Numerical investigation of deposition mechanism of submarine debris flow

Abstract

Submarine debris flow can damage oil and gas transport pipelines with potentially adverse consequences to the environment and to the industrial activity itself. The deposition process of submarine debris flow, which is related to the flow viscosity, is complex due to the slurry diffusion process that happens during the interaction of water and slurry. In addition, a quantitative characterization of the characterize the flow mechanism as influenced by the material density during the deposition process remains a scientific challenge. To fundamentally understand the mechanisms of solid-fluid interactions in fast-flowing submarine debris flows, a series of three-dimensional (3D) numerical simulations using Computational Fluid Dynamics (CFD) were conducted. The Herschel- Bulkley (HB) model was used to define the submarine slurry’s rheological characterization as calibrate through simple rheological experiment. Results reveal that deposition is a mass diffusion process. Shear stress at the bottom and at the top of the slurry leads to velocity differences in the vertical direction which in turn generates a huge vortex, which contributed to a separation of slurry into two parts: the frontal head, and the tail. The velocity difference in vertical direction is helpful for hydroplaning. For higher slurry viscosity case, the flow profile is longer and thicker with a front head that has a lower averaged densities and sharper head angles. In addition, highly viscous slurries have lower average frontal velocities during the deposition process. The mixture density decreases in two stages: quick decreasing stage and stable decreasing stage. In the first stage, the slurry expands quicker than the second stage. Higher viscosities also lead to larger volume expansions which consequently leads to quicker density decrease.