Optimization And Experimental Study On The Top Form Of Urban Elevated Road Noise Barrier

With the gradual improvement of urban integrated multidimensional transportation network,urban elevated road system brings ever-growing contraction between traffic noise pollution and unbalanced and inadequate development.As one of the most significant approaches to reduce overhead road noise pollution which has been proved in theory and practice that the top design of noise barrier has the advantages of intensive space occupation,lower construction cost and rare efficient in noise reduction compared with the improvement of noise barrier body.Therefore,this paper combines the advantage theory of the top design of noise barrier.The top design was optimized to improve the low frequency noise reduction performance of the barrier and take advantage of the structural characteristics rather than the material characteristics.In the first part of the paper,by summarizing the theoretical research progress of noise barrier such as geometric diffraction boundary improvement,acoustic soft surface cavity improvement and Schroeder diffuser improvement,the research and optimization of parameter design based on QRD type diffuser top and the cavity modification based on optimal diffraction boundary Y type are selected as the main research directions: For the design and optimization of the top of QRD diffuser,the influences of independent variables such as chamber width,design order,design frequency and cycle number on the effective frequency of diffuser are summarized,so as to establish the components with design frequency of 400 Hz and order of fifth or seventh order as standard type.Meanwhile,folding transformation and sequence number coefficient transformation are applied to the standard type.Virtual.Lab boundary element was used to simulate the sound field at the top of diffuser,and the difference of noise reduction performance before and after the reconstruction was preliminary detected.The third part is based on the dominant geometric diffraction type Y highlighted in the research,using its structural cavity for cavity transformation,derived Y-shaped derived top,such as Y-1l,Y-3l,Y-3x and tree structure,and compared the performance of the derived structure with the top foundation type,such as T-shaped,Y-shaped and vertical.The top of the sound barrier is regarded as the starting point of the virtual sound source that the noise acts on behind the barrier,and the directional diagram of the top sound pressure level is used to reflect the directional changes of each type of top to the sound source,so as to preliminary detect the optimized quality of the top.Finally,the 1:10 scale model was used to predict the insertion loss of various tops in multiple areas and multiple measuring points under the condition of the sound source of the elevated road.The results show that the comprehensive noise reduction performance of the Y-derived tree structure is the best,and the average improvement of the tree structure is 3.81～4.84 d B compared with that of the isometric vertical structure at measuring points,and the main noise reduction frequency is the low-frequency part of 100～400Hz.Both the folding improvement and coefficient improvement at the top of the QRD model can achieve the same overall noise reduction level as the standard model in the range of 100～2k Hz,and its dominant frequency band is mainly concentrated in the middle and low frequency,achieving similar effects with a smaller volume,which can provide a simplified design idea for engineering practice.