Modal analysis of asymmetric rotor system with isotropic stator using modulated coordinates

A new modal analysis method for rotor systems with periodically time-varying parameters is proposed. The essence of the method is to introduce the modulated coordinates such that the periodically time-varying linear differential equations can be effectively transformed to the equivalent time-invariant linear differential equations. This paper presents the modal analysis procedure for the asymmetric rotor system, of which rotating and stationary parts possess asymmetric and isotropic properties, respectively. With a simple asymmetric rotor model, the analytical modal analysis procedure is illustrated and compared with the conventional method based on formulation in the rotating coordinates. A numerical example with a flexible asymmetric rotor model is also provided to demonstrate the effectiveness of the proposed method.