Distributed Potential Theory and its Application for Spar-Type Floating Offshore Wind Turbines

Coupled aero-hydro-servo-elastic time-domain analysis is required for robust design and engineering of Floating Offshore Wind Turbines (FOWTs). For spar-type FOWTs, it is convenient to adopt a nonlinear beam finite element formulation in order to capture the coupled structural response of substructure, tower, blades and mooring lines accurately. The Distributed Potential Theory (DPT) approach applies first-order frequency-dependent added mass, radiation damping and excitation loads distributed over all submerged beam elements in the coupled time-domain simulation, as obtained from diffraction/radiation analysis. This approach therefore includes frequency-dependent diffraction effects for all wavelengths, while keeping the substructure flexible, thus enabling hydro-elastic coupling and extraction of internal sectional loads along the substructure. This paper demonstrates the use of DPT in coupled aero-hydro-servo-elastic time-domain analysis of a spar-type FOWT and illustrates the effect on tower and substructure fatigue life compared to using the classical Morison approach.