A 2-zn-high, 4-zn-wide rectangular advertisement panel is attached to a 4-rn-wide. 0.15-rn-high rectangular concrete block (density = 2300 kg/m3) by two 5-cm-diameter. 4-m-high (exposed part) poles, as shown in Fig. 11-96. If the sign is to withstand 150 kin/h winds from any direction, determine (a) the maximum drag force on the panel. (b) the drag force acting on the poles, and (c) the minimum length L of the concrete block for the panel to resist the winds. Take the density of air to be 1.30 kg/m3.
(a)
The maximum drag force on the panel.
Answer to Problem 96P
The maximum drag force on the panel is
Explanation of Solution
Given information:
The height of the rectangular advertisement panel is
Write the expression for the drag force for the panel.
Here, the drag force coefficient is
Write the expression for the frontal area of the panel.
Here, the height of the rectangular advertisement panel is
Calculation:
The drag coefficient for the turbulent flow for the thin rectangular plate is
Substitute
Substitute
Conclusion:
The maximum drag force on the panel is
(b)
The drag force acting on the pole.
Answer to Problem 96P
The drag force acting on the pole is
Explanation of Solution
Write the expression for the frontal area of the pole.
Here, the diameter of the pole is
Write the expression for the drag force for the pole.
Calculation:
The drag coefficient for the turbulent flow for circular rod is
Substitute
Substitute
Conclusion:
The drag force acting on the pole is
(c)
The minimum length
Answer to Problem 96P
The minimum length
Explanation of Solution
Draw the diagram for the side view of the advertisement panel.
Figure-(1)
Write the expression for the moment about point A.
Here, the minimum length of the concrete block for the panel to resist the winds is
Write the expression for the weight of the concrete block.
Here, the mass of the block is
Write the expression for the volume of the block.
Here, the height of the rectangular concrete block is
Write the expression for the mass of the block.
Here, the density of the concrete block is
Substitute
Substitute
Calculation:
Substitute
Substitute
Conclusion:
The minimum length
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Chapter 11 Solutions
Fluid Mechanics: Fundamentals and Applications
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