Design And Noise Reduction Performance Of A New Composite Phononic Crystal Window

With the acceleration of urbanization,the urban transport system becomes more and more dense and complex.The psychological and physical harm of traffic noise to the residents living around urban railway lines,high-speed rail lines and expressways is becoming more and more prominent.In order to mitigate traffic noise,the most popular way is to install noise barriers.Nevertheless,it usually has large installation space and poor natural ventilation and daylighting which prevent them from being installed directly on the facade of civil or commercial buildings as part of a window.To overcome these issues,the present study introduces a new concept of composite sonic crystals(SCs)window structure which can be used to balance noise attenuation,natural daylighting and ventilation performance.Numerical and experimental studies have shown that the SCs window structure exhibits good noise attenuation performance in the frequency range of urban traffic noise(frequency range: 630-1000 Hz).In order to meet the design requirements of civil or commercial buildings,effort has been made to reduce the thickness of SCs window by optimising the structure and arrangement of the sonic crystals together with installing supplementary sound-absorbing materials.The main work and results of this study are as follows:(1)Structural optimization of SCs windows.By applying the acoustic module of COMSOL Multiphysics as a numerical experiment platform,the Taguchi method and ANOVA analysis were combined to optimize the structure and arrangement parameters of the locally resonant SCs whithin the SCs window.According to the noise attenuation mechanism of the local resonant SCs structure,the geometric structure parameters were firstly analyzed and the critical design parameters were determined.For the optimization,the numerical experimental matrix was designed using the Taguchi method,and the S/N ratio and ANOVA analysis were carried out to determine the optimal configuration of the 3-rows of SCs window.The results show that the optimized 3-rows SCs window design has achieved the significant noise attenuation performance improvement in the overall traffic noise frequency range.This indicates that the proposed structural optimization method can contribute to the design of applications applying similar SCs.(2)Design and numerical simulation of a new concept of composite sonic crystal window.In order to further improve the noise attenuation performance of the optimized SCs window,a new concept of composite SCs window was proposed to install supplementary sound-absorbing materials on SCs to obtain better noise attenuation performance.Firstly,five common soundabsorbing materials were selected,namely felt,melamine foam,EVA foam,copper foam and nickel foam.The sound absorption coefficients of the sound-absorbing materials were obtained by the impedance tube measurement experiments.After a comprehensive analysis,the felt material with a thickness of 5 mm was selected as the supplementary sound-absorbing material to be adhered to the inner wall of the SCs.COMSOL simulations were carried out to investigate the overall noise attenuation performance of the new composite SCs window by importing the sound-absorbing material parameters obtained from the experiment.The result shows that the noise attenuation performance of the composite SCs window was improved compared to the original 3-rows SCs window,and the noise attenuation performance in the frequency range 630-1000 Hz was even better than that of the 4-rows SCs window.(3)Experimental study.The original and optimized SCs window prototypes were fabricated according to the original and optimized design parameters respectively.Experimental measurements of the noise attenuation performance of the original and optimised window prototypes were carried out by building an experimental platform in a semi-anechoic chamber.The reliability of the numerical simulation is firstly verified by comparing the experimental and numerical results.The composite SCs window performed better noise attenuation performance than the 4-rows SCs window in the frequency range of 630-1000 Hz.The composite SCs window can attenuate the traffic noise by 4.87 d BA,6.49 d BA,5.01 d BA and 5.35 d BA for the frequencies of 630 Hz,800 Hz,1000 Hz and the frequency range 630-1000 Hz,respectively.