Numerical investigation of the local scour around a coconut tree root foundation under wave-current joint actions

Abstract

A novel type of marine structure foundation is developed, namely, the coconut tree root foundation (CTRF). In this paper, a numerical wave-current tank is established using FLOW-3D to investigate the local scour characteristics around the CTRF under wave-current joint actions. The wave-current and scour models in the numerical tank are validated using the relative analytical solution and experimental data, respectively. Then, the scour progress and hydrodynamic characteristics around the CTRF are studied. The results show that two butterfly-wing-shaped scour pits form on the left and right sides of the primary root of the CTRF, and fan- and valley-shaped depositions form on the upstream and downstream sides of the CTRF, respectively. Moreover, the effects of the factors influencing the scour are discussed, including the still water depth, current velocity, wave height, Keulegan-Carpenter (KC) number, and relative wave-current velocity (Ucw). The increasing current velocity and wave height can make the scour around the CTRF stronger. With the increasing water depth, the maximum scour depth is decreased but the maximum scour pit area is increased. When KC < 1.1 and Ucw > 0.5, the maximum scour depth shows a slight negative correlation with KC but a positive correlation with Ucw.