Coupled bending vibration analysis of flexible rotors by using the assumed modes and substructure synthesis method

Abstract

Along with the recent demand for high precision, performance and efficiency of rotating machines such as the turbine and the hard disk drives of the personal computer, the design of such machines has a tendency to high capacity, light weight, and wide operating speed range so that the machines become more sophisticated than ever. As a result, before designing they should be analyzed in more complicate method before designing them. Since, some parts of a rotor was assumed to be rigid, its analytical result did not accurately reflect the behaviors of rotors in many cases. In order to predict accurately the dynamic characteristics of rotors, the rotor systems should be modeled as assemblies, whose parts are not considered to be rigid any more and to be coupled to each other. Many analytical methods have been developed and applied to the rotating machines in the industry. Most of them have been used to analyze the dynamic characteristics of the individual components without considering the possibility of coupling among them. These methods can cause some potentially signigicant drawback to remain inadequately investigated or completely ignored when the coupling effects of components on assemblies are notable due to the flexibility of components. Recently, FEM has been used to consider the coupling effects of components. However, the method requires the large number of degrees of freedom and the relatively large computational effort, which makes the parametric study rather difficult. In addition it is very difficult to reformulate the equations of motion when modifying the analytical model. In this work, an analytical method has been developed to investigate the dynamic characteristics of rotor systems. The method is based on the combination of the "substructure synthesis method" and the "assumed modes method," and it is applied to the two types of rotor systems: One is composed of a shaft, a disk and blades which are attached on the edge of disk such as gas or ste...