Study On Influence Of Temperature/Frequency Variation Characteristics Of Fasteners On Vibration And Noise Of Box Girder Structure In Rail Transit

The main structure providing rigidity and damping in fastener system is elastic backing plate.As viscoelastic damping material,its mechanical properties have obvious correlation between ambient temperature and excitation frequency.When a train passes through a bridge,vibration energy generated by wheel-rail irregularity excitation is transmitted to the bridge at the lower part through rail structures such as rail fasteners,which induces vibration of the bridge structure and thus radiates noise outward.In the past researches on vehicle-track-bridge coupling vibration and radiated noise of bridge structures,the stiffness and damping of fasteners are usually simplified by linear method,which leads to results that are not consistent with the actual situation.The purpose of this paper is to find out the influence law of temperature and frequency on the mechanical properties of fastener elastic pad through experiments,and to study the influence of temperature/frequency variation characteristics of elastic pad on the vibration and noise of rail transit box girder structure based on frequency domain algorithm,so as to further provide theoretical support and technical guidance for accurate and rapid prediction of vehicle-track-bridge coupling vibration and radiation noise of bridge structure and design of damping track.This paper takes WJ-7B fastener constant resistance elastic pad for high-speed railway as the research object,and adopts the method of combining experimental analysis and theoretical modeling to study the influence of temperature/frequency variation characteristics of WJ-7B fastener constant resistance elastic pad on vehicle-track-bridge coupling vibration and bridge structure radiation noise.The main work and achievements are as follows:(1)Through consulting domestic and foreign literatures,the dynamic characteristics of viscoelastic materials,vehicle-track-bridge coupling vibration and radiation noise of bridge structures at home and abroad are systematically summarized and summarized,and the research content and context are clarified.(2)Because the models used by scholars in the past cannot accurately describe the mechanical properties of rubber materials,in order to better characterize the temperature/frequency variation dynamic characteristics of the elastic pad of rail fastener,this paper combines the high-order fractional derivative FVMP model with the temperature-frequency equivalent principle to obtain the temperature/frequency variation dynamic mechanical model(TFDV model)of the elastic pad containing both temperature factor and frequency factor.Through the temperature scanning test of the elastic backing plate in the range of-60 ? 40?,it is shown that the dynamic parameters of the elastic backing plate have obvious low temperature sensitivity and high temperature stability.Combined with TFDV model,temperature change test data and genetic algorithm,a three-dimensional curved surface diagram of storage modulus and loss factor considering temperature and frequency changes is drawn.It shows that the trend of storage modulus and loss factor is larger at low temperature and high frequency and smaller at high temperature and low frequency within a certain temperature and frequency range.(3)The TFDV model established in(2)is substituted into the vehicle-track-bridge coupling vibration analysis model established by dynamic compliance method,and the vibration response of the vehicle and track-bridge system is solved by virtual excitation method,so as to calculate the influence of temperature/frequency variation characteristics and parameter frequency variation characteristics of the elastic pad on the random vibration response of the vehicle-track-bridge coupling system.(4)The dynamic characteristics of temperature/frequency variation of elastic plate of fastener have certain influence on random vibration of vehicle-track-bridge coupling.Considering the temperature/frequency variation of the elastic pad,the lower the temperature,the higher the energy storage stiffness of the elastic pad,the smaller the minimum value of the total dynamic compliance,and the frequency of the minimum value of the total dynamic compliance will shift to the high frequency direction;The vibration transmission attenuation rate of track-bridge system decreases with the decrease of temperature in low frequency band.The amplitude of vibration acceleration power spectrum of car body and bogie is basically not affected.Acceleration power spectrum of wheel pair,track-bridge and discrete spring force peak frequency of each connecting layer move to high frequency.The frequency-varying characteristics of the elastic plate parameters of fasteners have certain influence on the random vibration of vehicle-track-bridge coupling.The stiffness varies with frequency,the smaller the minimum value of total dynamic compliance is,and the frequency of the minimum value of total dynamic compliance will shift to high frequency.Frequency variation of loss factor will only reduce the dynamic compliance and phase angle amplitude near the peak value in high frequency band.Stiffness frequency variation causes the vibration transmission attenuation rate of track-bridge system to increase in high frequency band.Frequency variation of loss factor has little effect on vibration transmission attenuation rate of track-bridge system.The frequency variation of the parameters of the elastic backing plate has little influence on the amplitude of the vibration acceleration power spectrum of the vehicle body.Stiffness frequency variation causes the power spectrum of bogie vibration acceleration in this frequency band to increase in the middle and high frequency bands,and loss factor frequency variation causes the power spectrum of bogie vibration acceleration near the peak value to decrease.The frequency-varying characteristics of elastic pad parameters have the same influence on the vibration acceleration power spectrum of wheel-rail force,wheel pair,track-bridge and discrete spring force amplitude curve of each connecting layer.The frequency-varying stiffness causes the peak frequency of the power spectrum curve to shift to high frequency,while the frequency-varying loss factor causes the vibration response near the peak value to decrease.(5)The temperature/frequency variation of the elastic backing plate has great influence on the sound pressure level of each field point in the sound field of the bridge structure wheelset 1 position and the bridge mid-span position,and the influence rules are consistent.The lower the ambient temperature of the elastic backing plate of the fastener,the higher the dominant peak frequency of the sound pressure level of each field point moves to high frequency.This is because the lower the ambient temperature,the higher the stiffness of the elastic backing plate of the fastener,which leads to the larger overall stiffness of the track-bridge coupling system,thus affecting the high frequency migration of the sound pressure level of the field point of the bridge structure.The frequency variation of elastic pad parameters has a great influence on the sound pressure level of each field point in the sound field of the bridge structure wheelset 1 position and the bridge mid-span position,and the influence rules are consistent.The frequency variation of the fastener elastic pad stiffness has the greatest influence on the main frequency and amplitude of the sound pressure level of each field point,and the dominant peak frequency of the sound pressure level of each field point moves to high frequency.This is because the stiffness of the fastener elastic pad increases with the frequency,which leads to the overall stiffness of the track-bridge coupling system becoming larger,thus affecting the transfer of the sound pressure level of the bridge structure field point to high frequency.The influence of frequency variation of loss factor of fastener elastic backing plate on the sound pressure level of each field point is mainly reflected in the peak frequency band.This is because the loss factor increases slowly with the frequency variation,resulting in the influence on the sound pressure level of each field point is only reflected in the peak frequency band with higher noise intensity.