A series of experiments was conducted for a ship model of 3-ft length in a water tank. The relevant variables are the length of the model, L, water density, p, tawing velocity, V, the viscosity, μ, and the gravitational acceleration, g. The experimental result was V (ft/s) 10 D (lbf) 0.022 20 30 40 50 60 0.079 0.169 0.281 0.45 0.618 70 0.731

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Chapter5: Analysis Of Convection Heat Transfer
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1. A series of experiments was conducted for a ship model of 3-ft length in a water
tank. The relevant variables are the length of the model, L, water density, p, tawing
velocity, V, the viscosity, µ, and the gravitational acceleration, g. The experimental
result was
V (ft/s) 10
20
D (lbf) 0.022 0.079
50
30 40
0.169 0.281 0.45
=
60
0.618
70
0.731
The full-size ship is 150 ft long and designed to cruise at 15 knots and 20 knots in a
freshwater lake (1 knot = 1.68781 ft/s).
a. How many dimensionless groups can be obtained? Why?
b. Use dimensional analysis to prove that the functional relationship of the drag
force D=f(p, V, L, g, µ) can be simplified to Cd=f(Fr, Re), where
D
V
Ca
-, Fr=
PVL
Re=
√gL
μl
PV²12
c.
If the drag coefficient and Fr number are conserved, estimate the drag force
for the full-size ship at the two cruising velocities.
d. If the drag coefficient and Re number are conserved, estimate the drag force
for the full-size ship at the two cruising velocities.
Transcribed Image Text:1. A series of experiments was conducted for a ship model of 3-ft length in a water tank. The relevant variables are the length of the model, L, water density, p, tawing velocity, V, the viscosity, µ, and the gravitational acceleration, g. The experimental result was V (ft/s) 10 20 D (lbf) 0.022 0.079 50 30 40 0.169 0.281 0.45 = 60 0.618 70 0.731 The full-size ship is 150 ft long and designed to cruise at 15 knots and 20 knots in a freshwater lake (1 knot = 1.68781 ft/s). a. How many dimensionless groups can be obtained? Why? b. Use dimensional analysis to prove that the functional relationship of the drag force D=f(p, V, L, g, µ) can be simplified to Cd=f(Fr, Re), where D V Ca -, Fr= PVL Re= √gL μl PV²12 c. If the drag coefficient and Fr number are conserved, estimate the drag force for the full-size ship at the two cruising velocities. d. If the drag coefficient and Re number are conserved, estimate the drag force for the full-size ship at the two cruising velocities.
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