Evaluating the workability of On-Site Assembly of a 15MW Wind Turbine Blade on a Semi-Submersible Floating Wind Turbine Using a Crane Vessel

Abstract

Offshore wind energy is poised for significant growth, with three major trends emerging: larger wind turbines, offshore wind farm sites in deeper waters further from the coast, and a shift towards floating offshore wind energy. While current floating wind turbines are installed using a tow-to-site strategy, the increasing size of turbines and foreseen implementation scale raises the question if on-site installation will be more a viable option. This research investigates the operational feasibility of on-site installation of the NREL 15 MW wind turbine blade on a semi-submersible floating wind turbine using a floating monohull crane vessel. This study uses a simplified frequency-domain multi-body model to assess the workability of installing blades on the GustoMSC Tri-floater using a floating monohull crane vessel. The model assumed first order potential flow, rigid body motions for the Tri-floater and the crane vessel, and neglected wind and current loads. The comparison of the multibody and single-body models revealed that positioning the crane vessel next to the Tri-floater resulted in shielding, diffraction, radiation and reflection effects, which were also observed vice versa for the crane vessel but to a lesser degree. Results show that the workability for floating-to-floating operations is 31%, compared to a workability for a fixed-to-fixed operation of 87%. The relative surge was limiting, caused by the crane vessel roll angle. A sensitivity analysis on wave direction showed that the wave direction has significant impact on the relative motion and the workability. This optimal wave orientation resulted in a floating-to-floating workability of 51%. The workability of a floating-to-fixed operation was found comparable to that of a floating-to-floating operation. The preliminary findings indicate that on-site installation for floating-to-floating operations is more challenging than fixed-to-fixed operations. However, workability is comparable to floating-to-fixed operations, suggesting little impact from floating wind turbines. Further research, including wind loads, is recommended to understand the difference between installations. Another area for study is the development of a specialized blade installation tool to aid floating wind turbine installation.