Predicting Oil Film performance in a Journal Bearing based on Modulation Signal Bispectrum analysis of Vibration Signals

Abstract

This paper presents a study of the lubricant starvation of a journal bearing based on vibration signal analysis by modulation bispectrum. A vibration model is modified to includes conventional hydrodynamic effects, asperity churns and collisions excitations and shaft unbalance. It has been found by modulation signal bispectrum analysis of vibration responses from different levels of lubricant oil in the bearing reservoir shows that vibration characteristics are different in terms of frequency bands and magnitudes, which can be based on to differentiate between degrees of oil film thickness. The instable oil whirls can affect the measured vibration responses in the frequency range from 3.5kHz to 5.5kHz. This can be a good indication for detecting the instability of the rotor system supported by the bearing. Moreover, the structural resonances in the high frequency range of from 5.5kHz to 11kHz can better reflect the effect of the excitations and result in a more agreeable separation of different levels under wide operating conditions.