Nonlinear Vibration Analysis of a Rotor-Hydrodynamic Bearing System: Gear and Thermal Bow-Induced Vibration

Abstract

This dissertation presents a novel approach for modeling and analyzing a geared rotor-bearing system including nonlinear forces in the gear set and the supporting fluid film journal bearings. Co-existing, steady-state, autonomous and non-autonomous responses are obtained in an accurate and computationally efficient manner utilizing the multiple shooting and continuation algorithms. The results reveal a dependence of the gear set contact conditions and system nonlinear response characteristics, i.e. jump, coexisting responses, subharmonic resonances and chaos on the choice of journal bearing parameters. The Morton effect is caused by uneven viscous heating of the journal in a fluid film bearing, which causes thermal bending, especially in rotors with an overhung disc or coupling weight. This work investigates the influence of misaligned journal bearing effects on the thermally induced rotor instability problem. The simulation results indicate that the amplitude of the misalignment angle affects the instability speed range caused by the Morton effect under certain conditions. This work also treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper may change the rotor’s critical speed location, damping and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies. The influence of SFD cage stiffness is evaluated. The influence of tilting pad journal bearing’s pivot design on the severity and instability speed range of the ME vibration was investigated. The friction between pad and pivot, which only exists in the spherical pivot, is taken into account and its impact on the ME is also tested. Nonlinear transient simulations are carried out for a wide operating speed range with varying pivot design parameters. Simulation results indicate that the predicted ME instability is sensitive to the pivot shape, pivot flexibility, and padpivot friction. The Morton effect test rig was built, and its vibration test results are presented. The vibration increases of the rotor at constant operating speed reveals that the existence of the Morton effect in the designed rotor-bearing test rig