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。

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.

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