Design And Noise Reduction Performance Of Periodic Sound Barriers Based On Nested Structures

While expressway has brought great benefits to people’s lives,the traffic noise has a serious impact on the health and quality of life of residents living along route.The noise reduction effect of traditional sound barriers is based on the law of "mass density".And the noise reduction effect mainly depends on the surface density of the screen material.It is not possible to control different traffic noise frequency bands.And the effect of controlling low frequency noise is poor.Therefore,a new type of sound barrier with "new principle and new material" is urgently needed.In this study,the Bragg Scattering,the Cavity Resonance and the Porous Absorption were coupled as the theoretical basis.It was used to design structural parameters and study noise reduction performance of periodic sound barriers with nested structures.Firstly,the traffic noise spectrum was measured at the site of Guangzhou-Shenzhen Expressway.The main frequency characteristics of traffic noise on the Guangshen Expressway were obtained.Secondly,the influence of structural parameters and material types on the band structure of sonic crystals was comparatively studied.And finally,finite element simulations were carried out from the twodimension infinite model to the two-dimension finite model and finally to the threedimension infinite model.Then the noise reduction effect was combined for optimal structural design.The structural parameters of the periodic noise barrier based on nested structure were proposed.The main conclusions of this study are as follows:(Ⅰ)Under certain conditions,traffic volume and proportion of small cars are positively correlated with SPL(sound pressure level)of traffic noise.When driving on asphalt,small vehicles mainly generate medium and high frequency noise.And medium and large vehicles mainly generate medium and low frequency noise.The main nosie frequency band of traffic noise is315-2500 Hz.And the traffic noise SPL of the Guangzhou-Shenzhen Expressway only has a peak at 1000 Hz.(Ⅱ)For nested structures,the number and width of complete band gaps in a triangular lattice arrangement of scatterers is significantly greater than in a square lattice arrangement.And the cavity inside the scatterer can effectively improve the control of low frequency noise.(Ⅲ)In the two-dimensional infinite period model,the noise reduction effect increases with the number of scatterer rows in the 400-800 Hz.So the number of scatterer rows for sonic crystal sound barriers should be more than 3.And the filling of the scatterer with a porous sound absorbing materials enhances the noise reduction performance of the barrier in the frequency bands 100 to 400 Hz and 800 to 2500 Hz.(Ⅳ)In the three-dimensional infinite period model,gradient height layout of scatterers can enhance the control of noise in the 400-800 Hz.And the porous sound absorbing materials inside the internal open circular tube plays a major role in noise reduction.Compared to the non-filled porous sound absorbing materials,the noise reduction in the 100-2500 Hz increases by 2 to 27 d B(A).And then compared to compared to the traditional metal plate noise barrier and the traditional lightweight concrete noise barrier,the nested structure-based sonic crystal noise barrier has a significant improvement in noise reduction in 125-2500 Hz.The noise reduction effect can be improved by 10-28 d B(A)especially in 200-500 Hz and 800-2500 Hz.The nested structured periodic noise barrier can couple Bragg scattering with other noise reduction theories to achieve targeted noise reduction and control of low frequency noise.At the same time,it can be combined with the natural road surroundings to produce a good landscape and aesthetic benefits.So it has broad potential for application and promotion in the field of traffic noise control.