Managing Advanced Synchronization Aspects in Logistics Systems

In this thesis, we model various complex logistics problems and develop appropriate techniques to solve them. We improve industrial practices by introducing synchronized solutions to problems that were previously solved independently. The first part of this thesis focuses on cross-docks. We simultaneously optimize supplier orders and cross-docking operations to either reduce the storage space required or evenly distribute workload over the week. The second part of this thesis is devoted to transport problems in which two types of vehicles are synchronized, one of which can be transported by the other. The areas of application range from home services to parcel delivery to customers. After analyzing the complexity associated with these synchronized solutions (i.e., largescale problems for which the decisions depend on each other), we design algorithms based on the "destroy-and-repair" principle to find efficient solutions. We also introduce mathematical programs for all the considered problems. The problems under study arose directly from collaborations with various industrial partners. In this respect, our achieved solutions have been benchmarked with current industrial practice. Depending on the problem, we have been able to reduce the environmental impact generated by the industrial activities, the overall cost, or the social impact. The achieved gains compared to current industrial practice range from 10 to 70%, depending on the application. -- Dans cette thèse, nous modélisons divers problèmes logistiques complexes et développons des techniques appropriées pour les résoudre. Nous cherchons à améliorer certaines pratiques industrielles en introduisant des solutions synchronisées à des problèmes qui étaient auparavant résolus indépendamment. La première partie de cette thèse porte sur les cross-docks. Nous optimisons simultanément les commandes fournisseurs et les opérations au sein de la plateforme de logistique pour réduire l’espace de stockage requis ou répartir uniformément la charge de travail sur la semaine. La deuxième partie de cette thèse est consacrée aux problèmes de transport dans lesquels deux types de véhicules sont synchronisés, l’un pouvant être transporté par l’autre. Les domaines d’application vont du service à domicile à la livraison de colis chez des clients. Après avoir analysé la complexité des solutions synchronisées (c’est-à-dire des problèmes de grandes dimensions pour lesquels les décisions dépendent les unes des autres), nous concevons des algorithmes basés sur le principe de "destruction / reconstruction" pour trouver des solutions efficaces. Nous modélisons également les problèmes considérés avec la programmation mathématique. Les problèmes à l’étude viennent de collaborations avec divers partenaires industriels. A cet égard, les solutions que nous présentons sont comparées aux pratiques industrielles actuelles. En fonction du problème, nous avons pu réduire l’impact environnemental généré par les activités industrielles, le coût global, ou l’impact social des solutions. Les gains obtenus par rapport aux pratiques industrielles actuelles varient de 10 à 70%, selon l’application. Mot-clefs: Logistique, Synchronisation, Problème de transport, Tournée de véhicules, Plateforme de Cross-dock (transbordement), Programmation Mathématiques, Métaheuristiques, Matheuristiques, Instances Réelle

Assessment of structural and transport properties in fibrous C/C composite preforms as digitized by X-ray CMT. Part I : Image acquisition and geometrical properties

International audienceRaw and partially infiltrated carbon-carbon composite preforms have been scanned by high-resolution synchrotron radiation X-ray CMT. 3D high-quality images of the pore space have been produced at two distinct resolutions and have been used for the computation of geometrical quantities : porosity, internal surface area, pore sizes, and their distributions, as well as local and average fiber directions. Determination of the latter property makes use of an originalalgorithm. All quantities have been compared to experimental data, with good results. Structural models appropriate for ideal families of cylinders are shown to represent adequately the actual pore space

Direct 3D microscale imaging of C/C composites with computed holotomography

International audienceAs part of the modelling of CVI (Chemical Vapor Infiltration), one of the processing techniques of Carbon - Carbon composites, a better understanding of the relation between fiber architecture and transport properties is required. An excellent starting point for the pore-scale modeling of heat and gas transport is the acquisition of 3D images of the porous media through Computed Micro Tomography at various densification stages. Due to the low X-ray absorption rate of light materials such as carbon, a poor image contrast is obtained with absorption tomography. On the other hand, phase contrast imaging is readily feasible using the coherence properties of modern synchrotron beams. Holotomography has been performed on these materials and it provides quantitative density images where fibers and pyrocarbon matrix deposit are easily distinguishable. Such images are appropriate for the pore-scale computation of many effective transport properties

La responsabilidad social de los medios de comunicación en la protección del medio ambiente

El presente trabajo es un análisis sobre la cobertura y el tipo de tratamiento que se le da a la información relacionada con la protección del medio ambiente en los medios de comunicación. Como objeto de estudio selecciona tres semanarios impresos de diferentes países y realidades: Time de USA, Visão de Portugal y Proceso de México. La observación abarca seis meses, correspondientes a tres meses previos y tres posteriores a la Cumbre sobre el Cambio Climático realizada en Cancún, México (COP16/CMP6), del 29 de noviembre al 10 de diciembre de 2010. Primeramente se hará un breve recorrido sobre la historia del periodismo y las principales teorías que han analizado los procesos de producción de este medio de comunicación. Posteriormente se hablará sobre el papel de los medios de comunicación y los organismos oficiales e internacionales frente a la problemática ecológica. En el análisis empírico, se propone como metodología de estudio una tabla con categorías definidas para la recolección y organización de datos. Finalmente se hará un análisis comparativo de los resultados arrojados por cada uno de los semanarios y por último, se hará una reflexión sobre el ejercicio de esta investigación y la información obtenida.This dissertation analysis the coverage and the type of treatment that is given by the media to information related to environmental protection. The study focuses on three printed newsmagazines from different countries: Time from USA, Visão from Portugal and Proceso from Mexico. The observation covers six months, which correspond to the three months previous and the three months after the Summit of Climate Change that took place in Cancun, Mexico (COP16 / CMP6), held from November 29 to December 10 2010. The study starts with a brief overview of the history of journalism, its evolution and the main theories that have analyzed the production processes of the media. The following chapters address the role of the media in the creation of a public awarness about ecological problems. In the last chapters, the results of content analysis will be presented, comparing the coverage of each newsmagazine and reflecting on how the media frame ecological issues

Simulation of chemical vapor infiltration and deposition based on 3D images: a local scale approach

International audienceA numerical solution for the simulation of chemical vapor infiltration of ceramic matrix composites is presented. This computational model requires a 3D representation of the preform. Gas transport and chemical reaction are simulated by a Monte Carlo random walk technique. The developed algorithm can also be used for determination of effective transport and reaction properties in a porous medium. It is firstly validated by considering the simple case of diffusion and reaction in a flat pore. Results of infiltration of an actual fiber arrangement are described and discussed. Extension to deposition on a thin substrate with asperities is also studied

Contribution of X-ray CMT and image processing to the modelling of pyrocarbon Chemical Vapour Infiltration

International audienceThe Chemical Vapour Infiltration (CVI) process is used to fabricate the pyrocarbon matrices of C/C composites. This process involves complex physico-chemical phenomena such as the transport of precursor, carrier, and by-product gases in the reactor and inside a fibrous preform, heat transfer, chemical reactions (pyrolysis and deposition), and the structural evolution of the preform. It is able to provide high-quality materials because the processing conditions are rather mild with respect to the fibres; however it is expensive and sometimes difficult to optimize. This process has been the object of extensive modelling efforts, because of imperative optimization needs. The present work presents an approach suited to the exploitation of computerized microtomographs of C/C composites, which features image acquisition, computation of geometrical and transport properties, and infiltration modelling, as applied to the infiltration of needled carbon fibre fabrics. Another application to the reinforcement of carbon foams is also presented, as an example of inserting this approach in a global modelling strategy

Study of zircaloy-4 cladding air degradation at high temperature

Prix de la Meilleure Communication EuropéenneInternational audienceZircaloy cladding, providing the first containment of UO2 fuel in Pressurised Water Reactors, can be exposed to air during accidental situations. This might occur during reactor operation (in case of a core meltdown accident with subsequent reactor pressure vessel breaching), under shutdown conditions with the upper head of the vessel removed, in spent fuel storage pools after accidental loss of cooling or during degraded transport situations. The fuel assemblies inadequately cooled, heat up and as a result, corrosion of Zircaloy claddings takes place. This paper is devoted to the kinetic analysis of Zy4 corroded at 850°C in 20% oxygen - 80% nitrogen partial pressure atmosphere to support the comprehension of the degradation mechanisms involved during the post-transition stage

Modelling Chemical Vapour Infiltration in C/C composites: numerical tools based on µ-CT images

ISBN 978-3-00-032049-1International audienceIn the production of high-quality Ceramic-Matrix Composites, matrix preparation is often made by Chemical Vapor Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modeling tools.In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools.The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, surface and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modeling step.The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program.Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed