Osmania University (OU) 2009 B.E Mechanical Engineering Dynamics of machines - Question Paper

B.E. 2/4 (MECH) one SEM. MAIN EXAMINATION, NOV/DEC-2009
DYNAMICS OF MACHINES
ans all ques. of Part A. ans 5 ques. from Part B
PART-A
1. Give examples of gyroscopic motion in daily life.
2. What is the effect of friction in governors?
3. Differentiate ranging from engine flywheels and machine flywheels.
4. What is partial balancing of reciprocating parts? What is its effect?
5. How is balancing achieved in multi-cylinder engines?
6. Explain the whirling phenomenon in shafts.
7. Explain different conditions of daming in damped natural vibrations.
8. What is logarithmic decrement? discuss its use.
9. Why is Dunkerley's method approximate?
10. What is the function of vibration isolator? Name different materials used for vibration isolation.
PART-B
11. A propeller shaft of an aero-engine is rotating at 2000 rpm. The distance ranging from the bearings of the propeller shaft is 0.75m and the radius of gyration of propeller is 0.75m. obtain the extra pressure on the bearings, when the aeroplane is whirling round in a horizontal circle of 300m radius at a speed of 300kmph. The weight of the propeller is 55kg.
12. A porter governor has all the 4 arms 300mm long. The upper arms are pivoted on the axis of rotation, while the lower arms are attached to the sleeve at a distance of 35mm from the axis of rotation. The mass of every ball is 7kg and the mass of the sleeve is 54kg. compute the equilibrium speed when the radius of rotation is 190mm.
13. A punching machine having a stroke of 10cm, punches 1.25cm hole once in every 10 seconds in a one cm thick steel plate. During punching operation, it does 600 Nm of work per square cm of shaded area. The maximum linear speed of the fly wheel rim is not to exceed 30m/s.
14. A rigid rotor has all its unbalance in 1 plane and can be considered to consist of 3 masses m1=5kg; m2=3kg at angle of 165' c.c.w from m1 and m3=8kg at an angle of 85degrees c.w. from m1. The radii a1=20cm a2=8cm; a3=14cm; Determine the balancing mass at a radius of 10cm. Specify its location with respect to m1.
15. A mass of 100kg. is suspended on a spring having k=19600 N/m, and is acted up on by a harmonic force of 39.2N at the undamped natural frequency. The damping may be considered to be viscous with a coefficient of 98N.sec/m. determine (a) the damped natural frequency (b) amplitude of vibration of the mass. (c) the phase differences, ranging from the force and the displacement.
16. In a 3 – rotor system, an engine drives a centrifugal pump through gears. The length of the shaft from engine flywheel to the gear is one meter with dia. 8cm and the length of the shaft from pinion to impeller is 40cm with dia. 6cm. The ratio of engine and pump speed is ?. Take moments of inertia of engine flywheel, gear wheel, pinion and pump impeller are 100, 11, 1.25 kg m^2 respectively. The modulus of rigidity of shaft material is 0.8*10^11 N/m^2. obtain the fundamental and the 2 mode frequencies of the free torsional oscillations.
17. Give short note on:
a. Stability of governors.
b. Function of governor and flywheel.
c. Direct and Reserve crank method.

Earning:   Approval pending.