Nonlinear analysis of rotor system supported by oil lubricated bearings subjected to base movements

Abstract

Response analysis of rotor system subjected to the base movements in a large rotational machinery is a complex high-dimensional nonlinear problem. In this paper, rotor system of a centrifugal pump with a pair of oil lubricated bearings is modeled as a six-degrees-of-freedom nonlinear system by the Lagrange method. The Runge–Kutta–Felburg method with variable step size is applied to solve the equations based both on nonlinear bearing model and on linearized bearing model. Poincaré maps, phase trajectories, bifurcation diagrams, and cascade diagrams are used to illustrate the dynamics of the rotor with the two bearing models. The responses of these two kinds of systems under El Centro seismic wave are obtained. The acceleration data of the seismic wave are used as the input of base movements. The short bearing model is applied to express the nonlinear oil film force. Compared to the system with model of linearized bearing, the nonlinear bearing–rotor system can accurately reflect the dynamics of the system. Furthermore, trigonometric functions are employed to express the base movements, and the responses of nonlinear bearing–rotor system subject to the base movements are obtained. The fast Fourier transform is used to analyze the nonlinear bearing–rotor system with effects of the base movements. The results reveal not only the dynamic behavior of the rotor of the centrifugal pump supported by two nonlinear bearings, but also the responses of the nonlinear bearing–rotor system with the combined effects of centrifugal force and base movements.