Effect of nonlinearities on response characteristics of rotor systems with residual shaft bow

When rotor systems operate near resonance points, the amplitudes of the system become very large. Therefore, the dynamic characteristics of the system are determined by various nonlinearities that depend on the displacements. In this paper, the nonlinear forces caused by the fluid-film of the squeeze-film damper (SFD) and the cubic nonlinearity of the system are considered as sources of nonlinearity in the rotor systems. In addition, no matter how precisely the rotor system is manufactured, there will certainly exist some faults; therefore, such faults should be reflected in the system model, in order to accurately analyze the dynamic behavior of the system. In this paper, cubic nonlinearity and nonlinearity in SFD is together considered in the rotor systems with initial bow and used to study the dynamic behavior of the system. The equation of motion of the system is solved by combining the classical incremental harmonic balance (IHB) method and the modified IHB method, and stability analysis of the solutions of rotor systems is performed using the Floquet theory. Frequency–response curves, time histories, Poincaré sections and disk-centered whirl orbits according to the change of system parameters are constructed. The calculated results can contribute to studying the response characteristics of rotor systems with an initial bow.