title: Theory of Vibration: An Introduction (Mechanical Engineering Series) (Vol 1)
author: A.A. Shabana
description: "The text is particularly easy to read and moves from one section to the next with no major changes in style. It is obvious that the structure of the material is...based on a set of mature class notes...a very worthwhile addition to the vibration literature" - Proceedings of the Institution of Mechanical Engineers
zlib_text: CHAPTER 5
  SELF-EXCITED VIBRATION
  F. F. Ehrich
  INTRODUCTION
  Self-excited systems begin to vibrate of their own accord spontaneously,the amplitude
  increasing until some nonlinear effect limits any further increase. The energy supply-
  ing these vibrations is obtained from a uniform source of power associated with the
  system which, due to some mechanism inherent in the system, gives rise to oscillating
  forces.The nature of self-excited vibration compared to forced vibration is:1
  In self-excited vibration the alternating force that sustains the motion is created
  or controlled by the motion itself; when the motion stops, the alternating force dis-
  appears.
  In a forced vibration the sustaining alternating force exists independent of the
  motion and persists when the vibratory motion is stopped.
  The occurrence of self-excited vibration in a physical system is intimately associ-
  ated with the stability of equilibrium positions of the system. If the system is dis-
  turbed from a position of equili