Prediction of Wake Flows Induced by an Offshore Wind Turbine Foundation: Understanding its Environmental Impact - Phase 2: Floating Platforms

Abstract

The deployment of Floating Offshore Wind Turbine(s) (FOWTs) requires methods to evaluate their hydrodynamic response and wake characteristics. This thesis ap plies the Immersed Boundary Method (IBM), implemented as the Virtual Body Method (VBM) in Simcenter STAR-CCM+, to simulate the UMaine VolturnUS-S semi-submersible platform. The methodology was validated against the dynamic Fluid-Body Interaction (DFBI) with overset meshing technique. For a 2D floating box in waves, the VBM reproduced heave and pitch natural periods with differences of 0.65% and 0.24%, respectively, while surge exhibited a 12% deviation. In 3D free-decay simulations of the UMaine VolturnUS-S foundation, the platform’s heave natural period agreed within 0.73%, whereas the pitch period deviated by 0.22% . Even with noticeable deviations, this VBM notably reduced computational costs by nearly 40% in core-hours per million elements for free decay case, when com pared to the DFBI cases with overset meshing. Applying the validated framework to full-scale conditions, multiphase simulations of the platform in a thermally strat ified environment were conducted. The results demonstrated that the multi-column structure generates a complex near-wake recirculation zone with persistent flow re versal. Thermal mixing was predominantly observed near the surface, resulting in a maximum mean temperature increase by 5.82K at a depth of 3.83m below the free surface, with mixing effects decaying rapidly in deeper waters. The findings validate the VBM as a functional fixed-grid alternative for simulating platform kinemat ics and provide a baseline for future environmental wake investigations involving FOWTs.