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Accueil > Actualités > Séminaires > Séminaires 2016

Mardi 2 février 2016 à 11h00 en salle K118

Ilias Sigbatullin, Moscow State University, Moscow

Titre/Title : Instabilities in stratified media : penetrative convection and internal wave attractors

Contact : Bruno Voisin (équipe MEIGE)

Résumé/Abstract :
Coexistence of stably and unstably stratified media can drastically change the behavior of convective motion. A classical example is convection in water layer when temperature interval comprises point of density maximum. It is known that in this case appearance of convection is subcritical. We have investigated bifurcations of regimes with the increase of supercriticality and showed that transition from periodic to quasiperiodic regimes is carried out trough subcritical bifurcations of Neimark-Sacker. Convective structures and their development are different from classical RB convection. With further increase of supercriticality intermittency appears with stochastic bursts on the background of quasiperiodic solutions.
We have applied spectral element approach to problems of internal wave attractors, and made careful investigations of instability developments with increase of the forcing amplitude. First, we confirmed numerically that triadic resonance is the primary instability on the most energetic ray of the attractor. Next, we investigated cascades of triadic resonances in a numerical setup which corresponds to the experiments being carried out at ENS de Lyon. The correspondence between experiments and DNS is remarkable. We have investigated dissipation effects from the lateral walls in the experiments, and estimated the contribution of 3D effects to the synthetic schlieren measurements applied to nominally 2D problem. This contribution was found to be negligible. The validation of the numerical code makes us confident about the numerical results. As a further step, we explore numerically the quantities and phenomena which are hard to measure experimentally, and now the numerical experiments are being carried out which correspond more closely to real oceanological environments. We have used our own pseudospectral code for convections problems and nek5000 for spectral-element approach.