BEST DESIGN FOR A FASTEST CELLS SELECTING PROCESS

International audienceWe consider a cell sorting process based on negative dielectrophoresis. The goal is to optimize the shape of an electrode network to speed up the positioning. We first show that the best electric field to impose has to be radial in order to minimize the average time for a group of particles. We can get an explicit formula in the specific case of a uniform distribution of initial positions, through the resolution of the Abel integral equation. Next,we use a least-square numerical procedure to design the electrode's shape

A multi-criteria model for the evaluation of business benefits in horizontal collaborative networks

Despite many advantages that could be gained through belonging to enterprise networks, only a few networks continue running businesses after the governments stop their funding. One of the reasons is the lack of a model that evaluates the benefits from the firm's point of view. The objective of this work is to develop a model that estimates the benefits in horizontal collaborative networks, for a considered business opportunity, and determines the optimal network configuration in terms of the selected enterprises. We propose a method for evaluating the profits for a collaborative network based on a combination of product realisation graph and core competences identification. Through the case study of a Swiss horizontal collaborative network, the proposed approach proves its efficiency in selecting the optimal network of partners and evaluating their corresponding turnover and profit

A partitioned resolution for concurrent fluid flow and stress analysis during solidification: application to steel ingot casting

International audienceIn simulation of solidification processes, an open issue is the concurrent modelling of fluid flow and solid mechanics. This is critical for the prediction of cracks formed in solidified regions during the filling stage of ingot casting, or in the mould during continuous casting. The proposed approach consists of a partitioned two-step resolution strategy

Wavelet cross-correlation analysis of wind speed series generated by ANN based models

International audienceTo obtain, over medium term periods, wind speed time series on a site, located in the southern part of the Paris region (France), where long recording are not available, but where nearby meteorological stations provide large series of data, use was made of ANN based models. The performance of these models have been evaluated by using several commonly used statistics such as average absolute error, root mean square error, normalized mean square error, and correlation coefficient. Such global criteria are good indicators of the "robustness" of the models but are unable to provide useful information about their "effectiveness" in accurately generating wind speed fluctuations over a wide range of scales. Therefore a complementary wavelet cross coherence analysis has been performed. Wavelet cross coherence, wavelet cross-correlation and spectral wavelet cross-correlation coefficients, have been calculated and displayed as functions of the equivalent Fourier period. These coefficients provide quantitative measures of the scale-dependence of the model performance. In particular the spectral wavelet cross coherence coefficient can be used to have a rapid and efficient identification of the validity range of the models. The results show that the ANN models employed in this study are only effective in computing large-scale fluctuations of large amplitude. To obtain a more representative time series, with much higher resolution, small-scale fluctuations have to be simulated by a superimposed statistical model. By combining ANN and statistical models, both the high and the low-frequency segments of the wind velocity spectra can be simulated, over a range of several hours, at the target site.Pour générer des signaux synthétiques représentatifs du vent, sur un site situé dans le sud de la région parisienne (France) où très peu de données étaient disponibles, nous avons utilisé des données météo enregistrées dans des stations météorologiques voisines et des modèles basés sur des réseaux de neurones artificiels (RNA). Les performances de tels modèles sont généralement évaluées à l'aide d’indicateurs statistiques, tels que l'erreur absolue moyenne, l'erreur quadratique moyenne, l'erreur quadratique moyenne normalisée et le coefficient de corrélation. Ces indicateurs globaux servent à mesurer la « robustesse » des modèles, mais ils ne permettent pas, à priori, de mesurer leur aptitude à restituer l’ensemble des échelles contenues dans un signal multi-échelles. Aussi, nous avons proposé de mesurer leur efficacité à l’aide des propriétés temps-échelles des transformées en ondelettes continues. Pour cela, nous avons calculé, à différentes échelles, les fonctions de corrélation croisée en ondelettes, de cohérence croisée en ondelettes et les coefficients de corrélation croisée en ondelettes. Ces coefficients fournissent des mesures quantitatives, à chaque échelle, de la performance du modèle. Ils permettent, en particulier, de définir rapidement et efficacement la gamme de fluctuation que le modèle est apte à restituer. Les résultats ont montré que les modèles RNA utilisés dans cette étude ne reconstruisent correctement que les grandes échelles du vent, qui correspondent aux fluctuations lentes. Pour reconstruire les fluctuations turbulentes, rapides, un modèle classique de génération de processus stochastique a été utilisé. Ainsi, en combinant les deux types de modèles, sur le site considéré, toutes les gammes de fluctuation ont pu être simulées, sur des périodes de plusieurs heures

Protection of cobalt-based refractory alloys by chromium deposition on surface. Part II: Behaviour of the coated alloys in oxidation at hightemperature

International audienceA high chromium content, typically 30wt.%, is generally considered as necessary for cobalt-based alloys to allow them resisting oxidation by hot gases. Cobalt alloys with a bulk poorer in chromium may become resistant against high temperature oxidation if they are enriched in chromium on surface. The aim of this second part of the work is to expose to air at 1200°C three low-chromium cobalt-based alloys (Co-10Cr, Co-10Cr-0.25C-4.4Ta and Co-10Cr-0.5C-8.7Ta in wt.%), previously enriched in chromium on surface by pack-cementation, in order to examine if the applied cementation treatments are enough to ensure a good behavior on long time. The initial surface enrichment in chromium of the Ta-containing alloys, characterized by a maximal content on surface of about 30wt.%Cr and a depth of enrichment of several hundreds of micrometers, gives them a good resistance to oxidation at 1200°C, despite the very low chromium content in the bulk. This is also due to the interdendritic TaC carbides which may facilitate outward diffusion of chromium during oxidation as they facilitated its inward diffusion during cementation. In contrast, the CoCr alloy, enriched in chromium in the same conditions did not display a so good oxidation behavior

Protection of cobalt-based refractory alloys by chromium deposition on surface. Part I: Sub-surface enrichment in chromium by packcementationand diffusion

International audienceThe feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature. A binary Co-10Cr alloy, two ternary Co-10Cr-0.5C and Co-10Cr-1.0C alloys and two TaC-containing Co-10Cr-based alloys were elaborated by foundry for the study. 7.5h-long and 15h-long cementations at 1050°C, followed or not by a 75h-long heat treatment at 1200°C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis-Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Cr-enriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co-10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30wt.%Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation

A Monolithic Finite Element Approach to Compute Permeabilityatc Microscopic Scales in LCM Processes

International audienceIn this paper, a numerical approach for permeability determination at the mesoscopic and microscopic scales is proposed. In an eulerian framework, the computational domain (corresponding to the elementary cell) is composed of one single mesh, where the interface between the fibres (microscopic scale) or the yarns composing the fabric (mesoscopic scale) and fluid is captured through a level set approach. At the microscopic scale, Stokes equations are considered. At the mesoscopic scale, resolution of a coupled Stokes (in the fluid)Darcy (in the yarn) flow is necessary and is performed using also a mixed finite element technique, providing a single system of equations. Stabilization of the Brinkman flow is attained using the P1+/P1 element. Results on permeability computation at the microscopic scale, as well as sensitivity analysis, illustrate the methodology followed

Etudes numériques et expérimentales sur les suspensions de fibres et de sphères solides

International audienceUne méthode numérique a été développé afin de permettre le calcul du mouvement de particules solides dans un fluide en cisaillement. Les calculs sur un volume élémentaire permettent d'étudier l'évolution de l'orientation de particules allongées pour un fluide chargés en particules sphériques. Finalement, des observations expérimentales sont faites en utilisant des outils de rhéooptique

Numerical and Experimental Studies of Suspensions of Fiber and Spherical Solid Particles

Coupled Problems 2009 is one of the Thematic Conferences of the European Community in Computational Methods in Applied Sciences (ECCOMAS).International audienceThis paper is devoted the behavior of suspension of fiber-spheres particles. We pointed out by experimental and numerical observations that the Jeferry approximation is no more valid as the sphere particle concentration increases

Simulation of Rotating Continuous Casting of Steel: Thermo-hydrodynamics and Particles Motion

International audienceIn Rotating Continuous Casting (RCC), the vertical billet, the mould and the support rolls rotate at about 1 rotation/sec. The mould is fed by a liquid steel free plunging jet. A numerical modelling of the RCC has been developed. The aim of this article is to study the effects of the free plunging jet and of the rotation on : the fluid flow, the thermal state, the solidification and on the particles motion. The modelling of the RCC uses a levelset method to capture the interface between the liquid steel and argon. A stabilized Navier-Stokes method is used to compute the fluid flow. A stabilized thermal solver is used to study the thermal field and the solidification of steel. A Euler-Lagrange approach is used to solve the motion of argon bubbles and inclusions. Hydrodynamics and particles motion are confronted to observations made on a cold water model. All developed methods are validated and applied to the RCC