Directional cyclic demodulation with application to identification of rotor oil‐film instability fault coupled with rub–impact

Abstract

In the state of oil-film instability coupled with rub–impact, the vibration signal of rotor-bearing system generally presents the weak non-linear frequency modulation (FM) features. In order to get a deep insight into the complicated FM phenomenon, the mechanism analysis is carried out on the motion model of non-linear Jeffcott rotor in oil-film instability coupled with rub–impact fault. The method of directional cyclic demodulation is proposed to extract the weak FM information embodied in the strong oil-film instability vibration. In this method, the directional cyclic autocorrelation density (DCRD) is adopted to infuse the information of two-directional vibration signals, and then is sliced along the cyclic frequency axis. The FM features and rotor motion direction are extracted from the slice of DCRD. Then the experimental research on the rotor-bearing system demonstrates the validity of the proposed method.