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Morphogenese et Dynamique des Barchanes

Abstract : Barchans are crescentic and mobile dunes which develop on a firm ground under a (roughly) mono directionnal wind. Since the Pioneering work of R. A. Bagnold, many studies have been performed; directly on the field or with the help of numerical models. However, barchans have a very striking property : no barchans smaller than, typically ten meters wide and long, have been observed in sand deserts. Therefore, no laboratory experiment was able to study barchans at a small scale. Here, we present and analyse a very convenient and practical experimetal setup which overwhelms this limitation. Basically the experiment consists of studing barchans directly under water rather than in the air. These subaqueous dunes develop the same shape and dynamics than eolian ones but at a 1/1000 scale. Combined with a numerical modeling, which shows that the crescentic shape comes from the lateral deflexion of grains rolling on the dune's surface, this experiment opens the way to explore new aspects of the physics of dunes. Nucleation of barchans, their interactions and their evolution in macroscale structure called ”corridor of dunes”, as well as the collisions of barchans and the effect of wind turnover are studied both experimentally and numerically. These studies provide us with a general understanding of barchans behavior. In the end, we discuss the stability of barchans, on short and long timescales, showing the high sensibility of these barchans to the properties of the sand flux. Besides, we describe an experimental work about a famous phenomenon known as the singing dunes.
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https://tel.archives-ouvertes.fr/tel-00008602
Contributor : Hersen Pascal <>
Submitted on : Tuesday, March 1, 2005 - 4:29:42 AM
Last modification on : Monday, December 14, 2020 - 9:51:03 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:32:40 PM

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  • HAL Id : tel-00008602, version 1

Citation

Pascal Hersen. Morphogenese et Dynamique des Barchanes. Dynamique des Fluides [physics.flu-dyn]. Université Paris-Diderot - Paris VII, 2004. Français. ⟨tel-00008602⟩

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