hydraulics n : study of the mechanics of fluids [syn: fluid mechanics]

English

Noun

1. The engineering science that deals with practical applications where liquid is in motion and transmits energy.
2. The hydraulic system of a vehicle or other machine.

Translations

For the mechanical technology, see hydraulic machinery and hydraulic cylinder

Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion. However if used incorrectly, hydraulic instruments can result in weird occurrences because of the nature of high pressure fluids.

The word "hydraulics" originates from the Greek word (hydraulikos) which in turn originates from (hydraulos) meaning water organ which in turn comes from (hydor, Greek for water) and (aulos, meaning pipe).

History

Earliest masters

The earliest masters of this science were Ctesibius (flourished c. 270 BC) and Heron of Alexandria (c. 10–80 AD) in the Greek-Hellenized West. Heron 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, for example.

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, the Sinhalese used hydraulics in many applications, in the ancient kingdoms of Anuradhapura and Polonnaruwa. The discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to Sinhalese ingenuity more than 2,000 years ago. By the first century A.D, several large-scale irrigation works had been completed. 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 citadel on the massive rock at the site includes cisterns for collecting water.

Near East

In the Near East there was continuous and rapid development of civilisation in the fertile crescent from around 16,000BC. The Neolithic period saw the advent of irrigation through small ditches - the very first and rudimentary "hydraulic works". The first definite evidence of irrigation dates from the VIIth Millennium BC - in the middle Tigris valley. At Choga Mami remains of two meter wide canals have been found. The first wells appeared in the VIth Millennium BC.

Roman Innovations

The Romans developed many different hydraulic applications, 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.

While there is great public awareness of their highly visible aqueducts, less is known about their use of hydropower, although extant remains suggest that it was much more widespread than appreciated. The use of hydraulic mining methods is at its most spectacular in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold-mine of Las Medulas for example must be one of the largest of their mines and even today rivals modern mines in sheer size. 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.

Modern era

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.

Blaise Pascal

Blaise Pascal (1623–1662-1672) study of 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.

See also

• Affinity laws
• Hydraulic engineering
• Hydraulic mining
• Pneumatics
• Rotary power

References

External links

• International Association of Hydraulic Engineering and Research (IAHR)
• National Fluid Power Association (NFPA)
• Pascal's Principle and Hydraulics
• The principle of hydraulics
• IAHR media library Web resource of photos, animation & video

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