Dynmamics And Vibration Characteristics Of Misaligned Rotor Systems

Rotor system is the key part of rotating machinery, the common faults of which include imbalance, misalignment, rub-impact, oil whipping, shaft cracks, pedestal looseness. The faults often lead to serious abnormal vibrations, even cause catastrophic consequences. After imbalance, misalignment is accepted as the second most commonly observed disturbance source in rotor system. Misalignment is drawn more and more attention, because it may cause excessive vibrations of rataing machinery and premature failure of bearings and coupling, and also shaft failure from cyclic fatigue, and so on. The dynamic of misaligned rotor sytem is still unsolved, especially for bearing misalignment and coupling misalignment. As is known, misalignment has great effects on the natural frequencies and vibration responses of rotor system. And the dynamics of misaligned rotor system is one of the important issues in the field of rotor dynamic theory and engineering technology which are needed in deep study.Specific to two-support rotor system with bearing misalignment and three-support rotor system with gear coupling misalignment, dynmiac models of misaligned rotor system are investigated with analytical and finite element methods and experimental studies are also carried out. The works finished in this paper are as follows:(1) Based on the Hertz contact theory and the structural analysis of angular contact ball bearing, a 5 DOF analytical stiffness model of rolling bearing is derived, which considers the bearing bias and offset the normal state and abnormal state respectively in engineering field. And angular and parallel misalignments are introduced in the proposed 5 DOF analytical model. Secondly, the influences of misalignment on rolling bearing stiffness characteristics are investigated. Finally, the analyitical model is confirmed with finite element method and experimental mothod.(2) A dynamics modeling approach of two-support rotor system with bearing misalignment is proposed by Lagrange equations, in which the 5-DOF rolling bearing stiffness model is introduced considering beaaring misalignment factors. Secondly, based on the analytical model, excitation principles of rotor system with bearing misalignment are analyzed and additional excitation forces caused by misalignment are obtained. And it analyzes vibration responses of misaligned rotor system with the fourth-order variable step Runge-Kutta method, and then the influence of bearing misalignment on vibration responses and its characteristics are obtained.(3) A dynamics modeling approach of two-support rotor system with bearing misalignment is proposed by finite element method. Vibration response time-frequency characteristics and orbital characteristics of two-support rotor system with bearing misalignment are obtained. Comparations of theoretical results and FEM simulation results and experimental results are finished.(4) According to meshing and axial contact features of gear coupling, a 5-DOF stiffness model considering the lateral stiffness, bending stiffness and axial stiffness are set up. And then it derives an analytical model of three-support rotor system with coupling misalignment by Lagrange equation, which introduces the 5-DOF gear coupling stiffness stiffness model. Based on the analytical model, exciting incentive of coupling misalignment is analyzed, and additional excitation forces caused by gear coupling misalignment are obtained. Finally, it analyzes vibration responses of misaligned rotor system with Newmark method, and then gets vibration responses characteristics of misaligned rotor system.(5) A finite element model of a three-support rotor system with gear coupling misalignment is proposed and experimental studies to investigate the rotor vibration characteristics related to coupling misalignment are performed. Finally, theoretical results and FEM simulation results and experimental results are compared.As to the misaligned rotor system, excitation principles of bearing misalignment and coupling misalignment are investigated with three methods including analytical method, FEM method and experimental method. Lateral and axial vibration characteristics of misaligned rotor system are grasped, all of which have great value for vibrations predicted, evaluated and controled for misaligned rotor system.