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Floaters on Faraday waves: Clustering and heterogeneous flow

[ jeudi 26-03-2015 12:00 | anglais ]Floaters on Faraday waves: Clustering and heterogeneous flow Ceyda Sanli CompleXity and Networks, naXys, University of Namur, Belgium
Résumé :
Floating objects are found in our daily life: From bubbles in our drinks to plants on a river surface. We partly understand how things float thanks to Archimedes' principle, which explains the upward force on an object. However, this principle does not account for observed horizontal drift and so it cannot explain why bubbles in a drink drift to the wall of a glass or how plants bob along the waves of a river. Furthermore, Archimedes’ principle does not consider any interaction among these small floaters and a dynamic surface such as waves. In this study, we suggest an experimental system giving us a chance to examine cumulative effects of the horizontal drift on a periodically driven interface such as floating macroscopic plastic spheres on water waves. Our main focus is to quantify the resultant collective behavior systematically by increasing the number of the millimeter-sized hydrophilic spheres on a wave surface. We perform two distinct experiment series: (i) Standing gravity-capillary wave (ii) Erratic capillary wave. We find that (i) horizontal drift to the wave peaks (anti-nodes) inverts its direction to the locations where the water is stationary (nodes) when we create a floating carpet by adding large number of the floaters to the surface. Therefore, the antinode clusters in low floater numbers turn into the node clusters in high floater numbers [1]. On the other hand, (ii) this floating carpet interacting with the underlying erratic wave presents heterogeneous flow in space and irregular dynamics in time. In addition, we observe complex floater group formation. Borrowing the techniques such as the four-point dynamic susceptibility and the four-point correlation function, we are able to partially quantify the heterogeneous flow and the group formation [2]. In my talk, I will describe these two aspects of our experimental system.
[1] C. Sanli, D. Lohse, and D. van der Meer, Phys. Rev. E 89, 053011 (2014)
[2] C. Sanli, K. Saitoh, S. Luding, and D. van der Meer, Phys. Rev. E 90, 033018 (2014)
(Collaboration work with D. Lohse and D. van der Meer from Physics of Fluids, University of Twente, the Netherlands.)