Optimization of offshore wind turbine support structures using analytical gradient-based method

Design optimization of the offshore wind turbine support structure is an expensive task; due to the highly-constrained, non-convex and non-linear nature of the design problem. This report presents an analytical gradient-based method to solve this problem in an efficient and effective way. The design sensitivities of the objective and constraint functions are evaluated analytically while the optimization of the structure is performed, subject to sizing, eigenfrequency, extreme load and fatigue load constraints. A case study is carried out for the OC4 jacket substructure to evaluate the method. Results shows that an optimal jacket design with 52 percent structural mass reduction is attained in 27 iterations, while satisfying all design constraints under the simplified load cases used. Besides, it is shown that the analytical sensitivity analysis is more accurate and efficient than the often used finite difference approximations. It can avoid numerical artifacts that typically occur in the analysis of extreme load constraint sensitivities