Investigating the relevance of considering structural flexibility in model tests of floating wind turbine systems

The floating offshore wind market is evolving rapidly towards larger wind turbines, posing new challenges to present numerical and experimental methodologies used in the development and evaluation of floating offshore wind turbine (FOWT) designs. The inclusion of flexibility effects becomes increasingly important as wind turbines grow in size; nonetheless, small-scale model tests in wave basins are currently performed with rigid models. Ongoing work focuses on reflecting the structural flexibility characteristics of the floating support structure by advancing manufacturing approaches. This paper investigates the structural elasticity of the blades and tower as well as its impact on the dynamic system responses of different FOWT systems. The relevance of considering structural flexibility is evaluated in a comprehensive sensitivity study based on time-domain numerical simulations. Critical system parameters are compared for increasing wind turbine MW classes, two distinct floater types, different structural flexibility settings, and typical dynamic motions in representative sea states. It is found that consideration of structural flexibility has a substantial impact on fatigue loads of wind turbine systems of 10 MW and larger. Aeroelastic effects due to the blades’ flexibility, in addition to the tower's flexibility, are relevant for specific system parameter. Corresponding additional efforts should therefore be carefully weighed against the relevance of the affected parameters.