(SEM VI) THEORY EXAMINATION 2017-18 DYNAMICS OF MACHINES

Dynamics of Machines (NME-603)

Complete Section-Wise Explanation – B.Tech Semester VI

Introduction to the Subject

Dynamics of Machines deals with the study of forces acting on machine parts while they are in motion. Unlike Theory of Machines, which focuses mainly on motion, this subject emphasizes forces, inertia effects, vibrations, balancing, governors, gyroscopic effects, brakes, and dynamometers.

This subject is extremely important because it explains:

Why machines vibrate                                     How engines are balanced

How governors control speed                         How flywheels store energy

How brakes and dynamometers work             How gyroscopic effects influence ships, aircraft, and turbines

The question paper is divided into three sections: A, B, and C, and all sections must be attempted as per instructions.

SECTION A – Fundamental Concepts (Short Answer)

Pattern:
Attempt all questions
10 questions × 2 marks = 20 marks

Nature of Section A

Section A tests your basic understanding and definitions. Answers should be short, direct, and conceptually correct. These questions are easy scoring if definitions are clear.

Explanation of Section A Questions

Piston Effort
Piston effort is the force exerted by the gas pressure on the piston minus the inertia force of the reciprocating parts. It is the net force transmitted to the connecting rod.

Coefficient of Fluctuation of Energy
It is the ratio of the maximum fluctuation of energy to the mean energy of the flywheel. It indicates how much energy variation the flywheel can absorb.

Planes and Axes in Gyroscopic Effect
Gyroscopic motion involves three mutually perpendicular axes: the axis of spin, the axis of precession, and the axis of applied torque. These axes explain how gyroscopic couples are generated.

Natural Frequency of Longitudinal Vibration
The natural frequency of longitudinal vibration depends on stiffness, mass, and length of the rod. It represents the frequency at which the system vibrates freely without external force.

Partial Balancing
Partial balancing means balancing only a fraction of the reciprocating mass to reduce unbalanced forces without introducing excessive hammer blow.

Coupled and Uncoupled Locomotives
In coupled locomotives, driving wheels are connected by coupling rods, whereas in uncoupled locomotives, wheels are independent.

Classification of Governors
Governors are classified as centrifugal governors and inertia governors. Centrifugal governors are further classified into Watt, Porter, Proell, Hartnell, etc.

Sensitiveness and Stability of Governors
Sensitiveness indicates how easily a governor responds to speed change. Stability means the governor has only one equilibrium position for each speed.

Differential Brake
A differential brake is a band brake where the two ends of the band are attached on opposite sides of the fulcrum, resulting in different tensions.

Transmission Type Dynamometer
Transmission dynamometers measure power transmitted through a shaft, such as belt, rope, or torsion dynamometers.

SECTION B – Theory & Numerical Problems

Pattern:
Attempt any three questions
3 × 10 marks = 30 marks

Nature of Section B

Section B requires detailed explanations and numerical solutions. Proper derivations, assumptions, and step-by-step calculations are essential.

Explanation of Section B Questions

Forces in Slider-Crank Mechanism

This question involves analyzing forces acting on piston, connecting rod, and crank. Gas force, inertia force, thrust on cylinder walls, and forces at bearings are explained. Understanding free-body diagrams is crucial here.
 

Vibratory System with Viscous Damping (Numerical)

This problem tests vibration concepts. Given that amplitude reduces over cycles, logarithmic decrement is used to calculate damping coefficient. It checks understanding of damped vibration and energy dissipation.
 

Dynamic Balancing of Rotating Masses (Numerical)

This is a high-level balancing problem involving four masses in different planes. You must apply conditions of complete dynamic balance, using vector summation of forces and couples to find unknown masses, distances, and angular positions.
 

Porter Governor – Effort and Power

This question requires derivation of expressions for effort (force required to move sleeve) and power (work done at sleeve). A clear understanding of centrifugal force, geometry, and sleeve movement is required.
 

Band and Block Brake Tension Ratio

This question involves derivation of the ratio of maximum and minimum tensions considering friction and angle of contact. It tests braking theory and friction principles.
 

SECTION C – Advanced Theory & Applied Numericals
 

Pattern:
Attempt any one part from each question
5 questions × 10 marks = 50 marks

This section carries the highest weightage and determines overall performance.

Question 3 – Flywheel & Turning Moment

Derivation of Flywheel Dimensions
This question requires deriving expressions relating flywheel mass, radius, coefficient of fluctuation of energy, and speed. The derivation is based on energy storage and speed regulation.

Turning Moment Numerical (Steam Engine)
This numerical calculates effective turning moment considering steam pressures, inertia forces, crank position, and geometry. It combines thermodynamics with dynamics.

Question 4 – Gyroscopic Effects

Gyroscopic Effect on Aeroplane
This theory question explains how gyroscopic couple affects aircraft during pitching, rolling, and yawing. It is important to explain direction of motion and stability effects.

Gyroscopic Couple on Ship (Numerical)
This numerical involves calculating gyroscopic couple for steering and pitching conditions. It tests understanding of angular velocity, precession, and stability effects on ships.

Question 5 – Locomotive Dynamics

Tractive Effort, Swaying Couple & Hammer Blow
This theory question explains:

Variation in tractive effort due to crank rotation

Swaying couple caused by unbalanced forces

Hammer blow and its effect on rails and safe speed

Locomotive Balancing Numerical
This numerical determines fraction of reciprocating mass balanced, tractive effort variation, and maximum swaying couple under given speed and constraints.

Question 6 – Governors

Porter Governor with Friction (Numerical)
This problem calculates friction force at sleeve and speed range, considering equal speeds at rising and falling positions. It tests equilibrium and friction effects.

Hartnell Governor Numerical
This question involves spring-loaded governor analysis. You calculate spring compression and equilibrium speed at a given radius. Understanding of lever geometry and centrifugal force is essential.

Question 7 – Brakes & Dynamometers

Absorption and Transmission Dynamometers
This theory question explains working principles, construction, and applications of absorption and transmission type dynamometers with examples.

Differential Band Brake Numerical
This numerical calculates maximum load supported by a brake using friction theory, lever equilibrium, and tension ratios. Careful unit handling and force balance are required.