Low-velocity granular drag in reduced gravity

Costantino, D. J.; Bartell, Jason; Scheidler, Krysten; Schiffer, P.

doi:10.1103/physreve.83.011305

Cited by 52 publications

(43 citation statements)

References 22 publications

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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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Section: Introductionmentioning

confidence: 99%

Drag law for an intruder in granular sediments

2017

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“…gð1 À U=U c Þ, where U c is the fluidization airspeed where the upflow exactly balances gravity. Thus, without actually changing gravitational acceleration [10,22,23], the effective gravity loading is reduced by a subfluidizing upflow, 0 < U < U c , similarly, it is enhanced by a downflow, U < 0. The motion loading of contacts, and the inertial drag force, ought not be affected by airflow.…”

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confidence: 99%

Depth-Dependent Resistance of Granular Media to Vertical Penetration

2013

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“…For context, we note that studies of steady state drag on level granular surfaces reveal that force is proportional to plate width, w, and depth squared, d 2 (31). To make the first measurements of drag force F dependence on θ, d and w, we performed drag force measurements on granular inclines (23).…”

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confidence: 99%

Sidewinding with minimal slip: Snake and robot ascent of sandy slopes

Marvi

Gong

Gravish

et al. 2014

Science

241

229

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Limbless organisms like snakes can navigate nearly all terrain. In particular, desert-dwelling sidewinder rattlesnakes (C. cerastes) operate effectively on inclined granular media (like sand dunes) that induce failure in field-tested limbless robots through slipping and pitching. Our laboratory experiments reveal that as granular incline angle increases, sidewinder rattlesnakes increase the length of their body in contact with the sand. Implementing this strategy in a physical robot model of the snake enables the device to ascend sandy slopes close to the angle of maximum slope stability. Plate drag experiments demonstrate that granular yield stresses decrease with increasing incline angle. Together these three approaches demonstrate how sidewinding 1 arXiv:1410.2945v1 [physics.bio-ph] 11 Oct 2014 with contact-length control mitigates failure on granular media.The majority of terrestrial mobile robots are restricted to laboratory environments, in part because such robots are designed to roll on hard flat surfaces. It is difficult to systematically improve such terrestrial robots because we lack understanding of the physics of interaction with complex natural substrates like sand, dirt and tree bark. We are thus limited in our ability to computationally explore designs for potential all-terrain vehicles; in contrast, many of the recent developments in aerial and aquatic vehicles have been enabled by sophisticated computationaldynamics tools that allow such systems to be designed in silico (1).Compared with human-made devices, organisms such as snakes, lizards, and insects move effectively in nearly all natural environments. In recent years, scientists and engineers have sought to systematically discover biological principles of movement and implement these in robots (2). This "bioinspired robotics" approach (3) has proved fruitful to design laboratory robots with new capabilities (new gaits, morphologies, control schemes) including rapid running (2, 4), slithering (5), flying (6), and swimming in sand (7). Fewer studies have transferred biological principles into robust field-ready devices (4, 8) capable of operating in, and interacting with, natural terrain.Limbless locomotors like snakes are excellent systems to study to advance real-world allterrain mobility. Snakes are masters of most terrains: they can move rapidly on land (9, 10) and through water (11), burrow and swim through sand and soil (12), slither through tiny spaces (13), climb complex surfaces (14), and even glide through the air (15). Relative to legged locomotion, limbless locomotion is less studied, and thus broad principles which govern multi-environment movement are lacking. Recently developed limbless robotic platforms (5), based generally on the snake body plan, are appealing for multi-functional robotics study because they are also capable of a variety of modes of locomotion. These robots can traverse confined spaces, climb trees and pipes, and potentially dive through loose material. However, 2 the gaits that carry these robots across fir...

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Low-velocity granular drag in reduced gravity

Cited by 52 publications

References 22 publications

Drag law for an intruder in granular sediments

Drag law for an intruder in granular sediments

Depth-Dependent Resistance of Granular Media to Vertical Penetration

Sidewinding with minimal slip: Snake and robot ascent of sandy slopes

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