Elementary Mechanics of Fluids

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Elementary Mechanics of Fluids

• CE 319 F
• Daene McKinney

Pressure
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Pressure

• Fluid at rest can not support shear stress
• Normal stress on any plane is pressure ( for
  compression)

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Example (3.4)

• Prob. 3.4 How many bolts are needed at B-B?

20 bolts, 2.5 cm dia
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Pressure, Absolute Gage
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Pressure Variation with Elevation

• Static fluid pressure varies only with
  elevation in the fluid.

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Pressure Variation with Elevation

• If g is a constant

z z1, p p1
z z2, p p2
z 0
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Piezometric Head
Open Tank
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Piezometric Head
Pressurized Tank
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Example (3.6)

• Tank contins fluid with gA gt gB
• Which graph depicts the correct pressure
  distribution?

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Leaking Storage Tank

• Water has seeped in to the depth shown
• Find Pressure at gas-water interface, pressure
  at bottom of tank
• Assume Fluids are at rest

17 ft
GasolineSG0.68
water
3 ft
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Example (3.5)

• Find l
• Forces at surface inside tube

d0.5 mm
Fa
l
Fw
water
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Example (3.8)

• What is maximum force F2 that can be supported?

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Compressible Fluids

• Density is nearly proportional to pressure

• For perfect gasses

• Need to know T T(z)
• Constant (Isothermal)
• Linear

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Compressible Fluids

• Assume constant and integrate

• Assume linear and integrate

Temperature variation with altitude for the U.S.
standard atmosphere