Research On The Device With Wells On The Top Of Noise Barrier

Traffic noise pollution is increasingly serious caused by the traffic network becomes increasingly intensive and the flow and speed of the vehicles is increasing.At present,there are still many areas where the quality of the acoustic environment cannot meet the standard requirements,which has caused serious disturbance to the normal life of residents on both sides of the road.For traffic noise control,noise barriers have been applied widely in the world as a economic and effective measure,and the development of barriers with high noise reduction performance is a persistent goal in the research and development of barrier technology.At the present stage,an effective method to improve the acoustic performance of the barrier without significantly increasing the height of the barrier is to install a top device on the top of the barrier.A top device usually contains the acoustic mechanism to reduce the noise,and the structure is usually complicated.Although extensive research has been conducted on the top devices and a lot of results have been obtained,there is still a lack of guilding fruit for the development of the top device with wells.Therefore,this paper mainly conducts a research on the top device composed of the wells.The prediction of noise reduction effect of the barrier is an important work in the design stage of barriers.Based on the structure of the top device and the geometrical diffraction theory,with the consideration of the sound insulation of the main body of the barrier,a method for predicting the insertion loss of barrier with well on the top is proposed.The insertion loss calculated by the proposed method agrees well with the experimental results.The noise reduction effect of the barrier with wells on the top is compared with the noise reduction effect of the veritcal barrier and the barrier without wells on the top.The results show that the performance of barrier with wells on the top is excellent,especially in the middle and high frequency ranges.And the insertion loss of the barrier is mainly depends on the structure of the top device.The noise reduction performance of the top device is affected by parameters such as the depth and width of the wells.The top device composed of wells contains multiple technical parameters,such as the opening direction of the well,the depth of the well,the width of the well and the arrangement of the wells,and the noise reduction effect of the top device is closely related to these parameters.In order to investigate the effect of the design parameters to the noise reduction effect of the barrier.With different design paramenters,the noise reduction effects of barrier with wells on the top were calculated,experiments were also conducted in a semi-anechoic chamber,and the results show that,the opening direction of the well would affect the noise reduction effect of the barrier at the middle and high frequencies,when the opening direction of the well is vertically upward,it is beneficial to improve the noise reduction effect in the middle and high frequency range.Increasing the width of the well can improve the noise reduction effect of the barrier,the width of the well had better not be less than 1/ 3^1/2 of the depth of the well.The effect of the layout of the wells on the noise reduction effect is related to the location of the receiver,it is less important when the receiver located in the “dark area”.And the effect on the high frequency range is small when there are multiple wells on the top.When the well is close to the source side,it is more conducive to play its role in a wider area.When the top of the barrier is non-flat,the layout of the walls of the well would have a significant impact on the noise reduction effect of the barrier.The height of the apex of the wall of the well from the ground should be arranged in the order of increasing from the source side to the receiving side.In order to further improve the noise reduction effect of the top device,baced on the method of the diffraction of the acoustic,two structure improvement designs,namely the improvement of the top edge of the wall of the well and the improvement of the well,are proposed,which would improve the diffraction loss of the barrier.The recearch on the improved top devices show that,improvement the top edge of the wall of the well,the noise reduction effect of the barrier at high frequencies can be improved.And when the width of the well is greater than 0.12 m,the drum-shaped well could immprove the noise reduction effect of the barrier in a wide frequency range,especially in middle and high frequencies compared with a equal-section well.When the ratio of the opening width to the maximum width of the drum-shaped well is 1:2,the noise reduction effect of barrier with drum-shaped well on the top has an optimal value.Sound absorption material is normally adopted to improve the performance of the barrier.The noise reduction characteristics were calculated when barrier is under different conditions.The effect of the size and position of the sound absorption material on the noise reduction effect were analyzed.Full scale model was also conducted and experiments were carried out in a semi-anechoic chamber.The experimental results were in good agreement with the calculation results.The results show that laying the sound absorption material to the surface of the top device would improve the noise reduction effect of the barrier in middle and high frequency range.When the sound absorption material is partially adopted,it should be laid on the top of the surface and close to the source side.When the size of the sound absorption material is constant,compared with increasing the number of surface of laid,make the size of the sound absorption material on the surface of laying larger could obtain a better noise reduction effect.Top device consists of wells is studied in this paper.The insertion loss prediction method was proposed.The noise reduction characteristics and the effect of the design parameters of the wells to the noise reduction effect were investigated,as well as the effect of the sound absorption material laying on the surface of the top device.The improvement structure were also proposed.The research has practical significance for developing high-efficiency top device.