Research On Adaptive Vibration And Noise Control Of Track Based On Dynamic Vibration Absorption Principle

As an important part of urban transportation network,rail transit has developed rapidly in recent years,and gradually bears daily transportation pressure of major cities.However,with the increase of operation years and the continuous development of urban underground space,the environmental vibration and noise caused by train operation becomes more and more prominent.As one of the typical application examples,the rail vibration damper(RVD)inherits the advantages of dynamic vibration absorber as an additional secondary system,which is easy to install and replace.It can also transfer and dissipate vibration energy from the main system through coupling resonance.In addition,the parameters such as mass,stiffness and damping can be designed to meet the requirements of vibration and noise reduction under different working conditions specificially.In view of the environmental vibration and noise problems caused by the actual train operation,this paper puts forward a design scheme of adaptive RVD,whose purpose is to suppress the noise radiation by controlling the structural vibration of track from the source.The main contents of this paper are as follows:(1)Dynamic modal of rail-RVD coupling systemA dynamic modeling method for finite non-periodic discrete supported beam is proposed.In this method,the beam element between two supports is modeled by segments,and then the modified mode function and natural frequency of discrete supported beam are obtained by different boundary conditions.Compared with the simplified mode used in original track dynamic model,the modified mode can accurately represent the discrete distribution characteristics of supports,which solves the problem that frequency information contained in the simplified vibration mode is inconsistent with actual situation.The application range of the original track dynamic model is also extended.Furthermore,a dynamic model of 60 rail-RVD system is built based on the modified mode superposition method.By comparing the dynamic response changes of system before and after installing RVD,it is demonstrated that RVD can effectively restrain 60 rail vibration and noise under the fixed frequency,movement and impact load.(2)Rail noise radiation modelThe rail noise is regarded as moving line sound source.And the rail noise radiation model is constructed based on the definition of line sound power.The calculation formula of mean square sound pressure at the observation point for a period of time is given to explore the correlation between rail noise and surface vibration velocity.Furthermore,the frequency relationship between noise and rail structural vibration is revealed by structure-acoustics coupling finite element model,which lays a theoretical foundation for reducing vibration and noise from source by RVD.(3)Integrated design of adaptive RVDStarting from the rail side at vibration source,a design scheme of RVD which can adjust the natural frequency adaptively according to the variation of external excitation frequency is proposed.The dynamic model is established based on Euler and Timoshenko beam theory,and the relationship between natural frequency of RVD and structural parameters such as the length of simply supported beam is also given.Further,by optimizing the structural parameters,the adaptive stiffness adjustment can be realized at high frequency resolution over a large effective working bondwidth in order to match the real-time frequency variation of rail resonance peak more accurately.After that,the principle prototype is designed and manufactured for different target objects(20a-channel steel and 60 rail).(4)Experimental research on vibration and noise reduction of principle prototypeThe experimental platform is built with 20a-channel steel and 60 rail as target objects to test the reduction effect of RVD on structural vibration and noise under fixed and variable frequency conditions respectively.Further parameter analysis is carried out on performance indexes such as frequency resolution and effective working bandwidth.The experimental results show that under fixed frequency excitation,the maximum amplitude attenuation of 20a-channel steel is 16.26 d B and the insertion loss(maximum sound pressure level attenuation)is 19.97 d B.While the maximum amplitude attenuation of 60 rail is 4.31 d B and the insertion loss(maximum sound pressure level attenuation)is 4.27 d B.The vibration and noise reduction effect of RVD is remarkable.Besides 60 rail,the relevant model and theory in this paper also has reference and application value for other engineering objects such as discrete supported beam structure.