Study Of Nonlinear Dynamic Characteristic Of Gas-lubricated Bearing-rotor System

Gas-lubricated bearings are widely used in all kinds of rotating machinery,especially in high-speed operating condition,including auxiliary power units,air circulators,turbine generators,small generators and other turbine machinery due to the small size,high temperature resistance,low wear,low power loss and no fuel pollution.Gas-lubricated bearing-rotor system is the critical component of rotating machinery,the differences of performance of different types of rotors with gas-lubricated bearings support have a non-negligible influence on the overall system.Taking different gas-lubricated bearing-rotor systems as the objects,the performance of the nonlinear dynamic characteristics of rotor systems supported by different types of gas-lubricated bearings are studied in this dissertation.The influences of their respective specific structure parameters on the performance of gas-lubricated bearings-rotor systems are analyzed,the motion stability of rotor systems is improved through parameter optimization.The main contents of the dissertation are as follows:(1)The nonlinear dynamic characteristics of the rigid stepped rotor and the rod-fastened rotor systems’ are studied by taking the double and three fixing-pad gas-lubricated bearings as supports.The lubrication governing equation of fixing-pad gas-lubricated bearing is solved by block matrix iteration method.Considering the recovery force of the disk,the dynamic model of the rod-fastened rotor system is constructed.Taking rotational velocity as bifurcation parameter,the nonlinear dynamic characteristics and bifurcation behavior of rigid stepped rotor and rod-fastened rotor systems are studied,and the influence laws of position angle of fixing-pad and mass eccentricity are obtained.(2)The nonlinear dynamic characteristics of stepped rotor system are studied by using three tilting pad and fixing-tiling pad gas-lubricated bearings as supports.Considering the influence of flexure pivot on the swing of tilting pad,the dynamic characteristics of flexure pivot tilting pad gas-lubricated bearing with small perturbation are analyzed.The influence of the moment of inertia of tilting pad on nonlinear dynamic behavior of the fixing-tilting pad gas-lubricated bearing-rigid stepped rotor system is studied.Considering shear deformation,gyro effect,power transfer and axial torque,a nonlinear dynamic model of the flexible stepped rotor system is constructed.Based on different rotating velocities,bearing structure parameters and rotor mass eccentricity,the nonlinear dynamic response and bifurcation characteristics of tilting pad gas-lubricated bearing-flexible stepped rotor system are obtained.(3)Considering the influence of centrifugal growth of rotor on gas film thickness,the nonlinear dynamic characteristics of double-foil gas-lubricated bearing-rigid stepped rotor system are studied.According to the structural characteristics of the double-foil,the deformation model of the double-foil structure is established,and the dynamic characteristic coefficients equation of the double-foil gas-lubricated bearing is obtained.Considering the centrifugal growth of rotor and the deformation model of the double-foil structure,the coupling model of the gas film thickness is constructed,and the influence law of the centrifugal growth on static and dynamic characteristics of double-foil gas-lubricated bearing is analyzed.By applying disturbance compensation Newmark method,the nonlinear dynamic response of double-foil gas-lubricated bearing-rigid stepped rotor system is obtained.(4)In order to improve the computational efficiency,based on the rational function approximation and vector fitting method,a rational function approximation method is proposed to solve the transient gas film force and nonlinear dynamic response simultaneously.Based on the rational function approximation and inverse Fourier transform of dynamic characteristic coefficients,the rational function approximation model of gas-lubricated bearing is established,and the corresponding database of rational function coefficients is obtained.Coupling the rational function approximation model of the gas-lubricated bearing with the motion model of the flexible Jeffcott rotor system,an approximate fitting dynamic model of the gas-lubricated bearing-flexible Jeffcott rotor system is constructed,the complex nonlinear dynamic characteristics of the flexible Jeffcott rotor system is obtained.