Incorporating grain-scale processes in macroscopic sediment transport models

Abstract

Sediment transport simulations face the challenge of accounting for vastly different scales in space and time that cannot be tackled by a unifying approach. Instead, processes are subdivided into a microscale at the particle level, a mesoscale of a large finite number of particles, and a macroscale that computes the sediment motion by means of advection–diffusion equations. The different processes occurring at different scales are simulated using different computational approaches. However, modeling sediment transport at multiple scales with high fidelity requires proper closure arguments that interconnect the different processes. Ultimately, we will need efficient macroscale models that can readily be utilized for engineering practices covering, e.g., entire river reaches or even estuaries. In recent years, highly resolved simulations have become a valuable tool to provide these closure arguments for sediment transport models on the continuum scale. In this paper, we will review the most relevant approaches to simulate sediment transport at different scales and discuss the perspectives of four most promising modeling techniques that can help to improve sediment transport modeling. On the grain scale, these enhancements include the impact of mechanical properties of cohesion and biocohesion as well as the shape of non-spherical sediment grains on fluid–particle and particle–particle interactions. On larger scales, we review constitutive equations for the macroscopic rheological behavior of sediment beds that may decouple the relevant scales for fluid and sediment motion. Furthermore, we discuss machine learning strategies as an efficient means to derive scaling arguments across multiple scales.

Investigating cohesive sediment dynamics in open waters via grain-resolved simulations

“…In addition, as reviewed by Vowinckel (2021), recent advances in the field of pr-DNS have introduced techniques to relax the assumption of spherical particles (Ardekani & Brandt, 2019; Eshghinejadfard, Zhao, & Thévenin, 2018; Jain, Tschisgale, & Fröhlich, 2021; Voth & Soldati, 2017). Such considerations could further complicate the picture of cohesive sediment dynamics with important implications that are yet to be investigated.…”

“…Computational approaches that solve the Eulerian equations of motion for the fluid, while tracking the particles in a Lagrangian fashion, are commonly referred to as Euler–Lagrange frameworks. These can be further categorized according to the way in which they account for the coupling of fluid and particle motion (Balachandar & Eaton, 2010; Vowinckel, 2021). A one-way coupled system is obtained if the fluid motion remains unaffected by the particles, which are driven solely by their inertia, fluid drag and gravity, without interacting with each other.…”

Phase‐resolving direct numerical simulations of particle transport in liquids—From microfluidics to sediment

“…It relates the mean fluid shear stress at the bottom, 𝜏 w = 𝜌u 2 𝜏 , potentially mobilizing a particle, to the gravitational forces retaining a particle in place. An overview over numerical approaches for sediment transport has recently been compiled by Vowinckel [137]. Classical simulation approaches generally treat the flow separately and employ a specific model equation for the transport of bedload concentration [104].…”

“…An overview over numerical approaches for sediment transport has recently been compiled by Vowinckel [137]. Classical simulation approaches generally treat the flow separately and employ a specific model equation for the transport of bedload concentration [104].…”

Impact of the Salt Concentration and Biophysical Cohesion on the Settling Behavior of Bentonites

“…This is an important aspect as it may help to manage and mitigate sediment transport processes. It can also be useful in the modeling of cohesive sediments by means of continuum models (Jarvis et al, 2005;Verney et al, 2011;Kuprenas et al, 2018;Hsu et al, 2021) and newly emerging techniques of particle-resolved simulations (Vowinckel et al, 2019a,b;Vowinckel, 2021;Zhao et al, 2021, Zhu et al, 2022.…”