Spatio-temporal analysis of scour around complex offshore foundations under clear water and live bed conditions

Abstract

This study investigates scour around offshore wind foundations, focusing on two complex structures with varying degrees of flow blockage: a novel hybrid gravity-based jacket (structure “A") and a conventional four-legged jacket (structure “B"). As offshore structures like jackets become more prevalent, mainly due to their structural stability and growth of offshore wind energy in general, understanding scouring phenomena around complex structures is crucial. Laboratory tests under steady flow clear-water and live-bed conditions, with measurements of 3D laser scans for test durations of 15, 90, and 420 min were conducted. In addition the scour development over time was measured and analyzed with eight echo sounders. The findings confirm that scouring around complex structures displays significant variability in dependency of the structure type, making standardization a challenging task. However, some common trends can be derived. Under live-bed conditions, both types of structures exhibit global erosion, regardless of the complexity or flow obstruction of the structure. The spatial erosion depth, relative to the footprint, is markedly higher (2.5 times) for the gravity-based structure as opposed to the jacket structure. In clear-water conditions, no global scour was observed for both structures and a very similar spatial erosion depth was reached after 420 min.