Beyond OC5 – Further advances in floating wind turbine modelling using Bladed

Floating wind turbines offer the potential to harness the considerable wind energy resource located at deep water offshore locations. Accurate numerical modelling of floating wind turbines is of utmost importance given its prominence in the design process. DNV GL's aero-hydro-servo-elastic modelling package 'Bladed' was one of the tools validated as part of the Offshore Code Comparison Collaboration Continuation with Correlation (OC5) project [1] and gave favourable results alongside the other participants. However, in common with all of the participants using a Boundary Element Method hydrodynamic approach, the majority of the loads were under-predicted (whilst over-predicted by Morison-only approaches). In particular, the low frequency excitation was not fully captured in the Bladed numerical simulations. This paper describes the implementation and results of new simulations in which additional modelling features are implemented in the DNV GL Bladed OC5 model. The results show that including instantaneous hydrostatics and Froude-Krylov forcing produces a better match with experimental spectral energy density for platform pitch and surge motion, which in turns leads to improvements in tower base shear force predictions.