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Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of . At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concerns . Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation, control, and transmission of power by the use of pressure liquids. Hydraulic topics range through some parts of science and most of engineering modules, and they cover concepts such as pipe flow, dam design, fluidics, and fluid control circuitry. The principles of hydraulics are in use naturally in the human body within the vascular system and erectile tissue.
Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in , , , estuary, and . Its sub-field open-channel flow studies the flow in open channels.
The Qanat spread to neighboring areas, including the Armenian highlands. There, starting in the early 8th century BC, the Urartu undertook significant hydraulic works, such as the Menua Canal.
The earliest evidence of and date back to the ancient Near East in the 4th century BC,Terry S. Reynolds, Stronger than a Hundred Men: A History of the Vertical Water Wheel, JHU Press, 2002 , p. 14 specifically in the Persian Empire before 350 BCE, in the regions of Iraq, Iran, and Egypt.
In Greco-Roman Egypt, the construction of the first hydraulic machine automata by Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10 – 80 AD) is notable. Hero describes several 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.Museum, Victoria and Albert. "Catalogue of the mechanical engineering collection in the Science Division of the Victoria and Albert Museum, South Kensington, with descriptive and historical notes." Ulan Press. 2012.
In the Roman Empire, 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 . 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 of the largest of their mines. At least seven long aqueducts worked it, and the water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content.
Al-Jazari (1136–1206) described designs for 50 devices, many of them water-powered, in his book, The Book of Knowledge of Ingenious Mechanical Devices, including water clocks, a device to serve wine, and five devices to lift water from rivers or pools. These include Scoop wheel and a reciprocating device with hinged valves.
The earliest programmable machines were water-powered devices developed in the Muslim world. A music sequencer, a programmable musical instrument, was the earliest type of programmable machine. The first music sequencer was an automated water-powered flute player invented by the Banu Musa brothers, described in their Book of Ingenious Devices, in the 9th century. In 1206, Al-Jazari invented water-powered programmable automata/. He described four automaton musicians, including drummers operated by a programmable drum machine, where they could be made to play different rhythms and different drum patterns.Professor Noel Sharkey, A 13th Century Programmable Robot (Archive), University of Sheffield.
Blaise Pascal (1623–1662) studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids. His discovery on the theory behind hydraulics led to his invention of the hydraulic press, which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure (or exact 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 end in the container, i.e., any change in pressure applied at any point of the liquid is transmitted undiminished throughout the fluids.
A French physician, Poiseuille (1797–1869) 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.Sutera and Skalak, Salvatore and Richard. The History of Poiseuille's Law. Annu. Rev. Fluid Mech. 1993. 25: 1-19.
Several cities developed citywide hydraulic power networks in the 19th century, to operate machinery such as lifts, cranes, capstans and the like. Joseph Bramah (1748–1814) was an early innovator and William Armstrong (1810–1900) perfected the apparatus for power delivery on an industrial scale. In London, the London Hydraulic Power Company was a major supplier its pipes serving large parts of the West End of London, City and the London Docks, but there were schemes restricted to single enterprises such as docks and railway .
The conservation of mass requirement combined with fluid compressibility yields a fundamental relationship between pressure, fluid flow, and volumetric expansion, as shown below:
Assuming an incompressible fluid or a "very large" ratio of compressibility to contained fluid volume, a finite rate of pressure rise requires that any net flow into the collected fluid volume create a volumetric change.
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