臺灣博碩士論文加值系統

本文利用數值模型求解2-D RANS 以及k-ε 紊流模式並且利用VOF 追蹤自由液面。模擬孤立波由近岸至沖刷區域之傳遞過程。本研究著重水平流速、底床剪應力以及紊流動能於沖刷帶內隨時間變化過程。接著透過流場圖以及紊流動能分布圖討論孤力波孤立波由近岸至沖刷區域傳遞過程之變化。
由於沖刷區域內常因斜坡而產生非矩形網格，為了解決非矩形網格所造成之計算誤差，本文將座標軸旋轉平行於斜坡以解決沖刷區域固體邊界的問題。接著，在此座標系統下與孤立波理論解(Grimshaw,1971) 進行波型與水平流速之驗證，經由與實驗量測 (黃冠勳, 2012) 之壓力、水平流速與底床剪應力驗證，可知數值模擬結果與實驗量測之變化趨勢相同。
在驗證數值模式後，本文進行兩項研究。第一，分別改變底床粗糙度以及坡度來探討對水平流速、底床剪應力以及紊流動能的影響。第二，透過流場與紊流動能分布圖來了解孤立波由近岸到沖刷區域傳遞過程中之變化過程。若將底床粗糙度增加時，可發現到水平流速極值會隨之下降而底床剪應力與紊流動能會隨之增加。若將底床粗糙度增加時，可發現到水平流速、底床剪應力與紊流動能之及極值會隨之增加。透過流場圖與紊流動能分布圖，可發現到底床粗糙度增加時在溯升與溯降之邊界層流速度曲線會越趨明顯，而底床坡度增加時孤立波碎波形式與碎波點皆會改變，並且紊流動能生成方式也會隨之改變。底床坡度增加會使得孤立波從溢波碎波變為湧波形式，且紊流動能產生湧波前端接觸到底床時明顯生成而後逐漸擴散至整個水體。

In this study, the dynamic process of solitary wave propagating from shore to swash zone is investigated numerically by using a 2-D Reynolds Averaged Navier-Stokes (RANS) solver. The turbulence field is described by using a non-linear k-ε turbulence closure model and the free surface configuration is tracked by the Volume Of Fluid (VOF) method. To validate the numerical model, the results were compared with theoretical solution and existing experimental data. The result of the validation shows good agreement. Besides, the numerical model is applied to investigate the horizontal velocity, bottom shear stress, turbulence kinetic energy (TKE) and boundary layer in the swash zone of the different bed roughness and bed slopes.
The results show that the maximum velocity, bottom shear stress and turbulence kinetic energy exerted by uprush, and the maximum bottom shear stress and turbulence kinetic energy increase with the bed roughness and bed slope increase. The maximum velocity decreases as the bed roughness increase, but increases with the bed slope increases. The boundary layer vanishes during flow reversal and then grows during the backwash, and becomes depth limited at the end of the swash cycle. From the analysis of the velocity and turbulence field, the boundary layer flow was observed obviously as the bed roughness increases. When the bed slope increases the solitary wave in the form of spilling breaker to surging breaker.

摘要 1
Abstract II
誌謝 III
目錄 IV
圖目錄 VII
表目錄 X
符號表 XI
第一章 序論 1
1-1 研究目的 1
1-2 文獻回顧 2
1-2-1 現地量測 2
1-2-2 實驗室量測 2
1-2-3數值模擬 3
1-3 本文組織架構 5
第二章 數值方法 6
2-1 數值模式簡介 6
2-2 控制方程式 6
2-3 k-ε紊流閉合模式 8
2-4起始條件與邊界條件 11
2-4-1起始條件 11
2-4-2造波邊界條件 12
2-4-3固體結構物與自由液面條件 13
2-5流體體積法(Volume of fluid method) 14
2-6部分網格(partial cell) 16
2-7旋轉坐標軸 17
2-8 剪應力計算 19
第三章 模式驗證 20
3-1 實驗量測沖刷帶內底床剪應力(黃冠勳 2012) 20
3-1-1 試驗佈置 20
3-1-2 實驗底床剪應力計算 22
3-2 數值模擬沖刷帶內之數值模擬 24
第四章 結果與討論 29
4-1沖刷帶內流速時序變化 31
4-2沖刷帶內剪應力時序列變化 33
4-3沖刷帶內紊流動能時序列變化 35
4-4沖刷帶內之速度剖面與邊界層厚度 37
4-4-1比較Case1、Case4、Case6之流速剖面 37
4-4-2比較Case1、Ｃase4、Case6之邊界層厚度 39
4-5沖刷帶內流場圖與紊流動能分布 41
4-5-1淺化現象 41
4-5-2碎波現象 42
4-5-3溯升現象 43
4-5-4溯降現象 44
第五章 結論與建議 66
5-1 結論 66
5-2 建議 68
參考文獻 69

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