Numerical simulation of early stages of scour around a submarine pipeline using a two-phase flow model

Current-induced scour around a submarine pipeline during onset and tunnel erosion are investigated in both clear-water and live-bed regimes using an Eulerian-Eulerian two-phase model for sediment transport. The Hybrid Fictitious Domain-Immersed Boundary (HFD-IB) method is adopted to simulate the pipeline structure. The model is validated against two published experimental data: (1) flow past a pipeline near a rigid bed and (2) scour around a pipeline over a sand-bed, showing favorable results for the flow and scour patterns around the pipe. The driving mechanisms of the onset and tunnel erosion are investigated by examining the detailed fluid-sediment interactions around the pipe in both regimes. The driving mechanisms for the onset and tunnel erosion are found similar in both regimes, except their time and magnitude scales. The onset is triggered by the piping mechanism induced by the upstream-downstream pressure gradient beneath the pipe. Meanwhile, the jet flow is the driving mechanism for the tunnel erosion. The simulated live-bed condition shows a higher upstream-downstream pressure gradient beneath the pipe, faster piping mechanism, more intense jet flow velocity and sediment flux compared to the clear-water condition. The model well capture these underlying mechanisms, suggesting its promising capability as a predictive tool for scouring.

Automated summary

This study investigates current-induced scour and tunnel erosion around a submarine pipeline in both clear-water and live-bed regimes using a two-phase model. The model is validated with experimental data and reveals similar driving mechanisms for onset and tunnel erosion in both regimes, with differences in time and magnitude scales.