fluid_mechanics

Problems 571
fast will this wave travel across the ocean surface if the ocean depth
is 3000 m?
Section 10.3 Energy Considerations
10.15 Water flows in a 10-m-wide open channel with a flowrate
of 5 m 3 s. Determine the two possible depths if the specific energy
of the flow is E 0.6 m.
10.16 Water flows in a rectangular channel with a flowrate per
unit width of q 2.5 m 2 s. Plot the specific energy diagram for
this flow. Determine the two possible depths of flow if E 2.5 m.
10.17 Water flows radially outward on a horizontal round disk as
shown in Video V10.12 and Fig. P10.17. (a) Show that the specific
energy can be written in terms of the flowrate, Q, the radial distance
from the axis of symmetry, r, and the fluid depth, y, as
E y a Q 2
2pr b 1
2gy 2
(b) For a constant flowrate, sketch the specific energy diagram.
Recall Fig. 10.7, but note that for the present case r is a variable.
Explain the important characteristics of your sketch. (c) Based on the
results of Part (b), show that the water depth increases in the flow
direction if the flow is subcritical, but that it decreases in the flow
direction if the flow is supercritical.
q 4 m 2 s. The channel bottom contour is given by z B 0.2e x2 ,
where z B and x are in meters. The water depth far upstream of the
bump is y 1 2 m. Plot a graph of the water depth, y y1x2, and
the surface elevation, z z1x2, for 4 m x 4 m. Assume onedimensional
flow.
z
V 1
y 1
y(x)
z(x)
x
0
z B = 0.2e –x2
F I G U R E P10.22
*10.23 Repeat Problem 10.22 if the upstream depth is 0.4 m.
10.24 Water in a rectangular channel flows into a gradual
contraction section as is indicated in Fig. P10.24. If the flowrate
is Q 25 ft 3 s and the upstream depth is y 1 2 ft, determine the
downstream depth, y 2 .
V 1
b 1 = 4 ft
b 2 = 3 ft V 2
r
V
y
V
Top view
r
V 1
y 1 y 2 V 2
F I G U R E P10.17
(1)
Side view
F I G U R E P10.24
(2)
10.18 Water flows in a 10-ft-wide rectangular channel with a flowrate
of 200 ft 3 /s. Plot the specific energy diagram for this flow. Determine
the two possible flowrates when the specific energy is 6 ft.
10.19 Water flows in a rectangular channel at a rate of
q 20 cfsft. When a Pitot tube is placed in the stream, water in
the tube rises to a level of 4.5 ft above the channel bottom.
Determine the two possible flow depths in the channel. Illustrate
this flow on a specific energy diagram.
10.20 Water flows in a 5-ft-wide rectangular channel with a
flowrate of Q 30 ft 3 s and an upstream depth of y 1 2.5 ft as
is shown in Fig. P10.20. Determine the flow depth and the surface
elevation at section 122.
V
Q
1
y 2 V 2
y 1
(1)
F I G U R E P10.20
0.2 ft (2)
10.21 Repeat Problem 10.20 if the upstream depth is y 1 0.5 ft.
*10.22 Water flows over the bump in the bottom of the rectangular
channel shown in Fig. P10.22 with a flowrate per unit width of
10.25 Sketch the specific energy diagram for the flow of Problem
10.24 and indicate its important characteristics. Note that q 1 q 2 .
10.26 Repeat Problem 10.24 if the upstream depth is y 1 0.5 ft.
Assume that there are no losses between sections 112 and 122.
10.27 Water flows in a rectangular channel with a flowrate per
unit width of q 1.5 m 2 s and a depth of 0.5 m at section 112. The
head loss between sections 112 and 122 is 0.03 m. Plot the specific
energy diagram for this flow and locate states 112 and 122 on this
diagram. Is it possible to have a head loss of 0.06 m? Explain.
10.28 Water flows in a horizontal rectangular channel with a
flowrate per unit width of q 10 ft 2 s and a depth of 1.0 ft at the
downstream section 122. The head loss between section 112 upstream
and section 122 is 0.2 ft. Plot the specific energy diagram for this
flow and locate states 112 and 122 on this diagram.
10.29 Water flows in a horizontal, rectangular channel with an
initial depth of 1 m and an initial velocity of 4 ms. Determine the
depth downstream if losses are negligible. Note that there may be
more than one solution.
10.30 A smooth transition section connects two rectangular
channels as shown in Fig. P10.30. The channel width increases
from 6.0 to 7.0 ft and the water surface elevation is the same in
each channel. If the upstream depth of flow is 3.0 ft, determine h,
the amount the channel bed needs to be raised across the transition
section to maintain the same surface elevation.