| description abstract | Fast time-varying (FTV) phenomena, such as significant speed changes, FTV stiffness, and vibration signals with fast-oscillated instantaneous frequency (IF), carry critical fault information of high-speed rotating machines. However, the mechanism of FTV phenomenon remains unclear, and conventional methods cannot characterize the FTV features. In this study, the FTV vibration mechanism for rotor–stator contact systems is first revealed, and then, a novel fast-modulation-based rub-impact detection method (FRiDM) is significantly developed to extract the FTV features and thus promote the effectiveness of rub-impact diagnosis. The FTV vibration mechanism indicates that the fast-oscillated modulation of the vibration signal is the physical property, and the fast oscillation of IF is the mathematical nature. By theoretical and experimental study, it is demonstrated that the FTV features of the rotor–stator contact system are periodic for the periodic motion but aperiodic for the quasi-periodic and chaotic motions. Finally, the validity of the proposed FTV vibration mechanism and FRiDM is verified by the application to the rub-impact diagnosis of a bearing life testing rig and a dual-rotor turbine engine. The study results provide a potential way to nonlinear behavior identification and fault localization of sophisticated rotor systems. | |
