Discussion of solutions for basin model tests of FOWTs in combined waves and wind

Model testing of offshore floating wind turbines (FOWTs) needs to account for the hydrodynamics of the floater at the same time as the aerodynamics of the rotor, and their interactions. Testers have followed two distinct paths to solve the challenge of modelling these two dissimilar physical phenomena. One path has consisted of building physical models at basin scale that resembled the actual FOWT: a ‘‘full approach’‘. With this approach, every component of the model test needs to comply with Froude scaling laws: wind generators have been improved, dedicated scaled turbines designed and a method known as performance scaling developed. The second path consisted of mimicking the most relevant components of the wind turbine loads and applying them to the floater (at the wind turbine tower top): a ‘‘simplified approach’‘. With this approach, a specific experimental set-up is designed to transfer the wind turbine loads, which, in the case of hybrid testing are calculated by an aerodynamic simulation code. This article reviews the state of the art of testing FOWTs in basins, with a focus on the most complete examples of each testing approach. Limitations, similarities, differences and complementarities between the approaches are described and discussed. To continue improving testing techniques, there is an acute need for more comparisons between different testing approaches and validation against full-scale measurement campaigns.