Modelling the impact of particle removal on granular material behaviour

ABSTRACT With the flourishing number of small body missions that involve surface interactions, understanding the mechanics of spacecraft – surface interactions is crucial for improving our knowledge about the landing phases of space missions, for preparing spacecraft operations, and for interpreting the results of measurements made during the surface interactions. Given their regolith-covered surfaces, the process of landing on a small body can be considered as an impact at low-velocity on to a granular material in reduced-gravity. In order to study the influence of the surface material, projectile shape, and gravity on the collision dynamics, we used two experimental configurations (one for terrestrial gravity experiments and one for reduced-gravity experiments) to perform low-velocity collisions into different types of granular materials: quartz sand, and two different sizes of glass beads (1.5 and 5 mm diameter). Both a spherical and a cubic projectile (with varying impact orientation) were used. The experimental data support a drag model for the impact dynamics composed of both a hydrodynamic drag force and quasi-static resistance force. The hydrodynamic and quasi-static contributions are related to the material frictional properties, the projectile geometry, and the gravity. The transition from a quasi-static to a hydrodynamical regime is shown to occur at lower impact velocities in reduced-gravity trials than in terrestrial gravity trials, indicating that regolith has a more fluid-like behaviour in low-gravity. The reduced quasi-static regime of a granular material under low-gravity conditions leads to a reduction in the strength, resulting in a decreased resistance to penetration and larger penetration depths.

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High-speed filtration using highly porous fiber media for advanced and compact particle removal

Water Science & Technology Water Supply ◽

10.2166/ws.2014.028 ◽

2014 ◽

Vol 14 (5) ◽

pp. 735-742 ◽

Cited By ~ 2

Author(s):

Heidi B. Guerra ◽

Siping Niu ◽

Kisoo Park ◽

Youngchul Kim

Keyword(s):

High Speed ◽

Filtration Rate ◽

Polypropylene Fiber ◽

High Rate ◽

High Porosity ◽

Particle Removal ◽

Polyaluminum Chloride ◽

Operating Variables ◽

The Impact ◽

Highly Porous

Since its recent introduction to the filtration industry, one of the major concerns about the use of fiber in water treatment has been its applicability for high-rate filtration while minimizing the build-up of headloss. In this study, a compact, modular filter employing non-woven, highly porous polypropylene fiber as filter media was investigated for the treatment of turbid water under high filtration rates. The impact of different operating variables such as polyaluminum chloride (PAC) dose and filtration rate on the effluent turbidity and headloss were investigated. Due to the fiber's high porosity, the filter was able to retain solids at a filtration rate of up to 1,500 m/day without headloss. When PAC was added, the effluent turbidity decreased significantly with the lowest observed when the dose was 1 mg/L. Furthermore, the effluent turbidity was found to increase with the filtration rate. During all the experiments, no headloss was observed except when the filtration rate was 2,250 m/day or when the PAC dose was 5 mg/L. In terms of its compactness and applicability at very high filtration rates, the polypropylene fiber filter can have a considerable advantage compared to other filters.

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When does a granular material behave like a continuum fluid?

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.226 ◽

2012 ◽

Vol 704 ◽

pp. 1-4 ◽

Cited By ~ 3

Author(s):

John R. de Bruyn

Keyword(s):

Granular Material ◽

Temporal Resolution ◽

High Speed ◽

High Impact ◽

High Temporal Resolution ◽

Granular Bed ◽

Fluid Limit ◽

High Speed Imaging ◽

Impact Energies ◽

The Impact

AbstractA flowing granular material can behave like a collection of individual interacting grains or like a continuum fluid, depending in large part on the energy imparted to the grains. As yet, however, we have no general understanding of how or under what conditions the fluid limit is reached. Marston, Li & Thoroddsen (J. Fluid Mech., this issue, vol. 704, 2012, pp. 5–36) use high-speed imaging to investigate the ejection of grains from a granular bed due to the impact of a spherical projectile. Their high temporal resolution allows them to study the very fast processes that take place immediately following the impact. They demonstrate that for very fine grains and high impact energies, the dynamics of the ejecta is both qualitatively and quantitatively similar to what is seen in analogous experiments with fluid targets.

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Laboratory testing and granular material behaviour

Pavements Unbound ◽

10.4324/9780203026663_laboratory_testing_and_granular_material_behaviour ◽

2010 ◽

pp. 3-12

Keyword(s):

Granular Material ◽

Laboratory Testing ◽

Material Behaviour

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Granular jets and hydraulic jumps on an inclined plane

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.2 ◽

2011 ◽

Vol 675 ◽

pp. 87-116 ◽

Cited By ~ 34

Author(s):

C. G. JOHNSON ◽

J. M. N. T. GRAY

Keyword(s):

Granular Material ◽

Numerical Solutions ◽

Slope Angle ◽

Three Dimensional ◽

Breaking Wave ◽

Hydraulic Jumps ◽

Inclined Plane ◽

Steady Regime ◽

Diverse Range ◽

The Impact

A jet of granular material impinging on an inclined plane produces a diverse range of flows, from steady hydraulic jumps to periodic avalanches, self-channelised flows and pile collapse behaviour. We describe the various flow regimes and study in detail a steady-state flow, in which the jet generates a closed teardrop-shaped hydraulic jump on the plane, enclosing a region of fast-moving radial flow. On shallower slopes, a second steady regime exists in which the shock is not teardrop-shaped, but exhibits a more complex ‘blunted’ shape with a steadily breaking wave. We explain these regimes by consideration of the supercritical or subcritical nature of the flow surrounding the shock. A model is developed in which the impact of the jet on the inclined plane is treated as an inviscid flow, which is then coupled to a depth-integrated model for the resulting thin granular avalanche on the inclined plane. Numerical simulations produce a flow regime diagram strikingly similar to that obtained in experiments, with the model correctly reproducing the regimes and their dependence on the jet velocity and slope angle. The size and shape of the steady experimental shocks and the location of sub- and supercritical flow regions are also both accurately predicted. We find that the physics underlying the rapid flow inside the shock is dominated by depth-averaged mass and momentum transport, with granular friction, pressure gradients and three-dimensional aspects of the flow having comparatively little effect. Further downstream, the flow is governed by a friction–gravity balance, and some flow features, such as a persistent indentation in the free surface, are not reproduced in the numerical solutions. On planes inclined at a shallow angle, the effect of stationary granular material becomes important in the flow evolution, and oscillatory and more general time-dependent flows are observed. The hysteretic transition between static and dynamic friction leads to two phenomena observed in the flows: unsteady avalanching behaviour, and the feedback from static grains on the flowing region, leading to levéed, self-channelised flows.

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