204. An airship is to operate at 20 m/s in air at standard conditions (p 1.225 kg/m³, p 101,300 Pa). Amodel is constructed to scale and tested in a variable-pressure wind tunnel at the same air temperature to=determine the drag.GOOD YEARThe Goodyear Blimp is an example of an airship.(a) What criterion should be used to determine dynamic similarity? (You may assume that roughness is notimportant for this problem.)(b) If the model is tested at 20 m/s, what pressure should be used in the wind tunnel?(c) If the model drag force is found to be 250 N, what will be the drag of the full-scale airship?

Answered: 20 4. An airship is to operate at 20…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

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A one-fortieth-scale model of a ship’s propeller is tested in a tow tank at 1250 r/min and exhibits a power output of 1.9 ft·lbf/s. According to Froude scaling laws, what should the revolutions per minute of the prototype propeller be under dynamically similar conditions? According to Froude scaling laws, what should the horsepower output of the prototype propeller be under dynamically similar conditions?
Drop-load (I)This exercise is part of a series of problems aimed at modeling a situation by progressively refining our model to take into account more and more parameters. This progressive approach is very close to what professional scientists do! context We want to lower a suspended load in a controlled way, so that it hits the ground with a speed whose modulus is not too great. To do this, the suspended load (B) is connected by a rope passing through a pulley to another mass (A), which can move on a horizontal surface. To slow down the descent, we added a spring behind the mass (A). Information The masses of the charges A and B are known.The mass of the rope itself is negligible (very small compared to the loads).The pulley has negligible mass and can rotate without friction.The charge ? is initially stationary and is at a known height h.The surface on which mass A is placed is horizontal.There is no friction between mass A and the surface on which it is placed.The string attached…
A prototype ship is 50 m long and designed for cruising speed of 10 m/s. The drag is to be simulated by a 1-m-long model that will be towed in a towing tank. Using Froude scaling, determine the tow speed and the ratio of the model to prototype drag and power.
Drop-load (I)This exercise is part of a series of problems aimed at modelling a situation by progressively refining our model to consider more and more parameters. This progressive approach is very close to what professional scientists do! Context We want to lower a suspended load in a controlled way so that it hits the ground with a speed whose modulus is not too great. To do this, the suspended load (B) is connected by a rope passing through a pulley to another mass (A), which can move on a horizontal surface. Information The masses of the charges A and B are known.The pulley is a ring of mass mp and radius R that can rotate without friction.The surface on which mass A is placed is horizontal.There is no friction between mass A and the surface on which it is placed.The string attached to mass A is perfectly parallel to the surface on which the mass rests. SchematizationDraw a diagram of each object that interests us. Draw x- and y-axes for each object. Draw and name each force…
For the drag force of an Aerobee rocket, D=0.00056v (Ib], obtain a linear model near v = 800 ft/sec and find the velocity below 800 ft/sec that the model prediction error becomes greater than 2%. Enter an answer in a whole number in ft/sec.
Wind tunnel test section km/h Model FD Moving belt Drag balance The aerodynamic drag of a new Volvo FH truck is to be predicted at a speed of 85 km/h at an air temperature of 25°C (p=1.184 kg/m³, u=1.849x10-5kg/m-s). Volvo engineers build a 1/2 scale model of the FH to test in a wind tunnel. The temperature of the wind tunnel is also 25°C. The drag force is measured with a drag balance, and the moving belt is used to simulate the moving ground. Determine how fast the engineers should run the wind tunnel to achieve similarity between the model and the prototype.
A dam 75 ft wide, with a nominal flow rate of 260 ft 3 , is tobe studied with a scale model 3 ft wide, using Froude scaling.( a ) What is the expected flow rate for the model?( b ) What is the danger of only using Froude scaling for thistest? ( c ) Derive a formula for a force on the model as comparedto a force on the prototype.
The drag on a 2-m-diameter satellite dish due to an 69-km/hr wind is to be determined through a wind tunnel test using a geometrically similar 0.4-m-diameter model dish. Assume standard air for both model and prototype. (a) At what air speed should the model test be run? (b) With all similarity conditions satisfied, the measured drag on the model was determined to be 152 N. What is the predicted drag on the prototype dish? (a) Vm = (b) D = i i km/hr N
2. A student team is to design a human-powered submarine for a design competition. The overall length of the prototype submarine is 4.85 m, and its student designers hope that it can travel fully submerged through water at 0.440 m/s. The water is freshwater (a lake) at T = 15 °C. The design team builds a one-fifth scale model to test in their university's wind tunnel, as shown in the Fig. A shield surrounds the drag balance strut so that the aerodynamic drag of the strut itself does not influence the measured drag. The air in the wind tunnel is at 25 °C and at one standard atmosphere pressure. At what air speed do they need to run the wind tunnel in order to achieve similarity? Take for water at T = 15 °C and atmospheric pressure, p = 999.1 kg/m³ and µ = 1.138 × 10-³ Pa.s. Take for air at T = 25 °C and atmospheric pressure, p = 1.184 kg/m³ and µ = 1.849 × 105 Pa.s. Wind tunnel test section V Poo, P Model Shield FD Drag balance Strut
Do 1st 3

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