omniomni/omni-engineering huggingface dataset:
Cyclic stress. Cyclic stress  is the distribution of forces (aka stresses) that change over time in a repetitive fashion. As an example, consider one of the large wheels used to drive an aerial lift such as a ski lift. The wire cable wrapped around the wheel exerts a downward force on the wheel and the drive shaft supporting the wheel. Although the shaft, wheel, and cable move, the force remains nearly vertical  relative to the ground. Thus a point on the surface of the drive shaft will undergo tension when it is pointing towards the ground and compression when it is pointing to the sky.

Types of cyclic stress 

Cyclic stress  is frequently encountered in rotating machinery where a bending moment is applied to a rotating part. This is called a cyclic bending stress  and the aerial lift above is a good example. However, cyclic axial stresses and cyclic torsional stresses also exist. An example of cyclic axial stress would be a bungee cord (see bungee jumping), which must support the mass of people as they jump off structures such as bridges. When a person reaches the end of a cord, the cord deflects elastically and stops the person's descent. This creates a large axial stress in the cord. A fraction of the elastic potential energy stored in the cord is typically transferred back to the person, throwing the person upwards some fraction of the distance he or she fell. The person then falls on the cord again, inducing stress in the cord. This happens multiple times per jump. The same cord is used for several jumps, creating cyclical stresses in the cord that could eventually cause failure if not replaced.

Cyclic stress and material failure 

When cyclic stresses are applied to a material, even though the stresses do not cause plastic deformation, the material may fail due to fatigue. Fatigue failure is typically modeled by decomposing cyclic stresses into mean and alternating components. Mean stress is the time average of the principal stress. The definition of alternating stress varies between different sources. It is either defined as the difference between the minimum and the maximum stress, or the difference between the mean and maximum stress. Engineers try to design mechanisms whose parts are subjected to a single type (bending, axial, or torsional) of cyclic stress because this more closely matches experiments used to characterize fatigue failure in different materials.

References

Materials science
Mechanics
Howard Petch. Howard Earle Petch,  (12 May 1925 – 26 November 2018) was a Canadian academic administrator. Petch was the President of the University of Waterloo and the University of Victoria.

He received a Bachelor of Science, honours in physics and chemistry from McMaster University in 1949. He received his Ph.D. in physics from the University of British Columbia in 1952. He joined the department of physics at McMaster University in 1954. From 1958 to 1961 he was the chairman of the department of metallurgical engineering and was the Director of Research from 1961 to 1963.  From 1963 to 1967, he was the Principal of Hamilton College.

In 1967, he became the Vice-President (academic) and a Professor of physics at the University of Waterloo. From 1969 to 1970, he was the President pro tem of the University of Waterloo. In 1975, he became President and Vice-Chancellor of the University of Victoria. He also was a Professor of physics. He retired in 1990.

In 1990, he was awarded the Order of British Columbia. He was a Fellow of the Royal Society of Canada.

The Petch building at the University of Victoria, which houses the department of Biochemistry and Microbiology, was named in his honour.

See also
 List of University of Waterloo people

References

 

1925 births
2018 deaths
Canadian university and college vice-presidents
Canadian physicists
Fellows of the Royal Society of Canada
Members of the Order of British Columbia
Presidents of the University of Waterloo
McMaster University alumni
University of British Columbia alumni
Presidents of the Canadian Association of Physicists
P. A. Yeomans. Percival Alfred Yeomans (1905 - November 1984) was an Australian inventor known for the Keyline system for the development of land and increasing the fertility of that land. As a mining engineer and gold assayer, Yeomans had developed a keen sense of hydrology and equipment design. Upon his brother-in-law's death in a grass fire, P.A. Yeomans assumed management of a large tract of land he later named Nevallan in New South Wales. There he developed improved methods and equipment for cultivation. His designs won him The Prince Philip Design Award Australia in 1974.

His Keyline principles or concepts (Keyline Design) have been adopted by farm owners in almost every country in the world. Yeomans' Keyline concepts are now part of the curriculum of many sustainable agriculture courses in colleges and universities across the world. His ideas have also been a key factor in the development of permaculture design. P.A. Yeomans wrote four books: The Keyline Plan, The Challenge of Landscape, Water For Every Farm and The City Forest.

See also
 Keyline design
 Permaculture
 Allan Yeomans

External links
 Yeomans Plow Co
 Keyline.com.au

References

1905 births
1984 deaths
20th-century Australian inventors
Australian mining engineers
Minimum total potential energy principle. The minimum total potential energy principle is a fundamental concept used in physics and engineering. It dictates that at low temperatures a structure or body shall deform or displace to a position that (locally) minimizes the total potential energy, with the lost potential energy being converted into kinetic energy (specifically heat).

Some examples
 A free proton and free electron will tend to combine to form the lowest energy state (the ground state) of a hydrogen atom, the most stable configuration. This is because that state's energy is 13.6 electron volts (eV) lower than when the two particles separated by an infinite distance. The dissipation in this system takes the form of spontaneous emission of electromagnetic radiation, which increases the entropy of the surroundings.
 A rolling ball  will end up stationary at the bottom of a hill, the point of minimum potential energy. The reason is that as it rolls downward under the influence of gravity, friction produced by its motion transfers energy in the form of heat to the surroundings with an attendant increase in entropy.
 A protein folds into the state of lowest potential energy. In this case, the dissipation takes the form of vibration of atoms within or adjacent to the protein.

Structural mechanics
The total potential energy, , is the sum of the elastic strain energy, , stored in the deformed body and the potential energy, , associated to the applied forces:

This energy is at a stationary position when an infinitesimal variation from such position involves no change in energy:

The principle of minimum total potential energy may be derived as a special case of the virtual work principle for elastic systems subject to conservative forces.

The equality between external and internal virtual work (due to virtual displacements) is:

where
  = vector of displacements
  = vector of distributed forces acting on the part  of the surface
  = vector of body forces

In the special case of elastic bodies, the right-hand-side of () can be taken to be the change, , of elastic strain energy  due to infinitesimal variations of real displacements.
In addition, when the external forces are conservative forces, the left-hand-side of () can be seen as the change in the potential energy function  of the forces. The function  is defined as:

where the minus sign implies a loss of potential energy as the force is displaced in its direction. With these two subsidiary conditions,  becomes:

This leads to () as desired. The variational form of () is often used as the basis for developing the finite element method in structural mechanics.

References

Thermodynamics
Solid mechanics
John T. Parsons. John T. Parsons (October 11, 1913April 18, 2007) pioneered numerical control (NC) for machine tools in the 1940s. 

These developments were done in collaboration with his Chief Engineer and Vice President of Engineering, Frank L. Stulen, who Parsons hired when he was head of the Rotary Wing Branch of the Propeller Lab at Wright-Patterson Air Force Base, in April 1946. Together, they were the first to use computer methods to solve machining problems, in particular, the accurate interpolation of the curves describing helicopter rotor blades. In 1946, "computer" still meant a punched-card operated calculation machine. In 1948, Parsons' company, "Parsons Corporation" of Traverse City, Michigan, was awarded a contract to make the challenging tapered wings for military aircraft; they won the contract because they developed the computer support to do the difficult three-dimensional interpolation for the complex shapes, as well as the 800 steps long production cycle for the wing manufacturing. IBM was one of the subcontractors, as was MIT, which took care of the servomechanisms. The latter lab boosted the developments of numerical control machining in the following decades, by developing reliable servo control in 1952 and the APT (Automatic Programmed Tool) programming language for NC machines. 

Parsons, however, quickly saw the potential of connecting computers to the machine motors. On January 14, 1958, he received a patent for a Motor Controlled Apparatus for Positioning Machine Tool (patent number 2,820,187, filed on May 5, 1952).

The initial developments of NC machines, however, had been so expensive that Parsons was fired from his own company because the funding of the MIT developments was too much for the company. Parsons was reinstated as president of the company after royalties on the patent had generated significant amounts of money. (Bendix Corporation was an initial licensee of the patent, in 1955, and eventually bought all the rights to it.)

In 1985, Parsons and Stulen received the National Medal of Technology.  In 1988 he received an honorary Doctor of Engineering degree from the University of Michigan. In 1993, Parsons (but not Stulen) was inducted into the National Inventors Hall of Fame for inventing numerical control.

Parsons died on April 18, 2007, at the Grand Traverse Pavilions. He was 93. He had six children.

References

1913 births
2007 deaths
National Medal of Technology recipients
People from Detroit
Paul Horn (computer scientist). Paul M. Horn (born August 16, 1946) is an American computer scientist and solid state physicist who has made contributions to pervasive computing, pioneered the use of copper and self-assembly in chip manufacturing, and he helped manage the development of deep computing, an important tool that provides business decision makers with the ability to analyze and develop solutions to very complex and difficult problems.

Horn was elected a member of the National Academy of Engineering in 2007 for leadership in the development of information technology products, ranging from microelectronics to supercomputing.

Early life and education
Horn was born on August 16, 1946, and graduated from Clarkson University in 1968 with a Bachelor of Science degree. He obtained his PhD from the University of Rochester in physics in 1973.

Career
Horn has, at various times, been Senior Vice President of the IBM Corporation and executive director of Research. While at IBM, he initiated the project to develop Watson, the computer that competed successfully in the quiz show Jeopardy!.

He is currently a New York University (NYU) Distinguished Scientist in Residence and NYU Stern Executive in Residence. He is also a professor at NYU Tandon School of Engineering. In 2009, he was appointed as the Senior Vice Provost for Research at NYU.

Awards
 Industrial Research Institute (IRI) Medal in honor of his contributions to technology leadership, 2005
 American Physical Society, George E. Pake Prize, 2002
 Hutchison Medal from the University of Rochester, 2002
 Distinguished Leadership award from the New York Hall of Science, 2000
 Bertram Eugene Warren Award from the American Crystallographic Association, 1988

References

External links 
 IBM Bio

1946 births
Living people
Clarkson University alumni
New York University faculty
American computer scientists
Computer hardware researchers
Computer systems researchers
IBM employees
Members of the United States National Academy of Engineering
Polytechnic Institute of New York University faculty
Fellows of the American Physical Society
PKP class SU46. SU46 (new symbol 5 630) is the name for a diesel universal purpose locomotive working for Polish PKP. Cegielski has produced 52 machines in years 1974-1977 and 2 modified in 1985.

History
The 302D (class SP47) and 303D type (class SU46) locomotives are heavily improved version of 301Db type (class SP/SU45) diesel locomotive. Both of them has similar shape, but SP47 is a bit longer because of its 2116SSF diesel engine. SU46 uses a similar diesel engine as SP/SU45, but traction motors are totally different (this was enforced by usage of 3 kV electrical heating). Construction of SU46 was stopped in 1977, most likely due to communist government decisions. In 1985 additional two units of this class were built (numbers 053 and 054). They are slightly modified version of previous locomotives.

Operation
Order of this locomotive was connected with increasing in 1970s demand on freight and passenger services on non-electrified railway lines. SU46 has a very universal characteristic, so it was possible to use them in passenger service and freight.

Today they are used in service on west Polish border (passenger and goods) and in Warmia and Masuria (goods train). Previously they were used also in passenger service on Hel Peninsula.

See also
Polish locomotives designation

References

External links 
Rail Service
Chabówka Rail Museum

Diesel–electric locomotives of Poland
Standard gauge locomotives of Poland
Co′Co′ locomotives
Railway locomotives introduced in 1974
Energy principles in structural mechanics. Energy principles in structural mechanics express the relationships between stresses, strains or deformations, displacements, material properties, and external effects in the form of energy or work done by internal and external forces. Since energy is a scalar quantity, these relationships provide convenient and alternative means for formulating the governing equations of deformable bodies in solid mechanics. They can also be used for obtaining approximate solutions of fairly complex systems, bypassing the difficult task of solving the set of governing partial differential equations.

General principles
 Virtual work principle
Principle of virtual displacements
Principle of virtual forces
Unit dummy force method
 Modified variational principles

Elastic systems
 Minimum total potential energy principle
 Principle of stationary total complementary potential energy
 Castigliano's first theorem (for forces)

Linear elastic systems
 Castigliano's second theorem (for displacements)
 Betti's reciprocal theorem
 Müller-Breslau's principle

Applications
 Governing equations by variational principles
 Approximate solution methods
 Finite element method in structural mechanics

Bibliography
Charlton, T.M.; Energy Principles in Theory of Structures, Oxford University Press, 1973.  
Dym, C. L. and I. H. Shames; Solid Mechanics: A Variational Approach, McGraw-Hill, 1973.
Hu, H. Variational Principles of Theory of Elasticity With Applications; Taylor & Francis, 1984.  
Langhaar, H. L.; Energy Methods in Applied Mechanics, Krieger, 1989.
Moiseiwitsch, B. L.; Variational Principles, John Wiley and Sons, 1966. 
Mura, T.; Variational Methods in Mechanics, Oxford University Press, 1992.  
Reddy, J.N.; Energy Principles and Variational Methods in Applied Mechanics, John Wiley, 2002.  
Shames, I. H. and Dym, C. L.; Energy and Finite Element Methods in Structural Mechanics, Taylor & Francis, 1995,  
Tauchert, T.R.; Energy Principles in Structural Mechanics, McGraw-Hill, 1974. 
Washizu, K.; Variational Methods in Elasticity and Plasticity, Pergamon Pr, 1982.  
Wunderlich, W.; Mechanics of Structures: Variational and Computational Methods, CRC, 2002. 

Structural analysis
Calculus of variations
PKP class SM04. The SM04 (factory designation 409Da) is a low power, Polish built shunter, formerly operated by PKP (Polish National Railways) and is an improved version of the SM03.

History
Built between 1972 and 1978, the SM04 differed from its predecessor in that its construction allowed for the installation of a more powerful diesel engine, built under licence from Henschel. Originally, this engine was to be the 10H6, which had a power output of 160 bhp; however the 180 bhp 14H6 was used instead.

The SM04 was mainly sold to industry, where they carried their factory designation of 409Da. A mere 2 examples were acquired by PKP at the beginning of the 1990s. Both locomotives had been salvaged from Zakłady Naprawcze Taboru Kolejowego w Sędziszowie (Sędziszów Rolling Stock Reparation Plant), but were removed from PKP's inventory in 2000. One of these is now stationed as an exhibit at the railway museum in Chabówka.

Locomotive assignment

See also
Polish locomotives designation

External links
Modern Locos Gallery
Rail Service
Mikoleje
Chabówka Rail Museum

Railway locomotives introduced in 1972
Diesel locomotives of Poland
B locomotives
Standard gauge locomotives of Poland
Shunting locomotives
Raymond Peters. Raymond Harry Peters (19 February 1918 – 15 July 1995) was Professor of Polymer and Fibre Science, University of Manchester, 1955-1984, then professor emeritus.

He was educated at Ilford County High School, King's College London and the University of Manchester.

He worked for Imperial Chemical Industries, 1941-1946 and 1949-1955.  After retirement, he was visiting professor at UMIST, 1984-1986 and the University of Strathclyde, 1984.  He was president of the Society of Dyers and Colourists, 1967-1968.

References
 Who was Who

1918 births
1995 deaths
People educated at Ilford County High School
Imperial Chemical Industries people
British chemists
Alumni of King's College London
PKP class SM31. SM31 (production model 411D) is a Polish series of diesel shunting locomotives used by PKP and industry.

History
The SM31 class was designed for shunting heavy freight trains in large freight stations, works and harbours. The design was elaborated in Fablok in 1973, mainly on the basis of SM42 locomotive. Production of this series lasted between 1976 and 1981, as well as between 1983 and 1985. In this period PKP bought 167 units. About 200 locomotives were produced in total, with the rest of them servicing Polish industry, chiefly mining. The first 2 prototypes (SM31-001 and SM31-002) were sold to industrial works, and PKP's last locomotive was re-bought from an industrial user (SM31-170).

As the main purpose of this series was shunting heavy freight trains, after its introduction PKP possessed shunters suited for all purposes. For extremely light trains mainly SM03 locomotives were used. Medium light trains were shunted by SM30 series, medium weight trains were left for SM42 engines. The last thing to be done was the introduction of heavy shunter able to work in severe climatic conditions, what did not happen before SM48 were brought to Poland.

Today SM31 locomotives are mainly to be found on Upper Silesia railway tracks, pulling heavy freight trains from works to marshalling yards in Łazy, Jaworzno, Szczakowa, Tarnowskie Góry and Rybnik. Other engines are deployed at the stations of Łódź, Nowy Sącz, Poznań, Szczecin and Wrocław.

Technical data 
SM31 is a Co-Co locomotive, what means it runs on two bogies, each equipped with three axles. Bogies are similar in construction to those used in SU45 and SU46 locomotives. This gives SM31 locomotive good performance on highland tracks. Being a typical shunter, SM31 has a single crew compartment of the same height as the machine and electric compartments.
The engine (V8, compression-ignition) is in fact a developed version of SM42 locomotive engine, with its total power increased by about 50%. The engine drives the main alternator, which powers six  traction motors.

Nicknames 
Trumna (En.: Coffin) – from locomotive's angular shape.

References 

Diesel–electric locomotives of Poland
Co′Co′ locomotives
Standard gauge locomotives of Poland
Railway locomotives introduced in 1976
Shunting locomotives
Helicopter carrier. A helicopter carrier is a type of aircraft carrier whose primary purpose is to operate helicopters. It has a large flight deck that occupies a substantial part of the deck, which can extend the full length of the ship like  of the Royal Navy (RN), or extend only partway, usually aft, as in the Soviet Navy's  or in the Chinese Navy's Type 0891A. It often also has a hangar deck for the storage and maintenance of rotorwing aircraft.

Pure helicopter carriers are difficult to define in the 21st century. The advent of STOVL aircraft such as the Harrier jump jet, and now the F-35, have complicated the classification; the United States Navy's , for instance, carries six to eight Harriers as well as over 20 helicopters. Only smaller carriers unable to operate the Harrier, and older, pre-Harrier-era carriers, can be regarded as true helicopter carriers. In many cases, other carriers, able to operate STOVL aircraft, are classified as "light aircraft carriers". Other vessels, such as the Wasp class, are also capable of embarking troops such as marines and landing them ashore; they are classified as landing helicopter docks.

Helicopter carriers have been used as anti-submarine warfare carriers and amphibious assault ships.

 and two of her sisters were 22,000 ton fleet carriers converted to "commando carriers" only able to operate helicopters. Hermes was later converted to a STOVL carrier.

Helicopter carriers by country

Helicopter carriers

Helicopter carriers currently in service

Retired helicopter carriers

   (Royal Navy) – converted from light carrier and operating in helicopter carrier role from 1962 to 1973
   (Italian Navy) – an  helicopter cruiser active from 1964 to 1992
   (United States Navy) –  landing helicopter dock, active 1998–2020
   (Royal Navy) – converted from light carrier and operating in helicopter carrier role from 1960 to 1981
   (Italian Navy) - an Andrea Doria-class helicopter cruiser active from 1964 to 1989
   (US Coast Guard), decommissioned in 1946 – world's first helicopter carrier.
   (Royal Navy) – an  light aircraft carrier, which operated as a helicopter carrier when HMS Ocean was being refitted.
   (United States Navy) – lead of the seven-ship , active from the early 1960s to the early 2000s
   (French Navy), decommissioned in 2010
   (Soviet Navy) – second of the two-ship  - active 1969–1991
   (Soviet Navy) – lead of the two-ship Moskva class, active 1967–1991
  ex- (Royal Navy) – helicopter carrier 1998–2018, decommissioned March 2018.
Sold to Brazil in February 2018, renamed Atlântico
   (Italian Navy) – a helicopter cruiser active from 1969 to 2003

See also
 Amphibious transport dock
 Amphibious warfare ship
 Aviation-capable naval vessel
 List of STOVL carriers

Notes

References

External links

Aircraft carriers
Aircraft carriers by type