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Biomedical subjects

M Ammi

Publications and source records attributed to M Ammi.

6 recordsLinked to original sources
PubMed2005

Discrete Element Method studies of the collision of one rapid sphere on 2D and 3D packings.

We performed numerical simulations of one-bead collision on the surface of a static granular medium. The simulations have been done for two- and three-dimensional packings of beads. The effect of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings and only disordered 3D packings. The 2D results are in good agreement with experimental available data. The 3D simulations give good preliminaries results about the shock-wave propagation through the stacking and provides new insights in the ejection process ("Splash function").

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PubMed2003

Friction and rotation modes in a packing of cylinders under shear stress.

We study the influence of collective processes such as rotations on the effective friction of sheared granular media made of two-dimensional array of cylinders. An original experimental device allows us to measure simultaneously grain rotations and the global friction force between the packing and the basal plane. It is shown that the correlation between these two quantities can be analyzed at two different time scales: 1. Averaging over the duration of a whole experiment, the mean sliding behavior of the first row on the base of the packing describes satisfactorily the global friction force. 2. At short-time, description of this correlation requires the knowledge of the propagation of rotation perpendicularly to the shear direction.

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PubMed2000

Collective response of an array of rotating particles to fluctuating confining forces

We study the influence of fluctuations of confining forces on the rotation patterns in a dense array of cylinders. Our theoretical studies are motivated by new results from detailed time-resolved experimental measurements. In order to calculate the system's evolution in time at each moment, a molecular-dynamics code adapted to the system is developed. The numerical procedure is tested by a comparison with rigorous predictions derived analytically. The chain's reaction on oscillating confining forces is analyzed numerically for different typical cases. Our theoretical results reproduce the striking features of the experimental data. A quantitative analysis of the experimental data is performed by a computation of their power spectrum and of spatial and temporal correlation functions. From our comparison of the theoretical and experimental results we conclude that the experimental rotation patterns result of random superpositions of different steady-state patterns ("collective random walk").

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