The collapse dynamics and runout of columns of elongated grains in two dimensions are
numerically investigated in dry and immersed conditions, by means of an unresolved finite
elements/discrete elements model. The elongated grains are modeled as rigid aggregates
of disks. The column aspect ratio is systematically varied from 0.125 to 16 in order
to span short and tall columns. To analyze the effect of the initial grain orientation,
columns with an initial grain orientation that is either random or aligned with a given
direction are both considered. Collapse dynamics, both in dry and immersed cases, are
found analogous to that previously observed for circular grain columns, particularly with
respect to the power law dependency for the runout as a function of the column aspect
ratio. The effect of the fluid mainly results in a decrease of the runout distance. Inter-
estingly, the collapse dynamics and runout are not significantly affected by the initial
orientation of the grains, except maybe in the extreme case where the grains are all
horizontally oriented, which geometrically prevents the collapse. Finally, a scaling based
on the front propagation energy is proposed allowing one to unify the runout of short to
tall and dry to immersed columns in a single description, regardless of the initial grain
orientation.

For more details, check the publications section!

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This paper is devoted to the investigation of the density sorting of grains using water jigging. Experiments achieved in a laboratory scale water jig for two initial binary bed configurations are studied and compared to numerical results. The vertical composition of the deposit is estimated after different number of water pulses to represent the sorting evolution in time. Simulations are based on a multiscale model in which the fluid is solved at a larger scale than the grain diameter using the finite element method, while the grains are considered as rigid bodies and solved using the nonsmooth contact dynamics. Key parameters are numerically varied and observed to determine the sensitivity of the process.

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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.

The post New Article : Numerical analysis of the drag on a rigid body in an immersed granular flow appeared first on MigFlow Project.

Experiments were achieved in a Hele-Shaw cell to observe the gas invasion paths and to calibrate the numerical multiscale model. A phase indicator function is used to dissociate the gas and the liquid constituting the fluid and to compute the density and viscosity of the fluid at each position. The experiments are supported by simulations in two dimensions to refine the study and the understanding of the invasion dynamics at short times.

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