| It is recognized that noise pollution has become a serious problem as the progress of industrialization and urbanization,especially the hazard of noise pollution from transportation.Recently,the combination of new-type materials for noise absorption and the design of acoustic structure is becoming the main trend to improve the sound-absorption property of sound-absorption materials.In order to reduce the noise level in a tunnel,the sound absorption capacity and environmental tolerance of the material must be considered.Therefore,the inorganic noise-reducing material which is cement-based composite sound-absorbing material with rigid frame is chosen as the research object.With the investigation of the noise pollution in tunnels,the factors of the contribution of traffic noise in tunnels are found.And the influence of the noise in the tunnel is explained by analyzing the factors that affect the noise pollution in the tunnel.Several common acoustic models and their characteristic parameters for porous materials are compared.The test methods and theoretical reckoning methods of the acoustic parameters are described.The acoustic model(John-Allard model and Johnson-Lafarge model)suited for porous material of girid frame are found by discussing.Based on COMSOL Multiphysics which is a finite element software,the tunnel acoustic finite element model is established.The influence of the material on the noise of the tunnel model is obtained by simulating the tunnel with cement-based composite sound-absorbing material set on the tunnel wall.The simulation results show that the cement-based composite sound-absorbing material has an improved influence on the tunnel noise reduction.A variety of architectural sound-absorbing materials are selected to simulate the noise reduction of the tunnel model with different wall materials,and the comparison between the noise level(by A-weighted sound level and relative noise reduction)is analysised.The tunnel noise reduction capability of the cement-based composite sound-absorbing material is better at 500 Hz and 1000 Hz than others.With the simulation of different installing locations of the sound-absorbing material layout,it is found that the proportion of 4/5 installing with the material is better than the whole wall installing in the case of economy.If the installation of cement-material area is limited,considering installing on the middle area of the wall for sound reduction is needed.Simulation tests of cement-based composite sound-absorbing materials are carried out by simulating the standing-wave tube test with digital platform.The pore system and acoustic structure of cement-based composite sound-absorbing material are studied.It is found that the improvement of the pore structure can improve the sound absorption capacity of the material at the same frequency,but it is difficult to broaden the absorption frequency band.The acoustic structure can improve both the sound absorption frequency band and the sound absorption coefficient of the material.The cross section model of the tunnel is simulated.It is found that the coupling design of the wave-shaped structure,the multi-layer structure and the cavity structure can reduce the noise level in the tunnel model in the best efficience. |
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