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Theses

Instabilités dans un milieu granulaire : tôle ondulée sur un lit de sable, et ségrégation au sein des astéroïdes lâches

Abstract : This thesis, consisting of two parts, is focusing on instabilities into a granular assembly.The first part deals with washboard road instability, which is the growth of a ripplepattern on a track subjected to repeated passages of vehicles. Our experimental work aswell as soft spheres numerical simulations provide us a better understanding of this phenomenon.In the case of a rigid wheel dragged at constant velocity, we quantitatively studiedthe impact of the cohesion into the granular media on the main features of the instability :critical velocity, wavelength and growth rates. Finally, we have begun preliminary studieson a yield stress fluid, namely a carbopol microgel.The second part is devoted to the granular segregation in asteroids. Several keys showthat a significant part of them are rubble-piles, without internal cohesion and held togetherby their weak self-gravity. The distribution of grains is heterogeneous : while some regionsconsist in fine sand or powder, large boulders seem to accumulate in other parts. Wenumerically simulated a granular pile and subjected it to repeated quakes : we managedto reproduce segregation. We studied the influence of physical and numerical parameterson the segregation level and the dynamics of the phenomenon. We also investigate variouscauses of the segregation : granular convection, kinetic sieving, depletion pressure, etc.Finally, we highlighted an azimuthal segregation which can explain observations duringspatial missions.
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Submitted on : Tuesday, October 23, 2018 - 5:41:06 PM
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Charles-Edouard Lecomte. Instabilités dans un milieu granulaire : tôle ondulée sur un lit de sable, et ségrégation au sein des astéroïdes lâches. Physique [physics]. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSEN024⟩. ⟨tel-01902750⟩

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