Fractional-Frequency Rotor Motion Due to Nonsymmetric Clearance Effects

[+] Author and Article Information
D. W. Childs

Mechanical Engineering Department, Texas A&M University, College Station, Texas 77843

J. Eng. Power 104(3), 533-541 (Jul 01, 1982) (9 pages) doi:10.1115/1.3227312 History: Received December 15, 1980; Online September 28, 2009


Analysis based on the Jeffcott model is presented to explain 1/2 speed and 1/3 speed whirling motion occurring in rotors which are subject to periodic normal-loose or normal-tight radial stiffness variations. The normal-loose stiffness variation results due to bearing-clearance effects, while normal-tight stiffness variations result from rubbing over a portion of a rotor’s orbit. The results demonstrate that 1/2 speed subharmonic motion can be explained as either a linear parametric-excitation phenomenon or as a stable nonlinear subharmonic motion. The 1/3 speed motion is shown to be possible due to the radial stiffness nonlinearity. A linear parametric-excitation analysis demonstrates that during a normal-light rubbing condition, Coulumb damping significantly widens the potential range of unstable speeds.

Copyright © 1982 by ASME
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