Shutdown orientation induced load transfer and risk redistribution in a floating vertical-axis wind turbine under extreme wind and wave conditions

The survivability of floating vertical axis wind turbines (VAWTs) under extreme parked conditions is strongly affected by the transfer of aerodynamic loads through the rotor, floating platform, mooring system, and critical structural regions. However, the role of rotor shutdown orientation in this system-level load transfer process remains insufficiently understood. In this study, a high-fidelity CFD method coupled with a third-party CAE implicit solver is used to establish a two-way fluid structure interaction framework, in which the rotor, platform, and mooring lines are treated as flexible structures. A two-bladed H type floating VAWT mounted on a semi-submersible platform is investigated. Under the 50-year extreme wind speed and a representative severe sea condition, the fully coupled dynamic responses are compared for three shutdown orientations, namely 0°, 45°, and 90°. The results show that the 0° orientation produces the strongest flow separation and vortex shedding, together with the largest rotor thrust, platform pitch, and ML2 peak tension. The maximum rotor stress is concentrated at the blade support arm connection. The 45° orientation reduces the mean thrust but introduces stronger asymmetric loading, leading to larger sway, roll, yaw, mooring tension redistribution, and twisting of the side mooring lines. The 90° orientation shows the lowest aerodynamic loads, platform motion, blade deformation, and overall mooring tension, but shifts the local mooring risk toward the seabed contact region. This study provides guidance for shutdown orientation selection and future degradation driven survivability assessment of floating wind systems.