可變孔徑槽孔型設計於管道聲場內消音性能分析

Analysis on the Acoustic Performance for the Changeable Aperture Design in Duct

張嘉良(Chia-Liang Chang)

指導教授 ： 陳國在

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.11147

摘要

本研究主要探討，當聲音經過槽孔結構時，槽孔相關的幾何參數對聲音衰減的影響。因此本文希望以模擬軟體為平台，孔徑大小為參數，設計出一可變孔徑的共鳴型消音器，其功能端視環境需求，藉由旋轉內管來改變孔隙率，以得到不同的最高消音頻率及頻帶範圍。
本研究利用聲場模擬軟體，針對槽孔型圓管進行非耦合情況下之穩態流場 ，進行模擬計算分析。假定流體為理想非黏性介質，聲音在管道中以平面波傳遞，將模擬數據、J.W. Sullivan and M. J. Crocker文獻以及一簡單型槽孔消音器之實驗結果做比較，以驗證模擬軟體之可靠度。
根據上述成果，本研究持續對不同孔隙率之消音能力進行模擬分析，顯示孔隙率越高消音頻帶越往高頻移動，且當孔隙率超過約30%時，整體的消音頻帶的移動趨勢漸緩。
本文之研究結果顯示，依據所需消音頻帶，透過模擬軟體可計算出適當之孔隙率，並設計出多種配合的可變孔徑之共鳴型消音器，而達到不同噪音環境的最佳消音效果。

關鍵字

傳遞損失 ； 共鳴型消音器 ； 孔隙率 ； 有限元素法 ； 可變孔徑

並列摘要

This study is to examine the influence of structure parameters on the acoustic attenuation when the air passes through perforated muffler. Therefore this dissertation thesis is hopefully to use simulation package as basis and the perforation aperture of silencer as parameter to design some resonant muffler with variable-aperture such that its function can match the environmental requirements. Accordingly it is possible to determine the frequencies and the frequency criteria at extremely acoustic attenuation by turning inner duct to change the corresponding porosity.
This study is to use the acoustic simulation software-LMS Virtual.Lab to make acoustic simulation on a perforated duct in a uncoupled steady fluid flow. Here, the fluid flow is assumed to be ideal and non-viscous, and the plane wave propagation in duct is also assumed. To verify the reliability of simulation software, the comparison of the simulation results with that of study worked out by J.W. Sullivan and M. J. Crocker is also made in this study.
Based on the results as obtained, this study continually makes simulation in progress on the acoustic performance of silencer with various porosities. The corresponding result clearly shows the frequency at the extreme attenuation shifts higher for greater porosity of perforation. The above situation will become more smoothly when the perforated porosity of silencer is greater than 30%.
The result of the dissertation thesis is clearly to show that it is possible to calculate by using acoustic simulation software an appropriate porosity of perforated silencer for some required performance at the expected frequency. Accordingly, the design of resonant muffler for changeable perforation to reach extremely acoustic attenuation in various environments can be expectant.

並列關鍵字

transmission loss ； resonant muffler ； porosity ； finite element method ； variable-aperture

參考文獻

[4] 林士淳, “可變容積消音器消音能力之模擬分析,” 生物產業機電工程研究所, 台灣大學, 台北, 2010.

[1] L. L. Beranek, “Noise and vibration control,” New York; McGraw-Hill, pp. 362-405, 1971.

[2] 劉仁超, “可變容積式共鳴消音器之設計,” 生物產業機電工程研究所, 台灣大學, 台北, 2005.

[3] M. L. Munjal, Acoustics of ducts and mufflers with application to exhaust and ventilation system design, New York: John Wiley & Sons, 1987.

[5] D. D. Davis, “Theoretical and experimental investigation of mufflers with comments on engine-exhaust muffler design.,” 1954.