Author(s): Lu Jing
Linked Author(s):
Keywords: Grain sorting; Sediment dynamics; Granular segregation; Multiscale modeling
Abstract: Grain sorting in sediment dynamics has significant implications for scour, erosion, geomorphology and biological processes in fluvial and coastal environments. Coarsening of the river bed and seabed, for example, adds additional difficulties for accurate prediction of sediment transport rate under certain flow and current conditions, which is expected to compromise scour and erosion control measures designed based on classic approaches. Grain sorting involves a wide range of mechanisms due to the complex actions of gravity, fluid flows, and particle interactions. As such, seemingly contradictory phenomena occur under different conditions and forcing, and a unified understanding of grain sorting in sediment dynamics is still missing. Here, we present recent advances in a multiscale framework of grain sorting (Jing et al. 2017, 2021, 2022), in which the driving and resistive forces of sorting (or, particle-size segregation in the context of granular flows) at the grain level are formulated, leading to a general description of gravity-, shear-, and fluid flow-induced segregation flux in dense granular flows. This description is compatible with state-of-the-art sediment-fluid two-phase flow continuum models from which the relevant granular flow fields can be obtained. Figure 1 presents test results of the model in a rather idealized granular systems where creeping and inertial flows are simulated using the discrete element method (DEM). Results indicate that predictions of the “tracer” particle migration velocity agree well with the DEM data, demonstrating the potential applicability of the model in a wide range of sediment transport conditions. The presented framework of grain sorting modeling rests on a foundation of physical principles at the grain level. Therefore, it should be sufficiently versatile to be applied to more realistic situations, such as those involving size-polydispersity, non-spherical particle shapes, cohesion, and interstitial fluid effects. The potential applicability of the proposed framework in the simulation of grain sorting, as well as its impact on sediment transport modeling during wave- and current-induced scour around river and marine structures, will be discussed.
Year: 2023