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系統識別號 U0026-1407202010340200
論文名稱(中文) 以重疊網格進行浮動式離岸結構物之流固耦合數值模擬
論文名稱(英文) Numerical Analysis of Floating Offshore Structures Using Overset Method
校院名稱 成功大學
系所名稱(中) 水利及海洋工程學系
系所名稱(英) Department of Hydraulics & Ocean Engineering
學年度 108
學期 2
出版年 109
研究生(中文) 李醒亞
研究生(英文) Sing-Ya Li
學號 N86074209
學位類別 碩士
語文別 英文
論文頁數 91頁
口試委員 指導教授-蕭士俊
召集委員-葉博弘
口試委員-楊瑞源
口試委員-林鼎傑
中文關鍵字 流固耦合  OpenFOAM  重疊網格法 
英文關鍵字 FSI  OpenFOAM  Overset method 
學科別分類
中文摘要 本研究使用重疊網格法(Overset grid approach) 來探討流體和浮動式結構物之間的交互作用,以提高計算效率且避免由於網格過度變形而引起模式發散。本研究以開放源計算流體力學工具包OpenFOAM 的求解器overInterDyMFoam 為基底,加入數值吸波區,改良其成為overInterFoamSponge,以降低波浪反射造成數值水槽內波浪震盪的問題。
本研究藉由一系列驗證(包括升沈衰減測試,側傾衰減測試以及波浪與浮動式結構物之交互作用等)確定了此模式的準確性。並討論了重疊區域特性對模擬精度的影響,以及比較此模式和動態網格求解器計算得出的結果。最後進一步使用此模式模擬波浪與不同形狀的三維浮動潛沒式結構物之交互作用,並分析結構物之運動行為、纜繩張力變化以及波浪反射及穿透狀況。
英文摘要 The consciousness of global warming gradually transforms the energy dependency from fossil fuels to renewable energy resources such as waves, wind, solar, and geothermal heat. The flexible deployment range of floating offshore wind turbines makes this technology more popular in the offshore wind energy sector recently. However, this technique is still under development and the fluid-structure interaction (FSI) needs to be further investigated to improve the design of the floating wind turbine platform. Due to the significant evolvement of computer and numerical methods in recent years, computational fluid dynamics (CFD) has been widely applied to solve FSI problems. Grid morphing technique is commonly used to solve FSI problems; however, using this technique to deal with large body displacement problems will lead to large grid deformation and consequently induce numerical instabilities.
In this study, overset grid was used to explore the interaction between fluid and floating structures to avoid calculation divergence due to excessive grid deformation. A modified open-source CFD solver, overInterFoamSponge, was developed based on OpenFOAM overset grid Navier-Stokes solver, overInterDyMFoam, to diminish the wave reflection problem that the original solver can not handle. The accuracy of the developed model was validated using a series of benchmark tests including heave decay test, roll decay test, and a floating structure subject to different wave conditions. The influences of the overlapping zone properties on the model accuracy were discussed and the results obtained by the current study and those computed by dynamic grid solver were compared. Overall, the computed results presented in this study show good agreement with the results of the benchmark tests. Finally, this model is further used to understand the interaction between waves and three-dimensional floating submerged structures with different shapes, and to analyze the dynamic motion of the structures, the tension of the mooring line, and the reflection and transmission of waves.
論文目次 摘要i
Abstract ii
誌謝iv
Table of Contents v
List of Tables vii
List of Figures viii
Nomenclature xi
Chapter 1 Introduction 1
1.1 Motivation and Objective . . . . . . . . . . . . . .1
1.2 Literature Survey . . . . . . . . . . . . . . . . ..2
1.3 Methodology . . . . . . . . . . . . . . . . . . . . 6
1.4 Outline . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 2 Numerical Tools 9
2.1 Introduction . . . . . . . . . . . . . . . . . . . 9
2.2 Computational Fluid Dynamics . . . . . . . . . . . .9
2.2.1. Governing Equations . . . . . . . . . . . . . . 10
2.2.2. Turbulence Model . . . . . . . . . . . . . . . .11
2.2.3. Volume of Fluid method . . . . . . . . . . . . .12
2.2.4. Rigid Body Motion . . . . . . . . . . . . . . . 13
2.2.5. Numerical Wave Generation . . . . . . . . . . . 14
2.3 OpenFOAM . . . . . . . . . . . . . . . . . . . . . 15
2.4 Dynamic Grid Approach . . . . . . . . . . . . . . .16
2.5 Overset Grid Approach . . . . . . . . . . . . . . .18
2.6 Numerical Sponge Layer . . . . . . . . . . . . . . 21
Chapter 3 Model Validation 23
3.1 Introduction . . . . . . . . . . . . . . . . . . . 23
3.2 Free Heave Decay of a Two-Dimensional Floating Cylinder . . . . . . . . . . 23
3.2.1. Numerical Set-up . . . . . . . . . . . . . . . .24
3.2.2. Comparison of Dynamic and Overset Grids for 2D Free Heaving Test 25
3.3 Free Pitch Decay of a Two-Dimensional Floating Box . . . . . . . . . .27
3.3.1. Numerical Set-up . . . . . . . . . . . . . . . .27
3.3.2. Comparison of Dynamic and Overset Grids for 2D Free Pitch Decay Test . . . . . . . . . . . . . . . . .29
3.3.3. Effects of the Body-fitted Grid Domain Size in Overset Grid Approach . . . . . . . . . . . . . . . . .31
3.3.4. Effects of Overset Ratio . . . . . . . . . . . .32
3.4 Two-Dimensional Solitary Wave Over Fixed Submerged Horizontal Plate . . . . . . . . . . . . . . . . . . . 36
3.4.1. Numerical Set-up . . . . . . . . . . . . . . . .36
3.4.2. Numerical Wave Generation . . . . . . . . . . . 38
3.4.3. Water Surface Elevation . . . . . . . . . . . . 39
3.4.4. Pressure on Top of the Plate and Beneath . . . .41
3.4.5. Wave Force on the Plate . . . . . . . . . . . . 43
3.5 Two-Dimensional Wave Structure Interaction . . . . 45
3.5.1. Numerical Set-up . . . . . . . . . . . . . . . .45
3.5.2. Numerical Wave Generation . . . . . . . . . . . 47
3.5.3. Interaction between Wave and 2D Floating Box . .48
3.6 Response of a Three-Dimensional Floating Vertical Cylinder . . . . . . . . . . . . . . . . . . . . . . . 49
3.6.1. Numerical Set-up . . . . . . . . . . . . . . . .50
3.6.2. 3D Free Heave Decay Test . . . . . . . . . . . .51
3.6.3. 3D Free Pitch Decay Test . . . . . . . . . . . .52
3.7 Response of a Three-Dimensional Moored Floating Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
3.7.1. Numerical Set-up . . . . . . . . . . . . . . . .53
3.7.2. Dynamic Motion of the Moored Floating Box . . . 56
3.7.3. Tension of the Simplified Mooring Line . . . . .59
3.8 Summary . . . . . . . . . . . . . . . . . . . . . .61
Chapter 4 Results and Discussion . . . . . . . . . . . 63
4.1 Investigation of Moored Floating Structures with Different Wave Conditions . . . . . . . . . . . . . . .63
4.1.1. Numerical Set-up . . . . . . . . . . . . . . . .63
4.1.2. Numerical Wave Generation . . . . . . . . . . . 67
4.1.3. Dynamic Motion of the Structure . . . . . . . . 68
4.1.4. Tension of the Simplified Mooring Line . . . . .72
4.1.5. Wave Reflection and Transmission . . . . . . . .74
4.2 Comparisons Between Different Shapes of Moored Floating Structures . . . . . . . . . . . . . . . . . .78
4.2.1. Moored Double Floating Cylinder . . . . . . . . 78
4.2.2. Dynamic Motion of the Structure . . . . . . . . 80
4.2.3. Tension of the Simplified Mooring Line . . . . .83
4.2.4. Wave Reflection and Transmission . . . . . . . .84
4.2.5. Summary . . . . . . . . . . . . . . . . . . . . 86
Chapter 5 Conclusion and Future Work . . . . . . . . . 87
5.1 Conclusion . . . . . . . . . . . . . . . . . . . . 87
5.2 Future Work . . . . . . . . . . . . . . . . . . . .88
References . . . . . . . . . . . . . . . . . . . . . . 89
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