Vibration of Continuous Systems, 2nd Edition

1Introduction: Basic Concepts and Terminology

1.1 CONCEPT OF VIBRATION

Any repetitive motion is called vibration or oscillation. The motion of a guitar string, motion felt by passengers in an automobile traveling over a bumpy road, swaying of tall buildings due to wind or earthquake, and motion of an airplane in turbulence are typical examples of vibration. The theory of vibration deals with the study of oscillatory motion of bodies and the associated forces. The oscillatory motion shown in Fig. 1.1(a) is called harmonic motion and is denoted as

(1.1)

where X is called the amplitude of motion, is the frequency of motion, and t is the time. The motion shown in Fig. 1.1(b) is called periodic motion, and that shown in Fig. 1.1(c) is called nonperiodic or transient motion. The motion indicated in Fig. 1.1(d) is random or long‐duration nonperiodic vibration.

Figure 1.1 Types of displacements (or forces): (a) periodic, simple harmonic; (b) periodic, nonharmonic; (c) nonperiodic, transient; (d) nonperiodic, random.

The phenomenon of vibration involves an alternating interchange of ...