Nonlinear Dynamics of a Magnetically Supported Flexible Rotor in Auxiliary Bearings

Abstract

Abstract The results of a numerical simulation on the nonlinear dynamics of a flexible rotor mounted on magnetic and auxiliary bearings are presented in this work. The focus of this work was to investigate the effect of shaft flexibility on the rotor response during load sharing operation between the magnetic and auxiliary bearings. For the range of parameters considered herein, results from the numerical simulation showed that the stiffness ratio, which represented the contact stiffness of the auxiliary bearing, was a more effective parameter, as compared to the Coulomb sliding friction coefficient, for the suppression of sub-synchronous and non-synchronous vibrations in the rotor’s response. Sub-synchronous vibrations of period-2, period-4, period-8 and period-16 were observed in the response of the rotor. Non-synchronous vibration which was also seen in the rotor’s response was determined to be chaos. For the case of the rotor response with variation of the stiffness ratio, the route to chaos was found to be due to a sequence of period-doubling bifurcations, where the synchronous or period-1 response bifurcated into period-2, period-4, period-8 and period-16 responses, culminating into chaotic vibration. Vibrations which are of sub-synchronous and non-synchronous nature are best avoided in the rotor’s response during operation, whereby the load is shared between magnetic and auxiliary bearings, as they produce stress reversals. Such stresses can potentially cause fatigue failure of the rotors and their associated structures.