Comparative Study: Linear and Nonlinear Transient Stability Analysis for Meso Scale Rotor with Gas Foil Journal Bearings

Abstract

A comparative study on linear and nonlinear transient stability analysis of a meso scale rotor supported on gas foil journal bearings is carried out. Steady and unsteady Reynolds equations are solved by using the control volume formulation with a power law scheme and the Gauss–Seidel method. The modal impedance and the time domain orbit simulation are used to obtain the stability parameter: the threshold rotor mass for the linear and nonlinear transient methods respectively. The modal impedance is calculated by using the linear stiffness and damping coefficients. However, the orbit simulation solves explicitly the journal equations of motion, the compressible unsteady Reynolds equation and the equation of foil deformation. The threshold rotor mass which gives the stability threshold value for a given operating speed and load is obtained. It is found that there is a significant difference between the values of threshold rotor mass predicted by the linear and nonlinear transient stability methods.