Stability and nonlinear dynamic analysis of gas-lubricated system with elastomer suspension

Abstract

This paper presents the dynamic behavior of a rigid rotor supported by a pair of self-acting gas-lubricated bearings which is used in a turbo-expander, the key equipment in a large-scale cryogenic system. In order to restrict the vibration of the rotor relative to bearings, elastomers are mounted between bearings and shell. A finite difference method has been employed to solve the Reynolds equation in time-dependent states. The center orbits of the rotor are got by solving the motion equations. The system state trajectory, Poincare maps, logarithmic spectra maps and bifurcation diagrams are used to analyze the dynamic behavior of the system. The effect of the elastomer suspension to absorb the vibration is verified by comparison with the system with rigid suspension. A set of mass values, damping exponent values and stiffness of elastomer are calculated and compared in this paper. The results show that the rotor center loses its regular behavior gradually with the increase in the rotor mass. The square damping exponent model of the elastomer shows more stability than linear damping suspension model, and the quadratic damping exponent model has a similar motion behavior compared with a linear model. A suitable stiffness of the elastomer is important to the stability of the system. The elastomer with a low stiffness may cause the large amplitude of the vibration, and the system may lose its regular behavior when the stiffness is large enough.