SUBJECT - DYNAMICS OF MACHINERY
CODE - 04 606
SEMESTER - SIXTH
BRANCH - ME
UNIVERSITY - CALICUT
YEAR - 2013
Part A
Answer all Questions
1. Define shaking force.
2. Two masses in different planes are necessary to rectify the dynamic unbalance. Comment.
3. Define the term transmissibility. *
4. Whether the frequency of a non-linear system,a constant ? If not, why ?
5. Resonance, usually, does not occur ih non linear systems. Why ?
(5x2=10 marks)
Part B
Answer any four questions
Each question carries 5 marks
6.Write down the expression for finding thrust on sides of cylinder, crank effort and thrust on bearings in terms of effective piston force,F.
7.For a single cylinder resiprocating engine,mass of rotating parts is 30 kg, mass of reciprocating parts is 40 kg,and stroke is 350 mm and speed 150r.p.m.Determine the balance mass required at a radius of 320 mm and unbalanced force When the crank has turned 450 from TDC, if 60% of the reciprocating parts and all of the revolving parts are to be balanced.
8.An aeroplane flying at 240 km/h turns towards the left and completes a quarter circle of 60 m radius.The mass of the rotary engine and propeller of the plane is 450 kg with radius of gyration of 320 mm. The engine speed is 2000 r.p.m`. clockwise when viewed from the rear. Determine the gyroscopic couple on the aircraft and state its effect.
9.An unknown mass of is attached to one end of a spring of stiffness V having natural frequency of 6 Hz. When 1 kg mass is attached With mass, 'm' the natural frequency of the system is lowered by 20%. Determine 'm' and 'k'
10.A damper offers resistance 0.05N at constant velocity 0.04 m/s.The damper is used with k=9 N/m.Determine the frequency of damped vibration if the mass of the system is 0.1 kg.
11.Determine the error in an accelerometer reading if natural frequency of accelerometer is 5 times the frequency of observed motion.Neglect damping.
(4x5=20 marks)
Part C
Answer all questions.
Each question carries 10 marks.
12. A slider crank mechanism with the following dimension is acted upon by a force F = 2 kN as shown below. OA = 100 mm, AB » 450 mm. the inpiit torque on the link OA for the static equilibrium of the mechanism.
Or
13. ABCD is a four-bar chain with AB as the fixed link. The lengths of the links are AB = 7.5 cm, BC = 33.75 cm, CD = 15 cm and DA = 37.5 cm. Link AB turns with a uniform speed of 120 r.p ra. in acw direction. The mass of link BC is 0)5 kg and its C.G. is 11.25 cm from B and its radius of gyration about an axis through the C.G. is 13.5 cm. For the configuration in whichthe angle BAD is 30° and B and G lie on opposite sides of B.B, find the angular acceleration ofi£© and the torque
. which must be exerted on AB in order to overcome the inertia of the link BC.
14. The cranks and connecting rods of a four cylinder inline engine running at 1800 Are 60 Dim and 240 mm respectively and the cylinders are spaced 150 mm apart. The cylinders are numbered 1 to 4 in sequence from one end | the cranks appear at intervals of 90° in an end view in the order 1-4-2-3. The reciprocating mass corresponding to each cylinder is 1.5 kg. Determine the unbalanced primary and secondary forces and unbalanced primary and secondary couples with reference to central plane of the engine.
Or
15.The rotor of the turbine of a ship has a mass of 2500 kg and rotates at a speed of 3200 r.p.m. counter clockwise when viewed from stern.The rotor has a radius of gyration of 0.4m.Determine the gyroscopic couples and its effects when
(a) The ship steers to the left in a curve of 80 m radius at a speed of 15 knots.
(b) The ship pitches 5 degrees above and 5 degrees below the normal position and the bow is descending with its maximum velocity-the pitching motion is simple harmonic with a periodic time 40 seconds.
(c) The ship rolls and at the instant its angular velocity is 0.4 rad/s clockwise when viewed from stern.Also find the maximum angular acceleration during pitching
16. A coil of spring stiffness 4 N/mm supports vertically a mass of 20 kg at the free end. The motion is resisted by the oil dashpot. It is found that the amplitude at the beginning of the fourth cycle is 0.8 times the amplitude of the previous vibration. Determine the damping force per unit velocity. Also-find the ratio of the frequency of damped and undamped vibrations.
Or
17. A shaft of 2.5 cm diameter, freely supported by bearings 75 cm apart, carries a single concentrated load of 196.2 N midway between the bearings. Determine the first critical speed. Assume, that shaft material has a density of 8 gm/cm^3 and: E is 2.1 x 10€ kgf/cm^2.
18. A steel shaft AJBCD 1.5 m long has flywheel- at its ends A and D. The mass of the flywheel A is
600 kg and has a radius of gyration of 0.6 m. The mass of the flywheel D is 800 kg and has a radius of gyration of 0.9 m. The connecting- shaft has a diameter of 50 mm for the portion AB which is 0.4 m long and has a diameter of 60 mm for the portion BC which is 0.5 m long and has a diameter d mm for the portion CD which is 0.6 tn long. .Determine the diameter d so that the node of the torsional vibration of the system will be centre of length BC and the natural frequency of the torsional vibration. Take G = 80 GPa.
Or
19. Write a short note on :
(a) Vibrometer and tb) Accelerometer.
(4 x 10 = 40 marks)
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