07 octobre 2021

Wébinaire Javier Jimenez

Javier Jiménez is a Professor of Fluid Mechanics at the School of Aeronautics and currently a distinguished research Professor at the U. Politécnica de Madrid, Spain. He received his PhD in Applied Mathematics at the California Institute of Technology (USA) in 1973. He had been a Visiting Fellow at Kavli Inst. Theoretical Physics (UC Santa Barbara, CA) in 2016 and at the Sidney-Sussex College (U. Cambridge, UK) in 2015. Between 1989 and 2012 he joined the CTR Turbulence Res. (Stanford U. and NASA Ames) as Senior Research Fellow, and from 1999 and 2005, he held the position of Professor of Mechanics at Ecole Polytechnique, Palaiseau, France. Among the several national and international awards, he received the Annual prize of the Spanish Academy of Sciences (1998), the Biennial Fluid mechanics prize, Euromech (2018). Since 2005 he is member of the Spanish Academy of Engineering, and since 2008 he is member of the Spanish Academy of Sciences. He was awarded of three European Research Council Advanced Grants, from 2011 to 2015, from 2016 to 2021, and from 2021 to 2026. He co-authored more than 140 international refereed journal papers, 9 books and lecture notes and 95 among invited lectures and book chapters.
Collective structures in two-dimensional turbulence

Abstract: Although different from the three-dimensional case, two-dimensional turbulence is a plausible surrogate for some geophysical and stratified flows, and has served as a laboratory model for the analysis of high-dimensional nonlinear dynamical systems. Discouragingly, although theory correctly identifies important aspects of the flow, some predictions have turned out to be wrong in detail. The reason is that the flow organises into vortices that are too coherent to be treated by mean-field theory, but not permanent enough to be considered permanent ‘objects’. This talk deals with a further turn of the theoretical screw, showing that a subset of the vortices organise themselves into a collective superstructure (a ‘crystal’), that evolves more slowly than could be expected from the mean-field model. This object, whose evolution controls the flow, and whose formation is equivalent to the cascade of energy towards large scales, tends to minimise energy through mutual screening, but it is kept from reaching equilibrium by the occasional merging of like-signed vortices. This investigation stems from a computer search among random experiments for ‘things that have some effect on the flow evolution’. At least one of the candidates identified was interesting in the sense of not being trivially expected, but converting this ‘suggestion’ into a theory required human intervention using classical techniques. Part of the seminar will reflect on how long will computers stay limited to the role of suggesting research, and whether we can expect something else in future.

07 octobre 2021, 16h3017h30
Contacter Francesco Romano pour le lien

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08 décembre 2022

Webinaire Fabian Denner

Fabian Denner a obtenu son doctorat à l'Imperial College de Londres en 2013 sur les méthodes numériques pour les écoulements multiphasiques avec tension de surface, suivi d'un post-doc à l'Imperial College. En 2015, Fabian a obtenu une bourse prestigieuse

Fabian Denner a obtenu son doctorat à l'Imperial College de Londres en 2013 sur les méthodes numériques pour les écoulements multiphasiques avec tension de surface, suivi d'un post-doc à l'Imperial College. En 2015, Fabian a obtenu une bourse prestigieuse du Conseil de recherche en ingénierie et en sciences physiques (EPSRC) du Royaume-Uni, avec laquelle il a poursuivi ses travaux fructueux sur les écoulements avec tension de surface et a étendu ses recherches à de nouveaux domaines, tels que les écoulements compressibles et chargés de tensioactifs. Depuis 2018, Fabian est professeur junior de modélisation des écoulements multiphasiques à l'Otto-von-Guericke-Université de Magdebourg (Allemagne). Ses recherches tournent autour du développement de méthodes numériques et d'outils logiciels pour prédire les écoulements multiphasiques, et de l'application de ces méthodes pour répondre aux questions liées à la physique et aux applications de ces écoulements. Actuellement, les travaux de Fabian se concentrent sur les écoulements interfaciaux avec des surfactants, les écoulements viscoélastiques, les écoulements multiphasiques dans les applications biomédicales, ainsi que sur la cavitation et l'acoustique.