Micromechanics of intruder motion in wet granular medium

Abstract

We investigate the effective friction encountered by an intruder moving through a sedimented medium which consists of transparent granular hydrogels immersed in water, and the resulting motion of the medium. We show that the effective friction µ e on a spherical intruder is captured by the inertial number I given by the ratio of the time scale over which the intruder moves and the inertial time scale of the granular medium set by the overburden pressure. Further, µ e is described by the function µ e (I) = µ s + αI β , where µ s is the static friction, and α and β are material dependent constants which are independent of intruder depth and size. By measuring the mean flow of the granular component around the intruder, we find significant slip between the intruder and the granular medium. The motion of the medium is strongly confined near the intruder compared with a viscous Newtonian fluid and is of the order of the intruder size. The return flow of the medium occurs closer to the intruder as its depth is increased. Further, we study the reversible and irreversible displacement of the medium by not only following the medium as the intruder moves down but also while returning the intruder back up to its original depth. We find that the flow remains largely reversible in the quasi-static regime, as well as when µ e increases rapidly over the range of I probed. * akudrolli@clarku.edu 1 arXiv:1807.07833v1 [physics.flu-dyn] 20 Jul 2018Recently, it was demonstrated [21] that a sphere dragged through granular hydrogels immersed in water can be described by an effective friction which scales with inertial number I [22], and increases non-linearly from a non-zero static value. The form was found to be similar to that derived from the Herschel and Bulkley model [23], which is used to describe non-Newtonian fluids and muds [24]. Building on that study, we probe the dynamics of an intruder settling through granular hydrogels immersed in water as a model of wet granular medium or mud consisting of soft granular medium immersed in water. This is a much

Effective drag of a rod in fluid-saturated granular beds

“…Indeed, studies on spherical intruders moving through granular-hydrogels immersed in water found that the effective friction µ e , given by the ratio of the drag and the overburden pressure acting on the intruder, varied from being nearly constant at vanishing speeds to increasing rapidly with increasing speed [19]. It has been also found that the granular component of the medium is essentially fluidized over the scale of the sphere diameter and the decay of the medium speed is much faster compared with a viscous Newtonian fluid [20]. The granular medium used in those experiments were almost neutrally arXiv:1906.10046v1 [cond-mat.soft] 24 Jun 2019 buoyant, nearly frictionless, and limited to the inertia dominated regime.…”

Drag acting on an intruder in a three-dimensional granular environment

“…2 without any fitting parameters. It should be noted that some previous experiments also reported that the drag is proportional to the cross section [26,27].…”

Jamming transition and emergence of fracturing in wet granular media

“…Immiscible fluid-fluid displacement in porous media is important in many natural and industrial processes, including the displacement of air by water during rainfall infiltration [1], storage of carbon dioxide in deep saline aquifers [2], contaminant soil remediation [3], enhanced oil recovery [4], and design of microfluidic devices [5]. While fluid-fluid displacement in rigid porous media has been studied in depth, fundamental gaps remain in our understanding of the interplay between multiphase flow in a granular medium and the displacement of the grain particles [6,7]. This interplay can lead to a wide range of patterns, including fractures [8][9][10][11][12][13][14], desiccation cracks [15,16], labyrinth structures [17], and granular and frictional fingers [18][19][20][21].…”