本研究利用Acoustic Doppler Velocimeter (ADV)、流剖儀、波浪儀等儀器，在淺水珊瑚礁的後壁湖及後灣沿岸海域進行底邊界層紊流的量測，探討紊流動能消散率ε以及剪應力τ等紊流特性。首先進行ADV資料前置處理項目，包含：Despike、數據有效性判斷、座標系轉換以及消除波浪訊號。
紊流具有時間與空間上的廣闊分佈範圍，對此現象常採用能譜來做分析，而斜率-5/3的能譜走向以及慣性區間涵蓋範圍與平均流的大小有正向關係。觀察紊流動能消散率ε的變化，後壁湖珊瑚礁實驗是屬於碎波帶以淺，海流很小且為波浪主導的海域，由於受到粗糙底床的影響，ε的觀測值約為 W/kg，它會隨著水位和波高的大小而有正向的週期變化。後灣實驗則是屬於潮流和風浪所主導的海域，海流較強，底床剪切造成擾流，ε的觀測值約為 W/kg。另一方面，利用ε可計算整個水體的平均紊流動能消散率 ，結果得知淺水珊瑚礁海域的波浪能量消散 和紊流動能消散率具有高度的關連性。
利用三種方法計算底床剪應力τ，藉由修正過後的摩擦速度 其值增加約60%，使ID法所計算出的τ，在高雷諾數且紊流發展較完全的淺水珊瑚礁海域，能與波高趨勢吻合；但由於慣性區間的擷取上不具公式性、系統性，其準確度可能隨著低雷諾數或紊流發展不完全等因素而逐漸降低；在EC法方面，當雷諾數太小時，會使得底床剪應力等於雷諾應力之假設不成立，導致EC法計算結果不準確。故本文認為，利用變動速度所計算出的紊流動能(TKE)來討論τ應是最理想、最通用的方式。拖曳係數Cd與平均流速變化存有明顯的對應關係，因此並不適用於受波浪影響明顯的海域。

In this study, Acoustic Doppler Velocimeter (ADV), current profiler and wave gauge were used to measure the turbulent kinetic energy dissipation rate (ε) and shear stress (τ) in Hobi shallow coral reef and Howan coastal waters. Data pre-processing including despike, data quality check, coordinate transformation and filtering of wave signal were applied.
The inertial dissipation (ID) method is commonly used to estimate the turbulence due to its broad distribution in the frequency domain. The spectral slope of -5/3 and its frequency range within the inertial sub-range can be clearly seen with the increasing flow speed. At the Hobi coral reef which is situated shoreward of the surf zone characterized by small currents and large waves, the observed values of ε are O(〖10〗^(-5)-〖10〗^(-3))W/kg and vary in phase with the tide and wave height. On the other hand, the Howan experiment is dominated by unidirectional flows and wind waves, turbulence is generated at the bed by shear flows, and the observed values of ε are O(〖10〗^(-5)-〖10〗^(-4))W/kg. The average turbulent kinetic energy dissipation rate ε_BL, estimated directly from the observed ε with a bottom boundary layer scaling, indicates that a close correlation exists between the wave energy dissipation rate D_wave and turbulence dissipation.
Three methods were used to estimate the bed shear stress and their results are inter-compared. When the Reynolds number is smaller and wave-current interaction is important, correction of the friction velocity u_* by the ID method is required. As a result, an increase of τ by approximately 60 percent shows better correlation with the wave height. However, the applicability and reliability of the ID method become worse as the Reynolds number decrease and turbulence is not fully developed. The EC method will not produce reasonable values of bed shear stress when the Reynolds number is not sufficiently high and the turbulence is not fully developed. Finally, estimating τ by the turbulent kinetic energy (TKE) method with velocity fluctuations is considered be the best and most common method for this study. The drag coefficient Cd is found to be close correlated with the mean flow, but it is not suited for the wave-dominated shallow reefs.

摘要 i
Abstract ii
目錄 iv
圖目錄 vi
表目錄 ix
緒論……………………………………………………………………………1
1-1. 前言…………………………………………………………………………1
1-2. 底床邊界層動力結構………………………………………………………1
1-3. 前人研究……………………………………………………………………2
1-4. 研究動機……………………………………………………………………4
實驗設計………………………………………………………………………6
2-1. 實驗地點……………………………………………………………………6
2-2. 儀器介紹……………………………………………………………………6
2-3. 實驗配置……………………………………………………………………7
2-4. 氣候資料來源………………………………………………………………8
2-5. 回聲強度……………………………………………………………………9
數據前置處理…………………………………………………………………15
3-1. ADV數據處理……………………………………………………………15
3-2. Despike……………………………………………………………………15
3-2.1. Spike判斷…………………………………………………………15
3-2.2. Spike替代…………………………………………………………17
3-3. 數據有效性判斷…………………………………………………………21
3-4. 座標系轉換………………………………………………………………25
3-5. 消除波浪訊號……………………………………………………………28
3-5.1.Butterworth…………………………………………………………28
3-5.2. 快速傅立葉轉換…………………………………………………28
3-6. ADV資料處理程序………………………………………………………33
分析方法………………………………………………………………………34
4-1. 剪應力……………………………………………………………………34
4-1.1. 渦流相關法………………………………………………………34
4-1.2. 紊流動能法………………………………………………………35
4-1.3. 慣性消散法………………………………………………………35
五、結果與討論………………………………………………………………………40
5-1. 三個實驗的海流特性……………………………………………………40
5-1.1. 垂直剖面下的海流狀態…………………………………………41
5-1.2. 垂直剖面回聲強度變化…………………………………………42
5-2. 能量消散…………………………………………………………………46
5-2.1. 波浪能量消散……………………………………………………46
5-2.2. 底床摩擦消散率…………………………………………………47
5-2.3. 近岸淺水珊瑚礁海域的平均紊流動能消散率…………………52
5-2.4. 利用頻譜計算示性波高…………………………………………53
5-3. 底床邊界層紊流動能消散率……………………………………………54
5-3.1. 三個實驗的能譜與ε結果分析……………………………………54
5-3.2. 平均紊流動能消散率(ε^* 、ε_BL)與D_wave之結果比較……………60
5-4. 底床剪應力………………………………………………………………65
5-4.1. 三個實驗的底床剪應力結果分析………………………………65
5-4.2. 拖曳係數…………………………………………………………70
六、結論………………………………………………………………………………72
七、參考文獻…………………………………………………………………………74

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