Hydrodynamic Response of Semi-Submersible FOWT Floaters: A Numerical Investigation of Wave and Mooring Parameter Dependencies

Abstract

Floating wind turbines have enormous potential in harnessing high wind speeds in deep ocean locations. Compared with bottom-fixed technology, the latter is limited by the depth to which it can be installed. These turbines are designed to be deployed in deep waters and rely on specialized floaters such as spar buoys, semi-submersibles, and tension leg platforms to provide structural support. These floaters are tethered to the seabed using mooring lines, which regulate their movements and maintain stability. However, the existing literature lacks in-depth studies that comprehensively analyze how waves and mooring lines impact the motion of a semi-submersible floater. To address this gap, computational fluid dynamics (CFD) simulations are conducted using the overset methodology to replicate the actual loads experienced by semi-submersible floaters accurately. The study accurately predicts the six degrees of freedom (DOF) of the platform’s motion. The mooring lines are modeled using static or moving boundaries, and their interaction with the floater surface has been modeled using contact forces. The approach can simulate the impact of waves and mooring lines on the floater’s motion. The study uses the specifications depicted in the OC5 semi-submersible platform with mooring in test conditions and compares it with available experimental data to validate the numerical model. Once validated, the model is used to explore the hydrodynamic behavior of the floating structure across a range of waves characterized by varying amplitudes, periods, and directions. Similarly, in the case of the mooring lines, variations in critical parameters such as stiffness, pre-tension, and free length are introduced. This systematic manipulation of parameters enables a comprehensive investigation into their respective impacts on the dynamic response and motion of the floating platform.