337513(37)
B.E (Fifth Semester) Examination,
Nov.-Dec., 2008
(Mechanical Branch)
DYNAMICS OF MACHINES
Time allowed : THREE Hours
Maximum Marks : 80
Minimum Pass Marks : 28
1. (a) Explain the term 'height' of governor. 2
(b) Explain the following terms relating to governors: 4
Sensitiveness
Hunting
(c) In a Porter governor, the upper and lower arms are each 250 mm long and are pivoted on the axis of rotation. the massof each rotating ball is 3 kg and the mass of the sleeve is 20kg. the sleeve is in its lowest position when the arms are inclined at 30o to thegovernor axis. The lift of the sleeve is 36mm. Find the force of frictionat the sleeve, if the speed at the moment it falls from the highest position. Also find the range of speed of the governor. ...........................................10
OR
(d) The radius of rotation of the balls of a Hartnell governor is 80mm at the minimum speed of 300 rpm. Neglecting obliquity effect, determine the speed after the sleeve has lifted by 60 mm. Also determine the initial compression of spring, the governor effort and the power.
The particulars of the governor are :
Length of ball arm =150 mm; length of sleeve arm =100 mm; mass of each ball = 4 kg; stiffness of the spring = 25 N/mm; and mass on the sleeve = 20 kg. ....................................10
2. (a) State any one problem encountered in high-speed machinery due to unbalanced forces. 2
(b) A shaft is rotating at a uniform angular speed. two masses of 300 kg and 450 kg are attached rigidly to the shaft. the masses are rotating in the same plane. The corresponding radius of rotation are 200 mm and 150 mm. the angle between two masses is 90o, find magnitude and direction of balancing mass in same plane, if its radius of rotation is 200 m. 4
(c) Two outer cranks of a four-crank engine are set at 120o to each other with each reciprocating mass as 400 kg. The spacing between the planes of rotation of adjacent cranks are 450 mm, 750 mm and 600 mm. Determine the reciprocating mass and the relative angular position of each of the inner cranks if the engine is to be in complete primary balance. Also determine the maximum secodary unbalanced force if the length of the crank and the connecting rod are 300 mm and 1200 mm respectively and the speed is 240 rpm.10
OR
(d) The three cylinders of an air compressor have their axes 120o to the another, and their connecting rods are coupled to a single crank. The stroke is 100 mm and the length of each connecting rod is 150 mm. The mass of the reciprocating parts per cylinderis 1.5 kg. Find the maximum primary and secondary forces acting on the frame of the compressor when running at 3000 rpm. Describe clearly a method by which such forces may be balanced. 10
