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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER-VI EXAMINATION WINTER 2018
Subject Code:X61902 Date: 20/11/2018
Subject Name: Dynamics of Machinery
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

Explain the terms Static and Dynamic balancing with suitable example.
07

A shaft carries four weights S of 120 200 300 N and 160 N respectively spaced 18 cm apart. Measuring clockwise from Q is 240º, R is 135º and S is 270º. The radiuses are 15 cm, 12 cm, 6 cm and 18 cm. The speed of shaft is 120 rpm.
Find the magnitude and direction relative to P of the resultant moment at a plane midway between P and Q.
07
Q.2

A twin cylinder V-engine has the cylinder axes at 90º and the connecting rods operate a common crank. The reciprocating masses per cylinder is 2 kg and the crank radius is 80 mm. The length of connecting rods is 320 mm. Show that the engine may be balanced for primary forces by means of a revolving balance mass. If the engine speed is 600 rpm, what is the value of the maximum resultant secondary force?
07

Explain briefly energy method to find out characteristic equation for free vibration of single degree of freedom system.
07
OR

Find the differential equation of motion and the natural frequency of vibration for a system shown in Fig. 1.
Fig. 1
07
Q.3

An under damped shock absorber is to be designed for two wheeler vehicle of mass 250 kg such that during a road bump, the damped period of vibration is limited to 3 sec and the amplitude of vibration should reduce to one eighteenth in one cycle. Find: The stiffness of spring required; and The damping co-efficient of the shock absorber.
07

What do you mean by damping? What are the various types of damping methods?
07
OR
Q.3

Explain logarithmic decrement. Derive an expression for it.
07

Discuss the effect of damping on vibratory systems. What is meant by under damping, critical damping and over damping?
07
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Q.4

What do you meant by transient vibrations and steady-state vibrations? Also explain the term dynamic magnifier.
07

A motor cycle moves over a road surface having approximately the sinusoidal profile with a wave length of 10 m and an amplitude of 80 mm. The motor cycle is moving with a velocity of 55 km/hr. Calculate the critical speed of the motor cycle, if the amplitude of vibration is 25 mm and mass of vehicle is 50 kg.
07
OR
Q.4

How natural frequency of torsional vibration of three rotor system is determined?
07

Derive an expression for Torsionally Equivalent shaft system.
07
Q.5

Explain Holzer's method to determine natural frequency of multi-rotor system.
07

Explain Dunkerly's method to determine the natural frequency of shaft carrying number of point loads.
07
OR
Q.5

Explain the method to determine the critical speed of shaft carrying single rotor, neglecting damping.
07

List the various types of amplitude measuring instruments. Explain any one in detail with neat sketch.
07