Abstract: Based on the finite element method, three dynamic models are established considering pedestal looseness, rub-impact between rotor and stator, coupling fault of both, respectively. The pedestal looseness fault is simulated using piecewise linear stiffness and damping models, the rub-impact fault is simulated by adopting a point-point contact model. By adopting the augmented Lagrangian method to deal with contact constraint conditions and revised coulomb friction model to simulate rotor-stator frictional characteristics, the responses of the rotor system with three faults are analyzed at different rotating speeds, respectively. And similarities and differences for three faults are compared. The results show that rub-impact is in a dominant position and pedestal looseness subordinate position due to its effect only involving local scope of loose pedestal; the responses of coupling fault is the same as the single rub-impact at lower and higher speeds, different at intermediate speeds; the lower frequency vibrations caused by pedestal looseness disappear and high frequency components appear due to the effect of rub-impact comparing with single pedestal looseness. The results can provide a theoretical foundation for the diagnosis of coupled rub-impact fault.

Key words: Coupling fault, Finite element, Pedestal looseness, Rotor system, Rub-impact