Stability of Rotors in Bearings

  • N. F. Rieger
Part of the International Centre for Mechanical Sciences book series (CISM, volume 273)


A rotor is said to be unstable when the shaft orbit increases with time, without apparent limit. Instability begins when the rotor speed exceeds a so-called “threshold” speed. Stable operation usually resumes when the speed is again decreased below this threshold speed. Unstable whirl motions can cause mechanical problems such as rubbing between journal and bearing, seal rubbing, and blade/stator rub contacts, and may result in substantial machine damage. Unstable motions can also themselves introduce additional dynamic forces within the bearing which stabilize the whirling at a limiting whirl radius. Such whirl motions are called “bounded” instabilities.


Critical Speed Journal Bearing Rotor Mass Threshold Speed Whirl Motion 
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© Springer-Verlag Wien 1984

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  • N. F. Rieger

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