Research On Sound Field Distribution Of Active Control Of Low-Frequency Traffic Noise In Highway Tunnel

In recent years,with the rapid development of highway traffic construction,more and more highway tunnels,especially super long tunnels are built in our country.More and more attention has been paid to the traffic noise pollution in the tunnel.The sound pressure level(SPL)of the noise is more than 90dB in the long highway tunnels.The noise-reducing pavement and the sound absorbing material sprayed on the tunnel wall are the traditional passive noise-reducing techniques in the highway field.The active noise control methodology is an aspiring attempt to solve the noise control problem in the highway tunnels.In order to determine the applicable conditions,the realization method and the effect of the active noise-reducing technology in the highway tunnel,the active noise-reducing model in highway tunnel with asphalt concrete pavement was constructed,through method of combining theoretical derivation and finite element imitation.The effects of noise source frequency,active noise source location and other factors on the noise-reducing effect of the tunnel were analyzed.The active noise reduction equipment was researched and developed.The active noise reduction experiment was carried out The simulation results were consistent with the experimental results of the active noise-reducing tests.Main research conclusions are:(1)The experimental results show that the tunnel asphalt concrete pavement noise concentrated in 80Hz?150Hz band noise sound pressure level of the highest value is 90dB?100dB,very few cases there will be 130dB.(2)A multi-point synchronous acquisition system has been developed independently to achieve precise location of sensors in space and collect and store acoustic signals simultaneously at multiple measuring points.It can only collect direct noise and avoid reverberation noise.The computer controls the opening and closing of sensors.The data collected by sensors are stored in the wireless acquisition front end data box.After that,the stored signals are transmitted to the computer automatically through WiFi.(3)According to the active sound source computer programming,circuit theory and practical tunnel environment of independent research and development of application in highway tunnel,directional sound sensor installed on the active acoustic source,receiving direct noise acoustic information to the control box,reverse acoustic signal control box based on the information.The release of acoustic noise control loudspeaker.Real time noise control has been realized,and there are no related products at home and abroad.(4)When the source frequency is low,the distribution of sound pressure in the tunnel is uneven,and the phenomenon of acoustic pressure increasing or decreasing in the whole area will appear in the whole tunnel.With the sound source frequency increases to a certain extent,the field distribution in the tunnel tends to be stable and uniform,appear at the same time sound field in the tunnel wall and close to the disturbance of road surface within a certain range,the acoustic disturbance area,the tunnel wall or ground reflector is near the sound wave reflection has just completed the superposition with the direct wave interference by other smaller waves,so the reflected wave and direct wave superposition phenomenon is very obvious.(5)When the location of the noise source and the noise reduction area are known,the optimal placement of the active sound source can be determined,according to height limit,the regulation that active sound source should be located on the axis of the tunnel section,the space position relation formula of noise source,active noise source and noise reduction position.(6)The lower the noise frequency is,the better the noise reduction effect is.The active noise-reducing technology has a significant effect on the noise-reducing effect in highway tunnel with asphalt concrete pavement,whose noise frenquency is about 100Hz.(7)The active sound source is arranged on the axis of the tunnel section.When noise frequency is 125Hz,the noise-reducing region can be realized at the ear height of the workers in the walking area.The noise-reducing range is 6-10dB.The achievement can be referred for the subsequent implement of the active noise control devices in the highway tunnel.