Fundamentals of Mechanical Vibration

Chandan Kumar

LecturerMechanical Engineering

CUTM, Bhubaneswar

Chandan Kumar

LecturerMechanical Engineering

CUTM, Bhubaneswar

What is Vibration?In its simplest form, vibration can be considered to be the oscillation or repetitive motion of an object around an equilibrium position. The equilibrium position is the position the object will attain when the force acting on it is zero.

Vibration is occasionally "desirable". For example the motion of a tuning fork, the reed in a woodwind instrument or harmonica, or the cone of a loudspeaker is desirable vibration, necessary for the correct functioning of the various devices.

More often, vibration is undesirable, wasting energy and creating unwanted sound – noise. For example, the vibrational motions of engines, electric motors, or any mechanical device in operation are typically unwanted.

The main reasons of vibrations are• Unbalance centrifugal force in the system. This is caused because of non-uniform material distribution in the rotating machine parts.• Elastic nature of the system.• External excitation applied on the system.

Importance of vibration study in engineering

•Due to faulty design and poor manufacture there is unbalance in the engines which causes excessive and unpleasant stresses in the rotating system because of vibration

•The vibration causes rapid wear of machine parts such as bearings and gears.

•Many building s, structures and bridges falls because of vibration.

•Because of heavy vibration proper readings of instruments cannot be taken.

Parts of vibrating system

•Mass : Energy is stored by mass in the form of K.E

•Spring : Energy is stored by mass in the form of P.E

•Damper: Dissipate the energy in the form of heat

Parts of vibrating system

Vibrating System

K Spring

xM Mass

C Damper

Basic Concepts of Vibration

All the bodies having mass and elasticity are capable of vibration .The mass is inherent of the body.Elasticity causes relative motion among its parts.

When body particles are displaced by the application of external force , the internal forces in the form of elastic energy are presented in the body . These forces try to bring the body to its original position. At equilibrium position, the hole of the elastic energy is converted in to kinetic energy and body continues to move in the opposite direction because of it. The whole of the kinetic energy is again converted into elastic or strain energy due to which the body returns to the equilibrium position. In this way vibratory motion is repeated.

Types of vibration

Free vibration and forced vibrationWhen the motion is maintained by the restoring forces only, the vibration is described as free vibration. When a periodic force is applied to the system, the motion is described as forced vibration.

Damped undamped vibrationWhen the frictional dissipation of energy is neglected, the motion is said to be undamped. Actually, all vibrations are damped to some degree.

Methods of reducing vibration

•Removing external excitation if possible.

•Use shock absorber.

•Dynamic absorber.

•Resting the system on proper vibration isolators.

Methods of Vibration Analysis

•Energy Method :Sum of the energies associated with the system is constant.

•Rayleigh’s Method: This method is the extension of energy method. The method is based on the principle that the total energy of a vibrating system is equal to the maximum potential energy

•Equilibrium Method : Algebraic sum of the forces and moments acting on the system must be zero.

The end!

Thank You