The Optimized Design of Broadband Sound Absorption Structure using Simulated Annealing

Abstract

For traditional passive sound absorbing structure to absorb low frequency noise the structure is usually thick and has a small sound absorption bandwidth Therefore this study intent to improve the shortcomings of the traditional sound absorbing structure Mainly focuses on designing sound absorbing structures with small thickness high average sound absorption and broadband sound absorption Aiming at the low frequency range of 300~3000 Hz which is sensitive to human ears The simulated annealing method is used to optimize the size of the sound absorbing structure Two broadband sound absorbing structures are proposed in this research The first structure consists of five serial connected straight circular tubes with the optimized frequency division section and two quarter-wavelength tubes in parallel (SA_SPT) The circular section is changed to a rectangular section and folded in space to reduce structure thickness; The second structure is composed of four parallel quarter-circle micro-perforated plates optimized with segmented frequency and combined with two pancake structures (SA_MPP-Pan) We design the optimized size of various sound absorbing structures (quarter-wavelength tubes serial connected tubes micro-perforated plates) based on acoustic theory and simulated annealing method And calculate the sound absorption coefficient of the optimized structures in the impedance tubes with COMSOL Multiphysics and compare with the theoretical prediction value The influence of cross-sectional shape on the sound absorption characteristics of serial connected tubes and pancake structures is also discussed Finally the acoustic impedance tube measurement system is set up and the sound absorption coefficient of the structure is measured by the two microphone method For the two design structures the micro-perforated plate is made of aluminum plate with laser processing and the rest are manufactured by 3D printing The measurements are verified by comparing with the numerical simulation results From the results of numerical simulation and experimental measurement it is found that the second structure composed of micro-perforated plates and pancake structures has a very good sound absorption effect in the target frequency range and the average sound absorption coefficient in the experiment is 0 82 With a structure thickness of only 7 15 cm it can absorb low frequency noise with a wavelength of about 1 m and can be widely used in indoor and outdoor buildings

Date of Award	2020
Original language	English
Supervisor	I-Ling Chang (Supervisor)