CFD modelling of local scour around Tri-USAF in sand with different arrangements under steady current

Abstract

The complex offshore foundation is required to adapt to the extreme marine climate, such as tripile, tripod, pile group foundations. For this reason, it is of great importance to consider an advanced tri-USAF, analogous to tripile, since previous studies only take into account monoUSAF in which scouring tests of a USAF were performed and influences of steady currents, waves, as well as the combination of waves and currents were evaluated. In this work, a series of scouring tests were conducted computationally by using a VOF method to capture the sharp interface and finite-volume-finite-difference method to solve RANS equations combined with sediment transport equations, in order to explore the characteristics of local scour around a tri-USAF, with different arrangements, in sand seabed under steady current state. The three-dimensional scour model was established and validated against available experimental data reported in the literature and own measured data. Furthermore, parametric analysis was performed regarding the influence of spacing ratio and Froude number. The predicted results imply that flow field and scour characteristics involving a tri-USAF are more complicated than those of monoUSAF, and the impact of the neighbouring structure is interpreted differently compared with piles, as tri-USAF possesses several specific components.