Torsional oscillations of a rotor with continuous stator contact

In this work, torsional vibrations of a Jeffcott rotor subjected to continuous stator contact are analytically and numerically studied for both forward and backward whirling motions. Torsional oscillations of this system are complex due to nonlinear coupling with lateral vibrations, and nonlinearities originating from frictional forces between the rotor and stator. The phenomena observed in numerical simulations of the three degree-of-freedom Jeffcott rotor are explained through analysis of a derived reduced-order equation. It is found that during forward whirling, torsional oscillations are unlikely to exist in both the full and reduced-order models. Special consideration is provided to the torsional response during high-speed backward whirling. Although the rotor is subject to discontinuous friction, during high-speed backward whirling, it is found that the predictions from the full system and reduced-order models for the torsional oscillations are smooth in nature. Further analysis of the reduced-order system reveals that high-frequency forcing acts to smoothen out the discontinuity on the slow scale. Additionally, a centrifugal stiffening effect is experienced by the torsional motions during both forward and backward whirling.