Nos séminaires avec cadence mensuelle ont lieu les jeudis en début d'après-midi, ou exceptionnellement dans d'autres jours/horaire pour les professeurs et chercheurs invités.
Les séminaires sont organisés par Stefano Berti email@example.com , responsable pour la mécanique des fluides, et par Toufik Kanit firstname.lastname@example.org , responsable pour la mécanique des solides.
À venir :
- jeudi 16 mai, Alexis Duchesne (IEMN, U. Lille)
jeudi 4 avril, Karim Kandil (UML, U. Lille)
- jeudi 21 mars, , au bat. M6 à 13h
Vojtech Patocka (DLR German Aerospace Centre, Berlin, Germany)
Viscoelastic mantle convection
Present thermochemical convection models of planetary evolution often assume a purely viscous or viscoplastic rheology. Ignoring elasticity in the cold, outer boundary layer is, however, questionable since elastic effects may play an important role there and affect surface topography as well as the stress distribution within the stiff cold lithosphere. We present a modelling study focused on the combined effects of Maxwell viscoelastic rheology and a free surface in the stagnant lid planetary convection. We perform thermal convection models of the cooling planetary mantles and demonstrate that while the global characteristics of the mantle flow do not change significantly when including viscoelasticity, the stress state of the cold lithosphere may be substantially different. Transient cooling of an initially thin upper thermal boundary layer results in a complex layered stress structure due to the memory effects of viscoelastic rheology. The stress state of the lid may thus contain a record of the planetary thermal evolution.
- vendredi 15 février , au bat. M6 à 14h
Himani Garg - Soutenance de thèse / PhD defence Particle laden inhomogeneous elastic turbulence
- jeudi 29 novembre, au bat. M6 à 13h
Alexei Sentchev (Université du Littoral - Côte d'Opale, Laboratoire d'Océanologie et de Géosciences, UMR 8187-LOG)
Assessing coastal ocean dynamics by using modeling and remote sensing: Application in La Manche
Recent research activities conducted in LOG in the field of coastal ocean circulation assessment will be presented. Two approaches are used for understanding the major features of coastal water dynamics and its variability at different space/time scales: modeling and remote sensing. Examples of high resolution modeling in La Manche will be used to illustrate some practical applications in the domain of coastal water resource management. More recent work is focused on the assessment of tidal energy resource in La Manche and off the western Brittany coast (Iroise Sea) by using the remote sensing of coastal currents and modeling. A method of improving the results of modeling by merging the model and the underway velocity measurements will be presented. It allows to considerably decrease the discrepancy between the modeled and observed velocities at a highly energetic site in Normandy – Raz Blanchard. Possibilities of joint research could be also discussed.
- jeudi 25 octobre, au bat. M6 à 13h
Nader Ben-Cheikh (University of Tunis El-Menar, Tunisia)
A Multigrid Technic adapted to Large Eddy Simulation and Convection-Radiation of Incompressible Fluids
A finite-volume method is used to discretize the Navier–Stokes and energy equations. The advective terms are discretized by way of a QUICK third-order scheme in the momentum equation and a second order central differencing one in the energy equation. The discretized momentum and energy equations are solved using the red and black successive over relaxation method RBSOR, while the Poisson pressure correction equation is solved using a full multigrid method.The numerical method is first applied to the study of turbulent incompressible flows in lid driven cubical cavities using Large Eddy Simulation and two sub-grid scale models, i.e., the WALE (Wall Adapting Local Eddy-viscosity) model and the corresponding dynamic sub-grid model (DSGS).In a second step, a numerical tool for coupling natural convection in cavities with surface radiation and computations are presented for an air-filled square cavity whose four walls have the same emissivity.
- jeudi 18 octobre, au bat. M6 à 13h
Leonardo Santos de Brito Alves (Fluminense Federal University, Rio de Janeiro, Brazil)
Linear and nonlinear stability analyses to detect unsteady disturbance growth in Darcy-Bénard mixed convection under the influence of viscous dissipation
The present work investigates the linear and nonlinear disturbance growth in time induced by viscous dissipation and external heating from below in a porous media flow. In order to do so, we employed linear and local stability analysis as well as nonlinear analysis, by means of a direct numerical simulation of the governing equations. Linear stability analysis consists in decomposing all variables of the problem in two parts: a steady state, around which the stability is analyzed, and infinitesimal disturbances. Furthermore, two different linear stability analyzes are employed here: modal and non-modal. Matrix forming using the Generalized Integral Transform Technique is used to generate the generalized eigenvalue problem whereas the fully nonlinear problem is solved using high-order finite differences. The non-modal analysis reveals that viscous dissipation makes the linear operator non-normal, but transient energy growth is small, which means non-monotonicity is weak. Hence, an asymptotic behavior in time is assumed to dominate and a modal analysis is performed to evaluate absolute stability. Viscous dissipation introduces new modes that compete to trigger transition from convective to absolute instability. A nonlinear analysis is then performed in order to validate and better understand the linear results. Since both modal and non-modal linear analyses are dominated by transverse modes, a 2D DNS is used. The transition from stable to convectively unstable is in agreement between the two approaches, but the transition from convective to absolute instability only agrees when viscous dissipation effects are weak, i.e. low velocities and low viscosity. When these effects become important, the results from linear analysis are no longer recovered. In this scenario, transition to absolute instability takes place in subcritical conditions, where a nonlinear group velocity is observed. In other words, the flow transitions from linearly convectively unstable to nonlinearly absolutely unstable.
jeudi 4 octobre, 13h-14h , bâtiment M6
Youssef Hammi (Mississippi State University, USA)
Fatigue Modeling of a Powder Metallurgy Main Bearing Cap
Developing the ability to predict density distribution, monotonic plasticity, damage and the cyclic damage progression is imperative for the design of Powder Metallurgy (PM) components that will experience overloads during in-service life due to impacts, rough ground, and crash environments. In this paper, mathematical-based models for PM manufacturing process are developed, validated and implemented in user material subroutines Vumat and Umat to model the compaction and sintering processes. The material history is initially captured and carried throughout the compaction and sintering processes in order to predict the density distribution. Knowing the density distribution, mechanical properties are mapped in the PM sintered part using tension, compression, and torsion mechanical tests performed on samples at different densities, temperatures and strain rates. A finite element analysis of an experimental fatigue fixture that reproduces similar loading conditions than those of in-service life conditions is performed. Using a Multi-Stage Fatigue (MSF) model implemented in Abaqus, the fatigue life is evaluated on a PM automotive component, the main bearing cap (MBC), and results are compared to experimental fatigue tests.
jeudi 20 juin, 13h-14h, bâtiment M6.
Thomas Gomez (LMFL, Univ. Lille)
Analytical closure and helical turbulence
Since the first studies on turbulent flows, researchers’ attention has been drawn to helic- ity. Indeed, because the helicity is a non-viscous invariant of the 3D turbulent dynamics as well as energy or enstrophy in 2D, it is expected that its dynamics has a strong influence on inter-scales energy exchanges. Helical turbulence is also important because it corresponds to a first step towards more complex flows in which the homogeneous turbulence is no longer fully isotropic. This case denoted as skew-isotropic corresponds to a turbulence in which the mirror symmetry is broken. More recent results have shown that helicity is also involved in complex physical phenomena such as the dynamo effect in magnetohydrody- namics. After having defined the helicity and described its main properties, we will give an overview of the different models of analytical closure with special attention for the EDQNM model (Eddy Damped Quasi Normal Markonvian) introduced by Orszag in 1970 that we will use to illustrate the influence of helicity on the dynamics of free decaying turbulence.
jeudi 12 avril, bâtiment M6 à 12h45
Abdelghani Saouab (Laboratoire Ondes et Milieux Complexes, Université Le Havre Normandie)
Numerical Modeling and Simulation of Liquid Composites Molding Processes
For several years now, liquid composite molding (LCM) processes present a well‐established class of manufacturing technics for processing semi-structural and structural fiber-reinforced composite parts. These technics are widely used in many industrial domains and particularly in transportation (automotive, aeronautical, marine, etc.). Their principle is to inject or infuse a liquid within a fibrous preform, where the main objective is to reach a full impregnation as the liquid moves along between and inside the fiber bundles. The impregnation driving force is usually resulting from pressure gradient. During the LCM process, there is a strong coupling between the liquid flow, the preform compressibility, and the heat transfer between the liquid, the mold, and the fibrous medium. In this seminar, we will present our numerical modelling approach developed in this context, it concerns in particular the modeling of air bubble dynamics. In addition, a set of numerical and experimental results is presented to: validate the model, identify its parameters, and show some of its applications.
jeudi 15 mars, bâtiment M6 à 12h45
Wouter Bos (Laboratoire de Mécanique des Fluides et d’Acoustique, Lyon)
Recent experiments and simulations have shown that unsteady turbulent flows, before reaching a dynamic equilibrium state, display a universal behaviour. We show that the observed universal non-equilibrium scaling can be derived in a fairly simple manner. Given the universality of the experimental observations, the ideas presented here lay the foundation for the modeling of a wide class of unsteady turbulent flows and we show how engineering turbulence models (e.g. the k-epsilon model) can be modified to take this into account.
jeudi 15 février, salle d'Arsonval à Polytech à 13h
Moufid Mouwakeh (Department of Applied Mechanics, University of Aleppo, Syria)
Ductile Fracture of Cracked Pipes Using Limit Load Analysis
Using cracked pipes design codes and finite element (FE) analysis, limit load solutions of pipes containing surface cracks is determined. The study is performed on 5 pipes of different diameters with a constant crack length and depth. The crack geometry is semi-elliptical surface crack. The cracked pipes are subjected to internal pressures which are obtained from formulas of cracked pipes design codes. Due to ductile behavior of polyethylene pipes, failure occurs when the critical net stress reaches a value equal to ultimate tensile strength multiplied by constraint factor. Constraint factor is calculated and its evolution with pipe diameter is analyzed. Three different definitions of constraint factor based on global or local approach are also compared, so that a new failure criterion can be obtained. The new failure criterion enables us to predict the remaining life of the cracked pipes which allows programming the works of maintenance and replacement.
vendredi 15 décembre, Amphi Migeon à Polytech à 10h
Fouad Erchiqui (Université du Québec en Abitibi-Témiscaminque (UQAT), Canada)
Caractérisation, modélisation et optimisation en thermoformage
La simulation numérique des procédés de mise en forme des plastiques (thermoformage, moulage par soufflage, etc. ) nécessite une bonne connaissance, d’une part, du comportement des matériaux utilisés et, d’autre part, des intervalles en températures et en pressions (thermoformabilité) pour des applica! tions industrielles de ces matériaux en plasturgie. Ces matériaux sont souvent des polymères thermoplastiques (avec ou sans fibres) chauffés entre la température de transition vitreuse et de fusion pour être ensuite mis en forme. C’est dans ce contexte que la présentation est orientée et elle concerne trois volets : i) identification viscoélastique en grandes déformations des matériaux thermoplastiques (réseaux de neurones); ii) modélisation intégrée de thermoformage (étapes de chauffage infrarouge, de formage et de refroidissement) et iii) optimisation (métaheuristique).
jeudi 30 novembre, bâtiment M6 à 13h
Roney Thompson (Université Fédérale de Rio de Janeiro, Brésil)
Modeling thixotropic elasto-viscoplastic materials: ideas and challenges
There are examples of applied materials with high complexity that combine a diversity of aspects of material behavior. Recently, the scientific community started the endeavor to model these materials despite the fact that there are still unsolved problems in simpler materials. In this presentation we explore some ideas on modeling thixotropic elasto-viscoplastic materials and how a specific model in these lines perform in transient motions of free-surface problems. Challenges on developing even more generic models encompasses temperature dependency, better representation of microstructure, inclusion of non-viscometric data, transient experiments, transient microstructure evolution modeling, among others.
jeudi 9 novembre, bâtiment M6 à 13h
Louise Watremez (LOG, U. Lille)
Observation et modélisation géodynamique des structures extensives
Les plaques tectoniques sont considérées rigides et se déforment à leurs frontières. Il existe trois types de frontières de plaques tectoniques : les frontières convergentes (zones de subduction ou de collision continentale), les frontières coulissantes (failles décrochantes) et les frontières divergentes (rift continental ou océanique). L’étude de l’extension continentale est donc une des clés pour la compréhension des processus géodynamiques à grande échelle. Cette extension peut conduire à la formation (1) de grandes zones de lithosphère continentale amincie immergées dans lesquelles on retrouve notamment une grande partie des ressources pétrolières mondiales, voire (2) d'un nouvel océan. Cette étude, effectuée grâce à la combinaison de méthodes d’imagerie sismique à l’échelle de la croûte terrestre (~30 premiers kilomètres sous la surface) et de modélisation numérique thermomécanique à l’échelle de la lithosphère, permet de comprendre les processus entrant en jeu lors de la dislocation d’un continent ainsi que leur chronologie.