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1 Applied Mechanics and Engineering

1 1998

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Nonlinear transient analysis of point rub effects in a flexible rotor

Lee C. C., Allaire P. E.

Applied Mechanics and Engineering

1998

Vol. 3, no 4

571-588

Rubs occur in industrial rotating machinery in common practice. However, the vibration spectrum produced by different rub conditions is very different and not always easy to interpret. This paper presents a nonlinear analysis of a single mass rotor subject to a point rub with dry friction (Coulomb damping) and compares the results to experimental data. Experimentally, subsynchronous vibrations occur at whirl ratios of 1/N(N=2,3,4...) relative to operating speed with shaft orbits of complicated Lissajous shapes. These results have not been fully explained in the literature. A point rub dry friction model is used, different from previous authors. The nonlinear point rub transient analysis used numerical integration of the equations of motion forward in time to determine the rotor response. The results obtained matched the experimental results relatively well in terms of both whirl ratios of 1/N and the Lissajous shapes. Shaft orbits were found to be a mix of forward and backward precession, rather than the strictly backward whirl often cited in the literature for rubs. Orbit frequency spectrums were found using a Fast Fourier transform numerical algorithm. At the whirl ratio of 1/3, the analysis showed that the rotor only hit the point rub during every two out of three shaft revolutions. It was also found that the rub friction coefficient had little effect on the nonlinear transient results for this rotor and rub model.