Description du sujet de thèse

At CNRS, on the Futuroscope site, the Pprime Institute is recruiting a PhD student to work on a French National Research Agency (ANR)-funded research project.

During the PhD, we will identify the characteristics of periodic layering that can lead to the formation of band gaps. We will develop a new approach to studying the edge states formed by internal waves, using existing methodologies in multilayer photonic systems or topological insulators. Secondly, we will explore other wave phenomena such as Anderson localization in disordered stratifications or feedback phenomena in nonlinear regimes.

This research project proposes to develop a novel framework to investigate the interplay between internal
waves and complex environments using methods inspired from condensed matter physics. Drawing analogies from
a variety of systems describing wave-matter interactions, such as multi-layered photonic materials and topological
insulators, we aim to identify the physical mechanisms that govern internal wave transport in complex geophysical
environments, while exploring the existence of surface states and localization transition-like phenomena in fluids.
Periodic density stratifications will be prepared in laboratory experiments using traditional double-bucket method to
create non-uniform stratification by varying the mixing ratio of salt- and sweet-water periodically over time with a
computer-controlled pump. The interplay between double-diffusive convection and internal wave band formation
will be explored by controlling the temperature profile in addition to salinity differences in the tank. Flow velocity
fields measurements will be performed using particle image velocimetry (PIV), along with filtering and spectral
analysis methods to determine the internal wave dynamics. In parallel, we will perform numerical simulations
combined with experimentally measured stratification profiles to determine the wave field in the linear
approximation. The experiments will be carried out at Institut Pprime in close collaboration with Dr. Michel Fruchart
at ESPCI (Paris) where the theoretical approaches are being developed.

Contexte de travail

Internal gravity waves are mechanical waves that propagate in the bulk of stratified fluids, such as the ocean or the atmosphere. They can transport energy and momentum far from the surface and over large distances and affect large-scale circulation patterns. When the density stratification is not uniform, internal waves can exhibit resonances, tunneling, and frequency-dependent transmissions. In the Arctic Ocean, global warming has been driving rapid ice cover loss, and led to an increased seasonal internal gravity wave generation by atmospheric
perturbations. In this region, the interplay between heat diffusion and salt diffusion can lead to the formation of
extended regions with spatially periodic density profiles known as thermohaline staircases.
Periodic environments can strongly alter wavepropagation and energy transfer phenomena , yet the effect of these periodically stratified thermohaline structures on internal wave transmission in the ocean are incompletely understood. We recently showed with preliminary laboratory experiments.the existence of internal wave band gaps and surface states in periodically stratified fluids. The occurrence of such banded internal wave transmission hrough periodic thermohaline structures could profoundly affect energy transport processes in the ocean, and their modeling poses a fundamental challenge that requires the development of pluri-disciplinary approaches.

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*- REQUIRED SKILLS:
Candidates should hold a master degree in mechanics or equivalent and possess the following skills:
- have a taste for experimental research and physical modeling,
- have a basic knowledge in Python or Matlab,
- have a background in physics, fluid mechanics or soft matter.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

- Registration with the Université of Poitiers doctoral school: ED-MIMME
- Travel to ESPCI (Paris) is required.