Ship collision against a 10 MW semi-submersible floating offshore wind turbine

Abstract

The number of installed offshore wind turbines is continuously expanding worldwide in recent years. Floating offshore wind farms are generally located near the coast close to traffic lanes and are exposed to the risk of collisions from visiting and passing ships. Extreme ship collision events may cause large structural damage, collapse of turbine tower and flooding of compartments, leading to capsizing of turbine platforms. This paper investigates ship collision responses of a semi-submersible floating offshore wind turbine (FOWT), i.e. the OO-STAR floater with DTU 10 MW blades, using the nonlinear finite element code USFOS. The OO-STAR floater is made of post-tensioned concrete designed by Dr. techn. Olav Olsen. The striking ship is selected to be a modern supply vessel of 7500 tons. Modelling of the FOWT in USFOS is described in detail including the OO-STAR floater, the DTU 10 MW turbine blade, the turbine tower and the mooring system. Eigenmode analysis of the turbine model is performed to verify the modelling. Global collision response analyses of the FOWT were performed in both parked and operating conditions. The ship resistance is modeled as nonlinear springs in USFOS containing force - displacement curves established in LS-DYNA. The results are discussed with respect to global responses of the FOWT and energy absorption.