Page 42 - Singiresu S. Rao-Mechanical Vibrations in SI Units, Global Edition-Pearson (2017)

1.3 importanCe oF the study oF Vibration 39

FiGure 1.6 Nature of wind-induced vibration experienced by Tacoma Narrows bridge before
its failure. The bridge opened on July 1, 1940, and collapsed on November 7, 1940.

Whenever the natural frequency of vibration of a machine or structure coincides with
the frequency of the external excitation, there occurs a phenomenon known as resonance,
which leads to excessive deflections and failure. The literature is full of accounts of system
failures brought about by resonance and excessive vibration of components and systems.
As an example, Fig. 1.6 shows the nature of vibration experienced (with amplitude of over
8 m) by the Tacoma Narrows bridge before it collapsed into the river below. The cause
of the failure was determined to be aerodynamic instability. Because of the devastating
effects that vibrations can have on machines and structures, vibration testing [1.18] has
become a standard procedure in the design and development of most engineering systems
(see Fig. 1.7).
In many engineering systems, a human being acts as an integral part of the system. The
transmission of vibration to human beings results in discomfort and loss of efficiency. The
vibration and noise generated by engines causes annoyance to people and, sometimes,
damage to property (Fig. 1.8). Vibration of instrument panels can cause their malfunction
or difficulty in reading the meters [1.19]. Thus one of the important purposes of vibration
study is to reduce vibration through proper design of machines and their mountings. In this