Wind Turbine Control with Active Damage Reduction through Energy Dissipation

In this paper we propose an active damage reduction control strategy for wind turbines based on dissipated energy. To this end we rely on the equivalences relating both damage in the rainflow counting sense and dissipated energy to the variations of Preisach hysteresis operators. Since dissipation theory is well suited for control systems, we adopt the dissipated energy of a Duhem hysteresis model that is described by a differential equation. Accordingly, we incorporate the dissipated energy into the optimal control problem formulation as a proxy to the damage. Lastly, the proposed strategy is evaluated with NREL’s FAST high-fidelity non-linear wind turbine

Frequency-Domain Hydrodynamic Modelling of Dense and Sparse Arrays of Wave Energy Converters

In this work, we develop a frequency-domain model to study the hydrodynamic behaviour of a floater blanket (FB), i.e., an array of floater elements individually connected to power take-off (PTO) systems, which constitutes the core technology of the novel Ocean Grazer (OG) wave energy converter (WEC). The boundary element method open-source code NEMOH is used to solve the scattering and radiation problem. The aforementioned floater elements that comprise the FB are mechanically interconnected via (cylindrical, revolutional or spring) joints, which add extra constraint equations to the multibody problem. Various scenarios are investigated to understand the hydrodynamic response of the FB. The variation of the capture factor, PTO damping coeffcients, q-factor and response amplitude operator (RAO) of each scenario are analysed, in order to quantify the device performance. A new concept based on a negative-stiffness spring joint is proposed to increase the energy output of the FB. Attention is also paid to the anti-resonance that is found in the numerical simulations. This study provides further insight into the hydrodynamic behaviour of dense or sparse, interconnected arrays of WECs, which is fundamental for the design and optimisation of the OG-WEC