Hydraulic engineering as a sub-discipline of civil
engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One
feature of these systems is the extensive use of gravity as the motive force to
cause the movement of the fluids. This area of civil engineering is intimately
related to the design of bridges, dams,
channels, canals, and levees, and to both
sanitary and environmental engineering.
Hydraulic engineering is the application of fluid mechanics
principles to problems dealing with the collection, storage, control, transport,
regulation, measurement, and use of water. Before beginning a hydraulic
engineering project, one must figure out how much water is involved. The hydraulic engineer is concerned with the
transport of sediment by the river, the interaction of the water with its
alluvial boundary, and the occurrence of scour and deposition. "The
hydraulic engineer actually develops conceptual designs for the various
features which interact with water such as spillways and outlet works for dams,
culverts for highways, canals and related structures for irrigation projects,
and cooling-water facilities for thermal power plants."
Fundamental principles
A few examples of the fundamental principles of hydraulic
engineering include fluid mechanics, fluid flow, behavior
of real fluids, hydrology, pipelines, open channel hydraulics, mechanics of
sediment
transport, physical modeling, hydraulic machines, and drainage hydraulics.
Fluid mechanics
Fundamentals of Hydraulic Engineering defines
hydrostatics as the study of fluids at rest. In a fluid at rest, there exists a
force, known as pressure, that acts upon the fluid's surroundings. This
pressure, measured in N/m2, is not constant throughout the body of
fluid. Pressure, p, in a given body of fluid, increases with an increase in
depth. Where the upward force on a body acts on the base and can be found by equation:
where,
ρ = density of water
g = specific gravity
y = depth of the body of liquid
Rearranging this equation gives you the pressure
head p/ρg = y. Four basic devices for pressure measurement are a piezometer,
manometer,
differential manometer, Bourdon gauge, as well as an inclined manometer.
As Prasuhn states:
On undisturbed submerged bodies, pressure acts along all surfaces
of a body in a liquid, causing equal perpendicular forces in the body to act
against the pressure of the liquid. This reaction is known as equilibrium. More
advanced applications of pressure are that on plane surfaces, curved surfaces,
dams, and quadrant gates, just to name a few.
Behavior of real fluids
Real and ideal fluids
The main difference between an ideal fluid and a real fluid
is that for ideal flow p1 = p2 and for real
flow p1 > p2. Ideal fluid is
incompressible and has no viscosity. Real fluid has viscosity.Ideal fluid is
only an imaginary fluid as all fluids that exist have some viscosity.
Viscous flow
A viscous fluid will deform continuously under a shear
force, whereas an ideal fluid doesn't deform.
Laminar flow and turbulence
The various effects of disturbance on a viscous flow are
stable, transition and unstable.
Bernoulli's equation
For an ideal fluid, Bernoulli's equation holds along streamlines.
p/ρg + u²/2g = p1/ρg
+ u1²/2g = p2/ρg + u2²/2g
Boundary layer
Assuming a flow is bounded on one side only, and that a
rectilinear flow passing over a stationary flat plate which lies parallel to
the flow, the flow just upstream of the plate has a uniform velocity. As the
flow comes into contact with the plate, the layer of fluid actually 'adheres'
to a solid surface. There is then a considerable shearing action between the
layer of fluid on the plate surface and the second layer of fluid. The second
layer is therefore forced to decelerate (though it is not quite brought to
rest), creating a shearing action with the third layer of fluid, and so on. As
the fluid passes further along the plate, the zone in which shearing action
occurs tends to spread further outwards. This zone is known as the 'boundary
layer'. The flow outside the boundary layer is free of shear and
viscous-related forces so it is assumed to act like an ideal fluid. "The
intermolecular cohesive forces in a fluid are not great enough to hold fluid
together. Hence a fluid will flow under the action of the slightest stress and
flow will continue as long as the stress is present. The flow inside the layer
can be either viscous or turbulent, depending on Reynolds number.
Applications
Common topics of design for hydraulic engineers include
hydraulic structures such as dams, levees, water distribution networks, water collection
networks, sewage collection networks, storm water
management, sediment transport, and various other topics
related to transportation engineering and geotechnical engineering. Equations
developed from the principles of fluid
dynamics and fluid mechanics are widely utilized by other
engineering disciplines such as mechanical, aeronautical and even traffic engineers.
Related branches include hydrology and
rheology
while related applications include hydraulic modeling, flood mapping, catchment
flood management plans, shoreline management plans, estuarine strategies,
coastal protection, and flood alleviation.
History
Earliest uses of hydraulic engineering were to irrigate crops
and dates back to the Middle East and Africa.
Controlling the movement and supply of water for growing food has been used for
many thousands of years. One of the earliest hydraulic machines, the water clock
was used in the early 2nd millennium BC. Other early examples of using gravity
to move water include the Qanat system in ancient Persia and the very similar Turpan water system in ancient China as well as
irrigation canals in Peru.
In ancient China, hydraulic engineering was highly
developed, and engineers constructed massive canals with levees and dams to
channel the flow of water for irrigation, as well as locks to allow ships to
pass through. Sunshu
Ao is considered the first Chinese hydraulic engineer. Another important
Hydraulic Engineer in China, Ximen Bao was credited of starting the practice of large
scale canal irrigation during the Warring States period
(481 BC-221 BC), even today hydraulic engineers remain a respectable
position in China. Before becoming President, Hu Jintao
was a hydraulic engineer and holds an engineering degree from Tsinghua University
Eupalinos of Megara, was an ancient
Greek engineer
who built the Tunnel of Eupalinos on Samos in the 6th
century BC, an important feat of both civil and hydraulic engineering. The
civil engineering aspect of this tunnel was the fact that it was dug from both
ends which required the diggers to maintain an accurate path so that the two
tunnels met and that the entire effort maintained a sufficient slope to allow
the water to flow.
Hydraulic engineering was highly developed in Europe under
the aegis of the Roman Empire where it was especially applied to the
construction and maintenance of aqueducts to supply water to and remove
sewage from their cities.[3]
In addition to supplying the needs of their citizens they used hydraulic
mining methods to prospect and extract alluvial gold deposits in a
technique known as hushing, and applied the methods to other ores such as those
of tin and lead.
In the 15th century, the Somali
Ajuran
Empire was the only hydraulic empire in Africa. As a hydraulic empire,
the Ajuran State monopolized the water
resources of the Jubba and Shebelle
Rivers. Through hydraulic engineering, it also constructed many of the limestone wells and
cisterns of
the state that are still operative and in use today. The rulers developed new
systems for agriculture and taxation, which
continued to be used in parts of the Horn
of Africa as late as the 19th century.
Further advances in hydraulic engineering occurred in the Muslim
world between the 8th to 16th centuries, during what is known as the Islamic Golden Age. Of particular importance was
the 'water management technological
complex' which was central to the Islamic Green Revolution and, by
extension, a precondition for the emergence of modern technology. The various
components of this 'toolkit' were developed in different parts of the Afro-Eurasian
landmass, both within and beyond the Islamic world. However, it was in the
medieval Islamic lands where the technological complex was assembled and
standardized, and subsequently diffused to the rest of the Old World. Under the
rule of a single Islamic Caliphate, different regional hydraulic technologies were
assembled into "an identifiable water
management technological complex that was to have a global impact."
The various components of this complex included canals, dams, the qanat system
from Persia, regional water-lifting devices such as the noria, shaduf and screwpump
from Egypt, and
the windmill
from Islamic Afghanistan. Other original Islamic developments included
the saqiya
with a flywheel
effect from Islamic Spain, the reciprocating suction pump and crankshaft-connecting
rod mechanism from Iraq,
the geared and hydropowered
water supply system from Syria, and the water purification methods of Islamic chemists.
Modern times
In many respects the fundamentals of hydraulic engineering
haven't changed since ancient times. Liquids are still moved for the most part
by gravity through systems of canals and aqueducts, though the supply
reservoirs may now be filled using pumps. The need for water has steadily
increased from ancient times and the role of the hydraulic engineer is a
critical one in supplying it. For example, without the efforts of people like William Mulholland the Los Angeles area would
not have been able to grow as it has because it simply doesn't have enough
local water to support its population. The same is true for many of our world's
largest cities. In much the same way, the central valley of California could
not have become such an important agricultural region without effective water
management and distribution for irrigation. In a somewhat parallel way to what
happened in California the creation of the Tennessee Valley Authority(TVA) brought
work and prosperity to the South by building dams to generate cheap electricity
and control flooding in the region, making rivers navigable and generally
modernizing life in the region.
Leonardo da Vinci (1452–1519) performed experiments,
investigated and speculated on waves and jets, eddies and streamlining. Isaac
Newton (1642–1727) by formulating the laws of motion and his law of viscosity,
in addition to developing the calculus, paved the way for many great
developments in fluid mechanics. Using Newton's laws of motion, numerous
18th-century mathematicians solved many frictionless (zero-viscosity) flow
problems. However, most flows are dominated by viscous effects, so engineers of
the 17th and 18th centuries found the inviscid flow solutions unsuitable, and
by experimentation they developed empirical equations, thus establishing the
science of hydraulics.
Late in the 19th century, the importance of dimensionless
numbers and their relationship to turbulence was recognized, and dimensional
analysis was born. In 1904 Ludwig Prandtl published a key paper, proposing that
the flow fields of low-viscosity fluids be divided into two zones, namely a
thin, viscosity-dominated boundary layer near solid surfaces, and an
effectively inviscid outer zone away from the boundaries. This concept
explained many former paradoxes, and enabled subsequent engineers to analyze
far more complex flows. However, we still have no complete theory for the
nature of turbulence, and so modern fluid mechanics continues to be combination
of experimental results and theory.
The modern hydraulic engineer uses the same kinds of computer-aided design (CAD) tools as many of
the other engineering disciplines while also making use of technologies like computational fluid dynamics to
perform the calculations to accurately predict flow characteristics, GPS mapping to assist in locating the
best paths for installing a system and laser-based surveying tools to aid in
the actual construction of a system.
SUBSCRIBERS - ( LINKS) :FOLLOW / REF / 2 /
findleverage.blogspot.com
Krkz77@yahoo.com
+234-81-83195664
No comments:
Post a Comment