THEORY EXAMINATION (SEM–VI) 2016-17 DYNAMICS OF MACHINE

DYNAMICS OF MACHINE – NME603

B.Tech (SEM VI) | Section-wise Solved Answers

SECTION – A

(10 × 2 = 20 marks)

(a) Hammer blow

Hammer blow is the unbalanced dynamic force produced by the rotating masses of a locomotive wheel acting on the rails. It causes vertical vibration and increased rail wear.

(b) Gyroscope

A gyroscope is a rotating body that resists any change in the direction of its axis of rotation. It operates on the principle of conservation of angular momentum.

(c) Turning moment diagram of four-stroke I.C. engine

A turning moment diagram shows the variation of torque produced during one complete cycle (two revolutions) of a four-stroke engine. It helps in flywheel design.

(d) Coefficient of fluctuation of energy

It is the ratio of maximum fluctuation of energy to the mean energy of the flywheel during a cycle of operation.

(e) Governor vs Flywheel

A governor controls the mean speed of an engine over long periods.
A flywheel controls the speed fluctuation within a cycle.

(f) Height of governor

The height of a governor is the vertical distance between the center of the governor ball and the spindle axis. It influences speed regulation.

(g) Stability of governor

A governor is stable if the radius of rotation of balls increases with an increase in speed and decreases with a decrease in speed.

(h) Brakes vs Dynamometers

Brakes absorb mechanical energy and dissipate it as heat.
Dynamometers measure power output of engines.

(i) Hunting of governor

Hunting is the continuous oscillation of the governor balls and sleeve due to over-correction of speed.

(j) Free vs Forced vibration

Free vibration occurs without external force after initial disturbance.
Forced vibration occurs due to continuous external excitation.

SECTION – B

(Attempt any five – 5 × 10 = 50 marks)

(a) Balancing of masses in same plane

Balancing is achieved by vectorially summing centrifugal forces using a force polygon. The resultant force is made zero by adding a balancing mass.

(b) Balancing of four revolving masses (Numerical)

The given masses, radii, angles, and plane distances are represented graphically using force and couple polygons.
Balancing masses in planes X and Y are calculated by resolving forces and moments.

(c) Height of Watt governor

For Watt governor:

h=gω2h=\frac{g}{\omega^2}h=ω2g​

Limitations include low speed operation and neglect of friction effects.

(d) Tractive force & hammer blow

Tractive force varies sinusoidally due to reciprocating masses.
Hammer blow is derived by resolving centrifugal force components acting vertically.

(e) Single-cylinder engine dynamics

The net piston force is obtained by considering inertia and gas forces.
Crank effort is derived by resolving forces along crank direction.

(f) Function and types of governors

Governors regulate engine speed by adjusting fuel supply.
Types include Watt, Porter, Proell, Hartnell, and Wilson-Hartnell governors.

(g) Flywheel mass calculation

Maximum fluctuation of energy is obtained from turning moment diagram areas.
Using coefficient of speed fluctuation, flywheel mass is calculated.

(h) Damped vibration system

Critical damping coefficient, damping factor, logarithmic decrement, and amplitude ratio are calculated using standard vibration equations.

SECTION – C

(Attempt any two – 2 × 15 = 30 marks)

(3) Balancing of locomotive engine

Balancing masses are calculated by resolving rotating and reciprocating forces.
Swaying couple is determined using crank speed and spacing between wheels.

(4) Height of Proell governor

The height of Proell governor is derived considering centrifugal force, controlling force, and geometry. It allows higher operating speeds compared to Watt governor.

(5) Gyroscopic effects on four-wheel vehicle

During a turn, gyroscopic couple causes load transfer between wheels.
Using vehicle dimensions, speed, and moment of inertia, wheel loads are calculated.