Investigation on the Modal Characteristics of the Rubbing Rotor System With Additional Constraint

Abstract

The rub-impact can bring about the impact load and friction force onto the rotor, and produce the additional constraint effect as well. The additional constraint effect, which is also called stiffness effect, can increase the stiffness of the rotor system. Consequently, the modal characteristics of the rotor system are changed. This paper aims to understand the modal characteristics of the rubbing rotor system with additional constraint. The governing equation for a modified Jeffcott rotor with additional constraint is established first. Based on the complex nonlinear modes concept and harmonic balance method, the solution method for nonlinear modes of the rubbing rotor system is derived, then the method is validated through a 2-dof collision system. Finally, the modal characteristics of the rubbing rotor and influence of the key parameters are analyzed in detail. The results reveal that the rubbing rotor system possesses two potential mode motions, i.e. forward whirl with positive modal frequency and backward whirl with negative modal frequency. Both the modal frequency values of these two mode motions increase with the modal amplitude increases, but their values are limited to an interval range. The modal damping of the forward whirl mode motion is always greater than zero, while the modal damping of the backward whirl mode motion may be less than zero, indicating the backward whirl mode motion can be unstable in some cases.