The coupled action of wind and wave on the stability of floating offshore wind turbines (FOWT) tremendously affects the lifespan of these energy systems and their energy output. Passive control systems reduce such loads but can only mitigate the loading over a small range of excitation frequencies. To improve this, an active control system (ACS) is needed. The aim of this research is a digital twin proof of concept allowing the diagnosis of current and upcoming environmental events and re-tuning the ACS based on a tuned mass dampers system (TMD) to minimize wave-induced response at the frequency range of interest. This is accomplished through a series of numerical investigations supported by laboratory measurements in a wave basin made on a scale model of a 15MW FOWT. The numerical models are implemented via the multi-physics, multi-fidelity code: OpenFAST, that enables coupled nonlinear aero-hydro-servo-elastic simulation in time domain. The code is modified to enable ACS implementation and ease of communication between the controller and OpenFAST. After validating the model, an open-loop controller is designed to allow multiple stiffness and damping entries targeting first-order wave-frequency region. Two methods of data acquisition are investigated: the Current Sea-State Controller (CSSC) where sea-state prediction is governed by past wave elevation data points using a polynomial weighted buffer that leverages more recent data, and the Future Sea-State Controller (FSSC) that, additionally utilizes reconstruction/prediction model of the upcoming wave to investigate the effect of reduced latency in the controller response. Both controllers are optimized through a genetic algorithm scheme. Results show reduction in wave excitations ranging between 10s to 20s under varying sea-state when future wave elevation data is fed to the controller.
Wind energy is being recognized as a central factor in attaining Paris agreement (COP21) goals of 1.5°C global warming by the year 2100. Specifically, offshore wind energy is the most commercially well-established marine renewable form with a relatively mature technology (Astariz and Iglesias, 2016). This motivates more industry to be included in the picture and is the reason behind a year-over-year (YoY) growth of 12% in the year 2021 which was the wind industry's second-best year after 2020. Onshore wind market added 72.5 GW worldwide whereas offshore installations represented 22.5% of all new installations in the year 2021, bringing the world's total offshore capacity to 57GW (Council, 2022).
