Multi-objective optimization of orthogonal TLCDs for reducing fatigue and extreme loads of a floating offshore wind turbine

Floating offshore wind turbines have substantial potential to harness energy in deep-water locations, however, compared to fixed-bottom offshore wind turbines, they also have more complicated dynamic behavior that may lead to larger structural loads. In this paper, structural control using tuned liquid column dampers (TLCDs) is applied to a tension leg platform type floating offshore wind turbine in order to improve the structural response and reliability of the system. A structural control module in the aero-hydro-servo-elastic wind turbine simulator, FASTv8, is developed that enables the analysis of passive orthogonal tuned liquid column dampers with variable cross-sectional areas. Multi-objective optimization using the nondominated sorting genetic algorithm II is solved to provide an optimal Pareto front that can be used to select designs of the orthogonal TLCDs. With the optimal designs, non-linear fully-coupled time marching simulations are conducted to evaluate the impacts of the orthogonal TLCDs on reducing fatigue and extreme loads. The simulation results demonstrate the effectiveness of the orthogonal TLCDs on reducing the fore-aft and side-to-side fatigue and extreme loadings.