TABLE OF CONTENTS There are many examples in engineering where vibration levels can become so high that they threaten the structural integrity of the machine or structure concerned, the reliability of essential electronic equipment, or the health and efficiency of those exposed to it. In some cases it can be said that a high level of vibration is inherent in the design of a machine or vehicle, and measures to reduce it or isolate it are almost always needed, for example:
Reciprocating engines inevitably generate periodic forces that must be isolated from the vehicle interior in nearly all cases, and crankshaft torsional vibrations often have to be reduced, simply to prolong the life of the component.
Helicopter rotors can rarely be balanced well enough to avoid unacceptable periodic vibration in fuselage areas, and vibration reduction techniques are practically always required.
Combat aircraft often generate broad-band random vibration of sufficient severity to make vibration isolation necessary.
In a case of severe vibration response, if the source cannot be removed, the obvious first move is to try to increase the damping of the mode or modes affected. This is often not possible, and vibration isolation and vibration absorption may then be considered.
Vibration isolation uses the properties of a single-DOF system, either to isolate sensitive equipment from a severe vibration environment or to isolate an environment, such as the interior of a vehicle, from vibration forces developed within, say, the engine. Vibration isolation can be used with any form of vibration input.
