Nonlinear effects of induced unbalance in the rod fastening rotor-bearing system considering nonlinear contact

Rod fastening rotor (RFR) is characterized by discontinuity of contact interface and unbalance of multiple disks. There are few researches that focus on unbalance effect including magnitude and phase difference on the nonlinear dynamic characteristics of RFR considering contact feature. A typical RFR model is proposed to investigate the nonlinear dynamic characteristics. The nonlinear motion governing equation considering unbalance excitation, nonlinear oil-film force and nonlinear contact characteristics between disks is derived by D'Alembert principle. The contact effects are simulated by bending spring with nonlinear stiffness. The research focuses on the effects of unbalance on the onset of low-frequency instability and nonlinear response of RFR. The obtained results evidently show the distinct phenomena brought about by the variations of unbalance, which confirms that unbalance magnitude and phase difference are critical parameters for the RFR system response. To restrain large amplitude of nonsynchronous vibration and retard the occurrence of instability, the unbalance magnitude of rotor is suggested to be kept at range from U5 to U6. Meaningfully, RFR can operate relatively well with small vibration and higher instability threshold when the residual unbalance between disks is controlled at an enough-reasonable unbalance phase difference. Phase difference adjustment can accomplish active balance. The total vibration and nonsynchronous components could be reduced, and onset speed of instability could be delayed effectively by using the proposed method, which is helpful for the dynamic design, assembly, balance and vibration control of such RFR.