| Rotor systems are widely used in various fields of rotating machineries,such as steam turbines,turbomachineries and generators.In the operation of rotating machinery,unhealthy vibrations of rotor systems will reduce the fatigue life of rotating machineries,and even lead to the failure of mechanical parts and safety accidents.Bearing is the key supporting part of the rotor system.Error and dimension design parameters of bearings significantly affect the vibration characteristics of the rotor systems.Due to the effect of the unbalanced mass and gyroscopic moment,the rotor will occur bending deformation.Rotor system vibration responses between various components are different.Rigid rotor model is difficult to study the rotor vibration characteristics of different components.Therefore,it is urgent to study the multi degree of freedom of flexible rotor-bearing systems dynamics modeling,which can provide an analysis method to study vibration responses of rotor system components.The contact loads between raceways and rolling elements have time-varying excitations on the rotor with the influence of manufacturing errors.However,the indirect influence of manufacturing errors on the vibration characteristics of rotor is unknown.Therefore,it is urgent to study the dynamic characteristics of rotor-bearing systems with manufacturing errors,which can provide a reference for the study of rotor system vibration characteristics.Bearing internal relative sliding and friction can change lubrication properties.Moreover,the movements and the stress distributions of bearing internal components are complex.Therefore,it is difficlut to predict bearing vibration response characteristics.And it is hard for the bearing friction mathematical model to consider the effect of time-varying excitations.Therefore,it is urgent to carry out the research of bearing friction and lubrication model considering time-varying excitations and the study of the effect of installation errors on vibration characteristics of rotor-bearing systems.It can provide a new reference for the prediction of dynamic characteristics of rotor systems.The main research contents of this paper are as follows:(1)The rigid model can not obtain complete vibration responses.To overcome this problem,a six dgrees-freedom dynamic model of flexible rotor systems considering rotor stiffness is proposed.The vibration responses of different nodes on the rigid and flexible models are studied.The vibration behavior differences of rigid and flexible models at different rotational speeds are analyzed.(2)The indirect effect of waviness of bearing raceway and rolling elements on the vibration characteristics of rotor components is unclear.To solve this problem,a six dgrees-freedom dynamic model of flexible rotor systems considering waviness and friction monments is established.The effect of waviness amplitudes on vibration characteristics of the rotor system is studied.The mathematical relationships between waviness orders and vibration characteristic frequencies are analyzed.(3)The internal friction mechanism and lubrication characteristics of bearings are unclear.The effect of dynamic loads on vibration characteristics is unclear.To overcome these problems,a time-varying friction torque calculation method considering elastohydrodynamic lubrication,elastic hysteresis and differential sliding is proposed and a six dgrees-freedom dynamic model of flexible rotor systems considering time-varying friction moments and lubrication is established.The effect of rotor offset and radial clearance on the amplitude-frequency characteristics of the rotor system with time-varying friction moments is studied.The relationship between bearing stiffness and positions and the critical speed of the rotor system is analyzed.(4)To solve the vibration optimization design problem of rotor systems,an optimization method for vibration characteristics of flexible rotor systems is proposed.The finite element model of the rotor system is established to study the natural frequencies and mode shapes of the rotor system.The frequency characteristic equation and dynamic model of the rotor system are established to determine the optimal combination of bearing supports,which can solve the vibration optimization problem of the rotor system. |
PDF Full Text Request