Advanced analysis of rotor-bearing systems for stability and response

Rotor dynamics has become an integral part in the analysis and design of industrial turbo machinery. Rotor dynamics deals predominantly with the evaluation of the stability and damped critical speeds, and the response to an unbalance excitation, of turbomachinery. The majority of the industries which deal with rotor dynamics use the conventional and proven transfer matrix methods to solve the dynamics. However, the recent advances in computer technology and the distinct advantages of the finite element method make it an attractive tool to model complex rotor bearing systems.

This research has developed a PC-based finite element analysis program capable of modeling rotors supported not only on fluid film bearings, but also on Active Magnetic Beatings (AMB). Methods are described by which the non-synchronous bearing properties can be used to evaluate the stability of the rotors supported on AMB. The effect of sensor noncollocation on general elliptic orbit response and stability has also been studied, as compared to the circular response of the existing programs. A design procedure for the stability of rotors supported on squeeze film dampers has been outlined. The unbalance response of rotors supported on squeeze film dampers can be predicted using the new iterative solution method which accounts for the nonlinear behavior of the damper. Multilevel analysis, essential for systems such as aircraft jet engines and certain other classes of turbo machinery, can be performed using this new computer program. A post processor for viewing/animating the damped mode-shapes and force:d response of a rotor, in 3-dimensions, has been developed. This ability to view the animated complex modes of forward, backward, and mixed forward-backward whirl of the rotor adds a new dimension in understanding the dynamics of rotating machinery.

With the increasing demand for more accurately predicting the dynamic response and stability of high performance critical path turbomachinery, it is essential to develop advanced capability computer programs. The new PC-based finite element program developed in this research has the advanced capabilities required to model such complex rotating machinery.