Performance of large diameter steel tubes from a floating offshore wind turbine under lateral impact loads

Abstract

Floating offshore wind turbines (FOWTs) are expected to be increasingly installed in the world to harvest wind power in deep waters. Offshore wind turbines are often located near the coasts close to the traffic lanes and are exposed to safety threats from collisions by passing and visiting ships. It is therefore of great importance to investigate the impact mechanics in ship-FOWT collisions and propose practical design methods to protect from the collision loads. This paper presents a series of experimental and numerical studies on the performance of steel tubes from a NREL 5 MW spar-type FOWT under lateral impact loads. The experiments are designed and conducted at a scale of 1:30, where a rigid indenter mounted on a pendulum system is accelerated to collide into the scaled tubes. Global motions of the impacted tubes are accounted for an equivalent single-degree-of-freedom (SDOF) model for the rigid FOWT motions. Finite element (FE) models were established in LS-DYNA software. The effects of impact velocity as a crucial factor on the performance of the tubes against impact loads were discussed. Existing theoretical solutions for the lateral indentation resistance of the tubes were compared to the experimental and numerical results.