Modal analysis of asymmetric rotor with anisotropic stator using modulated coordinates

Abstract

Modern rotating machines have a tendency to increase capacity, reduce weight and obtain high operating speed. So the machines become more and more sophisticated and intelligent ever. But still there exists many factors not recognized by modeling techniques of the entire rotor system. Even for a carefully designed rotating machinery having high performance, broad stability with highly qualified materials, unexpected excessive vibrations may be produced and eventually result in fatigue failure or damage during their operating life. Therefore, early stage preventive detection for the system faults becomes increasingly important. Many monitoring methods for early detection of symptoms for various failure modes are developed until now. But they do not clearly match the needs of the industry, because the time-varying parameter in the model of the rotors are not modeled adequately. In this research work, a new modeling and modal analysis method for rotor systems usable in industry is proposed for the purpose of innovation of the theoretical technology for the early monitoring and detecting the critical dynamic failure modes of the rotating machineries. 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. The modal analysis procedure for the asymmetric rotor system, of which rotating and stationary parts possess asymmetric and isotropic properties is investigated in the first stage. 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 modeling method. In the second stage, the method is extended for asymmetric rotors with anisotropy, so call...