Research On The Sound Wave Propagation In Phononic Crystal Pipe

Air pipe systems are widely used in industrial system,aerospace and military fields,which are important components of central air-conditioning,large-scale gas pipe,and ventilation pipe systems.Due to the interference from the external factors,some noise can be transmitted in the pipe inevitably,which will affect the comfort of the equipment operator and lead to a certain effect on the normal function of the equipment.Furthermore,long-term noise interference may cause serious damage to the internal equipment structure.With the continuous development of the engineering technology,higher requirements for pipe noise control are also put forward.The traditional measures in pipe noise control are limited by space and size which cannot inhibit the propagation of low-frequency noise effectively.It is an urgent issue to be addressed on how to realize the noise control of low-frequency,wide-band and strong attenuation in pipe systems.In recent years,the design idea of Phononic Crystals(PC)is introduced into pipe design,and the control of noise by using the special properties of PC has been widely studied.The concept of PC is proposed by analogy with Photonic Crystals.It refers to a class of materials/structures with elastic band gaps composed of periodically arranged units of specially designed artificial structures.When the elastic wave propagates in the PC,the propagation of the wave in the band gap will be restrained,and the elastic wave control at a specific frequency can be realized by the band gap characteristics of the PC.Combining the design idea of PC with the pipe,the corresponding acoustic band gap will be generated when propagating in the pipe due to the interaction of periodic cells,thus achieving the effective control of noise.The main work of the paper is as follows:1.Based on the modal matching theory,the two-dimensional transfer matrix method for calculating the band gap of the PC pipe is improved,which provides an effective algorithm for analyzing the acoustic wave propagation characteristics of the PC pipe.2.The acoustic propagation characteristics of the PC pipe consisting of expansion chamber with extended inlet/outlet are studied.Firstly,the two-dimensional transfer matrix method is used to calculate the transmission loss of the expansion chamber with extended inlet/outlet,then the results are compared with those of the one-dimensional method and COMSOL method to verify the previous algorithm.Furthermore,the acoustical properties of the muffler are investigated.Finally,the band structure of the PC pipe consisting of expansion chamber with extended inlet/outlet is calculated and analyzed by the two-dimensional transfer matrix method,and the convergence of the two-dimensional algorithm is also studied.Based on this,the effect of the parameters on the band gap and band gap coupling is analyzed.3.A new type of Helmholtz Resonator(HR)muffler with built-in diaphragm and insert tube is designed,and the acoustic wave propagation characteristics of this kind of PC pipe are studied.Firstly,the transmission loss characteristics of a new type of HR muffler are investigated.Then the band structure characteristics of the PC pipe with periodically attached new type of HR are analyzed based on the two-dimensional transfer matrix method.The mechanism of band gap formation is revealed,and the effects of structural parameters on band gap and band gap coupling are analyzed.4.The samples are fabricated,and the experimental test system of the PC pipe is established to verify the acoustic propagation characteristic of the new HR PC pipe.In conclusion,the two-dimensional transfer matrix method for calculating the acoustic band gap of the PC pipe is improved in this paper.The band structures of PC pipe with two different structures are calculated and studied.The formation mechanism of the band gap and the effect of the structure parameters on the band gap and the band gap coupling are analyzed in detail.All the work is expected to provide new ideas and ways for band gap calculation and structural design in PC pipe.