Mardi 27 Mars 2012
14 h 00 salle de réunion CEAT
Professor of Mathematics
Department of Mathematics & Statistics
McMaster University, Hamilton, Canada
Invité par Bernd Noack
I will survey wavelet-based techniques that have been developed over the last 20 years for the analysis and computation of turbulent flows. The analysis techniques allow the measurement of local spectral and singular properties associated with particular flow structures, such as vortices. Wavelet filtering, which uses the compression and denoising properties of wavelets, forms the basis of a group of techniques for dynamically adaptive computation of turbulent flows and fluid-structure interaction. These techniques range from wavelet direct numerical simulation, to a local form of large eddy simulation called SCALES. Examples will include experimental mixing layer data (from Poitiers!), vortex interaction, fluid-structure interaction, two-dimensional turbulence and shallow water turbulence.
Lundi 26 Mars 2012
14 h 00 salle de réunion CEAT
Research Scientist
DLR German Aerospace Center
Institute of Aerodynamics and Flow Technology
Invité par Peter Jordan
Tip vortices generated by a helicopter rotor are highly dynamic velocity fields which remain close to the rotor plane for several revolutions. The passing blades interact with the tip vortices, resulting in a phenomenon known as blade-vortex interaction (BVI). The interaction is accompanied by significant airloads and noise generation. One of the governing parameters to reduce the induced BVI noise is the blade position with respect to a wake. The position can be changed actively by using a constantly moving flap located close to the blade tip. For the measurements of the spatial position of the blade tip as well as of the whole blade due to the motion of the flap, a stereo pattern recognition (SPR) technique can be applied. The main idea of this technique is based on the 3d object reconstruction by known positions of markers attached to the region of the interest and captured by cameras. For the case reported here, the markers were distributed over the entire length of the blade and the blade tip and were illuminated during the measurements by stroboscopic light. The stereo pattern recognition is proved to be a reliable technique for detection of spatial coordinates. The results obtained with the SPR can be easily used for further evaluation of blade motion parameters in flap, lead-lag and torsion.
Mardi 20 Mars 2012
14 h 00 salle de réunion Branche Fluides
Directeur de Recherche
Laboratoire de Physique et Mécanique des Milieux Hétérogènes - UMR CNRS 7636
Invité par Bernd R. Noack
Pour l'étude des instabilités hydrodynamiques et de la transition à la turbulence, nous nous concentrons sur le rôle des structures cohérentes présentes dans les écoulements. Celles ci, avec vorticité transversale et longitudinale, prennent la forme de rouleaux, de stries et de hairpins. Ces structures jouent un rôle important dans la dynamique des écoulements dit ouverts, comme dans les tubes, les canaux ou les parois ainsi que pour le contrôle des écoulements.
Nous présenterons des expériences mettant en jeu un mécanisme tridimensionnel et nonlinéaire, d'auto-entretien de la turbulence (Self-Sustaining Process), qui semble générique dans les écoulements cisaillés. Ces travaux ont été réalisés au laboratoire PMMH de l'ESPCI, avec J.L. Aider, T. Duriez, S. Goujon-Durand et G. Lemoult.
Short bio: José Eduardo Wesfreid, Directeur de Recherche au CNRS, est au laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH) de l'ESPCI. Il s'intéresse aux études expérimentales sur les instabilités hydrodynamiques, la transition à la turbulence et le contrôle des écoulements.
Mardi 6 Mars 2012
14 h 00 salle de réunion CEAT
PhD student
Duke University, Mechanical Engineering
Invité par Bernd Noack
It has often been remarked that turbulence is the last unsolved problem in Newtonian physics. The aggregate cost to our society resulting from our incomplete understanding of turbulence is quite staggering. Consider, for example, the environmental and economic costs associated with sub-optimal performance of virtually every fluid-thermal system such as the internal combustion engine and heat exchangers. The turbulence problem might appear puzzling to the outsider. After all, the equations governing turbulent flow, the Navier-Stokes equations, have been known for over a century and are deterministic and relatively compact. Turbulence remains a problem today because the only truly reliable tool for its approximation - direct numerical simulation - is computationally prohibitive. In this talk, I will summarize a new projection-based approach to model order reduction of the Navier-Stokes equations.
Short bio: Maciej (Mike) Balajewicz is a Ph.D. candidate in Mechanical Engineering in Duke University under the supervision or Professor Earl Dowell. He completed his M.S. and B.Eng. in Aerospace Engineering in Carleton University in Canada. His research interests include Applied Mathematics, Fluid-Structure Interactions and Fluid Dynamics.
Lundi 5 Mars 2012
10 h 00 salle de réunion CEAT
Department of Mathematics & Statistics
McMaster University, Canada
Invité par Bernd R. Noack
Short bio: Dr. Protas is an applied mathematician interested in problems combining theoretical and computational fluid dynamics with the theory of optimization and control. He holds a Ph.D. awarded jointly by the Warsaw University of Technology and Universite Pierre et Marie Curie (PARIS VI) in 2000. After post-doctoral experience at the University of California, San Diego, he joined the Department of Mathematics and Statistics at McMaster University in Canada as SHARCNET Chair in Scientific Computing, and has since been on the faculty there. Dr. Protas is a receipient of Ontario's Early Researcher Award and serves on the Editorial Board of the International Journal of Computer Mathematics (Section B).
Lundi 5 Mars 2012
14 h 00 salle de réunion CEAT
Department of Mathematics & Statistics
McMaster University, Canada
Invité par Bernd R. Noack
Short bio: Dr. Protas is an applied mathematician interested in problems combining theoretical and computational fluid dynamics with the theory of optimization and control. He holds a Ph.D. awarded jointly by the Warsaw University of Technology and Universite Pierre et Marie Curie (PARIS VI) in 2000. After post-doctoral experience at the University of California, San Diego, he joined the Department of Mathematics and Statistics at McMaster University in Canada as SHARCNET Chair in Scientific Computing, and has since been on the faculty there. Dr. Protas is a receipient of Ontario's Early Researcher Award and serves on the Editorial Board of the International Journal of Computer Mathematics (Section B).
Mercredi 22 Février 2012
14 h 00 salle de réunion Branche Fluides
Department of Mathematics & Statistics
McMaster University, Canada
Invité par Bernd R. Noack
In the presentation we will review recent results and discuss some emerging research directions concerning application of the modern methods of PDE-constrained optimization to address two classes of fundamental problems in turbulence research. The first class of problems is related to the applicability of some statistical theories, such as the Kraichnan-Leith-Batchelor (KLB) theory of the forced homogeneous isotropic two-dimensional turbulence, whereas the second class of problems concerns sharpness of certain mathematical estimates, such as the bounds on the maximum enstrophy growth in 3D flows. The latter issue is intimately related to the question of spontaneous singularity formation, known as the ``blow-up'' problem. We demonstrate how new insights concerning these problems can be obtained by formulating them as variational PDE optimization problems which can be solved computationally using adjoint-based gradient descent (or ascent) methods. In offering a systematic approach to finding flow solutions closest to the predictions of a given theory, the proposed paradigm provides a bridge between theory and computation. In the presentation we will show a number of new results concerning 2D Navier-Stokes flows characterized by the maximal growth of palinstrophy, and will discuss their relation to the available theoretical bounds obtained with rigorous methods of mathematical analysis. [joint work with D. Ayala]
Short bio: Dr. Protas is an applied mathematician interested in problems combining theoretical and computational fluid dynamics with the theory of optimization and control. He holds a Ph.D. awarded jointly by the Warsaw University of Technology and Universite Pierre et Marie Curie (PARIS VI) in 2000. After post-doctoral experience at the University of California, San Diego, he joined the Department of Mathematics and Statistics at McMaster University in Canada as SHARCNET Chair in Scientific Computing, and has since been on the faculty there. Dr. Protas is a receipient of Ontario's Early Researcher Award and serves on the Editorial Board of the International Journal of Computer Mathematics (Section B).
Lundi 9 Janvier 2012
14 h 00 salle de réunion Branche Fluides
Professor of Mechanical Engineering
University of Michoacan, Mexico
Invité par Gérard Touchard
L'interaction entre les contraintes mécaniques dans les matériaux solides et la polarisation des charges électriques au sein de ces matériaux a été mise en évidence depuis le début du XIX siècle par les phénomènes piézoélectriques.
Les applications industrielles des dispositifs piézoélectriques ont vu une évolution exponentielle dans les dernières décennies ; toutefois, l'étude de l'amorçage et de la propagation de fissures dans des matériaux solides soumis à des contraintes mécaniques a été développée principalement à partir de modèles mécaniques-énergétiques : le facteur d'intensité de contrainte, l'intégrale J, Loi de Paris,...
Etant donné que l'amorçage et la propagation de fissures constituent un phénomène essentiellement énergétique (énergie de déformation élastique et plastique, dissipation de chaleur, relaxation des contraintes,...), quelques études ont été dirigées pour comprendre la relation entre les phénomènes thermiques et l'amorçage et la propagation de fissures ; toutefois, très peu d'études ont abordé le couplage entre la variation des propriétés électriques des matériaux solides dans la zone de fissure et la dynamique de propagation de celle-ci.
L'objectif de ce séminaire est d'apporter quelques réflexions sur les possibilités de mettre en place l'étude sur l'amorçage et la propagation de fissures dans des matériaux solides, en associant le phénomène mécanique aux propriétés électriques dans le matériau à l'échelle macroscopique et de micro-plasticité.
Short bio: Doctor Gonzalo M. Dominguez-Almaraz is Professor at the University of Michoacan (UMSNH), Mexico. His main research interests are actually in ultrasonic fatigue tests (gigacycle fatigue tests) on metallic alloys: steels, cast irons, aluminums,... and high strength plastics and the interaction with the environment: corrosion, humidity, natural and artificial pitting holes, temperature, stress concentration and fretting fatigue under ultrasonic testing. Applications range from fatigue life evaluation on mechanical elements and systems attaining the very high cycle fatigue regime (>108 cycles), present in most of modern industries: aeronautical, energy production, automotive, oil, high speed trains... to the analysis of fracture surface to determine the failure origin and the interaction with the manufacturing, environmental, machining, and loading parameters of testing materials. He has developed an ultrasonic fatigue machine to carry out these tests.
Laurent Cordier Dernière modification le 31/01/2011