Nonlinear responses analysis caused by slant crack in a rotor-bearing system

A finite element model of a slant cracked rotor system attached with two disks is presented. A slant crack model is adopted to simulate time-varying stiffness caused by shaft crack. Two types of bearing force (linear and nonlinear bearing forces) are used for simulating the bearing. This study focuses on the effects of eccentric phase differences of two disks on the nonlinear responses of the rotor-bearing system under steady-state process (constant rotating speed) and run-up process. The results show that for the lateral vibration, the superharmonic resonance phenomenon related to the first bending critical speed can be observed under linear bearing forces; however, it is almost unseeable under nonlinear bearing forces. For the torsional vibration, the superharmonic resonance phenomena related to the first torsional natural frequency appear under linear and nonlinear bearing forces. Large eccentric phase differences of two disks can decrease the rotor vibration and restrain the oil-film instability, and the angular acceleration can restrain the oil-film instability due to the tangential inertia force. Moreover, the large torsional amplitude of the second harmonic frequency can also be identified as a typical feature during run-up.