Unstable Drainage of Frictional Fluids and Magnetic Control of the Mechanical Behavior of Confined Granular Media
| Quand ? |
Le 30/11/2021, de 11:00 à 12:00 |
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| Où ? | Salle des thèses |
| Participants |
Louison Thorens |
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The transport of immersed grains in confined media relevant for many industrial and natural situations highlights the complex interaction between capillary and granular stress. In this thesis, we have studied the triggering of a bulldozing instability, leading to the formation of granular plugs during the slow drainage of a frictional fluid, a mixture of a liquid and grains sedimented in a capillary. We could reveal a new unstable regime leading to the periodic formation of dunes. Furthermore, we have developed an original method to control the frictional interactions at the origin of this bulldozing instability, by using ferromagnetic particles: submitted to a magnetic field, they acquire a magnetic moment, leading to tunable interactions of pairs of magnetic dipoles. We demonstrated the emergence of a radial force along the walls of the container, whose amplitude and direction are determined by the applied magnetic field. This "magnetic Janssen effect" allows controlling the apparent mass of the granular column, paving the way towards the design of granular meta-materials, whose mechanical (un)jamming properties can be remotely controlled or even programmed.