Session: 09-01-07 Wind Energy: Aero-hydrodynamics 7

Paper Number: 132884

132884 - Integrated Load Analysis of a Floating Offshore Wind Turbine Under Extreme Sea States Using Hydroqus: Fully Coupled Aero-Hydro-Structure Interactions 

For the design of a floating offshore wind turbine (FOWT), time-domain integrated load analysis (ILA) including hydrodynamic forces, wind forces, and mooring forces is essential. Commonly used integrated load analysis programs and codes include OrcaFlex and OpenFAST, but they do not account for the elasticity of the substructure of the FOWT. To consider the elasticity of the floater, a finite element analysis program such as Abaqus is required, but it is difficult to consider the hydrodynamic forces acting on the wetted plate. In this study, we introduce a procedure for performing an integrated load analysis of a FOWT using Abaqus/Explicit, a finite element analysis program used for structural analysis, and HydroQus, a self-developed hydrodynamic force calculation plug-in.

The research was conducted for a 10MW capacity FOWT, consisting of a semi-submersible float with a displacement of approximately 10,000 tons and three catenary mooring lines The integrated load analysis was performed for the ultimate limit state, Design Load Case (DLC) 6.2. The environmental loads considered were wave height, wave period, current speed, and wind speed with a 50-year return period. The finite element analysis model for the ILA includes the rotor, tower, floater, mooring, and seabed. The rotor, tower, floater, and seabed were shell elements, and the mooring lines were composed of beam and joint elements. The shell element size is mostly the stiffener spacing. In DLC 6.2, the turbine is in a parked condition, so the wind forces acting on the rotor were ignored. To apply the wind and current forces due to wind speed acting on the tower and current speed acting on the floater, beam elements were placed along the tower centerline and floater column centerline. To consider the wave and radiation forces acting on the floater, the center of mass of the FOWT and the floater are connected by a load coupling element. Elastic catenary equation was used to determine the layout and discretized into beam elements and universal joint elements to model the mooring lines with no out-of-plane bending stiffness.

The results of the HydroQus-based integrated load analysis were validated against the commercial program OrcaFlex. The motion histories and mooring tension histories were in very good agreement, validating the accuracy of HydroQus. Large stress developments were observed at two interfaces: The floater column-deck interface and the tower-floater interface. In the future, HydroQus will be used to conduct various application research such as integrated load analysis but also collision analysis with passing ships. We will also port OpenFAST's AeroDyn and ServoDyn directly to HydroQus to perform ILAs for in-operation DLC for the FOWT.

Presenting Author: Dong Ho Yoon Inha University

Presenting Author Biography: Dong Ho Yoon is a Ph.D. student in the Department of Naval Architecture and Ocean Engineering at INHA university, South Korea.
He has been studying Fluid-Structure interaction techniques such as integrated load analysis of floating offshore wind turbine (FOWT).

Authors:

Dong Ho Yoon Inha University
Joonmo Choung Inha University