Study On Nonlinear Dynamic Behaviors Of Journal Bearing-Rotor System Based On Database

For large rotating machinery, the system's security is influenced by the operation stability of the rotor, which requires us to conduct a comprehensive analysis to the nonlinear dynamic response of the rotor. In this thesis, nonlinear dynamic systems of the rotor supported by hydrodynamic journal bearing are analyzed. The contents are as follows:1. Nonlinear oil film force database method is discussed here in detail. Based on the dynamic Reynolds equation with Reynolds boundary condition, the Castelli method was employed to solve the Reynolds equation for oil lubrication upon bearings. By special treatment to the dynamic Reynolds equation, a profile of nonlinear oil film force of single-pad journal bearing is established. At the same time, the structure of the database, as well as fast retrieval and accurate interpolation method are introduced. Taking fixed-pad bearing as the object, and the calculation of the geometric parameters and the assembly calculation of static characteristics of bearing are introduced. By comparison of the results of a variety of fixed-pad journal bearings, the database method is validated to be rapid and accurate.2. The nonlinear oil film forces of tilting-pad journal bearing and fixed-tilting pads journal bearing are calculated. A single pad coordinate system is established, and then the geometric parameters in the bearing coordinate system are transformed into the geometric parameters in a single pad coordinate system. According to the geometric parameters and the pad equilibrium condition in a single pad coordinate system, the nonlinear oil film forces are calculated by calling the nonlinear oil film forces database. The nonlinear oil film force of the tilting pad bearing is obtained by the assembly method. The calculation program for the static characteristics of tilting pad bearing is verified, and then the nonlinear oil film force of the fixed-tilting pads combination bearing is calculated.3. The dynamic model of a symmetric rigid rotor supported by fixed-tilting pads journal bearing is established. The unbalanced responses of the symmetrical rigid rotor dynamic system supported by fixed-tilting pads journal bearings are analyzed by self-adaptive Runge-Kutta method and Poincare mapping. The numerical results reveal nonlinear behaviors of the system, such as periodic, periodic-doubling, quasi-periodic, etc. The effects of the pivot ratio and the preload on the stability of the rotor system are analyzed. The results show that the pivot ratio and the preload have an important influence on the system's stability. Therefore, when selecting the system parameters, the appropriate preload and pivot ratio should be chosen.4. The dynamic model of a symmetric flexible rotor supported by fixed-tilting pads journal bearing is established. As for symmetrical flexible Jeffcott rotor systems supported by combination journal bearings, the. nonlinear motions of the center of the rotor are calculated by self-adaptive Runge-Kutta method and Poincare mapping during different rotational speed tests, . when the pivot ratio is 0.5 or 0.6, and the preload is 0.4. Numerical results reveal nonlinear behaviors, such as periodic, periodic-doubling, quasi-periodic, etc.The preceding research provides theoretical references for analyzing and settling nonlinear and stability problems of a practical rotor system supported by fixed-tilting pads journal bearings..