TABLE OF CONTENTS The existence of vibrating elements in any mechanical system produces unwanted noise, high stresses, wear, poor reliability, and, frequently, premature failure of one or more of the parts. The moving parts of all machines are inherently vibration producers, and for this reason engineers must expect vibrations to exist in the devices they design. But there is a great deal they can do during the design of the system to anticipate a vibration problem and to minimize its undesirable effects.
Sometimes it is necessary to build a vibratory system into a machine a vibratory conveyor, for example. Under these conditions the engineer must understand the mechanics of vibration in order to obtain an optimal design.
Any motion that exactly repeats itself after a certain interval of time is a periodic motion and is called a vibration. Vibrations may be either free or forced. A mechanical element is said to have a free vibration if the periodic motion continues after the cause of the original disturbance is removed, but if a vibratory motion persists because of the continuing existence of a disturbing force, then it is called a forced vibration. Any free vibration of a mechanical system will eventually cease because of loss of energy. In vibration analysis we often take account of these energy losses by using a single factor called the damping factor. Thus, a heavily damped system is one in which the vibration decays rapidly. The period of a...
