Comparative Study On Exterior Noise Characteristics Of High-speed Train At Bridge Section And Embankment Section

With an increase of train running speed,the control of exterior noise of train has become an important issue in the development and operation of high-speed trains.The exterior noise of high-speed train varies with different forms of high-speed railway lines.In order to make an in-depth comparison and study on the differences in the characteristics of the exterior noise generated by high-speed trains passing through bridges and embankments and their internal mechanisms,in this thesis,a bridge section and a embankment section adjacent to the bridge one on the same line are selected,and the high-speed train noise test is carried out in a targeted manner.Through the combination of line test and numerical simulation,the characteristics of exterior noise of high-speed trains of these two sections are systematically compared.The specific content is as follows:(1)The pass-by noises test of the high-speed train passing through the bridge section and the embankment section are carried out.Based on the FFT-NNLS deconvolution beamforming algorithm,a microphone array with 78 channels is used to identify external sources of high-speed trains experimentally.Based on the test results of the the pass-by noise and the identification of the sound source of high-speed train,the noise characteristics of the high-speed train at the two forms of the bridge and the embankment are systematically compared and analyzed.The results show that under the same operating conditions,the pass-by noise of high-speed train running on the embankment section is 0.1 to 1.2 dBA higher than that of the bridge section,and this difference will enlarge with the increase of train running speed.For the distribution characteristics of sound sources of the vehicle,the prominent sound sources at the two sections have the same position,mainly in the pantograph and bogie area.In contrast,the noise of the bogie area of the bridge section is higher than that of the embankment section,and the noise of the surface area of the embankment section is higher than that of the bridge section.(2)Based on the test results of vehicle vibration noise,wheel-rail roughness and track dynamic characteristics,and simulation calculation,the cause of the difference in noise characteristics between the two lines is analyzed.When the train runs on the bridge section,the bogie area noise is higher than the embankment section,which mainly related to the higher rail roughness level of the test bridge.For the two sections,the significant frequency range of the difference of the noise in the bogie area is 400-2500 Hz.The influence of the under-rail foundation structure of the bridge and embankment on the rail vibration lies in the frequence range less than 200 Hz,which has less influence on the difference of the noise in the bogie area.Based on the exterior noise test of the high-speed train,the geometric sound line method is used to establish the simulation model of the external noise of the high-speed trains on the bridge section and the embankment one.The influence of ground reflection on the exterior noise of high-speed trains is investigated.It is found that during the train operation on the embankment section,the noise on the surface of the train body and the pass-by noise are higher,which are related to the ground reflection in the embankment section.(3)Based on the simulation model of the external noise of the high-speed trains,the influence of line structure changes on the exterior noise of high-speed trains is investigated.The results show that when train running at a speed of 300 km/h,the embankment height changing from 1 m to 8 m makes the noise of the standard point M2(25 m away from the track centerline and 3.5 m away from the top of the rail)decrease by 1.4 dBA.When the embankment height is higher than 8 m,the height has no effect on the standard point noise.When the height of the embankment is 2 m,the noise absorption on the ground is smaller,the noise of each field is higher.Compared with the fully sound-absorbing ground,the noise of the standard point M2 can be increased by 2.2 dBA when the ground is totally reflected.With an increase of the dip angle of the embankment,the noise level of each field point decreases gradually.The noise of the standard point M2 in the bridge section does not vary with the height of the bridge.When the height of the bridge is 10.05 m,the increase of the height of the collision wall from 0 m to 1 m can reduce the noise of each field point outside the vehicle by about 1 dBA.The relevant research results can provide reference for the development of high-speed train exterior noise evaluation standards,high-speed railway line selection design and noise control.