波浪與潛沒平板之交互作用

Interaction of Water Waves and a Submerged Flat Plate

李政賢(Cheng-Hsien Lee) ； 陳志欣(Chin-Hsin Chen) ； 黃清哲(Ching-Jer Huang)

《海洋工程學刊》 6卷2期 (2006/12) Pp. 41-61

https://doi.org/10.6266/JCOE.2006.0602.03

摘要

本文發展數值模式求解二維時變的Navier-Stokes方程及完整的自由液面邊界條件，探討波浪與潛沒平板的交互作用。數值計算域中放置一直推式造波板來產生入射波，下游採用延伸網格避免波浪反射。本文模擬波浪通過平板時所得6個不同位置的水位時序列資料，經與Kojima et al.(1994)的實驗結果比較非常吻合，證明本數值模式的準確性。在確認模式的準確性後，本文探討不同波浪與平板幾何條件下，高頻波生成、反射率與透射率、及平板附近流場的特性。此外，為了呈現平板與一般常用的潛堤的差異，上述部份結果也與波浪通過矩形潛堤的結果比較。本文數值結果顯示當波浪通過平板時，平板下方會產生類似震盪流的流況；震盪流的相位若與平板兩端的波浪相位不同時，會在平板四周產生複雜的流場。此外，平板長度控制得宜時，波浪能量可以藉由流場經由平板下方往離岸方向傳遞，達到比潛堤更好的反射波能的效果。

關鍵字

潛沒平板 ； 高頻波 ； 反射率 ； 渦流

並列摘要

A numerical model was developed to solve the unsteady, two-dimensional Navier-Stokes equations and the exact free surface boundary conditions for investigating the interaction of water waves and a submerged flat plate. A piston-type wavemaker was set up in the computational domain to generate the incident water waves. The accuracy of the numerical model was verified by comparing the numerical results of water surface elevation with the experimental data. After having verified the accuracy of the numerical model, the wave and flow fields produced as waves propagate over a submerged flat plate were discussed in terms of the higher harmonics, the reflection and transmission coefficients, and the vortices. The corresponding results for a submerged breakwater were also provided for comparing the hydrodynamic efficiency between a plate and a breakwater. The numerical results show that as waves propagate over a submerged flat plate, the flow beneath the plate behaves like an oscillatory flow. This flow induces complicated flow fields if it is not in phase with the waves at the two edges of the plate. Furthermore, at appropriate plate lengths, the wave energy can be transmitted offshore through the flows beneath the plate, and thus results in a better wave reflection than in the case of a submerged breakwater.

並列關鍵字

Submerged flat plate ； Higher harmonics ； Reflection coefficients ； coefficients ； Vortices