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研究生：	鮑俊宏 Pao, Chun-Hung
論文名稱：	碎波帶底部邊界層流場之實驗研究 Experimental study of the boundary layer flow in surf zone
指導教授：	黃煌輝 Hwung, Hwung-Hweng
學位類別：	碩士 Master
系所名稱：	工學院 - 水利及海洋工程學系 Department of Hydraulic & Ocean Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	108
中文關鍵詞：	碎波帶、質點影像測速儀、邊界層
外文關鍵詞：	surf zone, PIV, wave bottom boundary layer
相關次數：	點閱：72 下載：6
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邊界層流 (boundary layer flow) 一直以來被視為兩相流的學理基礎，在淺水區域也是扮演底質懸浮、傳輸的重要力學機制，尤其是位於碎波帶的底部邊界層流，除了因本身流況不穩定而產生的局部較小紊流，尚有因碎波而產生於波峰區域的強烈外部紊流，隨著水舌衝擊水體的過程而往底部區域傳遞。此帶有大量能量的外部紊流，以渦流的形式向下傳遞並於底部邊界層區域產生動量交換，也可能導致更多底質的懸浮，因此，外部強烈紊流與局部較小紊流之間的關聯性，是需要進一步去探討的。然而，像是碎波產生的渦流，因缺乏適合量測的儀器，以至於較少有著重於此方面的研究，也因此，使得近十年來蓬勃發展的新量測技術，質點影像測速儀 (PIV，Particle Image Velocimetry)，非常適用於此關聯性的探討，同時也是個新課題。本文旨在使用PIV量測邊界層流，分析於兩種碎波條件、兩個不同測點情況下的邊界層流場。

本實驗於成功大學水工試驗所的造波水槽 (25m*0.3m*0.7m) 所進行，內置坡度1/20的透明斜坡，為避免表面水體因碎波捲入的氣泡將光源散射，雷射光頁由水槽玻璃側壁入射，經45度的鏡子反射，於底部流場區域提供照明。藉裝置一高放大率的鏡頭，相機的空間解析度提昇為6.7958 µm/pixel，若邊界層厚度為1mm，一垂直速度剖面可解析出約有9個向量分佈。本實驗另建立一可精確控制的資料擷取系統 (DAQ system，Data acquisition system)，得以用來決定欲量測的波浪相位，而此一量測系統所發展的起始點平移方法 (Shift method)，也成功地增加PIV量測的波浪相位兩倍，於溢波 (spilling breaker) 碎波的情況下，一個週期約有20個相位可解析，而捲波 (plunging breaker) 約有28個。實驗結果顯示在捲波衝擊點 (plunging point) 的位置無論是何種碎波型態，底部邊界層流場保持類似層流的行為，而渦流延展 (vortex-stretching) 明顯的區域，溢波碎波情況下仍維持類似前一測點的運動現象，捲波碎波條件下則發現於波峰後的2/14相位，有一較大渦流 (a large-scale eddy) 侵入邊界層流場，隨著相位速度傳遞並且逐漸消散。

The boundary layer flow has been considered an essential knowledge for two phase flow and plays an important role on sediment transport especially in the shallow water region. It has been observed that turbulences generated in the crest region will be propagated downward to the interior region during the breaking process in the surf zone. The descending turbulence may bring intense energy and lead momentum to exchange in the boundary layer region. The relationship between the characteristics of boundary layer flow and the externally driven fluid motions needs to be considered further. Coherent fluid motions, such as large eddies produced by wave breaking, were plausible mechanisms but have received little attention because of a lack of suitable measurements. Accordingly, this fact made PIV (Particle Image Velocimetry) measurement technique so enchanting because of the instantaneously full-field vectors and non-intrusive flow-field measurements. The objective of this paper was to investigate the near-bed flow using PIV. The measurements were conducted in two different positions under two types of breaker.

The experiment were carried out on a 1/20 slope in a glass-side walled wave flume in Tainan Hydraulics Laboratory. The laser light sheet was delivered beneath the transparent slope to avoid uncontrollable scattering of light sheet from the effect of free-surface. The resolution of CCD camera is 6.7958 µm/pixel which allows nine vectors being distributed vertically since the thickness of boundary layer flow is about 1 mm. A well-controlled DAQ (Data acquisition) system succeeded in doubling the measuring phases which resolved 20 phases during one period for spilling breaker and 28 phases for plunging breaker. The results show that boundary layer flow remained laminar-like behaviors in the plunging point regardless of types of breaker. Similar motions also revealed in the vortex-stretching region under spilling breaker, whereas a large-scale eddy struck the boundary layer flow and changed the original characteristics under plunging breaker.

Abstract (English)	i
Abstract (Chinese)	ii
Acknowledgment	iii
Contents	iv
List of Figures	vii
List of Tables	xi

Chapter 1 Introduction
1.1 Background	1
1.2 Literature review	4
1.2.1 WBBL in oscillatory flow	5
1.2.2 WBBL in field observations	7
1.2.3 Surf zone dynamics	10
1.3 Outline	20
Chapter 1 Introduction	20
Chapter 2 Experiments	20
Chapter 3 Experimental procedure	20
Chapter 4 Results	21
Chapter 5 Conclusions	21

Chapter 2 Experiments
2.1 Facilities	22
2.1.1 Wave flume	22
2.1.2 Slope	22
2.1.3 Wave gauges	23
2.1.4 3-D traversing table	24
2.1.5 PIV measuring system	24
2.2 DAQ system	28
2.3 Measuring techniques	29
2.3.1 Path of light sheet	29
2.3.2 High-magnification camera lens	30
2.3.3 Seeding concentration	31
2.3.4 Bottom boundary effects	32
2.4 Experimental set-up	33
2.4.1 Distribution of wave gauges	33
2.4.2 Measuring resolution	34
2.4.3 Measuring positions	34
2.4.4 Experimental conditions	38

Chapter 3 Experimental procedure
3.1 DAQ procedure	40
3.2 Shift method	41
3.3 Calibration of external trigger signal	43
3.4 Principle and process of PIV	46
3.4.1 Image quality	47
3.4.2 Theorem of evaluation	51
3.4.3 Setting for evaluation	53
3.4.4 Post processing	57

Chapter 4 Results
4.1 Estimation of Reynolds number	59
4.2 Vectors field in P1	60
4.3 Vectors field in P2	62
4.4 Non-dimensional profile	65

Chapter 5 Conclusions
5.1 Conclusions	102
5.2 Suggestions	103

References	104
Vita	108
                                    

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校內：2010-08-14公開
校外：2012-08-14公開

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