Grain-resolving simulations of submerged cohesive granular collapse

Abstract

We investigate the submerged collapse of weakly polydisperse, loosely packed cohesive granular columns, as a function of aspect ratio and cohesive force strength, via grain-resolving direct numerical simulations. The cohesive forces act to prevent the detachment of individual particles from the main body of the collapsing column, reduce its front velocity, and yield a shorter and thicker final deposit. All of these effects can be captured accurately across a broad range of parameters by piecewise power-law relationships. The cohesive forces reduce significantly the amount of available potential energy released by the particles. For shallow columns, the particle and fluid kinetic energy decreases for stronger cohesion. For tall columns, on the other hand, moderate cohesive forces increase the maximum particle kinetic energy, since they accelerate the initial free-fall of the upper column section. Only for larger cohesive forces does the peak kinetic energy of the particles decrease. Computational particle tracking indicates that the cohesive forces reduce the mixing of particles within the collapsing column, and it identifies the regions of origin of those particles that travel the farthest. The simulations demonstrate that cohesion promotes aggregation and the formation of aggregates. Furthermore, they provide complete information on the temporally and spatially evolving network of cohesive and direct contact force bonds. While the normal contact forces are aligned primarily in the vertical direction, the cohesive bonds adjust their preferred spatial orientation throughout the collapse. They result in a net macroscopic stress that counteracts deformation and slows the spreading of the advancing particle front.

Cohesive sediment: intermediate shear produces maximum aggregate size

“…We remark that the present one-way coupled approach is sometimes referred to as ‘three-way coupled’, while the current two-way coupling is also regarded as ’particle-resolved four-way coupling’ by some previous researchers (Zhu et al. 2022). Additional information on the two-way coupled simulations is provided in Appendix B.…”

“…For the two-way coupling approach, we employ the immersed boundary method implemented in Vowinckel et al (2019) to describe the particle-fluid interactions, and we use the spectral approach of Eswaran & Pope (1988) to generate statistically stationary turbulence. We remark that the present one-way coupled approach is sometimes referred to as 'three-way coupled', while the current two-way coupling is also regarded as 'particle-resolved four-way coupling' by some previous researchers (Zhu et al 2022). Additional information on the two-way coupled simulations is provided in Appendix B.…”

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

“…In contrast, submerged cohesive collapses have received considerably less attention to date, in spite of their relevance for industrial and environmental applications including sediment transport problems (Baas, Best, & Peakall, 2011; Hampton, 1972; Kuenen, 1951; Marr, Harff, Shanmugam, & Parker, 2001). Very recently, Zhu, He, Zhao, Vowinckel, and Meiburg (2022) took a first step in this direction, by employing particle-resolved simulations, as will be discussed below.…”

“…Such simulations, which were initially developed for non-cohesive grains (Kempe, Vowinckel, & Fröhlich, 2014; Kidanemariam & Uhlmann, 2017; Uhlmann, 2005; Vowinckel, Kempe, & Fröhlich, 2014), can currently deal with up to grains, so that they can capture a significant range of scales. In recent years they have been extended to cohesive grains as well (Vowinckel, Biegert, Luzzatto-Fegiz, & Meiburg, 2019a; Vowinckel et al., 2019b; Zhu et al., 2022). Tracking the cohesive primary particles in space and time enables us to study, among other things, the microstructure of individual flocs as a function of local shear conditions, or the packing density and stability of sediment deposits, in order to gain a quantitative understanding of the interplay between hydrodynamic and particle contact stresses.…”

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.…”