In this paper, the exemplary results of the IEA Wind Task 30 "Offshore Code Comparison Collaboration Continuation" (OC4) Project - Phase 1, focused on the coupled simulation of an offshore wind turbine (OWT) with a jacket support structure, are presented. The focus of this task has been the verification of OWT modeling codes through code-to-code comparisons. The discrepancies between the results are shown and the sources of the differences are discussed. The importance of the local dynamics of the structure is depicted in the simulation results. Furthermore, attention is given to aspects such as the buoyancy calculation and methods of accounting for additional masses (such as hydrodynamic added mass). Finally, recommendations concerning the modeling of the jacket are given.
The analysis of offshore wind turbines relies on aero-hydro-servo-elastic simulation codes. These coupled time-domain-based tools take into account an interaction of various environmental conditions and the entire structural assembly of the turbine, including its control system. Due to the complexity of the models, verification and validation of the codes is required. Limited availability of measurement data impedes the validation of these simulation tools. Therefore, there is a need to perform code-to-code comparisons (verification) instead. The first international project dedicated to verification of simulation tools for wind turbines, including hydrodynamic loads, was undertaken within the "Offshore Code Comparison Collaboration" (OC3) Project (Jonkman and Musial, 2010). The cooperation was focused on coupled simulations of an offshore wind turbine supported by a variety of support structures. Further research needs triggered a follow-on project, the "Offshore Code Comparison Collaboration Continuation" (OC4) Project. The OC4 project was formed under the International Energy Agency (IEA) Wind Task 30 in 2010 to investigate wind turbine coupled simulations with a jacket support structure and a semisubmersible platform. Complex hydrodynamics of the latter and local vibration phenomena of the former have not been broadly studied yet, and therefore, their analysis is of interest.