2024A-OS4-4 3D Tracking of Mooring Lines of Floating Offshore Wind Turbines by Autonomous Underwater Vehicle

Abstract

This paper presents an method for inspecting mooring lines of Floating Offshore Wind Turbines (FOWTs) using an Autonomous Underwater Vehicle (AUV) equipped with a tilt-controlled Multibeam Imaging Sonar (MBS). The method allows the AUV to estimate mooring line positions and safely track them. Using the tilt angle of the MBS and a pre-trained YOLO model, the AUV determines 3D positions of mooring chains from sonar imagery. The tracking system maintains a safe distance from the chains by dynamically adjusting surge and sway velocities based on real-time detection. Continuous tracking enables the AUV to reconstruct the entire mooring line structure using position data estimated through dead reckoning. The method was tested with the hovering type AUV, Tri-TON, during a sea trial at the FOWT Hibiki in Kitakyushu, Japan, validating the method to track mooring lines for 343 seconds and successfully reconstruct their entire structure.