Force and flow at the onset of drag in plowed granular media

Gravish, Nick; Umbanhowar, Paul B.; Goldman, Daniel I.

doi:10.1103/physreve.89.042202

Cited by 45 publications

(51 citation statements)

References 40 publications

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“…This is due to the free surface flow of the GM; a pile of sand above the surface, like those created by the snakes, appeared at the leading face of the intruder at the onset of drag and increased in volume until reaching a balance between the new grains being encountered and those flowing around the edges of the plate. Previous studies of plate drag at the surface (at β d = 90 deg) measured a similar drag distance dependent force and observed a wedge-shaped region of GM, beginning at the bottom edge of the plate and extending above the surface, whose constituent grains were flowing forward and up against gravity [34, 35].…”

Section: Granular Drag Measurementsmentioning

confidence: 77%

Mitigating memory effects during undulatory locomotion on hysteretic materials

Schiebel

Astley

Rieser

et al. 2019

Preprint

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10Undulatory swimming in flowing media like water is well-studied, but little is known about loco-11 motion in environments that are permanently deformed by body-substrate interactions like snakes in 12 sand, eels in mud, and nematode worms in rotting fruit. We study the desert-specialist snake Chion-13 actis occipitalis traversing granular matter and find body inertia is negligible despite rapid transit 14 and speed dependent granular reaction forces. New surface resistive force theory (RFT) calculation 15 reveals how this snakes wave shape minimizes memory effects and optimizes escape performance 16 given physiological limitations (power). RFT explains the morphology and waveform dependent 17 performance of a diversity of non-sand-specialist, but overpredicts the capability of snakes with 18 high slip. Robophysical experiments recapitulate aspects of these failure-prone snakes and elucidate 19 how reencountering previously remodeled material hinders performance. This study reveals how 20 memory effects stymied the locomotion of a diversity of snakes in our previous studies [Marvi et 21 al, Science, 2014] and suggests the existence of a predictive model for history-dependent granular 22 physics. 23 I. INTRODUCTION 24Movement is critical to the survival of many organisms and a necessary ability in robots used in fields like medicine 25 [1], search and rescue [2], and extraterrestrial exploration [3]. This complex phenomenon emerges from the interplay 26 between a locomotor's internal body shape changes and the physics of the surroundings. Successful locomotion 27 thus depends on the execution of self-deformations which generate appropriate reaction forces from the terrain; a 28 relationship which can be further complicated if the body motion permanently changes the state of the substrate. 29 Much of our knowledge of terrestrial locomotion is in the regime of rigid materials where the terrain is not affected 30 by passage of the animal [4-7], leading to the development of robots which are effective on hard ground [8-10].31 Little is known about locomotion in non-rigid materials which are plastically deformed by the movement of animals 32 or robots, leaving tracks or footprints. Deformable terrains inhabit a spectrum from materials like water which 33 continuously flow toward the undisturbed, zero shear state [11] to those which are remodeled by the interaction, like 34 sand. Most work on motion in yielding materials has been on systems in which disturbances dissipate (fluids) [12-14]; 35 the impact of soft material hysteresis on locomotion is not well-understood [15]. 36 At one end of the spectrum, where deformations are short-lived [16], small fluid swimmers like the nematode 37 Caenorhabditis elegans [17], spermatazoa [18], and bacteria in water [19] and macroscale frictional-fluid swimmers like 38 the sandfish lizard and shovel-nosed snake moving subsurface through sand [5] use the resistance of the surrounding 39 material to the motion of their body shape changes to propel themselves. The fluid in these...

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Section: Granular Drag Measurementsmentioning

confidence: 77%

Mitigating memory effects during undulatory locomotion on hysteretic materials

Schiebel

Astley

Rieser

et al. 2019

Preprint

Self Cite

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“…While a number of studies have investigated the force acting on an object moving through non-cohesive granular matter in air [2][3][4][5][6] and in liquids [7], a robust friction law for the drag encountered by the intruder is not available. In the case of granular medium immersed in a liquid where grains are always in contact, friction encountered has been found to be unchanged from the dry case [8].…”

Section: Introductionmentioning

confidence: 99%

Drag law for an intruder in granular sediments

2017

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We investigate the drag experienced by a spherical intruder moving through a medium consisting of granular hydrogels immersed in water as a function of its depth, size, and speed. The medium is observed to display a yield stress with a finite force required to move the intruder in the quasistatic regime at low speeds before rapidly increasing at high speeds. In order to understand the relevant time scales that determine drag, we estimate the inertial number I given by the ratio of the time scales required to rearrange grains due to the overburden pressure and imposed shear, and the viscous number J given by the ratio of the time scales required to sediment grains in the interstitial fluid and imposed shear. We find that the effective friction µ e encountered by the intruder can be parameterized by I = ρ g /P p v i , where ρ g is the density of the granular hydrogels, v i is the intruder speed, and P p is the overburden pressure due to the weight of the medium, over a wide range of I where the Stokes Number St = I 2 /J 1. We then show that µ e can be described by the function µ e (I) = µ o + α I β , where µ o , α and β are constants which depend on the medium.This formula can be used to predict the drag experienced by an intruder of a different size at a different depth in the same medium as a function of its speed.

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“…Therefore, the shape and diameter of the crater rim must be affected by the packing fraction mainly in a later stage. This gives the impression that events occurring after the opening of the crater, such as splashing [19,25] and avalanches [26][27][28], shape the final crater rim diameter in a profound way. Furthermore, Fig.…”

Section: Crater Evolutionmentioning

confidence: 99%

Crater formation during raindrop impact on sand

2017

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After a raindrop impacts on a granular bed, a crater is formed as both drop and target deform. After an initial, transient, phase in which the maximum crater depth is reached, the crater broadens outwards until a final steady shape is attained. By varying the impact velocity of the drop and the packing density of the bed, we find that avalanches of grains are important in the second phase and hence, affect the final crater shape. In a previous paper, we introduced an estimate of the impact energy going solely into sand deformation and here we show that both the transient and final crater diameter collapse with this quantity for various packing densities. The aspect ratio of the transient crater is however altered by changes in the packing fraction.

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Force and flow at the onset of drag in plowed granular media

Cited by 45 publications

References 40 publications

Mitigating memory effects during undulatory locomotion on hysteretic materials

Mitigating memory effects during undulatory locomotion on hysteretic materials

Drag law for an intruder in granular sediments

Crater formation during raindrop impact on sand

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