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A new Monte Carlo-based approach for addressing stiff chemical kinetics
No full textInternational audienceNew pointwise Monte Carlo method for chemical kinetics modeling.Effectiveness of handling the quasi-steady state situation by Monte Carlo.Addressing the partial equilibrium situation via the use of importance sampling
Monte Carlo Simulation of Atmospheric Radiative Forcings Using A Path-Integral Formulation Approach for Spectro-Radiative Sensitivities
No full textInternational audienceWe present recent advances in path-integral formulations designed for unbiased Monte Carlo sensitivity estimation (in the form of partial derivatives) within a coupled physics model. We establish the theoretical foundation and illustrate the approach by estimating instantaneous atmospheric radiative forcings. In climate studies, these quantities amount for the change in top-of-atmosphere (TOA) net radiative flux induced by an isolated change in surface or atmospheric constitution. Based on a path-integral framework, our approach results in estimations consistent with well-established radiative forcings in the climate community. We highlight how physics coupling through path-integral formulations yields unbiased sensitivity estimation of a radiative quantity (integrated TOA flux) to a spectroscopic parameter (fraction change in gas concentration). Furthermore, we emphasize the method's scalability, demonstrating its compatibility with computer science acceleration techniques. These latter play a key role in rendering the computational time weakly sensitive to the system's multidimensional and multiphysics complexity
Three approaches on estimating geometric sensitivities in radiative transfer with Monte Carlo
No full textInternational audienceThe Monte Carlo method, renowned for its ability to handle the spectral and geometric complexities of 3D radiative transfer, is extensively utilized across various fields, including concentrated solar power design, atmospheric science, and computer graphics. The success of this method also extends to the estimation of sensitivity—the derivative of an observable with respect to a given system parameter, which is, however, particularly challenging when these parameters involve geometric deformation. Bridging statistical physics and computer graphics, distinct methodologies have emerged within these fields for estimating geometric sensitivity, each employing unique terminologies and mathematical frameworks, leading to seemingly disparate approaches. In this paper, we review the three main approaches to sensitivity estimation: (1) Expectation Differentiation, which employs a vectorized Monte Carlo algorithm to simultaneously estimate the intensity and its sensitivity; (2) Differentiable Rendering, predominantly used in computer graphics and applied in numerous contexts; (3) Transport Model for Sensitivity, which conceptualizes sensitivity as a physical quantity with its own transport equations and boundary conditions, thereby facilitating engineering and physics analyses. We aim to enhance readers’ ability to tackle sensitivity-related challenges by providing a comparative understanding of these three perspectives. We achieve this through a simplified one-dimensional radiative transfer case study, offering an accessible platform for comparing and classifying these approaches based on their theoretical underpinnings and practical application in Monte Carlo algorithm
Material Forming. The 27th International ESAFORM Conference on Material Forming
No full textInternational audienceThese ESAFORM 2024 conference proceedings cover a wide range of topics: Additive manufacturing; Composites forming processes; Extrusion and drawing; Forging and rolling; Formability of metallic materials; Friction and wear in metal forming; Incremental and sheet metal forming; Innovative joining by forming technologies; Optimization and inverse analysis in forming; Machining, Cutting and severe plastic deformation processes; Material behavior modelling; New and advanced numerical strategies for material forming; Non-conventional processes; Polymer processing and thermomechanical properties; Sustainability on material forming
Centrifugation Effect on Olive Mill Wastewater Treatment by Coagulation-Flocculation Using Ca(OH)2-Pectin System
No full textInternational audienceThe aim of this research was the study of the centrifugation effect on olive mill wastewater (OMW) treatment by coagulation-flocculation using the Ca(OH)2-pectin system. To separate the treated OMW from the residual sludge, two methods were used: gravity decantation and centrifugation. Efficiency of the treatment was evaluated following the evolution of the OMW treated volumes and the reduction rates of dry matter (DM) and phenolic compounds (PC) and other parameters related to residual toxicity. Compared to gravity decantation, centrifugal separation significantly enhances the treatment of the OMW studied. Additionally, this separation method reduces considerably the treatment duration compared to gravity decantation i.e. 10 min instead of 4 h. The lime-pectin system improved OMW purification. Optimal doses of lime and pectin were respectively 10 g/L and 0.2 g/L. Under these conditions, centrifugal separation allowed to obtain a volume of treated OMW about 78.2% of the raw effluent volume and reduced the rates of DM by 38% and of PC by 79%. The COD was also reduced by 60.0%. These results show that the resulting sludge may be used for production of fertilizers or land augmentation, thus avoiding costly disposal
Using constraint programming to address the operational aircraft line maintenance scheduling problem
No full textInternational audienceMaintenance plays a major role in air transport management. Airlines are looking to reduce aircraft unavailability. Optimizing maintenance is a perspective to increase the operational potential of aircraft and offers novel managerial implications. Maintenance tasks are traditionally organized in periodic blocks of activities. In the modern aviation, more and more maintenance jobs can be performed between two flights, which is called Line Maintenance Scheduling Problem (LMSP). The expected goal of our paper is to propose an operational schedule that can be directly executed by maintainers, i.e. assigning a start time to each elementary activity and a resource to perform it. This new problem is named Operational Aircraft Line Maintenance Scheduling Problem (OALMSP). A scheduling assistant could help airlines to reduce maintenance costs and resource management. Planners have to respect task deadlines imposed by regulations, precedence constraints between certain operations and also ensure the availability of resources in order to perform specific actions. This problem is an extension of a Resource Constrained Project Scheduling Problem (RCPSP). In this article, we propose an industrial application of an automatic aircraft line maintenance scheduler based on a Constraint Programming (CP) model. The flexibility of our approach means we can easily adapt to airline use cases without changing the properties of the model. The optimization problem is generally made up of several objectives ordered according to their importance. The objectives are respectively to plan as many tasks as possible according to their priority, then to minimize both the use of resources and the deviation time between scheduled dates and target dates of tasks. The lexicographical order enables the use of human reasoning and the management of business priorities. A constructive search strategy is designed to compute a satisfying schedule within an acceptable execution time for industry application. A practical use case based on real airline data is presented and the results are compared with those found by an industrial solver taken as a reference
Etude de l'influence de la microstructure sur le comportement tribologique d'un superalliage base nickel obtenu par fabrication additive
No full textThis research project is a prospective study examining the relationships between specific microstructures and their associated tribological behaviors. The aim is to understand the impact of morphological and crystallographic anisotropy on the tribological behavior of surfaces, while maintaining a consistent chemical composition. To achieve this, the Laser Powder Bed Fusion (L-PBF) process is employed for its ability to generate multi-scale characteristic microstructures. The material under investigation is ABD-900AM, a nickel-based superalloy specifically developed for additive manufacturing, known for its defect-free printability across a wide range of process parameters. The microstructural features studied include the grain structure (size, morphology, crystallographic texture) and the cellular structure. To generate these characteristic microstructures, various laser scanning strategies are employed. The process parameters are selected by modifying the laser path and the orientation of the parts within the build chamber, while keeping key laser settings (power, speed) constant. The microstructures are primarily characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). For the grain structures, a range of sizes, from a few hundred to several thousand µm², and crystallographic textures ((200), (220), (111), combinations of multiple textures, and non-textured) were achieved. The cellular structure was also modified according to the laser scanning strategy, resulting in variations in thickness (from 0.61 ± 0.13 µm to 0.85 ± 0.31 µm), morphologies (columnar or equiaxed), and degrees of homogeneity. Tribological tests were conducted at room temperature using a ball-on-flat reciprocating sliding configuration with a normal load of 30 N, a frequency of 1 Hz, and a sliding distance of 10 mm. Various test durations (120 s, 600 s, 1800 s, and 3600 s) were examined to track the evolution of wear mechanisms over time. Under these loading conditions, only the 3600 s tests were able to effectively distinguish between different microstructures. The wear resistance of the microstructures was linked to the development of interfacial layers on the wear tracks and the ability of the microstructures to maintain these layers at the surface. The size and homogeneity of the cellular structure were identified as the key microstructural factors that enabled the retention of these interfacial layers by reinforcing the matrix. A phenomenological wear model based on the analysis of wear tracks for different test durations concludes this project.Ce projet de recherche est une étude prospective des liens entre des microstructures types et ses comportements tribologiques associés. Il s'agit de comprendre l'impact de l'anisotropie morphologique et cristalline sur le comportement tribologique de surfaces, tout en conservant la même chimie. Pour cela, le procédé fusion laser sur lit de poudre (L-PBF) est utilisé pour sa capacité à générer des microstructures types multi-échelles. Le matériau d'étude est l'ABD-900AM, un superalliage base nickel spécialement développé pour la fabrication additive qui est imprimable sans défaut sur une large gamme de paramètres procédé. Les différentes caractéristiques microstructurales étudiées sont la structure granulaire (taille, morphologie, texture cristallographique) et la structure cellulaire. Afin de générer ces microstructures types, différentes stratégies de lasage sont employées. Le choix de paramètre procédé consiste en une modification du parcours du laser et de l'orientation des pièces dans la chambre de fabrication, sans modifier les paramètres de lasage (puissance, vitesse). Les microstructures sont essentiellement caractérisées par les techniques DRX, MEB et EBSD. En termes de structures granulaires, différentes tailles de structure allant de quelques centaines à quelques milliers de µm² et de textures cristallographiques ((200), (220), (111) combinaison de plusieurs textures et non texturées) sont obtenues. La structure cellulaire est aussi modifiée selon la stratégie de lasage, et permet d'accéder à différentes épaisseurs (de 0,61 ± 0,13 µm à 0,85 ± 0,31 µm) et morphologies (colonnaire ou équiaxe) et de générer des différences d'homogénéités. Les essais tribologiques sont menés à température ambiante en configuration bille/plan en mouvement alterné avec une charge normale de 30 N, une fréquence de 1 Hz, et une distance de glissement de 10 mm. Différentes durées d'essais (120 s, 600 s, 1800 s et 3600 s) pour suivre l'évolution des mécanismes d'usure au cours du temps sont étudiées. Dans ces conditions de chargements, seuls les essais de 3600 s permettent de discriminer les microstructures. Ainsi, la tenue à l'usure des microstructures est associée au développement des couches interfaciales sur les traces d'usure, et à la capacité des microstructures à maintenir ces couches interfaciales à la surface. La taille et l'homogénéité de la structure cellulaire sont les éléments microstructuraux prépondérants qui permettent de maintenir ces couches interfaciales par le renforcement qu'elles apportent à la matrice. Un modèle d'usure phénoménologique basé sur l'analyse des traces d'usure pour différentes durées d'essais conclut ce projet
Impact de la configuration de l’alimentation sur le démarrage du procédé de mélange de poudres en continu
No full textNational audienc
Corrélation entre l'imprimabilité des formulations à base de gel et leur comportement rhéologique
No full textNational audienceLa rhéologie est une méthode relativement rapide et très utile pour évaluer l'imprimabilité des formulations destinées à l'impression 3D par extrusion. Les chercheurs effectuent actuellement différentes mesures rhéologiques, de la mesure traditionnelle de la viscosité aux techniques plus avancées telles que les études de cisaillement à amplitude oscillatoire. Avec ces volumes importants d'observations, les informations obtenues peuvent devenir énormes, en particulier pour les personnes inexpérimentées (Elbadawi et al., 2020). Cette étude fait partie de travaux déjà publiés (Aina et al., 2024), dans lesquels nous avons examiné les propriétés rhéologiques de formulations d'agar (A), d'hydroxypropylméthylcellulose (H), de sucrose (S) et de caféine (C) comme médicament modèle, tout en explorant leur imprimabilité (1) en tant que formulations gélifiées. Nous avons caractérisé les échantillons à l'aide d'expériences rhéologiques en oscillation et en rotation, qui ont donné lieu à 11 variables (Aina et al., 2024).</div
Devenir de l'azote lors de la combustion de biomasse dans le lit d'une chaudière à grille (thèse sous embargo)
No full textBiomass combustion in industrial-scale biomass grate-fired boilers produces several types of pollutants, including nitrogen oxides. These species, also known as NOx, are harmful to the environment because they cause acid rain and are greenhouse gases. These pollutants are mostly formed by the oxidation of the nitrogen that was initially present in the biomass. NOx emissions are a primary concern for biomass boiler manufacturers. Modeling is a great help in reducing NOx emissions. The gas phase chemistry of nitrogen is well known so gas phase reactions involving NOx species above the bed are not a problem. However, the chemistry governing the heterogeneous combustion of the fuel bed remains poorly understood. In particular, the nature of the nitrogen gases exiting the bed is not accurately predicted. The objective of this work is to provide a bed model capable of predicting the gas phase composition at the exit of the bed, with a particular focus on nitrogen species. To this end, a bed model was developed using MATLAB. This model is based on the BASIC model developed by the University of Aalborg. This is a 1D Euler-Euler bed that employs the walking column approach to simulate a biomass grate-fired boiler bed. Two significant modifications were made to the model: the incorporation of thermal non-equilibrium and the inclusion of nitrogen chemistry. To validate the model, experiments were conducted in a cross-fired fixed bed reactor. An existing experimental device was adapted to enable the quantification of nitrogen in all products. Three series of experiments were conducted. The first series compared the fate of nitrogen of three agrofuels during the pyrolysis and combustion. The second series investigated the influence of particle size and temperature on the fate of nitrogen during particleboard combustion and pyrolysis. The third series focused on the influence of chemical treatment on NOx emissions for three chemically treated particleboards. The results obtained with the experimental setup allowed us to fix some kinetic data for the model. This model represents a first step towards the prediction of nitrogen gas production in a biomass bed.La combustion de biomasse dans des chaudières industrielles à grille produit plusieurs espèces polluantes dont les oxydes d'azote, aussi appelés NOx. Ces molécules sont nocives pour l'environnement (causes de pluies acides, gaz à effet de serre). Ces polluants sont majoritairement formés par l'oxydation de l'azote initialement contenu dans la biomasse. La limitation de leurs émissions est donc un enjeu important dans le domaine de la combustion de biomasse. Pour y parvenir, le recours à la modélisation est courant. La chimie de l'azote en phase gaz est bien connue ; la modélisation du devenir de l'azote dans la phase gaz au-dessus du lit ne pose donc pas de problème. En revanche, les phénomènes régissant la combustion hétérogène du lit de biomasse restent mal connus. Cela se traduit par une mauvaise prédiction de la forme de l'azote en sortie de lit. L'objectif de cette thèse est alors de proposer un modèle de lit permettant de fournir des données d'entrée fiables à un modèle numérique de chaudière ne simulant que la phase gaz. Pour ce faire, un modèle a été développé sur MATLAB à partir du code BASIC développé par l'Université de Aalborg. Ce modèle de lit est un modèle de type 1D Euler-Euler pouvant modéliser le lit d'une chaudière biomasse via l'approche de la colonne mobile. La chimie de l'azote a été ajoutée à ce modèle et un modèle à deux températures a également été implémenté. Pour confronter le modèle, des expériences en lit fixe traversé ont été réalisées. Pour cela, un dispositif expérimental existant a été adapté afin de pouvoir quantifier l'azote dans les différents produits de la combustion. Trois séries d'expériences ont été réalisées sur ce dispositif expérimental. La première consistait à comparer le devenir de l'azote de trois agrocombustibles lors de leur pyrolyse et de leur combustion. La deuxième série consistait en une étude paramétrique sur l'influence de la taille des particules et de la température de combustion sur les émissions de NOx lors de la combustion de panneaux de particules. La troisième série est une étude de l'influence du traitement chimique de panneaux de particules sur les émissions de NOx lors d'une pyrolyse ou d'une combustion. Les résultats des expériences en lit fixe traversé ont permis de caler certains paramètres cinétiques du modèle 1D. Le modèle développé constitue une première étape dans la modélisation des émissions d'espèces azotées lors de la combustion d'un lit de biomasse