Optimization of floating wind turbine support structures using frequency-domain analysis and analytical gradients

A framework for conceptual optimal design of floating wind turbine support structures including mooring system is proposed. A four degree-of-freedom frequency-domain model is used for the dynamic response of the floating wind turbine subjected to wind and wave loads. The framework allows for integrated design optimization involving the geometrical properties of the floater and the mooring system and inclusion of long realizations of multiple load cases in the analysis. Analytical design sensitivities of the governing frequency-domain equations and the design requirements are developed. This ensures that modern numerical optimization methods can efficiently be used to solve the design problem. The framework is applied to sizing optimization of a spar-buoy floater including the mooring system. The inclusion of dynamic constraints in the design optimization is demonstrated. The optimization provides designs accurately satisfying optimality conditions in minutes.