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Soutenance de Corentin Pacary

Dynamics of stratified or rotating media: Axisymmetric wave attractors and non-linear interaction
When Jul 07, 2023
from 02:30 to 04:30
Where Amphi Physique Chimie
Contact Name Corentin Pacary
Attendees Corentin Pacary
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Inertia-gravity waves propagate in stratified and/or rotating media and are of great importance in the geophysical context, particularly in the ocean, due to the transport and the dissipation of the energy injected by tidal forces, and to maintain its stratification. Their peculiar dispersion relation, linking frequency and propagation angle, also makes them an interesting object of study.

This relation causes, during the reflection on an inclined slope, the focusing of a wave beam and therise of structures, called attractors, on which the energy is concentrated. We study numerically by raytracing the conditions of formation of these attractors, already well studied in two dimensions, in a three-dimensional geometry, restricted to the axisymmetric case.

An experimental study confirms the formation of these attractors, and their use to reach the weakly non-linear regime. In particular, the resonant triadic instability is observed, with differences between a stratified fluid at rest and a homogeneous rotating fluid, due to the possibility of interaction with standing wave modes. The presence of the axis of symmetry increases the dissipation in the system and prevents the occurrence of a wave turbulence type of energy cascade.

In the ocean, waves can propagate in the form of vertical propagative modes and the stratification is non-linear. With such a stratification in the laboratory, a mode can interact with itself to form a wave with double the frequency.

A final section looks at the dynamics of plumes in a uniform rotating ambient fluid. Under certain conditions, the plume is no longer deviated from its axis but is laminarised to form a cylindrical vortex, like a tornado, which could have consequences for the transport by these plumes.