Detailed simulation of morphodynamics: 2. Sediment pickup, transport, and deposition

Abstract

[1] The paper describes a numerical model for simulating sediment transport with eddyresolving 3-D models. This sediment model consists of four submodels: pickup, transport over the bed, transport in the water column and deposition, all based on a turbulent flow model using large-eddy simulation. The sediment is considered as uniform rigid spherical particles. This is usually a valid assumption for sand-bed rivers where underwater dune formation is most prominent. Under certain shear stress conditions, these particles are picked up from the bed due to an imbalance of gravity and flow forces. They either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow. Sooner or later, the suspended particles settle on the bed again. Each of these steps is modeled separately, yielding a physics-based process model for sediment transport, suitable for the simulation of bed morphodynamics. The sediment model is validated with theoretical findings such as the Rouse profile as well as with empirical relations of sediment bed load and suspended load transport. The current model shows good agreement with these theoretical and empirical relations. Moreover, the saltation mechanism is simulated, and the average saltation length, height, and velocity are found to be in good agreement with experimental results.

Computational Modeling of Flow and Scour around Two Cylinders in Staggered Array

“…We employed our previously developed LES model, combined with sediment transport and morphodyanmic models [23][24][25][26] to simulate the coupled hydrodynamic and morphodynamic processes around two circular cylinders in a staggered array. The numerical model was composed of three submodels including hydrodynamic, sediment transport, and morphodynamic models.…”

“…These submodels were coupled to simulate the local scouring process around the two cylinders in a physics-based manner. As the details of the numerical model have already been documented [23][24][25][26], only a brief description of the submodel is given here.…”

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

“…Eddy-resolving simulation techniques such as large-eddy simulation (LES) and detached eddy simulation (DES), or lattice Boltzmann methods, then become necessary. The utility of eddy-resolving methods has been demonstrated by the explosion of the number of studies in the last few years, with applications to flow around channel obstacles and their associated scour holes [Kirkil et al, 2008;Koken and Constantinescu, 2009], flow through vegetation [Kim and Stoesser, 2011], as well as sediment transport [Nabi et al, 2012[Nabi et al, , 2013aSchmeeckle, 2014] and flow over bed forms [Nabi et al, 2013b;Chang and Constantinescu, 2013;Omidyeganeh and Piomelli, 2013], and flow through channel confluences [Constantinescu et al, 2011a]. See Keylock et al [2005] for an early introduction to the use of LES in channel flow hydraulics and Keylock et al…”

Computational modeling of dissipation and regeneration of fluvial sand dunes under variable discharges

“…It involves modeling of sediment pickup, transport in suspension, deposition, and sliding. The sediment transport was modeled in a Lagrangian framework and was based on new concepts that are best suited for relatively small spatial and temporal scales [ Nabi et al , ]. The sediment particles were modeled as small rigid spheres in the water.…”

“…The shear stress, τ in equation , was calculated by projecting the flow forces in the tangential direction of the bed, and the critical shear stress, τ c r , was estimated by calculating the force (and its associated shear stress) at which the particle starts its initial rotation. The volume of sediment pickup in a time interval Δ t from an area A will be [ Nabi et al , ], …”