Abstract
The paper presents the results of demonstration towing tests conducted on a 1:40 scale model of the INO WINDMOOR semisubmersible floating wind turbine at SINTEF Ocean’s Ocean Basin. The primary focus of the experiments was to observe and analyze flow-induced motion (FIM), specifically vortex-induced motion (VIM) and galloping. FIM is a complex, non-linear fluid structure interaction, where the dynamic response is influenced by the interaction between the structure and the wake due to flow separation and interference. Understanding FIM is crucial for floating wind turbines, as these motions can significantly impact the integrity, stability, fatigue life of the platform and substructures. The natural periods of sway and yaw motion of the towing arrangement were significantly large, which, combined with the constraints of the basin’s dimensions, resulted in limited towing distances and durations. As a result, the measured signals only captured a few non-stationary, incomplete cycles, making the data challenging to analyse using conventional methods. Additionally, transient effects were observed in the measurements due to the short towing period. These conditions require alternative data analysis techniques capable of handling non-linear, non-stationary signals. The paper applies the Hilbert-Huang Transform (HHT), a time frequency analysis tool designed specifically for non-stationary and non-linear data. By employing HHT, the study aims to establish a systematic procedure for analysing FIM in semi-submersible floating wind turbines during towing operations. The results contribute to improving the analysis and prediction of FIM in real world floating wind turbine applications, helping to enhance their design and operational safety. This work provides insights into the challenges of measuring and analysing dynamic responses in scaled-down models, particularly when faced with limited experimental conditions.