臺灣博碩士論文加值系統

　　本文旨在探討潛沒式沙丘在不同波浪條件及不同佈置之演變過程、底床質傳輸及其對波浪產生之影響。實驗在二維波浪水槽進行，底質材料採用中值粒徑為0.32mm，比重為2.45之玻璃沙。沙丘幾何形狀隨時間變化之地形量測乃使用影像處理之方式以獲得砂丘表面高程曲線，其過程包含影像之擷取、分析及高程之轉換等。

　　因次分析及實驗結果顯示Shields參數在底床質傳輸中極為重要。本文採用無因次累計傳輸量(消失率)來探討沙丘之初始佈置與波浪條件之關係，以利於工程之實際應用。由實驗結果可知沙丘之變遷過程係以形成沙漣之方式並伴隨對流效應逐漸往兩旁擴展。在固定波浪及堤寬條件下，沙丘之高度對波浪反射係數有正向之趨勢，然而當堤寬由小增至約半波長時，反射係數有隨堤寬增加而減小之走向，堤寬及堤高之增長皆會減低波浪之透過率。在不等水深產生不等傳輸營力之影響下，沙丘之傳輸率隨著高度的降低而有減緩之傾向，最終而達到近乎動力平衡之穩定狀態。

　　沙丘之高度及寬度對於底床質之傳輸有不同之影響。藉由無因次平均傳輸率與Shields參數之關係，本文建立適用於潛沒式沙丘之傳輸率經驗式，而臨界可動之Shields參數值(0.032)可利用來區分沙丘為穩定或可動狀態。本文亦建立Shields參數與平衡狀態之沙丘消失率之經驗式。

　　The objectives of this study are to investigate the effects of the berm geometries and wave conditions on the accumulative transport rate and the evolution process of submerged berms. The experiments were conducted in a wave flume under a constant water depth condition. The bathymetry was obtained by the image processing method which includes the image formation, image analysis and image interpretation. The results were discussed in two main categories which were the analysis of the sediment transport and the wave transformation. It was demonstrated that the berm evolution process accompanied with the formations of sand ripples and the sediment would be convected away the original placed while it diffused.Under the same wave condition and berm width, the berm height was an important element of the wave reflection. However, the reflection coefficient declined as the berm bottom-width is one half to the incoming wave length.Under the same wave condition, both the extensions of the berm height and the berm width reduced the wave transmission. For berm application, an average dimensionless transport rate was formulated in terms of the Shields parameter. The critical Shield parameter, , was employed to distinguish whether the berm was stable or movable. Results also showed that the disappearing rate decreased while the berm was broader and more sand would be transported away as the berm height is extended. Finally, a formula was suggested to predict the disappearing rate of the berm at the quasi-equilibrium state.

Acknowledgement i
English Abstract ii
Chinese Abstract iii
List of Tables vi
List of Figures vii
Notations ix

Chapter 1 Introduction 1
1.1 Background 1
1.2 Literature Review 4
1.2.1 Field Application Studies 5
1.2.2 Physical Model Studies 9
1.2.3 Theoretical and Numerical Studies 13

Chapter 2 Dimensional Analysis 18
2.1 Dimensional Analysis 18
2.2 Definition of the Transport Rate and the Disappearing Rate 22

Chapter 3 Experiments 27
3.1 Experimental Facilities and Setup 27
3.2 Image Processing Method 29
3.3 Testing Conditions 31
3.4 Experimental Procedures 32

Chapter 4 Results and Discussions 41
4.1 Analysis on Sediment Transport 41
4.1.1 Evolution of the Submerged Berm 42
4.1.2 Relation between the Maximum Elevation and Transport Rate 43
4.1.3 Relations between the Shields Parameter and Transport Rate 44
4.1.4 Effects of the Berm Geometries on the Disappearing Rate 46
4.1.5 Relation between the Quasi-Equilibrium Maximum Elevation and
Shields Parameter 47
4.1.6 Relation between the Disappearing Rate and Shields Parameter 48
4.1.7 Evolution of the Normalized Disappearing Rate 49
4.2 Analysis on Wave Transformation 49
4.2.1 Evolution of the Reflection Coefficient and Transmission Coefficient 50
4.2.2 Effects of the Berm Geometries on the Wave Reflection and
Transmission 51
4.2.3 Evaluation of the difference on the transmission coefficient between
submerged berms and submerged breakwaters 52

Chapter 5 Conclusions and Recommendation of Further Research 64
5.1 Conclusions 64
5.2 Recommendation of Further Research 65

References 66

Vita 69

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