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Séminaires internes
Chaque semaine un séminaire interne informel dans l’équipe. 20min de présentation
Jeudi à 12h15.
S’inscrire sur Doodle.
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 :
Mesures et caractérisation de la couche limite turbulente sur le glacier du Zongo, Bolivie
Maxime Litt (LTHE), 04/10/2012
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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 (...)
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 (...)
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 (...)
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, (...)
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 (...)
Unspontaneous loss of balance
Achim Wirth, 31/05/2012
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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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
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 (...)
