Response evaluation of imbalance-rub-pedestal looseness coupling fault on a geometrically nonlinear rotor system

In order to achieve the purpose of condition monitoring and the appropriate design of rotating structure, analyzing the dynamic performance associated with rotor-stator rub coupling fault is of high significance. Due to large imbalance excitation and pedestal looseness, the whirling motion appears with larger amplitude and then the geometrical nonlinearity of shaft becomes impossible to ignore. In order to reveal the inner interaction between coupling fault commonly appearing in the rotating machine and geometrical nonlinearity of shaft, a geometrical nonlinear rotor system with imbalance-rub-pedestal looseness coupling fault is proposed in this paper. The mechanical mechanism of rotor-stator normal impact is represented in terms of a novel force model and its different modifications. Meanwhile, the friction between them is assumed to be a tangential dry Coulomb force, which is proportional to the impact force. After that the vibration features of the rotor system are analyzed with respect to the effects of geometrical nonlinearity, rotor-stator rub and pedestal looseness. The change rules of resonant characteristic and rub region are revealed under different loose stiffness. What is more, the dynamic variation routes of the rotor system are analyzed by the bifurcation diagram, time waveform, whirl orbit, and Poincaré section, respectively. At last, the vibration experiment is performed on a rotor test rig and the typical signals of coupling fault are obtained at different rotational speeds.