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題名 | 有限寬度潛式矩形立方體之三維繞射效應=Three-Dimensional Wave Diffraction by a Submerged Cuboid of Finite Width |
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作者 | 陳誠宗; 李兆芳; | 書刊名 | 海洋工程學刊 |
卷期 | 11:2 2011.12[民100.12] |
頁次 | 頁149-169 |
分類號 | 443.31 |
關鍵詞 | 三維邊界元素模式; 繞射; 潛堤; 立方體; Three-dimensional boundary element model; Wave diffraction; Submerged breakwater; Cuboid; |
語文 | 中文(Chinese) |
中文摘要 | 本研究藉由所建立三維邊界元素模式,探討三維海洋結構物受波浪作用的繞射問題,以及一般利用二維模式計算三維問題的適用性。所考慮問題為線性波浪通過潛式矩形立方體,控制方程式為Laplace方程式,邊界積分式為由Green定理推導得到。數值模式中使用常數元素作計算,配合使用自由水面、結構物表面、底床和輻射邊界條件代入矩陣式求解。為驗證數值模式的正確性,本文數值模式計算結果與MacCamy and Fuchs(1954)所提出波浪通過突出水面直立圓柱繞射理論解,以及與波浪通過圓形淺灘問題的試驗結果(Williams et al., 1980)作比較,比較結果相當一致,顯示所建立模式的正確性。計算過程中也說明當輻射邊界置於八倍水深處時,計算結果已足以正確呈現。對於所探討波浪通過矩形潛堤繞射問題,計算例中矩形寬度逐步加大,隨同模擬領域也逐漸加大,但是潛堤兩端繞射現象繼續存在。在矩形立方體寬長比為3:1,潛堤前方堤寬中間點的反射波可以用二維模擬的結果表示,但是堤後方繞射聚焦現象,則無法以二維呈現。 |
英文摘要 | In this study a three-dimensional boundary element model is developed to calculate wave diffractions by submerged rectangular cuboids, and the criteria of whether three-dimensional effects can be simulated by two-dimensional ones are investigated. In the numerical model, a boundary integral equation is derived using the Green's Identity for the governing Laplace equation. All the boundary conditions are then implemented into the solution matrix equations. Constant element is used in the calculation, and a simple grid generation program is developed to facilitate the numerical computation. To verify the numerical model, the present results are compared with the diffraction theory of a vertical circular cylinder (MacCamy and Fuchs, 1954), and experimental results of circular shoal by Williams et al. (1980), respectively. The comparisons show favorable agreements which indicate accuracy of the present model. Computational results also demonstrate that the position of radiation boundary placed at eight times the water depth is enough to obtain accurate results. In the computation of wave diffraction by a rectangular cuboid, diffraction effects on two ends of the structure exist persistently. For the ratio of width to length of the rectangular cuboid being 3:1, wave reflection at the centerline in front of the structure can be duplicated by the two dimensional results. However, wave diffraction and focusing behind the structure cannot be calculated by a two-dimensional model. |
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