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Production scientifique
Mécanique statistique des systèmes désordonnés, en particulier inspirés par des systèmes à l'interface avec la biologie
(2) Production(s) de l'année 2024
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Effect of viscosity on wind-driven gravitation waves 
Auteur(s): Chaubet C., Kern N., Manna M.
(Article) Publié:
Physics Of Fluids, vol. 36 p.103976 (2024)
Ref HAL: hal-04773731_v1
DOI: 10.1063/5.0221941
Exporter : BibTex | endNote
Résumé: We address the question of how viscosity impacts the growth of gravitation waves, such as those on the ocean, when they are driven by wind. There is so far no general rigorous theory for this energy transfer. We extend Miles' approach [J. W. Miles, “On the generation of surface waves by shear flows,” J. Fluid Mech. 3, 185–204 (1957)], using the same logarithmic wind profile, to incorporate bulk viscosity and derive modified growth rates. Exploiting the fact that water waves fall into the “weak viscosity” regime, we produce analytical expressions for the growth rate, which we solve using the numerical method proposed by Beji and Nadaoka [“Solution of Rayleigh's instability equation for arbitrary wind profiles,” J. Fluid Mech. 500, 65–73 (2004)]. Our results confirm that corrections to the growth rates are significant for wavelengths below a meter, and for weak to modest wind strengths. We show that all wave growth is suppressed, due to viscous effects, below a critical wind strength. We also show that the wave age corresponding to a developed sea is reduced by viscosity. We quantitatively characterize the zones, in terms of wind strength and wavelength, for which the wave growth is suppressed by viscosity.
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Emerging Mesoscale Flows and Chaotic Advection in Dense Active Matter
Auteur(s): Keta Y.-E., Klamser J., Jack Robert, Berthier L.
(Article) Publié:
Physical Review Letters, vol. 132 p.218301 (2024)
Texte intégral en Openaccess : 
Ref HAL: hal-04603641_v1
Ref Arxiv: 2306.07172
DOI: 10.1103/PhysRevLett.132.218301
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We study two models of overdamped self-propelled disks in two dimensions, with and without aligning interactions. Both models support active mesoscale flows, leading to chaotic advection and transport over large length scales in their homogeneous dense fluid states, away from dynamical arrest. They form streams and vortices reminiscent of multiscale flow patterns in turbulence. We show that the characteristics of these flows do not depend on the specific details of the active fluids, and result from the competition between crowding effects and persistent propulsions. This observation suggests that dense active suspensions of self-propelled particles present a type of “active turbulence” distinct from collective flows reported in other types of active systems. Published by the American Physical Society 2024
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