Nonlinear modal analysis of rotor systems considering gyroscopic and dry friction effects

Part looseness is a common fault in rotor systems, which may lead to serious dynamic problems. Rotor system with part looseness turns to be a complicated nonlinear problem, with gyroscopic and dry friction effects occurring simultaneously. The analysis of nonlinear systems is in general confronted with two key challenges: complicated calculation method and long calculation time. This work has developed a fast and efficient numerical scheme based on nonlinear modal analysis. By employing the proposed nonlinear modal analysis strategy, the essential gyroscopic effect, as well as the dry friction influence caused by part looseness, are both taken into account when analyzing the dynamic behavior of rotor systems. First, the theoretical aspects and the analysis approach considering the nonlinear force and the gyroscopic effect are proposed for a general rotor system. Second, by employing the proposed nonlinear modal strategy, simulations are conducted on a general rotor system considering the gyroscopic effect and dry friction caused by part looseness. Third, modal parameters such as resonance frequencies and modal damping ratios are carefully investigated as functions of rotation speed and modal amplitude. In the realization of a nonlinear modal analysis of a rotor system, the key point is to establish the relationship between modal parameters with both modal amplitude and rotation velocity. The proposed strategy can help better analyzing and interpreting the dynamic characteristics of rotor systems from the modal overview.