Numerical investigation of local scour around USAF with different hydraulic conditions under currents and waves

Abstract

An umbrella suction anchor foundation (USAF) is a new foundation type used for offshore wind turbines. In this paper, a three-dimensional numerical model was established in FLOW-3D to study the local scour characteristics under the coupled effects of waves and currents. RANS equations, closed with an RNG k-ε turbulence model, were established for simulating the flow field around pile groups. The simulation results were compared with a 1:40 model test and showed good agreement. Then, the effects of different hydraulic conditions and dimensionless parameters such as water depth, wave height, velocity, Keulegan-Carpenter number (KC) and the ratio of relative wave-current velocity (Ucw) on the maximum scour depth were considered in detail, and compared with the results of other scholars. This study found that the local scour shape of a USAF is different from that of a monopile foundation. Its maximum scour depth appears downstream behind the USAF, and the anchoring structure effectively blocks the scour in front of the USAF. The shallower water depth, the higher wave height and the faster flow velocity result in a more intense scour. When KC < 7 and Ucw <0.7, the maximum scour depth of the USAF increases with increasing KC number and Ucw.