裙礁流場之數值分析與消能特性之探討

裙礁為一種典型之珊瑚礁型式，主要由珊瑚礁灘(reef flat)和珊瑚礁坡(reef slope)所組合而成。其中珊瑚礁灘通常存在於較淺之海岸邊並且毗鄰陸地，其坡度較礁坡為平緩，可對波浪有消能效果。珊瑚礁坡離海岸較遠，坡度亦較為陡峭，因波浪由深水段傳遞到較淺之珊瑚礁灘上時經常直接造成波浪反射和伴隨碎波之產生。為了深入了解能量消散機制，本研究透過理想化珊瑚礁之實驗與數值模擬來探討其流場特性。在數值模擬方面，採用Large-Eddy Simulation (LES) 紊流模型並搭配Volume of Fluid (VOF) 法，為精準描述實驗室造波機所產生之入射波，本研究使用moving-solid algorithm (MSA)模擬造波機推板之運動，並針對無ridge之案例進行三維數值分析。其結果顯示，數值模擬與實驗比對良好，自由液面和半水深之流速比對中，流速誤差均於5%以內。在沒有ridge之不同前斜坡坡度之案例中顯示，1:10之前斜坡能量消散率較1:1前斜坡之能量消散率大12%。在沒有ridge不同之靜水深給予相同之波浪條件下，靜水深之改變對能量消散率並無太大之影響，靜水深0.4公尺之能量消散率僅較靜水深0.5公尺之能量消散率大1.2%。在固定相同之靜水深條件下，本模擬給予不同週期之波浪條件，其能量消散率隨將週期增長。無ridge之三維模擬結果呈現波浪破碎後之三維現象，且相較於二維模擬，波速及波高之比對上皆小約5%，而能量消散率部分則小約1%。詳細之分析結果與方法將於論文全文中呈現。

關鍵字

裙礁；大渦模擬；能量消散；流體體積法；珊瑚礁脊；三維模擬

並列摘要

The fringing reef is a common type of coral reef which is mainly by the reef flat and reef slope. The reef flat is usually found in the shallow water area with a mild slope. Because the reef flat is adjacent to land, it plays an important role on dissipating the wave energy. Reef slope, on the other hand, is often quite steep which reflects the wave energy directly and introducing wave breaking. In order to have profound understanding on the energy dissipating mechanism, we idealize the reef setup and explore the flow field numerically. We performed the numerical simulation by solving the Large-Eddy Simulation (LES) model with volume of fluid (VOF) interface tracking algorithm. To accurately describe the incident wave generated by a piston-type wavemaker, we utilized the moving-solid algorithm (MSA). Furthermore, the case without a ridge was chosen for demonstrating the 3-D effect of the flow field. By comparing the numerical result and the experimental data, the differences of flow velocity at middle depth and free surface-elevation were less than 5%. Energy dissipation rate for 1:10 slope is 12% greater than on the 1:1 slope. Dissipation rate of the still water depth 0.4m is 1.2% greater than the one of the still water depth 0.5m. Also, Long wave period has lager energy dissipation rate. In the case of 3-D simulation, the results show that the 3-D effect was observed after wave breaking. The differences between the 2-D and 3-D are less than 5% in terms of both the wave height and velocities. Energy dissipation rate between 2-D and 3-D simulations is less than 1%. Detailed analysis are shows in the context.

並列關鍵字

fringing reef ； LES ； energy dissipation rate ； VOF ； ridge ； 3-D simulation

參考文獻

[46] 王豪偉，黃清哲， “孤立波通過三維潛堤所衍生之波場與流場”，海洋工程期刊，第6卷，第2期, pp. 1-22, 2006.

[51] 陳孟志，”以三維賓漢留數值模式模擬海嘯沖刷坑之發展”，碩士論文，國立中央大學水文與海洋科學研究所，2011.

[45] 柯鈞瀚，蔡清標，陳盈圻 “潛堤與海堤間波流場數值模擬”，第34屆海洋工程研討會, pp. 213-218, 2012.

[2] Chen, Y., Lin, B.-L., Jiang, C.-B., and Liu Y., “Predicting near-field dam-break flow and impact force using a 3D model.” Journl of Hydraulic Research Vol. 48, No. 6, pp. 784-792, 2010.

[4] Skotner, C Apelt, C.J., “Application of a Boussinesq model for the computation of breaking waves. Part 2: Wave-induced setdown and set-up on a submerged coral reef.” Ocean Engineering 26, pp. 927-947, 1999.

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裙礁流場之數值分析與消能特性之探討

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