Nonlinear Dynamic Behavior Of Wear Bearing

Bearings play a vital role in rotating machinery systems,which involve many nonlinear factors.As an inevitable defect in the bearing structure,wear has a non-negligible influence on the nonlinear dynamic behavior and dynamic performance characteristics of the bearing,which affects the stability of the entire system,and can induce a direct or indirect economic loss.In this paper,worn sliding bearings and foil bearings are analyzed by using the non-linear dynamics theory and method.The main contents are as follows:Based on the elastohydrodynamic theory,the nonlinear dynamic behavior of worn oil-lubricated bearing is explored,and the dynamic response including the trajectory of the axis center,the accelerated speed,and the film thickness is analyzed.The discrete iterative method and implicit Euler method are combined to solve the Reynolds equation and dynamic equations simultaneously.The wear effect of bearing subjected to a step load is also examined in detail.It is found that the orbit and the stabilized point show significant variation with the worn depth,and the wear effect is also quite related to the rolling speed and the direction.The pressure and the change rate of film thickness increase when wear gets deeper.And the pressure and orbit vary with the depth of wear under the step load excitation.The worn model is represented by the worn depth in the top foil of oil-lubricated foil bearing.The Iordanoff model is used to solve the foil stiffness and the friction coefficient is modified based on the VALVFC model considering the friction interface.The wear effects on pressure,film thickness,and orbit were studied through numerical calculations.The perturbation method is used to calculate the dynamic parameters,and the dynamic response of bearing is analyzed by the nonlinear dynamics theory.The results indicate that the wear enhances pressure and makes axis trajectory converges faster,but reduces dynamic stiffness and damping,which decreasing bearing capacity and stability.The response of journal center changes with parameters to be periodic,multi-periodic,and almost periodic,which represents a highly nonlinear behavior.The nonlinear dynamics problems of gas-lubricated foil bearings are investigated.Reynolds equation for compressible gas of gas foil bearing is solved by adopting the Alternating Direction Implicit method(ADI).Motion parameters are evaluated by solving the motion equations,and orbits of the journal center are obtained by adopting Newmark-? method and iterative scheme in the time domain.The dynamic stiffness and damping coefficients of the bearing were obtained by the perturbation method,and the wear effects on the nonlinear dynamic response of the system are studied with different system parameters.The results show that the wear decreases the stiffness and damping coefficients.The analysis reals highly nonlinear behavior with the periodic,multi-periodic,and quasiperiodic motion of the journal center,and system motion behaviors like bifurcation with a lower imbalance value when wear occurs.