A Numerical Study on the Influence of Wave Breaking and Bragg Reflection on Wave Run-Up by Submerged Breakwaters

本研究旨在以計算流體力學模擬並探討波浪於潛堤上碎波及發生布拉格反射效應對波浪溯升影響情形，及分析波流場差異、堤前反射率、堤後透射率及後方溯升高度。數值模擬係以非定常雷諾平均方程式(Reynolds Averaged Navier-Stokes Equation, RANS)及k-ε turbulent model紊流模式，藉由FLOW-3D求解模擬。由Ting and Kirby(1994)及Mase et al. (1995)之實驗數據及模擬結果進行本文數值模式驗證，結果顯示本模式模擬波浪於斜波上波高變化結果及波浪受沙漣底床布拉格反射效應，均有精確性。本研究結果顯示，布拉格反射佈置系列潛堤，隨著潛堤個數增加，堤前反射率增大、紊流消散增加、堤後後射波高降低、溯升高度也隨之降低。發生碎波現象潛堤，由於潛堤高度較高有較大反射率，及波浪碎波造成大量能量消散，使堤後透射率大幅降低。若比較潛堤上碎波及布拉格反射配置系列潛堤對後方波浪溯升影響，因碎波所造成能量損失效益較為顯著，因此潛堤碎波佈置較能有效降低溯升高度。The purpose of this study is aimed to investigate the influence of wave breaking and Bragg reflection on the wave run-up by submerged breakwaters. This study used computational fluid dynamics to analyze the characteristics of wave flow field, reflection coefficient, transmittion coefficient and run-up height. The numerical model is based on general Reynolds-averaged Navier-Stokes equations associated with renormalization group turbulent closure model by using volume of fluid technique, which are implemented by FLOW-3D. The experimental data by Ting and Kirby (1994) and Mase et al. (1995) were used to verify numerical result. The results showed good agreement between the numerical simulation and experiment of the variations of wave height along the slope and Bragg reflection effect respectively. The results show that wave reflection coefficient and turbulent dissipation rate increased with the increasing of series submerged breakwaters numbers, but wave transmission coefficient and run-up height displayed decreased with the increasing of series submerged breakwaters numbers. Due to wave breaking phenomenon on the higher submerged breakwaters, it leads to higher wave reflection coefficient and lower wave transmission coefficient caused by wave turbulent energy dissipation.摘要 i Abstract ii 目錄 iii 表目錄 vi 圖目錄 vii 符號說明 xi 第一章 緒論 1 1-1 前言 1 1-2 文獻回顧 2 1-3 研究目的 6 1-4 本文組織 7 第二章 數值模式 8 2-1 控制方程式 8 2-2 Two-equation k-ε turbulent transport 紊流模式 9 2-3 流體邊界和自由液面 10 2-4 Flow-3D介紹 10 2-4.1 多區域結構性網格(Multi-Block Grids) 10 2-4.2 流體體積法(Volume of Fluid, VOF) 11 2-4.3 FAVOR 11 (Fraction Area/Volume Obstacle Representation) 11 2-4.4 網格處理方式 12 2-4.5 邊界條件設定 12 2-5 模擬步驟與參數設定 13 第三章 模式驗證 16 3-1 波浪於斜坡底床驗證 16 3-2 布拉格反射驗證 20 第四章 數值模擬與結果分析 23 4-1 模擬條件 23 4-2 無潛堤佈置分析 26 4-3 潛堤布拉格反射佈置分析 29 4-3.1 布拉格反射模擬分析 29 4-3.2 不同潛堤個數之影響 33 4-4 潛堤碎波佈置分析 46 4-5 潛堤碎波及布拉格反射效應比較 53 4-5.1 反射率比較 55 4-5.2 透射波高比較 55 4-5.3 斜坡上碎波波高與溯升高度比較 57 4-5.4 潛堤後方及斜坡上方流場變化 59 第五章 結論與建議 72 5-1 結論 72 5-2 建議 73 參考文獻 7