hydraulics

hydraulics, branch of engineering concerned mainly with moving liquids. The term is applied commonly to the study of the mechanical properties of water, other liquids, and even gases when the effects of compressibility are small. Hydraulics can be divided into two areas, hydrostatics and hydrokinetics. Hydrostatics, the consideration of liquids at rest, involves problems of buoyancy and flotation, pressure on dams and submerged devices, and hydraulic presses. The relative incompressibility of liquids is one of its basic principles. Hydrodynamics, the study of liquids in motion, is concerned with such matters as friction and turbulence generated in pipes by flowing liquids, the flow of water over weirs and through nozzles, and the use of hydraulic pressure in machinery.

Branch of science concerned with the practical applications of fluids, primarily liquids, in motion. It is related to fluid mechanics, which in large part provides its theoretical foundation. Hydraulics deals with such matters as the flow of liquids in pipes, rivers, and channels and their confinement by dams and tanks. Some of its principles apply also to gases, usually when variations in density are relatively small. The scope of hydraulics extends to such mechanical devices as actuators and control systems. Seealso Bernoulli's principle, Pascal's law, pump.

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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, fluidics and 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 ὑδραυλικός (hydraulikos) which in turn originates from ὕδραυλος (hydraulos) meaning water organ which in turn comes from ὕδωρ (hydor, Ancient Greek for water) and αὐλός (aulos, meaning pipe).

Ancient and medieval era

Ancient Near East

In the Near East there was continuous and rapid development of civilization 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 7th 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.

Hellenistic world

The earliest masters of hydraulics in the Greek-Hellenized West were Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10–80 AD). 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.

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.

Muslim innovations

In the medieval Islamic world, the advances in in fluid mechanics by Muslim physicists such as Abū Rayhān al-Bīrūnī (973-1048) and Al-Khazini (who invented the hydrostatic balance in 1121), led to innovations in hydraulics by Arabic engineers and inventors. The Arab Empire had advanced domestic water systems such as water cleaning systems and advanced water transportation systems resulting in better agriculture, something that helped in issues related to Islamic hygienical jurisprudence.

Muslim engineers made a number of innovative uses of watermills between the 8th and 13th centuries, including: the bridge mill, a unique type of mill that was built as part of the superstructure of a bridge; geared gristmill with trip hammers; hydropowered forge and finery forge; milling dam, used to provide additional power for milling; paper mill; shipmill, powered by water wheels mounted on the sides of large ships moored in midstream; spiral scoop-wheel, a device which raises large quantities of water to ground level with a high degree of efficiency; sugar refinery; the situation of watermills in the underground irrigation tunnels of a qanat and on the main canals of valley-floor irrigation systems; and the water turbine. The first factory milling installations were also built by Muslim engineers throughout every city and urban community in the Islamic world. For example, the factory milling complex in 10th century Baghdad could produce 10 tonnes of flour every day.

In the 9th century, the Banū Mūsā brothers introduced the use of differential pressures in their hydraulic devices. They also invented "the earliest known mechanical musical instrument", in this case a hydropowered organ which played interchangeable cylinders automatically. According to Charles B. Fowler, this "cylinder with raised pins on the surface remained the basic device to produce and reproduce music mechanically until the second half of the nineteenth century. They also invented an automatic water-powered flute player which appears to have been the first programmable machine. Al-Jazari (1136-1206) created the first recorded designs of programmable humanoid robots, which were driven by hydraulics and were part of a boat with four automatic musicians that floated on a lake to entertain guests at royal drinking parties. According to Charles B. Fowler, the automata were a "robot band" which performed "more than fifty facial and body actions during each musical selection. He also invented a hand washing automaton incorporating a flush mechanism now used in modern flush toilets. It features a female humanoid automaton standing by a basin filled with water. When the user pulls the lever, the water drains and the female automaton refills the basin. His "peacock fountain" was a more sophisticated hand washing device featuring humanoid automata as servants which offer soap and towels, dirven by advanced hydraulic-powered mechanisms.

The mechanical flywheel, used to smooth out the delivery of power from a driving device to a driven machine, was invented by Ibn Bassal (fl. 1038-1075) of Islamic Spain for use in the chain pump (saqiya) and noria. Al-Jazari invented a variety of machines for raising water in 1206, as well as water mills and water wheels with cams on their axle used to operate automata in the late 12th century. His invention of the crankshaft and connecting rod mechanism, which is central to modern machinery such as the internal combustion engine, was first employed in his water-raising machines, which included crank-driven and hydropowered saqiya chain pumps, and the first double-action suction piston pump with reciprocating motion. The concept of minimizing intermittency is also first implied in one of al-Jazari's saqiya chain pumps.

The monumental water clocks constructed by medieval Muslim engineers employed complex gear trains, arrays of automata, and weight-drives, while the escapement mechanism was present in the hydraulic controls they used to make heavy floats descend at a slow and steady rate. The on/off switch, an important feedback control principle, was invented by Muslim engineers between the 9th and 12th centuries, and it was employed in a variety of water-powered automata and water clocks. In 1206, Al-Jazari invented monumental water-powered astronomical clocks such as the "castle clock", a hydraulics-powered programmable analog computer, which could re-program the length of day and night every day, display moving models of the Sun, Moon, and stars, and had a pointer which travelled across the top of a gateway and caused automatic doors to open every hour. His hydraulics-powered elephant clock was the first to feature an automaton, flow regulator, and closed-loop system. The float regulator was later employed in domestic water systems during the Industrial Revolution.

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
• International Association of Hydraulic Engineering and Research

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