Global limit states for the design of floating wind turbine support structures

Reliability is an essential parameter for offshore wind turbines which are located some distance from the coast in mostly quite harsh environments. Limited weather windows for maintenance and repair work indicate the relevance for using reliability-based methods during the design process of wind turbine structures. This is even more crucial but also more challenging for floating devices due to the highly complex system dynamics and interactions. In this work, the use of global limit states for the design of floating support structures is elaborated. Reliability criteria which are essential for floating wind turbine systems are selected and their critical values are defined. Based on these, the global limit state functions can be set up. Furthermore, the dependencies and predefined boundary conditions of the parameters for the design of floating support structure have to be worked out, so that the modifiable variables can be identified and their effect on the global limit state functions and reliability criteria analysed. This study should serve as basis for developing a reliability-based optimisation tool for the design of floating wind turbine support structures, which uses global limit states and could be extended to consider local characteristics as well.