https://scholars.lib.ntu.edu.tw/handle/123456789/71968
標題: | 管壁引致聲源於管道聲場之主動控制 Active Control on the Acoustic Fields in Duct Using the Wall-Vibration Induced Acoustic Sources |
作者: | 陳宗志 Chen, Tsung-Chih |
關鍵字: | 主動聲場控制;管壁引致聲源;Active control;Wall-vibration induced acoustic sources | 公開日期: | 2009 | 摘要: | 噪音控制分為被動式及主動式兩種。而本文提出ㄧ種新的作法於主動管道噪音控制中,即是利用壓電片給予管道管壁一振動之激振力,藉由管壁振動使管道產生一與主要噪音聲源反向之聲波,進而達到下游聲壓衰減之目的。此作法不需要再準備第二聲源所需之設備(例如揚聲器或平板),僅需利用本身管道系統和壓電片,大大地節省了器材成本及設備所須的配置空間。 本文中,利用FIR(Finite Impluse Response)數位濾波器作為系統控制之主體架構並直接以訊號產生器產生之單頻或雙頻訊號作為控制之參考輸入,再利用LMS(Least Mean Square)演算法來即時修正濾波器之係數,以期能達到最佳的控制效果。 另外,會再分析由於無限長圓柱殼體振動所造成之聲輻射。 在結果方面,本實驗於各管聲幅射能力較佳之單頻率進行主動聲場控制時,皆能約有40dB左右之音壓衰減量;而對於各管聲幅射能力較佳之雙頻率進行主動聲場控制時,皆能有15~35dB左右之不錯的音壓衰減量,可見此方法之可行性。但當激振力為管道聲幅射能力較差之頻率時,則主動聲場控制的效果不佳。在最後的章節將會對其控制的效果作ㄧ探討,並加以討論。 There are two techniques in noise control,which are passive and active noise control.This thesis is to provide another approach to active noise control(ANC).It is to use a piezoelectric transducer(PZT) to excite the duct wall.The wall-vibration induced feedback sound wave can combine with primary noise to reduce the downstream sound pressure.Accordingly,only a duct and a piezoelectric tr-nsducer are wanted in this approach.Thus the cost and the space required for the apparatus to be wanted are saved much more. In experiment,we use a FIR digital filter as the main structure of the control system and meanwhile take a single-frequency or a dual-frequency signal as the reference input directly produced by a function generator.Weighting coefficients of the digital filter are adjusted by using LMS algorithm in order to achieve the best performance.Besides,the sound radiation by vibrating an infinite cylindrical shell will be analyzed. The result of this study shows great attenuation of downstream sound pressure level by about 40 dB will be obtained at some frequencies.Similar situation occurs for dual frequencies at which greater radiation from duct wall exists,the attenuation of downstream sound pressure levels by about 15~35dB is obtained.The actuality as discussed can demonstrate it is feasible to use wall-vibration induced source to adaptively active control on the sound transmissi-n in a circular duct. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/188994 |
顯示於: | 工程科學及海洋工程學系 |
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ntu-98-R96525067-1.pdf | 23.53 kB | Adobe PDF | 檢視/開啟 |
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