三維數值模擬之格點重訂技術

Abstract

FOR3D程式經常被使用於計算三維的聲場環境。由於其座標為圓柱座標系統，故隨著計算距離遠離聲源時則計算格點間距會逐漸變寬，以至於當計算到達遠場時，無法算得在水文或地形上方位角耦合(θ-coupling)的效應，因此會從原本三維計算變成以N×2D來做計算，若地形或水文變化過大時則不易呈現出聲場能量分佈。此外，在遠場計算時格點數量的不足亦會造成解析度變差。因此吾人想利用在遠場時以內插的方式增加格點，再以內插後的聲場作為初始聲場向下一個聲場繼續作計算，如此一來即使計算距離再遠因為格點增加的關係，使得方位角耦合(θ-coupling)的效應不會被忽略較能呈現聲音能量的分佈情況，且在遠場的解析度亦可改善。本文的重點在於當計算距離超過所設定的門檻距離時，如何做內插增加格點使得聲場的三維效應完整呈現。

FOR3D has been used to simulate sound propagation. The system of FOR3D is cylindrical coordinate. While it computes away from source, the distance between two grid points become too large to catch θ-coupling effect and the 3D transfers to Nx2D . Moreover, the resolution becomes low because of less grid points. The main idea to improve the limitation is increasing grid points in the far field. Hence, the θ-coupling terms would not be ignored. The study in this thesis is how to decide the re-grid distance and how to deal with the sound field after re-grid.