臺灣博碩士論文加值系統

本論文探討負壓沉箱施作過程對海洋底質動態反應之影響，其理論來自於海洋運動方程式與多孔介質淤沙環境之控制方程式，並由有限差分法求得海洋底質土體之超額孔隙水壓、固液兩相之速度分量、海洋底質中固體水平與垂直方向之正向應力與剪應力的數值解。
在基準驗證後測試不同的邊界條件產生之結果並提出了最合理的邊界條件。假設幾個沉貫深度並利用兩個不同的吸入壓力導致之應力來研究整體橫向阻力和可能發生管湧的潛力。
隨著沉貫深度的增加，沉箱壁內正規化超額孔隙水壓梯度的分佈與牆壁對齊，同時沉箱尖端的超額孔隙水壓力變小，而正應力和剪應力則隨著沉貫深度的增加而增加，且最大應力發生在沉箱尖端。
吸力引起的應力將導致沉箱內的摩擦應力減小，而沉箱外側則增加。然而有效土應力的減量最多是在沉貫深度到達2.5米且承受臨界吸力時，位於沉箱內側尖端的位置，此處管湧潛力為31.52%。

The objective of this study is the mechanical behavior of suction bucket caisson under loadings. The formulations are derived based on the fundamental theories of ocean hydrodynamic and flow in porous medium and they are solved by the finite-difference methods. A benchmark validation was made before further simulation cases. Several penetration depths were assumed and two different suction pressures were given. Different boundary conditions were tested and the most reasonable one was suggested.
Suction induced stresses in response to various suction pressures and penetration depths were studied. The overall lateral resistance and possible piping potential were investigated.
As the penetration depth increases, the distribution of the normalize excess water pressure gradient inside the caisson wall is aligned with the wall and the excess water pressure at the caisson tip become smaller, whereas the normal stress and shear stress increase as does the penetration depth and the maximums stress is on the caisson tips.
The suction induced stress will lead the friction stress within the caisson decrease, and the outer parts will increase. However, the maximum decrement of the effective soil stress at the inner corner of the caisson tip and the piping potential is 31.52 % in full penetration depth.

論文審定書 i
摘要 ii
ABSTRACT iii
TABLE OF CONTENTS iv
LIST OF FIGURE viii
LIST OF TABLE xiv
NOMENCLATURE xv
INTRODUCTION 1
1.1 Background 1
1.2 Offshore wind turbine development 2
1.2.1 Denmark 2
1.2.2 UK 2
1.2.3 Germany 3
1.3 Offshore Wind Power 4
1.3.1 Offshore wind power system 4
1.3.2 Types of Foundations 5
1.4 Summary of chapter 9
LITERATURE REVIEW 11
2.1 Development of Suction Caissons 11
2.2 Analysis of Suction Caissons 11
2.3 Installation analysis 14
THEORETICAL AND NUMERICAL METHODS 18
3.1 Governing equations 18
3.1.1 Seawater 18
3.1.2 Sediment 19
3.1.3 Boundary conditions 21
3.1.4 Initial conditions 22
3.2 Numerical Methods 22
3.2.1 Finite difference numerical solution 23
3.2.2 Grid system 23
3.2.3 Pressure wave equation processing 26
3.2.4 Pressure wave equation boundary processing 27
3.2.5 Velocity field of sediment 29
3.2.6 Stress field and porosity of sediment 31
3.3 Computational process and Convergence Conditions 32
STABILITY ANALYSIS AND THE BENCHMARK TESTS 34
4.1 Mesh and domain size 37
4.1.1 Domain parameter 38
4.1.2 Domain parameter 38
4.1.3 The clustering parameter 39
4.1.4 Number of the mesh 40
4.2 Benchmark problem 41
4.2.1 Excess pore pressure 42
4.2.2 The suction induced stress 46
4.2.3 Velocity 50
INFLUENCE OF BOUNDARY CONDITIONS 54
5.1 Outside of boundary 54
5.2 B.C. of the interface between seawater and sediment 56
5.3 B.C. of the interface between sediment and bottom 58
5.4 Summary of Chapter 61
THE OVERALL SOIL RESISTANCE 68
6.1 Friction stress in self-weight penetration depth 70
6.1.1 Passive-Active state 77
6.1.2 Active-Passive state 78
6.1.3 The rest state 79
6.2 Friction stress in full penetration depth 80
6.2.1 Passive-Active state 86
6.2.2 Active-Passive state 87
6.2.3 The rest state 87
6.3 The vertical Bearing stress 88
6.3.1 The piping potential on the whole domain 88
6.3.2 The piping potential at the caisson tip 90
6.4 Summary of chapter 93
CONCLUDING REMARKS 96
7.1 Conclusions 96
7.2 Recommendations for the future research 97
REFERENCES 99

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