Study On Nonlinear Dynamic Characteristics Of Fixed-Tilting Pads Journal Bearing-Rotor System

Nonlinear dynamics of a bearing-rotor system become the main contents of rotordynamics due to the increasing demand on high speed, high efficiency for the rotary machinery. Therefore, it is important to study nonlinear dynamic behaviors of fixed-tilting pads journal bearing-rotor system and analyze the dynamic characteristics of fixed-tilting pads journal bearing by nonlinear dynamics and rotordynamics.The main contents in the dissertation are as follows:1. According to the physical characteristics of the oil film, an isoparametric finite element with eight nodes method is used to convert the Reynolds equation. This is done continuously to the discrete form of finite dimensional algebraic variational equations and their disturbation equations satisfying certain constraint conditions. The nonlinear oil force of journal bearing is calculated by the proposed method, and its Jacobian matrix was calculated simultaneously and compatiable accuracy was obtained without increasing computational costs.2. The geometric parameters in the bearing coordinate system is transformed into the geometric parameters in a single pad coordinate system. According to the geometric parameters in a single pad coordinate system and the pad equilibrium conditions, the oil film force and its Jacobian matrix are calculated by calling the finite element computational program in a single pad coordinate system. The oil force, damping, and stiffness coefficients of the bearing are obtained by the assembly method.The program of the oil force and dynamic coefficients of tilting-pads journal bearing are verified respectively. The oil force and dynamic coefficients of fixed-tilting pads journal bearing are also analyzed.3. A symmetrical rigid rotor supported by fixed-tilting pads journal bearings is modeled. The unbalanced responses of the symmetrical rigid rotor dynamic system supported by fixed-tilting pads journal bearings are analyzed by the Runge-Kutta method and a Poincare map. The numerical results reveal complex nonlinear behaviors of the system, such as periodic, period-doubling, quasi-periodic, etc. The effects of the width-to-diameter ratio of bearing, the pivot ratio and the preload on the stability of the rotor system are also analyzed.4. The complete dynamic model of fixed-tilting pads journal bearing is established. The oil force, dynamic coefficients involving pad flutter in the complete dynamic model are also obtained by the assembly method at the equilibrium position. Then, the oil force and dynamic coefficients of fixed-tilting pads journal bearing in the complete dynamic model are analyzed.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.