The Nonlinear Analysis On The Mechanism Of Instability Of Rotor System Excited By Internal Damping Of Material And Seal Fluid

Rotor systems involve many types of nonlinearities, which may lead to a lotof complex dynamic behavior, and cause problems of stability in high speed rotating Rotors. The self—excited destabilizing forces contribute more directly to the destabilization of the rotor system. Numerous cases in actual machinery have shown that more than half of serious failure happened in rotating machinery arising from the instability growth of low—frequency ( or subharmonic ) vibrations. So it is badly in need of the study on the mechanism of low—frequency (subharmonic) vibration of rotor excited by various types of nonlinear destabilizing forces and techniques of instability controlling.The theory and techniques of nonlinear dynamics are used in the thesis, to study the mechanism of instability of rotors' whirling motion affected by the nonlinear destabilizing forces, such as internal damping of material and seal fluid forces. In addition, the transient evolution of rotor—easing rub events is analyzed by numerical method. Several parts included in the thesis are as follow:1. The study on the nonlinear dynamics of rotor at broad and.home is summarized in an all—round way. Besides, the direction for further study in this field, in these days and days to come, is indicated.2. The vibrational characteristics affected by the destabilizing forces of internal damping of material is studied. The Hamilton principle and the Galerkin's method are applied in deducing the equations of motion of the shaft with nonlinearity of internal damping of material and rigid of bending. The studies by using methods of nonlinear dynamics include the following aspects: the stability of the rotor in any modes of primary resonances, the local bifurcations of the normal motion as well as the self—excited whirling motion, and the mechanism of instability of low—frequency self—excited vibrations, in cases of non—resonance and 1 / 3—order subharmonic resonance, etc. The study shows that an unfavouvable impact can cause rotor instable when it operates at supercritical speed, then the self-excited vibration occurring through Hopf bifurcation. The effective methods of controlling this type of self—excited whirling motion are enhancing of external damping and well balanced of the rotor.3. The study on the dynamical characteristics of seal is summarized briefly. The...