Effective drag of a rod in fluid-saturated granular beds

Allen, Benjamin; Kudrolli, Arshad

doi:10.1103/physreve.100.022901

Cited by 14 publications

(20 citation statements)

References 34 publications

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“…The latter decreases with increasing friction, as the walls are able to support a larger fraction of the load. This Janssen effect should be taken into account in the choice of the dimensionless quantity F * , sometimes referred to as the effective friction [6,40]: with P = σ yy (x c ) computed with Eq. 26.…”

Section: Impact Of Friction Coefficientsmentioning

confidence: 99%

“…This decreases the value of the drag force [19] and the Froude number, leading to an earlier fluidization. The ratio between the drag force and the average weight of the grains on the object was observed to vary as a power law of a so-called viscous number J = η γ /P with η the viscosity of the fluid, γ the shear rate and P the pressure in the granular material [6,37].…”

Section: Introductionmentioning

confidence: 99%

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Numerical analysis of the drag on a rigid body in an immersed granular flow

et al. 2021

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The drag exerted on an object moving in a granular medium is subject to many studies: in dry grains, it depends on the stress -often due to gravity -inside the grains. For Froude numbers less than 10, the drag is independent of the velocity. In immersed grains, it is proportional to the apparent weight of the grains and it depends on both velocity and fluid viscosity. In this paper, the drag on a cylinder in dry and immersed granular flow is simulated with a multi-scale FEM-DEM model. The Janssen stress saturation effect before the flow and velocity independence of the drag are both reproduced. The semi-circular orientation of the stress field supports the hypothesis of a spherical zone of influence of the cylinder. This orientation does not significantly change upon flowing. The results show the velocity independence of the drag is due to particle friction. In the immersed case, the fluid contribution is negligible on its own. A dimensional analysis suggests that shear thickening should be taken into account. The transition between the quasi-static and the fluidized regime is accompanied by a decrease of the stress field downstream of the cylinder and a change in the shape of the shear zone. KeywordsGranular drag • Janssen effect • Nonsmooth contact dynamics • Unresolved model • MigFlow B Nathan Coppin

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Section: Impact Of Friction Coefficientsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical analysis of the drag on a rigid body in an immersed granular flow

et al. 2021

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“…The dynamic force resulting from granular collisions becomes important with speed and has been calculated in dry granular materials [17]. Presence of interstitial liquid influences the drag in granular beds [18][19][20], but remains relatively less studied compared to the dry granular case [21,22]. Various ξ have been reported in studies with granular beds composed of dry glass beads including ξ ≈ 3 in experiments with rods with L/D ≈ 2.5 after subtracting end effects [5,23,24].…”

Section: Introductionmentioning

confidence: 99%

Drag anisotropy of cylindrical solids in fluid-saturated granular beds

Pal,

Kudrolli

2021

Preprint

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We study the direction-dependent drag acting on a cylindrical solid intruder with length L and diameter D as it moves in water-saturated granular beds at constant depth. Polysterene and hydrogel grains with diameter d are used to investigate materials which have high contact friction and those which are nearly frictionless, respectively. The drag on the intruder is measured while oriented perpendicular F ⊥ and parallel F to its axis as a function of speed U from the quasi-static to the rate-dependent regime. We find that the drag anisotropy ξ = F ⊥ /F is not constant, and increases significantly with driving rate and L/D in both mediums. In particular for L/D = 40, ξ increases from 2.6 to 4.5, and from 7.0 to 8.2 in the high and low friction beds, respectively, as the nondimensional Froude number F r = U/ g(D + d) is varied between 10 −4 and 2 × 10 −2 . On average, ξ is observed to increase logarithmically with L/D for L/D1. Exploiting the index-matched nature of hydrogel grains in water, we further show that the sediment flow around the cylinder in the two orientations is consistent with skin friction dominated drag. The relative contributions of the cylindrical side and the circular flat-ends on ξ are estimated with thin disks to understand the observed variation of drag with aspect ratio and surface friction.

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“…It is long established that the drag of the body used by the swimmer to propel itself forward can be dominated by viscous forces at low speeds and by inertia at high speeds, as measured by the Reynolds number (11,12). Measurements with spheres and rods moving in water-saturated soft sediments have found that the drag scaled by the buoyancy-subtracted weight of the grains can be used to define an effective friction µe which approaches a constant value µo at vanishing speeds and increases many-fold with speed (13)(14)(15). While inertia and fluid viscosity can in general both play a role in determining the rate dependence, it has been found that inertial effects dominate in the case of millimetersized grains immersed in relatively low-viscosity fluids like water (13)(14)(15).…”

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confidence: 99%

“…In this case, µe = µo + kI n , where k and n are materialdependent constants, and I is the inertial number. For rods (15),…”

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confidence: 99%

Burrowing dynamics of aquatic worms in soft sediments

Kudrolli

Ramirez

2019

Proc. Natl. Acad. Sci. U.S.A.

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We investigate the dynamics ofLumbriculus variegatusin water-saturated sediment beds to understand limbless locomotion in the benthic zone found at the bottom of lakes and oceans. These slender aquatic worms are observed to perform elongation–contraction and transverse undulatory strokes in both water-saturated sediments and water. Greater drag anisotropy in the sediment medium is observed to boost the burrowing speed of the worm compared to swimming in water with the same stroke using drag-assisted propulsion. We capture the observed speeds by combining the calculated forms based on resistive-force theory of undulatory motion in viscous fluids and a dynamic anchor model of peristaltic motion in the sediments. Peristalsis is found to be effective for burrowing in noncohesive sediments which fill in rapidly behind the moving body inside the sediment bed. Whereas the undulatory stroke is found to be effective in water and in shallow sediment layers where anchoring is not possible to achieve peristaltic motion. We show that such dual strokes occur as well in the earthwormEisenia fetidawhich inhabits moist sediments that are prone to flooding. Our analysis in terms of the rheology of the medium shows that the dual strokes are exploited by organisms to negotiate sediment beds that may be packed heterogeneously and can be used by active intruders to move effectively from a fluid through the loose bed surface layer which fluidizes easily to the well-consolidated bed below.

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Effective drag of a rod in fluid-saturated granular beds

Cited by 14 publications

References 34 publications

Numerical analysis of the drag on a rigid body in an immersed granular flow

Numerical analysis of the drag on a rigid body in an immersed granular flow

Drag anisotropy of cylindrical solids in fluid-saturated granular beds

Burrowing dynamics of aquatic worms in soft sediments

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