Experimental Modeling and Investigation of Seabed Liquefaction at Large Scale, Part II: Wave-Structure Interaction

The design challenges of offshore wind are multifaceted, comprising techno-socio-enviro-economic aspects. Among the technological design challenges, seabed dynamics and seabed response to wave-induced and structural loading are of significant importance. While a number of studies are focused on the morphodynamics and scour around, for instance, monopolies, much less research has been dedicated to the liquefaction around marine structures and offshore wind installations in particular. Novel ocean structures such as floating offshore wind installations require complex anchoring systems for station keeping; thus, seabed liquefaction needs to be considered during the design phase. This study, together with the companion paper Part I, aims to provide unique insights into seabed liquefaction around a gravity-based, tension leg platform-type floating offshore wind system. To that end, experiments in the large wave-current flume, GWK⁺, at the Coastal Research Centre, Hannover, Germany, were performed at a very large length scale of 1:15.56. The results show, for the first time, the severity of compound wave-induced and structural loading. Small wave heights in the order of 0.56 m (model scale) trigger seabed liquefaction and lead to significant structural displacement in the order of meters (model scale). In addition, a discussion on model effects and uncertainties provides suggestions for future improvements of the experimental setup.