Study On Characteristics Of Micro-pressure Wave And Propagation Of Initial Compression Wave In Rail Transit Tunnels

When the head of train enters into the tunnel,the initial compression wave will radiate outward when it propagates along the tunnel with local sound speed to the exit of the tunnel,forming micro pressure wave at the exit of the tunnel,and the sound explosion generated when the intensity is high will have a serious impact on the surrounding environment and residents of the tunnel.The strength of the micro pressure wave is directly proportional to the pressure gradient of the compression wave at the exit of the tunnel.In order to estimate the strength of the micro pressure wave reasonably,it is necessary to accurately predict the initial compression wave and the characteristics of intensification and attenuation in the process of propagation in the tunnel.In this thesis,based on the study of the initial compression wave generated by the 160~200km/h medium speed maglev,400km/h high-speed wheel-rail and 600km/h high-speed maglev train entering the tunnel from three-dimensional distribution to one-dimensional plane wave,a one-dimensional compressible unsteady non-isentropic flow model is used to improve the generalized Riemannian variable characteristic line method.The characteristics of the initial compression wave propagation in the tunnel under different conditions are studied,and the pressure gradient intensification in the compression wave propagation is proposed for the maximum critical length,the basic characteristics of the intensification and attenuation of the compression wave propagation in the tunnels of medium speed maglev,high speed wheel-rail and high speed maglev train are obtained,which provides the basis for further study of the micro pressure wave strength.In this thesis,the solid angle model formula and the Ozawa correction formula are derived,and the Ozawa correction formula is optimized and improved during the derivation process.The Ozawa correction formula and the optimized formula are programmed using MATLAB software,and verified its correctness.Finally,the relationship between the compression wave at the exit of the medium speed maglev,high speed wheel-rail and high speed maglev train tunnel and the micro pressure wave outside the tunnel is studied by using them.The main conclusions are as follows:(1)When the train enters the tunnel with different blocking ratios at the same speed,the maximum pressure amplitude and the maximum pressure gradient of the initial compression wave increase with the increase of blocking ratio.When the train enters the tunnel with the same clearance area at different speeds,the maximum pressure amplitude corresponding to the initial compression wave will increase with the increase of train speed,and the maximum pressure gradient will also increase with the increase of speed.(2)Under different conditions,when the initial compression wave generated by the train entering the tunnel propagates in the long tunnel,the peak pressure of the compression wave decreases with the increase of the propagation distance,and the maximum pressure gradient corresponding to the compression wave increases first and then decreases,and the increasing trend becomes steeper with the increase of the train speed.(3)When the speed of the medium speed maglev train is in the range of 160~200km/h,the critical length of the compression wave propagation increases with the train speed from 160km/h to 200km/h and also increases from 2km to 4km.Comparing the critical length of the 400km/h high-speed wheel-rail train and the 600km/h high-speed maglev train passing through the non-buffer structure,it can be found that as the speed increases from 400km/h to 600km/h,the corresponding critical length also decreases from 5km to 2km.(4)When the speed of the high-speed maglev train is 600km/h,although the opening buffer structure can greatly reduce the maximum pressure gradient of the initial compression wave,for the long tunnel,due to the intensification of the compression wave during the propagation process,the open buffer structure actually has a significant weakening effect on the alleviation of the micro pressure wave,and it is recommended that the possibility of mitigation of intensification such as shafts should also be taken.(5)In addition,this thesis further studies the distribution characteristics of the micro pressure waves of the three train models under different conditions in tunnels of different lengths.Taking the micro-pressure wave control standard as the constraint condition,the specific values of the critical tunnel lengths under different conditions are obtained,which provides a certain practical reference for engineering design.