Experimental Identification of an Advanced Spar’s Low Frequency Drag Damping in Waves

Abstract

Abstract Climate change and increasing population growth are accelerating the need for new clean renewable energy generation. One such proposed type of renewable energy is offshore floating wind, which has yet to reach a convergence as to the optimum type of floating platform to support a wind turbine. To date there has been numerous proposals of novel floating platforms with unique hull characteristics. One such type is the advanced spar, which has a large area of sharp edges and therefore considerably different hydrodynamic viscous effects than typical cylindrical platforms. Prediction of a floating body’s low frequency drag damping is crucial to successfully predicting the horizontal motions. Calculation of the viscous effects have been seen to have the most uncertainty. Published literature shows that the viscous drag effects of floating bodies either increase or decrease with increasing wave severity as compared to still water decay tests. In this paper a combined experimental and numerical method for identifying low frequency viscous damping effects on the hull of a moored platform is introduced. An initial offset is applied to the platform, which is then released in still water and regular sinusoidal waves. The experimental results will then be compared to a weakly nonlinear time domain model in order to identify how the drag coefficients vary with wave conditions. Discussions on Keulegan–Carpenter (KC) number dependent damping are given. Finally simulations using results from these experiments are compared against a full scale deployed floating platform in multi-directional waves, current and wind.