To reach the full potential of offshore wind energy, the evaluation of the hydrodynamic performance of offshore wind turbine semi-submersible platforms is of vital importance. This study, known as the 1st FOWT Comparative Study (Ransley et al. 2022), aims to achieve this target by using a 1:70 scale model of the IEA 15MW reference wind turbine (Gaertner et al. 2020) and the UMaine VolturnUS-S semi-submersible platform (Allen et al. 2020). The numerical model used in this comparative study is an in-house hybrid CFD model (QaleFOAM) coupled with the dynamic mooring model (MoorDyn). QaleFOAM is a domain decomposition model that combines the Quasi-arbitrary Lagrangian-Eulerian finite element method (QALE-FEM) in the far-field subdomain and a two-phase Navier-Stokes model (NS) solver Open-FOAM/InterDyMFoam in the confined near-structure subdomain. By simulating the static equilibrium load cases, moored decay tests, and a pair of focused wave cases in both operational and extreme sea state conditions, the dynamic responses of this semi-submersible platform are evaluated. Furthermore, the reliability and accuracy of the adopted hybrid model are validated against the experimental measurement, and its numerical uncertainties and efficiency are examined in this study.


Offshore wind is expected to play a crucial role in the global shift towards renewable energy, with the Global Wind Energy Council predicting a 57-fold increase in worldwide capacity between 2020 and 2050 (James et al, 2022). According to the International Renewable Energy Agency, harnessing 2 TW of offshore wind energy will be necessary to limit global warming to 1.5° by 2050 (James et al, 2022). As about 80% of the ocean's wind resource potential is located in areas where the seabed is too deep for traditional bottom-fixed solutions, floating wind turbines are believed to hold great commercial potential and are expected to become competitive by 2030. In the UK alone, it is projected that by 2023, there will be over 10 GW of floating wind capacity, which is expected to reach over 70 GW by 2040 (James et al, 2022).

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