open recirculating evaporative cooling water systems, domestic hot water systems, fountains, and similar disseminators that tap into a public water supply. Natural sources include freshwater ponds and creeks.
Cooling tower and water discharge of a nuclear power plant
French researchers found that Legionella bacteria travelled up to 6 kilometres through the air from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. That outbreak killed 21 of the 86 people who had a laboratory-confirmed infection.[9] Drift (or windage) is the term for water droplets of the process flow allowed to escape in the cooling tower discharge. Drift eliminators are used in order to hold drift rates typically to 0.001%-0.005% of the circulating flow rate. A typical drift eliminator provides multiple directional changes of airflow while preventing the escape of water droplets. A well-designed and well-fitted drift eliminator can greatly reduce water loss and potential for Legionella or other chemical exposure. Many governmental agencies, cooling tower manufacturers and industrial trade organizations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers. Below is a list of sources for such guidelines: • Centers for Disease Control and Prevention [10]PDF (1.35 MB) - Procedure for Cleaning Cooling Towers and Related Equipment (pages 239 and 240 of 249) • Cooling Technology Institute [11]PDF (240 KB) - Best Practices for Control of Legionella, July, 2006 • Association of Water Technologies [12]PDF (964 KB) - Legionella 2003 • California Energy Commission [13]PDF (194 KB) - Cooling Water Management Program Guidelines For Wet and Hybrid Cooling Towers at Power Plants • SPX Cooling Technologies [14]PDF (119 KB) - Cooling Towers Maintenance Procedures • SPX Cooling Technologies [15]PDF (789 KB) - ASHRAE Guideline 12-2000 - Minimizing the Risk of Legionellosis • SPX Cooling Technologies [16]PDF (83.1 KB) - Cooling Tower Inspection Tips {especially page 3 of 7} • Tower Tech Modular Cooling Towers [17]PDF (109 KB) - Legionella Control • GE Infrastructure Water & Process Technologies Betz Dearborn [18]PDF (195 KB) - Chemical Water Treatment Recommendations For Reduction of Risks Associated with Legionella in Open Recirculating Cooling Water Systems
Cooling tower
Cooling tower fog Under certain ambient conditions, plumes of water vapor (fog) can be seen rising out of the discharge from a cooling tower, and can be mistaken as smoke from a fire. If the outdoor air is at or near saturation, and the tower adds more water to the air, saturated air with liquid water droplets can be discharged—which is seen as fog. This phenomenon typically occurs on cool, humid days, but is rare in many climates. This phenomenon can be prevented by decreasing the relative humidity of the saturated discharge air. For that purpose, in hybrid towers, saturated discharge air is mixed with heated low relative humidity air. Some air enters the tower above drift eliminator level, passing through heat exchangers. The relative humidity of the dry air is even more decreased instantly as being heated while entering the tower. The discharged mixture has a relatively lower relative humidity and the fog is invisible.
Cooling tower operation in freezing weather Cooling towers with malfunctions can freeze during very cold weather. Typically, freezing starts at the corners of a cooling tower with a reduced or absent heat load. Increased freezing conditions can create growing volumes of ice, resulting in increased structural loads. During the winter, some sites continuously operate cooling towers with 40 °F (4 °C) water leaving the tower. Basin heaters, tower draindown, and other freeze protection methods are often employed in cold climates. • Do not operate the tower unattended. • Do not operate the tower without a heat load. This can include basin heaters and heat trace. Basin heaters maintain the temperature of the water in the tower pan at an acceptable level. Heat trace is a resistive element that runs along water pipes located in cold climates to prevent freezing. • Maintain design water flow rate over the fill. • Manipulate airflow to maintain water temperature above freezing point.[19]
Some commonly used terms in the cooling tower industry • Drift - Water droplets that are carried out of the cooling tower with the exhaust air. Drift droplets have the same concentration of impurities as the water entering the tower. The drift rate is typically reduced by employing baffle-like devices, called drift eliminators, through which the air must travel after leaving the fill and spray zones of the tower. Drift can also be reduced by using warmer entering cooling tower temperatures. • Blow-out - Water droplets blown out of the cooling tower by wind, generally at the air inlet openings. Water may also be lost, in the absence of wind, through splashing or misting. Devices such as wind screens, louvers, splash deflectors and water diverters are used to limit these losses. • Plume - The stream of saturated exhaust air leaving the cooling tower. The plume is visible when water vapor it contains condenses in contact with cooler ambient air, like the saturated air in one's breath fogs on a cold day. Under certain conditions, a cooling tower plume may present fogging or icing hazards to its surroundings. Note that the water evaporated in the cooling process is "pure" water, in contrast to the very small percentage of drift droplets or water blown out of the air inlets. • Blow-down - The portion of the circulating water flow that is removed in order to maintain the amount of dissolved solids and other impurities at an acceptable level. It may be noted that higher TDS (total dissolved solids) concentration in solution results in greater potential cooling tower efficiency. However the higher the TDS concentration, the greater the risk of scale, biological growth and corrosion. The amount of blow-down is primarily designated by the electrical conductivity of the circulating water. Biological growth, scaling and corrosion can be prevented by chemicals (Biocid, Sulfric Acid, corrosion inhibitor). On the other hand, the only way to decrease the electrical conductivity is increasing the amount of blow-down and subsequently increasing the amount of make up.
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Cooling tower • Make up - The water that is needed to be added to the circulating water system in order to compensate water losses such as, evaporation, drift loss, blow-out, etc. • Leaching - The loss of wood preservative chemicals by the washing action of the water flowing through a wood structure cooling tower. • Noise - Sound energy emitted by a cooling tower and heard (recorded) at a given distance and direction. The sound is generated by the impact of falling water, by the movement of air by fans, the fan blades moving in the structure, and the motors, gearboxes or drive belts. • Approach - The approach is the difference in temperature between the cooled-water temperature and the entering-air wet bulb temperature (twb). Since the cooling towers are based on the principles of evaporative cooling, the maximum cooling tower efficiency depends on the wet bulb temperature of the air. The wet-bulb temperature is a type of temperature measurement that reflects the physical properties of a system with a mixture of a gas and a vapor, usually air and water vapor • Range - The range is the temperature difference between the water inlet and water exit. • Fill - Inside the tower, fills are added to increase contact surface as well as contact time between air and water. Thus they provide better heat transfer. The efficiency of the tower also depends on them. There are two types of fills that may be used: • Film type fill (causes water to spread into a thin film) • Splash type fill (breaks up water and interrupts its vertical progress) • Full-Flow Filtration- Full-flow filtration continuously strains the entire system flow. For example, in a 100-ton system, the flow rate would be roughly 300 gal/min. A filter would be selected to accommodate the entire 300 gal/min flow rate. In this case, the filter typically is installed after the cooling tower on the discharge side of the pump. While this is the preferred method of filtration, for higher flow systems, it may be cost prohibitive. • Side-Stream Filtration- Side-stream filtration, although popular, does not provide complete protection, but it can be effective. With side-stream filtration, a portion of the water is filtered continuously. This method works on the principle that continuous particle removal will keep the system clean. Manufacturers typically package side-stream filters on a skid, complete with a pump and controls. For high flow systems, this method is cost-effective. Properly sizing a side-stream filtration system is critical to obtain satisfactory filter performance. There is some debate over how to properly size the side-stream system. Many engineers size the system to continuously filter the cooling tower basin water at a rate equivalent to 10% of the total circulation flow rate. For example, if the total flow of a system is 1,200 gal/min (a 400-ton system), a 120 gal/min side-stream system is specified. • Cycle of concentration - Maximum allowed multiplier for the amount of miscellaneous substances in circulating water by the amount of those substances in make-up water. • Treated timber - A structural material for cooling towers which was largely abandoned about 10 years ago. It is still used due to its low costs. The life of treated timber varies a lot, depending on the operating conditions of tower, such as frequency of stops, treatment of the circulating water, etc. Considering proper working conditions, estimated life of treated timber structural member is about 10 years. • Pultruded FRP - A common structure material for cooling towers, known for its high corrosion resistance capabilities. Pultuded FRP is produced using pultrusion technology and became the most common structure material for cooling towers as it offers lower costs and requires less maintenance compared to reinforced concrete.
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Cooling tower
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Fire hazards Cooling towers which are constructed in whole or in part of combustible materials can support propagating internal fires. The resulting damage can be sufficiently severe to require the replacement of the entire cell or tower structure. For this reason, some codes and standards[20] recommend combustible cooling towers be provided with an automatic fire sprinkler system. Fires can propagate internally within the tower structure during maintenance when the cell is not in operation (such as for maintenance or construction), and even when the tower is in operation, especially those of the induced-draft type because of the existence of relatively dry areas within the towers.[21]
Stability Being very large structures, they are susceptible to wind damage, and several spectacular failures have occurred in the past. At Ferrybridge power station on 1 November 1965, the station was the site of a major structural failure, when three of the cooling towers collapsed owing to vibrations in 85 mph (137 km/h) winds. Although the structures had been built to withstand higher wind speeds, the shape of the cooling towers meant that westerly winds were funnelled into the towers themselves, creating a vortex. Three out of the original eight cooling towers were destroyed and the remaining five were severely damaged. The towers were rebuilt and all eight cooling towers were strengthened to tolerate adverse weather conditions. Building codes were changed to include improved structural support, and wind tunnel tests introduced to check tower structures and configuration.
Ferrybridge power station
European Market The Cooling Tower market is composed of one third of "close wet" units and two thirds of "open wet" units, and reaches in 2010 a total of 190,24M€.[22] The market by country is splitted in 2010 as following:
Countries
Two hyperboloid cooling towers on Kharkov Power Station #5
[23]
Sales Volume in M€
Share
Benelux
18.70
9.8%
France
22.48
11.8%
Germany
41.40
21.8%
Greece
1.82
1.0%
Italy
20.48
10.8%
Poland
6.31
3.3%
Portugal
2.72
1.4%
Russia, Ukraine and CIS countries
16.59
8.7%
Scandinavia
4.64
2.4%
Spain
9.47
5.0%
Cooling tower
155 Switzerland
5.33
2.8%
Turkey
8.50
4.5%
UK and Ireland
13.66
7.2%
Eastern Europe
18.16
9.5%
References [1] UK Patent No. 108,863 (http:/ / v3. espacenet. com/ publicationDetails/ biblio?KC=A& date=19180411& NR=108863A& DB=EPODOC& locale=en_V3& CC=GB& FT=D) [2] "Power Plant Cooling Towers Like Big Milk Bottle" Popular Mechanics, February 1930 (http:/ / books. google. com/ books?id=p-IDAAAAMBAJ& pg=PA201& dq=Popular+ Science+ 1930+ plane+ "Popular+ Mechanics"& hl=en& ei=kHFkTvrWBK3G0AHHlemCCg& sa=X& oi=book_result& ct=result& resnum=9& sqi=2& ved=0CEsQ6AEwCA#v=onepage& q& f=true) bottom-left of pg 201 [3] U.S. Environmental Protection Agency (EPA). (1997). Profile of the Fossil Fuel Electric Power Generation Industry (http:/ / www. epa. gov/ compliance/ resources/ publications/ assistance/ sectors/ notebooks/ fossil. html) (Report). Washington, D.C. . Document No. EPA/310-R-97-007. p. 79. [4] Cooling System Retrofit Costs (http:/ / www. epa. gov/ waterscience/ presentations/ maulbetsch. pdf) EPA Workshop on Cooling Water Intake Technologies, John Maulbetsch, Maulbetsch Consulting, May 2003 [5] Thomas J. Feeley, III, Lindsay Green, James T. Murphy, Jeffrey Hoffmann, and Barbara A. Carney (2005). "Department of Energy/Office of Fossil Energy’s Power Plant Water Management R&D Program." (http:/ / 204. 154. 137. 14/ technologies/ coalpower/ ewr/ pubs/ IEP_Power_Plant_Water_R& D_Final_1. pdf) U.S. Department of Energy, July 2005. [6] Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st Edition ed.). John Wiley and Sons. LCCN 67019834. (available in many university libraries) [7] Ryan K.J.; Ray C.G. (editors) (2004). Sherris Medical Microbiology (4th Edition ed.). McGraw Hill. ISBN 0-8385-8529-9. [8] |url=http:/ / www. cdc. gov/ ncidod/ eid/ vol4no3/ v4n3. pdf Centers for Disease Control and Prevention - Infectious Diseases (page 495) [9] Airborne Legionella May Travel Several Kilometres (http:/ / www. medscape. com/ viewarticle/ 521680) (access requires free registration) [10] http:/ / www. cdc. gov/ ncidod/ dhqp/ pdf/ guidelines/ Enviro_guide_03. pdf [11] http:/ / www. cti. org/ downloads/ WTP-148. pdf [12] http:/ / www. awt. org/ Legionella03. pdf [13] http:/ / www. energy. ca. gov/ 2005publications/ CEC-700-2005-025/ CEC-700-2005-025. PDF [14] http:/ / spxcooling. com/ pdf/ M99-1342. pdf [15] http:/ / spxcooling. com/ pdf/ guide12. pdf [16] http:/ / spxcooling. com/ pdf/ M92-1474C. pdf [17] http:/ / www. towertechinc. com/ documents/ Legionella_Control_White_Paper_05072004. pdf [18] http:/ / www. gewater. com/ pdf/ tech73. pdf [19] SPX Cooling Technologies: Operating Cooling Towers in Freezing Weather (http:/ / spxcooling. com/ pdf/ H-003B. pdf)PDF (1.45 MB) [20] National Fire Protection Association (NFPA). NFPA 214, Standard on Water-Cooling Towers (http:/ / www. nfpa. org/ aboutthecodes/ AboutTheCodes. asp?DocNum=214). [21] NFPA 214, Standard on Water-Cooling Towers. (http:/ / www. nfpa. org/ aboutthecodes/ AboutTheCodes. asp?DocNum=214) Section A1.1 [22] Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ [23] Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/
External links • What is a cooling tower? (http://www.cti.org/whatis/coolingtowerdetail.shtml) - Cooling Technology Institute • "Cooling Towers" - includes diagrams (http://www.nucleartourist.com/systems/ct.htm) - Virtual Nuclear Tourist
Coupling
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Coupling A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime.
Rotating coupling
Uses Shaft couplings are used in machinery for several purposes, the most common of which are the following.[1] • To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alterations. • To provide for misalignment of the shafts or to introduce mechanical flexibility. • To reduce the transmission of shock loads from one shaft to another. • To introduce protection against overloads. • To alter the vibration characteristics of rotating units.
Types Rigid A rigid coupling is a unit of hardware used to join two shafts within a motor or mechanical system. It may be used to connect two separate systems, such as a motor and a generator, or to repair a connection within a single system. A rigid coupling may also be added between shafts to reduce shock and wear at the point where the shafts meet. When joining shafts within a machine, mechanics can choose between flexible and rigid couplings. While flexible units offer some movement and give between the shafts, rigid couplings are the most effective choice for precise alignment and secure hold. By precisely aligning the two shafts and holding them firmly in place, rigid couplings help to maximize performance and increase the expected life of the machine. These rigid couplings are available in two basic designs to fit the needs of different applications. Sleeve-style couplings are the most affordable and easiest to use. They consist of a single tube of material with an inner diameter that's equal in size to the shafts. The sleeve slips over the shafts so they meet in the middle of the coupling. A series of set screws can be tightened so they touch the top of each shaft and hold them in place without passing all the way through the coupling. Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold.Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life. Examples:
Coupling
157
• Sleeve or muff coupling • Clamp or split-muff or compression coupling
Flexible Flexible couplings are used to transmit torque from one shaft to another when the two shafts are slightly misaligned. Flexible couplings can accommodate varying degrees of misalignment up to 3°. In addition to allowing for misalignment, flexible couplings can also be used for vibration damping or noise reduction. Flexible couplings are designed to transmit torque while permitting some radial, axial, and angular misalignment. Flexible couplings can accommodate angular misalignment up to a few degrees and some parallel misalignment. Beam
A beam coupling
A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion, of one shaft relative to the other. This design utilizes a single piece of material and becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of helical shape. Since it is made from a single piece of material, the Beam Style coupling does not exhibit the backlash found in some multi-piece couplings. Another advantage of being an all machined coupling is the possibility to incorporate features into the final product while still keep the
single piece integrity. Changes to the lead of the helical beam provide changes to misalignment capabilities as well as other performance characteristics such as torque capacity and torsional stiffness. It is even possible to have multiple starts within the same helix. The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical and aerospace. Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steel and titanium. The most common applications are attaching encoders to shafts and motion control for robotics.
A beam coupling with optional features machined into it
Increasing number of coils allows for greater angular misalignment
Coupling
158
Constant velocity There are various types of constant-velocity (CV) couplings: Rzeppa joint, Double cardan joint, and Thompson coupling. Diaphragm Diaphragm couplings transmit torque from the outside diameter of a flexible plate to the inside diameter, across the spool or spacer piece, and then from inside to outside diameter. The deforming of a plate or series of plates from I.D. to O.D accomplishes the misalignment. Disc Disc couplings transmit torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts. Gear A gear coupling is a mechanical device for transmitting torque between two shafts that are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.
A gear coupling
Each joint consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth.
Gear couplings and universal joints are used in similar applications. Gear couplings have higher torque densities than universal joints designed to fit a given space while universal joints induce lower vibrations. The limit on torque density in universal joints is due to the limited cross sections of the cross and yoke. The gear teeth in a gear coupling have high backlash to allow for angular misalignment. The excess backlash can contribute to vibration. Gear couplings are generally limited to angular misalignments, i.e., the angle of the spindle relative to the axes of the connected shafts, of 4-5°. Universal joints are capable of higher misalignments. Single joint gear couplings are also used to connected two nominally coaxial shafts. In this application the device is called a gear-type flexible, or flexible coupling. The single joint allows for minor misalignments such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings are generally limited to angular misalignments of 1/4-1/2°. Oldham An Oldham coupling has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue and groove on one side is perpendicular to the tongue and groove on the other. The middle disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between input and output shafts. Often springs are used to reduce backlash of the mechanism. An advantage to this type of Animated Oldham coupler
Coupling
159
coupling, as compared to two universal joints, is its compact size. The coupler is named for John Oldham who invented it in Ireland, in 1820, to solve a paddle placement problem in a paddle steamer design.
Oldham coupler, assembled
Oldham coupler, disassembled
Rag joint Rag joints are commonly used on automotive steering linkages and drive trains. When used on a drive train they are sometimes known as giubos. Universal joint Universal joints are also known as Cardan joints. Others • Bellows coupling — low backlash • Elastomeric coupling • Bushed pin coupling • Donut coupling • Spider or jaw coupling (or lovejoy coupling) • Resilient coupling • Roller chain and sprocket coupling
Requirements of good shaft alignment / good coupling setup • it should be easy to connect or disconnect the coupling. • it does allow some misalignment between the two adjacent shaft rotation axes. • it is the goal to minimise the remaining misalignment in running operation to maximise power transmission and to maximise machine runtime (coupling and bearing and sealings lifetime). • it should have no projecting parts. • it is recommended to use manufacturer's alignment target values to set up the machine train to a defined non-zero alignment, due to the fact that later when the machine is at operation temperature the alignment condition is perfect
Coupling
Coupling maintenance and failure Coupling maintenance is generally a simple matter, requiring a regularly scheduled inspection of each coupling. It consists of: • Performing visual inspections, checking for signs of wear or fatigue, and cleaning couplings regularly. • Checking and changing lubricant regularly if the coupling is lubricated. This maintenance is required annually for most couplings and more frequently for couplings in adverse environments or in demanding operating conditions. • Documenting the maintenance performed on each coupling, along with the date.[2] Even with proper maintenance, however, couplings can fail. Underlying reasons for failure, other than maintenance, include: • Improper installation • Poor coupling selection • Operation beyond design capabilities.[2] The only way to improve coupling life is to understand what caused the failure and to correct it prior to installing a new coupling. Some external signs that indicate potential coupling failure include: • Abnormal noise, such as screeching, squealing or chattering • Excessive vibration or wobble • Failed seals indicated by lubricant leakage or contamination.[2]
Checking the coupling balance Couplings are normally balanced at the factory prior to being shipped, but they occasionally go out of balance in operation. Balancing can be difficult and expensive, and is normally done only when operating tolerances are such that the effort and the expense are justified. The amount of coupling unbalance that can be tolerated by any system is dictated by the characteristics of the specific connected machines and can be determined by detailed analysis or experience.[2]
References [1] http:/ / www. totalpumps. co. nz/ products/ couplings/ [2] Boyle, B.(2008) "Tracking the causes of coupling failure" Plant Services (http:/ / www. plantservices. com/ articles/ 2008/ 197. html) Explore coupling maintenance and the telltale signs of failure to maximize coupling life and ensure reliable system operations.
External links • • • •
Shaft Coupling Glossary (http://www.unionmillwright.com/shaft.html) List of coupling types (http://www.roymech.co.uk/Useful_Tables/Drive/Drive_Couplings.html) Flash Animation of Oldham coupler (http://www.mekanizmalar.com/oldham.html) Biography of Oldham at Cornell University (http://kmoddl.library.cornell.edu/biographies/Oldham/index. php) • Animation Video of a shaft coupling (http://www.mayr.com/en/service/videoportal/primeflex/)
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Crank (mechanism)
161
Crank (mechanism) A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod. The end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion, in and out. The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crankset or a brace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. Often there is a bar perpendicular to the other end of the arm, often with a freely rotatable handle on it to hold in the hand, or in the case of operation by a foot (usually with a second arm for the other foot), with a freely rotatable pedal.
Examples Familiar examples include:
Hand-powered cranks • Mechanical pencil sharpener • Fishing reel and other reels for cables, wires, ropes, etc. • Manually operated car window • The crank set that drives a trikke through its handles.
Foot-powered cranks
A crank
• The crankset that drives a bicycle via the pedals. • Treadle sewing machine
Engines Almost all reciprocating engines use cranks to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft. Hand crank on a pencil sharpener
Crank (mechanism)
162
Mechanics The displacement of the end of the connecting rod is approximately proportional to the cosine of the angle of rotation of the crank, when it is measured from top dead center (TDC). So the reciprocating motion created by a steadily rotating crank and connecting rod is approximately simple harmonic motion:
where x is the distance of the end of the connecting rod from the crank axle, l is the length of the connecting rod, r is the length of the crank, and α is the angle of the crank measured from top dead center (TDC). Technically, the reciprocating motion of the connecting rod departs slightly from sinusoidal motion due to the changing angle of the connecting rod during the cycle. The mechanical advantage of a crank, the ratio between the force on the connecting rod and the torque on the shaft, varies throughout the crank's cycle. The relationship between the two is approximately:
where is the torque and F is the force on the connecting rod. For a given force on the crank, the torque is maximum at crank angles of α = 90° or 270° from TDC. When the crank is driven by the connecting rod, a problem arises when the crank is at top dead centre (0°) or bottom dead centre (180°). At these points in the crank's cycle, a force on the connecting rod causes no torque on the crank. Therefore if the crank is stationary and happens to be at one of these two points, it cannot be started moving by the connecting rod. For this reason, in steam locomotives, whose wheels are driven by cranks, the two connecting rods are attached to the wheels at points 90° apart, so that regardless of the position of the wheels when the engine starts, at least one connecting rod will be able to exert torque to start the train.
History Western World Classical Antiquity
Roman crank handle from Augusta Raurica, [1] dated to the 2nd century AD
The eccentrically mounted handle of the rotary handmill which appeared in 5th century BC Celtiberian Spain and ultimately spread across the Roman Empire constitutes a crank.[2] [3] [4] A Roman iron crankshaft of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica, Switzerland. The 82.5 cm long piece has fitted to one end a 15 cm long bronze handle, the other handle being lost.[5] [1]
A ca. 40 cm long true iron crank was excavated, along with a pair of shattered mill-stones of 50−65 cm diameter and diverse iron items, in Aschheim, close to Munich. The crank-operated Roman mill is dated to the late 2nd century AD.[6] An often cited modern reconstruction of a bucket-chain pump driven by hand-cranked flywheels from the Nemi ships has been dismissed though as "archaeological fantasy".[7]
Crank (mechanism)
The earliest evidence, anywhere in the world, for the crank combined with a connecting rod in a machine appears in the late Roman Hierapolis sawmill from the 3rd century AD and two Roman stone sawmills at Gerasa, Roman Syria, and Ephesus, Asia Minor (both 6th century AD).[8] On the pediment of the Hierapolis mill, a waterwheel fed by a mill race is shown powering via a gear train two frame saws which cut rectangular blocks by the way of some kind of connecting rods and, through mechanical necessity, cranks. The accompanying inscription is in Greek.[9]
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Roman Hierapolis sawmill from the 3rd century AD, the earliest known machine to combine a [8] crank with a connecting rod.
The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train.[10] [11] In ancient literature, we find a reference to the workings of water-powered marble saws close to Trier, now Germany, by the late 4th century poet Ausonius;[8] about the same time, these mill types seem also to be indicated by the Christian saint Gregory of Nyssa from Anatolia, demonstrating a diversified use of water-power in many parts of the Roman Empire[12] The three finds push back the date of the invention of the crank and connecting rod back by a full millennium;[8] for the first time, all essential components of the much later steam engine were assembled by one technological culture: With the crank and connecting rod system, all elements for constructing a steam engine (invented in 1712) — Hero's aeolipile (generating steam power), the cylinder and piston (in metal force pumps), non-return valves (in water pumps), gearing (in water mills and clocks) — were known in Roman times.[13] Middle Ages A rotary grindstone − the earliest representation thereof −[14] which is operated by a crank handle is shown in the Carolingian manuscript Utrecht Psalter; the pen drawing of around 830 goes back to a late antique original.[15] A musical tract ascribed to the abbot Odo of Cluny (ca. 878−942) describes a fretted stringed instrument which was sounded by a resined wheel turned with a crank; the device later appears in two 12th century illuminated manuscripts.[14] There are also two pictures of Fortuna cranking her wheel of destiny from this and the following century.[14] Vigevano's war
The use of crank handles in trepanation drills was depicted in the 1887 edition of the carriage Dictionnaire des Antiquités Grecques et Romaines to the credit of the Spanish Muslim surgeon Abu al-Qasim al-Zahrawi; however, the existence of such a device cannot be confirmed by the original illuminations and thus has to be discounted.[16] The Benedictine monk Theophilus Presbyter (c. 1070−1125) described crank handles "used in the turning of casting cores".[17] The Italian physician Guido da Vigevano (c. 1280−1349), planning for a new crusade, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels (center of image).[18] The Luttrell Psalter, dating to around 1340, describes a grindstone which was rotated by two cranks, one at each end of its axle; the geared hand-mill, operated either with one or two cranks, appeared later in the 15th century;[19] Medieval cranes were occasionally powered by cranks, although more often by windlasses.[20]
Crank (mechanism)
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Renaissance
15th century paddle-wheel boat whose paddles are turned by single-throw crankshafts (Anonymous of the Hussite Wars)
The crank became common in Europe by the early 15th century, often seen in the works of those such as the German military engineer Konrad Kyeser.[19] Devices depicted in Kyeser's Bellifortis include cranked windlasses (instead of spoke-wheels) for spanning siege crossbows, cranked chain of buckets for water-lifting and cranks fitted to a wheel of bells.[19] Kyeser also equipped the Archimedes screws for water-raising with a crank handle, an innovation which subsequently replaced the ancient practice of working the pipe by treading.[21] The earliest evidence for the fitting of a well-hoist with cranks is found in a miniature of c. 1425 in the German Hausbuch of
the Mendel Foundation.[22] The first depictions of the compound crank in the carpenter's brace appear between 1420 and 1430 in various northern European artwork.[23] The rapid adoption of the compound crank can be traced in the works of the Anonymous of the Hussite Wars, an unknown German engineer writing on the state of the military technology of his day: first, the connecting-rod, applied to cranks, reappeared, second, double compound cranks also began to be equipped with connecting-rods and third, the flywheel was employed for these cranks to get them over the 'dead-spot'. One of the drawings of the Anonymous of the Hussite Wars shows a boat with a pair of paddle-wheels at each end turned by men operating compound cranks (see above). The concept was much improved by the Italian Roberto Valturio in 1463, who devised a boat with five sets, where the parallel cranks are all joined to a single power source by one connecting-rod, an idea also taken up by his compatriot Francesco di Giorgio.[24] German crossbowman cocking his weapon with a cranked rack-and-pinion device (ca. 1493)
Crank (mechanism)
165 In Renaissance Italy, the earliest evidence of a compound crank and connecting-rod is found in the sketch books of Taccola, but the device is still mechanically misunderstood.[25] A sound grasp of the crank motion involved demonstrates a little later Pisanello who painted a piston-pump driven by a water-wheel and operated by two simple cranks and two connecting-rods.[25] The 15th century also saw the introduction of cranked rack-and-pinion devices, called cranequins, which were fitted to the crossbow's stock as a means of exerting even more force while spanning the missile weapon (see right).[26] In the textile industry, cranked reels for winding skeins of yarn were introduced.[19]
Water-raising pump powered by crank and connecting rod mechanism (Georg Andreas Böckler, 1661)
Around 1480, the early medieval rotary grindstone was improved with a treadle and crank mechanism. Cranks mounted on push-carts first appear in a German engraving of 1589.[27]
From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period: Agostino Ramelli's The Diverse and Artifactitious Machines of 1588 alone depicts eighteen examples, a number which rises in the Theatrum Machinarum Novum by Georg Andreas Böckler to 45 different machines, one third of the total.[28]
Far East The earliest true crank handle in Han China occurs, as Han era glazed-earthenware tomb models portray, in an agricultural winnowing fan,[29] dated no later than 200 AD.[30] The crank was used thereafter in China for silk-reeling and hemp-spinning, in the water-powered flour-sifter, for hydraulic-powered metallurgic bellows, and in the well windlass.[31] However, the potential of the crank of converting circular motion into reciprocal one never seems to have been fully realized in China, and the crank was typically absent from such machines until the turn of the 20th century.[32]
Middle East While the US-American historian of technology Lynn White could not find "firm evidence of even the simplest application of the crank until al-Jazari's Tibetan operating a quern (1938). The book of A.D. 1206",[19] the crank appears according to Beeston in the mid-9th perpendicular handle of such rotary century in several of the hydraulic devices described by the Banū Mūsā [3] [4] handmills works as a crank. [33] brothers in their Book of Ingenious Devices. These devices, however, made only partial rotations and could not transmit much power,[34] although only a small modification would have been required to convert it to a crankshaft.[35] Al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machine in two of his water-raising machines.[36] His twin-cylinder pump incorporated a crankshaft,[37] but the device was unnecessarily complex indicating that he still did not fully understand the concept of power conversion.[38] After al-Jazari cranks in Islamic technology are not traceable until an early 15th century copy of the Mechanics of the ancient Greek engineer Hero of Alexandria.[16] Cranks were formerly common on some machines in the early 20th century; for example almost all phonographs before the 1930s were powered by clockwork motors wound with cranks, and internal combustion engines of
Crank (mechanism) automobiles were usually started with cranks (known as starting handles in the UK), before electric starters came into general use.
References [1] [2] [3] [4] [5] [6] [7] [8]
Schiöler 2009, pp. 113f. Date: Frankel 2003, pp. 17–19 Ritti, Grewe & Kessener 2007, p. 159 Lucas 2005, p. 5, fn. 9 Laur-Belart 1988, p. 51–52, 56, fig. 42 Volpert 1997, pp. 195, 199 White, Jr. 1962, pp. 105f.; Oleson 1984, pp. 230f. Ritti, Grewe & Kessener 2007, p. 161:
Because of the findings at Ephesus and Gerasa the invention of the crank and connecting rod system has had to be redated from the 13th to the 6th c; now the Hierapolis relief takes it back another three centuries, which confirms that water-powered stone saw mills were indeed in use when Ausonius wrote his Mosella. [9] Ritti, Grewe & Kessener 2007, pp. 139–141 [10] Ritti, Grewe & Kessener 2007, pp. 149–153 [11] Mangartz 2006, pp. 579f. [12] Wilson 2002, p. 16 [13] Ritti, Grewe & Kessener 2007, p. 156, fn. 74 [14] White, Jr. 1962, p. 110 [15] Hägermann & Schneider 1997, pp. 425f. [16] White, Jr. 1962, p. 170 [17] Needham 1986, pp. 112–113. [18] Hall 1979, p. 80 [19] White, Jr. 1962, p. 111 [20] Hall 1979, p. 48 [21] White, Jr. 1962, pp. 105, 111, 168 [22] White, Jr. 1962, p. 167; Hall 1979, p. 52 [23] White, Jr. 1962, p. 112 [24] White, Jr. 1962, p. 114 [25] White, Jr. 1962, p. 113 [26] Hall 1979, pp. 74f. [27] White, Jr. 1962, p. 167 [28] White, Jr. 1962, p. 172 [29] N. Sivin; Needham, Joseph (August 1968), "Review: Science and Civilisation in China by Joseph Needham", Journal of Asian Studies (Association for Asian Studies) 27 (4): 859–864 [862], doi:10.2307/2051584, JSTOR 2051584 [30] White, Jr. 1962, p. 104 [31] Needham 1986, pp. 118–119. [32] White, Jr. 1962, p. 104:
Yet a student of the Chinese technology of the early twentieth century remarks that even a generation ago the Chinese had not 'reached that stage where continuous rotary motion is substituted for reciprocating motion in technical contrivances such as the drill, lathe, saw, etc. To take this step familiarity with the crank is necessary. The crank in its simple rudimentary form we find in the [modern] Chinese windlass, which use of the device, however, has apparently not given the impulse to change reciprocating into circular motion in other contrivances'. In China the crank was known, but remained dormant for at least nineteen centuries, its explosive potential for applied mechanics being unrecognized and unexploited. [33] A. F. L. Beeston, M. J. L. Young, J. D. Latham, Robert Bertram Serjeant (1990), The Cambridge History of Arabic Literature, Cambridge University Press, p. 266, ISBN 0521327636 [34] al-Hassan & Hill 1992, pp. 45, 61 [35] Banu Musa, Donald Routledge Hill (1979), The book of ingenious devices (Kitāb al-ḥiyal), Springer, pp. 23–4, ISBN 9027708339
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Crank (mechanism) [36] Ahmad Y Hassan. The Crank-Connecting Rod System in a Continuously Rotating Machine (http:/ / www. history-science-technology. com/ Notes/ Notes 3. htm). [37] Sally Ganchy, Sarah Gancher (2009), Islam and Science, Medicine, and Technology, The Rosen Publishing Group, p. 41, ISBN 1435850661 [38] White, Jr. 1962, p. 170:
However, that al-Jazari did not entirely grasp the meaning of the crank for joining reciprocating with rotary motion is shown by his extraordinarily complex pump powered through a cog-wheel mounted eccentrically on its axle.
Bibliography • Frankel, Rafael (2003), "The Olynthus Mill, Its Origin, and Diffusion: Typology and Distribution", American Journal of Archaeology 107 (1): 1–21 • Hall, Bert S. (1979), The Technological Illustrations of the So-Called "Anonymous of the Hussite Wars". Codex Latinus Monacensis 197, Part 1, Wiesbaden: Dr. Ludwig Reichert Verlag, ISBN 3-920153-93-6 • Hägermann, Dieter; Schneider, Helmuth (1997), Propyläen Technikgeschichte. Landbau und Handwerk, 750 v. Chr. bis 1000 n. Chr. (2nd ed.), Berlin, ISBN 3-549-05632-X • al-Hassan, Ahmad Y.; Hill, Donald R. (1992), Islamic Technology. An Illustrated History, Cambridge University Press, ISBN 0-521-422396 • Lucas, Adam Robert (2005), "Industrial Milling in the Ancient and Medieval Worlds. A Survey of the Evidence for an Industrial Revolution in Medieval Europe", Technology and Culture 46 (1): 1–30, doi:10.1353/tech.2005.0026 • Laur-Belart, Rudolf (1988), Führer durch Augusta Raurica (5th ed.), Augst • Mangartz, Fritz (2006), "Zur Rekonstruktion der wassergetriebenen byzantinischen Steinsägemaschine von Ephesos, Türkei. Vorbericht", Archäologisches Korrespondenzblatt 36 (1): 573–590 • Needham, Joseph (1991), Science and Civilisation in China: Volume 4, Physics and Physical Technology: Part 2, Mechanical Engineering, Cambridge University Press, ISBN 0521058031. • Oleson, John Peter (1984), Greek and Roman Mechanical Water-Lifting Devices: The History of a Technology, University of Toronto Press, ISBN 90-277-1693-5 • Volpert, Hans-Peter (1997), "Eine römische Kurbelmühle aus Aschheim, Lkr. München", Bericht der bayerischen Bodendenkmalpflege 38: 193–199, ISBN 3-7749-2903-3 • White, Jr., Lynn (1962), Medieval Technology and Social Change, Oxford: At the Clarendon Press • Ritti, Tullia; Grewe, Klaus; Kessener, Paul (2007), "A Relief of a Water-powered Stone Saw Mill on a Sarcophagus at Hierapolis and its Implications", Journal of Roman Archaeology 20: 138–163 • Schiöler, Thorkild (2009), "Die Kurbelwelle von Augst und die römische Steinsägemühle", Helvetia Archaeologica 40 (159/160): 113–124
External links • Crank highlight: Hypervideo of construction and operation of a four cylinder internal combustion engine courtesy of Ford Motor Company (http://www.asterpix.com/console?as=1187646878192-e57383c789) • Kinematic Models for Design Digital Library (KMODDL) (http://kmoddl.library.cornell.edu/index.php) Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library (http://kmoddl.library.cornell.edu/e-books.php) of classic texts on mechanical design and engineering.
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Critical speed
Critical speed In solid mechanics, in the field of rotordynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller, leadscrew, or gear. As the speed of rotation approaches the object's natural frequency, the object begins to resonate which dramatically increases systemic vibration. The resulting resonance occurs regardless of orientation. When the rotational speed is equal to the numerical value of the natural vibration then that speed is called critical speed.
References • • • • •
Damping Oscillate Natural Frequency Resonance Vibration
Cryogenic engineering Cryogenic engineering is a branch of mechanical engineering which deals with cryogenics. and related very low temperature processes such as air liquefaction, cryogenic engines (for rocket propulsion), cryogenic surgery, et cetera. Generally, temperatures below the boiling point of Nitrogen (77°K) comes under the purview of cryogenic engineering. This field of science also looks at what happens to a wide variety of materials from metals to gases when they are exposed to these temperatures. Cryogenic engineering is nothing but the branch of engineering which uses cryogenics for various domestic, commercial, scientific, medical and defense applications and cryogenics basically deals with the production of very low temperatures and the effects of these temperatures on different substances and materials.Tepperature concerned with cryogenic does not occur in nature,usually below -243.67 degrees Fahrenheit (120 Kelvin) which is used for liquification gases in air like oxygen, hydrogen, nitrogen, methane, argon, helium and neon etc. For example, the Ground Support Systems at Kennedy Space Center for the Ares-I and Ares-V rockets in support of the NASA manned space program. Another is the DOE's Office of Electric Transmission and Distribution to develop advanced cryogenic refrigeration systems for cooling the next generation of electric power equipment based upon high-temperature superconductors. Cryogenic engineering plays an important role in unmanned aerial vehicle systems, infrared search and track sensors, missile warning receivers, satellite tracking systems, and a host of other commercial and military systems. Cryogenic engineering has been used to liquefy atmospheric gases such as Oxygen, Hydrogen, Nitrogen, Methane, Argon, Helium, and Neon. The gases are condensed, collected, distilled and separated. Methane is used in liquid natural gas (LNG), and oxygen, hydrogen and nitrogen are used in rocket fuels and other aerospace and defense applications, in metallurgy and in various chemical processes. Helium is used in diving decompression chambers and to maintain suitably low temperatures for superconducting magnets, and neon is used in lighting. • INTRODUCTION: Cryogenics has given big impetus to the traditional fields,such as oxygen production for chemistry & metallurgy. But this technology is enhanced day by day & opens the newer divisions for 'Science and Technology' such as 'CRYOGENIC POWER GENERATION'. CRYOGENIC TEMPERATURE have come to be essential in the fields like physics,instrumentation, astronautics,biology and medicine and have been instrumental in the
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Cryogenic engineering development of specialized fields of cryogenics such as 1. 2. 3. 4.
CRYOPHYSICS CRYOELECTRONICS CRYOSURGERY CRYOGENIC ENGINEERING
• Origin Of Cryogenic Engineering: The word "cryogenic" is derived from the Greek words kruos for frost and genos for origin of creation which gradually refers to the technology and art of producing low temperatures.Cryogenics has come to describe the the study of phenomenon,techniques, and concepts occurring at or pertaining to temperature below 120K. many applications such as POWER ENGINEERING,NUCLEAR ENGINEERING,AEROSPACE TECHNOLOGY,AGRICULTURE, MEDICINE,FOOD PROCESSING needs the gases like oxygen , nitrogen , carbon dioxide, helium, crypton methane, etc . the liquified gases have very low boiling points lying in the cryogenic range. some materials ,when cooled to very low temperatures,some materials show super conductivity and some liquids, superfluidity. • Applications: Cryogenic engineering is important because it plays a major role in modern industry and science.Today, cryogenically cooled electrical machines and superconductors are widely used in power generation , instrumentation, transport and some of the newer fields of technology. Large-scale air separation plants use cryogenics to break down air into its component elements for industrial and medical uses. For efficiency the resulting products are frequently transported and stored as cryogenic fluids. Also for the long range space communication , infrared, and laser systems can hardly be overestimated. Magnetic resonance imaging (MRI) systems that use superconducting magnets cooled by liquid helium have become a common feature in modern hospitals.Deep Freezing , Cryogenic condensation, and Cryosorption offer powerful tools for producing ultra high vacuum. recent medical and biological experiments have discovered that,when exposed to cryogenic temperatures, living tissue and biological material show hitherto unknown properties which in fact opens up a very challenging and brilliant fields for researches in biology , medicine and farming.In space technology, cryogenics is found in the liquid hydrogen and oxygen fuels used in rocket engines and in applications such as the Cosmic Background Explorer (COBE) satellite, whose superfluid (He II) cooled sensors have detected remnants of the Big Bang. • Historical Review: The history of cryogenics is inseparable from advances in physics. The rapidly growing field of application for low temperatures,on other hand,has been governing developmaents in the field of cryogenic apparatus and plant.before,cryogenic air separation had been dominated the industrial area and was capable of operation down to 70 K. The rapid expansion in the commrcial production of hydrogen and helium systems operating down to 4K The more recent years have seen a massive expansion in the liquefaction , handling , and storage of natural gas. There is steady increase in the consumption of argon,neon and other rare gases. New cryogenic cooling systems have been designed for the superconducting windings of electrical machines and magnets masers and lasers .There have appeared plants to purify gases by low temperature sorption and distillation,high vacuum cryogenic pumps, instruments and apparatus for cryosurgery,etc. in addition to big 'tonnage-production' liquifiers and cryogenerators ,electronics and cryogenic apparatus. Now, 'mycrogenics' is a field in its own right .
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Cryogenic engineering
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References Book : 1)Theory & Design of Cryogenic Systems by A.Arkharov I.Marfenina Ye.Mikulin http:/ / books. google. com/ books/ about/ Theory_and_design_of_cryogenic_systems. html?id=ReceAQAAIAAJ 2)Cryogenic Enineering by Thomas A. Flynn http:/ / books. google. com/ books/ about/ Cryogenic_engineering. html?id=1OC8zeol7uMC 3)Introduction to Cryogenic Engineering http:/ / www. slac. stanford. edu/ econf/ C0605091/ present/ CERN. PDF 4)www.wisegeek.com 5)www.google.com
d'Alembert–Euler condition In mathematics and physics, especially the study of mechanics and fluid dynamics, the d'Alembert-Euler condition is a requirement that the streaklines of a flow are irrotational. Let x = x(X,t) be the coordinates of the point x into which X is carried at time t by a (fluid) flow. Let
be the second material derivative of x. Then the
d'Alembert-Euler condition is:
The d'Alembert-Euler condition is named for Jean le Rond d'Alembert and Leonhard Euler who independently first described its use in the mid-18th century. It is not to be confused with the Cauchy-Riemann conditions.
References • Truesdell, Clifford A. (1954). The Kinematics of Vorticity. Bloomington, IN: Indiana University Press. See sections 45–48. • d'Alembert–Euler conditions [1] on the Springer Encyclopedia of Mathematics
References [1] http:/ / eom. springer. de/ c/ c020970. htm
D-value (transport)
D-value (transport) In transport, D-value is a rating in kN that is typically attributed to mechanical couplings, and reflects dynamic loading limits between a towing vehicle and a trailer. The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is: D (kN) = 9.81 x (Gross Vehicle Mass X Gross Trailer Mass)/(Gross Combination Mass). The vehicle masses are in tonnes, and the 9.81 factor converts this to kN. GVM refers to the towing vehicle (including any vertical loads passed on to the towing vehicle via the coupling), GTM refers to the axle loads only of the towed vehicle, and GCM refers to the total mass of the combination.
Damper (flow) A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air handling equipment. A damper may be used to cut off central air conditioning (heating or cooling) to an unused room, or to regulate it for room-by-room temperature and climate control. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate airflow constantly and are operated by electric or pneumatic motors, in turn controlled by a thermostat or building automation system. In a chimney flue, a damper closes off the flue to keep the weather (and birds and other animals) out and warm or cool Opposed blade dampers in a mixing duct. air in. This is usually done in the summer, but also sometimes in the winter between uses. In some cases, the damper may also be partly closed to help control the rate of combustion. The damper may be accessible only by reaching up into the fireplace by hand or with a woodpoker, or sometimes by a lever or knob that sticks down or out. On a woodburning stove or similar device, it is usually a handle on the vent duct as in an air conditioning system. Forgetting to open a damper before beginning a fire can cause serious smoke damage to the interior of a home, if not a house fire.
Automated zone dampers
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Damper (flow)
A zone damper (also known as a Volume Control Damper or VCD) is a specific type of damper used to control the flow of air in an HVAC heating or cooling system. In order to improve efficiency and occupant comfort, HVAC systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to cool down.
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An opposed-blade, motor-closed, motor-opened zone damper. The damper is shown in the "open" position.
Zone dampers as used in home HVAC systems are usually electrically powered. In large commercial installations, vacuum or compressed air may be used instead. In either case, the motor is usually connected to the damper via a mechanical coupling. For electrical zone dampers, there are two principal designs. In one design, the motor is often a small shaded-pole synchronous motor combined with a rotary switch that can disconnect the motor at either of the two stopping points ("damper open" or "damper closed"). In this way, applying power to the "open damper" terminal causes the motor to run until the damper is open while applying power at the "close Close-up of the motor connections. This damper can switch the electrical power to control additional "slave" dampers, damper" terminal causes the motor to run until the damper is minimizing the electrical load on the damper's control closed. The motor is commonly powered from the same 24 circuitry and power transformer volt ac power source that is used for the rest of the control system. This allows the zone dampers to be directly controlled by low-voltage thermostats and wired with low-voltage wiring. Because simultaneous closure of all dampers might harm the furnace or air handler, this style of damper is often designed to only obstruct a portion of the air duct, for example, 75%. Another style of electrically powered damper uses a spring-return mechanism and a shaded-pole synchronous motor. In this case, the damper is normally opened by the force of the spring but can be closed by the force of the motor. Removal of electrical power re-opens the damper. This style of damper is advantageous because it is "fail safe"; if the control to the damper fails, the damper opens and allows air to flow. However, in most applications "fail safe" indicates the damper will close upon loss of power thus preventing the spread of smoke and fire to other areas. These dampers also may allow adjustment of the "closed" position so that they only obstruct, for example, 75% of the air flow when closed. For vacuum- or pneumatically-operated zone dampers, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded rubber diaphragm to move and actuate the damper. As with the second style of electrical zone dampers, these dampers automatically return to the default position without the application of any power, and the default position is usually "open", allowing air to flow. Like the second style of electrical zone damper, these dampers may allow adjustment of the "closed" position. Highly sophisticated systems may use some form of building automation such as BACnet or LonWorks to control the zone dampers. The dampers may also support positions other than fully open or fully closed and are usually capable of reporting their current position and, often, the temperature and volume of the air flowing past the smart damper.
Damper (flow) Regardless of the style of damper employed, the systems are often designed so that when no thermostat is calling for air, all dampers in the system are opened. This allows air to continue to flow while the heat exchanger in a furnace cools down after a heating period completes.
Comparison to multiple furnaces/air handlers Multiple zones can be implemented using either multiple, individually-controlled furnaces/air handlers or a single furnace/air handler and multiple zone dampers. Each approach has advantages and disadvantages.
Multiple furnaces/air handlers Advantages: • Simple mechanical and control design ("SPST thermostats") • Redundancy: If one zone furnace fails, the others can remain working Disadvantages: • Cost. Furnaces cost much more than zone dampers • Power consumption. Operating furnaces draw power whereas a zone damper only draws power while in motion from one state to the other (or, in some cases, a very small amount of power while holding closed).
Zone dampers Advantages: • Cost. • Power consumption. Disadvantages: • New US residential building codes require permanent access to dampers through ceiling access panels. • Zone dampers are not 100% reliable. The motor-to-open/motor-to-closed style of electrically operated zone dampers aren't "fail safe" (that is, they do not fail to the open condition). However, zone dampers that are of the "Normally Open" type are fail-safe, in that they will fail to the open condition. • No inherent redundancy for the furnace. A system with zone dampers is dependent upon a single furnace. If it fails, the system becomes completely inoperable. • Low total flow when only some dampers are open can cause inefficient operation. • Supply and return ducts need dampers to avoid pressurization of portions of the building. • The system can be harder to a design, requiring both "SPDT" thermostats (or relays) and the ability of the system to withstand the fault condition whereby all zone dampers are closed simultaneously. Pneumatic actuation is preferred for these dampers. It is easier to provide zone-classified solenoid valves for pneumatic actuation, as compared to electrical actuation. The physical size of such solenoid valves have come down very considerably over the years
Fire dampers Fire dampers are fitted where ductwork passes through fire compartment walls / fire curtains as part of a fire control strategy. In normal circumstances, these dampers are held open by means of fusible links. When subjected to heat, these links fracture and allow the damper to close under the influence of the integral closing spring. The links are attached to the damper such that the dampers can be released manually for testing purposes. The damper is provided with an access door in the adjacent ductworks for the purpose of inspection and resetting in the event of closure.
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Damper (flow)
External links • Flextor Dampers FAQ [1]
References [1] http:/ / www. dampersandexpansionjoints. com/ frequently-asked-questions. html
Damping matrix In applied mathematics, a damping matrix is a matrix corresponding to any of certain systems of linear ordinary differential equations. A damping matrix is defined as follows. If the system has n degrees of freedom un and is under application of m damping forces. Each force can be expressed as follows:
It yields in matrix form;
where C is the damping matrix composed by the damping coefficients:
References • (fr) Mechanics of structures and seisms [1]
References [1] http:/ / www. enpc. fr/ fr/ formations/ ecole_virt/ cours/ Pecker2009_2010/ poly/ Chapitre6. pdf
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Demister (vapor)
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Demister (vapor) A demister, is a device often fitted to vapor liquid separator vessels to enhance the removal of liquid droplets entrained in a vapor stream. Demisters may be a mesh type coalescer, vane pack or other structure intended to aggregate the mist into droplets that are heavy enough to separate from the vapor stream. Demisters can reduce the residence time required to separate a given liquid droplet size thereby reducing the volume and associated cost of separator equipment. Demisters are often used where vapor quality is important in regard to entrained liquids particularly where separator equipment costs are high (e.g., high pressure systems) or where space or weight savings are advantageous. For example, in the process of brine desalination on marine vessels, brine is flash heated into vapor. In flashing, vapor carries over droplets of brine which have to be separated before condensing, otherwise the distillate vapor would be contaminated with salt. This is the role of the demister. Demisted vapor condenses on tubes in the desalination plant, and product water is collected in the distillate tray.
A typical, large-scale, vapor-liquid separator as used in oil refineries, petrochemical and chemical plants
Design and manufacturing of gears
Design and manufacturing of gears Gear design is the process of designing a gear. Designing is done prior to manufacturing and includes calculation of the gear geometry, taking into account gear strength, wear characteristic of the gear teeth, material selection, gear alignment and provision for lubrication of gear.
Gear A gear is a rotating machine part which has cut teeth, that mesh with another toothed part in order to transmit torque. The cut teeth are also called 'cogs'. Gears are one of the most important parts of any machine or a mechanism. Some of the sectors in which gears play a vital role are: • • • •
Turbine plant Hot and Cold Rolling Construction machinery Elevator industry
Gear tooth terminology
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Design and manufacturing of gears
Standard system of Gear Teeth In a gear drive, two types of curves, the cycloidal and the involute, are generally used. In a gear drive, the shape of the tooth depends upon the pressure angle. Gears of involute profile with 14.5°,20° full-depth and 20° stub pressure angles are most commonly used in industries. A 20° pressure angle full-depth involute gear tooth has various advantages over the other pressure angles. BIS has recommended the use of 20° pressure angle full depth involute gear tooth.
Design Considerations[1] The accuracy of the output of a gear depends on the accuracy of its design and manufacturing.The correct manufacturing of a gear requires a number of prerequisite calculations and design considerations.The design considerations taken into account before manufacturing of gears are: • Strength of the gear in order to avoid failure at staring torques or under dynamic loading during running conditions. • Gear teeth must have good wear characteristics. • Selection of material combination. • Proper alignment and compactness of drive • Provision of adequate and proper lubrication arrangement.
Selection of Materials The gear material should have the following properties: • • • •
High tensile strength to prevent failure against static loads High endurance strength to withstand dynamic loads Low coefficient of friction Good manufacturability
Generally cast iron,steel,brass and bronze are preferred for manufacturing metallic gears with cut teeth.Where smooth action is not important,cast iron gears with cut teeth may be employed.Commercially cut gears have a pitch line velocity of about 5 metre/second.For velocities larger than this,gear sets with non metallic pinions as one member are used to eliminate vibration and noise.Non-metallic materials are made of various materials such as treated cotton pressed and and moulded at high pressure,synthetic resins of the phenol type and raw hide.Moisture affects raw hide pinions.gears made of phenolic resins are self supporting on the other hand other two types are supported by metal side plates at both ends of the plate.Large wheels are made with fretting rings to save alloy steels.Wheel centre is commonly cast from cast iron.The ring is forged or roll expanded from steel of the respective grade specified by the tooth design.
Gear wheel proportions A gear has three important parts • Hub • Web or arms • Rim Hub of gears are of two types,solid or split.The advantage of split hub is that it reduces the cooling stresses in the gear and facilitates the mounting of the gear on the shaft.The solid hub gear is to be mounted overhung on the shaft.The key is placed under the arm in case of solid hub while in case of split hub,the key is placed at right angles to the hub joint. Small gears up to 250 mm pitch circle diameter are built with a web,which joins the hub and the rim.The thickness of the web of the gear should be such that it is capable of transmitting the torque without shearing off at the hub where it joins.The gear is designed such that the thickness of its web is equal to half the circular
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Design and manufacturing of gears
178
pitch.Gear of larger diameter are provided with arms.The number of arms depends on the pitch circle diameter of the gear.Following are the prevailing practices of the number of arms and gear diameters Gear diameter(mm)
Arms
300-500
4-5
500-1500
6
1500-2400
8
>2400
10-12
While calculating the dimensions of the arms it is assumed that they transmit the stalling torque safely.Elliptical cross sections are preferred for lighter loads while remaining cross sections are used for large and heavy gears.The following aspects are considered while determining cross sectional diameter of the arm.
Empirical formulas are used to determine the rim thickness.
where
is the number of teeth and
are the number of arms.
A good design is a one in which the rim has a central rib of thickness equal to half the circular pitch. If the lay out of the shaft is known,the diameter of the gear shaft can be calculated.Toothed wheels fixed on the shaft are fitted by interference-for example,press or light press fit.For impact load or speeds above 2000 r.p.m. press fit is employed.If the wheel is to be removed from the shaft medium fit are used. The following types of gears are most commonly used in industry for power transmission purposes: • Spur gears
Design and manufacturing of gears
179
• Helical gears • Bevel gears • Worm and worm gears
Spur Gear[2] A gear having straight teeth along the axis is called a spur gear.They are used to transmit power between two parallel shafts as shown in the adjacent figure.A rack is a straight tooth gear which can be thought of as a segment of spur gear of infinite diameter.
Design of spur gear The prime requirement of a gear drive is to transmit power at a particular velocity ratio for certain working condition,such as,operating time,nature of load,etc.The following points must be considered while designing a gear drive:
Representation of spur gear
• Highest static load acting on the gear tooth due to high starting torque • Dynamic load at normal running conditions due to profile error on the tooth. • Wear characteristics of the tooth for increasing its life Besides the above basic requirements,the following aspects are also considered: • • • •
Lubrication of teeth alignment of gears Stress concentration at the root of the teeth Deflection of gear teeth and shaft should be specified
Force Analysis In a gear drive,power is transmitted by means of a force exerted by the tooth of the driving gear on the mating tooth of the driven gear.The law of gearing states that,the exerted force is always normal to the tooth surface and acts along the pressure angle line.
Design and manufacturing of gears
The normal force
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as shown in the above figure,acting along the pressure line,can be resolved into two
components,tangential force and radial force .Thus, = cosα and = sinα= tanα where α is the pressure angle. is responsible for transmitting torque and hence the power while the
is called the separating force,which
always acts towards the centre of the gear. In the force analysis of a gear drive,an assumption is made that the tangential force remains constant in magnitude as the contact between two teeth moves from top of the tooth to its bottom.The torque transmitted by with respect to the centre of the gear is
Also by using the relation P =
×v, the tangential force responsible for transmitting power can be obtained,where
is the power(kW) is the pitch line velocity(m/s) is tangential force(kN).
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Beam strength of spur gear tooth The continuous change in the point of application of load on the tooth profile and the change in magnitude and direction of the applied load make accurate stress analysis of a gear tooth a complicated problem.In 1892,Wilfred Lewis published a paper titled,"The investigation of the strength of gear tooth",in which he derived an equation for determining the approximate stress in a gear tooth by treating it as a cantilever beam of uniform strength. The following assumptions are made for the beam strength calculation: • The tangential component,
,is uniformly distributed across the face width.But practically the distribution is
non- uniform.This assumption is valid for small face widths 9.5m≤ • • • •
Force acting on a gear tooth
,i.e.
≤12.5m, where m is the module of the gear.
The effect of the radial component ,which produces direct compressive strength ,is neglected. The maximum stress is assumed to occur when the entire load is at the tip of the tooth. The tooth is assumed to be a simple cantilever beam. The effect of stress concentration and manufacturing error are neglected.
References [1] Pandya, N.C. (1981). Elements of Machine Design. India: Charotar Publishing House. pp. 713–735. [2] Sharma, C.S. (2010). Design of Machine Elements. India: PHI Learning Private Limited. pp. 399–426. ISBN 978-81-203-1955-4.
External links • http://www.explainthatstuff.com/gears.html
Design for manufacturability for CNC machining
Design for manufacturability for CNC machining Design for manufacturability (DFM) describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce its manufacturing costs. DFM will allow potential problems to be fixed in the design phase which is the least expensive place to address them. The design of the component can have an enormous effect on the cost of manufacturing. Other factors may affect the manufacturability such as the type of raw material, the form of the raw material, dimensional tolerances, and secondary processing such as finishing.
Material type The most easily machined types of metals include aluminum, brass, magnesium, and softer metals. As materials get harder, denser and stronger, such as steel, stainless steel, titanium, and exotic alloys, they become much harder to machine and take much longer, thus being less manufacturable. Most types of plastic are easy to machine, although additions of fiberglass or carbon fiber can reduce the machinability. Plastics that are particularly soft and gummy may have machinability problems of their own.
Material form Metals come in all forms. In the case of aluminum as an example, bar stock and plate are the two most common forms from which machined parts are made. The size and shape of the component may determine which form of material must be used. It is common for engineering drawings to specify one form over the other. Bar stock is generally close to 1/2 of the cost of plate on a per pound basis. So although the material form isn't directly related to the geometry of the component, cost can be removed at the design stage by specifying the least expensive form of the material.
Tolerances A significant contributing factor to the cost of a machined component is the geometric tolerance to which the features must be made. The tighter the tolerance required, the more expensive the component will be to machine. When designing, specify the loosest tolerance that will serve the function of the component. Tolerances must be specified on a feature by feature basis. There are creative ways to engineer components with lower tolerances that still perform as well as ones with higher tolerances.
Design and shape As machining is a subtractive process, the time to remove the material is a major factor in determining the machining cost. The volume and shape of the material to be removed as well as how fast the tools can be fed will determine the machining time. When using milling cutters, the strength and stiffness of the tool which is determined in part by the length to diameter ratio of the tool will play the largest role in determining that speed. The shorter the tool is relative to its diameter the faster it can be fed through the material. A ratio of 3:1 (L:D) or under is optimum.[1] If that ratio cannot be achieved, a solution like this depicted here can be used.[2] For holes, the length to diameter ratio of the tools are less critical, but should still be kept under 10:1. There are many other types of features which are more or less expensive to machine. Generally chamfers cost less to machine than radii on outer horizontal edges. Undercuts are more expensive to machine. Features that require smaller tools, regardless of L:D ratio, are more expensive.
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Design for manufacturability for CNC machining
References [1] http:/ / www. efunda. com/ processes/ machining/ mill_design. cfm [2] http:/ / procnc. com/ images/ content/ Design_Guide_Rev_C. pdf
External links • Arc Design for Manufacturability Tips (http://www.arctechinc.com/wp-content/uploads/2010/06/ Arc-Design-for-Manufacturability-Tips.pdf) • DFM Concept Explained (http://www.empf.org/empfasis/archive/104dfm.htm) • Design for Manufacturing and Analysis (http://www.dfma.com/index.html) • List of DFM links (http://www.npd-solutions.com/designguidelines.html)
Dexel Dexel ("depth pixel") is a concept used for a discretized representation of functions defined on surfaces used in geometrical modeling and physical simulation,[1] sometimes also referred to as multilevel Z-map[2] . Dexel is a nodal value of a scalar or vector field on a meshed surface. Dexels are used in simulation of manufacturing processes (such as turning[3] , milling[4] or rapid prototyping[5] ), when workpiece surfaces are subject to modifications. It is practical to express the surface evolution by dexels especially when the surface evolution scale is very different from the structural finite element 3D model discretization step (e.g. in machining the depth of cut variation is often several orders of magnitude smaller (1..10 microns) than the FE model mesh step (1 mm)).
References [1] Zhao, Wei; Xiaoping Qian (2009-01-01). "Mathematical Morphology in Multi-Dexel Representation" (http:/ / link. aip. org/ link/ abstract/ ASMECP/ v2009/ i48999/ p733/ s1). ASME Conference Proceedings 2009 (48999): 733–742. doi:10.1115/DETC2009-87722. . Retrieved 2011-07-07. [2] Choi, Byoung K.; Robert B. Jerard (1998). Sculptured surface machining: theory and applications. Kluwer Academic. ISBN 9780412780202. [3] Lorong, Philippe; Arnaud Larue, Alexis Perez Duarte (2011-04). "Dynamic Study of Thin Wall Part Turning" (http:/ / www. scientific. net/ AMR. 223. 591). Advanced Materials Research 223: 591–599. doi:10.4028/www.scientific.net/AMR.223.591. ISSN 1662-8985. . Retrieved 2011-05-31. [4] Assouline, S.; E. Beauchesne, G. Coffignal, P. Lorong, A. Marty (2002). "Numerical simulation of machining at the macroscopic scale: Dynamic models of the workpiece". Mecanique et Industries 3 (4): 389–402. ISSN 12962139 (ISSN). [5] Xinrui Gao; Shusheng Zhang, Zengxuan Hou (2007-08-24). "Three Direction DEXEL Model of Polyhedrons and Its Application". Third International Conference on Natural Computation, 2007. ICNC 2007. 5. Third International Conference on Natural Computation, 2007. ICNC 2007. IEEE. pp. 145-149. doi:10.1109/ICNC.2007.777. ISBN 978-0-7695-2875-5.
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Disc coupling
Disc coupling Disc coupling: by definition, transmits torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts. A disc coupling is a high performance motion control (Servo) coupling designed to be the torque transmitting element (by connecting two shafts together) while accommodating for shaft misalignment. It is designed to be flexible, while remaining torsionally strong under high torque loads. Typically, disc couplings can handle speeds up to 10,000 RPM. There are two different styles of disc coupling: Single Disc Style couplings are composed of two hubs (the ends of the coupling, which are typically made from aluminum, but stainless steel is used as well) and a single, flat, stainless steel disc spring. Double Disc Style coupling is also composed of two hubs, but has an additional center spacer sandwiching two disc springs. The center spacer can be made out of the same material as the hubs, but is sometimes available in insulating acetal, which makes the coupling electrically isolating.
The difference between the two styles is that single disc couplings cannot accommodate parallel misalignment due to the complex bending that would be required of the lone disc. Double disc styles allow the two discs to bend in opposite directions to better manage parallel offset. The discs are fastened to the hubs (and center spacer on double disc styles) with tight fitting pins that do not allow any play or backlash between the disc and the hubs. The discs can be bent easily and as a result, disc couplings have some of the lowest bearing loads available in a motion control coupling. Torsionally stiff and still flexible, disc couplings are a great solution for high speed applications. The downside is that they are more delicate than the average coupling and can be damaged if misused. Special care should be taken to ensure that misalignment is within the ratings of the coupling.
References
184
Docking sleeve
Docking sleeve In mechanical engineering, a docking sleeve or mounting boss is a tube or enclosure used to couple two mechanical components together, or to retain two components together; this permits two equally-sized appendages to be connected together via insertion and fixing within the construction. Docking sleeves may be physically solid or flexible, their implementation varying widely according to the required application of the device. The most common application is the plastic appendage that receives a screw in order to attach two parts.
Drive by wire Drive-by-wire, DbW, by-wire, or x-by-wire technology in the automotive industry replaces the traditional mechanical control systems with electronic control systems using electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators. Hence, the traditional components such as the steering column, intermediate shafts, pumps, hoses, belts, coolers and vacuum servos and master cylinders are eliminated from the vehicle. Examples include electronic throttle control and brake-by-wire.
Advantages Safety can be improved by providing computer controlled intervention of vehicle controls with systems such as Electronic Stability Control (ESC), adaptive cruise control and Lane Assist Systems. Ergonomics can be improved by the amount of force and range of movement required by the driver and by greater flexibility in the location of controls. This flexibility also significantly expands the number of options for the vehicle's design. Parking can be made easier with reduced lock-to-lock steering wheel travel as with BMW's Active Steering System, or semi-automatic]] which is available in Ford/Lincoln vehicles in the US, some Toyota Prius in Japan, Lexus LS460 models worldwide and newer European Volkswagen models. Although neither of these are strictly Steer-by-Wire (SbW) because they retain mechanical linkages, they show the capabilities that are possible.
Disadvantages The cost of DbW systems is often greater than conventional systems. The extra costs stem from greater complexity, development costs and the redundant elements needed to make the system safe. Failures in the control system could theoretically cause a runaway vehicle, although this is no different from the throttle return spring snapping on a traditional mechanical throttle vehicle. The vehicle could still be stopped by turning the ignition off if this occurred. Another disadvantage is that manufacturers often reduce throttle sensitivity in the low-mid throttle range to make the car easier or safer to control - or to protect the drivetrain (gearbox, clutch, etc.) from driver abuse. The feeling to the driver is that the throttle feels less responsive. There are aftermarket electronic kits to increase throttle sensitivity, to re-gain a more direct-feeling relationship between pedal position and throttle valve opening.
Steer by Wire This is currently used in electric forklifts and stockpickers and some tractors [1]. Its implementation in road vehicles is limited by concerns over reliability although it has been demonstrated in several concept vehicles such as ThyssenKrupp Presta Steering's Mercedes-Benz Unimog, General Motors' Hy-wire and Sequel and the Mazda Ryuga. A rear wheel SbW system by Delphi called Quadrasteer is used on some pickup trucks but has had limited commercial success. This is not to be confused with Electric Power Steering.
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Drive by wire
Passenger car state-of-the-art Electronic fuel injection metering in diesel and gasoline engines is now widely used. Electronic throttle control is also in widespread use for gasoline engine control. Purely electronic brake and steering systems have yet to find widespread application in passenger cars. This is primarily because of the significant safety implications of steering or braking systems without a redundant mechanical backup in case of failure of the DbW system. Although it is technically feasible to address these concerns with multiple redundant electronic systems (as in fly-by-wire systems used by many airliners and military aircraft), the additional cost and service requirements have made these systems commercially uncompetitive to date. Hybrid electric vehicles employ limited electronically controlled regenerative braking, but the standard hydraulic braking system is retained. The growth in sales of hybrid and electric vehicles is likely to become an enabling factor for drive-by-wire systems in the future cars because of the availability of high power electrical supplies required for the new electrical actuators.
The future Some fanciful theories and applications abound as to what the ultimate implications of DbW technology might be. It has been suggested that DbW might allow a car to become completely separate from its controls, meaning that a car of the future might theoretically be controlled by any number of different control systems: push buttons, joysticks, steering wheels, or even voice commands — whatever device that designers could come up with.
External links • Missing data compensation for safety-critical components in a drive-by wire system [2] • Fusion of redundant information in brake-by-wire systems, using a fuzzy Voter [3] • Position sensing in by-wire brake callipers using resolvers [4] [1] [2] [3] [4]
http:/ / www. motionsystemdesign. com/ Issue/ Article/ 47436/ ArticleDraw. aspx http:/ / www. ses. swin. edu. au/ ~rhoseinnezhad/ ieee_tvt_1. pdf http:/ / www. isif. org/ 2075D04. pdf http:/ / www. ses. swin. edu. au/ ~rhoseinnezhad/ ieee_tvt_2. pdf
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Duality (mechanical engineering)
187
Duality (mechanical engineering) In mechanical engineering, many terms are associated into pairs called duals. A dual of a relationship is formed by interchanging force (stress) and deformation (strain) in an expression. Here is a partial list of mechanical dualities: • force — deformation • stress — strain • stiffness method — flexibility method
Examples Constitutive relation • stress and strain (Hooke's law.)
References • Fung, Y. C., A First Course in CONTINUUM MECHANICS, 2nd edition, Prentice-Hall, Inc. 1977
Dunkerley's method Dunkerley's method is used in mechanical engineering to determine the critical speed of a shaft-rotor system. Other methods include the Rayleigh–Ritz method.
Whirling of a shaft No shaft can ever be perfectly straight or perfectly balanced. When an element of mass is a distance ‘ ’ from the axis of rotation, centrifugal force, will tend to pull the mass outward. The elastic properties of the shaft will act to restore the “straightness”. If the frequency of rotation is equal to one of the resonant frequencies of the shaft, whirling will occur. In order to save the machine from failure, operation at such whirling speeds must be avoided. Whirling is a complex phenomenon that can include harmonics but we are only going to consider synchronous whirl, where the frequency of whirling is the same as the rotational speed.
Dunkerley’s formula (approximation) The whirling frequency of a symmetric cross section of a given length between two points is given by: RPM where E = young's modulus, I = Second moment of area, m = mass of the shaft, L= length of the shaft between points A shaft with weights added will have an angular velocity of N (rpm) equivalent as follows:
Dunkerley's method
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Background information • Vibration • Mechanical resonance
Duty cycle In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration.[1] The term is often used pertaining to electrical devices, e.g., switching power supplies. A 60% duty cycle means the power is on 60% of the time and off 40% of the time. The "on time" for a 60% duty cycle could be a fraction of a second – or for say, irrigation pumps, days – depending on how long the device's period is. Here one period is the length of time it takes for the device to go through a complete on/off cycle. The term "duty cycle" has no agreed meaning for aperiodic devices.
Definition In a periodic event, duty cycle is the ratio of the duration of the event to the total period.
The duty cycle D is defined as the ratio between the pulse duration ( ) and the period ( ) of a rectangular waveform
duty cycle
[2]
where is the duration that the function is active is the period of the function.
Duty cycle
Examples Electrical machines A motor runs for one out of 100 seconds, or 1/100 of the time, and therefore its duty cycle is 1/100, or 1 percent.[3]
Electronics In an ideal pulse train (one having rectangular pulses), the duty cycle is the pulse duration divided by the pulse period.[4] For example, a pulse train in which the pulse duration is 1 μs and the pulse period is 4 μs has a duty cycle of 25%. The pulse duration is normally calculated for positive pulses unless "negative duty cycle" is specified. The duty cycle of a non-rectangular waveform, such as a sine or triangle wave, is defined as the fraction of the period the waveform spends above 0.[5]
Digital signal processing In a continuously variable slope delta (CVSD) modulation converter, the mean proportion of binary "1" digits at the converter output in which each "1" indicates a run of a specified number of consecutive bits of the same polarity in the digital output signal.
Electronic music Music synthesizers vary the duty cycle of their audio-frequency oscillators to obtain a subtle effect on the tone colors. This technique is known as pulse-width modulation (PWM).
Welding In a welding power supply, the maximum duty cycle is defined as the percentage of time in a 10 minute period that it can be operated continuously before overheating.[6]
Printers and copiers In the printer / copier industry, the duty cycle specification refers to the rated throughput (that is, printed pages) of a device per month.
References [1] "Definition: duty cycle" (http:/ / www. its. bldrdoc. gov/ fs-1037/ dir-013/ _1849. htm), Institute for Telecommunication Sciences, Boulder, Colorado, accessed 2011-03-23; from Federal Standard 1037C, "Telecommunications: Glossary of Telecommunication Terms", 1996 [2] "555 timer" (http:/ / www. doctronics. co. uk/ 555. htm), Doctronics, accessed 2011-03-23 [3] "Electric Motors" (http:/ / www. electricmotors. machinedesign. com/ guiEdits/ Content/ bdeee1/ bdeee1_3. aspx), Machine Design, accessed 2011-03-23 [4] "Clock Positive Duty Cycle" (http:/ / www. aubraux. com/ jitter/ meas-clock-positive-duty-cycle. php), Aubrax, accessed 2011-03-23 [5] MAX038 High-Frequency Function Generator Data Sheet 19-0266; Rev 7; 8/07 (http:/ / datasheets. maxim-ic. com/ en/ ds/ MAX038. pdf), Maxim Integrated Products, Inc., accessed 2011-03-23 [6] "What does the term duty cycle mean?" (http:/ / www. zena. net/ htdocs/ FAQ/ dutycycle. shtml), ZENA, Inc. welding systems
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Dynamometer For the dynamometer used in railroading, see dynamometer car. A dynamometer or "dyno" for short, is a device for measuring force, moment of force (torque), or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM). A dynamometer can also be used to determine the torque and power required to operate a driven machine such as a pump. In that case, a motoring or driving dynamometer is used. A dynamometer that is designed to be driven is called an absorption or passive dynamometer. A dynamometer that can either drive or absorb is called a universal or active dynamometer.
Early hydraulic dynamometer, with dead-weight torque measurement.
In addition to being used to determine the torque or power characteristics of a machine under test (MUT), dynamometers are employed in a number of other roles. In standard emissions testing cycles such as those defined by the US Environmental Protection Agency (US EPA), dynamometers are used to provide simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer). In fact, beyond simple power and torque measurements, dynamometers can be used as part of a testbed for a variety of engine development activities such as the calibration of engine management controllers, detailed investigations into combustion behavior and tribology. In the medical terminology, hand-held dynamometers are used for routine screening of grip and hand strength and initial and ongoing evaluation of patients with hand trauma or dysfunction. They are also used to measure grip strength in patients where compromise of the cervical nerve roots or peripheral nerves is suspected. In the rehabilitation, kinesiology, and ergonomics realms, force dynamometers are used for measuring the back, grip, arm, and/or leg strength of athletes, patients, and workers to evaluate physical status, performance, and task demands. Typically the force applied to a lever or through a cable are measured and then converted to a moment of force by multiplying by the perpendicular distance from the force to the axis of the level.[1]
Principles of operation of torque power (absorbing) dynamometers An absorbing dynamometer acts as a load that is driven by the prime mover that is under test (e.g. Pelton wheel). The dynamometer must be able to operate at any speed and load to any level of torque that the test requires. Absorbing dynamometers are not to be confused with "inertia" dynamometers, which calculate power solely by measuring power required to accelerate a known mass drive roller and provide no variable load to the prime mover. An Absorption dynamometer is usually equipped with some means of measuring the operating torque and speed. The dynamometer's Power Absorption Unit absorbs the power developed by the prime mover. The power absorbed by the dynamometer is converted into heat and the heat generally dissipates into the ambient air or transfers to cooling water that dissipates into the air. Regenerative dynamometers, in which the prime mover drives a DC motor as a generator to create load, make excess DC power and potentially, using a DC/AC inverter, can feed AC power back into the commercial electrical power grid - where the power produced is eventually converted back into heat (as in an oven or light bulb, etc.). Absorption dynamometers can be equipped with two types of control systems to provide different main test types. Constant Force The dynamometer has a "braking" torque regulator, the PAU (Power Absorption Unit) is configured to provide a set braking force torque load while the prime mover is configured to operate at whatever throttle opening, fuel delivery
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rate or any other variable it is desired to test. The prime mover is then allowed to accelerate the engine through the desired speed or RPM range. Constant Force test routines require the PAU to be set slightly torque deficient as referenced to prime mover output to allow some rate of acceleration. Power is calculated based on rotational speed x torque x constant. The constant varies depending on the units used. Constant Speed If the dynamometer has a speed regulator (human or computer), the PAU provides a variable amount of braking force (torque) that is necessary to cause the prime mover to operate at the desired single test speed or RPM. The PAU braking load applied to the prime mover can be manually controlled or determined by a computer. Most systems employ eddy current, oil hydraulic or DC motor produced loads because of their linear and quick load change ability. Power is calculated based on rotational speed x torque x constant, constant varies depending on output unit desired and input units used. A motoring dynamometer acts as a motor that drives the equipment under test. It must be able to drive the equipment at any speed and develop any level of torque that the test requires. In common usage, AC or DC motors are used to drive the equipment or "load" device. In most dynamometers power (P) is not measured directly; it must be calculated from torque (τ) and angular velocity (ω) values or force (F) and linear velocity (v):
or
where P is the power in watts τ is the torque in newton metres ω is the angular velocity in radians per second F is the force in newtons v is the linear velocity in metres per second Division by a conversion constant may be required depending on the units of measure used. For imperial units,
where Php is the power in horsepower τlb·ft is the torque in pound-feet ωRPM is the rotational velocity in revolutions per minute For metric units,
where PkW is the power in kilowatts τN·m is the torque in newton metres ωrpm is the rotational velocity in revolutions per minute
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Detailed dynamometer description A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in a housing. The rotor is coupled to the engine or other equipment under test and is free to rotate at whatever speed is required for the test. Some means is provided to develop a braking torque between dynamometer's rotor and housing. The means for developing torque can be frictional, hydraulic, electromagnetic etc. according to the type of absorption/driver unit.
Electrical dynamometer setup showing engine, torque measurement arrangement and tachometer
One means for measuring torque is to mount the dynamometer housing so that it is free to turn except that it is restrained by a torque arm. The housing can be made free to rotate by using trunnions connected to each end of the housing to support the dyno in pedestal mounted trunnion bearings. The torque arm is connected to the dyno housing and a weighing scale is positioned so that it measures the force exerted by the dyno housing in attempting to rotate. The torque is the force indicated by the scales multiplied by the length of the torque arm measured from the center of the dynamometer. A load cell transducer can be substituted for the scales in order to provide an electrical signal that is proportional to torque. Another means for measuring torque is to connect the engine to the dynamometer through a torque sensing coupling or torque transducer. A torque transducer provides an electrical signal that is proportional to torque. With electrical absorption units, it is possible to determine torque by measuring the current drawn (or generated) by the absorber/driver. This is generally a less accurate method and not much practiced in modern times, but it may be adequate for some purposes. When torque and speed signals are available, test data can be transmitted to a data acquisition system rather than being recorded manually. Speed and torque signals can also be recorded by a chart recorder or plotter.
Types of dynamometers In addition to classification as Absorption, Motoring or Universal as described above, dynamometers can be classified in other ways. A dyno that is coupled directly to an engine is known as an engine dyno. A dyno that can measure torque and power delivered by the power train of a vehicle directly from the drive wheel or wheels (without removing the engine from the frame of the vehicle), is known as a chassis dyno. Dynamometers can also be classified by the type of absorption unit or absorber/driver that they use. Some units that are capable of absorption only can be combined with a motor to construct an absorber/driver or universal dynamometer. The following types of absorption/driver units have been used:
Dynamometer
Types of absorption/driver units • • • • • • • • •
Eddy current or electromagnetic brake (absorption only) Magnetic Powder brake (absorption only) Hysteresis Brake (absorption only) Electric motor/generator (absorb or drive) Fan brake (absorption only) Hydraulic brake (absorption only) Mechanical friction brake or Prony brake (absorption only) Water brake (absorption only) Compound dyno (usually an absorption dyno in tandem with an electric/motoring dyno)
Eddy current type absorber EC dynamometers are currently the most common absorbers used in modern chassis dynos. The EC absorbers provide the quick load change rate for rapid load settling. Most are air cooled, but some are designed to require external water cooling systems. Eddy current dynamometers require an electrically conductive core, shaft or disc, moving across a magnetic field to produce resistance to movement. Iron is a common material, but copper, aluminum and other conductive materials are usable. In current (2009) applications, most EC brakes use cast iron discs, similar to vehicle disc brake rotors, and use variable electromagnets to change the magnetic field strength to control the amount of braking. The electromagnet voltage is usually controlled by a computer, using changes in the magnetic field to match the power output being applied. Sophisticated EC systems allow steady state and controlled acceleration rate operation.
Powder dynamometer A powder dynamometer is similar to an eddy current dynamometer, but a fine magnetic powder is placed in the air gap between the rotor and the coil. The resulting flux lines create "chains" of metal particulate that are constantly built and broken apart during rotation creating great torque. Powder dynamometers are typically limited to lower RPM due to heat dissipation issues.
Hysteresis dynamometers Hysteresis dynamometers, use a steel rotor that is moved through flux lines generated between magnetic pole pieces. This design, as in the usual "disc type" eddy current absorbers, allows for full torque to be produced at zero speed, as well as at full speed. Heat dissipation is assisted by forced air. Hysteresis and "disc type" EC dynamometers are one of the most efficient technologies in small (200 hp (150 kW) and less) dynamometers. A hysteresis brake is an eddy current absorber that, unlike most "disc type" eddy current absorbers, puts the electromagnet coils inside a vented and ribbed cylinder and rotates the cylinder, instead of rotating a disc between electromagnets. The potential benefit for the hysteresis absorber is that the diameter can be decreased and operating RPM of the absorber may be increased.
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Electric motor/generator dynamometer Electric motor/generator dynamometers are a specialized type of adjustable-speed drives. The absorption/driver unit can be either an alternating current (AC) motor or a direct current (DC) motor. Either an AC motor or a DC motor can operate as a generator that is driven by the unit under test or a motor that drives the unit under test. When equipped with appropriate control units, electric motor/generator dynamometers can be configured as universal dynamometers. The control unit for an AC motor is a variable-frequency drive and the control unit for a DC motor is a DC drive. In both cases, regenerative control units can transfer power from the unit under test to the electric utility. Where permitted, the operator of the dynamometer can receive payment (or credit) from the utility for the returned power. In engine testing, universal dynamometers can not only absorb the power of the engine, but also drive the engine for measuring friction, pumping losses and other factors. Electric motor/generator dynamometers are generally more costly and complex than other types of dynamometers.
Fan brake A fan is used to blow air to provide engine load. The torque absorbed by a fan brake may be adjusted by changing the gearing or the fan itself, or by restricting the airflow through the fan. It should be noted that, due to the low viscosity of air, this variety of dynamometer is inherently limited in the amount of torque that it can absorb.
Hydraulic brake The hydraulic brake system consists of a hydraulic pump (usually a gear type pump), a fluid reservoir and piping between the two parts. Inserted in the piping is an adjustable valve and between the pump and the valve is a gauge or other means of measuring hydraulic pressure. In simplest terms, the engine is brought up to the desired RPM and the valve is incrementally closed and as the pump's outlet is restricted, the load increases and the throttle is simply opened until at the desired throttle opening. Unlike most other systems, power is calculated by factoring flow volume (calculated from pump design specs), hydraulic pressure and RPM. Brake HP, whether figured with pressure, volume and RPM or with a different load cell type brake dyno, should produce essentially identical power figures. Hydraulic dynos are renowned for having the absolute quickest load change ability, just slightly surpassing the eddy current absorbers. The downside is that they require large quantities of hot oil under high pressure and the requirement for an oil reservoir.
Water brake type absorber The water brake absorber is sometimes mistakenly called a "hydraulic dynamometer." Water brake absorbers are relatively common, having been manufactured for many years and noted for their high power capability, small package, light weight, and relatively low manufacturing cost as compared to other, quicker reacting "power absorber" types. Their drawbacks are that they can take a relatively long period of time to "stabilize" their load amount and the fact that they require a constant supply of water to the "water brake housing" for cooling. In many parts of the country, environmental regulations now prohibit "flow through" water and large water tanks must be installed to prevent contaminated water from entering the environment. The schematic shows the most common type of water brake, the variable level type. Water is added until the engine is held at a steady RPM against the load. Water is then kept at that level and replaced by constant draining and refilling, which is needed to carry away the heat created by absorbing the horsepower. The housing attempts to rotate in response to the torque produced but is restrained by the scale or torque metering cell that measures the torque.
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This schematic shows a water brake, which is actually a fluid coupling with a housing restrained from rotating—similar to a water pump with no outlet.
Compound Dynamometers In most cases, motoring dynamometers are symmetrical; a 300 kW AC dynamometer can absorb 300 kW as well as motor at 300 kW. This is an uncommon requirement in engine testing and development. Sometimes, a more cost-effective solution is to attach a larger absorption dynamometer with a smaller motoring dynamometer; alternatively, a larger absorption dynamometer and a simple AC or DC motor may be used in a similar manner with the electric motor only providing motoring power when required and no absorption. The (cheaper) absorption dynamometer is sized for the maximum required absorption, whereas the motoring dynamometer is sized for motoring. A typical size ratio for common emission test cycles and most engine development is approximately 3:1. Torque measurement is somewhat complicated since there are two machines in tandem; an inline torque transducer is the preferred method of torque measurement in this case. An eddy-current or waterbrake dynamometer with electronic control combined with a variable frequency drive and AC induction motor is a commonly used configuration of this type. Disadvantages include requiring a second set of test cell services (electrical power and cooling), and a slightly more complicated control system. Attention must be paid to the transition between motoring and braking in terms of control stability.
How dynamometers are used for engine testing Dynamometers are useful in the development and refinement of modern day engine technology. The concept is to use a dyno to measure and compare power transfer at different points on a vehicle, thus allowing the engine or drivetrain to be modified to get more efficient power transfer. For example, if an engine dyno shows that a particular engine achieves 400 N·m (300 lbf·ft) of torque, and a chassis dynamo shows only 350 N·m (260 lbf·ft), one would know to look to the drivetrain for the major improvements. Dynamometers are typically very expensive pieces of equipment, reserved for certain fields that rely on them for a particular purpose.
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Types of dynamometer systems A brake dynamometer applies variable load on the Prime Mover (PM) and measures the PM's ability to move or hold the RPM as related to the "braking force" applied. It is usually connected to a computer that records applied braking torque and calculates engine power output based on information from a "load cell" or "strain gauge" and RPM (speed sensor). An inertia dynamometer provides a fixed inertial mass load and calculates the power required to accelerate that fixed, known mass and uses a computer to record RPM and acceleration rate to calculate torque. The engine is generally tested from somewhat above idle to its maximum RPM and the output is measured and plotted on a graph.
Dyno graph 1
A motoring dynamometer provides the features of a brake dyne system, but in addition, can "power" (usually with an AC or DC motor) the Prime Mover (PM) and allow testing of very small power small outputs. Example, duplicating speeds and loads that are experienced when operating a vehicle traveling downhill or on/off throttle operations.
There are essentially 3 types of dynamometer test procedures 1. Steady state (only on brake dynamometers), where the engine is held at a specified RPM (or series of usually sequential RPMs) for a desired amount of time by the variable brake loading as provided by the PAU (power absorber unit) Dyno graph 2 2. Sweep test (on inertia or brake dynamometers), where the engine is tested under a load (inertia or brake loading), but allowed to "sweep" up in RPM in a continuous fashion, from a specified lower "starting" RPM to a specified "end" RPM 3. Transient test (usually on AC or DC dynamometers), where the engine power and speed are varied throughout the test cycle. Different test cycles are used in different jurisdictions. Chassis test cycles include the US light-duty UDDS, HWFET, US06, SC03, ECE, EUDC, and CD34. Engine test cycles include ETC, HDDTC, HDGTC, WHTC, WHSC, and ED12.
Dynamometer Types of Sweep Tests: 1. Inertia sweep: An inertia dyno system provides a fixed inertial mass flywheel and computes the power required to accelerate the flywheel (load) from the starting to the ending RPM. The actual rotational mass of the engine or engine and vehicle in the case of a chassis dyno is not known and the variability of even tire mass will skew power results. The inertia value of the flywheel is "fixed," so low power engines are under load for a much longer time and internal engine temperatures are usually too high by the end of the test, skewing optimal "dyno" tuning settings away from the outside world's optimal tuning settings. Conversely, high powered engines, commonly complete a common "4th gear sweep" test in less than 10 seconds, which is not a reliable load condition as compared to operation in the outside world. By not providing enough time under load, internal combustion chamber temps are unrealistically low and power readings, especially past the power peak, are skewed low. 1. Loaded Sweep Tests (brake dyno type) consist of 2 types: 1. Simple fixed Load Sweep Test: A fixed load, of somewhat less than the engine's output, is applied during the test. The engine is allowed to accelerate from its starting RPM to its ending RPM, varying in its own acceleration rate, depending on power output at any particular rotational speed point. Power is calculated using rotational speed x torque x constant + the power required to accelerate the dyno and engine's / vehicle's rotating mass. 2. Controlled Acceleration Sweep Test: Similar in basic usage as the above Simple fixed Load Sweep Test, but with the addition of active load control that targets a specific rate of acceleration. Commonly, 20fps/ps is used Controlled Acceleration Rate test is that the acc. rate used is controlled from low power to high power engines and over extension and contraction of "test duration" is avoided, providing more repeatable tests and tuning results. In every Sweep Test, there is still the remaining issue of potential power reading error due to the variable engine / dyno / vehicle total rotating mass. Many modern computer controlled brake dyno systems are capable of deriving that "inertial mass" value to eliminate the error. Interestingly, A "sweep test" will always be suspect, as many "sweep" users ignore the rotating mass factor and prefer to use a blanket "factor" on every test, on every engine or vehicle. Simple inertia dyne systems aren't capable of deriving "inertial mass" and are forced to use the same assumed inertial mass on every vehicle. Using Steady State testing eliminates a Sweep Test rotating inertial mass error , as there is no acceleration during a Steady State test. Transient Test Characteristics: Aggressive throttle movements, engine speed changes, and engine motoring are characteristics of most transient engine tests. The usual purpose of these tests are for vehicle emissions development and homologation. In some cases, the lower-cost eddy-current dynamometer is used to test one of the transient test cycles for early development and calibration. An eddy current dyne system offers fast load response, which allows rapid tracking of speed and load, but does not allow motoring. Since most required transient tests contain a significant amount of motoring operation, a transient test cycle with an eddy-current dyno will generate different emissions test results. Final adjustments are required to be done on a motoring-capable dyno.
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Engine dynamometer An engine dynamometer measures power and torque directly from the engine's crankshaft (or flywheel), when the engine is removed from the vehicle. These dynos do not account for power losses in the drivetrain, such as the gearbox, transmission or differential etc.
HORIBA engine dynamometer TITAN
Chassis dynamometer A chassis dynamometer measures power delivered to the surface of the "drive roller" by the drive wheels. The vehicle is often parked on the roller or rollers, which the car then turns and the output is measured. Modern roller type chassis dyne systems use the Salvisberg roller,[2] which improved traction and repeatability over smooth or knurled drive rollers. On a motorcycle, typical power loss at higher power levels, mostly through tire flex, is about 10% and gearbox chain and other power transferring parts are another 2% to 5% .
Saab 96 on chassis dynamometer
Other types of chassis dynamometers are available that eliminate the potential wheel slippage on old style drive rollers and attach directly to the vehicle's hubs for direct torque measurement from the axle. Hub mounted dynos include units made by Dynapack and Rototest. Chassis dynos can be fixed or portable. Modern chassis dynamometers can do much more than display RPM, horsepower, and torque. With modern electronics and quick reacting, low inertia dyne systems, it is now possible to tune to best power and the smoothest runs, in realtime.
Example: 48" Chassis Dynamometer
In retail settings it is also common to "tune the air fuel ratio" , using a wideband oxygen sensor that is graphed along with RPM. Some, dyne systems can also add vehicle diagnostic information to the dyno graph as well. This is done by gathering data directly from the vehicle using on-board diagnostics communication.[3] Emissions development and homologation dynamometer test systems often integrate emissions sampling, measurement, engine speed and load control, data acquisition, and safety monitoring into a complete test cell system. These test systems usually include complex emissions sampling equipment (such as constant volume samplers or raw exhaust gas sample preparation systems), and exhaust emissions analyzers. These analyzers are much more sensitive and much faster than a typical portable exhaust gas analyzer. Response times of well under one second are common and required by many transient test cycles. Integration of the dynamometer control system along with automatic calibration tools for engine system calibration is often found in development test cell systems. In these test cell systems, the dynamometer load and engine speed
Dynamometer are varied to many engine operating points, and selected engine management parameters are varied and the results recorded automatically. Later analysis of this data may then be used to generate engine calibration data used by the engine management software. Because of frictional and mechanical losses in the various drivetrain components, the measured rear wheel brake horsepower is generally 15-20 percent less than the brake horsepower measured at the crankshaft or flywheel on an engine dynamometer.[4] Other sources, after researching several different "engine" dyno software packages, found that the engine dyno user can integrally add "frictional loss" channel factors of +10% to +15% to the flywheel power, raising the claim that 20% to 25% or even more power is actually lost between the crankshaft at high power outputs.
Common misconceptions about dynos Drag racing: 1/4 mile prediction based on dynamometer measured power Horsepower figures are a strong predictor but do not guarantee a specific 0-60 mph, 1/4 mile elapsed time (ET) or 1/4 mile speed. An engine accelerating in a vehicle experiences different conditions than on a dyno. G forces and different temperatures as well as different modes of vibration in a vehicle can cause significant differences in power output. Inexpensive "inertia dynamometers" commonly provide insufficient loading, and complete their "test" in less time than the real world 1/4 mile takes, causing inherent power value errors, due to unrealistic internal engine temperatures. More sophisticated dyno systems are capable of "loaded testing," which can potentially recreate the same temperatures as on the drag strip. In engineering units, the power figures used should be "True" or "Effective" horsepower scale. Engine damage: Can dyno testing damage engines? A brake dyno, in steady state mode only provides a load that is equal the amount of power that the engine is making at any specifically selected RPM point. If the engine makes 200 brake HP at 5000 RPM, the dynamometer's brake or power absorber will provide exactly 200 hp (150 kW) of load against it, keeping the RPM at 5000 RPM. That's a realistic load that simulates a vehicle pulling a large trailer up a hill. It should be no problem on the dyno if there's no problem on the road. Apprehension over dyno testing and engine damage has solid roots in fact. Old style dynamometers commonly used an inexpensive water brake type of power absorber. Load was increased or decreased by filling and draining water in the housing to change the amount of internal water volume to change the load, all the while draining and refilling the water to keep the water from boiling. It would sometimes take some time for the operator or computer to stabilize inflow and outflow rates. That extra time could pose a risk to engines. Water brakes are still commonly used in applications where their small size and light weight are important and engine torque curves are relatively straight, as in large automotive and boats. Engine testing may damage engines primarily due to insufficient instrumentation, insufficient safety monitoring systems, and insufficient cooling. An engine on a dyno does not receive air cooling due to engine speeds. Automotive engines are not typically designed for wide-open throttle operation for extended periods of time; internal components may overheat and fail.
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History Graham-Desaguliers Dynamometer. Invented by George Graham and mentioned in the writings of John Desagulier in 1719[5] . Desaguliers modified the dynamometer and it became known as Graham-Desaguliers dynamometer. Regnier dynamometer. Invented and made public in 1798 by Edme Régnier a French rifle maker and engineer. [6] the Régnier dynamomter. Marriot's patent weighing Machine [7] , patent dated June 1817[8] to Siebe and Marriot of Fleet Street, London for an improved weighing machine. Gaspard de Prony invented the de Prony brake in 1821. Macneill's road indicator. Invented by John Macneill in late 1820s and further developing Marriot's patent weighing machine. Froude Hofmann of Worcester, UK, manufactures engine and vehicle dynamometers. They credit William Froude with the invention of the hydraulic dynamometer in 1877 and say that the first commercial dynamometers were produced in 1881 by their predecessor company, Heenan & Froude. In 1928, the German company "Carl Schenck Eisengießerei & Waagenfabrik" built the first vehicle dynamometers for brake tests with the basic design of the today's vehicle test stands. The eddy current dynamometer was invented by Martin and Anthony Winther in about 1931. At that time, DC Motor/generator dynamometers had been in use for many years. A company founded by the Winthers, Dynamatic Corporation, manufactured dynamometers in Kenosha, Wisconsin until 2002. Dynamatic was part of Eaton Corporation from 1946 to 1995. In 2002, [9] Dyne Systems of Jackson, Wisconsin acquired the Dynamatic dynamometer product line. Starting in 1938, Heenan & Froude manufactured eddy current dynamometers for many years under license from Dynamatic and Eaton.[10]
Notes [1] (http:/ / www. health. uottawa. ca/ biomech/ courses/ apa4311/ dynamometry. pps) Dynamometry [2] http:/ / patft. uspto. gov/ netacgi/ nph-Parser?Sect1=PTO2& Sect2=HITOFF& p=1& u=%2Fnetahtml%2FPTO%2Fsearch-bool. html& r=10& f=G& l=50& co1=AND& d=PTXT& s1=salvisberg& OS=salvisberg& RS=salvisberg [3] Elisa Faustrum. "DynoJet Data-Link Module" (http:/ / web. archive. org/ web/ 20070928063127/ http:/ / www. modularfords. com/ articles/ DynoJet_DataLink_Module/ 1. html). Modular Fords. Archived from the original (http:/ / www. modularfords. com/ articles/ DynoJet_DataLink_Module/ 1. html) on September 28, 2007. . Retrieved June 14, 2007. [4] John Dinkel, "Chassis Dynamometer," Road and Track Illustrated Automotive Dictionary, (Bentley Publishers, 2000) p. 46. [5] Burton, Allen W. and Daryl E. Miller, 1998, Movement Skill Assessment [6] Régnier, Edmé. Description et usage du dynamomètre, 1798. [7] Marriot's patent weighing machine (http:/ / books. google. com/ books?id=g0YOAAAAYAAJ& pg=PA757& dq=marriott's+ patent+ weighing+ machine& hl=no& ei=L-XITq_lLaiB4ASfo5jcAg& sa=X& oi=book_result& ct=result& resnum=2& ved=0CEwQ6AEwAQ#v=onepage& q=marriott's patent weighing machine& f=false) [8] Marriott's improved weighing machine (http:/ / books. google. com/ books?id=l1EoAAAAYAAJ& pg=PA345& lpg=PA345& dq=marriott+ patent+ weighing+ machine+ fleet+ street& source=bl& ots=dXpBfYJsnJ& sig=1RMSAuTtewKrTUHUSNaa55S_72k& hl=no& ei=bu7IToarB-n04QT1qKgw& sa=X& oi=book_result& ct=result& resnum=1& ved=0CCIQ6AEwAA#v=onepage& q=marriott patent weighing machine fleet street& f=false) [9] http:/ / www. dynesystems. com/ [10] Winther, Martin P. (1976). Eddy Currents. Cleveland, Ohio: Eaton Corporation.
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References • Winther, J. B. (1975). Dynamometer Handbook of Basic Theory and Applications. Cleveland, Ohio: Eaton Corporation. • Martyr, A; Plint M (2007). Engine Testing - Theory and Practice (Third ed.). Oxford, UK: Butterworth-Heinemann. ISBN 978-0-7506-8439-2.
Edmund Key Edmund Key is a variant of the Ortman Key it is a coupling device used to secure two adjacent cylindrical segments of a pressure vessel common in tactical rocket motors. The key is made of elongated rectangular metal bar stock, such as steel, and is inserted into juxtaposed anular grooves around the circumference of the mating parts. An Edmund Key also provides a feature at the end of the key to allow the key to be extracted from the groove for disassembly.
References • Patent number: 6729004 Nov 13, 2002 (http://www.google.com/patents?id=JT0QAAAAEBAJ& printsec=abstract&zoom=4#v=onepage&q&f=false)
Embedment Embedment is a phenomenon in mechanical engineering in which the surfaces between mechanical members of a loaded joint embed. It can lead to failure by fatigue as described below, and is of particular concern when considering the design of critical fastener joints.
Mechanism The mechanism behind embedment is different from creep. When the loading of the joint varies (e.g. due to vibration or thermal expansion) the protruding points of the imperfect surfaces will see local stress concentrations and yield until the stress concentration is relieved. Over time, surfaces can flatten an appreciable amount in the order of thousandths of an inch.
Consequences In critical fastener joints, embedment can mean loss of preload. Flattening of a surface allows the strain of a screw to relax, which in turn correlates with a loss in tension and thus preload. In bolted joints with particularly short grip lengths, the loss of preload due to embedment can be especially significant, causing complete loss of preload. Therefore, embedment can lead directly to loosening of a fastener joint and subsequent fatigue failure. In bolted joints, most of the embedment occurs during torquing. Only embedment that occurs after installation can cause a loss of preload, and values of up to 0.0005 inches can be seen at each surface mate, as reported by SAE.
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Prevention/Solutions Embedment can be prevented by designing mating surfaces of a joint to have high surface hardness and very smooth surface finish. Exceptionally hard and smooth surfaces will have less susceptibility to the mechanism that causes embedment. In most cases, some degree of embedment is inevitable. That said, short grip lengths should be avoided. For two bolted joints of identical design and installation, except the second having a longer grip length, the first joint will be more likely to loosen and fail. Since both joints have the same loading, the surfaces will experience the same amount of embedment. However, the relaxation in strain is less significant to the longer grip length and the loss in preload will be minimized. For this reason, bolted joints should always be designed with careful consideration for the grip length. If a short grip length can not be avoided, the use of conical spring washers (Belleville washers or disc springs) can also reduce the loss of bolt pre-load due to embedment.
References • Comer, Dr. Jess. (2005); "Source of Fatigue Failures of Threaded Fasteners", [1] • T. Jaglinski, et al. (2007); "Study of Bolt Load Loss in Bolted Aluminum Joints", [2]
External links • SAE Fatigue Design and Evaluation Committee [3]
References [1] http:/ / www. fatigue. org/ Minutes/ Spring-2005/ comer. pdf [2] http:/ / silver. neep. wisc. edu/ ~lakes/ BoltJEMT07. pdf [3] http:/ / www. fatigue. org/
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Engineering design process
Engineering design process The engineering design process is a formulation of a plan or scheme to assist an engineer in creating a product. The engineering design is defined as:[1] …component, or process to meet desired needs. It is a decision making process (often iterative) in which the basic sciences, mathematics, and engineering sciences are applied to convert resources optimally to meet a stated objective. Among the fundamental elements of the design process are the establishment of objectives and criteria, synthesis, analysis, construction, testing and evaluation. The engineering design process is a multi-step process including the research, conceptualization, feasibility assessment, establishing design requirements, preliminary design, detailed design, production planning and tool design, and finally production.[1] The sections to follow are not necessarily steps in the engineering design process, for some tasks are completed at the same time as other tasks. This is just a general summary of each step of the engineering design process.
Research A significant amount of time is spent on research, or locating, information.[2] Consideration should be given to the existing applicable literature, problems and successes associated with existing solutions, costs, and marketplace needs.[2] The source of information should be relevant, including existing solutions. Reverse engineering can be an effective technique if other solutions are available on the market.[2] Other sources of information include the Internet, local libraries, available government documents, personal organizations, trade journals, vendor catalogs and individual experts available.[2]
Conceptualization Once an engineering issue is clearly defined, solutions must be identified. These solutions can be found by using ideation, or the mental process by which ideas are generated. The following are the most widely used techniques:[1] • trigger word - a word or phrase associated with the issue at hand is stated, and subsequent words and phrases are evoked. For example, to move something from one place to another may evoke run, swim, roll, etc. • morphological chart - independent design characteristics are listed in a chart, and different engineering solutions are proposed for each solution. Normally, a preliminary sketch and short report accompany the morphological chart. • synectics - the engineer imagines him or herself as the item and asks, "What would I do if I were the system?" This unconventional method of thinking may find a solution to the problem at hand. • brainstorming - this popular method involves thinking of different ideas and adopting these ideas in some form as a solution to the problem
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Engineering design process
Feasibility assessment The purpose of a feasibility assessment is to determine whether the engineer's project can proceed into the design phase. This is based on two criteria: the project needs to be based on an achievable idea, and it needs to be within cost constraints. It is of utmost importance to have an engineer with experience and good judgment to be involved in this portion of the feasibility study, for they know whether the engineer's project is possible or not.[1]
Establishing the design requirements Establishing design requirements is one of the most important elements in the design process, and this task is normally performed at the same time as the feasibility analysis. The design requirements control the design of the project throughout the engineering design process. Some design requirements include hardware and software parameters, maintainability, availability, and testability.[1]
Preliminary design The preliminary design bridges the gap between the design concept and the detailed design phase. The preliminary design phase is also called embodiment design. In this task, the overall system configuration is defined, and schematics, diagrams, and layouts of the project will provide early project configuration. During detailed design and optimization, the parameters of the part being created will change, but the preliminary design focuses on creating the general framework to build the project on.[1]
Detailed design The detailed design portion of the engineering design process is the task where the engineer can completely describe a product through solid modeling and drawings. Some specifications include:[1] • • • • • • • • • • •
Operating parameters Operating and nonoperating environmental stimuli Test requirements External dimensions Maintenance and testability provisions Materials requirements Reliability requirements External surface treatment Design life Packaging requirements External marking
The advancement of computer-aided design, or CAD, programs have made the detailed design phase more efficient. This is because a CAD program can provide optimization, where it can reduce volume without hindering the part's quality. It can also calculate stress and displacement using the finite element method to determine stresses throughout the part. It is the engineer's responsibility to determine whether these stresses and displacements are allowable, so the part is safe.[3]
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Engineering design process
Production planning and tool design The production planning and tool design is nothing more than planning how to mass produce the project and which tools should be used in the manufacturing of the part. Tasks to complete in this step include selecting the material, selection of the production processes, determination of the sequence of operations, and selection of tools, such as jigs, fixtures, and tooling. This task also involves testing a working prototype to ensure the created part meets qualification standards.[1]
Production With the completion of qualification testing and prototype testing, the engineering design process is finalized. The part must now be manufactured, and the machines must be inspected regularly to make sure that they do not break down and slow production.[1]
References [1] Ertas, A. & Jones, J. (1996). The Engineering Design Process. 2nd ed. New York, N.Y., John Wiley & Sons, Inc. [2] A.Eide, R.Jenison, L.Mashaw, L.Northup. Engineering: Fundamentals and Problem Solving. New York City: McGraw-Hill Companies Inc.,2002 [3] Widas, P. (1997, April 9). Introduction to finite element analysis. Retrieved from http:/ / www. sv. vt. edu/ classes/ MSE2094_NoteBook/ 97ClassProj/ num/ widas/ history. html
• "abet, criteria for accrediting engineering programs, Engineering accrediting commission: Baltimore, MD 2003" • Ullman, David G. (2009) The Mechanical Design Process, Mc Graw Hill, 4th edition • Eggert, Rudolph J. (2010) Engineering Design, Second Edition, High Peak Press, Meridian, Idaho www.highpeakpress.com
Engineering Equation Solver Engineering Equation Solver (EES) is a commercial software package used for solution of systems of simultaneous non-linear equations. It provides many useful specialised functions and equations for the solution of thermodynamics and heat transfer problems, making it a useful and widely-used program for mechanical engineers working in these fields. The program is developed by F-Chart Software, a commercial spin-off of Prof Sanford A Klein from Department of Mechanical Engineering University of Wisconsin-Madison. EES is included as attached software for a number of undergraduate thermodynamics, heat-transfer and fluid mechanics textbooks from McGraw-Hill. It integrates closely with the dynamic system simulation package TRNSYS, by some of the same authors.
External Links • Official site [1]
References [1] http:/ / www. fchart. com/ ees/
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Engineering fit
Engineering fit Fit refers to the mating of two mechanical components. Manufactured parts are very frequently required to mate with one another. They may be designed to slide freely against one another or they may be designed to bind together to form a single unit. The most common fit found in the machine shop is that of a shaft in a hole. There are three general categories of fits: 1) Clearance fits for when it may be desirable for the shaft to rotate or slide freely within the hole, this is usually referred to as a "sliding fit." 2) Interference fits for when it is desirable for the shaft to be securely held within the hole, this is usually referred to as an interference fit and 3) Transition fits for when it is desirable that the shaft to be held securely, yet not so securely that it cannot be disassembled, this is usually referred to as a Location or Transition fit. Within each category of fit there are several classes ranging from high precision and narrow tolerance (allowance) to lower precision and wider tolerance. The choice of fit is dictated first by the use and secondly by the manufacturability of the parts.
Interference fits Force fits FN 1 to FN 5
Transition fits LC 1 to LC 11 LT 1 to LT 6 LN 1 to LN 3
Locational fits RC 1 to RC 9
Free running fits Clearance fit: It is gap between two mating parts.
ISO Metric fits ISO-R286 and ANSI B4.2-1978
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Envelope (motion)
Envelope (motion) In mechanical engineering, an envelope is a solid representing all positions which may be occupied by an object during its normal range of motion. Another (jargon) word for this is a "flop".
Wheel envelope In automobile design, a wheel envelope may be used to model all positions a wheel and tire combo may be expected to occupy during driving. This will take into account the maximum jounce and rebound allowed by the suspension system and the maximum turn and tilt allowed by the steering mechanism. Minimum and maximum tire inflation pressures and wear conditions may also be considered when generating the envelope. This envelope is then compared with the wheel housing and other components in the area to perform an interference/collision analysis. The results of this analysis tell the engineers whether that wheel/tire combo will strike the housing and components under normal driving conditions. If so, either a redesign is in order, or that wheel/tire combo will not be recommended. A different wheel envelope must be generated for each wheel/tire combo for which the vehicle is rated. Much of this analysis is done using CAD/CAE systems running on computers. Of course, high speed collisions, during an accident, are not considered "normal driving conditions", so the wheel and tire may very well contact other parts of the vehicle at that time.
Robot's working envelope In robotics, the working envelope or work area is the volume of working or reaching space . Some factors of a robot's design (configurations, axes or degrees of freedom) influence its working envelope.[1]
References [1] OSHA TECHNICAL MANUAL - SECTION IV: CHAPTER 4 (http:/ / www. osha. gov/ dts/ osta/ otm/ otm_iv/ otm_iv_4. html)
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ERF damper
ERF damper An ERF damper or electrorheological fluid damper, is a type of quick-response active non-linear damper used in high-sensitivity vibration control.[1]
References [1] Zhu, Yu; Jia, Songtao; Chen, Yaying; Li, Guang (2008). "Electrorheological damper for the ultra-precision air bearing stage". Frontiers of Mechanical Engineering in China 3: 158. doi:10.1007/s11465-008-0031-4.
Euler–Bernoulli beam equation Euler–Bernoulli beam theory (also known as engineer's beam theory, classical beam theory or just beam theory)[1] is a simplification of the linear theory of elasticity which provides a means of calculating the load-carrying and deflection characteristics of beams. It covers the case for small deflections of a beam which is subjected to lateral loads only. It is thus a special case of Timoshenko beam theory which accounts for shear deformation and is applicable for thick beams. It was first enunciated circa 1750,[2] but was not applied on a large scale until the This vibrating glass beam may be modeled as a cantilever beam with acceleration, variable linear density, variable section modulus, some kind of development of the Eiffel Tower and the dissipation, springy end loading, and possibly a point mass at the free end. Ferris wheel in the late 19th century. Following these successful demonstrations, it quickly became a cornerstone of engineering and an enabler of the Second Industrial Revolution. Additional analysis tools have been developed such as plate theory and finite element analysis, but the simplicity of beam theory makes it an important tool in the sciences, especially structural and mechanical engineering.
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EulerBernoulli beam equation
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History Prevailing consensus is that Galileo Galilei made the first attempts at developing a theory of beams, but recent studies argue that Leonardo da Vinci was the first to make the crucial observations. Da Vinci lacked Hooke's law and calculus to complete the theory, whereas Galileo was held back by an incorrect assumption he made.[3] The Bernoulli beam is named after Jacob Bernoulli, who made the significant discoveries. Leonhard Euler and Daniel Bernoulli were the first to Schematic of cross-section of a bent beam showing the neutral axis. put together a useful theory circa [4] 1750. At the time, science and engineering were generally seen as very distinct fields, and there was considerable doubt that a mathematical product of academia could be trusted for practical safety applications. Bridges and buildings continued to be designed by precedent until the late 19th century, when the Eiffel Tower and Ferris wheel demonstrated the validity of the theory on large scales. For practical purposes, such as in the European design codes, it has now been superseded by the Perry Robertson formula which takes account of initial deflection of the beam.[5]
Static beam equation The Euler-Bernoulli equation describes the relationship between the beam's deflection and the applied load[6] :
Bending of an Euler-Bernoulli beam. Each cross-section of the beam is at 90 degrees to the neutral axis.
The curve
describes the deflection
one-dimensional object).
of the beam at some position
(recall that the beam is modeled as a
is a distributed load, in other words a force per unit length (analogous to pressure being a
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210
force per area); it may be a function of Note that
,
, or other variables.
is the elastic modulus and that
is the second moment of area.
must be calculated with respect to
the centroidal axis perpendicular to the applied loading. For an Euler-Bernoulli beam not under any axial loading this axis is called the neutral axis. Often,
,
, and EI is a constant, so that:
This equation, describing the deflection of a uniform, static beam, is used widely in engineering practice. Tabulated expressions for the deflection for common beam configurations can be found in engineering handbooks. For more complicated situations the deflection can be determined by solving the Euler-Bernoulli equation using techniques such as the "slope deflection method", "moment distribution method", "moment area method, "conjugate beam method", "the principle of virtual work", "direct integration", "Castigliano's method", "Macaulay's method" or the "direct stiffness method". Successive derivatives of • • • •
have important meanings:
is the deflection. is the slope of the beam. is the bending moment in the beam. is the shear force in the beam.
The stresses in a beam can be calculated from the above expressions after the deflection due to a given load has been determined. A number of different sign conventions can be found in the literature on the bending of beams and care should be taken to maintain consistency.[6] In this article, the sign convention has been chosen so the coordinate system is right handed. Forces acting in the positive and directions are assumed positive. The sign of the bending moment is chosen so that a positive value leads to a tensile stress at the bottom cords. The sign of the shear force has been chosen such that it matches the sign of the bending moment.
Dynamic beam equation The dynamic beam equation is the Euler-Lagrange equation for the following action
Finite element method model of a vibration of a wide-flange beam (I-beam).
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The first term represents the kinetic energy where
is the mass per unit length; the second one represents the
potential energy due to internal forces (when considered with a negative sign) and the third term represents the potential energy due to the external load . The Euler-Lagrange equation is used to determine the function that minimizes the functional
. For a dynamic Euler-Bernoulli beam, the Euler-Lagrange equation is
Derivation of Euler–Lagrange equation for beams Since the Lagrangian is
the corresponding Euler-Lagrange equation is
Now,
Plugging into the Euler-Lagrange equation gives
or,
which is the governing equation for the dynamics of an Euler-Bernoulli beam.
Stress Besides deflection, the beam equation describes forces and moments and can thus be used to describe stresses. For this reason, the Euler–Bernoulli beam equation is widely used in engineering, especially civil and mechanical, to determine the strength (as well as deflection) of beams under bending. Both the bending moment and the shear force cause stresses in the beam. The stress due to shear force is maximum along the neutral axis of the beam (when the width of the beam, t, is constant along the cross section of the beam; otherwise an integral involving the first moment and the beam's width needs to be evaluated for the particular cross section), and the maximum tensile stress is at either the top or bottom surfaces. Thus the maximum principal stress in the beam may be neither at the surface nor at the center but in some general area. However, shear force stresses are negligible in comparison to bending moment stresses in all but the stockiest of beams as well as the fact that stress concentrations commonly occur at surfaces, meaning that the maximum stress in a beam is likely to be at the surface.
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Simple or symmetrical bending For beam cross-sections that are symmetrical about a plane perpendicular to the neutral plane, it can be shown that the tensile stress experienced by the beam may be expressed as:
Element of a bent beam: the fibers form concentric arcs, the top fibers are compressed and bottom fibers stretched.
Here,
is the distance from the neutral axis to a point of interest; and
is the bending moment. Note that this
equation implies that pure bending (of positive sign) will cause zero stress at the neutral axis, positive (tensile) stress at the "top" of the beam, and negative (compressive) stress at the bottom of the beam; and also implies that the maximum stress will be at the top surface and the minimum at the bottom. This bending stress may be superimposed with axially applied stresses, which will cause a shift in the neutral (zero stress) axis.
Maximum stresses at a cross-section The maximum tensile stress at a cross-section is at the location and the maximum compressive stress is at the location where the height of the cross-section is . These stresses are
Quantities used in the definition of the section modulus of a beam.
EulerBernoulli beam equation The quantities
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are the section moduli[6] and are defined as
The section modulus combines all the important geometric information about a beam's section into one quantity. For the case where a beam is doubly symmetric, and we have one section modulus .
Strain in an Euler–Bernoulli beam We need an expression for the strain in terms of the deflection of the neutral surface to relate the stresses in an Euler-Bernoulli beam to the deflection. To obtain that expression we use the assumption that normals to the neutral surface remain normal during the deformation and that deflections are small. These assumptions imply that the beam bends into an arc of a circle of radius (see Figure 1) and that the neutral surface does not change in length during the deformation.[6] Let
be the length of an element of the neutral surface in the undeformed state. For small deflections, the element
does not change its length after bending but deforms into an arc of a circle of radius subtended by this arc, then
. If
is the angle
.
Let us now consider another segment of the element at a distance above the neutral surface. The initial length of this element is . However, after bending, the length of the element becomes . The strain in that segment of the beam is given by
where is the curvature of the beam. This gives us the axial strain in the beam as a function of distance from the neutral surface. However, we still need to find a relation between the radius of curvature and the beam deflection .
Relation between curvature and beam deflection Let P be a point on the neutral surface of the beam at a distance
from the origin of the
The slope of the beam, i.e., the angle made by the neutral surface with the
Therefore, for an infinitesimal element
, the relation
Hence the strain in the beam may be expressed as
-axis, at this point is
can be written as
coordinate system.
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Stress-strain relations For a one-dimensional linear elastic material, the stress is related to the strain by
where
is the Young's
modulus. Hence the stress in an Euler-Bernoulli beam is given by
Note that the above relation, when compared with the relation between the axial stress and the bending moment, leads to
Since the shear force is given by
, we also have
Boundary considerations The beam equation contains a fourth-order derivative in
. To find a unique solution
we need four
boundary conditions. The boundary conditions usually model supports, but they can also model point loads, distributed loads and moments. The support or displacement boundary conditions are used to fix values of displacement ( ) and rotations ( ) on the boundary. Such boundary conditions are also called Dirichlet boundary conditions. Load and moment boundary conditions involve higher derivatives of momentum flux. Flux boundary conditions are also called Neumann boundary conditions. As an example consider a cantilever beam that is built-in at one end and free at the other as shown in the adjacent figure. At the built-in end of the beam there cannot be any displacement or rotation of the beam. This means that at the left end both deflection and slope are zero. Since no external bending moment is applied at the free end of the beam, the bending moment at that location is zero. In addition, if there is no external force applied to the beam, the shear force at the free end is also zero.
and represent
A cantilever beam.
Taking the coordinate of the left end as and the right end as (the length of the beam), these statements translate to the following set of boundary conditions (assume
is a constant):
A simple support (pin or roller) is equivalent to a point force on the beam which is adjusted in such a way as to fix the position of the beam at that point. A fixed support or clamp, is equivalent to the combination of a point force and a point torque which is adjusted in such a way as to fix both the position and slope of the beam at that point. Point
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forces and torques, whether from supports or directly applied, will divide a beam into a set of segments, between which the beam equation will yield a continuous solution, given four boundary conditions, two at each end of the segment. Assuming that the product EI is a constant, and defining where F is the magnitude of a point force, and where M is the magnitude of a point torque, the boundary conditions appropriate for some common cases is given in the table below. The change in a particular derivative of w across the boundary as x increases is denoted by followed by that derivative. For example, of
where
is the value of
at the lower boundary of the up
at the upper boundary of the lower segment. When the values of the particular derivative are not only continuous
across the boundary, but fixed as well, the boundary condition is written e.g. equations (e.g.
which actually constitutes two separate
= fixed). Boundary Clamp Simple support Point force Point torque Free end Clamp at end Simply supported end
fixed
fixed fixed
Point force at end Point torque at end
Note that in the first cases, in which the point forces and torques are located between two segments, there are four boundary conditions, two for the lower segment, and two for the upper. When forces and torques are applied to an end of the beam, there are two boundary conditions given which apply at that end.
Loading considerations Applied loads may be represented either through boundary conditions or through the function
which
represents an external distributed load. Using distributed loading is often favorable for simplicity. Boundary conditions are, however, often used to model loads depending on context; this practice being especially common in vibration analysis. By nature, the distributed load is very often represented in a piecewise manner, since in practice a load isn't typically a continuous function. Point loads can be modeled with help of the Dirac delta function. For example, consider a static uniform cantilever beam of length with an upward point load applied at the free end. Using boundary conditions, this may be modeled in two ways. In the first approach, the applied point load is approximated by a shear force applied at the free end. In that case the governing equation and boundary conditions are:
Alternatively we can represent the point load as a distribution using the Dirac function. In that case the equation and boundary conditions are
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Note that shear force boundary condition (third derivative) is removed, otherwise there would be a contradiction. These are equivalent boundary value problems, and both yield the solution
The application of several point loads at different locations will lead to
being a piecewise function. Use of the
Dirac function greatly simplifies such situations; otherwise the beam would have to be divided into sections, each with four boundary conditions solved separately. A well organized family of functions called Singularity functions are often used as a shorthand for the Dirac function, its derivative, and its antiderivatives. Dynamic phenomena can also be modeled using the static beam equation by choosing appropriate forms of the load distribution. As an example, the free vibration of a beam can be accounted for by using the load function:
where
is the linear mass density of the beam, not necessarily a constant. With this time-dependent loading, the
beam equation will be a partial differential equation:
Another interesting example describes the deflection of a beam rotating with a constant angular frequency of
This is a centripetal force distribution. Note that in this case,
:
is a function of the displacement (the dependent
variable), and the beam equation will be an autonomous ordinary differential equation.
Examples Three-point bending The three point bending test is a classical experiment in mechanics. It represents the case of a beam resting on two roller supports and subjected to a concentrated load applied in the middle of the beam. The shear is constant in absolute value: it is half the central load, P / 2. It changes sign in the middle of the beam. The bending moment varies linearly from one end, where it is 0, and the center where its absolute value is PL / 4, is where the risk of rupture is the most important. The deformation of the beam is described by a polynomial of third degree over a half beam (the other half being symmetrical). The bending moments ( ) , shear forces ( ), and deflections ( ) for a beam subjected to a central point load and an asymmetric point load are given in the table below.[6] Distribution Simply supported beam with central load
Max. value
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Simply supported beam with asymmetric load
at
Cantilever beams Another important class of problems involves cantilever beams. The bending moments (
) , shear forces (
),
and deflections ( ) for a cantilever beam subjected to a point load at the free end and a uniformly distributed load are given in the table below.[6] Distribution
Max. value
Cantilever beam with end load
Cantilever beam with uniformly distributed load
Solutions for several other commonly encountered configurations are readily available in textbooks on mechanics of materials and engineering handbooks.
Statically indeterminate beams The bending moments and shear forces in Euler-Bernoulli beams can often be determined directly using static balance of forces and moments. However, for certain boundary conditions, the number of reactions can exceed the number of independent equilibrium equations.[6] Such beams are called statically indeterminate. The built-in beams shown in the figure below are statically indeterminate. To determine the stresses and deflections of such beams, the most direct method is to solve the Euler–Bernoulli beam equation with appropriate boundary conditions. But direct analytical solutions of the beam equation are possible only for the simplest cases. Therefore, additional techniques such as linear superposition are often used to solve statically indeterminate beam problems. The superposition method involves adding the solutions of a number of statically determinate problems which are chosen such that the boundary conditions for the sum of the individual problems add up to those of the original problem.
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(a) Uniformly distributed load q. (b) Linearly distributed load with maximum q0
(d) Moment M0 (c) Concentrated load P
Another commonly encountered statically indeterminate beam problem is the cantilevered beam with the free end supported on a roller.[6] The bending moments, shear forces, and deflections of such a beam are listed below. Distribution
Max. value
Extensions The kinematic assumptions upon which the Euler-Bernoulli beam theory is founded allow it to be extended to more advanced analysis. Simple superposition allows for three-dimensional transverse loading. Using alternative constitutive equations can allow for viscoelastic or plastic beam deformation. Euler-Bernoulli beam theory can also be extended to the analysis of curved beams, beam buckling, composite beams, and geometrically nonlinear beam deflection. Euler-Bernoulli beam theory does not account for the effects of transverse shear strain. As a result it underpredicts deflections and overpredicts natural frequencies. For thin beams (beam length to thickness ratios of the order 20 or more) these effects are of minor importance. For thick beams, however, these effects can be significant. More advanced beam theories such as the Timoshenko beam theory (developed by the Russian-born scientist Stephen Timoshenko) have been developed to account for these effects.
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Large deflections The original Euler-Bernoulli theory is valid only for infinitesimal strains and small rotations. The theory can be extended in a straightforward manner to problems involving moderately large rotations provided that the strain remains small by using the von Kármán strains.[7] The Euler-Bernoulli hypotheses that plane sections remain plane and normal to the axis of the beam lead to displacements of the form
Euler-Bernoulli beam
Using the definition of the Lagrangian Green strain from finite strain theory, we can find the von Karman strains for the beam that are valid for large rotations but small strains. These strains have the form
From the principle of virtual work, the balance of forces and moments in the beams gives us the equilibrium equations
where
is the axial load,
is the transverse load, and
To close the system of equations we need the constitutive equations that relate stresses to strains (and hence stresses to displacements). For large rotations and small strains these relations are
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where
The quantity
is the extensional stiffness,
is the coupled extensional-bending stiffness, and
is the
bending stiffness. For the situation where the beam has a uniform cross-section and no axial load, the governing equation for a large-rotation Euler-Bernoulli beam is
Notes [1] Timoshenko, S., (1953), History of strength of materials, McGraw-Hill New York [2] Truesdell, C., (1960), The rational mechanics of flexible or elastic bodies 1638-1788, Venditioni Exponunt Orell Fussli Turici. [3] Ballarini, Roberto (April 18, 2003). "The Da Vinci-Euler-Bernoulli Beam Theory?" (http:/ / www. memagazine. org/ contents/ current/ webonly/ webex418. html). Mechanical Engineering Magazine Online. . Retrieved 2006-07-22. [4] Seon M. Han, Haym Benaroya and Timothy Wei (March 22, 1999) (PDF). Dynamics of Transversely Vibrating Beams using four Engineering Theories (http:/ / csxe. rutgers. edu/ research/ vibration/ 51. pdf). final version. Academic Press. . Retrieved 2007-04-15. [5] McKenzie, William (2006). Examples in Structural Analysis. Taylor & Francis. [6] Gere, J. M. and Timoshenko, S. P., 1997, Mechanics of Materials, PWS Publishing Company. [7] Reddy, J. N., (2007), Nonlinear finite element analysis, Oxford University Press.
References • E.A. Witmer (1991-1992). "Elementary Bernoulli-Euler Beam Theory". MIT Unified Engineering Course Notes. pp. 5–114 to 5–164.
Fan coil unit
Fan coil unit A fan coil unit (FCU) is a simple device consisting of a heating or cooling coil and fan. It is part of an HVAC system found in residential, commercial, and industrial buildings. Typically a fan coil unit is not connected to ductwork, and is used to control the temperature in the space where it is installed, or serve multiple spaces. It is controlled either by a manual on/off switch or by thermostat. Due to their simplicity, fan coil units are more economical to install than ducted or central heating systems with air handling units. However, they can be noisy because the fan is within the same space. Unit configurations are numerous including horizontal (ceiling mounted) or vertical (floor mounted).
Design and operation It should be first appreciated that 'Fan Coil Unit' is a generic term that is applied to a range of products. Also, the term 'Fan Coil Unit' will mean different things to users, specifiers and installers in different countries and regions, particularly in relation to product size and output capability. A fan coil unit may be concealed or exposed within the room or area that it serves. An exposed fan coil unit may be wall mounted, freestanding or ceiling mounted, and will typically include an appropriate enclosure to protect and conceal the fan coil unit itself, with return air grille and supply air diffuser set into that enclosure to distribute the air. A concealed fan coil unit will typically be installed within an accessible ceiling void or services zone. The return air grille and supply air diffuser, typically set flush into the ceiling, will be ducted to and from the fan coil unit and thus allows a great degree of flexibility for locating the grilles to suit the ceiling layout and/or the partition layout within a space. It is quite common for the return air not to be ducted and to use the ceiling void as a return air plenum. The coil receives hot or cold water from a central plant, and removes heat from or adds heat to the air through heat transfer. Traditionally fan coil units can contain their own internal thermostat, or can be wired to operate with a remote thermostat. However, and as is common in most modern buildings with a Building Energy Management System (BEMS), the control of the fan coil unit will be by a local digital controller or outstation (along with associated room temperature sensor and control valve actuators) linked to the BEMS via a communication network, and therefore adjustable and controllable from a central point, such as a supervisors head end computer. Fan coil units circulate hot or cold water through a coil in order to condition a space. The unit gets its hot or cold water from a central plant, or mechanical room containing equipment for removing heat from the central building's closed-loop. The equipment used can consist of machines used to remove heat such as a chiller or a cooling tower and equipment for adding heat to the building's water such as a boiler or a commercial water heater. Fan coil units are divided into two types: Two-pipe fan coil units or four-pipe fan coil units. Two-pipe fan coil units have one (1) supply and one (1) return pipe. The supply pipe supplies either cold or hot water to the unit depending
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Fan coil unit on the time of year. Four-pipe fan coil units have two (2) supply pipes and two (2) return pipes. This allows either hot or cold water to enter the unit at any given time. Since it is often necessary to heat and cool different areas of a building at the same time, due to differences in internal heat loss or heat gains, the four-pipe fan coil unit is most commonly used. Fan coil units may be connected to piping networks using various topology designs, such as "direct return", "reverse return", or "series decoupled". See ASHRAE Handbook "2008 Systems & Equipment", Chapter 12. Depending upon the selected chilled water temperatures and the relative humidity of the space, it is likely that the cooling coil will dehumidify the entering air stream, and as a by product of this process, it will at times produce a condensate which will need to be carried to drain. The fan coil unit will contain a purpose designed drip tray with drain connection for this purpose. The simplest means to drain the condensate from multiple fan coil units will be by a network of pipework laid to falls to a suitable point. Alternatively a condensate pump may be employed where space for such gravity pipework is limited. Speed control of the fan motors within a fan coil unit is effectively used to control the heating and cooling output desired from the unit. Some manufacturers accomplish speed control by adjusting the taps on an AC transformer supplying the power to the fan motor. Typically this would require adjustment at the commissioning stage of the building construction process and is therefore set for life. Other manufacturers provide custom-wound Permanent Split Capacitor (PSC) motors with speed taps in the windings, set to the desired speed levels for the fan coil unit design. A simple speed selector switch (Off-High-Medium-Low) is provided for the local room occupant to control the fan speed. Typically this speed selector switch is integral to the room thermostat, and is set manually or is controlled automatically by the digital rooom thermostat. Building Energy Management Systems can be used for automatic fan speed and temperature control. Fan motors are typically AC Shaded Pole or Permanent Split Capacitor. More recent developments include brushless DC designs with electronic commutation. While these motors do offer significant energy savings, initial cost and return-on-investment should be carefully considered.
DC \ EC Motor Powered Fan Coil Units These motors are sometimes called DC motors, sometimes called EC motors and occasionally EC/DC motors. DC stands for Direct Current and EC stands for Electronically Commutated. DC motors allow the speed of the fans within a Fan Coil Unit to be controlled by means of a 0-10 Volt input 'Signal' to the motor/s, the transformers and speed switches associated with AC Fan Coils are not required. Up to a signal voltage of 2.5Volts (which may vary with different fan / motor manufacturers) the fan will be in a stopped condition but as the signal voltage is increased, the fan will seamlessly increase in speed until the maximum is reached at a signal Voltage of 10 Volts. Fan Coils will generally operate between approximately 4 Volts and 7.5 Volts because below 4 Volts the air volumes are ineffective and above 7.5 Volts the Fan Coil is likely to be too noisy for most commercial applications. The 0-10 Volt signal voltage can be set via a simple potentiometer and left or the 0-10 Volt signal voltage can be delivered to the fan motors by the terminal controller on each of the Fan Coil Units. The former is very simple and cheap but the latter opens up the opportunity to continuously alter the fan speed depending on various external conditions / influences. These conditions / criteria could be the 'real time' demand for either heating or cooling, occupancy levels, window switches, time clocks or any number of other inputs from either the unit itself, the Building Management System or both. The reason that these DC Fan Coil Units are, despite their apparent relative complexity, becoming more popular is their improved energy efficiency levels compared to their AC motor driven counterparts of only a few years ago. A straight swap, AC to DC, will reduce electrical consumption by 50% but applying Demand and Occupancy dependant fan speed control can take the savings to as much as 80%. In areas of the world where there are legally enforceable energy efficiency requirements for Fan Coils (such as the UK), DC Fan Coil Units are rapidly becoming the only choice.
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Fan coil unit
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Examples of EC\DC Fan Coil Units: • Ability EC\DC technical pages [1]
Areas of use Fan coil units are typically used in spaces where economic installations are preferred such as unoccupied storage rooms, corridors, loading docks. In high-rise buildings, fan coils may be stacked, located one above the other from floor to floor and all interconnected by the same piping loop. Fan coil units are an excellent delivery mechanism for hydronic chiller boiler systems in large residential and light commercial applications. In these applications the fan coil units are mounted in bathroom ceilings and can be used to provide unlimited comfort zones - with the ability to turn off unused areas of the structure to save energy.
Installation In high-rise residential construction, typically each fan coil unit requires a rectangular through-penetration in the concrete slab on top of which it sits. Usually, there are either 2 or 4 pipes made of ABS, steel or copper that go through the floor. The pipes are usually insulated with refrigeration insulation, such as acrylonitrile butadiene/polyvinyl chloride (AB/PVC) flexible foam (Rubatex or Armaflex brands) on all pipes or at least the cool lines.
Unit Ventilator A unit ventilator is a fan coil unit that is used mainly in classrooms, hotels, apartments and condominium applications. A unit ventilator can be a wall mounted or ceiling hung cabinet, and is designed to use a fan to blow air across a coil, thus conditioning the space which it is serving. Examples of unit ventilators: • • • • •
McQuay [2] Nesbitaire [3] Trane [4] International Environmental [5] Williams [www.wfc-fc.com]
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European Market The Fan Coil market is composed of one quarter of 2-pipe-units and three quarters of 4-pipe-units, and the most sold products are "with casing" (35%), "without casing" (28%), "cassette" (18%) and "ducted" (16%).[6] The market by country is splitted in 2010 as following: Countries
[7] Sales Volume in units
Share
Benelux
33 725
2.6%
France
168 028
13.2%
Germany
63 256
5.0%
Greece
33 292
2.6%
Italy
409 830
32.1%
Poland
32 987
2.6%
Portugal
22 957
1.8%
Russia, Ukraine and CIS countries
87 054
6.8%
Scandinavia and Baltic countries
39 124
3.1%
Spain
91 575
7.2%
Turkey
70 682
5.5%
UK and Ireland
69 169
5.4%
Eastern Europe
153 847
12.1%
References [1] [2] [3] [4] [5] [6] [7]
http:/ / www. abilityprojects. com/ matrixTechnology/ upClose. php http:/ / www. mcquay. com/ McQuay/ ProductInformation/ UnitVent/ UnitVentilators http:/ / www. nesbittaire. com/ na_vents_903. html http:/ / www. trane. com/ Commercial/ Dna/ View. aspx?i=1094 http:/ / www. iec-okc. com Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/ Eurovent Market Intelligence https:/ / www. eurovent-marketintelligence. eu/
Feedwater heater
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Feedwater heater A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler.[1] [2] [3] Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system.[4] This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle. Many of the locomotive systems are ACFI type. In a steam power plant (usually modeled as a modified Rankine cycle), feedwater heaters allow the feedwater to be brought up to the saturation temperature very gradually. This minimizes the inevitable irreversibilities associated with heat transfer to the working fluid (water). See the article on the Second Law of Thermodynamics for a further discussion of such irreversibilities.
Cycle discussion and explanation
A Rankine cycle with two steam turbines and a single open feedwater heater.
The energy used to heat the feedwater is usually derived from steam extracted between the stages of the steam turbine. Therefore, the steam that would be used to perform expansion work in the turbine (and therefore generate power) is not utilized for that purpose. The percentage of the total cycle steam mass flow used for the feedwater heater is termed the extraction fraction[4] and must be carefully optimized for maximum power plant thermal efficiency since increasing this fraction causes a decrease in turbine power output. Feedwater heaters can also be open and closed heat exchangers. An open feedwater heater is merely a direct-contact heat exchanger in which extracted steam is allowed to mix with the feedwater. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure. A deaerator is a special case of the open feedwater heater which is specifically designed to remove non-condensable gases from the feedwater. Closed feedwater heaters are typically shell and tube heat exchangers where the feedwater passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feedwater to the pressure of the extracted steam as with an open heater. However, the extracted steam (which is most likely almost fully condensed after heating the feedwater) must then be throttled to the condenser pressure, an isenthalpic process that results in some entropy gain with a slight penalty on overall cycle efficiency. Many power plants incorporate a number of feedwater heaters and may use both open and closed components. Feedwater heaters are used in both fossil- and nuclear-fueled power plants. Smaller versions have also been installed on steam locomotives, portable engines and stationary engines. An economiser serves a similar purpose to a feedwater heater, but is technically different. Instead of using actual cycle steam for heating, it uses the
Feedwater heater
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lowest-temperature flue gas from the furnace (and therefore does not apply to nuclear plants) to heat the water before it enters the boiler proper. This allows for the heat transfer between the furnace and the feedwater to occur across a smaller average temperature gradient (for the steam generator as a whole). System efficiency is therefore further increased when viewed with respect to actual energy content of the fuel.
References [1] British Electricity International (1991). Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-040510-X. [2] Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st edition ed.). ISBN 0-9634570-0-4. [3] Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997). Standard Handbook of Powerplant Engineering (2nd edition ed.). McGraw-Hill Professional. ISBN 0-07-019435-1. [4] Fundamentals of Steam Power (http:/ / www. personal. utulsa. edu/ ~kenneth-weston/ chapter2. pdf) by Kenneth Weston, University of Tulsa
External links • Power plant diagram (http://www.tva.gov/power/coalart.htm)
Fillet (mechanics) In mechanical engineering, a fillet ( /ˈfɪlɪt/) is a concave easing of an interior corner of a part design. A rounding of an exterior corner is called a "round" or a "chamfer".[1]
Applications • Stress concentration is a problem of load-bearing mechanical parts which is reduced by employing fillets on points and lines of expected high stress. These features effectively make the parts more durable and capable of bearing larger loads. • For considerations in aerodynamics, fillets are employed to reduce interference drag where aircraft components such as wings, struts, and other surfaces meet one another.
Example of a non-filleted pole (left) and a filleted pole (right)
• For manufacturing, concave corners are sometimes filleted to allow the use of round-tipped end mills to cut out an area of a material. This has a cycle time benefit if the round mill is simultaneously being used to mill complex curved surfaces. • Rounds are used to eliminate sharp edges that can be easily damaged or that can cause injury when the part is handled.[2]
Design process Fillets can be quickly designed onto parts using 3d solid modeling engineering CAD software by invoking the function and picking edges of interest. Once these features are included in the CAD design of a part, they are often manufactured automatically using computer-numerical control.
It is common to find a fillet where two parts are welded together
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Different packages use different names for the same operations. CATIA, Vectorworks, Autodesk Inventor and Solidworks refer to both concave and convex rounded edges as fillets, while referring to angled cuts of edges and concave corners as chamfers. Unigraphics and CADKEY refer to concave and convex rounded edges as blends. Pro/Engineer refers to rounded edges simply as rounds. Other 3D solid modeling software programs outside of engineering, such as gameSpace, have similar functions. Smooth edges connecting two simple flat features are generally simple for a computer to create and fast for a human user to specify.
Notes [1] Madsen et al., "Engineering Drawing and Design" page 179. Delmar, 2004 ISBN 0-7668-1634-6 [2] Visualization, modeling, and graphics for engineering design By Dennis Kenmon Lieu, Sheryl Sorby, Page 6-31
External links • Welding fillets (http://www.unified-eng.com/scitech/weld/fillet.html)
Flange A flange is an external or internal ridge, or rim (lip), for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel. Thus flanged wheels are wheels with a flange on one side to keep the wheels from running off the rails. The term "flange" is also used for a kind of tool used to form flanges. Pipes with flanges can be assembled and disassembled easily.
Flanged railway wheel
Flange
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Railway wheel flange, left & tram wheel flange, right
Plumbing or piping A flange can also be a plate or ring to form a rim at the end of a pipe when fastened to the pipe (for example, a closet flange). A blind flange is a plate for covering or closing the end of a pipe. A flange joint is a connection of pipes, where the connecting pieces have flanges by which the parts are bolted together. Although the word flange generally refers to the actual raised rim or lip of a fitting, many flanged plumbing fittings are themselves known as 'flanges': Common flanges used in plumbing are the Surrey flange or Danzey flange, York flange, Sussex flange and Essex flange. Surrey flange Surrey and York flanges fit to the top of the hot water tank allowing all the water to be taken without disturbance to the tank. They are often used to ensure an even flow of water to showers. An Essex flange requires a hole to be drilled in the side of the tank. There is also a Warix flange which is the same as a York flange but the shower output is on the top of the flange and the vent on the side. The York and Warix flange have female adapters so that they fit onto a male tank, whereas the Surrey flange connects to a female tank. A closet flange provides the mount for a toilet.
Pipe flanges There are many different flange standards to be found worldwide. To allow easy functionality and inter-changeability, these are designed to have standardised dimensions. Common world standards include ASA/ANSI (USA), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean). In most cases these are not interchangeable (e.g. an ANSI flange will not mate against a JIS flange). Further, many of the flanges in each standard are divided into "pressure classes", allowing flanges to be capable of taking different pressure ratings. Again these are not generally interchangeable (e.g. an ANSI 150 will not mate with an ANSI 300). These pressure classes also have differing pressure and temperature ratings for different materials. Unique pressure classes for piping can also be developed for a process plant or power generating station; these may be specific to the corporation, engineering procurement and construction (EPC) contractor, or the process plant owner. The flange faces are also made to standardized dimensions and are typically "flat face", "raised face", "tongue and groove", or "ring joint" styles, although other obscure styles are possible.
Flange Flange designs are available as "welding neck", "slip-on", "boss", "lap joint", "socket weld", "threaded", and also "blind".
ASME standards (U.S.) Pipe flanges that are made to standards called out by ASME B16.5 or ASME B16.47 are typically made from forged materials and have machined surfaces. B16.5 refers to nominal pipe sizes (NPS) from ½" to 24". B16.47 covers NPSs from 26" to 60". Each specification further delineates flanges into pressure classes: 150, 300, 400, 600, 900, 1500 and 2500 psi for B16.5; B16.47 delineates its flanges into pressure classes 75, 150, 300, 400, 600, 900. The gasket type and bolt type are generally specified by the standard(s); however, ASME type flange on a gas pipeline sometimes the standards refer to the ASME Boiler and Pressure Vessel Code (B&PVC) for details (see ASME Code Section VIII Division 1 - Appendix 2). These flanges are recognized by ASME Pipe Codes such as ASME B31.1 Power Piping, and ASME B31.3 Process Piping. Materials for flanges are usually under ASME designation: SA-105 (Specification for Carbon Steel Forgings for Piping Applications), SA-266 (Specification for Carbon Steel Forgings for Pressure Vessel Components), or SA-182 (Specification for Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service). In addition, there are many "industry standard" flanges that in some circumstance may be used on ASME work.
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Flange
230
Other countries Flanges in other countries also are manufactured according to the standards for materials, pressure ratings, etc. Such standards include DIN, BS, and/or ISO standards.
Vacuum flanges A vacuum flange is a flange at the end of a tube used to connect vacuum chambers, tubing and vacuum pumps to each other.
Microwave RF In microwave telecommunications, a flange is a type of cable joint which allows different types of waveguide to connect. Several different microwave RF flange types exist, such as CAR, CBR, OPC, PAR, PBJ, PBR, PDR, UAR, UBR, UDR, icp and UPX.
References Further reading • ASME B16.5 Standard Pipe Flanges up to and including 24 inches nominal • ASME B16.47 Standard Pipe Flanges above 24 inches Form factor of PDR and CBR flanges.
• ASME Section II (Materials), Part A - Ferrous Material Specifications • Nayyar, Mohinder (1999). Piping Handbook, Seventh Edition. New York: McGraw-Hill. ISBN 0070471061.
Float (liquid level)
Float (liquid level) Liquid level floats, also known as float balls, are spherical, cylindrical, oblong or similarly-shaped objects, made from either rigid or flexible material, that are buoyant in water and other liquids. They are non-electrical hardware frequently used as visual sight-indicators for surface demarcation and level measurement. They may also be incorporated into switch mechanisms or translucent fluid-tubes as a component in monitoring or controlling liquid level. Liquid level floats use the principle of material buoyancy (differential densities) to follow fluid levels. Solid floats are often made of plastics with a density less than water or other application liquid, and so they float. Hollow floats filled with air are much less dense than water or other liquids, and are appropriate for some applications.[1]
References [1] "Learn More About Liquid Level Floats" (http:/ / www. globalspec. com/ LearnMore/ Sensors_Transducers_Detectors/ Level_Sensing/ Liquid_Level_Floats). globalspec.com. .
Flow stress Flow stress is defined as the instantaneous value of stress required to continue deforming the material - to keep the metal flowing. It is the yield strength of the metal as a function of strain, which can be expressed:[1] Yf = Ken • • • •
Yf = Flow stress, MPa e = True strain K = Strength Coefficient, MPa n = Strain hardening exponent
Hence, Flow stress can also be defined as the stress required to sustain plastic deformation at a particular strain. The flow stress is a function of plastic strain. Flow stresses occur when a mass of flowing fluid induces a dynamic pressure on a conduit wall. The force of the fluid striking the wall acts as the load. This type of stress may be applied in an unsteady fashion when flow rates fluctuate. Water hammer is an example of a transient flow stress. The following properties that have an effect on flow stress: chemical composition, purity, crystal structure, phase constitution, exit microstructure, grain size, and heat treatment.[2]
References [1] Mikell P. Groover, 2007, "Fundamentals of Modern Manufacturing; Materials, Processes, and Systems," Third Edition, John Wiley & Sons Inc. [2] Flow Stress (http:/ / www. metalpass. com/ metaldoc/ paper. aspx?docID=3)
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Fluid power
Fluid power Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is subdivided into hydraulics using a liquid such as mineral oil or water, and pneumatics using a gas such as air or other gases. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.
Practical use A fluid power system has a pump driven by a prime mover (such as an electric motor or IC engine) that converts mechanical energy into fluid energy. This fluid flow is used to actuate a devices such as: • A Hydraulic cylinder or Pneumatic cylinder, provides force in a linear fashion • A Hydraulic motor or Pneumatic motor, provides continuous rotational motion or torque • A Rotary actuator provides rotational motion of less than 360 degrees.
Application The choice of liquid or gas as the fluid power medium is governed by the application requirements: • Cost: Pneumatics are considerably more expensive to build and operate. For one, air is used as the compressed medium, so no reservoir is needed to store fluid, nor is there any need to provide means to drain or recover fluid. With increasing working pressures, pneumatics require larger parts than hydraulics. • Precision: Unlike liquids, gases change volume significantly when pressurized making it difficult to achieve precision. • Safety: Compressed gases tend to expand at high velocities when decompressed, thus pneumatics are typically limited in utilities with a working pressure up to around 100 psi (7 bar).
References • Esposito, Anthony, Fluid Power with Applications, ISBN 0-13-010225-3 • Hydraulic Power System Analysis, A. Akers, M. Gassman, & R. Smith, Taylor & Francis, New York, 2006, ISBN 0-8247-9956-9
External links • National Fluid Power Association web-site nfpa.com [1] • Using Equivalent Lengths of Valves and Fittings [2] • Fluid Power Net International, a scientific association in the field of fluid power [3]
References [1] http:/ / www. nfpa. com [2] http:/ / www. cheresources. com/ eqlength. shtml [3] http:/ / www. fluidpower. net
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Formability
Formability Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged. The plastic deformation capacity of metallic materials, however, is limited to a certain extent. Processes affected by the formability of a material include: rolling, extrusion, forging, rollforming, stamping, and hydroforming
Fracture strain A general parameter that indicates the formability and ductility of a material is the fracture strain which is determined by a uniaxial tensile test (see also fracture toughness). The strain identified by this test is defined by elongation with respect to a reference length (e. g. 80 mm for the standardized uniaxial test of flat specimens pursuant to EN 10002). It is important to note that deformation is homogeneous up to uniform elongation. Strain subsequently localizes until fracture occurs. Fracture strain is not an engineering strain since distribution of the deformation is inhomogeneous within the reference length. Fracture strain is nevertheless a rough indicator of the formability of a material. Typical values of the fracture strain are 7% for ultra-high-strength material and well over 50% for mild-strength steel.
Forming limits for sheet forming One main failure mode is caused by tearing of the material. This is typical for sheet forming applications.[1] [2] [3] A neck may appear at a certain forming stage. This is an indication of localized plastic deformation. Whereas more or less homogeneous deformation takes place in and around the subsequent neck location in the early stable deformation stage, almost all deformation is concentrated in the neck zone during the quasistable and instable deformation phase. This leads to material failure manifested by tearing. Forming limit curves depict the extreme but still possible deformation a sheet material may undergo during any stage of the stamping process. These limits depend on the deformation mode and the ratio of the surface strains. The major surface strain has a minimum value when plane strain deformation occurs, which means that the corresponding minor surface strain is zero. Forming limits are a specific material property. Typical plane strain values range from 10% for high-strength grades and 50% and above for mild-strength materials and those with very good formability.
Deep drawability A classic form of sheetforming is deep drawing, which is done by drawing a sheet by means of a punch tool pressing on the inner region of the sheet, whereas the side material held by a blankholder can be drawn toward the center. It has been observed that materials with outstanding deep drawability behave anisotropically (anisotropy). Plastic deformation in the surface is much more pronounced than in the thickness. The lankford coefficient ( r ) is a specific material property indicating the ratio between width deformation and thickness deformation in the uniaxial tensile test. Materials with very good deep drawability have an r value of 2 and above. The positive aspect of formability with respect to the forming limit curve (forming limit diagram) is seen in the deformation paths of the material that are concentrated in the extreme left of the diagram where the forming limits become very large.
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Formability
Ductility Another failure mode that may occur without any tearing is ductile fracture after plastic deformation (ductility). This may occur as a result of bending or shear deformation (inplane or through the thickness). The failure mechanism may be due to void nucleation and expansion on a microscopic level. Microcracks and subsequent macrocracks may appear when deformation of the material between the voids has exceeded the limit. Extensive research has focused in recent years on understanding and modeling ductile fracture. The approach has been to identify ductile forming limits using various small-scale tests that show different strain ratios or stress triaxialities.[4] [5] An effective measure of this type of forming limit is the minimum radius in roll-forming applications (half the sheet thickness for materials with good and three times the sheet thickness for materials with low formability).
Use of formability parameters Knowledge of the material formability is very important to the layout and design of any industrial forming process. Simulations using the finite-element method and use of formability criteria such as the forming limit curve (forming limit diagram) enhance and, in some cases, are indispensable to certain tool design processes (see also sheet metal forming analysis).
IDDRG One major objective of the international deep drawing research group (IDDRG) is the investigation, exchange and dissemination of knowledge and experience about the formability of sheet materials.
References [1] Pearce, R.: “Sheet Metal Forming”, Adam Hilger, 1991, ISBN 0-7503-0101-5. [2] Koistinen, D. P.; Wang, N.-M. edts.: „Mechanics of Sheet Metal Forming – Material Behavior and Deformation analysis“, Plenum Press, 1978, ISBN 0-306-40068-5. [3] Marciniak, Z.; Duncan, J.: “The Mechanics of Sheet Metal Forming”, Edward Arnold, 1992, ISBN 0-340-56405-9. [4] Hooputra, H.; Gese, H.; Dell, H.; Werner, H.: "A comprehensive failure model for crashworthiness simulation of aluminium extrusions", IJ Crash 2004 Vol 9, No. 5, pp. 449-463. [5] Wierzbicki, T.; Bao, Y.; Lee, Y.-W.; Bai, Y.: “Calibration and Evaluation of Seven Fracture Models”, Int. J. Mech. Sci., Vol. 47, 719 – 743, 2005.
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Fretting Wear
Fretting Wear Fretting wear is the repeated cyclical rubbing between two surfaces, which is known as fretting, over a period of time which will remove material from one or both surfaces in contact. It occurs typically in bearings, although most bearings have their surfaces hardened to resist the problem. Another problem occurs when cracks in either surface are created, known as fretting fatigue. It is the more serious of the two phenomena because it can lead to catastrophic failure of the bearing. An associated problem occurs when the small particles removed by wear are oxidised in air. The oxides are usually harder than the underlying metal, so wear accelerates as the harder particles abrade the metal surfaces further. Fretting corrosion acts in the same way, especially when water is present. Unprotected bearings on large structures like bridges can suffer serious degradation in behaviour, especially when salt is used during winter to deice the highways carried by the bridges. The problem of fretting corrosion was involved in the Silver Bridge tragedy and the Mianus River Bridge accident.
Friction loss Friction loss refers to that portion of pressure lost by fluids while moving through a pipe, hose, or other limited space. In mechanical systems such as internal combustion engines, it refers to the power lost overcoming the friction between two moving surfaces.
Causes Friction loss has several causes, including: • Frictional losses depend on the conditions of flow and the physical properties of the system. • Movement of fluid molecules against each other • Movement of fluid molecules against the inside surface of a pipe or the like, particularly if the inside surface is rough, textured, or otherwise not smooth • Bends, kinks, and other sharp turns in hose or piping In pipe flows the losses due to friction are of two kinds: skin-friction and form-friction. The former is due to the roughness of the inner part of the pipe where the fluid comes in contact with the pipe material, while the latter is due to obstructions present in the line of flow--perhaps a bend, control valve, or anything that changes the course of motion of the flowing fluid.
Firefighting Applications While friction loss has multiple applications, one of the most common is in the realm of firefighting. With the advent of modern power-takeoff (PTO) fire pumps, pressures created can sometimes overwhelm the ability of water to flow through a hose of a given diameter. As the velocity of water inside a hose increases, so does the friction loss. This resulting increase occurs as an exponential rate, thus an increase in the flow by a factor of X will result in an increase in friction loss by a factor of X2. For example, doubling the flow through a hose will quadruple the friction loss. Ultimately, as the pressure created by a fire pump goes higher and higher the amount of water actually flowing through a hose to a given point lessens, threatening firefighting operations. Conversely, friction loss can restrict the distance which water can be lifted during fire department drafting operations.
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Friction loss
External links • Pipe pressure drop calculator [1] for single phase flows. • Pipe pressure drop calculator for two phase flows. [2] • Open source pipe pressure drop calculator. [3]
References [1] http:/ / www. enggcyclopedia. com/ welcome-to-enggcyclopedia/ fluid-dynamics/ line-sizing-calculator [2] http:/ / www. enggcyclopedia. com/ welcome-to-enggcyclopedia/ fluid-dynamics/ pipe-pressure-drop-calculator-phase [3] http:/ / pfcalc. sourceforge. net
Galling Galling usually refers to the adhesive wear and transfer of material between metallic surfaces in relative converging contact during sheet metal forming and other industrial operations. In engineering science and in other technical aspects, the term galling is widespread. The influence of acceleration in the contact zone between materials have been mathematically described and correlated to the exhibited friction mechanism found in the tracks during empiric observations of the galling phenomenon, (see figures 1,2,3 and 4). Due to problems with previous incompatible definitions and test methods, better means Figure 1 An electron microscope image shows transferred of measurements in coordination with greater sheet-material accumulated on a tool surface during sliding contact understanding of the involved frictional mechanisms, under controlled laboratory conditions. The outgrowth of material or localized, roughening and creation of protrusions on the tool surface have led to the attempt to standardize or redefine the is commonly referred to as a lump. term galling to enable a more generalized use. ASTM International has formulated and established a common definition for the technical aspect of the galling phenomenon in the ASTM G40 standard: "Galling is a form of surface damage arising between sliding solids, distinguished by microscopic, usually localized, roughening and creation of protrusions, (i.e. lumps, see figure 1), above the original surface".[1]
Mechanism When two metallic surfaces are pressed against each other the initial interaction and the mating points are the asperities or high points found on each surface. An asperity may penetrate the opposing surface if there is a converging contact and relative movement. The contact
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between the surfaces, initiates friction or plastic deformation and induces pressure and energy in a small area or volume called the contact zone. The elevation in pressure increases the energy density and heat level within the deformed volume. This leads to greater adhesion between the surfaces which initiate material transfer, galling build-up, lump growth and creation of protrusions above the original surface. An example of accumulated transferred material or “lump growth” on a tool surface can be seen in figure 1. The initial asperity/asperity contact and surface damage on the opposing sheet-metal surface can be seen in figure 2. If the lump (or protrusion of transferred material to one surface) grows to a height of several microns, it may penetrate the opposing surface oxide layer and cause damage to the underlying bulk material. Damage in the bulk material is a prerequisite for plastic flow that is found in the deformed volume which surrounds the lump. The geometry and the nominal sliding velocity of the lump defines how the flowing material will be transported, accelerated and decelerated around the lump. This torrent or material flow is critical when defining the contact pressure, energy density and developed temperature during sliding. The mathematical function describing acceleration and deceleration of flowing material is thereby defined by the geometrical constraints, deduced or given by the lump's surface contour. The contact damage from deformation of bulk material is seen in figure 3.
Figure 2 The damage on the metal sheet, wear mode, or characteristic pattern shows no breakthrough of the oxide surface layer, which indicates a small amount of adhesive material transfer and a flattening damage of the sheet's surface. This is the first stage of material transfer and galling build-up.
Figure 3 The damage on the metal sheet or characteristic pattern illustrates continuous lines or stripes, indicating a breakthrough of the oxide surface layer. This type of contact can, in different proportions, be found simultaneously with the pattern found in Figure 4. Both characteristic patterns found in figure 3 and 4 arise as a consequence and are sequential to the pattern in figure 2.
If the right conditions are met, such as geometric constraints of the lump that cause less energy transfer away from the contact zone than what is added by movement and plastic deformation, an accumulation of energy can cause a clear change in the sheet materials contact and plastic behaviour; generally this increases adhesion and the friction force needed for further advancement. The sheet damage from this type of high energy contact can be seen in figure 4. In dynamic contact and sliding friction, increased compressive stress is proportionally equal to a rise in potential energy and temperature within the contact zone or "the system of the mechanics". The reasons for accumulation of energy during sliding can be the lesser
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loss of energy away from the contact zone due to a small surface area on the system boundary and low heat conductivity. Another reason is the amount of energy that is continuously forced into the system, which is a product of the acceleration of mass and developed pressure. In cooperation these mechanism allows a constant accumulation of energy and increased energy density and temperature in the contact zone during sliding. The process and contact found in figure 4 can be compared to cold welding or friction welding, because cold welding is not truly cold and the fusing points exhibit an increase in temperature and energy density derived from applied pressure and plastic deformation in the contact zone.
Figure 4 The damage on the metal sheet or characteristic pattern illustrates an "uneven surface", a change in the sheet material's plastic behaviour and involves a larger deformed volume compared to flattening of the surface oxides seen in figure 2. This type of contact is associated and usually found in different proportions simultaneously with the pattern in figure 3.
Incidence and location Galling or adhesive wear is often found between metallic surfaces where direct contact and relative motion have occurred. Sheet metal forming, thread manufacturing and other industrial operations may include made parts of stainless steel, aluminium and titanium[2] that are particularly susceptible to galling. In metalworking that involves cutting (primarily turning and milling), galling is often used to describe a wear phenomenon which occurs when cutting soft metal. The work material is transferred to the cutter and develops a "lump". The developed lump changes the contact behavior between the two surfaces, which usually increases adhesion and resistance to further advancement and, due to created vibrations, can be heard as a distinct sound. An example of a change in material behavior can be seen in figure 4. Galling often occurs with aluminium compounds and is a common cause of tool breakdown. Aluminium is a ductile metal, which means it possesses the ability for plastic flow with relative ease, which presupposes a relatively consistent and large plastic zone. In comparison, brittle fractures exhibit a momentary and unstable plastic zone around the cutter, which gives a discontinuous fracture mechanism that deters the accumulation of heat. High ductility and flowing material can be considered a general prerequisite for excessive material transfer and galling build-up because frictional heating is closely linked to the constitution (physique) of plastic zones around penetrating objects and, as mentioned, brittle fractures seldom generate a great amount of heat. Galling can occur even at relatively low loads and velocities because it is the real local pressure or energy density in the system that induces a phase transition, which often leads to an increase in material transfer and higher friction.
Galling
Prevention Adhesive wear and material transfer from one surface to another during sliding, so called galling, occur for a number of different materials and frictional systems. Generally there are two major frictional systems which effect adhesive wear or galling. In terms of prevention, they work in dissimilar ways and set different demands on the surface structure, alloys and crystal matrix used in the materials. The two frictional systems are: • Solid surface contact (unlubricated conditions) • Lubricated contact In solid surface contact or unlubricated conditions, the initial contact is characterised by interaction between asperities and the exhibition of two different sorts of attraction. Cohesive surface energy or chemical attraction between atoms or molecules connect and adhere the two surfaces together, notably even if they are separated by a measurable distance. Direct contact and plastic deformation generates another type of attraction through the constitution of a plastic zone with flowing material where induced energy, pressure and temperature allow bonding between the surfaces on a much larger scale than cohesive surface energy. In metallic compounds and sheet metal forming, the asperities are usually oxides and the plastic deformation mostly consists of brittle fracture, which presupposes a very small plastic zone. The accumulation of energy and temperature is low due to the discontinuity in the fracture mechanism. However, during the initial asperity/asperity contact, wear debris or bits and pieces from the asperities adhere to the opposing surface, creating microscopic, usually localized, roughening and creation of protrusions (in effect lumps) above the original surface. The transferred wear debris and created lumps penetrate the opposing oxide surface layer and cause damage to the underlying bulk material, allowing continuous plastic deformation, plastic flow, and accumulation of energy and temperature. With regard to the previously defined difference between the initial two types of attraction in "solid surface contact" or unlubricated conditions, the prevention of adhesive material transfer is accomplished by the following or similar approaches: • Less cohesive or chemical attraction between surface atoms or molecules. • Avoiding continuous plastic deformation and plastic flow, for example through a thicker oxide layer on the subject material in sheet metal forming (SMF). • Coatings deposited on the SMF work tool, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD) and titanium nitride (TiN) or diamond-like carbon coatings exhibit low chemical reactivity even in high energy frictional contact, where the subject material's protective oxide layer is breached, and the frictional contact is distinguished by continuous plastic deformation and plastic flow. Lubricated contact sets other demands on the materials surface structure, and the main issue is to withhold the protective lubrication thickness and avoid plastic deformation. This is important because plastic deformation raises the temperature of the oil or lubrication fluid and changes the viscosity. Any eventual material transfer or creation of protrusions above the original surface will also deteriorate the ability to withhold a protective lubrication thickness. A proper protective lubrication thickness can be withheld by the following: • Surface cavities (or small holes) can create a favourable geometric situation for the oil to withhold a protective lubrication thickness in the contact zone. • Cohesive forces on the surface can increase the chemical attraction between the surface and used lubrication and enhance the lubrication thickness. • Oil additives may reduce the tendency for galling or adhesive wear.
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Clarification and limitations Galling should not be confused with attraction between surfaces without involving plastic deformation. This type of attraction should only be compared with adhesive surface forces or surface energy theories. Different energy potentials at the surfaces can develop adhesive bonds or cohesive forces that may hold the two surfaces together, but surface energy and the cohesive force phenomenon is not the same as galling and only partly correlate. Because galling involves plastic deformation of at least one surface. However, the present research generally lacks a clear distinction between energy derived from plastic deformation and the adjacent counterpart cohesive surface forces and chemical attraction between atoms or surface molecules. The latter is likely involved in the initial material transfer, as shown in figure 2, where only surface-oxide asperities are in contact. But it is hard to distinguish these adhesive forces from more severe attractions caused by accumulated energy and increased pressure from plastic deformation. Oxides are brittle and it is probable that most of the energy in the fracture mechanism is consumed in brittle fracture, but the created wear debris will instantaneously penetrate the opposing surface. This means that the transferred oxide material will instantly act as a penetrating body and the concentration of energy, pressure and frictional heating is immediate, and without this accumulation of energy, the tendency for material transfer will certainly decrease. The formation and constitution (physique) of plastic zones around penetrating objects are arguably a prerequisite and the main factor for excessive material transfer, lump growth and galling build-up even in the initial contact process (see figure 2).
References [1] ASTM standard G40 (2006) [2] http:/ / www. estainlesssteel. com/ gallingofstainless. html
Gear A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear, however a gear can also mesh a non-rotating toothed part, called a rack, thereby producing translation instead of rotation. The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping. When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.
Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster. Although the larger gear is rotating less quickly, its torque is proportionally greater. One subtlety of this particular arrangement is that the linear speed at the rim is the same on both gears.
In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission.[1]
Gear
241 The earliest known reference to gears was circa A.D. 50 by Hero of Alexandria,[2] but they can be traced back to the Greek mechanics of the Alexandrian school in the 3rd century B.C. and were greatly developed by the Greek polymath Archimedes (287–212 B.C.).[3] The Antikythera mechanism is an example of a very early and intricate geared device, designed to calculate astronomical positions. Its time of construction is now estimated between 150 and 100 BC.[4]
Comparison with drive mechanisms The definite velocity ratio which results from having teeth gives gears an advantage over other drives (such as traction drives and V-belts) in precision machines such as watches that depend upon an exact velocity ratio. In cases where driver and follower are in close proximity gears also have an advantage over other drives in the reduced number of parts required; the downside is that gears are more expensive to manufacture and their lubrication requirements may impose a higher operating cost. The automobile transmission allows selection between gears to give various mechanical advantages.
Definition of gear terminology.
Types External vs internal gears An external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is one with the pitch angle exceeding 90 degrees. Internal gears do not cause direction reversal.[5]
Internal gear
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Spur Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts.
Spur gear
Helical Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling causes the tooth shape to be a segment of a helix. Helical gears can be meshed in a parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration are sometimes known as "skew gears". The angled teeth engage more gradually than do spur gear teeth causing them to run more smoothly and quietly.[6] With parallel helical gears, each pair of Helical gears Top: parallel configuration teeth first make contact at a single point at one side of the gear wheel; a Bottom: crossed configuration moving curve of contact then grows gradually across the tooth face to a maximum then recedes until the teeth break contact at a single point on the opposite side. In spur gears teeth suddenly meet at a line contact across their entire width causing stress and noise. Spur gears make a characteristic whine at high speeds. Whereas spur gears are used for low speed applications and those situations where noise control is not a problem, the use of helical gears is indicated when the application involves high speeds, large power transmission, or where noise abatement is important. The speed is considered to be high when the pitch line velocity exceeds 25 m/s.[7] A disadvantage of helical gears is a resultant thrust along the axis of the gear, which needs to be accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth, often addressed with additives in the lubricant. Skew gears For a 'crossed' or 'skew' configuration the gears must have the same pressure angle and normal pitch, however the helix angle and handedness can be different. The relationship between the two shafts is actually defined by the helix angle(s) of the two shafts and the handedness, as defined:[8] for gears of the same handedness for gears of opposite handedness Where
is the helix angle for the gear. The crossed configuration is less mechanically sound because there is only
a point contact between the gears, whereas in the parallel configuration there is a line contact.[8] Quite commonly helical gears are used with the helix angle of one having the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal angles. The two
Gear
243 equal but opposite angles add to zero: the angle between shafts is zero – that is, the shafts are parallel. Where the sum or the difference (as described in the equations above) is not zero the shafts are crossed. For shafts crossed at right angles the helix angles are of the same hand because they must add to 90 degrees. • 3D Animation of helical gears (parallel axis) [9] • 3D Animation of helical gears (crossed axis) [10]
Double helical Double helical gears, or herringbone gear, overcome the problem of axial thrust presented by "single" helical gears by having two sets of teeth that are set in a V shape. Each gear in a double helical gear can be thought of as two standard mirror image helical gears stacked. This cancels out the thrust since each half of the gear thrusts in the opposite direction. Double helical gears are more difficult to manufacture due to their more complicated shape. For each possible direction of rotation, there are two possible arrangements of two oppositely-oriented helical gears or gear faces. In one possible orientation, the helical gear faces are oriented so that the axial force generated by each is in the axial direction away from the center of the gear; this Double helical gears arrangement is unstable. In the second possible orientation, which is stable, the helical gear faces are oriented so that each axial force is toward the mid-line of the gear. In both arrangements, when the gears are aligned correctly, the total (or net) axial force on each gear is zero. If the gears become misaligned in the axial direction, the unstable arrangement generates a net force for disassembly of the gear train, while the stable arrangement generates a net corrective force. If the direction of rotation is reversed, the direction of the axial thrusts is reversed, a stable configuration becomes unstable, and vice versa. Stable double helical gears can be directly interchanged with spur gears without any need for different bearings.
Bevel A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes also intersect at this point, forming an arbitrary non-straight angle between the shafts. The angle between the shafts can be anything except zero or 180 degrees. Bevel gears with equal numbers of teeth and shaft axes at 90 degrees are called miter gears. Bevel gear
The teeth of a bevel gear may be straight-cut as with spur gears, or they may be cut in a variety of other shapes. Spiral bevel gear teeth are curved along the tooth's length and set at an angle, analogously to the way helical gear teeth are set at an angle compared to spur gear teeth. Zerol bevel gears have teeth which are curved along their length, but not angled. Spiral bevel gears have the same advantages and disadvantages relative to their straight-cut cousins as helical gears do to spur gears. Straight bevel gears are generally used only at speeds below 5 m/s (1000 ft/min), or, for small gears, 1000 r.p.m.[11] • 3D Animation of two bevel gears [12]
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Hypoid
Hypoid gear
Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution.[13] [14] Hypoid gears are almost always designed to operate with shafts at 90 degrees. Depending on which side the shaft is offset to, relative to the angling of the teeth, contact between hypoid gear teeth may be even smoother and more gradual than with spiral bevel gear teeth. Also, the pinion can be designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and higher are feasible using a single set of hypoid gears.[15] This style of gear is most commonly found driving mechanical differentials; which are normally straight cut bevel gears; in motor vehicle axles.
Crown Crown gears or contrate gears are a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points on a crown. A crown gear can only mesh accurately with another bevel gear, although crown gears are sometimes seen meshing with spur gears. A crown gear is also sometimes meshed with an escapement such as found in mechanical clocks.
Crown gear
Worm Worm gears resemble screws. A worm gear is usually meshed with a spur gear or a helical gear, which is called the gear, wheel, or worm wheel. Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1.[16] A disadvantage is the potential for considerable sliding action, leading to low efficiency.[17] Worm gears can be considered a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction; and it is these attributes which give it screw like Worm gear qualities. The distinction between a worm and a helical gear is made when at least one tooth persists for a full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. If that tooth persists for several turns around the helix, the worm will appear, superficially, to have more than one tooth, but what one in fact sees is the same tooth reappearing at intervals along the length of the worm. The usual
Gear
245 screw nomenclature applies: a one-toothed worm is called single thread or single start; a worm with more than one tooth is called multiple thread or multiple start. The helix angle of a worm is not usually specified. Instead, the lead angle, which is equal to 90 degrees minus the helix angle, is given. In a worm-and-gear set, the worm can always drive the gear. However, if the gear attempts to drive the worm, it may or may not succeed. Particularly if the lead angle is small, the gear's teeth may simply lock against the worm's teeth, 4-start worm and wheel because the force component circumferential to the worm is not sufficient to overcome friction. Worm-and-gear sets that do lock are called self locking, which can be used to advantage, as for instance when it is desired to set the position of a mechanism by turning the worm and then have the mechanism hold that position. An example is the machine head found on some types of stringed instruments. If the gear in a worm-and-gear set is an ordinary helical gear only a single point of contact will be achieved.[18] If medium to high power transmission is desired, the tooth shape of the gear is modified to achieve more intimate contact by making both gears partially envelop each other. This is done by making both concave and joining them at a saddle point; this is called a cone-drive.[19] Worm gears can be right or left-handed following the long established practice for screw threads.[5] • 3D Animation of a worm-gear set [20]
Non-circular Non-circular gears are designed for special purposes. While a regular gear is optimized to transmit torque to another engaged member with minimum noise and wear and maximum efficiency, a non-circular gear's main objective might be ratio variations, axle displacement oscillations and more. Common applications include textile machines, potentiometers and continuously variable transmissions.
Non-circular gears
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Rack and pinion A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely large radius of curvature. Torque can be converted to linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a straight line. Such a mechanism is used in automobiles to convert the rotation of the steering wheel into the left-to-right motion of the tie rod(s). Racks also feature in the theory of gear geometry, where, for instance, the tooth shape of an interchangeable set of gears may be specified for the rack (infinite radius), and the tooth shapes for gears of particular actual radii then derived from that. The rack and pinion gear type is employed in a rack railway.
Rack and pinion gearing
Epicyclic In epicyclic gearing one or more of the gear axes moves. Examples are sun and planet gearing (see below) and mechanical differentials.
Epicyclic gearing
Sun and planet Sun and planet gearing was a method of converting reciprocating motion into rotary motion in steam engines. It was famously used by James Watt on his early steam engines in order to get around the patent on the crank. The Sun is yellow, the planet red, the reciprocating arm is blue, the flywheel is green and the driveshaft is grey.
Sun (yellow) and planet (red) gearing
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Harmonic drive A harmonic drive is a specialized gearing mechanism often used in industrial motion control, robotics and aerospace for its advantages over traditional gearing systems, including lack of backlash, compactness and high gear ratios.
Harmonic drive gearing
Cage gear A cage gear, also called a lantern gear or lantern pinion has cylindrical rods for teeth, parallel to the axle and arranged in a circle around it, much as the bars on a round bird cage or lantern. The assembly is held together by disks at either end into which the tooth rods and axle are set.
Nomenclature Cage gear in Pantigo Windmill, Long Island
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General nomenclature
Rotational frequency, n Measured in rotation over time, such as RPM. Angular frequency, ω Measured in radians per second.
rad/second
Number of teeth, N How many teeth a gear has, an integer. In the case of worms, it is the number of thread starts that the worm has. Gear, wheel The larger of two interacting gears or a gear on its own. Pinion The smaller of two interacting gears. Path of contact Path followed by the point of contact between two meshing gear teeth. Line of action, pressure line Line along which the force between two meshing gear teeth is directed. It has the same direction as the force vector. In general, the line of action changes from moment to moment during the period of engagement of a pair of teeth. For involute gears, however, the tooth-to-tooth force is always directed along the same line—that is, the line of action is constant. This implies that for involute gears the path of contact is also a straight line, coincident with the line of action—as is indeed the case. Axis Axis of revolution of the gear; center line of the shaft.
Gear
249 Pitch point, p Point where the line of action crosses a line joining the two gear axes. Pitch circle, pitch line Circle centered on and perpendicular to the axis, and passing through the pitch point. A predefined diametral position on the gear where the circular tooth thickness, pressure angle and helix angles are defined. Pitch diameter, d A predefined diametral position on the gear where the circular tooth thickness, pressure angle and helix angles are defined. The standard pitch diameter is a basic dimension and cannot be measured, but is a location where other measurements are made. Its value is based on the number of teeth, the normal module (or normal diametral pitch), and the helix angle. It is calculated as: in metric units or
in imperial units.[21]
Module, m A scaling factor used in metric gears with units in millimeters whose effect is to enlarge the gear tooth size as the module increases and reduce the size as the module decreases. Module can be defined in the normal (mn), the transverse (mt), or the axial planes (ma) depending on the design approach employed and the type of gear being designed.[21] Module is typically an input value into the gear design and is seldom calculated. Operating pitch diameters Diameters determined from the number of teeth and the center distance at which gears operate.[5] Example for pinion:
Pitch surface In cylindrical gears, cylinder formed by projecting a pitch circle in the axial direction. More generally, the surface formed by the sum of all the pitch circles as one moves along the axis. For bevel gears it is a cone. Angle of action Angle with vertex at the gear center, one leg on the point where mating teeth first make contact, the other leg on the point where they disengage. Arc of action Segment of a pitch circle subtended by the angle of action. Pressure angle, The complement of the angle between the direction that the teeth exert force on each other, and the line joining the centers of the two gears. For involute gears, the teeth always exert force along the line of action, which, for involute gears, is a straight line; and thus, for involute gears, the pressure angle is constant. Outside diameter, Diameter of the gear, measured from the tops of the teeth. Root diameter Diameter of the gear, measured at the base of the tooth. Addendum, a Radial distance from the pitch surface to the outermost point of the tooth. Dedendum, b Radial distance from the depth of the tooth trough to the pitch surface.
Gear
250 Whole depth, The distance from the top of the tooth to the root; it is equal to addendum plus dedendum or to working depth plus clearance. Clearance Distance between the root circle of a gear and the addendum circle of its mate. Working depth Depth of engagement of two gears, that is, the sum of their operating addendums. Circular pitch, p Distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the pitch circle. Diametral pitch, Ratio of the number of teeth to the pitch diameter. Could be measured in teeth per inch or teeth per centimeter. Base circle In involute gears, where the tooth profile is the involute of the base circle. The radius of the base circle is somewhat smaller than that of the pitch circle. Base pitch, normal pitch, In involute gears, distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the base circle. Interference Contact between teeth other than at the intended parts of their surfaces. Interchangeable set A set of gears, any of which will mate properly with any other.
Helical gear nomenclature Helix angle, Angle between a tangent to the helix and the gear axis. It is zero in the limiting case of a spur gear, albeit it can considered as the hypotenuse angle as well. Normal circular pitch, Circular pitch in the plane normal to the teeth. Transverse circular pitch, p Circular pitch in the plane of rotation of the gear. Sometimes just called "circular pitch". Several other helix parameters can be viewed either in the normal or transverse planes. The subscript n usually indicates the normal.
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Worm gear nomenclature Lead Distance from any point on a thread to the corresponding point on the next turn of the same thread, measured parallel to the axis. Linear pitch, p Distance from any point on a thread to the corresponding point on the adjacent thread, measured parallel to the axis. For a single-thread worm, lead and linear pitch are the same. Lead angle, Angle between a tangent to the helix and a plane perpendicular to the axis. Note that it is the complement of the helix angle which is usually given for helical gears. Pitch diameter, Same as described earlier in this list. Note that for a worm it is still measured in a plane perpendicular to the gear axis, not a tilted plane. Subscript w denotes the worm, subscript g denotes the gear.
Tooth contact nomenclature
Line of contact
Path of action
Line of action
Plane of action
Lines of contact (helical gear)
Arc of action
Length of action
Limit diameter
Face advance
Zone of action
Point of contact Any point at which two tooth profiles touch each other. Line of contact
Gear
252 A line or curve along which two tooth surfaces are tangent to each other. Path of action The locus of successive contact points between a pair of gear teeth, during the phase of engagement. For conjugate gear teeth, the path of action passes through the pitch point. It is the trace of the surface of action in the plane of rotation. Line of action The path of action for involute gears. It is the straight line passing through the pitch point and tangent to both base circles. Surface of action The imaginary surface in which contact occurs between two engaging tooth surfaces. It is the summation of the paths of action in all sections of the engaging teeth. Plane of action The surface of action for involute, parallel axis gears with either spur or helical teeth. It is tangent to the base cylinders. Zone of action (contact zone) For involute, parallel-axis gears with either spur or helical teeth, is the rectangular area in the plane of action bounded by the length of action and the effective face width. Path of contact The curve on either tooth surface along which theoretical single point contact occurs during the engagement of gears with crowned tooth surfaces or gears that normally engage with only single point contact. Length of action The distance on the line of action through which the point of contact moves during the action of the tooth profile. Arc of action, Qt The arc of the pitch circle through which a tooth profile moves from the beginning to the end of contact with a mating profile. Arc of approach, Qa The arc of the pitch circle through which a tooth profile moves from its beginning of contact until the point of contact arrives at the pitch point. Arc of recess, Qr The arc of the pitch circle through which a tooth profile moves from contact at the pitch point until contact ends. Contact ratio, mc, ε The number of angular pitches through which a tooth surface rotates from the beginning to the end of contact.In a simple way, it can be defined as a measure of the average number of teeth in contact during the period in which a tooth comes and goes out of contact with the mating gear. Transverse contact ratio, mp, εα The contact ratio in a transverse plane. It is the ratio of the angle of action to the angular pitch. For involute gears it is most directly obtained as the ratio of the length of action to the base pitch. Face contact ratio, mF, εβ The contact ratio in an axial plane, or the ratio of the face width to the axial pitch. For bevel and hypoid gears it is the ratio of face advance to circular pitch.
Gear
253 Total contact ratio, mt, εγ The sum of the transverse contact ratio and the face contact ratio.
Modified contact ratio, mo For bevel gears, the square root of the sum of the squares of the transverse and face contact ratios.
Limit diameter Diameter on a gear at which the line of action intersects the maximum (or minimum for internal pinion) addendum circle of the mating gear. This is also referred to as the start of active profile, the start of contact, the end of contact, or the end of active profile. Start of active profile (SAP) Intersection of the limit diameter and the involute profile. Face advance Distance on a pitch circle through which a helical or spiral tooth moves from the position at which contact begins at one end of the tooth trace on the pitch surface to the position where contact ceases at the other end.
Tooth thickness nomeclature
Tooth thickness
Thickness relationships
Span measurement
Long and short addendum teeth
Chordal thickness
Circular thickness Length of arc between the two sides of a gear tooth, on the specified datum circle. Transverse circular thickness Circular thickness in the transverse plane. Normal circular thickness
Tooth thickness measurement over pins
Gear
254 Circular thickness in the normal plane. In a helical gear it may be considered as the length of arc along a normal helix. Axial thickness In helical gears and worms, tooth thickness in an axial cross section at the standard pitch diameter. Base circular thickness In involute teeth, length of arc on the base circle between the two involute curves forming the profile of a tooth. Normal chordal thickness Length of the chord that subtends a circular thickness arc in the plane normal to the pitch helix. Any convenient measuring diameter may be selected, not necessarily the standard pitch diameter. Chordal addendum (chordal height) Height from the top of the tooth to the chord subtending the circular thickness arc. Any convenient measuring diameter may be selected, not necessarily the standard pitch diameter. Profile shift Displacement of the basic rack datum line from the reference cylinder, made non-dimensional by dividing by the normal module. It is used to specify the tooth thickness, often for zero backlash. Rack shift Displacement of the tool datum line from the reference cylinder, made non-dimensional by dividing by the normal module. It is used to specify the tooth thickness. Measurement over pins Measurement of the distance taken over a pin positioned in a tooth space and a reference surface. The reference surface may be the reference axis of the gear, a datum surface or either one or two pins positioned in the tooth space or spaces opposite the first. This measurement is used to determine tooth thickness. Span measurement Measurement of the distance across several teeth in a normal plane. As long as the measuring device has parallel measuring surfaces that contact on an unmodified portion of the involute, the measurement will be along a line tangent to the base cylinder. It is used to determine tooth thickness. Modified addendum teeth Teeth of engaging gears, one or both of which have non-standard addendum. Full-depth teeth Teeth in which the working depth equals 2.000 divided by the normal diametral pitch. Stub teeth Teeth in which the working depth is less than 2.000 divided by the normal diametral pitch. Equal addendum teeth Teeth in which two engaging gears have equal addendums. Long and short-addendum teeth Teeth in which the addendums of two engaging gears are unequal.
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Pitch nomenclature Pitch is the distance between a point on one tooth and the corresponding point on an adjacent tooth.[5] It is a dimension measured along a line or curve in the transverse, normal, or axial directions. The use of the single word pitch without qualification may be ambiguous, and for this reason it is preferable to use specific designations such as transverse circular pitch, normal base pitch, axial pitch.
Pitch
Tooth pitch
Base pitch relationships
Principal pitches
Circular pitch, p Arc distance along a specified pitch circle or pitch line between corresponding profiles of adjacent teeth. Transverse circular pitch, pt Circular pitch in the transverse plane. Normal circular pitch, pn, pe Circular pitch in the normal plane, and also the length of the arc along the normal pitch helix between helical teeth or threads. Axial pitch, px Linear pitch in an axial plane and in a pitch surface. In helical gears and worms, axial pitch has the same value at all diameters. In gearing of other types, axial pitch may be confined to the pitch surface and may be a circular measurement. The term axial pitch is preferred to the term linear pitch. The axial pitch of a helical worm and the circular pitch of its worm gear are the same. Normal base pitch, pN, pbn An involute helical gear is the base pitch in the normal plane. It is the normal distance between parallel helical involute surfaces on the plane of action in the normal plane, or is the length of arc on the normal base helix. It is a constant distance in any helical involute gear. Transverse base pitch, pb, pbt In an involute gear, the pitch on the base circle or along the line of action. Corresponding sides of involute gear teeth are parallel curves, and the base pitch is the constant and fundamental distance between them along a common normal in a transverse plane. Diametral pitch (transverse), Pd Ratio of the number of teeth to the standard pitch diameter in inches.
Normal diametral pitch, Pnd Value of diametral pitch in a normal plane of a helical gear or worm.
Angular pitch, θN, τ
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256 Angle subtended by the circular pitch, usually expressed in radians. degrees or
radians
Backlash Backlash is the error in motion that occurs when gears change direction. It exists because there is always some gap between the trailing face of the driving tooth and the leading face of the tooth behind it on the driven gear, and that gap must be closed before force can be transferred in the new direction. The term "backlash" can also be used to refer to the size of the gap, not just the phenomenon it causes; thus, one could speak of a pair of gears as having, for example, "0.1 mm of backlash." A pair of gears could be designed to have zero backlash, but this would presuppose perfection in manufacturing, uniform thermal expansion characteristics throughout the system, and no lubricant. Therefore, gear pairs are designed to have some backlash. It is usually provided by reducing the tooth thickness of each gear by half the desired gap distance. In the case of a large gear and a small pinion, however, the backlash is usually taken entirely off the gear and the pinion is given full sized teeth. Backlash can also be provided by moving the gears farther apart. The backlash of a gear train equals the sum of the backlash of each pair of gears, so in long trains backlash can become a problem. For situations in which precision is important, such as instrumentation and control, backlash can be minimised through one of several techniques. For instance, the gear can be split along a plane perpendicular to the axis, one half fixed to the shaft in the usual manner, the other half placed alongside it, free to rotate about the shaft, but with springs between the two halves providing relative torque between them, so that one achieves, in effect, a single gear with expanding teeth. Another method involves tapering the teeth in the axial direction and providing for the gear to be slid in the axial direction to take up slack.
Shifting of gears In some machines (e.g., automobiles) it is necessary to alter the gear ratio to suit the task. There are several methods of accomplishing this. For example: • Manual transmission • Automatic transmission • Derailleur gears which are actually sprockets in combination with a roller chain • Hub gears (also called epicyclic gearing or sun-and-planet gears) There are several outcomes of gear shifting in motor vehicles. In the case of vehicle noise emissions, there are higher sound levels emitted when the vehicle is engaged in lower gears. The design life of the lower ratio gears is shorter so cheaper gears may be used (i.e. spur for 1st and reverse) which tends to generate more noise due to smaller overlap ratio and a lower mesh stiffness etc. than the helical gears used for the high ratios. This fact has been utilized in analyzing vehicle generated sound since the late 1960s, and has been incorporated into the simulation of urban roadway noise and corresponding design of urban noise barriers along roadways.[22]
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Tooth profile
Profile of a spur gear
Undercut
A profile is one side of a tooth in a cross section between the outside circle and the root circle. Usually a profile is the curve of intersection of a tooth surface and a plane or surface normal to the pitch surface, such as the transverse, normal, or axial plane. The fillet curve (root fillet) is the concave portion of the tooth profile where it joins the bottom of the tooth space.2 As mentioned near the beginning of the article, the attainment of a non fluctuating velocity ratio is dependent on the profile of the teeth. Friction and wear between two gears is also dependent on the tooth profile. There are a great many tooth profiles that will give a constant velocity ratio, and in many cases, given an arbitrary tooth shape, it is possible to develop a tooth profile for the mating gear that will give a constant velocity ratio. However, two constant velocity tooth profiles have been by far the most commonly used in modern times. They are the cycloid and the involute. The cycloid was more common until the late 1800s; since then the involute has largely superseded it, particularly in drive train applications. The cycloid is in some ways the more interesting and flexible shape; however the involute has two advantages: it is easier to manufacture, and it permits the center to center spacing of the gears to vary over some range without ruining the constancy of the velocity ratio. Cycloidal gears only work properly if the center spacing is exactly right. Cycloidal gears are still used in mechanical clocks. An undercut is a condition in generated gear teeth when any part of the fillet curve lies inside of a line drawn tangent to the working profile at its point of juncture with the fillet. Undercut may be deliberately introduced to facilitate finishing operations. With undercut the fillet curve intersects the working profile. Without undercut the fillet curve and the working profile have a common tangent.
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Gear materials Numerous nonferrous alloys, cast irons, powder-metallurgy and plastics are used in the manufacture of gears. However steels are most commonly used because of their high strength to weight ratio and low cost. Plastic is commonly used where cost or weight is a concern. A properly designed plastic gear can replace steel in many cases because it has many desirable properties, including dirt tolerance, low speed meshing, and the ability to "skip" quite well.[23] Manufacturers have employed plastic gears to make consumer items affordable in items like copy machines, optical storage devices, VCRs, cheap dynamos, consumer audio equipment, servo motors, and printers.
The module system Countries which have adopted the metric system generally use the module system. As a result, the term module is usually understood to mean the pitch diameter in millimeters divided by the number of teeth. When the module is based upon inch measurements, it is known as the English module to avoid confusion with the metric Wooden gears of a historic windmill module. Module is a direct dimension, whereas diametral pitch is an inverse dimension (like "threads per inch"). Thus, if the pitch diameter of a gear is 40 mm and the number of teeth 20, the module is 2, which means that there are 2 mm of pitch diameter for each tooth.[24]
Manufacture Gears are most commonly produced via hobbing, but they are also shaped, broached, cast, and in the case of plastic gears, injection molded. For metal gears the teeth are usually heat treated to make them hard and more wear resistant while leaving the core soft and tough. For large gears that are prone to warp a quench press is used.
Inspection Gear geometry can be inspected and verified using various methods such as industrial CT scanning, coordinate-measuring machines, white light scanner or laser scanning. Particularly useful for plastic gears, industrial CT scanning can inspect internal geometry and imperfections such as porosity.
Gear Cutting simulation (length 1m35s) faster, high bitrate version.
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Gear model in modern physics Modern physics adopted the gear model in different ways. In the nineteenth century, James Clerk Maxwell developed a model of electromagnetism in which magnetic field lines were rotating tubes of incompressible fluid. Maxwell used a gear wheel and called it an "idle wheel" to explain the electrical current as a rotation of particles in opposite directions to that of the rotating field lines.[25] More recently, quantum physics uses "quantum gears" in their model. A group of gears can serve as a model for several different systems, such as an artificially constructed nanomechanical device or a group of ring molecules.[26] The Three Wave Hypothesis compares the wave–particle duality to a bevel gear.[27]
References [1] [2] [3] [4]
Howstuffworks "Transmission Basics" (http:/ / auto. howstuffworks. com/ cvt1. htm) Norton 2004, p. 462 M.J.T. Lewis: "Gearing in the Ancient World", Endeavour, Vol. 17, No. 3 (1993), pp. 110–115 (110) " The Antikythera Mechanism Research Project: Why is it so important? (http:/ / www. antikythera-mechanism. gr/ faq/ general-questions/ why-is-it-so-important)", Retrieved 2011-01-10 Quote: "The Mechanism is thought to date from between 150 and 100 BC" [5] ANSI/AGMA 1012-G05, "Gear Nomenclature, Definition of Terms with Symbols". [6] Khurmi, R.S, Theory of Machines, S.CHAND [7] Doughtie and Vallance give the following information on helical gear speeds: "Pitch-line speeds of 4,000 to 7,000 fpm [20 to 36 m/s] are common with automobile and turbine gears, and speeds of 12,000 fpm [61 m/s] have been successfully used." -- p.281. [8] Helical gears (http:/ / www. roymech. co. uk/ Useful_Tables/ Drive/ Hellical_Gears. html), , retrieved 2009-06-15. [9] http:/ / www. youtube. com/ watch?v=Qcgjsor1Q-Y [10] http:/ / www. youtube. com/ watch?v=ZpJuyK842RQ [11] McGraw Hill Encyclopedia of Science and Technology, "Gear", p. 742. [12] http:/ / www. youtube. com/ watch?v=o-Kdj_f6WCQ [13] Canfield, Stephen (1997), "Gear Types" (http:/ / gemini. tntech. edu/ ~slc3675/ me361/ lecture/ grnts4. html), Dynamics of Machinery, Tennessee Tech University, Department of Mechanical Engineering, ME 362 lecture notes, . [14] Hilbert, David; Cohn-Vossen, Stephan (1952), Geometry and the Imagination (2nd ed.), New York: Chelsea, pp. 287, ISBN 978-0-8284-1087-8. [15] McGraw Hill Encyclopedia of Science and Technology, "Gear, p. 743. [16] Vallance Doughtie, p. 287. [17] Vallance Doughtie, pp. 280, 296. [18] Doughtie and Vallance, p. 290; McGraw Hill Encyclopedia of Science and Technology, "Gear", p. 743. [19] McGraw Hill Encyclopedia of Science and Technology, "Gear", p. 744. [20] http:/ / www. youtube. com/ watch?v=mNI0TwHKNi4 [21] ISO/DIS 21771:2007 : "Gears - Cylindrical Involute Gears and Gear Pairs - Concepts and Geometry", International Organization for Standardization, (2007) [22] C Michael Hogan and Gary L Latshaw,The Relationship Between Highway Planning and Urban Noise , Proceedings of the ASCE, Urban Transportation Division Specialty Conference by the American Society of Civil Engineers, Urban Transportation Division, May 21 to 23, 1973, Chicago, Illinois (http:/ / www. worldcatlibraries. org/ wcpa/ top3mset/ 2930880) [23] Plastic gears are more reliable when engineers account for material properties and manufacturing processes during design. Zan Smith: Motion System Design, July 2000. (http:/ / motionsystemdesign. com/ mechanical-pt/ plastic-gears-more-reliable-0798/ index. html), [24] Oberg, E; Jones, F.D.; Horton, H.L.; Ryffell, H.H. (2000), Machinery's Handbook (26th ed.), Industrial Press, pp. 2649, ISBN 978-0-8311-2666-7. [25] Innovation in Maxwell's Electromagnetic Theory: Molecular Vortices, Displacement Current, and Light Daniel M. Siegel. University of Chicago Press (1991) [26] Angus MacKinnon arxiv (2002) http:/ / arxiv. org/ abs/ cond-mat/ 0205647v2 [27] M. I. Sanduk, Does the Three Wave Hypothesis Imply Hidden Structure? Apeiron, 14, No. 2, pp. 113-125 (2007)
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Bibliography • American Gear Manufacturers Association; American National Standards Institute (2005), Gear Nomenclature, Definitions of Terms with Symbols (ANSI/AGMA 1012-F90 ed.), American Gear Manufacturers Association, ISBN 9781555898465. • McGraw-Hill (2007), McGraw-Hill Encyclopedia of Science and Technology (10th ed.), McGraw-Hill Professional, ISBN 978-0071441438. • Norton, Robert L. (2004), Design of Machinery (http://books.google.com/?id=iepqRRbTxrgC) (3rd ed.), McGraw-Hill Professional, ISBN 9780071214964. • Vallance, Alex; Doughtie, Venton Levy (1964), Design of machine members (4th ed.), McGraw-Hill.
Further reading • Buckingham, Earle (1949), Analytical Mechanics of Gears, McGraw-Hill Book Co.. • Coy, John J.; Townsend, Dennis P.; Zaretsky, Erwin V. (1985), Gearing (http://ntrs.nasa.gov/archive/nasa/ casi.ntrs.nasa.gov/20020070912_2002115489.pdf), NASA Scientific and Technical Information Branch, NASA-RP-1152; AVSCOM Technical Report 84-C-15.
External links • Geararium. Museum of gears and toothed wheels (http://geararium.org) Antique, vintage, contemporary gears, sprockets, gear-related objects and interesting connections. • Kinematic Models for Design Digital Library (KMODDL) (http://kmoddl.library.cornell.edu/index.php) Movies and photos of hundreds of working models at Cornell University • Mathematical Tutorial for Gearing (Relating to Robotics) (http://www.societyofrobots.com/mechanics_gears. shtml) • Animation of an Involute Rack and Pinion (http://www.brockeng.com/mechanism/RackNPinion.htm) • Explanation Of Various Gears & Their Applications (http://www.geardesign.co.uk) • "Gearology" – A short introductory course on gears and related components (http://www.bostongear.com/ training/gearology.asp) • American Gear Manufacturers Association website (http://www.agma.org) • Gear Solutions Magazine, Your Resource for Machines Services and Tooling for the Gear Industry (http://www. gearsolutions.com) • Gear Technology, the Journal of Gear Manufacturing (http://www.geartechnology.com) • "Wheels That Can't Slip." (http://books.google.com/books?id=AyEDAAAAMBAJ&pg=PA120& dq=popular+science+1930&hl=en&ei=4dTRTu6lLsvUgAed8uifDQ&sa=X&oi=book_result&ct=result& resnum=5&ved=0CEIQ6AEwBDhG#v=onepage&q&f=true) Popular Science, February 1945, pp. 120-125.
Gudgeon pin
Gudgeon pin In internal combustion engines, the gudgeon pin (UK, wrist pin US) is that which connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot upon as the piston moves.[1] In very early engine designs (including those driven by steam and also many very large stationary or marine engines), the gudgeon pin is located in a sliding crosshead that connects to the piston via a rod. The gudgeon pin is typically a forged short hollow rod made of a steel alloy of high strength and hardness that may be physically separated from both the connecting rod and piston or crosshead.[1] The design of the Gudgeon pin connection at connecting rod. Gudgeon pin fits into gudgeon pin, especially in the case of small, gudgeons inside piston. high-revving automotive engines is challenging. The gudgeon pin has to operate under some of the highest temperatures experienced in the engine, with difficulties in lubrication due to its location, while remaining small and light so as to fit into the piston diameter and not unduly add to the reciprocating mass. The requirements for lightness and compactness demand a small diameter rod that is subject to heavy shear and bending loads, with some of the highest pressure loadings of any bearing in the whole engine. To overcome these problems, the materials used to make the gudgeon pin and the way it is manufactured are amongst the most highly engineered of any mechanical component found in internal combustion engines.
Design options Gudgeon pins use two broad design configurations: semi-floating and fully floating.[1] In the semi-floating configuration, the pin is usually fixed relative to the piston by an interference fit with the journal in the piston. (This replaced the earlier set screw method.[2] ) The connecting rod small end bearing thus acts as the bearing alone. In this configuration, only the small end bearing requires a bearing surface, if any. If needed, this is provided by either electroplating the small end bearing journal with a suitable metal, or more usually by inserting a sleeve bearing or needle bearing into the eye of the small end, which has an interference fit with the aperture of the small end. During overhaul, it is usually possible to replace this bearing sleeve if it is badly worn. The reverse configuration, fixing the gudgeon pin to the connecting rod instead of to the piston, is implemented using an interference fit with the small end eye instead, with the gudgeon pin journals in the piston functioning as bearings.[3] This arrangement is usually more difficult to manufacture and service because two bearing surfaces or inserted sleeves complicate the design. In addition, the pin must be precisely set so that the small end eye is central. Because of thermal expansion considerations, this arrangement was more usual for single-cylinder engines as opposed to multiple cylinder engines with long cylinder blocks and crankcases, until precision manufacturing became more commonplace. In the fully floating configuration, a bearing surface is created both between the small end eye and gudgeon pin and the journal in the piston. The gudgeon pins are usually secured with circlips.[3] No interference fit is used in any instance and the pin 'floats' entirely on bearing surfaces. The average rubbing speed of each of the three bearings is halved and the load is shared across a bearing that is usually about three times the length of the semi-floating design with an interference fit with the piston.
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Notes [1] Nunney, Malcolm James (2007) "The Reciprocating Piston Petrol Engine: Gudgeon pins and their location" Light and heavy vehicle technology (4th ed.) Butterworth-Heinemann, Oxford, UK, p. 28 (http:/ / books. google. co. uk/ books?id=I90NpNQUzJ4C& pg=PA28), ISBN 978-0-7506-8037-0 [2] Williamson, W.D. (16 March 1916) "The Sizes of Motors for Trucks and Outline of British Practice in This Field: Part Two: Outline of British Truck Motor Design" The Automobile [Automotive industries] The Class Journal Company, New York, Vol. XXXIV, pp. 502–504, p. 502 (http:/ / books. google. co. uk/ books?id=0sgqAAAAMAAJ& pg=PA502), OCLC 5276931 (http:/ / www. worldcat. org/ oclc/ 5276931) [3] Hillier, Victor Albert Walter and Pittuck, Frank William (1991) "The Petrol Engine: Gudgeon pins" Fundamentals of Motor Vehicle Technology (4th ed.) Stanley Thornes Pub., Cheltenham, England, p. 34 (http:/ / books. google. co. uk/ books?id=2_QQtv4pFoIC& pg=PA34) ISBN 0-7487-0531-7
Heat transfer Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as required by the second law of thermodynamics. Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is sometimes called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means. The final major form of heat transfer is by radiation, which occurs in any transparent medium (solid or fluid) but may also even occur across vacuum (as when the Sun heats the Earth). Radiation is the transfer of energy through space by means of electromagnetic waves in much the same way as electromagnetic light waves transfer light. The same laws that govern the transfer of light govern the radiant transfer of heat.[1]
Overview Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system. It is a characteristic of a process and is not statically contained in matter. In engineering contexts, however, the term heat transfer has acquired a specific usage, despite its literal redundancy of the characterization of transfer. In these contexts, heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (caloric) that can be transferred by various causes,[2] and that is also common in the language of laymen and everyday life. Fundamental methods of heat transfer in engineering include conduction, convection, and radiation. Physical laws describe the behavior and characteristics of each of these methods. Real systems often exhibit a complicated combination of them. Heat transfer methods are used in numerous disciplines, such as automotive engineering, thermal management of electronic devices and systems, climate control, insulation, materials processing, and power plant engineering.
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Heat transfer Various mathematical methods have been developed to solve or approximate the results of heat transfer in systems. Heat transfer is a path function (or process quantity), as opposed to a state quantity; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process. Heat flux is a quantitative, vectorial representation of the heat flow through a surface.[3] Heat transfer is typically studied as part of a general chemical engineering or mechanical engineering curriculum. Typically, thermodynamics is a prerequisite for heat transfer courses, as the laws of thermodynamics are essential to the mechanism of heat transfer.[3] Other courses related to heat transfer include energy conversion, thermofluids, and mass transfer. The transport equations for thermal energy (Fourier's law), mechanical momentum (Newton's law for fluids), and mass transfer (Fick's laws of diffusion) are similar[4] [5] and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.[5]
Mechanisms The fundamental modes of heat transfer are: Conduction or diffusion The transfer of energy between objects that are in physical contact Convection The transfer of energy between an object and its environment, due to fluid motion Radiation The transfer of energy to or from a body by means of the emission or absorption of electromagnetic radiation Mass transfer The transfer of energy from one location to another as a side effect of physically moving an object containing that energy
Conduction On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact.[6] Steady state conduction (see Fourier's law) is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further.[7] In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out.[6] Transient conduction (see Heat equation) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.[6]
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Convection Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids. (In physics, the term fluid means any substance that deforms under shear stress; it includes liquids, gases, plasmas, and some plastic solids.) Bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid.[8] Convection is usually the dominant form of heat transfer in liquids and gases. Although often discussed as a third method of heat transfer, convection actually describes the combined effects of conduction and fluid flow.[9] Free, or natural, convection occurs when the fluid motion is caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is when the fluid is forced to flow over the surface by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.[10] Convective heating or cooling in some circumstances may be described by Newton's law of cooling: "The rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings." However, by definition, the validity of Newton's law of cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients, and in some cases is strongly nonlinear. In these cases, Newton's law does not apply.
Radiation Thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy that all matter possesses that has a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.[11]
A red-hot iron object, transferring heat to the surrounding environment primarily through thermal radiation.
Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface.
Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation. For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F).
Mass Transfer In mass transfer, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another.[12] This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics.
Convection vs. conduction In a body of fluid that is heated from underneath its container, conduction and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy, while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On the other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong. The Rayleigh number (
) is a measure determining the result of this competition.
Heat transfer
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where • g is acceleration due to gravity • • • • • •
ρ is the density with being the density difference between the lower and upper ends μ is the dynamic viscosity α is the Thermal diffusivity β is the volume thermal expansivity (sometimes denoted α elsewhere) T is the temperature and ν is the kinematic viscosity.
The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system. The buoyancy force driving the convection is roughly
, so the corresponding pressure is roughly
.
In steady state, this is canceled by the shear stress due to viscosity, and therefore roughly equals , where V is the typical fluid velocity due to convection and
the order of its timescale.
The conduction timescale, on the other hand, is of the order of . Convection occurs when the Rayleigh number is above 1,000–2,000. For example, the Earth's mantle, exhibiting non-stable convection, has Rayleigh number of the order of 1,000, and Tconv as calculated above is around 100 million years.
Phase changes Transfer of heat through a phase transition in the medium—such as water-to-ice, water-to-steam, steam-to-water, or ice-to-water—involves significant energy and is exploited in many ways: steam engines, refrigerators, etc.[13] For example, the Mason equation is an approximate analytical expression for the growth of a water droplet based on the effects of heat transport on evaporation and condensation.
Boiling Heat transfer in boiling fluids is complex, but of considerable technical importance. It is characterized by an S-shaped curve relating heat flux to surface temperature difference.[14] At low driving temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling, and is a very efficient heat transfer mechanism. At high bubble generation rates, the bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling, or DNB). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux, or CHF). The regime of falling heat transfer that follows is not easy to study, but is believed to be characterized by alternate periods of nucleate and film boiling. Nucleate boiling slows the heat transfer due to gas bubbles on the heater's surface; as mentioned, gas-phase thermal conductivity is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier". At higher temperatures still, the hydrodynamically-quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low, but rise slowly with temperature. Any contact between fluid and the surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation").
Heat transfer
Condensation Condensation occurs when a vapor is cooled and changes its phase to a liquid. Condensation heat transfer, like boiling, is of great significance in industry. During condensation, the latent heat of vaporization must be released. The amount of the heat is the same as that absorbed during vaporization at the same fluid pressure. There are several types of condensation: • Homogeneous condensation, as during a formation of fog. • Condensation in direct contact with subcooled liquid. • Condensation on direct contact with a cooling wall of a heat exchanger: This is the most common mode used in industry: • Filmwise condensation is when a liquid film is formed on the subcooled surface, and usually occurs when the liquid wets the surface. • Dropwise condensation is when liquid drops are formed on the subcooled surface, and usually occurs when the liquid does not wet the surface. Dropwise condensation is difficult to sustain reliably; therefore, industrial equipment is normally designed to operate in filmwise condensation mode.
Modeling approaches Complex heat transfer phenomena can be modeled in different ways.
Heat equation The heat equation is an important partial differential equation that describes the distribution of heat (or variation in temperature) in a given region over time. In some cases, exact solutions of the equation are available; in other cases the equation must be solved numerically using computational methods. For example, simplified climate models may use Newtonian cooling, instead of a full (and computationally expensive) radiation code, to maintain atmospheric temperatures.
Lumped system analysis System analysis by the lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady state system. That is, the method assumes that the temperature within the object is completely uniform, although its value may be changing in time. In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the object's boundary, known as the Biot number, is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into the object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object. Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newton's law of cooling.
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Applications and techniques Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances.
Insulation and radiant barriers Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both. Radiant barriers are materials that reflect radiation, and therefore reduce the flow of heat from radiation sources. Good insulators are not necessarily good radiant barriers, and vice versa. Metal, for instance, is an excellent reflector and a poor insulator. The effectiveness of an insulator is indicated by its R-value, or resistance value. The R-value of a material is the inverse of the conduction coefficient (k) multiplied by the thickness (d) of the insulator. In most of the world, R-values are measured in SI units: square-meter kelvins per watt (m²·K/W). In the United States, R-values are customarily given in units of British thermal units per hour per square-foot degrees Fahrenheit (Btu/h·ft²·°F).
Car exhausts usually require some form of heat barrier, especially high performance exhausts where a ceramic coating is often applied.
Heat exposure as part of a fire test for firestop products.
Rigid fiberglass, a common insulation material, has an R-value of four per inch, while poured concrete, a poor insulator, has an R-value of 0.08 per inch.[15] The tog is a measure of thermal resistance, commonly used in the textile industry, and often seen quoted on, for example, duvets and carpet underlay. The effectiveness of a radiant barrier is indicated by its reflectivity, which is the fraction of radiation reflected. A material with a high reflectivity (at a given wavelength) has a low emissivity (at that same wavelength), and vice versa. At any specific wavelength, reflectivity = 1 - emissivity. An ideal radiant barrier would have a reflectivity of 1, and would therefore reflect 100 percent of incoming radiation. Vacuum flasks, or Dewars, are silvered to approach this ideal. In the vacuum of space, satellites use multi-layer insulation, which consists of many layers of aluminized (shiny) Mylar to greatly reduce radiation heat transfer and control satellite temperature.
Heat transfer Critical insulation thickness Low thermal conductivity (k) materials reduce heat fluxes. The smaller the k value, the larger the corresponding thermal resistance (R) value. Thermal conductivity is measured in watts-per-meter per kelvin (W·m−1·K−1), represented as k. As the thickness of insulating material increases, the thermal resistance—or R-value—also increases. However, adding layers of insulation has the potential of increasing the surface area, and hence the thermal convection area. For example, as thicker insulation is added to a cylindrical pipe, the outer radius of the pipe-and-insulation system increases, and therefore surface area increases. The point where the added resistance of increasing insulation thickness becomes overshadowed by the effect of increased surface area is called the critical insulation thickness. In simple cylindrical pipes, this is calculated as a radius:[16]
Heat exchangers A heat exchanger is a tool built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are in direct contact. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface. Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions; and in cross flow, the fluids move at right angles to each other. Common constructions for heat exchanger include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate. When engineers calculate the theoretical heat transfer in a heat exchanger, they must contend with the fact that the driving temperature difference between the two fluids varies with position. To account for this in simple systems, the log mean temperature difference (LMTD) is often used as an "average" temperature. In more complex systems, direct knowledge of the LMTD is not available, and the number of transfer units (NTU) method can be used instead.
Heat dissipation A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems, and the radiator in a car (which is also a heat exchanger). Heat sinks also help to cool electronic and optoelectronic devices such as CPUs, higher-power lasers, and light-emitting diodes (LEDs). A heat sink uses its extended surfaces to increase the surface area in contact with the cooling fluid. Buildings In cold climates, houses with their heating systems form dissipative systems. In spite of efforts to insulate houses to reduce heat losses via their exteriors, considerable heat is lost, which can make their interiors uncomfortably cool or cold. For the comfort of the inhabitants, the interiors must be maintained out of thermal equilibrium with the external surroundings. In effect, these domestic residences are oases of warmth in a sea of cold, and the thermal gradient between the inside and outside is often quite steep. This can lead to problems such as condensation and uncomfortable air currents, which—if left unaddressed—can cause cosmetic or structural damage to the property. Such issues can be prevented by use of insulation techniques for reducing heat loss. Thermal transmittance is the rate of transfer of heat through a structure divided by the difference in temperature across the structure. It is expressed in watts per square meter per kelvin, or W/m²K. Well-insulated parts of a
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Heat transfer building have a low thermal transmittance, whereas poorly-insulated parts of a building have a high thermal transmittance. A thermostat is a device capable of starting the heating system when the house's interior falls below a set temperature, and of stopping that same system when another (higher) set temperature has been achieved. Thus, the thermostat controls the flow of energy into the house, that energy eventually being dissipated to the exterior.
Thermal energy storage Thermal energy storage refers to technologies that store energy in a thermal reservoir for later use. They can be employed to balance energy demand between daytime and nighttime. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment. Applications include later use in space heating, domestic or process hot water, or to generate electricity. Most practical active solar heating systems have storage for a few hours to a day's worth of heat collected.
Evaporative cooling Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect. A simple example of natural evaporative cooling is perspiration, or sweat, which the body secretes in order to cool itself. An evaporative cooler is a device that cools air through the simple evaporation of water.
Radiative cooling Radiative cooling is the process by which a body loses heat by radiation. It is an important effect in the Earth's atmosphere. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere, making it available for radiative transport at higher altitudes.
Laser cooling Laser cooling refers to techniques in which atomic and molecular samples are cooled through the interaction with one or more laser light fields. The most common method of laser cooling is Doppler cooling. In Doppler cooling, the frequency of the laser light is tuned slightly below an electronic transition in the atom. Thus, the atoms would absorb more photons if they moved towards the light source, due to the Doppler effect. If an excited atom then emits a photon spontaneously, it will be accelerated. The result of the absorption and emission process is to reduce the speed of the atom. Eventually the mean velocity, and therefore the kinetic energy of the atoms, will be reduced. Since the temperature of an ensemble of atoms is a measure of the random internal kinetic energy, this is equivalent to cooling the atoms. Sympathetic cooling is a process in which particles of one type cool particles of another type. Typically, atomic ions that can be directly laser-cooled are used to cool nearby ions or atoms. This technique allows cooling of ions and atoms that cannot be laser cooled directly.
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Magnetic cooling Magnetic evaporative cooling is a technique for lowering the temperature of a group of atoms. The process confines atoms using a magnetic field. Over time, individual atoms will become much more energetic than the others due to random collisions, and will escape—removing energy from the system and reducing the temperature of the remaining group. This process is similar to the familiar process by which standing water becomes water vapor.
Heat Transfer in the Human Body The principles of heat transfer in engineering systems can be applied to the human body in order to determine how the body transfers heat. Heat is produced in the body by the continuous metabolism of nutrients which provides energy for the systems of the body.[17] The human body must maintain a consistent internal temperature in order to maintain healthy bodily functions. Therefore, excess heat must be dissipated from the body to keep it from overheating. When a person engages in elevated levels of physical activity, the body requires additional fuel which increases the metabolic rate and the rate of heat production. The body must then use additional methods to remove the additional heat produced in order to keep the internal temperature at a healthy level. Heat transfer by convection is driven by the movement of fluids over the surface of the body. This convective fluid can be either a liquid or a gas. For heat transfer from the outer surface of the body, the convection mechanism is dependent on the surface area of the body, the velocity of the air, and the temperature gradient between the surface of the skin and the ambient air.[18] The normal temperature of the body is approximately 37°C. Heat transfer occurs more readily when the temperature of the surroundings is significantly less than the normal body temperature. This concept explains why a person feels “cold” when not enough covering is worn when exposed to a cold environment. Clothing can be considered an insulator which provides thermal resistance to heat flow over the covered portion of the body.[19] This thermal resistance causes the temperature on the surface of the clothing to be less than the temperature on the surface of the skin. This smaller temperature gradient between the surface temperature and the ambient temperature will cause a lower rate of heat transfer than if the skin were not covered. In order to ensure that one portion of the body is not significantly hotter than another portion, heat must be distributed evenly through the bodily tissues. Blood flowing through blood vessels acts as a convective fluid and helps to prevent any buildup of excess heat inside the tissues of the body. This flow of blood through the vessels can be modeled as pipe flow in an engineering system. The heat carried by the blood is determined by the temperature of the surrounding tissue, the diameter of the blood vessel, the thickness of the fluid, velocity of the flow, and the heat transfer coefficient of the blood. The velocity, blood vessel diameter, and the fluid thickness can all be related with the Reynolds Number, a dimensionless number used in fluid mechanics to characterize the flow of fluids. Latent heat loss, also known as evaporative heat loss, accounts for a large fraction of heat loss from the body. When the core temperature of the body increases, the body triggers sweat glands in the skin to bring additional moisture to the surface of the skin. The liquid is then transformed into vapor which removes heat from the surface of the body.[20] The rate of evaporation heat loss is directly related to the vapor pressure at the skin surface and the amount of moisture present on the skin.[18] Therefore, the maximum of heat transfer will occur when the skin is completely wet. The body continuously loses water by evaporation but the most significant amount of heat loss occurs during periods of increased physical activity.
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Other A heat pipe is a passive device constructed in such a way that it acts as though it has extremely high thermal conductivity. Heat pipes use latent heat and capillary action to move heat, and can carry many times as much heat as a similar-sized copper rod. Originally invented for use in satellites, they have applications in personal computers. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control, and can also be used to convert heat into electric power. A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of thermocouples. Thermopiles do not measure the absolute temperature, but generate an output voltage proportional to a temperature difference. Thermopiles are widely used, e.g., they are the key component of infrared thermometers, such as those used to measure body temperature via the ear. A thermal diode or thermal rectifier is a device that preferentially passes heat in one direction: a "one-way valve" for heat.
References [1] Geankoplis, Christie John (2003). Transport processes and separation process principles : (includes unit operations) (4th ed. ed.). Upper Saddle River, NJ: Prentice Hall Professional Technical Reference. ISBN 013101367X. [2] Lienhard, John H., IV; Lienhard, John H., V (2008). A Heat Transfer Textbook (3rd ed.). Cambridge, Massachusetts: Phlogiston Press. ISBN 9780971383531. OCLC 230956959. [3] New Jersey Institute of Technology, Chemical Engineering Dept. "B.S. Chemical Engineering" (http:/ / catalog. njit. edu/ undergraduate/ programs/ chemicalengineering. php). NJIT. . Retrieved 9 April 2011. [4] Welty, James R.; Wicks, Charles E.; Wilson, Robert Elliott (1976). Fundamentals of momentum, heat, and mass transfer (http:/ / books. google. be/ books?cd=3& hl=en& id=hZxRAAAAMAAJ) (2 ed.). New York: Wiley. ISBN 9780471933540. OCLC 2213384. . [5] Faghri, Amir; Zhang, Yuwen; Howell, John (2010). Advanced Heat and Mass Transfer. Columbia, MO: Global Digital Press. ISBN 978-0984276004. [6] Abbott, J.M. Smith, H.C. Van Ness, M.M. (2005). Introduction to chemical engineering thermodynamics (7th ed. ed.). Boston ; Montreal: McGraw-Hill. ISBN 0073104450. [7] "Thermal-FluidsPedia | Heat conduction" (https:/ / www. thermalfluidscentral. org/ encyclopedia/ index. php/ Heat_Conduction). [8] Çengel, Yunus A. (2003). Heat Transfer: a practical approach (http:/ / books. google. be/ books?id=nrbfpSZTwskC& dq=9780072458930& hl=en& ei=1q7YTNKMJ8OqlAe25_CSCQ& sa=X& oi=book_result& ct=result& resnum=1& ved=0CCkQ6AEwAA). McGraw-Hill series in mechanical engineering (2nd ed.). Boston: McGraw-Hill. ISBN 9780072458930. OCLC 300472921. . Retrieved 2009-04-20. [9] "Thermal-FluidsPedia | Convective heat transfer" (https:/ / www. thermalfluidscentral. org/ encyclopedia/ index. php/ Convective_Heat_Transfer) [10] "Convection — Heat Transfer" (http:/ / www. engineersedge. com/ heat_transfer/ convection. htm). Engineers Edge. Engineers Edge. . Retrieved 2009-04-20. [11] "Thermal-FluidsPedia | Radiation" (https:/ / www. thermalfluidscentral. org/ encyclopedia/ index. php/ Radiation) [12] "Thermal-FluidsPedia | Mass transfer" (https:/ / www. thermalfluidscentral. org/ encyclopedia/ index. php/ Mass_Transfer) [13] "Thermal-FluidsPedia | Multiphase systems" (https:/ / www. thermalfluidscentral. org/ encyclopedia/ index. php/ Multiphase_systems) [14] Kay, John Menzies; Nedderman, R. M. (1985). Fluid Mechanics and Transfer Processes (2nd ed.). CUP Archive. p. 529. ISBN 9780521316248. [15] Martin, Randy L. (2008-07-29). "R-Value Table" (http:/ / coloradoenergy. org/ procorner/ stuff/ r-values. htm). ColoradoENERGY.org. Windsor, Colorado: R. L. Martin & Associates, Inc.. . Retrieved 2010-11-08. [16] Balku, Şaziye (2007-05-22). "Steady Heat Transfer and Thermal Resistance Networks" (http:/ / mechatronics. atilim. edu. tr/ courses/ mece310/ ch9mechatronics. ppt) PPT Course notes: Mece 310: Thermodynamics and Heat Transfer. p. 20. Ankara, Turkey: Atılım University. Retrieved 2010-11-08. [17] Hartman,Carl and Bibb, Lewis. "The Human body and its enemies: a textbook of physiology hygiene and sanitation", World Book Co., 1913, p.232. [18] Cengel, Yunus A. and Ghajar, Afshin J. "Heat and Mass Transfer: Fundamentals and Applications." , McGraw-Hill, 4th Edition, 2010. [19] Tao, Xiaoming. "Smart fibres, fabrics, and clothing" , Woodhead Publishing, 2001 [20] Wilmore, Jack H., Costill, David L., Kenney, Larry, "Physiology of sport and exercise", Human Kinetics, 2008, p.256.
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Further reading • Frontiers in Heat and Mass Transfer (https://www.thermalfluidscentral.org/e-journals/index.php/ Heat_Mass_Transfer) • Heat Transfer Engineering (http://www.tandf.co.uk/journals/titles/01457632.asp) • Experimental Heat Transfer (http://www.tandf.co.uk/journals/titles/08916152.asp) • International Journal of Heat and Mass Transfer (http://www.sciencedirect.com/science/journal/00179310) • ASME Journal of Heat Transfer (http://scitation.aip.org/dbt/dbt.jsp?KEY=JHTRAO) • Numerical Heat Transfer Part A (http://www.tandf.co.uk/journals/titles/10407782.asp) • Numerical Heat Transfer Part B (http://www.tandf.co.uk/journals/titles/10407790.asp) • Nanoscale and Microscale Thermophysical Engineering (http://www.tandf.co.uk/journals/titles/15567265. asp) • Journal of Enhanced Heat Transfer (http://www.begellhouse.com/journals/4c8f5faa331b09ea.html)
External links • Advanced Heat and Mass Transfer (https://www.thermalfluidscentral.org/e-books/book-intro.php?b=37) - A textbook for free online reading. • Thermal-FluidsPedia (https://www.thermalfluidscentral.org/encyclopedia/index.php/Main_Page) - An online thermal fluids encyclopedia. • COMSOL Heat Transfer Module (http://www.comsol.com/products/ht/) - CAD software that models and simulates heat transfer problems. • Heat Transfer Tutorial (http://www.spiraxsarco.com/resources/steam-engineering-tutorials/ steam-engineering-principles-and-heat-transfer/heat-transfer.asp) Modes of heat transfer (conduction, convection, radiation) within or between media are explained, together with calculations and other issues such as heat transfer barriers - Spirax Sarco • Heat Transfer Podcast - Arun Majumdar - Department of Mechanical Engineering - University of California, Berkeley (http://webcast.berkeley.edu/courses/archive.php?seriesid=1906978353) • Heat Transfer Basics (http://www.cheresources.com/heat_transfer_basics.shtml) - Overview • A Heat Transfer Textbook (http://web.mit.edu/lienhard/www/ahtt.html) - Downloadable textbook (free) • Thermal Resistance Circuits (http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node118. html) - Overview • Hyperphysics Article on Heat Transfer (http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html) Overview • Interseasonal Heat Transfer (http://www.icax.co.uk/thermalbank.html) - a practical example of how heat transfer is used to heat buildings without burning fossil fuels. • Heat transfer fundamentals (http://www.hrs-heatexchangers.com/en/resources/ heat-transfer-fundamentals-01-05.aspx) • Aspects of Heat Transfer, Cambridge University (http://www.msm.cam.ac.uk/phase-trans/2007/HT/ heat_transfer.html) • Thermal-Fluids Central (https://www.thermalfluidscentral.org/)
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Heisler Chart Heisler Charts are a graphical analysis tool for the evaluation of heat transfer in thermal engineering. They are a set of two charts per included geometry introduced in 1947 by M. P. Heisler[1] which were supplemented by a third chart per geometry in 1961 by H. Gröber. Heisler Charts permit evaluation of the central temperature for transient heat conduction through an infinitely long plane wall of thickness 2L, an infinitely long cylinder of radius ro, and a sphere of radius ro. Although Heisler-Gröber Charts are a faster and simpler alternative to the exact solutions of these problems, there are some limitations. First, the body must be at uniform temperature initially. Additionally, the temperature of the surroundings and the convective heat transfer coefficient must remain constant and uniform. Also, there must be no heat generation from the body itself.[2] [3] [4]
Infinitely long plane wall These first Heisler-Gröber Charts were based upon the first term of the exact Fourier Series solution for an infinite plane wall: ,[2] where Ti is the initial temperature of the slab, T∞ is the constant temperature imposed at the boundary, x is the location in the plane wall, λn is π(n+1/2), and α is thermal diffusivity. The position x=0 represents the center of the slab. The first chart for the plane wall is plotted using 3 different variables. Plotted along the vertical axis of the chart is dimensionless temperature at the midplane, θo*
. Plotted along the horizontal axis is the Fourier
Number, Fo=αt/L2 . The curves within the graph are a selection of values for the inverse of the Biot Number, where "Bi = hL/k. k is the thermal conductivity of the material and h is the heat transfer coefficient."[2] [5]
The second chart is used to determine the variation of temperature within the plane wall for different Biot Numbers. The vertical axis is the ratio of a given temperature to that at the centerline θ/θo curve is the position at which T is taken. The horizontal axis is the value of Bi−1.
where the x/L
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[5]
The third chart in each set was supplemented by Gröber in 1961 and this particular one shows the dimensionless heat transferred from the wall as a function of a dimensionless time variable. The vertical axis is a plot of Q/Qo , the ratio of actual heat transfer to the amount of total possible heat transfer before T=T∞ . On the horizontal axis is the plot of (Bi2)(Fo), a dimensionless time variable.
[5]
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Infinitely long cylinder For the infinitely long cylinder, the Heisler chart is based on the first term in an exact solution to a Bessel function.[2] Each chart plots similar curves to the previous examples, and on each axis is plotted a similar variable.
[5]
[5]
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[5]
Sphere (of radius ro) The Heisler Chart for a sphere is based on the first term in the exact Fourier series solution: [2]
These charts can be used similar to the first two sets and are plots of similar variables.
[5]
Heisler Chart
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[5]
[5]
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Modern alternatives Currently there are programs that provide numerical solutions to the same problems, without using transcendental functions or infinite series. Examples of these programs can be found here [6][7] or here [8].[9]
References [1] Transactions ASME, 69, 227-236, 1947 [2] Cengel, Yunus A. (2007). Heat and Mass Transfer: A Practical Approach (3rd edition ed.). McGraw Hill. pp. 231-236. ISBN 978-0-07-312930-3. [3] http:/ / www. slideshare. net/ erlaurito/ unsteady-state-basics-presentation [4] http:/ / www. scribd. com/ doc/ 17462198/ Heat-conduction-in-cylinder [5] Lee Ho Sung, http:/ / www. mae. wmich. edu/ faculty/ Lee/ me431/ ch05_supp_heisler. pdf [6] http:/ / faculty. virginia. edu/ ribando/ modules/ OneDTransient/ [7] http:/ / faculty. virginia. edu/ ribando/ modules/ OneDTransient/ [8] http:/ / www. che. utexas. edu/ cache/ newsletters/ summer2006_JAVA. pdf [9] http:/ / www. che. utexas. edu/ cache/ newsletters/ summer2006_JAVA. pdf
Mechanical Engineering Heritage (Japan) The Mechanical Engineering Heritage (Japan) (機械遺産 kikaiisan) is a list of sites, landmarks, machines, and documents that made significant contributions to the development of mechanical engineering in Japan. Items in the list are certified by the Japan Society of Mechanical Engineers (JSME) (日本機械学会 Nihon Kikai Gakkai).
Overview The Mechanical Engineering Heritage program was inaugurated in June 2007 in connection with the 110th anniversary of the founding of the JSME. The program recognizes machines, related systems, factories, specification documents, textbooks, and other items that had a significant impact on the development of mechanical engineering. When a certified item can no longer be maintained by its current owner, the JSME acts to prevent its loss by arranging a transfer to the National Science Museum of Japan or to a local government institution.
Myriad year Japanese clock, Heritage No. 22
The JSME plans to certify approximately a hundred items of high heritage value over ten years.
Categories Items in the Mechanical Engineering Heritage (Japan) are classified into four categories: 1. Sites: Historical sites that contain heritage items. 2. Landmarks: Representative buildings, structures, and machinery. 3. Collections: Collections of machinery, or individual machines. 4. Documents: Machinery-related documents of historical significance. Each item is assigned a Mechanical Engineering Heritage number.
Mechanical Engineering Heritage (Japan)
Items certified in 2007 Sites • No. 1: Steam engines and hauling machinery at the Kosuge Ship Repair Dock, (built in 1868). - Nagasaki Prefecture
Landmarks • No. 2: Memorial workshop and machine tools at Kumamoto University, (built in 1908). - Kumamoto Prefecture
Collections • • • •
No. 3: Forged iron treadle lathe (made in 1875 by Kaheiji Ito). - Aichi Prefecture No. 4: Industrial steam turbine (Parsons steam turbine), (made in 1908). - Nagasaki Prefecture No. 5: 10A rotary engine (made in 1967). - Hiroshima Prefecture No. 6: Honda CVCC engine (first engine to meet emission standards of Clean Air Act (1970)). - Tochigi Prefecture • No. 7: FJR710 jet engine (made in 1971). - Tokyo • • • • • • • • • • • • • • • •
No. 8: Yanmar small horizontal diesel engine, Model HB (made in 1933). - Shiga Prefecture No. 9: Prof. Inokuchi's centrifugal pump, (made in 1912). - Aichi Prefecture No. 10: High frequency generator (made in 1929 by German AEG). - Aichi Prefecture No. 11: 0-Series Tōkaidō Shinkansen electric multiple units (operated 1964–1978). - Osaka Prefecture No. 12: Class 230 No.233 2-4-2 steam tank locomotive (made 1902–1909). - Osaka Prefecture No. 13: YS11 passenger airplane (flown 1964–2009). - Tokyo No. 14: Cub Type F, Honda bicycle engine (1952). - Tochigi Prefecture No. 15: Chain stitch sewing machine for the production of straw hats (made in 1928). - Aichi Prefecture No. 16: Non-stop shuttle change automatic loom, Toyoda Type G (made in 1924). - Aichi Prefecture No. 17: Hand operated letterpress printing machine (made in 1885). - Tokyo No. 18: Komatsu bulldozer G40 (made in 1943). - Shizuoka Prefecture No. 19: Olympus gastrocamera GT-I (made in 1950). - Tokyo No. 20: Buckton[1] universal testing machine (installed in 1908). - Hyōgo Prefecture No. 21: Mutoh Drafter manual drafting machine, MH-I (made in 1953). - Tokyo No. 22: Myriad year clock, (made in 1851). - Tokyo No. 23: The Chikugo River Lift Bridge (opened in 1935). - Between Fukuoka and Saga Prefecture
Documents • No. 24: JSME publications from the early days of the society, (published in 1897, 1901 and 1934). - Tokyo • No. 25: "Hydraulics and Hydraulic Machinery", lecture notes by Professors Bunji Mano and Ariya Inokuchi at Imperial University of Tokyo (1905). - Tokyo
Items certified in 2008 Sites • No. 26: Sankyozawa hydroelectric power station and related objects, (operating since 1888). - Miyagi Prefecture • No. 27: Hydraulic lock (made in United Kingdom, operating since 1908) and floating steam crane (operated 1905–2008), Miike Port. - Fukuoka Prefecture
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Collections • No. 28: “Entaro” bus (Ford TT type), (1923, adapted from chassis imported from United States). - Saitama Prefecture • No. 29: Mechanical telecommunication devices (made in 1947 by Shinko Seisakusho Co.). - Iwate Prefecture • No. 30: Mechanical calculator, (Yazu Arithmometer, patented in 1903). - Fukuoka Prefecture[2] • No. 31: Induction motor and design sheet (made in 1910, in the earliest days of the Japanese electrical machinery industry). - Ibaraki Prefecture
Items certified in 2009 Sites • No. 32: Mechanical Device of Sapporo Clock Tower, (clock mechanism imported/installed from E. Howard & Co. in 1881, moved in 1906). - Hokkaidō
Landmarks • No. 33: Minegishi Watermill, (installed in 1808, in operation till 1965). - Tokyo
Collections • No. 34: The Master Worm Wheel of the Hobbing Machine HRS-500, (machining by Hobbing machine of Rhein-Neckar from Germany in 1943). - Shizuoka Prefecture • No. 35: Locomobile, The oldest private Steam Automobile in Japan, (one of eight imported from Locomobile Company of America in 1902, failured in 1908, discovered in 1978 then only boiler was replaced and operable in 1980). - Hokkaidō • No. 36: Arrow-Gou, The oldest Japanese-made Car, (one of Japanese fundamental vehicle technology made in 1916). - Fukuoka Prefecture • No. 37: British-made 50 ft Turn Table, (imported from Ransomes & Rapier made in 1897, but installed location was unknown before moved in 1941 then further moved to Ōigawa Railway in 1980, in operation. Two others are deemed also imported and still in operation in other locations, these historical details is not known). - Shizuoka Prefecture
Items certified in 2010 Landmarks • NO. 38: Carousel El Dorado of Toshimaen, the oldest in Japan and oldest class in worldwide, produced by Hugo Haase (German, 1857-1933) in 1907, travelled in Europe, then moved to Steeplechase Park of Coney Island, New York in 1911, operated till 1964, then purchased, refurbished and operate in Toshimaen since 1971. - Tokyo[3] [4] • No. 39: Revolving stage and its slewing mechanism of old Konpira Grand Theatre. - Kagawa Prefecture Carousel El Dorado in Toshimaen. Heritage No. 38
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Collections • No. 40: Electric vehicle TAMA (E4S-47 I), produced by Tachikawa Aircraft Company Ltd in 1947, to overcome oil shortage after World War II. The car is with single motor of 36V, 120A, run 65km by single charge, max. speed 35km/h. The second model in 1949 run 200km. Used as taxi in Tokyo. Production had quitted due to cost up of battery by Korean War. - Kanagawa Prefecture • No. 41: The first made in Japan forklift truck with internal combustion engine, max. load 6,000 pound, in 1949, learned from Clark Material Handling Company's 4,000 pound type. - Shiga Prefecture
Electric vehicle TAMA, Heritage No. 40.
• No. 42: Takasago and Ebara type Centrifugal Refrigerating machine. - Kanagawa Prefecture • No. 43: Automated Ticket Gate (Turnstile), OMRON and Kintetsu jointly studied from 1964, model PG-D120 operated from 1973 after prototype evaluation from 1967. - Kyoto Prefecture
Items certified in 2011 Landmarks • NO. 44: Seikan Train Ferry and Moving Rail Bridge. The ferry service started between Aomori Station of Honshu and Hakodate Station of Hokkaido in 1908, and became train ferry service from 1925 till Seikan Tunnel operated in 1988. Landmark is both Hakkoda Maru ( 八甲田丸) and moving rail bridge at Aomori Station, and Mashū Maru (摩周丸) and moving rail bridge at Hakodate Station. - Aomori Prefecture and Hokkaidō
Collections
Mashū Maru, Heritage No. 44.
• NO. 45: Type ED15 Electric Locomotive. This direct current locomotive is the first Japan made one in 1924 and operation till 1960. It is functionally equal to imported electric locomotive with specification of maximum speed 65 km/h with 820 KW by four main motors. - Ibaraki Prefecture • NO. 46: Silk reeling machines of the Okaya Silk Museum (岡谷蚕糸博物館), several types of silk reeling machines. Machines are; 2 silk reeling machines out of 300 machines imported by French engineer Paul Brunat (ポール・ブリューナ) for Tomioka silk mill which operated from 1872, Japan made machine based on French and Italian technologies, and some other Japan made improved and innovated machines. - Nagano Prefecture • NO. 47: Toyoda Power Loom. Looms power by steam engine type and electric motor types invented by Sakichi Toyoda in 1897 and patented next year. Machine's productivity is 20 times high and 1/20 of low in machine cost compared to imported machines, widely used through out Japan. - Aichi Prefecture • NO. 48: Hydraulic Excavator UH03 is the first evolved type, made in Japan in 1965, having double hydraulic pumps and double valves with bucket size 0.35 m³ and engine output 58 hp. The excavators made in Japan before UH03 are single hydraulic pump and single valve type under technical tieb up with Europe. - Ibaraki Prefecture • NO. 49: Zipper chain machine (YKK-CM6) is YKK Group first made in Japan machine in 1953, evolved from imported machine from U.S. in 1950. - Toyama Prefecture • NO. 50: Ticket Vending Machine is the first train ticket vending machine consisted by 250 piece of relay, developed in 1962. This machine is capable to print various train fee per destination on a roll paper and cut as a
Mechanical Engineering Heritage (Japan) ticket, to accepts Japanese coin and sorting then storage, returns change and detects fake coins. The improved type made in 1969 was installed in Bankokuhaku-chūōguchi station (万国博中央口駅) of Expo '70 in Suita, Osaka. - Nagano Prefecture
References [1] Buckton machine (http:/ / www. civil. usyd. edu. au/ about/ history_department_trahair. shtml):See fig.3 and its description. [2] The History of Japanese Mechanical Calculating Machines (http:/ / www. xnumber. com/ xnumber/ japanese_calculators. htm) [3] "Collections: American Art: Lion, from the El Dorado Carousel, Coney Island, Brooklyn" (http:/ / www. brooklynmuseum. org/ opencollection/ objects/ 90656/ Lion_from_the_El_Dorado_Carousel_Coney_Island_Brooklyn). Brooklyn Museum. . Retrieved 2010-07-26. [4] The carousel King, Hugo Haase (http:/ / my. opera. com/ skunks/ blog/ hugo-haase-the-carousel-king)
External links • The Japan Society of Mechanical Engineers, JSME (http://www.jsme.or.jp/English/) • The Mechanical Engineering Heritage (Japan) list (http://www.jsme.or.jp/kikaiisan/data/list.html) — official website, in Japanese with English titles
User:Hg82/Larry Howell Larry Howell received a B.S. degree in mechanical engineering from Brigham Young University and M.S. and Ph.D. degrees from Purdue University. His Ph.D. advisor was Ashok Midha, who is regarded as the "Father of Compliant Mechanisms." [1] Howell is currently a professor at Brigham Young University where his research includes compliant mechanisms and microelectromechanical systems. More recently, Howell has conducted research in lamina emergent mechanisms and nanoinjection.
Biography Howell joined the BYU faculty in 1994 and served as Chair of the Department of Mechanical Engineering from 2001 to 2007[2] . Prior to joining BYU, he was a Visiting Professor at Purdue University, a Finite-Element Analyst for Engineering Methods, Inc., and he was an engineer on the design of the YF-22, the first prototype of the U.S. Air Force F-22 Raptor. His patents and technical publications focus on compliant mechanisms and microelectromechanical systems. He is the author of the book Compliant Mechanisms[3] , which is available in English and Chinese. Dr. Howell is a Fellow of the American Society of Mechanical Engineers (ASME), the Past Chair of the ASME Mechanisms and Robotics Committee, and a past Associate Editor for the Journal of Mechanical Design. His research has been recognized by the BYU Maeser Research Award, the National Science Foundation CAREER Award [4] , and the ASME Mechanisms and Robotics Award, among others.
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Books Howell, L.L., Compliant Mechanisms, John Wiley & Sons, New York, NY, 2001. Chinese Translation of Compliant Mechanisms published (under agreement with Wiley), by Higher Education Press, an official publisher of the State Education Department of China. Translator: Professor Yue-Qing Yu.
Selected Articles Ferrell, D.B., Isaac, Y.F., Magleby, S.P., Howell, L.L., "Development of Criteria for Lamina Emergent Mechanism Flexures with Specific Application to Metals", Journal of Mechanical Design, Vol. 133, pp. 031009-1 to 031009-9, March 2011. Howell, L.L., DiBiasio, C.M., Cullinan, M.A., Panas, R., and Culpepper, M.L., “A Pseudo-Rigid-Body Model for Large Deflections of Fixed-Clamped Carbon Nanotubes,” Journal of Mechanisms & Robotics, Vol. 2, No. 3, 034501-1 to 034501-5. David, R.A., Jensen, B.D., Black, J. L., Burnett, S. H., Howell, L. L., "Modeling and Experimental Validation of DNA Motion in Uniform and Nonuniform DC Electric Fields", Journal of Nanotechnology in Engineering and Medicine, Vol. 1, October 2010. Chen, G., Aten, Q.T., Zirbel, S., Jensen, B.D., Howell, L.L., “A Tristable Mechanism Configuration Employing Orthogonal Compliant Mechanisms,” J. Mechanisms and Robotics, vol. 2,pp. 14501-1–14501-6, Feb. 2010. Jacobsen, J.O., Winder, B.G., Howell, L.L., Magleby, S.P., "Lamina Emergent Mechanisms and their Basic Elements", Journal of Mechanisms and Robotics, Vol. 2, February 2010. Halverson, P.A., Howell, L.L., and Magleby, S.P., “Tension-Based Multi-stable Compliant Rolling-contact Elements,” Mechanism & Machine Theory, Vol. 45, No. 2, pp. 147-156, 2010. Winder, B.G., Magleby, S.P., and Howell, L.L., “Kinematic Representations of Pop-up Paper Mechanisms,” Journal of Mechanisms & Robotics, Vol. 1, No. 2, 021009-1 to 021009-10, 2009. (Also presented in Proceedings of IDETC/CIE 2007 as part of the 2007 ASME Mechanisms and Robotics Conference, Las Vegas, NV, Sept. 4-7, 2007, DETC2007-35505.) Anderson, C.S., Magleby, S.P., Howell, L.L., "Principles and Preliminary Concepts for Compliant Mechanically Reactive Armor", ASME/IFToMM International Conference on Reconfigurable Mechanisms and Robots, 2009. Dibiasio, C.M., Culpepper, M.L., Panas, R., Howell, L.L., and Magleby, S.P., “Comparison of Molecular Simulation and Pseudo-Rigid-Body Model Predictions for a Carbon Nanotube-Based Compliant Parallel-Guiding Mechanism,” Journal of Mechanical Design, Vol. 130, April 2008. Berglund, M., Magleby, S., and Howell, L.L., “Design Rules for Selecting and Designing Compliant Mechanisms for Rigid-Body Replacement Synthesis,” Proceedings of the 26th Design Automation Conference, at the 2000 ASME Design Engineering Technical Conference, Baltimore, Maryland, DETC2000/DAC-14225. Murphy, M.D., Midha, A., and Howell, L.L., “The Topological Synthesis of Compliant Mechanisms,” Mechanism and Machine Theory, Vol. 31, No. 2, pp. 185-199, 1996. Howell, L.L. and Midha, A., “A Loop-Closure Theory for the Analysis and Synthesis of Compliant Mechanisms,” Journal of Mechanical Design, Trans. ASME, Vol. 118, pp. 121-125, March 1996.
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Selected Patents Compliant bistable micromechanism US Pat. 7075209 Compliant, ortho-planar, linear motion spring US Pat. 6983924 Micromechanical positional state sensing apparatus method and system US Pat. 7616013 Bistable micromechanical devices US Pat. 7554342 Compliant overrunning clutch with centrifugal throw-out US Pat. 6148979
References [1] [2] [3] [4]
http:/ / www. seas. upenn. edu/ ~gksuresh/ mylinks. html http:/ / me. byu. edu/ faculty/ larryhowell http:/ / www. wiley. com/ WileyCDA/ WileyTitle/ productCd-047138478X. html Journal of Mechanical Design, Vol. 126, No. 6, pp. 941–942, November 2004
External links • Compliant Mechanism Research Group (http://research.et.byu.edu/llhwww/)
Hinge A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components. In biology, many joints function as hinges.
Door hinges There are many types of door hinges. The main types include: Barrel hinge which is a sectional barrel secured by a pivot. A barrel is a component of a hinge, that has a hollow cylinder shaped section where the rotational bearing force is applied to the pivot, and may also have a screw shaped section for fastening and/or driving the pivot.
A barrel hinge
Pivot hinges which pivot in openings in the floor and the top of the door frame. Also referred to as a double-acting floor hinge. This type is found in ancient dry stone buildings. Butt/Mortise hinges usually in threes or fours, which are inset (mortised) into the door and frame. Most residential hinges found in the U.S. are made of steel, although mortise hinges for exterior doors are often made of brass or stainless steel to prevent corrosion. Case hinges Case hinges are similar to a butt hinge however usually more of a decorative nature most commonly used in suitcases, briefcases and the like.
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Continuous hinges, or piano hinges This type of hinge is also known as a piano hinge. It runs the entire length of the door, panel, or box. Continuous hinges are manufactured with or without holes. These hinges also come in various thicknesses, pin diameters, and knuckle lengths. Concealed hinges used for furniture doors (with or without self-closing feature, and with or without dampening systems). They are made of 2 parts: One part is the hinge cup and the arm; the other part is the mounting plate. Also Euro/cup hinge. Butterfly hinges, or Parliament (UK) Hinges These were known as dovetail hinges from the 17th century onwards and can be found on old desks and cabinets from about 1670 until the 18th century. The form of these hinges varied slightly between manufacturers, and their size ranged from the very large for heavy doors to the tiniest decorative hinge for use on jewellery boxes. Many hinges of this type were exported to America to support the home trade's limited supply. They are still found to be both fairly cheap and decorative, especially on small items. Flag hinges a flag hinge can be taken apart with a fixed pin on one leaf. Flag hinges can also swivel a full 360 degrees around the pin. Flag hinges are manufactured as a right hand and a left hand configuration. Strap hinges Strap hinges are an early hinge and used on many kinds of interior and exterior doors and cabinets. H hinges Shaped like an H and used on flush-mounted doors. Small H hinges (3–4 in/76–100 mm) tend to be used for cabinets hinges, while larger hinges (6–7 in/150–180 mm) are for passage doors or closet doors. HL hinges Large HL hinges were common for passage doors, room doors and closet doors in the 17th, 18th and even 19th centuries. On taller doors H hinges were occasionally used in the middle along with the HL hinges. Other types include: • • • • • • • • • • • •
Counterflap hinge Flush hinge Coach hinge Rising Butt hinge Double action spring hinge Tee hinge Friction hinge Security hinge Cranked hinge or stormproof hinge Lift-off hinge Self closing hinge Butt hinge
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Building access hinges Since at least medieval times there have been hinges to draw bridges for defensive purposes for fortified buildings. Hinges are used in contemporary architecture where building settlement can be expected over the life of the building. For example, the Dakin Building, California was designed with its entrance ramp on a large hinge to allow settlement of the building built on piles over bay mud. This device has been effective.
Other hinges Butler tray hinge Fold to 90 degrees and also snap flat. They are for tables that have a tray top for serving. Card table hinge Mortised into edge of antique or reproduction card tables and allow the top to fold onto itself. Drop leaf table hinge Mounted under the surface of a table with leaves that drop down. They are most commonly used with rule joints. Piano hinge a long hinge, originally used for piano lids, but now used in many other applications where a long hinge is needed.
Old construction of hinges in the dry stone wall near Bignasco.
A flushed door hinge.
A barrel hinge made of wrought iron.
Increasing the number of loops to 3 allows the butt hinge axis to be fixed from both ends.
Door in furniture with spring to lock door in closed and totally open position. It hides completely behind the door.
Rusty hinges on a building exterior.
A barrel hinge made of bronze strap.
Hydraulics
Hydraulics Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, [1] Hydraulics and other studies control, and transmission of power by the use of pressurized liquids. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluidics and fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, canals, lakes, estuaries and seas. Its sub-field open channel flow studies the flow in open channels. The word "hydraulics" originates from the Greek word ὑδραυλικός (hydraulikos) which in turn originates from ὕδωρ (hydor, Greek for water) and αὐλός (aulos, meaning pipe).
Ancient and medieval era Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient China.
Greek / Hellenistic world Greeks continued and sophisticated the construction of water and hydraulic power systems. An example is the construction by Eupalinos, under a public contract, of a watering channel for Samos. An early example of the usage of hydraulic wheel, probably the earliest in Europe, is the Perachora wheel (3rd c. BC).[2] Notable is the construction of the first hydraulic automata by Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10–80 AD). Hero describes a number of working machines using hydraulic power, such as the force pump, which is known from many Roman sites as having been used for raising water and in fire engines.
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China In ancient China there was Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 - 139 AD), and Ma Jun (200 - 265 AD), while medieval China had Su Song (1020 - 1101 AD) and Shen Kuo (1031–1095). Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation.
Sri Lanka In ancient Sri Lanka, hydraulics were widely used in the ancient kingdoms of Anuradhapura and Polonnaruwa.[3] The discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to ingenuity more than 2,000 years ago.[4] By the first century A.D, several large-scale irrigation works had been completed.[5] Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya, Sri Lanka. The coral on the massive rock at the site includes cisterns for collecting water.
Moat and gardens at Sigirya.
Innovations in Ancient Rome In Ancient Rome many different hydraulic applications were developed, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining. They were among the first to make use of the siphon to carry water across valleys, and used hushing on a large scale to prospect for and then extract metal ores. They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae. Hydraulic mining was used in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold-mine of Las Medulas was one Aqueduct of Segovia of the largest of their mines. It was worked by at least 7 long aqueducts, and the water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content.
Hydraulics
Modern era (c. 1600–1870) Benedetto Castelli In 1619 Benedetto Castelli (1576 - 1578–1643), a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e., management of rivers in the Papal States, beginning in 1626.[6]
Blaise Pascal Blaise Pascal (1623–1662) studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids. His inventions include the hydraulic press, which multiplied a smaller force acting on a larger area into the application of a larger force totaled over a smaller area, transmitted through the same pressure (or same change of pressure) at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force. This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the container, i.e., any change in pressure applied at any point of the fluid is transmitted undiminished throughout the fluids.
Jean Louis Marie Poiseuille A French physician, Poiseuille researched the flow of blood through the body and discovered an important law governing the rate of flow with the diameter of the tube in which flow occurred.
In the UK Several cities developed city-wide hydraulic power networks in the 19th century, to operate machinery such as lifts, cranes, capstans and the like. Joseph Bramah[7] was an early innovator and William Armstrong[8] perfected the apparatus for power delivery on an industrial scale. In London, the London Hydraulic Power Company[9] was a major supplier its pipes serving large parts of the West End of London, City and the Docks, but there were schemes restricted to single enterprises such as docks and railway goods yards.
Notes [1] NEZU Iehisa (1995), Suirigaku, Ryutai-rikigaku, Asakura Shoten, p. 17, ISBN 4-254-26135-7. [2] The Perachora Waterworks: Addenda, R. A. Tomlinson, The Annual of the British School at Athens, Vol. 71, (1976), pp. 147-148 (http:/ / www. jstor. org/ pss/ 30103359) [3] "SriLanka-A Country study" (http:/ / www. marines. mil/ news/ publications/ Documents/ Sri Lanka Study_1. pdf). USA Government, Department of Army. 1990. . Retrieved 09 November 2011. [4] "SriLanka - History" (http:/ / asia. isp. msu. edu/ wbwoa/ south_asia/ sri_lanka/ history. htm). Asian Studies Center, Michigan State University. . Retrieved 09 November 2011. [5] "Traditional SriLanka or Ceylon" (http:/ / www. shsu. edu/ ~his_ncp/ SriLanka. html). Sam Houston State University. . Retrieved 09 November 2011. [6] Benedetto Castelli (1576-1578-1643) (http:/ / galileo. rice. edu/ sci/ castelli. html), The Galileo Project (http:/ / galileo. rice. edu/ ) [7] http:/ / www. robinsonlibrary. com/ technology/ engineering/ biography/ bramah. htm [8] http:/ / www. victorianweb. org/ technology/ engineers/ armstrong. html [9] http:/ / www. subbrit. org. uk/ sb-sites/ sites/ h/ hydraulic_power_in_london/ index. shtml
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References • Rāshid, Rushdī; Morelon, Régis (1996), Encyclopedia of the history of Arabic science, London: Routledge, ISBN 978-0-415-12410-2.
External links • International Association of Hydraulic Engineering and Research (IAHR) (http://www.iahr.org) • National Fluid Power Association (NFPA) (http://www.nfpa.com) • Pascal's Principle and Hydraulics (http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/ Pascals_principle.html) • The principle of hydraulics (http://www.hydraulicmania.com) • IAHR media library Web resource of photos, animation & video (http://www.iahrmedialibrary.net) • Basic hydraulic equations (http://hydraulik.empass.biz) • MIT hydraulics course notes (http://ocw.mit.edu/courses/civil-and-environmental-engineering/ 1-060-engineering-mechanics-ii-spring-2006/lecture-notes/)
Hydrogen pinch Hydrogen pinch analysis (HPA) is a hydrogen management method that originates from the concept of heat pinch analysis. HPA is a systematic technique for reducing hydrogen consumption and hydrogen generation through integration of hydrogen-using activities or processes in the petrochemical industry, petroleum refineries hydrogen distribution networks and hydrogen purification.[1]
Principle A mass analysis is done by representing the purity and flowrate for each stream from the hydrogen consumers (sinks), such as hydrotreaters, hydrocrackers, isomerization units and lubricant plants and the hydrogen producers (sources), such as hydrogen plants and naphtha reformers, streams from hydrogen purifiers, membrane reactors, pressure swing adsorption and continuous distillation and off-gas streams from low- or high-pressure separators. The source-demand diagram shows bottlenecks, surplus or shortages. The hydrogen pinch is the purity at which the hydrogen network has neither hydrogen surplus nor deficit.[2] [3] After the analysis REFOPT from the Centre for Process Integration at The University of Manchester is used as a tool for process integration with which the process is optimized.[4] The methodology was also developed into commercial software by companies such as Linnhoff March and AspenTech. The Aspen product incorporated the work of Nick Hallale (formerly a lecturer at University of Manchester) and was the first method to consider multiple components, rather than a pseudo-binary mixture of hydrogen and methane.
History The first assessment based on cost and value composite curves of hydrogen resources of a hydrogen network was proposed by Tower et al. (1996). Alves developed the hydrogen pinch analysis approach based on the concept of heat pinch analysis in 1999.[5] Nick Hallale and Fang Liu extended this original work, adding pressure constraints and mathematical programming for optimisation. This was followed by developments at AspenTech, producing commercial software for industrial application.
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References [1] Hydrogen optimization at minimal investment (http:/ / www. aspentech. com/ publication_files/ PTQ_Spring_2003_Hydrogen_Optimization. pdf) [2] Pinch Analysis- (http:/ / www. bfe. admin. ch/ php/ modules/ publikationen/ stream. php?extlang=en& name=en_23130289. pdf) [3] Pinch Analysis- (http:/ / www. bfe. admin. ch/ php/ modules/ publikationen/ stream. php?extlang=en& name=en_23130289. pdf) [4] REFOPT (http:/ / www. ceas. manchester. ac. uk/ research/ centres/ centreforprocessintegration/ software/ packages/ refopt/ ) [5] Multi-period hydrogen management (http:/ / www. aidic. it/ pres09/ webpapers/ 203Ahmad. pdf)
Nick Hallale, Ian Moore, Dennis Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003)
External links • Hydrogen Pinch made easy (http://www.design.che.vt.edu/h2pinch/h2pinch.html)
Hydrogen turboexpander-generator A hydrogen turboexpander-generator or generator loaded expander for hydrogen gas is an axial flow turbine or radial expander for energy recovery through which a high pressure hydrogen gas is expanded to produce work that is used to drive a electrical generator. It replaces the control valve or regulator where the pressure drops to the appropriate pressure for the low pressure network.
Description Per stage 200 bar is handled with up to 15,000 kW power and a maximum expansion ratio of 14, the generator loaded expander for hydrogen gas is fitted with automatic thrust balance, a dry gas seal and a programmable logic control with remote monitoring and diagnostics.[1]
Application The hydrogen turboexpander-generators are used for hydrogen pipeline transport in combination with hydrogen compressors and for the recovery of energy in underground hydrogen storage. A variation are the compressor loaded turboexpanders which are used in the liquefaction of gases such as liquid hydrogen[2]
References [1] Turbo generators (http:/ / www. geoilandgas. com/ businesses/ ge_oilandgas/ en/ literature/ en/ downloads/ turbo_generators. pdf) [2] Achieving and demonstrating vehicle technologies engine fuel efficiency milestones-Pag.18 (http:/ / www1. eere. energy. gov/ vehiclesandfuels/ pdfs/ merit_review_2009/ advanced_combustion/ ace_16_wagner. pdf)
External links • A preliminary inventory of the potential for electricity generation-2005 (http://www.osti.gov/bridge/servlets/ purl/843010-3bxGVs/native/843010.pdf)
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Ideal machine
Ideal machine The term ideal machine refers to a mechanical system in which energy and power are not lost or dissipated through friction, deformation, wear, or other inefficiencies. Ideal machines have the theoretical maximum performance, and therefore are used as a baseline for evaluating the performance of real machine systems.[1] [2] A simple machine, such as a lever, pulley, or gear train, is "ideal" if the power in is equal to the power out of the device, which means there are no losses. In this case, the mechanical efficiency is 100%. Mechanical efficiency is the performance of the machine compared to its theoretical maximum as performed by an ideal machine. The mechanical efficiency of a simple machine is calculated by dividing the actual power output by the ideal power output. This is usually expressed as a percentage. Power loss in a real system can occur in many ways, such as through friction, deformation, wear, heat losses, incomplete chemical conversion, magnetic and electrical losses.
Criteria A machine consists of a power source and a mechanism for the controlled use of this power. The power source often relies on chemical conversion to generate heat which is then used to generate power. Each stage of the process of power generation has a maximum performance limit which is identified as ideal. Once the power is generated the mechanism components of the machine direct it toward useful forces and movement. The ideal mechanism does not absorb any power, which means the power in is equal to the power out. An example is the automobile engine (internal combustion engine) which burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston.[3] The movement of the piston rotates the crank shaft. The remaining mechanical components such as the transmission, drive shaft, differential, axles and wheels form the power transmission mechanism that directs the power from the engine into friction forces on the road to move the automobile. The ideal machine has the maximum energy conversion performance combined with a lossless power transmission mechanism that yields maximum performance.
References [1] J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York. [2] B. Paul, 1979, Kinematics and Dynamics of Planar Machinery, Prentice Hall. [3] "Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 998 .
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Idler An idler is a mechanical device such as an idler pulley or idler wheel that is secondary to the main transfer of power in a mechanical system. They are support rollers on which conveyor belts move. They are cylindrical in shape and support the weight of the belt and the materials being transported on it.
Idler-wheel An idler-wheel drive is a system used to transmit the rotation of the main shaft of a motor to another rotating device. For example the platter of a record-reproducing turntable or the crankshaft-to-camshaft gear train of an automobile. An idler gear is a gear wheel that is inserted between two or more other gear wheels. The purpose of an idler gear can be two-fold. Firstly, the idler gear will change the direction of rotation of the output shaft. Secondly, an idler gear can assist to reduce the size of the input/output gears whilst maintaining the spacing of the shafts. An idler gear does not affect the gear ratio between the input and output shafts. Note that in a sequence of gears chained together, the ratio depends only on the number of teeth on the first and last gear. The intermediate gears, regardless of their size, do not alter the overall gear ratio of the chain. But, of course, the addition of each intermediate gear reverses the direction of rotation of the final gear. An intermediate gear which doesn't drive a shaft to perform any work is called an idler gear. Sometimes, a single idler gear is used to reverse the direction, in which case it may be referred to as a reverse idler. For instance, the typical automobile manual transmission engages reverse gear by means of inserting a reverse idler between two gears. Idler gears can also transmit rotation among distant shafts in situations where it would be impractical to simply make the distant gears larger to bring them together. Not only do larger gears occupy more space, but the mass and rotational inertia (moment of inertia) of a gear is quadratic in the length of its radius. Instead of idler gears, of course, a toothed belt or chain can be used to transmit torque over distance. A gear wheel placed between two other gears to transmit motion from one to the other. It does not alter the speed of the output, but it does alter the direction it turns. It is used to ensure that the rotation of two gears is the same. An idler gear is placed between two gears. The idler gear rotates in the opposite direction as the driver gear, and the follower gear rotates in the opposite direction of the idler, the same direction of the driver. It is also used to change the spacing between the input and output axles. It does not change the gear ratio between the input and output gears. All the gears and wheels that turn inside the treads of a battle tank are all idler gears that transfer power from the input gear to the output gear to move the tread and move the tank forward. The power take off mechanism includes a gear train with an input idler gear, a first intermediate idler gear, a second intermediate idler gear and an output gear. The input idler gear receives a rotary input and the first intermediate idler gear meshes with the input gear and the second intermediate idler gear. The output gears transmit rotary power to one of the first and second axles.
Index of mechanical engineering articles
Index of mechanical engineering articles This is an alphabetical list of articles pertaining specifically to mechanical engineering. For a broad overview of engineering, please see List of engineering topics. For biographies please see List of engineers.
A Acceleration -- Accuracy and precision -- Actual mechanical advantage -- Aerodynamics -- Agitator (device) -- Air handler -- Air conditioner -- American Machinists' Handbook -- American Society of Mechanical Engineers -Ampere -- Applied mechanics -- Antifriction -- Archimedes' screw -- Artificial intelligence -- Automaton clock -Automobile -- Automotive engineering -- Axle --
B Backlash -- Balancing -- Beale Number -- Bearing -- Belt (mechanical) -- Bending -- Biomechatronics -- Bogie -Brittle -- Buckling -- Bus-- Bushing -- Boilers & boiler systems
C CAD -- CAM -- CAID -- Calculator -- Calculus -- Car handling -- Carbon fiber -- Classical mechanics -- Clean room design -- Clock -- Clutch -- CNC -- Coefficient of thermal expansion -- Coil spring -- Combustion -- Composite material -- Compression ratio -- Compressive strength -- Computational fluid dynamics -- Computer -Computer-aided design -- Computer-aided industrial design -- Computer-numerically controlled -- Conservation of mass -- Constant-velocity joint -- Constraint -- Continuum mechanics -- Control theory -- Corrosion -- Cotter pin -Crankshaft -- Cybernetics --
D Damping -- Deformation (engineering) -- Delamination -- Design -- Diesel Engine -- Differential -- Dimensionless number -- Diode -- Diode and laser -- Drafting -- Drifting -- Driveshaft -- Dynamics -- Design for Manufacturability for CNC machining --
E Elasticity -- Electric motor -- Electrical engineering -- Electrical circuit -- Electrical network -- Electromagnetism -Electronic circuit -- Electronics -- Energy -- Engine -- Engineering -- Engineering cybernetics -- Engineering drawing -- Engineering economics -- Engineering ethics -- Engineering management -- Engineering society -Exploratory engineering --
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Index of mechanical engineering articles
F ( Fits and tolerances)--- Factor of safety -- False precision -- Fast fracture -- Fatigue -- Fillet -- Finite element analysis -- Fluid mechanics -- Flywheel -- Force -- Force density -- Four-stroke cycle -- Four wheel drive -- Friction -- Front wheel drive -- Fundamentals of Engineering exam -- Fusible plug -- Fusion Deposition Modelling -- forging process-- fluid mechanics--
G Gas compressor -- Gauge -- Gauge (engineering) -- Gauge, rail -- Gear -- Gear coupling -- Gear ratio -- Granular material --
H Heat engine -- Heat transfer -- Heating and cooling systems -- Hinge -- Hooke's law -- Hotchkiss drive -- HVAC -Hydraulics -- Hydrostatics --
I Ideal machine -- Ideal mechanical advantage -- Imperial College London -- Inclined plane -- Independent suspension -- Inductor -- Industrial engineering -- Inertia -- Institution of Mechanical Engineers -- Instrumentation -- Integrated circuit -- Invention --
J Joule --
K Kelvin -- Kinematic determinacy -- Kinematics --
L Laser -- Leaf spring -- Lever -- Liability -- Life cycle cost analysis -- Limit state design -- Live axle -- Load transfer -- Locomotive -- Lubrication --
M Machine -- Magnetic circuit -- Margin of safety -- Mass transfer -- Materials -- Materials engineering -- Material selection -- Mechanical advantage -- Mechanical Biological Treatment -- Mechanical efficiency -- Mechanical engineering -- Mechanical equilibrium -- Mechanical work -- Mechanics -- Mechanochemistry -- Mechanosynthesis -- Mechatronics -- Micromachinery -- Microprocessor -- Microtechnology -- modules of rigidity-- Molecular assembler -- Molecular nanotechnology -- Moment -- Moment of inertia -- Multi-link suspension --
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Index of mechanical engineering articles
N Nanotechnology -- Normal stress -- Nozzle --
O (orientation)--Overdrive -- Oversteer --
P Pascal (unit) -- Physics -- Pinion -- Piston -- Pitch drop experiment -- Plasma processing -- Plasticity -- Pneumatics -Poisson's ratio -- Position vector -- Potential difference -- Power -- Power stroke -- Pressure -- Prime mover -Process control -- Product Lifecycle Management -- Professional Engineer -- Project management -- Pulley -- Pump --
Q Quality -- Quality control-- quality assurance
R Rack and pinion -- Rack railway -- Railcar -- Rail gauge -- Railroad car -- Railroad switch -- Rail tracks -- Reaction kinetics -- Rear wheel drive -- Refrigeration -- Reliability engineering -- Relief valve -- RepRap Project -- Resistive force -- Resistor -- Reverse engineering -- Rheology -- Rigid body -- Robotics -- Roller chain -- Rolling -Rotordynamics --
S Safety engineering -- Screw theory -- Seal -- Semiconductor -- Series and parallel circuits -- Shear force diagrams -Shear pin -- Shear strength -- Shear stress -- Simple machine -- Simulation -- Slide rule -- Society of Automotive Engineers -- Solid mechanics -- Solid modeling -- Sprung mass -- Statics -- Steering -- Steam Systems -Stress-strain curve -- Structural failure -- Student Design Competition -- Surveying -- Suspension -- Switch --
T Technical drawing -- Technology -- Tensile strength -- Tensile stress -- Testing Adjusting Balancing -- Theory of elasticity -- Thermodynamics -- Toe -- Torque -- Torsion beam suspension -- Torsion spring -- Toughness -Tramway track -- Transmission -- Truck -- Truck (railway) -- Turbine -- Tribology -- Time travel-- touch screen--tear-- Tyre production--
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Index of mechanical engineering articles
U Understeer -- Unibody -- Unsprung weight --
V Verification and Validation -- Valve -- Vector -- Vertical strength -- Viscosity -- Volt -- Vibration -- Velocity diagrams --
W Wear -- Wedge -- Weight transfer -- Wheel -- Wheel and axle -- Wheelset --
X x bar charts
Y Yield strength -- Young's modulus --
Z zerothlaw
Indexing (motion) Indexing in reference to motion is moving (or being moved) into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its location is known to within a few hundredths of a millimeter (thousandths of an inch), or often even to within a few thousandths of a millimeter (ten-thousandths of an inch), despite the fact that no elaborate measuring or layout was needed to establish that location. Indexing is a necessary kind of motion in many areas of mechanical engineering and machining. A part that indexes, or can be indexed, is said to be indexable. Usually when the word indexing is used, it refers specifically to rotation. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number of degrees. For example, Machinery's Handbook, 25th edition, in its section on milling machine indexing,[1] says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing."[2] In addition to that most classic sense of the word, the swapping of one part for another, or other controlled movements, are also sometimes referred to as indexing, even if rotation is not the focus.
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Indexing (motion)
Examples from everyday life There are various examples of indexing that laypersons (non-engineers and non-machinists) can find in everyday life. These motions are not always called by the name indexing, but the idea is essentially similar: • The motion of pins inside a pin tumbler lock, which the correct key can move quickly and easily but also rather precisely into the correct position to allow the lock's cylinder to turn • Indexable driver bits for screwdrivers • The motion of a retractable utility knife blade, which often will have well-defined discrete positions (fully retracted, ¼-exposed, ½-exposed, ¾-exposed, fully exposed) • The indexing of a revolver's cylinder with each shot
Manufacturing applications Indexing is vital in manufacturing, especially mass production, where a well-defined cycle of motions must be repeated quickly and easily—but precisely—for each interchangeable part that is made. Without indexing capability, all manufacturing would have to be done on a craft basis, and interchangeable parts would have very high unit cost because of the time and skill needed to produce each unit. In fact, the evolution of modern technologies depended on the shift in methods from crafts (in which toolpath is controlled via operator skill) to indexing-capable toolpath control.
How indexing is achieved in manufacturing Indexing capability is provided in two fundamental ways: with or without IT. Non-IT-assisted physical guidance Non-IT-assisted physical guidance was the first means of providing indexing capability, via purely mechanical means. It allowed the Industrial Revolution to progress into the Machine Age. It is achieved by jigs, fixtures, and machine tool parts and accessories, which control toolpath by the very nature of their shape, physically limiting the path for motion. Some archetypal examples, developed to perfection before the advent of the IT era, are drill jigs, the turrets on manual turret lathes, indexing heads for manual milling machines, rotary tables, and various indexing fixtures and blocks that are simpler and less expensive than indexing heads, and serve quite well for most indexing needs in small shops.[3] Although indexing heads of the pre-CNC era are now mostly obsolete in commercial manufacturing, the principle of purely mechanical indexing is still a vital part of current technology, in concert with IT, even as it has been extended to newer uses, such as the indexing of CNC milling machine toolholders or of indexable cutter inserts, whose precisely controlled size and shape allows them to be rotated or replaced quickly and easily without changing overall tool geometry. IT-assisted physical guidance IT-assisted physical guidance (for example, via NC, CNC, or robotics) has been developed since the World War II era and uses electromechanical and electrohydraulic servomechanisms to translate digital information into position control. These systems also ultimately physically limit the path for motion, as jigs and other purely mechanical means do; but they do it not simply through their own shape, but rather using changeable information.
References [1] Green 1996, pp. 1873–1916. [2] Green 1996, p. 1873. [3] Bulgin 2011.
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Indexing (motion)
Bibliography • Bulgin, J. Randolph (March/April 2011), "Indexing basics" (http://www.homeshopmachinist.net/), The Home Shop Machinist (Traverse City, MI, USA: Village Press) 30 (2): 66–69. • Green, Robert E. et al. (eds) (1996), Machinery's Handbook (http://www.worldcat.org/title/ machinerys-handbook/oclc/473691581) (25 ed.), New York, NY, USA: Industrial Press, ISBN 978-0-8311-2575-2.
Injector An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and entrains a suction fluid. After passing through the throat of the injector, the Diagram of a typical modern ejector. mixed fluid expands and the velocity is reduced which results in recompressing the mixed fluids by converting velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream.[1] [2] The adjacent diagram depicts a typical modern ejector. It consists of a motive fluid inlet nozzle and a converging-diverging outlet nozzle. Water, air, steam, or any other fluid at high pressure provides the motive force at the inlet. An injector is a more complex device containing at least three cones. That used for delivering water to a steam locomotive boiler takes advantage of the release of the energy contained within the latent heat of evaporation to increase the pressure to above that within the boiler. The Venturi effect, a particular case of Bernoulli's principle, applies to the operation of this device. Fluid under high pressure is converted into a high-velocity jet at the throat of the convergent-divergent nozzle which creates a low pressure at that point. The low pressure draws the suction fluid into the convergent-divergent nozzle where it mixes with the motive fluid. In essence, the pressure energy of the inlet motive fluid is converted to kinetic energy in the form of velocity head at the throat of the convergent-divergent nozzle. As the mixed fluid then expands in the divergent diffuser, the kinetic energy is converted back to pressure energy at the diffuser outlet in accordance with Bernoulli's principle. Depending on the specific application, an injector is commonly also called an Eductor-jet pump, a water eductor, a vacuum ejector, a steam-jet ejector, or an aspirator.
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Injector
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Key design parameters The compression ratio of the injector, pressure of the suction fluid
, is defined as ratio of the injectors's outlet pressure
to the inlet
.
The entrainment ratio of the injector,
, is defined as the amount of motive fluid
(in kg/hr) required to
entrain and compress a given amount (in kg/hr) of suction fluid.. The compression ratio and the entrainment ratio are key parameters in designing an injector or ejector.
History The injector was invented by a Frenchman, Henri Giffard in 1858[3] and patented in the United Kingdom by Messrs Sharp Stewart & Co. of Glasgow. Motive force was provided at the inlet by a suitable high-pressure fluid.
Feedwater injectors The injector was originally used in the boilers of steam locomotives for injecting or pumping the boiler A- Steam from boiler, B- Needle valve, C- Needle valve handle, D- Steam and water feedwater into the boiler. The injector combine, E- Water feed, F- Combining cone, G- Delivery nozzle and cone, H- delivery chamber and pipe, K- Check valve, L- Overflow consisted of a body containing a series of three or more nozzles, "cones" or "tubes". The motive steam passed through a nozzle that reduced its pressure below atmospheric and increased the steam velocity. Fresh water was entrained by the steam jet, and both steam and water entered a convergent "combining cone" which mixed them thoroughly so that the water condensed the steam. The condensate mixture then entered a divergent "delivery cone" which slowed down the jet, and thus built up the pressure to above that of the boiler. An overflow was required for excess A more modern drawing of the injector used in steam locomotives. steam or water to discharge, especially during starting. There was at least one check valve between the exit of the injector and the boiler to prevent back flow, and usually a valve to prevent air being sucked in at the overflow.
Injector
After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation, the injector was widely adopted as an alternative to mechanical pumps in steam-driven locomotives. The key to understanding how it works is to appreciate that steam, having a much lower density than water, attains a much higher velocity than water would do in flowing from a high pressure to a low pressure through the steam cone. Steam injector of a steam locomotive boiler. When this jet of steam meets cold water in the combining cone, the principle of conservation of momentum applies. The steam is condensed by mixing with the cold water but the flow of water is accelerated by absorbing the momentum of the high velocity water molecules condensed from the steam. Since the steam, in condensing, gives up its latent heat energy, this causes the temperature of the resultant jet of water to be raised. When this accelerated jet of water passes through the delivery cone, it is capable to developing a much higher pressure than that of the original supply of steam and is thus able to overcome the boiler pressure at the check valve, thereby allowing water to enter the boiler. Furthermore, the addition of heat to the flow of water lessens the effect of the injected water in cooling the water in the boiler compared to the case of cold water injected via a mechanical feed pump. Most of the heat energy in the condensed steam is therefore returned to the boiler, increasing the thermal efficiency of the process. Injectors were therefore simple and reliable and also thermally efficient. Efficiency was further improved by the development of a multi-stage injector which was powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise have gone to waste. Injectors could be troublesome under certain running conditions, when vibration caused the combined steam and water jet to "knock off". Originally the injector had to be restarted by careful manipulation of the steam and water controls, and the distraction caused by a malfunctioning injector was largely responsible for the 1913 Ais Gill rail accident. Later injectors were designed to automatically restart on sensing the collapse in vacuum from the steam jet, for example with a spring-loaded delivery cone.
Vacuum ejectors An additional use for the injector technology was in vacuum ejectors in continuous train braking systems, which were made compulsory in the UK by the Regulation of Railways Act 1889. A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. Vacuum brakes have been superseded by air brakes in modern trains, which use pumps, as diesel and electric locomotives no longer have a suitable working fluid for vacuum ejectors.
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Injector
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Modern uses The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example: • To inject chemicals into the boiler drums of small, stationary, low pressure boilers. In large, high-pressure modern boilers, usage of injectors for chemical dosing is not possible due to their limited outlet pressures. • In thermal power stations, they are used for the removal of the boiler bottom ash, the removal of fly ash from the hoppers of the electrostatic precipitators used to remove that ash from the boiler flue gas, and for creating a vacuum pressure in steam turbine exhaust condensers. • Jet pumps have been used in boiling water nuclear reactors to circulate the coolant fluid.[4] • For use in producing a vacuum pressure in steam jet cooling systems. • For the bulk handling of grains or other granular or powdered materials. • The construction industry uses them for pumping turbid water and slurries. • Some aircraft (mostly earlier designs) use an ejector attached to the fuselage to provide vacuum for gyroscopic instruments such as an attitude indicator. Similar devices called aspirators based on the same operating principle are used in laboratories to create a partial vacuum and for medical use in suction of mucus or bodily fluids.
Well pumps Jet pumps are commonly used to extract water from water wells. The main pump, often a centrifugal pump, is powered and installed at ground level. Its discharge is split, with the greater part of the flow leaving the system, while a portion of the flow is returned to the jet pump installed below ground in the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high-energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass flow which is then piped to the inlet of the main pump. Shallow well pumps are those in which the jet assembly is attached directly to the main pump and are limited to a depth of approximately 5-8m to prevent cavitation. Deep well pumps are those in which the jet is located at the bottom of the well. The maximum depth for deep well pumps is determined by the inside diameter of and the velocity through the jet. The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g., electric/petrol motor, rotating The S type pump is useful for removing water from a well or container. impellers) at the ground surface for easy maintenance. The advent of the electrical submersible pump has partly replaced the need for jet type well pumps, except for driven point wells or surface water intakes.
Injector
Multi-stage steam ejectors In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency; both barometric and shell-and-tube surface condensers are used.
Construction materials Injectors or ejectors are made of carbon and stainless steel, titanium, PTFE, carbon and other materials.
References [1] Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook (8th Edition ed.). McGraw Hill. ISBN 0-07-142294-3. [2] Power, Robert B. (1993). Steam Jet Ejectors For The Process Industries (First Edition ed.). McGraw-Hill. ISBN 0-07-050618-3. [3] Strickland L. Kneass (1894). Practice and Theory of the Injector. John Wiley & Sons (Reprinted by Kessinger Publications, 2007 ). ISBN 0-548-47587-3. [4] "Steam-assisted jet pump" (http:/ / www. freepatentsonline. com/ 4847043. html). General Electric. . Retrieved 17 March 2011. "United States Patent 4847043 ... recirculation of a coolant in a nuclear reactor"
Additional reading • J.B. Snell (1973). Mechanical Engineering: Railways. Arrow Books. ISBN 0-09-908170-9. • J.T. Hodgson and C.S. Lake (1954). Locomotive Management (Tenth Edition ed.). Tothill Press.
External links • Use of Eductor for Lifting Water (http://www.muleshoe-eng.com/sitebuildercontent/sitebuilderfiles/Eductor. pdf)
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Interference fit
Interference fit An interference fit, also known as a press fit or friction fit,[1] is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening. For metal parts in particular, the friction that holds the parts together is often greatly increased by compression of one part against the other, which relies on the tensile and compressive strengths of the materials the parts are made from. Typical examples of interference fits are the press fitting of shafts into bearings or bearings into their housings and the attachment of watertight connectors to cables. An interference fit also results when pipe fittings are assembled and tightened.
Introducing interference between parts An interference fit is generally achieved by shaping the two mating parts so that one or the other (or both) slightly deviate in size from the nominal dimension. The word interference refers to the fact that one part slightly interferes with the space that the other is taking up. For example: A shaft may be ground slightly oversize, and the hole in the bearing (through which it is going to pass with an interference fit) may be ground slightly undersized. When the shaft is pressed into the bearing, the two parts interfere with each others occupation of space; the result is that they elastically deform slightly, each being compressed, and the interface between them is one of extremely high friction—so high that even large amounts of torque cannot turn one of them relative to the other; they are locked together and they turn in unison.
Tightness of fit is controlled by amount of interference ("allowance") Formulas exist to compute the "allowance" (planned difference from nominal size) that will result in various strengths of fit such as loose fit, light interference fit, and interference fit. The value of the allowance depends on which material is being used, how big the parts are, and what degree of tightness is desired. Such values have already been worked out in the past for many standard applications, and they are available to engineers in the form of tables, obviating the need for re-derivation. Thus if a loose fit is desired for a 10 mm (0.394 in) shaft made of 303 stainless steel, the engineer can look up the needed allowance in a reference book or computer program, rather than using a formula to calculate it.
Assembling an oversize shaft into an undersized hole There are two basic methods for assembly, sometimes used in combination: force, and thermal expansion or contraction.
Force There are at least three different terms used to describe an interference fit created via force: press fit, friction fit, and hydraulic dilation.[2] [3] Press fit is achieved with presses that can press the parts together with very large amounts of force. The presses are generally hydraulic, although small hand-operated presses (such as arbor presses) may operate by means of the mechanical advantage supplied by a screw jack or by a gear reduction driving a rack and pinion. The amount of force applied in hydraulic presses may be anything from a few pounds for the tiniest parts to hundreds of tons for the largest parts. Often the edges of shafts and holes are chamfered (beveled). The chamfer forms a guide for the pressing movement, helping (a) to distribute the force evenly around the circumference of the hole, (b) to allow the compression to occur gradually instead of all at once, thus helping the pressing operation to be smoother, to be more easily controlled, and to require less power (less force at any one instant of time), and (c) to assist in aligning the shaft parallel with the
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Interference fit hole it is being pressed into.
Thermal expansion or contraction Most materials expand when heated and shrink when cooled. Enveloping parts are heated (e.g., with torches or gas ovens) and assembled into position while hot, then allowed to cool and contract back to their former size, except for the compression that results from each interfering with the other. This is also referred to as shrink-fitting. Railroad axles, wheels, and tires are typically assembled in this way. Alternatively, the enveloped part may be cooled before assembly such that it slides easily into its mating part. Upon warming, it expands and interferes. Cooling is often preferable as it is less likely than heating to change material properties, e.g. assembling a hardened gear onto a shaft, where heating the gear would alter its hardness.
References [1] Alan O. Lebeck (1991). Principles and design of mechanical face seals (http:/ / books. google. com/ books?id=RnOZ4zl6CRMC& pg=PA232& dq="Friction+ fit"+ "interference+ fit"+ "press+ fit"& lr=& ei=8YNkS4L2KJH2NPGp_IsO& cd=1#v=onepage& q="Friction fit" "interference fit" "press fit"& f=false). Wiley-Interscience. p. 232. ISBN 978-0471515333. . [2] Heinz P. Bloch (1998). Improving machinery reliability (http:/ / books. google. com/ books?id=pBhKQu8WwL8C& pg=PA216& dq="Friction+ fit"+ "interference+ fit"& lr=& ei=f4BkS4HmAabuNN3AvYoO& cd=2#v=onepage& q="Friction fit" "interference fit"& f=false) (3rd ed.). Gulf Professional Publishing. p. 216. ISBN 978-0884156611. . [3] "Coupling Design and Selection" (http:/ / www. emerson-ept. com/ EPTRoot/ kopflex/ Engineered/ FAQ/ design. htm). . Retrieved 2010-01-30.
External links • Diagram of an interference fit (http://engineeronadisk.com/notes_manufact/assemblya3.html) • Interference fitting (http://www.eminebea.com/content/html/en/engineering/bearings/shaftbrg_10.shtml) formulae for calculating clearance reductions when using interference fits for bearings on shafts and in housings
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ITA Iscar Tool Advisor
ITA – Iscar Tool Advisor ITA - Iscar Tool Advisor is a computer software that is developed for the needs of mechanical engineers operating especially in metalworking industry. The software is constructed upon a complex mathematical algorithm. [1] This algorithm provides an effective process of narrowing down all possible alternatives. Consequently, the software guides the end-users towards specific recommendations indicating the most suitable cutting tools, cutting conditions and machining strategies. The output data provided by the software comprises: inserts and tool designations, carbide grades, recommended machining conditions, required machine power, net operation time and material removal rate. This information can be sorted according to user preference. [2] The user ability to define preferences is one of the features that the ITA software provides. Details such as tool diameter, solid carbide vs. indexable tooling, product family, grade and tool designations can be defined, as well as user restrictions like clamping stability, long overhang, type of cut, machine power limitation, and all settings that could influence cutting data. Since release in early 2010, tens of thousands of mechanical engineers, technologists [3] and foremen are using this software on a daily basis in more than 100 countries [4] around the globe. The software is available free of charge 24/7.
References [1] eFunda: The Ultimate Online Reference for Engineers (http:/ / www. efunda. com/ home. cfm) [2] Cutting Tool Engineering, January 2011 (http:/ / www. cuttingtoolengineering. com/ product. search. php?proid=707) [3] European Tool&Mould Making, February 2011 (http:/ / www. etmm-online. com/ nw. php?2487) [4] Metal Working（MW）magazine, Japan, February 2011 (http:/ / www. metalworking1950. com/ html/ 2011-2/ mw_art433816266. shtml)
External links • ITA Iscar Tool Advisor software (http://www.iscar.com/ita) • Iscar Metalworking
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Jaw coupling
Jaw coupling A jaw coupling is a type of motion control (servo) coupling designed to transmit torque (by connecting two shafts) while damping system vibrations, which protects other components from damage. Jaw couplings are composed of three parts: two metallic hubs and an elastomer insert called an element, but commonly referred to as a "spider". The three parts press fit together with a jaw from each hub fitted alternately with the lobes of the spider. The curved jaws of the hubs reduce deformation of the spider to maintain the zero-backlash fit. The elastomer of the spider can be made in different hardnesses, which Computer drawing of a curved jaw coupling allows the user to customize the coupling so that it absorbs more or less vibration. The more damping ability the coupling has, the less torsional strength it possesses. Jaw couplings are best suited for applications that rely on a stop-and-go type of movement, where accuracy needs to take place upon stopping in order to perform any number of precision tasks, such as taking a high resolution picture (machine vision system). Absorbing vibrations decreases the settling time the system needs, which increases through-put. The jaw coupling is less suited for applications that rely on a constant scanning type of motion, where accuracy is required during movement, which requires a torsionally stronger coupling. The drawback of the jaw coupling is the lack of misalignment capability. Too much axial motion will cause the coupling to come apart, while too much angular or parallel misalignment will result in bearing loads that are higher than most other servo/motion control couplings. Jaw couplings are also considered fail-safe. If the spider fails, the jaws of the two hubs will mate, much like teeth on two gears, and continue to transmit torque. This may or may not be desirable to the user depending on the application. Jaw couplings are well balanced and able to tolerate high RPM. With its damping capability and interchangeable spiders, jaw couplings make a great solution for shock absorption.
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JIC fitting
JIC fitting JIC fittings, defined by the SAE J514 and MIL-F-18866 standards, are a type of flare fitting machined with a 37-degree flare seating surface. JIC (Joint Industry Council) fittings are widely used in fuel delivery and fluid power applications, especially where extremely high pressure is involved. The SAE J514 standard replaces the MS16142 military specification, although some tooling is still listed under MS16142. JIC fittings are dimensionally identical to AN (Army-Navy) fittings, but are produced to less exacting tolerances and are generally less costly. 45-degree flare fittings are similar in appearance, but are not interchangeable. JIC fitting systems have three components that make a tubing assembly: fitting, flare nut, and sleeve. As with other flared connection systems, the seal is achieved through metal-to-metal contact between the finished surface of the fitting nose and the inside diameter of the flared tubing. The sleeve is used to evenly distribute the compressive forces of the flare nut to the flared end of the tube. Materials commonly used to fabricate JIC fittings include forged carbon steel, forged stainless steel, forged brass, machined brass, Monel and nickel-copper alloys.
External links • IHS [1]
References [1] http:/ / aero-defense. ihs. com/ document/ abstract/ FSCNGBAAAAAAAAAA
Kinematic coupling Kinematic coupling describes fixtures designed to exactly kinematically constrain the part in question. A canonical example of a kinematic coupling consists of three radial v-groves in one part that mate with three hemispheres in another, credited to Maxwell. Each hemisphere has two contact points for a total of six contact points, enough to constrain all six of the part's degrees of freedom. One alternative, favored by Kelvin, consists of three hemispheres on one part that fit respectively into a tetrahedral dent, a v groove, and a flat.
References External links • http://pergatory.mit.edu/perg/research/archive/Culpepper/kincouple.htm • http://pergatory.mit.edu/kinematiccouplings/
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Kinematic determinacy
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Kinematic determinacy Kinematic determinacy is a term used in structural mechanics to describe a structure where material compatibility conditions alone can be used to calculate deflections. A kinematically determinate structure can be defined as a structure where, if it is possible to find nodal displacements compatible with member extensions, those nodal displacements are unique. The structure has no possible mechanisms, i.e. nodal displacements, compatible with zero member extensions, at least to a first-order approximation. Mathematically, the mass matrix of the structure must have full rank. Kinematic determinacy can be loosely used to classify an arrangement of structural members as a structure (stable) instead of a mechanism (unstable). The principles of kinematic determinacy are used to design precision devices such as mirror mounts for optics, and precision linear motion bearings.
Kinematic diagram
PUMA robot
and its kinematic diagram
Kinematic diagram or kinematic scheme is diagram of a mechanism or machine that shows its moving parts and their relationships to each other. Elements of Kinematic diagrams include the frame, which is the frame of reference for all the moving components, as well as links, and joints. Primary Joints include pins, sliders and other elements that allow pure rotation or pure linear motion. Higher order joints also exist that allow a combination of rotation or linear motion. Kinematic diagrams also include points of interest, and other important components. Kinematic diagrams allow one to determine the geometric consequences of a mechanical design. For instance, in two dimensional space the degree of freedom can be determined using the Chebychev–Grübler–Kutzbach criterion from the number of links, the number of primary joints, and the number of higher order joints. A kinematic diagram is sometimes called a joint map or a skeleton diagram. For instance, the following diagram distinguishes between the various functions that arise in four-bars according to the lengths of their links:
Types of four-bar linkages, s = shortest link, ℓ = longest link
Laboratory for Energy Conversion
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Laboratory for Energy Conversion LEC Zurich, Switzerland Established 1892 Type
Public
Location
Zurich, Canton of Zurich, Switzerland 47°22′35.10″N 8°32′53.17″E
Campus
Urban
Website
[1]
The Laboratory for Energy Conversion (LEC) formerly known as Turbomachinery Laboratory (LSM) was founded in 1892 by Aurel Boleslaw Stodola. As part of the Federal Institute of Technology Zurich (ETH). The laboratory has been headed by some of the most prominent mechanical engineers in the history of turbomachinery.
Areas of research The current research projects at LEC cover the fields of: • • • • • • • • •
performance and reliability of wind energy minimizing high-cycle fatigue failure of compressors efficiency improvements of turbomachines aircraft noise suppression cooling and thermal management laser produced plasma source (EUV) and debris mitigation development of a mobile power pack novel measurement techniques biomedical diagnostics
Awards Amongst many noted achievements, LEC has recently developed the FENT probe[2] . This probe, for the first time, enables measurement of entropy generation in Turbomachinery. The highly rated peer-review journal Measurement Science and Technology recognised[3] the development of this probe as the most outstanding contribution in the field of fluid mechanics in 2008.
Professors since 1892 • • • • •
1892 - 1929 Aurel Boleslaw Stodola 1929 - 1954 Henri Quiby 1954 - 1983 Prof. Walter Traupel 1983 - 1998 George Gyarmathy 1998 - Prof. Reza Abhari
Laboratory for Energy Conversion
Industry partners • • • • • • • • • •
ABB Group, Switzerland BKW FMB Energie AG, Switzerland EOS Holding, Switzerland General Electric, US MAN Turbo AG, Switzerland Mitsubishi Heavy Industries, Japan MTU, Germany Siemens, US, Germany Swisselectric Research, Switzerland [4] Toshiba, Japan
References [1] http:/ / www. lec. ethz. ch [2] "Time-resolved entropy measurements using a fast response entropy probe" (http:/ / iopscience. iop. org/ 0957-0233/ 19/ 11/ 115401). Measurement Science and Technology. 17 September 2008. . [3] "Announcing the 2008 Measurement Science and Technology Outstanding Paper Awards" (http:/ / iopscience. iop. org/ 0957-0233/ 20/ 5/ 050101). Measurement Science and Technology. 1 May 2009. . [4] http:/ / www. swisselectric-research. ch/ E/ home/ home. html
External links • • • •
ETH Zurich (http://www.ethz.ch) Laboratory for Energy Conversion (http://www.lec.ethz.ch) Adlyte (http://www.adlyte.com) New Enterprise for Engineers (http://www.nefe.ethz.ch)
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Lamina emergent mechanisms (LEMs)
Lamina emergent mechanisms (LEMs) Lamina Emergent Mechanisms also known as LEMs are a subset of compliant mechanisms fabricated from planar materials (lamina) and have motion emerging from the fabrication plane. LEMs use compliance, or the deflection of flexible members to achieve motion.[1]
Background Ortho-Planar Mechanisms are an earlier concept similar to LEMs. [2] More well known LEMs include pop-up books [3] , flat-folding origami mechanisms, origami stents [4] , and deployable mechanisms. The research in LEMs also overlaps with deployable structures[5] , origami, kirigami, compliant mechanisms, Microelectromechanical systems, packaging engineering[6] , robotics[7] , paper engineering and more.
References [1] Jacobsen, J.O., Howell, L.L., Magleby, S.P., “Fundamental Components for Lamina Emergent Mechanisms,” Proceedings of the 2007 ASME International Mechanical Engineering Congress and Exposition, November 10-16, 2007, Seattle, WA, IMECE2007-42311. [2] Parise, J.J., Howell, L.L., and Magleby, S.P., “Ortho-Planar Mechanisms,” Proceedings of the 26th Biennial Mechanisms and Robotics Conference, at the 2000 ASME Design Engineering Technical Conference, Baltimore, Maryland, DETC2000/MECH-14193. [3] Winder, B.G., Magleby, S.P., and Howell, L.L., “Kinematic Representations of Pop-up Paper Mechanisms,” Proceedings of IDETC/CIE 2007 as part of the 2007 ASME Mechanisms and Robotics Conference, Las Vegas, NV, Sept. 4-7, 2007, DETC2007-35505. [4] http:/ / www. tulane. edu/ ~sbc2003/ pdfdocs/ 0257. PDF [5] Albrechtsen, N. B., Magleby, S.P., and Howell, L.L. "Identifying Potential Applications for Lamina Emergent Mechanisms Using Technology Push Product Development" Proceedings of IDETC/CIE2010 as part of the 2010 ASME Mechanisms and Robotics Conference, Montreal, Canada, Aug. 15-18, 2010, DETC2010-28531. [6] J.S. Dai and F. Cannella, Stiffness Characteristics of Carton Folds for Packaging, Transactions of the ASME: Journal of Mechanical Design, vol. 130, no. 2, page 022305_1-7, 2008. [7] Devin Balkcom, "Robotic Origami Folding," doctoral dissertation, tech. report CMU-RI-TR-04-43, Robotics Institute, Carnegie Mellon University, August, 2004
External links • • • •
Compliant Mechanism Research Group at BYU (http://research.et.byu.edu/llhwww/) Motion Structure research at Oxford (http://www-civil.eng.ox.ac.uk/people/zy/research/res.html) Rigid Origami Structure research by Tomohiro Tachi (http://www.tsg.ne.jp/TT/cg/index.html) Metamorphic Mechanism research at King's College London (http://www.kcl.ac.uk/nms/depts/engineering/ research/Robotics/researchprojects/kinematics.aspx) • Robotic Origami Folding research at Carnegie Mellon (http://www.ri.cmu.edu/publication_view. html?pub_id=4822)
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Larry Howell
Larry Howell Dr. Larry L. Howell received a B.S. degree in mechanical engineering from Brigham Young University and M.S. and Ph.D. degrees from Purdue University. His Ph.D. advisor was Ashok Midha, who is regarded as the "Father of Compliant Mechanisms." [1] Howell is currently a professor at Brigham Young University where his research includes compliant mechanisms and microelectromechanical systems. More recently, Howell has conducted research in lamina emergent mechanisms and nanoinjection.
Biography Howell joined the BYU faculty in 1994 and served as Chair of the Department of Mechanical Engineering from 2001 to 2007.[2] Prior to joining BYU, he was a Visiting Professor at Purdue University, a Finite-Element Analyst for Engineering Methods, Inc., and he was an engineer on the design of the YF-22, the first prototype of the U.S. Air Force F-22 Raptor. His patents and technical publications focus on compliant mechanisms and microelectromechanical systems. He is the author of the book Compliant Mechanisms,[3] which is available in English and Chinese. Dr. Howell is a Fellow of the American Society of Mechanical Engineers (ASME), the Past Chair of the ASME Mechanisms and Robotics Committee, and a past Associate Editor for the Journal of Mechanical Design. His research has been recognized by the BYU Maeser Research Award, the National Science Foundation CAREER Award,[4] and the ASME Mechanisms and Robotics Award, among others. Dr. Howell is originally from Portage, a small city in Northern Utah with a 2000 census population of 257 people.
Books Howell, L.L., Compliant Mechanisms, John Wiley & Sons, New York, NY, 2001. Chinese Translation of Compliant Mechanisms published (under agreement with Wiley), by Higher Education Press, an official publisher of the State Education Department of China. Translator: Professor Yue-Qing Yu.
Selected Articles Ferrell, D.B., Isaac, Y.F., Magleby, S.P., Howell, L.L., "Development of Criteria for Lamina Emergent Mechanism Flexures with Specific Application to Metals", Journal of Mechanical Design, Vol. 133, pp. 031009–1 to 031009-9, March 2011. Howell, L.L., DiBiasio, C.M., Cullinan, M.A., Panas, R., and Culpepper, M.L., “A Pseudo-Rigid-Body Model for Large Deflections of Fixed-Clamped Carbon Nanotubes,” Journal of Mechanisms & Robotics, Vol. 2, No. 3, 034501-1 to 034501-5. David, R.A., Jensen, B.D., Black, J. L., Burnett, S. H., Howell, L. L., "Modeling and Experimental Validation of DNA Motion in Uniform and Nonuniform DC Electric Fields", Journal of Nanotechnology in Engineering and Medicine, Vol. 1, October 2010. Chen, G., Aten, Q.T., Zirbel, S., Jensen, B.D., Howell, L.L., “A Tristable Mechanism Configuration Employing Orthogonal Compliant Mechanisms,” J. Mechanisms and Robotics, vol. 2,pp. 14501–1–14501-6, Feb. 2010. Jacobsen, J.O., Winder, B.G., Howell, L.L., Magleby, S.P., "Lamina Emergent Mechanisms and their Basic Elements", Journal of Mechanisms and Robotics, Vol. 2, February 2010. Halverson, P.A., Howell, L.L., and Magleby, S.P., “Tension-Based Multi-stable Compliant Rolling-contact Elements,” Mechanism & Machine Theory, Vol. 45, No. 2, pp. 147–156, 2010.
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Larry Howell Winder, B.G., Magleby, S.P., and Howell, L.L., “Kinematic Representations of Pop-up Paper Mechanisms,” Journal of Mechanisms & Robotics, Vol. 1, No. 2, 021009-1 to 021009-10, 2009. (Also presented in Proceedings of IDETC/CIE 2007 as part of the 2007 ASME Mechanisms and Robotics Conference, Las Vegas, NV, Sept. 4-7, 2007, DETC2007-35505.) Anderson, C.S., Magleby, S.P., Howell, L.L., "Principles and Preliminary Concepts for Compliant Mechanically Reactive Armor", ASME/IFToMM International Conference on Reconfigurable Mechanisms and Robots, 2009. Dibiasio, C.M., Culpepper, M.L., Panas, R., Howell, L.L., and Magleby, S.P., “Comparison of Molecular Simulation and Pseudo-Rigid-Body Model Predictions for a Carbon Nanotube-Based Compliant Parallel-Guiding Mechanism,” Journal of Mechanical Design, Vol. 130, April 2008. Berglund, M., Magleby, S., and Howell, L.L., “Design Rules for Selecting and Designing Compliant Mechanisms for Rigid-Body Replacement Synthesis,” Proceedings of the 26th Design Automation Conference, at the 2000 ASME Design Engineering Technical Conference, Baltimore, Maryland, DETC2000/DAC-14225. Murphy, M.D., Midha, A., and Howell, L.L., “The Topological Synthesis of Compliant Mechanisms,” Mechanism and Machine Theory, Vol. 31, No. 2, pp. 185–199, 1996. Howell, L.L. and Midha, A., “A Loop-Closure Theory for the Analysis and Synthesis of Compliant Mechanisms,” Journal of Mechanical Design, Trans. ASME, Vol. 118, pp. 121–125, March 1996.
Selected Patents Compliant bistable micromechanism US Pat. 7075209 Compliant, ortho-planar, linear motion spring US Pat. 6983924 Micromechanical positional state sensing apparatus method and system US Pat. 7616013 Bistable micromechanical devices US Pat. 7554342 Compliant overrunning clutch with centrifugal throw-out US Pat. 6148979
References [1] [2] [3] [4]
http:/ / www. seas. upenn. edu/ ~gksuresh/ mylinks. html http:/ / me. byu. edu/ faculty/ larryhowell http:/ / www. wiley. com/ WileyCDA/ WileyTitle/ productCd-047138478X. html Journal of Mechanical Design, Vol. 126, No. 6, pp. 941–942, November 2004
External links • Compliant Mechanism Research Group (http://cmr.byu.edu/)
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Light Aid Detachment
Light Aid Detachment A Light Aid Detachment is an attached independent minor unit of the Royal Electrical and Mechanical Engineers or Detachment of Royal Canadian Electrical and Mechanical Engineers operating as a sub-unit of the supported unit. These units provide dedicated logistic support to every field unit of the British Army or Canadian Army. REME and RCEME were created in October 1942 out of elements of the Royal Army Ordnance Corps, Royal Engineers, Royal Corps of Signals, Royal Army Service Corps and Royal Canadian Ordnance Corps who previously handled functions such as the repair of weapons, optics and vehicles.[1] In the RCEME LADs were divisions of larger units known as Workshops.[1] In the British Army the title Workshop (Wksp) is used both for major REME units (Field for Brigades or Armoured for Divisions) and for those minor units which provide some 2nd Line support to the parent regiment. The term LAD is therefore restricted to only those minor REME units which solely provide 1st Line support, typically this is Armour and Infantry units. REME minor units supporting RA, R Signals, RE, RLC etc. are normally titled as Wksp as they also provide some degree of 2nd line support to the parent unit. Typically composed of around 60-80 personnel they are attached to a host battalion. Typical field deployment would split the LAD/Wksp into a regimental "B Echelon" contingent of about 30 men and 4 "fitter sections" of about 7-12 men, each of which is attached to a company/squadron. The fitter sections are part of the A Echelon HQ of the company/squadron. This average configuration does, of course, vary widely dependent on the parent unit and their equipment.
References [1] RCEME article (http:/ / www. canadiansoldiers. com/ mediawiki-1. 5. 5/ index. php?title=RCEME)
Limits and fits In mechanical engineering, limits and fits are a set of rules how many thousandths of an inch a part's measurement is to be under or over the theoretical size to achieve various sorts of fit (sliding fit, rotating fit, non-sliding fit, loose fit, etc.)
External links • http://mechanical-design-handbook.blogspot.com/2009/10/standards-of-limits-and-fits-for-mating.html • http://gometricusa.org/metric-limits-and-fits-convert.html
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List of gear nomenclature
316
List of gear nomenclature Gears have a wide range of unique terminology known as gear nomenclature. Many of the terms defined cite the same reference work.[1]
Addendum The addendum is the height by which a tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line; also, the radial distance between the pitch circle and the addendum circle.[1]
Addendum angle Addendum angle in a bevel gear, is the angle between elements of the face cone and pitch cone.[1]
Principal dimensions
Addendum circle The addendum circle coincides with the tops of the teeth of a gear and is concentric with the standard (reference) pitch circle and radially distant from it by the amount of the addendum. For external gears, the addendum circle lies on the outside cylinder while on internal gears the addendum circle lies on the internal cylinder.[1]
Internal gear diameters
Root circle
List of gear nomenclature
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Apex to back Apex to back, in a bevel gear or hypoid gear, is the distance in the direction of the axis from the apex of the pitch cone to a locating surface at the back of the blank.[1]
Back angle The back angle of a bevel gear is the angle between an element of the back cone and a plane of rotation, and usually is equal to the pitch angle.[1] Apex to back
Mounting distance
Back cone The back cone of a bevel or hypoid gear is an imaginary cone tangent to the outer ends of the teeth, with its elements perpendicular to those of the pitch cone. The surface of the gear blank at the outer ends of the teeth is customarily formed to such a back cone.[1]
Back cone distance Back cone distance in a bevel gear is the distance along an element of the back cone from its apex to the pitch cone.[1] Principal dimensions
List of gear nomenclature
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Base circle The base circle of an involute gear is the circle from which involute tooth profiles are derived.[1]
Involute teeth
Base cylinder The base cylinder corresponds to the base circle, and is the cylinder from which involute tooth surfaces are developed.[1]
Base cylinder
Base diameter The base diameter of an involute gear is the diameter of the base circle.[1]
Bull gear The term bull gear is used to refer to the larger of two spur gears that are in engagement in any machine. The smaller gear is usually referred to as a pinion.
Base diameter
List of gear nomenclature
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Center distance Center distance (operating) is the shortest distance between non-intersecting axes. It is measured along the mutual perpendicular to the axes, called the line of centers. It applies to spur gears, parallel axis or crossed axis helical gears, and worm gearing.[1]
Center distance
Central plane The central plane of a worm gear is perpendicular to the gear axis and contains the common perpendicular of the gear and worm axes. In the usual case with axes at right angles, it contains the worm axis.[1]
Central plane
Composite action test The composite action test (double flank) is a method of inspection in which the work gear is rolled in tight double flank contact with a master gear or a specified gear, in order to determine (radial) composite variations (deviations). The composite action test must be made on a variable center distance composite action test device.[1]
Schematic of the composite action test
List of gear nomenclature
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Cone distance Cone distance in a bevel gear is the general term for the distance along an element of the pitch cone from the apex to any given position in the teeth.[1] Outer cone distance in bevel gears is the distance from the apex of the pitch cone to the outer ends of the teeth. When not otherwise specified, the short term cone distance is understood to be outer cone distance. Mean cone distance in bevel gears is the distance from the apex of the pitch cone to the middle of the face width. Inner cone distance in bevel gears is the distance from the apex of the pitch cone to the inner ends of the teeth. Cone distance
Conjugate gears Conjugate gears transmit uniform rotary motion from one shaft to another by means of gear teeth. The normals to the profiles of these teeth, at all points of contact, must pass through a fixed point in the common centerline of the two shafts.[1]
Crossed helical gear A crossed helical gear is a gear that operate on non-intersecting, non-parallel axes. The term crossed helical gears has superseded the term spiral gears. There is theoretically point contact between the teeth at any instant. They have teeth of the same or different helix angles, of the same or opposite hand. A combination of spur and helical or other types can operate on crossed axes.[1]
Crossing point The crossing point is the point of intersection of bevel gear axes; also the apparent point of intersection of the axes in hypoid gears, crossed helical gears, worm gears, and offset face gears, when projected to a plane parallel to both axes.[1]
Crown circle The crown circle in a bevel or hypoid gear is the circle of intersection of the back cone and face cone.[1]
Crowned teeth
List of gear nomenclature
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Crowned teeth have surfaces modified in the lengthwise direction to produce localized contact or to prevent contact at their ends.[1]
Dedendum angle Dedendum angle in a bevel gear, is the angle between elements of the root cone and pitch cone.[1]
Crowned gear
Equivalent pitch radius Equivalent pitch radius is the radius of the pitch circle in a cross section of gear teeth in any plane other than a plane of rotation. It is properly the radius of curvature of the pitch surface in the given cross section. Examples of such sections are the transverse section of bevel gear teeth and the normal section of helical teeth. Back cone equivalent
Face (tip) angle Face (tip) angle in a bevel or hypoid gear, is the angle between an element of the face cone and its axis.[1]
Face cone The face cone, also known as the tip cone is the imaginary surface that coincides with the tops of the teeth of a bevel or hypoid gear.[1]
Face gear A face gear set typically consists of a disk-shaped gear, grooved on at least one face, in combination with a spur, helical, or conical pinion. A face gear has a planar pitch surface and a planar root surface, both of which are perpendicular to the axis of rotation.[1] It can also be referred to as a face wheel, crown gear, crown wheel, contrate gear or contrate wheel.
Face worm gear
List of gear nomenclature
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Face width The face width of a gear is the length of teeth in an axial plane. For double helical, it does not include the gap.[1] Total face width is the actual dimension of a gear blank including the portion that exceeds the effective face width, or as in double helical gears where the total face width includes any distance or gap separating right hand and left hand helices. For a cylindrical gear, effective face width is the portion that contacts the mating teeth. One member of a pair of gears may engage only a portion of its mate. For a bevel gear, different definitions for effective face width are applicable.
Face width
Form diameter Form diameter is the diameter of a circle at which the trochoid (fillet curve) produced by the tooling intersects, or joins, the involute or specified profile. Although these terms are not preferred, it is also known as the true involute form diameter (TIF), start of involute diameter (SOI), or when undercut exists, as the undercut diameter. This diameter cannot be less than the base circle diameter.[1]
Front angle The front angle, in a bevel gear, denotes the angle between an element of the front cone and a plane of rotation, and usually equals the pitch angle.[1]
Form diameter
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Front cone The front cone of a hypoid or bevel gear is an imaginary cone tangent to the inner ends of the teeth, with its elements perpendicular to those of the pitch cone. The surface of the gear blank at the inner ends of the teeth is customarily formed to such a front cone, but sometimes may be a plane on a pinion or a cylinder in a nearly flat gear.[1]
Gear center A gear center is the center of the pitch circle.[1]
Heel The heel of a tooth on a bevel gear or pinion is the portion of the tooth surface near its outer end. The toe of a tooth on a bevel gear or pinion is the portion of the tooth surface near its inner end.[1]
Helical rack A helical rack has a planar pitch surface and teeth that are oblique to the direction of motion.[1]
Heel and toe
Index deviation The displacement of any tooth flank from its theoretical position, relative to a datum tooth flank. Distinction is made as to the direction and algebraic sign of this reading. A condition wherein the actual tooth flank position was nearer to the datum tooth flank, in the specified measuring path direction (clockwise or counterclockwise), than the theoretical position would be considered a minus (-) deviation. A condition wherein the actual tooth flank position was farther from the datum tooth flank, in the specified measuring path direction, than the theoretical position would be considered a plus (+) deviation. The direction of tolerancing for index deviation along the arc of the tolerance diameter circle within the transverse plane.[1]
List of gear nomenclature
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Inside cylinder The inside cylinder is the surface that coincides with the tops of the teeth of an internal cylindrical gear.[1]
Diameters, Internal Gear
Inside diameter Inside diameter is the diameter of the addendum circle of an internal gear, this is also known as minor diameter.[1]
Internal gear diameters
Involute polar angle Expressed as θ, the involute polar angle is the angle between a radius vector to a point, P, on an involute curve and a radial line to the intersection, A, of the curve with the base circle.[1]
Involute polar angle
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Involute roll angle Expressed as ε, the involute roll angle is the angle whose arc on the base circle of radius unity equals the tangent of the pressure angle at a selected point on the involute.[1]
Involute roll angle
Involute teeth Involute teeth of spur gears, helical gears, and worms are those in which the profile in a transverse plane (exclusive of the fillet curve) is the involute of a circle.[1]
Involute teeth
Lands Bottom land The bottom land is the surface at the bottom of a gear tooth space adjoining the fillet.[1]
Top land Top land is the (sometimes flat) surface of the top of a gear tooth.[1] Top and bottom lands
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Line of centers The line of centers connects the centers of the pitch circles of two engaging gears; it is also the common perpendicular of the axes in crossed helical gears and wormgears. When one of the gears is a rack, the line of centers is perpendicular to its pitch line.[1]
Mounting distance Mounting distance, for assembling bevel gears or hypoid gears, is the distance from the crossing point of the axes to a locating surface of a gear, which may be at either back or front.[1]
Normal module Normal module is the value of the module in a normal plane of a helical gear or worm.[1] Mounting distance
Normal plane A normal plane is normal to a tooth surface at a pitch point, and perpendicular to the pitch plane. In a helical rack, a normal plane is normal to all the teeth it intersects. In a helical gear, however, a plane can be normal to only one tooth at a point lying in the plane surface. At such a point, the normal plane contains the line normal to the tooth surface. Important positions of a normal plane in tooth measurement and tool design of helical teeth and worm threads are:
Planes at a pitch point on a helical tooth
1. the plane normal to the pitch helix at side of tooth; 2. the plane normal to the pitch helix at center of tooth; 3. the plane normal to the pitch helix at center of space between two teeth In a spiral bevel gear, one of the positions of a normal plane is at a mean point and the plane is normal to the tooth trace.[1]
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Offset Offset is the perpendicular distance between the axes of hypoid gears or offset face gears.[1] In the diagram to the right, (a) and (b) are referred to as having an offset below center, while those in (c) and (d) have an offset above center. In determining the direction of offset, it is customary to look at the gear with the pinion at the right. For below center offset the pinion has a left hand spiral, and for above center offset the pinion has a right hand spiral.
Offset
Outside cylinder The outside (tip or addendum) cylinder is the surface that coincides with the tops of the teeth of an external cylindrical gear.[1]
Cylindrical surfaces
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Outside diameter The outside diameter of a gear is the diameter of the addendum (tip) circle. In a bevel gear it is the diameter of the crown circle. In a throated wormgear it is the maximum diameter of the blank. The term applies to external gears, this is can also be known from major diameter.[1]
Wormgear diameters
Pitch angle Pitch angle in bevel gears, is the angle between an element of a pitch cone and its axis. In external and internal bevel gears, the pitch angles are respectively less than and greater than 90 degrees.[1]
Pitch circle A pitch circle (operating) is the curve of intersection of a pitch surface of revolution and a plane of rotation. It is the imaginary circle that rolls without slipping with a pitch circle of a mating gear.[1] These are the outline off the imaginary smooth roller or friction discs in every pair of mating gear. Many important measurement are taken on and from these circle.[1]
Angle relationships
Angles
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Pitch cone A pitch cone is the imaginary cone in a bevel gear that rolls without slipping on a pitch surface of another gear.[1]
Pitch cones
Pitch cylinder A pitch cylinder is the imaginary cylinder in a spur or helical gear that rolls without slipping on a pitch plane or pitch cylinder of another gear.[1]
Pitch cylinder
Pitch helix The pitch helix is the intersection of the tooth surface and the pitch cylinder of a helical gear or cylindrical worm.[1]
Base helix The base helix of a helical, involute gear or involute worm lies on its base cylinder. Tooth helix
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Base helix angle Base helix angle is the helix angle on the base cylinder of involute helical teeth or threads.
Base lead angle Base lead angle is the lead angle on the base cylinder. It is the complement of the base helix angle.
Outside helix The outside (tip or addendum) helix is the intersection of the tooth surface and the outside cylinder of a helical gear or cylindrical worm.
Outside helix angle Outside helix angle is the helix angle on the outside cylinder.
Outside lead angle Outside lead angle is the lead angle on the outside cylinder. It is the complement of the outside helix angle.
Normal helix A normal helix is a helix on the pitch cylinder, normal to the pitch helix.
Pitch line
Normal helix
The pitch line corresponds, in the cross section of a rack, to the pitch circle (operating) in the cross section of a gear.[1]
Pitch point The pitch point is the point of tangency of two pitch circles (or of a pitch circle and pitch line) and is on the line of centers.[1]
Pitch surfaces
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Pitch surfaces are the imaginary planes, cylinders, or cones that roll together without slipping. For a constant velocity ratio, the pitch cylinders and pitch cones are circular.[1]
Pitch surfaces
Planes
Pitch cones
Pitch plane The pitch plane of a pair of gears is the plane perpendicular to to the axial plane and tangent to the pitch surfaces. A pitch plane in an individual gear may be any plane tangent to its pitch surface. The pitch plane of a rack or in a crown gear is the imaginary planar surface that rolls without slipping with a pitch cylinder or pitch cone of another gear. The pitch plane of a rack or crown gear is also the pitch surface.[1]
Transverse plane The transverse plane is perpendicular to the axial plane and to the pitch plane. In gears with parallel axes, the transverse and the plane of rotation coincide.[1]
Pitch planes
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Principal directions Principal directions are directions in the pitch plane, and correspond to the principal cross sections of a tooth. The axial direction is a direction parallel to an axis. The transverse direction is a direction within a transverse plane. The normal direction is a direction within a normal plane.[1]
Principal directions
Profile radius of curvature Profile radius of curvature is the radius of curvature of a tooth profile, usually at the pitch point or a point of contact. It varies continuously along the involute profile.[1]
Fillet radius
Radial composite deviation Tooth-to-tooth radial composite deviation (double flank) is the greatest change in center distance while the gear being tested is rotated through any angle of 360 degree/z during double flank composite action test. Tooth-to-tooth radial composite tolerance (double flank) is the permissible amount of tooth-to-tooth radial composite deviation.
Total composite variation trace
Total radial composite deviation (double flank) is the total change in center distance while the gear being tested is rotated one complete revolution during a double flank composite action test. Total radial composite tolerance (double flank) is the permissible amount of total radial composite deviation.[1]
List of gear nomenclature
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Root angle Root angle in a bevel or hypoid gear, is the angle between an element of the root cone and its axis.[1]
Root circle The root circle coincides with the bottoms of the tooth spaces.[1]
Internal gear diameters
Root cone The root cone is the imaginary surface that coincides with the bottoms of the tooth spaces in a bevel or hypoid gear.[1]
Root cylinder The root cylinder is the imaginary surface that coincides with the bottoms of the tooth spaces in a cylindrical gear.[1]
Principal dimensions
Shaft angle A shaft angle is the angle between the axes of two non-parallel gear shafts. In a pair of crossed helical gears, the shaft angle lies between the oppositely rotating portions of two shafts. This applies also in the case of worm gearing. In bevel gears, the shaft angle is the sum of the two pitch angles. In hypoid gears, the shaft angle is given when starting a design, and it does not have a fixed relation to the pitch angles and spiral angles.[1]
Spiral gear See: Crossed helical gear.
Shaft angle
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Spur gear A spur gear has a cylindrical pitch surface and teeth that are parallel to the axis.[1]
Spur rack A spur rack has a planar pitch surface and straight teeth that are at right angles to the direction of motion.[1]
Standard pitch circle The standard pitch circle is the circle which intersects the involute at the point where the pressure angle is equal to the profile angle of the basic rack.[1]
Standard pitch diameter The standard reference pitch diameter is the diameter of the standard pitch circle. In spur and helical gears, unless otherwise specified, the standard pitch diameter is related to the number of teeth Spur gear and the standard transverse pitch. The diameter can be roughly estimated by taking the average of the diameter measuring the tips of the gear teeth and the base of the gear teeth.[1] The pitch diameter is useful in determining the spacing between gear centers because proper spacing of gears implies tangent pitch circles. The pitch diameters of two gears may be used to calculate the gear ratio in the same way the number of teeth is used.
Where
is the total number of teeth,
is the circular pitch,
is the diametrical pitch, and
is the helix angle
for helical gears.
Standard reference pitch diameter The standard reference pitch diameter is the diameter of the standard pitch circle. In spur and helical gears, unless otherwise specified, the standard pitch diameter is related to the number of teeth and the standard transverse pitch. It is obtained as:[1]
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Test radius The test radius (Rr) is a number used as an arithmetic convention established to simplify the determination of the proper test distance between a master and a work gear for a composite action test. It is used as a measure of the effective size of a gear. The test radius of the master, plus the test radius of the work gear is the set up center distance on a composite action test device. Test radius is not the same as the operating pitch radii of two tightly meshing gears unless both are perfect and to basic or standard tooth thickness.[1]
Throat diameter The throat diameter is the diameter of the addendum circle at the central plane of a wormgear or of a double-enveloping wormgear.[1]
Throat form radius Throat form radius is the radius of the throat of an enveloping wormgear or of a double-enveloping worm, in an axial plane.[1]
Wormgear diameters
Tip radius Tip radius is the radius of the circular arc used to join a side-cutting edge and an end-cutting edge in gear cutting tools. Edge radius is an alternate term.[1]
Tip radius
Tip relief
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Tip relief is a modification of a tooth profile whereby a small amount of material is removed near the tip of the gear tooth.[1]
Tip relief
Tooth surface
Profile of a spur gear
Notation and numbering for an external gear
Notation and numbering for an internal gear
The tooth surface (flank) forms the side of a gear tooth.[1] It is convenient to choose one face of the gear as the reference face and to mark it with the letter “I”. The other non-reference face might be termed face “II”. For an observer looking at the reference face, so that the tooth is seen with its tip uppermost, the right flank is on the right and the left flank is on the left. Right and left flanks are denoted by the letters “R” and “L” respectively.
References [1] Gear Nomenclature, Definition of Terms with Symbols. American Gear Manufacturers Association. ISBN 1-55589-846-7. OCLC 65562739. ANSI/AGMA 1012-G05.
Machine (mechanical)
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Machine (mechanical) The mechanical properties of a machine manage power to achieve desired forces and movement. A machine consists of a power source and actuators that generate forces and movement, and a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. Modern machines often include computers and sensors that monitor performance and plan movement, and are called mechanical systems. The meaning of the word "machine" is traced by the Oxford English Dictionary[1] to an independently functioning structure and by Merriam-Webster Dictionary[2] to something that has been constructed. This includes human design into the meaning of machine. The adjective "mechanical" refers to skill in the practical application of an art or science, as well as relating to or caused by movement, physical forces, properties or agents such as is dealt with by mechanics.[1] Similarly Merriam-Webster Dictionary[2] defines "mechanical" as relating to machinery or tools. Power flow through a machine provides a way to understand the performance of devices ranging from levers and gear trains to automobiles and robotic systems. The German mechanician Franz Reuleaux[3] wrote "a machine is a combination of resistant bodies so arranged that by their means the mechanical forces of nature can be compelled to do work accompanied by certain determinate motion." Notice that forces and motion combine to define power. More recently, Uicker et al.[4] state that a machine is "a device for applying power or changing its direction." And McCarthy and Soh[5] describe a machine as a system that "generally consists of a power source and a mechanism for the controlled use of this power."
Simple machines The idea that a machine can be decomposed into simple movable elements led Archimedes to define the lever, pulley and screw as simple machines. By the time of the Renaissance this list increased to include the wheel and axle, wedge and inclined plane. The modern approach to characterizing machines focusses on the components that allow movement, known as joints. Theo Jansen's kinetic sculpture Strandbeest. A wind-driven walking machine.
Machine (mechanical)
338 Wedge (hand axe): Perhaps the first example of a device designed to manage power is the hand axe, also see biface and Olorgesailie. A hand axe is made by chipping stone, generally flint, to form a bifacial edge, or wedge. A wedge is a simple machine that transforms lateral force and movement of the tool into a transverse splitting force and movement of the workpiece. The available power is limited by the effort of the person using the tool, but because power is the product of force and movement, the wedge amplifies the force by reducing the movement. This amplification, or mechanical advantage is the ratio of the input speed to output speed. For a wedge this is given by 1/tanα, where α is the tip angle. The faces of a wedge are modeled as straight lines to form a sliding or prismatic joint.
Lever: The lever is another important and simple device for managing power. This is a body that pivots on a fulcrum. Because the velocity of a point farther from the pivot is greater than the velocity of a point near the pivot, forces applied far from the pivot are amplified near the pivot by the associated decrease in speed. If a is the distance from the pivot to the point where the input force is applied and b is the distance to the point where the output force is applied, then a/b is the mechanical advantage of the lever. The fulcrum of a lever is modeled as a hinged or revolute joint. Flint hand axe found in Winchester
Wheel: The wheel is clearly an important early machine, such as the chariot. A wheel uses the law of the lever to reduce the force needed to overcome friction when pulling a load. To see this notice that the friction associated with pulling a load on the ground is approximately the same as the friction in a simple bearing that supports the load on the axle of a wheel. However, the wheel forms a lever that magnifies the pulling force so that it overcomes the frictional resistance in the bearing.
Power sources Natural forces such as wind and water powered larger mechanical systems. Waterwheels appeared around the world around 300 BC to use flowing water to generate rotary motion, which was applied to milling grain, and powering lumber, machining and textile operations. Modern water turbines use water flowing through a dam to drive an electric generator. Early windmills captured wind power to generate rotary motion for milling operations. Modern wind turbines also drives a generator. This electricity in turn is used to drive motors forming the actuators of mechanical systems. The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices. See Merriam-Webster's definition of engine [6]. A steam engine uses heat to boil water contained in a pressure vessel; the expanding steam drives a piston or a turbine. This principle can be seen in the aeolipile of Hero of Alexandria. This is called an external combustion engine. An automobile engine is called an internal combustion engine because it burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston. A jet engine uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft, and so is also an "internal combustion engine." [7] The heat from coal and natural gas combustion in a boiler generates steam that drives a steam turbine to rotate an electric generator. A nuclear power plant uses heat from a nuclear reactor to generate steam and electric power. This power is distributed through a network of transmission lines for industrial and individual use. Electric motors use either AC or DC electric current to generate rotational movement. Electric servomotors are the actuators for mechanical systems ranging from robotic systems to modern aircraft. Hydraulic and pneumatic systems use electrically driven pumps to drive water or air respectively into cylinders to power linear movement.
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Mechanisms A machine consists of an actuator input, a system of mechanisms that generate the output forces and movement, and an interface to the user. Electric motors, hydraulic and pneumatic actuators provide the input forces and movement. This input is shaped by mechanisms consisting of gears and gear trains, belt and chain drives, cam and follower mechanisms, and linkages as well as friction devices such as brakes and clutches. Structural components consist of the frame, fasteners, bearings, springs, lubricants and seals, as well as a variety of specialized machine elements such as splines, pins and keys.[3] [4] The user interface ranges from switches and buttons to programmable logic controllers and includes the covers that provide texture, color and styling.
Gears and gear trains The transmission of rotation between contacting toothed wheels can be traced back to the Antikythera mechanism of Greece and the South Pointing Chariot of China. Illustrations by the renaissance scientist Georgius Agricola show gear trains with cylindrical teeth. The implementation of the involute tooth yielded a standard gear design that provides a constant speed ratio. Some important features of gears and gear trains are: • The ratio of the pitch circles of mating gears defines the speed ratio and the mechanical advantage of the gear set.
The Antikythera mechanism (main fragment)
• A planetary gear train provides high gear reduction in a compact package. • It is possible to design gear teeth for gears that are
non-circular, yet still transmit torque smoothly. • The speed ratios of chain and belt drives are computed in the same way as gear ratios. See bicycle gearing.
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Cam and follower mechanisms A cam and follower is formed by the direct contact of two specially shaped links. The driving link is called the cam (also see cam shaft) and the link that is driven through the direct contact of their surfaces is called the follower. The shape of the contacting surfaces of the cam and follower determines the movement of the mechanism.
Linkages A linkage is a collection of links connected by joints. Generally, the links are the structural elements and the joints allow movement. Perhaps the single most useful example is the planar four-bar linkage. However, there are many more special linkages: • Watt's linkage is a four-bar linkage that generates an approximate straight line. It was critical to the operation of his design for the steam engine. This linkage also appears in vehicle suspensions to prevent side-to-side movement of the body relative to the wheels. Also see the article Parallel motion. • The success of Watt's linkage lead to the design of similar approximate straight-line linkages, such as Hoeken's linkage and Chebyshev's linkage. • The Peaucellier linkage generates a true straight-line output from a rotary input.
Schematic of the actuator and four-bar linkage that position an aircraft landing gear.
• The Sarrus linkage is a spatial linkage that generates straight-line movement from a rotary input. Select this link for an animation of the Sarrus linkage [8] • The Klann linkage and the Jansen linkage are recent inventions that provide interesting walking movements. They are respectively a six-bar and an eight-bar linkage.
Flexure mechanisms A flexure mechanism consisted of a series of rigid bodies connected by compliant elements (also known as flexure joints) that is designed to produce a geometrically well-defined motion upon application of a force.
Structural components A number of machine elements provide important structural functions such as the frame, bearings, splines, spring and seals. • The recognition that the frame of a mechanism is an important machine element changed the name three-bar linkage into four-bar linkage. Frames are generally assembled from truss or beam elements. • Bearings are components designed to manage the interface between moving elements and are the source of friction in machines. In general, bearings are designed for pure rotation or straight line movement. • Splines and keys are two ways to reliably mount an axle to a wheel, pulley or gear so that torque can be transferred through the connection.
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• Springs provides forces that can either hold components of a machine in place or acts as a suspension to support part of a machine. • Seals are used between mating parts of a machine to ensure fluids, such as water, hot gases, or lubricant do not leak between the mating surfaces. • Fasteners such as screws, bolts, spring clips, and rivets are critical to the assembly of components of a machine. Fasteners are generally considered to be removable. In contrast, joining methods, such as welding, soldering, crimping and the application of adhesives, usually require cutting the parts to disassemble the components
Mechanics Usher[9] reports that Hero of Alexandria's treatise on Mechanics focussed on the study of lifting heavy weights. Today mechanics refers to the mathematical analysis of the forces and movement of a mechanical system, and consists of the study of the kinematics and dynamics of these systems.
Kinematics of Mechanisms Kinematics applies geometry to the analysis of movement in a mechanical system. The rotation and sliding movement central to mechanical systems are modeled mathematically as Euclidean, or rigid, transformations. The set of rigid transformations in three dimensional space forms a Lie group, denoted as SE(3). Planar mechanisms: While all mechanisms in a mechanical system are three dimensional, they can be analyzed using plane geometry, if the movement of the individual components are constrained so all point trajectories are parallel to a plane. In this case the system is called a planar mechanism. The kinematic analysis of planar mechanisms uses the subset of SE(3) consisting of planar rotations and translations, denote SE(2). The group SE(2) is three dimensional, which means that every position of a body in the plane is defined by three parameters. The parameters are often the x and y coordinates of the origin of a coordinate frame in M measured from the origin of a coordinate frame in F, and the angle measured from the x-axis in F to the x-axis in M. This is often described saying a body in the plane has three degrees-of-freedom. The pure rotation of a hinge and the linear translation of a slider can be identified with subgroups of SE(2), and define the two joints one degree-of-freedom joints of planar mechanisms. The cam joint formed by two surfaces in sliding and rotating contact is a two degree-of-freedom joint. Select this link to see Theo Jansen's Strandbeest linkages
[10]
walking machine with legs constructed from planar eight-bar
Spherical mechanisms: It is possible to construct a mechanism such that the point trajectories in all components lie in concentric spherical shells around a fixed point. An example is the gimbaled gyroscope. These devices are called spherical mechanisms.[5] Spherical mechanisms are constructed by connecting links with hinged joints such that the axes of each hinge passes through the same point. This point becomes center of the concentric spherical shells. The movement of these mechanisms is characterized by the group SO(3) of rotations in three dimensional space. Other examples of spherical mechanisms are the automotive differential and the robotic wrist. Select this link for an animation of a Spherical deployable mechanism [11]. The rotation group SO(3) is three dimensional. An example of the three parameters that specify a spatial rotation are the roll, pitch and yaw angles used to define the orientation of an aircraft. Spatial mechanisms: A mechanism in which a body moves through a general spatial movement is called a spatial mechanism. An example is the RSSR linkage, which can be viewed as a four-bar linkage in which the hinged joints of the coupler link are replaced by rod ends, also called spherical joints or ball joints. The rod ends allow the input and output cranks of the RSSR linkage to be misaligned to the point that they lie in different planes, which causes the coupler link to move in a general spatial movement. Robot arms, Stewart platforms, and humanoid robotic systems are also examples of spatial mechanisms.
Machine (mechanical) Select this link for an animation of Bennett's linkage [12], which is a spatial mechanism constructed from four hinged joints. The group SE(3) is six dimensional, which means the position of a body in space is defined by six parameters. Three of the parameters define the origin of the moving reference frame relative to the fixed frame. Three other parameters define the orientation of the moving frame relative to the fixed frame.
References [1] [2] [3] [4] [5] [6] [7]
Oxford English Dictionary Merriam-Webster Dictionary Definition of machine (http:/ / www. merriam-webster. com/ dictionary/ machine) Reuleaux, F., 1876 'The Kinematics of Machinery,' (trans. and annotated by A. B. W. Kennedy), reprinted by Dover, New York (1963) J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York. J. M. McCarthy and G. S. Soh, 2010, Geometric Design of Linkages, Springer, New York. http:/ / www. merriam-webster. com/ dictionary/ engine "Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 998 . [8] http:/ / mechanicaldesign101. com/ 2009/ 04/ 27/ c-j-sangwins-linkage-movies/ [9] A. P. Usher, 1929, A History of Mechanical Inventions, Harvard University Press, (reprinted by Dover Publications 1968). [10] http:/ / mechanicaldesign101. com/ 2010/ 06/ 11/ theo-jansens-site/ [11] http:/ / mechanicaldesign101. com/ 2009/ 04/ 27/ spherical-rhombus-linkage-assembly/ [12] http:/ / mechanicaldesign101. com/ 2009/ 04/ 27/ linkage-animations-on-sythetica
Further reading • Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain. ed. Machinery's Handbook (26th edition ed.). New York: Industrial Press Inc.. ISBN 0-8311-2635-3. • Reuleaux, Franz; (trans. and annotated by A. B. W. Kennedy) (1876). The Kinematics of Machinery. New York: reprinted by Dover (1963). • Uicker, J. J.; G. R. Pennock and J. E. Schigley (2003). Theory of Machines and Mechanisms. New York: Oxford University Press.
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Machinery's Handbook Machinery's Handbook for machine shop and drafting-room; a reference book on machine design and shop practice for the mechanical engineer, draftsman, toolmaker, and machinist (the full title of the 1st edition) is a classic reference work in mechanical engineering and practical workshop mechanics in one volume published by Industrial Press, New York, since 1914. The first edition was created by Erik Oberg (1881–1951) and Franklin D. Jones (1879–1967), who are still mentioned on the title page of the 28th edition (2008). Recent editions of the handbook contain chapters on mathematics, mechanics, materials, measuring, toolmaking, manufacturing, threading, gears, and machine elements, combined with excerpts from ANSI standards.
Machinery's Encyclopedia, 1917
In 1917, Oberg and Jones also published Machinery's Encyclopedia in 7 volumes. The handbook and encyclopedia are named after the monthly magazine Machinery (Industrial Press, 1894–1973), where the two were consulting editors. Today, the phrases "machinist's handbook" or "machinists' handbook" are almost always imprecise references to Machinery's Handbook. During the decades from World War I through World War II, these phrases could refer to either of two competing reference books: "Boiler", Machinery's Encyclopedia, 1917 McGraw-Hill's American Machinists' Handbook or Industrial Press's Machinery's Handbook. The former book ceased publication after the 8th edition (1945). (One short-lived spin-off appeared in 1955.) The latter book, Machinery's Handbook, is still regularly revised and updated, and it continues to be a "bible of the metalworking industries" today. Machinery's Handbook is apparently the direct inspiration for similar works in other countries, such as Sweden's Karlebo handbok (1st ed. 1936).
External links • Industrial Press [1] official site • History of the Machinery's Handbook [2], on the publisher's official site
References [1] http:/ / www. industrialpress. com/ [2] http:/ / new. industrialpress. com/ node/ 1003
Maintenance engineering
Maintenance engineering Maintenance Engineering is the discipline and profession of applying engineering concepts to the optimization of equipment, procedures, and departmental budgets to achieve better maintainability, reliability, and availability of equipment. Maintenance, and hence maintenance engineering, is increasing important due to rising amounts of equipment, systems, machineries and infrastructures. Since the Industrial Revolution devices, equipment, machinery and structures have grown increasingly complex, requiring a host of personnel, vocations and related systems needed to maintain them.[1] Prior to 2006, the United States spent approximately US$300 billion annually on plant maintenance and operations alone.[1] A person practising Maintenance Engineering is known as a Maintenance Engineer.
Maintenance Engineer's Essential Knowledge A Maintenance Engineer shall possess significant knowledge of statistics, probability and logistics, and additionally in the fundamentals of the operation of the equipment and machinery he or she is responsible for. A Maintenance Engineer shall als possess high interpersonal, communication and management skills.
Typical Maintenance Engineering Responsibilities Typical responsibilities include:[2] • • • • • • • • • •
Assure optimization of the Maintenance Organization structure Analysis of repetitive equipment failures Estimation of maintenance costs and evaluation of alternatives Forecasting of spare parts Assessing the needs for equipment replacements and establish replacement programs when due Application of scheduling and project management principles to replacement programs Assessing required maintenance tools and skills required for efficient maintenance of equipment Assessing required skills required for maintenance personnel Reviewing personnel transfers to and from maintenance organizations Assessing and reporting safety hazards associated with maintenance of equipment
Maintenance Engineering Education There is Bachelor Degree program for Maintenance Engineering,at the German Jordanian University in Amman. However, Maintenance Engineers usually hold a degree in Mechanical Engineering, Industrial Engineering, or other Engineering Disciplines.
References [1] Dhillon, Balbir S. (2006) Maintainability, Maintenance, and Reliability for Engineers (http:/ / books. google. com/ books?id=nxT-wxeVVIQC), CRC Press, 2006, ISBN 0849372437, ISBN 9780849372438; [2] Mobley, Keith R. & Higgins, Lindley R. & Wikoff, Darrin J. (2008) Maintenance Engineering Handbook (http:/ / books. google. ca/ books?hl=en& id=O8Fcf-VIliwC& dq=maintenance+ engineering+ handbook& printsec=frontcover& source=web& ots=64-5OGeEgg& sig=hspdMJ5Oe5Hz4T0qyjdh0XUoYoE& sa=X& oi=book_result& resnum=1& ct=result), McGraw-Hill Professional, Seventh Edition, 2008, ISBN 0071546464, ISBN 9780071546461;
http://www.gju.edu.jo/page.aspx?id=36&type=s&lng=en&page=159
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External links • MaintenanceOnline.org (http://www.maintenanceonline.org/maintenanceonline) • Maintenance-engineering.eu (http://www.maintenance-engineering.eu/)
Maintenance, repair, and operations Maintenance, repair, and operations[1] (MRO) or maintenance, repair, and overhaul[2] involves fixing any sort of mechanical or electrical device should it become out of order or broken (known as repair, unscheduled or casualty maintenance). It also includes performing routine actions which keep the device in working order (known as scheduled maintenance) or prevent trouble from arising (preventive maintenance). MRO may be defined as, "All actions which have the objective of retaining or restoring an item in or to a state in which it can perform its required function. The actions include the combination of all technical and corresponding administrative, managerial, and supervision actions." [3]
Mechanical repair
MRO operations can be categorised by whether the product remains the property of the customer, i.e. a service is being offered, or whether the product is bought by the reprocessing organisation and sold to any customer wishing to make the purchase. (Guadette, 2002) The former of these represents a closed loop supply chain and usually has the scope of maintenance, repair or overhaul of the product. The latter of the categorisations is an open loop supply chain and is typified by refurbishment and remanufacture. The main characteristic of the closed loop system is that the demand for a product is matched with the supply of a used product. Neglecting asset write-offs and exceptional activities the total population of the product between the customer and the service provider remains constant
Engineering In telecommunication, and engineering in general, the term maintenance has the following meanings: 1. Any activity – such as tests, measurements, replacements, adjustments and repairs — intended to retain or restore a functional unit in or to a specified state in which the unit can perform its required functions.[4] 2. For material — all action taken to retain material in a serviceable condition or to restore it to serviceability. It includes inspection, testing, servicing, classification as to serviceability, repair, rebuilding, and reclamation.[4] 3. For material — all supply and repair action taken to keep a force in condition to carry out its mission.[4] 4. For material — the routine recurring work required to keep a facility (plant, building, structure, ground facility, utility system, or other real property) in such condition that it may be continuously used, at its original or designed capacity and efficiency for its intended purpose.[4] Manufacturers and Industrial Supply Companies often refer to MRO as opposed to Original Equipment Manufacture (OEM). OEM includes any activity related to the direct manufacture of goods, where MRO refers to any maintenance and repair activity to keep a manufacturing plant running. Industrial supply companies can generally be sorted into two types: • the ones who cater to the MRO market generally carry a broad range of items such as fasteners, conveyors, cleaning goods, plumbing, and tools to keep a plant running. • OEM supply companies generally provide a smaller range of goods in much larger quantities with much lower prices, selling materials that will be regularly consumed in the manufacturing process to create the finished item.
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Maintenance types Generally speaking, there are two types of maintenance in use: • Preventive maintenance, where equipment is maintained before break down occurs. This type of maintenance has many different variations and is subject of various researches to determine best and most efficient way to maintain equipment. Recent studies have shown that Preventive maintenance is effective in preventing age related failures of the equipment. For random failure patterns which amount to 80% of the failure patterns, condition monitoring proves to be effective. • Corrective maintenance, where equipment is maintained after break down. This maintenance is often most expensive because worn equipment can damage other parts and cause multiple damage.
Preventive maintenance Preventive maintenance is maintenance performed in an attempt to avoid failures, unnecessary production loss and safety violations. As equipment cannot be maintained at all times, some way is needed to decide when it is proper to perform maintenance. Normally, this is done by deciding some inspection/maintenance intervals, and sticking to this interval more or less affected by what you find during these activities. The result of this is that most of the maintenance performed is unnecessary; it even adds substantial wear to the equipment. Also, you have no guarantee that the equipment will continue to work even if you are maintaining it according to the maintenance plan. The effectiveness of a preventive maintenance schedule depends on the RCM analysis which it was based on, and the ground rules used for cost-effectivity.[5] Further information: Planned maintenance
Corrective maintenance Corrective maintenance is probably the most commonly used approach, but it is easy to see its limitations. When equipment fails, it often leads to downtime in production. In most cases this is costly business. Also, if the equipment needs to be replaced, the cost of replacing it alone can be substantial. It is also important to consider health, safety and environment (HSE) issues related to malfunctioning equipment. Corrective maintenance can be defined as the maintenance which is required when an item has failed or worn out, to bring it back to working order. Corrective maintenance is carried out on all items where the consequences of failure or wearing out are not significant and the cost of this maintenance is not greater than preventive maintenance.
Repair shop
Maintenance, repair, and operations
MRO software In many organizations because of the number of devices or products that need to be maintained or the complexity of systems, there is a need to manage the information with software packages. This is particularly the case in aerospace (e.g. airline fleets), military installations, large plants (e.g. manufacturing, power generation, petrochemical) and ships. These software tools help engineers and technicians in increasing the system availability and reducing costs and repair times as well as reducing material supply time and increasing material availability by improving supply chain communication. As MRO involves working with an organization’s products, resources, suppliers and customers, MRO packages have to interface with many enterprise business software systems (PLM, EAM, ERP, SCM, CRM). One of the functions of such software is the configuration of bills of materials or BOMs, taking the component parts list from engineering (eBOM) and manufacturing (mBOM) and updating it from “as delivered” through “as maintained” to “as used”. Another function is project planning logistics, for example identifying the critical path on the list of tasks to be carried out (inspection, diagnosis, locate/order parts and service) to calculate turnaround times (TAT). Other tasks that software can perform: • • • •
Planning operations, Managing execution of events, Management of assets (parts, tools and equipment inventories), Knowledge-base data on: • • • • •
Maintenance service history, Serial numbered parts, Reliability data: MTBF, MTTB (mean time to breakdown), MTBR (mean time between removals), Maintenance and repair documentation and best practices, Warranty/guarantee documents.
Many of these tasks are addressed in Computerized Maintenance Management Systems (CMMS). Data standards have been developed around these activities, most notably EAMXML and MIMOSA.
MRO goods MRO goods are typically defined as any goods used in the creation of a product but not in the final product itself. Examples include: • the machinery used to make a product • spare parts for the machinery that creates the product, and • items used to maintain the facility in which the product is made.
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References [1] Defense Logistics Agency (http:/ / www. dscp. dla. mil/ gi/ mro/ ) [2] Lockheed Martin press release (http:/ / www. lockheedmartin. com/ news/ press_releases/ 2008/ 0122ae_u2sanantonio. html) Kelly Aviation Center, L.P. [3] European Federation of National Maintenance Societies (http:/ / www. EFNMS. org) [4] Federal Standard 1037C and from MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms [5] Tain Inc (http:/ / www. mtain. com/ logistics/ logrcm. htm) RCM analysis
Marks' Standard Handbook for Mechanical Engineers Marks' Standard Handbook for Mechanical Engineers is a comprehensive handbook for the field of mechanical engineering. It was first published in 1916 by Lionel S. Marks. In 2007, it was in its 11th edition, and published by McGraw-Hill. Lionel S. Marks was a professor of Mechanical Engineering at Harvard University and Massachusetts Institute of Technology in the early 1900s.[1]
Topics In the 11th edition, there are 20 sections: 1. Mathematical Tables and Measuring Units 2. Mathematics 3. Mechanics of Solids and Fluids 4. Heat 5. Strength of Materials 6. Materials of Engineering 7. Fuels and Furnaces 8. Machine Elements 9. Power Generation 10. Materials Handling 11. Transportation 12. Building Construction and Equipment 13. Manufacturing Processes 14. Fans, Pumps, and Compressors 15. Electrical and Electronics Engineering 16. Instruments and Controls 17. Industrial Engineering 18. The Regulatory Environment 19. Refrigeration, Cyrogenics, and Optics 20. Emerging Technologies
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References [1] "Harvard Professors at MIT" (http:/ / books. google. com/ books?id=JyTPAAAAMAAJ& pg=PA79& lpg=PA79& dq=lionel+ s. + marks+ harvard+ mit& source=bl& ots=_6LCf_ev9U& sig=ffsR0ATsUsuhq7ep0-A1bMsRSu4& hl=en& ei=2r03TfCBMY3rgQf8yMiNCQ& sa=X& oi=book_result& ct=result& resnum=1& ved=0CBYQ6AEwAA#v=onepage& q=lionel s. marks harvard mit& f=false), Harvard Alumni Bulletin, Volume 17, n.5, Harvard Alumni Association, Associated Harvard Clubs, October 28, 1914.
• Avallone, Eugene A., Theodore Baumeister III, and Ali M. Sadegh, eds. (2007). Marks' Standard Handbook for Mechanical Engineers. 11th ed. New York: McGraw-Hill. ISBN 9780071428675.
External links • Publisher's description (http://www.mhprofessional.com/product.php?isbn=0071428674) • Marks' Standard Handbook For Mechanical Engineers (http://www.jaredzone.info/2011/06/ marks-standard-handbook-for-mechanical.html)
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Mass transfer Part of a series on
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Mass transfer is the net movement of mass from one location, usually meaning a stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, adsorption, drying, precipitation, membrane filtration, and distillation. Mass transfer is used by different scientific disciplines for different processes and mechanisms. The phrase is commonly used in engineering for physical processes that involve diffusive and convective transport of chemical species within physical systems.
Mass transfer Some common examples of mass transfer processes are the evaporation of water from a pond to the atmosphere, the purification of blood in the kidneys and liver, and the distillation of alcohol. In industrial processes, mass transfer operations include separation of chemical components in distillation columns, absorbers such as scrubbers, adsorbers such as activated carbon beds, and liquid-liquid extraction. Mass transfer is often coupled to additional transport processes, for instance in industrial cooling towers. These towers couple heat transfer to mass transfer by allowing hot water to flow in contact with hotter air and evaporate as it absorbs heat from the air.
Astrophysics In astrophysics, mass transfer is the process by which matter gravitationally bound to a body, usually a star, fills its Roche lobe and becomes gravitationally bound to a second body, usually a compact object (white dwarf, neutron star or black hole), and is eventually accreted onto it. It is a common phenomenon in binary systems, and may play an important role in some types of supernovae and pulsars.
Chemical Engineering Mass transfer finds extensive application in chemical engineering problems. It is used in reaction engineering, separations engineering, heat transfer engineering, and many other sub-disciplines of chemical engineering. The driving force for mass transfer is typically a difference in chemical potential, when it can be defined, though other thermodynamic gradients may couple to the flow of mass and drive it as well. A chemical species moves from areas of high chemical potential to areas of low chemical potential. Thus, the maximum theoretical extent of a given mass transfer is typically determined by the point at which the chemical potential is uniform. For single phase-systems, this usually translates to uniform concentration throughout the phase, while for multiphase systems chemical species will often prefer one phase over the others and reach a uniform chemical potential only when most of the chemical species has been absorbed into the preferred phase, as in liquid-liquid extraction. While thermodynamic equilibrium determines the theoretical extent of a given mass transfer operation, the actual rate of mass transfer will depend on additional factors including the flow patterns within the system and the diffusivities of the species in each phase. This rate can be quantified through the calculation and application of mass transfer coefficients for an overall process. These mass transfer coefficients are typically published in terms of dimensionless numbers, often including Péclet numbers, Reynolds numbers, Sherwood numbers and Schmidt numbers, among others[1] .
Analogies between heat, mass, and momentum transfer There are notable similarities in the commonly used approximate differential equations for momentum, heat, and mass transfer.[1] The molecular transfer equations of Newton's law for fluid momentum at low Reynolds number (Stokes flow), Fourier's law for heat, and Fick's law for mass are very similar, since they are all linear approximations to transport of conserved quantities in a flow field. At higher Reynolds number, the analogy between mass and heat transfer and momentum transfer becomes less useful due to the nonlinearity of the Navier-Stokes equation (or more fundamentally, the general momentum conservation equation), but the analogy between heat and mass transfer remains good. A great deal of effort has been devoted to developing analogies among these three transport processes so as to allow prediction of one from any of the others.
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Mass transfer
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References [1] Welty, James R.; Wicks, Charles E.; Wilson, Robert Elliott (1976). Fundamentals of momentum, heat, and mass transfer (http:/ / books. google. be/ books?cd=3& hl=en& id=hZxRAAAAMAAJ) (2 ed.). Wiley. .
Mating connection A mating connection is any method of assembling of two or more component parts with mutually complementing shapes that, with some imagination, resembles the way two animals, male and female, are physically connected during the act of mating. In such connections one of the two components acts as male and the other as female, although more complex relationships exist.[1] Any electrical connector, bolted joint, and jigsaw puzzle is an example of assembling based on mating connection.
References [1] Webster, Len F. The Wiley Dictionary of Civil Engineering and Construction Professional Series (http:/ / books. google. ca/ books?id=u7nAYkS9lGcC), Wiley Professional, Wiley-Interscience, 1997, ISBN 0471181153, ISBN 9780471181156.
Internal and external threads illustrated using a common nut and bolt, as an example of a mating connection.
McKinley Climatic Laboratory
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McKinley Climatic Laboratory McKinley Climatic Laboratory U.S. National Register of Historic Places
F-117A, 84-0824, on ice at McKinley Climatic Laboratory in 1991.
Nearest city:
Fort Walton Beach, Florida
Coordinates:
30°28′33″N 86°30′27″W
Built:
1944
Architect:
US Army Air Corps of Engineers
Architectural style: Late 19th And Early 20th Century American Movements, Other Governing body:
US Air Force
NRHP Reference#: 97001145[1] Added to NRHP:
October 06, 1997
The McKinley Climatic Laboratory is both an active laboratory and a historic site located in Building 440 on Eglin Air Force Base, Florida. The laboratory is part of the 46th Test Wing. In addition to Air Force testing, it can be used by other US government agencies and private industry.[2] On October 6, 1997, it was added to the U.S. National Register of Historic Places.[1] The laboratory was named a National Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers in 1987.[3] [4]
McKinley Climatic Laboratory
History In 1940, the US Army Air Force designated Ladd Field in Fairbanks, Alaska as a cold-weather testing facility. Because sufficiently cold weather was not predictable and often of short duration, Ashley McKinley suggested a refrigerated airplane hangar be built. The facilities were constructed at Eglin Field.[4] The first tests started in May 1947. Airplanes that were tested included the B-29 Superfortress, C-82 Packet, P-47 Thunderbolt, P-51 Mustang, P-80 Shooting Star, and the Sikorsky H-5D helicopter.[4] More recently, it has tested the C-5 Galaxy,[4] the F-117,[5] the F-22[6] and the Boeing 787.[7] On 12 June 1971, the hangar was dedicated at the McKinley Climatic Hangar in honor of Col. Ashley McKinley, who suggested the facility and served at Eglin during its construction.[4]
Buildings The Building 440 is an insulated, refrigerated hangar. There is an office and instrumentation building, a cold-weather engine test cell, the refrigeration system, mechanical-draft cooling towers, and a steam-heating plant.[4] The main chamber is 252 feet (77 m) wide, 201 feet (61 m) deep, and 70 feet (21 m) tall at the center of the hangar. It was constructed to hold aircraft as large a B-29, its size also fitting the larger Convair B-36 Peacemaker. In 1968, a 60 feet (18 m) by 85 feet (26 m) extension was added. It now has 55000 square feet (5100 m2) working area. This allows it to test aircraft as large as a C-5A. Under hot conditions, it can achieve 165 °F (74 °C).[4] [8] The All-Weather Room is 42 feet (13 m) by 22 feet (7 m). It has a temperature range from −80 °F (−62 °C) to 170 °F (77 °C). Rainfall can be as high as 15 inches (380 mm) per hour and the wind can be as high as 60 knots (31 m/s). Snow can be made in the chamber.[4] The Temperature-Altitude Chamber is 13.5 feet (4.1 m) by 9.5 feet (2.9 m) with a height of 6.9 feet (2.1 m). Altitudes up to 80000 feet (24 km) can be simulated. The temperature range is −80 °F (−62 °C) to 140 °F (60 °C).[4] The engine test cell was originally used for aircraft engines. It was about 130 feet (40 m) by 30 feet (9 m) with a height of 25 feet (8 m). It is now called the Equipment Test Chamber and is used mainly for tanks, trucks, and other equipment. The original building had small tests rooms for desert, hot, marine, and jungle conditions. These have been eliminated.[2] [4] The original floor of the building was constructed of reinforced-concrete slabs that were 12 inches (30 cm) thick and 12.5 feet (3.8 m) square. The slabs rested on 13 inches (33 cm) of cellular glass blocks over reinforced concrete. In 1990, much of this floor was replaced with 25 feet (7.6 m) square slabs. The walls and door are insulated with 13 inches (33 cm) of glass-wool board sheathed in galvanized steel. To seal the doors, they are pulled against foam rubber seals. The ceiling insulation is on a corrugated steel deck, which is suspended from the roof trusses by chains.[4] [8]
Refrigeration system The original coolant was R-12 refrigerant. Liquid refrigerant is held in a low-pressure surge tank. The pressure in this tank is maintained at the saturation pressure for the desired temperature for the cooling coils. Vapor from this tank is compressed to a gage pressure of 20 psi (138 kPa) by the first-stage compressor. The compressed vapor is expanded into an intermediate, desuperheater tank. Liquid condensed in this expansion is drained back the to the surge tank. The remaining vapor is compressed in a high-stage compressor to a gage pressure of about 150 psi (1 MPa). Heat is transferred from the hot vapor to cooling water. Any condensed liquid is returned to the intermediate tank, the surge tank, or the supply tank. Liquid refrigerant from the surge tank is pumped through the cooling coils at sufficient pressure to avoid vaporization. Warmed liquid is returned to the surge tank. As its pressure is reduced, a portion of this liquid will flash into vapor.[4]
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McKinley Climatic Laboratory There are three such refrigeration systems. Each low-stage compressor is powered by a 1000 horsepower (746 kW) motor and each high-stage compressor is powered by a 1250 horsepower (932 kW) motor. The system was built by York Corporation. The original motors were Allis-Chalmers induction motors. They have been replaced by variable frequency, synchronous motors manufactured by EMICC that operate between 350 and 1800 rpm.[4] Recent efforts have been made to change from ozone-depleting refrigerants.[8] For engine tests, there is need for makeup air. The system originally could cool 200 pounds (91 kg) per second of humid air. In 1966, this was increased to 450 pounds (204 kg) per second. Air is also cooled by a two-stage heat exchanger. The first stage uses 110000 US gallons (416 m3) of 20% calcium chloride brine pre-cooled to 24 °F (−4 °C). The second stage uses 137500 US gallons (520 m3) of methylene chloride pre-cooled to −97 °F (−72 °C). This can cool 450 pounds (204 kg) per second of humid air from 80 °F (27 °C) to −65 °F (−54 °C) for 40 minutes.[4]
References [1] "National Register Information System" (http:/ / nrhp. focus. nps. gov/ natreg/ docs/ All_Data. html). National Register of Historic Places. National Park Service. 2008-04-15. . [2] "McKinley Climatic Laboratory" (http:/ / www. aiaa. org/ tc/ gt/ facility_database/ Climatic2008. pdf). 46th Test Wing Fact Sheet. US Air Force. . Retrieved 2009-01-16. [3] "McKinley Climatic Laboratory" (http:/ / www. asme. org/ Communities/ History/ Landmarks/ McKinley_Climatic_Laboratory. cfm). Landmarks. American Society of Mechanical Engineers. . Retrieved 2009-01-06. [4] "McKinley Climatic Laboratory, Eglin Air Force Base, Florida" (http:/ / files. asme. org/ ASMEORG/ Communities/ History/ Landmarks/ 5590. pdf) (PDF). McKinley Climatic Laboratory brochure. ASME. . Retrieved 2009-01-06. [5] "F-117 on ice at McKinley Climatic Laboratory" (http:/ / www. eglin. af. mil/ photos/ media_search. asp?q=mckinley& page=1). Eglin Air Force Base Photos. US Air Force. . Retrieved 2009-01-16. [6] "F-22 endures 3-week, cold-weather test at Eielson" (http:/ / www. af. mil/ news/ story. asp?id=123077428). Air Force Link. US Air Force. . Retrieved 2009-01-16. [7] Gates, Dominic (2010-04-22). "Boeing 787 test plane is chilling in Florida" (http:/ / seattletimes. nwsource. com/ html/ businesstechnology/ 2011674665_787cold23. html). The Seattle Times. . Retrieved 2010-04-25. [8] "McKinley Climatic Laboratory" (http:/ / www. nps. gov/ history/ nr/ travel/ aviation/ mck. htm). Aviation: From Sand Dunes to Sonic Booms. US National Park Service. . Retrieved 2009-01-06.
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Mechanical advantage device
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Mechanical advantage device A simple machine that exhibit mechanical advantage is called a mechanical advantage device - e.g.: • Lever: The beam shown is in static equilibrium around the fulcrum. This is due to the moment created by vector force "A" counterclockwise (moment A*a) being in equilibrium with the moment created by vector force "B" clockwise (moment B*b). The relatively low vector force "B" is translated in a relatively high vector force "A". The force is thus increased in the ratio of the forces A : B, which is equal to the ratio of the distances to the fulcrum b : a. This ratio is called the mechanical advantage. This idealised situation does not take into account friction.
Beam balanced around a fulcrum
• Wheel and axle motion (e.g. screwdrivers, doorknobs): A wheel is essentially a lever with one arm the distance between the axle and the outer point of the wheel, and the other the radius of the axle. Typically this is a fairly large difference, leading to a proportionately large mechanical advantage. This allows even simple wheels with wooden axles running in wooden blocks to still turn freely, because their friction is overwhelmed by the rotational force of the wheel multiplied by the mechanical advantage. • A block and tackle of multiple pulleys creates mechanical advantage, by having the flexible material looped over several pulleys in turn. Adding more loops and pulleys increases the mechanical advantage. • Screw: A screw is essentially an inclined plane wrapped around a cylinder. The run over the rise of this inclined plane is the mechanical advantage of a screw.[1]
Pulleys Consider lifting a weight with rope and pulleys. A rope looped through a pulley attached to a fixed spot, e.g. a barn roof rafter, and attached to the weight is called a single pulley. It has an MA = 1 (assuming frictionless bearings in the pulley), meaning no mechanical advantage (or disadvantage) however advantageous the change in direction may be.
Examples of rope and pulley systems illustrating mechanical advantage.
A single movable pulley has an MA of 2 (assuming frictionless bearings in the pulley). Consider a pulley attached to a weight being lifted. A rope passes around it, with one end attached to a fixed point above, e.g. a barn roof rafter, and a pulling force is applied upward to the other end with the two lengths parallel. In this situation the distance the lifter must pull the rope becomes twice the distance the weight travels, allowing the force applied to be halved. Note: if an additional pulley is used to change the direction of the rope, e.g. the person doing the work wants to stand on the ground instead of on a rafter, the mechanical advantage is not increased. By looping more ropes around more pulleys we can continue to increase the mechanical advantage. For example if we have two pulleys attached to the rafter, two pulleys attached to the weight, one end attached to the rafter, and someone standing on the rafter pulling the rope, we have a mechanical advantage of four. Again note: if we add
Mechanical advantage device another pulley so that someone may stand on the ground and pull down, we still have a mechanical advantage of four. Here are examples where the fixed point is not obvious: • A velcro strap on a shoe passes through a slot and folds over on itself. The slot is a movable pulley and the MA = 2. • Two ropes laid down a ramp attached to a raised platform. A barrel is rolled onto the ropes and the ropes are passed over the barrel and handed to two workers at the top of the ramp. The workers pull the ropes together to get the barrel to the top. The barrel is a movable pulley and the MA = 2. If there is enough friction where the rope is pinched between the barrel and the ramp, the pinch point becomes the attachment point. This is considered a fixed attachment point because the rope above the barrel does not move relative to the ramp. Alternatively the ends of the rope can be attached to the platform. • Block and tackle: MA = 2 or more, depending on design (see above)
Screws The theoretical mechanical advantage for a screw can be calculated using the following equation:[2]
where dm = the mean diameter of the screw thread l = the lead of the screw thread Note that the actual mechanical advantage of a screw system is greater, as a screwdriver or other screw driving system has a mechanical advantage as well. • Inclined plane: MA = length of slope ÷ height of slope
References Notes [1] Fisher, pp. 69–70. [2] United States Bureau of Naval Personnel, p. 5-4.
Bibliography • Fisher, Len (2003), How to Dunk a Doughnut: The Science of Everyday Life (http://books.google.com/ ?id=VuK7m3LU8rgC), Arcade Publishing, ISBN 9781559706803. • United States Bureau of Naval Personnel (1971), Basic machines and how they work (http://books.google.com/ ?id=yDKzy4rKEg0C) (Revised 1994 ed.), Courier Dover Publications, ISBN 9780486217093.
External links • Gears and pulleys (http://www.technologystudent.com/gears1/geardex1.htm) • Mechanical engineering — pulleys (http://www.swe.org/iac/lp/pulley_03.html) • Mechanical advantage — video (http://ca.youtube.com/watch?v=yfAdmRJDKIc)
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Mechanical efficiency
Mechanical efficiency Mechanical efficiency measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement. Efficiency is measured as a ratio of the measured performance to the performance of an ideal machine,
The efficiency of energy conversion of the power plant of a machine is often considered separately from the efficiency of the mechanism that transmits this power to achieve a particular force and movement. Because the power transmission system or mechanism does not generate power, its ideal performance occurs when the output power equals the input power, that is when there are no losses. Real devices dissipate power through friction, part deformation and wear. The ideal transmission or mechanism has an efficiency of 100%, because there is no power loss. Real devices will have efficiencies less than 100% because rigid and frictionless systems do not exist. The power losses in a transmission or mechanism are eventually dissipated as heat.
Mechanical engineering technology Mechanical engineering technology is the application of physical principles and current technological developments to the creation of useful machinery and operation design. Technologies such as solid models may be used as the basis for finite element analysis (FEA) and / or computational fluid dynamics (CFD) of the design. Through the application of computer-aided manufacturing (CAM), the models may also be used directly by software to create "instructions" for the manufacture of objects represented by the models, through computer numerically controlled (CNC) machining or other automated processes, without the need for intermediate drawings. Mechanical engineering technologists are also expected to understand and be able to apply concepts from the chemical and electrical engineering fields. Mechanical engineering technologists are expected to apply current technologies and principals to machine and product design, production, and manufacturing processes.
Mechanical Engineering Technology coursework Fundamental subjects of mechanical engineering technology include: • • • • • • • • • • • •
Dynamics Statics Fluid mechanics/fluid dynamics Applied thermodynamics Machine design and kinematics Material science Manufacturing process Engineering drafting and standard familiarization classes Electronic circuit and electrical analysis Instrumentation and measurement HVAC Hydraulics and pneumatics
• Quality assurance • Technical communications and tec
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Mechanical engineering technology • Project management/Operations management The above subjects are usually the core subjects of MET programs/courses globally, because of the multi disciplinary nature of MET the most obvious and precise application of the above modules are Mechatronics Engineering or courses/programs that are at BSc level which emphasizes the application of mechanical engineering because Mechanical engineering (BEng) is usually involved with highly complex conceptual calculations, In the UK as graduates of both BSc (mechanical and similar bias) and BEng degrees are recognised as Professional Engineers, with a theoretical distinction of BSc (IEng) and BEng (IEng with much easier access to gain CEng)
External links • List of Mechanical Engineering Technology Programs [1]
References [1] http:/ / www. abet. org/ accredittac. asp
Mechanical singularity In engineering, a mechanical singularity is a position or configuration of a mechanism or a machine where the subsequent behaviour cannot be predicted, or the forces or other physical quantities involved become infinite or nondeterministic. When the underlying engineering equations of a mechanism or machine are evaluated at the singular configuration (if any exists), then those equations exhibit mathematical singularity. Examples of mechanical singularities are gimbal lock and in static mechanical analysis, an under-constrained system.
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Mechanical system
Mechanical system A mechanical system manages power to accomplish a task that involves forces and movement. Mechanical is derived from the Latin word machina,[1] which in turn derives from the Doric Greek μαχανά (machana), Ionic Greek μηχανή (mechane) "contrivance, machine, engine"[2] and that from μῆχος (mechos), "means, expedient, remedy".[3] The Oxford English Dictionary[4] defines the adjective mechanical as skilled in the practical application of an art or science, of the nature of a machine or machines, and relating to or caused by movement, physical forces, properties or agents such as is dealt with by Mechanics. Similarly Merriam-Webster Dictionary[5] defines "mechanical" as relating to machinery or tools. A mechanical system consists of (i) a power source and actuators that generate forces and movement, (ii) a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement, and (iii) a controller with sensors that compares the output to a performance goal and then directs the actuator input. This can be seen in Watt's steam engine (see the illustration) in which the power is provided by steam expanding to drive the piston. The walking beam, coupler and crank transform the linear movement of the piston into rotation of the output pulley. Finally, the pulley rotation drives the flyball governor which controls the valve for the steam input to the piston cylinder. Power flow through a mechanical system provides a way to understand the performance of devices ranging from levers and gear trains to automobiles and robotic systems.
Power Sources Human and animal effort were the original power sources for early machines. Natural forces such as wind an water powered larger mechanical systems. Waterwheel: Waterwheels appeared around the world around 300 BC to use flowing water to generate rotary motion, which was applied to milling grain, and powering lumber, machining and textile operations. Modern water turbines use water flowing through a dam to drive an electric generator. Windmill: Early windmills captured wind power to generate rotary motion for milling operations. Modern wind turbines also drives a generator. This electricity in turn is used to drive motors forming the actuators of mechanical systems. Engine: The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices. See Merriam-Webster's definition of engine [6]. A steam engine uses heat to boil water contained in a pressure vessel; the expanding steam drives a piston or a turbine. This principle can be seen in the aeolipile of Hero of Alexandria. This is called an external combustion engine. An automobile engine is called an internal combustion engine because it burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston. A jet engine uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft, and so is also an "internal combustion engine." [6] Power plant: The heat from coal and natural gas combustion in a boiler generates steam that drives a steam turbine to rotate an electric generator. A nuclear power plant uses heat from a nuclear reactor to generate steam and electric power. This power is distributed through a network of transmission lines for industrial and individual use. Motors: Electric motors use either AC or DC electric current to generate rotational movement. Electric servomotors are the actuators for mechanical systems ranging from robotic systems to modern aircraft. Fluid Power: Hydraulic and pneumatic systems use electrically driven pumps to drive water or air respectively into cylinders to power linear movement.
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Mechanical system
Mechanisms The mechanism of a mechanical system is assembled from components called machine elements. These elements provide structure for the system and control its movement. The structural components are, generally, the frame members, bearings, splines, springs, seals, fasteners and covers. The shape, texture and color of covers provide a styling and operational interface between the mechanical system and its users. The assemblies that control movement are also called "mechanisms." [7] [8] Mechanisms are generally classified as gears and gear trains, which includes belt drives and chain drives, cam and follower mechanisms, and linkages, though there are other special mechanisms such as clamping linkages, indexing mechanisms, escapements and friction devices such as brakes and clutches. The number of degrees of freedom (dof) or mobility of a mechanism depends on the number of links and joints and the types of joints used to construct the mechanism. The general mobility of a mechanism is the difference between the unconstrained freedom of the links and the number of constraints imposed by the joints. It is described by the Chebychev-Grübler-Kutzbach criterion.
Controllers Controllers combine sensors, logic, and actuators to maintain the performance of components of a machine. Perhaps the best known is the flyball governor for a steam engine. Examples of these devices range from a thermostat that as temperature rises opens a valve to cooling water to speed controllers such the cruise control system in an automobile. The programmable logic controller replaced relays and specialized control mechanisms with a programmable computer. Servomotors that accurately position a shaft in response to an electrical command are the actuators that make robotic systems possible.
References [1] The American Heritage Dictionary, Second College Edition. Houghton Mifflin Co., 1985. [2] "μηχανή" (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=mhxanh/ ), Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus project [3] "μῆχος" (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=mh=xos), Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus project [4] Oxford English Dictionary [5] Merriam-Webster Dictionary Definition of mechanical (http:/ / www. merriam-webster. com/ dictionary/ mechanical) [6] "Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 998 . [7] Reuleaux, F., 1876 The Kinematics of Machinery, (trans. and annotated by A. B. W. Kennedy), reprinted by Dover, New York (1963) [8] J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York.
Further reading • Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain. ed. Machinery's Handbook (26th edition ed.). New York: Industrial Press Inc.. ISBN 0-8311-2635-3. • Reuleaux, Franz; (trans. and annotated by A. B. W. Kennedy) (1876). The Kinematics of Machinery. New York: reprinted by Dover (1963). • Uicker, J. J.; G. R. Pennock and J. E. Schigley (2003). Theory of Machines and Mechanisms. New York: Oxford University Press.
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Metallurgical failure analysis
Metallurgical failure analysis Metallurgical failure analysis is the process by which a metallurgist determines the mechanism that has caused a metal component to fail. Typical failure modes involve various types of corrosion and mechanical damage. It has been estimated that the direct annual cost of corrosion alone in the United States is a staggering 276 billion, approximately 3.1% of GDP.[1] Metal components fail as a result of the environmental conditions to which they are exposed to as well as the mechanical stresses that they experience. Often a combination of both environmental conditions and stress will cause failure. Metal components are designed to withstand the environment and stresses that they will be subjected to. The design of a metal component involves not only a specific elemental composition but also specific manufacturing processes such as heat treatments, machining processes, etc.… The huge arrays of different metals that result all have unique physical properties.[2] Specific properties are designed into metal components to make them more robust to various environmental conditions. These differences in physical properties will exhibit unique failure modes. A metallurgical failure analysis takes into account as much of this information as possible during analysis. Analysis of a failed part can be done using destructive testing or non-destructive testing. Destructive testing involves removing a metal component from service and sectioning the component for analysis. Destructive testing gives the failure analyst the ability to conduct the analysis in a laboratory setting and perform tests on the material that will ultimately destroy the component. Non destructive testing is a test method that allows certain physical properties of metal to be examined without taking the samples completely out of service. NDT is generally used to detect failures in components before the component fails catastrophically. There is no standardized list of metallurgical failure modes and different metallurgists might use a different name for the same failure mode. The Failure Mode Terms listed below are those accepted by ASTM,[3] ASM,[4] and/or NACE[5] as distinct metallurgical failure mechanisms.
Metallurgical Failure Modes Caused By Corrosion and Stress • • • • • • • • •
Stress Corrosion Cracking[6] Corrosion Fatigue Caustic Cracking (ASTM term) Caustic Embrittlement (ASM term) Stress Corrosion (NACE term) Sulfide Stress Cracking (ASM, NACE term) Stress Accelerated Corrosion (NACE term) Hydrogen Stress Cracking (ASM term) Hydrogen Assisted Stress Corrosion Cracking (ASM term)
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Metallurgical failure analysis
Metallurgical Failure Modes Caused By Stress • • • • • •
Fatigue (ASTM, ASM term) Mechanical Overload Creep Rupture Cracking (NACE term) Embrittlement
Metallurgical Failure Modes Caused by Corrosion • • • • • • •
Erosion Corrosion Oxygen Pitting Hydrogen Embrittlement Hydrogen Induced Cracking (ASM term) Corrosion Embrittlement (ASM term) Hydrogen Disintegration (NACE term) Hydrogen Assisted Cracking (ASM term)
• Hydrogen Blistering • Corrosion
References [1] ‘Corrosion Costs and Preventive Strategies in the United States,’ Report FHWA-RD-01-156, contact the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161; phone: 703/605-6000. [2] M&M Engineering Conduit Fall 2007 “Ferrous Metallurgy 101,” (http:/ / mmengineering. com/ pdf files/ Conduit-Fall 2007. pdf) [3] “Standard Terms Relating to Corrosion and Corrosion Testing” (G 15), Annual Book of ASTM Standards, ASTM, Philadelphia, PA. [4] ASM-International Metals Handbook, Ninth Edition, Corrosion, ASM-International, Metals Park, OH [5] NACE-International NACE Basic Corrosion Course, NACE-International, Houston, TX [6] M&M Engineering Conduit Fall 2007 “Chloride Pitting and Stress Corrosion Cracking of Stainless Steel Alloys,” (http:/ / mmengineering. com/ pdf files/ Conduit-Fall 2007. pdf)
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Microelectromechanical systems
Microelectromechanical systems Microelectromechanical systems (MEMS) (also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems) is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines (in Japan), or micro systems technology – MST (in Europe). MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm) and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre. They usually consist of a central unit that processes data, the microprocessor and several components that interact with the outside such as microsensors.[1] At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass. The potential of very small machines was appreciated before the technology existed that could make them—see, for example, Richard Feynman's famous 1959 lecture There's Plenty of Room at the Bottom. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing small devices. An early example of a MEMS device is the resonistor – an electromechanical monolithic resonator.[2] [3]
Materials for MEMS manufacturing The fabrication of MEMS derived from the process technology in semiconductor device fabrication, i.e. the basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes.[4]
Silicon Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking.
Polymers Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to produce. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding, embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.
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Metals Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability. Metals can be deposited by electroplating, evaporation, and sputtering processes. Commonly used metals include gold, nickel, aluminium, copper, chromium, titanium, tungsten, platinum, and silver.
Ceramics The nitrides of silicon, aluminium and titanium as well as silicon carbide and other ceramics are increasingly applied in MEMS fabrication due to advantageous combinations of material properties. AlN crystallizes in the wurtzite structure and thus shows pyroelectric and piezoelectric properties enabling sensors, for instance, with sensitivity to normal and shear forces.[5] TiN, on the other hand, exhibits a high electrical conductivity and large elastic modulus allowing to realize electrostatic MEMS actuation schemes with ultrathin membranes.[6] Moreover, the high resistance of TiN against biocorrosion qualifies the material for applications in biogenic environments and in biosensors.
MEMS basic processes This chart is not complete : Basic Process Deposition
Patterning
Etching
Deposition processes One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometres to about 100 micrometres. Physical deposition There are two types of physical deposition processes.They are as follows. Physical vapor deposition (PVD) Physical vapor deposition consists of a process in which a material is removed from a target, and deposited on a surface. Techniques to do this include the process of sputtering, in which an ion beam liberates atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and Evaporation (deposition), in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in a vacuum system. Chemical deposition Chemical deposition techniques include chemical vapor deposition ("CVD"), in which a stream of source gas reacts on the substrate to grow the material desired. This can be further divided into categories depending on the details of the technique, for example, LPCVD (Low Pressure chemical vapor deposition) and PECVD (Plasma Enhanced chemical vapor deposition). Oxide films can also be grown by the technique of thermal oxidation, in which the (typically silicon) wafer is exposed to oxygen and/or steam, to grow a thin surface layer of silicon dioxide.
Microelectromechanical systems
Patterning Patterning in MEMS is the transfer of a pattern into a material. Lithography Lithography in MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs. This exposed region can then be removed or treated providing a mask for the underlying substrate. Photolithography is typically used with metal or other thin film deposition, wet and dry etching. Photolithography KrF ArF Immersion EUV Electron beam lithography Electron beam lithography (often abbreviated as e-beam lithography) is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film (called the resist),[7] ("exposing" the resist) and of selectively removing either exposed or non-exposed regions of the resist ("developing"). The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. It was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures. The primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer regime. This form of maskless lithography has found wide usage in photomask-making used in photolithography, low-volume production of semiconductor components, and research & development. The key limitation of electron beam lithography is throughput, i.e., the very long time it takes to expose an entire silicon wafer or glass substrate. A long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. Also, the turn-around time for reworking or re-design is lengthened unnecessarily if the pattern is not being changed the second time. Ion beam lithography It is known that focused-ion-beam lithography has the capability of writing extremely fine lines (less than 50 nm line and space has been achieved) without proximity effect. However, because the writing field in ion-beam lithography is quite small, large area patterns must be created by stitching together the small fields. Ion track technology Ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. It is capable to generate holes in thin films without any development process. Structural depth can be defined either by ion range or by material thickness. Aspect ratios up to several 104 can be reached. The technique can shape and texture materials at a defined inclination angle. Random pattern, single-ion track structures and aimed pattern consisting of individual single tracks can be generated.
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Microelectromechanical systems X-ray lithography X-ray lithography, is a process used in electronic industry to selectively remove parts of a thin film. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist," on the substrate. A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist.
Etching processes There are two basic categories of etching processes: wet etching and dry etching. In the former, the material is dissolved when immersed in a chemical solution. In the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant.[8] [9] for a somewhat dated overview of MEMS etching technologies. Wet etching Wet chemical etching consists in selective removal of material by dipping a substrate into a solution that dissolves it. The chemical nature of this etching process provides a good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully. Isotropic etching Etching progresses at the same speed in all directions. Long and narrow holes in a mask will produce v-shaped grooves in the silicon. The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate. Anisotropic etching Some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate. This is known as anisotropic etching and one of the most common examples is the etching of silicon in KOH (potassium hydroxide), where Si <111> planes etch approximately 100 times slower than other planes (crystallographic orientations). Therefore, etching a rectangular hole in a (100)-Si wafer results in a pyramid shaped etch pit with 54.7° walls, instead of a hole with curved sidewalls as with isotropic etching. HF etching Hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide (SiO2, also known as BOX for SOI), usually in 49% concentrated form, 5:1, 10:1 or 20:1 BOE (buffered oxide etchant) or BHF (Buffered HF). They were first used in medieval times for glass etching. It was used in IC fabrication for patterning the gate oxide until the process step was replaced by RIE. Hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. It penetrates the skin upon contact and it diffuses straight to the bone. Therefore the damage is not felt until it is too late. Electrochemical etching Electrochemical etching (ECE) for dopant-selective removal of silicon is a common method to automate and to selectively control etching. An active p-n diode junction is required, and either type of dopant can be the etch-resistant ("etch-stop") material. Boron is the most common etch-stop dopant. In combination with wet anisotropic etching as described above, ECE has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. Selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon.
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Microelectromechanical systems Dry etching Vapor etching Xenon difluoride etching Xenon difluoride (XeF2) is a dry vapor phase isotropic etch for silicon originally applied for MEMS in 1995 at University of California, Los Angeles.[10] [11] Primarily used for releasing metal and dielectric structures by undercutting silicon, XeF2 has the advantage of a stiction-free release unlike wet etchants. Its etch selectivity to silicon is very high, allowing it to work with photoresist, SiO2, silicon nitride, and various metals for masking. Its reaction to silicon is "plasmaless", is purely chemical and spontaneous and is often operated in pulsed mode. Models of the etching action are available,[12] and university laboratories and various commercial tools offer solutions using this approach. Plasma etching Reactive ion etching (RIE) In reactive ion etching (RIE), the substrate is placed inside a reactor, and several gases are introduced. A plasma is struck in the gas mixture using an RF power source, which breaks the gas molecules into ions. The ions accelerate towards, and react with, the surface of the material being etched, forming another gaseous material. This is known as the chemical part of reactive ion etching. There is also a physical part, which is similar to the sputtering deposition process. If the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction. It is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. By changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical. RIE can be deep (Deep RIE or deep reactive ion etching (DRIE)). Deep RIE (DRIE) is a special subclass of RIE that is growing in popularity. In this process, etch depths of hundreds of micrometres are achieved with almost vertical sidewalls. The primary technology is based on the so-called "Bosch process",[13] named after the German company Robert Bosch, which filed the original patent, where two different gas compositions alternate in the reactor. Currently there are two variations of the DRIE. The first variation consists of three distinct steps (the Bosch Process as used in the Plasma-Therm tool) while the second variation only consists of two steps (ASE used in the STS tool). In the 1st Variation, the etch cycle is as follows: (i) SF6 isotropic etch; (ii) C4F8 passivation; (iii) SF6 anisoptropic etch for floor cleaning. In the 2nd variation, steps (i) and (iii) are combined. Both variations operate similarly. The C4F8 creates a polymer on the surface of the substrate, and the second gas composition (SF6 and O2) etches the substrate. The polymer is immediately sputtered away by the physical part of the etching, but only on the horizontal surfaces and not the sidewalls. Since the polymer only dissolves very slowly in the chemical part of the etching, it builds up on the sidewalls and protects them from etching. As a result, etching aspect ratios of 50 to 1 can be achieved. The process can easily be used to etch completely through a silicon substrate, and etch rates are 3–6 times higher than wet etching.
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Die preparation After preparing a large number of MEMS devices on a silicon wafer, individual dies have to be separated, which is called die preparation in semiconductor technology. For some applications, the separation is preceded by wafer backgrinding in order to reduce the wafer thickness. Wafer dicing may then be performed either by sawing using a cooling liquid or a dry laser process called stealth dicing.
MEMS manufacturing technologies Bulk micromachining Bulk micromachining is the oldest paradigm of silicon based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures.[9] Silicon is machined using various etching processes. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that have changed the shape of the sensor industry in the 80's and 90's.
Surface micromachining Surface micromachining uses layers deposited on the surface of a substrate as the structural materials, rather than using the substrate itself.[14] Surface micromachining was created in the late 1980s to render micromachining of silicon more compatible with planar integrated circuit technology, with the goal of combining MEMS and integrated circuits on the same silicon wafer. The original surface micromachining concept was based on thin polycrystalline silicon layers patterned as movable mechanical structures and released by sacrificial etching of the underlying oxide layer. Interdigital comb electrodes were used to produce in-plane forces and to detect in-plane movement capacitively. This MEMS paradigm has enabled the manufacturing of low cost accelerometers for e.g. automotive air-bag systems and other applications where low performance and/or high g-ranges are sufficient. Analog Devices have pioneered the industrialization of surface micromachining and have realized the co-integration of MEMS and integrated circuits.
High aspect ratio (HAR) silicon micromachining Both bulk and surface silicon micromachining are used in the industrial production of sensors, ink-jet nozzles, and other devices. But in many cases the distinction between these two has diminished. A new etching technology, deep reactive-ion etching, has made it possible to combine good performance typical of bulk micromachining with comb structures and in-plane operation typical of surface micromachining. While it is common in surface micromachining to have structural layer thickness in the range of 2 µm, in HAR silicon micromachining the thickness can be from 10 to 100 µm. The materials commonly used in HAR silicon micromachining are thick polycrystalline silicon, known as epi-poly, and bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also have been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining. The consensus of the industry at the moment seems to be that the flexibility and reduced process complexity obtained by having the two functions separated far outweighs the small penalty in packaging. A comparison of different high-aspect-ratio microstructure technologies can be found in the HARMST article. A forgotten history regarding surface micromachining revolved around the choice of polysilicon A or B. Fine grained (<300A grain size, US4897360), post strain annealed pure polysilicon was advocated by Prof Henry Guckel (U. Wisconsin); while a larger grain, doped stress controlled polysilicon was advocated by the UC Berkeley group.
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Applications In one viewpoint MEMS application is categorized by type of use. • Sensor • Actuator • Structure In another view point MEMS applications are categorized by the field of application (commercial applications include): • Inkjet printers, which use piezoelectrics or thermal bubble ejection to deposit ink on paper.
microelectromechanical systems chip, sometimes called "lab on a chip"
• Accelerometers in modern cars for a large number of purposes including airbag deployment in collisions. • Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone, various Nokia mobile phone models, various HTC PDA models)[15] and a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs to park the hard disk head when free-fall is detected, to prevent damage and data loss. • MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger dynamic stability control[16] • MEMS microphones in portable devices, e.g., mobile phones, head sets and laptops. • Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors • Displays e.g., the DMD chip in a projector based on DLP technology, which has a surface with several hundred thousand micromirrors • Optical switching technology, which is used for switching technology and alignment for data communications • Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemosensor) • Interferometric modulator display (IMOD) applications in consumer electronics (primarily displays for mobile devices), used to create interferometric modulation − reflective display technology as found in mirasol displays • Fluid acceleration such as for micro-cooling Companies with strong MEMS programs come in many sizes. The larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics. The successful small firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins. In addition, both large and small companies work in R&D to explore MEMS technology.
Industry structure The global market for micro-electromechanical systems, which includes products such as automobile airbag systems, display systems and inkjet cartridges totaled $40 billion in 2006 according to Global MEMS/Microsystems Markets and Opportunities, a research report from SEMI and Yole Developpement and is forecasted to reach $72 billion by 2011.[17] MEMS devices are defined as die-level components of first-level packaging, and include pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, micro fluidic devices, etc. The materials and equipment used to manufacture MEMS devices topped $1 billion worldwide in 2006. Materials demand is driven by substrates, making up over 70 percent of the market, packaging coatings and increasing use of chemical mechanical planarization (CMP). While MEMS manufacturing continues to be dominated by used semiconductor equipment, there is a migration to 200 mm lines and select new tools, including etch and bonding for certain MEMS
Microelectromechanical systems applications.
References [1] Waldner, Jean-Baptiste (2008). Nanocomputers and Swarm Intelligence. London: ISTE John Wiley & Sons. p. 205. ISBN 1848210094. [2] Electromechanical monolithic resonator, US patent 3614677 (http:/ / www. google. com/ patents/ about?id=hpcBAAAAEBAJ& dq=ELECTROMECHANICAL+ MONOLITHIC+ RESONATOR), Filed April 29, 1966; Issued October 1971 [3] R.J. Wilfinger, P. H. Bardell and D. S. Chhabra: The resonistor a frequency selective device utilizing the mechanical resonance of a substrate, IBM J. 12, 113–118 (1968) [4] R. Ghodssi, P. Lin (2011). MEMS Materials and Processes Handbook. Berlin: Springer. ISBN 978-0-387-47316-1. [5] T. Polster, M. Hoffmann (2009). "Aluminium nitride based 3D, piezoelectric, tactile sensors". Proc. Chem. 1: 144–147. doi:10.1016/j.proche.2009.07.036. [6] M. Birkholz, K.-E. Ehwald, P. Kulse, J. Drews, M. Fröhlich, U. Haak, M. Kaynak, E. Matthus, K. Schulz, D. Wolansky (2011). "Ultrathin TiN Membranes as a Technology Platform for CMOS-Integrated MEMS and BioMEMS Devices" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1002/ adfm. 201002062/ pdf). Adv. Func. Mat. 21: 1652–1656. doi:10.1002/adfm.201002062. . [7] McCord, M. A.; M. J. Rooks (2000). "2" (http:/ / www. cnf. cornell. edu/ cnf_spietoc. html). SPIE Handbook of Microlithography, Micromachining and Microfabrication. . [8] Williams, K.R.; Muller, R.S. (1996). "Etch rates for micromachining processing". Journal of Microelectromechanical Systems 5 (4): 256. doi:10.1109/84.546406. [9] Kovacs, G.T.A.; Maluf, N.I.; Petersen, K.E. (1998). "Bulk micromachining of silicon". Proceedings of the IEEE 86 (8): 1536. doi:10.1109/5.704259. [10] Chang, Floy I. (1995). Gas-phase silicon micromachining with xenon difluoride. 2641. pp. 117. doi:10.1117/12.220933. [11] Chang, Floy I-Jung. 1995. Xenon difluoride etching of silicon for MEMS. Thesis (M.S.) University of California, Los Angeles, 1995. [12] Brazzle, J.D.; Dokmeci, M.R.; Mastrangelo, C.H. (2004). Modeling and characterization of sacrificial polysilicon etching using vapor-phase xenon difluoride. pp. 737. doi:10.1109/MEMS.2004.1290690. [13] Laermer, F.; Urban, A. (2005). Milestones in deep reactive ion etching. 2. pp. 1118. doi:10.1109/SENSOR.2005.1497272. [14] J. M. Bustillo, R. T. Howe, and R. S. Muller, "Surface micromachining for microelectromechanical systems" (http:/ / citeseerx. ist. psu. edu/ viewdoc/ download;jsessionid=D3FB771FA48AB37E17C2F58B3082E65A?doi=10. 1. 1. 120. 4059& rep=rep1& type=pdf) Proceedings of the IEEE, vol. 86, pp. 1552−1574, 1998. [15] Johnson, R. Collin. There's more to MEMS than meets the iPhone (http:/ / www. eetimes. com/ showArticle. jhtml?articleID=200900669), EE Times, (2007-07-09). Retrieved 2007-07-10. [16] Cenk Acar, Andrei M. Shkel (2008). MEMS Vibratory Gyroscopes: Structural Approaches to Improve Robustness (http:/ / books. google. com/ books?id=WgFPvZyApd0C& pg=PA111). pp. 111 ff. ISBN 0387095357. . [17] Worldwide MEMS Systems Market Forecasted to Reach $72 Billion by 2011 (http:/ / www. azonano. com/ news. asp?newsID=4479)
External links • Online course on An Introduction to BioMEMS and Bionanotechnology (http://nanohub.org/resources/180)
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User:Mkoronowski/turbomachinery Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. The two types of machines are governed by the same basic relationships including Newton's second Law of Motion and Euler's energy equation for compressible fluids. This is illustrated by the horizontal axis of of both Figure_0.2 and 0.3. Centrifugal pumps are also turbomachines that transfer energy from a rotor to a fluid, usually a liquid, while turbines and compressors usually work with a gas.[1] In actuality, there are two overall kinds of turbomachines are encountered in practice. Those that are open and those that are closed turbomachines. Open machines such as propellers, windmills, and unshrouded fans act as isolated airfoils within an infinite (boundary condition) extent of fluid. Conversely, closed machines operate more similarly as an infinite number of airfoils within a finite (boundary condition) quantity of fluid as it passes through a housing or casing (control volume). As a result open turbo-machines have historically been designed and analyzed using wing theory. However, recent advances in CFD has shrunk the gap in applied mathematics such that unducted fans, as used on prototype aircraft engines, are closely related to their closed counterparts.
Figure_0.1 Mounting of a steam turbine
Figure_0.2 -- Aero-Thermo Domain of Turbo-Machinery
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Historical Contributions, The Pioneers The above explanation may seem trivial, but it is actually quite complex. Over this past 100 years, applied scientists like Stodola (1903, 1927-1945[2] ), Pfleiderer (1952[3] ), Hawthorne (1964[4] ), Shepard (1956[5] ), Lakshminarayana (1996[6] ) and Japikse (numerous texts including, 1997[7] ) have tried to educate young engineers in the fundamentals of turbomachinery which apply to all dynamic, continuous-flow, axisymmetric pumps, fans, blowers, and compressors in axial, mixed-flow and radial/centrifugal configurations. Figure_0.3 -- Physical Domain of
This relationship is why advances in turbines and axial compressors Turbo-Machinery frequently find their way into other turbomachinery including centrifugal compressors. Figures 1.1 and 1.2, illustrate the domain of turbomachinery with labels showing centrifugal compressors. Improvements in centrifugal compressors has not been achieved through large discoveries. Rather, improvements have been achieved through understanding and applying incremental pieces of knowledge discovered by many individuals. Figure_1.1 represents the aero-thermo domain of turbomachinery. The horizontal axis represents the energy equation derivable from The First Law of Thermodynamics. The verticle axis, which can be characterized by Mach Number, represents the range of fluid compressibility (or elasticity). The Zed axis, which can be characterized by Reynolds Number, represents the range of fluid viscosities (or stickiness). Mathematicians and Physicists that established the foundations of this aero-thermo domain include: Sir Isaac Newton, Daniel Bernoulli, Leonard Euler, Claude-Louis Navier, Sir George Gabriel Stokes, Ernst Mach, Nikolay Yegorovich Zhukovsky, Martin Wilhelm Kutta, Ludwig Prandtl, Theodore von Karman, Paul Richard Heinrich Blasius, and Henri Coandă. Figure_1.2 represents the physical or mechanical domain of turbomachinery. Again, the horizontal axis represents the energy equation with turbines generating power to the left and compressors absorbing power to the right. Within the physical domain the vertical axis differentiates between high speeds and low speeds depending upon the turbomachinery application. The Zed axis differentiates between axial-flow geometry and radial-flow geometry within the physical domain of turbomachinery. It is implied that mixed-flow turbomachinery lie between axial and radial. Key contributors of technical achievements that pushed the practical application of turbomachinery forward include: Denis Papin[8] , Kernelien Le Demour, Daniel Gabriel Fahrenheit, John Smeaton, Dr. A. C. E. Rateau[9] , John Barber, Alexander Sablukov, Sir Charles Algernon Parsons, Ægidius Elling, Sanford Moss, Willis Carrier, Adolf Busemann, Hermann Schlichting, and Frank Whittle.
Partial Time-Line
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<1689 Early Turbomachines
Pumps, blowers, fans
1689
Denis Papin
Origin of the centrifugal compressor
1754
Leonhard Euler
Euler's "Pump & Turbine" equation
1791
John Barber
First gas turbine patent
1899
Dr. A. C. E. Rateau
First practical centrifugal compressor
1927
Aurel Boleslav Stodola
Formalized "slip factor"
1928
Adolf Busemann
Derived "slip factor"
1937
Frank Whittle
First gas turbine using centrifugal compressor
>1970 Modern Turbomachines 3D-CFD, rocket turbo-pumps, heart assist pumps, turbocharged fuel cells
Turbomachines may be further classified into two additional categories: those that absorb energy to increase the fluid pressure, i.e. pumps, fans, and compressors, and those that produce energy such as turbines by expanding flow to lower pressures. Of particular interest are applications which contain pumps, fans, compressors and turbines. These components are essential in almost all mechanical equipment systems, such as power and refrigeration cycles.[10]
Dimensional analysis To weigh the advantages between centrifugal compressors it is important to compare 8 parameters classic to turbomachinery. Specifically, pressure rise (p), flow (Q), speed (N), power (P), density (ρ), diameter (D), viscosity (mu) and elasticity (e). This creates a practical problem when trying to experimentally determine the effect of any single parameter. This is because it is nearly impossible to change one of these parameters independently.
A steam turbine from MAN SE subdidiary MAN Turbo
The method of procedure known as Buckingham's Pi-Therom can help solve this problem by generating 5 dimensionless forms of these parameters.[5] [7] [11] These Pi parameters provide the foundation for "similitude" and the "affinity-laws" in turbomachinery. They provide for the creation of additional relationships (being dimensionless) found valuable in the characterization of performance. For the examples below Head will be substituted for pressure and sonic velocity will be substituted for elasticity.
Π theorem The three independent dimensions used in this procedure for turbomachinery are: •
Mass (Force is an alternative)
•
Length
•
Time
According to the theorem each of the eight primary parameters are equated to its independent dimensions as follows:
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Flow:
ex. = m^3/s
Head:
ex. = kg*m/s^2
Speed:
ex. = m/s
Power:
ex. = kg*m^2/s^3
Density:
ex. = kg/m^3
Viscosity:
ex. = kg/(m*s)
Diameter:
ex. = m
Speed of sound:
ex. = m/s
Classic turbomachinery similitude Completing the task of following the formal procedure results in generating this classic set of five dimensionless parameters for turbomachinery. Full similitude is achieved when each of the 5 Pi-parameters are equivalent. This of course would mean the to turbo-machines being compared are geometrically similar and running at the same operating point. Flow coefficient: Head coefficient: Speed coefficient: Power coefficient:
Reynolds coefficient:
Turbomachinery analysts gain tremendous insight into performance by comparisons of these 5 parameters with efficiencies and loss coefficients which are also dimensionless. In general application, the flow coefficient and head coefficient are considered of primary importance. Generally, for centrifugal compressors, the velocity coefficient is of secondary importance while the Reynolds coefficient is of tertiary importance. In contrast, as expected for pumps, the Reynolds number becomes of secondary importance and the velocity coefficient almost irrelevant.
Other dimensionless combinations Demonstrated in the table below is another value of dimensional analysis. Any number of new dimensionless parameters can be calculated through exponents and multiplication. For example, a variation of the first parameter shown below is popularly used in aircraft engine system analysis. The third parameter is a simplified dimensional variation of the first and second. This third definition is applicable with strict limitations. The fourth parameter, specific speed, is very well known and useful in that it removes diameter. The fifth parameter, specific diameter, is a less frequently discussed dimensionless parameter found useful by Balje[12] .
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Corrected mass flow coefficient:
Alternate#1 equivalent Mach form:
Alternate#2 simplified dimensional form:
Specific speed coefficient:
Specific diameter coefficient:
Affinity laws The following "affinity laws" are derived from the five Pi-parameters shown above. They provide a simple basis for scaling turbomachinery from one application to the next. From flow coefficient:
From head coefficient:
From power coefficient:
From flow coefficient:
From head coefficient:
From power coefficient:
Turbomachinery There are numerous types of dynamic continuous flow turbomachinery that can be referenced within Wikipedia. Below is a partial list of these entries. What is notable about this collection is that the fundamentals that apply to centrifugal compressors also apply to each of these entries. Certainly there are significant differences between these machines and between the types of analysis that are typically applied to specific cases. This does not negate the fact that they are unified by the same underlying physics of fluid dynamics, gas dynamics, aerodynamics, hydrodynamics, and thermodynamics.
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•
Axial compressor
•
Radial turbine
•
Axial fan
•
Turbocharger
•
Centrifugal fan
•
Turboexpander
•
Centrifugal pump
•
Turbofans
•
Centrifugal type supercharger
•
Turbojet
•
Francis turbine
•
Turbomachinery
•
Turboprop
•
Turbopump
•
Turboshaft
•
Turbines
See also • Secondary flow in turbomachinery • Exoskeletal engine - an inside-out turbine • Turbocharger
Sources • Sydney Lawrence Dixon, Fluid mechanics and thermodynamics of turbomachinery, 1998 • Earl Logan (1993). Turbomachinery: basic theory and applications [13]. CRC Press. ISBN 9780824791384. • Erian A. Baskharone (2006). Principles of turbomachinery in air-breathing engines [14]. Cambridge University Press. ISBN 9780521858106.
References [1] [2] [3] [4]
Logan, p.1 Aurel Stodola (1945). Steam and Gas Turbines. New York: P. Smith. OL18625767M. Pfleiderer, C. (1952). Turbomachines. New York: Springer-Verlag. W. R. Hawthorne (1964). Aerodynamics Of Turbines and Compressors. Princeton New Jersey: Princeton University Press. ISBN LCCN 58-5029. [5] Shepard,Dennis G. (1956). Principles of Turbomachinery. McMillan. ISBN 0 - 471 - 85546 - 4. LCCN 56002849. [6] Lakshminarayana, B. (1996). Fluid Dynamics and Heat Transfer of Turbomachinery. New York: John Wiley & Sons Inc.. ISBN 0-471-85546-4. [7] Japikse, David & Baines, Nicholas C. (1997). Introduction to Turbomachinery. Oxford: Oxford University press. ISBN 0-933283-10-5. [8] Engeda, Abraham (1999). "From the Crystal Palace to the pump room" (http:/ / www. memagazine. org/ backissues/ membersonly/ february99/ features/ crystal/ crystal. html). Mechanical Engineering. ASME. . [9] Elliott Company. "Past, Present, Future, 1910-2010" (http:/ / www. elliott-turbo. com/ Files/ Admin/ 100th Anniversary/ 1930s - O Line Blowers. pdf). Elliott. . Retrieved 1 May 2011. [10] Baskharone, p.6 [11] Streeter, Victor L. (1971). Fluid Mechanics fifth edition. New York: McGraw Hill Book Company. ISBN 07-062191-8. [12] Balje, O. E. (1961). Turbo Machines; a Guide to Design, Selection, and Theory. New York: John Wiley & Sons. ISBN 0-471-06036-4. [13] http:/ / books. google. com/ books?id=s4Qfa1AWGGkC& printsec=frontcover& dq=turbomachinery& source=bl& ots=U_mTFto9da& sig=8zz82kSRJZT6uYdBpqKxcNwNNik& hl=en& ei=ND23TMudHMSclgfGpqi9DA& sa=X& oi=book_result& ct=result& resnum=4& sqi=2& ved=0CCgQ6AEwAw#v=onepage& q& f=false [14] http:/ / books. google. com/ books?id=dY6a4bZg-LsC& pg=PA10& lpg=PA10& dq=Turbomachinery+ classification& source=bl& ots=YcpNwn4tO-& sig=Lz-l5x3cLfhmvVPLT-BbbCoiDWU& hl=en& ei=LkO3TLOhCIOglAf17a27DA& sa=X& oi=book_result& ct=result& resnum=1& ved=0CBIQ6AEwAA#v=onepage& q& f=false
User:Mkoronowski/turbomachinery
External links • Basic hydraulic equations (http://hydraulik.empass.biz) • MIT hydraulics course notes (http://ocw.mit.edu/courses/civil-and-environmental-engineering/ 1-060-engineering-mechanics-ii-spring-2006/lecture-notes/) • Hydrodynamics of Pumps (http://caltechbook.library.caltech.edu/22/01/pumps.htm)
Modal analysis Modal analysis is the study of the dynamic properties of structures under vibrational excitation. Modal analysis is the field of measuring and analysing the dynamic response of structures and or fluids when excited by an input. Examples would include measuring the vibration of a car's body when it is attached to an electromagnetic shaker, or the noise pattern in a room when excited by a loudspeaker. Modern day modal testing systems are composed of transducers (typically accelerometers and load cells), or non contact via a Laser vibrometer, an analog-to-digital converter frontend (to digitize analog instrumentation signals) and a host PC (personal computer) to view the data and analyze it. Classically this was done with a SIMO (single-input, multiple-output) approach, that is, one excitation point, and then the response is measured at many other points. In the past a hammer survey, using a fixed accelerometer and a roving hammer as excitation, gave a MISO (multiple-input, single-output) analysis, which is mathematically identical to SIMO, due to the principle of reciprocity. In recent years MIMO (multi-input, multiple-output) has become more practical, where partial coherence analysis identifies which part of the response comes from which excitation source. Typical excitation signals can be classed as impulse, broadband, swept sine, chirp, and possibly others. Each has its own advantages and disadvantages. The analysis of the signals typically relies on Fourier analysis. The resulting transfer function will show one or more resonances, whose characteristic mass, frequency and damping can be estimated from the measurements. The animated display of the mode shape is very useful to NVH (noise, vibration, and harshness) engineers. The results can also be used to correlate with finite element analysis normal mode solutions.
Structures In structural engineering, modal analysis uses a structure's overall mass and stiffness to find the various periods that it will naturally resonate at. These periods of vibration are very important to note in earthquake engineering, as it is imperative that a building's natural frequency does not match the frequency of expected earthquakes in the region in which the building is to be constructed. If a structure's natural frequency matches an earthquake's frequency, the structure could continue to resonate and experience structural damage. Although modal analysis is usually carried out by computers, it is possible to hand-calculate the period of vibration of any high-rise building by idealizing it as a fixed-ended cantilever with lumped masses. For a more detailed explanation, see "Structural Analysis" by Ghali, Neville, and Brown, as it provides an easy-to-follow approach to idealizing and solving complex structures by hand.
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Modal analysis
Electrodynamics The basic idea of a modal analysis in electrodynamics is the same as in mechanics. The application is to determine which electromagnetic wave modes can stand or propagate within conducting enclosures such as waveguides or resonators.
References • D. J. Ewins: Modal Testing: Theory, Practice and Application • Jimin He, Zhi-Fang Fu (2001). Modal Analysis, Butterworth-Heinemann. ISBN 0-7506-5079-6.
External links • • • • • •
Experimental Modal Analysis [1] Structural Dynamics Testing/Modal Analysis [2] A Brief Introduction to Modal Analysis [3] An Introduction on the Topic from The Society for Experimental Mechanics [4] International Modal Analysis Conference (IMAC) [5] International Seminar on Modal Analysis (ISMA) [6]
• NAFEMS - Modal Analysis in Virtual Prototyping and Product Validation [7] • An Integrated Approach to the Dynamic Testing of Aerospace Structures [8] • Free Excel sheets to estimate modal parameters [9]
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
http:/ / www. polytec. com/ us/ applications/ automotive-transportation/ experimental-modal-analysis/ http:/ / www. mpihome. com/ pdf/ soa_structural_dynamics_testing. pdf http:/ / www. lmsintl. com/ modal-analysis http:/ / www. sem. org/ ArtDownLoad/ msma98. pdf http:/ / www. sem. org/ CONF-IMAC-TOP. asp http:/ / www. isma-isaac. be http:/ / www. nafems. org/ events/ nafems/ 2009/ modal/ http:/ / www. lmsintl. com/ dynamic-testing-aerospace-structures http:/ / www. noisestructure. com/ products/ MPE_SDOF. php
379
Motion ratio
Motion ratio The motion ratio of a mechanism is the ratio of the displacement of the point of interest to that of another point. The most common example is in a vehicle's suspension, where it is used to describe the displacement and forces in the springs and shock absorbers. The force in the spring is (roughly) the vertical force at the contact patch divided by the motion ratio, and the wheel rate is the spring rate divided by the motion ratio squared. This is described as the Installation Ratio in the reference. Motion Ratio is the more common term in the industry, but sometimes is used to mean the inverse of the above definition. Motion ratio in suspension of a vehicle describes the amount of shock travel for a given amount of wheel travel. Mathematically it is the ratio of shock travel and wheel travel. The amount of force transmitted to the vehicle chassis reduces with increase in motion ratio. A motion ratio close to one is desired in vehicle for better ride and comfort. One should know the desired wheel travel of the vehicle before calculating motion ratio which depends much on the type of track the vehicle will run upon. How to decide the motion ratio? It basically depends on 3 factors a)Bending Moment: To reduce the bending moment the strut point should be near to the wheel. b)Suspension Stiffness: The suspension tends to get stiff when its inclination of the shock absorber to horizontal tends to 90 deg. c)Half Shafts: In Rear suspension the wheel travel is constrained by the angle limitations of the universal joints of the half shafts. Design the motion ratio such that at maximum bounce and rebound shocks are the first components that bottom out by hitting bump stops.
References • Milliken and Milliken "Race Car Vehicle Dynamics" • Carol Smith "Tune to win"
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Multi-function structure
Multi-function structure Multi-function material is a composite material. The traditional approach to the development of structures is to address the loadcarrying function and other functional requirements separately. Recently, however, there has been increased interest in the development of load-bearing materials and structures which have integral non-load-bearing functions, guided by recent discoveries about how multifunctional biological systems work[1] .
Introduction With conventional structural materials, it has been difficult to achieve simultaneous improvement in multiple structural functions, but the increasing use of composite materials has been driven in part by the potential for such improvements. The multi-functions can vary from mechanical to electrical and thermal functions. The most widely used composites have polymer matrix materials, which are typically poor conductors. Enhanced conductivity could be achieved with reinforcing the composite with carbon nanotubes for instance.[2] [3]
Functions Among the many functions that can be attained are Electrical/thermal conductivity, Sensing and actuation, Energy harvesting/storage, Self-healing capability, Electromagnetic interference (EMI) shielding and recyclability and biodegradability. See also Functionally graded materials(FGM) which are composite materials where the composition or the microstructure are locally varied so that a certain variation of the local material properties is achieved [4] . However, FGM can be designed for specific function and applications.
Applications Touchscreens Smart structures[5] are one of many applications.
References [1] [2] [3] [4] [5]
A review of recent research on mechanics of multifunctional composite, Journal of Composite Structures 92 (2010) 2793–2810 "Sensors and actuators based on carbon nanotubes and their composite" J. Composites Science and Technology 68 (2008) 1227–1249 Challenges and opportunities in multifunctional nanocomposite structures for aerospace applications. MRS Bull 2007;32(4):324-34 O. Kolednik, Functionally Graded Materials, 2008 (http:/ / www. oeaw. ac. at/ esi/ english/ research/ materials/ comp/ fgms. html) http:/ / science. howstuffworks. com/ engineering/ structural/ smart-structure. htm
381
Multiphase heat transfer
382
Multiphase heat transfer Definitions A multiphase system is one characterized by the simultaneous presence of several phases, the two-phase system being the simplest case. The term ‘two-component’ is sometimes used to describe flows in which the phases consist of different chemical substances. For example, steam-water flows are two-phase, while air-water flows are two-component. Some two-component flows (mostly liquid-liquid) technically consist of a single phase but are identified as two-phase flows in which the term “phase” is applied to each of the components. Since the same mathematics describes two-phase and two-component flows, the two expressions can be treated as synonymous.
Multiphase flow versus heat transfer The analysis of multiphase systems can include consideration of multiphase flow and multiphase heat transfer. When all of the phases in a multiphase system exist at the same temperature, multiphase flow is the only concern. However, when the temperatures of the individual phases are different, interphase heat transfer also occurs.
Phase-change heat transfer If different phases of the same pure substance are present in a multiphase system, interphase heat transfer will result in a change of phase, which is always accompanied by interphase mass transfer. The combination of heat transfer with mass transfer during phase change makes multiphase systems distinctly more challenging than simpler systems. Based on the phases that are involved in the system, phase change problems can be classified as: (1) solid–liquid phase change (melting and solidification), (2) solid–vapor phase change (sublimation and deposition), and (3) liquid–vapor phase change (boiling/evaporation and condensation). Melting and sublimation are also referred to as fluidification because both liquid and vapor are regarded as fluids.
References Faghri, A., and Zhang, Y., 2006, Transport Phenomena in Multiphase Systems Burlington, MA.
[1]
, ISBN: 0-12-370610-6, Elsevier,
Lock, G.S.H., 1994, Latent Heat Transfer, Oxford Science Publications, Oxford University, Oxford, UK.
References [1] http:/ / www. elsevier. com/ wps/ find/ bookdescription. cws_home/ 707571/ description?navopenmenu=4
Non-synchronous transmission
383
Non-synchronous transmission Transmission types Manual • • •
Sequential manual Non-synchronous Preselector Automatic
•
Manumatic Semi-automatic
Electrohydraulic Dual clutch • Saxomat • •
Continuously variable Bicycle gearing • •
Derailleur gears Hub gears
A non-synchronous transmission is a form of transmission based on gears that do not use synchronizing mechanisms. They are found primarily in various types of agricultural, and commercial vehicles. Because the gear boxes are engineered without "cone and collar" synchronizing technology, the non-synchronous transmission type requires an understanding of gear range, torque, engine power, range selector, multi-functional clutch, and shifter functions. Engineered to pull tremendous loads, often equal to or exceeding 40 tons, some vehicles may also use a combination of transmissions for different mechanisms. An example would be a PTO.[1]
History In 1842, the reversing lever was invented and patented as the Walschaerts valve gear in Belgium, and reversing lever descriptions exist in British, and American mechanics' diagrams.[2] In 1890, Panhard used a chain-drive with a Daimler engine in a horseless carriage. Industrial marketing has since then coined spectacular names for various vehicle parts. Changing from the Locomobile,[3] a 1906 race-car to what is now called the automobile, advertisers used design wording from the engineering departments to give new ideas a desirable appeal for sales promotions. From 1932, synchronizer mechanisms began to appear in automotive transmissions. The split off of automotive transmission types that has prevailed in engineering designs uses three major categories: automatic, manual, and non-synchronous. Some of the differences are improvements, including the continuously variable transmission installed in hybrid vehicles that are powered partly by an internal combustion engine, and partly by an electric motor. The concepts of transmission continue to employ methods for transferring the most conceivably efficient use of power.
Non-synchronous transmission
How non-synchronization works Non-synchronous transmissions are engineered[4] with the understanding that a trained operator will be shifting gears in a known coordination of timing. Commercial vehicle operators use a double-clutching technique that is taught in driver's trade schools. The most skillful drivers can shift these transmissions without using the clutch by bringing the engine to exactly the right rpm in neutral before attempting to complete a shift, a technique called "float-shifting." With payloads of cargo ranging in commercial freight of 80,000 lbs (40 tons (short) or 36.3 tonnes) or more, some heavy haulers have over 24 gears that an operator will shift through before reaching a top cruising speed of 70 mph (113 km/h). Many low-low (creeper) gears are used in farm Diagram of a non-synchronous transmission equipment to plow, till, or harvest. Also see Engineering vehicle. An showing gear fork, gear box, and gears that would inexperienced operator would suddenly find a piece of heavy be used in a commercial motor vehicle equipment stuck in gear under full power, or even worse unable to shift into gear a runaway vehicle in neutral headed down a steep slope, unless he understood the synchronizing skill, and torque issues in non-synchronous transmissions. Many mountain roads require heavy equipment operators to remain in gear and not shift while passing down a steep grade. For more details about steep grade operation see either jake brake, or engine brake. Many other circumstances face operators of non-synchronous transmissions. Safety and operator skills need to be learned before operating any of these types of vehicles.
Double clutching (commercial motor vehicle) Operators of 18-wheelers, farm equipment, tractors and other heavy equipment learn to float the transmission in and out of gear, beginning with dis-engaging the clutch by pressing the clutch pedal only part way, enough to pull the transmission out of gear, re-engaging the clutch in neutral (between gears by letting the clutch pedal all the way back out) to let the engine revolutions decelerate enough for the idle sprockets to shift, and free gear shafts to slow their revolutions per minute (RPM), then dis-engage the clutch again (by pressing the clutch pedal only part way to the floor) a 2nd time, and float the higher gear into engaging the drive coupling and fly wheel and engaging the clutch plates. Professional operators of heavy equipment take extensive safety training before ever learning how to double-clutch. Once an operator is Cut-away view of a commercial motor vehicle familiar with range, range selector, rpm, velocity, and torque of heavy non-synchronous transmission equipment like an 18-wheeler, they can begin to anticipate when to shift gears. Operators become familiar with ranges of gears. They also learn not to leave their foot on the clutch while driving, because these types of transmissions use the clutch for several very different purposes. The depth the clutch is depressed to the floor will determine what the clutch will be doing as a synchronizing function.
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Non-synchronous transmission
Clutch brake Unlike any other type of transmission, non-synchronous transmissions often have a mechanism for slowing down, or stopping an idle gear. In commercial motor vehicles, this mechanism is called the clutch brake, and is used by depressing the clutch all the way to the floor. This is useful in 18-wheelers that have just started their diesel engines, and are releasing parking locks, and engaging the transmission from a stop. The clutch brake not only slows or stops the idle gear axis, but can also prevent shifting into gear until the clutch is lifted a few inches off the floor. In order to shift into gear, the clutch must be half way off the floor, otherwise the clutch brake will prevent the transmission from being shifted into or out of gear. Mechanics must often repair or replace the clutch brake in a non-synchronous transmission when an inexperienced operator wears it out, it becomes inoperable, or has lost its function.
Comparison of transmissions Non-synchronous transmissions[5] are designed to depend upon an operator experienced in changing gears. The operators must understand how to shift the transmission into and out of gear. Many learn how to do this in certifying schools. All automatic transmissions have synchronizing mechanisms. Most manual transmissions also have synchronizers.[6] But there are still other types of transmissions used mostly in commercial applications that are non-synchronous. Fully synchronous, hydrau-pneumatic systems are designed to change gears based on engine performance and other velocity indicators, delivering torque to drive wheels. These transmissions have synchronizing mechanisms (called cone and collar synchronizers) that are designed to keep gear dog-teeth from being broken off. Heavy equipment for industrial, military, or farm use have different torque and load issues. They have unique stress from massive horsepower that would make converter faces shear. For the reasons of engineering a dependable, longer-life piece of equipment, these machines often use non-synchronous transmissions. Any transmission that requires the operator to manually synchronize engine crank-shaft revolutions (RPM) with drive-shaft revolutions is non-synchronous.
Notes [1] [2] [3] [4] [5]
"6-10 Bolt Mechanical Power Takeoff" (http:/ / news. thomasnet. com/ fullstory/ 10489/ 1723). . Retrieved 2007-07-16. The reversing lever, or Johnson Bar (http:/ / books. google. com/ books?id=jCJMAAAAMAAJ& pg=PA209). . Retrieved 2009-08-14. "Edison & Ford Museum" (http:/ / www. thehenryford. org). . Retrieved 2007-07-19. "transmission parts news: index" (http:/ / news. thomasnet. com/ news/ 1620). . Retrieved 2007-07-16. "Sec.13Pg13-3Vehicles equipped with Non-synchronous transmission" (http:/ / www. nh. gov/ safety/ divisions/ dmv/ documents/ nhcdm. pdf) (PDF). . Retrieved 2007-07-18. [6] "Synchronizers; graphic illustration of how they work" (http:/ / www. howstuffworks. com/ transmission3. htm). . Retrieved 2007-07-18.
References • Core Transmissions (http://www.coresuppliers.com/transmission_core_supplier.htm)-for display only: this is not an endorsement • ATA - American Trucking Association (http://www.truckline.com)- not a global reference • PTDI acronym for Professional Truck Driver Institute - pertains to U.S. only • Federal Motor Carrier Safety Administration (http://www.nh.gov/safety/divisions/dmv/documents/nhcdm. pdf) New Hampshire Dept. of Motor Vehicles 2005 Commercial Driver's License Manual, sec. 13.1.11 Section 13 page 13-3 says Double clutch if vehicle is equipped with non-synchronized transmission. (note: this file is a complete manual in Adobe Acrobat format with a file size of over 10 Megabytes).
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Nutation
Nutation Nutation (from Latin: nūtāre, to nod) is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behavior of a mechanism. A pure nutation is a movement of a rotational axis such that the first Euler angle (precession) is constant.
Astronomy The nutation of a planet happens because of tidal forces that cause the precession of the equinoxes to vary over time so that the speed of precession is not constant. The nutation of the axis of the Earth was discovered in 1728 by the British astronomer James Bradley, but this nutation was not explained in detail until 20 years later.[1] Because the dynamic motions of the planets are so well-known, their Rotation (green), Precession (blue) and nutations can be calculated to within arcseconds over periods of many Nutation in obliquity (red) of the Earth decades. There is another disturbance of the Earth's rotation called polar motion that can be estimated for only a few months into the future because it is influenced by rapidly and unpredictably varying things such as ocean currents, wind systems, and motions in the liquid nickel-iron core of the Earth. Values of nutations are usually divided into components parallel and perpendicular to the ecliptic. The component that works along the ecliptic is known as the nutation in longitude. The component perpendicular to the ecliptic is known as the nutation in obliquity. Celestial coordinate systems are based on an "equator" and "equinox," which means a great circle in the sky that is the projection of the Earth's equator outwards, and a line, the Vernal equinox intersecting that circle, which determines the starting point for measurement of right ascension. These items are affected both by precession of the equinoxes and nutation, and thus depend on the theories applied to precession and nutation, and on the date used as a reference date for the coordinate system. In simpler terms, nutation (and precession) values are important in observation from Earth for calculating the apparent positions of astronomical objects.
Earth In the case of the Earth, the principal sources of tidal force are the Sun and Moon, which continuously change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes. However, there are other significant periodical terms that must be calculated depending on the desired accuracy of the result. A mathematical description (set of equations) that represents nutation is called a "theory of nutation" (see, e.g., [2]). In the theory, parameters are adjusted in a more or less ad hoc method to obtain the best fit to data. As can be seen from the IERS publication just cited, nowadays simple rigid-body mechanics do not give the best theory; one has to account for deformations of the solid Earth.
386
Nutation Values The principal term of nutation is due to the regression of the moon's nodal line and has the same period of 6798 days (18.6 years). It reaches plus or minus 17″ in longitude and 9″ in obliquity. All other terms are much smaller; the next-largest, with a period of 183 days (0.5 year), has amplitudes 1.3″ and 0.6″ respectively. The periods of all terms larger than 0.0001″ (about as accurately as one can measure) lie between 5.5 and 6798 days; for some reason they seem to avoid the range from 34.8 to 91 days, so it is customary to split the nutation into long-period and short-period terms. The long-period terms are calculated and mentioned in the almanacs, while the additional correction due to the short-period terms is usually taken from a table.
In mechanical engineering A nutating motion can be seen in a swashplate mechanism. In general, a nutating plate is carried on a skewed bearing on the main shaft and does not itself rotate, whereas a swashplate is fixed to the shaft and rotates with it. The motion is similar to the motions of coin or a tire wobbling on the ground after being dropped with the flat side down. The nutating motion is widely employed in flowmeters and pumps. The displacement of volume for one revolution is first determined. The speed of the device in revolutions per unit time is measured. In the case of flowmeters, the product of the rotational speed and the displacement per revolution is then taken to find the flow rate.
In physiology In upright vertebrates, the sacrum is capable of slight independent movement along the sagittal plane. When you bend backward the top (base) of the sacrum moves forward relative to the ilium; when you bend forward the top moves back.[3] The anterior motion of the sacral base is called nutation, and the posterior motion is counter-nutation.[4]
External links • Nutating Disk Displacement Flowmeter [5]
References [1] The Nodding Sphere and the Bird's Beak: D'Alembert's Dispute with Euler (http:/ / mathdl. maa. org/ mathDL/ ?pa=content& sa=viewDocument& nodeId=962& bodyId=1147) [2] http:/ / www. iers. org/ nn_10382/ IERS/ EN/ Science/ Recommendations/ resolutionB3. html [3] Maitland, J (2001). Spinal Manipulation Made Simple. Berkeley: North Atlantic Books, p. 72. [4] Joseph D. Kurnik, DC. "The AS Ilium Fixation, Nutation, and Respect" (http:/ / www. chiroweb. com/ archives/ 14/ 26/ 18. html). . [5] http:/ / www. engineersedge. com/ instrumentation/ nutating_disk_displacment_meter. htm
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Orifice plate
388
Orifice plate An orifice plate is a device used for measuring the volumetric flow rate. It uses the same principle as a Venturi nozzle, namely Bernoulli's principle which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. When the velocity increases, the pressure decreases and vice versa.
Description An orifice plate is a thin plate with a hole in the middle. It is usually placed in a pipe in which fluid flows. When the fluid reaches the orifice plate, with the hole in the middle, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracta point (see drawing to the right). As it does so, the velocity and the pressure changes. Beyond the vena contracta, the fluid expands and the velocity and pressure change once again. By measuring the difference in fluid pressure between the normal pipe section and at the vena contracta, the volumetric and mass flow rates can be obtained from Bernoulli's equation.
Uses
Flat-plate, sharp-edge orifice
ISO 5167 Orifice Plate
Orifice plates are most commonly used for continuous measurement of fluid flow in pipes. They are also used in some small river systems to measure flow rates at locations where the river passes through a culvert or drain. Only a small number of rivers are appropriate for the use of the technology since the plate must remain completely immersed i.e the approach pipe must be full, and the river must be substantially free of debris. A restrictive flow orifice, a type of orifice plate, is a safety device to control maximum flow from a compressed gas cylinder. [1] In the natural environment large orifice plates are used to control onward flow in flood relief dams. In these structures a low dam is placed across a river and in normal operation the water flows through the orifice plate unimpeded as the orifice is substantially larger than the normal flow cross section. However, in floods, the flow rate rises and floods out the orifice plate which can then only pass a flow determined by the physical dimensions of the orifice. Flow is then held back behind the low dam in a temporary reservoir which is slowly discharged through the orifice when the flood subsides.
Orifice plate
389
Incompressible flow through an orifice By assuming steady-state, incompressible (constant fluid density), inviscid, laminar flow in a horizontal pipe (no change in elevation) with negligible frictional losses, Bernoulli's equation reduces to an equation relating the conservation of energy between two points on the same streamline:
or:
By continuity equation: or
Solving for
and
:
:
and:
The above expression for
gives the theoretical volume flow rate. Introducing the beta factor
as the coefficient of discharge
as well
:
And finally introducing the meter coefficient
which is defined as
to obtain the final equation
for the volumetric flow of the fluid through the orifice: Multiplying by the density of the fluid to obtain the equation for the mass flow rate at any section in the pipe:[2] [3] [4] [5]
where: = volumetric flow rate (at any cross-section), m³/s = mass flow rate (at any cross-section), kg/s = coefficient of discharge, dimensionless = orifice flow coefficient, dimensionless = cross-sectional area of the pipe, m² = cross-sectional area of the orifice hole, m² = diameter of the pipe, m = diameter of the orifice hole, m = ratio of orifice hole diameter to pipe diameter, dimensionless
Orifice plate
390 = upstream fluid velocity, m/s = fluid velocity through the orifice hole, m/s = fluid upstream pressure, Pa with dimensions of kg/(m·s² ) = fluid downstream pressure, Pa with dimensions of kg/(m·s² ) = fluid density, kg/m³
Deriving the above equations used the cross-section of the orifice opening and is not as realistic as using the minimum cross-section at the vena contracta. In addition, frictional losses may not be negligible and viscosity and turbulence effects may be present. For that reason, the coefficient of discharge is introduced. Methods exist for determining the coefficient of discharge as a function of the Reynolds number.[3] is often referred to as the velocity of approach factor[2] and dividing the coefficient of
The parameter
discharge by that parameter (as was done above) produces the flow coefficient determining the flow coefficient as a function of the beta function
. Methods also exist for
and the location of the downstream pressure
sensing tap. For rough approximations, the flow coefficient may be assumed to be between 0.60 and 0.75. For a first approximation, a flow coefficient of 0.62 can be used as this approximates to fully developed flow. An orifice only works well when supplied with a fully developed flow profile. This is achieved by a long upstream length (20 to 40 pipe diameters, depending on Reynolds number) or the use of a flow conditioner. Orifice plates are small and inexpensive but do not recover the pressure drop as well as a venturi nozzle does. If space permits, a venturi meter is more efficient than an orifice plate.
Flow of gases through an orifice In general, equation (2) is applicable only for incompressible flows. It can be modified by introducing the expansion factor to account for the compressibility of gases.
is 1.0 for incompressible fluids and it can be calculated for compressible gases.[3]
Calculation of expansion factor The expansion factor
, which allows for the change in the density of an ideal gas as it expands isentropically, is
[3]
given by:
For values of
less than 0.25,
approaches 0 and the last bracketed term in the above equation approaches 1.
Thus, for the large majority of orifice plate installations:
Orifice plate
391
where: = Expansion factor, dimensionless = = specific heat ratio (
), dimensionless
Substituting equation (4) into the mass flow rate equation (3):
and:
and thus, the final equation for the non-choked (i.e., sub-sonic) flow of ideal gases through an orifice for values of β less than 0.25:
Using the ideal gas law and the compressibility factor (which corrects for non-ideal gases), a practical equation is obtained for the non-choked flow of real gases through an orifice for values of β less than 0.25:[4] [5] [6]
Remembering that
and
(ideal gas law and the compressibility factor)
where: = specific heat ratio (
), dimensionless
= mass flow rate at any section, kg/s = upstream real gas flow rate, m³/s = orifice flow coefficient, dimensionless = cross-sectional area of the orifice hole, m² = upstream real gas density, kg/m³ = upstream gas pressure, Pa with dimensions of kg/(m·s²) = downstream pressure, Pa with dimensions of kg/(m·s²) = the gas molecular mass, kg/mol (also known as the molecular weight) = the Universal Gas Law Constant = 8.3145 J/(mol·K) = absolute upstream gas temperature, K = the gas compressibility factor at
and
, dimensionless
A detailed explanation of choked and non-choked flow of gases, as well as the equation for the choked flow of gases through restriction orifices, is available at Choked flow.
Orifice plate
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The flow of real gases through thin-plate orifices never becomes fully choked. "Cunningham (1951) first drew attention to the fact that choked flow will not occur across a standard, thin, square-edged orifice."[7] The mass flow rate through the orifice continues to increase as the downstream pressure is lowered to a perfect vacuum, though the mass flow rate increases slowly as the downstream pressure is reduced below the critical pressure.[8]
Permanent pressure drop for incompressible fluids For a square-edge orifice plate with flange taps[9] :
where: = permanent pressure drop = indicated pressure drop at the flange taps
And rearranging the formula near the top of this article:
References [1] [2] [3] [4]
[5]
[6] [7] [8] [9]
restrictive flow orifice (http:/ / www. mathesongas. com/ pdfs/ products/ Restrictive-Flow-Orifices. pdf) Lecture, University of Sydney (http:/ / www. aeromech. usyd. edu. au/ aero/ cvanalysis/ node3. shtml#node43) Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook (Sixth Edition ed.). McGraw Hill. ISBN 0-07-049479-7. Handbook of Chemical Hazard Analysis Procedures, Appendix B, Federal Emergency Management Agency, U.S. Dept. of Transportation, and U.S. Environmental Protection Agency, 1989. Handbook of Chemical Hazard Analysis, Appendix B (http:/ / nepis. epa. gov/ Exe/ ZyNET. exe/ 10003MK5. TXT?ZyActionD=ZyDocument& Client=EPA& Index=1986+ Thru+ 1990& Docs=& Query=& Time=& EndTime=& SearchMethod=1& TocRestrict=n& Toc=& TocEntry=& QField=pubnumber^"OSWERHCHAP"& QFieldYear=& QFieldMonth=& QFieldDay=& UseQField=pubnumber& IntQFieldOp=1& ExtQFieldOp=1& XmlQuery=& File=D:\zyfiles\Index Data\86thru90\TXT\00000003\10003MK5. TXT& User=ANONYMOUS& Password=anonymous& SortMethod=h|-& MaximumDocuments=10& FuzzyDegree=0& ImageQuality=r75g8/ r75g8/ x150y150g16/ i425& Display=p|f& DefSeekPage=x& SearchBack=ZyActionL& Back=ZyActionS& BackDesc=Results page& MaximumPages=1& ZyEntry=1& SeekPage=x) Click on PDF icon, wait and then scroll down to page 391 of 520 PDF pages. Risk Management Program Guidance For Offsite Consequence Analysis, U.S. EPA publication EPA-550-B-99-009, April 1999. Guidance for Offsite Consequence Analysis (http:/ / yosemite. epa. gov/ oswer/ ceppoweb. nsf/ vwResourcesByFilename/ oca-all. pdf/ $file/ oca-all. pdf?OpenElement) Methods For The Calculation Of Physical Effects Due To Releases Of Hazardous Substances (Liquids and Gases), PGS2 CPR 14E, Chapter 2, The Netherlands Organization Of Applied Scientific Research, The Hague, 2005. PGS2 CPR 14E (http:/ / vrom. nl/ pagina. html?id=20725) Cunningham, R.G., "Orifice Meters with Supercritical Compressible Flow", Trans. ASME, Vol. 73, pp. 625-638, 1951 Section 3 -- Choked Flow (http:/ / www. engsoft. co. kr/ download_e/ steam_flow_e. htm) Catalog section by AVCO (http:/ / www. avcovalve. com/ products/ pdfs/ Orifice Plates. pdf)
External Links • Orifice flow calculators (http://tierling.home.texas.net/)
Ortman Key
Ortman Key Ortman Key is a coupling device used to secure two adjacent cylindrical segments of a pressure vessel common in tactical rocket motors. An Ortman Key is made of elongated rectangular metal bar stock, such as steel, and is inserted into juxtaposed anular grooves around the circumference of the mating parts. The Ortman Key assembly is used in high pressure applications where packaging, strength and mass are important. Edmund Key is a common variant of the Ortman Key which is similar except has a feature added to the end of the key to aid in extraction of the key from the assembly.
References • Google Patent Search Ortman Key G. Nathan 1961 (http://www.google.com/patents/ about?id=AcdEAAAAEBAJ&dq=ortman+key) • Google Patent Search Rocket Motor 1961 (http://www.google.com/patents?id=4OxiAAAAEBAJ& printsec=abstract&zoom=4#v=onepage&q&f=false)
Oscillating reciprocation Oscillating reciprocation is an action where a body's displacement 'reciprocates' in a given axis or defined displacement vector and 'oscillates' along that axis usually perpendicular to the defined displacement. eg. the new Sabre Saw's on the market are reciprocating saw's which also oscillate the blade in an up and down fashion perpendicular to the cutting stroke.
Overspeed (engine) Overspeed is a condition in which an engine is allowed or forced to turn beyond its design limit. The consequences of running an engine too fast vary by engine type and model and depend upon several factors, chief amongst them the duration of the overspeed and by the speed attained. With some engines even a momentary overspeed can result in greatly reduced engine life or even catastrophic failure. The speed of an engine is ordinarily measured in revolutions per minute (RPM).
Examples of overspeed • In aircraft an engine overspeed will occur if the propeller - ordinarily connected directly to the engine - is forced to turn too fast by high speed airflow while the aircraft is in a dive. • In jet aircraft an overspeed results when the axial compressor exceeds its maximum operating RPM - this often leads to the mechanical failure of turbine blades, flameout and complete destruction of the engine. • In vehicles an engine can be forced to turn too quickly by changing to an inappropriately low gear. • Most unregulated engines will overspeed should there be no or little load while power is applied.
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Overspeed (engine)
Overspeed protection Sometimes a regulator or governor is fitted to make engine overspeed impossible or less likely. For example: • Many steam engines use a centrifugal governor which centrifugally close a throttle to restrict steam flow as engine speed increases. • In motor vehicles automatic gearboxes will change gear to prevent the engine from turning too quickly. • Some aircraft have constant speed units which automatically change propeller pitch to keep the engine running at the optimum speed. Large diesel engines are sometimes fitted with a secondary protection device [1] which operates if the governor fails. This consists of a flap valve in the air intake. If the engine overspeeds, the air flow through the intake will rise to an abnormal level. This causes the flap valve to snap shut, starving the engine of air and shutting it down.
References [1] AirTek Systems (http:/ / www. airteksystems. com/ pages/ positive. html)
Parallel motion The parallel motion is a mechanical linkage invented by the Scottish engineer James Watt in 1784 for his double-acting steam engine. In previous engines built by Newcomen and Watt, the piston pulled one end of the walking beam downwards during the power stroke using a chain, and the weight of the pump pulled the other end of the beam downwards during the recovery stroke using a second chain, the alternating forces producing the rocking motion of the beam. In Watt's new double-acting engine, the piston produced power on both the upward and downward strokes, so a chain could not be used to transmit the force to the beam. Watt designed the parallel motion to transmit force in both directions whilst keeping the piston rod vertical. He called it "parallel motion" because both the piston and the pump rod were required to move vertically, parallel to one another. In a letter to his son in 1808, James Watt wrote "I am more proud of the parallel motion than of any other invention I have ever made."[1] See the diagram on the right. A is the journal (bearing) of the walking beam KAC, which rocks up and down about A. H is the piston, which is required to move vertically but not horizontally. The heart of the design is the four-bar linkage consisting of AB, BE and EG and the base link is AG, both joints on the framework of the engine. As the beam rocks, point F (which is drawn to aid this explanation, but which is not visible on the machine itself) describes an elongated figure-of-eight in mid-air. Since the motion of the walking beam is constrained to a small angle, F describes only a short section of the Schematic of Watt's parallel motion figure-of-eight, which is quite close to a vertical straight line. The figure-of-eight is symmetrical as long as arms AB and EG are equal in length, and straightest when the ratio of BF to FE matches that of AB to EG. If the stroke length (that is, the maximum travel of F) is S, then the straight section is longest when BE is around 2/3 S and AB is 1.5 S.[2]
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It would have been possible to connect F directly to the piston rod, but this would have made the machine an awkward shape, with G a long way from the end of the walking beam. To avoid this, Watt added the parallelogram linkage BCDE to form a pantograph. This guarantees that F always lies on a straight line between A and D, and therefore that the motion of D is a magnified version of the motion of F. D is therefore the point to which the piston rod DH is attached. The addition of the pantograph also made the mechanism shorter and so the building containing the engine could be smaller. An example of a parallel motion where there is no pantograph and point F does connect to the piston rod can be found on the high and intermediate pressure piston rod of the Crossness engines. In these engines, the low pressure piston rod uses the more conventional arrangement, but the high and intermediate pressure rod does not connect to the end of the beam so there is no requirement to save space. As already noted, the path of F is not a perfect straight line, but merely an approximation. Watt's design produced a deviation of about one part in 4000 from a straight line. Later, in the 19th century, perfect straight-line linkages were invented, beginning with the Peaucellier–Lipkin linkage of 1864.
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Watt parallel motion on a pumping engine
Hand-drawn diagram by James Watt (1808) in a letter to his son, describing how he arrived at the [1] design.
References [1] Franz Reuleaux, The Kinematics of Machinery (1876), page 4. [2] Neil Sclater and Nicholas P. Chironis, Mechanisms and Mechanical Devices Sourcebook Third Edition (2001), page 136.
• Linkages article in Encyclopædia Britannica, 1958. • Parallel Motion article in Encyclopædia Britannica, 1911. • Robert Stuart, A Descriptive History of the Steam Engine (http://books.google.com/ books?id=J_sJAAAAIAAJ&printsec=frontcover), London, J. Knight and H. Lacey, 1824.
Particle damping
Particle damping Particle damping is the use of particles moving freely in a cavity to produce a damping effect.
Introduction Active and passive damping techniques are common methods of attenuating the resonant vibrations excited in a structure. Active damping techniques are not applicable under all circumstances due, for example, to power requirements, cost, environment, etc. Under such circumstances, passive damping techniques are a viable alternative. Various forms of passive damping exist, including viscous damping, viscoelastic damping, friction damping, and impact damping. Viscous and viscoelastic damping usually have a relatively strong dependence on temperature. Friction dampers, while applicable over wide temperature ranges, may degrade with wear. Due to these limitations, attention has been focused on impact dampers, particularly for application in cryogenic environments or at elevated temperatures. Particle damping technology is a derivative of impact damping with several advantages. Impact damping refers to only a single (somewhat larger) auxiliary mass in a cavity, whereas particle damping is used to imply multiple auxiliary masses of small size in a cavity. The principle behind particle damping is the removal of vibratory energy through losses that occur during impact of granular particles which move freely within the boundaries of a cavity attached to a primary system. In practice, particle dampers are highly nonlinear dampers whose energy dissipation, or damping, is derived from a combination of loss mechanisms. Because of the ability of particle dampers to perform through a wide range of temperatures and survive for a longer life, they have been used in applications such as the weightless environments of outer space,[1] [2] in aircraft structures, to attenuate vibrations of civil structures,[3] and even in tennis rackets.[4]
Advantages of particle dampers • They can perform through a large range of temperatures • They can survive for a long life Therefore, they are suited for applications where there is a need for long service in harsh environments.
Analysis of particle damping The analysis of particle dampers is mainly conducted by experimental testing, simulations by discrete element method or finite element method, and by analytical calculations.
Research literature review A significant amount of research has been carried out in the area of analysis of particle dampers. Olson [5] presented a mathematical model that allows particle damper designs to be evaluated analytically. The model utilized the particle dynamics method and took into account the physics involved in particle damping, including frictional contact interactions and energy dissipation due to viscoelasticity of the particle material. Fowler et al [6] discussed results of studies into the effectiveness and predictability of particle damping. Efforts were concentrated on characterizing and predicting the behaviour of a range of potential particle materials, shapes, and sizes in the laboratory environment, as well as at elevated temperature. Methodologies used to generate data and extract the characteristics of the nonlinear damping phenomena were illustrated with test results. Fowler et al [7] developed an analytical method, based on the particle dynamics method, that used characterized particle damping data to predict damping in structural systems. A methodology to design particle damping for dynamic structures was discussed. The design methodology was correlated with tests on a structural component in
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the laboratory. Mao et al [8] utilized DEM for computer simulation of particle damping. By considering thousands of particles as Hertz balls, the discrete element model was used to describe the motions of these multi-bodies and determine the energy dissipation.
External links • Particle damping DEM simulation video [9]
References [1] H.V. Panossian, Structural damping enhancement via non-obstructive particle damping technique, Journal of Vibration and Acoustics, 114 (1992), pp. 101–105. [2] R. Ehrgott, H. Panossian & G. Davis, Modelling techniques for evaluating the effectiveness of particle damping in turbomachinery, Pratt & Whitney Rocketdyne, Canoga Park, CA. PDF (http:/ / ntrs. nasa. gov/ archive/ nasa/ casi. ntrs. nasa. gov/ 20090023611_2009022946. pdf) [3] S.S. Simonian, Particle beam damper, Proceedings of the SPIE, 2445 (1995), pp. 149–160. [4] S. Ashley, A new racket shakes up tennis, Mechanical Engineering, 117 (1995), pp. 80–81. [5] Steven E. Olson, An analytical particle damping model, Journal of Sound and Vibration, 264 (2003), pp. 1155–1166. doi:10.1016/S0022-460X(02)01388-3 [6] Bryce L. Fowler, Eric M. Flint, Steven E. Olson, Effectiveness and Predictability of Particle Damping, Proceedings of SPIE Volume 3989, Smart Structures and Materials 2000, Damping and Isolation, 2000. PDF (http:/ / www. brycefowler. com/ published_papers/ SPIE/ Fowler_SPIE_3989-38. pdf) [7] Bryce L. Fowler, Eric M. Flint, Steven E. Olson, Design Methodology for Particle Damping, SPIE Conference on Smart Structures and Materials, 2001. PDF (http:/ / www. brycefowler. com/ published_papers/ SPIE/ Fowler_SPIE_4331-20. pdf) [8] Kuanmin Mao, Michael Yu Wang, Zhiwei Xu, Tianning Chen, DEM simulation of particle damping, Powder Technology, 142 (2004), pp. 154– 165. doi:10.1016/j.powtec.2004.04.031 [9] http:/ / www. youtube. com/ watch?v=fkJpZfME0EU
Photoelasticity Photoelasticity is an experimental method to determine the stress distribution in a material. The method is mostly used in cases where mathematical methods become quite cumbersome. Unlike the analytical methods of stress determination, photoelasticity gives a fairly accurate picture of stress distribution even around abrupt discontinuities in a material. The method serves as an important tool for determining the critical stress points in a material and is often used for determining stress concentration factors in irregular geometries. A picture of plastic utensils created using photoelasticity
History The photoelastic phenomena was first described by the scottish physicist David Brewster[1] .[2] Photoelasticity developed at the beginning of the twentieth century with the works of E.G.Coker and L.N.G Filon of University of London. Their book Treatise on Photoelasticity published in 1930 by the Cambridge Press became a standard text on the subject. Between 1930 and 1940 many other books in Russian, German and French appeared on the subject.
Photoelasticity
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At the same time a lot of development was made in field. Great improvements were achieved in the technique and the equipment was simplified. With the improvement in technology the scope of photoelasticity was also extended to three dimensional state of stress. Many practical problems were solved using photoelasticity and it soon became very popular. A number of photoelastic laboratories were then setup in both educational institutions and industries. With the advent of digital polariscope using LEDs, continuous monitoring of structures under load became possible. This led to the development of dynamic photoelasticity. Dynamic photoelasticity has contributed greatly to the study of complex phenomena of fracture of materials.
Principles The method is based on the property of birefringence, which is exhibited by certain transparent materials. Birefringence is a property by virtue of which a ray of light passing through a birefringent material experiences two refractive indices. The property of birefringence or double refraction is exhibited by many optical crystals. But photoelastic materials exhibit the property of birefringence only on the application of stress and the magnitude of the refractive indices at each point in the material is directly related to the state of stress at that point. Thus, the first task is to develop a model made out of such materials. The model has a similar geometry to that of the structure on which stress analysis is to be performed. This ensures that the state of the stress in the model is similar to the state of the stress in the structure.
Tension lines in plastic protractor seen under cross polarized light.
When a ray of plane polarised light is passed through a photoelastic material, it gets resolved along the two principal stress directions and each of these components experiences different refractive indices. The difference in the refractive indices leads to a relative phase retardation between the two component waves. The magnitude of the relative retardation is given by the stress optic law:
where R is the induced retardation, C is the stress optic coefficient, t is the specimen thickness, σ11 is the first principal stress, and σ22 is the second principal stress. The two waves are then brought together in a polariscope. The phenomena of optical interference takes place and we get a fringe pattern, which depends on relative retardation. Thus studying the fringe pattern one can determine the state of stress at various points in the material.
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Isoclinics and isochromatics Isoclinics are the locus of the points in the specimen along which the principal stresses are in the same direction. Isochromatics are the locus of the points along which the difference in the first and second principal stress remains the same. Thus they are the lines which join the points with equal maximum shear stress magnitude.
Two-dimensional photoelasticity Photoelasticity can be applied both to three dimensional and two dimensional state of stress. But the application of photoelasticty to the three dimensional state of stress is more involved as compared to the state of two dimensional / plane stress system. So the present section deals with application of photoelasticity in investigation of a plane stress system. This condition is achieved when the thickness of the prototype is much smaller as compared to dimensions in the plane. Thus one is only concerned with stresses acting parallel to the plane of the model, as other stress components are zero. The experimental setup varies from experiment to experiment. The two basic kinds of setup used are plane polariscope and circular polariscope.
Photoelasticity
Plane polariscope The setup consists of two linear polarizers and a light source. The light source can either emit monochromatic light or white light depending upon the experiment. First the light is passed through the first polarizer which converts the light into plane polarized light. The apparatus is set up in such a way that this plane polarized light then passes through the stressed specimen. This light then follows, at each point of the specimen, the direction of principal stress at that point. The light is then made to pass through the analyzer and we finally get the fringe pattern. The fringe pattern in a plane polariscope setup consists of both the isochromatics and the isoclinics. The isoclinics change with the orientation of the polariscope while there is no change in the isochromatics.
Circular polariscope In a circular polariscope setup two quarter-wave plates are added to the experimental setup of the plane polariscope. The first quarter-wave plate is placed in between the polariser and the specimen and the second quarter-wave plate is placed between the specimen and the analyser. The effect of adding the quarter-wave plates is that we get circularly polarised light.
Transmission Circular Polariscope The same device functions as a plane polariscoe when quarter wave plates are taken aside or rotated so their axes parallel to polarization axes
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The basic advantage of a circular polariscope over a plane polariscope is that in a circular polariscope setup we only get the isochromatics and not the isoclinics. This eliminates the problem of differentiating between the isoclinics and the isochromatics.
Applications Photoelasticity has been used for a variety of stress analyses and even for routine use in design, particularly before the advent of numerical methods, such as for instance finite elements or boundary elements.[3] Photoelasticity can successfully be used to investigate the highly localized stress state within masonry[4] [5] or in proximity of a rigid line inclusion (stiffener) embedded in an elastic medium.[6] In the former case, the problem is nonlinear due to the contacts between bricks, while in the latter case the elastic solution is singular, so that numerical methods may fail to provide correct results. These can be obtained through photoelastic techniques.
References
Photoelastic experiment to validate the stiffener model. Isochromatic fringe patterns around a steel platelet in a photo-elastic two-part epoxy resin.
[1] D. Brewster, Experiments on the depolarization of light as exhibited by various mineral, animal and vegetable bodies with a reference of the phenomena to the general principle of polarization, Phil. Tras. 1815, pp.29-53. [2] D. Brewster, On the communication of the structure of doubly-refracting crystals to glass, murite of soda, flour spar, and other substances by mechanical compression and dilation, Phil. Tras. 1816, pp.156-178. [3] Frocht, M.M., 1965. Photoelasticity. J. Wiley and Sons, London [4] D. Bigoni and G. Noselli, Localized stress percolation through dry masonry walls. Part I - Experiments. European Journal of Mechanics A/Solids, 2010, 29, 291-298. (http:/ / www. ing. unitn. it/ ~bigoni) [5] D. Bigoni and G. Noselli, Localized stress percolation through dry masonry walls. Part II - Modelling. European Journal of Mechanics A/Solids, 2010, 29, 299-307. (http:/ / www. ing. unitn. it/ ~bigoni) [6] G. Noselli, F. Dal Corso and D. Bigoni, The stress intensity near a stiffener disclosed by photoelasticity. International Journal of Fracture, 2010, 166, 91–103. (http:/ / www. ing. unitn. it/ ~bigoni)
External links • University of Cambridge Page on Photoelasticity. (http://www.doitpoms.ac.uk/tlplib/photoelasticity/history. php) • Photograph of photoelastic stress pattern using plane-polarized white light. (http://public.fotki.com/ ROBERT1010/scitech/photoelasticstress4.html) • Laboratory for Physical Modeling of Structures and Photoelasticity (University of Trento, Italy) (http://ssmg. ing.unitn.it) • Reflection Photoelasticity Appartus. (http://www.photostress.com)
Pinch analysis
Pinch analysis Pinch analysis is a methodology for minimising energy consumption of chemical processes by calculating thermodynamically feasible energy targets (or minimum energy consumption) and achieving them by optimising heat recovery systems, energy supply methods and process operating conditions. It is also known as process integration, heat integration, energy integration or pinch technology. The process data is represented as a set of energy flows, or streams, as a function of heat load (kW) against temperature (deg C). These data are combined for all the streams in the plant to give composite curves, one for all hot streams (releasing heat) and one for all cold streams (requiring heat). The point of closest approach between the hot and cold composite curves is the pinch point (or just pinch) with a hot stream pinch temperature and a cold stream pinch temperature. This is where the design is most constrained. Hence, by finding this point and starting the design there, the energy targets can be achieved using heat exchangers to recover heat between hot and cold streams in two separate systems, one for temperatures above pinch temperatures and one for temperatures below pinch temperatures. In practice, during the pinch analysis of an existing design, often cross-pinch exchanges of heat are found between a hot stream with its temperature above the pinch and a cold stream below the pinch. Removal of those exchangers by alternative matching makes the process reach its energy target.
History The techniques were first developed in late 1977 by Ph.D. student Bodo Linnhoff under the supervision of Dr John Flower at the University of Leeds[1] . In 1977 Linnhoff joined Imperial Chemical Industries (ICI) where he led practical applications and further method development. In 1982 he joined University of Manchester Institute of Technology (UMIST, present day University of Manchester) to continue the work. In 1983 he set up a consultation firm known as Linnhoff March International later acquired by KBC Energy Services.[2] Many refinements have been developed since and used in a wide range of industries, including extension to heat and power systems and non-process situations. Both detailed and simplified (spreadsheet) programs are now available to calculate the energy targets. A commonly used, free pinch analysis program is PinchLeni. In recent years, Pinch analysis has been extended beyond energy applications. It now includes: • Mass Exchange Networks (El-Halwagi and Manousiouthakis, 1987) • Water pinch (Yaping Wang and Robin Smith, 1994; Nick Hallale, 2002; Prakash and Shenoy, 2005) • Hydrogen pinch (Nick Hallale et al., 2003; Agrawal and Shenoy, 2006)
References [1] Ebrahim, M. (2000). "Pinch technology: an efficient tool for chemical-plant energy and capital-cost saving". Applied Energy 65: 45–40. doi:10.1016/S0306-2619(99)00057-4. [2] http:/ / www. kbcenergyservices. com/ default. energy. asp?id=1
• El-Halwagi, M. M. and V. Manousiouthakis, 1989, "Synthesis of Mass Exchange Networks", AIChE J., 35(8), 1233-1244. • Kemp, I.C. (2006). Pinch Analysis and Process Integration: A User Guide on Process Integration for the Efficient Use of Energy, 2nd edition. Includes spreadsheet software. Butterworth-Heinemann. ISBN 0750682604. (1st edition: Linnhoff et al., 1982). • Shenoy, U.V. (1995). "Heat Exchanger Network Synthesis: Process Optimization by Energy and Resource Analysis". Includes two computer disks. Gulf Publishing Company, Houston, TX, USA. ISBN 0884153916. • Hallale, Nick. (2002). A New Graphical Targeting Method for Water Minimisation. Advances in Environmental Research. 6(3): 377-390
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• Nick Hallale, Ian Moore, Dennis Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003) • Agrawal, V. and U. V. Shenoy, 2006, "Unified Conceptual Approach to Targeting and Design of Water and Hydrogen Networks", AIChE J., 52(3), 1071-1082. • Wang, Y. P. and Smith, R. (1994). Wastewater Minimisation. Chemical Engineering Science. 49: 981-1006 • Prakash, R. and Shenoy, U.V. (2005) Targeting and Design of Water Networks for Fixed Flowrate and Fixed Contaminant Load Operations. Chemical Engineering Science. 60(1), 255-268.
Pinch analysis software • Pinchleni - Freeware developed by Laboratoire d'Energétique Industrielle de l'Ecole Polytechnique Fédérale de Lausanne, Switzerland Pinchleni (http://www.stenum.at/en/?id=software/pinchlenisoftware/ pinchlenifreeware) • Online Pinch Analysis Tool (http://www.uic-che.org/pinch/) - Free for personal and educational use, hosted by the College of Chemical Engineering at the University of Illinois at Chicago
Piping For other uses, see Piping (erosion), Piping (sewing), Bagpiping, or Pipe (fluid conveyance), or Pipe. Within industry, piping is a system of pipes used to convey fluids (liquids and gases) from one location to another. The engineering discipline of piping design studies the efficient transport of fluid.[1] [2] Industrial process piping (and accompanying in-line components) can be manufactured from wood, fiberglass, glass, steel, aluminum, plastic, copper, and concrete. The in-line components, known as fittings, valves, and other devices, typically sense and control the pressure, flow rate and temperature of the transmitted fluid, and usually are included in the field of Piping Design (or Piping Engineering). Piping systems are documented in piping and instrumentation diagrams (P&IDs). If necessary, pipes can be cleaned by the tube cleaning process. "Piping" sometimes refers to Piping Design, the detailed specification of the physical piping layout within a process plant or commercial building. In earlier days, this was sometimes called Drafting, Technical drawing, Engineering Drawing, and Design but is today commonly performed by Designers who have learned to use automated Computer Aided Drawing / Computer Aided Design (CAD) software.
Large-scale piping system in an HVAC mechanical room
Plumbing is a piping system that most people are familiar with, as it constitutes the form of fluid transportation that is used to provide potable water and fuels to their homes and business. Plumbing pipes also remove waste in the form of sewage, and allow venting of sewage gases to the outdoors. Fire sprinkler systems also use piping, and may
Piping transport nonpotable or potable water, or other fire-suppression fluids. Piping also has many other industrial applications, which are crucial for moving raw and semi-processed fluids for refining into more useful products. Some of the more exotic materials of construction are Inconel, titanium, chrome-moly and various other steel alloys.
Engineering subfields Generally, Industrial Piping Engineering has three major subfields: • Piping Material • Piping Design • Stress Analysis
Stress analysis Process piping and power piping are typically checked by Pipe Stress Engineers to verify that the routing, nozzle loads, hangers, and supports are properly placed and selected such that allowable pipe stress is not exceeded under different situation such as sustain, operating, hydro test etc as per the ASME or any other legislative code and local government standards. It is necessary to evaluate the mechanical behavior of the piping under regular loads (internal pressure and thermal stresses) as well under occasional and intermittent loading cases such as earthquake, high wind or special vibration, and water hammer.[3] [4] This evaluation is usually performed with the assistance of a specialized (finite element) pipe stress analysis computer program such as CAESAR II [5], ROHR2, CAEPIPE [6] and AUTOPIPE [7].
Wooden piping history Early wooden pipes were constructed out of logs that had a large hole bored lengthwise through the center. Later wooden pipes were constructed with staves and hoops similar to wooden barrel construction. Stave pipes have the advantage that they are easily transported as a compact pile of parts on a wagon and then assembled as a hollow structure at the job site. Wooden pipes were especially popular in mountain regions where transport of heavy iron or concrete pipes would have been difficult. Wooden pipes were easier to maintain than metal, because the wood did not expand or contract with temperature changes as much as metal and so consequently expansion joints and bends were not required. The thickness of wood afforded some insulating properties to the pipes which helped prevent freezing as compared to metal pipes. Wood used for water pipes also does not rot very easily. Electrolysis, that bugbear of many iron pipe systems, doesn't affect wood pipes at all, since wood is a much better electrical insulator. In the Western United States where redwood was used for pipe construction, it was found that redwood had "peculiar properties" that protected it from weathering, acids, insects, and fungus growths. Redwood pipes stayed smooth and clean indefinitely while iron pipe by comparison would rapidly begin to scale and corrode and could eventually plug itself up with the corrosion. [8]
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Materials The material with which a pipe is manufactured often forms as the basis for choosing any pipe. Materials that are used for manufacturing pipes include: • • • • •
Carbon Steel (CS) Low Temperature Service Carbon Steel (LTCS) Stainless Steel (SS) Non Ferrous Metals (Inconel, Incoloy, Cupro-nickel, etc.) Non Metallic (GRE, PVC, HDPE, tempered glass, etc.)
Standards There are certain standard codes that need to be followed while designing or manufacturing any piping system. Organizations that promulgate piping standards include: • • • •
ASME - The American Society of Mechanical Engineers ASTM - American Society for Testing and Materials API - American Petroleum Institute AWS - American Welding Society
• • • • •
AWWA - American Water Works Association MSS – Manufacturers' Standardization Society ANSI - American National Standards Institute NFPA - National Fire Protection Association EJMA - Expansion Joint Manufacturers Association
References [1] Editors: Perry, R.H. and Green, D.W. (1984). Perry's Chemical Engineers' Handbook (6th Edition ed.). McGraw-Hill Book Company. ISBN 0-07-049479-7. [2] Editor: McKetta, John J. (1992). Piping Design Handbook. Marcel Dekker, Inc.. ISBN 0-8247-8570-3. [3] Process Piping: ASME B31.3 (http:/ / catalog. asme. org/ books/ PrintBook/ Process_Piping_Complete_Guide. cfm) [4] Power Piping: ASME B31.1 (http:/ / catalog. asme. org/ Codes/ PrintBook/ B311_2004_Power_Piping. cfm) [5] http:/ / www. coade. com/ products/ caesarii [6] http:/ / www. sstusa. com/ caepipe. php [7] http:/ / www. bentley. com/ AutoPIPE/ [8] Piping water through miles of Redwood, Popular Science monthly, December 1918, page 74, Scanned by Google Books: http:/ / books. google. com/ books?id=EikDAAAAMBAJ& pg=PA74
Further reading • ASME B31.3 Process Piping Guide, Revision 1 (http://engstandards.lanl.gov/engrman/6mech/pdfs/ D20-AppA-ASME_B31.3-r1a.pdf) from Los Alamos National Laboratory Engineering Standards Manual OST220-03-01-ESM • Seismic Design and Retrofit of Piping Systems, July 2002 (http://www.americanlifelinesalliance.org/pdf/ Seismic_Design_and_Retrofit_of_Piping_Systems.pdf) from American Lifelines Alliance website • Engineering and Design, Liquid Process Piping (http://www.usace.army.mil/publications/eng-manuals/ em1110-1-4008/entire.pdf) U.S. Army Corps of Engineers, EM 1110-l-4008, May 1999
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External links • Building services piping links (http://www.dmoz.org//Construction_and_Maintenance/ Materials_and_Supplies/Mechanical/Building_Services_Piping//) at the Open Directory Project
Piston motion equations The motion of a non-offset piston connected to a crank through a connecting rod (as would be found in internal combustion engines), can be expressed through several mathematical equations. This article shows how these motion equations are derived, and shows an example graph.
Crankshaft geometry Definitions l = rod length (distance between piston pin and crank pin) r = crank radius (distance between crank pin and crank center, i.e. half stroke) A = crank angle (from cylinder bore centerline at TDC) x = piston pin position (upward from crank center along cylinder bore centerline) v = piston pin velocity (upward from crank center along cylinder bore centerline) a = piston pin acceleration (upward from crank center along cylinder bore centerline) ω = crank angular velocity in rad/s
Diagram showing geometric layout of piston pin, crank pin and crank center
Angular velocity The crankshaft angular velocity is related to the engine revolutions per minute (RPM):
Triangle relation As shown in the diagram, the crank pin, crank center and piston pin form triangle NOP. By the cosine law it is seen that:
Piston motion equations
Equations with respect to angular position (Angle Domain) The equations that follow describe the reciprocating motion of the piston with respect to crank angle. Example graphs of these equations are shown below.
Position Position with respect to crank angle (by rearranging the triangle relation):
Velocity Velocity with respect to crank angle (take first derivative, using the chain rule):
Acceleration Acceleration with respect to crank angle (take second derivative, using the chain rule and the quotient rule):
Equations with respect to time (Time Domain) Angular velocity derivatives If angular velocity is constant, then
and the following relations apply:
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Piston motion equations
Converting from Angle Domain to Time Domain The equations that follow describe the reciprocating motion of the piston with respect to time. If time domain is required instead of angle domain, first replace A with ωt in the equations, and then scale for angular velocity as follows:
Position Position with respect to time is simply:
Velocity Velocity with respect to time (using the chain rule):
Acceleration Acceleration with respect to time (using the chain rule and product rule, and the angular velocity derivatives):
Scaling for angular velocity You can see that x is unscaled, x' is scaled by ω, and x" is scaled by ω². To convert x' from velocity vs angle [inch/rad] to velocity vs time [inch/s] multiply x' by ω [rad/s]. To convert x" from acceleration vs angle [inch/rad²] to acceleration vs time [inch/s²] multiply x" by ω² [rad²/s²]. Note that dimensional analysis shows that the units are consistent.
Velocity maxima/minima Acceleration zero crossings The velocity maxima and minima do not occur at crank angles (A) of plus or minus 90°. The velocity maxima and minima occur at crank angles that depend on rod length (l) and half stroke (r), and correspond to the crank angles where the acceleration is zero (crossing the horizontal axis).
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Crank-Rod angle not right angled The velocity maxima and minima do not necessarily occur when the crank makes a right angle with the rod. Counter-examples exist to disprove the idea that velocity maxima/minima occur when crank-rod angle is right angled.
Example For rod length 6" and crank radius 2", numerically solving the acceleration zero-crossings finds the velocity maxima/minima to be at crank angles of ±73.17615°. Then, using the triangle sine law, it is found that the crank-rod angle is 88.21738° and the rod-vertical angle is 18.60647°. Clearly, in this example, the angle between the crank and the rod is not a right angle. (Sanity check, summing the angles of the triangle 88.21738° + 18.60647° + 73.17615° gives 180.00000°) A single counter-example is sufficient to disprove the statement "velocity maxima/minima occur when crank makes a right angle with rod".
Example graph of piston motion The graph shows x, x', x" with respect to crank angle for various half strokes, where L = rod length (l) and R = half stroke (r): Pistons motion animation with same rod length and crank radius values in graph above :
The vertical axis units are inches for position, [inches/rad] for velocity, [inches/rad²] for acceleration. The horizontal axis units are crank angle degrees.
Pistons motion animation with various half strokes
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References • http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm
Further reading • John Benjamin Heywood, Internal Combustion Engine Fundamentals, McGraw Hill, 1989. • Charles Fayette Taylor, The Internal Combustion Engine in Theory and Practice, Vol. 1 & 2, 2nd Edition, MIT Press 1985.
External links • • • •
http://www.animatedengines.com/otto.shtml youtube [1] Rotating chevy 350 short block. youtube [2] 3D animation of a V8 ENGINE youtube [3] Inside a V8 Engine at Idle Speed
References [1] http:/ / www. youtube. com/ watch?v=stuaK5bk_Ck [2] http:/ / www. youtube. com/ watch?v=lMIxKOM6jRA [3] http:/ / www. youtube. com/ watch?v=sLQWEnQmmyY
Power engineering Power engineering, also called power systems engineering, is a subfield of engineering that deals with the generation, transmission and distribution of electric power as well as the electrical devices connected to such systems including generators, motors and transformers. Although much of the field is concerned with the problems of three-phase AC power - the standard for large-scale power transmission and distribution across the modern world - a significant fraction of the field is concerned with the conversion between AC and DC power as well as the development of specialised power systems such as those used in aircraft or for electric railway networks.
A steam turbine used to provide electric power.
Power engineering
History Electricity became a subject of scientific interest in the late 17th century with the work of William Gilbert.[1] Over the next two centuries a number of important discoveries were made including the incandescent lightbulb and the voltaic pile.[2] [3] Probably the greatest discovery with respect to power engineering came from Michael Faraday who in 1831 discovered that a change in magnetic flux induces an electromotive force in a loop of wire—a principle known as electromagnetic induction that helps explain how generators and transformers work.[4] In 1881 two electricians built the world's first power station at Godalming in England. The station employed two waterwheels to produce an alternating current that was used to supply seven Siemens arc lamps at 250 volts and thirty-four incandescent lamps at 40 volts.[5] However supply was intermittent and in 1882 Thomas Edison and his company, The Edison Electric Light Company, developed the first steam-powered electric power station on Pearl Street in New York City. The Pearl Street Station consisted of several generators and initially powered around 3,000 lamps for 59 customers.[6] [7] The power station used direct current A sketch of the Pearl Street Station and operated at a single voltage. Since the direct current power could not be easily transformed to the higher voltages necessary to minimise power loss during transmission, the possible distance between the generators and load was limited to around half-a-mile (800 m).[8] That same year in London Lucien Gaulard and John Dixon Gibbs demonstrated the first transformer suitable for use in a real power system. The practical value of Gaulard and Gibbs' transformer was demonstrated in 1884 at Turin where the transformer was used to light up forty kilometres (25 miles) of railway from a single alternating current generator.[9] Despite the success of the system, the pair made some fundamental mistakes. Perhaps the most serious was connecting the primaries of the transformers in series so that switching one lamp on or off would affect other lamps further down the line. Following the demonstration George Westinghouse, an American entrepreneur, imported a number of the transformers along with a Siemens generator and set his engineers to experimenting with them in the hopes of improving them for use in a commercial power system. One of Westinghouse's engineers, William Stanley, recognised the problem with connecting transformers in series as opposed to parallel and also realised that making the iron core of a transformer a fully enclosed loop would improve the voltage regulation of the secondary winding. Using this knowledge he built a much improved alternating current power system at Great Barrington, Massachusetts in 1886.[10] Then in 1887 and 1888 another engineer called Nikola Tesla filed a range of patents related to power systems including one for a two-phase induction motor. Although Tesla cannot necessarily be attributed with building the first induction motor, his design, unlike others, was practical for industrial use.[11] By 1890 the power industry had flourished and power companies had built literally thousands of power systems (both direct and alternating current) in the United States and Europe - these networks were effectively dedicated to providing electric lighting. During this time a fierce rivalry known as the "War of Currents" emerged between Edison, Westinghouse and Tesla over which form of transmission (direct or alternating current) was superior. In 1891, Westinghouse installed the first major power system that was designed to drive an electric motor and not just provide electric lighting. The installation powered a 100 horsepower (75 kW) synchronous motor at Telluride,
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Colorado with the motor being started by a Tesla induction motor.[12] On the other side of the Atlantic, Oskar von Miller built a 20 kV 176 km three-phase transmission line from Lauffen am Neckar to Frankfurt am Main for the Electrical Engineering Exhibition in Frankfurt.[13] In 1895, after a protracted decision-making process, the Adams No. 1 generating station at Niagara Falls began transmitting three-phase alternating current power to Buffalo at 11 kV. Following completion of the Niagara Falls project, new power systems increasingly chose alternating current as opposed to direct current for electrical transmission.[14] Although the 1880s and 1890s were seminal decades in the field, developments in power engineering continued throughout the 20th and 21st century. In 1936 the first commercial HVDC (high voltage direct current) line using Mercury arc valves was built between Schenectady and Mechanicville, New York. HVDC had previously been achieved by installing direct current generators in series (a system known as the Thury system) although this suffered from serious reliability issues.[15] In 1957 Siemens demonstrated the first solid-state rectifier (solid-state rectifiers are now the standard for HVDC systems) however it was not until the early 1970s that this technology was used in commercial power systems.[16] In 1959 Westinghouse demonstrated the first circuit breaker that used SF6 as the interrupting medium.[17] SF6 is a far superior dielectric to air and, in recent times, its use has been extended to produce far more compact switching equipment (known as switchgear) and transformers.[18] [19] Many important developments also came from extending innovations in the information technology and telecommunications field to the power engineering field. For example, the development of computers meant load flow studies could be run more efficiently allowing for much better planning of power systems. Advances in information technology and telecommunication also allowed for much better remote control of the power system's switchgear and generators.
Basics of electric power Electric power is the mathematical product of two quantities: current and voltage. These two quantities can vary with respect to time (AC power) or can be kept at constant levels (DC power). Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power (the digital devices you plug into the mains typically have an internal or external power adapter to convert from AC to DC power). AC power has the advantage of being easy to transform between voltages and is able to be generated and utilised by brushless machinery. DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages (see HVDC).[20] [21]
An external AC to DC power adapter used for household appliances
The ability to easily transform the voltage of AC power is important for two reasons: Firstly, power can be transmitted over long distances with less loss at higher voltages. So in power networks where generation is distant from the load, it is desirable to step-up the voltage of power at the generation point and then step-down the voltage near the load. Secondly, it is often more economical to install turbines that produce higher voltages than would be used by most appliances, so the ability to easily transform voltages means this mismatch between voltages can be easily managed.[20] Solid state devices, which are products of the semiconductor revolution, make it possible to transform DC power to different voltages, build brushless DC machines and convert between AC and DC power. Nevertheless devices utilising solid state technology are often more expensive than their traditional counterparts, so AC power remains in widespread use.[22]
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Power Power Engineering deals with the generation, transmission and distribution of electricity as well as the design of a range of related devices. These include transformers, electric generators, electric motors and power electronics. The power grid is an electrical network that connects a variety of electric generators to the users of electric power. Users purchase electricity from the grid avoiding the costly exercise of having to generate their own. Power engineers may work on the design and maintenance of the power grid as well as the power systems that connect to it. Such systems are called on-grid power systems and may supply the grid with additional power, draw power from the grid or do both.
Transmission lines transmit power across the grid.
Power engineers may also work on systems that do not connect to the grid. These systems are called off-grid power systems and may be used in preference to on-grid systems for a variety of reasons. For example, in remote locations it may be cheaper for a mine to generate its own power rather than pay for connection to the grid and in most mobile applications connection to the grid is simply not practical. Today, most grids adopt three-phase electric power with alternating current. This choice can be partly attributed to the ease with which this type of power can be generated, transformed and used. Often (especially in the USA), the power is split before it reaches residential customers whose low-power appliances rely upon single-phase electric power. However, many larger industries and organizations still prefer to receive the three-phase power directly because it can be used to drive highly efficient electric motors such as three-phase induction motors. Transformers play an important role in power transmission because they allow power to be converted to and from higher voltages. This is important because higher voltages suffer less power loss during transmission. This is because higher voltages allow for lower current to deliver the same amount of power, as power is the product of the two. Thus, as the voltage steps up, the current steps down. It is the current flowing through the components that result in both the losses and the subsequent heating. These losses, appearing in the form of heat, are equal to the current squared times the electrical resistance through which the current flows, so as the voltage goes up the losses are dramatically reduced. For these reasons, electrical substations exist throughout power grids to convert power to higher voltages before transmission and to lower voltages suitable for appliances after transmission.
Components Power engineering is a network of interconnected components which convert different forms of energy to electrical energy. Modern power engineering consists of three main subsystems: the generation subsystem, the transmission subsystem, and the distribution subsystem. In the generation subsystem, the power plant produces the electricity. The transmission subsystem transmits the electricity to the load centers. The distribution subsystem continues to transmit the power to the customers.
Power engineering
Generation Generation of electrical power is a process whereby energy is transformed into an electrical form. There are several different transformation processes, among which are chemical, photo-voltaic, and electromechanical. Electromechanical energy conversion is used in converting energy from coal, petroleum, natural gas, uranium into electrical energy. Of these, all except the wind energy conversion process take advantage of the synchronous AC generator coupled to a steam, gas or hydro turbine such that the turbine converts steam, gas, or water flow into rotational energy, and the synchronous generator then converts the rotational energy of the turbine into electrical energy. It is the turbine-generator conversion process that is by far most economical and consequently most common in the industry today. The AC synchronous machine is the most common technology for generating electrical energy. It is called synchronous because the composite magnetic field produced by the three stator windings rotate at the same speed as the magnetic field produced by the field winding on the rotor. A simplified circuit model is used to analyze steady-state operating conditions for a synchronous machine. The phasor diagram is an effective tool for visualizing the relationships between internal voltage, armature current, and terminal voltage. The excitation control system is used on synchronous machines to regulate terminal voltage, and the turbine-governor system is used to regulate the speed of the machine. However, in highly interconnected systems, such as the "Western system", the "Texas system" and the "Eastern system", one machine will usually be assigned as the so-called "swing machine", and which generation may be increased or decreased to compensate for small changes in load, thereby maintaining the system frequency at precisely 60 Hz. Should the load dramatically change, as which happens with a system separation, then a combination of "spinning reserve" and the "swing machine" may be used by the system's load dispatcher. The operating costs of generating electrical energy is determined by the fuel cost and the efficiency of the power station. The efficiency depends on generation level and can be obtained from the heat rate curve. We may also obtain the incremental cost curve from the heat rate curve. Economic dispatch is the process of allocating the required load demand between the available generation units such that the cost of operation is minimized. Emission dispatch is the process of allocating the required load demand between the available generation units such that air pollution occurring from operation is minimized. In large systems, particularly in the West, a combination of economic and emission dispatch may be used.
Transmission The electricity is transported to load locations from a power station to a transmission subsystem. Therefore we may think of the transmission system as providing the medium of transportation for electric energy. The transmission system may be subdivided into the bulk transmission system and the sub-transmission system. The functions of the bulk transmission are to interconnect generators, to interconnect various areas of the network, and to transfer electrical energy from the generators to the major load centers. This portion of the system is called "bulk" because it delivers energy only to so-called bulk loads such as the distribution system of a town, city, or large industrial plant. The function of the sub-transmission system is to interconnect the bulk power system with the distribution system. Transmission circuits may be built either underground or overhead. Underground cables are used predominantly in urban areas where acquisition of overhead rights of way are costly or not possible. They are also used for transmission under rivers, lakes and bays. Overhead transmission is used otherwise because, for a given voltage level, overhead conductors are much less expensive than underground cables. The transmission system is a highly integrated system. It is referred to the substation equipment and transmission lines. The substation equipment contain the transformers, relays, and circuit breakers. Transformers are important static devices which transfer electrical energy from one circuit with another in the transmission subsystem. Transformers are used to step up the voltage on the transmission line to reduce the power loss which is dissipated on the way.[23] A relay is functionally a level-detector; they perform a switching action when the input voltage (or current) meets or exceeds a specific and adjustable value. A circuit breaker is an automatically operated electrical
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Power engineering switch designed to protect an electrical circuit from damage caused by overload or short circuit. A change in the status of any one component can significantly affect the operation of the entire system. There are three possible causes for power flow limitations to a transmission line. These causes are thermal overload, voltage instability, and rotor angle instability. Thermal overload is caused by excessive current flow in a circuit causing overheating. Voltage instability is said to occur when the power required to maintain voltages at or above acceptable levels exceeds the available power. Rotor angle instability is a dynamic problem that may occur following faults, such as short circuit, in the transmission system. It may also occur tens of seconds after a fault due to poorly damped or undamped oscillatory response of the rotor motion. As long as the equal area criteria is maintained, the interconnected system will remain stable. Should the equal area criteria be violated, it becomes necessary to separate the unstable component from the remainder of the system.
Distribution The distribution system transports the power from the transmission system to the customer. The distribution systems are typically radial because networked systems are more expensive. The equipment associated with the distribution system includes the substation transformers connected to the transmission systems, the distribution lines from the transformers to the customers and the protection and control equipment between the transformer and the customer. The protection equipment includes lightning protectors, circuit breakers, disconnectors and fuses. The control equipment includes voltage regulators, capacitors, relays and demand side management equipment.
References [1] "Pioneers in Electricity and Magnetism: William Gilbert" (http:/ / www. magnet. fsu. edu/ education/ tutorials/ pioneers/ gilbert. html). National High Magnetic Field Laboratory. . Retrieved 2008-05-25. [2] "The History Of The Light Bulb" (http:/ / www. thehistoryof. net/ the-history-of-the-light-bulb. html). Net Guides Publishing, Inc.. 2004. . Retrieved 2007-05-02. [3] Greenslade, Thomas. "The Voltaic Pile" (http:/ / physics. kenyon. edu/ EarlyApparatus/ Electricity/ Voltaic_Pile/ Voltaic_Pile. html). Kenyon College. . Retrieved 2008-03-31. [4] "Faraday Page" (http:/ / www. rigb. org/ heritage/ faradaypage. jsp). The Royal Institute. . Retrieved 2008-03-31. [5] "Godalming Power Station" (http:/ / www. engineering-timelines. com/ scripts/ engineeringItem. asp?id=744). Engineering Timelines. . Retrieved 2009-05-03. [6] Williams, Jasmin (2007-11-30). "Edison Lights The City" (http:/ / www. nypost. com/ seven/ 11302007/ news/ cextra/ edison_lights_the_city_514905. htm). New York Post. . Retrieved 2008-03-31. [7] Grant, Casey. "The Birth of NFPA" (http:/ / www. nfpa. org/ itemDetail. asp?categoryID=500& itemID=18020& URL=About Us/ History& cookie_test=1). National Fire Protection Association. . Retrieved 2008-03-31. [8] "Bulk Electricity Grid Beginnings" (http:/ / www. pearlstreetinc. com/ NYISO_bulk_elect_beginnings. pdf) (Press release). New York Independent System Operator. . Retrieved 2008-05-25. [9] Katz, Evgeny (2007-04-08). "Lucien Gaulard" (http:/ / web. archive. org/ web/ 20080422072336/ http:/ / people. clarkson. edu/ ~ekatz/ scientists/ gaulard. html). Archived from the original (http:/ / people. clarkson. edu/ ~ekatz/ scientists/ gaulard. html) on 2008-04-22. . Retrieved 2008-05-25. [10] Blalock, Thomas (2004-10-02). "Alternating Current Electrification, 1886" (http:/ / www. ieee. org/ web/ aboutus/ history_center/ stanley. html). IEEE. . Retrieved 2008-05-25. [11] Petar Miljanic, Tesla's Polyphase System and Induction Motor, Serbian Journal of Electrical Engineering, p121-130, Vol. 3, No. 2, November 2006. [12] Foran, Jack. "The Day They Turned The Falls On" (http:/ / ublib. buffalo. edu/ libraries/ projects/ cases/ niagara. htm). . Retrieved 2008-05-25. [13] Voith Siemens (company) (2007-02-01). HyPower (http:/ / www. more-powerful-solutions. com/ media/ ScreenPDF_Hypower_15_72dpi. pdf). pp. 7. . [14] "Adams Hydroelectric Generating Plant, 1895" (http:/ / www. ieee. org/ web/ aboutus/ history_center/ adams. html). IEEE. . Retrieved 2008-05-25. [15] "A Novel but Short-Lived Power Distribution System" (http:/ / www. ieee. org/ organizations/ pes/ public/ 2005/ may/ peshistory. html). IEEE. 2005-05-01. . Retrieved 2008-05-25. [16] Gene Wolf (2000-12-01). "Electricity Through the Ages" (http:/ / tdworld. com/ mag/ power_electricity_ages/ ). Transmission & Distribution World. .
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[17] John Tyner, Rick Bush and Mike Eby (1999-11-01). "A Fifty-Year Retrospective" (http:/ / tdworld. com/ mag/ power_fiftyyear_retrospective/ ). Transmission & Distribution World. . [18] "Gas Insulated Switchgear" (http:/ / www. abb. com/ product/ us/ 9AAC710047. aspx). ABB. . Retrieved 2008-05-25. [19] Amin, Sayed. "SF6 Transformer" (http:/ / www. sayedsaad. com/ Transformer/ SF6_Transformer/ sf6_transformer_main. htm). . Retrieved 2008-05-25. [20] All About Circuits (http:/ / www. allaboutcircuits. com/ ) [Online textbook], Tony R. Kuphaldt et al., last accessed on 17 May 2009. [21] Roberto Rudervall, J.P. Charpentier and Raghuveer Sharma (March 7–8, 2000). High Voltage Direct Current (HVDC) Transmission Systems Technology Review Paper (http:/ / library. abb. com/ GLOBAL/ SCOT/ scot221. nsf/ VerityDisplay/ 9E64DAB39F71129BC1256FDA004F7783/ $File/ Energyweek00. pdf). World Bank. . (also here (http:/ / www. trec-uk. org. uk/ elec_eng/ world_bank_hvdc. pdf)) [22] Ned Mohan, T. M. Undeland and William P. Robbins (2003). Power Electronics: Converters, Applications, and Design. United States of America: John Wiley & Sons, Inc.. ISBN 0-471-22693-9. [23] Transformers (http:/ / www. bbc. co. uk/ schools/ gcsebitesize/ physics/ electricity_and_magnetism/ electromagnetic_inductionrev5. shtml)
External links • IEEE Power Engineering Society (http://www.ieee.org/portal/site/pes) • Jadavpur University, Department of Power Engineering (http://www.jaduniv.edu.in/view_department. php?deptid=63) • Power Engineering International Magazine Articles (http://pepei.pennnet.com/articles/print_toc. cfm?Section=ARTCL&p=17) • Power Engineering Magazine Articles (http://pepei.pennnet.com/articles/print_toc.cfm?Section=ARTCL& p=6) • American Society of Power Engineers, Inc. (http://www.asope.org/) • National Institute for the Uniform Licensing of Power Engineer Inc. (http://www.niulpe.org/)
Precision engineering Precision engineering is a subdiscipline of electrical engineering, electronics engineering, mechanical engineering, and optical engineering concerned with designing machines, fixtures, and other structures that have exceptionally low tolerances, are repeatable, and are stable over time. These approaches have applications in machine tools, MEMS, NEMS, optoelectronics design, and many other fields.
Overview One of the fundamental principles in precision engineering is that of determinism. System behavior is fully predictable even to nanometer-scale motions.
NIST Precision engineering research. Measurement of API Rotary Master [1] Gauge on CMM.
"The basic idea is that machine tools obey cause and effect relationships that are within our ability to understand and control and that there is nothing random or probabilistic about their behavior. Everything happens for a reason and the list of reasons is small enough to manage." - Jim Bryan "By this we mean that machine tool errors obey cause-and-effect relationships, and do not vary randomly for no reason. Further, the causes are not esoteric and uncontrollable, but can be explained in terms of familiar engineering
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principles." - Bob Donaldson Professors Hiromu Nakazawa and Pat McKeown provide the following list of goals for precision engineering: " 1. 2. 3. 4. 5. 6. 7. 8.
Create a highly precise movement. Reduce the dispersion of the product's or part's function. Eliminate fitting and promote assembly, especially automatic assembly. Reduce the initial cost. Reduce the running cost. Extend the life span. Enable the design safety factor to be lowered. Improve interchangeability of components so that corresponding parts made by other factories or firms can be used in their place. 9. Improve quality control through higher machine accuracy capabilities and hence reduce scrap, rework, and conventional inspection. 10. Achieve a greater wear/fatigue life of components. 11. Make functions independent of one another. 12. Achieve greater miniaturization and packing densities. 13. Achieve further advances in technology and the underlying sciences."[2]
Technical Societies • American Society for Precision Engineering • euspen - European Society for Precision Engineering and Nanotechnology [3] • JSPE- The Japan Society for Precision Engineering [4]
References This article incorporates public domain material from websites or documents Standards and Technology.
[5]
of the National Institute of
[1] NIST Manufacturing Engineering (2008). NIST Programs of the Manufacturing Engineering Laboratory (http:/ / www. mel. nist. gov/ programs/ pbookweb. pdf). March 2008. [2] Venkatesh, V. C. and Izman, Sudin, Precision Engineering, Tata McGraw-Hill Publishing Company Limited, 2007, page 6. [3] http:/ / www. euspen. eu [4] http:/ / www. jspe. or. jp/ english/ [5] http:/ / www. nist. gov
External links • Precision Engineering, the Journal of the International Societies for Precision Engineering and Nanotechnology (http://www.elsevier.com/wps/find/journaldescription.cws_home/525017/description#description) • Precision Engineering Centre at Cranfield University (http://www.cranfield.ac.uk/sas/precisionengineering) • History of Precision Engineering (http://www.cranfieldprecision.com/history.php) • Precision Engineering in Yorkshire (http://precisionengineeringyorkshire.co.uk/)
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Pressure exchanger A pressure exchanger transfers pressure energy from a high pressure fluid stream to a low pressure fluid stream. Many industrial processes operate at elevated pressures and have high pressure waste streams. One way of providing a high pressure fluid to such a process is to transfer the waste pressure to a low pressure stream using a pressure exchanger. One particularly efficient type of pressure Schematics of a rotary pressure exchanger. A: High pressure side, B: Low pressure exchanger is a rotary pressure exchanger. side, C: Rotor rotation, D: Sealed area, 1:High pressure reject water inflow, 2:Pressurized sea water, 3: Low pressure sea water inflow, 4: Low pressure reject This device uses a cylindrical rotor with water drain, : Reject water / concetrate, : Piston / barrier, : Sea water longitudinal ducts parallel to its rotational axis. The rotor spins inside a sleeve between two end covers. Pressure energy is transferred directly from the high pressure stream to the low pressure stream in the ducts of the rotor. Some fluid that remains in the ducts serves as a barrier that inhibits mixing between the streams. This rotational action is similar to that of an old fashioned machine gun firing high pressure bullets and it is continuously refilled with new fluid cartridges. The ducts of the rotor charge and discharge as the pressure transfer process repeats itself. The performance of a pressure exchanger is measured by the efficiency of the energy transfer process and by the degree of mixing between the streams. The energy of the streams is the product of their flow rates and pressures. Efficiency is a function of the pressure differentials and the volumetric losses (leakage) through the device computed with the following equation:
where Q is flow, P is pressure, L is leakage flow, HDP is high pressure differential, LDP is low pressure differential, the subscript B refers to the low pressure feed to the device and the subscript G refers to the high pressure feed to the device. Mixing is a function of the concentrations of the species in the inlet streams and the ratio of flow rates to the device. Equation 2 is an expression for volumetric mixing that was derived by mass balance. Where C is the concentration of a dissolved species and the subscript D refers to the high-pressure outlet of the device. Reverse Osmosis with Pressure Exchangers One application in which pressure exchangers are widely used is reverse osmosis (RO). In an RO system, pressure exchangers are used as energy recovery devices (ERDs). As illustrated in Figure 3, high pressure membrane concentrate from the membranes is directed to the ERD. Pressure transfers from the high pressure concentrate stream [G] to a low pressure feedwater stream [B]. Pressurized feedwater flows from the ERD [D], driven by a circulation pump. This stream merges with the output of a high pressure pump [C] to form the membrane feed stream [E]. The concentrate leaves the ERD at low pressure [H], expelled by the incoming feedwater flow [B]. Figure 3 – Schematic Diagram of an RO Process with Pressure Exchanger Energy Recovery Devices Pressure exchangers save energy in these systems by reducing the load on the high pressure pump. In a seawater RO system operating at a 40% membrane water recovery rate, the ERD supplies 60% of the membrane feed flow. Energy is consumed by the circulation pump, however, because this pump merely circulates and does not pressurize water, its energy consumption is almost negligible: less than 3% of the energy consumed by the high pressure pump.
Pressure exchanger Therefore, nearly 60% of the membrane feed flow is pressurized with almost no energy input.
Energy Recovery and Pressure Exchange Systems Seawater desalination plants have produced potable water for many years. However, until recently desalination had been used only in extreme circumstances because of the very high-energy consumption of the process. Early designs for desalination plants made use of various evaporation technologies. The most advanced, however, are the multi-stage flash distillation seawater evaporation desalinators which made use of multiple Schematics of a reverse osmosis system (desalination) using a pressure exchanger. stages have an energy consumption of over 1:Sea water inflow, 2: Fresh water flow (40%), 3:Concentrate Flow (60%), 4:Sea 9 kWh per cubic meter of potable water water flow (60%), 5: Concentrate (drain), A: High pressure pump flow (40%), B: produced. For this reason large seawater Circulation pump, C:Osmosis unit with membrane, D: Pressure exchanger desalters were initially constructed in locations with very low energy costs, such as the Middle East or next to process plants with available waste heat. In the 1970s the seawater reverse osmosis (SWRO) process was developed which made potable water from seawater by forcing it under high pressure through a tight membrane thus filtering out salts and impurities. These salts and impurities are discharged from the SWRO device as a concentrated brine solution in a continuous stream, which contains a large amount of high-pressure energy. Most of this energy can be recovered with a suitable device. Many early SWRO plants built in the 1970s and early 1980s had an energy consumption of over 6.0 kWh per cubic meter of potable water produced, due to low membrane performance, pressure drop limitations and the absence of energy recovery devices. An example where a pressure exchange engine finds application is in the production of potable water using the reverse osmosis membrane process. In this process, a feed saline solution is pumped into a membrane array at high pressure. The input saline solution is then divided by the membrane array into super saline solution (brine) at high pressure and potable water at low pressure. While the high pressure brine is no longer useful in this process as a fluid, the pressure energy that it contains has high value. A pressure exchange engine is employed to recover the pressure energy in the brine and transfer it to feed saline solution. After transfer of the pressure energy in the brine flow, the brine is expelled at low pressure to drain. Nearly all reverse osmosis plants operated for the desalination of sea water in order to produce drinking water in industrial scale are equipped with an energy recovery system based on turbines. These are activated by the concentrate (brine) leaving the plant and transfer the energy contained in the high pressure of this concentrate usually mechanically to the high-pressure pump. In the pressure exchanger the energy contained in the brine is transferred hydraulically[1] [2] and with an efficiency of approximately 98% to the feed. This reduces the energy demand for the desalination process significantly and thus the operating costs. Therefrom results an economic energy recovery, amortization times for such systems varying between 2 and 4 years depending on the place of operation. Reduced energy and capital costs mean that for the first time ever it is possible to produce potable water from seawater at a cost below $1 per cubic meter in many locations worldwide. Although the cost may be a bit higher on islands with high power costs, the PE has the potential to rapidly expand the market for seawater desalination. By means of the application of a pressure exchange system, which is already used in other domains, a considerably higher efficiency of energy recovery of reverse osmosis systems may be achieved than with the use of reverse
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Pressure exchanger running pumps or turbines. The pressure exchange system is suited, above all, for bigger plants i.e. approx. ≥ 2000 m3/d permeate production.
References [1] NO 870016 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=NO870016), Leif J. Hauge [2] US patent 4887942 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=US4887942), Leif J. Hauge, "Pressure exchanger for liquids", issued 1988-09-02
Energy Recovery Device Performance Analysis by Richard L. Stover Ph. D. (http:/ / www. energyrecovery. com/ news/pdf/ERDPerformance.pdf) Ghalilah SWRO Plant by Richard L. Stover Ph. D. (http:/ / www. energyrecovery. com/ news/ pdf/ aww_ghalilah_cover_reprint_oct_05.pdf) http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2006020679&DISPLAY=STATUS http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2006020679&DISPLAY=DESC http://www.energyrecovery.com/news/documents/ERDsforSWRO.pdf http://www.energyrecovery.com/news/pdf/eri_launches_advanced_swro.doc http://www.patentstorm.us/patents/7306437-description.html http://www.sciencedirect.com/
Proactive maintenance Proactive maintenance is a maintenance strategy for stabilizing the reliability of machines or equipment. Its central theme involves directing corrective actions aimed at failure root causes, not active failure symptoms, faults, or machine wear conditions. A typical proactive maintenance regimen involves three steps: • (1) setting a quantifiable target or standard relating to a root cause of concern (e.g., a target fluid cleanliness level for a lubricant), • (2) implementing a maintenance program to control the root cause property to within the target level (e.g., routine exclusion or removal of contaminants), • and (3) routine monitoring of the root cause property using a measurement technique (e.g., particle counting) to verify the current level is within the target.[1]
References [1] Jim C. Fitch, Proactive maintenance. The cost-reduction strategy for the 90s, in Diesel & Gas Worldwide, June 1992, p. 48
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Process integration
Process integration Process integration is a term in chemical engineering which has two possible meanings. 1. A holistic approach to process design which emphasizes the unity of the process and considers the interactions between different unit operations from the outset, rather than optimising them separately. This can also be called integrated process design or process synthesis. El-Halwagi (1997 and 2006) and Smith (2005) describe the approach well. An important first step is often product design (Cussler and Moggridge 2003) which develops the specification for the product to fulfil its required purpose. 2. Pinch analysis, a technique for designing a process to minimise energy consumption and maximise heat recovery, also known as heat integration, energy integration or pinch technology. The technique calculates thermodynamically attainable energy targets for a given process and identifies how to achieve them. A key insight is the pinch temperature, which is the most constrained point in the process. The most detailed explanation of the techniques is by Linnhoff et al. (1982), Shenoy (1995) and Kemp (2006). This definition reflects the fact that the first major success for process integration was the thermal pinch analysis addressing energy problems and pioneered by Linnhoff and co-workers. Later, other pinch analyses were developed for several applications such as mass-exchange networks (El-Halwagi and Manousiouthakis, 1989), water minimization (Wang and Smith, 1994), and material recycle (El-Halwagi et al., 2003). A very successful extension was "Hydrogen Pinch", which was applied to refinery hydrogen management (Nick Hallale et al., 2002 and 2003). This allowed refiners to minimise the capital and operating costs of hydrogen supply to meet ever stricter environmental regulations and also increase hydrotreater yields. In the context of chemical engineering, Process Integration can be defined as a holistic approach to process design and optimization, which exploits the interactions between different units in order to employ resources effectively and minimize costs. Note that Process Integration is not limited to the design of new plants, but it also covers retrofit design (e.g. new units to be installed in an old plant) and the operation of existing systems. Nick Hallale (2001), in his article in Chemical Engineering Progress provided a state of the art review. He explained that process integration far wider scope and touches every area of process design. Industries are making more money from their raw materials and capital assets while becoming cleaner and more sustainable. Source: http://www.allbusiness.com/manufacturing/chemical-manufacturing/1128450-1.html#ixzz1Wij9OVl5 The main advantage of process integration is to consider a system as a whole (i.e. integrated or holistic approach) in order to improve their design and/or operation. In contrast, an analytical approach would attempt to improve or optimize process units separately without necessarily taking advantage of potential interactions among them. For instance, by using process integration techniques it might be possible to identify that a process can use the heat rejected by another unit and reduce the overall energy consumption, even if the units are not running at optimum conditions on their own. Such an opportunity would be missed with an analytical approach, as it would seek to optimize each unit, and thereafter it wouldn’t be possible to re-use the heat internally. Typically, process integration techniques are employed at the beginning of a project (e.g. a new plant or the improvement of an existing one) to screen out promising options to optimize the design and/or operation of a process plant. Also it is often employed, in conjunction with simulation and mathematical optimization tools to identify opportunities in order to better integrate a system (new or existing) and reduce capital and/or operating costs. Most process integration techniques employ Pinch analysis or Pinch Tools to evaluate several processes as a whole system. Therefore, strictly speaking, both concepts are not the same, even if in certain contexts they are used interchangeably. The review by Nick Hallale (2001) explains that in the future, several trends are to be expected in the field. In the future, it seems probable that the boundary between targets and design will be blurred and that these
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Process integration will be based on more structural information regarding the process network. Second, it is likely that we will see a much wider range of applications of process integration. There is still much work to be carried out in the area of separation, not only in complex distillation systems, but also in mixed types of separation systems. This includes processes involving solids, such as flotation and crystallization. The use of process integration techniques for reactor design has seen rapid progress, but is still in its early stages. Third, a new generation of software tools is expected. The emergence of commercial software for process integration is fundamental to its wider application in process design. OA
References Cussler, E.L. and Moggridge, G.D. (2001). Chemical Product Design. Cambridge University Press (Cambridge Series in Chemical Engineering). ISBN 0521791839 El-Halwagi, M. M., (2006) "Process Integration", Elsevier El-Halwagi, M. M., (1997) "Pollution Prevention through Process Integration", Academic Press El-Halwagi, M. M., F. Gabriel, and D. Harell, (2003) “Rigorous Graphical Targeting for Resource Conservation via Material Recycle/Reuse Networks”, Ind. Eng. Chem. Res., 42, 4319-4328 El-Halwagi, M. M., and Manousiouthakis, V. (1989). Synthesis of mass exchange networks. AIChE J. 35(8), 1233-1244. Hallale, Nick, (2001), "Burning Bright: Trends in Process Integration", Chemical Engineering Progress, July 2001 Nick Hallale, I Moore, D. Vauk (2002), "Hydrogen: Liability or Asset?", Chemical Engineering Progress, September 2002 [1] Hallale, N. Ian Moore, Dennis Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003) Kemp, I.C. (2006). Pinch Analysis and Process Integration: A User Guide on Process Integration for the Efficient Use of Energy, 2nd edition. Butterworth-Heinemann. ISBN 0750682604. Includes downloadable spreadsheet software. Linnhoff, B., D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy and R.H. Marsland, (1982) “A User Guide on Process Integration for the Efficient Use of Energy," IChemE UK Shenoy, U.V. (1995). "Heat Exchanger Network Synthesis: Process Optimization by Energy and Resource Analysis". Includes two computer disks. Gulf Publishing Company, Houston, TX, USA. ISBN 0884153916. Smith, R. (2005). Chemical Process Design and Integration. John Wiley and Sons. ISBN 0471486809 Wang, Y. P. and R. Smith (1994). Wastewater Minimisation. Chem. Eng. Sci., 49, 981-1006
References [1] http:/ / www. allbusiness. com/ manufacturing/ chemical-manufacturing/ 1000302-1. html
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Pulverizer
Pulverizer A pulverizer or grinder is a mechanical device for the grinding of many different types of materials. For example, they are used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.
Types of pulverizers Coal pulverizers may be classified by speed, as follows:[1] • Low Speed • Medium Speed • High Speed
Low Speed Ball and tube mills A ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length, containing a charge of tumbling or cascading steel balls, pebbles, or rods. A tube mill is a revolving cylinder of up to five diameters in length used for fine pulverization of ore, rock, and other such materials; the material, mixed with water, is fed into the chamber from one end, and passes out the other end as slime (slurry). Both types of mill include liners that protect the cylindrical structure of the mill from wear. Thus the main wear parts in these mills are the balls themselves, and the liners. The balls are simply "consumed" by the wear process and must be re-stocked, whereas the liners must be periodically replaced. The ball and tube mills are low-speed machines that grind the coal with steel balls in a rotating horizontal cylinder. Due to its shape only, people call it as Tube Mill and due to use of Grinding Balls for crushing, it is called Ball Mill. Hence, is the name Ball Tube Mill. These Mills are also designated as BBD-4772, Where- B – Broyer (Name of inventor). B – Boulet (French word for Balls). D – Direct firing. 47 – Diameter of shell (in Decimeters) i.e. 4.7m dia. 72 – Length of shell (in Decimeters) i.e. 7.2 m length By the name the grinding in the ball and tube mill is produced by rotating quantity of steel balls by their fall and lift due to rotation of tube. The ball charge may occupy one third to half of the total internal volume of the shell. The significant feature incorporated in the BBD mills is its double end operation, each end catering to one elevation of a boiler. The system facilitated entry of raw coal and outlet of pulverized fuel from same end simultaneously. This helps in reducing the number of installations per unit.
Mill Constructions And Details A ball Tube mill may be described as a cylinder made of steel plate having separate heads or trunion attached to the ends with the trunion resting on suitable bearings for supporting the machine. The trunion are hollow to allow for the introduction of discharge of the materials undergoing reduction in size. The mill shell is lined with chilled iron, carbon steel, manganese steel, High Chrome liners attached to shell body with counter sunk bolts.These liners are made in different shapes so that the counter inside surface of the mill is suited for requirement of application. The Shells are of three pieces. The Intermediate shell connects to the end shells by flange joints and the total length of shell is 7.2 m. The liners are fastened to the inner side of mill shell (cylindrical part) to protect the shell from the impact of steel balls. There are 600 nos. of liners of ten variants in each shell weighing 60.26 MT. The original lift value of the liners is 55 mm. and the minimum lift allowed is 20 mm.
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Pulverizer
Working Primary air in the case of Tube Mill have dual function to perform. It is used as drying as well as transporting media and by regulating the same the Mill output is regulated. Governed by the pulverize fuel outlet temperature requirement the combination of cold air and hot air dampers are regulated to have proper primary air temperature. In addition to raising the coal temperature Inside the Mill for drying and better grinding the same air works carrying media for pulverized coal through annular space between fixed trunnion tube and rotating hot air tube on way to classifier. Coal-laden air passing through Double cone static classifiers with adjustable classifier vanes for segregation Into pulverized fuel of desired fineness and coarse particles continues its journey towards coal burners for combustion. Coarse particles rejected in classifier find their way back to mill for another cycle of grinding. In order to avoid excess sweeping of coal from Mill Only Part Of the primary air, directly proportional to the boiler load demand is passed through Mill. Further to ensure and maintain sufficient velocity of pulverized fuel and to avoid settling in P.F. pipes an additional quantity of primary air is fed in to mixing box on raw coat circuit. This by-pass air tapped from the primary air duct going in Mill makes appreciable contribution for drying of raw coal by flash drying effect in addition to picking pp the pulverized fuel from Mill outlet for its transportation towards classifiers. Tube mill output while responding to boiler load demand is controlled by regulating primary air-flow. Such regulation by sweeping away of pulverized fuel from Mill being very fast rather well comparable with oil firing response, needs coal level to be maintained in the Mill. Mill level control circuit sensing the decreased coat level in Mill increases the speed of raw coal feeder and vice versa. Maintaining the coal level in Mill offers built-in-capacity cushion of pulverized fuel to take care of short interruption in raw coal circuit. The mill is pressurised and the tightness is ensured by plenum chambers around the rotating trunnion filled with pressurised seal air. Bleading seal air from plenum chamber to Mill provides air cushion between pulverized fuel in the Mill and the outside atmosphere. Inadequacy or absence of seal air will allow escape of pulverized fuel into atmosphere. On the other hand excess of seal air leaking into Mill will affect the Mill outlet temperature. As such the seal air is controlled by a local control damper by maintaining just sufficient differential pressure for sealing.
Medium Speed Ring and ball mill This type of mill consists of two rings separated by a series of large balls, like a thrust bearing. The lower ring rotates, while the upper ring presses down on the balls via a set of spring and adjuster assemblies, or pressurised rams. The material to be pulverized is introduced into the center or side of the pulverizer (depending on the design). As the lower ring rotates, the balls to orbit between the upper and lower rings, and balls roll over the bed of coal on the lower ring. The pulverized material is carried out of the mill by the flow of air moving through it. The size of the pulverized particles released from the grinding section of the mill is determined by a classifer separator - if the coal is fine enough to be picked up by the air, it is carried through the classifier. Coarser particles return to be further pulverized.
Vertical roller mill Similar to the ring and ball mill, this mill uses large "tires" to crush the coal. These are usually found in utility plants. Raw coal is gravity-fed through a central feed pipe to the grinding table where it flows outwardly by centrifugal action and is ground between the rollers and table. Hot primary air for drying and coal transport enters the windbox plenum underneath the grinding table and flows upward through a swirl ring having multiple sloped nozzles surrounding the grinding table. The air mixes with and dries coal in the grinding zone and carries pulverized coal particles upward into a classifier. Fine pulverized coal exits the outlet section through multiple discharge coal pipes leading to the burners, while oversized coal particles are rejected and returned to the grinding zone for further grinding. Pyrites and extraneous
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Pulverizer dense impurity material fall through the nozzle ring and are plowed, by scraper blades attached to the grinding table, into the pyrites chamber to be removed. Mechanically, the vertical roller mill is categorized as an applied force mill. There are three grinding roller wheel assemblies in the mill grinding section, which are mounted on a loading frame via pivot point. The fixed-axis roller in each roller wheel assembly rotates on a segmentally-lined grinding table that is supported and driven by a planetary gear reducer direct-coupled to a motor. The grinding force for coal pulverization is applied by a loading frame. This frame is connected by vertical tension rods to three hydraulic cylinders secured to the mill foundation. All forces used in the pulverizing process are transmitted to the foundation via the gear reducer and loading elements. The pendulum movement of the roller wheels provides a freedom for wheels to move in a radial direction, which results in no radial loading against the mill housing during the pulverizing process. Depending on the required coal fineness, there are two types of classifier that may be selected for a vertical roller mill. The dynamic classifier, which consists of a stationary angled inlet vane assembly surrounding a rotating vane assembly or cage, is capable of producing micron fine pulverized coal with a narrow particle size distribution. In addition, adjusting the speed of the rotating cage can easily change the intensity of the centrifugal force field in the classification zone to achieve coal fineness control real-time to make immediate accommodation for a change in fuel or boiler load conditions. For the applications where a micron fine pulverized coal is not necessary, the static classifier, which consists of a cone equipped with adjustable vanes, is an option at a lower cost since it contains no moving parts. With adequate mill grinding capacity, a vertical mill equipped with a static classifier is capable of producing a coal fineness up to 99.5% or higher <50 mesh and 80% or higher <200 mesh, while one equipped with a dynamic classifier produces coal fineness levels of 100% <100 mesh and 95% <200 mesh, or better. Bowl mill Similar to the vertical roller mill, it also uses tires to crush coal. There are two types, a deep bowl mill, and a shallow bowl mill.
High Speed Attrition Mill Rotor, Stationary Pegs Hammer Mill Used on farms for grinding grain and chaff for feed
Demolition pulverizer An attachment fitted to an excavator. Commonly used in demolition work to break up large pieces of concrete.
References [1] Coal Pulverising Mill Types, by Glenn Schumacher, 2010
Bibliography • Schumacher, Glenn (201). Coal Pulverising Mill Types. ISBN 9780646537597.
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Radiation properties
Radiation properties Conduction and convection are heat transfer processes that require the presence of a medium.[1] Radiation heat transfer is characteristically different from the other two in which it does not require a medium and, in fact it reaches maximum efficiency in a vacuum. Electromagnetic radiation has some proper characteristics depending on the frequency and wavelengths of the radiation, as shown in Figure 1. The phenomenon of radiation is not yet fully understood. Two theories have been used to explain radiation; however neither of them is perfectly satisfactory. First, the earlier theory which originated from the concept of a hypothetical medium referred as ether. Ether supposedly fills all evacuated or non evacuated spaces. The transmission of light or of radiant heat are allowed by the propagation of Schematic of the electromagnetic spectrum. electromagnetic waves in the ether.[2] Electromagnetic waves have similar characteristics to television and radio broadcasting waves they only differ in wavelength.[3] All electromagnetic waves travel at the same speed; therefore, shorter wavelengths are associated with high frequencies. Since every body or fluid is submerged in the ether, due to the vibration of the molecules, any body or fluid can potentially initiate an electromagnetic wave. All bodies generate and receive electromagnetic waves at the expense of its stored energy [4] The second theory of radiation is best known as the quantum theory and was first offered by Max Planck in 1900.[5] According to this theory, energy emitted by a radiator is not continuous but is in the form of quanta. Planck claimed that quantities had different sizes and frequencies of vibration similarly to the wave theory.[6] The energy E is found by the expression:h=6.626069E-34 Js(Plank's constant) and ν is the frequency. Higher frequencies are originated by high temperatures and create an increase of energy in the quantum. The propagation of electromagnetic waves of all wave lengths is often referred as "radiation" thermal radiation is constrained to the visible and infrared regions in Figure 1. However, the term radiation refers to thermal radiation only. For engineering purposes, it mat be stated that thermal radiation is a form of electromagnetic radiation which varies on the nature of a surface and its temperature.[7] Radiation waves may travel in unusual patterns compare to conduction heat flow. Radiation allows waves to travel from a heated body through a cold nonabsorbing or partially absorbing medium and reach a warmer body again.[8] This is the case of the radiation waves that travel from the sun to the earth.
Properties Emissivity (ε) The emissivity of a given surface is the measure of its ability to emit radiation energy in comparison to a blackbody at the same temperature. The emissivity of a surface varied between zero and one. This is a property that measures how much a surface behaves as a blackbody. The emissivity of a real surface varies as a function of the surface temperature, the wavelength, and the direction of the emitted radiation.[9] The fundamental emissivity of a surface at a given temperature is the spectral directional emissivity, which is defined as the ratio of the intensity of radiation emitted by the surface at a specified wavelength and direction to that emitted by a blackbody under the same
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Radiation properties conditions.[10] The total directional emissivity is defined in the same fashion by using the total intensities integrated over all wavelengths. In practice a more convenient method is used, hemispherical properties. These properties are spectrally and directionally averaged.[11] The emissivity of a surface at a specified wavelength may vary as temperature changes since the spectral distribution of emitted radiation changes with temperature. Finally the total hemispherical emissivity is defined in terms of the radiation energy emitted over all wavelengths in all directions. Radiation is a complex phenomenon, the dependability of its properties in wavelength and direction makes it even more complicated. Therefore, the gray and diffuse approximation methods are commonly used to perform radiation calculations.[12] A gray surface is characterized by having properties independent of wavelength, and a diffuse surface has properties independent of direction.
Absorptivity (α), Reflectivity (ρ) , and Transmissivity (t) If the amounts of radiation energy absorbed, reflected, and transmitted when radiation strikes a surface are measured in percentage of the total energy in the incident electromagnetic waves. The total energy would be divided into three groups (see Figure 2), they are called Absorptivity (α), Reflectivity (ρ) , and Transmissivity (t).[13] α + ρ + t = 1 (Equation 1) • Absorption is the fraction of irradiation absorbed by a surface. • Reflectivity is the fraction reflected by the surface. • Transmissivity is the fraction transmitted by the surface. A body is considered transmit some of the radiation waves falling on its surface. If electromagnetic waves are not transmitted through the substance it is therefore called opaque. When radiation waves hit the surface of an opaque body, some of the waves are reflected back while the other waves are absorbed by a thin layer of the material close to the surface. For engineering purposes all materials are thick enough that they can be considered opaque reducing Equation 1 to: α + ρ = 1 (Equation 2) Reflectivity deviates from the other properties in that it is bidirectional in nature. In other words, this property depends on the direction of the incident of radiation as well as the direction of the reflection. Therefore, the reflected rays of a radiation spectrum incident on a real surface in a specified direction forms an irregular shape that is not easily predictable. In practice, surfaces are assumed to reflect in a perfectly specular or diffuse manner. In a specular reflection (see Figure 3a), the angles of reflection and incidence are equal. In diffuse reflection (see Figure 3b), radiation is reflected equally in all directions. Reflection from smooth and polished surfaces can be assumed to be specular reflection, whereas reflection from rough surfaces approximates diffuse reflection.[14] In radiation analysis a surfaces is defined as smooth if the height of the surface roughness is much smaller relative to the wavelength of the incident radiation.
Conclusion Radiation is considered as the third model of heat transfer which is characteristically different from conduction and convection. Radiation is freely transmitted in air though partially absorbed by other gases, and in general, is partially reflected and partially absorbed by solids.[15] Transmission of radiation may occur in solids as well as in fluids is an interesting phenomenon because it may occur through a cold non-absorbing medium between two hotter bodies. Thus the surface of the earth is radiated by the sun, even though the atmosphere at high altitude is extremely cold. Radiation also deviates from conduction and convection in that the temperature level is a controlling factor. The properties of radiation are: Emissivity (ε),Absorptivity (α), Reflectivity (ρ) , and Transmissivity (t)
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Radiation properties
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References [1] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [2] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [3] Becker, Martin. Heat Transfer a Modern Approach New York: Plenum Publishing Corporation, 1986. [4] Becker, Martin. Heat Transfer a Modern Approach New York: Plenum Publishing Corporation, 1986. [5] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [6] Yunus, Cengel. Heat and Mass Transfer.New York: Mc Graw Hill, 2007. [7] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [8] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [9] Yunus, Cengel. Heat and Mass Transfer. New York: Mc Graw Hull, 2007. [10] Edwards, D.K. Radiation Heat Transfer. New York: Hemisphere Publishing Corporation, 1981. [11] Edwards, D.K. Radiation Heat Transfer. New York: Hemisphere Publishing Corporation, 1981. [12] Yunus, Cengel. Heat and Mass Transfer. New York: Mc Graw Hull, 2007. [13] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [14] Hsu, Shao Ti. Engineering Heat Transfer. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962. [15] Simonson, John R. " An Introduction to Engineering Heat Transfer." London: Mc Graw Hill,1967.
Railworthiness Railworthiness[1] [2] is the property or ability of a locomotive, passenger car, freight car, train or any kind of railway vehicle to be in proper operating condition or to meet acceptable safety standards of project, manufacturing, maintenance and railway use for transportation of persons, luggage or cargo.
References [1] Railworthiness Directives. In: Tank Car Safety Initiatives. Pg 2. (http:/ / www. fra. dot. gov/ downloads/ safety/ federal_safety_initiatives_april_2002. pdf) Federal Railroad Administration (FRA) (http:/ / www. fra. dot. gov/ ). United States Department of Transportation (DOT). Government Regulations. April 2002. T59.1. (visited on April 03, 2011)
TGV, Rennes, France.
[2] Registered Unit Standard: Manage the operation of railway on track maintenance machines. (http:/ / regqs. saqa. org. za/ showUnitStandard. php?id=255954) South African Qualifications Authority (SAQA). (visited on April 03, 2011)
JR-Maglev, MLX01, Yamanashi test rail, Japan.
Range of motion
Range of motion Range of motion (or ROM), is the distance (linear or angular) that a movable object may normally travel while properly attached to another object. It is also called range of travel, particularly when talking about mechanical devices and in mechanical engineering fields. For example, a volume knob (a rotary fader) may have a 300° range of travel from the "off" or muted (fully attenuated) position at lower left, going clockwise to its maximum-loudness position at lower right. As used in the biomedical and weightlifting communities, range of motion refers to the distance and direction a joint can move between the flexed position and the extended position. The act of attempting to increase this distance through therapeutic exercises (range of motion therapy—stretching from flexion to extension for physiological gain) is also sometimes called range of motion.
Measuring range of motion Each specific joint has a normal range of motion that is expressed in degrees. Devices to measure range of motion in the joints of the body include the goniometer and inclinometer which use a stationary arm, protractor, fulcrum, and movement arm to measure angle from axis of the joint. As measurement results will vary by the degree of resistance, two levels of range of motion results are recorded in most cases.
Limited range of motion Limited range of motion refers to a joint that has a reduction in its ability to move. The reduced motion may be a mechanical problem with the specific joint or it may be caused by injury or diseases such as osteoarthritis, rheumatoid arthritis, or other types of arthritis. Pain, swelling, and stiffness associated with arthritis can limit the range of motion of a particular joint and impair function and the ability to perform usual daily activities.
Range of motion exercises Physical therapy can help to improve joint function by focusing on range of motion exercises. The goal of these exercises is to gently increase range of motion while decreasing pain, swelling, and stiffness. There are three types of range of motion exercises: • Passive range of motion (or PROM) - Therapist or equipment moves the joint through the range of motion with no effort from the patient. • Active assistive range of motion (or AAROM) - Patient uses the muscles surrounding the joint to perform the exercise but requires some help from the therapist or equipment (such as a strap). • Active range of motion (or AROM) - Patient performs the exercise to move the joint without any assistance to the muscles surrounding the joint.
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Reciprocating compressor
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Reciprocating compressor A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.[1] [2] The intake gas enters the suction manifold, then flows into the compression cylinder where it gets compressed by a piston driven in a reciprocating motion via a crankshaft, and is then discharged. Applications include oil refineries, gas pipelines, chemical plants, natural gas processing plants and refrigeration plants. One specialty application is the blowing of plastic bottles made of Polyethylene Terephthalate (PET). A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders.
Portable compressors Reciprocating compressors were formerly used for powering portable tools such as pneumatic drills. The unit was mounted on a trailer or a lorry and comprised a reciprocating compressor driven, through a centrifugal clutch, by a diesel engine. The engine's governor provided only two speeds: • idling, when the clutch was disengaged • maximum, when the clutch was engaged and the compressor was running Modern versions use rotary compressors and have more sophisticated variable governors.
References [1] Bloch, H.P. and Hoefner, J.J. (1996). Reciprocating Compressors, Operation and Maintenance. Gulf Professional Publishing. ISBN 0-88415-525-0. [2] (http:/ / www. machinerylubrication. com/ Read/ 775/ reciprocating-compressor) Adam Davis, Noria Corporation, Machinery Lubrication, July 2005
External links • Calculation of required cylinder compression for a multistage reciprocating compressor (http://www. globmaritime.com/200907034744/marine-engineering/ calculation-of-required-cylinder-compression-for-a-multistage-reciprocating-compressor.html)
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Reciprocating motion Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes. A crank can be used to convert circular motion into reciprocating motion, or conversely turn reciprocating motion into circular motion. For example, inside an internal combustion engine (a type of reciprocating engine), the expansion of burning fuel in the cylinders periodically pushes the piston down, which, through the connecting rod, turns the crankshaft. The continuing rotation of the crankshaft drives the piston back up, ready for the next cycle. The piston moves in a reciprocating motion, which is converted into circular motion of the crankshaft, which ultimately propels the vehicle or does other useful work. The vibrations felt when the engine is running are a side effect of the reciprocating motion of the pistons. Reciprocating motion is clearly visible in early steam engines, particularly horizontal stationary engines and outside-cylindered steam locomotives, as the crank and connecting-rod usually are not enclosed.
Double-acting stationary steam engine demonstrating conversion of reciprocating motion to rotary motion. The piston is on the left, the crank is mounted on the flywheel axle on the right.
Machine demonstrating conversion of rotary motion to reciprocating motion using gears. The bottom pair of gears drives the mechanism.
Mathematically, reciprocating motion is approximately sinusoidal simple harmonic motion. Technically, however, the reciprocating motion produced by a rotating crank departs slightly from simple harmonic motion due to the changing angle of the connecting rod during the cycle.
Recuperator
Recuperator A recuperator is a special purpose counter-flow energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the waste heat . The image, right, shows the three major configurations.
Description Types of recuperator, or cross plate Heat exchanger. In many types of processes, combustion is used to generate heat, and the recuperator serves to recuperate, or reclaim this heat, in order to reuse or recycle it. The term recuperator refers as well to liquid-liquid counterflow heat exchangers used for heat recovery in the chemical and refinery industries and in closed processes such as ammonia-water or LiBr-water absorption refrigeration cycles.
Recuperators are often used in association with the burner portion of a heat engine, to increase the overall efficiency. For example, in a gas turbine engine, air is compressed, mixed with fuel, which is then burned and used to drive a turbine. The recuperator transfers some of the waste heat in the exhaust to the compressed air, thus preheating it before entering the fuel burner stage. Since the gases have been pre-heated, less fuel is needed to heat the gases up to the turbine inlet temperature. By recovering some of the energy usually lost as waste heat, the recuperator can make a heat engine or gas turbine significantly more efficient.
Energy transfer process Normally the heat transfer between airstreams provided by the device is termed as 'sensible', which is the exchange of energy, or enthalpy, resulting in a change in temperature of the medium (air in this case), but with no change in moisture content. However, if moisture or relative humidity levels in the return air stream are high enough to allow condensation to take place in the device, then this will cause 'latent' heat to be released and the heat transfer material will be covered with a film of water. Despite a corresponding absorption of latent heat, as some of the water film is evaporated in the opposite airstream, the water will reduce the thermal resistance of the boundary layer of the heat exchanger material and thus improve the heat transfer coefficient of the device, and hence increase efficiency. The energy exchange of such devices now comprises both sensible and latent heat transfer; in addition to a change in temperature, there is also a change in moisture content of the exhaust air stream. However, the film of condensation will also slightly increase pressure drop through the device, and depending upon the spacing of the matrix material, this can increase resistance by up to 30%. If the unit is not laid to falls, and the condensate not allowed to drain properly, this will increase fan energy consumption and reduce the seasonal efficiency of the device.
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Recuperator
Use in Ventilation systems In heating, ventilation and air-conditioning systems, HVAC, recuperators are commonly used to re-use waste heat from exhaust air normally expelled to atmosphere. Devices typically comprises a series of parallel plates of aluminium, plastic, stainless steel, or synthetic fibre, alternate pairs of which are enclosed on two sides to form twin sets of ducts at right angles to each other, and which contain the supply and extract air streams. In this manner heat from the exhaust air stream is transferred through the separating plates, and into the supply air stream. Manufacturers claim gross efficiencies of up to 80% depending upon the specification of the unit. The characteristics of this device are attributable to the relationship between the physical size of the unit, in particular the air path distance, and the spacing of the plates. For an equal air pressure drop through the device, a small unit will have a narrower plate spacing and a lower air velocity than a larger unit, but both units may be just as efficient. Because of the cross-flow design of the unit, its physical size will dictate the air path length, and as this increases, heat transfer will increase but pressure drop will also increase, and so plate spacing is increased to reduce pressure drop, but this in turn will reduce heat transfer. As a general rule a recuperator selected for a pressure drop of between 150 and 250Pa will have a good efficiency, whilst having a small effect on fan power consumption, but will have in turn a higher seasonal efficiency than that for physically smaller, but higher pressure drop recuperator. When heat recovery is not required, it is typical for the device to be bypassed by use of dampers arranged within the ventilation distribution system. Assuming the fans are fitted with inverter speed controls, set to maintain a constant pressure in the ventilation system, then the reduced pressure drop leads to a slowing of the fan motor and thus reducing power consumption, and in turn improves the seasonal efficiency of the system.
Other types of air-to-air heat exchangers • Run around coil • Thermal Wheel, or rotary heat exchanger (including enthalpy wheel and desiccant wheel) • Heat pipe
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Reel
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Reel A reel is an object around which lengths of another material (usually long and flexible) are wound for storage. Generally a reel has a cylindrical core and walls on the sides to retain the material wound around the core. In some cases the core is hollow, although other items may be mounted on it, and grips may exist for mechanically turning the reel.
Construction The size of the core is dependent on several factors. A smaller core will obviously allow more material to be stored in a given space. However, there is a limit to how tightly the stored material can be wound without damaging it and this limits how small the core can be. Other issues affecting the core size include:
A 250V-16A electrical wire on a reel
• Mechanical strength of the core (especially with large reels) • Acceptable turning speed (for a given rate of material moving on or off the reel a smaller core will mean that an almost empty reel has to turn faster) • any functional requirements of the core e.g. • For a reel that must be mechanically turned the size of the grips that mount it on the mechanical turning device. • The size of the mountings needed to support the core during unwinding. • Anything mounted on the cores (e.g. the sockets on an extension reel) With material such as photographic film that is flat and long but is relatively wide, the material generally is stored in successive single layers. In cases where the material is more uniform in cross-section (for example, a cable), the material may be safely wound around a reel that is wider than its width. In this case, several windings are needed to create a layer on the reel. An irrigation reel with travelling sprinkler
Uses Reel has potentially limitless uses, but major ones include: • A fishing reel is used on a fishing rod to wind the fishing line up. • Kite lines frequently are operated from reels. • Specialized reels for holding tow line for hang glider, glider, and sailplane launching • Laying of communications table use giant reels • Winches wind cables on reels • Webbing barriers that allow mobile post positions collect Electric wire reel reused as a table in a Rio de tensionally excess webbing. Janeiro decoration fair • Tow trucks hold steel cable on reels. • Garden hoses reeled solve hose kink problems. • Rope, wire and cable is often supplied on reels.
Reel
434 • Badge reels are used to hold badges, ski passes and the like. • A cave diving reel is safety equipment used for running a guideline.[1]
A badge reel
Motion picture terminology It is traditional to discuss the length of theatrical motion pictures in terms of "reels." The standard length of a 35 mm motion picture reel is 1000 feet (300 m). This length runs approximately 11 minutes at sound speed (24 frames per second) and slightly longer at silent movie speed (which may vary from approximately 16 to 22 frames per second). Most films have visible cues which mark the end of the reel. This allows projectionists running reel-to-reel to change-over to the next reel on the other projector. A so-called "two-reeler" would have run about 20–24 minutes since 35mm film reels and boxes the actual short film shipped to a movie theater for exhibition may have had slightly less (but rarely more) than 1000 ft (about 305 m) on it. Most modern projectionists use the term "reel" when referring to a 2000-foot (610 m) "two-reeler," as modern films are rarely shipped by single 1000-foot (300 m) reels. A standard Hollywood movie averages about five 2000-foot reels in length. The "reel" was established as a standard measurement because of considerations in printing motion picture film at a film laboratory, for shipping (especially the film case sizes) and for the size of the physical film magazine attached to the motion picture projector. Had it not been standardized (at 1000 feet (300 m) of 35 mm film) there would have been many difficulties in the manufacture of the related equipment. A 16 mm "reel" is 400 feet (120 m). It runs, at sound speed, approximately the same amount of time (11–12 minutes) as a 1000-foot 35 mm reel. A "split reel" is a motion picture film reel in two halves that, when assembled, hold a specific length of motion picture film that has been wound on a plastic core. Using a split reel allows film to be shipped or handled in a lighter and smaller form than film would on a "fixed" reel. In silent film terminology, two films on one reel. As digital cinema catches on, the physical reel is being replaced by a virtual format called Digital Cinema Package, which can be distributed using any storage media (such as hard drives) or data transfer medium (such as the Internet or satellite links) and projected using a digital projector instead of a conventional movie projector.
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Demo reels A "demo reel", or "show reel", is the motion picture or video equivalent of an artist's portfolio. It is typically used as a tool to promote the artist's skill, talent, and experience in a selected field, such as acting, directing, cinematography, editing, special effects, animation, or video games and other graphics. The demo reel is frequently submitted with a résumé to a prospective employer. When a reel contains scenes from actual productions, a shot list or credit list may also be submitted to describe the artist's specific involvement in each portion of the reel. While the usage of video excerpts on such showreels can be regarded as a breach of copyright, it is generally accepted in the film industry to do so, as it is the only tool of an artist to actually self-promote his/her work.[2] [3]
References [1] Devos, Fred; Le Maillot, Chris; Riordan, Daniel (2004). "Introduction to Guideline Procedures Part 1: Equipment" (http:/ / www. gue. com/ files/ page_images/ expeditions/ Mexico/ guideline1. pdf). DIRquest (Global Underwater Explorers) 5 (3). . Retrieved 2009-04-05. [2] Thompson, Pamela (May 1, 2000). "The Career Coach: Demo Reel DOs and DON'Ts" (http:/ / mag. awn. com/ index. php?ltype=search& sval=How+ to+ Make+ Sure+ Your+ Demo+ Ree& article_no=16). awn.com. Retrieved May 3, 2007. [3] "The Perfect Showreel How-To" (http:/ / www. clipland. com/ Blog/ 16-perfect-showreel-howto. html). clipland.com. August 2, 2006.
Relief valve For similar articles see Relief valve (disambiguation) The relief valve (RV) is a type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurised fluid to flow from an auxiliary passage out of the system. The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the set pressure is exceeded, the relief valve becomes the "path of least resistance" as the valve is forced open and a portion of the fluid is diverted through the auxiliary route. The diverted fluid (liquid, gas or liquid–gas mixture) is usually routed through a piping system known as a flare header or relief header to a central, elevated gas flare where it is usually burned and the resulting combustion gases are released to the atmosphere. As the fluid is diverted, the pressure inside the vessel will drop. Once it reaches the valve's reseating pressure, the valve will close. The blowdown is usually stated as a percentage of set pressure and refers to how much the pressure needs to drop before the valve reseats. The blowdown can vary from roughly 2–20%, and some valves have adjustable blowdowns.
A relief valve
In high-pressure gas systems, it is recommended that the outlet of the relief valve is in the open air. In systems where the outlet is connected to piping, the opening of a relief valve will give a pressure build up in the piping system downstream of the relief valve. This often means that the relief valve will not re-seat once the set pressure is reached. For these systems often so called "differential" relief valves are used. This means that the pressure is only working on an area that is much smaller than the openings area of the valve. If the valve is opened the pressure has to
Relief valve decrease enormously before the valve closes and also the outlet pressure of the valve can easily keep the valve open. Another consideration is that if other relief valves are connected to the outlet pipe system, they may open as the pressure in exhaust pipe system increases. This may cause undesired operation.[1] In some cases, a so-called bypass valve acts as a relief valve by being used to return all or part of the fluid discharged by a pump or gas compressor back to either a storage reservoir or the inlet of the pump or gas compressor. This is done to protect the pump or gas compressor and any associated equipment from excessive pressure. The bypass valve and bypass path can be internal (an integral part of the pump or compressor) or external (installed as a component in the fluid path). Many fire engines have such relief valves to prevent the overpressurization of fire hoses. In other cases, equipment must be protected against being subjected to an internal vacuum (i.e., low pressure) that is lower than the equipment can withstand. In such cases, vacuum relief valves are used to open at a predetermined low pressure limit and to admit air or an inert gas into the equipment so as control the amount of vacuum.
Technical terms In the petroleum refining, petrochemical and chemical manufacturing, natural gas processing and power generation industries, the term relief valve is associated with the terms pressure relief valve (PRV), pressure safety valve (PSV) and safety valve. In practice, people often do not stick to the technical distinctions between the most common abbreviations: SRV, PRV, SV and RV Pressure relief valve (PRV) or pressure safety valve (PSV). The difference being that PSVs have a manual lever to activate the valve in case of emergency. Most PRV are spring operated. At lower pressures some use a diaphragm in place of a spring. The oldest PRV designs use a weight to seal the valve. Set pressure: When increasing system pressure reaches this value the PRV opens. Accuracy of set pressure often follows guidelines set by the ASME. Relief valve (RV): A valve used on a liquid service, which opens proportionally as the increasing pressure overcomes the spring pressure. Safety valve (SV): Used in gas service. Most SV are full lift or snap acting, they pop open all the way. Safety relief valve (SRV): A PRV that can be used for gas or liquid service. But set pressure will usually only be accurate for one type of fluid at a time (the type it was set with). Pilot-operated relief valve (POSRV, PORV, POPRV): device that relieves by remote command from a pilot valve that is connected to the upstream system pressure. Low-pressure safety valve (LPSV): automatic system that relieves by static pressure on a gas. The pressure is small and near the atmospheric pressure. Vacuum pressure safety valve (VPSV): automatic system that relieves by static pressure on a gas. The pressure is small, negative and near the atmospheric pressure. Low and vacuum pressure safety valve (LVPSV): automatic system that relieves by static pressure on a gas. The pressure is small, negative or positive and near the atmospheric pressure. Snap acting: The opposite of modulating, refers to a valve that "pops" open, it goes into full lift in milliseconds. Usually accomplished with a skirt on the disc so that the fluid passing the seat suddenly affects a larger area and creates more lifting force. Modulating: Opens in proportion to the overpressure formed.
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Relief valve
Legal and code requirements in industry In most countries, industries are legally required to protect pressure vessels and other equipment by using relief valves. Also in most countries, equipment design codes such as those provided by the American Society of Mechanical Engineers (ASME), American Petroleum Institute (API) and other organizations like ISO (ISO 4126) must be complied with and those codes include design standards for relief valves.[2] [3] The main standards, laws or directives are: • ASME (American Society of Mechanical Engineers) Boiler & Pressure Vessel Code, Section VIII Division 1 and Section I • API (American Petroleum Institute) Recommended Practice 520/521, API Standard 2000 et API Standard 526 • ISO 4126 (International Organisation for Standardisation) • EN 764-7 (European Standard based on pressure Equipment Directive 97/23/EC) • AD Merkblatt (German) • PED 97/23/EC [4] (Pressure Equipment Directive – European Union)
DIERS Formed in 1976, the Design Institute for Emergency Relief Systems[5] was a consortium of 29 companies under the auspices of the American Institute of Chemical Engineers (AIChE) that developed methods for the design of emergency relief systems to handle runaway reactions. Its purpose was to develop the technology and methods needed for sizing pressure relief systems for chemical reactors, particularly those in which exothermic reactions are carried out. Such reactions include many classes of industrially important processes including polymerizations, nitrations, diazotizations, sulphonations, epoxidations, aminations, esterifications, neutralizations and many others. Pressure relief systems can be difficult to design, not least because what is expelled can be gas/vapour, liquid, or a mixture of the two – just as with a can of carbonated drink when it is suddenly opened. For chemical reactions, it requires extensive knowledge of both chemical reaction hazards and fluid flow. DIERS investigated the two-phase vapor–liquid onset / disengagement dynamics and the hydrodynamics of emergency relief systems with extensive experimental and analysis work.[6] Of particular interest to DIERS were the prediction of two-phase flow venting and the applicability of various sizing methods for two-phase vapor-liquid flashing flow. DIERS became a user's group in 1985. European DIERS Users’ Group (EDUG)[7] is a group of mainly European industrialists, consultants and academics who use the DIERS technology. The EDUG started in the late 1980s and has an annual meeting. A summary of many of key aspects of the DIERS technology has been published in the UK by the HSE.[8]
References [1] Beychok, Milton R. (2005). Fundamentals Of Stack Gas Dispersion (4th Edition ed.). author-published. ISBN 0-9644588-0-2. See Chapter 11, Flare Stack Plume Rise. [2] List of countries accepting the ASME Boiler & Pressure Vessel Code (http:/ / www. onetb. com/ asme_code_countries. htm) [3] API 5210-1, Sizing and Selection of Pressure-Relieving Devices (http:/ / www. techstreet. com/ cgi-bin/ detail?product_id=235758) [4] http:/ / ec. europa. eu/ enterprise/ pressure_equipment/ ped/ index_en. html [5] DIERS (http:/ / www. iomosaic. com/ diersweb/ home. aspx) [6] H.G. Fisher, H.S. Forrest, Stanley S. Grossel, J. E. Huff, A. R. Muller, J. A. Noronha, D. A. Shaw, B. J. Tilley (1992). Emergency Relief System Design Using DIERS Technology: The Design Institute for Emergency Relief Systems (DIERS) Project Manual. ISBN 0-8169-0568-3. [7] EDUG: European DIERS Users’ Group (http:/ / www. edug. eu) [8] CRR 1998/136 Workbook for chemical reactor relief system sizing (http:/ / www. hse. gov. uk/ research/ crr_htm/ 1998/ crr98136. htm)
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External links • Pressure relief valve sizing calculator (http://www.enggcyclopedia.com/calculators/ psv-sizing-calculator-blocked-liquid-discharge) PSV sizing calculator for liquid blocked outlet case. • PSV sizing calculator for blocked gas outlet case. (http://www.enggcyclopedia.com/calculators/ psv-sizing-calculator-blocked-gas-discharge) PSV sizing calculator for blocked gas discharge. • PSV sizing calculator – fire case for gas filled vessel (http://www.enggcyclopedia.com/calculators/ instrument-sizing/psv-sizing-calculator-fire-case-gas-filled-vessel/) • PSV sizing calculator – fire case for liquid filled vessel (http://www.enggcyclopedia.com/calculators/ instrument-sizing/psv-sizing-calculator-fire-case-liquid-filled-vessel/)
Residual stress Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. They remain along a cross section of the component, even without the external cause. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Another example occurs during semiconductor fabrication and microsystem fabrication when thin film materials with different thermal and crystalline properties are deposited sequentially under different process conditions. The stress variation through a stack of thin film materials can be very complex and can vary between compressive and tensile stresses from layer to layer.
Premature failure Castings may also have large residual stresses due to uneven cooling. Residual stress is often a cause of premature failure of critical components, and was one factor in the collapse of the suspension bridge at Silver Bridge in West Virginia, United States in December 1967. The eyebar links were castings which showed high levels of residual stress, which in one Ibar, encouraged crack growth. When the crack reached a critical size, it grew catastrophically, and from that moment, the whole structure started to fail in a chain reaction. Because the structure failed in less than a minute, 46 drivers and passengers in cars on the bridge at the time were killed as the suspended roadway fell into the river below.
The collapsed Silver Bridge, as seen from the Ohio side
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Controlled residual stress While uncontrolled residual stresses are undesirable, some designs rely on them. For example, toughened glass and pre-stressed concrete depend on residual stress to prevent brittle failure. A demonstration of the effect is shown by Prince Rupert's Drop, where a molten glass globule is quenched to produce a toughened outer layer. Bolted joints use residual stress to avoid subjecting bolts to fatigue. A gradient in martensite formation leaves residual stress in some swords with particularly hard edges (notably the katana), which can prevent the opening of edge cracks.
Prince Rupert's Drops
In certain types of gun barrels made with two tubes forced together, the inner tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. Parts are often heated or dropped into liquid nitrogen to aid assembly.
Press fits Press fits are the most common intentional use of residual stress. Automotive wheel studs, for example are pressed into holes on the wheel hub. The holes are smaller than the studs, requiring force to drive the studs into place. The residual stresses fasten the parts together. Nails are another example where the stress created by penetration of wood then helps to keep the nail in place.
Compressive residual stress (metal alloy) See shot peening
Measurement techniques There are several techniques that are used to measure the residual stress. They can be classified as destructive and non-destructive methods. Mechanical methods or dissection uses the release of stress and its associated strain after doing a cut, hole or crack. Nonlinear elastic methods as ultrasonic or magnetic techniques requires a reference sample. X-ray diffraction is a non-destructive method which allows the measurement of residual stress in isolated spots spaced distances as small as 100 micrometres.[1] [2] [3] Neutron diffraction is an alternative non-destructive method which allows measurement of residual stress in isolated spots. The choice between these two techniques depends on the design of the mechanical part to be tested.
References [1] Khan, Z. et al. (2005). "Ceramic rolling elements with ring crack defects—A residual stress approach". Materials Science and Engineering: A 404: 221. doi:10.1016/j.msea.2005.05.087. [2] Khan, Z. et al. (2006). "Residual stress variations during rolling contact fatigue of refrigerant lubricated silicon nitride bearing elements". Ceramics International 32: 751. doi:10.1016/j.ceramint.2005.05.012. [3] Khan, Z. et al. (2007). "Manufacturing induced residual stress influence on the rolling contact fatigue life performance of lubricated silicon nitride bearing materials". Materials & Design 28: 2688. doi:10.1016/j.matdes.2006.10.003.
Further reading • Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
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External links • - Energy-saving technology and computerized equipment for vibration stabilization of residual stress (the only CIS 35-year-old Scientific School, who presented in 1988, the world's first installation of computer diagnostics) are intended to stabilize the residual stresses in welds, castings and other non-rigid dynamic metal (http://www. minetek.donetsk.ua) • Residual stresses at The Welding Institute (http://www.twi.co.uk/j32k/protected/band_3/ksrhl001.html) • Comprehensive resources on Residual stresses at Cambridge University (http://www.msm.cam.ac.uk/ phase-trans/residual.html)
Reynolds transport theorem Reynolds' transport theorem (also known as the Leibniz-Reynolds' transport theorem), or in short Reynolds theorem, is a three-dimensional generalization of the Leibniz integral rule which is also known as differentiation under the integral sign. The theorem is named after Osborne Reynolds (1842–1912). It is used to recast derivatives of integrated quantities and is useful in formulating the basic equations of continuum mechanics. Consider integrating
over the time-dependent region
that has boundary
, then taking the
derivative with respect to time:
If we wish to move the derivative under the integral sign there are two issues: the time dependence of introduction of and removal of space from
, and the
due to its dynamic boundary. Reynolds' transport theorem provides the
necessary framework.
General form Reynolds' transport theorem, derived in [1] [2] , is:
in which and
is the outward-pointing unit-normal, are volume and surface elements at
, and
is a point in the region and is the variable of integration, is the velocity of the area element. The function
may be vector or scalar valued. Note that the integral on the left hand side is a function solely of time, and so the total derivative has been used.
Form for a Material Element In continuum mechanics this theorem is often used for material elements, which are parcels of fluids or solids which no material enters or leaves. If is a material element then there is a velocity function and the boundary elements obey This condition may be substituted to obtain [3]
Proof for a Material Element Let deformation gradient be given by
be reference configuration of the region
. Let the motion and the
Reynolds transport theorem
Let
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. Then, integrals in the current and the reference configurations are related by
That this derivation is for a material element is implicit in the time constancy of the reference configuration: it is constant in material coordinates. The time derivative of an integral over a volume is defined as
Converting into integrals over the reference configuration, we get
Since
is independent of time, we have
Now, the time derivative of
is given by [4]
Therefore,
where is the material time derivative of . Now, the material derivative is given by
Therefore,
or,
Using the identity
we then have
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Using the divergence theorem and the identity
we have
Erroneous sources This theorem is widely quoted, incorrectly, as being the form specific to material volumes. See the planetmath external link below for an example. Clearly, if the material volume form is applied to regions other than material volumes, errors will ensue.
A special case If we take
to be constant with respect to time, then
and the identity reduces to
as expected. This simplification is not possible if an incorrect form of the Reynolds transport theorem is used.
Interpretation and reduction to one dimension The theorem is the higher dimensional extension of Differentiation under the integral sign and should reduce to that expression in some cases. Suppose is independent of & , and that is a unit square in the plane and has
limits
and
. Then Reynolds transport theorem reduces to
which is the expression given on Differentiation under the integral sign, except that there the variables x and t have been swapped.
Notes [1] L. G. Leal, 2007, p. 23. [2] O. Reynolds, 1903, Vol. 3, p. 14 [3] T. Belytschko, W. K. Liu, and B. Moran, 2000, Nonlinear Finite Elements for Continua and Structures, John Wiley and Sons, Ltd., New York. [4] Gurtin M. E., 1981, An Introduction to Continuum Mechanics. Academic Press, New York, p. 77.
References L. G. Leal, 2007, Advanced transport phenomena: fluid mechanics and convective transport processes, Cambridge University Press, p. 912. O. Reynolds, 1903, Papers on Mechanical and Physical Subjects, Vol. 3, The Sub-Mechanics of the Universe, Cambridge University Press, Cambridge.
Reynolds transport theorem
External links • Osborne Reynolds, Collected Papers on Mechanical and Physical Subjects, in three volumes, published circa 1903, now fully and freely available in digital format: Volume 1 (http://www.archive.org/details/papersonmechanic01reynrich) Volume 2 (http://www.archive.org/details/papersonmechanic02reynrich) Volume 3 (http://www.archive.org/details/papersonmechanic03reynrich) • http://www.catea.org/grade/mecheng/mod6/mod6.html#slide1 • http://planetmath.org/encyclopedia/ReynoldsTransportTheorem.html
Roadworthiness Roadworthiness[1] [2] [3] [4] or streetworthiness is a property or ability of a car, bus, truck or any kind of automobile to be in a suitable operating condition or meeting acceptable standards for safe driving and transport of people, baggage or cargo in roads or streets.
Reference list [1] Roadworthiness. (http:/ / www. dvtani. gov. uk/ compliance/ roadworthiness. asp) Site of Driver & Vehicle Agency, Department of Environment, United Kingdom Government. (visited on March 8, 2011) [2] Certificate of Roadworthiness. (http:/ / www. vicroads. vic. gov. au/ Home/ Registration/ BuySellTransferVehicles/ CertificateOfRoadworthiness/ ) Site of VicRoads. State Government of Victoria. Australia. (visited on March 08, 2011) [3] Guide to maintaining roadworthiness. Commercial goods and passenger vehicles. (http:/ / www. businesslink. gov. uk/ Transport_files/ 070051_Guide to Maintaining Roadworthiness. pdf) PDF file available on the site of BusinessLink, United Kingdom Government. (visited on March 08, 2011) [4] Road Worthiness. (http:/ / www. brohns. co. za/ drivealive/ road-worthiness) "Drive Alive" site. (visited on April 10, 2011)
443
Roark's Formulas for Stress and Strain
444
Roark's Formulas for Stress and Strain Roark's Formulas for Stress and Strain Author(s)
Warren Young and Richard Budynas
Language
English
Subject(s)
Engineering
Publisher
McGraw-Hill Companies, The
Publication date September 2001 (7th Edition) Media type
Hardback
Pages
832
ISBN
007072542X
Roark's Formulas for Stress and Strain was first published in 1938 and the most current seventh edition was published in September 2001. The subjects covered in the book include: joints, bearing and shear stress, experimental stress analysis, and stress concentrations, as well as material behavior coverage and stress and strain measurement. Also included are expanded tables and cases; improved notations and figures with in the tables; consistent table and equation numbering and verification of correction factors. The book organizes the formulas into tables in a hierarchical format – chapter, table, case, subcase—providing diagrams for each case and subcase. Here are the topics covered in the 7th Edition: Chapter 1 – Introduction Chapter 2 – Stress and Strain: Important Relationships Chapter 3 – The Behavior of Bodies Under Stress Chapter 4 – Principles and Analytical Methods Chapter 5 – Numerical Methods Chapter 6 – Experimental Methods Chapter 7 – Tension, Compression, Shear, and Combined Stress Chapter 8 – Beams; Flexure of Straight Bars Chapter 9 – Bending of Curved Beams Chapter 10 – Torsion Chapter 11 – Flat Plates Chapter 12 – Columns and Other Compression Members Chapter 13 – Shells of Revolution; Pressure Vessels; Pipes Chapter 14 – Bodies in Contact Undergoing Direct Bearing and Shear Stress Chapter 15 – Elastic Stability Chapter 16 – Dynamic and Temperature Stresses Chapter 17 – Stress Concentration Factors Appendix A – Properties of a Plane Area Appendix B – Glossary Appendix C – Composite Materials In all, there are over 5000 formulas for over 1500 different load/support conditions for various structural members.
Roark's Formulas for Stress and Strain
Editions • • • • • • • •
1st Edition 1938 2nd Edition 1943 3rd Edition 1954 4th Edition 1965 5th Edition 1975 6th Edition 1989 7th Edition September 13, 2001 (851 Pages) 8th Edition December 20, 2011 (1072 Pages)
Biography Warren C. Young is professor emeritus in the department of mechanical engineering at the University of Wisconsin, Madison, where he was on the faculty for over 40 years. Dr. Young has also taught as a visiting professor at Bengal Engineering College in Calcutta, India, and served as chief of the Energy Manpower and Training Project sponsored by USAir in Bandung, Indonesia. Richard G. Budynas is professor of mechanical engineering at Rochester Institute of Technology. He is author of a newly revised McGraw-Hill textbook, Applied Strength and Applied Stress Analysis, 2nd Edition.
Rotary feeder Rotary feeders, also known as rotary airlocks or rotary valves, are commonly used in industrial and agricultural applications as a component in a bulk or specialty material handling system. Rotary feeders are primarily used for discharge of bulk solid material from hoppers/bins, receivers, and cyclones into a pressure or vacuum-driven pneumatic conveying system. Components of a rotary feeder include a rotor shaft, housing, head plates, and packing seals and bearings. Rotors have large vanes cast or welded on and are typically driven by small internal combustion engines or electric motors.
Use Rotary airlock feeders have wide application in industry wherever dry free-flowing powders, granules, crystals, or pellets are used. Typical materials include: cement, ore, sugar, minerals, grains, plastics, dust, fly ash, flour, gypsum, lime, coffee, cereals, pharmaceuticals, etc. Industries requiring this type include cement, asphalt, chemical, mining, plastics, food, etc. Rotary feeders are ideal for pollution control applications in wood, grain, food, textile, paper, tobacco, rubber, and paint industries, the Standard Series works beneath dust collectors and cyclone separators even with high temperatures and different pressure differentials.
445
Rotary feeder
Rotary valves are available with square or round inlet and outlet flanges. Housing can be fabricated out of sheet material or cast. Common materials are cast iron, carbon steel, 304 SS, 316 SS, and other materials. Rotary airlock feeders are often available in standard and heavy duty models, the difference being the head plate and bearing configuration. Heavy duty models use an outboard bearing in which the bearings are moved out away from the head plate. Housing inlet and discharge configurations are termed drop-thru or side entry. Different wear protections are available such as hard chrome or ceramic plating on the inner housing surfaces. Grease and air purge fittings are often provided to prevent contaminants from entering the packing seals.
Uses • Rotary airlock The basic use of the rotary airlock feeder is as an airlock transition point, sealing pressurized systems against loss of air or gas while maintaining a flow of material between components with different pressure and suitable for air lock applications ranging from gravity discharge of filters, rotary valves, cyclone dust collectors, and rotary airlock storage devices to precision feeders for dilute phase and continuous dense phase pneumatic convey systems. • Rotary valve Rotary airlock feeders/ rotary airlock valves are used in pneumatic conveying systems, dust control equipment, and as volumetric feed-controls. • Volumetric feeder Rotary airlock valves are also widely used as volumetric feeders for metering materials at precise flow rates from bins, hoppers, or silos onto conveying or processing systems.
Types Rotary airlock feeders Drop through rotary airlock feeders are designed for rugged applications that require an outboard bearing style unit where contamination and /or an abrasive product cannot be handled with an inboard bearing style. The outboard bearing feeders is engineered for use in high pressure pneumatic conveying systems, with high temperatures where more of an effective seal is required due to high or excessive wear that is experienced with a simple dust collector.
Blow-thru rotary airlock feeder The blow-thru rotary airlock feeder is ideal for pneumatic conveying applications in food, grain, chemical, milling, baking, plastics and pharmaceutical industries. The blow-thru airlocks feature a low profile with large capacity. High pressure differentials integral mounting feet, and retrofit competitive units. The blow-thru valves are available with 10-vane open-end rotor; outboard bearings and replaceable shaft seals.
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Rotary feeder
Easy clean rotary feeder The easy-clean series rotary feeders can be fast and simply disassembled, thoroughly quick cleaned, sanitized and inspected or maintenance in a minimum amount of time without the use of tools or removal from service, thereby reducing downtime and increasing system production. Reassembly without tools is accomplished in minutes. Internal clearances are automatically re-established every time. The Clean-in-place rotary feeder is a special purpose valve designed for where cross-contamination is a major concern and lengthy shut-downs for clean-out are cost-prohibitive, suited for Dairy, Pharmaceutical industries, Food, Baking, Chemical, Plastics, Paint, and Powder Coating plants. It is ideal for batch mixing systems such as those handling different colored resins which demand regular cleaning between cycles.
Filter valve The filter valve is a low-cost solution designed for light duty dust collector applications.
Knife rotary feeder This type of feeder is used for discharge of secondary fuel as for example: plastics or wood. The knife is cutting the oversize material and is preventing the rotor from blockage.
External links • The Powder and Bulk Channel - Solutions for the Powder and Bulk Industry [1]
References [1] http:/ / www. powderbulkchannel. com
447
Rotor
448
Rotor Rotor may refer to: • A rotating part of a mechanical device, for example in an electric motor, generator, alternator or pump. In engineering: • Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element called the stator. • Helicopter rotor, the rotary wing(s) of a rotorcraft such as a helicopter • ROTOR, a former radar project in the UK following the Second World War • Rotor (turbine), the rotor of a turbine powered by fluid pressure • Rotor (crank), a variable-angle bicycle crank • Rotor (brake), the disc of a disc brake, in U.S. terminology • Rotor (brake mechanism), a device that allows the handlebars and fork to revolve indefinitely without tangling the rear brake cable • Rotor (distributor), a component of the ignition system of an internal combustion engine • Rotor (engine), the powered part of a pistonless rotary engine • Rotor (antenna), an electric motor that rotates an antenna to the direction of transmission or reception In computing: • Rotor machine, the rotating wheels used in certain cipher machines, such as the German Enigma machine • Rotor (software project), the former code name for Microsoft's shared source implementation of its Common Language Infrastructure In medicine: • Rotor syndrome, a rare liver disorder In biology and chemistry: • The rotating part of a centrifuge, which also holds the samples In other fields: • • • • • • • • •
SC Rotor Volgograd, a Russian football club Rotor (Sonic the Hedgehog), a fictional character from the Sonic the Hedgehog universe Rotor (ride), the trade name for an amusement ride Rotor (meteorology), a turbulent horizontal vortex that forms in the trough of lee waves Rotor (mathematics), an n-blade object in geometric algebra, which rotates another n-blade object about a fixed or translated point Curl (mathematics), known as rotor in some countries, a vector operator that shows a vector field's rate of rotation Rotor, a space colony in Isaac Asimov's novel Nemesis R.O.T.O.R., a 1989 science fiction/action movie Vibrator (sex toy), a Japanese usage of similar sounds in English. Also spelt as rotar.
Run-around coil
449
Run-around coil A run-around coil is a type of energy recovery heat exchanger most often positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, to recover the heat energy. Generally, it refers to any intermediate stream used to transfer heat between two streams that are not directly connected for reasons of safety or practicality. It may also be referred to as a run-around loop, a pump-around coil or a liquid coupled heat exchanger.[1]
Description
A run-around coil installation, serving air handling units on the roof of an office building
A typical run-around coil system comprises two or more multi-row finned tube coils connected to each other by a pumped pipework circuit. The pipework is charged with a heat exchange fluid, normally water, which picks up heat from the exhaust air coil and gives up heat to the supply air coil before returning again. Thus heat from the exhaust air stream is transferred through the pipework coil to the circulating fluid, and then from the fluid through the pipework coil to the supply air stream. The use of this system is generally limited to situations where the air streams are separated and no other type of device can be utilised since the heat recovery efficiency is lower than other forms of air-to-air heat recovery. Gross efficiencies are usually in the range of 40 to 50%, but more significantly seasonal efficiencies of this system can be very low, due to the extra electrical energy used by the pumped fluid circuit. The fluid circuit, as well as containing the circulating pump, will also contain an expansion vessel, to accommodate changes in fluid pressure; a fill device, to ensure the system remains charged; controls to bypass and shut down the system when not required, and various other safety devices and ancillaries. Pipework runs should be kept as short as possible and should be sized for low velocities to keep frictional losses to a minimum, and hence reduce pump energy consumption. It is possible however to recover some of this energy in the form of heat given off by the motor if a glandless pump is used, where a water jacket surrounds the motor stator, thus water passing through the pump will pick up some of its heat. The pumped fluid will have to be protected from freezing in certain climates, and as such is normally treated with a glycol based anti-freeze. This also reduces the specific heat capacity of the fluid and increases the viscosity, increasing pump power consumption, further reducing the seasonal efficiency of the device. For example, a 20% glycol mixture will provide protection down to −10 °C (14 °F), but will increase system resistance by 15%. For the finned tube coil design, there is a performance maximum corresponding to an eight- or ten-row coil, above this the fan and pump motor energy consumption increases substantially and seasonal efficiency starts to drop off. The main cause of increased energy consumption lies with the fan, for the same face velocity, fewer coil rows will decrease air pressure drop and increase water pressure drop but the total energy consumption will usually be less than that for a greater number of coil rows with higher air pressure drops and lower water pressure drops.
Run-around coil
Energy transfer process Normally the heat transfer between airstreams provided by the device is termed as 'sensible', which is the exchange of energy, or enthalpy, resulting in a change in temperature of the medium (air in this case), but with no change in moisture content.
Other types of air-to-air heat exchangers • Thermal wheel, or rotary heat exchanger (including enthalpy wheel and desiccant wheel) • Recuperator, or cross plate heat exchanger • Heat pipe
References [1] D. A. REAY (1980), A Review of Gas–Gas Heat Recovery Systems, Heat Recovery Systems, Volume 1, No. 1, Pergamon Press Ltd., pgs 18 – 21
Sacrificial part A sacrificial part is a part of a machine or product that is intentionally engineered to fail under excess mechanical stress, electrical stress, or other unexpected and dangerous situations. The sacrificial part is engineered to fail first, and thus protect other parts of the system. Examples of sacrificial part include: • • • •
Electrical fuses Over-pressure burst disks Mechanical shear pins Galvanic anodes
450
Screw theory
451
Screw theory Screw theory refers to the algebra and calculus of pairs of vectors, such as forces and moments and angular and linear velocity, that arise in the kinematics and dynamics of rigid bodies.[1] [2] The conceptual framework was developed by Sir Robert Stawell Ball in 1876 for application in kinematics and statics of mechanisms (rigid body mechanics).[3] The value of screw theory derives from the central role that the geometry of lines plays in three dimensional mechanics, where lines form the screw axes of spatial movement and the lines of action of forces. The pair of vectors that form the Plücker coordinates of a line define a unit screw, and general screws are obtained by multiplication by a pair of real numbers and addition of vectors. A remarkable result of screw theory is that geometric calculations for points using vectors have parallel geometric calculations for lines obtained by replacing vectors with screws. This is termed the transfer principle.[4] Screw theory notes that all rigid-body motion can be represented as rotation about an axis along with translation along the same axis; this axis need not be coincident with the object or particle undergoing displacement. In this framework, screw theory expresses displacements, velocities, forces, and torques in three dimensional space. Recently screw theory has become an important tool in robot mechanics,[5] [6] mechanical design, computational geometry and multibody dynamics. This is in part because of the relationship between screws and dual quaternions which have been used to interpolate rigid-body motions.[7] Based on screw theory, an efficient approach has also been developed for the type synthesis of parallel mechanisms (parallel manipulators or parallel robots) [8] Fundamental theorems include Poinsot's theorem (Louis Poinsot, 1806) and Chasles' theorem (Michel Chasles, 1832). Other prominent contributors include Julius Plücker, W. K. Clifford, F. M. Dimentberg, Kenneth H. Hunt, J. R. Phillips.
Basic concepts Here we describe screw, twist, and wrench in general terms, and save the mathematics for the following sections.
Screw A spatial displacement of a rigid body can be defined by a rotation about a line and a translation along the same line, called a screw displacement. This is known as Chasles' theorem. The six parameters that define a screw displacement are the four independent components of the Plucker vector that defines the screw axis, together with the rotation angle about and linear slide along this line, and form a pair of vectors called a screw. For comparison, the six parameters that define a spatial displacement can also be given by three Euler Angles that define the rotation and the three components of the translation vector.
The pitch of a pure screw relates rotation about an axis to translation along that axis.
The points in a body undergoing a constant screw motion trace helices in the fixed frame. If this screw motion has zero pitch then the trajectories trace circles, and the movement is a pure rotation. If the screw motion has infinite pitch then the trajectories are all straight lines in the same direction.
Screw theory
Twist A twist represents the velocity of a rigid body as an angular velocity around an axis and a linear velocity along this axis. All points in the body have the same component of the velocity along the axis, however the greater the distance from the axis the greater the velocity in the plane perpendicular to this axis. Thus, the helicoidal field formed by the velocity vectors in a moving rigid body flattens out the further the points are radially from the twist axis.
Wrench The force and torque vectors that arise in applying Newton's laws to a rigid body can be assembled into a screw called a wrench. A force has a point of application and a line of action, therefore it defines the Plucker coordinates of a line in space and has zero pitch. A torque, on the other hand, is a pure moment that is not bound to a line in space and is an infinite pitch screw.
Algebra of Screws Let a screw be an ordered pair S=(S, V), where S and V are three dimensional real vectors. The sum and difference of these ordered pairs are computed componentwise. Screws are often called dual vectors. Now, introduce the ordered pair of real numbers â=(a, b) called dual scalars. Let the addition and subtraction of these numbers be componentwise, and define multiplication as
The multiplication of a screw S=(S, V) by the dual scalar â=(a, b) is computed componentwise to be,
Finally, introduce the dot and cross products of screws by the formulas:
and
The dot and cross products of screws satisfy the identities of vector algebra, and allow computations that directly parallel computations in the algebra of vectors. Let the dual scalar ẑ=(φ, d) define a dual angle, then the infinite series definitions of sine and cosine yield the relations
In general, the function of a dual variable is defined to be f(ẑ)=(f(φ), df′(φ)), where f′(φ) is the derivative of f(φ). These definitions allow the following results: • Unit screws are Plucker coordinates of a line and satisfy the relation
• Let ẑ=(φ, d) be the dual angle, where φ is the angle between the axes of S and T around their common normal, and d is the distance between these axes along the common normal, then
• Let N be the unit screw that defines the common normal to the axes of S and T, and ẑ=(φ, d) is the dual angle between these axes, then
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Screw theory
Wrench A common example of a screw is the wrench associated with a force acting on a rigid body. Let P be the point of application of the force F and let P be the vector locating this point in a fixed frame. The wrench W=(F, P×F) is a screw. The resultant force and moment obtained from all the forces Fi i=1,...,n, acting on a rigid body is simply the sum of the individual wrenches Wi, that is
Notice that the case of two equal but opposite forces F and -F acting at points A and B respectively, yields the resultant R=(F-F, A×F - B× F) = (0, (A-B)×F). This shows that screws of the form M=(0, M) can be interpreted as pure moments.
Twist In order to define the twist of a rigid body, we must consider its movement defined by the parameterized set of spatial displacements, D(t)=([A(f)],d(f)), where [A] is a rotation matrix and d is a translation vector. This causes a point p that is fixed in moving body to trace a curve P(t) in the fixed frame given by,
The velocity of P is
where v is velocity of the origin of the moving frame, that is dd/dt. Now substitute p= [AT](P-d) into this equation to obtain, where [Ω]=[dA/dt][AT] is the angular velocity matrix and ω is the angular velocity vector. The screw
is the twist of the moving body. The vector V=v + d×ω is the velocity of the point in the body that corresponds with the origin of the fixed frame. There are two important special cases: (i) when d is constant, that is v=0, then the twist is a pure rotation about the line L=(ω, d×ω), and (ii) when [Ω]=0, that is the body does not rotate but only slides in the direction v, then the twist is a pure slide given by L=(0, v).
Screws and spatial displacements The coordinate transformations for screws are easily understood by beginning with the coordinate transformations of the Plücker vector of line, which in turn are obtained from the transformations of the coordinate of points on the line. Let the displacement of a body be defined by D=([A], d), where [A] is the rotation matrix and d is the translation vector. Consider the line in the body defined by the two points p and q, which has the Plücker coordinates,
then in the fixed frame we have the transformed point coordinates P=[A]p+d and Q=[A]q+d, which yield.
Thus, a spatial displacement defines a transformation for Plücker coordinates of lines given by
453
Screw theory
454
The matrix [D] is the skew symmetric matrix that performs the cross product operation, that is [D]y=d×y. The 6×6 matrix [Â]=([A], [DA]) obtained from the spatial displacement D=([A], d) operates on a screw s=(s.v) to obtain:
The dual matrix [Â]=([A], [DA]) has determinant 1 and is called a dual orthogonal matrix.
Transformations Twists The velocities of each particle within a rigid body define a helical field called the velocity twist. To move representation from point A to point B, one must account for the rotation of the body such that:
In screw notation velocity twists transform with a 6x6 transformation matrix
Where: • • • •
denotes the linear velocity at point A denotes the linear velocity at point B denotes the angular velocity of the rigid body denotes the 3×3 cross product matrix
Screw theory
455
Wrenches Similarly the equipolent moments expressed at each location within a rigid body define a helical field called the force wrench. To move representation from point A to point B, once must account for the forces on the body such that:
In screw notation force wrenches transform with a 6x6 transformation matrix
Where: denotes the equipollent (link: wikibooks.org [9] ) moment at point A denotes the equipollent (link: wikibooks.org [9] ) moment at point B
• • •
denotes the total force applied to the rigid body
•
denotes the 3×3 cross product matrix
Twists as general displacements Given an initial configuration
, and a twist
location and orientation can be computed with the following formula: where
represents the parameters of the transformation.
Calculating twists Twists can be easily calculated for certain common robotic joints.
, the homogeneous transformation to a new
Screw theory
456
Revolute Joints For a revolute joint, given the axis of revolution
and a point
on that axis, the twist for the joint
can be calculated with the following formula:
Prismatic Joints For a prismatic joint, given a vector
pointing in the direction of translation, the twist for the joint can be
calculated with the following formula:
Screws by reflection In transformation geometry, the elemental concept of transformation is the reflection (mathematics). In planar transformations a translation is obtained by reflection in parallel lines, and rotation is obtained by reflection in a pair of intersecting lines. To produce a screw transformation from similar concepts one must use planes in space: the parallel planes must be perpendicular to the screw axis, which is the line of intersection of the intersecting planes that generate the rotation of the screw. Thus four reflections in planes effect a screw transformation. The tradition of inversive geometry borrows some of the ideas of projective geometry and provides a language of transformation that does not depend on analytic geometry.
Reciprocity of twist and wrench A wrench
acting on a rigid body moving with a twist
are reciprocal if the motion generated no power against
the force:
References [1] F. M. Dimentberg, The Screw Calculus and Its Applications in Mechanics, (Foreign Technology Division translation FTD-HT-23-1632-67) 1965 [2] A.T. Yang (1974) "Calculus of Screws" in Basic Questions of Design Theory, William R. Spillers, editor, Elsevier, pages 266 to 281. [3] R. S. Ball, The Theory of Screws: A study in the dynamics of a rigid body, Hodges, Foster & Co., 1876 (http:/ / books. google. com/ books?id=Qu9IAAAAMAAJ& ots=wwsm6pBaJa& dq=The theory of screws: A study in the dynamics of a rigid body& pg=PR3#v=onepage& q& f=false) [4] J. M. McCarthy and G. S. Soh, Geometric Design of Linkages. 2nd Edition, Springer 2010 (http:/ / books. google. co. uk/ books?id=jv9mQyjRIw4C& printsec=frontcover& dq=geometric+ design+ of+ linkages& hl=en& ei=3L_5TcvZGaHV0QG2wMiDAw& sa=X& oi=book_result& ct=result& resnum=1& ved=0CDMQ6AEwAA#v=onepage& q& f=false) [5] R. Featherstone, Robot Dynamics Algorithms, Springer, 1987. (http:/ / books. google. com/ books?id=c6yz7f_jpqsC& printsec=frontcover& source=gbs_ge_summary_r& cad=0#v=onepage& q& f=false) [6] R. Featherstone, Robot Dynamics Algorithms, Springer, 2008. (http:/ / books. google. com/ books?id=UjWbvqWaf6gC& printsec=frontcover& source=gbs_ge_summary_r& cad=0#v=onepage& q& f=false) [7] J. M. Selig, "Rational Interpolation of Rigid Body Motions," Advances in the Theory of Control, Signals and Systems with Physical Modeling, Lecture Notes in Control and Information Sciences, 2011 Volume 407/2011 213-224, DOI: 10.1007/978-3-642-16135-3_18 Springer. [8] X. Kong, Type Synthesis of Parallel Mechanisms, Springer, 2007. (http:/ / books. google. co. uk/ books?id=II9_FbbpkL0C& printsec=frontcover& dq=type+ synthesis+ of+ parallel+ mechanisms& hl=en& ei=AwDVTr63Hsyg8gORlsScAg& sa=X& oi=book_result& ct=result& resnum=1& ved=0CDgQ6AEwAA#v=onepage& q=type synthesis of parallel mechanisms& f=false) [9] http:/ / en. wikibooks. org/ wiki/ Statics/ Resultants_of_Force_Systems_(contents)
Screw theory • Ball, R. S. (1876). The theory of screws: A study in the dynamics of a rigid body (http://books.google.com/ books?id=Qu9IAAAAMAAJ&dq=The theory of screws: A study in the dynamics of a rigid body& pg=PR3#v=onepage&q&f=false). Hodges, Foster. • William Kingdon Clifford (1873), "Preliminary Sketch of Biquaternions", Paper XX, Mathematical Papers, p. 381. • A.T. Yang (1974) "Calculus of Screws" in Basic Questions of Design Theory, William R. Spillers, editor, Elsevier, pages 266 to 281. • Roy Featherstone (1987). Robot Dynamics Algorithms. Springer. ISBN 0898382300.
External links • Joe Rooney William Kingdon Clifford (http://oro.open.ac.uk/8455/01/chapter4(020507).pdf), Department of Design and Innovation, the Open University, London.
Self-exciting oscillation Self-exciting oscillation is a phenomenon in many fields, including engineering, economics and biology.
Mathematical basis Self-exciting oscillations are a logical consequence of systems which are described by a closed loop of time-lagged differential equations, i.e. where a change in variable N is driven by a change in variable N+1 but only after a time delay, a change in variable N+1 is driven by a change in variable N+2 but only after a time delay, … a change in variable N is driven by a change in variable N+x but only after a time delay.
Examples in engineering Railway and automotive wheels Hunting oscillation in railway wheels and shimmy in automotive tires can cause an uncomfortable wobbling effect, which in extreme cases can derail trains and cause cars to lose grip.
Central heating thermostats Early central heating thermostats were guilty of self-exciting oscillation because they responded too quickly. The problem was overcome by hysteresis, i.e., making them switch state only when the temperature varied from the target by a specified minimum amount.
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Self-exciting oscillation
Automatic transmissions Self-exciting oscillation occurred in early automatic transmission designs when the vehicle was traveling at a speed which was between the ideal speeds of 2 gears. In these situations the transmission system would switch almost continuously between the 2 gears, which was both annoying and hard on the transmission. Such behavior is now inhibited by introducing hysteresis into the system.
Steering of vehicles when course corrections are delayed There are many examples of self-exciting oscillation caused by delayed course corrections, ranging from light aircraft in a strong wind to erratic steering of road vehicles by a driver who is inexperienced or drunk.
SEIG (Self Excited Induction Generator) If an asynchronous motor is connected to a capacitor and the shaft turns with above critical speed, an electric hunting occurs which appears as line voltage on the terminals and provides useful function. See Exciter [1], an open source generator that is built on this principle.
Examples in other fields Population cycles in biology For example a reduction in population of a herbivore species because of predation, this makes the populations of predators of that species decline, the reduced level of predation allows the herbivore population to increase, this allows the predator population to increase, etc. Closed loops of time-lagged differential equations are a sufficient explanation for such cycles - in this case the delays are caused mainly by the breeding cycles of the species involved.
References [1] http:/ / ronja. twibright. com/ exciter/
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Shear pin
459
Shear pin A shear pin is a safety device designed to shear in the case of a mechanical overload, preventing other, more-expensive parts from being damaged. As a mechanical sacrificial part, it is the analogue of an electric fuse. The pin itself may be a plain metal rod inserted through a hub and axle; the diameter of the rod is carefully chosen to allow the shearing action when the desired breakaway force or shock is reached. A cotter pin may also be used as a low-tech shear pin. They are most commonly used in drive trains, such as a snow blower's auger or the propellers attached to marine engines.
A sailor checks the outside diameter of a shear pin in the machinery repair shop aboard the Nimitz-class aircraft carrier USS John C. Stennis
Another use is in pushback bars used for large aircraft. In this operation, if the pilot accidentally commands the front wheel - in which the bar is engaged - to steer, the shear pin breaks the bar, preventing it to swivel to the sides, which could be dangerous to both the pushback tractor and the personnel working nearby the plane.
Shear strength Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shear. In structural and mechanical engineering the shear strength of a component is important for designing the dimensions and materials to be used for the manufacture/construction of the component (e.g. beams, plates, or bolts) In a reinforced concrete beam, the main purpose of stirrups is to increase the shear strength. For shear stress
applies
where is major principal stress is minor principal stress In general: ductile materials fail in shear (ex. aluminum), whereas brittle materials (ex. cast iron) fail in tension. See tensile strength. To calculate: Given total force at failure and the force-resisting area (e.g. the cross-section of a bolt loaded in shear), shear strength is:
As a very rough guide[1] :
Shear strength
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Material
Ultimate Strength Relationship
Yield Strength Relationship
Steels
USS = approx. 0.75*UTS
SYS = approx. 0.58*TYS
Ductile Iron
USS = approx. 0.9*UTS
SYS = approx. 0.75*TYS
Malleable Iron USS = approx. 1.0*UTS Wrought Iron
USS = approx. 0.83*UTS
Cast Iron
USS = approx. 1.3*UTS
Aluminiums
USS = approx. 0.65*UTS
SYS = approx. 0.55*TYS
USS: Ultimate Shear Strength, UTS: Ultimate Tensile Strength, SYS: Shear Yield Stress, TYS: Tensile Yield Stress
References [1] http:/ / www. roymech. co. uk/ Useful_Tables/ Matter/ shear_tensile. htm
Sieving coefficient In mass transfer, the sieving coefficient is a measure of equilibration between the concentrations of two mass transfer streams. It is defined as the mean pre- and post-contact concentration of the mass receiving stream divided by the pre- and post-contact concentration of the mass donating stream.
where • S is the sieving coefficient • Cr is the mean concentration mass receiving stream • Cd is the mean concentration mass donating stream A sieving coefficient of unity implies that the concentrations of the receiving and donating stream equilibrate, i.e. the out-flow concentrations (post-mass transfer) of the mass donating and receiving stream are equal to one another. Systems with sieving coefficient that are greater than one require an external energy source, as they would otherwise violate the laws of thermodynamics. Sieving coefficients less than one represent a mass transfer process where the concentrations have not equilibrated. Contact time between mass streams in important in consider in mass transfer and affects the sieving coefficient.
In kidney In renal physiology, the sieving coefficient can be expressed as: sieving coefficient = clearance / ultrafiltration rate[1]
References [1] Sieving coefficient in drug clearance (http:/ / www. aic. cuhk. edu. hk/ web8/ Renal replacement therapy - CVVH. htm) - cuhk.edu.hk
Sight glass
Sight glass A sight glass or water gauge is a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within.
Liquid in tanks Simple sight glasses may be just a plastic or glass tube connected to the bottom of the tank at one end and the top of the tank at the other. The level of liquid in the sight glass will be the same as the level of liquid in the tank. Today, however, sophisticated float switches have replaced sight glasses in many such applications.
Steam boilers If the liquid is hazardous or under pressure, more sophisticated arrangements must be made. In the case of a boiler, the pressure of the water below and the steam above is equal, so any change in the water level will be seen in the gauge. The transparent tube (the “glass” itself) may be mostly enclosed within a metal or toughened glass shroud to prevent it from being damaged through scratching or impact and offering Water gauge on a steam locomotive. Here the water is at the “top protection to the operators in the case of breakage. This nut”, the maximum working level. Note the patterned backplate to help reading and toughened glass shroud. usually has a patterned backplate to make the magnifying effect of the water in the tube more obvious and so allow for easier reading. In some locomotives where the boiler operated at very high pressures, the tube itself would be made of metal-reinforced toughened glass.[1] It is important to keep the water at the specified level, otherwise the top of the firebox will be exposed, creating an overheat hazard and causing damage and possibly catastrophic failure. To check that the device is offering a correct reading and the connecting pipes to the boiler are not blocked by scale, the water level needs to be “bobbed” by quickly opening the taps in turn and allowing a brief spurt of water through the drain cock.[2]
Failure The gauge glass on a boiler needs to be inspected periodically and replaced if it is seen to have worn thin in the vicinity of the gland nuts, but a failure in service can still occur. Drivers are expected to carry two or three glass tubes, pre-cut to the required length, together with hemp or rubber seals, to replace the tubes on the road.[1] Familiarity with this disquieting occurrence was considered so important that a glass would often be smashed deliberately while a trainee driver was on the footplate, to give them practice in fitting a new tube.[3] Although automatic ball valves are fitted in the mounts to limit the release of steam and scalding water, these can fail through accumulation of limescale. It was standard procedure to hold the coal scoop in front of the face while the other hand, holding the cap for protection, reached to turn off the valves at both ends of the glass.
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Sight glass
Repair of a broken glass The following is the generally accepted procedure of safely fitting a new tubular glass on a steam boiler in industrial applications. Leather work gloves and a full face shield should be worn while working with the glass; this to prevent burns, cuts, and protect the operator's eyesight. 1. 2. 3. 4. 5. 6. 7.
8. 9.
Shut both the valves and open the glass drain cock Loosen and remove both gland nuts Remove any broken glass or other debris from glass valve body Place gland nuts and new seals on the precut glass Install glass in upper valve first and loosely tighten the nut. Pull glass down to bottom so that the gap in upper and lower valve body is even (this allows for expansion of the glass) Hand tighten both nuts, and then using a wrench, give each nut an additional quarter turn. Crack open steam side valve and allow the steam to lightly blow through to warm the glass. This prevents the glass from being subject to sudden thermal shock. (Should the glass be subject to thermal shock the effects may not be noticed immediately. However, the glass may then be much more brittle and even a slight bump might shatter it.) Close drain valve and crack open valve on water side of glass Observe gland for leakage and tighten as required
10. Open both valves fully.
Reflex Gauges A reflex gauge is more complex in construction but can give a clearer distinction between gas (steam) and liquid (water). Instead of containing the media in a glass tube, the gauge consists of a vertically-oriented slotted metal body with a strong glass plate mounted on the open side of the slot facing the operator. The rear of the glass, in contact with the media, has grooves moulded into its surface, running vertically. The grooves form a zig-zag pattern with 90° angles. Incident light entering the glass is refracted at the rear surface in contact with the media. In the region that is contact with the gas, most of the light is reflected from the surface of one groove to the next and back towards the operator, appearing silvery white. In the region that is in contact with the liquid, most of the light is refracted into the liquid causing this region to appear almost black to the operator. Well-known makes of reflex gauge are Penberthy, Jerguson, Klinger, and Cesare-Bonetti. Due to the caustic nature of boiler anti-scaling treatments ("water softeners"), reflex gauges tend to become relatively rapidly etched by the water and lose their effectivess at displaying the liquid level. Therefore, bi-colour gauges are recommended for certain types of boiler, particularly those operating at pressure above 60 bar.
Bi-Colour Gauges A bi-colour gauge is generally preferred for caustic media in order to afford protection to the glass. The gauge consists of a vertically-oriented slotted metal body with a strong plain glass to the front and the rear. The front and rear body surfaces are in non-parallel vertical planes. Behind the gauge body are light sources with two quite different wavelengths, typically red and green. Due to the different refraction of the red and green light, the liquid region appears green to the operator, while the gas region appears red. Unlike the reflex gauge, the glass has a plane surface which it does not need to be in direct contact with the media and can be protected with a layer of a caustic-resistant transparent material such as silica.
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Sight glass
Magnetic Gauges In a magnetic gauge a float on the surface of the liquid contains a permanent magnet. The liquid is contained in a chamber of strong, non-magnetic material avoiding the use of glass. The level indicator consists of a number of pivoting magnetic vanes arranged one above the other and placed close to the chamber containing the float. The two faces of the vanes are differently coloured. As the magnet passes up and down behind the vanes it cause them to rotate, displaying one colour for the region containing the liquid and another for the region containing gas. Magnetic gauges are stated in various manufacturers' literature to be most suitable for very high pressure and / or temperature and for aggressive liquids.
History The first locomotive to be fitted with the device was built in 1829 by John Rastrick at his Stourbridge works.[4]
Modern Industrial Sight Glass Industrial observational instruments have changed with industry itself. More structurally sophisticated than the water gauge, the contemporary sight glass — also called the sight window or sight port — can be found on the media vessel at chemical plants and in other industrial settings, including pharmaceutical, food, beverage and bio gas plants. Sight glasses enable operators to visually observe processes inside tanks, pipes, reactors and vessels. The modern industrial sight glass is a glass disk held between two metal frames, which are secured by bolts and gaskets, or the glass disc is fused to the metal frame during manufacture. The glass used for this purpose is either soda lime glass or borosilicate glass, and the metal, usually a type of stainless steel, is chosen for desired properties of strength. Borosilicate glass is superior to other formulations in terms of chemical corrosion resistance and temperature tolerance, as well as transparency. Fused sight glasses are also called mechanically prestressed glass, because the glass is strengthened by compression of the metal ring. Heat is applied to a glass disc and its surrounding steel ring, causing a fusion of the materials. As the steel cools, it contracts, compressing the glass and making it resistant to tension. Because glass typically breaks under tension, mechanically prestressed glass is unlikely to break and endanger workers. The strongest sight glasses are made with borosilicate glass, because of the greater difference in its coefficient of expansion.[5]
References [1] [2] [3] [4] [5]
Bell, A.M. (1950). Locomotives. London: Virtue and Company Limited. pp. 38; 284. Unidentified author (1957). Handbook for steam locomotive enginemen. London: British Transport Commission. Gasson, Harold (1973). Firing Days. Oxford: Oxford Publishing Company. p. 20. ISBN 0902888250. Snell, John B (1971). Mechanical Engineering: Railways. London: Longman. "Chemical and Pharmaceutical Sight Glass: Application Handbook" (http:/ / www. chemicalprocessing. com/ wp_downloads/ pdf/ LJ_Star_handbook. pdf). L.J. Star, Inc. (2009) (Retrieved June 4, 2010)
External links Reflex gauges with diagrams, application examples and photographs - Cesare-Bonetti: (http:/ / www. cesare-bonetti. it/Products/Level/livrflx.htm) Bi-Colour gauges with diagrams, application examples and photographs - Cesare-Bonetti: (http:/ / www. cesare-bonetti.it/Products/Level/bicol01.htm) Magnetic gauges: - Klinger: (http://www.klinger.kfc.at/resourcesklinger/shop/default/6539.pdf)
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Simple machine
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Simple machine A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that provide mechanical advantage (also called leverage).[2] Usually the term refers to the six classical simple machines which were defined by Renaissance scientists:[3] • • • • • •
Lever Wheel and axle Pulley Inclined plane Wedge Screw
These simple machines fall into two classes; those dependent on the vector resolution of forces (inclined plane, wedge, screw) and those in which there is an equilibrium of torques (lever, pulley, wheel). A simple machine is an elementary device that has a specific movement (often called a mechanism), which can be combined with other devices and movements to form a machine. The view of machines as decomposable into simple machines arose in the Renaissance as an interpretation of Greek texts on technology.[4] Simple machines are the elementary "building blocks" of more complicated machines. For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle.[5]
Table of simple mechanisms, from Chambers' Cyclopedia, [1] 1728. Simple machines provide a "vocabulary" for understanding more complex machines.
A page from a 1728 text by Ephraim Chambers[1] (see figure to the right) shows more simple machines. By the late 1800's Franz Reuleaux[6] identified hundreds of simple machines. Models of these devices can be found at Cornell's KMODDL site [7].
History The idea of a "simple machine" originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the "Archimedean" simple machines: lever, pulley, and screw.[2] [8] He discovered the principle of mechanical advantage in the lever.[9] Later Greek philosophers defined the classic five simple machines (excluding the inclined plane) and were able to roughly calculate their mechanical advantage.[4] Heron of Alexandria (ca. 10–75 AD) in his work Mechanics lists five mechanisms that can "set a load in motion"; lever, windlass, pulley, wedge, and screw,[8] and describes their fabrication and uses.[10] However the Greeks' understanding was limited to the statics of simple machines; the balance of forces, and did not include dynamics; the tradeoff between force and distance, or the concept of work. During the Renaissance the dynamics of the Mechanical Powers, as the simple machines were called, began to be studied from the standpoint of how much useful work they could perform, leading eventually to the new concept of mechanical work. In 1586 Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, and it was included with the other simple machines. The complete dynamic theory of simple machines was worked
Simple machine
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out by Italian scientist Galileo Galilei in 1600 in Le Meccaniche ("On Mechanics").[11] understand that simple machines do not create energy, only transform it.[11]
[12]
He was the first to
The classic rules of sliding friction in machines were discovered by Leonardo Da Vinci (1452–1519), but remained unpublished in his notebooks. They were rediscovered by Guillaume Amontons (1699) and were further developed by Charles-Augustin de Coulomb (1785).[13]
Mechanical advantage A simple machine has an applied force that works against a load force. If there are no friction losses, the work done on the load is equal to the work done by the applied force. This allows an increase in the output force at the cost of a proportional decrease in the distance moved by the load. The ratio of the output force to the input force is the mechanical advantage of the machine. If the simple machine does not dissipate or absorb energy, then its mechanical advantage can be calculated from the machine's geometry. For example, the mechanical advantage of a lever is equal to the ratio of its lever arms. A simple machine with no friction or elasticity is often called an ideal machine.[14] [15] In an ideal simple machine, the rate of energy in, or power in, equals the rate of energy out, or power out. Power is defined as the force multiplied by the velocity of its point of application. So the applied force times the velocity the input point moves, , must be equal to the load force times the velocity the load moves, :
or
So the ratio of output to input force, the mechanical advantage, of a frictionless machine is equal to the "velocity ratio"; the ratio of input velocity to output velocity: (Ideal Mechanical Advantage) In the screw, which uses rotational motion, the input force should be replaced by the torque, and the velocity by the angular velocity the shaft is turned.
Compound machine A compound machine is a machine formed from a set of simple machines connected in series with the output force of one providing the input force to the next. For example a bench vise consists of a lever (the vise's handle) in series with a screw, and a simple gear train consists of a number of gears (wheels and axles) connected in series. The mechanical advantage of a compound machine is the ratio of the output force exerted by the last machine in the series divided by the input force applied to the first machine, that is
Because the output force of each machine is the input of the next,
and
, this
mechanical advantage is also given by,
Thus, the mechanical advantage of the compound machine is equal to the product of the mechanical advantages of the series of simple machines that form it,
Simple machine
Energy losses and efficiency Machines lose energy through friction, deformation and wear, which is dissipated as heat. This means the power out of the machine is less than power in. The ratio of power out to power in is the efficiency η of the machine, and is a measure of the energy losses,
The velocity ratio of a machine is fixed by its dimensions, so it is the mechanical advantage that is reduced by the losses, that is
So in non-ideal machines, the mechanical advantage is always less than the velocity ratio by the product with the efficiency η. So a machine that includes losses such as friction, deformation and wear, will not be able to move as large a load as a corresponding ideal machine using the same input force. The efficiency of a compound machine is the product of the efficiencies of the series of simple machines that form it,
References [1] Table of Mechanicks, from Ephraim Chambers (1728) Cyclopaedia, A Useful Dictionary of Arts and Sciences, Vol. 2, London, p.528, Plate 11. [2] Asimov, Isaac (1988). Understanding Physics (http:/ / books. google. com/ books?id=pSKvaLV6zkcC& pg=PA88& dq=Asimov+ simple+ machine& cd=1#v=onepage& q& f=false). New York: Barnes & Noble. p. 88. ISBN 0880292512. . [3] Anderson, William Ballantyne (1914). Physics for Technical Students: Mechanics and Heat (http:/ / books. google. com/ books?id=Pa0IAAAAIAAJ& pg=PA112). New York, USA: McGraw Hill. pp. 112–122. . Retrieved 2008-05-11. [4] Usher, Abbott Payson (1988). A History of Mechanical Inventions (http:/ / books. google. com/ books?id=xuDDqqa8FlwC& pg=PA196#v=snippet& q=wedge and screw& f=false). USA: Courier Dover Publications. pp. 98. ISBN 048625593X. . [5] Prater, Edward L. (1994), Basic Machines (http:/ / www. constructionknowledge. net/ public_domain_documents/ Div_1_General/ Basic_Skills/ Basic Machines NAVEDTRA 14037 1994. pdf), Naval Education and Training Professional Development and Technology Center, NAVEDTRA 14037 [6] Reuleaux, F., 1876 'The Kinematics of Machinery,' (trans. and annotated by A. B. W. Kennedy), reprinted by Dover, New York (1963) [7] http:/ / kmoddl. library. cornell. edu/ rx_collection. php [8] Chiu, Y.C. Chiu (2010). An introduction to the History of Project Management (http:/ / books. google. com/ books?id=osNrPO3ivZoC& pg=PA42& dq="heron+ of+ alexandria"+ + load+ motion#v=onepage& q="heron of alexandria" load motion& f=false). Delft: Eburon Academic Publishers. pp. 42. ISBN 9059724372. . [9] Ostdiek, Vern; Bord, Donald (2005). Inquiry into Physics (http:/ / books. google. com/ books?id=7kz2pd14hPUC& pg=PA123). Thompson Brooks/Cole. p. 123. ISBN 0534491685. . Retrieved 2008-05-22. [10] Strizhak, Viktor; Igor Penkov, Toivo Pappel (2004). "Evolution of design, use, and strength calculations of screw threads and threaded joints" (http:/ / books. google. com/ books?id=FqZvlMnjqY0C& printsec=frontcover& dq="archimedean+ simple+ machine"& source=gbs_summary_r& cad=0). HMM2004 International Symposium on History of Machines and Mechanisms. Kluwer Academic publishers. p. 245. ISBN 1402022034. . Retrieved 2008-05-21. [11] Krebs, Robert E. (2004). Groundbreaking Experiments, Inventions, and Discoveries of the Middle Ages (http:/ / books. google. com/ books?id=MTXdplfiz-cC& pg=PA163& dq="mechanics+ Galileo+ analyzed"#v=onepage& q="mechanics Galileo analyzed"& f=false). Greenwood Publishing Group. p. 163. ISBN 0313324336. . Retrieved 2008-05-21. [12] Stephen, Donald; Lowell Cardwell (2001). Wheels, clocks, and rockets: a history of technology (http:/ / books. google. com/ books?id=BSfpFLV1nkAC& pg=PA86& dq="simple+ machine"+ galileo#v=onepage& q="simple machine" galileo& f=false). USA: W. W. Norton & Company. pp. 85–87. ISBN 0393321754. . [13] Armstrong-Hélouvry, Brian (1991). Control of machines with friction (http:/ / books. google. com/ books?id=0zk_zI3xACgC& pg=PA10& dq=friction+ leonardo+ da+ vinci+ amontons+ coulomb#v=onepage& q=friction leonardo da vinci amontons coulomb& f=false). USA: Springer. pp. 10. ISBN 0792391330. . [14] J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York. [15] B. Paul, 1979, Kinematics and Dynamics of Planar Machinery, Prentice Hall.
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Slip joint
Slip joint A slip joint is a mechanical construction allowing extension and compression in a linear structure.
General forms Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment from one temporarily fixed position to another. Examples of the latter are tripods, hiking poles, or similar telescoping device. The position is fixed using a clamping mechanism based on a cam, a set screw or similar locking mechanism. Slip joints can also be non-telescoping, such as the joints on some older wooden surveyor's levelling rods. These use a joint that keeps the sections offset from each other but able to be slid together for transport. Examples of continuous slip joints are given below.
Special purpose slip joints Civil Engineering Slip joints in large structures are used to allow independent motion of large components while enabling them to be joined in some way. For example, if two tall buildings are to be joined with a pedestrian skyway at some high level, there are two options in structural engineering. If the buildings are identical in mass and elasticity they will tend to respond similarly to ground motion induced by earthquakes. In this case it may be appropriate to construct a rigid connection between the buildings, although this may require additional supporting members within the structures. On the other hand, a lower cost connection may be made by using a lightweight structure that is not coupled rigidly but instead which is allowed to slide or "float" relative to one or both structures. This is especially suitable where the two structures may respond differently to ground motion. The structure will not be completely free to move but rather may use elastic materials to locate it near the center of its range of motion and viscous shock absorbers to absorb energy and to restrict the speed of relative motion. When a sliding connection is used it is extremely important that there be sufficient range of motion without failure to accommodate the maximum credible relative motion of the structures. Additional "fail safe" flexible connections may be added to ensure that the structure does not fall, although it may be damaged to a point of being unservicable or unrepairable Slip joints are common under conditions where temperature changes can cause expansion and contraction that may overstress a structure. These are generally referred to as expansion joints. Bridges and overpasses frequently have sliding joints that allow a deck to move relative to piers or abutments. The joints can be constructed with elastomeric pads that permit motion or can use rollers on flat surfaces to allow the ends to move smoothly. The exact details are limited by the imagination of the designer.
Mechanical Engineering Slip joints are sometimes found in tubular structures such as piping, but are generally avoided for this application due to requirements for sealing against leakage, instead using either a large loop that is allowed to flex or a semi-rigid bellows. Pipe supports often are slip joints to allow for the thermal expansion or contraction or the pipe relative to the support.
467
Slip line field
Slip line field A Slip Line Field or Slip line field theory, is a technique often used to analyze the stresses and forces involved in the major deformation of metals, using theories based around maximum shear stress.
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Society of Tribologists and Lubrication Engineers
469
Society of Tribologists and Lubrication Engineers Society of Tribologists and Lubrication Engineers Type
Non-Profit/Technical Society
Industry
Tribology and Lubrication Engineering
Founded
1944
Headquarters Park Ridge, Illinois Key people
Edward Salek, Executive Director
Website
www.stle.org
The Society of Tribologists and Lubrication Engineers [1] or "STLE" is the premier technical society that serves the needs of more than 10,000 individuals and 150 companies and organizations that comprise the tribology and lubrication engineering business sector, bringing together managers, engineers, scientists, technicians, academics, and government institutions from around the world to learn and share the “best practices” for the tribology and lubrication fields. This professional organization's stated mission [2] is to advance the science of tribology and the practice of lubrication engineering in order to foster innovation, improve the performance of equipment and products, conserve resources and protect the environment. Its stated vision [2] is to be a leader in the global network of individuals, institutions, societies and corporate entities with a common interest in advancing the science of tribology and the practice of lubrication engineering. This international and interdisciplinary society operates from its 9000 sq ft (840 m2). headquarters building located in Park Ridge, Illinois, a suburb located fifteen miles (24 km) northwest of downtown Chicago, where staff focus on areas of membership, certification, technical information and training, and publications to better support its members who influence the worldwide communities affected by tribology and lubricants.
History STLE is an individual membership society focusing on professional, technical and scientific issues and needs. It was founded on March 3, 1944, in Chicago as the American Society of Lubrication Engineers (ASLE). From these early days, into the 1980s, the organization’s primary audience was plant engineers in charge of lubrication for production equipment at major facilities like auto plans or steel mills. Major activities were technical conferences, peer-reviewed publishing and educational activities. To adapt and reflect evolving market and audience needs, the organization’s membership voted in 1987 to change the name to Society of Tribologists and Lubrication Engineers (STLE). This acknowledged a growing international participation and appealed to a more diverse audience that encompassed many aspects of engineering and tribology, as well as the traditional base of lubrication engineers and suppliers of liquid lubricants. Creation and dissemination of reliable technical information, STLE’s strength for 65 years, will continue defining the organization’s purpose and value in the future. As the world searches for solutions to environmental and energy challenges, many of which are tied to the fundamentals of tribology and lubricants, STLE stands ready to be the trusted source of information for an expanding audience of people looking for answers to these challenges.
Society of Tribologists and Lubrication Engineers
Organization STLE is incorporated in the State of Illinois. Structure and governance procedures are defined in a Constitution and Bylaws, which have recently been updated and revised. In addition, a strategic plan directs the ongoing activities of the Society. Annual budget is approximately $2.25 million. STLE’s elected leadership is provided by a 24-member Board of Directors. The President, who serves a one-year term, is the organization’s chief elected officer and the chairman of the Board of Directors. Complementing and extending the work of the Board is an impressive volunteer network that includes hundreds of individuals serving in a variety of ways. This might include participation in one of 23 technical committees and councils, an administrative committee, serving as an associate editor or reviewer for a Society journal or local Section activity. Working in concert with the elected leadership and volunteers is a 9-person professional staff who work out of its headquarters in Park Ridge. In its entirety, the STLE staff have combined experience of more than 100 years in association and organization management. STLE is recognized by the US Internal Revenue Service as a 501(c)(3)non-profit organization.
Membership Membership [3] in the STLE is open to anyone involved with tribology and lubrication issues, especially as they apply to industrial production and who want to acknowledge their professionalism and focus in these fields. There are 4 ways for an individual to become a member of the STLE; corporate membership, regular membership, associate membership, and student membership. Corporate membership provides opportunities for industry to stay at the forefront of their field. Included in this membership is the membership magazine TLT, plus online access to the full archives of Tribology Transactions and Tribology Letters. Also included are two free admissions to the annual meeting including two education courses. Corporate members receive discounts on exhibit booth space and Commercial Marketing Forum registrations, and are listed in the STLE Online Corporate Member Directory. Regular membership is available to the technical individual with an engineering or science degree or equivalent experience. Membership carries voting privileges and leadership opportunities on both the national and local levels, such as involvement in various committees through the organization or one of the local sections. Associate membership is open regardless of experience or educational background to anyone with an interest in lubrication engineering. Associate membership carries voting privileges and leadership opportunities on the local level, such as a local section of the STLE organization. Student membership is available for interested students studying in one of the education fields of lubrication engineering at a collegiate level, whether they be undergraduate or graduate and offers discounts for various STLE events, such as registration to the Annual Meeting or International Joint Tribology conferences each year.
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Society of Tribologists and Lubrication Engineers
Publications STLE's magazine "Tribology & Lubrication Technology" or TLT and its two scholarly journals, "Tribology Transactions" and "Tribology Letters" are respected sources for reliable technical and scientific information and peer-reviewed research papers, known throughout the tribology and lubrication industries. On top of these significant publications, STLE also offers a monthly e-newsletter [4] that can be accessed on the organization's website. Tribology & Lubrication Technology [5] is the official monthly magazine of STLE and is provided free as part of STLE membership. TLT was created to aid in the technical education and professional development of STLE members and industry colleagues. Each issue is filled with feature articles, case studies, best practice analysis, industry surveys, interviews with leading professionals, resources, lubrication fundamentals and more. TLT published its first issue in October 2003 and in June 2009 the magazine went digital [6], allowing for a total circulation of more than 13,000 print and online readers and articles that can be translated into 38 languages. Tribology Transactions [7] features scientific and technical papers in the field of tribology. Since its inception in 1957, the quarterly journal has published more than 2,000 papers of relevance to a wide variety of industries. Transactions is read and referenced by nearly 1,000 leaders in the field of tribology research in countries around the world. Tribology Letters [8] is devoted to the development of the science of tribology and its applications. It serves as a depository for new information on the properties of surfaces and interfaces in relative motion, among which are friction, lubrication, wear, adhesion, failure and contact phenomena. The journal facilitates communication and exchange of seminal ideas among thousands of practitioners who are engaged worldwide in the pursuit of tribology-based science and technology. Coverage spans all areas of industrial and academic tribology. Tribology Letters fosters the cross-fertilization of ideas by rapid dissemination of the results of frontier research and development
Education and Certification Professional development activities are at the heart of the STLE's programs. Technical professionals working in tribology and the lubricants industry expect that organizations like the STLE will remain as their primary source of continuing education. The STLE offers educational programs in several different venues and formats, such as the annual meeting, local sections, online education, certifications, and education partners. The Annual Meeting [9] is a week long conference that occurs each May in various cities across the U.S., where one-day technical education courses are taught by professionals who have in-depth knowledge of current trends in their respective fields. Local Sections often conduct education days during the year, using a format similar to the Annual Meeting courses. The STLE also implementing online education in 2010 to the betterment of its members and it also works in conjunction with Education partners who have recommended training programs to further the success of the individual in the lubrication industry. The STLE is also proud to offer credentialing in 3 areas of expertise with sponsored certifications exams. The value of STLE certification has been proven in the market place with increased income and immediate respect and credibility with buyers and peers. These certifications are designed to be consistent with the standards of the National Organization for Competency Assurance (NOCA), ISO 17024, and also distinguish between a credible real professional and a “self-proclaimed” expert. These 3 exams are the Certified Lubrication Specialist (CLS), Oil Monitoring Analyst (OMA I and OMA II), and Certified Metalworking Fluids Specialist (CMFS). Certified Lubrication Specialist [10] (CLS) is the only independent certification for the lubrication professional that verifies your broad lubrication engineering knowledge. Certification recognizes those individuals who possess current knowledge of lubrication fundamentals and best practices in lubrication maintenance in industrial settings. Certified individuals must have at least three years of experience in the field of lubrication.
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Society of Tribologists and Lubrication Engineers Oil Monitoring Analyst [11] (OMA) is the certification for the Predictive Maintenance Professional that demonstrates competence in the field of machinery oil monitoring. Oil monitoring in this context consists of sampling and analyzing the oil properties to assess whether the oil needs service and/or to assess the mechanical health of the equipment being monitored. There are two types of OMA certifications. OMA I is for the oil sampler, the individual on the shop floor with responsibility for sampling the oil and the overall care of the equipment. OMA II is for the oil analyzer, the individual in the laboratory responsible for properly running the appropriate tests, data interpretation, program management, and related activities. Certified Metalworking Fluids Specialist [12] (CMFS) verifies knowledge, experience and education in this specialized and growing field. The certification is intended for individuals with overall responsibility for metal removal or forming fluids management; for specialists with on-site responsibility for metal removal or forming systems, and for others involved with research, instruction, evaluation, analysis, selection, technical management, application and handling of metalworking fluids and related materials.
External links • Official website [1]
References [1] http:/ / www. stle. org [2] http:/ / www. stle. org/ about/ default. aspx? [3] http:/ / www. stle. org/ join/ benefits. aspx? [4] http:/ / www. stle. org/ research/ update/ default. aspx? [5] http:/ / www. stle. org/ research/ membership/ default. aspx? [6] http:/ / onlinedigitalpublishing. com/ publication/ ?m=5716& l=1 [7] http:/ / www. stle. org/ research/ transactions/ default. aspx? [8] http:/ / www. stle. org/ research/ tribology_letters. aspx? [9] http:/ / www. stle. org/ events/ annual/ details. aspx? [10] http:/ / www. stle. org/ certifications/ cls/ program. aspx [11] http:/ / www. stle. org/ certifications/ oma/ program. aspx [12] http:/ / www. stle. org/ certifications/ cmfs/ definitions. aspx
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South-pointing chariot
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South-pointing chariot
Exhibit in the Science Museum in London, England. This conjectural model chariot incorporates a differential gear.
South-pointing chariot Traditional Chinese
指南車
Simplified Chinese
指南车
Transcriptions Mandarin - Hanyu Pinyin zhi3 nan2 che1 Cantonese (Yue) - Jyutping
zi2 naam4 ce1
The south-pointing chariot (or carriage) was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the south, no matter how the chariot turned. Usually, the pointer took the form of a doll or figure with an outstretched arm. The chariot was supposedly used as a compass for navigation, and may also have had other purposes. There are legends of earlier south-pointing chariots, but the first reliably documented one was created by Ma Jun (c. 200–265 CE) of Cao Wei during the Three Kingdoms, about eight hundred years before the first navigational use of a magnetic compass. No ancient chariots still exist, but many extant ancient Chinese texts mention them, saying they were used intermittently until about 1300 CE. Some include information about their inner components and workings. There were probably several types of south-pointing chariot which worked differently. In most or all of them, the rotating road wheels mechanically operated a geared mechanism to keep the pointer aimed correctly. The mechanism had no magnets and did not automatically detect which direction was south. The pointer was aimed southward by hand at the start of a journey, then, whenever the chariot turned, the mechanism rotated the pointer relative to the body of the chariot to counteract the turn and keep the pointer aiming in a constant direction, to the south. Thus the mechanism did a kind of directional dead reckoning, which is inherently prone to cumulative errors and uncertainties. Some chariots' mechanisms may have had differential gears. If so, it was probably the first use of differentials anywhere in the world.
South-pointing chariot
Legend and history Legend Legend has it that Huangdi, credited as being the founder of the Chinese nation, lived in a magnificent palace in the Kunlun Mountains. There was also at this time another tribal leader, Chi You, who was skilled at making weapons and waging war. He attacked the tribe of Yandi, driving them into the lands of Huangdi. Huangdi was angered by this and went to war with Yandi, initially suffering several defeats. At some stage in the fighting Chi You conjured up a thick fog to confound Huangdi's men. They used the south-pointing chariot to find their way and they were ultimately victorious.
History It was recorded in the Sanguo Zhi (Records of the Three Kingdoms) that the 3rd century CE mechanical engineer Ma Jun from the Kingdom of Wei was the inventor of the south-pointing chariot (also called the south-pointing carriage). After being mocked by Permanent Counsellor Gaotang Long and the Cavalry General Qin Lang that he could not reproduce what they deemed a non-historical and nonsensical pursuit, Ma Jun retorted "Empty arguments with words cannot (in any way) compare with a test which will show practical results". After inventing the device and proving those who were doubtful wrong, he was praised by many, including his contemporary Fu Xuan, a noted poet of his age. After Ma Jun the south-pointing chariot was re-invented by Zu Chongzhi (429–500 CE), after the details of its instructions had been lost temporarily in China. During the Tang Dynasty (618–907 CE) and Song Dynasty (960–1279 CE) the south-pointing chariot was combined with another mechanical wheeled vehicle, the distance-measuring odometer. Some early historical records state that the south-pointing chariot was invented around the first millennium BCE, but such evidence is obscure.
Historical texts for south-pointing chariot Earliest sources The south-pointing chariot, a mechanical-geared wheeled vehicle used to discern the southern cardinal direction (without magnetics), was given a brief description by Ma's contemporary Fu Xuan.[1] The contemporary 3rd century CE source of the Weilüe, written by Yuan Huan also described the south-pointing chariot of Ma Jun.[2] The Jin Dynasty (265–420 CE) era text of the Shu Zheng Ji (Records of Military Expeditions), written by Guo Yuansheng, recorded that south-pointing chariots were often stored in the northern gatehouse of the Government Workshops (Shang Fang) of the capital city.[2] However, the later written Song Shu (Book of Song) (6th century CE) recorded the south-pointing chariot's design and use in further detail, as well as created background legend of the device's (supposed) use long before Ma's time, in the Western Zhou Dynasty (1050–771 BCE). The book also provided description of the south-pointing chariot's re-invention and use in times after Ma Jun and the Three Kingdoms. The 6th century CE text reads as follows. (In this translation, by Needham, the south-pointing chariot is referred to as the south-pointing carriage. Also, he uses "AD" to denote dates in the Common Era, and "BC" for dates Before the Common Era.):
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The south-pointing carriage was first constructed by the Duke of Zhou (beginning of the 1st millennium BC) as a means of conducting homewards certain envoys who had arrived from a great distance beyond the frontiers. The country to be traversed was a boundless plain, in which people lost their bearings as to east and west, so (the Duke) caused this vehicle to be made in order that the ambassadors should be able to distinguish north and south. The Gui Gu Zi book says that the people of the State of Zheng, when collecting jade, always carried with them a 'south-pointer', and by means of this were never in doubt (as to their position). During the Qin and Former Han dynasties, however, nothing more was heard of the vehicle. In the Later Han period, Zhang Heng re-invented it, but owing to the confusion and turmoil at the close of the [3] dynasty it was not preserved.
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In the State of Wei, (in the San Guo period) Gaotong Long and Qin Lang were both famous scholars; they disputed about the south-pointing carriage before the court, saying that there was no such thing, and that the story was nonsense. But during the Qing-long reign period (233–237 AD) the emperor Ming Di commissioned the scholar Ma Jun to construct one, and he duly succeeded. This again was lost during [4] the troubles attending the establishment of the Jin Dynasty.
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Later on, Shi Hu (emperor of the Jie Later Zhao Dynasty) had one made by Xie Fei, and again Linghu Sheng made one for Yao Xing (emperor of the Later Qin dynasty). The latter was obtained by emperor An Di of the Jin in the 13th year of the Yi-xi reign-period (417 AD), and it finally came into the hands of emperor Wu Di of the Liu Song Dynasty when he took over the administration of Chang'an. Its appearance and construction was like that of a drum-carriage (odometer). A wooden figure of a man was placed at the top, with its arm raised and pointing to the south, (and the mechanism was arranged in such a way that) although the carriage turned round and round, the pointer-arm still indicated [5] the south. In State processions, the south-pointing carriage led the way, accompanied by the imperial guard.
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These vehicles, constructed as they had been by barbarian (Qiang) workmen, did not function particularly well. Though called south-pointing carriages, they very often did not point true, and had to negotiate curves step by step, with the help of someone inside to adjust the machinery. The ingenious man from Fanyang, Zi Zu Chongzhi frequently said, therefore, that a new (and properly automatic) south-pointing carriage ought to be constructed. So towards the close of the Sheng-Ming reign period (477–479 AD) the emperor Shun Di, during the premiership of the Prince of Qi, commissioned (Zi Zu Chongzhi) to make one, and when it was completed it was tested by Wang Seng-qian, military governor of Tanyang, and Liu Hsiu, president of the Board of Censors. The workmanship was excellent, and although the carriage was twisted and turned in a hundred directions, the hand never failed to point to the south. Under the Jin, moreover, there had also been a south-pointing [5] ship.
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The last sentence of the passage is of great interest for navigation at sea, since the magnetic compass used for seafaring navigation was not used until the time of Shen Kuo (1031–1095). Although the Song Shu text describes earlier precedents of the south-pointing chariot before the time of Ma Jun, this is not entirely credible, as there are no pre-Han or Han Dynasty era texts that describe the device.[6] In fact, the first known source to describe stories of its legendary use during the Zhou period was the Gu Jin Zhu book of Cui Bao (c. 300 CE), written soon after the Three Kingdoms era.[2] Cui Bao also wrote that the intricate details of construction for the device were once written in the Shang Fang Gu Shi (Traditions of the Imperial Workshops), but the book was lost by his time.[2]
Japan The invention of the south-pointing chariot also made its way to Japan by the 7th century. The Nihon Shoki (The Chronicles of Japan) of 720 CE described the earlier Chinese Buddhist monks Zhi Yu and Zhi You constructing several south-pointing Chariots for Emperor Tenji of Japan in 658 CE.[7] This was followed up by several more chariot devices built in 666 CE as well.[7]
Children's instructive toy chariot in Chinese display at Expo 2005 in Japan
South-pointing chariot
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South-pointing chariot in Song Shi The south-pointing chariot was also combined with the earlier Han Dynasty era invention of the odometer (also Greco-Roman), a mechanical device used to measure distance traveled, and found in all modern automobiles. It was mentioned in the Song Dynasty (960–1279 CE) historical text of the Song Shi (compiled in 1345) that the engineers Yan Su (in 1027 CE) and Wu Deren (in 1107 CE) both created south-pointing chariots, which it details as follows. [8] (In Needham's translation, inches and feet (ft) are used as units of distance. 1 inch is 25.4 millimetres. 1 ft is 12 inches or 304.8 mm.)
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In the 5th year of the Tian-Sheng reign period of the emperor Renzong (1027 AD), Yan Su, a Divisional Director in the Ministry of Works, made a south-pointing carriage. He memorialised the throne, saying, [after the usual historical introduction]: 'Throughout the Five Dynasties and until the reigning dynasty there has been, so far as I know, no one who has been able to construct such a vehicle. But now I have invented [8] a design myself and have succeeded in completing it'.
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'The method involves using a carriage with a single pole (for two horses). Above the outside framework of the body of the carriage let there be a cover in two stories. Set a wooden image of a xian (immortal) at the top, stretching out its arm to indicate the south. Use 9 wheels, great and small, with a total of 120 teeth, i.e. 2 foot-wheels (i.e. road-wheels, on which the carriage runs) 6 ft. high and 18 ft. in circumference, attached to the foot wheels, 2 vertical subordinate wheels, 2.4 ft. in diameter and 7.2 ft. in circumference, each with 24 teeth, the teeth being at intervals [8] of 3 inches apart.
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'...Then below the crossbar at the end of the pole, two small vertical wheels 3 inches in diameter and pierced by an iron axle, to the left 1 small horizontal wheel, 1.2 feet in diameter, with 12 teeth, to the right 1 small horizontal wheel, 1.2 ft. in diameter, with 12 teeth, in the middle 1 large horizontal wheel, of diameter 4.8 ft. and circumference 14.4 ft., with 48 teeth, the teeth at intervals of 3 inches apart; in the middle a vertical shaft piercing the center (of the large horizontal wheel) 8 ft. high and 3 inches in diameter; at the top carrying the wooden figure of the [8] xian'.
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'When the carriage moves (southward) let the wooden figure point south. When it runs (and goes) eastwards, the (back end of the) pole is pushed to the right; the subordinate wheel attached to the right road-wheel will turn forward 12 teeth, drawing with it the right small horizontal wheel one revolution (and so) pushing the central large horizontal wheel to revolve a quarter turn to the left. When it has turned around 12 teeth, the carriage moves eastwards, and the wooden figure stands crosswise and points south. If (instead) it turns (and goes) westwards, the (back end of the) pole is pushed to the left; the subordinate wheel attached to the left road-wheel will turn forward with the road-wheel 12 teeth, drawing with it the left small horizontal wheel one revolution, and pushing the central large horizontal wheel to revolve a quarter turn to the right. When it has turned round 12 teeth, the carriage moves due west, but still the wooden figure stands crosswise and points south. If one [9] wishes to travel northwards, the turning round, whether by east or west, is done in the same way'.
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After this initial description of Yan Su's device, the text continues to describe the work of Wu Deren, who crafted a wheeled device that would combine the odometer and south-pointing chariot:
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It was ordered that the method should be handed down to the (appropriate) officials so that the machine might be made. In the first year of the Da-Guan reign period (1107 AD), the Chamberlain Wu Deren presented specifications of the south-pointing carriage and the carriage with the [10] li-recording drum (odometer). The two vehicles were made, and were first used that year at the great ceremony of the ancestral sacrifice.
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The body of the south-pointing carriage was 11.15 ft. (long), 9.5 ft. wide, and 10.9 ft. deep. The carriage wheels were 5.7 ft. in diameter, the carriage pole 10.5 ft. long, and the carriage body in two stories, upper and lower. In the middle was placed a partition. Above there stood a figure of a xian holding a rod, on the left and right were tortoises and cranes, one each on either side, and four figures of boys each holding a tassel. In the upper story there were at the four corners trip-mechanisms, and also 13 horizontal wheels, each 1.85 ft. in diameter, 5.55 ft. in [10] circumference, with 32 teeth at intervals of 1.8 inches apart. A central shaft, mounted on the partition, pierced downwards.
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In the lower story were 13 wheels. In the middle was the largest horizontal wheel, 3.8 ft. in diameter, 11.4 ft. in circumference, and having 100 teeth at intervals of 2.1 inches apart. (On vertical axles) reaching to the top (of the compartment) left and right, were two small horizontal wheels which could rise and fall, having an iron weight (attached to) each. Each of these was 1.1 ft. in diameter and 3.3 ft. in circumference, with 17 teeth, at intervals of 1.9 inches apart. Again, to left and right, were attached wheels, one on each side, in diameter 1.55 ft., in [10] circumference 4.65 ft., and having 24 teeth, at intervals of 2.1 inches.
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Left and right, too, were double gear-wheels (lit. tier-wheels), a pair on either side. Each of the lower component gears was 2.1 ft. in diameter and 6.3 ft. in circumference, with 32 teeth, at intervals of 2.1 inches apart. Each of the upper component gears was 1.2 ft. in diameter and 3.6 ft. in circumference, with 32 teeth, at intervals of 1.1 inches apart. On each of the road-wheels of the carriage, left and right, was a vertical wheel 2.2 ft. in diameter, 6.6 ft. in circumference, with 32 teeth at intervals of 2.25 inches apart. Both to left and right at the back end of the pole there were small wheels without teeth (pulleys), from which hung bamboo cords, and both were tied above the left and right (ends of the) [10] axle (of the carriage) respectively.
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If the carriage turns to the right, it causes the small pulley to the left of the back end of the pole to let down the left-hand (small horizontal) wheel. If it turns to the left, it causes the small pulley to the right of the back end of the pole to let down the right (small horizontal) wheel. However, the carriage moves the xian and the boys stand crosswise and point south. The carriage is harnessed with two red horses, bearing [10] frontlets of bronze.
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Chariots with differential gears Background and explanation There is a widely believed hypothesis that most, if not all, south-pointing chariots worked by means of differential gears. A differential is an assembly of gears, nowadays used in almost all automobiles except some electric and hybrid-electric ones, which has three shafts linking it to the external world. They are conveniently labelled A, B, and C. The gears cause the rotation speed of Shaft A to be proportional to the sum of the rotation speeds of Shafts B and C. There are no other limitations on the rotation speeds of the shafts. In an automobile, Shaft A is connected to the engine An illustration of a differential between the drive shaft (Shaft A, at bottom right) and driving wheels of an automobile. For animation, click (through the transmission), and Shafts B and C are [11] here . connected to two road wheels, one on each side of the vehicle. When the vehicle turns, the wheel going around the outside of the turning curve has to roll further and rotate faster than the wheel on the inside. The differential permits this to happen while both wheels are being driven by the engine. If the sum of the speeds of the wheels is constant, the speed of the engine does not change. In a south-pointing chariot, according to the hypothesis, Shaft B was connected to one road wheel and Shaft C was connected through a direction-reversing gear to the other road wheel. This made Shaft A rotate at a speed that was proportional to the difference between the rotation speeds of the two wheels. The pointing doll was connected (possibly through intermediate gears) to Shaft A. When the chariot moved in a straight line, the two wheels turned at equal speeds, and the doll did not rotate. When the chariot turned, the wheels rotated at different speeds (for the same reason as in an automobile), so the differential caused the doll to rotate, compensating for the turning of the chariot.
South-pointing chariot The hypothesis that there were south-pointing chariots with differential gears originated in the 20th Century. People who were familiar with modern, e.g. automotive, uses of differentials interpreted some of the ancient Chinese descriptions in ways that agreed with their own ideas. Essentially, they re-invented the south-pointing chariot, as it had previously been re-invented several times in antiquity. Working chariots that use differentials have been constructed in recent decades. Whether any such chariots existed previously is not known with certainty. If the hypothesis is true, then the Chinese probably knew about differentials centuries before Europeans. There has been speculation that the ancient Greeks knew about them in about 100 BCE, but this is now considered unlikely. The first true differential gear definitely known to have been used in the Western world was by Joseph Williamson in 1720.[12] He used a differential for correcting the equation of time for a clock that displayed both mean and solar time.[12] Even then, the differential was not fully appreciated in Europe until James White emphasized its importance and provided details for it in his Century of Inventions (1822).[12]
Geometrical properties If the south-pointing chariot were built perfectly accurately, using a differential gear, and if it travelled on an Earth that was perfectly smooth, it would have interesting properties. It would be a mechanical compass that transports a direction, given by the pointer, along the path it travels. Mathematically the device performs parallel transport along the path it travels. The chariot can be used to detect straight lines or geodesics. A path on a surface the chariot travels along is a geodesic if and only if the pointer does not rotate with respect to the base of the chariot. Because of the non-Euclidean geometry of the Earth's surface (due to it being curved around as a globe), the chariot would generally not continue to point due south as it moves. For example, if the chariot moves along a geodesic (as approximated by any great circle) the pointer should instead stay at a fixed angle to the path. Also, if two chariots travel by different routes between the same starting and finishing points, their pointers, which were aimed in the same direction at the start, usually do not point in the same direction at the finish. Likewise, if a chariot goes around a closed loop, starting and finishing at the same point on the Earth's surface, its pointer generally does not aim in the same direction at the finish as it did at the start. The difference is the holonomy of the path, and is proportional to the enclosed area. If the journeys are short compared with the radius of the Earth, these discrepancies are small and may have no practical importance. Nevertheless they show that this type of chariot, based on differential gears, would be an imperfect compass even if constructed exactly and used in ideal conditions.
Lack of precision, and implications Real machines are never built perfectly accurately. Simple geometry shows that if the chariot's mechanism is based on a differential gear and if, for example, the width of the track of the chariot (the separation between its wheels) is three metres, and if the wheels are intended to be identical but actually differ in diameter by one part in a thousand, then if the chariot travels one kilometre in a straight line, the "south-pointing" figure will rotate nearly twenty degrees. If it initially points exactly to the south, at the end of the one-kilometre trip it will point almost to the south-southeast or south-southwest, depending on which wheel is the larger. If the chariot travels nine kilometres, the figure will end up pointing almost due north. Obviously, this would make it useless as a south-pointing compass. To be a useful navigational tool, the figure would have to rotate no more than, say, a couple of degrees over a journey of a hundred kilometres, but this would require the chariot's wheels to be equal in diameter to within one part in a million. Even if the process of manufacturing the wheels were capable of this precision (which would not be possible with ancient Chinese methods), it is doubtful that the equality of the wheels could be maintained for long as they are subjected to the wear and tear of travelling across open country. Irregularity of the ground would add further errors to the device's functioning. Considerable scepticism is therefore warranted as to whether this type of south-pointing chariot, using a differential gear for the whole time, was used in practice to navigate over long distances. Conceivably, the south-pointing doll
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South-pointing chariot was fixed to the body of the chariot while it was travelling in straight lines, and coupled to the differential only when the chariot was turning. The charioteer could have operated a control to do this just before and after making each turn, or maybe shouted commands to someone inside the chariot who connected and disconnected the doll and the differential. This could have been done without stopping the chariot. If turns were brief and rare, this would have greatly reduced the pointing errors, since they would have accumulated only during the short periods when the doll and differential were connected. However, it raises the problem of how the chariot could have been kept travelling in straight lines with sufficient accuracy without using the pointing doll. If the real purposes of the chariot and the accounts of it were amusement and impressing visiting foreigners, rather than actual long-distance navigation, then its inaccuracy might not have been important.
Chariots without differential gears Although the hypothesis that the south-pointing chariot used differential gears has gained wide acceptance, it should be recognized that functional south-pointing chariots without differential gears are possible. The ancient descriptions are often unclear, but they suggest that the Chinese implemented several different designs, at least some of which did not include differentials.
Mechanical designs Some of the ancient descriptions suggest that some south-pointing chariots could move in only three ways: straight ahead, or turning left or right with a fixed radius of curvature. A third wheel might have been used to fix the turning radius. If the chariot was turning, the pointing doll was connected by gears to one or other of the two main road wheels (e.g. whichever was on the outside of the curve around which the chariot was moving) so the doll rotated at a fixed speed, relative to the rate of the chariot's movement, to compensate for the predetermined rate of turn. The doll turned in opposite directions depending on which road wheel was connected to it, so its rotation compensated for the chariot turning left or right. This design would have been simpler than using a differential gear. The chariots of Yan Su and Wu Deren appear to have used this type of mechanism. (See descriptions quoted from the Song Shi, above.) Apart from the presence of components in Wu Deren's vehicle to make it function as an odometer, there were only minor differences between them. In each chariot, the two main road wheels were attached to vertical gear wheels. A large horizontal gear wheel was linked (possibly via intermediate gearing) to the pointing doll, and was positioned so a diameter almost spanned the space between the uppermost points of the vertical gear wheels. When the chariot was moving straight ahead, there was no connection between these gears, but when the chariot turned, a small gear wheel was lowered into contact with the horizontal gear and one of the vertical gears, thus linking the doll to one of the road wheels. Two small gear wheels were available, one to connect the horizontal gear to each of the vertical ones. Of course, they were not used simultaneously. The small gear wheels were raised and lowered by an arrangement of weights, pulleys and cords which were attached to the pole to which the horses that pulled the chariot were harnessed. When the horses moved to one side or the other, in order to turn the chariot, the pole moved and the cords lowered the appropriate small gear wheel into its working position. When the horses returned to walking straight ahead, the small gear wheel was raised out of contact with the main horizontal and vertical gears. Thus the system functioned automatically. The mirror-symmetry of the vertical gears being linked by the small gears to the horizontal gear at diametrically opposite points caused the horizontal gear to rotate in opposite directions depending on which road wheel was linked to it, thus rotating the pointing doll in opposite directions when the chariot turned left and right. The description does not mention a third road wheel to fix the turning radius, but it is possible that such a wheel was present. No gears would have been attached to it, so perhaps the author of the description did not mention it because he did not realize that it was an important part of the mechanism. Putting such a wheel on the chariot and making it function properly would not have been difficult. It might have been attached to the pole to which the horses were harnessed. Stops would have been provided to limit the motions of the pole to left and right.
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South-pointing chariot If a third road wheel was included, this type of south-pointing chariot could have worked quite accurately as a compass when used for short journeys under good conditions, but if used for long journeys it would have been subject to cumulative errors, like chariots using the differential mechanism. If in fact there was no third road wheel, the chariot might have functioned as a compass if turns were always made so that one of the two wheels was stationary and only the other rotated, with the pointing doll connected to it by gears. The charioteer could have kept the stationary wheel from turning by controlling the horses appropriately. (A brake would have helped, but there is no mention of one in the description.) The radius of the curve around which the rotating wheel moved would have equalled the track-width of the chariot, and the gears turning the doll would have been chosen accordingly. This design would have worked as a compass for short journeys, but would have suffered from cumulative errors if used for long ones. Also, the chariot would have been slow and awkward to turn. This might not have mattered if turns were rarely executed. The Song Shi description of the gears in Yan Su's chariot, and the numbers of teeth on them, suggests that it worked this way, without a third road wheel. The gear ratios would have been correct if the pointing doll was attached directly to the large horizontal gear wheel, and the track-width of the chariot equalled the diameter of the road wheels. Wu Deren's chariot also appears to have been designed to work this way. The width of the chariot, and therefore presumably the track-width, was greater than the diameter of the wheels. The gear ratios were appropriate for these dimensions. The charioteer would have had to use great skill to ensure that the radius of each turn of the chariot was correct to make one of the wheels exactly stop rotating. Unless he did this correctly, the pointing doll would not have kept aiming to the south. He would have been able to adjust the direction in which it aimed by making turns that were more or less sharp. This would sometimes have given him opportunities to use the chariot dishonestly. If it was being demonstrated to spectators, for example, and was being driven around in front of them, making many turns, the charioteer, who would have known which way was south, would have been able to make the chariot appear to work extremely accurately as a compass for long periods. The spectators could have been shown the machinery, and would have seen that the charioteer could not manipulate the doll. They would presumably have been impressed by the apparent accuracy of the mechanism. It is possible that this type of chariot was sometimes constructed with the prime purpose of fraudulently impressing spectators. Possibly, people who built these chariots deceived their own employers with them, which could have gained them fame and fortune provided nobody tried using the chariots for real navigation. Maybe it is not surprising that the chariots were "lost" when conflicts flared up! Other mechanical designs for the south-pointing chariot are also possible, including ones that employ a device that is used today, the gyro compass. However, there is no indication that the ancient Chinese knew of these.
Non-mechanical possibilities Some south-pointing chariots may not have been purely mechanical devices. Someone riding inside the chariot may have used some non-mechanical method of determining the compass directions, and turned the doll on top of the chariot accordingly. There are several methods that could have been used, for example: • By using a magnetic compass. The Chinese were using this for navigation by the 11th Century CE, when south-pointing chariots were still being made and used. • By using astronomical observations of the sun and/or stars, e.g. the Pole Star. Chinese astronomical knowledge was extensive. • By using local knowledge. The person in the chariot may have known the area, or had a map or description of it. • By observing the polarization of light from the sky. At about the same time, the Vikings are thought to have used birefringent crystals of Iceland Spar to navigate across the Atlantic Ocean by this method. Iceland Spar is found in China as well as in Iceland and some other places. Insects such as bees can respond to sky polarization and use it to find their way home. Whether the Chinese used it is hypothetical, but it is certainly possible.
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• By observing light that had been refracted by the earth's atmosphere. This is one of the techniques that were used by Polynesian navigators to steer ships among Pacific islands. When the surface of the earth, ocean or ground, is colder than the air above it, a dense layer of air is formed near the surface which refracts light downward. The result is that light can go around the curvature of the earth, allowing things to be seen at much greater distances than simple geometry would predict. The images are very distorted, but they can be recognized by skilled navigators. Certain other Polynesian techniques can also be used on land, and may have been employed by the Chinese. Unlike mechanisms that rely on the rotation of road wheels, most of these methods can be used at sea. This may account for the mention (see "Earliest sources", above) that a marine version of the south-pointing chariot existed. These methods can work accurately over long distances, unlike the mechanical designs for the chariot.
Necessity of non-mechanical orientation Some non-mechanical method of finding the south must have been used when a mechanical south-pointing chariot was initialized, aiming its pointer to the south at the start of a journey. Any of the methods mentioned above in "Non-mechanical possibilities" could have been used. If any south-pointing chariot was really used for long-distance navigation, it must have relied (after initialization) on a non-mechanical direction-finding method. It might have been operated non-mechanically by someone riding in it, as outlined above. Alternatively, if it had a mechanical mechanism, it must have been frequently re-initialized non-mechanically to eliminate accumulated errors and uncertainties. The only chariots that might not have needed non-mechanical methods of finding the south would have been those that were never used for long-distance navigation. If some chariots were used only for amusement or fraud, they could have worked purely mechanically. Even initialization could have been avoided by simply declaring some arbitrary direction to be "south".
Timeline The south-pointing chariot has been invented and reinvented at many times throughout Chinese history. Below is a partial timeline of the major events; Year
Event
2634 BCE
According to Legend, the Yellow Emperor designs the south-pointing chariot. It is built for him by the craftsman Fang Bo.
1115 BCE
During the reign of the Duke of Chou, the duke gives five such devices (called Zhinan) to ambassadors of Yueshang to get them back home.
120 .. 139 CE
Zhang Heng might have reinvented the vehicle.
233 .. 237
Ma Jun constructs a working vehicle for Emperor Ming of Wei.
300
Cui Bao reports that the construction is described in a book (not preserved) named Shang Fang Ku Shih.
334 .. 349
Xie Fei makes one for Later Zhao Jie state Emperor Shi Jilong (石季龍, aka Shi Hu)
394 .. 416
Linghu Sheng makes one for Emperor Xiaowu of Jin China.
417
Linghu Sheng's vehicle is captured by Emperor An of Jin. It is reported that, at this time, there is no machinery, but only a man inside who turns the figure.
423 .. 452
Guo Shanming fails to make one for Emperor Taiwu of Northern Wei.
South-pointing chariot
423 .. 452
Ma Yue succeeds, but he is killed by Guo Shanming.
478
Zu Chongzhi makes a new improved (bronze gears) vehicle for Emperor Shun of Liu Song.
658
Buddhist monk Chiyu constructs vehicle for Japanese Emperor Tenji
666
Monk Chiyu constructs another vehicle for Japanese Emperor Tenji.
806 .. 821
Jin Gongli presents a south-pointing carriage to Emperor Xianzong of Tang.
1027
Engineer Yan Su (member of the "Board of Works") describes his construction (5 cogged, 4 non-cogged gear wheels, 18 soldier-drivers).
1107
Chamberlain Wu Deren presents a specification (24 cogged, 4 non-cogged gear wheels), which is successfully built twice.
1341
Chu Tê-Jun describes a jade figure as part of a miniature south-pointing carriage.
1720
Joseph Williamson uses a differential gear in a clock.
1834
Julius Klaproth writes to Alexander von Humboldt, noting the south-pointing chariot chih-nan-ch´ê, but assumes that a magnetic compass is hidden in the little doll.
1879
James Starley first uses a differential gear in a vehicle.
1909
Professor Giles points out that the directional property of the south-pointing chariot was effected by a mechanical system, and not by magnetism.
1909
Professor Bertram Hopkinson (Cambridge) remarks that some mechanism would have been required to ensure that the gears connected to the chariot wheels at right and left were engaged or disengaged when the chariot turned right or left. After some years of study, he declares that Yen Su's specification is insufficient to build a working model.
1910
The first mechanical navigation aide, "Jones Live Map", is invented. Like in the south-pointing chariot, the movement of the road wheels is geared down, but this time to show the relative position of the vehicle on a map.
1924
Rev. A. C. Moule (Cambridge) proposes a realization of Wu Tê-Jen's specification, where the chariot is allowed to drive only in straight lines. For each turn it is stopped, a gear connected and the turn done on the spot, the pointer now being corrected automatically.
1924
K. T. Dykes is the first to propose a differential gearing, arguing that the clutch mechanism proposed by Moule is "slow and complicated to drive".
1932
Dr. J.B.Kramer discovers references to the mechanical nature of the south-pointing chariot and declares that the Chinese therefore did not invent the magnetic compass, unaware that the magnetic compass had been described by Shen Kuo about 200 years before its (re)invention in Europe.
1932
George Lanchester (chief engineer at Lanchester Motor Company) proposes that the ancient machines (Ma Jun notably) embodied some kind of differential gear. He builds a working model to prove his concept.
1937
Wang Zhenduo proposes a realization of Yan Su's specification and builds a working model from it.
1948
Bao Sihe proposes another reconstruction.
1955
F.W. Cousins introduces the Lanchester reconstruction to a broader public, namely the Meccano fans.
1956
J. Coales points out that by hanging a carrot from the emperor's hand, the south-pointing chariot would become self-steering!
1977
Professor André Wegener Sleeswyk publishes a scientific essay on the historic chariots. He proves their feasibility exactly to the words in the ancient texts.
1978
Dr. Alan Partridge starts a contest in Meccano Magazine for the design with the fewest gears. It is shown subsequently that no gears are necessary at all!
1979
Dr. Noel C. Ta'Bois (LDS RCS Eng) publishes a concise treatise on the theoretical aspects. Working specimens are shown, which do not adhere to the "width equals wheel diameter" rule.
1979
Lu Zhiming produces three reconstructions based on differential gears.
1980
Mr. Don Frantz from New York re-discovers the south-pointing chariot, builds models along the Lanchester path and manages to place them in the Museum of the Province of Xian.
1982
Yan Zhiren builds another model, stressing that only differential gears provide the accuracy reported by the old writings.
482
South-pointing chariot
1991
Mr. M. Santander from Spain proposes to use the chariot to teach students the basic concepts of parallel transport and curvature. En passant a mathematical model is given for Mr. Nuttall's design.
Where they can be seen While none of the historic south-pointing chariots remain, full sized replicas can be found. The History Museum in Beijing, China holds a replica based on the mechanism of Yen Su (1027). The National Palace Museum in Taipei, Taiwan holds a replica based on the Lanchester mechanism of 1932. Referred to as the "southern pointing man", two replicas can also be seen (and physically experimented with) at the Ontario Science Centre in Toronto Canada.
Notes [1] Needham, Volume 4, Part 2, 40. [2] Needham, Volume 4, Part 2, 288 [3] Needham, Volume 4, Part 2, 286. [4] Needham, Volume 4, Part 2, 286–287. [5] Needham, Volume 4, Part 2, 287. [6] Needham, Volume 4, Part 2, 287–288. [7] Needham, Volume 4, Part 2, 289. [8] Needham, Volume 4, Part 2, 291. [9] Needham, Volume 4, Part 2, 291–292. [10] Needham, Volume 4, Part 2, 292. [11] http:/ / www. youtube. com/ watch?v=vBm-SzO3ggE [12] Needham, Volume 4, Part 2, 298.
References • The Chinese South-Seeking chariot: A simple mechanical device for visualizing curvature and parallel transport (http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf& id=AJPIAS000060000009000782000001&idtype=cvips&ident=freesearch&prog=search) M. Santander, American Journal of Physics – September 1992 – Volume 60, Issue 9, pp. 782–787 • Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 2. Taipei: Caves Books, Ltd. • Kit Williams, Engines of Ingenuity, Gingko Press (February 2002), ISBN 978-1584231066
External links • South Pointing Things (http://www.odts.de/southptr/) – Useful site with lot of info, images and plans (http:// www.odts.de/southptr/reposito.htm) for building chariots • RLT (http://www.ancientengineering.com/14201) – Fully functional model kit • A video of a 3D model of an open differential (http://www.youtube.com/watch?v=vBm-SzO3ggE)
483
Split pin
484
Split pin A split pin, also known in U.S. usage as a cotter pin or cotter key,[1] is a metal fastener with two tines that are bent during installation, similar to a staple or rivet. Typically made of thick wire with a half-circular cross section, split pins come in multiple sizes and types. The British definition of "cotter pin" is equivalent to U.S. term "cotter", which can be a cause for confusion when companies of both countries work together. There are signs that manufacturers and stockists are increasingly listing both names together to avoid confusion; this led to the term split cotter sometimes being used for a split pin.
A split pin (UK usage) / cotter pin (USA usage) holding a rod in place with a washer.
Construction A new split pin (see figure A) has its flat inner surfaces touching for most of its length so that it appears to be a split cylinder (figure D). Once inserted, the two ends of the pin are bent apart, locking it in place (figure B). When they are removed they are supposed to be discarded and replaced, because of fatigue from bending.[2] Split pins are typically made of soft metal, making them easy to install and remove, but also making it inadvisable to use them to resist strong shear forces. Common materials include mild steel, brass, bronze, stainless steel, and aluminium.[3]
Split pins: A: New B: Installed C: Spring type D: Cross-section of traditional design
Types
As shown above, there are different types of ends available on split pins. The most common is the extended prong with a square cut, but extended prongs are available with all of the other types of ends. The extended prong type is popular because it makes it easier to separate the tines. To ease insertion into a hole the longer tine may be slightly curved to overlap the tip of the shorter tine or it is beveled. The length, L, of the split pin is defined as the distance from the end of the shortest tine to the point of the eyelet that contacts the hole.[3]
Split pin
485
Hammer lock split pins are properly installed by striking the head with a hammer to secure the pin. This forces the shorter tine forward, spreading the pin.[4] • Standard • Humped • Clinch
Sizes The diameter of split pins are standardized. American split pins start at 1⁄32 in and end at 3⁄4 in.[4]
Metric split pin sizes[5] Nominal diameter [mm]
Hole size [mm]
For bolt size [mm]
1.5
1.9
6
2
2.4
8
2.5
2.8
10
3
3.4
12, 14
4
4.5
20
5
5.6
24, 28
6
6.3
30, 36, 42
8
8.5
48
9 ^^
American split pin sizes[4] [5] Nominal diameter [in]
Hole size [in]
For bolt size [in]
1
3
3
1
1
5
1
5
3
5
3
7
3
7
1
1
9
1
9
5
5
5
11
3
3
13
1, 1.125
7
15
1.25, 1.375
1
17
1.5
5
5
1.75
3
3
⁄32 ⁄64 ⁄16 ⁄64 ⁄32 ⁄64 ⁄8 ⁄64 ⁄32 ⁄16 ⁄32 ⁄4 ⁄16 ⁄8
⁄64 ⁄16 ⁄64 ⁄32 ⁄64
⁄4 ⁄16 ⁄8
⁄8 ⁄64 ⁄32 ⁄64 ⁄64 ⁄64 ⁄64
⁄16 ⁄8
⁄2 ⁄8 ⁄4
Split pin
486
7
7
1
1
5
5
3
3
⁄16 ⁄2 ⁄8 ⁄4
⁄16 ⁄2 ⁄8 ⁄4
Applications Split pins are frequently used to secure other fasteners, e.g. clevis pins, as well as being used in combination with hardboard discs as a traditional joining technique for teddy bears.[6] Split pins may be used in some applications as low-tech shear pins. A common application of this is when used to secure a castellated nut. One problem with this type of use is that the castles on the nut must line up with the hole in the mating part so that the split pin can be installed. When the nut is torqued properly, but the holes still do not line up, it is preferable to over-tighten the nut than under-tighten it.[7]
A car hub showing a castellated nut cover and split pin (near center).
References [1] [2] [3] [4] [5] [6] [7]
U.S. Patent 4298299 (http:/ / www. google. com/ patents?vid=4298299) Welsch 2005, p. 141. Soled 1957, p. 312. Cotter pins (http:/ / www. sizes. com/ tools/ cotter_pins. htm), , retrieved 2009-08-17. Jensen 2001, p. 234. Baby Pip Teddy Bear (http:/ / www. craftbits. com/ viewProject. do?projectID=1524) at CraftBits.com Reithmaier 1999, p. 151.
===Bibliography • Jensen, Cecil Howard (2001), Interpreting Engineering Drawings (http://books.google.com/ ?id=n5AZcpo5IFcC) (6th ed.), SteinerBooks, ISBN 9780766828971. • Reithmaier, Lawrence W. (1999), Standard aircraft handbook for mechanics and technicians (http://books. google.com/?id=a3bloqOeFhkC) (6th ed.), McGraw-Hill Professional, ISBN 9780071348362. • Soled, Julius (1957), Fasteners handbooks (http://books.google.com/?id=8OdSAAAAMAAJ), Reinhold Publication Corporation. • Welsch, Roger (2005), From Tinkering to Torquing: A Beginner's Guide to Tractors and Tools (http://books. google.com/?id=J_xMHJSIvL0C), MBI Publishing Company, ISBN 9780760320822.
Standard conditions for temperature and pressure
Standard conditions for temperature and pressure Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards. Other organizations have established a variety of alternative definitions for their standard reference conditions. In chemistry, IUPAC established standard temperature and pressure (informally abbreviated as STP) as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm),[1] An unofficial, but commonly used standard is standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 101.325 kPa (14.696 psi, 1 atm). International Standard Metric Conditions for natural gas and similar fluids[2] is 288.15 K and 101.325 kPa. In industry and commerce, standard conditions for temperature and pressure are often necessary to define the standard reference conditions to express the volumes of gases and liquids and related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure). However many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them, often leading to confusion and errors. Good practice is to incorporate the reference conditions wherever ambiguity is possible, e.g. V(273.15 K, 101.325 kPa)m3.
Definitions Past use In the last five to six decades, professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being 0 °C (273.15 K; 32.00 °F) and 101.325 kPa (1 atm or 760 Torr). During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was 60 °F (15.56 °C; 288.71 K) and 14.696 psi (1 atm) because it was almost universally used by the oil and gas industries worldwide. The above definitions are no longer the most commonly used in either system of units.
Current use Many different definitions of standard reference conditions are currently being used by organizations all over the world. The table below lists a few of them, but there are more. Some of these organizations used other standards in the past. For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to their old standard of 0 °C and 101.325 kPa (1 atm).[3] Natural gas companies in Europe and South America have adopted 15 °C (59 °F) and 101.325 kPa (14.696 psi) as their standard gas volume reference conditions.[4] [5] [6] Also, the International Organization for Standardization (ISO), the United States Environmental Protection Agency (EPA) and National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations. In Russia, State Standard GOST 2939-63 sets the following standard conditions: 25 °C (298.15 K), 760 mmHg (101325 N/m2) and zero humidity.[7]
487
Standard conditions for temperature and pressure
488
Standard reference conditions in current use Temperature
Absolute pressure
Relative humidity
Publishing or establishing entity
°C
kPa
% RH
0
100.000
0
101.325
15
101.325
20
101.325
25
101.325
EPA
25
100.000
SATP
20
100.000
15
100.000
20
101.3
50
°F
psi
% RH
60
14.696
60
14.73
59
14.503
78
U.S. Army Standard Metro
59
14.696
60
ISO 2314, ISO 3977-2
°F
in Hg
% RH
70
29.92
0
59 (15c)
29.92 (1013.25 hPa)
[1]
IUPAC (STP) [8]
NIST, [10] [11]
[9]
[10]
0
[1]
ISO 10780,
ICAO's ISA,
formerly IUPAC [11]
ISO 13443, [14]
EPA,
NIST
[12]
EEA,
[13] EGIA
[15]
[16] [17]
[18]
0
CAGI SPE
[19] [20]
ISO 5011
[19]
[21]
SPE,
U.S. OSHA, [13]
EGIA,
[23]
OPEC,
SCAQMD
[22]
[24]
U.S. EIA
[25] [26] [27]
[28] [29]
AMCA,
air density = 0.075 lbm/ft³. This AMCA standard applies only to air. [30]
FAA, FAA's Pilot Handbook of Aeronautical Knowledge, Chapter 3
Notes: • EGIA: Electricity and Gas Inspection Act (of Canada) • SATP: Standard Ambient Temperature and Pressure
International Standard Atmosphere In aeronautics and fluid dynamics the "International Standard Atmosphere" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. The International Standard Atmosphere is representative of atmospheric conditions at mid latitudes. In the USA this information is specified the U.S. Standard Atmosphere which is identical to the "International Standard Atmosphere" at all altitudes up to 65,000 feet above sea level.
Standard laboratory conditions Due to the fact that many definitions of standard temperature and pressure differ in temperature significantly from standard laboratory temperatures (e.g., 0 °C vs. ~25 °C), reference is often made to "standard laboratory conditions" (a term deliberately chosen to be different from the term "standard conditions for temperature and pressure", despite its semantic near identity when interpreted literally). However, what is a "standard" laboratory temperature and pressure is inevitably culture-bound, given that different parts of the world differ in climate, altitude and the degree of use of heat/cooling in the workplace. For example, schools in New South Wales, Australia use 25 °C at 100 kPa
Standard conditions for temperature and pressure for standard laboratory conditions.[31] ASTM International has published Standard ASTM E41- Terminology Relating to Conditioning and hundreds of special conditions for particular materials and test methods. Other standards organizations also have specialized standard test conditions.
Molar volume of a gas It is equally as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas[32] as it is when expressing a gas volume or volumetric flow rate. Stating the molar volume of a gas without indicating the reference conditions of temperature and pressure has no meaning and it can cause confusion. The molar gas volumes can be calculated with an accuracy that is usually sufficient by using the universal gas law for ideal gases. The usual expression is:
…which can be rearranged thus:
where (in SI metric units): P = the absolute pressure of the gas, in Pa (pascal) n = amount of substance, in mol V = the volume of the gas, in m3 T = the absolute temperature of the gas, in K R = the universal gas law constant of 8.3145 m3·Pa/(mol·K)
The molar volume of any ideal gas may be calculated at various standard reference conditions as shown below: • • • • • •
V/n = 8.3145 × 273.15 / 101.325 = 22.414 m3/kmol at 0 °C and 101.325 kPa V/n = 8.3145 × 273.15 / 100.000 = 22.711 m3/kmol at 0 °C and 100 kPa V/n = 8.3145 × 298.15 / 101.325 = 24.466 m3/kmol at 25 °C and 101.325 kPa V/n = 8.3145 × 298.15 / 100.000 = 24.790 m3/kmol at 25 °C and 100 kPa V/n = 10.7316 × 519.67 / 14.696 = 379.48 ft3/lbmol at 60 °F and 14.696 psi (or about 0.8366 ft3/gram mole) V/n = 10.7316 × 519.67 / 14.730 = 378.61 ft3/lbmol at 60 °F and 14.73 psi
The technical literature can be confusing because many authors fail to explain whether they are using the universal gas law constant R, which applies to any ideal gas, or whether they are using the gas law constant Rs, which only applies to a specific individual gas. The relationship between the two constants is Rs = R / M, where M is the molecular weight of the gas. The US Standard Atmosphere uses 8.31432 m3·Pa/(mol·K) as the value of R for all calculations. (See Gas constant)
489
Standard conditions for temperature and pressure
References [1] A. D. McNaught, A. Wilkinson (1997). Compendium of Chemical Terminology, The Gold Book (http:/ / www. iupac. org/ goldbook/ S05910. pdf) (2nd ed.). Blackwell Science. ISBN 0865426848. . "Standard conditions for gases: Temperature, 273.15 K [...] and pressure of 105 pascals. The previous standard absolute pressure of 1 atm (equivalent to 1.01325 × 105 Pa) was changed to 100 kPa in 1982. IUPAC recommends that the former pressure should be discontinued." [2] ISO 13443 [3] A. D. McNaught, A. Wilkinson (1997). Compendium of Chemical Terminology, The Gold Book (http:/ / www. iupac. org/ goldbook/ S05921. pdf) (2nd ed.). Blackwell Science. ISBN 0865426848. . "Standard pressure: Chosen value of pressure denoted by po or p°. In 1982 IUPAC recommended the value 105 Pa, but prior to 1982 the value 101 325 Pa (= 1 atm) was usually used." [4] Gassco. "Concepts – Standard cubic meter (scm)" (http:/ / www. gassco. no/ sw3138. asp). . Retrieved 2008-07-25. "Scm: The usual abbreviation for standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1.01325 bar and a temperature of 15°C. This unit provides a measure for gas volume." [5] Nord Stream (October 2007). "Status of the Nord Stream pipeline route in the Baltic Sea" (http:/ / www. nord-stream. com/ uploads/ media/ Nord_Stream_Route_Status_ENGLISH. pdf). . Retrieved 2008-07-25. "bcm: Billion Cubic Meter (standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1 atm and a temperature of 15 °C.)" [6] Metrogas (June 2004). "Natural gas purchase and sale agreement" (http:/ / www. secinfo. com/ dsD7y. 1a. 7. htm). . Retrieved 2008-07-25. "Natural gas at standard condition shall mean the quantity of natural gas, which at a temperature of fifteen (15) Celsius degrees and a pressure of 101.325 kilopascals occupies the volume of one (1) cubic meter." [7] http:/ / www. docload. ru/ standart/ Pages_gost/ 27361. htm [8] NIST (1989). "NIST Standard Reference Database 7 – NIST Electron and Positron Stopping Powers of Materials Database" (http:/ / www. nist. gov/ srd/ WebGuide/ nist7/ 07_2. htm). . Retrieved 08-07-25. "If you want the program to treat the material as an ideal gas, the density will be assumed given by M/V, where M is the gram molecular weight of the gas and V is the mol volume of 22414 cm3 at standard conditions (0 deg C and 1 atm)." [9] ISO (1994). "ISO 10780:1994 : Stationary source emissions - Measurement of velocity and volume flowrate of gas streams in ducts" (http:/ / www. iso. org/ iso/ iso_catalogue/ catalogue_tc/ catalogue_detail. htm?csnumber=18855). [10] Robert C. Weast (Editor) (1975). Handbook of Physics and Chemistry (56th ed.). CRC Press. pp. F201–F206. ISBN 0-87819-455-X. [11] "Natural gas – Standard reference conditions", ISO 13443, International Organization for Standardization, Geneva, Switzerland ISO Standards Catalogue (http:/ / www. iso. org/ iso/ iso_catalogue. htm) [12] "Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels", Emission Inventory Guidebook B521, Activities 050201 050303, September 1999, European Environmental Agency, Copenhagen, Denmark Emission Inventory Guidebook (http:/ / reports. eea. eu. int/ EMEPCORINAIR3/ en/ B521vs3. 1. pdf) [13] "Electricity and Gas Inspection Act", SOR/86-131 (defines a set of standard conditions for Imperial units and a different set for metric units) Canadian Laws (http:/ / laws. justice. gc. ca/ en/ E-4/ SOR-86-131/ 95708. html) [14] "Standards of Performance for New Sources", 40 CFR--Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990 New Source Performance Standards (http:/ / a257. g. akamaitech. net/ 7/ 257/ 2422/ 08aug20051500/ edocket. access. gpo. gov/ cfr_2005/ julqtr/ pdf/ 40cfr60. 2. pdf) [15] "Design and Uncertainty for a PVTt Gas Flow Standard", Journal of Research of the National Institute of Standards and Technology, Vol.108, Number 1, 2003 NIST Journal (http:/ / www. cstl. nist. gov/ div836/ 836. 01/ PDFs/ 2003/ j80wri. pdf) [16] "National Primary and Secondary Ambient Air Quality Standards", 40 CFR--Protection of the Environment, Chapter I, Part 50, Section 50.3, 1998 National Ambient Air Standards (http:/ / a257. g. akamaitech. net/ 7/ 257/ 2422/ 08aug20051500/ edocket. access. gpo. gov/ cfr_2005/ julqtr/ pdf/ 40cfr50. 3. pdf) [17] "Table of Chemical Thermodynamic Properties", National Bureau of Standards (NBS), Journal of Physics and Chemical Reference Data, 1982, Vol. 11, Supplement 2. [18] "Glossary", 2002, Compressed Air and Gas Institute, Cleveland, OH, USA Glossary (http:/ / www. cagi. org/ toolbox/ glossary. htm) [19] The SI Metric System of Units and SPE Metric Standard (http:/ / www. spe. org/ spe-site/ spe/ spe/ papers/ authors/ Metric_Standard. pdf) (Notes for Table 2.3, on PDF page 25 of 42 PDF pages, define two different sets of reference conditions, one for the standard cubic foot and one for the standard cubic meter) [20] "Air Intake Filters", ISO 5011:2002, International Organization for Standardization, Geneva, Switzerland ISO (http:/ / www. iso. org/ iso/ en/ prods-services/ ISOstore/ store. html) [21] "Storage and Handling of Liquefied Petroleum Gases" and "Storage and Handling of Anhydrous Ammonia", 29 CFR--Labor, Chapter XVII--Occupational Safety and Health Administration, Part 1910, Sect. 1910.110 and 1910.111, 1993 Storage/Handling of LPG (http:/ / ecfr. gpoaccess. gov/ cgi/ t/ text/ text-idx?c=ecfr& sid=f169acd0f57a17565c9984fa0f57d285& rgn=div8& view=text& node=29:5. 1. 1. 1. 8. 8. 33. 10& idno=29) [22] "Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, USA SCAQMD Rule 102 (http:/ / www. aqmd. gov/ rules/ reg/ reg01/ r102. pdf) [23] "Annual Statistical Bulletin", 2004, Editor-in-chief: Dr. Omar Ibrahim, Organization of the Petroleum Exporting Countries, Vienna, Austria OPEC Statistical Bulletin (http:/ / www. opec. org/ library/ Annual Statistical Bulletin/ pdf/ ASB2004. pdf)
490
Standard conditions for temperature and pressure [24] "Natural Gas Annual 2004", DOE/EIA-0131(04), December 2005, U.S. Department of Energy, Energy Information Administration, Washington, D.C., USA Natural Gas Annual 2004 (http:/ / tonto. eia. doe. gov/ FTPROOT/ natgas/ 013104. pdf) [25] Sierra Bullets L.P.. "Chapter 3 – Effects of Altitude and Atmospheric Conditions" (http:/ / www. exteriorballistics. com/ ebexplained/ 5th/ 31. cfm). Rifle and Handgun Reloading Manual, 5th Edition. ."Effects of Altitude and Atmospheric Conditions", Exterior Ballistics Section, Sierra's "Rifle and Handgun Reloading Manual, 5th Edition", Sedalia, MO, USA [26] The pressure is specified as 750 mmHg. However, the mmHg is temperature dependant, as mercury expands as temperature goes up. Here the values for the 0-20°C range are given. [27] "Gas turbines – Procurement – Part 2: Standard reference conditions and ratings", ISO 3977-2:1997 and "Gas turbines - Acceptance tests", ISO 2314:1989, Edition 2, International Organization for Standardization, Geneva, Switzerland ISO (http:/ / www. iso. org/ iso/ en/ prods-services/ ISOstore/ store. html) [28] ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied here: http:/ / www. greenheck. com/ pdf/ centrifugal/ Plug. pdf when accessed on October 17, 2007 [29] The standard is given as 29.92 inHg at an unspecified temperature. This most likely corresponds to a standard pressure of 101.325 kPa, converted into ~29.921 inHg at 32 °F) [30] (http:/ / www. faa. gov/ library/ manuals/ aviation/ pilot_handbook/ media/ PHAK - Chapter 03. pdf) [31] Peter Gribbon (2001). Excel HSC Chemistry Pocket Book Years 11-12. Pascal Press. ISBN 1-74020-303-8. [32] Fundamental Physical Properties: Molar Volumes (http:/ / physics. nist. gov/ cgi-bin/ cuu/ Results?search_for=volume+ molar) (CODATA values for ideal gases as listed on a NIST website page)
External links • • • •
"Standard conditions for gases" (http://www.iupac.org/goldbook/S05910.pdf) from the IUPAC Gold Book. "Standard pressure" (http://www.iupac.org/goldbook/S05921.pdf) from the IUPAC Gold Book. "STP" (http://www.iupac.org/goldbook/S06036.pdf) from the IUPAC Gold Book. "Standard state" (http://www.iupac.org/goldbook/S05925.pdf) from the IUPAC Gold Book.
[[sh:
Steam rupture A steam rupture occurs within a pressurized system of super critical water when the pressure exceeds the design plus safety margin specification. A steam rupture can occur in any elevated temperature pressurized system, including, but not limited to: Automobile cooling systems, stationary power plants, mobile power plants, steam driven tools (such as some trip hammers), and even the delivery systems for application processes such as cleaning and fabric fullering.
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Stick-slip phenomenon
Stick-slip phenomenon The stick-slip phenomenon, also known as the slip-stick phenomenon or simply stick-slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other.
Cause Stick-slip is caused by the surfaces alternating between sticking to each other and sliding over each other, with a corresponding change in the force of friction. Typically, the static friction coefficient between two surfaces is larger than the kinetic friction coefficient. If an applied force is large enough to overcome the static friction, then the reduction of the friction to the kinetic friction can cause a sudden jump in the velocity of the movement. The attached picture shows symbolically an example of stick-slip.
V is a drive system, R is the elasticity in the system, and M is the load that is lying on the floor and is being pushed horizontally. When the drive system is started, the Spring R is loaded and its pushing force against load M increases until the static friction coefficient between load M and the floor is not able to hold the load anymore. The load starts sliding and the friction coefficient decreases from its static value to its dynamic value. At this moment the spring can give more power and accelerates M. During M’s movement, the force of the spring decreases, until it is insufficient to overcome the dynamic friction. From this point, M decelerates to a stop. The drive system however continues, and the spring is loaded again etc.
Examples Examples of stick-slip can be heard from hydraulic cylinders, honing machines etc. Special dopes can be added to the hydraulic fluid or the cooling fluid to overcome or minimize the stick-slip effect. Stick-slip is also experienced in lathes, mill centres, and other machinery where something slides on a slideway. Slideway oil typically lists "prevention of stick-slip" as one of their features. Other examples of the stick-slip phenomenon include the music that comes from bowed instruments, the noise of car brakes and tires, and the noise of a stopping train. Another example of the stick-slip phenomenon occurs when you play musical notes with a glass harp by rubbing a wet finger along the rim of a crystal wine glass. One animal that produces sound using stick-slip friction is the spiny lobster which rubs its antennae over smooth surfaces on its head. [1] . Another, more common example which produces sound using stick-slip friction is the grasshopper. Stick-slip can also be observed on the atomic scale using a friction force microscope[2] . In such case, the phenomenon can be interpreted using the Tomlinson model. The behaviour of seismically-active faults is also explained using a stick-slip model, with earthquakes being generated during the periods of rapid slip.[3] Stick-slip is responsible for the squeaking sound of chalk on a blackboard. The same phenomenon can also be used to create dashed lines using chalk, by holding the chalk at an angle.
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Stick-slip phenomenon
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One can move objects using the stick-slip effect. For example, one can take a piece of paper, put the paper on a solid surface, and place a heavy object on it. Put a mark on the paper to determine the initial position of the object. Now slowly move the paper to the left and suddenly slide it to the right. If you do this a few times then you should observe that the object will be to the left side of its initial position.
References [1] S. N. Patek (2001). "Spiny lobsters stick and slip to make sound". Nature 411 (6834): 153–154. doi:10.1038/35075656. PMID 11346780. [2] Atomic-scale friction of a tungsten tip on a graphite surface C.M. Mate, G.M. McClelland, R. Erlandsson, and S. Chiang Phys. Rev. Lett. 59, 1942 (1987) [3] Scholz, C.H. (2002). The mechanics of earthquakes and faulting (http:/ / books. google. co. uk/ books?id=JL1VM5wMbrQC& pg=PA82& dq="stick-slip"+ behaviour+ earthquake& hl=en& ei=iIXeTtuVCIPLtAbOv9jqCA& sa=X& oi=book_result& ct=result& resnum=3& ved=0CDYQ6AEwAjgK#v=onepage& q& f=false) (2 ed.). Cambridge University Press. pp. 81–84. ISBN 9780521655408. . Retrieved 6 December 2011.
External links • Simulation of stick-slip behaviour in a friction force microscope (movie) (http://www.youtube.com/ watch?v=idlHxu7TTWU)
Strain hardening exponent The strain hardening exponent (also called strain hardening index), noted as n, is a materials constant which is used in calculations for stress-strain behaviour in work hardening. In the formula σ = K ε n, σ represents the applied stress on the material, ε is the strain and K is the strength coefficient. The value of the strain hardening exponent lies between 0 and 1. A value of 0 means that a material is a perfectly plastic solid, while a value of 1 represents a 100% elastic solid. Most metals have an n value between 0.10 and 0.50.
Tabulation Tabulation of n and K Values for Several Alloys [1] Material
n
K (MPa)
Low-carbon steel (annealed)
0.21 600
4340 steel alloy (annealed)
0.12 2650
304 stainless steel (annealed)
0.44 1400
Copper (annealed)
0.44 530
Naval brass (annealed)
0.21 585
2024 aluminum alloy (heat treated—T3) 0.17 780 AZ-31B magnesium alloy (annealed)
0.16 450
Strain hardening exponent
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References [1] Callister, Jr., William D (2005), Fundamentals of Materials Science and Engineering (2nd ed.), United States of America: John Wiley & Sons, p. 199, ISBN 9780471470144
External links • More complete picture about the strain hardening exponent in the stress-strain curve on www.key-to-steel.com (http://steel.keytometals.com/Articles/Art42.htm) • A discourse on textbook prices by Kevin P. Siu (http://engsci.unavoidable.ca/bme210/)
Streamlines, streaklines, and pathlines Fluid flow is characterized by a velocity vector field in three-dimensional space, within the framework of continuum mechanics. Streamlines, streaklines and pathlines are field lines resulting from this vector field description of the flow. They differ only when the flow changes with time: that is, when the flow is not steady.[1] [2]
• Streamlines are a family of curves that are instantaneously tangent to the velocity vector of the flow. These show the direction a fluid element will travel in at any point in time. • Streaklines are the locus of points of all the fluid particles that have passed continuously through a particular spatial point in the past. Dye steadily injected into the fluid at a fixed point extends along a streakline.
The red particle moves in a flowing fluid; its pathline is traced in red; the tip of the trail of blue ink released from the origin follows the particle, but unlike the static pathline (which records the earlier motion of the dot), ink released after the red dot departs continues to move up with the flow. (This is a streakline.) The dashed lines represent contours of the velocity field (streamlines), showing the motion of the whole field at the same time. (See high resolution version.)
• Pathlines are the trajectories that individual fluid particles follow. These can be thought of as a "recording" of the path a fluid element in the flow takes over a certain period. The direction the path takes will be determined by the streamlines of the fluid at each moment in time.
• Timelines are the lines formed by a set of fluid particles that were marked at a previous instant in time, creating a line or a curve that is displaced in time as the particles move.
Streamlines, streaklines, and pathlines
By definition, different streamlines at the same instant in a flow do not intersect, because a fluid particle cannot have two different velocities at the same point. Similarly, streaklines cannot intersect themselves or other streaklines, because two particles cannot be present at the same location at the same instant of time; unless the origin point of one of the streaklines also belongs to the streakline of the other origin point. However, pathlines are allowed to intersect themselves or other pathlines (except the starting and end points of the different pathlines, which need to be distinct).
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Solid blue lines and broken grey lines represent the streamlines. The red arrows show the direction and magnitude of the flow velocity. These arrows are tangential to the streamline. The group of streamlines enclose the green curves ( and ) to form a stream surface.
Streamlines and timelines provide a snapshot of some flowfield characteristics, whereas streaklines and pathlines depend on the full time-history of the flow. However, often sequences of timelines (and streaklines) at different instants—being presented either in a single image or with a video stream—may be used to provide insight in the flow and its history. If a line, curve or closed curve is used as start point for a continuous set of streamlines, the result is a stream surface. In the case of a closed curve in a steady flow, fluid that is inside a stream surface must remain forever within that same stream surface, because the streamlines are tangent to the flow velocity. A scalar function whose contour lines define the streamlines is known as the stream function. Dye line may refer either to a streakline: dye released gradually from a fixed location during time; or it may refer to a timeline: a line of dye applied instantaneously at a certain moment in time, and observed at a later instant.
Mathematical description Streamlines Streamlines are defined as[3]
with "×" denoting the vector cross product and
is the parametric representation of just one streamline at one
moment in time. If the components of the velocity are written
and those of the streamline as
[3]
we deduce:
which shows that the curves are parallel to the velocity vector. Here is a variable which parametrizes the curve Streamlines are calculated instantaneously, meaning that at one instance of time they are calculated throughout the fluid from the instantaneous flow velocity field.
Streamlines, streaklines, and pathlines
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Pathlines Pathlines are defined by
The suffix
indicates that we are following the motion of a fluid particle. Note that at point
parallel to the flow velocity vector that time
the curve is
, where the velocity vector is evaluated at the position of the particle
at
.
Streaklines Streaklines can be expressed as,
where,
is the velocity of a particle
streakline
and
at location
, where
and time
. The parameter
, parametrizes the
is a time of interest.
Steady flows In steady flow (when the velocity vector-field does not change with time), the streamlines, pathlines, and streaklines coincide. This is because when a particle on a streamline reaches a point, , further on that streamline the equations governing the flow will send it in a certain direction . As the equations that govern the flow remain the same when another particle reaches particle reaches position
it will also go in the direction
. If the flow is not steady then when the next
the flow would have changed and the particle will go in a different direction.
This is useful, because it is usually very difficult to look at streamlines in an experiment. However, if the flow is steady, one can use streaklines to describe the streamline pattern.
Frame dependence Streamlines are frame-dependent. That is, the streamlines observed in one inertial reference frame are different from those observed in another inertial reference frame. For instance, the streamlines in the air around an aircraft wing are defined differently for the passengers in the aircraft than for an observer on the ground. When possible, fluid dynamicists try to find a reference frame in which the flow is steady, so that they can use experimental methods of creating streaklines to identify the streamlines. In the aircraft example, the observer on the ground will observe unsteady flow, and the observers in the aircraft will observe steady flow, with constant streamlines.
Applications Knowledge of the streamlines can be useful in fluid dynamics. For example, Bernoulli's principle, which describes the relationship between pressure and velocity in an inviscid fluid, is derived for locations along a streamline. The curvature of a streamline is related to the pressure gradient acting perpendicular to the streamline. The center of curvature of the streamline lies in the direction of decreasing radial pressure. The magnitude of the radial pressure gradient can be calculated directly from the density of the fluid, the curvature of the streamline and the local velocity. Engineers often use dyes in water or smoke in air in order to see streaklines, from which pathlines can be calculated. Streaklines are identical to streamlines for steady flow. Further, dye can be used to create timelines.[4] The patterns guide their design modifications, aiming to reduce the drag. This task is known as streamlining, and the resulting
Streamlines, streaklines, and pathlines design is referred to as being streamlined. Streamlined objects and organisms, like steam locomotives, streamliners, cars and dolphins are often aesthetically pleasing to the eye. The Streamline Moderne style, an 1930s and 1940s offshoot of Art Deco, brought flowing lines to architecture and design of the era. The canonical example of a streamlined shape is a chicken egg with the blunt end facing forwards. This shows clearly that the curvature of the front surface can be much steeper than the back of the object. Most drag is caused by eddies in the fluid behind the moving object, and the objective should be to allow the fluid to slow down after passing around the object, and regain pressure, without forming eddies. The same terms have since become common vernacular to describe any process that smooths an operation. For instance, it is common to hear references to streamlining a business practice, or operation.
Notes and references Notes [1] [2] [3] [4]
Batchelor, G. (2000). Introduction to Fluid Mechanics. Kundu P and Cohen I. Fluid Mechanics. Granger, R.A. (1995). Fluid Mechanics. Dover Publications. ISBN 0486683567., pp. 422–425. "Flow visualisation" (http:/ / modular. mit. edu:8080/ ramgen/ ifluids/ Flow_Visualization. rm) (realmedia). National Committee for Fluid Mechanics Films (NCFMF). . Retrieved 2009-04-20.
References • Faber, T.E. (1995). Fluid Dynamics for Physicists. Cambridge University Press. ISBN 0-521-42969-2.
External links • Streamline illustration (http://www.centennialofflight.gov/essay/Dictionary/streamlining/DI44.htm) • Tutorial - Illustration of Streamlines, Streaklines and Pathlines of a Velocity Field(with applet) (http://web.mit. edu/fluids-modules/www/potential_flows/LecturesHTML/lec02/tutorial/tutorial-spsl.html) • NPTEL web content (http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/ FLUID-MECHANICS/ui/Course_home-3.htm)
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Structural load
Structural load Structural loads or actions are forces, deformations or accelerations applied to a structure or its components.[1] [2] Loads cause stresses, deformations and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis. Excess load or overloading may cause structural failure, and hence such possibility should be either considered in the design or strictly controlled. Mechanical structures, such as aerospace vehicles (e.g. aircraft, satellites, rockets, space stations, etc...), marine craft (e.g. boats, submarines, etc.), and material handling machinery have their own particular structural loads and actions.[3] Engineers often evaluate structural loads based upon published regulations, contracts, or specifications. Accepted technical standards are used for acceptance testing and inspection.
Types of loads Dead loads are static forces that are relatively constant for an extended time. They can be in tensile or compression. The term can refer to a laboratory test method or to the normal usage of a material or structure. Live loads are usually unstable or moving loads. These dynamic loads may involve considerations such as impact, momentum, vibration, slosh dynamics of fluids, etc. Cyclic loads on a structure can lead to fatigue damage, cumulative damage, or failure. These loads can be repeated loadings on a structure or can be due to vibration.
Loads on Architectural and Civil Engineering Structures Building codes require that structures be designed and built to safely resist all actions that they are likely to face during their service life, while remaining fit for use.[4] Minimum loads or actions are specified in these building codes for types of structures, geographic locations, usage and materials of construction.[5] Structural loads are split into categories by their originating cause. Of course, in terms of the actual load on a structure, there is no difference between dead or live loading, but the split occurs for use in safety calculations or ease of analysis on complex models as follows: To meet the requirement that design strength be higher than maximum loads, Building codes prescribe that, for structural design, loads are increased by load factors. These load factors are, roughly, a ratio of the theoretical design strength to the maximum load expected in service. They are developed to help achieve the desired level of reliability of a structure[6] based on probabilistic studies that take into account the load's originating cause, recurrence, distribution, and static or dynamic nature.[7]
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Structural load
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Dead load The dead load includes loads that are relatively constant over time, including the weight of the structure itself, and immovable fixtures such as walls, plasterboard or carpet. Dead loads are also known as Permanent loads.[8] [9] [10] The designer can also be relatively sure of the magnitude of dead loads as they are closely linked to density and quantity of the construction materials. These have a low variance, and the designer himself is normally responsible for the specifications of these components.
Live loads Dead load
Live loads, or imposed loads, are temporary, of short duration, or moving. These dynamic loads may involve considerations such as impact, momentum, vibration, slosh dynamics of fluids, fatigue, etc. Live loads, sometimes referred to as probabilistic loads include all the forces that are variable within the object's normal operation cycle not including construction or environmental loads. Roof live loads are produced 1. during maintenance by workers, equipment and materials, and 2. during the life of the structure by movable objects such as planters and by people. Bridge live loads are produced by vehicles traveling over the deck of the bridge.
Imposed load
Environmental loads These are loads that act as a result of weather, topography and other natural phenomena. • Wind loads • Snow, rain and ice loads • Seismic loads • Temperature changes leading to thermal expansion cause thermal loads • Ponding loads • Lateral pressure of soil, ground water or bulk materials • Loads from fluids or floods • Dust loads
Live snow load
Structural load
Other loads Engineers must also be aware of other actions that may affect a structure, such as: • • • • • • •
Support settlement or displacement Fire Corrosion Explosion Creep or shrinkage Impact from vehicles or machinery Loads during construction
Load combinations A load combination results when more than one load type acts on the structure. Design codes usually specify a variety of load combinations together with Load factors (weightings) for each load type in order to ensure the safety of the structure under different maximum expected loading scenarios. For example, in designing a staircase, a dead load factor may be 1.2 times the weight of the structure, and a live load factor may be 1.6 times the maximum expected live load. These two "factored loads" are combined (added) to determine the "required strength" of the staircase. The reason for the disparity between factors for dead load and live load, and thus the reason the loads are initially categorized as dead or live is because while it is not unreasonable to expect a large number of people ascending the staircase at once, it is less likely that the structure will experience much change in its permanent load.
Aircraft Structural Loads For aircraft, loading is divided into two major categories: limit loads and ultimate loads. Limit loads are often just flight loads and are further divided into maneuvering loads and gust loads. Ultimate loads are crash loads. Maneuvering loads are determined based on the performance limits of the aircraft whether imposed by the flight manual or by the actual aerodynamic performance of aircraft. Gust loads are determined statistically are taken from guidelines or requirements given by the applicable regulatory agency. Crash loads are loosely bounded by the ability of humans to survive extreme accelerations and are also typically taken from regulations. Other loads that may be critical are pressure loads (for pressurized, high-altitude aircraft) and ground loads. Loads on the ground can be from adverse braking or maneuvering during taxi. Finally, you cannot discuss aircraft loading without hearing about fatigue and damage tolerance. Aircraft are constantly subjected to cyclic loading. These cyclic loads initiate cracks and cause them to grow. Thermal loading is rarely considered for the analysis of the primary structure of aircraft but it can become critical under extreme operating conditions and should be examined where materials of disparate coefficients of thermal expansion are joined.
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Structural load
References [1] ASCE/SEI 7-05 Minimum Design Loads for Buildings and Other Structures. American Society of Civil Engineers. 2006. pp. 1. ISBN 0-7844-0809-2. [2] "1.5.3.1". Eurocode 0: Basis of structural design EN 1990. Bruxelles: European Committee for Standarization. 2002. [3] Avallone, E.A., and Baumeister, T., ed. Mark's Standard Handbook for Mechanical Engineers (10th ed.). McGraw-Hill. pp. 11–42. ISBN 0-07-004997-1. [4] "2.2.1(1)". Eurocode 0: Basis of structural design EN 1990. Bruxelles: European Committee for Standarization. 2002. [5] "1604.2". International Building Code. USA: International Code Council. 2000. p. 295. ISBN 1-892395-26-6. [6] "2.2.5(b)". Eurocode 0: Basis of structural design EN 1990. Bruxelles: European Committee for Standarization. 2002. [7] Rao, Singiresu S. (1992). Reliability Based Design. USA: McGraw-Hill. pp. 214–227. ISBN 0-07-051192-6. [8] 2006 International Building Code Section 1602.1. [9] EN 1990 Euro code – Basis of structural design section 4.1.1 [10] EN 1991-1-1 Euro code 1: Actions on Structures – Part 1-1: General actions – densities, self-weight, imposed loads for buildings section 3.2
External links • Wind and Snow loads on Constructions (http://sites.google.com/site/erefhome/programi/opterecenja) • Types of loads of structure (http://www.grook.net/forum/civil-engineering/construction/ types-of-loads-structure)
External links • Luebkeman, Chris H., and Donald Petting "Lecture 17: Primary Loads". University of Oregon. 1996 (http:// darkwing.uoregon.edu/~struct/courseware/461/461_lectures/461_lecture17/461_lecture17.html) • Fisette, Paul, and the American Wood Council. "Understanding Loads and Using Span Tables". 1997. (http:// www.awc.org/technical/spantables/tutorial.htm)
Surface integrity Surface integrity is the surface condition of a workpiece after being modified by a manufacturing process. The term was coined by Michael Field[1] and John F. Kahles[2] in 1964.[3] The surface integrity of a workpiece or item changes the material's properties. The consequences of changes to surface integrity are a mechanical engineering design problem, but the preservation of those properties are a manufacturing consideration.[4] Surface integrity can have a great impact on a parts function; for example, Inconel 718 can have a fatigue limit as high as 540 MPa (78000 psi) after a gentle grinding or as low as 150 MPa (22000 psi) after electrical discharge machining (EDM).[5]
Definition There are two aspects to surface integrity: topography characteristics and surface layer characteristics. The topography is made up of surface roughness, waviness, errors of form, and flaws. The surface layer characteristics that can change through processing are: plastic deformation, residual stresses, cracks, hardness, overaging, phase changes, recrystallization, intergranular attack, and hydrogen embrittlement. When a traditional manufacturing process is used, such as machining, the surface layer sustains local plastic deformation.[3] [4] The processes that affect surface integrity can be conveniently broken up into three classes: traditional processes, non-traditional processes, and finishing treatments. Traditional processes are defined as processes where the tool contacts the workpiece surface; for example: grinding, turning, and machining. These processes will only damage the surface integrity if the improper parameters are used, such as dull tools, too high feed speeds, improper coolant
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Surface integrity or lubrication, or incorrect grinding wheel hardness. Nontraditional processes are defined as processes where the tool does not contact the workpiece; examples of this type of process include EDM, electrochemical machining, and chemical milling. These processes will always change the surface integrity no matter how well controlled; for instance, they can leave a stress-free surface, a remelted surface, or excessive surface roughness. Finishing treatments are defined as processes that negate surface finishes imparted by traditional and non-traditional processes or improve the surface integrity. For example, residual stress can be removed via peening or roller burnishing or the recast layer left by EDMing can be removed via chemical milling.[6] Finishing treatments can affect the workpiece surface in a wide variety of manners. Some clean and/or remove defects, such as scratches, pores, burrs, flash, or blemishes. Other processes improve or modify the surface appearance by improving smoothness, texture, or color. They can also improve corrosion resistance, wear resistance, and/or reduce friction. Coatings are another type of finishing treatment that may be used to plate an expensive or scarce material onto a less expensive base material.[6]
Variables Manufacturing processes have five main variables: the workpiece, the tool, the machine tool, the environment, and process variables. All of these variables can affect the surface integrity of the workpiece by producing:[3] • • • •
High temperatures involved in various machining processes Plastic deformation in the workpiece (residual stresses) Surface geometry (roughness, cracks, distortion) Chemical reactions, especially between the tool and the workpiece
References [1] Dr. Michael Field (http:/ / www. nae. edu/ nae/ naepub. nsf/ Members+ By+ UNID/ AA719535BA65B8E186257552006B36A1?opendocument), , retrieved 2009-08-28 [2] Micheal, Field, John F. Kahles (http:/ / books. nap. edu/ openbook. php?record_id=4779& page=121), , retrieved 2009-08-28 [3] Degarmo, Black & Kohser 2003, p. 778. [4] Degarmo, Black & Kohser 2003, p. 779. [5] Degarmo, Black & Kohser 2003, p. 777. [6] Degarmo, Black & Kohser 2003, p. 780.
Bibliography • Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4.
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Surface roughness
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Surface roughness Surface roughness, often shortened to roughness, is a measure of the texture of a surface. It is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small the surface is smooth. Roughness is typically considered to be the high frequency, short wavelength component of a measured surface (see surface metrology). Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces (see tribology). Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion. Although roughness is usually undesirable, it is difficult and expensive to control in manufacturing. Decreasing the roughness of a surface will usually increase exponentially its manufacturing costs. This often results in a trade-off between the manufacturing cost of a component and its performance in application.
Parameters A roughness value can either be calculated on a profile or on a surface. The profile roughness parameter (Ra, Rq,...) are more common. The area roughness parameters (Sa, Sq,...) give more significant values.
Profile roughness parameters Each of the roughness parameters is calculated using a formula for describing the surface. There are many different roughness parameters in use, but parameters include
,
countries. For example, the
, and
is by far the most common. Other common
. Some parameters are used only in certain industries or within certain
family of parameters is used mainly for cylinder bore linings, and the Motif
parameters are used primarily within France. Since these parameters reduce all of the information in a profile to a single number, great care must be taken in applying and interpreting them. Small changes in how the raw profile data is filtered, how the mean line is calculated, and the physics of the measurement can greatly affect the calculated parameter. By convention every 2D roughness parameter is a capital R followed by additional characters in the subscript. The subscript identifies the formula that was used, and the R means that the formula was applied to a 2D roughness profile. Different capital letters imply that the formula was applied to a different profile. For example, Ra is the arithmetic average of the roughness profile, Pa is the arithmetic average of the unfiltered raw profile, and Sa is the arithmetic average of the 3D roughness. Each of the formulas listed in the tables assumes that the roughness profile has been filtered from the raw profile data and the mean line has been calculated. The roughness profile contains ordered, equally spaced points along the trace, and is the vertical distance from the mean line to the data point. Height is assumed to be positive in the up direction, away from the bulk material.
Surface roughness
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Amplitude parameters Amplitude parameters characterize the surface based on the vertical deviations of the roughness profile from the mean line. Many of them are closely related to the parameters found in statistics for characterizing population samples. For example, Ra is the arithmetic average of the absolute values and Rt is the range of the collected roughness data points. The average roughness, Ra, is expressed in units of height. In the Imperial (English) system, 1 Ra is typically expressed in "millionths" of an inch. This is also referred to as "microinches" or sometimes just as "micro" (however the latter is just slang). The amplitude parameters are by far the most common surface roughness parameters found in the United States on mechanical engineering drawings and in technical literature. Part of the reason for their popularity is that they are straightforward to calculate using a computer. Parameter
Description
[1]
arithmetic average of absolute values
Ra,
Raa,
Formula [1]
Ryni Rq, RRMS
[1]
root mean squared [1]
Rv
maximum valley depth
Rp
maximum peak height
Rt
Maximum Height of the Profile
Rsk
skewness
Rku
kurtosis
RzDIN, Rtm
average distance between the highest peak and lowest valley in each sampling length, ASME Y14.36M - 1996 Surface Texture Symbols
RzJIS
Japanese Industrial Standard for
, where lengths, and
is
is the number of sampling
for the
sampling length.
, based on the five highest
peaks and lowest valleys over the entire sampling length.
, where
are the
highest peak, and lowest valley respectively.
Slope, spacing, and counting parameters Slope parameters describe characteristics of the slope of the roughness profile. Spacing and counting parameters describe how often the profile crosses certain thresholds. These parameters are often used to describe repetitive roughness profiles, such as those produced by turning on a lathe.
Surface roughness
505
Parameter
Rdq, R
q
Rda, R
a
i
Description
Formula
the RMS slope of the profile within the sampling length
the average absolute slope of the profile within the sampling length where delta i is calculated according to ASME B46.1
Bearing ratio curve parameters These parameters are based on the bearing ratio curve (also known as the Abbott-Firestone curve.) This includes the Rk family of parameters. Fractal theory The mathematician Benoît Mandelbrot has pointed out the connection between surface roughness and fractal dimension[2] .
Areal roughness parameters Areal roughness parameters are defined in the ISO 25178 series. The resulting values are Sa, Sq, Sz,... . At the moment many optical measurement instruments are able to measure the surface roughness over an area.
Sketches depicting surfaces with negative and positive skew. The roughness trace is on the left, the amplitude distribution curve is in the middle, and the bearing area curve (Abbott-Firestone curve) is on the right.
Practical effects In most cases, roughness is considered to be detrimental to part performance. As a consequence, most manufacturing prints establish an upper limit on roughness, but not a lower limit. An exception is in cylinder bores where oil is retained in the surface profile and a minimum roughness is required. Roughness is often closely related to the friction and wear properties of a surface. A surface with a large or a positive
value,
, will usually have high friction and wear quickly. The peaks in the roughness profile are not
always the points of contact. The form and waviness must also be considered.
References [1] Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 223, ISBN 0-471-65653-4. [2] Den Outer, A.; Kaashoek, J.F.; Hack, H.R.G.K. (1995). "Difficulties of using continuous fractal theory for discontinuity surfaces". International Journal of Rock Mechanics and Mining Science & Geomechanics Abstracts 32 (1): 3–9. doi:10.1016/0148-9062(94)00025-X.
External links • Roughness terminology (http://www.mfg.mtu.edu/cyberman/quality/sfinish/terminology.html)
Swivel
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Swivel A swivel is a connection that allows the connected object, such as a gun or chair, to rotate horizontally and/or vertically. A common design for a swivel is a cylindrical rod that can turn freely within a support structure. The rod is usually prevented from slipping out by a nut, washer or thickening of the rod. The device can be attached to the ends of the rod or the center. Another common design is a sphere that is able to rotate within a support structure. The device is attached to the sphere. A third design is a hollow cylindrical rod that has a rod that is slightly smaller than its inside diameter inside of it. They are prevented from coming apart by flanges. The device may be attached to either end.
A swivel in a chain link
A swivel joint for a pipe is often a threaded connection in between which at least one of the pipes is curved, often at an angle of 45 or 90 degrees. The connection is tightened enough to be water- or air-tight and then tightened further so that it is in the correct position.
A swivel in a link
Systematic Hierarchical Approach for Resilient Process Screening (SHARPS)
507
Systematic Hierarchical Approach for Resilient Process Screening (SHARPS) Systematic Hierarchical Approach for Resilient Process Screening (SHARPS)[1] is a cost screening technique to assist designers achieve a desired investment payback period during preliminary design of water-using systems. Heuristics involving equipment susbtitution and intensification are used to guide process changes. SHARPS method has been used to yield cost effective minimum water network for water-intensive facilities.
References [1] Wan Alwi, S. R. and Manan, Z. A. (2006). SHARPS – A New Cost-Screening Technique To Attain Cost-Effective Minimum Water Utilisation Network . AiChe Journal. 11 (52): 3981-3988.
Tail lift A tail lift is a mechanical device permanently fitted to the back of van or lorry, which is designed to facilitate the materials handling of goods from ground level or a loading dock to the level of the load bed of the vehicle, or vice versa. The majority of tail lifts are hydraulic or pneumatic in operation, although they can be mechanical, and are controlled by an operator using an electric relay switch. The use of a tail lift can obviate the need to use machinery such as a forklift truck in order to load heavy items on to a vehicle, or can be used to bridge the difference in height between a loading dock and the vehicle load bed.
A hydraulic cantilever tail lift on the back of a truck
Tail lifts are available for many sizes of vehicle, from standard vans to articulated lorries, and standard models can lift anywhere up to 2500kg.[1]
Types There are two key types of tail lift available to operators these are:
Column lifts Column lifts are often mechanical, although they can be hydraulic or pneumatic. They run on 'tracks' fitted to the rear of the vehicle. From the tracks, a folding platform extends, which can be taken up and down. Column lifts have the advantage of being able to lift to a higher level than the load bed (and are therefore suitable for loads over more than one level in the truck.[2] They are usually the easiest of the lift types to fit, as they require little structural work.
Four stages of deployment on an ambulance tail lift
Tail lift
508
The disadvantages of column lifts include that the platform is only usually able to operate at a 90° angle from the track, meaning that on uneven surfaces, the lift will not meet the ground properly.
Cantilever lifts The cantilever lift is the type first developed by Zepro. They operate only on a hydraulic or pneumatic system. The system works by a set of rams attached to the chassis of the vehicle. These rams are on hinges, allowing them to move angle as they expand or contract. By using the rams in sequence, the working platform can either be tilted, or raised and lowered. Cantilever lifts have the advantage of being able to tilt, which means they can often form a ramp arrangement, which may be more appropriate for some applications. It also means that it can be easier to load or unload on uneven ground. On tuckaway lifts, the ramp can be folded away under the load bed of the vehicle, leaving the option of it not being used when at a loading ramp, and giving access and egress for operatives without the need to operate the lift.
References [1] "Zepro Tail lifts product history" (http:/ / www. hiab. com/ taillifts). . Retrieved 2007-06-05. [2] "Ratcliff Double Tier Lift" (http:/ / www. ratcliff. co. uk/ palfinger/ 16461_EN. pdf). . Retrieved 2007-06-13.
Control for a tail lift
Thermal efficiency
509
Thermal efficiency In thermodynamics, the thermal efficiency (
) is a dimensionless performance measure of a device that uses
thermal energy, such as an internal combustion engine, a steam turbine or a steam engine, a boiler, a furnace, or a refrigerator for example.
Overview In general, energy conversion efficiency is the ratio between the useful output of a device and the input, in energy terms. For thermal efficiency, the input, , to the device is heat, or the heat-content of a fuel that is consumed. The desired output is mechanical work, , or heat,
, or possibly both. Because the input heat normally has
a real financial cost, a memorable, generic definition of thermal efficiency is[1]
Output energy is always lower than input energy
From the first law of thermodynamics, the energy output cannot exceed the input, so
When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Due to inefficiencies such as friction, heat loss, and other factors, thermal engines' efficiencies are typically much less than 100%. For example, a typical gasoline automobile engine operates at around 25% efficiency, and a large coal-fueled electrical generating plant peaks at about 46%. The largest diesel engine in the world peaks at 51.7%. In a combined cycle plant, thermal efficiencies are approaching 60%.[2] Such a real-world value may be used as a figure of merit for the device. For engines where a fuel is burned there two types of thermal efficiency: indicated thermal efficiency and brake thermal efficiency.[3] This efficiency is only appropriate in when comparing similar types or similar devices. For other systems the specifics of the calculations of efficiency vary but the no dimensional input is still the same. Efficiency = Output energy / input energy
Heat engines Heat engines transform thermal energy, or heat, Qin into mechanical energy, or work, Wout. They cannot do this task perfectly, so some of the input heat energy is not converted into work, but is dissipated as waste heat Qout into the environment
The thermal efficiency of a heat engine is the percentage of heat energy that is transformed into work. Thermal efficiency is defined as
The efficiency of even the best heat engines is low; usually below 50% and often far below. So the energy lost to the environment by heat engines is a major waste of energy resources, although modern cogeneration, combined cycle
Thermal efficiency
510
and energy recycling schemes are beginning to use this heat for other purposes. Since a large fraction of the fuels produced worldwide go to powering heat engines, perhaps up to half of the useful energy produced worldwide is wasted in engine inefficiency. This inefficiency can be attributed to three causes. There is an overall theoretical limit to the efficiency of any heat engine due to temperature, called the Carnot efficiency. Second, specific types of engines have lower limits on their efficiency due to the inherent irreversibility of the engine cycle they use. Thirdly, the nonideal behavior of real engines, such as mechanical friction and losses in the combustion process causes further efficiency losses.
Carnot efficiency The second law of thermodynamics puts a fundamental limit on the thermal efficiency of all heat engines. Surprisingly, even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work. The limiting factors are the temperature at which the heat enters the engine, , and the temperature of the environment into which the engine exhausts its waste heat,
, measured in an absolute scale, such as the Kelvin or Rankine
scale. From Carnot's theorem, for any engine working between these two temperatures:[4]
This limiting value is called the Carnot cycle efficiency because it is the efficiency of an unattainable, ideal, reversible engine cycle called the Carnot cycle. No device converting heat into mechanical energy, regardless of its construction, can exceed this efficiency. Examples of
are the temperature of hot steam entering the turbine of a steam power plant, or the temperature at
which the fuel burns in an internal combustion engine.
is usually the ambient temperature where the engine is
located, or the temperature of a lake or river that waste heat is discharged into. For example, if an automobile engine burns gasoline at a temperature of and the ambient temperature is , then its maximum possible efficiency is:
Due to the other causes detailed below, practical engines have efficiencies far below the Carnot limit; for example the average automobile engine is less than 35% efficient. As Carnot's theorem only applies to heat engines, devices that convert the fuel's energy directly into work without burning it, such as fuel cells, can exceed the Carnot efficiency. It can be seen that since
is fixed by the environment, the only way for a designer to increase the Carnot
efficiency of an engine is to increase
, the temperature at which the heat is added to the engine. This is a general
principle that applies to all heat engines: the efficiency increases with operating temperature. For this reason the operating temperatures of engines have increased greatly over the long term, and new materials such as ceramics to enable engines to stand higher temperatures are an active area of research.
Engine cycle efficiency The Carnot cycle is reversible and thus represents the upper limit on efficiency of an engine cycle. Practical engine cycles are irreversible and thus have inherently lower efficiency than the Carnot efficiency when operated between the same temperatures and . One of the factors determining efficiency is how heat is added to the working fluid in the cycle, and how it is removed. The Carnot cycle achieves maximum efficiency because all the heat is added to the working fluid at the maximum temperature
, and removed at the minimum temperature
. In
contrast, in an internal combustion engine, the temperature of the fuel-air mixture in the cylinder is nowhere near its peak temperature as the fuel starts to burn, and only reaches the peak temperature as all the fuel is consumed, so the average temperature at which heat is added is lower, reducing efficiency.
Thermal efficiency • Automobiles: Otto cycle The Otto cycle is the name for the cycle used in spark-ignition internal combustion engines such as gasoline and hydrogen fueled automobile engines. Its theoretical efficiency depends on the compression ratio r of the engine and the specific heat ratio γ of the gas in the combustion chamber.[4]
Hence, to improve efficiency, increase the compression ratio. However the compression ratio is limited by the need to prevent the uncontrolled combustion known as knocking. The specific heat ratio of the air-fuel mixture γ varies somewhat with the fuel, but is generally close to the air value of 1.4. This standard value is usually used in all the engine cycle equations below, and when this approximation is used the cycle is called an air-standard cycle. • Trucks: Diesel cycle In the Diesel cycle used in diesel truck and train engines, the fuel is ignited by compression in the cylinder. The efficiency of the Diesel cycle is dependent on r and γ like the Otto cycle, and also by the cutoff ratio, rc, which is the ratio of the cylinder volume at the beginning and end of the combustion process:[4]
The Diesel cycle is less efficient than the Otto cycle when using the same compression ratio. However, practical Diesel engines are 30% - 35% more efficient than gasoline engines.[5] This is because, since the fuel is not introduced to the combustion chamber until it is required for ignition, the compression ratio is not limited by the need to avoid knocking, so higher ratios are used than in spark ignition engines. • Power plants: Rankine cycle The Rankine cycle is the cycle used in steam turbine power plants. The overwhelming majority of the world's electric power is produced with this cycle. Since the cycle's working fluid, water, changes from liquid to vapor and back during the cycle, their efficiencies depend on the thermodynamic properties of water. The thermal efficiency of modern steam turbine plants with reheat cycles can reach 47%, and in combined cycle plants it can approach 60%.[4] • Gas turbines: Brayton cycle The Brayton cycle is the cycle used in gas turbines and jet engines. It consists of a compressor that increases pressure of the incoming air, then fuel is continuously added to the flow and burned, and the hot exhaust gasses are expanded in a turbine. The efficiency depends largely on the ratio of the pressure inside the combustion chamber p2 to the pressure outside p1[4]
Other inefficiencies The above efficiency formulas are based on simple idealized mathematical models of engines, with no friction and working fluids that obey simple thermodynamic rules called the ideal gas law. Real engines have many departures from ideal behavior that waste energy, reducing actual efficiencies far below the theoretical values given above. Examples are: • • • • • • •
friction of moving parts inefficient combustion heat loss from the combustion chamber departure of the working fluid from the thermodynamic properties of an ideal gas aerodynamic drag of air moving through the engine energy used by auxiliary equipment like oil and water pumps inefficient compressors and turbines
• imperfect valve timing
511
Thermal efficiency Another source of inefficiency is that engines must be optimized for other goals besides efficiency, such as low pollution. The requirements for vehicle engines are particularly stringent: they must be designed for low emissions, adequate acceleration, fast starting, light weight, low noise, etc. These require compromises in design (such as altered valve timing to reduce emissions) that reduce efficiency. The average automobile engine is only about 35% efficient, and must also be kept idling at stoplights, wasting an additional 17% of the energy, resulting in an overall efficiency of 18%.[5] Large stationary electric generating plants have fewer of these competing requirements as well as more efficient Rankine cycles, so they are significantly more efficient than vehicle engines, around 50% Therefore, replacing internal combustion vehicles with electric vehicles, which run on a battery that is charged with electricity generated by burning fuel in a power plant, has the theoretical potential to increase the thermal efficiency of energy use in transportation, thus decreasing the demand for fossil fuels. When comparing different heat engines as sources of power, such as electric power or the power to run vehicles, the engine efficiency alone is only one factor. To give a meaningful comparison, the overall efficiency of the entire energy supply chain from the fuel source to the consumer must be considered. Although the heat wasted by heat engines is usually the largest source of inefficiency, factors such as the energy cost of fuel refining and transportation, and energy loss in electrical transmission lines to transport it, may offset the advantage of a more efficient heat engine.
Energy conversion For a device that converts energy from a form other than thermal energy to another form (such as a boiler or furnace), the thermal efficiency is
where the
quantities are heat-equivalent values.
So, for a boiler that produces 210 kW (or 700,000 BTU/h) output for each 300 kW (or 1,000,000 BTU/h) heat-equivalent input, its thermal efficiency is 210/300 = 0.70, or 70%. This means that 30% of the energy is lost to the environment. An electric resistance heater has a thermal efficiency close to 100%.[6] When comparing heating units, such as a highly efficient electric resistance heater to an 80% efficient natural gas-fueled furnace, an economic analysis is needed to determine the most cost-effective choice.
Effects of fuel heating value The heating value of a fuel is the amount of heat released during an exothermic reaction (e.g., combustion) and is a characteristic of each substance. It is measured in units of energy per unit of the substance, usually mass, such as: kcal/kg, kJ/kg, J/mol, Btu/m³. The heating value for fuels is expressed as the HHV, LHV, or GHV to distinguish treatment of the heat of phase changes: • Higher heating value (HHV) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. This is the same as the thermodynamic heat of combustion. • Lower heating value (LHV) (or net calorific value) is determined by subtracting the heat of vaporization of the water vapor from the higher heating value. The energy required to vaporize the water therefore is not realized as heat. • Gross heating value accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning.
512
Thermal efficiency Which definition of heating value is being used significantly affects any quoted efficiency. Not stating whether an efficiency is HHV or LHV renders such numbers very misleading.[7]
Heat pumps and refrigerators Heat pumps, refrigerators and air conditioners use work to move heat from a colder to a warmer place, so their function is the opposite of a heat engine. The work energy (Win) that is applied to them is converted into heat, and the sum of this energy and the heat energy that is moved from the cold reservoir (QC) is equal to the total heat energy added to the hot reservoir (QH) Their efficiency is measured by a coefficient of performance (COP). Heat pumps are measured by the efficiency with which they add heat to the hot reservoir, COPheating; refrigerators and air conditioners by the efficiency with which they remove heat from the cold interior, COPcooling:
The reason for not using the term 'efficiency' is that the coefficient of performance can often be greater than 100%. Since these devices are moving heat, not creating it, the amount of heat they move can be greater than the input work. Therefore, heat pumps can be a more efficient way of heating than simply converting the input work into heat, as in an electric heater or furnace. Since they are heat engines, these devices are also limited by Carnot's theorem. The limiting value of the Carnot 'efficiency' for these processes, with the equality theoretically achievable only with an ideal 'reversible' cycle, is:
The same device used between the same temperatures is more efficient when considered as a heat pump than when considered as a refrigerator:
This is because when heating, the work used to run the device is converted to heat and adds to the desired effect, whereas if the desired effect is cooling the heat resulting from the input work is just an unwanted byproduct.
Energy efficiency The 'thermal efficiency' is sometimes called the energy efficiency. In the United States, in everyday usage the SEER is the more common measure of energy efficiency for cooling devices, as well as for heat pumps when in their heating mode. For energy-conversion heating devices their peak steady-state thermal efficiency is often stated, e.g., 'this furnace is 90% efficient', but a more detailed measure of seasonal energy effectiveness is the Annual Fuel Utilization Efficiency (AFUE).[8]
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Thermal efficiency
514
Energy Efficiency of heat exchangers A counter flow heat exchanger is generally, effectively 100% efficient in transferring heat energy from one circuit to the other, albeit at a slight loss in temperature.
References
[1] Fundamentals of Engineering Thermodynamics, by Howell and Buckius, McGraw-Hill, New York, 1987 [2] GE Power’s H Series Turbine (http:/ / www. ge-energy. com/ prod_serv/ products/ gas_turbines_cc/ en/ h_system/ index. htm) [3] The Internal Combustion Engine in Theory and Practice: Vol. 1 - 2nd Edition, Revised, MIT Press, 1985, Charles Fayette Taylor - Equation 1-4, page 9 [4] Holman, Jack P. (1980). Thermodynamics. New York: McGraw-Hill. pp. 217. ISBN 0-07-029625-1. [5] "Where does the energy go?" (http:/ / www. fueleconomy. gov/ feg/ atv. shtml). Advanced technologies and energy efficiency, Fuel Economy Guide. US Dept. of Energy. 2009. . Retrieved 2009-12-02. [6] http:/ / www. energysavers. gov/ your_home/ space_heating_cooling/ index. cfm/ mytopic=12520 [7] http:/ / www. claverton-energy. com/ the-difference-between-lcv-and-hcv-or-lower-and-higher-heating-value-or-net-and-gross-is-clearly-understood-by-all-energy-engineers-there-is-no-right-or-wrong html [8] HVAC Systems and Equipment volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, USA, 2004
Thermal engineering Heating or cooling of processes, equipment, or enclosed environments are within the purview of thermal engineering. One or more of the following disciplines may be involved in solving a particular thermal engineering problem: • • • •
Thermodynamics Fluid mechanics Heat transfer Mass transfer
Thermal engineering may be practiced by mechanical engineers and chemical engineers. One branch of knowledge used frequently in thermal engineering is that of thermofluids.
Applications • • • •
Engineering : HVAC Cooling of computer chips [1] Boiler design Solar heating
External links • Yahoo directory [2] • Thermal Engineering branch at Goddard Space Flight Center [3] • List of related fields in UNESCO thesaurus [4]
Thermal engineering
References [1] [2] [3] [4]
http:/ / www. aavidthermalloy. com/ technical/ papers/ engineering. shtml http:/ / dir. yahoo. com/ Science/ Engineering/ Mechanical_Engineering/ Thermal_Engineering/ http:/ / thermal. gsfc. nasa. gov/ http:/ / www. freethesaurus. info/ unesco/ index. php?tema=2116& / thermal-engineering
Thermal science Thermal science is the combined study of thermodynamics, fluid mechanics, heat transfer, and combustion.
Overview Introductory subjects studied in thermal science generally are focused on thermodynamics. These include studies of properties of pure substances, pressure-volume-temperature diagrams, the ideal gas law, heat and it relationship to work, heat transfer, the laws of thermodynamics, engine and refrigeration cycles, and combustion. Another area of concern in thermal science is fluid mechanics. These include fluid statics, fluid flows, e.g. laminar flow vs. turbulent flow, the Bernoulli equation. The applicability of this area is piping networks, turbo-machineries, airfoils. Heat transfer has applications for heat exchangers, heat engines, heating, ventilating, and air-conditioning, and cooling of microelectronics. Combustion involves both thermal effects and chemical reaction. Intensive study of thermal sciences requires additional knowledge and experience in other areas such as experimental techniques and numerical or computational methods.
References Potter, M. & Scott, E. (2003). Thermal Sciences: An Introduction to Thermodynamics, Fluid Mechanics, and Heat Transfer. New York: Thomson-Engineering. ISBN 0-534-38521-4 Faghri, A., Zhang, Y., and Howell, J. R. (2010). Advanced Heat and Mass Transfer. Global Digital Press, Columbia, MO. ISBN 978-0984276004
Further reading • Advanced Heat and Mass Transfer [1] - An free online textbook • Thermal Science [2] - International Scientific Journal
External links • Thermal-Fluids Central [3]
References [1] https:/ / www. thermalfluidscentral. org/ e-books/ book-intro. php?b=37 [2] http:/ / thermalscience. vinca. rs/ [3] https:/ / www. thermalfluidscentral. org/
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Thermo-mechanical fatigue
Thermo-mechanical fatigue Thermo-mechanical fatigue (short TMF) is the overlay of a cyclical mechanical loading, that leads to fatigue of a material, with a cyclical thermal loading. Thermo-mechanical fatigue is an important point that needs to be considered, when constructing turbine engines or gas turbines.
Failure Mechanisms There are three mechanisms acting in thermo-mechanical fatigue • Creep is the flow of material at high temperatures • Fatigue is crack growth and propagation due to repeated loading • Oxidation is a change in the chemical composition of the material due to environmental factors. The oxidized material is more brittle and prone to crack creation. Each factor has more or less of an effect depending on the parameters of loading. In phase (IP) thermo-mechanical loading (when the temperature and load increase at the same time) is dominated by creep. The combination of high temperature and high stress is the ideal condition for creep. The heated material flows more easily in tension, but cools and stiffens under compression. Out of phase (OP) thermo-mechanical loading is dominated by the effects of oxidation and fatigue. Oxidation weakens the surface of the material, creating flaws and seeds for crack propagation. As the crack propagates, the newly exposed crack surface then oxidizes, weakening the material further and enabling the crack to extend. A third case occurs in OP TMF loading when the stress difference is much greater than the temperature difference. Fatigue alone is the driving cause of failure in this case, causing the material to fail before oxidation can have much of an effect. [1] TMF still is not fully understood. There are many different models to attempt to predict the behavior and life of materials undergoing TMF loading. The two models presented below take different approaches.
Models of Thermo-Mechanical Fatigue There are many different models that have been developed in an attempt to understand and explain TMF. This page will address the two broadest approaches, constitutive and phenomenological models. Constitutive models utilize the current understanding of the microstructure of materials and failure mechanisms. These models tend to be more complex, as they try to incorporate everything we know about how the materials fail. These types of models are becoming more popular recently as improved imaging technology has allowed for a better understanding of failure mechanisms. Phenomenological models are based purely on the observed behavior of materials. They treat the exact mechanism of failure as a sort of "black box". Temperature and loading conditions are input, and the result is the fatigue life. These models try to fit some equation to match the trends found between different inputs and outputs.
Damage Accumulation Model The damage accumulation model is a constitutive model of TMF. It adds together the damage from the three failure mechanisms of fatigue, creep, and oxidation.
where
is the fatigue life of the material, that is, the number of loading cycles until failure. The fatigue life for
each failure mechanism is calculated individually and combined to find the total fatigue life of the specimen. [2] [3]
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Thermo-mechanical fatigue Fatigue The life from fatigue is calculated for isothermal loading conditions. It is dominated by the strain applied to the specimen.
where
and
are material constants found through isothermal testing. Note that this term does not account for
temperature effects. The effects of temperature are treated in the oxidation and creep terms. Oxidation The life from oxidation is affected by temperature and cycle time.
where
and Parameters are found by comparing fatigue tests done in air and in an environment with no oxygen (vacuum or argon). Under these testing conditions, it has been found that the effects of oxidation can reduce the fatigue life of a specimen by a whole order of magnitude. Higher temperatures greatly increase the amount of damage from environmental factors. [4] Creep
where
Benefit The damage accumulation model is one of the most in-depth and accurate models for TMF. It accounts for the effects of each failure mechanism. Drawback The damage accumulation model is also one of the most complex models for TMF. There are several material parameters that must be found through extensive testing. [5]
Strain-Rate Partitioning Strain-rate partitioning is a phenomenological model of thermo-mechanical fatigue. It is based on observed phenomenon instead of the failure mechanisms. This model deals only with inelastic strain and ignores plastic strain completely. It accounts for different types of deformation and breaks strain into four possible scenarios: [6] • • • •
PP – plastic in tension and compression CP – creep in tension and plastic in compression PC – plastic in tension and creep in compression CC – creep in tension and compression
The damage and life for each partition is calculated and combined in the model
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Thermo-mechanical fatigue
518
where and
etc, are found from variations of the equation
where A and C are material constants for individual loading. Benefit Strain-Rate Partitioning is a much simpler model than the damage accumulation model. Because it breaks down the loading into specific scenarios, it can account for different phases in loading. Drawback The model is based on inelastic strain. This means that it does not work well with scenarios of low inelastic strain, such as brittle materials or loading with very low strain. This model can be an oversimplification. Because it fails to account for oxidation damage, it may overpredict specimen life in certain loading conditions.
Looking Forward The next area of research is attempting to understand TMF of composites. The interaction between the different materials adds another layer of complexity. Seifert and Reidel are modeling hard graphite inclusions in cast iron as spherical inclusions in a matrix. Because the materials are brittle, crack development is assumed to occur early in the loading process. The fatigue life model is then based on a crack growth model, but is adjusted to account for effects from temperature. Their proposed model is
where
is the original crack size,
is the final crack size,
temperature, and hardening of the matrix.
is a material constant, and D is a function of stress,
[7]
Zhang and Wang are currently investigating the TMF of a unidirectional fiber reinforced matrix. They are using a finite element method that accounts for the known microstructure. They have discovered that the large difference in the thermal expansion coefficient between the matrix and the fiber is the driving cause of failure, causing high internal stress. [8]
References [1] Nagesha, A et al. "A comparative study of isothermal and thermomechanical fatigue on type 316L(N) austenitic stainless steel" (http:/ / dx. doi. org/ 10. 1016/ j. msea. 2010. 05. 082) Materials Science and Engineering: A, 2010 [2] Changan, Chai et al. "Recent Developments in the Thermomechanical Fatigue Life Prediction of Superalloys" (http:/ / www. tms. org/ pubs/ journals/ JOM/ 9904/ Cai/ Cai-9904. htm), JOM, April 1999 [3] "Thermo Mechanical Technical Background" (https:/ / www. efatigue. com/ hightemp/ background/ tmf. html) [4] Heckel, T. K. et al. "Thermomechanical Fatigue of the TiAl Intermetallic Alloy TNB-V2" (http:/ / www. springerlink. com/ content/ 7232j3t772580465/ fulltext. html) Experimental Mechanics, 2009 [5] Minichmayr, Robert et al. "Thermo-mechanical fatigue life assessment of aluminum components using the damage rate model of Sehitoglu" (http:/ / www. sciencedirect. com/ science?_ob=ArticleURL& _udi=B6V35-4NCJCRP-2& _user=571676& _coverDate=02/ 29/ 2008& _alid=1572321743& _rdoc=1& _fmt=high& _orig=search& _origin=search& _zone=rslt_list_item& _cdi=5721& _sort=r& _st=13& _docanchor=& view=c& _ct=1& _acct=C000029040& _version=1& _urlVersion=0& _userid=571676& md5=be6d57b6fac5d812e66d17e3afabb53b& searchtype=a) International Journal of Fatigue, 2008 [6] Zhuang, W. Z. et al. "Thermo-mechanical fatigue life prediction: A critical review" (http:/ / hdl. handle. net/ 1947/ 3887) Defence Science and Technology Organisation Publications, 1998 [7] Seifert, T and H. Riedel "Mechanism-based thermomechanical fatigue life prediction of cast iron. Part I: Models" (http:/ / dx. doi. org/ 10. 1016/ j. ijfatigue. 2010. 02. 004) International Journal of Fatigue, 2010
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[8] Zhang, Junqian and Fang Wang "Modeling of Damage Evolution and Failure in Fiber-Reinforced Ductile Composites Under Thermomechanical Fatigue Loading" (http:/ / ijd. sagepub. com/ content/ 19/ 7/ 851. abstract) International Journal of Damage Mechanics, 2010
Thermomechanical generator The Harwell TMG Stirling engine, an abbreviation for "Thermo-Mechanical Generator", was invented in 1967 by E. H. Cooke-Yarborough at the Harwell Labs of the United Kingdom Atomic Energy Authority[1] [2] [3] [4] . It was intended to be a remote electrical power source with low cost and very long life, albeit by sacrificing some efficiency. The TMG (model TMG120) was at one time the only Stirling engine sold by a manufacturer, namely HoMach Systems Ltd., England.[5] The engine has near isothermal cylinders because 1) the heater area covers the entire cylinder end, 2) it is a short stroke device, with wide shallow cylinders, yielding a high surface area to volume ratio, 3) the average thickness of the gas space is about 0.1 cm, and 4) the working fluid is Helium, a gas having good thermal properties for Stirling engines. The engine's displacer also has very low losses. These low-loss operating characteristics simplify the engine analysis, compared to more conventional Stirling engines.[5]
Freebody diagram; modeling the interaction of the piston with the case
The design has many advantages over conventional Stirling engines. The simplicity of the heater greatly reduces the cost by allowing the TMG to avoid the need for a brazed tubular or finned heater, which can account for 40% of the cost of a conventional Stirling engine. [6] The heat exchangers for the heater and cooler are mechanically trivial. The regenerator is a simple annulus, referred to as a "flat plate". Along with the cylinder wall and the displacer, there are a total of four regenerating surfaces. The TMG is a free piston engine. There are no rolling bearings or sliding seals, thus there is very little friction or wear. The working space is hermetically sealed, allowing it to contain pressurized helium gas for many thousands of hours. The displacer is a stainless steel can, 27 cm in diameter. It is suspended by a low-loss planer metal spring centered in a 27.4 cm diameter cylinder. The 2 mm radial clearance is divided into two concentric annular gaps by a thin, open-ended cylinder, which is fixed to the engine's cylinder. This annulus acts as the regenerator, which is much less costly than a wire-mesh type. The engine is a "free-cylinder" design, in which the entire engine is mounted on springs and allowed to vibrate slightly. This allows the displacer to be driven by positive feedback from the motion of the power piston and the magnets in the linear-alternator magnets, which have a combined weight of 10 kg.
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Engine Parameter
HoMach TMG 120 Spec
Indicated power
170 W
Shaft power
150 W
Heat input
1500 W
Thermal to mechanical efficiency
10%
Engine frequency
110 Hz
charge Pressure
0.2 MPa
Displacer diameter
26.0 cm
displacer stroke
0.2 cm
Displacer swept volume
110 cm³
Power piston diaphragm outer diameter
35.2 cm
Power piston diaphragm stroke
0.152 cm
Power piston diaphragm swept volume
110 cm³
Phase angle
~90 degrees
Moving mass (Power piston and alternator magnets)
10 kg
Total engine mass
~80 kg
Operating life
over 90000 hours
Helium replenishment (7 liters, at unknown pressure) every 22500 hours on average [5]
The unique power piston was invented by Cooke-Yarborough, and is called an "articulated diaphragm". It consists of a stainless steel annulus, with an outer diameter of 35 cm and an inner diameter of 26 cm. This annulus is clamped to the engine on the outer edge by two flexible rubber o-rings, and on the inner edge it is similarly clamped, in this case to a rigid center hub that makes up the piston's center. The o-rings flex but do not slide, thus no lubricant is needed and there is negligible wear in the entire machine. The compression space is located between the power-piston hub and the displacer, and this space is cooled by direct conduction through the power piston. A developmental model of the TMG contained a double articulated diaphragm containing cooling water, which was pumped by a thermosyphon. The depth of the compression space varies from 0.2 to 2.7 mm, as governed by the 2 mm displacer stroke and the 1.5 mm power piston stroke moving 90 degrees out of phase. The TMG engine successfully overcomes many of the economic and mechanical difficulties common in conventional Stirling engines. However, there are some limitations of this design. The simple, low-cost annular regenerator is inefficient compared to other types, (and this contributes to this engine's somewhat low thermal efficiency of only 10%). The mechanical limitations of the articulated diaphragm only allow a maximum stroke of an estimated 3 mm. These properties limit the maximum obtainable power to about 500 - 1000 Watts from an engine of this design.[5] Nevertheless, it is rare for a low-cost Stirling engine to obtain this high level of reliability and operating life, which can only be attributed to the ingenuity of the design.
Thermomechanical generator
References [1] [2] [3] [4] [5] [6]
GB 1252258 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=GB1252258), "Stirling-motor" GB 1397548 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=GB1397548), "Stirling cycle heat engines" GB 1539034 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=GB1539034), "Resilient coupling devices" GB 2136087 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=GB2136087), "Annular Spring" Colin D. West (1986). Principles and Applications of Stirling Engines. ISBN 0-442-29237-6. p. 195, 113, 109, 195 Clifford.M.Hargreaves (1991). The Philips Stirling Engine. ISBN 0444884637.
Timken OK Load Timken OK Load is a qualitative measure that indicates the possible performance of extreme pressure additives (EP Additives) in a lubricating grease or oil. The units of measure are pounds-force or kilograms-force and are determined using a special test machine. The test machine is based on a machine manufactured by the Timken Company from 1935 to 1972. It is now an industry standard test though the meaning of the qualitative measure has become less useful as the science of tribology has advanced. The test machine consists of a bearing race mounted on a tapered arbor rotating at high speed. The race is brought into contact with a square steel test block under load. The contact area is flooded with the lubricant being tested. The Timken OK Load is the load at which the spinning bearing race produces a score mark on the test block. Timken OK Loads are still listed on grease and oil property charts. It was once generally assumed that the measure and the film strength of the lubricant were directly related. Today, the primary purpose of the test is to determine whether EP additives are present and functioning. A measure of 35 pounds-force (16 kilograms-force or 155 newtons) or more means that EP additives are present and working. The Timken OK Load test specification is ASTM D-2509.
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Tip clearance Tip clearance is the distance between the tip of a rotating airfoil and a non-moving part. • Gas turbine: Rotor blade and casing[1] • Propeller (ship or aircraft): Propeller and structure[2] • Ground tip clearance [3] • Wind turbine: blade and tower [4]
References [1] Boyce, Meherwan P. (2002). Gas turbine engineering handbook (http:/ / books. google. de/ books?id=nEc2OxxT_uMC& pg=PA365& lpg=PA365& dq=gas+ turbine+ "tip+ clearance"& source=bl& ots=Bb7imzjkoM&
The inlet of an EJ200, showing rotor and stator blades. The narrow clearance between the rotor (first set of blades) and the casing is visible.
sig=M0YODKiSlOc6KtgpnhuxIYmPvGw& hl=en& ei=9zS-Sea1I8KPsAbi9vToDg& sa=X& oi=book_result& resnum=2& ct=result). Gulf Professional Publishing. p. 365. ISBN 0884157326. . Retrieved 2009-03-16. [2] Breslin, John P.; Poul Andersen (1996). Hydrodynamics of Ship Propellers (http:/ / books. google. de/ books?id=yV2QSl92TzcC& pg=PA424& lpg=PA424& dq=propeller+ "tip+ clearance"& source=bl& ots=08PGBL0BzI& sig=SfVsqZ-3ODCIC8moV5759JB7aiA& hl=en& ei=jTG-SaWZKoaPsAawisDoDg& sa=X& oi=book_result& resnum=3& ct=result). Cambridge University Press. p. 424. ISBN 0521574706. . Retrieved 2009-03-16. [3] http:/ / www. hartzellprop. com/ top_prop/ topprop_moreblade. htm [4] Burton, Tony; David Sharpe, Nick Jenkins, Ervin Bossanyi (2001). Wind Energy Handbook (http:/ / books. google. de/ books?id=4UYm893y-34C& pg=PA464& lpg=PA464& dq="tip+ clearance"+ "wind+ turbine"+ tower& source=bl& ots=2N4zZM45du& sig=bqjC36l4QGmAlCpnScd3IYNESP8& hl=en& ei=XIq7SfCGHYuRsAbyhcnoDg& sa=X& oi=book_result& resnum=10& ct=result). John Wiley and Sons. p. 464. ISBN 0471489972. . Retrieved 2009-03-16.
Tolerance analysis
Tolerance analysis Tolerance analysis is the general term for activities related to the study of accumulated variation in mechanical parts and assemblies. Its methods may be used on other types of systems subject to accumulated variation, such as mechanical and electrical systems. Engineers analyze tolerances for the purpose of evaluating geometric dimensioning and tolerancing (GD&T). Methods include 2D tolerance stacks, 3D Monte Carlo simulations, and datum conversions. Tolerance stackups or tolerance stacks are terms used to describe the problem-solving process in mechanical engineering of calculating the effects of the accumulated variation that is allowed by specified dimensions and tolerances. Typically these dimensions and tolerances are specified on an engineering drawing. Arithmetic tolerance stackups use the worst-case maximum or minimum values of dimensions and tolerances to calculate the maximum and minimum distance (clearance or interference) between two features or parts. Statistical tolerance stackups evaluate the maximum and minimum values based on the absolute arithmetic calculation combined with some method for establishing likelihood of obtaining the maximum and minimum values, such as Root Sum Square (RSS) or Monte-Carlo methods. While no official engineering standard covers the process or format of tolerance analysis and stackups, these are essential components of good product design. Tolerance stackups should be used as part of the mechanical design process, both as a predictive and a problem-solving tool. The methods used to conduct a tolerance stackup depend somewhat upon the engineering dimensioning and tolerancing standards that are referenced in the engineering documentation, such as American Society of Mechanical Engineers (ASME) Y14.5, ASME Y14.41, or the relevant ISO dimensioning and tolerancing standards. Understanding the tolerances, concepts and boundaries created by these standards is vital to performing accurate calculations. Tolerance stackups serve engineers by: • • • •
helping them study dimensional relationships within an assembly. giving designers a means of calculating part tolerances. helping engineers compare design proposals. helping designers produce complete drawings.
Concerns with tolerance stackups A safety factor is often included in designs because of concerns about: • • • • •
Operational temperature and pressure of the parts or assembly. Wear. Deflection of components after assembly. The possibility or probability that the parts are slightly out of specification (but passed inspection). The sensitivity or importance of the stack (what happens if the design conditions are not met).
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References • "Automation of Linear Tolerance Charts and Extension to Statistical Tolerance Analysis". Journal of Computing and Information Science in Engineering 3 (1): 95–99. March 2003. • ASME publication Y14.41-2003, Digital Product Definition Data Practices • Alex Krulikowski (1994), Tolerance Stacks using GD&T, ISBN 0-924520-05-1 • Bryan R. Fischer (2004), Mechanical Tolerance Stackup and Analysis, ISBN 0-8247-5379-8
Tooth Interior Fatigue Fracture Tooth Interior Fatigue Fracture, (TIFF), is a type of gear failure. The failure is characterised by a fracture at approximately mid-height on the tooth of the gear. This distinguishes it from a tooth root fatigue failure. The crack for a TIFF is initiated in the interior of the tooth. This distinguishes TIFF from other fatigue failures of gears. TIFF has been observed in case-hardened idlers (i.e. gear wheels loaded on both flanks during each revolution). The TIFF fracture surface has a distinct plateau in the central part along the tooth width and approximately mid-height of the tooth. In a close-up of the cross-section of the TIFF small wing cracks are observed. The presence of the wing crack indicates that the main crack has propagated from the centre of the tooth toward the tooth flank.
Tooth Interior Fatigue Fracture (TIFF) on intermediate gear
The crack-producing stresses of TIFF are twofold: i) constant residual tensile stresses in the interior of the tooth due to case hardening; and ii) alternating stresses due to the idler usage of the gear wheel. Contact fatigue begins with surface distress, which can grow to spalling. In severe cases a secondary crack can grow from a spalling crater through the tooth thickness and a part of the tooth can fall off. In contrast to the fracture of severe contact fatigue, spalling craters are not necessary at the flank surface for a TIFF. The TIFF fracture surface has a distinct plateau in the central part along the tooth width and approximately mid-height of the tooth.
References • MackAldener, Magnus; Mårten Olsson (2000). "Interior Fatigue Fracture of Gear Teeth". Fatigue and Fracture of Engineering Materials and Structures 23 (18): 283–292. • MackAldener, Magnus; Mårten Olsson (December 2002). "Analysis of crack propagation during tooth interior fatigue fracture". Engineering Fracture Mechanics (Elsevier Science Ltd.) 69 (18): 2147–2162. doi:10.1016/S0013-7944(02)00016-4.
Torque density
Torque density Torque density is a measure of the torque-carrying capability of a mechanical component. It is the ratio of torque capability to volume and is expressed in units of torque per volume. Torque density is a system property since it depends on the design of each element of the component being examined and their interconnection. Torque density is useful during the concept evaluation stage of mechanical designs, especially in power train design problems. Typically, it will be one of many factors used to assign potential success measures to each concept. For example, in the upgrade of a drive train for a set of rolls in a rolling mill, space is often dictated by the configuration of current components. There may be several types of devices that can perform the function of an existing component that must be replaced. The relative torque densities of the devices may be an important determinant for which design is ultimately selected, although it will often compete with other factors such as cost, ease of maintenance, time to install, operating costs and potential failure modes.
Units In SI units, torque density is expressed in joules per cubic metre or equivalently newton-metres per cubic metre (though dimensionally equivalent to the pascal, that is usually not used for this purpose). Small amounts can be expressed in newton-millimetres per cubic millimetre. In U.S. customary units, torque density is expressed in foot-pounds force per cubic foot, or inch-pounds force per cubic inch or ounce-force inches per cubic inch.
Total indicator reading Total indicator reading is the difference between the maximum and minimum measurements on the surface or plane of a part, effectively determining its flatness. [1] This measurement can also apply to cylindrical surfaces.
See Also • Flatness (manufacturing) • Metrology
References [1] http:/ / www. engineersedge. com/ engineering/ Engineering_Terms_Glossary/ T/ total_indicator_reading_tir_4448. htm
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Transmission (mechanics)
Transmission (mechanics) A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a live axle.[1] Often transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.[2] [3] In British English the term transmission 5-speed gearbox + reverse, the 1600 Volkswagen Golf (2009). refers to the whole drive train, including gearbox, clutch, prop shaft (for rear-wheel drive), differential and final drive shafts. In American English, however, the distinction is made that a gearbox is any device which converts speed and torque, whereas a transmission is a type of gearbox that can be "shifted" to dynamically change the speed:torque ratio, such as in a vehicle. The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and anywhere else rotational speed and torque needs to be adapted. Often, a transmission will have multiple gear ratios (or simply "gears"), with the ability to switch between them as speed varies. This switching may be done manually (by the operator), or automatically. Directional (forward and reverse) control may also be provided. Single-ratio transmissions also exist, which simply change the speed and torque (and sometimes direction) of motor output. In motor vehicle applications, the transmission will generally be connected to the crankshaft of the engine. The output of the transmission is transmitted via driveshaft to one or more differentials, which in turn drive the wheels. While a differential may also provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds (essential to avoid wheel slippage on turns) as it changes the direction of rotation. Conventional gear/belt transmissions are not the only mechanism for speed/torque adaptation. Alternative mechanisms include torque converters and power transformation (e.g., diesel-electric transmission, hydraulic drive system, etc.). Hybrid configurations also exist.
Explanation
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Transmission (mechanics)
527
Transmission types Manual • • •
Sequential manual Non-synchronous Preselector Automatic
•
Manumatic
• • •
Electrohydraulic Dual clutch Saxomat
Semi-automatic
Continuously variable Bicycle gearing • •
Derailleur gears Hub gears
Early transmissions included the right-angle drives and other gearing in windmills, horse-powered devices, and steam engines, in support of pumping, milling, and hoisting.
Interior view of Pantigo Windmill, looking up into cap from floor -- cap rack, brake wheel, brake and wallower. Pantigo Windmill is located on James Lane, East Hampton, Suffolk County, Long Island, New York.
Most modern gearboxes are used to increase torque while reducing the speed of a prime mover output shaft (e.g. a motor crankshaft). This means that the output shaft of a gearbox will rotate at a slower rate than the input shaft, and this reduction in speed will produce a mechanical advantage, causing an increase in torque. A gearbox can be set up to do the opposite and provide an increase in shaft speed with a reduction of torque. Some of the simplest gearboxes merely change the physical direction in which power is transmitted.
Many typical automobile transmissions include the ability to select one of several different gear ratios. In this case, most of the gear ratios (often simply called "gears") are used to slow down the output speed of the engine and increase torque. However, the highest gears may be "overdrive" types that increase the output speed.
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Uses Gearboxes have found use in a wide variety of different—often stationary—applications, such as wind turbines. Transmissions are also used in agricultural, industrial, construction, mining and automotive equipment. In addition to ordinary transmission equipped with gears, such equipment makes extensive use of the hydrostatic drive and electrical adjustable-speed drives.
Simple
The main gearbox and rotor of a Bristol Sycamore helicopter
The simplest transmissions, often called gearboxes to reflect their simplicity (although complex systems are also called gearboxes in the vernacular), provide gear reduction (or, more rarely, an increase in speed), sometimes in conjunction with a right-angle change in direction of the shaft (typically in helicopters, see picture). These are often used on PTO-powered agricultural equipment, since the axial PTO shaft is at odds with the usual need for the driven shaft, which is either vertical (as with rotary mowers), or horizontally extending from one side of the implement to another (as with manure spreaders, flail mowers, and forage wagons). More complex equipment, such as silage choppers and snowblowers, have drives with outputs in more than one direction.
The gearbox in a wind turbine converts the slow, high-torque rotation of the turbine into much faster rotation of the electrical generator. These are much larger and more complicated than the PTO gearboxes in farm equipment. They weigh several tons and typically contain three stages to achieve an overall gear ratio from 40:1 to over 100:1, depending on the size of the turbine. (For aerodynamic and structural reasons, larger turbines have to turn more slowly, but the generators all have to rotate at similar speeds of several thousand rpm.) The first stage of the gearbox is usually a planetary gear, for compactness, and to distribute the enormous torque of the turbine over more teeth of the low-speed shaft.[4] Durability of these gearboxes has been a serious problem for a long time.[5] Regardless of where they are used, these simple transmissions all share an important feature: the gear ratio cannot be changed during use. It is fixed at the time the transmission is constructed. For transmission types that overcome this issue, see Continuously Variable Transmission, also known as CVT.
Multi-ratio systems Many applications require the availability of multiple gear ratios. Often, this is to ease the starting and stopping of a mechanical system, though another important need is that of maintaining good fuel efficiency.
Automotive basics
Tractor transmission with 16 forward and 8 backward gears
The need for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. Engines typically operate over a range of 600 to about 7000 revolutions per minute (though this varies, and is typically less for diesel engines), while the car's wheels rotate between 0 rpm and around 1800 rpm.
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Furthermore, the engine provides its highest torque and power outputs unevenly across the rev range resulting in a torque band and a power band. Often the greatest torque is required when the vehicle is moving from rest or traveling slowly, while maximum power is needed at high speed. Therefore, a system that transforms the engine's output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits, is required. Transmissions perform this transformation. The dynamics of a car vary with speed: at low speeds, acceleration is limited by the inertia of vehicular gross mass; while at cruising or maximum speeds wind resistance is the dominant barrier. In the former torque is required to overcome inertia, in the latter power is needed to keep the car from being slowed down by wind resistance. Many transmissions and gears used in automotive and truck applications are contained in a cast iron case, though more frequently aluminium is used for lower weight especially in cars. There are usually three shafts: a mainshaft, a countershaft, and an idler shaft.
A diagram comparing the power and torque bands of a "torquey" engine versus a "peaky" one
The mainshaft extends outside the case in both directions: the input shaft towards the engine, and the output shaft towards the rear axle (on rear wheel drive cars- front wheel drives generally have the engine and transmission mounted transversely, the differential being part of the transmission assembly.) The shaft is suspended by the main bearings, and is split towards the input end. At the point of the split, a pilot bearing holds the shafts together. The gears and clutches ride on the mainshaft, the gears being free to turn relative to the mainshaft except when engaged by the clutches. Types of automobile transmissions include manual, automatic or semi-automatic transmission.
Manual Manual transmission come in two basic types: • a simple but rugged sliding-mesh or unsynchronized / non-synchronous system, where straight-cut spur gear sets are spinning freely, and must be synchronized by the operator matching engine revs to road speed, to avoid noisy and damaging "gear clash", • and the now common constant-mesh gearboxes which can include non-synchronised, or synchronized / synchromesh systems, where diagonal cut helical (and sometimes double-helical) gear sets are constantly "meshed" together, and a dog clutch is used for changing gears. On synchromesh boxes, friction cones or "synchro-rings" are used in addition to the dog clutch. The former type is commonly found in many forms of racing cars, older heavy-duty trucks, and some agricultural equipment. Manual transmissions are the most common type outside North America and Australia. They are cheaper, lighter, usually give better performance, and fuel efficiency (although automatic transmissions with torque converter lockup and advanced electronic controls can provide similar results). It is customary for new drivers to learn, and be tested, on a car with a manual gear change. In Malaysia and Denmark all cars used for testing (and because of that, virtually all those used for instruction as well) have a manual transmission. In Japan, the Philippines, Germany, Poland, Italy,
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Israel, the Netherlands, Belgium, New Zealand, Austria, Bulgaria, the UK,[6] [7] Ireland,[7] Sweden, Estonia, France, Spain, Switzerland, the Australian states of Victoria, Western Australia and Queensland, Finland and Lithuania, a test pass using an automatic car does not entitle the driver to use a manual car on the public road; a test with a manual car is required. Manual transmissions are much more common than automatic transmissions in Asia, Africa, South America and Europe. Many manual transmissions include both synchronized and unsynchronized gearing; it is not uncommon for the first/reverse gear to lack synchros. Those gears are meant to be shifted into only when the vehicle is stopped. Some manual transmissions have an extremely low ratio for first gear, which is referred to as a "creeper gear" or "granny gear". Such gears are usually not synchronized. This feature is common on pickup trucks tailored to trailer-towing, farming, or construction-site work. During normal on-road use, the truck is usually driven without using the creeper gear at all, and second gear is used from a standing start.
Non-synchronous There are commercial applications engineered with designs taking into account that the gear shifting will be done by an experienced operator. They are a manual transmission, but are known as non-synchronized transmissions. Dependent on country of operation, many local, regional, and national laws govern the operation of these types of vehicles (see Commercial Driver's License). This class may include commercial, military, agricultural, or engineering vehicles. Some of these may use combinations of types for multi-purpose functions. An example would be a power take-off (PTO) gear. The non-synchronous transmission type requires an understanding of gear range, torque, engine power, and multi-functional clutch and shifter functions. Also see Double-clutching, and Clutch-brake sections of the main article.
Automatic Most modern North American and Australian and many larger, high specification European and Japanese cars have an automatic transmission that will select an appropriate gear ratio without any operator intervention. They primarily use hydraulics to select gears, depending on pressure exerted by fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a fluid flywheel, or torque converter is placed in between the engine and transmission. It is possible for the driver to control the number of gears in use or select reverse, though precise control of which gear is in use may or may not be possible.
Epicyclic gearing or planetary gearing as used in an automatic transmission.
Automatic transmissions are easy to use. However, in the past, automatic transmissions of this type have had a number of problems; they were complex and expensive, sometimes had reliability problems (which sometimes caused more expenses in repair), have often been less fuel-efficient than their manual counterparts (due to "slippage" in the torque converter), and their shift time was slower than a manual making them uncompetitive for racing. With the advancement of modern automatic transmissions this has changed. Attempts to improve the fuel efficiency of automatic transmissions include the use of torque converters which lock up beyond a certain speed, or in the higher gear ratios, eliminating power loss, and overdrive gears which automatically actuate above certain speeds; in older transmissions both technologies could sometimes become intrusive, when conditions are such that they repeatedly cut in and out as speed and such load factors as grade or wind vary slightly. Current computerized transmissions possess very complex programming to both maximize fuel efficiency and eliminate any intrusiveness, and we are at a point in technological advancement where automatics are beginning to outperform manuals in both performance and efficiency. This is due to electronic advances however,
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rather than mechanical ones. For certain applications, the slippage inherent in automatic transmissions can be advantageous; for instance, in drag racing, the automatic transmission allows the car to be stopped with the engine at a high rpm (the "stall speed") to allow for a very quick launch when the brakes are released; in fact, a common modification is to increase the stall speed of the transmission. This is even more advantageous for turbocharged engines, where the turbocharger needs to be kept spinning at high rpm by a large flow of exhaust in order to keep the boost pressure up and eliminate the turbo lag that occurs when the engine is idling and the throttle is suddenly opened.
Semi-automatic The creation of computer control also allowed for a sort of cross-breed transmission where the car handles manipulation of the clutch automatically, but the driver can still select the gear manually if desired. This is sometimes called a "clutchless manual," or "automated manual" transmission. Many of these transmissions allow the driver to give full control to the computer. They are generally designed using manual transmission "internals", and when used in passenger cars, have synchromesh operated helical constant mesh gear sets. Specific type of this transmission includes: Easytronic, and Geartronic. A "dual-clutch" transmission uses two sets of internals which are alternately used, each with its own clutch, so that only the clutches are used during the actual "gearchange". Specific type of this transmission includes: Direct-Shift Gearbox. There are also sequential transmissions which use the rotation of a drum to switch gears.[8]
Bicycle gearing Bicycles usually have a system for selecting different gear ratios. There are two main types: derailleur gears and hub gears. The derailleur type is the most common, and the most visible, using sprocket gears. Typically there are several gears available on the rear sprocket assembly, attached to the rear wheel. A few more sprockets are usually added to the front assembly as well. Multiplying the number of sprocket gears in front by the number to the rear gives the number of gear ratios, often called "speeds". Hub gears use epicyclic gearing and are enclosed within the axle of the rear wheel. Because of the small space, they typically offer fewer different speeds, although at least one has reached 14 gear ratios and Fallbrook Technologies manufactures a transmission with technically infinite ratios.[9]
Shimano XT rear derailleur on a mountain bike
Causes for failure of bicycle gearing include: worn teeth, damage caused by a faulty chain, damage due to thermal expansion, broken teeth due to excessive pedaling force, interference by foreign objects, and loss of lubrication due to negligence.
Uncommon types Dual clutch transmission This arrangement is also sometimes known as a direct shift gearbox or powershift gearbox. It seeks to combine the advantages of a conventional manual shift with the qualities of a modern automatic transmission by providing different clutches for odd and even speed selector gears. When changing gear, the engine torque is transferred from one gear to the other continuously, so providing gentle, smooth gear changes without either losing power or jerking the vehicle. Gear selection may be manual, automatic (depending on throttle/speed sensors), or a 'sports' version
Transmission (mechanics) combining both options.
Continuously variable The Continuously Variable Transmission (CVT) is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios. The CVT should not be confused with the Infinitely Variable Transmission (IVT) (See below). The other mechanical transmissions described above only allow a few different gear ratios to be selected, but this type of transmission essentially has an infinite number of ratios available within a finite range. The CVT allows the relationship between the speed of the engine and the speed of the wheels to be selected within a continuous range. This can provide even better fuel economy if the engine is constantly running at a single speed. The transmission is in theory capable of a better user experience, without the rise and fall in speed of an engine, and the jerk felt when poorly changing gears.
Infinitely variable The IVT is a specific type of CVT that has an infinite range of input/output ratios in addition to its infinite number of possible ratios; this qualification for the IVT implies that its range of ratios includes a zero output/input ratio that can be continuously approached from a defined 'higher' ratio. A zero output implies an infinite input, which can be continuously approached from a given finite input value with an IVT. [Note: so-called 'low' gears are a reference to low ratios of output/input, which have high input/output ratios that are taken to the extreme with IVTs, resulting in a 'neutral', or non-driving 'low' gear limit.] Most (if not all) IVTs result from the combination of a CVT with an epicyclic gear system (which is also known as a planetary gear system) that facilitates the subtraction of one speed from another speed within the set of input and planetary gear rotations. This subtraction only needs to result in a continuous range of values that includes a zero output; the maximum output/input ratio can be arbitrarily chosen from infinite practical possibilities through selection of extraneous input or output gear, pulley or sprocket sizes without affecting the zero output or the continuity of the whole system. Importantly, the IVT is distinguished as being 'infinite' in its ratio of high gear to low gear within its range; high gear is infinite times higher than low gear. The IVT is always engaged, even during its zero output adjustment. The term 'infinitely variable transmission' does not imply reverse direction, disengagement, automatic operation, or any other quality except ratio selectability within a continuous range of input/output ratios from a defined minimum to an undefined, 'infinite' maximum. This means continuous range from a defined output/input to zero output/input ratio.
Electric variable The Electric Variable Transmission (EVT) is a transmission that achieves CVT action and in addition can use separate power inputs to produce one output. An EVT is usually designed around an epicyclic differential gear system (also known as a planetary gear system). The epicyclic gear acts as a differential, performing a "power-split" function; a portion of the mechanical power is carried directly through the gear set (the "mechanical path"). The rest of the power is converted to and from electrical energy by electric motor-generators (the "electrical path"). Hence, the EVT is a class of Power Split Transmission (PST). Many EVTs are linked to batteries or other electrical energy storage devices. This enables them to store or draw electrical power for better operation under various conditions. The pair of motor/generators forms an Electric Transmission in its own right, but at a lower capacity, than the EVT it is contained within. Generally the Electric Transmission capacity within the EVT is a quarter to a half of the capacity
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Transmission (mechanics) of the EVT. An EVT is often preferable to a pure electrical transmission because the mechanical transmission is cheaper, more compact, and more efficient than the electrical path. The EVT linked to a battery is the essential method for transmitting power in some hybrid vehicles, enabling an Internal Combustion Engine (ICE) to be used in conjunction with motor/generators for vehicle propulsion. Vehicle speed is controlled primarily by adjusting the amount of power flowing through the electrical as opposed to the mechanical path. The EVT may be used to generate electrical power for storage in a battery, especially through 'regenerative braking' during deceleration. Various configurations of power generation, usage and balance can be implemented with an EVT, enabling great flexibility in propelling hybrid vehicles. The Toyota single mode hybrid and General Motor 2 Mode hybrid are production systems that use EVTs. The Toyota system is in the Prius, Highlander, and Lexus RX400h and GS450h models. The GM system is used in the Allison Bus hybrid powertrains and the Tahoe and Yukon models. The Toyota system uses one power-split epicyclic differential gearing system over all driving conditions and is sized with an electrical path rated at approximately half the capacity of the EVT. The GM system uses two different EVT ranges: one designed for lower speeds with greater mechanical advantage, and one designed for higher speeds. The electrical path is rated at approximately a quarter of the capacity of the EVT. Other arrangements are possible and applications of EVTs are growing rapidly in number and variety. EVTs are capable of continuously modulating output/input speed ratios like mechanical CVTs, but offer the distinct difference and benefit of being able to also apportion power from two different sources to one output.
Hydrostatic See also Continuously variable transmission > Hydrostatic CVTs Hydrostatic transmissions transmit all power hydraulically, using the components of hydraulic machinery. Hydrostatic transmissions do not make use of the hydrodynamic forces of the fluid flow. There is no solid coupling of the input and output. The transmission input drive is a central hydraulic pump and final drive unit(s) is/are a hydraulic motor, or hydraulic cylinder (see:swashplate). Both components can be placed physically far apart on the machine, being connected only by flexible hoses. Hydrostatic drive systems are used on excavators, lawn tractors, forklifts, winch drive systems, heavy lift equipment, agricultural machinery, earth-moving equipment, etc. An arrangement for motor-vehicle transmission [10] was probably used on the Ferguson F-1 P99 racing car in about 1961. The Human Friendly Transmission of the Honda DN-01 is hydrostatic.
Hydrodynamic If the hydraulic pump and/or hydraulic motor make use of the hydrodynamic effects of the fluid flow, i.e. pressure due to a change in the fluid's momentum as it flows through vanes in a turbine. The pump and motor usually consist of rotating vanes without seals and are typically placed in close proximity. The transmission ratio can be made to vary by means of additional rotating vanes, an effect similar to varying the pitch of an airplane propeller. The torque converter in most automotive automatic transmissions is, in itself, a hydrodynamic transmission. It was possible to drive the Dynaflow transmission without shifting the mechanical gears. Hydrodynamic transmissions are used in many passenger rail vehicles. In this application the advantage of smooth power delivery may outweigh the reduced efficiency caused by turbulence energy losses in the fluid.
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Electric Electric transmissions convert the mechanical power of the engine(s) to electricity with electric generators and convert it back to mechanical power with electric motors. Electrical or electronic adjustable-speed drive control systems are used to control the speed and torque of the motors. If the generators are driven by turbines, such arrangements are called turbo-electric. Likewise installations powered by diesel-engines are called diesel-electric. Diesel-electric arrangements are used on many railway locomotives, ships, large mining trucks, and some bulldozers.
Virtual transmission Virtual Transmission allows for the same traction motor to be both a low-speed high torque and high-speed electric motor, using the winding/software that runs on the new electric motors.[11] This virtual transmission will require less complex engineering, and less weight. The alternator and starter for the Chevrolet Volt can be combined into a single armature, smaller and lighter than each alternator and starter individually.
References [1] http:/ / www. merriam-webster. com/ dictionary/ transmission Merriam-Webster definition of transmission [2] J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York. [3] B. Paul, 1979, Kinematics and Dynamics of Planar Machinery, Prentice Hall. [4] Stiesdal, Henrik (August 1999), The wind turbine: Components and operation (http:/ / www. windmission. dk/ workshop/ BonusTurbine. pdf), , retrieved 2009-10-06. [5] Musial, W.; Butterfield, S.; McNiff, B. (May 2007), National Renewable Energy Laboratory, http:/ / www. nrel. gov/ wind/ pdfs/ 41548. pdf. [6] Practical Driving Test FAQs (http:/ / www. dvtani. gov. uk/ practicaldrivingtest/ carfaqs. asp#15) [7] Graduated Licensing: Is it what it's meant to be? (http:/ / www. af1. ca/ gradlicensing. htm) [8] (http:/ / auto. howstuffworks. com/ sequential-gearbox. htm) Howstuffworks.com [9] Rohloff 14-speed hub (http:/ / www. rohloff. de/ en/ products/ index. html) [10] http:/ / pigeonsnest. co. uk/ stuff/ trilink/ trilink. html [11] http:/ / www. choruscars. com/ tech_summary. shtml
External links • Eco-friendly transmission (http://deseretnews.com/dn/view/1,1249,635179379,00.html) • How Manual Transmissions Work (http://auto.howstuffworks.com/transmission.htm) • The Transmission Bible (http://www.carbibles.com/transmission_bible.html)
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Treadle
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Treadle A treadle [from OE tredan = to tread] is a part of a machine which is operated by the foot to produce reciprocating or rotary motion in a machine such as a weaving loom (reciprocating) or grinder (rotary). Treadles can also be used to power water pumps (treadle pump)
Railways On a railway, a treadle or treatle is a device that detects the passing of a train, a bit like a track circuit and might be used to put a signal to 'stop'. Treadles are also used to start the sequence of automatic level crossings.
A sheep or dog treadle
Sewing machines Many of the early sewing machines were operated by a treadle mechanism linked to the machine by a leather belt.
Tribology Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is a branch of mechanical engineering.
Fundamentals The tribological interactions of a solid surface's exposed face with interfacing materials and environment may result in loss of material from the surface. The process leading to loss of material is known as "wear". Major types of wear include abrasion, friction (adhesion and cohesion), erosion, and corrosion. Wear can be minimized by modifying the surface properties of solids by one or more of "surface engineering" processes (also called surface finishing) or by use of lubricants (for frictional or adhesive wear). Estimated direct and consequential annual loss to industries in the USA due to wear is approximately 1-2% of GDP. (Heinz, 1987). Engineered surfaces extend the working life of both original and recycled and resurfaced equipments, thus saving large sums of money and leading to conservation of material, energy and the environment. Methodologies to minimize wear include systematic approaches to diagnose the wear and to prescribe appropriate solutions. Important methods include: • Terotechnology, where multidisciplinary engineering and management techniques are used to protect equipment and machinery from degradation (Peter Jost, 1972) • Horst Czichos's systems approach, where appropriate material is selected by checking properties against tribological requirements under operating environment (H. Czichos,1978) • Asset Management by Material Prognosis - a concept similar to terotechnology which has been introduced by the US Military (DARPA) for upkeep of equipment in good health and start-ready condition for 24 hours. Good health monitoring systems combined with appropriate remedies at maintenance and repair stages have led to improved performance, reliability and extended life cycle of the assets, such as advanced military hardware and civil aircraft. In recent years, micro- and nanotribology have been gaining ground. Frictional interactions in microscopically small components are becoming increasingly important for the development of new products in electronics, life sciences,
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chemistry, sensors and by extension for all modern technology.
Friction regimes Friction regimes for sliding lubricated surfaces have been broadly categorized into: 1. Solid/boundary friction 2. Fluid friction 3. Mixed friction on the basis of the “Stribeck curve”. These curves clearly show the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions. Stribeck and others systematically studied the variation of friction between two liquid lubricated surfaces as a function of a dimensionless lubrication parameter ηN/P, where η is the dynamic viscosity, N the speed (e.g. revolutions per minute of a bearing) and P the load projected on to the geometrical surface.[1]
A typical Stribeck curve obtained by Martens
The “Stribeck-curve” has been a classic teaching element in tribology classes.[2]
History Historically, Leonardo da Vinci (1452–1519) was the first to enunciate two laws of friction.[3] According to da Vinci, the frictional resistance was the same for two different objects of the same weight but making contacts over different widths and lengths. He also observed that the force needed to overcome friction is doubled when the weight is doubled. Similar observations were made by Charles-Augustin de Coulomb (1736–1806). The first reliable test on frictional wear was carried out by Charles Hatchett (1760–1820) using a simple Tribological experiments suggested by Leonardo da Vinci reciprocating machine to evaluate wear on gold coins. He found that compared to self-mated coins, coins with grits between them wore at a faster rate. The deciphering of da Vinci's work took several centuries, before the development of this branch of science, today called "tribology". The "Stribeck curve" or "Stribeck–Hersey curve" (named after Richard Stribeck[4] [5] [6] and Mayo D. Hersey[7] [8] ), used to categorize the friction properties between two surfaces, was developed in the first half of the 20th century. The research of Professor Richard Stribeck (1861–1950) was performed in Berlin at the Royal Prussian Technical Testing Institute (MPA, now BAM). Similar work was previously performed around 1885 by Prof. Adolf Martens (1850–1914) at the same Institute and in the mid 1870s by Dr. Robert H. Thurston [9] [10] at the Stevens Institute of Technology in the U.S. Prof. Dr. Thurston was therefore close to establishing the “Stribeck curve”, but he presented no “Stribeck”-like graphs, as he evidently did not fully believe in the relevance of this dependency. Since that time the “Stribeck-curve” has been a classic teaching element in tribology classes.[2] The graphs of friction force reported by Stribeck stem from a carefully conducted, wide-ranging series of experiments on journal bearings. Stribeck systematically studied the variation of friction between two liquid lubricated surfaces.[1] His results were presented on 5 December 1901 during a public session of the railway society and published on 6 September 1902. They clearly showed the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions. Stribeck studied different bearing materials and aspect
Tribology ratios D/L from 1:1 to 1:2. The maximum sliding speed was 4 m/s and the geometrical contact pressure was limited to 5 MPa. (These operating conditions were related to railway wagon journal bearings.) The reason why the form of the friction curve for liquid lubricated surfaces was later attributed to Stribeck, although both Thurston and Martens achieved their results considerably earlier, (Martens even in the same organization roughly 15 years before), may be because Stribeck published in the most important technical journal in Germany at that time, Zeitschrift des Vereins Deutscher Ingenieure (VDI, Journal of German Mechanical Engineers). Martens published his results “only” in the official journal of the Royal Prussian Technical Testing Institute, which has now become BAM. The VDI journal, as one of the most important journals for engineers, provided wide access to these data and later colleagues rationalized the results into the three classical friction regimes. Thurston however, did not have the experimental means to record a continuous graph of the coefficient of friction but only measured the friction at discrete points; this may be the reason why the minimum in the coefficient of friction was not discovered by him. Instead, Thurston's data did not indicate such a pronounced minimum of friction for a liquid lubricated journal bearing as was demonstrated by the graphs of Martens and Stribeck. The term tribology became widely used following The Jost Report in 1966, in which huge sums of money were reported to have been lost in the UK annually due to the consequences of friction, wear and corrosion. As a result several national centres for tribology were created in the UK. Since then the term has diffused into the international engineering field and many specialists now claim to be tribologists. There are now numerous national and international societies, such as the Society for Tribologists and Lubrication Engineers (STLE [1]) in the USA and the Institution of Mechanical Engineers' Tribology Group (IMechE Tribology Group [11]) in the UK or the German Society for Tribology (Gesellschaft für Tribologie, www.gft-ev.de). Most technical universities have a group working on tribology, often as part of their mechanical engineering departments. The limitations in tribological interactions are however no longer mainly determined by mechanical designs, but rather by material limitations so the discipline of tribology now counts at least as many materials engineers, physicists and chemists as it does mechanical engineers.
Etymology The word 'tribology' derives from the Greek root τριβ- of the verb τρίβω - tribo "Ι rub", and the suffix -logy.
Applications The study of tribology is commonly applied in bearing design but extends into almost all other aspects of modern technology, even to such unlikely areas as hair conditioners and cosmetics such as lipstick, powders and lipgloss. Any product where one material slides or rubs over another is affected by complex tribological interactions, whether lubricated like hip implants and other artificial prostheses, or unlubricated as in high temperature sliding wear in which conventional lubricants cannot be used but in which the formation of compacted oxide layer glazes have been observed to protect against wear. Tribology plays an important role in manufacturing. In metal-forming operations, friction increases tool wear and the power required to work a piece. This results in increased costs due to more frequent tool replacement, loss of tolerance as tool dimensions shift, and greater forces required to shape a piece. A layer of lubricant which eliminates surface contact virtually eliminates tool wear and decreases needed power by one third.
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References [1] R. Stribeck, Die wesentlichen Eigenschaften der Gleit- und Rollenlager (The basic properties of sliding and rolling bearings), Zeitschrift des Vereins Deutscher Ingenieure, 2002, Nr. 36, Band 46, p. 1341-1348, p. 1432-1438 and 1463-1470 [2] H. Czichos, K.-H. Habig, Tribologie-Handbuch (Tribology handbook), Vieweg Verlag, Wiesbaden, 2nd edition, 2003, ISBN 3-528-16354-2 [3] Palaci, Ismaël (2007), Atomic Force Microscopy Studies of Nanotribology and Nanomechanics. p. 52. (http:/ / biblion. epfl. ch/ EPFL/ theses/ 2007/ 3905/ EPFL_TH3905. pdf) [4] Stribeck, R. (1901), Kugellager für beliebige Belastungen (Ball Bearings for any Stress), Zeitschrift des Vereins Deutscher Ingenieure 45. [5] Stribeck, R. (1902), Die wesentlichen Eigenschaften der Gleit- und Rollenlager (Characteristics of Plain and Roller Bearings), Zeit. des VDI 46. [6] Jacobson, Bo (2003), The Stribeck memorial lecture. (http:/ / www. sciencedirect. com/ science?_ob=ArticleURL& _udi=B6V57-497HBKM-4& _user=10& _coverDate=11/ 30/ 2003& _rdoc=1& _fmt=high& _orig=search& _sort=d& _docanchor=& view=c& _searchStrId=1433619808& _rerunOrigin=google& _acct=C000050221& _version=1& _urlVersion=0& _userid=10& md5=634f43c7420d0709195dbd4ac5e8a719) [7] Hersey, M. D. (1914), The Laws of Lubrication of Horizontal Journal Bearings, J. Wash. Acad. Sci., 4, 542-552. [8] Biography of Mayo D. Hersey (http:/ / www. nndb. com/ people/ 221/ 000169711/ ) [9] Robert H. Thurston, Friction and lubrication - Determination of the laws and co-ëfficients of friction by new methods and with new apparatus, Trübner and Co., Ludgate Hill, London, 1879 [10] Robert H. Thurston, A treatise on friction and lost work in machinery and millwork, John Wiley&Sons, New York, 1894, fifth edition [11] http:/ / www. imeche. org. uk/ tribology/ index. asp
Bibliography • Surface Wear – Analysis, Treatment, and Prevention: R. Chattopadhyay, published by ASM-International, Materials Park, OH, 2001, ISBN 0-87170-702-0. • Advanced Thermally Assisted Surface Engineering Processes: Ramnarayan Chattopadhyay, Kluwer Academic Publishers, MA (now Springer, NY), 2004. • DeGarmo, E. Paul, J T. Black, and Ronald A. Kohser. Materials and Processes in Manufacturing. Upper Saddle River, New Jersey: Prentice Hall, 1997. ISBN 0-02-328621-0 • Zum Gahr, Karl-Heinz (1987). Microstructure and Wear of Materials. Tribology Series, 10. Elsevier. ISBN 0444427546. • Heshmat, Hooshang. Tribology of Interface Layers. CRC Press. ISBN 978-0824758325. • Litt, Fred. "Starting from Scratch: Tribology Basics Volume I" (http://www.stle.org/assets/document/ Starting_from_Scratch.pdf). STLE. Retrieved 2010-06-10.
External links • Tribology NL (http://www.tribology-abc.com/default.htm) an overview of tribology topics targeted at mechanical engineers. • IET Tribology Network (http://kn.theiet.org/communities/tribology/index.cfm?origin-wiki)
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Trunnion
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Trunnion A trunnion (from Old French "trognon", trunk[1] ) is a cylindrical protrusion used as a mounting and/or pivoting point. In a cannon, the trunnions are two projections cast just forward of the centre of mass of the cannon and fixed to a two-wheeled movable gun carriage.[2] As they allowed the muzzle to be raised and lowered easily, the integral casting of trunnions is seen by military historians as one of the most important advances in early field artillery.[3]
The trunnions are the protrusions from the side of the barrel that rest on the carriage.
Medieval history With the creation of larger and more powerful siege guns in the early 1400s, a new way of mounting them had to be specially designed. Stouter gun carriages were created with reinforced wheels, axles, and “trails” which extended behind the gun. Guns would be up to eight feet in length and shoot iron projectiles weighing from twenty-five to fifty pounds. These wrought iron balls when discharged were comparable in range and accuracy with stone-firing bombards.[4]
15th Century depiction of a cannon with trunnions
Trunnions were mounted near the center of mass to allow the barrel to be elevated to any desired angle, without having to dismount it from the carriage upon which it rested. Some guns had a second set of trunnions placed several feet back from the first pair, which could be used to allow for easier transportation.[5] The gun would recoil causing the carriage to move backwards several feet but men or a team of horses could put it back into firing position. It became easier to rapidly transport these large siege guns, maneuver them from transportation mode to firing position, and could go wherever a team of men or horses could pull them.[6]
Initial significance Due to its capabilities, the French and Burgundy designed siege gun, equipped with its trunnions, required little significant modification from around 1465 to the 1840s. King Charles VIII and the French army used this new gun in the 1494 invasion of Italy. Although deemed masters of war and artillery at that time, Italians had not anticipated the innovations in French siege weaponry. Prior to this, field artillery guns were huge, large-caliber bombards: superguns that, along with enormous stones or other projectiles, were dragged from destination to destination. These behemoths could only be used effectively in sieges, and more often than not provided just a psychological effect on the battlefield; owning these giant mortars did not
Trunnion guarantee any army a victory. The French saw the limitations of these massive weapons and focused their efforts on improving their smaller and lighter guns, which used smaller, more manageable projectiles combined with larger amounts of gunpowder. Equipping them with trunnions was key for two reasons: teams of horses could now move these cannons fast enough to keep up with their armies, without having to stop and dismount them from their carriages to achieve the proper range before firing. Francesco Guicciardini, an Italian historian and statesman, sometimes referred to as the “Father of History,” wrote that the cannons were placed against town walls so quickly, spaced together so closely and shot so rapidly and with such force that the amount of damage inflicted went from a matter of days (as with bombards) to a matter of hours.[4] For the first time in history, as seen in the 1512 battle of Ravenna and the 1515 Battle of Marignano, artillery weaponry played a very decisive part in the victory of the invading army over the city under siege.[7] Cities that had proudly withstood sieges for up to seven years fell swiftly with the advent of these new weapons. Defensive tactics and fortifications had to be altered since these new weapons could be transported so speedily and aimed with much more accuracy at strategic locations. Two such changes were the additions of a ditch and low, sloping ramparts of packed earth that would surround the city and absorb the impact of the cannon balls and the replacement of round watchtowers with angular bastions. These towers would be deemed trace Italienne.[8] Whoever could afford these new weapons had the tactical advantage over their neighbors and smaller sovereignties, which could not incorporate them into their army. Smaller states, such as the principalities of Italy, began to conglomerate. Preexisting stronger entities, such as France or the Hapsburg emperors, were able to expand their territories and maintain tighter control. With the threat of their land and castles being seized, the nobility began to pay their taxes and more closely follow their ruler’s mandates. With siege guns mounted on trunnions, stronger and larger states were formed, but because of this, struggles between neighboring governments with consolidated power began to ensue and would continue to plague Europe for the next few centuries.[6]
Usages In firearms • On firearms, the barrel is sometimes mounted in a trunnion, which in turn is mounted to the receiver. This usage is common for tubular or pressed metal frame guns, such as the AK-47, PPSh-41, Uzi, Sten, and others.
In vehicles • In older cars, the trunnion is part of the suspension and either allows free movement of the rear wheel hub in relation to the chassis[9] or allows the front wheel hub to rotate with the steering. On many cars (such as those made by the Triumph Motor Company[10] ) the trunnion is machined from a brass or bronze casting and is prone to failure if not greased properly.[11] American Motors used a molded rubber "Clevebloc" bushings on the upper trunnion to seal out dirt and retain silicone lubricant for the life of the car.[12] • In aviation, the term refers to the structural component that attaches the undercarriage or landing gear to the airframe.[13] For aircraft equipped with retractable landing gear, the trunnion is pivoted to permit rotation of the entire gear assembly.[14] • In heavy equipment, such as a bulldozer, the term refers to the protrusions on the vehicle frame on which the blade frame attaches and hinges allowing vertical movement. • In Chevrolet GMC C/K pickup trucks, the term refers to the tailgate attachment points. Rather than using conventional tailgate hinges, trunnions are used to permit quick toolless removal and installation of the pickup tailgate. • In trailers [15], the term refers to the type of suspension used on a two axle configuration with eight tires, i.e. four tires per axle. This type of trailer suspension is commonly used in the western United States and allows 60000 pounds (27000 kg) to be loaded on that axle group.
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Trunnion • In the valve train of a pushrod engine, the term refers to the fixed axle that acts as a pivot point for the valve rocker.
In other technology • In steam engines, they are supporting gudgeon pins on either side of an oscillating steam cylinder. They are usually tubular and convey steam. • On communication satellites, the antennas are usually mounted on a pair of trunnions to allow the beam pattern to be correctly pointed on the Earth from the geostationary orbit. • On stage lighting instruments, a trunnion is a bracket attached to both ends of a striplight that allows the striplight to be mounted on the floor. Sometimes trunnions are also equipped with casters to allow the striplight to be moved easily. • In woodworking, they are the assembly that holds a saw's arbor to the underside of the saw table. • In Waste Collection the trunnion is the bar on the front of a Dumpster that connects to the back of a garbage truck. • On the Space Shuttle, trunnion pins are affixed to the sides of payload items allowing them to be secured to receivers mounted on the sills of the payload bay. These receivers can be remotely commanded to secure and release selected items. Similar keel pins protrude from the nadir side of payload items, into matching holes in the bottom of the payload bay. • On hydraulic cylinders, a trunnion (either featuring external pins or internal pockets) can be an alternative body mounting type, as opposed to a flange or pin eye. • In steelmaking, on the Bessemer converter. There are trunnions on either side to be able to pour the molten steel out. • In surveying total stations and theodolites, the trunnion axis is the axis about which the telescope transits. It is parallel to the horizontal axis defined by the tubular spirit bubble. • In Dobsonian telescope designs. • In structural engineering, a type of Bascule bridge, with the road deck on one side of the trunnion, and the counterweight on the other. • In laboratory centrifuges, trunnions are used to pivot sample buckets in swinging-bucket rotors. • In nuclear power plants, when the steam generators are replaced, trunnions are used to upend them, to get them on the rail system, to shuttle them out of containment.
Trunnion bearings In avionics, these are self-contained concentric bearings that are designed to offer fluid movement in a critical area of the steering. The term is also used to describe the wheel that a rotating cylinder runs on. For example, a lapidary (stone-polishing) cylinder runs on a pair of rollers, similar to trunnions. The sugar industry uses rotating cylinders up to 22 feet (7 m) in diameter, 131 ft (40 m) long, and weighing around 1,000 tons. These rotate at around 30 revolutions per hour. They are supported on a pathring which runs on trunnions. Similar devices called rotary kilns are used in cement manufacturing. In mining, some refining plants utilise drum scrubbers in the process that are supported by a large trunnion and associated trunnion bearings at each end.
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Trunnion
References Inline [1] "trunnion - definition of trunnion by the Free Online Dictionary, Thesaurus and Encyclopedia" (http:/ / www. thefreedictionary. com/ trunnion). Thefreedictionary.com. . Retrieved 2010-08-23. [2] Duffy, Chris (1979) Siege Warfare: The Fortress in the Early Modern World 1494-1660. Routledge & Kegan Paul. ISBN 0-415-14649-6 [3] Keegan, John (1994). A History of Warfare. Vintage. ISBN 9780679730828 [4] Duffy, Chris (1979). Siege Warfare: The Fortress in the Early Modern World 1494-1660. Routledge & Kegan Paul. ISBN 0-415-14649-6 [5] Manucy, Albert (2008) Artillery Through the Ages. BiblioBazaar. ISBN: 0554395975 [6] McNeill, William H. (1982) The Pursuit of Power. University of Chicago Press. ISBN 0226561585 [7] Cipolla, Carlo M. (1965) Guns and Sails in the Early Phase of European Expansion 1400-1700. Collins Clear-Type Press, London. ISBN 0308600142 [8] Benedict, Phillip; Gutmann, Myran (2005) Early Modern Europe: From Crisis to Stability. Rosemont Publishing and Printing Corp. ISBN 0-87413-906-6 [9] Society of Automotive Engineers (1915). SAE transactions, Volume 10, Part 1 (http:/ / books. google. com/ books?id=rqnNAAAAMAAJ& pg=PA180& dq=Trunnion+ suspension& hl=en& ei=6hFzTJXkK4OglAf53uDPDw& sa=X& oi=book_result& ct=result& resnum=7& ved=0CE4Q6AEwBjgK#v=onepage& q=Trunnion suspension& f=false). p. 180. . Retrieved 23 August 2010. [10] Piggott, Bill; Clay, Simon (2003). Original Triumph TR4/4A/5/6: The Restorer's Guide (http:/ / books. google. com/ books?id=roAhcuSXL-sC& pg=PT88& dq=Trunnion+ front+ suspension& hl=en& ei=DhdzTMCRA4GdlgfF_symAQ& sa=X& oi=book_result& ct=result& resnum=3& ved=0CD0Q6AEwAg#v=onepage& q=Trunnion front suspension& f=false). MotorBooks International.. ISBN 9780760317389. . Retrieved 23 August 2010. [11] Piggott, Bill; Clay, Simon (2009). Collector's Originality Guide Triumph TR2 TR3 TR4 TR5 TR6 TR7 TR8 (http:/ / books. google. com/ books?id=ZVRq-KUY_bgC& pg=PA108& dq=Trunnion+ suspension& hl=en& ei=6hFzTJXkK4OglAf53uDPDw& sa=X& oi=book_result& ct=result& resnum=8& ved=0CFQQ6AEwBzgK#v=onepage& q=Trunnion suspension& f=false). MBI Publishing. p. 108. ISBN 9780760335765. . Retrieved 23 August 2010. [12] "American Motors" (http:/ / books. google. com/ books?id=m-06AAAAMAAJ& q=Trunnion+ suspension+ AMC& dq=Trunnion+ suspension+ AMC& hl=en& ei=lhRzTOaQB4O8lQfB6fTUCg& sa=X& oi=book_result& ct=result& resnum=4& ved=0CEsQ6AEwAw). Car Life 10: 57. 1963. . Retrieved 23 August 2010. [13] Lombardo, David A. (1993). Advanced Aircraft Systems. McGraw-Hill. p. 266. ISBN 9780070386037. [14] Currey, Norman S. (1988). Aircraft landing gear design: principles and practices (http:/ / books. google. com/ books?id=XMpdOeWeqq8C& pg=PA175& dq=Trunnion+ aircraft& hl=en& ei=ghtzTJXyC4GKlwfxkYWDAQ& sa=X& oi=book_result& ct=result& resnum=8& ved=0CFQQ6AEwBzgU#v=onepage& q=Trunnion aircraft& f=false). American Institute of Aeronautics & Astronautics. pp. 175–177. ISBN 9780930403416. . Retrieved 23 August 2010. [15] http:/ / www. murraytrailer. com/ images/ new/ Professional/ Professional_small. pdf
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Tuned mass damper
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Tuned mass damper A tuned mass damper, also known as an active mass damper (AMD) or harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure. They are frequently used in power transmission, automobiles, and buildings.
An animation showing the movement of a skyscraper versus the mass damper. The green indicates the hydraulic cylinders used to damp the motion of the skyscraper.
Principle Tuned mass dampers stabilize against violent motion caused by harmonic vibration. A tuned damper reduces the vibration of a system with a comparatively lightweight component so that the worst-case vibrations are less intense. Roughly speaking practical systems are tuned to either move the main mode away from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensive to damp directly. An example of the latter is a crankshaft torsional damper. Mass dampers are frequently implemented with a frictional or hydraulic component that turns mechanical kinetic energy into heat, like an automotive shock absorber. An electrical analogue is a LCR circuit. Given a motor with mass attached via motor mounts to the ground, the motor vibrates as it operates and the soft motor mounts act as a parallel spring and damper, and . The force on the motor mounts is
A schematic of a simple spring–mass–damper system used to demonstrate the tuned mass damper system.
. In order to reduce the maximum
force on the motor mounts as the motor operates over a range of speeds, a smaller mass, , is connected to a spring and a damper, and . is the effective force on the motor due to its operation.
by
Tuned mass damper
544 The graph shows the effect of a tuned mass damper on a simple spring–mass–damper system, excited by vibrations with an amplitude of one unit of force applied to the main mass, . An important measure of performance is the ratio of the force on the motor mounts to the force vibrating the motor, . This assumes that the system is
Response of the system excited by one unit of force, with (red) and without (blue) the 10% tuned mass. The peak response is reduced from 9 units down to 5.5 units. While the maximum response force is reduced, there are some operating frequencies for which the response force is increased.
linear, so if the force on the motor were to double, so would the force on the motor mounts. The blue line represents the baseline system, with a maximum response of 9 units of force at around 9 units of frequency. The red line shows the effect of adding a tuned mass of 10% of the baseline mass. It has a maximum response of 5.5, at a frequency of 7. As a side effect, it also has a second normal mode and will vibrate somewhat more than the baseline system at frequencies below about 6 and above about 10.
The heights of the two peaks can be adjusted by changing the stiffness of the spring in the tuned mass damper. Changing the damping also changes the height of the peaks, in a complex fashion. The split between the two peaks can be changed by altering the mass of the damper ( ). The Bode plot is more complex, showing the phase and magnitude of the motion of each mass, for the two cases, relative to F1. In the plots at right, the black line shows the baseline response ( ). Now considering , the blue line shows the motion of the damping mass and the red line shows the motion of the primary mass. The amplitude plot shows that at low frequencies, the damping mass resonates much more than the primary mass. The phase plot shows that at low frequencies, the two masses are in phase. As the frequency increases moves out of phase with until at around 9.5 Hz it is 180° out of phase with , maximizing the damping effect by maximizing the amplitude of , this maximizes the energy dissipated into
and simultaneously pulls on the primary
mass in the same direction as the motor mounts.
A Bode plot of displacements in the system with (red) and without (blue) the 10% tuned mass.
Mass dampers in automobiles Motorsport The tuned mass damper was introduced as part of the suspension system by Renault, on its 2005 F1 car (the R25), at the 2005 Brazilian Grand Prix. It was deemed to be legal at first, and it was in use up to the 2006 German Grand Prix. At Hockenheim, the mass damper was deemed illegal by the FIA, because the mass was not rigidly attached to the chassis and, due to the influence it had on the pitch attitude of the car, which in turn significantly affected the gap under the car and hence the ground effects of the car, to be a movable aerodynamic device and hence as a consequence, to be illegally influencing the performance of the aerodynamics. The Stewards of the meeting deemed it legal, but the FIA appealed against that decision. Two weeks later, the FIA International Court of Appeal deemed the mass damper illegal.[1] [2]
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Production cars Tuned mass dampers are widely used in production cars, typically on the crankshaft pulley to control torsional vibration and bending modes of the crankshaft, on the driveline for gearwhine, and other noises. They are also used on the exhaust, on the body and on the suspension. Almost all cars will have one mass damper, some may have 10 or more.
Mass dampers in spacecraft One proposal to reduce vibration on NASA's Ares solid fuel booster is to use 16 tuned mass dampers as part of a design strategy to reduce peak loads from 6g to 0.25 g, the TMDs being responsible for the reduction from 1 g to 0.25 g, the rest being done by conventional vibration isolators between the upper stages and the booster.[3] [4]
Dampers in power transmission lines High-tension lines often have small barbell-shaped Stockbridge dampers hanging from the wires to reduce the high-frequency, low-amplitude oscillation termed flutter.[5] [6]
Stockbridge dampers on power lines.
Dampers in buildings and related structures Typically, the dampers are huge concrete blocks or steel bodies mounted in skyscrapers or other structures, and moved in opposition to the resonance frequency oscillations of the structure by means of springs, fluid or pendulums.
Sources of vibration and resonance Unwanted vibration may be caused by environmental forces acting on a structure, such as wind or earthquake, or by a seemingly innocuous vibration source causing resonance that may be destructive, unpleasant or simply inconvenient.
Location of Taipei 101's largest tuned mass damper.
Earthquakes The seismic waves caused by an earthquake will make buildings sway and oscillate in various ways depending on the frequency and direction of ground motion, and the height and construction of the building. Seismic activity can cause excessive oscillations of the building which may lead to structural failure. To enhance the building's seismic performance, a proper building design is performed engaging various seismic vibration control technologies.
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Tuned mass damper atop Taipei 101.
Mechanical human sources Masses of people walking up and down stairs at once, or great numbers of people stomping in unison, can cause serious problems in large structures like stadiums if those structures lack damping measures. Vibration caused by heavy industrial machinery, generators and diesel engines can also pose problems to structural integrity, especially if mounted on a steel structure or floor. Large ocean going vessels may employ tuned mass dampers to isolate the vessel from its engine vibration. Wind
Dampers on the Millennium Bridge in London. The white disk is not part of the damper.
The force of wind against tall buildings can cause the top of skyscrapers to move more than a meter. This motion can be in the form of swaying or twisting, and can cause the upper floors of such buildings to move. Certain angles of wind and aerodynamic properties of a building can accentuate the movement and cause motion sickness in people. Examples of buildings and structures with tuned mass dampers Canada • One Wall Centre in Vancouver — It employs tuned liquid column dampers, at the time of its installation, a unique form of tuned mass damper. China • Shanghai World Financial Center in Shanghai, China Germany • Berlin Television Tower (Fernsehturm) — tuned mass damper located in the spire. Ireland • Dublin Spire in Dublin, Ireland — This narrow slender structure was designed with a tuned mass damper to ensure aerodynamic stability during a wind storm.
Tuned mass damper Japan • Akashi-Kaikyō Bridge, between Honshu and Shikoku in Japan, currently the world's longest suspension bridge, uses pendulums within its suspension towers as tuned mass dampers. • Tokyo Sky Tree, vertically placed two units (total 100 tons) in the housing as atop. • Yokohama Landmark Tower Russia • Sakhalin-I — An offshore drilling platform Taiwan • Taipei 101 skyscraper — Contains one of the world's largest tuned mass dampers, at 730 tons.[7] United Arab Emirates • Burj al-Arab in Dubai — 11 tuned mass dampers. United States of America • Bally's to Bellagio, Bally's to Caesars Palace, and Treasure Island to The Venetian Pedestrian Bridges in Las Vegas, NV • Bloomberg Tower/731 Lexington in New York City, NY • Citigroup Center in New York City, NY — Designed by William LeMessurier and completed in 1977, it was one of the first skyscrapers to use a tuned mass damper to reduce sway. Uses a concrete version. • Comcast Center in Philadelphia, PA — Contains the largest Tuned Liquid Column Damper (TLCD) in the world at 1,300 tons.[8] • Grand Canyon Skywalk, AZ • John Hancock Tower in Boston, MA — A tuned mass damper was added to it after it was built. • One Rincon Hill South Tower , San Francisco, CA— First building in California to have a liquid tuned mass damper • Park Tower in Chicago, IL — The first building in the United States to be designed with a tuned mass damper from the outset. • Random House Tower Uses two liquid filled dampers in New York City, NY • Theme Building at Los Angeles International Airport Los Angeles, CA • Trump World Tower in New York City, NY United Kingdom • London Millennium Bridge — 'The Wobbly Bridge'
References [1] Bishop, Matt (2006). "The Long Interview: Flavio Briatore". F1 Racing (October): 66–76. [2] "FIA bans controversial damper system" (http:/ / www. pitpass. com/ fes_php/ pitpass_news_item. php?fes_art_id=28765). Pitpass.com. . Retrieved 2010-02-07. [3] "Ares I Thrust Oscillation meetings conclude with encouraging data, changes" (http:/ / www. nasaspaceflight. com/ 2008/ 12/ ares-i-thrust-oscillation-meetings-encouraging-allowance-for-changes/ ). NASASpaceFlight.com. 2008-12-09. . Retrieved 2010-02-07. [4] "Shock Absorber Plan Set for NASA's New Rocket" (http:/ / www. space. com/ news/ 080819-nasa-ares1-vibration-update. html). SPACE.com. 2008-08-19. . Retrieved 2010-02-07. [5] "On the hysteresis of wire cables in Stockbridge dampers" (http:/ / cat. inist. fr/ ?aModele=afficheN& cpsidt=13772262). Cat.inist.fr. . Retrieved 2010-02-07. [6] "Cable clingers - 27 October 2007" (http:/ / www. newscientist. com/ backpage. ns?id=mg19626273. 000). New Scientist. . Retrieved 2010-02-07.
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[7] Taipei 101's 730-Ton Tuned Mass Damper (http:/ / www. popularmechanics. com/ technology/ industry/ 1612252. html), Popular Mechanics, May 2005. [8] "Comcast Center" (http:/ / www. rwdi. com/ cms/ publications/ 84/ pp_comcast_center. pdf). . Retrieved 2010-02-07.
Turboexpander A turboexpander, also referred to as a turbo-expander or an expansion turbine, is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is often used to drive a compressor.[1] [2] [3] Because work is extracted from the expanding high pressure gas, the expansion is approximated by an isentropic process (i.e., a constant entropy process) and the low pressure exhaust gas from the turbine is at a very low temperature, sometimes as low as −90 °C or less. Figure 1: Schematic diagram of a turboexpander driving a compressor.
Turboexpanders are very widely used as sources of refrigeration in industrial processes such as the extraction of ethane and natural gas liquids (NGLs) from natural gas,[4] the liquefaction of gases (such as oxygen, nitrogen, helium, argon and krypton)[5] [6] and other low-temperature processes. Turboexpanders currently in operation range in size from about 750 W to about 7.5 MW (1 hp to about 10,000 hp).
Turboexpander
Applications Although turboexpanders are very commonly used in low-temperature processes, they are used in many other applications as well. This section discusses one of the low temperature processes as well as some of the other applications.
Extracting hydrocarbon liquids from natural gas Raw natural gas consists primarily of methane (CH4), the shortest and lightest hydrocarbon molecule, as well as various amounts of heavier hydrocarbon gases such as ethane (C2H6), propane (C3H8), normal butane (n-C4H10), isobutane (i-C4H10), pentanes and even higher molecular weight hydrocarbons. The raw gas also contains various amounts of acid gases such as carbon dioxide (CO2), hydrogen sulfide (H2S) and mercaptans such as methanethiol (CH3SH) and ethanethiol (C2H5SH). When processed into finished by-products (see Natural gas processing), these heavier hydrocarbons are collectively referred to as NGL (natural gas liquids). The extraction of the NGL often involves a turboexpander[7] and a Figure 2: A schematic diagram of a demethanizer extracting hydrocarbon liquids from low-temperature distillation column natural gas. (called a demethanizer) as shown in Figure 2. The inlet gas to the demethanizer is first cooled to about −51 °C in a heat exchanger (referred to as a cold box) which partially condenses the inlet gas. The resultant gas-liquid mixture is then separated into a gas stream and a liquid stream. The liquid stream from the gas-liquid separator flows through a valve and undergoes a throttling expansion from an absolute pressure of 62 bar to 21 bar (6.2 to 2.1 MPa), which is an enthalpic process (i.e., a constant enthalpy process) that results in lowering the temperature of the stream from about −51 °C to about −81 °C as the stream enters the demethanizer. The gas stream from the gas-liquid separator enters the turboexpander where it undergoes an isentropic expansion from an absolute pressure of 62 bar to 21 bar (6.2 to 2.1 MPa) that lowers the gas stream temperature from about −51 °C to about −91 °C as it enters the demethanizer to serve as distillation reflux. Liquid from the top tray of the demethanizer (at about −90 °C) is routed through the cold box where it is warmed to about 0 °C as it cools the inlet gas, and is then returned to the lower section of the demethanizer. Another liquid stream from the lower section of the demethanizer (at about 2 °C) is routed through the cold box and returned to the demethanizer at about 12 °C. In effect, the inlet gas provides the heat required to "reboil" the bottom of the demethanizer and the turboexpander removes the heat required to provide reflux in the top of the demethanizer.
549
Turboexpander The overhead gas product from the demethanizer at about −90 °C is processed natural gas that is of suitable quality for distribution to end-use consumers by pipeline. It is routed through the cold box where it is warmed as it cools the inlet gas. It is then compressed in the gas compressor which is driven by the turbo expander and further compressed in a second-stage gas compressor driven by an electric motor before entering the distribution pipeline. The bottom product from the demethanizer is also warmed in the cold box, as it cools the inlet gas, before it leaves the system as NGL.
Power generation Figure 3 depicts an electric power generation system that uses a heat source, a cooling medium (air, water or other), a circulating working fluid and a turboexpander. The system can accommodate a wide variety of heat sources such as: • Geothermal hot water • Exhaust gas from internal combustion engines burning a variety of fuels (natural gas, landfill gas, diesel oil, or fuel oil) • A variety of waste heat sources (in the form of either gas or liquid) Referring to Figure 3, the circulating working fluid (usually an organic compound such as R-134a) is pumped to a high pressure and then vaporized in the evaporator by heat exchange with the available heat source. The resulting Figure 3: Schematic diagram of power generation system using a turboexpander. high-pressure vapor flows to the turboexpander where it undergoes an isentropic expansion and exits as a vapor-liquid mixture which is then condensed into a liquid by heat exchange with the available cooling medium. The condensed liquid is pumped back to the evaporator to complete the cycle. The system in Figure 3 is a Rankine cycle as is used in fossil fuel power plants where water is the working fluid and the heat source is derived from the combustion of natural gas, fuel oil or coal used to generate high-pressure steam. The high-pressure steam then undergoes an isentropic expansion in a conventional steam turbine. The steam turbine exhaust steam is next condensed into liquid water which is then pumped back to steam generator to complete the cycle. When an organic working fluid such as R-134a is used in the Rankine cycle, the cycle is sometimes referred to as an Organic Rankine Cycle (ORC).[8] [9] [10]
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Refrigeration system Figure 4 depicts a refrigeration system with a capacity of about 100 to 1000 tons of refrigeration (i.e., 350 to 3,500 kW). The system utilizes a compressor, a turboexpander and an electric motor. Depending on the operating conditions, the turboexpander reduces the load on the electric motor by some 6 to 15% as compared to a conventional vapor-compression refrigeration system that uses a throttling expansion valve rather than a turboexpander.[11] The system employs a high-pressure refrigerant (i.e., one with a low normal boiling point) such as:[11] • Chlorodifluoromethane (CHClF2) known as R-22, with a normal boiling point of −47 °C • 1,1,1,2-Tetrafluoroethane (C2H2F4) known as R-134a, with a normal boiling point of −26 °C.
Figure 4: Schematic diagram of a refrigeration system using a turboexpander, compressor and a motor.
As shown in Figure 4, refrigerant vapor is compressed to a higher pressure resulting in a higher temperature as well. The hot, compressed vapor is then condensed into a liquid. The condenser is where heat is expelled from the circulating refrigerant and is carried away by whatever cooling medium is used in the condenser (air, water, etc.). The refrigerant liquid flows through the turboexpander where it is vaporized and the vapor undergoes an isentropic expansion which results in a low-temperature mixture of vapor and liquid. The vapor-liquid mixture is then routed through the evaporator where it is vaporized by heat absorbed from the space being cooled. The vaporized refrigerant flows to the compressor inlet to complete the cycle.
Power recovery in fluid catalytic cracker The combustion flue gas from the catalyst regenerator of a fluid catalytic cracker is at a temperature of about 715 °C and at a pressure of about 2.4 barg (240 kPa gauge). Its gaseous components are mostly carbon monoxide (CO), carbon dioxide (CO2) and nitrogen (N2). Although the flue gas has been through two stages of cyclones (located within the regenerator) to remove entrained catalyst fines, it still contains some residual catalyst fines. Figure 5 depicts how power is recovered and utilized by routing the regenerator flue gas through a turboexpander. After the flue gas exits the regenerator, it is routed through a secondary catalyst separator containing swirl tubes designed to remove 70 to 90 percent of the residual catalyst fines.[12] This is required to prevent erosion damage to the turboexpander.
Figure 5: A schematic diagram of the power recovery system in a fluid catalytic cracking unit.
Turboexpander As shown in Figure 5, expansion of the flue gas through a turboexpander provides sufficient power to drive the regenerator's combustion air compressor. The electrical motor-generator in the power recovery system can consume or produce electrical power. If the expansion of the flue gas does not provide enough power to drive the air compressor, the electric motor-generator provides the needed additional power. If the flue gas expansion provides more power than needed to drive the air compressor, than the electric motor-generator converts the excess power into electric power and exports it to the refinery's electrical system.[13] The steam turbine shown in Figure 5 is used to drive the regenerator's combustion air compressor during start-ups of the fluid catalytic cracker until there is sufficient combustion flue gas to take over that task. The expanded flue gas is then routed through a steam-generating boiler (referred to as a CO boiler) where the carbon monoxide in the flue gas is burned as fuel to provide steam for use in the refinery.[13] The flue gas from the CO boiler is processed through an electrostatic precipitator (ESP) to remove residual particulate matter. The ESP removes particulates in the size range of 2 to 20 micrometers from the flue gas.[13]
History The possible use of an expansion machine for isentropically creating low temperatures was suggested by Carl Wilhelm Siemens (Siemens cycle), a German engineer in 1857. About three decades later, in 1885, Ernest Solvay of Belgium attempted to use a reciprocating expander machine but could not attain any temperatures lower than −98 °C because of problems with lubrication of the machine at such temperatures.[2] In 1902, Georges Claude, a French engineer, successfully used a reciprocating expansion machine to liquefy air. He used a degreased, burnt leather packing as a piston seal without any lubrication. With an air pressure of only 40 bar (4 MPa), Claude achieved an almost isentropic expansion resulting in a lower temperature than had before been possible.[2] The first turboexpanders seem to have been designed in about 1934 or 1935 by Guido Zerkowitz, an Italian engineer working for the German firm of Linde AG.[14] [15] In 1939, the Russian physicist Pyotr Kapitsa perfected the design of centrifugal turboexpanders. His first practical prototype was made of Monel metal, had an outside diameter of only 8 cm (3.1 in), operated at 40,000 revolutions per minute and expanded 1,000 cubic metres of air per hour. It used a water pump as a brake and had an efficiency of 79 to 83 percent.[2] [15] Most turboexpanders in industrial use since then have been based on Kapitsa's design and centrifugal turboexpanders have taken over almost 100 percent of the industrial gas liquefaction and low temperature process requirements.[2] [15] In 1978, Pyotr Kapitsa was awarded a Nobel physics prize for his body of work in the area of low-temperature physics.[16] In 1983, San Diego Gas and Electric was among the first to install a turboexpander in a natural gas letdown station for energy recovery[17]
Types Turboexpanders can be classified by loading device or bearings. Three main loading devices used in turboexpanders are centrifugal compressors, electrical generators or hydraulic brakes. With centrifugal compressors and electrical generators the shaft power from the turboexpander is recouped either to recompress the process gas or to generate electrical energy lowering utility bills. Hydraulic brakes are used when the turboexpander is very small and harvesting the shaft power is not economically justifiable. Bearings used are either oil bearings or magnetic bearings.
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Turboexpander
References [1] [2] [3] [4] [5] [6] [7]
Heinz Bloch and Claire Soares (2001). Turboexpanders and Process Applications. Gulf Professional Publishing. ISBN 0-88415-509-9. Frank G. Kerry (2007). Industrial Gas Handbook:Gas Separation and Purification. CRC Press. ISBN 0-8493-9005-2. Thomas Flynn (2004). Cryogenics Engineering (Second Edition ed.). CRC Press. ISBN 0-8247-5367-4. Demethanzer (http:/ / freepatentsonline. com/ US6915662. html) BOC (NZ) publication (http:/ / www. nzic. org. nz/ ChemProcesses/ production/ 1K. pdf): use search function for keyword "expansion" US Department of Energy Hydrogen Program (http:/ / www. hydrogen. energy. gov/ pdfs/ progress05/ v_e_1_shimko. pdf) Gas Processes 2002, Hydrocarbon Processing, pages 83-84, May 2002 (schematic flow diagrams and descriptions of the NGL-Pro and NGL Recovery processes) [8] ORC Technology for Waste Heat Applications (http:/ / www. akenergyauthority. org/ PDF files/ ArchiveConferenceMaterial/ ORC_Waste_Heat-Holdmann. pdf) [9] The Integrated Rankine Cycle Project (http:/ / www. csiro. au/ science/ ps4q. html) [10] The Rankine Cycle Turbogenerator at Altheim, Austria (http:/ / www. geothermie. de/ gte/ gte36-37/ altheim_gaia. htm) [11] Refrigeration apparatus with expansion turbine, European patent EP 0 676 600 B1, September 6, 2000, Joost J. Brasz, Carrier Corporation EP 0 676 600 B1 (http:/ / www. freepatentsonline. com/ EP0676600. pdf) (this website requires registration) [12] Alex C. Hoffnab and Lewis E. Stein (2002). Gas Cyclones and Swirl Tubes:Principles , Design and Operation (1st Edition ed.). Springer. ISBN 3-540-43326-0. [13] Reza Sadeghbeigi (2000). Fluid Catalytic Cracking Handbook (2nd Edition ed.). Gulf Publishing. ISBN 0-88415-289-8. [14] Turbine for Low Temperature Gas Separation, U.S. Patent 2,165,994, July 1939 (Continuation of an application in March 1934), Guido Zerkowitz, Linde AG United States Patent US2165994 (http:/ / www. freepatentsonline. com/ 2165994. pdf) (this website requires registration) [15] Ebbe Almqvist (2002). History of Industrial Gases (First Edition ed.). Springer. p. 165. ISBN 0-306-47277-5. [16] Pyotr Kapitsa, The Nobel Prize in Physics 1978 (http:/ / nobelprize. org/ nobel_prizes/ physics/ laureates/ 1978/ kapitsa-bio. html) [17] Turboexpanders: Harnessing the Hidden Potential of Our Natural Gas Distribution System (http:/ / jacobrheuban. com/ 2009/ 03/ 09/ turboexpanders-harnessing-the-hidden-potential-of-our-natural-gas-distribution-system/ )
External links • Use of Expansion Turbines in Natural Gas Pressure Reduction Stations (http://actamont.tuke.sk/pdf/2004/n3/ 27pozivil2.pdf) • Full load, full speed test of turboexpander-compressor with active magnetic bearings (http://turbolab.tamu.edu/ pubs/Turbo35/T35pg081.pdf) • Low-Temperature Geothermal Power Generation with HVAC Hardware (http://www.smu.edu/geothermal/ Oil&Gas/2007/Dickey_Halley Future of Field Installations UTC Power.pdf)
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Turbomachinery Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. The two types of machines are governed by the same basic relationships including Newton's second Law of Motion and Euler's energy equation for compressible fluids. Centrifugal pumps are also turbomachines that transfer energy from a rotor to a fluid, usually a liquid, while turbines and compressors usually work with a gas.[1]
Mounting of a steam turbine produced by Siemens, Germany
Classification In general, the two kinds of turbomachines encountered in practice are open and closed turbomachines. Open machines such as propellers, windmills, and unshrouded fans act on an infinite extent of fluid, whereas, closed machines operate on a finite quantity of fluid as it passes through a housing or casing. Turbomachines are also categorized according to the type of flow. When the flow is parallel to the axis of rotation, they are called axial flow machines, and when flow is perpendicular to the axis of rotation, they are referred to as radial (or centrifugal) flow machines. There is also a third category, called mixed flow machines, where both radial and axial flow velocity components are present. Turbomachines may be further classified into two additional categories: those that absorb energy to increase the fluid pressure, i.e. pumps, fans, and compressors, and those that produce energy such as turbines by expanding flow to lower pressures. Of particular interest are applications which contain pumps, fans, compressors and turbines. These components are essential in almost all mechanical equipment systems, such as power and refrigeration cycles.[2] Classification of fluid machinery in species and groups
A steam turbine from MAN SE subdidiary MAN Turbo
Turbomachinery
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machine type →
machinery
combinations of power and machinery
engines
group ↓ open turbomachine
propeller
wind turbines
hydraulic fluid machinery (≈ incompressible fluids)
centrifugal pumps turbopumps and fans
Fluid couplings and clutches (hydrodynamic gearbox); Voith Turbo-Transmissions; pump-turbines (in pumped-storage hydroelectricity)
water turbines
thermal turbomachinery (compressible fluid)
compressors
gas turbines (inlet of GT consists of a compressor)
steam turbines ← turbine jet engines
Dimensionless ratios to describe turbomachinery The following dimensionless ratios are often used for the characterisation of fluid machines. They allow a comparison of flow machines with different dimensions and boundary conditions. 1. Pressure range ψ 2. Flow number φ (including delivery or volume number called) 3. Performance numbers λ 4. Run number σ 5. Diameter Number δ
Sources • Sydney Lawrence Dixon, Fluid mechanics and thermodynamics of turbomachinery, 1998
A pelton wheel turbine wheel being installed into power generation equipment
• Earl Logan (1993). Turbomachinery: basic theory and applications [13]. CRC Press. ISBN 9780824791384. • Erian A. Baskharone (2006). Principles of turbomachinery in air-breathing engines [14]. Cambridge University Press. ISBN 9780521858106.
References [1] Logan, p.1 [2] Baskharone, p.6
External links • Hydrodynamics of Pumps (http://authors.library.caltech.edu/25019/)
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Undercut (manufacturing) In manufacturing, an undercut is a special type of recessed surface. In turning it refers to a recess in a diameter. In machining it refers to a recess in a corner. In molding it refers to a feature that cannot be molded using only a single pull mold. In printed circuit board construction it refers to the portion of the wafer that is etched away under the photoresist.
Turning On turned parts an undercut is also known as a neck. They are often used at the end of the threaded portion of a shaft or screw to provide clearance for the cutting tool. For proper usage the undercut should be at least 1.5 threads long and the diameter should be at least 0.015 in (0.38 mm) smaller than An example of a turned part with and without an undercut the minor diameter of the thread.[1] They are also often used on shafts that have diameter changes so that a mating part can seat against the shoulder. If an undercut is not provided there is always a small radius left behind even if a sharp corner is intended. These types of undercuts are called out on technical drawings by stating the width and either the depth or the diameter of the bottom of the neck.[2]
Molding Undercuts on molded parts are features that prevent the part from being directly ejected from the injection molding machine. They are categorized into internal and external undercuts, where external undercuts are on the exterior of the part and interior undercuts are on the inside of the part. Undercuts can still be molded, but require a side action or side pull.[3] This is an extra part of the mold that moves separately from the two halves. These can add 15 to 30% to the cost of the mold and also increase the cost of the molded part.[3] [4]
A simple example of molding an external undercut
undercuts.[3]
If the size of the undercut is small enough and the material is flexible enough a side action is not always required. In these cases the undercut is stripped or snapped out of the mold. When this is done usually a stripping plate or ring is used instead of stripper pins so that the part is not damaged. This technique can be used on internal and external
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Machining In machining the corners may be undercut to remove the radius that is usually left by the milling cutter. Examples of this use are linear bearings for square shafts (i.e. racks) and machined hexalobular sockets.
An example of a machining undercut
Etching Undercuts from etching are somewhat different than the undercuts explained above, because it is a side effect, not an intentional feature. Undercuts from etching can occur from two common causes. The first is over etching, which means the etchant was applied too long. The second is due to an isotropic etchant, which means the etchant etches in all directions equally. To overcome this problem an anisotropic etchant is used.[5]
References 1. An isotropic etchant that creates an undercut 2. An anisotropic etchant leaves no undercut
[1] "Thread relief and chamfers" (http:/ / www. pmpa. org/ technology/ design/ threadrelief. htm). PMPA's Designer's Guide. Precision Machined Products Association. . Retrieved 2009-07-19. [2] Taylor 2004, p. 194.
[3] Berins & Society of the Plastics Industry 1991, pp. 325–326. [4] Rosato et al. 2001, pp. 1405–1406. [5] Degarmo, Black & Kohser 2003, p. 897.
Bibliography • Berins, Michael L.; Society of the Plastics Industry (1991), SPI plastics engineering handbook of the Society of the Plastics Industry, Inc. (http://books.google.com/?id=FzPEJyDTqtEC) (5th ed.), Springer, ISBN 9780412991813. • Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4. • Rosato, Dominick V.; Plastics Institute of America; Schott, Nick R.; Rosato, Marlene G. (2001), Plastics Engineering, Manufacturing & Data Handbook (http://books.google.com/?id=2KSbTcdYv9QC), Springer, ISBN 9780792373162. • Taylor, David L. (2004), Machine Trades Blueprint Reading (http://books.google.com/?id=EWE-RK3F6mcC) (2nd ed.), Cengage Learning, ISBN 9781401899981.
Units conversion by factor-label
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Units conversion by factor-label Many, if not most, parameters and measurements in the physical sciences and engineering are expressed as a numerical quantity and a corresponding dimensional unit; for example: 1000 kg/m³, 100 kPa/bar, 50 miles per hour, 1000 Btu/lb. Converting from one dimensional unit to another is often somewhat complex and being able to perform such conversions is an important skill to acquire. The factor-label method, also known as the unit-factor method or dimensional analysis, is a widely used approach for performing such conversions.[1] [2] [3] It is also used for determining whether the two sides of a mathematical equation involving dimensions have the same dimensional units.
The factor-label method for converting units The factor-label method is the sequential application of conversion factors expressed as fractions and arranged so that any dimensional unit appearing in both the numerator and denominator of any of the fractions can be cancelled out until only the desired set of dimensional units is obtained. For example, 10 miles per hour can be converted to meters per second by using a sequence of conversion factors as shown below: 10 mile 1609 meter 1 hour -- ---- × ---- ----- × ---- -----1 hour 1 mile 3600 second
meter = 4.47 -----second
It can be seen that each conversion factor is equivalent to the value of one. For example, starting with 1 mile = 1609 meters and dividing both sides of the equation by 1 mile yields 1 mile / 1 mile = 1609 meters / 1 mile, which when simplified yields 1 = 1609 meters / 1 mile. So, when the units mile and hour are cancelled out and the arithmetic is done, 10 miles per hour converts to 4.47 meters per second. As a more complex example, the concentration of nitrogen oxides (i.e., NOx) in the flue gas from an industrial furnace can be converted to a mass flow rate expressed in grams per hour (i.e., g/h) of NOx by using the following information as shown below: NOx concentration = 10 parts per million by volume = 10 ppmv = 10 volumes/106 volumes NOx molar mass = 46 kg/kgmol (sometimes also expressed as 46 kg/kmol) Flow rate of flue gas = 20 cubic meters per minute = 20 m³/min The flue gas exits the furnace at 0 °C temperature and 101.325 kPa absolute pressure. The molar volume of a gas at 0 °C temperature and 101.325 kPa is 22.414 m³/kgmol. 10
m³ NOx
20 m³ gas
60 minute
1
kgmol NOx
46 kg NOx
1000 g
g NOx
--- ------ × -- ------ × -- ------ × ------ --------- × -- --------- × ---- -- = 24.63 ----106 m³ gas
1 minute
1 hour
22.414 m³ NOx
1 kgmol NOx
1 kg
hour
After cancelling out any dimensional units that appear both in the numerators and denominators of the fractions in the above equation, the NOx concentration of 10 ppmv converts to mass flow rate of 24.63 grams per hour.
Units conversion by factor-label
Checking equations that involve dimensions The factor-label method can also be used on any mathematical equation to check whether or not the dimensional units on the left hand side of the equation are the same as the dimensional units on the right hand side of the equation. Having the same units on both sides of an equation does not guarantee that the equation is correct, but having different units on the two sides of an equation does guarantee that the equation is wrong. For example, check the Universal Gas Law equation of P·V = n·R·T, when: • • • • •
the pressure P is in pascals (Pa) the volume V is in cubic meters (m³) the amount of substance n is in moles (mol) the universal gas law constant R is 8.3145 Pa·m³/(mol·K) the temperature T is in kelvins (K)
mol (Pa)(m³) K (Pa)(m³) = ----- × ---------- × --1 (mol)(K) 1 As can be seen, when the dimensional units appearing in the numerator and denominator of the equation's right hand side are cancelled out, both sides of the equation have the same dimensional units.
Limitations The factor-label method can convert only unit quantities for which the units are in a linear relationship intersecting at 0. Most units fit this paradigm. An example for which it cannot be used is the conversion between degrees Celsius and kelvins (or Fahrenheit). Between degrees Celsius and kelvins, there is a constant difference rather than a constant ratio, while between Celsius and Fahrenheit there is both a constant difference and a constant ratio. Instead of multiplying the given quantity by a single conversion factor to obtain the converted quantity, it is more logical to think of the original quantity being divided by its unit, being added or subtracted by the constant difference, and the entire operation being multiplied by the new unit. Mathematically, this is an affine transform ( ), not a linear transform ( ). Formally, one starts with a displacement (in some units) from one point, and ends with a displacement (in some other units) from some other point. For instance, the freezing point of water is 0° in Celsius and 32° in Fahrenheit, and a 5° change in Celsius correspond to a 9° change in Fahrenheit. Thus to convert from Fahrenheit to Celsius one subtracts 32° (displacement from one point), multiplies by 5 and divides by 9 (scales by the ratio of units), and adds 0 (displacement from new point). Reversing this yields the formula for Celsius; one could have started with the equivalence between 100° Celsius and 212° Fahrenheit, though this would yield the same formula at the end. [°F = 1.8(°C) + 32°] To convert Celsius to Fahrenheit, simply plug in the known numbers in the above formula. [°C = (°F-32°) ÷ 1.8] To convert Fahrenheit to Celsius (Centigrade), plug the known temperature into the above formula. EX. °F = 1.8(-40°C) + 32° = -40°F (Identical temperature point in °C and °F) EX. °C = (98.6°F-32°) ÷ 1.8 = 37°C (Known standard body temperature in °C and °F)
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References [1] David Goldberg (2006). Fundamentals of Chemistry (5th Edition ed.). McGraw-Hill. ISBN 0-07-322104-X. [2] James Ogden (1999). The Handbook of Chemical Engineering. Research & Education Association. ISBN 0-87891-982-1. [3] Dimensional Analysis or the Factor Label Method (http:/ / www. kentchemistry. com/ links/ Measurements/ dimensionalanalysis. htm)
External links • Unicalc Live web calculator doing units conversion by dimensional analysis (http://www.calchemy.com/ uclive.htm) • Math Skills Review (http://www.chem.tamu.edu/class/fyp/mathrev/mr-da.html) • U.S. EPA tutorial (http://www.epa.gov/eogapti1/toc/full_toc.htm) • A Discussion of Units (http://www.ncsu.edu/felder-public/kenny/papers/units.html) • Short Guide to Unit Conversions (http://www.astro.yale.edu/astro120/unitconv.pdf) • Cancelling Units Lesson (http://www.purplemath.com/modules/units.htm) • Chapter 11: Behavior of Gases (http://www.dentonisd.org/512125919103412/lib/512125919103412/_files/ chemChap11.pdf) Chemistry: Concepts and Applications, Denton Independent School District • Air Dispersion Modeling Conversions and Formulas (http://www.air-dispersion.com/formulas.html)
Variable air volume Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 55 °F (13 °C) supply air. Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. There are two primary advantages to VAV systems. The fan capacity control, especially with modern electronic variable-speed drives, reduces the energy consumed by fans, which can be a substantial part of the total cooling energy requirements of a building. Dehumidification is greater with VAV systems than it is with constant-volume system, which modulate the discharge air temperature to attain part load cooling capacity. The air blower's flow rate is variable. For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well. A VAV terminal unit[1] , often called a VAV box, is the zone-level flow control device. It is basically a quality, calibrated air damper with an automatic actuator. The VAV terminal unit is connected to either a local or a central control system. Historically, pneumatic control was commonplace, but electronic direct digital control systems are popular especially for mid-to-large size applications. Hybrid control, for example having pneumatic actuators with digital data collection, is popular as well. A common commercial application is shown in this diagram. This VAV system consists of a VAV box, ductwork, and four air terminals.
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Variable air volume Control of the system's fan capacity is critical in VAV systems. Without proper and rapid flow rate control, the system's ductwork, or its sealing, can easily be damaged by overpressurization. In the cooling mode of operation, as the temperature in the space is satisfied, a VAV box closes to limit the flow of cool air into the space. As the temperature increases in the space, the box opens to bring the temperature back down. The fan maintains a constant static pressure in the discharge duct regardless of the position of the VAV box. Therefore, as the boxes close, the fan slows down or restricts the amount of air going into the supply duct. As the boxes open, the fan speeds up and allows more air flow into the duct, maintaining a constant static pressure.
References [1] Systems and Equipment volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2004
Vibration isolation Vibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibrations.
Passive isolation Passive vibration isolation systems consist essentially of a mass, spring and damper (dash-pot).
Negative-Stiffness Vibration Isolator Negative-Stiffness-Mechanism (NSM) vibration isolation systems offer a unique passive approach for achieving low vibration environments and isolation against sub-Hertz vibrations. "Snap-through" or "over-center" NSM devices are used to reduce the stiffness of elastic suspensions and create compact six-degree-of-freedom systems with low natural frequencies. Practical systems with vertical and horizontal natural frequencies as low as 0.2 to 0.5 Hz provide isolation efficiencies one to two orders of magnitude better than top-performance air tables and pneumatic isolation systems. Electro-mechanical auto-adjust mechanisms compensate for varying weight loads and provide automatic leveling in multiple-isolator systems, similar to the function of leveling valves in pneumatic systems. All-metal systems can be configured which are compatible with high vacuums and other adverse environments such as high temperatures. These isolation systems enable vibration-sensitive instruments such as scanning probe microscopes, micro-hardness testers and scanning electron microscopes to operate in severe vibration environments sometimes encountered, for example, on upper floors of buildings and in clean rooms. Such operation would not be practical with pneumatic isolation systems. Similarly, they enable vibration-sensitive instruments to produce better images and data than those achievable with pneumatic isolators. The theory of operation of NSM vibration isolation systems is summarized, some typical systems and applications are described, and data on measured performance is presented. The theory of NSM isolation systems is explained in References 1 and 2. It is summarized briefly for convenience. Vertical-Motion Isolation A vertical-motion isolator is shown in Figure 1. It uses a conventional spring connected to an NSM consisting of two bars hinged at the center, supported at their outer ends on pivots, and loaded in compression by forces P. The spring is compressed by weight W to the operating position of the isolator, as shown in Figure 1. The stiffness of the isolator is K=KS-KN where KS is the spring stiffness and KN is the magnitude of a negative stiffness which is a function of the length of the bars and the load P. The isolator stiffness can be made to approach zero while the spring supports the weight W.
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Vibration isolation
Horizontal-Motion Isolation A horizontal-motion isolator consisting of two beam-columns is illustrated in Figure. 2. Each beam-column behaves like two fixed-free beam columns loaded axially by a weight load W. Without the weight load the beam-columns have horizontal stiffness KS With the weight load the lateral bending stiffness is reduced by the "beam-column" effect. This behavior is equivalent to a horizontal spring combined with an NSM so that the horizontal stiffness is K=KS-KN, and KN is the magnitude of the beam-column effect. Horizontal stiffness can be made to approach zero by loading the beam-columns to approach their critical buckling load.
Six-Degree-of-Freedom (six-DOF) Isolation A six-DOF NSM isolator typically uses three isolators stacked in series: a tilt-motion isolator on top of a horizontal-motion isolator on top of a vertical-motion isolator. Figure 3 shows a schematic of a vibration isolation system consisting of a weighted platform supported by a single six-DOF isolator incorporating the isolators of Figures 1 and 2. Flexures are used in place of the hinged bars shown in Figure 1. A tilt flexure serves as the tilt-motion isolator. A vertical-stiffness adjustment screw is used to adjust the compression force on the
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Vibration isolation negative-stiffness flexures thereby changing the vertical stiffness. A vertical load adjustment screw is used to adjust for varying weight loads by raising or lowering the base of the support spring to keep the flexures in their straight, unbent operating positions.
Vibration isolation of supporting joint The equipment and gears have joint with surrounding objects (the supporting joint - with the support; the unsupporting joint - the pipe duct or cable ). Vibration isolation of supporting joint is realized in the device named vibration-isolator (absorber). On an illustration presented dependence of difference is levels of vibrations which are measured before installation of the functioning gear on vibration-isolator and after installation in a wide range of frequencies.
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Vibration isolation The Vibration Isolator A device that reflects and absorbs waves of oscillatory energy, extending from the working gear or an electrical equipment, with the aid of effect of a vibration insulation. Vibration-isolator is established between a body transferring fluctuations and a body which defend (for example, between the gear and the foundation). On an illustration is presented the image vibration-isolator a series «ВИ» which are applied in shipbuilding of Russia. Shown «ВИ» allow loadings 5, 40 and 300 kg. They differ in the sizes, but have a similar structure . In a structure is used the rubber envelope, which is reinforced by a spring. Rubber and a spring are strongly connected during transformation of crude rubber into rubber envelope by a method of vulcanization. Under action of weight loading of the gear the rubber envelope is of deformation , and a spring are compressed or stretch. Thus, in springs cross section, occurs the twig twist with a material of rubber envelope, causing deformation of shift in rubber envelope. It is known, that the vibration insulation basically cannot be carried out without presence of vibration absorption . The size of deformation of shift in elastic material of vibration-isolator it basis for definition of size of absorption of fluctuations. At action of vibration or shock loadings of deformation increase. Being thus cyclic, it considerably strengthens efficiency of the given device. In the upper part of a design the sleeve, and in the lower part a flange by means of which the vibration-isolator fastens to the gear and the foundation.
Vibration isolator manufacturers • OOO "NPP "Poligon", Russia, Saint-Petersburg.
Vibration isolation of unsupporting joint Vibration isolation of unsupporting joint is realized in the device named branch pipe a of isolating vibration. Branch pipe a of isolating vibration Branch pipe a of isolating vibration is a part of a tube with elastic walls for reflection and absorption of waves of the oscillatory energy extending from the working pump over wall of the pipe duct. Is established between the pump and the pipe duct. On an illustration is presented the image a vibration-isolating branch pipe of a series «ВИПБ». In a structure is used the rubber envelope, which is reinforced by a spring. Properties of an envelope are similar envelope to a isolator vibration. Has the device reducing axial effort from action of internal pressure up to zero.
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Active isolation Active vibration isolation systems contain, along with the spring, a feedback circuit which consists of a piezoelectric accelerometer, a controller, and an electromagnetic transducer. The acceleration (vibration) signal is processed by a control circuit and amplifier. Then it feeds the electromagnetic actuator, which amplifies the signal. As a result of such a feedback system, a considerably stronger suppression of vibrations is achieved compared to ordinary damping.
Subframe isolation Another technique used to increase isolation is to use an isolated subframe. This splits the system with an additional mass/spring/damper system. This doubles the high frequency attenuation rolloff, at the cost of introducing additional low frequency modes which may cause the low frequency behaviour to deteriorate. This is commonly used in the rear suspensions of cars with Independent Rear Suspension (IRS), and in the front subframes of some cars. The graph (see illustration) shows the force into the body for a subframe that is rigidly bolted to the body compared with the red curve that shows a compliantly mounted subframe. Above 42 Hz the compliantly mounted subframe is superior, but below that frequency the bolted in subframe is better.
References
Subframe vibration isolation graph: force transmission on suspended body vs. frequency for rigidly and compliantly mounted subframes.
• Platus PhD, David L., SPIE International Society of Optical Engineering - July 1999, Optomechanical Engineering and Vibration Control Negative-Stiffness-Mechanism Vibration Isolation Systems • Harris, C., Piersol, A. , Harris Shock and Vibration Handbook, Fifth Edition, McGraw-Hill, (2002), ISBN 0-07-137081-1 • A.Kolesnikov «Noise and vibration». Russia. Leningrad. Publ.«Shipbuilding». 1988
Vibration isolation
External links • "Selecting a vibration/shock isolator" [1]PDF (372 KiB) at Lord Corporation • "Vibration isolation is the key to accuracy" [2] article at EngineeringTalk.com • White Paper on Active Vibration Isolation for Lithography and Imaging [3] • Fundamentals of Vibration Isolation [4]
References [1] [2] [3] [4]
http:/ / www. lord. com/ Portals/ 0/ VibrationMotionNoise/ selecting_a_vibration_shock_isolator. pdf http:/ / www. engineeringtalk. com/ news/ mqp/ mqp100. html http:/ / www. rdmag. com/ uploadedFiles/ RD/ White_Papers/ 2010/ 03/ PiezoVibrationIsolationMicroscopyLithography. pdf http:/ / www. cvimellesgriot. com/ Products/ Documents/ TechnicalGuide/ Fundamentals-Vibration-Isolation. pdf
Vibratory stress relief Vibratory Stress Relief, often abbreviated VSR, is a non-thermal stress relief method used by the metal working industry to enhance the dimensional stability and mechanical integrity of castings, forgings, and welded components, chiefly for two categories of these metal workpieces: • Precision components, which are machined or aligned to tight dimensional or geometric tolerances. Examples include machine tool bases or columns, components of paper mill, mining equipment, or other large-scale processing machinery, and centrifuge rotors. • Heavily loaded metal workpieces, which are components designed and built with the ability to withstand heavy loads. Examples include lifting yokes, clamshell buckets, crane bases, vibratory screening system frames, ingot processing, and rolling mill equipment. These stresses, called residual stresses[1] , because they reside within the metal workpiece, rather than as a result of external loading, are caused by rapid, unequal cooling. This unequal cooling occurs during welding, casting, forging, rough machining or hot rolling. These stresses often lead to distortion or warping of the structure during machining, assembly, testing, transport, field-use or over time. In extreme cases, residual stress can cause structural failure. Almost all vibratory stress relief equipment manufacturers and procedures use the workpiece’s own resonant frequency to boost the loading experienced by induced vibration, so to maximize the degree of stress relief achieved. Some equipment and procedures are designed to operate near, but not at, workpiece resonances (perhaps to extend equipment life), but independent research[2] has consistently shown resonant frequency vibration to be more effective. See references 4, 6, and 9.
Criteria for Effective VSR Treatment Effective vibratory stress relief treatment results from a combination of factors: 1. Material condition: The material must be ductile. Metal in the welded, cast, forged, or hot-rolled condition can be treated. Material that has been severely cold-rolled or through-hardened, which renders the metal non-ductile, will resist effective treatment. 2. Component gemoetry: Large workpieces lend themselves well to vibratory stress relief, likely due to their being more able to be resonated, however a variety of modest-sized workpieces (overall size less than 20" / 500 mm) have been effectively stress relieved, using vibration. 3. Setup for VSR Treatment involves several steps: • Placing workpiece upon load cushions. These cushions should be made of soft, yet resilient material, typically urethane or neoprene. The cushions should be placed away from the corners of the workpiece, so
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that workpiece damping is minimized, which promotes increased resonant response to vibration. • Positioning, orienting, and securely clamping vibrator on workpiece. The vibrator should be placed away from the corners of the workpiece, and oriented so that the force-field output of the vibrator, with rotary vibrators a plane perpendicular to the vibrator’s axis of rotation, can drive the workpiece into resonance. Dual-mount-flanged vibrators are helpful in achieving effective orientation. The vibrator must be securely clamped, typically with machinist-grade clamps or high-tensile bolts. • Positioning and orienting vibration sensor. The best location for this sensor is on one of the corners of the workpiece, and in-line with the force-plane of the vibrator (a plane perpendicular to the vibrator’s axis of rotation [AOR]). • Adjustment of the vibrator unbalance. The unbalance of the vibrator should be sufficient to drive the resonances of the workpiece, minimally to a level of a few g’s of acceleration. The unbalance might require further increase, to cause peak growth (discussed later) during stress relief treatment. 4. Finding Resonance(s). The vibrator speed range must reach high enough to be greater than the resonance(s) of the workpiece. A max speed capability of at least 6000 – 8000-RPM is recommended. Equally important is tight vibrator motor speed regulation (±0.25%), which greatly improves the ability to detect and drive the resonance(s) (abilities that are required for stress relieving to occur). Driving a resonance involves tuning the vibrator speed to the top of the resonance peak. This is increasingly challenging as workpiece rigidity increases, which causes resonances to become very narrow. To record such resonances, a slow, automated scan through the speed range and plotting of the vibration response of the workpiece is made. The scan rate must be slow, not only because the resonance peaks are narrow, but also due to the high-inertia of the workpiece. There is a significant time delay, caused by this high workpiece inertia, in the response to vibration. This can be best explained by first looking at the phenomenon known as ring time. Ring time is defined as the time period a resonating body continues to vibrate after resonant excitation is stopped. When the vibration is stopped, the waveform will decay, ie, reduce in amplitude, due to frictional losses. See Figure 1
[3]
Figure 1: A waveform that demonstrates ring time, which is the time period vibration continues, after resonant excitation ceases.
Most people have experienced ring time. A large bell, after being struck, continues to emit sound, but at decreasing (softer) sound levels. Over time, the sound level dissipates, as the vibration amplitude decays to an undetectable level. When vibration is the excitation causing resonance (rather than a hammer blow [such as the strike of a bell]), there is a time period between the beginning of vibration excitation, and the moment when full resonant amplitude is reached. During this time the amplitude is building-up or growing (the reverse of decaying), so this phenomenon is called reverse ring time, or RRT. For large metal structures that are commonly stress relieved with vibration, ring or reverse ring times (the time periods are the same, whether the amplitude is growing or decaying), can be 20 – 40 seconds or longer. See Figure 2.
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[4]
Figure 2: Reverse ring time, or RRT, is the time period between the start of vibration excitation, and full resonant amplitude.
The most frequently used method of finding the resonances of a workpiece during vibratory stress relief is to scan through the vibrator speed range, and record / plot the vibration amplitude vs. the vibrator speed. The effect of RRT, specifically the time delay between the beginning of resonant vibration and full resonant amplitude being achieved, dictates that the scan rate used to sweep through the vibrator speed range be slow, in order to make an accurate record of the resonance pattern. Scanning too quickly will result in resonant peaks not being fully depicted or being missed entirely, since the workpiece will not have sufficient time to reach full amplitude resonance before the vibrator speed increases (due to scanning) beyond the resonance frequency. A scan rate of 10-RPM / second has been found in practice to result in the accurate resonant peaks recording of many workpieces. As workpiece size increases, the scan rate might require being decreased, in order to fully capture accurate resonance data. See Figure 3.
Figure 3: The effects of scanning at different scan rates: 10 and 50-RPM/sec. Peaks that are scanned too quickly don't have enough time to reach full resonant amplitude, due to the RRT effect. The larger and heavier the structure, the greater the inertia, the longer the ring time (and reverse ring time): Thus, larger, heavier structures might require slower scan rates to plot accurate resonance patterns.
5. Tuning Vibrator Speed. The vibrator speed is then tuned upon the resonance(s) recorded during the scan, and the response of the workpiece to vibration is monitored. Fine tuning of the speed, plus tight speed regulation, enhances peak tuning and tracking capabilities. The most common responses to treatment are: Peak Growth - Typically the larger change.
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Peak Shift, in the direction of lower RPM - Percentage-wise, the smaller change. Typically resonance peaks are very narrow, causing any peak shifting to rapidly decrease the vibration amplitude, and hence, rapidly decrease of the rate of stress relief, since resonant amplitude is more effective in relieving stress. Thus, any peak shifting requires fine-tuning adjustment of the vibrator speed, in order to track the peak to its final, stable position. Each of these changes, which often combine, i.e., peak growth AND shifting, is consistent with a lowering of the rigidity of the workpiece. The workpiece rigidity is inflated by the presence of residual stress. In the example below, which depicts a common resonance pattern change that occurs during vibratory stress relief, the large peak grew by 47%, while simultaneously shifting to the left 28-RPM, which is less than 0.75%. See Figure 4. The equipment used to perform this stress relief had vibrator speed regulation of ± 0.02%, and speed increment fine-tuning of 1-RPM, which allowed even subtle shifting of the peaks to be accurately tracked to their final, stable locale. The pattern of change, i.e., how quickly the peaks grow and shift, is faster at the beginning of vibration treatment: As treatment continues, the rate of change decreases, eventually resulting in a new, stable resonance pattern. Stability of this new resonance pattern indicates that dimensional stability of the workpiece has been achieved.
Figure 4: VSR Treatment Chart consists of two plots: The upper plot is workpiece acceleration, the lower plot is vibrator input power, simultaneously plotted vertically vs. a common horizontal axis of vibrator speed. Peaks in the acceleration data depict resonances; growth and shifting of the peaks are the response of the workpiece to treatment.
The power plot is useful in both positioning and orienting the vibrator, and when adjusting the vibrator unbalance. Poor or inappropriate vibrator locations or orientations, or excessive vibrator unbalance settings, cause large peaks in the power plot. Use of higher-powered vibrator motors (above 2-kW) provides more "head-room" for peaks in power to be tolerated, and treatment to take place, which was the case here: The power peak at ≈ 3700-RPM was only half of the vibrator motor’s 2.3-kW power capacity (top of the power scale). A Pre-Treatment Scan, which functions as a base-line, is first recorded in green. The operator uses this green data set to tune upon the resonances, and monitor the growth and shifting of the resonance peaks. After peak growth and shifting have subsided, a Post-Treatment Scan is made (red). This data is superimposed on the original, green,
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Pre-Treatment Scan data, documenting the changes in resonance pattern. The stress relief treatment resulted in 47% growth of the original, large peak, while it shifted to the left 28-RPM (less than 0.75%).
Figure 5: Vibratory Stress Relief was performed on this mild steel weldment weighing almost 12 tons. Overall size was 17' × 15' × 2' (≈ 5.2 × 5.6 × 0.6 meters). Workpiece was supported on three, red urethane load cushions (two of which are circled), which are positioned far from the corners of the workpiece to minimize damping, thus promoting resonance, which is required for stress relief to be achieved. The vibrator can be seen in the left, mid-ground (circled), and the accelerometer (vibration sensor whose output is proportional to acceleration), can be seen in the central, left, foreground (circled).
After stress relief treatment, the braces (rust-colored, structural beams), which are used to maintain the desired shape during welding, were removed. The spacing between the two "arms" remained the same; no change was detectable (measured to 1/32" or less than 1 mm), and the spacing remained so throughout assembly, testing (to 60 ton test loads), transport, and installation.
When Should VSR be Considered and the Limits of TSR Historically, the first type of stress relief was performed on castings by storing them outside for months or even years. This was referred to as curing, a term used for long-term storage of freshly hewn wood. Fresh castings were referred to as being green, meaning, they were prone to distortion during precision machining, just as green wood bows during cutting. Later, thermal stress relief (TSR) was developed to alleviate the lengthy time requirements of curing. It has been known for many years, however, that TSR has limitations or shortcomings, specifically: • Furnace size: workpieces can be too large to fit. • Not effective on all alloys, among them austenitic stainless steels. • Should not be used on welded structures made of low-carbon, high-strength steels, which can suffer loss of physical properties and/or crack initiation if thermally stress relieved.[5] [6] • Cannot be used on workpieces that have been quenched and tempered (Q&T) without risking loss of physical properties. Vibratory stress relief can be successfully applied, if some level of ductility is present after Q&T, together with acceptable workpiece geometry (which determines resonant vibration frequency required). • Often not suitable for rough-machined components, due to difficulty in removing scale (rust-colored skin that develops on ferrous components while in-furnace), without damaging machined surfaces. • Asymmetrical-shaped workpieces, which are difficult to cool while maintaining uniform temperature, can develop new, unacceptably high-level, residual stress patterns during the last stage of TSR. Cooling rates can be slowed, but with increased costs. Metal components, whose function would be enhanced by stress relief, and fall into one or more of the above categories, are strong candidates for VSR for quality-related reasons.
Vibratory stress relief Further, there is a strong economic incentive to use vibratory stress relief on large workpieces, since stress relief using a furnace (thermal stress relief or TSR) is highly energy-intensive; consuming much natural gas, and hence, producing much CO2. The cost of TSR is approximately proportional to a metal component’s weight or overall size, estimated to be $ 2500 USD for the structure pictured, plus transportation costs, which might involve special transport permits, to and from a furnace. VSR Treatment would cost a company owning appropriate equipment less than 15% as much ( ≈ $ 400 ) as TSR Treatment, chiefly amortization of equipment investment plus labor, and a modest amount of electrical consumption, and treatment would take less than two hours, with no transport required.
References [1] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ mc_goldrick_saunders. pdf) R.T. McGoldrick and H. Saunders, Some Experiments in Stress-Relieving Castings and Structures by Vibration, Journal of the American Society of Naval Engineer., 55, 589-609 (1943) [2] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ dawson-moffat. pdf) R. Dawson and D.G. Moffat, Vibratory Stress Relief: A Fundamental Study of Effectiveness, Journal of Engineering Material and Technology, 102, 169-176 (1980) [3] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ walker_waddell_johnston. pdf) C.A. Walker, A.J. Waddell and D.J. Johnston, Vibratory Stress Relief - An Investigation of the Underlying Process, Proc. Inst. Mechanical Engineers., 209, 51-58 (1995) [4] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ shankar. pdf) S. Shakar, Vibratory Stress Relief of Mild Steel Weldments, PhD Dissertation, Oregon Graduate Center, U. of Oregon, 1982 [5] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ adams_klauba. pdf) B.B. Klauba and C.M. Adams, A Progress Report on the Use and Understanding of Vibratory Stress Relief, Proc. Winter Meeting of the ASME AMD 52, 47-57 (1982) [6] (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ hahn_william. pdf) W. Hahn, Report on Vibratory Stress and Modifications in Materials to Conserve Resources and Prevent Pollution, Afred University (NY), Center for Environmental and Energy Research (CEER), 2002
(http:/ / scitation. aip. org/ getabs/ servlet/ GetabsServlet?prog=normal& id=JMSEFK000126000002000388000001& idtype=cvips& gifs=yes& ref=no) D. Rao, J. Ge, and L. Chen, Vibratory Stress Relief in the Manufacturing the Rails of a Maglev System, J. of Manufacturing Science and Engineering, 126, Issue 2, 388-391 (2004) (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ adams_berry_klauba. pdf) B.B. Klauba, C.M. Adams, J.T. Berry, Vibratory Stress Relief: Methods Used to Monitor and Document Effective Treatment, A Survey of Users, and Directions for Further Research, Proc. of ASM, 7th International Conference: Trends in Welding Research 601-606 (2005) (http:/ / www. vsrtechnology. net/ wp-content/ uploads/ yang_jung_yancey. pdf) Y. Yang, G. Jung, and R. Yancey, Finite Element Modeling of Vibratory Stress Relief after Welding, Proc of ASM, 7th International Conference; Trends in Welding Research 547-552 (2005)
External links • Is Vibratory Stress Relief as Effective as Thermal Stress Relief? (http://www.esabna.com/us/en/twi/ Vibratory-Stress-Relief.cfm), ESBA Website • Energy Lost From Vibrations (http://www.lightandmatter.com/html_books/3vw/ch02/ch02.html#Section2. 2), Vibrations and Waves by Benjamin Crowell • Putting Energy Into Vibrations (http://www.lightandmatter.com/html_books/3vw/ch02/ch02.html#Section2. 3), Vibrations and Waves by Benjamin Crowell • Plate Specification Guide (http://www.arcelormittal.com/plateinformation/documents/en/Inlandflats/ ProductSpecification/2010 SPEC.GUIDE - FINAL WEB VERSION.pdf), ArcelorMittalUSA • How to Weld "T-1" Constructional Alloy Steels (http://www.arcelormittal.com/plateinformation/documents/ en/Inlandflats/Applications/ARCELORMITTAL HOW TO WELD.pdf), ArcelorMittalUSA
571
Victaulic
Victaulic Victaulic is a developer and producer of mechanical pipe joining systems.[1] Victaulic provides products for Fire Protection, Data Centers, Shipbuilding, Commercial Buildings, Mining, BioFuels, and Industrial Manufacturing.[2] Victaulic was founded in 1925 in New York City.[3] The company is currently headquartered in Easton, Pennsylvania, and employs more than 6,500 people worldwide. Victaulic main products are: • "Victaulic Couplings" [4] used to join mechanical pipes together.[5] The company produces a variety of these couplings and has done so since it was founded.[6] • The "Victaulic Vortex" Fire Suppression System, a product placed at critical locations like data centers. It emits a mix of water and nitrogen from a single Example of Victaulic Piping source that simultaneously cools the affected area and extinguishes the fire.[7] The Vortex is the only Fire Suppression system approved for use in areas containing flammable liquids & hazardous machinery.[8] • Victaulic Sprinker Heads / Sprinkler Systems,[9] Valves / Groove Fittings,[10] and Expansion Joints.[11]
References [1] "Victaulic to Provide Piping Systems for Four Landmark Buildings" (http:/ / news. thomasnet. com/ companystory/ Victaulic-to-Provide-Piping-Systems-for-Four-Landmark-Buildings-581300). ThomasNet News. . Retrieved August 24, 2011. [2] "Products - Victaulic" (http:/ / www. victaulic. com/ content/ Products. htm). . Retrieved August 24, 2011. [3] "Corporate History - Victaulic" (http:/ / www. victaulic. com/ content/ CorporateHistory. htm). . Retrieved August 24, 2011. [4] "Victaulic coupling" (http:/ / www. answers. com/ topic/ victaulic-coupling). Answers.com. . Retrieved August 24, 2011. [5] "Victaulic - Mechanical Pipe Joining Systems" (http:/ / www. power-technology. com/ contractors/ thermal_insulation/ victaulic/ ). power-technology.com. . Retrieved August 24, 2011. [6] "Victaulic Marks 80 Years Of Innovation" (http:/ / www. supplyht. com/ Articles/ HVACR_and_Hydronics_News/ 86c85f75f04a8010VgnVCM100000f932a8c0____). Supplyhouse Times. BNP Media. May 4, 2005. . Retrieved August 24, 2011. [7] "Fire Protection Systems" (http:/ / www. firesystems. biz/ Products/ VictaulicVortexFireSuppressionSystem/ tabid/ 78/ Default. aspx). Levitt=Safety. . Retrieved August 24, 2011. [8] "Technology Focus" (http:/ / memagazine. asme. org/ Articles/ 2010/ April/ Technology_Focus. cfm). Mechanical Engineering. American Society of Mechanical Engineers. . Retrieved August 24, 2011. [9] "Victaulic Sprinklers" (http:/ / www. guardianfireprotection. com/ victaulic-sprinklers. php). Guardian Fire Protection Service. . Retrieved August 24, 2011. [10] "Victaulic grooved fittings and Victaulic grooved valves" (http:/ / www. indpipe. com/ victaulic_grooved_fittings_d. htm). Independent Pipe and Supply Corp.. . Retrieved August 24, 2011. [11] "Victaulic Showcases Benefits of Grooved Piping in the Power Industry at #PowerGen" (http:/ / www. prweb. com/ releases/ Victaulic/ Power-Gen/ prweb4893674. htm). PRWeb. December 13, 2010. . Retrieved August 24, 2011.
572
Virtual work
Virtual work Virtual work arises in the application of the principle of least action to the study of forces and movement of a mechanical system. Historically, virtual work and the associated calculus of variations were formulated to analyze systems of rigid bodies,[1] but they have also been developed for the study of the mechanics of deformable bodies.[2] If a force acts on a particle as it moves from point A to point B, then, for each possible trajectory that the particle may take, it is possible to compute the total work done by the force along the path. The principle of virtual work, which is the form of the principle of least action applied to these systems, states that the path actually followed by the particle is the one for which the difference between the work along this path and other nearby paths is zero. The formal procedure for computing the difference of functions evaluated on nearby paths is a generalization of the derivative known from differential calculus, and is termed the calculus of variations. Let the function x(t) define the path followed by a point, then a nearby path can be defined by adding the function δx(t) to the original path, so the new path is given by x(t)+δx(t). The function δx(t) is called the variation of the original path, and each of the components of δx=(δx, δy, δz) is called a virtual displacement. This can be generalized to an arbitrary mechanical system defined by the generalized coordinates qi, i=1,..., n. In which case, the variation of the trajectory qi(t) is defined by the virtual displacements δqi, i=1,..., n. Virtual work can now be described as the work done by the applied forces and the inertial forces of a mechanical system as it moves through a set of virtual displacements.
History The formulation of virtual work implements the view that nature selects from a set of "tentative" realities in order to minimize a quantity. This is a version of the "simplicity hypothesis" that can be traced to Aristotle.[3] Another form of this hypothesis is Ockham's "razor" which states that "it is futile to employ many principles when it is possible to employ fewer." These ideas illustrate a view of physics that nature optimizes in some way. Leibnitz formulated Newton's laws of motion in terms of work and kinetic energy, or vis viva (living force), which are minimized as a system moves.[1] [3] Maupertuis adapted Liebnitz's ideas as the principle of least action that nature minimizes action. But it was Euler and Lagrange who provided the mathematical foundation of the calculus of variations and applied it to the study of the statics and dynamics of mechanical systems. Hamilton's reformulation of the principle of least action and Lagrange's equations yielded a theory of dynamics that is the foundation for modern physics and quantum mechanics.
Introduction In this introduction basic definitions are presented that will assist in understanding later sections. Consider a particle P that moves along a trajectory r(t) from a point A to a point B, while a force F is applied to it, then the work done by the force is given by the integral
where dr is the differential element along the curve that is the trajectory of P, and v is its velocity. It is important to notice that the value of the work W depends on the trajectory r(t). Now consider the work done by the same force on the same particle P again moving from point A to point B, but this time moving along the nearby trajectory that differs from r(t) by the variation δr(t)=εh(t), where ε is a scaling constant that can be made as small as desired and h(t) is an arbitrary function that satisfies h(t0)=h(t1)=0,
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Virtual work
The variation of the work δW associated with this nearby path, known as the virtual work, can be computed to be
Now assume that r(t) and h(t) depend on the generalized coordinates qi, i=1, ..., n, then the derivative of the variation δr=εh(t) is given by
then we have
The requirement that the virtual work be zero for an arbitrary variation δr(t)=εh(t) is equivalent to the set of requirements
The terms Fi are called the generalized forces associated with the virtual displacement δr.
Static equilibrium Static equilibrium is the condition in which the applied forces and constraint forces on a mechanical system balance such that the system does not move. The principle of virtual work states that the virtual work of the applied forces is zero for all virtual movements of the system from static equilibrium, that is, δW=0 for any variation δr.[4] This is equivalent to the requirement that the generalized forces for any virtual displacement are zero, that is Fi=0. Let the forces on the system be Fj, j=1, ..., m and let the virtual displacement of each point of application of these forces be δrj, j=1, ..., m, then the virtual work generated by a virtual displacement of these forces from the equilibrium position is given by
Now assume that each δrj depends on the generalized coordinates qi, i=1, ..., n, then
and
The n terms
are the generalized forces acting on the system. Kane[5] shows that these generalized forces can also be formulated in terms of the ratio of time derivatives,
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Virtual work where vj is the velocity of the point of application of the force Fj. In order for the virtual work to be zero for an arbitrary virtual displacement, each of the generalized forces must be zero, that is
Constraint forces An important benefit of the principle of virtual work is that only forces that do work as the system moves through a virtual displacement are needed to determine the mechanics of the system. There are many forces in a mechanical system that do no work during a virtual displacement, which means that they need not be considered in this analysis. The two important examples are (i) the internal forces in a rigid body, and (ii) the constraint forces at an ideal joint. Lanczos[1] presents this as the postulate: "The virtual work of the forces of reaction is always zero for any virtual displacement which is in harmony with the given kinematic constraints." The argument is as follows. The principle of virtual work states in equilibrium the virtual work of the forces applied to a system is zero. Newton's laws state that at equilibrium the applied forces are equal and opposite to the reaction, or constraint, forces. This means the virtual work of the constraint forces must be zero as well.
Couples A pair of forces acting on a rigid body can form a couple defined by the moment vector M. The virtual work of a moment vector is obtained from the virtual rotation of the rigid body. For planar movement, the moment acts perpendicular to the plane with magnitude M and the virtual work due to this moment is
where δφ is the virtual rotation angle of the body. In order to extend this to three dimensional rotations, use the angular velocity vector ω of the body to obtain the virtual work as
Now consider the moments Mj acting on m rigid bodies in a mechanical system. Let the angular velocity vectors ωj, j= 1,..., m of each body depend on the n generalized coordinates qj, i=1,... , n. Then the virtual work obtained from these moments for a virtual displacement from equilibrium is given by
Collect the coefficients of the virtual displacements δqi to obtain
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Virtual work
Forces and moments Combine the virtual work above for couples with the virtual work of forces in order to obtain the virtual work of a system of forces and moments acting on system of rigid bodies displaced from equilibrium as
where the generalized forces are now defined to be
The principle of virtual work requires that a system of rigid bodies acted on by the forces and moments Fj and Mj is in equilibrium if the generalized forces Fi are zero, that is
One degree-of-freedom mechanisms In this section, the principle of virtual work is used for the static analysis of one degree-of-freedom mechanical devices. Specifically, we analyze the lever, a pulley system, a gear train, and a four-bar linkage. Each of these devices moves in the plane, therefore a force F=(fx, fy) has two components and acts on a point with coordinates r= (rx, ry) and velocity v=(vx, vy). A moment, also called a torque, T acting on a body that moves in the plane has one component as does the angular velocity ω of the body. Assume the bodies in the mechanism are rigid and the joints are ideal so that the only change in virtual work is associated with the movement of the input and output forces and torques.
Applied Forces Consider a mechanism such as a lever that operates so that an input force generates an output force. Let A be the point where the input force FA is applied, and let B be the point where the output force FB is exerted. Define the position and velocity of A and B by the vectors rA, vA and rB, vB, respectively. Because the mechanism has one degree-of-freedom, there is a single generalized coordinate q that defines the position vectors rA(q) and rB(q) of the input and output points in the system. The principle of virtual work requires that the generalized force associated with this coordinate be zero, thus
The negative sign on the output force FB arises because the convention of virtual work assumes the forces are applied to the device.
Applied Torque Consider a mechanism such as a gear train that operates so that an input torque generates an output torque. Let body EA have the input moment TA applied to it, and let body EB exert the output torque TB. Define the angular position and velocity of EA and EB by θA, ωA and θB, ωB, respectively. Because the mechanism has one degree-of-freedom, there is a single generalized coordinate q that defines the angles θA(q) and θB(q) of the input and output of the system. The principle of virtual work requires that the generalized force associated with this coordinate be zero, thus
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Virtual work
577
The negative sign on the output torque TB arises because the convention of virtual work assumes the torques are applied to the device.
Law of the Lever A lever is modeled as a rigid bar connected a ground frame by a hinged joint called a fulcrum. The lever is operated by applying an input force FA at a point A located by the coordinate vector rA on the bar. The lever then exerts an output force FB at the point B located by rB. The rotation of the lever about the fulcrum P is defined by the rotation angle θ. Let the coordinate vector of the point P that defines the fulcrum be rP, and introduce the lengths
This is an engraving from Mechanics Magazine published in London in 1824.
which are the distances from the fulcrum to the input point A and to the output point B, respectively. Now introduce the unit vectors eA and eB from the fulcrum to the point A and B, so This notation allows us to define the velocity of the points A and B as where eA⊥ and eB⊥ are unit vectors perpendicular to eA and eB, respectively. The angle θ is the generalized coordinate that defines the configuration of the lever, therefore using the formula above for forces applied to a one degree-of-freedom mechanism, the generalized force is given by
Now, denote as FA and FB the components of the forces that are perpendicular to the radial segments PA and PB. These forces are given by
This notation and the principle of virtual work yield the formula for the generalized force as
The ratio of the output force FB to the input force FA is the mechanical advantage of the lever, and is obtained from the principle of virtual work as
Virtual work
578
This equation shows that if the distance a from the fulcrum to the point A where the input force is applied is greater than the distance b from fulcrum to the point B where the output force is applied, then the lever amplifies the input force. If the opposite is true that the distance from the fulcrum to the input point A is less than from the fulcrum to the output point B, then the lever reduces the magnitude of the input force. This is the law of the lever, which was proven by Archimedes using geometric reasoning.[6]
Gear train A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next. For this analysis, we consider a gear train that has one degree-of-freedom, which means the angular rotation of all the gears in the gear train are defined by the angle of the input gear. The size of the gears and the sequence in which they engage define the ratio of the angular velocity ωA of the input gear to the angular velocity ωB of the output gear, known as the speed ratio, or gear ratio, of the gear train. Let R be the speed ratio, then
Illustration from Army Service Corps Training on Mechanical Transport, (1911), Fig. 112 Transmission of motion and force by gear wheels, compound train
The input torque TA acting on the input gear GA is transformed by the gear train into the output torque TB exerted by the output gear GB. If we assume, that the gears are rigid and that there are no losses in the engagement of the gear teeth, then the principle of virtual work can be used to analyze the static equilibrium of the gear train. Let the angle θ of the input gear be the generalized coordinate of the gear train, then the speed ratio R of the gear train defines the angular velocity of the output gear in terms of the input gear, that is
The formula above for the principle of virtual work with applied torques yields the generalize force
Virtual work
579
The mechanical advantage of the gear train is the ratio of the output torque TB to the input torque TA, and the above equation yields
Thus, the speed ratio of a gear train also defines its mechanical advantage. This shows that if the input gear rotates faster than the output gear, then the gear train amplifies the input torque. And, if the input gear rotates slower than the output gear, then the gear train reduces the input torque.
Virtual work principle for a rigid body If the principle of virtual work for applied forces is used on individual particles of a rigid body, the principle can be generalized for a rigid body: When a rigid body that is in equilibrium is subject to virtual compatible displacements, the total virtual work of all external forces is zero; and conversely, if the total virtual work of all external forces acting on a rigid body is zero then the body is in equilibrium. The expression compatible displacements means that the particles remain in contact and displace together so that the work done by pairs of action/reaction inter-particle forces cancel out. Various forms of this principle have been credited to Johann (Jean) Bernoulli (1667-1748) and Daniel Bernoulli (1700-1782).
Virtual work principle for a deformable body Consider now the free body diagram of a deformable body, which is composed of an infinite number of differential cubes as shown in the figure. Let's define two unrelated states for the body: • The • The
-State (Fig.a): This shows external surface forces T, body forces f, and internal stresses -State (Fig.b): This shows continuous displacements and consistent strains .
in equilibrium.
The superscript * emphasizes that the two states are unrelated. Other than the above stated conditions, there is no need to specify if any of the states are real or virtual. Imagine now that the forces and stresses in the -State undergo the displacements and deformations in the -State: We can compute the total virtual (imaginary) work done by all forces acting on the faces of all cubes in two different ways: • First, by summing the work done by forces such as
which act on individual common faces (Fig.c): Since the
material experiences compatible displacements, such work cancels out, leaving only the virtual work done by the surface forces T (which are equal to stresses on the cubes' faces, by equilibrium). • Second, by computing the net work done by stresses or forces such as
,
which act on an individual cube,
e.g. for the one-dimensional case in Fig.(c):
where the equilibrium relation
has been used and the second order term has been neglected.
Integrating over the whole body gives: - Work done by the body forces f. Equating the two results leads to the principle of virtual work for a deformable body:
where the total external virtual work is done by T and f. Thus,
Virtual work
580
The right-hand-side of (d,e) is often called the internal virtual work. The principle of virtual work then states: External virtual work is equal to internal virtual work when equilibrated forces and stresses undergo unrelated but consistent displacements and strains. It includes the principle of virtual work for rigid bodies as a special case where the internal virtual work is zero.
Proof of Equivalence between the Principle of Virtual Work and the Equilibrium Equation We start by looking at the total work done by surface traction on the body going through the specified deformation:
Applying divergence theorem to the right hand side yields:
Now switch to indicial notation for the ease of derivation.
To continue our derivation, we substitute in the equilibrium equation
. Then
The first term on the right hand side needs to be broken into a symmetric part and a skew part as follows:
where is the strain that is consistent with the specified displacement field. The 2nd to last equality comes from the fact that the stress matrix is symmetric and that the product of a skew matrix and a symmetric matrix is zero. Now recap. We have shown through the above derivation that
Move the 2nd term on the right hand side of the equation to the left:
The physical interpretation of the above equation is, the External virtual work is equal to internal virtual work when equilibrated forces and stresses undergo unrelated but consistent displacements and strains. For practical applications:
Virtual work
581
• In order to impose equilibrium on real stresses and forces, we use consistent virtual displacements and strains in the virtual work equation. • In order to impose consistent displacements and strains, we use equilibriated virtual stresses and forces in the virtual work equation. These two general scenarios give rise to two often stated variational principles. They are valid irrespective of material behaviour.
Principle of virtual displacements Depending on the purpose, we may specialize the virtual work equation. For example, to derive the principle of virtual displacements in variational notations for supported bodies, we specify: • Virtual displacements and strains as variations of the real displacements and strains using variational notation such as and • Virtual displacements be zero on the part of the surface that has prescribed displacements, and thus the work done by the reactions is zero. There remains only external surface forces on the part that do work. The virtual work equation then becomes the principle of virtual displacements:
This relation is equivalent to the set of equilibrium equations written for a differential element in the deformable body as well as of the stress boundary conditions on the part of the surface. Conversely, (f) can be reached, albeit in a non-trivial manner, by starting with the differential equilibrium equations and the stress boundary conditions on , and proceeding in the manner similar to (a) and (b). Since virtual displacements are automatically compatible when they are expressed in terms of continuous, single-valued functions, we often mention only the need for consistency between strains and displacements. The virtual work principle is also valid for large real displacements; however, Eq.(f) would then be written using more complex measures of stresses and strains.
Principle of virtual forces Here, we specify: • Virtual forces and stresses as variations of the real forces and stresses. • Virtual forces be zero on the part forces on
of the surface that has prescribed forces, and thus only surface (reaction)
(where displacements are prescribed) would do work.
The virtual work equation becomes the principle of virtual forces:
This relation is equivalent to the set of strain-compatibility equations as well as of the displacement boundary conditions on the part . It has another name: the principle of complementary virtual work.
Virtual work
Alternative forms A specialization of the principle of virtual forces is the unit dummy force method, which is very useful for computing displacements in structural systems. According to D'Alembert's principle, inclusion of inertial forces as additional body forces will give the virtual work equation applicable to dynamical systems. More generalized principles can be derived by: • allowing variations of all quantities. • using Lagrange multipliers to impose boundary conditions and/or to relax the conditions specified in the two states. These are described in some of the references. Among the many energy principles in structural mechanics, the virtual work principle deserves a special place due to its generality that leads to powerful applications in structural analysis, solid mechanics, and finite element method in structural mechanics.
References [1] C. Lanczos, The Variational Principles of Mechanics, 4th Ed., General Publishing Co., Canada, 1970 (http:/ / books. google. com/ books?id=ZWoYYr8wk2IC& printsec=frontcover& source=gbs_ge_summary_r& cad=0#v=onepage& q& f=false) [2] Dym, C. L. and I. H. Shames, Solid Mechanics: A Variational Approach, McGraw-Hill, 1973. [3] W. Yourgrau and S. Mandelstam, Variational Principles in Dynamics and Quantum Theory, 3rd Ed., General Publishing Co., Canada, 1968 (http:/ / books. google. com/ books?id=OwTyrJJXZbYC& printsec=frontcover& source=gbs_ge_summary_r& cad=0#v=onepage& q& f=false) [4] Torby, Bruce (1984). "Energy Methods". Advanced Dynamics for Engineers. HRW Series in Mechanical Engineering. United States of America: CBS College Publishing. ISBN 0-03-063366-4. [5] T. R. Kane and D. A. Levinson, Dynamics: theory and applications, McGraw-Hill, New York, 1985 [6] A. P. Usher, 1929, A History of Mechanical Inventions, Harvard University Press, (reprinted by Dover Publications 1968).
Bibliography • • • • • • • • • • •
Bathe, K.J. "Finite Element Procedures", Prentice Hall, 1996. ISBN 0-13-301458-4 Charlton, T.M. Energy Principles in Theory of Structures, Oxford University Press, 1973. ISBN 0-19-714102-1 Dym, C. L. and I. H. Shames, Solid Mechanics: A Variational Approach, McGraw-Hill, 1973. Greenwood, Donald T. Classical Dynamics, Dover Publications Inc., 1977, ISBN 0-486-69690-1 Hu, H. Variational Principles of Theory of Elasticity With Applications, Taylor & Francis, 1984. ISBN 0-677-31330-6 Langhaar, H. L. Energy Methods in Applied Mechanics, Krieger, 1989. Reddy, J.N. Energy Principles and Variational Methods in Applied Mechanics, John Wiley, 2002. ISBN 0-471-17985-X Shames, I. H. and Dym, C. L. Energy and Finite Element Methods in Structural Mechanics, Taylor & Francis, 1995, ISBN 0-89116-942-3 Tauchert, T.R. Energy Principles in Structural Mechanics, McGraw-Hill, 1974. ISBN 0-07-062925-0 Washizu, K. Variational Methods in Elasticity and Plasticity, Pergamon Pr, 1982. ISBN 0-08-026723-8 Wunderlich, W. Mechanics of Structures: Variational and Computational Methods, CRC, 2002. ISBN 0-8493-0700-7
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VOICED
VOICED Virtual Organization for Innovative Conceptual Engineering Design (VOICED) is a virtual organization that promotes innovation in engineering design. This project is the collaborative work of researchers at five universities across the United States, and is funded by the National Science Foundation. The goal of this virtual organization is to facilitate the sharing of design information between often geographically dispersed engineers and designers through the use of a robust and sophisticated design repository. Additionally, functional data can be mapped to historical failure data[1] and possible components[2] to create a conceptual design. The end goal is to turn VOICED into a tool that allows engineers to create conceptual designs based on archived designs and detect failures in those design through an open design repository (Tumer & Stone, n.d.). VOICED is a fairly new organization, being about 3–4 years old, however the concepts that underlie the organization have been under development for much longer[3] .
Universities • Oregon State University • Missouri University of Science and Technology (team has moved to Oregon State) • Penn State • University of Texas • Texas A&M University
NSF Awards Collaborative Research: VOICED - A Virtual Organization for Innovative Conceptual Engineering Design • 0742677 [4] & 0742698 [5]
Software • Design Engineering Lab [6] • Design Repository [7] • FunctionCAD [8] is an open source application used for the visual representation of functional models. • SKDB [9] - " apt for hardware", see also open source hardware.
References [1] R.B. Stone, I.Y. Tumer, and M.E. Stock, “Linking product functionality to historic failures to improve failure analysis in design,” Research in Engineering Design, vol. 16, 2005, pp. 96-108. [2] *R.B. Stone and K.L. Wood, “Development of a Functional Basis for Design,” Journal of Mechanical Design, vol. 122, Dec. 2000, pp. 359-370. [3] http:/ / voiced. device. mst. edu [4] http:/ / www. nsf. gov/ awardsearch/ showAward. do?AwardNumber=0742677 [5] http:/ / www. nsf. gov/ awardsearch/ showAward. do?AwardNumber=0742698 [6] http:/ / designengineeringlab. org [7] http:/ / designengineeringlab. org/ delabsite/ repository. html [8] http:/ / function. device. mst. edu:16080/ FunctionCAD/ [9] http:/ / adl. serveftp. org/ dokuwiki/ skdb
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VOICED
External links • http://www.p2pfoundation.net/VOICED
Water cascade analysis Water cascade analysis (WCA) is a technique to calculate the minimum flowrate target for feedwater and wastewater for continuous water-using processes[1] .
Principle It is a tabular and numerical alternative to the water surplus diagram in Water Pinch which can be used to identify opportunities for reduction in feedwater usage and the design of water distribution networks. The WCA is done in three steps, a global analysis of water distribution and consumption in the network, establishing baseline minimum water targets and redesign of the water network to achieve these targets.
History WCA was first introduced by Manan, foo and Tan in 2004. [2] Since then, it has been widely used as a tool for water conservation in industrial process plants. A Time dependent water cascade analysis was presented later on[3] . A variation of the WCA is the gas cascade analysis (GCA)[4] .
References [1] Water cascade analysis technique for minimum flowrate targeting (http:/ / eprints. utm. my/ 6893/ ) [2] Manan, Z. A., Foo, C. Y. and Tan, Y. L. (2004). Targeting the Minimum Water Flowrate Using Water Cascade Analysis Technique, AIChE Journal, Volume 50, No. 12, 2004. [3] Time dependent water cascade analysis (http:/ / kolmetz. com/ pdf/ Foo/ Dominic Foo's thesis 2. pdf) [4] Setting the minimum utility gas flowrate targets using cascade analysis (http:/ / pubs. acs. org/ doi/ abs/ 10. 1021/ ie051322k)
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Water chiller
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Water chiller A water chiller[1] is a mechanical device used to facilitate heat exchange from water to a refrigerant in a closed loop system. The refrigerant is then pumped to a location where the waste heat is transferred to the atmosphere. In hydroponics, pumps, lights and ambient heat can warm the reservoir water temperatures, leading to plant root and health problems. For ideal plant health, a chiller can be used to lower the water temperature below ambient level; 68°F (20°C) is a good temperature for most plants. This results in healthy root production and efficient absorption of nutrients. In air conditioning, chilled water is often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel. A chiller lowers water temperature to between 40° and 45°F before the water is pumped to the location to be cooled.[2]
Notes [1] George F Van Patten. Hydroponic Basics. [2] How Stuff Works: How Air Conditioners Work-Chilled-water and Cooling-tower AC Units (http:/ / home. howstuffworks. com/ ac4. htm)
Water pinch analysis Water Pinch Analysis (WPA) originates from the concept of heat pinch analysis. WPA is a systematic technique for reducing water consumption and wastewater generation through integration of water-using activities or processes. WPA was first introduced by Wang and Smith[1] . Since then, it has been widely used as a tool for water conservation in industrial process plants. Water Pinch Analysis has recently been applied for urban/domestic buildings.[2] It was extended in 1998 by Nick Hallale at the University of Cape Town, who developed it as a special case of mass exchange networks for capital cost targeting. Techniques for setting targets for maximum water recovery capable of handling any type of water-using operation including mass-transfer-based and non-mass-transfer based systems include the source and sink composite curves (Nick Hallale (2002). A New Graphical Targeting Method for Water Minimisation. Advances in Environmental Research. 6(3): 377-390) and water cascade analysis (WCA).[3] The source and sink composite curves is a graphical tool for setting water recovery targets as well as for design of water recovery networks.[4]
References [1] Wang, Y. P. and Smith, R. (1994). Wastewater Minimisation. Chem. Eng. Sci. 49, 981–1006. [2] Manan, Z. A., Wan Alwi, S. R. and Ujang Z. (2006). Water pinch analysis for urban system: a case study on the Sultan Ismail Mosque at Universiti Teknologi Malaysia (UTM) . Desalination. 194: 52-68. [3] Manan, Z. A., Foo, C. Y. and Tan, Y. L. (2004). Targeting the Minimum Water Flowrate Using Water Cascade Analysis Technique, AIChE Journal, Volume 50, No. 12, 2004. [4] Wan Alwi, S. R. and Manan, Z. A. (2008). Generic Graphical Technique for Simultaneous Targeting and Design of Water Networks . Ind. Eng. Chem. Res. 47 (8): 2762-2777. DOI:10.1021/ie071487o. 5. Hallale, Nick. (2002). A New Graphical Targeting Method for Water Minimisation. Advances in Environmental Research. 6(3): 377-390
Wells turbine
Wells turbine The Wells turbine is a low-pressure air turbine that rotates continuously in one direction in spite of the direction of the air flow. Its blades feature a symmetrical airfoil with its plane of symmetry in the plane of rotation and perpendicular to the air stream. It was developed for use in oscillating-water-column wave power plants, in which a rising and falling water surface moving in an air compression chamber produces an oscillating air current. The use of this bidirectional turbine avoids the need to rectify the air stream by delicate and expensive check valve systems. Its efficiency is lower than that of a turbine with constant air stream direction and asymmetric airfoil. One reason for the lower efficiency is that symmetric airfoils have a higher drag coefficient than asymmetric ones, even under optimal conditions. Also, in the Wells turbine, the symmetric airfoil is used with a high angle of attack (i.e., low blade speed / air speed ratio), as it occurs during air velocity maxima in volatile flow. A high angle of attack causes a condition known as "stall" in which the airfoil loses lift. The efficiency of the Wells turbine in oscillating flow reaches values between 0.4 and 0.7. This simple but ingenious device was developed by Prof. Alan Arthur Wells of Queen's University Belfast in the late 1970s.
Annotation Another solution of the problem of stream direction independent turbine is the Darrieus wind turbine (Darrieus rotor).
External links • about wave power generation in general with part on wells turbine [1] (German) • Animation showing OWC wave power plant" [2]
References [1] http:/ / www. uni-leipzig. de/ ~grw/ lit/ texte_099/ 59__1999/ 59_1999_hansa. htm [2] http:/ / www. archipelago. co. uk/ our-work/ wave-power-animation
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West number
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West number The West number is an empirical parameter used to characterize the performance of Stirling engines, and other Stirling systems. It is very similar to the Beale number where a larger number indicates higher performance; however, the West number includes temperature compensation. The West number is often used to approximate of the power output of a Stirling engine. The average value is (0.25) [1] for a wide variety of engines, although it may range up to (0.35) [1], particularly for engines operating with a high temperature differential. The West number may be defined as:
where: • • • • •
Wn is the West number Wo is the power output of the engine (watts) P is the mean average gas pressure (Pa) or (MPa, if volume is in cm3) V is swept volume of the expansion space (m3) or (cm³, if pressure is in MPa) f is the engine cycle frequency (Hz)
• TH is the absolute temperature of the expansion space or heater (kelvins) • TK is the absolute temperature of the compression space or cooler (kelvins) • Bn is the Beale number for an engine operating between temperatures TH and TK When the Beale number is known, but the West number is not known, it is possible to calculate it. First calculate the West number at the temperatures TH and TK for which the Beale number is known, and then use the resulting West number to calculate output power for other temperatures. To estimate the power output of a new engine design, nominal values are assumed for the West number, pressure, swept volume and frequency, and the power is calculated as follows: [2]
For example, with an absolute temperature ratio of 2, the portion of the equation representing temperature correction equals 1/3. With a temperature ratio of 3, the temperature term is 1/2. This factor accounts for the difference between the West equation, and the Beale equation in which this temperature term is taken as a constant. Thus, the Beale number is typically in the range of 0.10 to 0.15, which is about 1/3 to 1/2 the value of the West number.
References [1] http:/ / www. ornl. gov/ ~webworks/ cppr/ y2001/ rpt/ 27113. pdf [2] ornl-tm-10475 (http:/ / www. ornl. gov/ ~webworks/ cppr/ y2001/ rpt/ 27113. pdf)
External links • Stirling Engine Performance Calculator (http://www.bekkoame.ne.jp/~khirata/academic/simple/simplee. htm)
Work (physics)
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Work (physics) Work SI symbol:
W
SI unit:
joule
Derivations from other quantities: W = F · d W=τθ
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Coriolis.[1] [2] If a constant force of magnitude F acts on a point that moves s in the direction of the force, then the work W done by this force is calculated W=Fs. For example, if a force of 10 newtons (F=10 N) acts along a path of 2 metres (s =2 m), it will do work W equal to W =(10 N)(2 m) = 20 N*m =20 J, where joule (J) is the SI unit for work (defined as the product N*m, so that a joule is a newton-meter). For moving objects, the quantity of work/time enters calculations as distance/time, or velocity. Thus, at any instant, the rate of the work done by a force (measured in joules/second, or watts) is the scalar product of the force (a vector) with the velocity vector of the point of application. This scalar product of force and velocity is called instantaneous power. Just as velocities may be integrated over time to obtain a total distance, by the fundamental theorem of calculus, the total work along a path is similarly the time-integral of instantaneous power applied along the trajectory of the point of application. The first law of thermodynamics states that when work is done to a system (and no other energy is subtracted in other ways), the system's energy state changes by the same amount of the work input. This equates work and energy. In the case of rigid bodies, Newton's laws can be used to derive a similar relationship called the work-energy theorem.
Units The SI unit of work is the joule (J), which is defined as the work done by a force of one newton acting over a distance of one metre. This definition is based on Sadi Carnot's 1824 definition of work as "weight lifted A baseball pitcher does positive work on the ball by transferring energy into it. through a height", which is based on the fact that early steam engines were principally used to lift buckets of water, through a gravitational height, out of flooded ore mines. The dimensionally equivalent newton-metre (N·m) is sometimes used for work, but this can be confused with the units newton-metre of torque. Non-SI units of work include the erg, the foot-pound, the foot-poundal, and the litre-atmosphere. Other non-SI units for work are the horsepower-hour, the therm, the BTU and Calorie. It is important to note that heat and work are measured using the same units.
Work (physics)
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Heat conduction is not considered to be a form of work, since the energy is transferred into atomic vibration rather than a macroscopic displacement. However, heat conduction can perform work by expanding a gas in a cylinder such as in the engine of an automobile.
Mathematical calculation Calculating the work as "force times straight path segment" can only be done in the simple circumstances described above. If the force is changing, if the body is moving along a curved path, possibly rotating and not necessarily rigid, then only the path of the application point of the force is relevant for the work done, and only the component of the force parallel to the application point velocity is doing work (positive work when in the same direction, and negative when in the opposite direction of the velocity). This component of the force can be described by the scalar quantity called scalar tangential component ( , where is the angle between the force and the velocity). And then the most general definition of work can be formulated as follows: Work of a force is the line integral of its scalar tangential component along the path of its application point. Simpler (intermediate) formulas for work and the transition to the general definition are described in the text below.
Force and displacement If a force F that is constant with respect to time acts on an object while the object is translationally displaced for a displacement vector d, the work done by the force on the object is the dot product of the vectors F and d:[3] (1) where
is the angle between the force and the displacement vector.
Gravity F=mg does work W=mgh along any descending path
Whereas the magnitude and direction of the force must remain constant, the object's path may have any shape: the work done is independent of the path and is determined only by the total displacement vector . A most common example is the work done by gravity – see diagram. The object descends along a curved path, but the work is calculated from , which gives the familiar result . More generally, if the force causes (or affects) rotation of the body, or if the body is not rigid, displacement of the point to which the force is applied (the application point) must be used to calculate the work. This is also true for the case of variable force (below) where, however, magnitude of can equally be interpreted as differential displacement magnitude or differential length of the path of the application point. (Although use of displacement vector most frequently can simplify calculation of work, in some cases simplification is achieved by use of the path length, as in the work of torque calculation below.) In situations where the force changes over time, equation (1) is not generally applicable. But it is possible to divide the motion into small steps, such that the force is well approximated as being constant for each step, and then to express the overall work as the sum over these steps. This will give an approximate result, which can be improved by
Work (physics)
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further subdivisions into smaller steps (numerical integration). The exact result is obtained as the mathematical limit of this process, leading to the general definition below. The general definition of mechanical work is given by the following line integral: (2) where: is the path or curve traversed by the application point of the force; is the force vector; is the position vector; and is its velocity. The expression
is an inexact differential which means that the calculation of
path-dependent and cannot be differentiated to give
is
.
Equation (2) explains how a non-zero force can do zero work. The simplest case is where the force is always perpendicular to the direction of motion, making the integrand always zero. This is what happens during circular motion. However, even if the integrand sometimes takes nonzero values, it can still integrate to zero if it is sometimes negative and sometimes positive. The possibility of a nonzero force doing zero work illustrates the difference between work and a related quantity, impulse, which is the integral of force over time. Impulse measures change in a body's momentum, a vector quantity sensitive to direction, whereas work considers only the magnitude of the velocity. For instance, as an object in uniform circular motion traverses half of a revolution, its centripetal force does no work, but it transfers a nonzero impulse.
Torque and rotation Work done by a torque can be calculated in a similar manner, as is easily seen when a force of constant magnitude is applied perpendicularly to a lever arm. After extraction of this constant value, the integral in the equation (2) gives the path length of the application point, i.e. the circular arc , and the work done is .
A force of constant magnitude and perpendicular to the lever arm
However, the arc length can be calculated from the angle of rotation ensuing product follows:
is equal to the torque
(expressed in radians) as
, and the
applied to the lever arm. Therefore, a constant torque does work as
Work (physics)
Work and kinetic energy According to the work-energy theorem, if one or more external forces act upon a rigid object, causing its kinetic energy to change from Ek1 to Ek2, then the work (W) done by the net force is equal to the change in kinetic energy. For translational motion, the theorem can be specified as:[4]
where m is the mass of the object and v is the object's velocity. The theorem is particularly simple to prove for a constant force acting in the direction of motion along a straight line. For more complex cases, however, it can be for variable force, we can use integration to get the same result. In rigid body dynamics, a formula equating work and the change in kinetic energy of the system is obtained as a first integral of Newton's second law of motion. To see this, consider a particle P that follows the trajectory X(t) with a force F acting on it. Newton's second law provides a relationship between the force and the acceleration of the particle as
where m is the mass of the particle. The scalar product of each side of Newton's law with the velocity vector yields
which is integrated from the point X(t1) to the point X(t2) to obtain
The left side of this equation is the work of the force as it acts on the particle along the trajectory from time t1 to time t2. This can also be written as
This integral is computed along the trajectory X(t) of the particle and is therefore path dependent. The right side of the first integral of Newton's equations can be simplified using the identity
which can be integrated explicitly to obtain the change in kinetic energy,
where the kinetic energy of the particle is defined by the scalar quantity,
The result is the work-energy principle for rigid body dynamics,
This derivation can be generalized to arbitrary rigid body systems.
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Work (physics)
Frame of reference The work done by a force acting on an object depends on the choice of reference frame because displacements and velocities are dependent on the reference frame in which the observations are being made.[5] The change in kinetic energy also depends on the choice of reference frame because kinetic energy is a function of velocity. However, regardless of the choice of reference frame, the work energy theorem remains valid and the work done on the object is equal to the change in kinetic energy.[6]
Zero work An important class of forces in mechanical systems perform zero work. These are constraint forces that restrict the relative movement of bodies. For example, the centripetal force exerted by a string on a ball in uniform circular motion does zero work because this force is perpendicular to the velocity of the ball. As a result the kinetic energy of the moving ball doesn't change. Another example is a book at rest on a table, the table does no work on the book despite exerting a force equivalent to mg upwards, because no energy is transferred into or out of the book. On the other hand, if the table moves upward, then it performs work on the book, since the force of the table on the book will be acting through a distance. A current that generates a magnetic field can also produce a magnetic force where a charged particle exerts a force on a magnetic field, but the magnetic force can do no work because the charge velocity is perpendicular to the magnetic field and in order for a force or an object to perform work, the force has to be in the same direction as the distance that it moves.
References [1] Jammer, Max (1957). Concepts of Force. Dover Publications, Inc.. ISBN 0-486-40689-X. [2] Sur une nouvelle dénomination et sur une nouvelle unité à introduire dans la dynamique, Académie des sciences, August 1826 [3] Resnick, Robert and Halliday, David (1966), Physics, Section 7-2 (Vol I and II, Combined edition), Wiley International Edition, Library of Congress Catalog Card No. 66-11527 [4] Tipler (1991), page 138. [5] Resnick, Robert and Halliday, David (1966), Physics, Section 1-3 (Vol I and II, Combined edition), Wiley International Edition, Library of Congress Catalog Card No. 66-11527 [6] Resnick, Robert and Halliday, David, Physics, Section 4-6
Bibliography • Serway, Raymond A.; Jewett, John W. (2004). Physics for Scientists and Engineers (6th ed. ed.). Brooks/Cole. ISBN 0-534-40842-7. • Tipler, Paul (1991). Physics for Scientists and Engineers: Mechanics (3rd ed., extended version ed.). W. H. Freeman. ISBN 0-87901-432-6.
External links • Work (http://www.lightandmatter.com/html_books/2cl/ch03/ch03.html) – a chapter from an online textbook
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Zero seek
Zero seek Zero seek is a mechanical engineering design component of most computer-controlled data storage devices, including floppy disk drives, tape drives, and early hard drives. Most early data storage devices were controlled primarily by stepper motors, which are able to move in very small, precise rotational movements. These movements were commonly used to define separate physical spaces where data is to be stored, such as the rotations being used to move a read/write head across the surface of a recording media to define tracks of cylinders of data on the media. Although the movement of the stepper is precise, when a device is first powered on, the computer usually cannot immediately determine where the stepper is positioned. It needs to do something in order to calibrate the movement of the stepper so that it can know where the stepper is positioned. The most common method of stepper synchronization is the zero seek, which is to move the stepper until it is able to find track zero. Once track zero has been located, that position is then used to locate all other positions, by continuously staying aware of the number steps the stepper motor has taken. In the event of a severe data error when either reading or writing, it is possible that there has been a sychronization failure and the computer has lost track of the correct position of the stepper. The computer will then perform a zero seek in order to realign the stepper on track zero and get it back in alignment, just in case that were the cause of the problem. Zero seeking takes two primary forms: the hard end-stop and the sensed end-stop. A hard end-stop is often nothing more than a physical barrier against which the stepper mechanism collides and cannot move further. Hard end-stops can be quite noisy because the stepper will usually attempt to advance as far as it ever possibly would normally advance, whether the end-stop is nearby or far way. If nearby, the mechanism collides with the end-stop and continues to attempt to move against it, causing considerable noise and vibration. In some cases the end-stop can go out of alignment after much of this pounding abuse by the sychronization process. A sensed end-stop uses some sort of electronic sensor to determine when the mechanism has reached track zero. The most common form of sensor is the light-beam sensor, using a light-emitting diode and a photosensor. An opaque blade attached to the mechanism cuts the lightbeam just as the mechanism reaches track zero, signalling that the mechanism has arrived and is in alignment. Sensed end-stops are silent because movement of the mechanism stops immediately after track zero has been found.
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Article Sources and Contributors
Article Sources and Contributors Dynamic Vibration Absorber Source: http://en.wikipedia.org/w/index.php?oldid=406364006 Contributors: Gipstar, Guoguo12, Seaphoto, 1 anonymous edits Entertainment engineering Source: http://en.wikipedia.org/w/index.php?oldid=454705166 Contributors: Locopingvin, Michael Hardy, Rjwilmsi, TheTito, Topbanana, West.andrew.g, 4 anonymous edits Mechanical engineering Source: http://en.wikipedia.org/w/index.php?oldid=465367057 Contributors: (3) Livonia Ave. Local, .:Ajvol:., 10metreh, 206504564, 21655, 3Coins, 45Factoid44, 9258fahsflkh917fas, ABF, AXRL, Abraham70, Ac44ck, Ace8101995, Adamblack21, AdjustShift, Admiral Roo, Agogino, Ahoerstemeier, Aiken drum, Aitias, Ajh16, Alansohn, Ale jrb, Ame Errante, Amirrad.en, Amit.phatak, Amitauti, Amrik, Andrea105, Andres, Andrew Jameson, Andy M. 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to experience good ride quality, Wiwalsh00, Wizard191, XJamRastafire, Xev lexx, Xionbox, YellowMonkey, Yuri r, रामा, 219 anonymous edits AFGROW Source: http://en.wikipedia.org/w/index.php?oldid=428841118 Contributors: Alex fx, Arnon Chaffin, Biktora, ChrisHodgesUK, Faycc, Raise exception, Shalom Yechiel, The wub, Will Beback Auto, 7 anonymous edits Agitator (device) Source: http://en.wikipedia.org/w/index.php?oldid=436149132 Contributors: Abush422, Aleenf1, Altenmann, Aushulz, Backonceagain, BrokenSphere, Chanchis2, Closedmouth, Eekerz, Jatkins, Leofric1, Lord Arador, Lotje, Melchoir, N Yo FACE, Nikthestoned, Nuberger13, Special-T, WikHead, 11 anonymous edits Air handler Source: http://en.wikipedia.org/w/index.php?oldid=465115585 Contributors: Anurag.airflowsales, Arthena, Atlant, Btyner, Cherry1212, DragonflySixtyseven, Drilnoth, Eurovent, Falcon8765, Flaktind, Gogo Dodo, Hapeace, Inwind, JLaTondre, Ja 62, Jm307, John of Reading, KurtRaschke, Larry Hopkins, Leeyiulun, Longhair, Marchinopv, Maurreen, McQuayMarcom, MikeWazowski, Mild Bill Hiccup, OlEnglish, P199, Pahazzard, Parksy, Plrk, RJASE1, Ray Van De Walker, Rexwilhoite, Smalljim, Snorlax sleepy, So God created Manchester, SpigotMap, Splash, Stamford spiney, WereSpielChequers, Yannick Lu-Cotrelle, Zvn, 111 anonymous edits Air preheater Source: http://en.wikipedia.org/w/index.php?oldid=461914844 Contributors: Alyhne, Ammubhave, AxelBoldt, Berkut, Biglovinb, BradBeattie, CRGreathouse, Chowbok, Claush66, Clicketyclack, DARTH SIDIOUS 2, Danno uk, Dore chakravarty, DreamGuy, Edward, Element16, Fallschirmjäger, Flewis, Fragmaheaters, Gaius Cornelius, Gimboid13, GorgeCustersSabre, Ground Zero, Hmains, Hooperbloob, Joost.vp, KVDP, Knulclunk, Lidingo, Mbeychok, Melvynflitman, Mikiemike, Patrom, Pigman, Quale, Rinkjustice, Rjwilmsi, Rtdrury, Sentinel75, Shadowjams, SimonP, StealthFox, Superslum, Trusilver, Unbitwise, Wongm, 49 anonymous edits Airshaft Source: http://en.wikipedia.org/w/index.php?oldid=439707573 Contributors: Crusoe8181, Friedo, Hanbrook, Janderson223, Jrcweb, Karada, Longhair, Orangemike, Parhamr, Peter Horn, 17 anonymous edits American Machinists' Handbook Source: http://en.wikipedia.org/w/index.php?oldid=442808189 Contributors: Graibeard, Lumbercutter, Pegship, Three-quarter-ten, Whitis, Wizard191, 3 anonymous edits Applied mechanics Source: http://en.wikipedia.org/w/index.php?oldid=463158790 Contributors: Academic Challenger, Agogino, Amaragijlili, Andareed, AndrewDressel, Another Stickler, Basar, Bbanerje, Blkutter, Brews ohare, Bryt, Cjlim, Cronholm144, DH85868993, David Eppstein, Didsomebodysayme, Dr eng x, Esmhead, Falcor84, Fs, Geschichte, Giftlite, GlassFET, Gsuhasini, Halpaugh, Headbomb, Inwind, Jpc4031, Kalivd, Kanesue, KathrynLybarger, Leppi, Lunch, Mdd4696, Michael Hardy, Mogtheforgetfulcat, MrOllie, Nitin Nehra, Nitya Dharma, Norrisandrew, Okedem, Open2universe, Peterlewis, Rettetast, Rockrolling, Strikehold, TStein, Tinavj, To011, Username11`1344, VanishedUser314159, Zhigangsuo, Âme Errante, Ʒ, 53 anonymous edits Atmosphere (unit) Source: http://en.wikipedia.org/w/index.php?oldid=464665889 Contributors: Acalamari, Adashiel, Ahoerstemeier, AirdishStraus, Andrejj, Andres, Anthony Appleyard, Aushulz, Badseed, Bastin, BigrTex, Bjankuloski06en, Bobblewik, Calair, Can't sleep, clown will eat me, Chemical Engineer, Chromaticity, Cleared as filed, Coolhandscot, Crissov, Cybercobra, Cyp, DBragagnolo, Dbeardsl, Doradus, Frokor, GTBacchus, Gene Nygaard, Gorank4, Greg L, Gutza, Happydude69 yo, Harry, HedgeHog, HenkvD, Henrygb, Hqb, Icairns, Jashiin, Jauerback, Jeltz, Joanjoc, Johndburger, Jrockley, Karelj, Keta, LeBofSportif, Light current, Lightmouse, Mbeychok, Mr. Stradivarius, Murtasa, Musiphil, Paulmewis, Peptuck, Puppy8800, R'son-W, Radiojon, Random832, RoyBoy, Ryanrs, Savidan, Sfo62, Sietse Snel, Simian, Spooky, Superm401, Tew3, The Rambling Man, Thrissel, Thunderbird2, UnbiasedHistory, Urhixidur, Vsmith, Werner X, Wikiborg, Woodstone, Wranadu2, 121 anonymous edits Automaton clock Source: http://en.wikipedia.org/w/index.php?oldid=452982868 Contributors: A2Kafir, David G Brault, Evilandi, Fanatix, Jongleur100, Kivaan, Longhair, Mild Bill Hiccup, Slash Backdrive Source: http://en.wikipedia.org/w/index.php?oldid=455165429 Contributors: ArnoldReinhold, Bearcat, Ron7684, 1 anonymous edits
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Article Sources and Contributors Ball detent Source: http://en.wikipedia.org/w/index.php?oldid=368586736 Contributors: ArmadilloFromHell, Edcolins, GRAHAMUK, GTBacchus, Integracer, Rolf the wolf, Van helsing, 6 anonymous edits Beale number Source: http://en.wikipedia.org/w/index.php?oldid=444607893 Contributors: AtholM, Aushulz, Dhollm, Gene Nygaard, Grutness, Iridescent, Linas, Mikiemike, Pegship, Rich257, Venny85, 1 anonymous edits Bearing surface Source: http://en.wikipedia.org/w/index.php?oldid=376081585 Contributors: ShelfSkewed, Three-quarter-ten, Wizard191 Bellcrank Source: http://en.wikipedia.org/w/index.php?oldid=442747614 Contributors: (npcserver), Aldis90, Andy Dingley, Ashlux, Beeblebrox, Caygeon pete, Firsfron, Head Injury, Malcolma, Maury Markowitz, Rbeas, Rich Farmbrough, SimonP, 10 anonymous edits Bimetallic strip Source: http://en.wikipedia.org/w/index.php?oldid=457604360 Contributors: 2D, 3R1C, Aleenf1, Alexknight12, Alphachimp, AngelOfSadness, Anna Frodesiak, Arakunem, Bemoeial, Bobo192, Bovineone, Buster2058, Caesura, Caltas, CambridgeBayWeather, Cburnett, Chem-awb, Epbr123, Finejon, Finlay McWalter, Flamingsheep1, Funkboy3, Headbomb, Heron, Hustvedt, Imjustmatthew, JSpung, JaviPrieto, Jdpipe, Karelj, King of Hearts, Leonard G., LilHelpa, Lumos3, Magioladitis, Mastrchf91, Maximus Rex, Mboverload, McGeddon, Michael Devore, Michał Sobkowski, Minimac, Moala, Moon Nectar, Palapala, Peter R Hastings, Poloko, Quadell, RB30DE, Riana, Romanm, Rumping, Sanjaymaster, Schumi4ever, SimDarthMaul, Slipperyweasel, Spongefrog, Swish2424, ThomasPusch, Unioneagle, Vareb002, Vicarious, Vsmith, Whiteandnerdy123, Wtshymanski, 134 anonymous edits Block and bleed manifold Source: http://en.wikipedia.org/w/index.php?oldid=412933465 Contributors: AndrewHowse, Basar, Dynaflow, Geozapf, Ghostrider7, Mikec alco, Moglex, NawlinWiki, O keyes, Postcard Cathy, Rich Farmbrough, Timtrent, Valve Solutions, 2 anonymous edits Blood viscoelasticity Source: http://en.wikipedia.org/w/index.php?oldid=440111838 Contributors: Bearcat, Caseydyck, DragonflySixtyseven, Muhandes, Wilhelmina Will, 5 anonymous edits Bolted joint Source: http://en.wikipedia.org/w/index.php?oldid=462999791 Contributors: Achalmeena, Andy Dingley, Arlingtonengineer, BananaManCanDance, Basar, BenFrantzDale, BoJosley, CarolGray, Chris the speller, Dachande, Daleh, Dougher, Drdrtoto, Duk, Długosz, EXcaliberZac, Felixksw, Graibeard, GreyCat, Grotte, Hemmingsen, Hooperbloob, Hudson Fasteners, Hyacinth, JLaTondre, Jhsompura, Justallofthem, Kwantus, LeadSongDog, Leonard G., Luigizanasi, MJ3600, Melesse, Mfwitten, Mighty librarian, Nbarth, Ohnoitsjamie, Paddyez, Pbroks13, Peter Horn, Polyparadigm, Qqzzccdd, R4943112, RJP, Rembecki, Rich Farmbrough, Rjwilmsi, Rlsheehan, Seraphimblade, Sietse Snel, Simian, Skarkkai, Slightlymighty, Slysplace, Sonett72, Spalding, Spiel496, Srinivasbala, SueHay, Sumsum2010, Superherongpogi, The Thing That Should Not Be, Tom harrison, UpstateNYer, VBGFscJUn3, Williampoetra, Wizard191, Wnt, Zeizmic, 71 anonymous edits Brake shoe Source: http://en.wikipedia.org/w/index.php?oldid=451836720 Contributors: ArnoldReinhold, Biscuittin, Bobywow, Buster7, CZmarlin, Citicat, E2eamon, ErikvanB, Kilgoretrout89, Malcolma, NawlinWiki, Ohnoitsjamie, Peter Horn, South Bay, Stusutcliffe, Tam0031, Thedukie7, Untitled0, 6 anonymous edits Break-in (mechanical run-in) Source: http://en.wikipedia.org/w/index.php?oldid=458945964 Contributors: DKwik, John of Reading, Malcolma, Mild Bill Hiccup, Pengo, Rettetast, RickO5, Rjwilmsi, Three-quarter-ten, Twinsday, Wizard191, Zee991, 3 anonymous edits Brinelling Source: http://en.wikipedia.org/w/index.php?oldid=460654457 Contributors: Andy Dingley, CK62, DMahalko, DragonflySixtyseven, Fossilfeatures, Michael Hardy, MuZemike, Peter Horn, Rumiton, Wizard191, 1 anonymous edits Built-up gun Source: http://en.wikipedia.org/w/index.php?oldid=443185802 Contributors: AustralianRupert, Bagheera, Kalmbach, Rcbutcher, Thewellman Bullwheel Source: http://en.wikipedia.org/w/index.php?oldid=456333741 Contributors: A2Kafir, AnnaFrance, Blob5824, EncMstr, Royalguard11, Sandstein, Tuzi, Xezbeth, 3 anonymous edits Burmester's theory Source: http://en.wikipedia.org/w/index.php?oldid=454834260 Contributors: Andy Dingley, Biscuittin, Gadanieli, Gavin.perch, Mcmahon251, Ospalh, Prof McCarthy, Rgdboer, Rich Farmbrough, VanBurenen, Wizard191 Burnishing (metal) Source: http://en.wikipedia.org/w/index.php?oldid=444213776 Contributors: Emok, J04n, Jprevey, Mockingbus, Pakaraki, Plrk, Tbr00, Thomasdiablo, Verdatum, Wizard191, 11 anonymous edits Bushing (isolator) Source: http://en.wikipedia.org/w/index.php?oldid=441604272 Contributors: A. Carty, ABF, Addshore, Ahunt, Alan.ca, Alansohn, Ale jrb, Andre Parent, Animeranger, Armadilloz, BenFrantzDale, BillC, Biscuittin, Breno, Christopher Parham, Dbenbenn, Drbreznjev, Ebenwalker, Elonka, Ethan Mitchell, Ezeu, Finlay McWalter, Fratrep, Fredcipriano, GRAHAMUK, Gaius Cornelius, Gogo Dodo, Greglocock, Grudd, Hooperbloob, Ironicon, J.delanoy, Jessup1010, Jimmymagee, Jodarom, John john john, Jpc4031, Knuckles, Light current, Mdebets, Mike R, Mitrius, Nburden, PenguiN42, Peter Horn, PigFlu Oink, Radagast83, Ranteng, Reedgs, Rmky87, Rvollmert, SWAdair, Salmanazar, Schbrownie, TastyPoutine, Three-quarter-ten, Thumperward, Thurth, Triton Rocker, Wizard191, Wolfkeeper, Xanzzibar, Xezbeth, 54 anonymous edits Calibrated orifice Source: http://en.wikipedia.org/w/index.php?oldid=401613762 Contributors: A2Kafir, Bearcat, Chris Chittleborough, Edward321, Malcolma, Wikilenox, Wolfkeeper, Woodshed, Zowie, 2 anonymous edits Cam Source: http://en.wikipedia.org/w/index.php?oldid=465129600 Contributors: 16@r, 2D, Addshore, Alansohn, Altafqadir, AndrewDressel, Angr, Anna Lincoln, Aoesc10291, Ark25, Arny, Astatine-210, Bdesham, Bennyking, Bifmason, Bobo192, Cameron is emo, Camster1508, Candlefrontin17, Carbuncle, Ccrrccrr, Christopher Mahan, Ciphers, Clairfar, Dhollm, Dictabeard, Dr.K., Drj, Dysprosia, Ed g2s, Egmontaz, Eiyuu Kou, Elsendero, Epbr123, Excirial, Ezhiki, Fayenatic london, Freelance Intellectual, Fromjarod, GB fan, Ghosty231, Gilliam, Glenn, Gun Powder Ma, Gurch, Hadal, HaeB, Hallows AG, Hayaku, Heqwm, Heron, Hintss, Ilario, Indon, J Di, Jagged 85, Jamesontai, Jeffrey Mall, JimVC3, JoanneB, John NRW, Jpc4031, Jusdafax, KVDP, Kieff, Kross, Kusma, LUKE1234, Lear's Fool, Longhair, Luk, Lumos3, Luna Santin, Marc Lacoste, Matthew Yeager, Mdd, Michael Hardy, Moechick101, NellieBly, Ninly, Norm, Ntveem, Oxymoron83, Palx, Patstuart, PericlesofAthens, Phgao, Philip Trueman, Philtodd, PierreAbbat, Pinethicket, Politepunk, Prof McCarthy, PuzzletChung, R'n'B, RONRON61093, RTC, Rebcop-NJITWILL, Renata, RetiredUser124642196, Rizzoandz, Rjwilmsi, SJP, Sango123, Sangwinc, Sarranduin, Sdfasdgasdg, Shadowjams, Shay420shay420, Sonett72, Superweapons, Tergum violinae, The sock that should not be, Three-quarter-ten, Timpersson, Tregoweth, Uirauna, Van helsing, Verloren, WLU, Wayne Slam, WelshMatt, Wikibofh, Wizard191, Ye olde minr, Yrithinnd, Yuri r, Zfr, Zureks, ﻣﺎﻧﻲ, 253 anonymous edits Cam follower Source: http://en.wikipedia.org/w/index.php?oldid=456924022 Contributors: ChrisHodgesUK, GoodOlRickyTicky4, J04n, Jigarpatel12345, Moloch09, Nick Number, Piledhigheranddeeper, Prari, Ronhjones, Serasuna, ShelfSkewed, SoWhy, StaticGull, Three-quarter-ten, VictorianMutant, West.andrew.g, Wikipelli, Wizard191, Wo0dstock79, Woohookitty, 25 anonymous edits Cam plastometer Source: http://en.wikipedia.org/w/index.php?oldid=404153875 Contributors: Carders, Crystallina, Gary King, Grantmidnight, SietskeEN, Wizard191 Campbell diagram Source: http://en.wikipedia.org/w/index.php?oldid=457826312 Contributors: Dontknowhow, Kosiakk, Omnipaedista, R'n'B, Radim.simanek, Redtricycle, Rjwilmsi, Sadads, Whoisjohngalt, 5 anonymous edits Central Mechanical Engineering Research Institute Source: http://en.wikipedia.org/w/index.php?oldid=437748413 Contributors: Abhi19july, Eastmain, IndianGeneralist, JamesAM, Rahulghose, TheCatalyst31, 1 anonymous edits Centrifugal-type supercharger Source: http://en.wikipedia.org/w/index.php?oldid=442377195 Contributors: Blake Burba, CJ DUB, Diceman, Doctormatt, Emt147, Fabiform, Fvw, Gaius Cornelius, Go229, Gzuckier, Hooperbloob, Impreziv, Joema, JohnOwens, JonRB, Kcds, Killer Raccoon, LMB, Maury Markowitz, Mkoronowski, Morven, Oo7565, Peter R Hastings, Rich becks, Rjones, Sfoskett, 24 anonymous edits Century tower clocks Source: http://en.wikipedia.org/w/index.php?oldid=417786913 Contributors: CMG, Doug Coldwell, GoingBatty, RFD, 2 anonymous edits Chilled water Source: http://en.wikipedia.org/w/index.php?oldid=450732282 Contributors: Aelius28, Edgar181, Mgreason, Michał Sobkowski, Paul24112, Vegaswikian, 6 anonymous edits Chiller Source: http://en.wikipedia.org/w/index.php?oldid=459983339 Contributors: A tomasi, Abce2, Adam Schloss, Adam850, Ahoerstemeier, Alan.ca, AndrewWatt, AnthonyQBachler, Arjiebarjie, Atlant, Aushulz, Bastien Sens-Méyé, Bobblewik, Bobdonnell, Booyabazooka, Cathodic, ChemGardener, Chris the speller, Chronulator, CohenTheBavarian, DVdm, Dabomb87, Ecb, Elassint, Epolk, Eurovent, Fastilysock, Flood78, Frédérick Lacasse, Fsiler, FusionNow, Gene Nygaard, Gralo, Hmvont, Hooperbloob, Hu12, IG-2000, Indefatigable, JALsnipe, Jason.cinema, Jeff Silvers, Jo Stainless, JoaoRicardo, John of Reading, Johnsjohn, Khalid hassani, Libro0, LightRobb, Longhair, Mbeychok, McQuayMarcom, MikeWazowski, MikeySq, Mononomic, Muffinon, Mygerardromance, NipponBill, Old Moonraker, P199, PL290, Pashute, Paul Raftery, Piano non troppo, Ppipr, Rick lightburn, Rjanag, Rrostrom, S Roper, SDC, Shawis, Shawnhath, Sneakernets, Solarusdude, Tasiosvas, ThefirstM, Thumperward, Tom harrison, Tombomp, Tracs Chillers, Vascer, Veinor, Viswaprabha, Wayne Slam, Yannick Lu-Cotrelle, Zaccuardi, 182 anonymous edits CILAS Source: http://en.wikipedia.org/w/index.php?oldid=409232452 Contributors: Cpsusinc, Fram, Micru, Rich Farmbrough, VSimonian, 35 anonymous edits
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Article Sources and Contributors Circle grid analysis Source: http://en.wikipedia.org/w/index.php?oldid=400216422 Contributors: Eqsgroup, Stormbay, Whpq, Wizard191, Yewlongbow Coefficient of performance Source: http://en.wikipedia.org/w/index.php?oldid=455164317 Contributors: AchromatReader, Alan Liefting, Allen3, Arn' E. Colobulous, ArnoldReinhold, BlaiseFEgan, Bodybagger, Casper Gutman, Dereckson, ESkog, Edcolins, Edward, Epbr123, FactsAndFigures, Fresheneesz, Imolk, JHunterJ, Jeh25, Johnbibby, Kaze0010, Krazywrath, Longhair, Mac Davis, MahmudAlam, Marshall Williams2, Mbeychok, Mejor Los Indios, Mikiemike, MrOllie, Muffinon, Oli Filth, Pieter Felix Smit, Salsb, Spitfired, Stephan Leeds, Tcncv, User A1, Wikipelli, Wogone, Wtshymanski, Ywaz, 61 anonymous edits Collapse action Source: http://en.wikipedia.org/w/index.php?oldid=332070479 Contributors: Alynna Kasmira, Dudegalea, Hooperbloob, RedWolf, The Anome, Watsonladd, 1 anonymous edits Combined cycle Source: http://en.wikipedia.org/w/index.php?oldid=464581616 Contributors: A man in space, Aaron north, Abtinb, Adamrush,
[email protected], Alureiter, BWDuncan, Beetstra, Bender235, Biscuittin, Chetvorno, Chris Henniker, DabMachine, Delirium, Dethroned Buoy, Dgianotti, Dhollm, DocKrin, Donebythesecondlaw, Edward, Eleman, Engineman, FearChild, Fletcher, Gaius Cornelius, GeeJo, Glenn, Gralo, Haseebsaqib, Hmains, Hooperbloob, Huggorm, Ian Pitchford, Ignignot, Imotorhead, Irooniqermez, J JMesserly, JaGa, Jensbn, Jimad, Joshv, Khalid hassani, Knotnic, Leonard G., LibLord, Liftarn, LilHelpa, Limulus, Linas, Linnormlord, M samadi, MGTom, MagiMaster, Magister Mathematicae, Male1979, Marc Lacoste, Mario Huerta, Mark.murphy, Materialscientist, Mbeychok, MikeL, Million Little Gods, Mion, MisterWeatherbee, Mrl98, Munay09, N5iln, NVAFDiscoStu, OnUrb, OtisF, Pakaraki, Pelle-Gnillot, Petri Krohn, Pjacobi, Plugwash, Quercus basaseachicensis, QuiteUnusual, Qwyrxian, Ragf18, Ray Van De Walker, Rjwilmsi, Robini 99, Roleplayer, Seano1, Sinus, Slogsweep, Spiffy sperry, Steve24, Surfersafari, Tobberoth, Toll booth, User A1, Valuethinker, WhiteDragon, Wikifedo, Wikiliki, Willbit, Wongm, Woohookitty, Woood, Wwoods, Xanzzibar, Yellowstone6, Zhou Yu, Zureks, 185 anonymous edits Compliant mechanism Source: http://en.wikipedia.org/w/index.php?oldid=460823933 Contributors: ArnoldReinhold, Biscuittin, Dirkbike, GeorgeLouis, Hegdesudarshan, Helle49, Hg82, J04n, Joshbm, Juangasa, Naveensmk, R'n'B, RHaworth, Tennisgirlchi, 14 anonymous edits Compound lever Source: http://en.wikipedia.org/w/index.php?oldid=458042637 Contributors: BD2412, EDSClikes2hunt, JimmyGuano, Nick Number Compression (physical) Source: http://en.wikipedia.org/w/index.php?oldid=463835821 Contributors: Allstarecho, Ancheta Wis, AshishG, Binksternet, Blackangel25, COMPFUNK2, Credema, Ddawson, Eeekster, EvilTeeth, Fnlayson, Gene Nygaard, J36miles, Jcronen1, Jormungandr, Jvbishop, Light current, Linas, MCTales, Mattisse, Melonie Smith, Mgnbar, Mystere, Nabla, Patrick, Rlsheehan, Ruy Pugliesi, Segv11, Siqbal, Sprite007, StefanosKozanis, Tagishsimon, Tommy2010, Wizard191, Zarniwoot, 60 anonymous edits Constant air volume Source: http://en.wikipedia.org/w/index.php?oldid=434164826 Contributors: Cmbronwing31, FactsAndFigures, Inwind, Rapidografek, Rjwilmsi, Rsoenneker, Vegaswikian, 5 anonymous edits Constrained-layer damping Source: http://en.wikipedia.org/w/index.php?oldid=336436523 Contributors: C4dn, MuffledThud Contact mechanics Source: http://en.wikipedia.org/w/index.php?oldid=465164791 Contributors: Bbanerje, BenFrantzDale, Edwinv1970, Gene93k, Huijssen2011, John of Reading, Jputhoff, LilHelpa, Luiz.bortolan, Michael Hardy, Ospalh, Reibungsphysik, Rich Janis, Rjwilmsi, Speed8ump, Wizard191, Woohookitty, Wriggers, 27 anonymous edits Frictional contact mechanics Source: http://en.wikipedia.org/w/index.php?oldid=464398633 Contributors: AndrewDressel, Cymru.lass, Edwinv1970, Fyrael, Iohannes Animosus, Khazar, 1 anonymous edits Cooling tower Source: http://en.wikipedia.org/w/index.php?oldid=464675563 Contributors: Abhijit033, AgentPeppermint, Alexabbrevoir, Alynna Kasmira, Ana.socev, Anonymous 57, Anwarulmaruf, Asterion, Auvi82, Barbirossa, BarkingFish, Black Stripe, Blainster, Blue387, Bogdangiusca, Buster2058, Bwnichols, CDM2, Carlos1873, Cathodic, Cenk Endustri, Chanbc, CharlesC, Cherrypj, CompRhetoric, Copeland.James.H, CopelandJim, Crosbiesmith, DJ Creamity, DanTheSeeker, Daniel.Cardenas, DanielCD, Deeptrivia, Deor, Dfeuer, Dirk Schlichting, DragonHawk, Dragunova, Duncan, EdC, Edreher, Edward, Emmanuelxp, Eotterman, ErkDemon, Eurovent, Farosdaughter, Foot, Fuhghettaboutit, Gamewizard71, Godal, Gogo Dodo, Goochelaar, Gralo, H Bruthzoo, Hair2leern, Hairy Dude, Herogamer, Hmains, Hobartimus, Hydrargyrum, Hydrogen Iodide, IanOfNorwich, Ikar.us, Intelshwets, Inwind, J JMesserly, Jackehammond, Jcthunder1, Jeyakumarjohn, Jidanni, Jnestorius, JohnJardine, Jon seah, KDS4444, Kilmer-san, Kkolmetz, Kku, Klow, KnowledgeOfSelf, Kostmo, Koysmile, Krevonims, Lightmouse, Linas, MER-C, MGTom, MONGO, MacBuzz, Mach10, Magister Mathematicae, MarcoTolo, Markus Schweiss, Materialscientist, Mattnad, Maxim, Mbeychok, MikeWazowski, MilestonebyMilestone, MinorProphet, Mion, Mmeijeri, Mononomic, Moreau1, Mr3641, Nekura, Neo-Jay, NewGuy4, Old Moonraker, Oleg Alexandrov, Orphan Wiki, Part Time Security, Pauli133, Peterlewis, PhilKnight, Plerlmoc, Pomte, Racklever, Ratarsed, Reaper Eternal, Remuel, Ritabest, Rjwilmsi, Robinashby, Ronz, Samw, Scwlong, Sean Tevis, Serknap, Sionus, Slov01, Snigbrook, Squeed, Stephan Leeds, SteveBaker, Strait, SunCreator, Sunny7218214, Sych, TJBlackwell, The Thing That Should Not Be, Theanphibian, Themfromspace, Tinton5, Tom harrison, Tony Fox, Tonydevito, TreeBread, Trublu, VQuakr, Velella, Vizu, Vrenator, Vsmith, Webmasterpct, Websites, Xnatedawgx, Yannick Lu-Cotrelle, Zonk43, 262 anonymous edits Coupling Source: http://en.wikipedia.org/w/index.php?oldid=465434565 Contributors: A. di M., A2Kafir, Alansohn, Andrewrp, Andy Dingley, Anthony, Army1987, Balaje07, Banaticus, BenFrantzDale, Biscuittin, Bongwarrior, Brian0918, Broetzner, Catsquisher, Cgumas, Cholaq, Choppingmall, Chrisbolt, Christoph Neuroth, Colonies Chris, Dan Guan, Dangherous, DanielVallstrom, Dcljr, Deor, Dhaluza, Diomidis Spinellis, Eghagstrom, Epbr123, Ewok Slayer, Excirial, FNQ, Fern33, Fibonacci, Gadykozma, Glenn, Golbez, Gwernol, Hadhuey, HappyCamper, Humanoc, Immunize, Jay, Johnbibby, Jrdioko, Jrtayloriv, Khalid hassani, Khendon, Le Fou, Ligulem, Lkinkade, Malvineous, Mattszeto, Mboverload, Mgros, Mikiemike, Mjolnir1984, Mononomic, Morwen, Mr Stephen, Mulad, Natrij, Nehautkur, Neparis, Oli Filth, P199, Peter Horn, Pietrasagh, Prizmman8, RKingsbury, Ram4eva, Reddi, Rjstott, Roadrunner, Robert.schmid, Roe T. Alstromer, Ryguy104gt, Schwallex, SilentC, Smbrown123, SteffenB, Syd1435, Tabatonga, TakuyaMurata, Traal, UserGoogol, V8rik, Van helsing, VanBurenen, Wizard191, YahoKa, Yeokaiwei, Your Lord and Master, 113 anonymous edits Crank (mechanism) Source: http://en.wikipedia.org/w/index.php?oldid=464093339 Contributors: Ahpook, Altermike, Ark25, AtholM, Axlq, Ayax el cronopio, Bensin, Billbeee, Biscuittin, Bnkausik, Chetvorno, ChrisHodgesUK, Christopherlin, CommonsDelinker, Cooksey, Dhollm, EdJogg, Email4mobile, Epolk, Euryalus, F l a n k e r, Fanatix, Gaius Cornelius, Garhowell, Glenn, Golgofrinchian, Graibeard, Gun Powder Ma, Gzuckier, Hqb, Husein Najmi, Infrogmation, JaGa, Jagged 85, Jpc4031, KVDP, Kilo-Lima, Lightmouse, LilHelpa, Luis Dantas, Martarius, Nik Sage, Pak21, Patrick, PericlesofAthens, Picapica, Pion, Quiddity, R'n'B, Sobol2222, Spacepotato, Tam0031, The Thing That Should Not Be, Tommy2010, Tualha, Tweenk, Van helsing, Wizard191, YolanCh, Білецький В.С., Лев Дубовой, 水水, 19 anonymous edits Critical speed Source: http://en.wikipedia.org/w/index.php?oldid=441562005 Contributors: Flopsy Mopsy and Cottonmouth, Fresheneesz, Halpaugh, Hamiltondaniel, J.delanoy, LilHelpa, Maayaavi, Pradipta vaskar, Spectraquest, Wiwalsh00, 16 anonymous edits Cryogenic engineering Source: http://en.wikipedia.org/w/index.php?oldid=464517243 Contributors: ANIKETDC.MECH, GrahamCrusty, IgnorantArmies, Iqu, Jovianeye, Malcolma, Nikhilkumarmk.mech, Patchy1, Postcard Cathy, RHaworth, RichardOSmith, Rohitbk.mech, Tabletop, Terrek, Vishalpb.mech, 2 anonymous edits d'Alembert–Euler condition Source: http://en.wikipedia.org/w/index.php?oldid=396328964 Contributors: AxelBoldt, Hmains, Legoktm, Lunch, Michael Hardy, Philip Trueman, Rakby, Tfl D-value (transport) Source: http://en.wikipedia.org/w/index.php?oldid=443786137 Contributors: Bakerwayne, Jamietw, Katharineamy, Mikael Häggström, Mr Sheep Measham, VernoWhitney Damper (flow) Source: http://en.wikipedia.org/w/index.php?oldid=461598680 Contributors:
[email protected], Atlant, BenFrantzDale, Bettia, CanadianLinuxUser, Ceyockey, David R. Ingham, Inwind, Longhair, Mikeblas, Nick Number, P199, Radagast83, Radiojon, Rinkjustice, Scott D, Spalding, Spangineer, Woodshed, 18 anonymous edits Damping matrix Source: http://en.wikipedia.org/w/index.php?oldid=416549938 Contributors: CharlesCo, Kuyabribri, Logan, Michael Hardy, Seddon, 1 anonymous edits Demister (vapor) Source: http://en.wikipedia.org/w/index.php?oldid=348605661 Contributors: AtholM, Aushulz, Davecrosby uk, Depictionimage, Euchiasmus, Graham87, Liface, Mbeychok, R.J.Oosterbaan, Scriberius, Shaddack, Thienz, Tucats, Warren oO, 10 anonymous edits Design and manufacturing of gears Source: http://en.wikipedia.org/w/index.php?oldid=463598554 Contributors: Aniketam.mech, Bearcat, Gunit31, Katharineamy, Kudpung Design for manufacturability for CNC machining Source: http://en.wikipedia.org/w/index.php?oldid=432093729 Contributors: Dfmcnc, Eadro, Elockid, Gfoley4, Hamiltondaniel, Jncraton, Jonathanwf, Kjkolb, Malcolma, Oracleconnect, Pietrow, Prashant chan, Rjwilmsi, Sweetness46, Tabletop, Wizard191, 15 anonymous edits Dexel Source: http://en.wikipedia.org/w/index.php?oldid=456538256 Contributors: Dontknowhow, Island Monkey, Nono64 Disc coupling Source: http://en.wikipedia.org/w/index.php?oldid=452379318 Contributors: Aruland, CommonsDelinker, NawlinWiki, P199, Soap, Three-quarter-ten, Ukexpat, 3 anonymous edits Docking sleeve Source: http://en.wikipedia.org/w/index.php?oldid=392000078 Contributors: AtholM, CommonsDelinker, Kingturtle, OlEnglish, ShakespeareFan00, Tristessa de St Ange, Wongm, Zephalis
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Article Sources and Contributors Drive by wire Source: http://en.wikipedia.org/w/index.php?oldid=452026548 Contributors: Babbage, Billheller, Bmoosani, Bobber100, Bram89, Davidgothberg, Dr. zedy, Edward, Frank Lofaro Jr., Fratrep, Harris000, IcemanJ256, Itinerant1, Jeodesic, JoniFili, Kallog, Krevnasty, Lightning12, Maclauk, Nihiltres, Ospalh, R'n'B, Rhoseinnezhad, Rl, Sfoskett, SkiDragon, Stillnotelf, Vegaswikian, Whisky drinker, 52 anonymous edits Duality (mechanical engineering) Source: http://en.wikipedia.org/w/index.php?oldid=449825309 Contributors: J04n, Vadmium, ﺳﻌﯽ Dunkerley's method Source: http://en.wikipedia.org/w/index.php?oldid=316180803 Contributors: Abcdefghayden, Biscuittin, Bmunden, Canis Lupus, Killercarpcatcher, Malcolma, Michael Hardy, 10 anonymous edits Duty cycle Source: http://en.wikipedia.org/w/index.php?oldid=462789980 Contributors: A. B., Aicchalmers, Amikake3, BD2412, Bearcat, Berserkerus, Breno, Charly Whisky, Compholio, CyrilB, Deville, Dicklyon, Endomion, Freddyjoejaeger, Frencheigh, Furrykef, Giftlite, Glenn, Gurch, Heron, Jennavecia, Katharineamy, MBisanz, Mortense, Mpfiz, NERIC-Security, NeoChaosX, Nigholith, Nmnogueira, Ohms law, OmarBradley, Omegatron, Phlake, Quercus basaseachicensis, Ruslik0, Ryk, ShotgunSanches, Skewmeister, Snottywong, SteinbDJ, Stephen Wilson, Stigmj, Suruena, Teslaton, Thomasgruebler, Toffile, Yamamoto Ichiro, Zdenekkrejci, Σ, ﺧﺎﻟﻘﯿﺎﻥ, 87 anonymous edits Dynamometer Source: http://en.wikipedia.org/w/index.php?oldid=461585384 Contributors: Ahoerstemeier, Andy Dingley, Anitahaase, AnnaFrance, ArglebargleIV, Arnie1066, Aude, BenFrantzDale, Beta34, Bjelleklang, Bobblewik, Brianhe, C J Cowie, CanisRufus, Cantaloupe2, CarlZenor, Cholycross, Chowells, Chris the speller, Crazedcougar, Crickel, D6, DYNO46, Daniel.Cardenas, Dennis Bratland, Dger, Dhollm, Djonen, Dodgeelkins, Dynoboy, Firsfron, Fraserb, Fuhghettaboutit, Gaius Cornelius, Gamewizard71, Gantvik, Gene Nygaard, GraemeL, Habensm, Hooperbloob, Hu12, IJB TA, ItsZippy, Jeff Relf, Jgodden, Jkelly, JoeSmack, JoshLMeyer, Jwinst, KGasso, Kaibabsquirrel, Kertmiller, Klparrot, Knotnic, Koavf, Kychan1958, Lightmouse, Mandarax, Marc Salvisberg, Materialscientist, Me0u9171, Michael Hardy, Mikeblas, Mikelantis, Mitch Ames, Motorhead, NeonMerlin, Netkinetic, Nopetro, Parajohnd, Pbroks13, Piano non troppo, Pilser, Pkgx, Posix memalign, Primetime, R'n'B, Remuel, Rjstott, Rmashhadi, Ruudse, S.orellanawps, Sammy Mu, Silent52, Skywalkar, Snowolf, Sonett72, Strike Engine, Susfele, Svtsnake03, SyntaxError55, Tide rolls, Vegaswikian, Veinor, Voidxor, Vometia, Wdwd, Wintonian, Wizard191, 201 anonymous edits Edmund Key Source: http://en.wikipedia.org/w/index.php?oldid=429928811 Contributors: Bearcat, Esourcemarketing, Wilhelmina Will, 1 anonymous edits Embedment Source: http://en.wikipedia.org/w/index.php?oldid=463005918 Contributors: BananaManCanDance, Dougher, Martin.medved, Nsaa, Shaddack, Wizard191, Woohookitty, 6 anonymous edits Engineering design process Source: http://en.wikipedia.org/w/index.php?oldid=461780644 Contributors: Acroterion, Alansohn, Allan McInnes, Alvestrand, Andyjsmith, Arthena, Avicennasis, BD2412, Belovedfreak, Boccobrock, Bsrboy, Buddhahopper, COMPFUNK2, Calmer Waters, CanadianLinuxUser, CarbonLifeForm, Coemgenus, Corruptcopper, DMS, Davidullman, Douglasr007, Epbr123, Esprit15d, Favonian, Frongle, GSMR, Graymornings, Intotherye, Inwind, J.delanoy, J04n, Jaredrkennard, Jeff3000, Jncraton, John of Reading, Johngee1, Kaebae1127, Khalcyon, Kilmer-san, Leaf7786, Lights, LilHelpa, MER-C, MKoltnow, Materialscientist, Mdd, Michael93555, Motyka, MrOllie, Nanomega, Nasa-verve, Nejuf, Nick Number, Obankston, Oicumayberight, Oneiros, Paul Silverman, Pdcook, Pen1234567, Piano non troppo, Piast93, Plunkerman, Quantpole, Rhondalorraine, Ronz, Roymcloud93, Ryoutou, S h i v a (Visnu), Scetoaux, ScottJ, Sellyme, Semaj Ydoc, Silly rabbit, StanGawlik-NJITWILL, StaticGull, The Thing That Should Not Be, Tide rolls, Underpants, Utcursch, Vipinhari, Wenttomowameadow, Woohookitty, Yeokaiwei, 218 anonymous edits Engineering Equation Solver Source: http://en.wikipedia.org/w/index.php?oldid=455870990 Contributors: Bearcat, Dawynn, Jain.dhrj, Jdpipe, Rpyle731, Xezbeth, 2 anonymous edits Engineering fit Source: http://en.wikipedia.org/w/index.php?oldid=457524544 Contributors: Andres, Epbr123, Gargoyle888, HPeugeot, Mifter, Rlsheehan, Wizard191, 10 anonymous edits Envelope (motion) Source: http://en.wikipedia.org/w/index.php?oldid=458581388 Contributors: Altermike, Chaosdruid, Chris the speller, DARTH SIDIOUS 2, El monty, Fortdj33, Inwind, Page Up, StuRat, 5 anonymous edits ERF damper Source: http://en.wikipedia.org/w/index.php?oldid=397864556 Contributors: Aarghdvaark, Bearcat, Cybercobra, Headbomb, J Milburn, Malcolma, Northamrtr Euler–Bernoulli beam equation Source: http://en.wikipedia.org/w/index.php?oldid=462233161 Contributors: Adamcone, Alangstone,
[email protected], Arthena, BahramH, Basar, Baxtrom, Bbanerje, Ben pcc, Bender235, Beren, Bkell, Black Falcon, BlueOrb, BoJosley, Buffetrand, CWenger, Carnildo, Chris the speller, Crowsnest, Dhollm, DonQ1906, Dsivil, Eerb, El C, Email4mobile, EndingPop, Gaius Cornelius, Gene Nygaard, Giftlite, Gmclureg, Gpayette, Headbomb, Heron, Hidekih, Hooperbloob, I do not exist, IanOfNorwich, IronGargoyle, Jcw69, Jeff G., JonnyJD, Kahoolie, Kallog, Kolyma, KraZug, Lar, Lightmouse, Ligulem, Mecanismo, Michael Belisle, Michael Hardy, Mintz l, Myasuda, Nostraticispeak, PAR, Piano non troppo, RG2, RJFJR, Raghu1202, Riceplaytexas, Riki, Rtyq2, Sam Hocevar, Seam.us, Sonett72, Srich32977, Tide rolls, Tkn20, UpstateNYer, Visor, Vladsinger, Wikiwide, Wilkn, YK Times, Ytrottier, Zhigangsuo, Zzyzx11, 青子守歌, 105 anonymous edits Fan coil unit Source: http://en.wikipedia.org/w/index.php?oldid=458484182 Contributors: AKB10,
[email protected], Beax, Bobdonnell, Ccrrccrr, EoGuy, Eurovent, Iridescent, Johntindale, McQuayMarcom, Melchoir, MikeWazowski, Muffinon, P199, Pahazzard, PeterQL, Ray Van De Walker, Rporter8555, Slady, Valdoria, Yannick Lu-Cotrelle, 23 anonymous edits Feedwater heater Source: http://en.wikipedia.org/w/index.php?oldid=385586804 Contributors: Bobblewik, EdJogg, Ettrig, Gabriel Kielland, Gjp23, Hooperbloob, Hugo999, Marminnetje, Mbeychok, MikeRiggs, Neurolysis, Signalhead, Slambo, Usafharvey, 16 anonymous edits Fillet (mechanics) Source: http://en.wikipedia.org/w/index.php?oldid=435225732 Contributors: Bapho, CheMechanical, Deflective, Dricherby, Hooperbloob, Interiot, Jackhmo, Jkuhl, Kafziel, Kwamikagami, Leonard G., Reubj, Rich Farmbrough, Wizard191, 16 anonymous edits Flange Source: http://en.wikipedia.org/w/index.php?oldid=464518745 Contributors: AGoon, Aarem, Acdx, ActivExpression, Addshore, Ahoerstemeier, Alex bartho, Alexius08, Alphachimp, Amikake3, Andrea105, Anilocra, Anna Frodesiak, Apparition11, Ashley Pomeroy, Aushulz, Ausxan, Basar, Biker Biker, Bk2204, Bobo192, Bornhj, Brambleclawx, Bryan Derksen, Bubba hotep, Can't sleep, clown will eat me, Catslash, Cfandrew, CheMechanical, Checco, Ckatz, Comenboy, Cst17, D, DMacks, DTOx, Dallyn21, Dong187, Dspradau, Duffbeerforme, ENeville, Edcolins, Epbr123, Falkonry, Flangeking, Flangemandrew, Food dude2007, Foucoult, Geologyguy, Gjp23, Gogo Dodo, GregorB, Gtdp, Guyinthenw, Gwernol, Gypsum Fantastic, Haemo, HappyInGeneral, Hellbus, Heron, Husond, IRP, Industrial Torque Tools, InstEng, Inzy, Iohannes Animosus, IronGargoyle, Isaac Rabinovitch, J.delanoy, JOHNJMAZUREK, Jigneshsteel123, Kainybbz, Kedi the tramp, Keilana, Khalid hassani, Kjoonlee, Kmccoy, Knucmo2, Kostmo, Kubigula, Kuru, Laurie299, LiamE, Life of Riley, Lost on belmont, MBK004, MER-C, Maffsham, Marc omorain, Mariegriffiths, MarnetteD, Mattisse, Mausy5043, Mcgeeflange, Mel Etitis, Menezies C, Mike51025, Miles underwood, Mintrick, MonoAV, Morenooso, Mpiff, Muckluck14, Nae'blis, Navid1366, NawlinWiki, Nixeagle, Nposs, Nsaa, O, Ohnoitsjamie, OrangeDog, Peter Horn, Phil Boswell, Preisler, Quasispace, Radiojon, Rautopia, Retired username, Rettetast, Riana, Rjstott, Rpresser, Samir, Samuel Blanning, Sango123, Skater333, Starnestommy, Steveprutz, Stybn, SusanJ, TastyPoutine, The Yeti, The undertow, Theda, Thewayforward, Three-quarter-ten, Thryduulf, TomGreen, Vanakaris, Velella, Vrenator, Wermac, Wiki alf, Xareu bs, Xx-sallz-xx, Yatra2yatra, Yettie0711, Zalgo, 260 anonymous edits Float (liquid level) Source: http://en.wikipedia.org/w/index.php?oldid=421540327 Contributors: Berek, Lawrence Kelley, Tbennert Flow stress Source: http://en.wikipedia.org/w/index.php?oldid=457670001 Contributors: Btilm, Burntsauce, J04n, Katharineamy, Mgizzle4shizzle, Shellingfordpku, SietskeEN, Submano, Wizard191, 15 anonymous edits Fluid power Source: http://en.wikipedia.org/w/index.php?oldid=461690311 Contributors: Alexknight71, Autoerrant, Biscuittin, Bluemoose, C1ay, Cbdorsett, Charles Matthews, Cholo733, Chris the speller, Conscious, Craig Pemberton, DV8 2XL, Daiyuxia, Davidljung, Drmbenj, Duk, Dwiki, Ectortapia, Eoy4, Giftlite, Greg Linn, Hydraulicinnovations, IW.HG, Ian Pitchford, Jehochman, JoD, KnowledgeOfSelf, LeaveSleaves, LizardJr8, Louis7, Manhartsgruber, Michael Devore, Michael Hardy, Niteowlneils, Nposs, Oda Mari, Orpheus, PL290, Paul Richter, Petri Krohn, RJP, RatOmeter, That Guy, From That Show!, The Holy Roman Emperor, Thonil, Van helsing, WP137, Wtshymanski, 62 anonymous edits Formability Source: http://en.wikipedia.org/w/index.php?oldid=459783696 Contributors: BD2412, Guoguo12, JHunterJ, MER-C, Magioladitis, Tilledw, Wizard191, 5 anonymous edits Fretting Wear Source: http://en.wikipedia.org/w/index.php?oldid=332354655 Contributors: AtholM, Canis Lupus, Hooperbloob, ImGz, Nihiltres, P.r.lewis, Woohookitty, 3 anonymous edits Friction loss Source: http://en.wikipedia.org/w/index.php?oldid=465222169 Contributors: Ac44ck, Alan Liefting, Aushulz, Bluap, Bobblehead, DarkFalls, Eliyak, Eplack, Hooperbloob, Jclemens, Lantonov, MER-C, Mattisse, Moribello, Pearle, Qwertyuiopaass, Rich Farmbrough, Sargas83, Shadowjams, Squids and Chips, Txgp17, Woohookitty, 16 anonymous edits Galling Source: http://en.wikipedia.org/w/index.php?oldid=460540145 Contributors: 6birc, A2Kafir, Alga, Argyriou, BenFrantzDale, Beyond My Ken, Bob House 884, Chris the speller, Clarityfiend, CommonsDelinker, Drbreznjev, Epicurus2112, Gail, GameOn, Haraldwallin, Holme053, JGreul, Jimfbleak, JohnBlackburne, Johnuniq, Kjkolb, Larryisgood, Manofthesea, Moxy, Neelix, Niels Olson, Phuzion, R M Dee, R'n'B, Ra1d3n, Radagast83, Rifleman 82, Samuel Blanning, SebastianHelm, Shaddack, Shearonink, Thumperward, Tournesol, Uusitunnus, Wcoole, WereSpielChequers, Wizard191, Ytrottier, Zingowner, 77 anonymous edits Gear Source: http://en.wikipedia.org/w/index.php?oldid=465419218 Contributors: 16@r, 2301700056mark, 28421u2232nfenfcenc, 360creep, 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Article Sources and Contributors Idler Source: http://en.wikipedia.org/w/index.php?oldid=460974656 Contributors: Hooperbloob, J.delanoy, Kathleen.wright5, KeithD, Perodicticus, Treekids, 5 anonymous edits Idler-wheel Source: http://en.wikipedia.org/w/index.php?oldid=368901380 Contributors: Bogey97, Collector57, Geniac, Hooperbloob, Longhair, SoCalSuperEagle, Speedferry, Tkynerd, 10 anonymous edits Index of mechanical engineering articles Source: http://en.wikipedia.org/w/index.php?oldid=461174167 Contributors: 3Coins, Alan Liefting, AndrewHowse, AnnaFrance, Avenue, Beetstra, Burgergary, Carolinahockey00, Commander Keane, Copeland.James.H, Dfmcnc, Ehudshapira, Ensign beedrill, GTBacchus, Giggy, HEL, Harryboyles, Hazelsct, Heegoop, Hongooi, Hoo man, J04n, LearnMore, Logicman1966, Materialscientist, Mausy5043, Mr pand, Mxn, Neparis, Notyouravgjoe, NuclearWarfare, Paolo.dL, Peter Horn, Pjvpjv, Quiddity, Rgdboer, Rjwilmsi, Ronz, Snoyes, Stef breukel, The Transhumanist, VikOlliver, Vortexrealm, Woohookitty, Zuejay, 139 anonymous edits Indexing (motion) Source: http://en.wikipedia.org/w/index.php?oldid=414799863 Contributors: Longhair, Three-quarter-ten, Wizard191 Injector Source: http://en.wikipedia.org/w/index.php?oldid=464257935 Contributors: 7severn7, 84user, A5b, Andy Dingley, Anthony Appleyard, Atlant, Bergsten, Bermicourt, CZmarlin, Claush66, DA3N, DePiep, Die Oubaas, DocKrin, Dore chakravarty, Drmies, E Wing, Ellehammer1904, France3470, GS3, Gertdam, Giraffedata, Globbet, H Padleckas, HarryHenryGebel, Hellbus, Hrm3319, Hydrargyrum, Incompetence, Interiot, Inwind, JohJak2, Kelly Martin, Ketiltrout, Kkmurray, KnowledgeOfSelf, LilHelpa, LouisCYUL, Lvranek, Magioladitis, Mbeychok, Mcapdevila, Miwanya, Nilsrk, Per Honor et Gloria, Peridon, PhilKnight, Pol098, Postrach, RJFJR, Rogerzilla, Rpresser, Rsajan1, Sabergum, Sean Whitton, SimonP, Sobhuev, Stahlkocher1, User A1, Varano, Velella, Wikiborg, Zhangzhe0101, 40 anonymous edits Interference fit Source: http://en.wikipedia.org/w/index.php?oldid=446141576 Contributors: A2Kafir, Anachron, AndrewDressel, BAxelrod, Balok, Bbaddorf, BenFrantzDale, Bigdumbdinosaur, Cstaffa, DerrickOswald, Dispenser, Evand, HPeugeot, Hashem62, Hooperbloob, Longhair, Lumbercutter, Otrfan, Peter Horn, Regofix, Rlsheehan, S Roper, Sameer pandya, SamuelRiv, Sole Soul, Sourgreentomatoes, Tagishsimon, Three-quarter-ten, VBGFscJUn3, Wizard191, Xchbla423, Ymulleneers, 25 anonymous edits ITA – Iscar Tool Advisor Source: http://en.wikipedia.org/w/index.php?oldid=443342312 Contributors: JaGa, Stkn, VQuakr Jaw coupling Source: http://en.wikipedia.org/w/index.php?oldid=451275834 Contributors: Aruland, CommonsDelinker, Crazyjoe, Deb, ESkog, Fabrictramp, Hooperbloob, Katharineamy, NawlinWiki, Ruslik0, Shkod, Triaged, Ukexpat, 5 anonymous edits JIC fitting Source: http://en.wikipedia.org/w/index.php?oldid=436835168 Contributors: Ale jrb, Bigdumbdinosaur, Evand, Fabrictramp, Frankl1000, Gary King, GregorB, Jerry, Rlandrum, Sbowers3, Scottanon, Wizard191, Zundark, 3 anonymous edits Kinematic coupling Source: http://en.wikipedia.org/w/index.php?oldid=455487678 Contributors: 1ForTheMoney, AtholM, Bearcat, BenFrantzDale, Fortdj33, Malcolma, Prof McCarthy, RHaworth, Rjwilmsi, 5 anonymous edits Kinematic determinacy Source: http://en.wikipedia.org/w/index.php?oldid=303203264 Contributors: BenFrantzDale, Longhair, NSR, Seihin, Srleffler, 2 anonymous edits Kinematic diagram Source: http://en.wikipedia.org/w/index.php?oldid=451528742 Contributors: Bearcat, CWenger, Nikola Smolenski, Osidge, R3owen, Rgdboer, Rich Farmbrough, TheTito, 4 anonymous edits Laboratory for Energy Conversion Source: http://en.wikipedia.org/w/index.php?oldid=423689458 Contributors: Banej, Biscuittin, Lec-newton, LilHelpa, 1 anonymous edits Lamina emergent mechanisms (LEMs) Source: http://en.wikipedia.org/w/index.php?oldid=458991814 Contributors: 78.26, Hg82 Larry Howell Source: http://en.wikipedia.org/w/index.php?oldid=434527700 Contributors: 78.26, Hg82, Tennisgirlchi Light Aid Detachment Source: http://en.wikipedia.org/w/index.php?oldid=415327937 Contributors: Cool Blue, Cyfal, Davecrosby uk, Gogogarry, Kernel Saunters, RJFJR, Rjwilmsi, Trevor Marron, 10 anonymous edits Limits and fits Source: http://en.wikipedia.org/w/index.php?oldid=459758240 Contributors: Anthony Appleyard, Bearcat, DexDor, LilHelpa, Malcolma, Mattslay, Yogeshmj.mech, 1 anonymous edits List of gear nomenclature Source: http://en.wikipedia.org/w/index.php?oldid=460434659 Contributors: Biscuittin, Catsquisher, ClickRick, Darkwind, Incnis Mrsi, JohnBlackburne, Michael Hardy, Mrbob715, Open2universe, Peter Horn, Tommy2010, We hope, Wizard191, 21 anonymous edits Machine (mechanical) Source: http://en.wikipedia.org/w/index.php?oldid=464405726 Contributors: Auntof6, Petershank, Prof McCarthy, R'n'B, Rgdboer, Wizard191 Machinery's Handbook Source: http://en.wikipedia.org/w/index.php?oldid=456814730 Contributors: ASCIIn2Bme, Alan Liefting, BenFrantzDale, Chris Capoccia, LA2, LP-mn, Lumbercutter, MakeRocketGoNow, Pegship, Peter Horn, Three-quarter-ten, Toastydeath, Utcursch, Wadems, Wizard191, 19 anonymous edits Maintenance engineering Source: http://en.wikipedia.org/w/index.php?oldid=464420923 Contributors: Ace Corona, Christian Lassure, Ciphers, Fabrictramp, Gaia Octavia Agrippa, Gaius Cornelius, Harryzilber, JaGa, Kijasa, Libro0, LilHelpa, Malcolma, Maurizio.Cattaneo, NCS2004, R'n'B, Xecide, 16 anonymous edits Maintenance, repair, and operations Source: http://en.wikipedia.org/w/index.php?oldid=458517231 Contributors: 16@r, Abisys, Adam850, Ahunt, Alansohn, Alex756, Altermike, Ashu unique, Beenturns23, Belovedfreak, Billdakelski, Bkbroilers, Bonadea, Brian Radwell, Brown.kj, CALR, COMPFUNK2, CRGreathouse, Capricorn42, Christian Lassure, Ckatz, CommonsDelinker, Crunchy Numbers, D.h, Damowe, Denturerepairlab, Dwo, EECavazos, Elonka, Energiie, Fredbauder, Freeformer, Glenn, GraemeMcRae, HECOTracRat, Haakon, HappyInGeneral, Harriv, Hasankachal, Hashem sfarim, Ignorance is strength, Jim.henderson, Jmax-, Kgorman-ucb, Kjkolb, Kuru, Kvng, Lasta, Leksey, Liao, Loftyideaz, Longhair, Lotje, Lowellian, MRC83, Mac, Maintman16, Mctim, MelSkunk, Miladtai, Mr Minchin, MrOllie, Mrg3105, Ngenox, No1lakersfan, Notinasnaid, Olegwiki, Pasajero, Przepla, R'n'B, Realization, Robert Weemeyer, Roux, SK8Rider, Sawireless2000, Shadowjams, Silverpop81, SimonArlott, SimonP, Sjagdish80, Skarebo, Sn4s, Software-surprise, SouthLake, Spalding, Sqush101, Stevertigo, The Thing That Should Not Be, Thumperward, Timdunfee, Tinton5, Tucvbif, Ukexpat, Valfontis, Vince, Viridae, Wikiped4ik, Williamborg, Woohookitty, Ysangkok, 109 anonymous edits Marks' Standard Handbook for Mechanical Engineers Source: http://en.wikipedia.org/w/index.php?oldid=436690125 Contributors: Phoebe, Wikiklrsc, 4 anonymous edits Mass transfer Source: http://en.wikipedia.org/w/index.php?oldid=452410883 Contributors: -- April, Acroterion, Ahasrh21, Alfio, AstroNomer, AvicAWB, BeastRHIT, Biglama, Bob, COGDEN, ChE Fundamentalist, Conversion script, Davey5505, Dhollm, Docu, Eat411, FactsAndFigures, Fanghong, Fingerz, Ghosts&empties, GregRM, Hesacon, Igoruha, Inwind, JHobbs103, Karol Langner, Ketiltrout, Mausy5043, Mirwin, NawlinWiki, Newuy, Okedem, Peter in s, Phmoreno, Physchim62, Ppntori, Radiant chains, RedWolf, Rifleman 82, Rnt20, Slashme, Squids and Chips, Srleffler, StephRichmond-NJITWILL, Sunilshamnur, Tunheim, Unconcerned, Δ, 37 anonymous edits Mating connection Source: http://en.wikipedia.org/w/index.php?oldid=434069304 Contributors: Biscuittin, Eivind, Harryzilber, Hooperbloob, Infoporfin, MichaelKor, 2 anonymous edits McKinley Climatic Laboratory Source: http://en.wikipedia.org/w/index.php?oldid=464797512 Contributors: Biruitorul, Brutaldeluxe, D6, Doncram, Dravecky, Ebyabe, Gaius Cornelius, Hermanoere, Jfknrh, Jllm06, KudzuVine, Mandarax, Mark Sublette, Mattsrevenge, Ridge Runner, Vegaswikian, 4 anonymous edits Mechanical advantage device Source: http://en.wikipedia.org/w/index.php?oldid=430267842 Contributors: Glenn Mechanical efficiency Source: http://en.wikipedia.org/w/index.php?oldid=455487935 Contributors: 95j, A Softer Answer, Aitias, Andy M. Wang, Astral, Bcrbbmx, BiH, CRGreathouse, Conscious, FreplySpang, Hooperbloob, Hut 8.5, Jetru, Materialscientist, Melah Hashamaim, Merovingian, OlEnglish, Paved, Perish Song, Philip Trueman, Prof McCarthy, Rios sk, Rmt2m, Rtdrury, Sbmehta, SmartyPanters, Takeitupalevel, TubeWorld, Wikiman65, WolfmanSF, 51 anonymous edits Mechanical engineering technology Source: http://en.wikipedia.org/w/index.php?oldid=451189984 Contributors: Alansohn, BD2412, BaomoVW, Chris the speller, DARTH SIDIOUS 2, Dolamite02, Edurant, EugeneZ, Falcon8765, Ladida, Pascal.Tesson, Pearle, Pekayer11, Pjvpjv, Pluemaster, Reluctance, Sheets.robert, Tabletop, 34 anonymous edits Mechanical singularity Source: http://en.wikipedia.org/w/index.php?oldid=341023096 Contributors: AtholM, Cohesion, Dr. Submillimeter, Knehcsa, Linas, Marcok, Michael Hardy, Mild Bill Hiccup, Nicesai, Nmajdan, Piet Delport, TheTito, 16 anonymous edits Mechanical system Source: http://en.wikipedia.org/w/index.php?oldid=455488030 Contributors: Akarkera, Armadilloz, Derek farn, GIMeer, Gavin.perch, LeyteWolfer, Prof McCarthy, 2 anonymous edits
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Article Sources and Contributors Metallurgical failure analysis Source: http://en.wikipedia.org/w/index.php?oldid=405163601 Contributors: Autoerrant, Berek, Katharineamy, Kingturtle, Nihiltres, Pascal666, Rextiama, Sachinvenga, Shoy, Wizard191 Microelectromechanical systems Source: http://en.wikipedia.org/w/index.php?oldid=464626186 Contributors: A. B., Abadel, Addihockey10, Aesalon, Andreareinhardt, Andrewrp, Antony-22, Anwar saadat, Apollonaire1980, Appliedmst, ArnoldReinhold, Arteitle, Aveclafaux, Average Earthman, Bachrach44, Barlian, Batlep1, Beatnik8983, BernardKevin, Berserkerus, Bknoblich, Bobblewik, Bontragerltd, Borgx, Brianhe, Cakepower, Calvin 1998, Canaima, Carl086, Chaiken, CharlesC, Christopher Thomas, Ciprianr, Coneal, Conversion script, Crowsnest, Cubic Hour, DEEJAY JPM, DReyes5, Dan100, Dana boomer, Dancter, Daneshwiki, Deli nk, Deodar, Derek Ross, Despotuli, Dhollm, Dicklyon, Dinofaralli, Donarreiskoffer, Dr-b-m, DrTorstenHenning, Dreftymac, Dspark76, Dtcdthingy, Ed g2s, Edgar181, Edison, Eeekster, Elipongo, Elkman, Epbr123, Erlingkjerlstrup, Fitzhugh, Freakofnurture, Fredrik, FrummerThanThou, Funandtrvl, GPS GIS, Georgewilliamherbert, Glaurung, Glengarry, Goanookie, Goeckeri, Gzuckier, Haasl, Hanjin, Hede2000, Heikki kuisma, HenrikP, Heron, Hu12, Hunturk, Inductiveload, Isnow, Ivisio, J.delanoy, Jackzhlin, JanKorvink, JasonWoof, Jbw2, Jessemundo, JimScott, Jll, JonHarder, Journals88, Jvkuijk, KD5TVI, Karnesky, Kcpenner, KenFehling, Kenyob, Kenyon, Kirchi edu, Kmaillot, Kruglick, Kurt Jansson, KurtRaschke, Latka, LouScheffer, MBirkholz, MC MasterChef, Markbegbie, MassimoAr, Materialscientist, Matt Britt, Mems1620, Memsconcepts, Mexcellent, Mhopeng, Michael Hardy, Michael-Zero, Michael.Forman, Michaelhuff, Mike Treder, Mike Van Emmerik, Mild Bill Hiccup, Mizouman, MrOllie, Nanotechadvisor, Nicopipo2, Nopetro, Nposs, Ohnoitsjamie, OllieFury, OsamaIsALiar, Pathoschild, Petiatil, Piano non troppo, Pierrot Lafouine, Pilarkitty, Polonium, Praveen pillay, Qantuss, R. S. Shaw, RJFJR, Rabarberski, Rchandra, Reimarspohr, Rh, Rich Farmbrough, Rjwilmsi, Rockoprem, Rspanton, Rubin joseph 10, Rulatir, Ryanhi, SPUI, Sakkaraju, Scarian, Semicolin, Shadowjams, Shawis, Sligocki, Smack, Snowfalcon cu, Soumyasch, Speck-Made, Speight, Sridutt3, StaticGull, Stiucsib86, Stockpotato, Stone, Stsanga, Supten, Suruena, Sutene84, Svick, Swk8173, THEN WHO WAS PHONE?, Techmemsnems, TheBendster, TheDoctor10, ThibaultB, Tinrobert, Toffile, Tommy2010, Torchwoodtwo, Twisp, Vatassery, Veinor, Vgy7ujm, Vortistic, Vspengen, W.F.Galway, WILFR, WLU, Welsh, Wernher, Whaa?, Whosasking, WikHead, Wikdwarlock, Wireless Keyboard, Wisden17, Wizard191, Wjbeaty, Woohookitty, Xiner, Zakblade2000, Zondor, Δ, ﻋﻠﯽ ﻭﯾﮑﯽ, 502 anonymous edits User:Mkoronowski/turbomachinery Source: http://en.wikipedia.org/w/index.php?oldid=430148113 Contributors: Mkoronowski Modal analysis Source: http://en.wikipedia.org/w/index.php?oldid=457749794 Contributors: BenFrantzDale, Binary TSO, Cgrislin, Dancter, Eaolsen, Gjwaldie, Greglocock, Hu, Inwind, Iyovan, Jmh649, KaiBorgeest, Kidcharles, LindsayH, Lzyvzl, Michael Hardy, Mild Bill Hiccup, Mitiit, Msb103, Omnipaedista, RaseaC, Reyk, Rwl10267, Sboesche, Shustov, Slffea, Steve Quinn, Vuara, Wa03, Wefer, Wiwalsh00, Zwilling, Zyxoas, 47 anonymous edits Motion ratio Source: http://en.wikipedia.org/w/index.php?oldid=448782166 Contributors: Douglaswweb, Ganeshunwired, Greglocock, Interiot, Postcard Cathy, ShelfSkewed, Unionhawk, 2 anonymous edits Multi-function structure Source: http://en.wikipedia.org/w/index.php?oldid=442654390 Contributors: Dr eng x, Frap, Rangoon11, Sopher99, Virtualerian Multiphase heat transfer Source: http://en.wikipedia.org/w/index.php?oldid=448396309 Contributors: Craxyxarc, Nick Number, RHaworth, Salih, Thinking of England, Tony1, Yuwenzmo, 5 anonymous edits Non-synchronous transmission Source: http://en.wikipedia.org/w/index.php?oldid=460622974 Contributors: -Majestic-, CZmarlin, Danhash, Eddiehimself, FEAR6655, Filemon, HamburgerRadio, JMBAXT, JimWae, Kevin, Leedeth, Makelelecba, Nnewton, One half 3544, Phil13, Rogerb67, StationNT5Bmedia, TJSwoboda, Tabletop, The Unknown Muncher, Thryduulf, Typ932, WazzaMan, 28 anonymous edits Nutation Source: http://en.wikipedia.org/w/index.php?oldid=462942441 Contributors: Andres, AndrewDressel, Andycjp, Arentath8, AvicAWB, BillC, Bruinfan12, Bryan Derksen, Conversion script, Cícero, DMG413, Doady, Drphilharmonic, Excirial, Firsfron, Globbet, HansHermans, Hesperian, Hinaen, Isnow, Izogi, JEBrown87544, Jonah22, Jonathanzung, Joseaperez, Jotaigna, Karada, Karol Langner, Levskaya, Lorenzarius, MrOllie, Mårten Berglund, Nahum Reduta, Nveitch, Oberst, Pdn, Portnadler, Rememberway, S.K., Svetsveti, Tamfang, Tauʻolunga, The Great Lamprey, Tim Zukas, Tjic, Tpheiska, Tzartzam, Unyoyega, Van helsing, Whosasking, Wolfkeeper, XJamRastafire, 42 anonymous edits Orifice plate Source: http://en.wikipedia.org/w/index.php?oldid=461990267 Contributors: Ac44ck, Aushulz, Billymac00, Brighterorange, Calvero JP, Caradoxical, Chase me ladies, I'm the Cavalry, Correogsk, Dan6hell66, Danny-w, ESkog, Edward321, Eugene Azarov, Fpunktz, Gaius Cornelius, Gastester, Hankwang, Info2139, J.delanoy, Jdpipe, Kdcarver, Kieff, Lakee911, Loughmsa, MajorVariola, Mausy5043, Mbeychok, Rotkäppchen, Salih, Samw, Shoefly, Tannkremen, Tarantinof, Ursus.Bear, User A1, Velella, Wdchk, Wikilenox, 73 anonymous edits Ortman Key Source: http://en.wikipedia.org/w/index.php?oldid=415371263 Contributors: Bearcat, Esourcemarketing, Miyagawa, 3 anonymous edits Oscillating reciprocation Source: http://en.wikipedia.org/w/index.php?oldid=364589106 Contributors: EdGl, Erlyrisa, Finell, Oleg Alexandrov, Sharkface217 Overspeed (engine) Source: http://en.wikipedia.org/w/index.php?oldid=423124406 Contributors: AtholM, Bigjimr, Biscuittin, Dolphin51, Psb777, Toohool, Uruiamme, X15, 9 anonymous edits Parallel motion Source: http://en.wikipedia.org/w/index.php?oldid=457005440 Contributors: Andy Dingley, Axel-berger, Carnildo, Ce1984, Charles Matthews, DonSiano, Duk, EdJogg, Equilibrial, Gaius Cornelius, Glenn, Heron, LA2, Linas, Mais oui!, Mdockrey, Michael Hardy, Mortice, Noetica, Ospalh, Sangwinc, Tanner Swett, Warofdreams, Wikiklrsc, Zlerman, 7 anonymous edits Particle damping Source: http://en.wikipedia.org/w/index.php?oldid=436808421 Contributors: Denzil Simoes, RHaworth Photoelasticity Source: http://en.wikipedia.org/w/index.php?oldid=464496452 Contributors: 17Drew, A. B., A13ean, Adam Krellenstein, Alai, Arnero, Basilicofresco, Berkut, Bluemoose, DIMS SSMG, Dhollm, DrBob, Eugene-elgato, Fox89, Gaurav1146, J.delanoy, Kirbytime, Laor, Liberatus, Lightmouse, Nigosh, Nord0306, Philippe, R'n'B, RainbowOfLight, RxS, SSMG-ITALY, Sanpaz, SpLoT, Stephan Leeds, The wub, Vikom, Wadems, 71 , לאורanonymous edits Pinch analysis Source: http://en.wikipedia.org/w/index.php?oldid=461475747 Contributors: Chemical Engineer, Cirt, Donebythesecondlaw, Ebaksa, Engineman, Hyperman 42, Inwind, J Milburn, Kirsted, Llywelyn2000, Mahbod 1363he, Mikaey, Mion, Od Mishehu, Prari, Punctilius, Rich Farmbrough, Roychai, Sharifah81, Softy, Sr wanalwi, Superp, TomasBat, Zainmanan, 25 anonymous edits Piping Source: http://en.wikipedia.org/w/index.php?oldid=460833301 Contributors: 2fort5r,
[email protected], Anabantidae, Bentogoa, Bonadea, Brimz, Ccknowles, Crowsnest, DMahalko, Dbhouston, Dekisugi, EdBever, El C, ElPeste, Electron9, Eliyak, Eptin, Erik9, Feinoha, Fluidflow, Foobar, Glassjunky, Gorsky, Graibeard, Herdingcats2, Jauhienij, KrakatoaKatie, La goutte de pluie, Macrakis, Mani1, Markus Schweiss, Mbeychok, Mikropedia, Mild Bill Hiccup, Mion, Munay09, NawlinWiki, Netalarm, Nosferatü, Notinasnaid, Oleg Alexandrov, P199, Peter Horn, Piping3d, Pipingdesigner, Pranav.patwardhan, R'n'B, RHaworth, Reify-tech, Roleplayer, Samwb123, SebastianHelm, Shoefly, Siroxo, Smithfarm, Solipsist, Sonett72, Sv1xv, Tlesher, Vanuan, Vornel, Wayne Slam, Wikfr, Woodshed, Ydadkhah, Ytrottier, Zuejay, 62 anonymous edits Piston motion equations Source: http://en.wikipedia.org/w/index.php?oldid=443698910 Contributors: Alphachimp, Greglocock, Hooperbloob, Icairns, JennyRad, Joecar, Kotepho, L Kensington, Patrhoue, Typ932, Van helsing, Zzyzx11, 94 anonymous edits Power engineering Source: http://en.wikipedia.org/w/index.php?oldid=462857504 Contributors: 2001beibei, Ahmed Khalel, Alan Liefting, Albedo, Altenmann, Auntof6, Bagbesh, Beland, BokicaK, CRGreathouse, Cedars, Chris the speller, Ciphers, Ckatz, Cometstyles, CyborgTosser, Daniel11, Dillard421, Dlrohrer2003, Dthomsen8, Dual Freq, Everyking, Gaius Cornelius, Glenn, Gurch, Hooperbloob, Iotaindia, Ipecac, Jammat, Joy, Jrneumann, Kait101, Kevbell, LaForge, Light current, Maji.pratap, Mani1, Mikeblas, Mion, Mohit.thatte, Nposs, Oh Snap, Oli Filth, Overand, Peterh5322, Pigman, Pinethicket, Plugwash, Random user 39849958, Rasputin243, Rklawton, Skaterdudex, Smart Viral, Smithfarm, Ssilvers, Steven Zhang, Tabletop, Teratornis, TexasAndroid, The Thing That Should Not Be, Tiraden, Toffile, TudorTulok, V1adis1av, Viriditas, We hope, Wtshymanski, Yk Yk Yk, Yupik, 95 anonymous edits Precision engineering Source: http://en.wikipedia.org/w/index.php?oldid=462422329 Contributors: BenFrantzDale, Ciphers, Dooglegoogle, Elongstaff, Magicka81, Mdd, Misarxist, Nelson50, Sludwick, Tstolber, WikiPrecisionYorks, Zarano, 10 anonymous edits Pressure exchanger Source: http://en.wikipedia.org/w/index.php?oldid=443804635 Contributors: Basherr, Chrkl, Drahkrub, JuJube, Mwarren us, NonNobisSolum, Pascal666, Peter in s, R.J.Oosterbaan, RHaworth, Sdrtirs, Telecineguy, Xp54321, 1 anonymous edits Proactive maintenance Source: http://en.wikipedia.org/w/index.php?oldid=418104182 Contributors: C12H22O11, Christian Lassure, Jim Fitch, Kjkolb, Longhair, Mramsey68, Nachoman-au, ProveIt, SimonP, The Thing That Should Not Be, 5 anonymous edits Process integration Source: http://en.wikipedia.org/w/index.php?oldid=462555977 Contributors: Falankas, Hyperman 42, Mikaey, Oaguila, Oicumayberight, Sr wanalwi, 11 anonymous edits Pulverizer Source: http://en.wikipedia.org/w/index.php?oldid=450769847 Contributors: Cst17, Erik9, Fortdj33, Goldenrowley, Gproud, Hmains, Joost.vp, Mbeychok, Motorcyclesfish, Razorflame, Runningonbrains, TheProject, Σ, 36 anonymous edits
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Article Sources and Contributors Radiation properties Source: http://en.wikipedia.org/w/index.php?oldid=423841164 Contributors: BD2412, ChrisHodgesUK, Grafen, Leoniceno, LilHelpa, Nyttend, Sergio01mendoza, Shadowjams, Welsh Railworthiness Source: http://en.wikipedia.org/w/index.php?oldid=441227095 Contributors: Future Perfect at Sunrise, JaGa, Sethemanuel, Suffusion of Yellow Range of motion Source: http://en.wikipedia.org/w/index.php?oldid=453885589 Contributors: AThing, Arcadian, Auntof6, BD2412, Balmung0731, Bronayur, DarkArcher25, Davwillev, Fram, GUllman, Ganeshk, Gunnar Hendrich, Huemxm, Karada, Lotje, Megan Hieatt, Mig77, Monkeyjunky, Nsaa, Piano non troppo, Radiojon, Stevenfruitsmaak, THB, Tmonzenet, Tyciol, Una Smith, WeaselADAPT, Wikipelli, Woohookitty, 47 anonymous edits Reciprocating compressor Source: http://en.wikipedia.org/w/index.php?oldid=463517378 Contributors: Alan.ca, Biscuittin, Bryan Derksen, Cantons-de-l'Est, Cyrius, Dogaroon, Edderso, Gaius Cornelius, Graibeard, Gurch, Hooperbloob, I h kazmi, Jncraton, Jonnat, Mark.murphy, Matt.S., Mbeychok, Meestaplu, Mellery, Mion, Muhends, Odie5533, OlEnglish, Pearle, Rich Farmbrough, The Rambling Man, Unixxx, Verdatum, Whpq, Wizard191, Zimin.V.G., 48 anonymous edits Reciprocating motion Source: http://en.wikipedia.org/w/index.php?oldid=464074431 Contributors: Alansohn, Ark25, Catsquisher, Chetvorno, Dangherous, EdJogg, Epbr123, Finell, Gaius Cornelius, GregorB, Inwind, Lumos3, Mcapdevila, Pharaoh of the Wizards, Radagast83, Rudimae, Score Under, Tanquai, 25 anonymous edits Recuperator Source: http://en.wikipedia.org/w/index.php?oldid=464075427 Contributors: Aldis90, AtholM, Bbpen, Dhollm, Drstuey, Francisco Quiumento, Hooperbloob, Jaganath, Khalid hassani, Leonard G., Maurreen, Mikiemike, Mion, Pahazzard, Pegship, Pinar, Queenmomcat, RussBlau, Vikom, Wolfkeeper, Єдлінська Уляна, 16 anonymous edits Reel Source: http://en.wikipedia.org/w/index.php?oldid=464922696 Contributors: Al Fecund, Alex Rio Brazil, Alexbak2,
[email protected], Binksternet, Bobblewik, CLW, Calebsg, Cleduc, Cmulrooney, Colin S, Daniel Bonniot de Ruisselet, EasilyAmused, Esn, Eveningmist, Eventer, Flyhighplato, FredR, Gaius Cornelius, Garion96, Gene Hobbs, GlikD, Gogo Dodo, Grandpafootsoldier, Herr Satz, IRP, Joefaust, Jorgenumata, KVDP, Kizzerdalz, Korg, Loggie, Martpol, Michael Bednarek, Movieresearch, Newabbey, Paul E Ester, Pearle, Peter S., Plugwash, Postoak, QofASpiewak, RHaworth, RJFJR, Rapsar, Reub2000, Sanguinity, Shanes, Shay351, SpacemanSpiff, Th1rt3en, Traveler100, Videoreel, Zoney, Zuckerberg, 41 anonymous edits Relief valve Source: http://en.wikipedia.org/w/index.php?oldid=453351550 Contributors: Andrewrost3241981, Aushulz, Biscuittin, Bookinvestor, CesarB, Cohesion, Dadude3320, DanMS, Darwinek, David alexandre 98, Dekisugi, Ettrig, Everyking, Grm wnr, HelenOswald, Hooperbloob, Jamclaassen, Jclemens, Kaleid, Lockley, Mbeychok, Microsoft Willy on Wheels!, Mikeblas, Mion, Nihaar, Paulmstone, Philip Trueman, Protegouk, Pushkar.gaikwad, Ruakh, Scarian, Slightlymighty, Sole Soul, Stillers, That Guy, From That Show!, Toevoeger, Tony1, Tresiden, Ufwuct, Wikidiscdoctor, WilfriedC, 74 anonymous edits Residual stress Source: http://en.wikipedia.org/w/index.php?oldid=458416860 Contributors: Aboalbiss, Apparition11, BenFrantzDale, Billlion, Chem-awb, Chongkian, Gilgunn, Gilliam, II MusLiM HyBRiD II, InvictaHOG, Jafet, John Vandenberg, Jprevey, Lightmouse, Linas, Materialscientist, Mike Rosoft, Misterlobat, Opheicus, Peteranderson6663, Peterlewis, Rich Farmbrough, Rjd2008, Rjwilmsi, Spangineer, Unara, Wizard191, XJamRastafire, Xornok, Zhou Yu, 52 anonymous edits Reynolds transport theorem Source: http://en.wikipedia.org/w/index.php?oldid=464341585 Contributors: !jim, AeonicOmega, Agricola44, AnthonyA7, Bbanerje, CXCV, Calmer Waters, Charlesreid1, Crowsnest, EMBaero, EndingPop, Freakband, Garethvaughan, Giftlite, Hoo0, Lechatjaune, Matador, Misterkong, P4lm0r3, SWGlassPit, Salih, Starryharlequin, Trevor.tombe, 44 anonymous edits Roadworthiness Source: http://en.wikipedia.org/w/index.php?oldid=428033820 Contributors: CKBrown1000, Malcolma, Paul A, Sethemanuel Roark's Formulas for Stress and Strain Source: http://en.wikipedia.org/w/index.php?oldid=461806320 Contributors: Aka042, AvicAWB, Jrtayloriv, Tabletop, Tedder, Tmlim526, UTSWeb, Wizard191 Rotary feeder Source: http://en.wikipedia.org/w/index.php?oldid=443395410 Contributors: BD2412, Brichter328, Gierczyk, Hooperbloob, Imasleepviking, Iridescent, John of Reading, Longhair, RJFJR, Rjwilmsi, Traveler100, Woohookitty, Zginder, 41 anonymous edits Rotor Source: http://en.wikipedia.org/w/index.php?oldid=461639228 Contributors: AlistairMcMillan, AndrewDressel, Arpingstone, Ask123, BAxelrod, Belirac, BenFrantzDale, Benet Allen, Bert Hickman, BlckKnght, Borgx, Born2flie, Bryan Derksen, Clicketyclack, Conscious, DV8 2XL, DexDor, Dhaluza, Dungodung, EdX20, Edward, Emilio Juanatey, Evan G, Glenn, Heron, Hu Totya, Inwind, Jschwa1, Kbdank71, KnightRider, Laurennnxo, Lommer, Lvzon, Mark83, Matt Crypto, Ojigiri, Pne, Quibik, Rar, Reddi, Rich Farmbrough, RottweilerCS, Rs14, Rtdrury, Saberwyn, Scwlong, Sehsuan, Skydivingdutch, Smithbrenon, Spike Wilbury, Stevenlw, TarenGarond, Thefox258, Tyomitch, UncleDouggie, Van helsing, Vanuan, Vasquezcp1, Vilkapi, Xyzzyplugh, 25 anonymous edits Run-around coil Source: http://en.wikipedia.org/w/index.php?oldid=454549750 Contributors: Khazar, Pahazzard, Pol098, Tony1, Ziqidel, 1 anonymous edits Sacrificial part Source: http://en.wikipedia.org/w/index.php?oldid=463622589 Contributors: Adam850, Elkman, Furrykef, Nbarth, VegKilla, VoxLuna, Winston Spencer, Wizard191 Screw theory Source: http://en.wikipedia.org/w/index.php?oldid=463122669 Contributors: BenFrantzDale, Ceyockey, Charles Matthews, Conscious, David Eppstein, Designprof, Dfeldmann, Diderot, Dmartins, Dontknowhow, Drm0hr, Elf, Eric Lengyel, HWU K, Hansamurai, Jalexiou, Kborer, Longhorn, Melchoir, Michael Devore, Nmnogueira, Open2universe, Paolo.dL, Phrood, Prof McCarthy, Rgdboer, Shannonbonannon, Silly rabbit, TheTito, Vishakha, 39 anonymous edits Self-exciting oscillation Source: http://en.wikipedia.org/w/index.php?oldid=458605287 Contributors: Avocado, Conscious, Cutler, Gordon Vigurs, Grutness, Hankwang, Ibroadfo, Inwind, Longhair, Maxal, Philcha, Riddley, William Avery, 9 anonymous edits Shear pin Source: http://en.wikipedia.org/w/index.php?oldid=460762176 Contributors: Atlant, Carders, Chipmunk2, EchetusXe, Freaky Fries, Hooperbloob, Rlsheehan, Wizard191, 7 anonymous edits Shear strength Source: http://en.wikipedia.org/w/index.php?oldid=451348787 Contributors: Aboalbiss, AdjustShift, Aitias, Amir136990, Argyriou, Basar, Colonies Chris, Covalent, FaWzY, Feydey, Fratrep, GeoEng, Hakeliha, Hemmingsen, Hooperbloob, Icairns, J.delanoy, Jjmatt33, Jpeeling, Jpvinall, Longhair, Lumos3, M3taphysical, Michael93555, Noclevername, Patrick, Physics is all gnomes, Robert Hack, Sonett72, Sorsanmetsastaja, TVBZ28, Tzm41, Ufwuct, VanBurenen, Vegaswikian, Vistaridge81, William.mu, Zuejay, 40 anonymous edits Sieving coefficient Source: http://en.wikipedia.org/w/index.php?oldid=416312008 Contributors: Foobarnix, Mikael Häggström, Nephron, 1 anonymous edits Sight glass Source: http://en.wikipedia.org/w/index.php?oldid=463045796 Contributors: Afluegel, Artemis84, Atlant, Bctwriter, CommonsDelinker, Edward, Ifor1966, MER-C, MKFI, Maurreen, Old Moonraker, Oli Filth, Petervdh, Saintmaster, Singforlife, Tabletop, Vsmith, Xyzzyplugh, Ytrottier, 17 anonymous edits Simple machine Source: http://en.wikipedia.org/w/index.php?oldid=464724702 Contributors: .:Ajvol:., 165.123.179.xxx, 192.101.175.xxx, A. di M., Adambro, Adashiel, Addshore, Adrian, Alansohn, Ali'i, Alpha 4615, Andrewpmk, Antandrus, Apau98, Arjun01, Asdfjkl1235, Atif.t2, Austin9801, AzaToth, B, Beland, Big Bird, Bobet, Bobo192, Bryan Derksen, Bubbles45, Buck Mulligan, Buster2058, Butros, CameronG6, Carders, Carnildo, Catgut, Chetvorno, Conversion 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Pinethicket, Pol098, Postoak, PranksterTurtle, Prof McCarthy, Psyche825, QueenCake, Quiddity, RabbitMuncher123, RainbowOfLight, Raoulduke25, Rapsar, Rasi2290, Reaper Eternal, Restre419, Rfc1394, RgVsTheWorld, Rich Farmbrough, Rico402, Rjwilmsi, Rob Lindsey, Robert Foley, Rompe Lapize, Ronbo76, Rossami, Rracecarr, SBKT, SJP, Scootey, Seaphoto, Seckelberry1, Secret of success, Simetrical, Sionus, Sirburnsalot, Sirlondon, Sjlewis, Skywalker999, Soccergirlsam, Someguy1221, Squids and Chips, Stardust8212, Stephenb, Taranet, Teo64x, Ternit, Terry2isback, Th1rt3en, The Evil Spartan, The Thing That Should Not Be, The wub, TheRealFennShysa, Theda, Thejerm, Tide rolls, Tiggerjay, Tom soldier, Toothpaste95, Treisijs, Tvoz, VanBurenen, Velella, Vrenator, Vsmith, WAvegetarian, Wavelength, Wayne Slam, Wiki alf, Wikipelli, Wimt, Wizard191, WojPob, Woohookitty, XxUltimateGodzXx, Yvesnimmo, Ziounclesi, 476 anonymous edits Slip joint Source: http://en.wikipedia.org/w/index.php?oldid=447207594 Contributors: Andy Dingley, Basar, BrownstoneKnockn, Bwpach, Gamewizard71, Hooperbloob, Leonard G., Longhair, Michael Daly, Sgeureka, Spoon!, 4 anonymous edits Slip line field Source: http://en.wikipedia.org/w/index.php?oldid=322275506 Contributors: Breakmonker, GregorB, J04n, Malcolma, Richardcavell, Wizard191
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Article Sources and Contributors Society of Tribologists and Lubrication Engineers Source: http://en.wikipedia.org/w/index.php?oldid=460076318 Contributors: Ashearer stle, AvicAWB, Beetstra, Dave Heenan, Eyrian, Gregzore, Lightmouse, Mean as custard, Mr.crabby, PeterHuntington, Pichpich, Redrose64, Sonicspike, Tassedethe, 9 anonymous edits South-pointing chariot Source: http://en.wikipedia.org/w/index.php?oldid=456463389 Contributors: AndrewH, Andy Dingley, AnonMoos, Balthazarduju, Barefact, Benjwong, BertK, Bueller 007, Calm, Cesiumfrog, Chill doubt, Cold Season, CommonsDelinker, Confuzion, Craig Pemberton, D6, DOwenWilliams, Deadkid dk, Disobey, DopefishJustin, Euchiasmus, Fratrep, Freechild, Gerbrant, Hmains, IanOsgood, Insouciance, Inwind, Jagged 85, KnowledgeOfSelf, Lombroso, LorenzoB, Magicmike, Michael Hardy, Mild Bill Hiccup, Mohammad k88, Monsted, Oxymoron83, PericlesofAthens, Philippe, ProfessorXY, RafaelG, RedWolf, Redmarkviolinist, Riana, Rjwilmsi, RxS, SebastianHelm, ShanRen, Stone, SwiftlyTilt, Tagforlife8, The Man in Question, TheParanoidOne, Tvarnoe, Valentinian, Wizard191, Yowhat, Yug, 68 anonymous edits Split pin Source: http://en.wikipedia.org/w/index.php?oldid=462426716 Contributors: A2Kafir, AKGwikiAcct, AMCKen, Alex holden, Altafqadir, Anthony Appleyard, Ashawley, Atlant, Bejnar, Castor8, Charles Matthews, Chris Cross, ClairSamoht, Daderot, Dogcow, Esradekan, Globbet, Gpvos, Graibeard, Jj137, Jsd, Justallofthem, Kamezuki, Kelisi, Kivaan, LilHelpa, Mdrag, Memestream, Modica4uall, Neclark, Peridon, Pissant, Pjbflynn, Polyparadigm, R'n'B, Royalbroil, Shaddack, Skipweasel, Someonesdad363616, Techtonik, Themightyseptopus, Wazronk, Wizard191, Zephyris, 29 anonymous edits Standard conditions for temperature and pressure Source: http://en.wikipedia.org/w/index.php?oldid=463538479 Contributors: 1266asdsdjapg, 84user, Ac44ck, Adam78, Adamrush, Alan Liefting, Alereon, Alex.muller, Android Mouse, Aritzo, AxelBoldt, AySz88, BMunage, Bardak, Bduke, Beetstra, Beetstra public, Belatulipo, Blainster, Bobblewik, Bplohr, BryanG, C.Fred, Canadian popcan, Carltzau, Chieron, Christian75, Coemgenus, Conversion script, Crissov, Cybercobra, Darrien, Dead3y3, Dolphin51, Donarreiskoffer, Eequor, Eilatybartfast, Emchau, Emudd, Equendil, Eric Kvaalen, Eric119, EryZ, Evolauxia, Ewen, Excirial, FHBridges, FJPB, Faixu, Farosdaughter, First-user, Flatline, Foxhunt king, GHe, Gazjo, Gene Nygaard, GradEngineer, GradEngr, Graham87, Greg L, Hairy Dude, Headbomb, Hectorthebat, Hede2000, HorsePunchKid, Hqb, Hullcrushdepth, Icairns, Itub, Ixfd64, Jake Wartenberg, Jimp, Joanjoc,
[email protected], Jusjih, Jzana, Kbh3rd, KrakatoaKatie, LarryMorseDCOhio, LilHelpa, Linuxlad, Looxix, Markus Kuhn, Martin451, Maurreen, Mausy5043, Maxim Razin, Mbeychok, Mets501, Mh, Mikael Häggström, Mike dill, Mimihitam, MimirZero, Morasdeta, Mormegil, Mr. Wheely Guy, NewEnglandYankee, Nguyen Thanh Quang, Nigholith, Nikonoff, Notkenreid, Obradovic Goran, Pearle, Pewwer42, Pflatau, Physchim62, PierreAbbat, Pizza Puzzle, Poccil, Porqin, Postglock, Potatoswatter, Prillen, QU, Ranveig, RexNL, Rlsheehan, Rogper, Ronhjones, Royjensen, Sadi Carnot, Shaggorama, Silverleaftree, Sjavitt84, Sl, Sodium, Stagyar Zil Doggo, Stan J Klimas, StefanosKozanis, Stemonitis, Stevertigo, Stuartwaudby, Suisui, Sverdrup, The Thing That Should Not Be, TheAmigo42, TheJC, Thermbal, Thunderbird2, Tide rolls, Toddst1, Tregoweth, Turbinator, UncleDouggie, Urhixidur, Vanished User 1004, Vicki Rosenzweig, Victor Blacus, Vsmith, Wavelength, Wereon, Wilhelm.peter, Wimt, Wtmitchell, Wyvyrn, Yerpo, Yk Yk Yk, Yyy, Zaf, 263 anonymous edits Steam rupture Source: http://en.wikipedia.org/w/index.php?oldid=448009904 Contributors: AvicAWB, Hooperbloob, Likeem, Samw, TheParanoidOne, 6 anonymous edits Stick-slip phenomenon Source: http://en.wikipedia.org/w/index.php?oldid=464465051 Contributors: Alchemist of Steel, Elderyang, Gregors, Hooperbloob, ILike2BeAnonymous, JForget, Jamclaassen, Jschwa1, Kuliphex, Mikenorton, Peterlewis, Recepkuyubasi, SamBuss, Stedewa, Tai89ch, Tamicat, Titeuf24, Trondos, W.F.Galway, Wizard191, 20 anonymous edits Strain hardening exponent Source: http://en.wikipedia.org/w/index.php?oldid=463778434 Contributors: 6hassan, Alex Bakharev, Basar, Hongooi, Jujutacular, LeaveSleaves, Nfette, SietskeEN, Wizard191, 8 anonymous edits Streamlines, streaklines, and pathlines Source: http://en.wikipedia.org/w/index.php?oldid=452039346 Contributors: AndrewHowse, Anthony Appleyard, BenFrantzDale, BigrTex, BoH, Bunnyhop11, Can't sleep, clown will eat me, Cayte, Charles Matthews, Crowsnest, DVirus101, Dolphin51, Doogleface, Feministo, Fi1Kaiv8, Fram, Func, Gaius Cornelius, Grace Xu, Harry S., IMSoP, Iwfyita, Jaganath, Janmiedzik, Jjalexand, Jon513, Josce, Kan8eDie, Kelly Martin, Lewisbalfour, Loren36, Ludatal, M1ss1ontomars2k4, Mark Foskey, Maury Markowitz, Mhowkins, Michael Hardy, Mira, Moink, Mulad, Mythealias, Natcase, Nikai, Oleg Alexandrov, Paolo.dL, Patrick, Paul.adams.jr, Petri Krohn, Phlebas, Picapica, Raspberrycoulis, Retaggio, Rex the first, Rracecarr, Sarav62, Tarquin, The Anome, The Thing That Should Not Be, Thegreatdr, Tobo, Twisp, User2004, Wesley, Zowie, 70 anonymous edits Structural load Source: http://en.wikipedia.org/w/index.php?oldid=465469269 Contributors: Addshore, Alexknight12, Amalas, AxelBoldt, Basar, Beezhive, Before My Ken, Binksternet, Butros, Ciphers, Clutjen, Craig Pemberton, DVD R W, DabMachine, Edderso, Erdenekhorloo, Esanchez7587, Excirial, Grafen, Guillaume2303, Hda3ku, Hooperbloob, Immunize, Ivanwhlau, J04n, Jasón, JerrySteal, JiFish, Kappa, Khazar, Kp kyak, Kps2, Kvetner, LinguistAtLarge, Mejor Los Indios, Methecooldude, Mindfrieze, MrOllie, Noq, Panchobook, Passportguy, PhilKnight, Pkgx, R'n'B, RA0808, Rlsheehan, SaveThePoint, Shoessss, Special-T, Stemonitis, StudierMalMarburg, Sue Rangell, TVBZ28, Torchwood5, VK35, VasilievVV, Vegaswikian, Xnuala, ZenoLuh, 85 anonymous edits Surface integrity Source: http://en.wikipedia.org/w/index.php?oldid=455218176 Contributors: Gatoclass, KConWiki, Mgiganteus1, Pdcook, Tamfang, TenthEagle, William Avery, Wizard191 Surface roughness Source: http://en.wikipedia.org/w/index.php?oldid=460266936 Contributors: 16@r, Andy Dingley, BenFrantzDale, Berland, BjoernBoeckle, DHill1977, DexDor, Emok, EricHeselmans, Fede.Campana, Femto, Fhelmli, Greglocock, Gregzore, Heron, HybridBoy, Jayeshmore77, JcCoPM, Jjmatt33, Kelisi, Mastersonb, MetrologyMan, Neuron1978, Nihiltres, Philip Trueman, Physchim62, Prunesqualer, Pstack12, Raggiante, Robert Hack, Rucha Mulawekar, Ruud Koot, Samlaw, Sandheep, Slon02, Spirko, The wub, Tomeasy, Towerman86, Wellfare - to experience good ride quality, Wizard191, Xorx, 54 anonymous edits Swivel Source: http://en.wikipedia.org/w/index.php?oldid=458299936 Contributors: 16@r, Al Silonov, Calg1, Chris the speller, Coolperson420, Eekerz, Fone4My, Guttlekraw, Kjkolb, Nick Number, Pavtron, Pearle, Rajah, Sus scrofa, Tosaka1, Wai Hong, Wizard191, 5 anonymous edits Systematic Hierarchical Approach for Resilient Process Screening (SHARPS) Source: http://en.wikipedia.org/w/index.php?oldid=217701867 Contributors: FrankTobia, Sharifah81, 3 anonymous edits Tail lift Source: http://en.wikipedia.org/w/index.php?oldid=454252796 Contributors: Comyu, Owain.davies, Paradoctor, Scriberius, 1 anonymous edits Thermal efficiency Source: http://en.wikipedia.org/w/index.php?oldid=463925080 Contributors: A930913, Andrew.Ainsworth, Arnero, BlaiseFEgan, Borgx, CRGreathouse, Chetvorno, Colonies Chris, Covington, DerrickOswald, Dhollm, Doradus, Dorkenergy, Ebyabe, Electron9, Elronxenu, Engineman, Ewlyahoocom, FactsAndFigures, Franamax, Gene Nygaard, Grandonia, Hamiltondaniel, Ideal gas equation, Inwind, Kjkolb, Mbeychok, Michael Devore, Mindmatrix, Mnmngb, Napalm Llama, Nick Number, NielLeon, Nosferatü, Pcarmour, Piperh, Rawheas, Rijkbenik, Rios sk, Rtdrury, Swpb, Teep111, TheBusiness, Wavelength, Wranadu2, 81 anonymous edits Thermal engineering Source: http://en.wikipedia.org/w/index.php?oldid=452753308 Contributors: Ac44ck, Chris857, Fryed-peach, PigFlu Oink, Turbojet, 2 anonymous edits Thermal science Source: http://en.wikipedia.org/w/index.php?oldid=457783977 Contributors: 3Coins, DVdm, Dejan Cvetinovic, Flarelocke, Karol Langner, Kbrose, Matt Smith4, Mike Dillon, Newuy, Niceguyedc, Rich Farmbrough, Rich257, Sadi Carnot, Scls19fr, Srleffler, Yuwenzmo, 9 anonymous edits Thermo-mechanical fatigue Source: http://en.wikipedia.org/w/index.php?oldid=401323948 Contributors: Nuetzel, Peter LaVigne, Robert Ullmann, Wizard191, Wronkiew, 2 anonymous edits Thermomechanical generator Source: http://en.wikipedia.org/w/index.php?oldid=372867077 Contributors: Alberisch, CSWarren, Glenn, Hydrogen Iodide, Mikiemike, Rich257, Schmloof, Soliloquial, Waitak, 1 anonymous edits Timken OK Load Source: http://en.wikipedia.org/w/index.php?oldid=418766289 Contributors: Ewlyahoocom, Gene Nygaard, Hooperbloob, Icairns, Open2universe, Physchim62, Srleffler, Vivers, 3 anonymous edits Tip clearance Source: http://en.wikipedia.org/w/index.php?oldid=464652035 Contributors: Burtonpe, Inwind, 1 anonymous edits Tolerance analysis Source: http://en.wikipedia.org/w/index.php?oldid=420248727 Contributors: Blanchardb, Dhollm, Jim.henderson, Magioladitis, Scientus, Wizard191, Zz9fy4, 4 ,א anonymous edits Tooth Interior Fatigue Fracture Source: http://en.wikipedia.org/w/index.php?oldid=272249555 Contributors: Fatal!ty, Itub, Mackaldener, Naerii, Nihiltres, Power.corrupts, WilliamH Torque density Source: http://en.wikipedia.org/w/index.php?oldid=332218401 Contributors: Fuhghettaboutit, Gene Nygaard, Hooperbloob, Icairns, MJCdetroit, Vivers Total indicator reading Source: http://en.wikipedia.org/w/index.php?oldid=421705275 Contributors: Bassplr19 Transmission (mechanics) Source: http://en.wikipedia.org/w/index.php?oldid=464928970 Contributors: 102orion, 16@r, 2301700056mark, A.Abdel-Rahim, A7N8X, A876, ABF, ARM-2805, AS, Achalmeena, AdrenalineRush23, Aenesidemos, Alansohn, Alureiter, Amzimuthis, Andy Dingley, Another Stickler, Antifumo, Appelsauce14, Arabigo, Arthena, Atlant, Attilios, Auntof6, Autoproonline, Bensaccount, Berserkerus, Biscuittin, Bjf, Bloodshedder, BlueDevil, Bobblewik, Brian Patrie, C J Cowie, Channelturbo, Choppingmall, Chris the speller, ChrisChiasson, Chrislonghurst, Christopherlin, Cinabrium, Closedmouth, Corti, Cryptic, DH85868993, DMacks, Damërung, David Oates, DeLarge, DeadEyeArrow, Dennis Bratland, Deor, DocWatson42, Downstream, DragonHawk, Duk, EagleFan, Erik9, Erud, Ervinpospisil, F.V.A Constantinus, F.bendik, Fabartus, Fenevad, Fratrep, Frosted14, Geometry guy, Giftlite, Glenn, Goodnightmush,
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Article Sources and Contributors Grafen, Graibeard, Grendelkhan, Gus Polly, Gzuckier, Hacktivist, HandyAndy, Hateless, Henry W. 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B., Basar, BenFrantzDale, Bryan H Bell, Christian75, Crissov, Frehley, Glenn L, Jabowery, Jackol, Mbeychok, Michael Hardy, Nbarth, NuclearEnergy, NuclearWarfare, Peter Horn, Samw, Sjuapseorn, Vinsfan368, WereSpielChequers, Wikiaegent, 31 anonymous edits Variable air volume Source: http://en.wikipedia.org/w/index.php?oldid=463233335 Contributors: Atlant, C J Cowie, Cyberwriter, Drphilharmonic, Elliott.engineer, FactsAndFigures, Hmains, Longhair, Marek69, P199, Rapidografek, Robertb-dc, Simon3637, Telecomtom, TreeBread, Vegaswikian, Waldir, Wwcorigan, 21 anonymous edits Vibration isolation Source: http://en.wikipedia.org/w/index.php?oldid=464304010 Contributors: Abdullah Köroğlu, Atlant, Auntof6, Beland, Biscuittin, Borissh07, CVIMG, CherryHintonBlue, Chovin, Chris the speller, Deeptrivia, Dicklyon, Djr32, Dr.K., Greglocock, Grubber, Halpaugh, HerzanLLC, Komusou, Lzyvzl, Materialscientist, Orion290754, Oskay, R'n'B, Rlsheehan, Scarlet Lioness, Sdv1120, Shustov, Solid Simulation, Spinningspark, Teapotgeorge, TenOfAllTrades, Three-quarter-ten, 17 anonymous edits Vibratory stress relief Source: http://en.wikipedia.org/w/index.php?oldid=428377873 Contributors: Airmatic, Autoerrant, Biscuittin, Chowbok, RHaworth, Sadads, Wilhelmina Will Victaulic Source: http://en.wikipedia.org/w/index.php?oldid=458208749 Contributors: Aclewell,
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