Effect of Increased Geometric Complexity on LoadActing on Floating Offshore Wind Turbine Platforms

Abstract

Renewable energy sources, including offshore wind energy, are fundamental to reducing fossil fuelconsumption and greenhouse gas emissions. Many countries are planning for a rapid and massive ex-pansion of the offshore wind sector to meet the NetZero goals. So far, the installation of offshore windturbines (OWT) has been restricted to near-shore shallow water (≤ 60m). However, future expansionof the sector will be in deep waters, away from the shore, where the wind speed is stronger and moreconsistent. Monopiles, the most commonly used foundations for OWT, become uneconomical or tech-nologically unfeasible in deep waters. Therefore, OWT supported by floating platforms is the way to goforward. The initial platform designs and construction were based on the experience obtained from theoil and gas industry (O&G). However, the load acting and the movement of the floating offshore windturbine (FOWT) platforms are vastly different from the O&G platforms. In addition to the aerodynamicloading, these platforms are subjected to hydrodynamic loading, making platform design a complex task.Evaluating the forces acting on these platforms, even under idealistic conditions, is challenging. Althoughsignificant progress has been made, platform, anchor, mooring, and turbine design improvement dependson accurate load calculation. Further, understanding hydrodynamic loading is essential to evaluate theenergy losses due to the FOWT system and, therefore, the mixing of the water column behind the struc-ture. In this research, the effect of increased geometric complexity on load acting on a semi-submersibleplatform is numerically investigated. Three unidirectional flow regimes of Reynolds number (Re) = 2900,43000, and 200000 are investigated, using the OC4 semi-submersible platform as the reference. The OC4semi-submersible platform was developed by the OC4-DeepCWind consortium to obtain experimentaldata and validate numerical models for FOWT. The results show that the drag force acting on the plat-form increases as the Re and number of members in the platform increases. These findings are importantin understanding the hydrodynamic loading on FOWT platforms under static conditions and designingthe platform, mooring and anchoring systems. Further, this is essential for the sustainable developmentof the offshore wind energy sector.