Modal Analysis and Error Estimates for Linearized Finite Journal Bearings

Abstract

The linearized model of a rigid symmetric rotor with finite bearings is solved using modal analysis. Important parameters of the finite bearing system are evaluated and these include the logarithmic decrement, damped natural frequencies, complex frequency response functions, and inclination angles of the orbits with the load direction. A chart of error measures giving the deviation of the linearized bearing stiffness and damping from those of the actual nonlinear system is provided. This chart can assist in obtaining a knowledge of the quality of a rotor response as calculated using linearized stiffness and damping and can be used to set acceptance boundaries for the linear model in different industrial applications because of the mathematical difficulties involved in a complete solution of the actual nonlinear representation of the rotor bearing system.

A Nonlinear Dynamic Model With Confidence Bounds for Hydrodynamic Bearings

“…Obviously, such a linearized approach would require an evaluation of the linearized error to set forth an acceptable bound for the linear solutions. Hashi and Sankar (1984) have attempted to estimate the linearized error. Deviations of linearized journal bearing coefficients from the nonlinear systems are calculated.…”