On the sensitivity of short design waves for semi-submersible wind platforms

Determining ultimate loads and platform motions is essential for both survivability and cost-effectiveness in the development of floating offshore wind. Current design standards utilise time-consuming methodologies that rely on irregular sea state simulations to determine design loads. Design waves offer the potential to accelerate the design process through the simulation of shorter wave profiles that specifically target extreme responses. However, it is not well understood how reliable design waves are for floating devices. Using a mid-fidelity numerical tool, this paper explores the characteristic loads produced by four design wave methods for a semi-submersible floating wind device over a wide range of environmental conditions, using the traditional approach as a benchmark. The results show that for most sea states there is a design wave method that is at least as conservative as the traditional approach. Furthermore, single design waves can be used to identify extreme sea states for more detailed analysis, saving considerable time at the early design stage. Finally, if the most efficient design wave is used for each sea state, there is potential for significant speed up within the design process, but this will rely on being able to reliably identify the method in advance.