Offres de Thèses et Postdocs

L’objectif de ce postdoc est de caractériser théoriquement et numériquement le couplage d’écoulements de sillages turbulents pour plusieurs corps présentant différentes géométries. Les approches seront multiples et permettront de comparer les modèles développés récemment avec des modèles classiques et des simulations numériques directes. Des comparaisons expérimentales seront réalisées dans le cadre du projet SILTURB à l’aide d‘expériences dédiées réalisées à l’UME de l’ENSTA. Les résultats de ces études ont pour objectif de proposer des modèles de fermeture nouveaux implémentables dans les codes CFD

The mechanical engineering department of the LISN lab invites applications for a one-yearpostdoctorate position to conduct cutting-edge research at the intersection of turbulent naturalconvection, convolutional neural networks (CNN), physics-informed machine learning, and high-performance computing (HPC). The successful candidate will work on advancing the field of super-resolution analysis for turbulent fluid flows using innovative approaches based on numerical andexperimental ombroscopy techniques.

L’originalité de ce travail consiste à passer de l’échelle laboratoire où différentsessais ont été menés pour caractériser l’érosion à une grande échelle sur laquelledifférentes études de terrain sont menées dans le cas de la thèse en cours surl’étude du transport sédimentaire en milieu instationnaire. L’objectif du postdoctorant sera de paramétrer les lois d’érosion et de transport en reproduisant lesexpériences laboratoire par des simulations numériques pour pouvoir ensuitealimenter des simulations numériques à plus grande échelle, réalisées avecTélémac.

The Department of Engineering at Reykjavik University is looking for a PhD student to work on the project “Wind Power Installations in Harsh Environments; an experimental study”.

L’étude proposée ici repose sur la comparaison de modèles numériques dédiées au transport sédimentaire pour identifier des modèles physiques locaux de transport sédimentaire. L’objectif est de comparer les résultats issus de simulations numériques sous OpenFoam à des mesures obtenues en laboratoire de transport sédimentaire à des échelles locales en temps et en espace. Ces mesures expérimentales ont été réalisées en configurations stationnaire et instationnaire pour différentes caractéristiques de sédiments. Des mesures de la réponse du lit sédimentaire, du taux d’érosion et des conditions hydrodynamiques (vitesses et hauteurs) ont été acquises et sont disponibles à partir des travaux de thèsefinancés par l’OFB et démarrés en Octobre 2022.

The post holder will work at the Department of Low Temperature Physics, within a project focusing on the experimental study of wall-bounded flows of liquid helium-4.

This postdoctorate investigates the question of the influence of large structures on small scales and their fluctuations and vice versa in atmospherics dynamics.In particular, this postdoctorate will consist especially in performing Direct Numerical Simulations (DNS) of an idealized geophysical flow in the strongly stratified turbulence (SST) regime (i.e. small Froude number and high buoyancy Reynolds number) containing large structures called vertically-sheared horizontal flow, internal gravity waves and eddies. In addition, he will have to apply a new method for extracting large strutures, waves and vortices, developed in our team (Lam et.al. atmos 2020 , JFM 2021 & JFM 2023) and calculate thevelocity increments for each part.

This Postdoc project aims at understanding the propagation of weakly nonlinear waves in anisotropic media. The isotropy of the system will emerge either from external sources (forcing) or might be intrinsic to the waves due to the physics of the problem. The main questions to understand is how non-linear wave interactions helps to recover isotropy and the stability of certain out-of-equilibrium solutions. The scientific problem will be addressed using the wave turbulence theory and studying solutions of the associated wave kinetic equations. To complement theoretical predictions, the successful applicant will perform numerical simulations of the wave kinetic equation and the original dynamical equation describing the whole physics. This postdoc position is, therefore, theoretical with an important numerical part using existent numerical codes.

We have funding for a Ph.D. position on fundamental turbulence modeling. The student will work in collaboration with the two advisors A. Alexakis in LPENS at École Normale Supérieure Paris, and S. Chibbaro LISN at Université Paris-Saclay. The goal of the Ph.D. would be to build and test a novel stochastic models using large-scale direct numerical simulations and machine learning. The potential candidate should have some familiarity with numerics, and motivation to study turbulent flows. For further information please see https://www.phys.ens.fr/~alexakis/StochasticModeling.html or contact us directly by email.

We are looking a postdoctoral researcher to work on the dynamics of quantum vortices in rotating superfluid helium in the framework the ANR QuantumVIW by joining the group in Nice. The QuantumVIW project aims at providing numerical and theoretical support to the experiment CryoLEM at LEGI Grenoble. This unique experiment is able to produce and visualise in real time a stable vortex lattice in rotating superfluid helium. The successful applicant is expected to perform numerical simulations of the self-consistent model FOUCAULT (and other related superfluid models), to develop analytical theories and strongly interact with all partners of the ANR QuantumVIW

This project focuses on the dynamics of quantum vortices in rotating superfluid helium. In particular, it aims to provide numerical and theoretical support to the experiment CryoLEM at LEGI Grenoble. This unique experiment can produce and visualise in real time a stable vortex lattice in rotating superfluid helium. The successful applicant is expected to perform numerical simulations of the self-consistent model FOUCAULT. This recently developed model can accurately describe the interaction between quantum vortices and the normal fluid. More precisely, the project aims to understand the effect of rotation and counterflow (mean relative velocity between the superfluid and the normal fluid) on the dynamics of quantum vortices and the normal fluid. Other superfluid models might be used to complement and answer related scientific questions. This project contains an important numerical part, but analytical theories will be developed whenever possible.

Analogue Gravity allows us to mimic the propagation of fields in curved spacetime with waves in a condensed matter system, thus making certain gravitational phenomena accessible to experiment. The best-known example of such a phenomenon is Hawking radiation, which is likely far too weak to be observed in an astrophysical context. The system of surface waves on an open channel flow is studied for this purpose at Institut Pprime in Poitiers. An analogue of the Hawking effect takes place at an effective horizon where the flow speed becomes faster than the wave speed. While this effect has been observed, the Hawking regime in which the scattering behaves in accordance with a thermal (Planck) spectrum has yet to be realized in a water wave system. The goal of this thesis will be to provide theoretical insight into how to reach the Hawking regime and the optimisation of the seeding of the Hawking process.

The aim of the Thesis is to characterize and better understand the interaction dynamics between a vortex ring and a freely moving body, for a panel of situations featuring vortex rings of well-controlled intensity and size interacting with bubbles, solid spheres, as well as rigid and flexible cylinders of various aspect ratios. The state-of-the-art time-resolved 3D-PTV technique coupled to a shadowgraphy technique will be used to capture simultaneously the bodykinematics, the body deformation as well as the surrounding fluid motion.

Proposition de thèseModélisation stochastique pour la dynamique des particules en turbulence hétérogèneEncadrants : Rémi Zamansky, Pascal Fede, Olivier SimoninContact : remi.zamansky@imft.fr pascale.fede@imft.fr olivier.simonin@imft.fr Financement : Contrats Doctoraux MESRI 2024-2027

The aim of this thesis is to develop new tools and methodology for modelling andcontrol of bistable flows from data, by coupling state-of-the-art machine learning techniques withdynamical system theory. Closed-loop control will be implemented using model predictive control.

The aim of the project is to develop and analyze a model reduction technique for the simulation of parametric incompressible turbulent (chaotic) flows. The point of departure is the stochastic closure modeling procedure ; we shall consider the efficient treatment of parametric boundary conditions and the development of efficient hyper-reduction techniques to handle nonlinear terms.Application to large-scale three-dimensional problems will be pursued by integrating the methodology in the C++ solver Ithaca FV.

The aim of the project is to develop, analyze, validate and compare reduced data assimilation technique for 3D incompressible turbulent flows. The point of departure is the stochastic closure modeling procedure and the existing code coupled with the C++ solver Ithaca FV. The PhD student will acquire a broad vision of the data assimilation process and its limitation: from the theory, to the implementation, the data qualification and the experiments. Both synthetic and experimental data will be considered. We shall also consider the efficient treatment of unknown turbulent inflow conditions and the development of efficient hyper-reduction techniques to handle nonlinear terms.

The coastline of Nouvelle Aquitaine region is not immune to erosion and submersion risks. The thunderstorms of 2023 served as reminders. Nouvelle Aquitaine region has undertaken a reflection on territorial planning and decided to fund the CORALI program, whose objective is to provide multidisciplinary scientific knowledge necessary for better predicting coastal changes and anticipating adaptations to erosion and coastal submersion. Within the CORALI program, CURIOSITY and M2N propose a PhD thesis on the numerical modeling of wave interaction with defense structures. The thesis will involve modifying Smooth Particle Hydrodynamics methods. Numerical simulations will provide corrections to empirical laws used to quantify the performance of defense structures, including reflection coefficient (wave transmission), crest height (wave run-up), overflow discharge (wave overtopping), and structure stability (wave pressure), by incorporating the characteristics of defense structures.

This PhD project aims at modelling the dynamics of long flexible fibers in wall-bounded turbulent flows, in particular close to the walls where the turbulence is inhomogeneous and anisotropic. To tackle this challenging problem, the project will primarily utilize an experimental approach complemented by direct numerical simulations and physical modelling.

he subject of this thesis is the understanding, modelling and numerical simulation of the transport of solutes, whether passive or reactive, in porous, permeable, heterogeneous and/or fractured media. The most immediate field of application is geological media, often with environmental concerns (sensitivity to contaminants, pollution clean-up), but geothermal energy also falls into this category if the solute is heat.One of the most decisive aspects, and one that is difficult to take into account in modelling, concerns mass transfers between zones of strongly contrasting properties, and in particular between fractures (which constitute the preferential paths) and the matrix (which contains most of the possible accumulation volume, and is the site of possible sorptions and/or reactions).