LEGI - UMR 5519
Laboratoire des Ecoulements Géophysiques et Industriels


Partenaires

CNRS
Université de Grenoble Alpes


Rechercher

Sur ce site

Sur le Web du CNRS


Accueil du site > Équipes > Equipe MEIGE : Modélisation, Expériences et Instrumentation pour la Géophysique et l’Environnement > Diffusion scientifique > Séminaires internes

Séminaires internes

Chaque semaine un séminaire interne informel dans l’équipe. 20min de présentation

Jeudi à 12h15.

Envoyer un courriel à : Maria-Eletta.Negretti  .

Spatially developing gravity currents onto concave slopes

Eletta Negretti, 04/12/14

Experimental results using a PIV measurement technique of gravity currents over concave slopes with different initial slope angles are presented. For large angles, the flow follows a periodic acceleration-deceleration cycle in which gravity and total friction (at the interface and at the bottom) interplay resulting in a strong spatial development of the gravity current. A theoretical model adapted for varying slope angles is presented and used for comparison with the experiments. (...)

Lire la suite

Wall plume in a cavity : an experimental investigation

Tobit Caudwell, 27/11/14

Wall convection produced by hot walls is of great interest to many industrial and environmental applications. In this experimental-theoretical investigation we consider a turbulent plume generated by an isothermal wall in an enclosure, and the formation of the heat stratification in the interior. The evolution of the plume near the wall and the temperature stratification are measured across a plane, using simultaneous LIF and PIV measurements that allows to give a precise description of the (...)

Lire la suite

UVMAT : a tool to process and organize experimental data

Joël Sommeria, 20/11/2014

The organization of experimental data is a recurring problem, especially on a large installation such as the Coriolis platform where data from multiple cameras and instruments are used by a group of researchers and must remain accessible several years after the experiments. The tool uvmat under Matlab provides processing programs likes PIV but it more generally proposes a systematic data organisation using the standard binary format netcdf and documenting the processing parameters by xml files. Furthermorte it gives access to the computer cluster in a way transparent for the user.

Characterization and modelling of internal tides

Natalia Shmakova, 06/11/2014

The interaction of tidal currents with ocean bottom topography results in the radiation of internal gravity waves into the ocean interior. These waves are called internal tides and their dissipation due to nonlinear wave breaking could play an important role in the mixing of the abyssal ocean, and hence in controlling the large-scale ocean circulation. We investigate internal waves generated by oscillating obstacles of different idealized geometries as a model of ocean topography, and (...)

Lire la suite

Pooling and Draining processes in deep Alpine valleys and their effect on pollutant dispersion

Gabriele Arduini, 23/10/14

The aim of my PhD work is to characterize pooling and draining processes in deep alpine valleys under decoupled stable conditions and quantify their effects on pollutant dispersion. Cold-air pools form in landscape depressions and can lead to particularly poor air quality. Such cold-air pools are characterized by very stable stratification and can trap air for many hours or even days, resulting in peak pollution episodes in and around urbanized areas, especially when they are intense, (...)

Lire la suite

Influence d’un rideau de bulles d’air sur le déferlement des vagues

Djalal Merkoune, 02/10/2014

Nous présentons les résultats expérimentaux, de l’influence d’un rideau de bulles d’air sur le déferlement des vagues, ce dernier est de type plongeant. Les expériences ont été réalisées en canal à houle à une profondeur d’eau constante. Une pompe à air a été utilisée pour générer les bulles d’air et contrôler leur concentration. Une faible concentration de bulles d’air provoque une dissipation d’énergie négligeable des vagues, cependant elle influence significativement la position du point de déferlement. A (...)

Lire la suite

Dynamics of gravity currents on concave and convex slopes

Ana-Marija Duranec, 03/07/2014

This presentation is dealing with dynamics of gravity currents on a slope and better understanding the instabilities appearing and leading to the turbulent state of the ow, such as Görtler vortices and Kelvin-Helmholtz vortices. Four different simulations were performed, using the LES (Large Eddy Simulation), for two different slopes - concave and convex. For the concave slope two simulations were performed coarse mesh and fine mesh. The differences were small enough so for the convex case (...)

Lire la suite

Modelling the multiscale interactions of the coupled atmosphere-ocean-sediment system, induced by Marine Renewable Energy Devices

Tim Nagel, 02/07/2014

While the world assist to an increasing development of offshore wind energy, the environmental impact of offshore wind farms remains still unknown. If some recent studies have recently light up the impact of offshore wind farms piles on the seabed morphodynamic or the slight influence of wind farm presence on regional climate, no one has, as far as we know, ever considered the turbine wake impact upon both ocean and sediment layers. The purpose of this internship was to study this (...)

Lire la suite

Simulations numériques de la rhéologie des suspensions denses avec un modèle couplé DEM-fluide

Donia Marzougui, 26/06/2014

Les suspensions denses de particules solides immergées dans un fluide se retrouvent dans de nombreux phénomènes naturels tels que le transport de sédiment ou les coulées de débris et de nombreuses applications industrielles comme la mise en oeuvre des bétons ou le transport d’hydrocarbures. La compréhension des lois rhéologiques qui les régissent a fait l’objet d’un important effort de recherche au cours du siècle dernier (Frankel and Acrivos, 1967 ; Brady and Bossis, 1988). Ce problème est complexe de (...)

Lire la suite

Oceanic Circulation and Dynamical Processes Around the Reykjanes Ridge. Numerical Simulations and Laboratory Experiments

Thibault Jougla, 25/06/2014

The Reykjanes ridge is situated between the Irminger basin and the Iceland basin, at the intersection of different flows determining the global ocean circulation. The flow coming from the Faroe Bank channel turns around the ridge. The aim of this project is to understand the dynamic processes around the ridge. To the best of our knowledge idealized studies on the circulation around sloping ridges, focusing on meso- and sub-meso-scale structures are scant. For this study, idealized (...)

Lire la suite

Experimental study of sheet flow regime in a laboratory flume

Thibaud Revil-Baudard, 24/04/2014

The sheet flow regime of sediment transport occurs when the shear stress exerted by the fluid flow on the sediment bed is high enough to set in motion a thick layer of particles. This phenomenon is very important for river and coastal morphodynamical evolution. However, the key mechanisms controlling this regime such as intergranular interactions or turbulent processes in dense fluid-sediment mixture are not well understood yet. For this purpose, an original laboratory experiment has been (...)

Lire la suite

Nonlinearities of waves propagating over a mild-slope beach : laboratory and numerical results

Mariana Rocha, 24/04/2014

As surface gravity waves propagate from deeper waters to the shore, their shape changes, primarily due to nonlinear wave interactions and further on due to breaking. The nonlinear effects amplify the higher harmonics and cause the oscillatory flow to transform from nearly sinusoidal in deep water, through velocity-skewed in the shoaling zone, to velocity asymmetric in the inner-surf and swash zones. In addition to short-wave nonlinearities, the presence of long waves and wave groups also (...)

Lire la suite

Utilisation de la Fluorescence Induite par Laser pour des mesures de température en convection naturelle

Tobit Caudwell, 23/01/2014

Laser Induced Fluorescence to measure temperature in natural convective flows Résumé : La Fluorescence Induite par Laser (LIF) permet d’avoir accès, de manière quantitative et non-intrusive, à diverses informations sur un scalaire au sein d’un écoulement. Cette technique s’appliquant notamment à des mesures de température, elle est particulièrement séduisante pour des expériences de convection naturelle dans lesquelles les gradients thermiques sont moteurs de l’écoulement. On peut en outre facilement (...)

Lire la suite

Experimental investigation of sediment transport in sheet-flow conditions

Thibaud Revil-Baudard, 28/11/2013

Abstract : In order to better understand the dominant physical mechanisms in intense bed-load transport (sheet flow) and the effect of the mobile layer on the turbulence (damping in the dense layer and modification in the dilute suspended layer), experiments have been performed over fixed rough bed and in sheet-flow conditions. These experiments have been performed in the LEGI open channel using an acoustic profiler together with high frequency digital images obtained from the side wall. (...)

Lire la suite

Effect of the Coriolis force on the drainage of a circular tank

Isabel Peinke, 18/07/2013

The aim of our experiment is to examine the impact of the Coriolis force on the drainage of a tank. We use a circular tank 2 m in diameter and a draining hole in the center. In 1856 Perrot talked the first time about the drainage of a circular tank to show the rotation of the Earth. Then in 1962 Shapiro built up an experiment we took as model. He visualised the effect of the Coriolis force by the rotation of a cross floating above the draining hole. Trefethen repeated this experiment in the (...)

Lire la suite

Focalisation linéaire d’ondes internes par un tore oscillant

Bruno Voisin, 04/07/2013

En collaboration avec Evgeny Ermanyuk, Jan-Bert Flór & Natalia Shmakova Parmi les phénomènes susceptibles de provoquer localement une intensification de l’amplitude des ondes internes de gravité dans un fluide stratifié, et ainsi de conduire au mélange, figure un phénomène spécifiquement tridimensionnel : la focalisation géométrique causée par la forme de l’émetteur. Cette configuration a reçu récemment quelque attention, aussi bien théoriquement pour l’émission de la marée interne par une topographie (...)

Lire la suite

A drag-induced barotropic instability in air-sea interaction.

Aimie Moulin, 20/06/2013

We discuss a new mechanism that induces barotropic instability in the ocean. It is due to air-sea interaction with a quadratic drag law and horizontal viscous dissipation in the atmosphere. We show that the instability spreads to the atmosphere. The preferred spatial scale of the instability is that of the oceanic baroclinic Rossby radius of deformation. It can only be represented in numerical models, when the dynamics at this scale is resolved in the atmosphere and the ocean. The dynamics (...)

Lire la suite

An Empirical Investigation of Non-linear Energy Transfer from the M2 tide to M2 Subharmonic Wave Motions in the Kauai Channel

Sherry Chou, 13/06/2013

Long-duration observations of horizontal currents throughout nearly the entire water column at a location in the Kauai Channel, Hawaii (21.75˚N, 158.75˚W), are used to test hypotheses about the existence of energetic oscillations driven by non-linear processes acting on the semi-diurnal tide. For decades it has been believed that three classes of resonant interactions, based on weakly interacting, non-linear wave theory, are the dominant mechanisms for moving energy through (...)

Lire la suite

Turbulent oceanic western-boundary layers at low latitude

Cataria Quam Cyrille AKUETEVI, 02/05/2013

Low latitude oceanic western-boundary layers range within the most turbulent regions in the worlds ocean. The Somali current system with the Great Whirl and the Brazilian current system with its eddy shedding are the most prominent examples. Results from analytical calculations and integration of a one layer reduced-gravity fine reso- lution shallow water model is used to entangle this turbulent dynamics. Two types of wind-forcing are applied : a remote Trade wind forcing with maximum shear (...)

Lire la suite

Free surface effects on the morphology of river dunes and their evolution to upper stage plane beds

Suleyman Naqshband, 04/04/2013

A large number of bed form data from literature is analyzed, showing significantly different evolution of dune height and length in flows with low Froude numbers (negligible free surface effects) and flows with high Froude numbers (large free surface effects). For high Froude numbers, relative dune heights are observed to grow only in bed load dominant transport regime and start to decay for u*/ws (suspension number) exceeding 1. Dunes in this case are not observed for suspension numbers (...)

Lire la suite

Comparison of sediment flux : in-situ measurements versus simulation.

Philippe Larroudé, 21/02/2013

I will present the abilities of numerical models to predict the morphodynamics over sandy beds. The flow field and the water depth are calculated using the depth-averaged hydrodynamic model. The work consisted in setting up the methodology of calculation. The principle is to make an external coupling of three codes : a swell propagation model ; a one to simulate the currents and one to determine the morphodynamic evolution. The basic principle of this external coupling is to make this loop (...)

Lire la suite

Modelling sedimentation-consolidation in the framework of a one-dimensional two-phase flow model

Julien Chauchat, 20/12/2012

During this short seminar, I will present a one-dimensional vertical two-phase flow model for sedimentation-consolidation process. The model is based on solving the continuity and momentum equations for both fluid and solid phases. After reviewing the main physical processes involved in the cohesive and non-cohesive cases I will show some validation results based on a comparison with detailled experimental datas. The reliability of the proposed model is illustrated from an analysis of the (...)

Lire la suite

UPDATED “GRAB AND DUMP” MODEL FOR SEDIMENT TRANSPORT UNDER ACCERELATION SKEWED WAVES

Tomoko Shimamoto, 12/11/2012

School of Civil Engineering, University of Queensland, Brisbane, Australia. Nielsen (1988) presented a simple “grab and dump” model for sediment transport over ripples, and found its performance in predicting the sediment transport rate was superior to more traditional models for data collected in the small-scale TU Delft flume in the 1970s. While the model performed well for fine sediment (d50=0.125mm), it performed less well for coarse sediment (d50=0.465mm). This presentation will (...)

Lire la suite

3D internal wave focusing

Evgeny V. Ermanyuk, 18/10/2012

The talk presents an experimental study of internal waves emitted by a horizontally oscillating torus in a linearly stratified fluid. Internal waves are measured via precise tracking of distortions of horizontal fluorescein-dye planes created in the test tank prior to experiments and illuminated by a vertical laser sheet (Voisin et al (JFM 2011), Ermanyuk et al (JFM 2011)). This approach gives an access to the Lagrangian measurements of local wave amplitudes and slopes, in contrast with (...)

Lire la suite

Convection naturelle et stockage thermique d’énergie solaire

Philippe Marty, 11/10/2012

Au cours de ce séminaire je vous présenterais le contexte du stockage thermique d’énergie solaire et les problèmes de convection naturelle que nous avons identifiés. Nous avons fait quelques manips préliminaires mais de jolies manips plus poussées seraient utiles. Les mêmes techniques que celles qu’utilisent Eletta Negretti pourraient être mises en œuvre (PIV par exemple). Il y a de la belle physique à y faire dans une configuration simple mais (...)

Dynamics of a Levitating Drop in a Faraday Experiment.

Tobit Caudwell, 19/07/2012

In a recent experiment, a drop has been introduced on top of a liquid layer which is forced to oscillate. The amplitude of the bath oscillations is close but below Faraday instability threshold. It has been observed that the drop avoids to collapse into the bath : it oscillates over the layer on an air film and generates capillary as well as attenuated Faraday waves in the layer2 . In a certain parameter range, the drop can even move via a coupling with theses waves. In this (...)

Lire la suite

Fine-scale modeling of the boudray layer wind field over complex topography

Charles Amory, 12/07/2012

This study dThis study describes the adaptation of wind fields to steep and complex alpine terrain using fine-scale numerical modeling and grid nesting technique. This work is motivated by the need of high-resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes. Applying the meteorological prediction model Méso-NH (developed by Météo-France and the Laboratoire d’Aérologie of Toulouse) over the complex topography of a benchmark site in terms of (...)

Lire la suite

Lagrangian drifter modelling on an experimental rip current

Leandro Suarez-Atias, 28/06/2012

When approaching the coast the propagation of random wave fields on uneven bathymetries triggers spatially non-uniform wave breaking, inducing energy dissipation gradients in the surf zone that generates mean currents. We aim at investigating and characterizing with a 2D non-linear shallow-water equations numerical model the nearshore circulation forced by a random wave field propagating over non-uniform bathymetry in comparison with 3D morphodynamic laboratory experiments of rip-channels. (...)

A two-phase model for sediment transport in sheet flow regime

Thibaud Rrevil-Baudard, 21/06/2012

A two-phase model having a μ(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the sheet flow regime of sediment transport. In the model two layers are considered, a dilute suspen- sion layer and a dense sediment bed layer. The concentration profile is obtained from the φ(I) phenomenological law in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity and concentration (...)

Lire la suite

LES katabatic flow modeling on realistic configuration.

Sebastien Blein, 14/06/2012

Turbulence in stable atmospheric boundary layer, and more precisely on the very close vicinity of the ground (first tens meters), is often parametrized on numerical atmospheric models commonly used. The aim of the present work is to better understand the behavior of the turbulence witch could be very strong into down-slope flows. We study such a realistic down-slope flow thanks to a very high resolution simulation. The french model, MesoNH (Meteo-France and Laboratoire d’Aerologie, (...)

Lire la suite

Generation of mean current by nonlinear internal gravity wave reflection

Matthieu Leclair, 07/06/2012

In this study, we investigate the generation of a mean horizontal current observed in laboratory experiments performed at the CORIOLIS facility. We reproduced this experimental setting in numerical simulations performed with the NHOES code. 2D simulations exhibit an along slope sheared mean current which is the opposite of the first harmonic Stokes drift. Hence, no Lagrangian transport is associated with it. On the contrary, we reproduced a large scale horizontal mean flow in 3D (...)

Lire la suite

Unspontaneous loss of balance

Achim Wirth, 31/05/2012

............................................................................................. ............................................................................................. ............................................................................................. ............................................................................................. ............................................................................................. (...)

Lire la suite

ECOUFLU meeting

24/05/2012

Le jeudi 24 mai, le séminaire interne sera annulé pour que l’équipe MEIGE puisse participer à la journée ECOUFLU. Le texte de l’annonce : Comme vous le savez peut-être, les membres du plateau ECOUFLU d’Envirhonalp organisent leur journée annuelle sous forme d’un mini-colloque le jeudi 24 mai à Grenoble sur le Campus Universitaire. Nous souhaitons que cette journée soit l’occasion la rassembler la communauté Rhône Alpine de l’hydraulique à la fois du secteur privé et public. Cette journée atelier (...)

Lire la suite

Fine-structure contamination by internal waves

Louis Gostiaux, 10/05/2012

Oceanic fine structure has been studied since the development of CTD and microstructure profilers allowed to resolve the vertical scales of temperature and salinity in the ocean. In the context of internal waves, it rapidly appeared that the advection of oceanic fine-structure may lead to erroneous interpretations of temperature measurements, and much theoretical work was achieved to distinguish real internal wave signal from the so-called fine-structure contamination. The pioneering work (...)

Lire la suite

Large Eddy Simulation of a Stably stratified Atmospheric Boundary Layer

Christophe Brun, 03/05/2012

In the present talk, Large Eddy Simulation of a Stably stratified Atmospheric Boundary Layer is performed. we focus on the specific role played by Görtler vortices in katabatic flows. A downslope jet is artificialy generated by ground surface cooling on a generic curved slope. Such turbulent shear flow has the structure of both wall turbulence in the inner-layer zone and shear layer turbulence in the outer-layer zone. Results are analysed to show how turbulent mixing mechanism is promoted by (...)

Experimental modelling of bistability in mid-latitude atmospheric jets

Manikandan Mathur, 12/04/2012

Bistability, a striking property of some climate features, can be obtained in purely hydrodynamic systems in turbulent regimes and can be explained in terms of statistical mechanics. Here, we report laboratory experiments reproducing mid-latitude atmospheric jets in an annular rotating tank. The jet is influenced by a non-axisymmetric bottom topography interfering with the natural wavy pattern of the jet, which is related to a barotropic instability. Two states emerge from this interaction (...)

Lire la suite

Impact des ondes de relief dans la circulation océanique

Pierre Labreuche, 05/04/2012

The Southern Ocean (SO) is home to some of the strongest of the world’s ocean currents. Recent observations and numerical experiments suggest that a fraction of the energy of SO currents is converted into internal lee waves (ILW) close to bottom topography. ILW breaking induces large scale motions through momentum deposition, which are bottom-trapped inertial oscillations (IO). These IOs trigger in turn ILW breaking thereby reinforcing the IO field. We shall investigate the vertical (...)

Lire la suite

Searching for Goertler rolls in a gravity flow : some preliminary tests

Eletta Negretti, 29/03/2012

Gravity flows are ubiquitous in several geophysical and industrail contexts and play an important role in turbulent kinetic energy transfer, as well as in turbulent transport and mixing with important consequences for climate modeling and pollution remediation. The behaviour of density currents at sudden channel slope changes and ambient stratification have been not investigated in detail yet. Whereas most previous studies concentrated on flows over flat or uniform sloping bottom, this (...)

Lire la suite

Internal wave–boundary layer coupling for a disc oscillating in a density-stratified fluid

Bruno Voisin, 22/03/2012

A horizontal circular disc oscillating in a density-stratified fluid radiates internal gravity waves. Viscosity affects both the propagation of the waves through the fluid and their generation at the disc. The second aspect, namely the coupling of the waves and the boundary layer at the disc, is seldom considered. For this, an assumption of large Stokes number is usually invoked. We compare the various linear theories of the problem — inviscid or viscous and with free-slip or no-slip (...)

Lire la suite

Part 2. Statiscal mechanics of 2D flows

Joel Sommeria, 08/03/2012

2D turbulence is naturally defined as a turbulent flow depending only on two space coordinates x,y or qlternqtively qs flow confined to a surface (which does not need to be plane, for instance a sphere). In the former case, there is a possibly non-zero third velocity component uz, along the z direction, but independent of z. Then the equation of motion states that this velocity component is passively transported (like the concentration of a chemical) by the flow ux, uy in the plane, so this (...)

Statistical Mechanics of 2-D flows

Joel Sommeria, 01/03/2012

2D turbulence is naturally defined as a turbulent flow depending only on two space coordinates x,y or qlternqtively qs flow confined to a surface (which does not need to be plane, for instance a sphere). In the former case, there is a possibly non-zero third velocity component uz, along the z direction, but independent of z. Then the equation of motion states that this velocity component is passively transported (like the concentration of a chemical) by the flow ux, uy in the plane, so this (...)

Part 2. Investigation of the mobile granular layer in bed-load transport

Julien Chauchat 02/02/2012

During this seminar I will present the results of of a join experimental, theoretical and numerical investigation of the bed-load layer in laminar shearing flow conditions. For this purpose we have set-up an indexed-matched experiment and we use PIV technique to measure the velocity profiles of the particles and the fluid. Based on the two-phase flow formalism we develop analytical and numerical solutions for this problem. The proposed two-phase model is based on the assumption of a (...)

Lire la suite

Part 2. Momentary liquefaction of coastal sands : Field observations and physical modelling

Hervé Michallet 26/01/2012

Wave forcing combined to coastline retreat may weaken or unsettle coastal and port structures. Coupling between dynamic flow and seabed mechanical properties at the vicinity of a coastal structure may trigger scour and liquefaction phenomena leading to easier erosion. Field experiments in a macrotidal environment have shown that air bubbles can be trapped within the sand bed, as the beach desaturates at low tide and partially saturates during rising tide. The seabed gas content is of major (...)

Lire la suite

Investigation of the mobile granular layer in bed-load transport

Julien Chauchat 19/01/2012

During this seminar I will present the results of of a join experimental, theoretical and numerical investigation of the bed-load layer in laminar shearing flow conditions. For this purpose we have set-up an indexed-matched experiment and we use PIV technique to measure the velocity profiles of the particles and the fluid. Based on the two-phase flow formalism we develop analytical and numerical solutions for this problem. The proposed two-phase model is based on the assumption of a (...)

Lire la suite

Momentary liquefaction of coastal sands : Field observations and physical modelling

Hervé Michallet 12/01/2012

Wave forcing combined to coastline retreat may weaken or unsettle coastal and port structures. Coupling between dynamic flow and seabed mechanical properties at the vicinity of a coastal structure may trigger scour and liquefaction phenomena leading to easier erosion. Field experiments in a macrotidal environment have shown that air bubbles can be trapped within the sand bed, as the beach desaturates at low tide and partially saturates during rising tide. The seabed gas content is of major (...)

Lire la suite

Internal waves measurements above Great Meteor seamount : turbulence and mixing

Louis Gostiaux 05/01/2012

Turbulent vertical eddy diffusivity () and dissipation rate () are estimated between 0.5 and 50 m above the sloping side of Great Meteor Seamount, Canary Basin, using 101 moored temperature sensors, 1-mK precision, sampling at 1 Hz. Effectively, detailed observed time-depth temperature images are split in two : a statically stable and a turbulence image. Tides dominate the temperature variations, but the local bottom slope is sub-critical to semidiurnal frequencies. Averaged over a (...)

Lire la suite

Second harmonic behavior in the 2D internal wave reflection problem.

Matthieu Leclair, 15/12/2011

The generation of the second harmonic wave is studied through a weakly non linear inviscid theory based on Thorpe (1987) and extended to finite width plane waves. It turns out that, contrary to what is claimed in TH87, a resonance for the second harmonic wave generation is impossible. Results are confronted to numerical experiments which validate the theory. Perspective : 3D Laboratory experiments at the CORIOLIS platform show that the main dynamical feature is the set up of a strong (...)

Lire la suite

Ekman boundary layer - a local stability analysis

Manikandan Mathur 08/12/2011

The Ekman boundary layer describes fluid flow near a solid boundary in the presence of background rotation. Ekman dynamics plays a critical role in the understanding of several atmospheric and oceanic processes. Two branches of instabilities, known in the literature as Type I and Type II instabilities, lead to the formation of roll structures in the laminar Ekman layer. In this talk, I will discuss the possibility of performing a "local stabilty analysis" (equivalently the geometric optics (...)

Lire la suite

Development and Implementation of a Wall Model for the Immersed Boundary Method

Florian Mintgen 12/2009

Florian Mintgen est en visite au LEGI/ERES dans le cadre d’un stage Master-Honour (3 mois) de l’université de Munich. Il a présenté vendredi 18 décembre 2009 les résultats de son projet de Master effectué sous la direction de M. Manhart (TUM) sur le sujet suivant :

Lire la suite

Destabilizing a seiche with an movable dam.

Hélène Scolan 12/2009

Volcanic tremors are seismic signals emanating from uid channels encased in rock. The understanding of the mechanism of this phenomenon is of great importance to improve evaluation of volcanic eruptions. Many possibilities have been advanced to understand the mechanism responsible for these low-frequency signals. It has been suggested recently that the seismicity could be the result of owdestabilized oscillations whose frequency is set by an adjacent reservoir in the rock. Thus, the (...)

Lire la suite

Quantum vortices in a glass of Bose-Einstein condensate

Grisouard 11/2009

Bose-Einstein condensation occurs for bosons when, for a temperature low enough (typically a few nanokelvins for a gaseous condensate), a macroscopic fraction of the bosons gathers in the quantum state of lowest energy, forming a Bose-Einstein condensate (BEC). In this case, the behavior of the fluid can be described in the case of a dilute gas by the nonlinear Schrödinger equation (NLS), also called the Gross-Pitaevskii equation. It can be shown that the dynamics of the NLS is very close to (...)

Lire la suite

Mecanique statistique d’écoulements océaniques

Antoine Venaille 06/2008

Two dimensional flows are known to organize themselves spontaneously into large scale coherent structures. The statistical theory of Robert-Sommeria-Miller predicts the final flow organization from any initial condition, when forcing and dissipation are neglected. Our aim is to compute such statistical equilibria, for simple, academic ocean models (1 layer quasi-geostrophic equations on a beta plane), to classify the different possible flow structures and to study the existence or not of (...)

Fronts de marée interne sur le "Great Meteor Seamount" et resuspension de sédiments

Louis Gostiaux 05/2008

We present a 19 days, high frequency record of temperature profiles above the eastern shelfbreak of the Great Meteor Seamount. We used a new "NIOZ-3" high sampling rate thermistor string developed at the Netherlands Institute for sea Research (www.nioz.nl), which consists of 100 independent thermistors sampling temperature at 1Hz with an accuracy of 1mK. Sensors were set 0.5m apart above a bottom-lander, allowing high resolution measurements of temperature both in space and time in the (...)

Lire la suite

Un modèle pour le mélange

Antoine Venaille 03/2008

Our aim is to obtain a simple, efficient model to describe the temporal evolution of the probability (PDF) to measure a given concentration of a passive tracer advected by a turbulent flow. This is of wide interest for environmental, industrial and geophysical applications. We present a phenomenological model based on a self-convolution process that mimic the effect of turbulent cascades. The model, as well as the underlying hypothesis are discussed and tested by laboratory (...)