JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year DYNAMICS OF MACHINERY Previous Question Paper (July - 2023 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
PART - A
What is the gyroscopic effect on aero-plane when it is steered right-hand side on horizontal plane?
Answer
When an aeroplane steers to the right, the gyroscopic couple acts to cause the nose of the aeroplane to pitch upwards. This occurs because the gyroscopic effect creates a reactive couple that acts in a plane perpendicular to the plane of spin and the plane of precession, resulting in a nose-up movement.
How is the static force analysis done? Which forces are considered, and which forces are not considered in this analysis?
Answer
Static force analysis is performed by applying the principles of D'Alembert's principle, which treats a dynamic system as a static one by introducing an inertial force. The analysis assumes that the mechanism is in static equilibrium, where the vector sum of all external forces and moments acting on each link is equal to zero.
The forces considered in this analysis include:
- Applied external forces and torques.
- Gravitational forces acting on the center of mass of each link.
- Reaction forces at the kinematic pairs (joints).
- Inertia forces and inertia torques, which are calculated as the product of mass and acceleration (or moment of inertia and angular acceleration) and applied in the opposite direction of acceleration.
Forces that are not considered in static force analysis include:
- Frictional forces at the joints (unless specifically included as an external resistance).
- Dynamic effects arising from time-varying velocity or acceleration profiles that are not captured by the instantaneous inertia force calculation.
What is the function of a flywheel in a prime mover?
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Explain the terms ‘piston effort’ and ‘crank effort’.
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What is the function of a clutch? How is it achieved?
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What is dynamometer? How does it differ from the brake?
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What is the difference between inside cylinder locomotive and outside cylinder locomotive?
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Write the differences between Porter governor and Proell Governor.
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What is the critical speed of a shaft if its natural frequency of transverse vibration is 2.85 Hz?
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What is the natural frequency of a simply supported beam of length l with mass M at its center, flexural rigidity EI, and negligible beam mass?
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PART - B
Describe the effect of the gyroscopic couple on a disc fixed at a certain angle to a rotating shaft.
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The length of the connecting rod of a gas engine is 500 mm and its center of gravity lies at 165 mm from the crank pin center. The rod has a mass of 80 kg and a radius of gyration of 182 mm about an axis through the center of mass. The stroke of piston is 225 mm, and the crank speed is 300 rpm. Determine the inertia force on the crankshaft when the crank has turned 300 from the inner dead center.
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A rear engine automobile is travelling along a curved track of 120 m radius. Each of the four wheels has a moment of inertia of 2.3 kg-m2 and an effective diameter of 600 mm. The rotating parts of the engine have a moment of inertia of 1.25 kg-m2. The gear ratio of the engine to the back wheel is 3.2. The engine axis is parallel to the rear axle and the crankshaft rotates in the same sense as the road wheels. The mass of the vehicle is 2500 kg and the center of mass is 520 mm above the road level. The width of the track is 1.6 m. What will be the limiting speed of the vehicle for all four wheels to maintain contact with the road surface?
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Twenty 1-cm holes are to be punched every minute in a 1.5 cm plate whose resistance to shear is 35316 N/cm2. The actual punching takes place in one-fifth of the interval between successive operations. The speed of the flywheel is 300 rpm. Making the usual assumptions, specify the dimensions of a suitable CI rimmed flywheel. Use coefficient of fluctuation of speed = 0.01 and V = 60 m/s.
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In a turning moment diagram, the areas above and below the mean torque line taken in order are 4400, 1150, 1300, and 4550 mm2 respectively. The scales of the turning moment diagram are: Turning moment: 1 mm = 100 N – m; Crank angle: 1 mm = 10. Find the mass of the flywheel required to keep the speed between 297 and 303 rpm, if the radius of the gyration is 0.525 m.
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A multi – disc clutch has 5 plates having four pairs of active friction surfaces. If the intensity of pressure is not to exceed 127 kN/m2, find the power in kW transmitted at 500 rpm, if the outer and inner radii of friction surfaces are 1.25 mm and 75 mm respectively. Assume uniform wear and take coefficient of friction as 0.3.
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Derive from first principles, the expression for the frictional moment (or torque due to friction) of a conical collar bearing, assuming uniform rate of wear.
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A thrust shaft of a ship has 6 collars of 600 mm external diameter and 300 mm internal diameter. The total thrust from the propeller is 100 kN. If the coefficient of friction is 0.12 and speed of the engine is 90 r.p.m., find the power absorbed in friction at the thrust block, assuming (i) uniform pressure, (ii) uniform wear.
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Calculate the range of speed of a porter governor which has equal arms of each 200 mm long and pivoted on the axis of rotation. The mass of each ball is 4 kg and the central load of the sleeve is 20 kg. The radius of rotation of the ball is 100 mm when the governor begins to lift and 130 mm when the governor is at maximum speed.
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The cranks of a two – cylinder, uncoupled inside cylinder locomotive are at right angles and are 300 mm long. The center lines of the cylinders are 700 mm apart. The rotating mass per cylinder is 150 kg at the crank pin, and the mass of the reciprocating parts per cylinder is 180 kg. The wheel center lines are 1.5 m apart. The whole of the rotating parts and 60% of the reciprocating masses are to be balanced, and the balance masses are to be placed in the planes of rotation of the driving wheels at a radius of 600 mm. If the dead weight on each wheel is 10 kN, and diameter of the wheels is 1.8 m, find the (a) maximum and minimum pressure on the rails, and (b) maximum speed of the locomotive (in km/h) without lifting the wheels from the rails.
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When does the Whirling of Shafts occur? Explain with a sketch. If the speed of operation of a machine shaft is above the whirling speed, how is this problem of passing over the whirling speed taken care of?
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A mass m is suspended from a spring of length l and spring constant k. The frequency of vibration of the mass is f1. The spring is cut into two equal parts, and the same mass is suspended from one of the parts. What is the new frequency of vibration of the mass?
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A shaft 12.5 mm diameter rotates in long bearings, and a disc of mass 16 kg is secured to the shaft at the middle of its length. The span of the shaft between the bearings is 0.5 m. The mass center of the disc is 0.5 mm from the axis of the shaft. Neglecting the mass of the shaft and taking E = 200 GN/m2, find the: (a) critical speed of rotation in rpm.; and (b) range of speed over which the stress in the shaft due to bending will not exceed 120 MN/m2. Take the static deflection of the shaft for a beam fixed at both ends, i.e.
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