On fault induced nonlinear rotary response and instability

Results of applying instantaneous frequency to the interpretation and characterization of bifurcation and evolution of instability are presented for a comprehensive rotor-journal bearing model incorporating translational and rotational inertia, bending stiffness, gyroscopic moments, shear deformation and disk imbalance. By designating rotor speed and the relative flexibility embodying the extent of surface crack development as the two controlled parameters, rich and complex nonlinear behaviors are observed as the model subjected to the combined exertion of slow crack breathing and bearing film pressure. Among them are that sub-harmonics attributable to the oil-film force are seen disappeared with crack opening and that the model system fails from one of the three possible scenarios: super-harmonic bifurcation, prolonged chaotic response, and large vibration amplitudes accompanied by no bifurcation. As a result of the investigation, a dynamic failure curve differentiating zones of stability and bifurcated instability from zones of dynamic failure is constructed and proposed as an alternative to the traditional stability chart.

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