Study On Dynamic Tribology And Friction-induced Vibration Mechanism Of Water-lubricated Bearing System

Water-lubricated bearing systems are widely used in the transmission systems of ships,submarines,underwater robots and shaftless propulsor.With the development of water-lubricated bearing systems towards to the direction of low noise,long life,high-depth watertightness,low runout,and high-power density.In addition,due to the emergence of subversive technologies for ship power-shaftless propulsion systems,more stringent performance requirements are put forward for water-lubricated bearing systems.The study of the dynamic tribology mechanism model can optimize the comprehensive performances,such as lubrication,contact,wear,dynamic,and avoid the risk of the medium and high frequency noise radiation,which can improve the concealment of underwater weapons,shortening the combat radius,and enhance the combat capability.Therefore,for the water-lubricated bearing system under dynamic service conditions,it is of the great theoretical and engineering significance to develop a multi-mechanism fusion mathematical model for water-lubricated bearing under dynamic service condition,including lubrication mechanics,contact mechanics,thermodynamics,wear theory,rotor dynamics and friction-induced vibration theory,This thesis primarily focuses on the basic theoretical modeling of tribology,dynamics,and friction-excited vibration of water-lubricated bearings.The basic theoretical study for water-lubricated bearings under dynamic service condition has been carried out,including transient wear,transient 3D temperature rise,transient mixed thermoelastohydrodynamic and friction-induced vibration.The main research work of the thesis includes:1The transient mixed thermoelastohydrodynamic model for water-lubricated bearing system is developed by coupling the generalized average Reynolds equation,Kogut-Etsion asperity model,transient 3D energy equation.Based on the model,the transient numerical predictions of hydrodynamic lubrication,asperity contact and 3D heat transfer can be achieved.2The transient wear and mixed thermoelastohydrodynamic coupling model of the water-lubricated bearing system is proposed by integrating the friction fatigue and wear model into the transient mixed thermoelastic-hydrodynamic model.The evolutions of lubrication,contact,thermal behavior and wear characteristics of water-lubricated bearings during service is studied,and the importance of 3D heat transfer characteristics in the prediction of transient wear of water-lubricated bearings is demonstrated.The influence of key structural parameters,surface characteristic parameters and material parameters of water-lubricated bearings on the coupling performance of transient wear-hybrid lubrication are systematically studied,which provides a theoretical guideline for predicting the transient wear performance of water-lubricated bearings and optimization of anti-wear performance in actual working conditions.3With consideration of the wear morphology,the transient tribo-dynamic model of water-lubricated bearing system is developed by integrating the transient mixed thermo-elastohydrodynamic model and the rotor dynamics model.Based on the second type of dynamic tribology model,the study on the tribo-dynamic coupling performance modeling of water-lubricated bearing systems under multiple operating conditions is performed.The interactions between the dynamic characteristics of the rotor and the mixed lubrication force of the bearing interface are revealed.The influences of rotor starting mode,starting parameters and transient mixed lubrication force on the starting characteristics of water-lubricated bearing are studied,and the applicability of the disturbance method in the prediction of tribo-dynamic performance of eccentric rotors is assessed.The critical speed and minimum effective clearance empirical formulas of grooved water-lubricated bearings during the start-up are proposed,and a structural optimization scheme for improving the anti-shock performance of water-lubricated bearings is proposed.4Based on the above proposed dynamic tribological models,the friction-induced vibration model of water-lubricated bearing system under mixed thermoelastohydrodynamic condition is established by further integrating the interface random displacement disturbance,water film stiffness,water film damping,and elastoplastic contact stiffness.Based on this model,the friction-induced vibration characteristics of water-lubricated bearings under mixed thermoelastic fluid conditions are simulated.Through the complex modal analysis method,the friction self-excited vibration amplification area and the friction vibration stability of the water-lubricated bearing system under multi-conditions and multi-parameter conditions are studied,and the critical parameters/works of friction self-excited amplification vibration and friction noise of the water-lubricated bearing Condition interval.It provides theoretical guidance for water-lubricated bearings to avoid friction-induced instability and medium and high frequency noise radiation.5The wear performance equivalent experiment among different water-lubricated materials is performed at the friction and wear tester manufactured by RTEC company(made in USA),and the dynamic tribology experiment for water-lubricated bearing was conducted at the comprehensive performance experimental platform.Based on the wear test,the transient wear characteristic among different water-lubricated materials under mixed friction condition are measured.Based on the dynamic tribology experiment,the dynamic axis orbit and friction coefficient of the water-lubricated rubber alloy bearing are tested.Subsequently,the experimental and the theoretical results are compared to further demonstrate the validity of the present model.