利用輻射模態之聲場輻射分析

Abstract

以往輻射模態通常是應用在主動式結構聲場控制（ASAC），在本研究中我們將使用輻射模態來分析聲場輻射。而本篇的聲場輻射分析主要分成兩部分，其中之一是聲功率的探討，另一個是聲場傳遞的探討。經由我們的模擬分析，我們發現以輻射模態為理論基礎的聲功率量測法，可以獲得相當好的結果。另外在低頻時，我們可以使用前面幾個主要輻射模態來簡化聲場計算之複雜度。當然在低頻時這樣處理並不影響準確性。我們也以實驗來驗證這個方法，並且與ISO的方法來比較。我們發現這個方法的效果比ISO具有較好的準確性與便利性。尤其是這個方法並不需要特殊的量測環境。另外我們也將輻射模態應用到聲場的傳遞探討。我們發現使用傳遞矩陣來重建該處之聲壓與傳遞距離和聲源頻率有關。當傳遞距離在遠場且聲源頻率低時，我們亦可用前面幾個主要的輻射模態來簡化整個傳遞矩陣，並且整個傳遞矩陣的維度不需太大。反之，若是傳遞距離在近場且聲源頻率高時，則需高維度的傳遞矩陣和需較多的輻射模態來重建該處之聲壓。

In the past, the Radiation modes were usually applied in active structural acoustical control. In this paper, we apply the radiation modes to analysis acoustic radiation. The acoustic radiation of this paper is divided into two parts; One is the analysis of estimating sound power, and another is the analysis of acoustic propagation. Through our simulation and analysis, we find that the radiation modes being applied in estimating sound power can obtain good approximation. Otherwise in low-frequency range, we can apply the first several dominative modes to simplify the complexity of acoustic calculation. Certainly, it does not reduce the accuracy of system. Furthermore, we also verify our method through experiment and compare it with ISO 3745. We find that the result of our method is better than ISO 3745. Especially, our method does not need special rooms, i.e. semi-anechoic chamber. In addition, we also apply the radiation mode in analyzing the far-field propagation. We find that reconstructing the sound pressure has relationship with the distance of propagation and the frequency of sound source. When the distance of propagation is in far field and the frequency of sound source is low, we can apply the first several modes to reconstruct the sound pressure and propagation matrix do not need high dimension.