Multi-objective Non-causal Optimal Control of an Active Pumping System for a Floating Wind Platform

Semi-submersible floating offshore wind turbines (FOWTs) are susceptible to undesirable wave- and wind-induced pitch motion which may be reduced by control strategies. Presently these mainly rely on passive damping, which becomes ineffective under varying sea states. To address this issue, this paper proposes an active pumping strategy for water ballast using multi-objective non-causal optimal controller to suppress pitch motion by pumping water among three columns, thereby generating a counteracting moment against wave and wind excitations. Firstly, the dynamic model of the triple-column VolturnUS floating platform, coupled with hydrodynamic and aerodynamic forces, is developed using the Euler–Lagrange method. Based on this model, a multi-objective non-causal optimal controller is developed to balance pitch motion suppression and pumping power. When pitch minimization is prioritized, compared with the conventional passive damping control, the proposed method reduces the pitch motion by 85% but with high power demand. When power consumption is penalized, the controller can still reduce the pitch by 82% while lowering power usage by 95%, indicating a trade-off between motion suppression and pump energy consumption.