Hydraulics

 Hydraulics, 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 in cases in which variations in density are relatively small. Consequently, the scope of hydraulics extends to such mechanical devices as fans and gas turbines and to pneumatic control systems.

Pascal's principle

Liquids in motion or under pressure did useful work for humanity for many centuries before French scientist-philosopher Blaise Pascal and Swiss physicist Daniel Bernoulli formulated the laws on which modern hydraulic power technology is based. Pascal’s principle, formulated about 1650, states that pressure in a liquid is transmitted equally in all directions; i.e, when water is made to fill a closed container, the application of pressure at any point will be transmitted to all sides of the container. In the hydraulic press, Pascal’s principle is used to gain an increase in force; a small force applied to a small piston in a small cylinder is transmitted through a tube to a large cylinder, where it presses equally against all sides of the cylinder, including the large piston.

Bernoulli’s theorem, formulated about a century later, states that energy in a fluid is due to elevation, motion, and pressure, and if there are no losses due to friction and no work done, the sum of the energies remains constant. Thus, kinetic energy, deriving from motion, can be partly converted to pressure energy by enlarging the cross section of a pipe, which slows down the flow but increases the area against which the fluid is pressing.

hydraulic mining

Until the 19th century it was not possible to develop velocities and pressures much greater than those provided by nature, but the invention of pumps brought a vast potential for application of the discoveries of Pascal and Bernoulli. In 1882 the city of London built a hydraulic system that delivered pressurized water through street mains to drive machinery in factories. In 1906 an important advance in hydraulic techniques was made when an oil hydraulic system was installed to raise and control the guns of the USS Virginia. In the 1920s, self-contained hydraulic units consisting of a pump, controls, and motor were developed, opening the way to applications in machine tools, automobiles, farm equipment, earth-moving machinery, locomotives, ships, airplanes, and spacecraft.

In hydraulic power systems there are five elements: the driver, the pump, the control valves, the motor, and the load. The driver may be an electric motor or an engine of any type. The pump acts mainly to increase pressure. The motor may be a counterpart of the pump, transforming hydraulic input into mechanical output. Motors may produce either rotary or reciprocating motion in the load.

In the operation and control of machine tools, farm machinery, construction machinery, and mining machinery, fluid power can compete successfully with mechanical and electrical systems (see fluidics). Its chief advantages are flexibility and the ability to multiply forces efficiently; it also provides fast and accurate response to controls.

Hydraulic power systems have become one of the major energy-transmission technologies used by all phases of industrial, agricultural, and defense activity. Modern aircraft, for example, use hydraulic systems to activate their controls and to operate landing gears and brakes. Virtually all missiles, as well as their ground-support equipment, use fluid power. Automobiles use hydraulic power systems in their transmissions, brakes, and steering mechanisms. Mass production and its offspring, automation, in many industries have their foundations in the use of fluid power systems. Hydraulic fracturing, better known as fracking, has allowed the extraction of natural gas and petroleum from previously inaccessible deposits.

Hydraulics (from Greek ὕδωρ (hydor) 'water', and αὐλός (aulos) 'pipe') is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. 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 pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, and 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 rivers, canals, lakes, estuaries and seas. Its sub-field open-channel flow studies the flow in open channels.

History

Ancient and medieval eras

Waterwheels

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 Central Asia.

Persian Empire

In the Persian Empire, the Persians constructed an intricate system of water mills, canals and dams known as the Shushtar Historical Hydraulic System. The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I, has been referred to by UNESCO as "a masterpiece of creative genius". They were also the inventors of the Qanat, an underground aqueduct. Several of Iran's large, ancient gardens were irrigated thanks to Qanats.

The earliest evidence of water wheels and watermills date back to the ancient Near East in the 4th century BC, specifically in the Persian Empire before 350 BCE, in the regions of Iraq, Iran, and Egypt.

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 Lank

Moat and gardens at Sigiriya

In ancient Sri Lanka, hydraulics were widely used in the ancient kingdoms of Anuradhapura and Polonnaruwa. The discovery of the principle of the valve tower, or valve pit, (Bisokotuwa in Sinhalese) for regulating the escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, 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 coral on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa (King Dhatusena), Parakrama Samudra (King Parakrama Bahu), Tisa Wewa (King Dutugamunu), Minneriya (King Mahasen)

Greco-Roman world

In Ancient Greece, the Greeks constructed sophisticated water and hydraulic power systems. An example is a construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of hydraulic wheel, probably the earliest in Europe, is the Perachora wheel (3rd century BC).

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.

Aqueduct of Segovia, a 1st-century AD masterpiece

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 ores. They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae.[citation needed]

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.

Arabic-Islamic world

In the Muslim world during the Islamic Golden Age and Arab Agricultural Revolution (8th–13th centuries), engineers made wide use of hydropower as well as early uses of tidal power, and large hydraulic factory complexes. A variety of water-powered industrial mills were used in the Islamic world, including fulling mills, gristmills, paper mills, hullers, sawmills, ship mills, stamp mills, steel mills, sugar mills, and tide mills. By the 11th century, every province throughout the Islamic world had these industrial mills in operation, from Al-Andalus and North Africa to the Middle East and Central Asia.Muslim engineers also used water turbines, employed gears in watermills and water-raising machines, and pioneered the use of dams as a source of water power, used to provide additional power to watermills and water-raising machines.

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 an endless belt with jugs attached 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/robots. 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.