Science of vibration

Vibration science is a subject which deals with oscillatory motion of dynamic systems and various forces associated with them. Vibration is a virtue in some areas while it is a cause of concern in some other areas. In machines and structures, vibration causes undesirable effects. But in some machines, presence of vibration is essential. Examples are washing machines, mechanical shakers, sorting devices, conveyors and compactors, musical instruments, some medical equipment and some stress relieving instruments. Some main causes of vibration are unbalance, misalignment, looseness, dry friction between two rubbing surfaces, wind induced vibration, oil whirl and external excitation. The four important vibration characteristics are vibration displacement, vibration velocity, vibration acceleration and phase. Vibration displacement is the total distance travelled by the vibrating part from one extreme limit of travel to the other extreme limit of travel. Vibration velocity and vibration acceleration changes with position of vibrating part. Velocity is maximum at neutral position and minimum at the extreme position. Acceleration is zero at neutral position and maximum at the extreme position. Phase is defined as the position of a vibrating part with respect to a fixed point or another vibrating part at the given instant.