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Accueil du site > Séminaires > Séminaires 2022 > MSC Seminar. May 30th 2022 at 11:30. Anaïs Abramian (IJLRDA, Sorbonne Université) : " From Chladni patterns to alluvial rivers : how diffusive transport of grains can shape macroscopic systems"..

MSC Seminar. May 30th 2022 at 11:30. Anaïs Abramian (IJLRDA, Sorbonne Université) : " From Chladni patterns to alluvial rivers : how diffusive transport of grains can shape macroscopic systems".

Sauf mention contraire, les séminaires et les soutenances se déroulent à 11h30 en salle 454A du bâtiment Condorcet.


There will be a live diffusion with Zoom.

Monday May 30th, 11h30

Contact Michael Berhanu to attend the visio-seminar.

From Chladni patterns to alluvial rivers : how diffusive transport of grains can shape macroscopic systems

Anaïs Abramian

L’ Institut Jean Le Rond d’Alembert Sorbonne Université, CNRS, Paris

At the microscopic scale, Brownian motion of a particle is the manifestation of successive collisions with the molecules of the surrounding liquid. Yet, grains can undergo macroscopic collisions, at larger scales, which also leads to random walks and induces diffusive fluxes. In this talk, I will describe two examples where diffusive fluxes can explain the shape of macroscopic systems.

The first example is the selection of the shape and the size of an alluvial river. The latter builds its own bed with the sediment it transports, through erosion and deposition of grains. Using laboratory experiments, we showed that, due to the roughness of the bed, the trajectory of a moving grain on the river bed fluctuates across the stream. Grains thus diffuse towards the banks and counteract gravity at the equilibrium, which selects the width of such rivers.

The second example deals with bouncing grains : when sand is sprinkled on a vibrated membrane, grains move until they eventually settle down in the nodes of vibration. These so-called "Chladni patterns" provide an easy visualization of the membrane’s modes. However, the mechanism by which bouncing grains migrate on the vibrated membrane lacks a quantitative description. We suggest that they act as random walkers, whose diffusivity depends on the membrane amplitude.


Contact : Équipe séminaires / Seminar team - Published on / Publié le 17 mai


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