Effect of the wind turbine floater geometry on the uncertainty associated with the hydrodynamic loading

Abstract

The study aims to contribute to the establishment of the reliability-based design for floating offshore wind turbines by quantifying the uncertainty in Morison's wave force in the extreme conditions for two floating wind turbine platforms, namely, the Spar and the OC4 DeepCwind semi-submersible. Numerical models are developed to estimate the wave forces on cylindrical members with different configurations and then to quantify the uncertainty in the output using the propagation law of uncertainty. Morison's coefficients are extracted from Sarpkaya's data as a function of relative roughness, Keulegan-Carpenter number, Reynolds number and the member inclination angle. The combined uncertainty for each input is investigated based on the gathered data from different sources of uncertainties. The First-Order Second-Moment method is then adopted to quantify the output uncertainty based on the uncertainty in the input variables. Furthermore, the contribution of each random variable to the total uncertainty is analysed. The study reveals that wave height is the most significant contributing random variable to the total uncertainty.