Nonlinear model of vibrations in a rotor-bearings system

This article presents a theoretical model for the nonlinear description of vibrations occurring in the rotor-bearings-supports system. A new approach to the determination of viscous-elastic properties of the oil film that does not draw on the commonly used principle of superposition of pressure or hydrodynamic forces in the bearing is put forward. The dynamic features of the oil film are determined by means of nonlinear coefficients of stiffness and damping calculated by using a fast and modified perturbation method. The method applied to describe the oil film properties enables us to take advantage of the equations of motion of the entire system derived on the basis of the finite element method. The theoretical model takes also into account the effect of heat transfer within the bearing. With regard to kinetostatic problems, the temperature distribution in the film is calculated on the basis of a sophisticated so-called diathermal model of the bearing that permits the determination of a mean dynamic viscosity of the oil, further applied to the problems of the system dynamics. A general calculation algorithm and a computer program consisting of two clearly separated parts, kinetostatic and dynamic, is described. This article also gives examples of experimental verification of the model at a special large-size test rig and presents the analysis of nonlinear vibrations of a real large turbo-set carried out with the help of the developed theoretical method and computer program.