| Because rail transit has the characteristics of large traffic volume,it is widely used in urban transportation in various countries,which is of great significance for solving traffic problems.With the increasing amount of urban rail construction every year,its noise will be a key issue that hinders its sustainable construction and development.The tunnel is an important part of the urban rail transit of Chongqing and other cities.When the subway train passes through a special underground tunnel environment,the vehicle sound source radiates noise outward,and the wall surface reflects in the nearly closed space,while the tunnel space section structure is mainly Divided into a rectangular section and a multi-center arc-cut surface,the structure of the reverberation sound generated in the tunnel is 10~20dB higher than the sound pressure outside the tunnel,the reverberation noise will last for about 10s~20s,and the vehicle leaving the tunnel is at the tunnel entrance.The noise formed nearby still affects the surrounding residents or passengers.Therefore,the finite element model of the noise sound field in the tunnel is created to obtain the tunnel sound field characteristics of different sound source locations,which provides a theoretical basis for the active noise control in the tunnel at the beginning of the tunnel construction.Secondly,starting from the passive noise reduction control measures,the tunnel is targeted.The noise generated by the free sound field rail transit vehicles and the noise reduction effect of different structural sound barriers have engineering value and practical significance for studying the increasingly serious noise pollution problems of rail transit tunnels.The main research work is as follows:(1)Study on noise field characteristics of urban rail transit tunnel noiseAccording to the characteristics of each component structure in the tunnel,the formation mechanism and influencing factors of noise are analyzed.The tunnel model was established by SolidWorks,and the distribution of sound field in the tunnel when the position of the vehicle sound source was changed was calculated by the finite element method in the acoustic analysis software Virtual.Lab.The distribution characteristics were studied.The research results show that when the train runs in a single-hole tunnel and the frequency of the sound source is 50Hz~400Hz,the overall sound pressure value of the train is 3m laterally from the centerline of the tunnel.When the vertical position is increased to 0.5m,the overall noise pressure is 0.5m.The value is lower.When the train runs in a double-hole tunnel,the relative distance of the sound source is from 3.5m to 7m.As the distance between the two line sources becomes larger at each sound source frequency,the overall sound pressure value of the sound field in the tunnel becomes smaller and then becomes larger.When the relative distance of the sound source is 5m,the sound pressure value of the sound field in the tunnel is the lowest.(2)Analysis of acoustic basic theoryBased on the basic theory of acoustics and Huygens-Fresnel theory,the principle of noise reduction and the factors affecting the noise reduction are analyzed from the three directions of reflection,diffraction and transmission.The theory of noise finite element calculation is discussed.The calculation principle and formula for the insertion loss of the sound insulation sound barrier.(3)Study on noise reduction performance of sound barriers with different top structuresThe finite element model of free sound field of sound barrier was established by using SolidWorks.The influence of train body on the insertion loss of sound barrier was analyzed.The noise reduction performance of 12 different top structure acoustic barriers was compared.The research shows that when the sound source structure sound source frequency range is 50~160Hz in the low frequency band and the peak frequency appears at 160 Hz,the 0.5m circular sound barrier has the best noise reduction effect,followed by the top camber 30° sound barrier and the top length.2mT type sound barrier,1m high,60° dip Y-type sound barrier. |
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