Dynamic Response Analysis And Vibration Control Of Oil Film Instability In Sliding Bearing-Rotor System~*

Sliding bearing-rotor system is the core component of many rotating machinery.Some Lunreasonable factors in design or operation may lead to oil film oscillation.According to the statistics of relevant departments,most of the high speed rotating machinery have some low frequency vibration components and some of that have oil film oscillation.If self-excited vibration occurs in the unit,the vibration amplitude will increase,which will lead to damage to the unmt to vary ing degrees.Moreover,because of the lar ge number of uncelrtain non-linear factors accompanying the operation of the unit,it is difficult to explore the internal mechanism of the vibration fault of the unit by traditional methods.Therefore,in order to reveal the influence of different non-linear factors on the stable operation of hydroelectric generating untnts,it is necessary to analyze and study the non-linear dynamics of sliding bearing-rotor system.Based on the theory and method of non-linear rotor dynamics,this pap er establishes the rotor dynamic model and differ,ential equation of motion under the action of oil film force support of non-linear short bearings,calculates the non-linear oil film force by numerical integration method,and then synthetically uses the bifurcation diagram of bearings and rotors,the amplitude diagram of rotors,Poincare section,axis trajectory diagram,time-domain waveform diagram and spectrum diagram to analyze the rotor.The influence of different system parmeters on the dynamic response of the sliding bearing-rotor system is studied,especially the influence of the change of oil film temperature on the vibration characteri stics of the system when oil film whirl and oil film oscillation occur at the second critical speed,and the effect of the sliding bearing plus NES on the vibration reduction effect and stability of the system.The main research contents and results are as follows.(1)Aiming at the problem of oil film instability of rotor system caused by strong non-linearity of oil film force in sliding bearings,a formula for calculating the non-linear oil film force of short bearings is derived from the Reynolds equation of oil film lubrication and under the assumption of Gumbel oil film boundary condition.At the same time,the mathematical model of sliding bearing-rotor system and the system differential equation are established(2)The vibration characteristics of a sliding bearing-rotor system are studied.The influence of the change of system parameters on the vibration characteristics of the system is analyzed.The results show that the increase of the mass eccentricity of the rotor is beneficial to the stable operation of the rotor at low speed,on the other hand,the increase of the mass eccentricity of the rotor will not prevent the oil film instability of the system at double critical speed,but will reduce the amplitude of the oil film whirl and oil film oscillation of the rotor;the journal clearance of the bearing also has a greater impact on the system,and the reduction of the sliding bearing clearance is also conducive to the stable operation of the system(3)By using Walther's empirical formula of viscosity-temperature,the dynamic response of the axle sliding bearing-rotor system under the change of lubricant temperature is analyzed,taking into account the change of lubricant viscosity when the lubricant temperature changes.The results show that when different lubricants are used,the lubricants with larger temperature-viscosity coefficient have better inhibition effect on the quasi-periodic and chaotic motion near the second critical speed of the rotor;the increase of lubricant temperature is beneficial to the stability of the rotor system in the low speed range,but the rotational speed region corresponding to the oil film whirl and oil film oscillation will be prolonged near the second critical speed.It is not conducive to the operation of the rotor-bearing system(4)In order to reduce the vibration of the rotor system by the non-linear energy Sinks(NES)?the dynamic response of the sliding bearing-rotor system is analyzed by considering the additional NES damper with cubic stiffness.The results show that the NES with cubic stiffness can only play a positive role in the attenuation of the amplitude of motion of the rotor-bearing system within a specific speed range,but it will not change the motion pattern of the system,the vibration attenuation of the bearing-rotor system will change sensitively with the change of the mass and damping of the NES mass block in a small parameter range,and the variation of parameters beyond this range has little effect on the effect of vibration reduction.