Experimental assessment of engineering models with CFD derived heave hydrodynamic coefficients for a shallow draft barge-type floating wind turbine

Abstract

Nonlinear hydrodynamic loading for barge-type floating wind turbines (FWTs) remains particularly challenging to capture accurately using engineering (mid-fidelity) models. This study examines the wave-induced responses of a barge-type FWT. Model tests are performed for the novel WindBarge 16 MW FWT under various wave conditions. The heave added mass and quadratic damping are estimated using CFD simulations under forced oscillation in still water. Several engineering models are established using the aero-hydro-servo-elastic tool SIMA. The first-order and second-order difference-frequency wave loads are calculated based on potential flow theory. To account for viscous effects associated with the bilge keels around the platform bottom, CFD-derived added mass and quadratic damping/drag force formulations in heave are incorporated into the engineering model, while experimentally calibrated damping terms are included where needed. Numerical simulations are performed to reproduce the experiments under decay tests, regular and irregular waves. Platform motions and tower base fore-aft bending moments are compared against the experimental results. The CFD-derived heave added mass markedly improves the prediction of the natural period in heave (reducing the error compared to experiments from -9.61% to -3.93%) and the heave response in the wave-frequency range. Furthermore, the CFD-informed drag model improves the agreement with the measured heave response, as well as the pitch and tower-base bending moments near the natural frequency in pitch under irregular wave conditions. The experimental RAOs reveal wave-height-dependent nonlinear effects in surge, pitch, and tower-base bending moments, while the numerical models reproduce the overall response levels reasonably well but do not fully capture these trends.