Research Of Interference Device At Top Of Near-rail Low-height Noise Barrier For Urban Rail Transit

Urban rail transit has the advantages of convenience,safety and so on.While the noise resulted from it has a serious negative impact on the daily life of residents along the line.So reducing the noise of urban rail transit has become an urgent problem to be solved.Setting noise barriers is an effective way to reduce the noise in its route of transmission.However,there are serious problems of noise barriers,such as blocking line of sight,affecting the beauty and safety and so on.In addition,the noise barrier cannot attenuate the medium and low frequency noise of urban rail transit.In addition,it will cause multiple reflections of acoustic waves between the noise barrier and body of the train,which will weaken the effect of noise barrier.Laying porous acoustic-absorbing material can effectively solve these problems.This paper replaces the traditional noise barrier with near-rail low-height barrier.By establishing the simulation prediction model about noise reduction effect of noise barriers for urban rail transit,this paper evaluates the noise reduction effect of noise barrier with different structure types and acoustic absorption conditions.In addition,this paper compares and analyzes four types porous acoustic absorbing materials,rock wool,foam glass,superfine glass wool and expanded perlite.The influence of acoustic-absorption track to noise reduction effect of the noise barrier is considered.Based on these researches,the interference device at the top of the noise barrier is designed to further improve noise reduction effect of noise barrier.This paper mainly carries out the following research work:(1)First,there is a review on the background and significance of the research on noise of urban rail transit and noise barriers.And the development of acoustic absorbing materials or structures is introduced.This paper investigates on the research methods of noise barriers.At last,the application prospects and research directions of low-height near-rail noise barriers for urban rail transit are discussed.(2)The simulation prediction model about noise reduction effect of noise barriers for urban rail transit is based on boundary element method.The two-dimensional geometric boundaries of train body and track are considered in this model.Besides,the multiple reflections of acoustic waves between train body,track and noise barriers are considered in this model.There is an assumption that the ground was rigid reflecting surface.And the noise source of wheel/rail noise is simplified to line source.Based on the measured data,the accuracy and reliability of results from the simulation prediction model are tested and verified.(3)From the amplitude of insertion loss,the spectral characteristic and the acoustic field distribution,the noise reduction effects of low-height near-rail noise barriers with different height,head shape and acoustic absorption conditions are investigated.In addition,this paper compares and analyzes four types porous acoustic absorbing materials,rock wool,foam glass,superfine glass wool and expanded perlite.The influence of acoustic-absorption track to noise reduction effect of the noise barrier is also considered.The results are achieved as follow: each 0.5 m increase of the height of the noise barrier will cause 1.6 dBA increase of average noise reduction.The installation of inverted L-type / T-type / Y-type head shape can further increase the average noise reduction of the noise barrier by 2.2~2.7 dBA.Furthermore,adding the acoustic absorbers to the interior side of noise barrier will increase the average noise reduction by 7.2 dBA.If the screen of noise barrier is covered with superfine glass wool,the average insertion loss will reach 12.1 dBA.Besides,acoustic-absorption track can increase the average noise reduction by 7.6~10.1 dBA.By analyzing and comparing the noise reduction effects of each scheme,this paper propose a composite scheme,which is based on material-structure integration.Adding the acoustic absorbers to the interior side of 2.0 m high vertical / L-type / T-type / Y-type no-absorption noise barrier,as well as to the track structure,the average insertion loss will reach 20.4 / 20.3 / 20.9 / 20.8 dBA.It can be seen that installing different head shaped at the top of 2.0 m high vertical noise barrier,which has acoustic absorbers over the interior side of noise barrier and the track structure,has little influence on the noise reduction effect.(4)Based on the mechanism of interference silencing,a U shaped interference device at the top of noise barrier is designed to improve the noise reduction effect of the composite scheme.The effects of the U shaped interference device with different depth,width and thickness on the noise reduction effect investigated from the amplitude of insertion loss,the spectral characteristic and the acoustic field distribution.At the same time,the influence of acoustic absorbers over the U shaped interference device is considered.The results are achieved as follow: the devices,whose depth are 42.5 / 53.1 / 212.5 / 270 mm,increase the average noise reduction by 0.4~0.9 dBA.Each 12 mm increase of the width of the device will cause 0.18 dBA increase of average noise reduction.While the thickness of the device has little effect.By analyzing and comparing the influence of different structure types on noise reduction effects,this paper proposes a composite device,and investigates on the influence of the composite device to the noise reduction effect of the composite scheme.It can be seen that the composite device can increase the average noise reduction by 4.8 dBA.Related results in this paper have theoretical and engineering guiding significance for the design of low-height near-rail noise barrier for for urban rail transit.