Force and Flow Transition in Plowed Granular Media

Abstract

We use plate drag to study the response of granular media to localized forcing as a function of volume fraction, φ. A bifurcation in the force and flow occurs at the onset of dilatancy, φc. Below φc rapid fluctuations in the drag force, FD, are observed. Above φc fluctuations in FD are periodic and increase with φ. Velocity field measurements indicate that the bifurcation in FD results from the formation of stable shear bands above φc which are created and destroyed periodically during drag. A friction-based model captures the dynamics for φ > φc.

Environmental interaction influences muscle activation strategy during sand-swimming in the sandfish lizard Scincus scincus

“…In the laboratory, ϕ can be systematically varied via an airfluidized bed Maladen et al, 2009;Gravish et al, 2010) (Fig.1B), and provides a controlled method to test the effects of compaction on locomotion. A less compact granular medium (low ϕ, loosely packed or LP) generates smaller forces on a rod intruder moving at constant speed than does a more compact granular medium (high ϕ, closely packed or CP) (Maladen et al, 2009;Gravish et al, 2010) (Fig.1C,D).…”

“…A less compact granular medium (low ϕ, loosely packed or LP) generates smaller forces on a rod intruder moving at constant speed than does a more compact granular medium (high ϕ, closely packed or CP) (Maladen et al, 2009;Gravish et al, 2010) (Fig.1C,D). Unlike fluids, the average force acting on an object moving at low speed (typically less than 0.5ms −1 ) through granular media increases proportionally with depth ( Fig.1C) and is approximately independent of speed ( Fig.1D) (Albert et al, 1999;Maladen et al, 2009).…”

The impact of raindrops on sand

“…Though the word 'dilation' describes a change of the volume, previous studies have shown that the dilatancy transition is accompanied by a force response transition [66,68,88,90]. As explained above, this force transition feature is already encapsulated by the factor (U 0 − U s )/U s representing momentum transfer, and the volume change of the substrate is supposed to give a transition at φ * as well.…”

“…It is well known that the rigidity of a granular substrate is very sensitive to its packing density, φ 0 [66,68,88,90]. In the previous chapter 2 we have discussed the dependence of the maximum droplet spreading diameter, D * d…”

“…In contrast, droplet impact on a solid surface or a liquid pool has been studied extensively [29,36,39]. However, a granular substrate can act both solid-like and fluid-like [56] and many experiments have been conducted to reveal the response of a granular packing to a solid object impact [68,71,75,80,82,87,88], where the intruder does not deform. Droplet impact on a granular substrate adds new challenges to the above: First, both the intruder and the target, not merely one of the two, deform during impact; second, the liquid composing the droplet may penetrate into the substrate during the impact and may, in the end, completely merge with the grains.…”