Stability and nonlinear response of rotor-bearing systems with squeeze film bearings

A Method of analyzing the first mode stability and unbalance response of multimass flexible rotors is presented whereby the multimass system is modeled as an equivalent single mass modal model including the effects of rotor flexibility, general linearized hydrodynamic journal bearings, squeeze film bearing supports and rotor aerodynamic cross coupling. Expressions for optimum bearing and support damping are presented for both stability and unbalance response. The method is intended to be used as a preliminary design tool to quickly ascertain the effects of bearing and support changes on rotor-bearing system performance. Since the method can be quickly applied, it should realize a time and cost savings in analyzing the class of rotors considered. Methods of calculating the nonlinear squeeze film bearing forces for finite length bearings are developed which are computationally faster than finite difference and finite element methods generally used.

Three industrial rotor systems are analyzed for stability and unbalance response. Linear and nonlinear analysis with squeeze film bearing supports are presented using nonlinear steady state and time transient techniques to verify the linear designs. The results indicate that the linear design method based on the optimum damping expressions presented herein leads to viable bearing and support designs for rotor-bearing stability and unbalanced response.