Author(s): H. Chen; J. S. Zhang; D. W. Guan
Linked Author(s): Hongyun Chen
Keywords: Jacket foundation; Scour; Wave-current interaction; Keulegan–Carpenter number; Shields parameter
Abstract: This paper presents the experimental results to investigate the scour around a jacket foundation under the combined, cyclically varied wave-current loading. Under such complicated hydrodynamic action, sediment transport and the resultant scour evolution around the jacket foundations are extremely complex compared to that around monopile foundations. This study investigates the effects of wave-current parameters, including flow strength and Keulegan–Carpenter number (KC), on the local scour characteristics around a jacket foundation through comprehensive laboratory experiments. The effect of the relative wave-current velocity (Ucw) on the clear-water and live-bed scours are examined. Results indicate that the scour pattern is dominated by the current and the jacket piles are surrounded by inverted-cone scour pit when Ucw exceeds 0.49 in this study. When Ucw is less than 0.49, the piles are surrounded by concentric circular scour pit. The relative scour depth, normalized by the pile diameter, increases linearly with the increase of KC number for a constant flow strength. However, the growth rate of the equilibrium scour depth decreases with the increase of flow strength. Fluctuations of the maximum scour depth with the Shields parameter θ and the Froude number Fra are also investigated. Experimental results show that the equilibrium scour depth increases as the Shields parameter increases when θ<θcr (corresponding to clear water scour condition), with a gradually decreasing growth rate. However, the correlation between the Shields parameter and the equilibrium scour depth exhibits a fluctuation pattern with two distinct upward and downward trends when θ>θcr, corresponding to live-bed scour condition. Moreover, the equilibrium scour depth increases with an increasing Fra, while the growth rate slows down as both KC number and flow strength increase. Notably, the equilibrium scour depth is greatly influenced by the composition of current and wave-induced flow.
Year: 2024