Download HW 5 Environmental Loading - essie-uf

OCE 3016
Home Work 5
Environmental Loading
1. Define the following:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
shear stress
normal stress
drag force
inertia force
buoyancy force
pressure drag
flow separation
wake vortex
horseshoe vortex
Reynold’s Number
2. Consider the water flow around the cylinder shown in the figure. Sketch the slow field
around the cylinder in both the side and top views.
3. Describe what happens to the drag force on a sphere when the surface is roughened.
4. Estimate the drag force (in lbf) on a score board at the end of a stadium when the wind is
blowing directly at the board at 50 miles/hr. The board is 20 ft tall and 30 ft long. The mass
density, ρa, and dynamic viscosity, µ, of the air are 0.076 lbm/ft3 and the 0.121 x 10-4 lbm/s ft
respectively. Use the attached graph to determine the drag coefficient.
5. Estimate the terminal velocity of a 130 lbf parachutist if the diameter of the parachute is 30
ft. The mass density and dynamic viscosity of the air is the same as in problem 4. If her 200
ibf friend uses the same parachute what will be his terminal speed?
a. A steady current of 6 knots (nautical miles per hour) is flowing past a piling in the water as
shown in the figure. If the water depth is 20 ft and the mass density and dynamic viscosity
are 62.27 lbm/ft3 and 6.733 x 10-4 lbm/s ft respectively estimate the drag force on the pile.
1 ft dia.
20
7. Compute the instantaneous force on the pile in problem 6 by a wave with a height of 8 ft and
a period of 6 s at the time when the crest is at the centerline of the pile. What would the
force be if the period of the wave were 8 s? What would the force be if the pile were 6 ft in
diameter (6 s period)?
ADVANCED PROBLEM
Consider the wind anemometer shown in the figure. The wind speed is related to the revolutions
per minute (rpms) of the cups. By measuring the rpms of the cups the wind speed can be
estimated.
2 in.
Hemispherical
Cup 1 in dia.
Top View
a. If the anemometer is locked in position shown in the figure what are the forces on the
cups and the moment about the axis of rotation when the wind speed is 20 miles/hr?
Assume ρa and µ are the same as in problem 4.
b. If the anemometer is now allowed to spin what is the terminal rpm of the cups when the
wind speed is 20 mi/hr? Assume that the friction in the bearings is negligible.
c. Determine the relationship between rpm and wind speed for this anemometer.