Non-Linear Tuned Mass-Damper-Inerters for Vibration Reduction and Energy Harvesting within Semi-Submersible Offshore Wind Platforms

Abstract Offshore floating wind turbines experience greater pitch and heave motions than their fixed counterparts, resulting in component fatigue that reduces the longevity of the turbine structure. While various vibration control systems have been proposed to reduce vibrations, this paper proposes a novel non-linear tuned mass-damper-inerter (TMDI) system within the columns of the semi-submersible platform that is able to simultaneously dampen vibrations and harvest power from the vibrations. As such, the design essentially incorporates three wave-energy converter power take-off systems within the floating platform structure. Modeling of three non-linear TMDIs within the system was completed using a Euler-Lagrangian approach and optimization was completed using pattern search in MATLAB. The nonlinear TMDIs performed better than the linear TMDIs and tuned mass-dampers (TMDs) over the broader frequency range but underperformed the linear TMDIs and TMDs at peak loading. This indicates promise for regions with highly variable wave conditions; however, the TMDs and linear TMDIs may still perform better on semi-submersible platforms in some offshore locations. For identical vibrational performance, the linear and non-linear TMDIs required lighter secondary masses than TMDs. Additionally, theoretical power potential from the TMDI generator increased with the introduction of nonlinearity for most design cases.