1. Elementary Mechanics of Fluids
CE 319 F
Daene McKinney
Elementary Mechanics of Fluids
Pressure

2. Pressure Fluid at rest – can not support shear stress
Normal stress on any plane is pressure (+ for compression)

3. Example (3.4) Prob. 3.4: How many bolts are needed at B-B?
20 bolts, 2.5 cm dia

4. Pressure, Absolute & Gage

5. Pressure Variation with Elevation
Static fluid – pressure varies only with elevation in the fluid.

6. Pressure Variation with Elevation
If g is a constant
z = z1, p = p1 1
z = z2, p = p2 2
Piezometric head
Elevation head
Pressure head
z = 0

7. Piezometric Head
z = 0 1 2
Open Tank

8. Piezometric Head
z = 0 3 2 1
Pressurized Tank

9. Example (3.6) Tank contins fluid with gA > gB
Which graph depicts the correct pressure distribution?

10. 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
Gasoline SG=0.68 1
water 2
3 ft

11. Example (3.5) Find l Forces at surface inside tube l Fw d=0.5 mm Fa
water Fw

12. Example (3.8)
What is maximum force F2 that can be supported?

13. Compressible Fluids Density is nearly proportional to pressure
For perfect gasses
Need to know T = T(z)
Constant (Isothermal):
Linear:

14. Temperature variation with altitude for the U.S. standard atmosphere
Compressible Fluids
Assume constant and integrate
Assume linear and integrate
Temperature variation with altitude for the U.S. standard atmosphere