Effects of working conditions on the nonlinear dynamic performances of a rigid rotor for air journal bearing

Abstract

The vibration of the rotor for an air journal bearing is extremely complicated, which always exhibits nonlinear dynamic performances. In this paper, the transient Reynolds equation is solved by the finite element method so that the pressure distribution of air film can also be obtained, which determines the transient force acting on the rotor. The dynamic equation of rotor motion with mass eccentricity and external harmonic force is derived. The trajectory of the rotor can be acquired by solving the two equations continuously through the weak-coupling solution method. Effects of working conditions including supply pressure and rotational speed on the nonlinear dynamic performances of an air journal bearing are studied based on the trajectory, Poincaré map, frequency spectrum diagram and bifurcation diagram. The results show that increasing the supply pressure can reduce the rotor vibration amplitude. The vibration amplitude shows an upward trend as the rotational speed increases. There always exists a vibration frequency corresponding to the external harmonic force, while the vibration amplitude is small.