Hydraulics for Civil Engineering Assignment

Hydraulics for Civil Engineering 1
HYDROSTATIC AND HYDRODYNAMIC PROBLEMS
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Hydraulics for Civil Engineering 2
TASK 1
Height above the city = Height = 100 m
Water Density = 1000 kg/m3
Gravitational pull = 9.8N/Kg
Pressure in pipe, P = 100 x 1000 x 10 N/m3
Pressure in pipe = 1,000,000N/m2
When converted into Bar: Pressure in Pipe = 10 Bar
(Diamantis, Papageorgiou, & Kosmatopoulos, 2010)
Since in open channel system the water flow due to the effects of atmospheric pressure, the
pressure bringing water into the city center is equal to the atmospheric pressure:
Therefore:
Atmospheric Pressure, PAtmo = Open Channel Pressure
PAtmo = 100,000 N/m2
Open Channel Pressure = 100,000N/m2
The pressure in pipe system is 1,000,000N/m2 while open channel pressure is 100,000N/m2,
this means that the pipe system pressure is higher compared to open channel pressure since in
pipe channel system may be flowing as a result of external pressure such as pumping action
(Bing & Yang, 2011).
The major forces of resistance to flow of water in pipes include boundary layer effect and
frictional force in water (viscosity). The effects of boundary layer is a resistive force that is
caused by sticking of fluid on the solid bordering it. This sticking effect in the boundary layer
reduces the velocity of fluid flow gradually and the fluid near the boundary do not flow at all.

Hydraulics for Civil Engineering 3
Viscosity of the frictional force in fluids and is caused by internal friction between the fluid
molecules themselves or between the fluid molecules and the surface of the container (Ercan
& Kavvas, 2013).
An increase in temperature may either increase or decrease the viscosity or the boundary layer
effect depending on the physical state of the water. An increase in temperature decreases the
viscosity effect on the flowing fluid since an increase in temperature decreases the cohesion
forces and increasing kinetic energies of the molecules hence reducing the viscosity of fluid. A
decrease in temperature affect the viscosity of fluid since the decrease in temperature
increases the cohesion forces and decreases the kinetic energies of the molecules hence
increasing the viscosity of the fluid.
The increase in temperature decreases the boundary layer effect of the fluid by increasing the
kinetic energies of the flowing fluid hence mobility of molecules is also increased. A decrease
in temperature increases the boundary effect of the fluid by decreasing the kinetic energies of
the flowing fluid hence mobility of molecules is also decreased (Zimmermann, 2010).
Laminar flow which is also referred to as streamline flow and occurs when fluid flows in
parallel layers without any disruptions between the fluid layers. At low velocities, there is a
tendency of the fluid to flow without mixing laterally. There are no swirls, eddies, or cross-
currents perpendicular to the flow direction (Friedrich & Stemmer, 2014).
Turbulent flow is a disorderly or chaotic flow resulting into variations in flow velocity and
pressure in time and space. The fluid does not flow in in layers as in the case of laminar flow.
The flows at Reynolds number greater than 4000 are generally turbulent (Widodo &
Pradhana, 2018).
The Reynolds number is fluid mechanic quantity used for the flow pattern prediction in
various fluid flow conditions. At low Reynolds number below 2300, the fluid flows is laminar
characterized by smooth and orderly flow while at high Reynolds number higher than 2300,
the fluid flow tend to be turbulent flow characterized by disorderly flow (Chamorro & Arndt,
2011).

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A boundary layer is a relatively thin layer of fluid close to the surface of the body neighboring
the fluid flow. The boundary layer tend to affect the flow of fluid by having a pull effect of the
flowing hence reducing the fluid velocity especially near the borders between the fluid and the
soil surface.
The physical state of the surface over which water is flowing influences the boundary layer
since a very smooth surface results in laminar flow of fluid over the surface since there are no
disturbances hence increasing the boundary layer. In case the surface in which water is
flowing over is rough, then there will be disorderly or turbulence which reduced the boundary
layer between fluid and the surface.
Some of the ways in which the resistance of water flow can be reduced in open channel system
or pipe system include:
Reducing water flow velocity: High velocity of water flow causes turbulence hence resulting
into resistance to the flow of water. By reducing the velocity, the flow of water will be smooth
without any resistance (Ghosh, Friedrich, & Stemmer, 2014).
Increasing the temperature of water flowing in the pipe: By increasing the temperature of the
flowing fluid, the viscosity will be reduced hence no resistance between water molecules or
between water molecules and the pipe surface.
Reducing the length of pipe: The longer the pipe, the higher the resistance between the fluid
molecules themselves and also between the fluid molecules and the surface of open channel or
pipe. Therefore, the resistance of water flow is reduced by reducing the length of the flow
channel.
Increasing the pipe diameter: The diameter of the pipe affects the velocity of water flowing
through the pipe. The larger the pipe diameter the lower the resistance of water flow (Garai,
Pardyjak, & Steeneveld, 2013).