Dresden 2011 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 22: Granular Matter/ Contact Dynamics
DY 22.1: Talk
Wednesday, March 16, 2011, 14:00–14:15, HÜL 186
Where to Dig for Gold? - Density Segregation inside Migrating Dunes — Christopher Groh1, Ingo Rehberg1, and •Christof A. Krülle1,2 — 1Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth, Germany — 2Maschinenbau und Mechatronik, Hochschule Karlsruhe - Technik und Wirtschaft, D-76133 Karlsruhe, Germany
Spatiotemporal patterns in nature, such as ripples or dunes, formed by a fluid streaming over a sandy surface show complex behavior despite their simple forms. Below the surface, the granular structure of the sand particles is subject to self-organization processes, exhibiting such phenomena as reverse grading when larger particles are found on top of smaller ones. Here we report results of an experimental investigation with downscaled model dunes revealing that, if the particles differ not in size but in density, the heavier particles, surprisingly, accumulate at the crest of migrating dunes while lighter particles are buried at the bottom. As a side effect we show that the migration velocity of bi-dense dunes scales with the mean density of the grains as a power law function with an exponent of -3/2. This insight into the sedimentology of dunes composed of different types of sand has, loosely speaking, the implication, that in a ripple or dune mixed of gold and sand, the gold nuggets are likely to be found at the top, close to the surface at the crest.