A 3-D finite element modeling method for time-varying rotor-support system based on rotating-fixed coordinates

Abstract

The asymmetry of rotor systems is sometimes evident, such as keyed shafts, crack rotors, two-pole generator rotors and especially shaft-disk-blade systems. Meanwhile, the coupling vibration problem between rotor and support structure is becoming more and more prominent due to the light weight of aero-engines. The design and analysis method for the dynamic characteristics of time-varying rotor-support system with detailed structure is needed. Therefore, a modeling method is proposed by using 3-D finite element for time-varying rotor-support system based on rotating-fixed coordinates. The rotor is modeled in rotating coordinate system and the support structure is modeled in fixed coordinate system respectively. The force, energy and displacement between rotor and support structure are transmitted by bearing mechanical parameters. Thus, the time-varying characteristics of the system are expressed explicitly by bearing mechanical parameters, and the dynamic equation of time-varying rotor-support system can be obtained. Then, Floquet theory and Hill infinite determinant method are used to analyze quasi-mode frequency characteristics and stability of time-varying rotor-support system. The results of a typical asymmetric rotor-support system got by the proposed method were compared with existed methods, and more coupling vibration characteristics such as the coupling vibration of rotor axial motion and support plate bending, the coupling vibration of shaft bending and support plate torsion were obtained.