Optimal control of wave energy systems considering nonlinear Froude-Krylov effects: control-oriented modelling and moment-based control

Motivated by the relevance of so-called nonlinear Froude-Krylov (FK) hydrodynamic effects in the accurate dynamical description of wave energy converters (WECs) under controlled conditions, and the apparent lack of a suitable control framework effectively capable of optimally harvesting ocean wave energy in such circumstances, we present, in this paper, an integrated framework to achieve such a control objective, by means of two main contributions. We first propose a data-based, control-oriented, modelling procedure, able to compute a suitable mathematical representation for nonlinear FK effects, fully compatible with state-of-the-art control procedures. Secondly, we propose a moment-based optimal control solution, capable of transcribing the energy-maximising optimal control problem for WECs subject to nonlinear FK effects, by incorporating the corresponding data-based FK model via moment-based theory, with real-time capabilities. We illustrate the application of the proposed framework, including energy absorption performance, by means of a comprehensive case study, comprising both the data-based modelling, and the optimal moment-based control of a heaving point absorber WEC subject to nonlinear FK forces.

Automated summary

Motivated by the relevance of nonlinear Froude-Krylov (FK) hydrodynamic effects in wave energy converters, this paper presents an integrated framework for accurately describing and optimizing the control of WECs under controlled conditions. The framework consists of a data-based modeling procedure to compute a suitable mathematical representation for nonlinear FK effects and a moment-based optimal control solution to transcribe the energy-maximizing optimal control problem. A comprehensive case study is used to illustrate the application of the proposed framework, including energy absorption performance.