三維水下音傳局部卡氏座標模式

Abstract

海洋環境複雜多變，導致我們很難得到任何時刻下的實際聲場，所以我們希望可以藉由模擬計算，來了解各種不同環境對聲場的影響。 由於圓柱座標適合用來描述聲音傳播現象，所以大多數的模擬計算都是以圓柱座標系來表示，但圓柱座標的弧長會隨距離而增加，若我們想要了解沿某一聲音傳遞路徑下，離聲源較遠處的區域內環境對聲波傳遞的影響，則可能會因計算間距過大導致無法完整描述此環境，甚至使得角度的耦合效應消失，但卡氏座標的間距並不會隨距離而增加。 本篇論文內容是以FOR3D(圓柱座標模式)為基礎，加入局部卡氏座標轉換而得之數值模式，以解決特定方位角之音傳路徑的局部卡氏座標模式，其適用範圍為5°以內。

As the complexity of the marine environment leads to the difficulty to get the actual sound field at any moment, so we hope to understand the influence of a variety of different environments on the sound field by numerical simulation. Cylindrical coordinate is adaptable to describe the phenomenon of sound propagation, so most of numerical model are based on cylindrical coordinate. However since the arc length in cylindrical coordinate is proportional to range, for receiving position far away for the source, the azimuthal coupling effect would not be incorporated for the distances between two neighboring grid points in the azimuthal direction are too large. In Cartesian coordinate, the arc length would not increase as the range increases. Numerical models in Cartesian coordinate could avoid this drawback as mentioned above. This thesis presents a modified version of FOR3D, which solves the acoustic field in local Cartesian coordinate system along a radial direction. The limitation of the azimuthal range is about five degrees.