Dimension Reduction And Nonlinear Dynamics Of Rotor Systems

Modern turbomachinery are increasingly designed in high power, high speed, high efficiency and high flexibility. A large number of vibration failures are closely related with the nonlinear factors of a rotor system in engineering fields. It has been attract to more attention of the researchers about the nonlinear dynamics of rotor system. Application the nonlinear dynamics theories and methods in this thesis, several important problems of the rotor system are researched. Merely purpose includes: 1. the study on the dimension reduce of the rotor dynamic system in the large turbo- machinery and the vibration characters of a continue rotor with nonlinear oil film forces and the seal fluid forces together. 2. It is revealed that the floating ring bearing-rigid rotor and the overhang rotor at the evolution of dynamics by researching the nonlinear vibration characters of floating ring bearing/rotor. 3. The friction degrees and the rich dynamic behaviors under the different system parameters for the rotor with the axial rubs. Several works and results included in the thesis are as follow:1. The dimension reduction methods, application and latest developed are summarized. Besides, the research methods, status and further trends in rotor dynamics are indicated.2. The approximately inertial manifold and nonlinear Galerkin method in a continue rotor system is studied. Comparing to the standard Galerkin method, the effectiveness is explained at the application of the nonlinear Galerkin method in a continue rotor system. Furthermore, the dynamic characters in a continue rotor/bearing/seal are analyzed. The investigation shows that the nonlinear Galerkin method has an advantage over the standard one with when the same order of truncations, transitions, or bifurcations, of the rotor whirl from being synchronous to non-synchronous as the unstable speed is exceeded. The non-synchronous oil/seal whirl is a quasi-periodic motion. In the regime of quasi-periodic motion, the"windows"of multi-periodic were found.3. The rigid rotor and overhung rotor with floating ring bearing supporting is researched at the vibration characters. The influence discipline of system stability is revealed by adopting the varying parameters of rotor and floating ring. Furthermore, a continuous overhung rotor with gyroscopic moment is studied by the post-process version of nonlinear Galerkin method. The results show that the dynamic behaviors include periodic motion, double-periodic motion, quasi-periodic motion and chaos. Several parameters as the thickness of floating ring, the ratio of inner/outer oil gap, viscosity of lubricating oil are influence on the stability of system. The dynamical response is also revealed in an overhung rotor system with gyroscopic moment.4. The study on lateral and torsional vibrations of a rotor system with axial rubs. The conclusions include that the lateral vibration of rotor experiences changes from being periodic to multi-periodic and chaotic eventually. At the same time the vibrational amplitude is also enlarged. The phase portrait of the torsional response becomes complex as many frequency components appear in amplitude-frequency spectrum. Due to the couple effect, more or less same frequency components appear both in the lateral and the torsional motions. The single disk contact/rubs have less influence to the rotor dynamics than the two disk rubs have.