臺灣博碩士論文加值系統

隨著水下海事工程的日漸發達，諸如挖砂及埋管等工作需求不斷，操控水下遙控載具的精準度也相對要求提高。本論文針對長期工作之載具其利用射流所造成的自挖填之相關問題，模擬移動式水射條件輔以實驗室量測及觀察水射對輸砂的影響，其中包含了砂與水複雜的互制行為、射流的捲增效應、沖刷及淤積現象等。除了實驗配置外並研究淺水波理論之於射流模擬之可行性，理論之建立除了架構於傳統的連續方程及動量守恆更嘗試聯立能量方程。初步以水面均勻射流及水下異重射流做理論根基的基礎，整合介面分層以及傳輸理論將統御方程延伸應用在曲線座標裡。並針對水下穩定的作業提供一維穩定解之操作模式。理論計算將和實驗資料一一驗證，除了寄望對於沖刷深度及長度等工程實際問題提供有效之模式預測，並發現模式可能之侷限性。雖然模式得以驗證水射之於輸砂具薄層流及水躍行為，經由實驗觀察，移動式水射所造成之溝渠流仍有可能發生超出模式之分離流等。

Underwater activities such as extracting sand beds or burying pipelines are getting more and more widespread and remotely operated vehicles (ROVs) are being increasingly used to reach deeper areas. The present thesis examines the behaviour of jetting onto the sediment sand bed by using a trencher-like machine. Complex phenomena of the interaction between water and sand are observed experimentally, including physical processes of erosion, suspension, entrainment and breaching. Starting with two simpler cases of surface current and bottom plume with a slope break, extensions of shallow flow theory are first presented and validated with analytic solutions. To further extend the theory to eroding turbid currents, interface transfer theory and concept of sub-layered shallow flow are integrated in a mathematical curvilinear formulation. The governing equations include conservation laws for continuity, momentum and energy. Simulating the steady flow, numerical calculations and approximate solutions are obtained in moving coordinates attached to the travelling jets. Comparison of theory and experiments include is made for the bed response profiles. Both in the model and the experiment, two possible pattern of flow are observed, with and without an internal hydraulic jump. In some of the experimental runs, however, phenomena such as flow separation and sand face breaching are observed, which exceed the current scope of the proposed theory.

ABSTRACT i
中文摘要 ii
LIST OF SYMBOLS iii
CONTENTS viii
LIST OF FIGURES xi
LIST OF TABLES xvii

1 INTRODUCTION 1

2 EXPERIMENTS 8
2.1 EXPLORATION EXPERIMENTS 8
2.2 SAND MATERIAL PROPERTIES 14
2.2.1 Material characterization tests 14
2.2.2 Settling column test 16
2.3 TANK 21
2.4 SUCTION DREDGE 24
2.5 JETTING HEADS 26
2.6 CARRIAGE AND ARM 29
2.7 IMAGING MEASUREMENTS 36

3 EXTENDED SHALLOW FLOW THEORY 40
3.1 SURFACE CURRENT 40
3.2 BOTTOM PLUME ALONG RIGID BED 43
3.3 SUB-LAYERED SHALLOW FLOW THEORY 48
3.3.1 Notations and assumptions 48
3.3.2 Governing equations 51
3.3.3 Interface transfer relations 53
3.3.4 Turbulent mass drift and shear stress functions 56
3.3.5 Balance of mechanical energy 58
3.3.6 Synthesis 60

4 STEADY AND TRAVELLING WAVE SOLUTIONS 62
4.1 SURFACE JETS 62
4.2 BOTTOM JETS ALONG RIGID BEDS 65
4.3 TRAVELLING WAVE SOLUTIONS 72
4.3.1 Equations in moving coordinates 72
4.3.2 Characteristic structure 74
4.3.3 Longitudinal flow structure 76
4.4 FLOW AND SOLUTION DETAILS 78
4.4.1 Jet expansion before impingement 78
4.4.2 Trenching front 80
4.4.3 Internal hydraulic jump 82
4.4.4 Passage through the critical section 84
4.4.5 Composite solutions 86

5 COMPARISON OF THEORY AND EXPERIMENTS 91
5.1 EXPERIMENTAL RESULTS 91
5.2 COMPARISON OF THEORY AND EXPERIMENTS 92
5.3 FLOW SEPARATION AND BREACHING EFFECTS 119

6 CONCLUSIONS AND FUTURE WORK 121
6.1 CONCLUSIONS 121
6.2 LIMITATIONS 123
6.3 FUTURE WORK 123

REFERENCES 127

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