Reliability-based optimization of floating wind turbine support structures

Floating offshore wind technology has high potential due to the renewable energy goals and the vast deep water ocean areas, however, still faces several challenges until achieving commercial market uptake. Floating concepts have to gain economic competitiveness and deal with more complex coupled system dynamics and greater uncertainties. This makes modeling, simulation, and reliability-based design optimization indispensable. However, reliability assessment and design optimization of floating wind turbines has not yet been coupled. - This is precisely the focus of this thesis. The overall aim is to derive guidelines for reliability-based design optimization of floating wind turbine support structures, taking target safety levels and failure mechanisms from existing standards into account and applying them in such novel concepts. To achieve this, reliability methods applied in the offshore and marine renewable energy industry are reviewed, classified, and investigated with respect to suitable procedures for reliability assessment of offshore wind turbine systems. Addressing the aspect of floating wind, the large diversity of existing floating support structures is assessed, focusing on their suitability for offshore wind farm deployment. Based on this, a reference floating wind turbine system is defined, for which an aero-hydro-servo-elastic coupled model of dynamics is developed and verified. Additionally, a holistic framework for automated simulation and optimization is developed and applied to different design optimization tasks: based on global limit states, addressing innovative design solutions or the future trend towards larger MW-class wind turbines, and finally including reliability criteria. The developed model, framework, and approaches - especially the concept for combining floating wind turbine design optimization with reliability assessment in a computationally and time-efficient manner - are of high value for both research and industry. The knowledge and outcomes of this thesis offer a broad range of future applications and pave the way towards economic and reliable floating support structure designs.Floating offshore wind technology has high potential due to the renewable energy goals and the vast deep water ocean areas, however, still faces several challenges until achieving commercial market uptake. Floating concepts have to gain economic competitiveness and deal with more complex coupled system dynamics and greater uncertainties. This makes modeling, simulation, and reliability-based design optimization indispensable. However, reliability assessment and design optimization of floating wind turbines has not yet been coupled. - This is precisely the focus of this thesis. The overall aim is to derive guidelines for reliability-based design optimization of floating wind turbine support structures, taking target safety levels and failure mechanisms from existing standards into account and applying them in such novel concepts. To achieve this, reliability methods applied in the offshore and marine renewable energy industry are reviewed, classified, and investigated with respect to suitable procedures for reliability assessment of offshore wind turbine systems. Addressing the aspect of floating wind, the large diversity of existing floating support structures is assessed, focusing on their suitability for offshore wind farm deployment. Based on this, a reference floating wind turbine system is defined, for which an aero-hydro-servo-elastic coupled model of dynamics is developed and verified. Additionally, a holistic framework for automated simulation and optimization is developed and applied to different design optimization tasks: based on global limit states, addressing innovative design solutions or the future trend towards larger MW-class wind turbines, and finally including reliability criteria. The developed model, framework, and approaches - especially the concept for combining floating wind turbine design optimization with reliability assessment in a computationally and time-efficient manner - are of high value for both research and industry. The knowledge and outcomes of this thesis offer a broad range of future applications and pave the way towards economic and reliable floating support structure designs