Fully-coupled wind turbine simulation including substructuring of support structure components

Offshore wind turbines (OWT) are currently designed and certified based on loads calculated in so called aero-servo-hydro-elastic simulation tools. Large sets of time domain simulations are run, especially in the certification process. In ADCoS-Offshore - the software used in this study - branched support structures are modeled with finite element (FE) beam members. These structures usually consist of hollow steel tubes connected by joints. As the representation of the joints using FE beam members is not too precise, ADCoS-Offshore was extended with a substructuring feature to model the joints more accurately. In this paper, a model of a 5MWOWT that includes a "basic" support structure model, and an OWT model incorporating superelements to represent the support structure's joints are briefly described. Furthermore, a heavily reduced fatigue load case set based on the respective standards combined with statistical data for a given site is presented. Based on these load c ases and with both, the basic beam model and the model incorporating superelements, the simulations are performed. Results are compared mainly in terms of post processed fatigue parameters and interpreted. Finally, conclusions are drawn indicating the necessary model fidelity for the fully-coupled simulations of this type of turbine under the given conditions.