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This paper analyzes the compaction behavior of assemblies composed of soft (elastic) spherical particles beyond the jammed state, using three-dimensional non-smooth contact dynamic simulations. The assemblies of particles are characterized using the evolution of the packing fraction, the coordination number, and the von Misses stress distribution within the particles as the confining stress increases. The packing fraction increases and tends toward a maximum value close to 1, and the mean coordination number increases as a square root of the packing fraction. As the confining stress increases, a transition is observed from a granular-like material with exponential tails of the shear stress distributions to a continuous-like material characterized by Gaussian-like distributions of the shear stresses. We develop an equation that describes the evolution of the packing fraction as a function of the applied pressure. This equation, based on the micromechanical expression of the granular stress tensor, the limit of the Hertz contact law for small deformation, and the power-law relation between the packing fraction and the coordination of the particles, provides good predictions from the jamming point up to very high densities without the need for tuning any parameters.

The compaction behavior of deformable grain packings beyond jamming is a process widelyinvestigated because of its great industrial and engineering significance, yet it remainsmisunderstood. Many numerical and experimental approaches have enabled the explorationof the physics of deformable granular media and the definition of some theoretical modelswith reliable predictions for the relations between pressure and density. However, thesemodels have some limitations such as the use of nonphysical parameters, the lack of accuracyat extreme pressures, and the missing physical derivation of the compaction equations. Westudy the compaction behavior of soft sphere packings beyond the jammed state by numericalsimulations (see Fig. 1) using the non-smooth contact dynamic method. The resultsshow that the evolution of packing fraction - as a function of the applied pressure - is welldescribed using only micromechanical parameters. This is obtained based on the stress tensor,together with the limit too small deformation of the particles' strain. Our work also suggeststhat it is possible to extrapolate the compaction behavior of an elementary Voronoi cell thatcontains a single particle to the packing scale.

Granular column collapse simulations are a benchmark in the study of transitional granular flows [1].The column collapse is a simplified version of occurring flows in highly varying scales, ranging innatural debris flows or industrial handling purposes. A characteristic among them is their occasionalsubmergence in a viscous fluid, resulting in strong grain-fluid interactions between particles ofdifferent sizes [2, 3, 4]. This work studies the effect of polydispersity in the runout of the collapse ofimmersed granular columns. For this purpose, we simulate a two-dimensional immersed granularcolumn employing a coupled discrete and finite element fluid model (DEM-FEM) [5]. In thisconfiguration, we study granular systems with different grain size distributions (GSD), varying theratio between the biggest and smallest particle from 1.2 to 10. We simulate dense granular columns,varying the initial column height H0 and initial column width L0 through three different aspect ratiosA = H0/L0 = (0.5, 1.0, 3.5). We show that the collapse mechanism and collapse duration stronglydepend on polydispersity. Increasing polydispersity reduces the kinematic energy of the collapse andreduces the final runout. For short columns A = (0.5, 1.0), the repose angle increases with thepolydispersity until it reaches a plateau near 17°. Our results highlight the effect on the final shape,flow mechanism, and fluid-grain interaction of increasing polydispersity in transitional immersedflows.

Granular asteroids are naturally occurring gravitational aggregates (rubble piles) bound together by gravitational forces. For this reason, it is reasonable to use the theoretical concepts and numerical tools developed for granular media to study them. In this paper, we extend the field of applicability of the Contact Dynamic (CD) method, a class of non smooth discrete element approach, for the simulation of three dimensional granular asteroids. The CD method is particularly relevant to address the study of dense granular assemblies of a large number of particles of complex shape and broad particles size distribution, since it does not introduces numerical artefacts due to contact stiffness. We describe how the open source software LMGC90, interfaced with an external library for the calculation of self-gravity, is used to model the accretion process of spherical and irregular polyhedral particles.