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Theses

Stabilité et dynamique de pentes sous-marines

Abstract : This thesis mainly consists in the experimental study of the dynamics of a tilted granular interface, sheared by a laminar continuous water flow. In the geometry-controlled duct, two kinds of sedimentary transport may be encountered: water erosion and avalanche.
A first study deals with onsets of motion. Experimental relations between motion thresholds by erosion or avalanche and water velocity or bedslope are consistent with simple modelling when taking into account gravity, inter-particular friction and water shear stresses.
The regime of underwater avalanches is then explored for high slopes above the angle of maximal stability. Measurements of the pile slope evolution and of the particle transport rate (by PIV) show that the avalanche rapidly exhibits a quasi-stationary behaviour. The grains speed depends only on the pile slope. The relation between velocity and slope is well predicted by a modelling including recent developments about the rheology of granular materials and wall effects.
In a third part, the deformation of the granular interface in a particular regime is studied. Vortex ripples are observed at the surface of the avalanche, when a water flow is imposed which tends to transport the particles in the opposite direction. A first stage of exponential growth is followed by the saturation of the amplitude of the ripples. The shape of the structures seems to be controlled by the recirculation bubble present at the rear of the ripple whereas the amplitude seems to be determined by the maximum quantity of particles transportable in the avalanche.
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Submitted on : Tuesday, October 24, 2006 - 3:17:18 PM
Last modification on : Monday, December 14, 2020 - 9:52:15 AM
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Delphine Doppler. Stabilité et dynamique de pentes sous-marines. Dynamique des Fluides [physics.flu-dyn]. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00109458⟩

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