Multidisciplinary design analysis and optimization of support structures for offshore wind turbines
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The purpose of this thesis was to implement complex optimization techniques developed in the aerospace industry for structural optimization of offshore wind turbine support structures. The OpenMDAO (Multidisciplinary analysis and optimization) framework developed by NASA (Na- tional Aeronautics and Space Administration) was used to develop a structural optimization pro- gram in combination with a finite element solver in order to reduce the weight of the support structure. The analysis is based on a bottom-fixed tower-jacket support structure. A selection of three different algorithms and two different analysis methods were developed and tested in a case study. Two of the algorithms were programmed to optimize both jacket and tower simultaneously, and one sequentially. Due to the complexity of the support structure, the simultaneous optimization gave larger weight reduction than the sequential optimization. One of the two simultaneous opti- mization algorithms used a two-stage approach. In the first stage the structure had both an upper and lower constraint for stress and fatigue damage. In the second stage, only an upper constraint for fatigue damage and stress was used. At the same time the relative dimensional ratio from the first stage was preserved. This algorithm performed best in terms of weight reduction. Both of the simultaneous optimization algorithms were recommended for further development.