近年來開發離岸風電為我國重要之能源政策之一，在一系列的規劃當中， 未來的開發風場位置會從近海走向深海的區域，而風機的設計也會從基樁式走向浮動式，因此海洋中浮式結構物的研究也會越來越重要。為此本研究將會模擬流固耦合的物理問題，除了與波浪交互作用外，更是針對了當繫纜束縛浮體時，浮體的運動軌跡與繩張力進行討論。

本研究利用開源計算流體力學軟體OpenFoam進行模擬。在流固耦合的部分使用Overset法，減少因網格變形所產生的計算量。繫纜模型則是採用有限元素法建立，可進行繫纜中每個質點的計算，是屬於利用動態模式模擬的繫纜。

在驗證時，分別會針對二維以及三維水槽的情形進行模擬，將測試不同的流場條件下，浮體以及繫纜模型的正確性，以及繩張力的變化。

最後在成果中，會設計三維的計算案例，討論動態模式求解繫纜模型時的優勢，包含繩張力的合理性。以及討論浮體繫上不同的繫纜模式時，若改變繫纜質量，張力及運動行為分別會如何變化。

關鍵字:浮式結構物，開源計算流體力學軟體，繫纜模型

In recent years, the development of offshore wind power has become one of the important energy policies in my country. In a series of plans, the future development of wind farms will move to the deep sea area, and the design of wind turbines will also change from pile-type to floating-type. Simulation of floating structures is necessary. For this reason, this study will investigate the interaction between the rigid body of the mooring cable and the fluid in the fluid-structure interaction problem.
In this study, OpenFoam is used to simulate, and the overset method is used to calculate the rigid body motion. The cable model developed by the predecessors is used to re-develop in the environment of openFoam. In the issue of fluid-structure interaction, the Overset is solved by the partition method, and the cable model is established by the finite element method, and the incremental displacement method is used to achieve convergence.
In the results, it will be designed in a three-dimensional numerical tank. We will discuss the advantages of dynamic mode in solving the mooring model and discuss how different cable modes will change the tension as the cable quality changes.

Keywords: Floating Structure, OpenFoam, Mooring Model

[ 1 ] J. Davidson, J. V. Ringwood. “Mathematical Modelling of Mooring Systems for Wave Energy Converters—A Review”, Special Issue "Marine Energy",2017.
[ 2 ] G. Hou, J. Wang, & A. Layton, “Numerical methods for fluid-structure interaction—a review”, Communications in Computational Physics., Vol 12, Issue 2, pp. 337 - 377, 2012.
[ 3 ] S. Itō. “Study of the transient heave oscillation of a floating cylinder”, Massachusetts Institute of Technology, Dept. of Ocean Engineering,1997.
[ 4 ] K. H. Jung, K. A. Chang, & H. J. Jo. “Viscous effect on the roll motion of a rectangular structure”, Journal of engineering mechanics., Vol 132, 2006.
[ 5 ] S. Y. Li, “Numerical Analysis of Floating Offshore Structures Using Overset Method”, Master’s thesis,NCKU,2020.
[ 6 ] T. Martin, H. Bihs, A. Kamath, “Modeling and Simulation of Moored-Floating Structures Using the Tension Element Method”, 37th International Conference on Ocean Offshore and Arctic Engineering,2018.
[ 7 ] Open CFD, “OpenFOAM user guide” OpenFOAM Foundation,2022.
[ 8 ] J. Palm, C. Eskilsson, G. M. Paredes, L. Bergdahl “Coupled mooring analysis for floating wave energy converters using CFD: Formulation and validation”, International Journal of Marine Energy, Vol 16, pp 83-99,2016.
[ 9 ] M. A. Rahman, N. Mizutani,“ Numerical modeling of dynamic responses and mooring forces of submerged floating breakwater”, Coastal Engineering, Vol 53, pp. 799-815, 2006.
[ 10 ] I. C. TSAI , “Numerical Simulation of 2-D Fluid-Structure Interaction with Tightly Coupled Solver and Establishment of the Mooring Model”, Master’s thesis,NCKU,2019.
[ 11 ] D. Zulli, A. Luongo, ” Mathematical Models of Beams and Cables”, Wiley-ISTE, 2013.