運用一維波動方程式特性之主動式噪音控制器設計

Abstract

本論文針對管路系統的主動式噪音消除，提出新的控制方法。本文利 用二階的偏微分方程式來描述一維的管路系統，並且引入兩側邊界條件的 影響，噪音源及控制聲源皆考慮為點聲源的型式。在控制法則設計方面， 本論文分別探討控制聲源為單極點聲源及雙極點聲源兩種情況下的設計方 式，控制法則設計的目標意欲在控制聲源處造成全反射的效果，進而在下 游位置達到漸進消音的目的。本文所採用的是前饋式的控制架構，噪音源 訊號的取得乃是利用兩顆前饋麥克風，由於只使用一顆控制喇叭，因此所 有的實驗皆是採用單極點聲源的控制法則。在實際執行上，喇叭及麥克風 的動態並非理想，所以必須將兩者之影響考慮在控制器的設計程序中，有 鑑於此，本論文利用喇叭與麥克風位置的巧妙安排，識別出兩者的動態， 並利用順向識別與逆向識別的技巧求得其反動態。實驗方面，本文嘗試在 靜態流場及風扇噪音兩種不同情況下的噪音消除，在靜態流場實驗，與所 預期的相同，消音的結果相當顯著；在風扇噪音方面也獲得相當程度的消 音。 In this thesis, a new controller design approach is proposed and experimented for active noise cancellationin in duct.The plant considered is governed by a linear one- dimensional second-order PDE with two boundary conditions. All disturbance and control sources are considered as point- type. In control laws design,monopole and dipole control sources are discussed.The objective is to design control laws such that the wave generatedby the noise source is blocked(total reflection) at the control source location. It means the response at any downstream location will go to zero asymptotically. The controller consists of a feedforward block with two microphones which serve as a noise observer.Because only one control loudspeaker is used,all control laws implemented are monopole-type. In reality, the dynamics of loudspeaker and microphones are not ideal, thus their effects must be introduced into the procedures of controller design. In order to get the characteristics of loudspeaker and microphone, the identification procedure is designed by carefully choosing the locations of measurement microphones.And then applying the techniques of forward and backward identificaton to find their inverse dynamics. Experimentation on static-flow field and practical fan noise are investigated. In the first one, as expected, the effectness of the controller is prominent. In the second case, the result is also satisfied.