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REEF2FAST: A coupling tool for enhanced floating offshore wind turbine analysis using REEF3D::NHFLOW and OpenFAST

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School of Engineering | Master's thesis

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en

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59

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The advancement of floating offshore wind turbines (FOWTs) requires simulation tools that can capture the interaction between atmospheric loading and realistic sea states. While established system-level tools like OpenFAST offer aero-hydro-servo-elastic modeling capabilities, their implemented wave modules may rely on simplified wave theory, which cannot fully capture complex sea conditions. To close this gap, this thesis introduces REEF2FAST, a non-invasive coupling pre-processor that integrates wave kinematics from the shock-capturing non-hydrostatic Navier-Stokes solver REEF3D::NHFLOW into OpenFAST. REEF2FAST employs a memory-efficient, time-step-streaming approach and a parallelized spatial interpolation scheme based on a k-d tree nearest neighbor search and inverse distance weighting (IDW). It enables the projection of high-fidelity NHFLOW wavefields onto OpenFAST's Cartesian grid, including wave crest regions above the still water level (SWL) using the Wheeler stretching method. Written in C++ and released as an open-source command-line application, REEF2FAST is designed for simple integration into coupled simulation pipelines. Verification tests demonstrate the accurate transmission of wave kinematics across various wave conditions. Validation against experimental platform motions from the OC5 DeepCWind Campaign Phase II confirms the tool's ability to reproduce realistic six-degree-of-freedom (6-DoF) dynamics under both second-order Stokes waves and the irregular JONSWAP spectrum. By enabling the use of externally computed wavefields, REEF2FAST expands OpenFAST's applicability to more complex hydrodynamic environments, such as shallow waters and higher-order wave theories. The modular design of REEF2FAST lays the groundwork for future developments, including two-way fluid-structure interaction and the implementation of complex bathymetries.

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Mikkola, Tommi

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Bihs, Hans

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Attachment notes Description: REEF2FAST GitHub Repository Attachments: Thesis_AronVogelsang_appendix1.zip

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