Research On Characteristics Of Interior Noise And Its Key Influence Factors For A Metro Vehicle In Tunnels

Acoustic environment in trains can directly affect passengers' riding comfort.Unlike high-speed trains running on the ground surface,metro trains are mainly running in tunnels.The interior noise level will be higher in a tunnel because the noise sources are reflected by the tunnel wall and the car body for many times,which in turn further decrease the passengers' riding comfort.Therefore,it is of great significance to control the interior noise when metro trains running in tunnels.In this paper,the main works are listed as following:(1)The current state and progress of the study on interior noise characteristics of metro trains and the spatial sound field characteristics of tunnels are summarized,future research directions on the interior noise control when metro trains running on ground surface,or running in tunnels with different boundary conditions are discussed.(2)Based on the line test,the differences of interior noise spectrum when metro trains running in tunnels or on the ground surface are studied,the significant frequency bands are both located in 315-1600 Hz under two running cases.Moreover,when the train running in a tunnel,the frequency band of the interior noise in 315~1000 Hz is more significant than the ground surface.In addition,the regional contribution rates of noise sources under these two running cases are analyzed.Results show that when the train running in tunnels,the distribution area of the significant sound sources will be expanded,the contribution rate of the upper part of the car body will be increased.(3)Based on the geometric sound ray method,the prediction model of sound field in a tunnel is established,the validity of the model is verified according to the line test data.The acoustic response of the car body is obtained.Comparisons between the two running cases on the distribution characteristics of the sound field of the car body and the cross section of the train are made.Results show that when the train running in a tunnel,the maximum sound pressure level is still located in the bogie area,and its sound pressure level distributes uniformly on the cross section of the train,however,when the train running on the ground surface,the sound energy can be propagated to the semi-infinite surroundings of the two sides thus the noise sources have little influence on the sound field of the train.(4)Based on the statistical energy analysis(SEA)method,the simulation models of vehicle interior noise under two running cases are established,and the validity of the model is verified by comparing with the experimental results.On this basis,contribution rates of the power input of the acoustic cavity subsystems at the end of the passenger compartment and their difference under the two running cases are analyzed.Results show that when the train running on the ground surface,the percentage of the air-borne sound is about 61.3%,mainly from the floor,while in a tunnel,the percentage is about 83.5%,mainly from the side wall.But the floor and roof areas are the main source of the structure-borne sound.(5)The influence factors such as blocking ratio,cross section shape and sound absorption of a tunnel wall on vehicle interior noise are investigated.The sound pressure level at the end of the passenger compartment decreases with the decrease of the blocking ratio of the tunnel;the circular tunnel is 1.2 dBA smaller than the rectangular tunnel when their cross-sectional areas are equal.With the increase of the area of sound absorbing materials,the noise reduction efficiency of the end of the passenger compartment decreases gradually,the noise reduction is about for 4.3 dBA when the sound-absorbing materials are laying on the ballast and the lower part of the tunnel wall,however,5.3 dBA when all the materials are applied.The sound pressure level at the end of the passenger compartment when the sound absorption material laying on the lower part of the tunnel wall is lower than that laying on the middle and upper part.In addition,based on acoustic sensitivity method,the effects of vehicle factors such as sound insulation and vibration of the car body,sound absorption of interior train under the two running cases are analyzed.When the train running on the ground surface,the noise at the end of the passenger compartment has the greatest sensitivity to floor sound insulation and floor vibration;however,when the train running in a tunnel,the noise at the end of the passenger compartment has the greatest sensitivity to door sound insulation and side wall vibration.There is little difference between the sensitivity of the noise to the sound absorption coefficient under the two running cases.Relevant analysis results can provide references for interior noise control when the train running in tunnels.