Influence of Hydrodynamic Damping Model on Floater and Mooring Responses of 10MW Class Floating Offshore Wind Turbine

Abstract

In this study, the influence of the hydrodynamic damping model of the semi-submersible type floating offshore wind turbine (FOWT) on the floater and mooring dynamics were verified numerically and experimentally. Most of the FOWT substructures currently being developed are semi-submersible type and consist of a combination of multiple pontoons and vertical columns. These structures submerged in the sea water undergo dynamic behavior in the fluid domain under the influence of waves and currents. The drag force due to the shape of the structure and the damping force due to the viscosity of the fluid act in a complex way to affect the dynamic motion of the floater. In the initial stage of design, an integrated load analysis is performed to estimate the response characteristics of the structure. At this time, if an appropriate level of drag coefficient or damping coefficient is not applied to the floating structure, the motion of the floating body may be underestimated or overestimated. Since this affects the reliability of the entire structure, it is very important to select an appropriate damping model that can simulate the damping characteristics of the actual structure as closely as possible. The floating substructure used in this study is a semi-submersible type composed of three outer columns and one center column, and a DTU 10MW turbine is mounted at the center column. To design the optimal damping model for the 1/36 scale model, a combination of experiments and Computational Fluid Dynamics (CFD) was used. The linear and quadratic damping coefficients were determined by analyzing the results of free decay experiments conducted in calm water. These coefficients were applicable to the time-domain solution. The nonlinear Morison drag coefficient was obtained through a uniform flow field test using CFD. The characteristics of the obtained damping models were compared, and an appropriate combination method was proposed. Its validity was confirmed by applying it to the floating substructure. Copyright © 2023 by ASME.