Development of numerical methods for the reactive transport of chemical species in a porous media : a nonlinear conjugate gradient method

In the framework of the evaluation of nuclear waste disposal safety, the French Atomic Energy Commission (CEA) is interested in modelling the reactive transport in porous media. At a given time step, the equation system of reactive-transport can be written as a system of nonlinear coupled equations F(x) = 0. In the computational code which is presently used, this system is solved using classical sequential iterative algorithms (SIA). We are currently investigating nonlinear conjugate gradient methods to improve the resolution of the system. Indeed, the handling of the coupling is improved by numerical derivation along the descent direction. The original feature of this method is the use of an explicit formula for the descent parameter. We choose an approach involving two distinct codes, that is one code for the chemistry and one code for the transport equations

Updating 3D acoustic models with the constitutive relation error method: A two-stage approach for absorbing material characterization

International audienceIn the global framework of improving vibro-acoustic numerical simulations together with the need to decrease the number of prototyping stages, improving the quality for acoustic models becomes increasingly important for many industries such as automotive companies, for instance. This paper focuses on achieving greater accuracy for acoustic numerical simulations by making use of a parametric updating technique, which enables tuning the model parameters inside physically meaningful boundaries. The improved model is used for the next prototyping stages, allowing more accurate results within reduced simulation times. The updating technique used in this paper is based on recent works dealing with the constitutive relation error (CRE) method applied to acoustics. The updating process focuses on improving the acoustic damping matrix related to the absorbing properties of the materials covering the borders of the acoustic domain.The present study proposes a 2-stage optimization process, which exhibits many advantages. Indeed, the computational time decreases, the frequency interpolation of the material absorbing properties outside the studied frequency range is easily performed, and comparing the correlation of several material absorbing constitutive equations with experimental records is fast.Additional originality of the work comes with the application of the CRE updating method to a concrete real-life device, while previous works addressed purely numerical setups without experimental data. The test-case is the TRICARMO setup engineered by LMS International in Leuven, Belgium. The TRICARMO setup is a simplified car cabin with rigid walls and car seats inside. Thanks to the 2-stage approach, the material property characterization of the seat is improved by running the updating simulation process using a physical absorbing material model

Development of numerical methods for the reactive transport of chemical species in a porous media : a nonlinear conjugate gradient method

In the framework of the evaluation of nuclear waste disposal safety, the French Atomic Energy Commission (CEA) is interested in modelling the reactive transport in porous media. At a given time step, the equation system of reactive-transport can be written as a system of nonlinear coupled equations F(x) = 0. In the computational code which is presently used, this system is solved using classical sequential iterative algorithms (SIA). We are currently investigating nonlinear conjugate gradient methods to improve the resolution of the system. Indeed, the handling of the coupling is improved by numerical derivation along the descent direction. The original feature of this method is the use of an explicit formula for the descent parameter. We choose an approach involving two distinct codes, that is one code for the chemistry and one code for the transport equations

Le rôle de l’urbanisation incontrôlée dans la genèse des vulnérabilités: Cas de la région du Sijoumi à Tunis

Tunis a connu depuis la seconde moitié du 20ème siècle une métamorphose importante causée par une urbanisation galopante et non-planifiée, due principalement à l'exode rural. Cette nouvelle population urbaine a été obligée de construire des logements anarchiques permanents sur des terres agricoles bon marché, situées aux abords de la capitale Tunisienne. Ces derniers dans la majorité des cas, étaient implantés sur des terres vulnérables exposées aux risques urbains majeurs, comme dans notre étude de cas, où tout un quartier d’habitat informel a été construit sur les rives du lac «Sijoumi» au sud-ouest de Tunis. Au fil du temps, au lieu de s’affirmer comme une source de progrès ou un véritable moteur de développement de la région environnante, la présence de ce plan d’eau s’est transformée, à cause des pressions d'origine météorologique, écologique mais aussi anthropique, en une source de nuisances et risques urbains menaçant la santé et vie de la population. La relation actuelle entre le lac et le quartier « Sidi Hssine » en particulier, implanté sur ses abords est devenue conflictuelle et nécessite une intervention urbaine urgente, inclusive et durable. Cet article examine brièvement les enjeux majeurs et défis urbains actuels de la région et la complexité du lien entre les deux milieux, naturel et urbain

Identification of Admittance Coefficients from in-situ Measurements in Acoustic Cavities

International audienceIn recent decades, sound intensity and quality is taking an increasingly important place in the design process of products like cars or aircrafts. Different types of absorbing materials have therefore been developed and used in such products to achieve this purpose. Acoustical calculations are quite heavy and industries generally have to use numerical tools to predict the influence of absorbing materials on the sound propagation inside cavities. In these ones, the acoustical properties of absorbing materials are described by the admittance (or impedance) coefficient, which is a simplification of the physical model. However, the limits of applicability of this model are not well known and the conditions in which its parameters are measured can differ significantly from the ones in which the materials are really used. In this paper, a model updating technique process is used to identify the parameters required to describe admittance coefficients from sound pressure measurements inside a closed cavity. Updating techniques have been used for many years to improve numerical models, and consist in minimizing an error between the numerical solutions and a set of experimental results. The technique based on the Constitutive Relation Error (CRE), initially proposed by Ladevèze [1] for structural dynamics problems, is an indirect method in which the cost function, called the CRE, is based on an energy norm. The main advantages of this method are that the updated parameters keep a physical meaning, that it allows taking into account the measurement error and that it allows locally evaluating the modeling and measurement errors [2]. In this paper the CRE-based updating technique is applied to the acoustical problem ([3], [4]) in order to identify the admittance coefficients and the local estimators are developed. The method is applied on real 2D (Kundt's tube) and 3D (concrete box) experimental data

Evolution du niveau d'agglomération de nanopoudres d'aluminium : une approche rhéologique

National audienceFrom micrometric size to nanometric size, the increase of the surface energies allows the agglomeration to be preponderant and then, the risks linked to powders are changed. When the toxicity, the inflammation and explosion risks of nanoparticles are mentioned, the agglomerates must be taken into account. The effect of agglomeration in the behavior of nanopowders has been studied from experimental observation of agglomerated nanopowders of aluminum subjected to shear in a powder rheometer. In order to understand the effect of deagglomeration on the powders, the agglomerate strength has been estimated thanks to the porosity of the powder bed contained in the rheometer cell. This one is ranged between 10 kPa and 1 MPa. The rheological tests show that, compared with the micrometric aluminum, the aluminum nanopowders have a peculiar behavior in the Geldart's classification, being in both class A and C. This fact is due to the facility of nanoparticles to agglomerate and to stay agglomerated.Lorsque l'on passe de la dimension micrométrique à la dimension nanométrique, l'augmentation importante des énergies de surface rend prépondérants les phénomènes d'agglomération. Ceci modifie l'appréhension des risques liés aux poudres. Pour parler de toxicité, de risques d'inflammation et d'explosion des nanoparticules, nous devons prendre en compte la présence d'agglomérats. L'effet de l'agglomération sur la dispersibilité des nanopoudres a été étudié à partir d'observations expérimentales de nanopoudres agglomérées d'aluminium soumises au cisaillement fourni par un rhéomètre à poudres. Pour comprendre l'effet de la désagglomération sur les poudres, nous avons déjà estimé la contrainte d'agglomération mise en jeu à partir de la porosité du lit de poudres contenues dans la cellule du rhéomètre. Cette contrainte est globalement ici comprise entre 10 kPa et 1MPa. Les tests en rhéologie ont montré qu'en comparaison avec une poudre d'aluminium micrométrique, les nanopoudres d'aluminium ont un comportement particulier vis-à-vis de la classification de Geldart, appartenant à la fois aux classes A et C, ceci étant du à la facilité des nanoparticules à s'agglomérer et à le rester

Modelling the rainfall-runoff response from a headwater wetland

info:eu-repo/semantics/publishe

The effect of agglomeration on the emission of particles from nanopowders flow

International audienceThis paper suggests an original method to evaluate the possible emission of particles from a nanopowder submitted to a shear stress in dense phase and the resulting degree of agglomeration of the particles released. The method is based upon the monitoring of the rheological signature of the nanopowders, thanks to a powder rheometer. As a function of the increasing shear rate, the powder flow will evolve from the newtonian state (dense powder) to the coulombian state (dense rheofluidified phase). If the shear rate is high enough, the powder will be set in suspension and the kinetic state (a leaner dense phase submitted to particles collisions) will be reached. The shear stress in this state is dependent on the particle or the agglomerate diameter for cohesive powders, which can be then calculated from rheograms. Carbon black and silica nanopowders have been tested and compared to other experiments carried out on non cohesive glass beads microparticles, chosen as reference. For the different glass beads powders, the average value of their 'agglomerate' diameter is 12% different of the primary diameter, indicating agglomeration of less than two particles. Nanometric agglomerates were found to be of hundred micrometers diameter. That is in line with the high tendency of the nanoparticles to agglomerate. This work can be used to evaluate the current safety tests, such as Hartmann's tube or 20 L sphere apparatuses, to verify whether the standard equipment for microparticles is suitable for the use of nanoparticles. This is linked to research projects like NanoSafe 2

Référentiels de compétences à l’université

La recherche présentée contribue à analyser le rôle des référentiels de compétences dans le pilotage de la formation à l’université et dans les pratiques d’enseignement et d’évaluation des enseignants. Elle explore également les liens entre le rôle joué par un référentiel et les conditions qui ont présidé à sa réalisation. L’étude croisée de dix cas dans différents pays permet de montrer que, dans la plupart des cas, les référentiels étudiés ont joué un rôle bien plus important dans le pilotage de la formation que dans les pratiques d’enseignement et d’évaluation.The aim of this paper is to present a research contributing to analyze the role of reference systems for competences in the management of training at university and in teachers’ teaching practices and assessment. This research also explores the links between the role played by a system of reference and the conditions which presided over its creation. A cross study of ten cases was carried out in various countries which enabled us to show that in most cases the analyzed systems of reference played a much more important part in the management of training than in teaching and assessment practices.La investigación presentada contribuye à analizar el papel de los referenciales de competencias en el pilotaje de la formación en la universidad y en las prácticas de docencia y de evaluación de los docentes. Explora igualmente los vínculos entre el papel desempeñado por un referencial y las condiciones que han presidido à su realización. El estudio cruzado de diez casos en diferentes países permite demostrar que en la mayoría de los casos, los referenciales han desempeñado un papel mucho más importante en el pilotaje de la formación que en las prácticas de docencia y de evaluación.Diese Forschungsarbeit trägt dazu bei, die Rolle der Bezugssysteme der Kompetenzen bei der Ausbildungssteuerung an der Universität und bei den Lehrtätigkeiten und der Evaluation der Lehrer zu analysieren. Sie erforscht auch die Verbindungen zwischen der von einem Bezugssystem gespielten Rolle und den Bedingungen, die es möglich gemacht haben. Mit der gekreuzten Studie von 10 Fällen in verschiedenen Ländern wird gezeigt, dass die Bezugssysteme meistens eine viel wichtigere Rolle bei der Ausbildungssteuerung gespielt haben als bei den Lehr-und Evaluationstätigkeiten

Transport Network Design for FrontHaul

International audienceThe evolution of LTE and advent of 5G networks increases further the bandwidth requirements for Radio Access Network (RAN). In parallel, the deployment of Centralized RAN architecture raises new challenges on the FrontHaul network. The inflexibility of the legacy Common Public Radio Interface (CPRI) is the primary challenge to Virtualized RAN deployments, and there is currently a strong trend towards the use of packetized transport methods, together with flexible split RAN based architectures. Functional splits within the real-time functions of the RAN have very stringent requirements on latency and jitter. This paper analyzes the jitter produced in the switching nodes of the FrontHaul network, and proposes dimensioning rules