Design Of Noise Reduction In Phononic Crystal Pipe

In the interior of aircraft and ship,there is a huge and complex pipeline system,which is usually used to transfer mass flow,momentum flow or energy flow.For air pipe system,air is the main medium.Noise features a long distance transmission and a slow decaying under the low-frequency.From this point,it poses a strongly bad effect on the equipment so to weaken the combat effectiveness.For the sake of the quietness of the equipment,the design has become a problem to solve urgently for the manufacture of equipment.Phononic Crystal(PC)is periodically composite structures or materials that have band gap(BG)characteristics and can suppress propagation of sound waves in the BGs.In this paper,the PC's BG theory is applied to the design and the application for air pipe noise reduction.The PC theory is adopted to design the periodical pipeline structure,and then to produce air pipeline with acoustic BGs.Therefore,we can control the characteristics of sound waves within a specific frequency,achieving the goal of low-frequency wideband noise reduction.The main work of this dissertation include:1.The study analyzed the acoustic characteristics the typical mufflers and their PC pipes.The acoustic characteristics of two typical mufflers,Helmholtz muffler and expansion chamber muffler,are presented.The further work exhibits the acoustic characteristics of the muffler under different structural parameters The transfer matrix method is performed to investigate the BG characteristics of two kinds of PC pipe installed in Helmholtz muffler and expansion chamber muffler,respectively.And then give an analysis on the characteristics of BGs under different lattice constants and different structural parameters.2.The work conducted a design for a combined cell PC pipe with low-frequency BGs,and then explored further for the characteristics of its acoustic BGs,and the conclusion is verified by experiment results.Based on the study of typical mufflers,the design is performed for the PC pipe with the combined cell of Helmholtz muffler and expansion chamber muffler.The analysis is given for the formation mechanism of acoustic BGs and parameter regulation.The influence of the distance between the two mufflers on the characteristics of the acoustic BG is verified,so to demonstrate the effect of this PC pipe on the low-frequency wideband noise reduction.3.A new type of perforated muffler with big hole is designed,which has a considerable reduction in low-frequency noise.The acoustic characteristics of this new muffler and its PC pipe are analyzed by Comsol Multiphysics simulation software.The acoustic characteristics of BGs in this PC pipe are investigated.Then the study performs a further discussion about the influence of the muffler structural parameters on the characteristics of BGs.Finally,the effectiveness of this new muffler in low-frequency noise reduction is illustrated by practical engineering test.It shows the fact that this combined cell PC pipe can achieve the wideband low-frequency noise reduction.This paper explored the suppression of low-frequency sound wave in PC pipe,which provides a new theoretical basis and technical support for wideband low-frequency noise control of air pipeline system.