PRESENTATIONON

“VIBRATION ISOLATIONAND

BASE EXCITATION”

DYNAMICS OF MACHINERY

SUBMITTED BY:HIMANSHI GUPTA (140120119057)/ ME/A2GUIDED BY:PROF. SAMEER RAVAL

(2161901)

GANDHINAGAR INSTITUTE OF TECHNOLOGY

INTRODUCTION

• Vibrations are produced in machines having unbalanced masses or forces

• High vibration levels can cause machinery failure, as well as objectionable noise levels

• A common source of objectionable noise in buildings is the vibration of machines that are mounted on floors or walls

SOURCES OF VIBRATION

EXAMPLES

 Rotating and reciprocating Unbalance Pumps, Turbines, Electric Generators, Compressors

Misalignment and wear of tools Manufacturing – machining 

 Seismic Vibrations Buildings, Bridges, Chimneys and Cooling Towers

Wind (Pressure loading) Tall Structures

Small magnitude vibrations E.g. Pedestal and vehicular traffic

Sensitive systems like optical instruments, microscopes, Nanofabrication 

Impact and shock loads Hammer and presses, in vehicles due to bumpy/ irregular nature of road

VIBRATION ISOLATION

• Vibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibration

• The effectiveness of isolation is expressed in terms of force or motion

• Lesser the amount of force or motion transmitted to the foundation greater is said to be the isolation

TYPESPASSIVE VIBRATION ISOLATION • Refers to vibration isolation or mitigation of

vibrations by passive techniques such as rubber pads or mechanical springs

ACTIVE VIBRATION ISOLATION• Also known as electronic force cancellation• Employs electric power, sensors, actuators, and

control systems for vibration isolation

OBJECTIVES

The basic objectives of vibration isolation are:• To protect the delicate machine from excessive

vibration transmitted to it from its supporting structure

• To prevent vibratory forces generated by machine from being transmitted to its supporting structure

MECHANISM OF VIBRATIONS TRANSMISSION

SOURCE

PATH

RECEIVER

VIBRATION ISOLATORS

• The vibration isolation may be obtained by placing materials, called vibration isolators in between the vibrating body and the supporting foundation or structure

PASSIVE VIBRATION ISOLATORS

METALLIC SPRING ISOLATION

PAD

ISOLATION HANGER PNEUMATIC ISOLATOR

ACTIVE VIBRATION ISOLATORS

FRAME MOUNTABLE ACTIVE HARD-MOUNT

PIEZOELECTRIC VIBRATION CONTROL

SYSTEM

ACTIVE VIBRATION ISOLATION TABLE

IMPORTANT CONSIDERATIONS WITH VIBRATION ISOLATOR SELECTION

1) Machine Location :• As far away from sensitive areas as possible• And on as rigid a foundation as possible

2) Proper sizing of isolator units :• Correct stiffness • Sufficient travel to prevent bottoming out during shock loads,

or during system startup and shutdown

3) Location of isolators :• Isolators should be equally loaded, and the machine should be

level

4) Stability :• Sideways motion should be restrained with snubbers• The diameter of the spring should also be greater than its compressed

height

5) Adjustment :• Springs should have free travel, should not be fully compressed, nor

hitting a mechanical stop

6) Eliminate vibration short circuits :• Any mechanical connection between machine and foundation which

bypasses the isolators, such as pipes, conduits, binding springs, poorly adjusted snubbers or mechanical stops

7) Safe operation :• To avoid a spring break, you must have mechanical supports on which

the machine can rest without tipping

VIBRATION ISOLATION MATERIALS

• The materials normally used for vibration isolation are rubber, felt, cork, metallic springs, etc.

• These are put between the foundation and the vibrating body

RUBBER FELT

CORK METALLIC SPRING

BASE EXCITATION

• It models the behavior of a vibration isolation system

• The base of the spring is given a prescribed motion, causing the mass to vibrate

• This system can be used to model a vehicle suspension system, or the earthquake response of a structure

FBD OF SDOF BASE EXCITATION SYSTEM

…(1)

 

• For a car,

• The steady-state solution is just the superposition of the two individual particular solutions

(system is linear)

(1)

PARTICULAR SOLUTION (SINE TERM)• With a sine for the forcing function,

PARTICULAR SOLUTION (COS TERM)  

• With a cosine for the forcing function, we showed

MAGNITUDE X/Y• Now add the sin and cos terms to get the magnitude

of the full particular solution

 EFFECT OF SPEED ON THE AMPLITUDE OF CAR VIBRATION

Thank You