Offshore Code Comparison Collaboration within IEA Wind Annex XXIII: Phase III Results Regarding Tripod Support Structure Modeling

Offshore wind turbines are designed and analyzed using comprehensive simulation codes that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the wind turbine, along with the incident waves, sea current, hydrodynamics, and foundation dynamics of the support structure. This paper presents an overview and describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration, which operates under Subtask 2 of the International Energy Agency Wind Annex XXIII. In the latest phase of the project, a variety of project participants using an assortment of codes have modeled the coupled dynamic response of a 5-MW wind turbine installed on a tripod substructure in 45 m of water. The code predictions from a set of load case simulations-each selected to test different features of the models-were compared side-by-side. The comparisons have resulted in a more thorough understanding of the modeling techniques and better knowledge of when various approximations are not valid. Importantly, the lessons learned from this exercise have been used to improve the codes of the participants, hence improving the standard of offshore wind turbine modeling.