Dynamic Response Optimization of Steel Jackets for Offshore Wind Turbines With Fatigue and Time-Dependent Constraints

Abstract

In this work, a methodology for the shape and sizing optimization of steel jackets for offshore wind turbines considering the full dynamic response of the structure in a fully-coupled model is presented. The coupled model includes the jacket, the transition piece, the tower of the turbine, the rotor-nacelle assembly and the blades. The rotation of the blades is also included in the model. Ultimate limit state (ULS), fatigue limit state (FLS) and natural frequency constraints are imposed to the model and the weight of the steel jacket is optimized using design variables that control the size of the elements and the overall geometry of the structure. A new formulation is introduced to deal with time-dependent ULS constraints allowing an efficient treatment of the constraints while being suitable for gradientbased optimization. The formulation reduces the size of the large-scale constrained optimization problem and the constraints are satisfied at every time-step of the dynamic analysis. This work represents the first optimization approach to tackle the optimization of the jackets in fully-coupled models with constraints in the complete dynamic response and in the fatigue damage. A numerical example is shown and optimized achieving a significant reduction of half of the weight of the structure and a considerable change in the overall geometry of the structure.