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Metaheuristics for solving the multi-stage hybrid flow shop scheduling problem with dedicated machines
No full textInternational audienceThis paper addresses the multi-stage hybrid flow shop scheduling problem with dedicated machines (HFSSP-DM), with more than three stages. The primary objective is to minimise the maximum completion time of jobs (makespan). We first formulate a mixed integer programming (MIP)-model for the problem and adapt three metaheuristic algorithms from the literature on two-stage hybrid flow shop with dedicated machines, simulated annealing (SA), Tabu search (TS), and genetic algorithm (GA). In addition, we introduce, for the first time in this context, a recent swarm-based algorithm, the reptile search algorithm (RSA), specifically tailored to tackle HFSSP-DM. To evaluate the effectiveness of these metaheuristics, we conduct a comprehensive set of computational experiments across various problem classes with different machine configurations and job sizes. The results show that RSA significantly outperforms GA, TS and SA, achieving near-optimal solutions with a very reasonable computational time. These findings underscore RSA’s potential as a powerful tool for solving complex hybrid flow shop scheduling problems and offer valuable insights for optimising resource allocation and minimising production time in multi-stage manufacturing environments
Discovering search behaviour in black garden ant trajectories
No full textExploration of space plays an important role in many animals, in particular for social insects who have to feed and protect a whole colony. In a laboratory study, Khuong et al (2013) studied how the workers of the black garden ant Lasius niger move around in an unknown environment. They assumed that, in a homogeneous arena with no visual cues, ants had no information about their position in space. Based on this hypothesis, they modelled their ants in a Boltzmann Walker framework which describes an ant's random walk as a series of straight segments separated by reorientation events. They assumed that on plain horizontal surfaces the ant's direction of movement would not influence their average speed, segment lengths and reorientation decisions, thus leading to diffusive trajectories. However, published experiments indicate that L. niger ants are not completely devoid of directional information even in standard laboratory setups with no obvious landmarks. Moreover, many ant species are known to develop specific search strategies when they want to find a particular place in space, a situation that may apply to the analysed data. We re-analyze Khuong et al ’s data on non-inclined surfaces, this timetaking into account the ant’s orientation in relation to its starting point in the arena. We discovered that, with this information taken into account, the ant’s trajectory is biased towards its starting point (biased random walk), revealing an advecto-diffusive process. In fact, the distributions of segment lengths and reorientation angles turned out to be modulated by the ant’s orientation in relation to its starting point. By simulating these biased trajectories, we show that this modulation halves the time it takes for an ant to come back towards its starting point. We conclude that not taking into account the animal’s cognitive abilities in data analysis may lead to incomplete or biased conclusions. The discovered search behaviour in L. niger can play a significant role in the colony’s exploration and foraging ecology
Alkali-promoted FeCo/TiO<sub>2</sub> catalysts for carbon dioxide hydrogenation to fuels
No full textInternational audienceA titania support has been modified in order to prepare alkali promoted cobalt-iron catalysts for the hydrogenation of carbon dioxide into long-chain hydrocarbons (C5+). Under mild reaction temperatures (220-250-270 °C), the partial substitution of cobalt by iron decreased the catalytic activity (CO2 conversion) but increased the selectivity into C5+, since iron is less active within this temperature range, but more selective for the reverse water-gas shift reaction. Alkali promotion (Na or K) further decreased the catalytic activity of cobalt-iron catalysts, albeit, strongly increasing the selectivity into CO and C5+ by decreasing CH4 production. This could be attributed to the high basicity of alkali promoted catalysts, their beneficial effect on CO2 dissociative adsorption, and their ability to limit H2 adsorption
Application of the coupled Eulerian-Lagrangian method to the roller compaction modelling
No full textInternational audienceThe roller compaction (RC) process of powders is a steady-state operation characterized by large deformationsand complex contact interactions. Traditionally, it is modelled using the Arbitrary Lagrangian–Eulerian (ALE)method, which requires frequent remeshing of the Lagrangian domain to preserve solution accuracy. To over-come this limitation, this study explores the Coupled Eulerian–Lagrangian (CEL) method, which can accom-modate large deformations without mesh distortion.The CEL approach is implemented in Abaqus/Explicit, with an imposed inlet feed velocity and zero outletpressure as Eulerian boundary conditions. A steady-state solution is achieved through a general transient (non-steady-state) simulation. To improve computational efficiency of the explicit analysis, the simulation time isartificially reduced by increasing the material density.The results highlight the strong potential of the CEL method to accurately predict the key characteristics of theroll compaction process, showing good agreement with both experimental measurements and ALE-based sim-ulations reported in the literature. The study also shows that while mesh size significantly affects interface ac-curacy, it does not influence the stable time increment. Overall, the CEL approach offers a promising alternativefor simulating roller compaction without mesh distortion and provides deeper insight into roller-powderinteractions
Satisfaction des Professionnels de Santé et Optimisation des Processus : Une Approche Intégrée
No full textInternational audienceÉtant leurs principaux clients, la satisfaction des médecins prescripteurs constitue un indicateur clé pour évaluer la qualité des services fournis par les laboratoires d’analyses médicales rattachés aux hôpitaux. Dans cette étude, nous nous intéressons à l’évaluation de la performance du laboratoire d’analyse d’un hôpital universitaire tunisien à travers l’évaluation de la satisfaction de ses médecins prescripteurs et l’analyse du processus de prise en charge. Après la collecte des données, une analyse approfondie a été menée en utilisant divers outils statistiques, notamment l’Analyse enComposantes Principales (ACP) afin d’extraire les informations les plus pertinentes des données issues d’une enquête de satisfaction. Sur la base des résultats obtenus et des points faibles identifiés, une cartographie des flux a été réalisée à l’aide de la cartographie de la chaine de valeur (Value Stream Mapping, VSM) pour analyser les processus du laboratoire et proposer des améliorations. Cette approche intégrée permet non seulement d’optimiser le fonctionnement du laboratoire, mais aussi d’améliorer l’expérience des médecins prescripteurs, en réduisant les inefficacités et en augmentant la qualité du service rendu
Mechanochromic sensor for measuring high strain
No full textInternational audienceDirect measurement of high strain is of great interest. Indirect optical methods are expensive anddifficult to transport. This is why many projects are focusing on the development of small sensors formeasuring high strains. The main objective of this study is to create a sensor capable of measuring 20%strain. This new sensor must meet specific criteria: it must be small, flexible and low-cost. After creatingsamples, this study focuses on photoluminescence characterization. Tensile tests coupled with an opticaltest bench provided the mechanical properties and light spectra of each sensor. Spectral analysisenabled us to calculate an intensity ratio indicating at what rate of deformation the mechanochromicphenomenon was triggered. Our results show that it is possible to generate mechanochromy in apolymer blend composed of 60%PP-40%POE doped at 1% by mass with the additive BBS. Deformationrates detected with this sensor are of the order of 20%. Our study concludes with the creation of amechanochromic threshold sensor capable of measuring large deformations while meeting our initialconstraints.La mesure directe des déformations importantes présente un grand intérêt. Les méthodes optiquesindirectes sont coûteuses et difficiles à transporter. C'est pourquoi de nombreux projets s’intéressent audéveloppement de petits capteurs pour mesurer des déformations élevées. L’objectif principal de cetteétude est de créer un capteur capable de mesurer 20% de déformation. Ce nouveau capteur doitrépondre à des critères spécifiques : être de petite taille, souple et à faible coût. Après la création deséchantillons, notre étude se concentre ici sur la photoluminescence. La réalisation d’essais de tractioncouplés avec un banc d’essai optique ont permis d’avoir les propriétés mécaniques et les spectreslumineux de chaque capteur. L’analyse spectrale a permis de calculer un ratio d’intensité nousindiquant à quel taux de déformation le phénomène de mécanochromie se déclenchait. Nos résultatsmontrent qu’il est possible de générer de la mécanochromie dans un mélange polymérique composé de60%PP-40%POE dopé à 1% en masse avec un additif le BBS. Les taux de déformations détectés avecce capteur sont de l’ordre de 20%. Notre étude se conclut par la création d’un capteurmécanochromique à seuil capable de mesurer des grandes déformations tout en répondant à noscontraintes initiales
Development of cyclic double virtual phase model for advanced packed bed solar-driven thermo-chemical reactor
No full textInternational audienceThe packed bed solar-driven thermo-chemical reactor suffers from hour-level changing solar heating conditions and extreme heat flux on the gas-solid interface, leading to difficulties for quick and stable modelling. To address this problem, the current study developed a novel model by virtual phase method (VPM), in which cyclic double virtual phases (DVP) are applied to track the non-uniform gas-solid interface. With this model, the usage of moving mesh and calculation of extra N-S equations for gravity-driven mass conversion can be avoided, improving the stability and efficiency of simulation. A 3–6 kW fin-enhanced solar-driven packed-bed reactor for carbonaceous feedstock gasification is modeled to assess the influence of key empirical parameters and operating conditions on numerical results. Results obtained by DVP model exhibit negligible deviations when empirical parameters are amplified by 0.5–2 times against standard cases validated by experiment. The model can stably run when the temperature on gas-solid interface varies from 293 K to 1800 K, covering the temperature range in commonly used solar reactor. Hour-level solar gasification processes in the packed bed reactor only require several hours of calculation with DVP model, indicating a good treatment of numerical oscillations caused by finite element method (FEM) during the density consumption
Effect of oxygen content on elastic properties of an oxygen-graded titanium: Experimental and computational analyses
No full textInternational audienceHigh-speed nanoindentation mapping (HSNM), electron backscatter diffraction (EBSD), electron microprobe analyses (EPMA), and high resolution – microscale laser induced breakdown spectroscopy (HR–LIBS), were used to characterize the evolution of the elastic anisotropy of a commercially pure titanium (CP-Ti) having a gradient of oxygen concentration. CP-Ti samples were pre-oxidized in air at 655 C for 120 h to create a 35 -deep gradient of oxygen within Ti, the oxygen-rich layer (ORL). Wedge-cut samples were prepared to spread the ORL over hundreds of micrometers instead of tens of micrometers for cross-sections. EPMA and HR–LIBS were used to quantify the oxygen distribution within the ORL in a relative and absolute manner, respectively. The Vlassak-Nix theory was used for inverse identification of the stiffness matrix terms as a function of the oxygen content. The stiffness matrix as a function of the oxygen concentration was used to simulate the stress–strain distribution at the sub-grain level in the ORL under tensile macroscopic loading. Configurations with and without external oxide were numerically tested to investigate the role of the oxide layer on the stress distribution within the ORL as well as the crystallographic texture
Comparing Borate Fusion and Microwave Digestion in the Challenging Dissolution and Quantification of Inorganic Elements from Bottom Ash
No full textInternational audienceMunicipal solid waste incineration bottom ash like many other solid wastes is a heterogeneous material, making complete mineralization and accurate quantification challenging, especially for samples containing silica, aluminum oxides, and related blends with other elements. This study aimed to compare the effectiveness of two mineralization processes: microwave-assisted acid digestion using a combination of hydrofluoric acid (HF), nitric acid (HNO3), and hydrogen peroxide (H2O2) under different digestion times (3, 6, and 9 h) and borate fusion using lithium metaborate (LiBO2) as a flux (1:4 ash-to-flux ratio) at high temperatures (900–1050 °C). Elemental quantification of Si, Ca, Fe, Al, Na, and K was performed using ICP-AES. Among the tested digestion times, the 6 h microwave digestion showed better mineralization and was therefore compared to the borate fusion. Silica recovery reached 189 ± 6 g/kg of ash when using borate fusion, compared to 156.5 ± 16 g/kg of ash with microwave digestion. A similar trend was observed for Ca, Fe, and Al. This effectiveness is attributed to the high temperatures (900–1050 °C) and strongly alkaline conditions, which enabled the effective decomposition of complex silicates and oxides. These findings show borate fusion as a reliable and efficient technique for the mineralization of complex materials such as bottom ash for further reliable quantitative analyses. This approach could favor the recovery of metal species from various waste streams and enable the circular management of metal resources
Investigation of Perfluorohexane as a Potential Physical Solvent for Flue Gas Cleaning: Experimental Vapour-Liquid Equilibrium Data and Modelling Conference Topics/Sessions: Phase Equilibria and Fluid Properties
No full textInternational audiencePerfluorocarbons possess atypical properties due to their strong carbon-fluorine bonds, providing exceptional chemical and thermal stability. Their high gas absorption capacity, among other properties, makes them promising candidates for use as physical solvents in industrial applications 1 . In this study, perfluorohexane was investigated as a potential physical solvent for flue gas cleaning in advanced power generation facilities, particularly integrated gasification combined cycle systems. A key factor in designing gas absorption systems is accurate vapour-liquid equilibrium (VLE) data 2 . However, VLE data for perfluorohexane with common flue gases are scarce. To address this scarcity, phase equilibrium data measurements were conducted for binary systems of perfluorohexane with CO, H₂ S, and C₂ H₆ using a static-analytical apparatus equipped with a capillary sampler for phase sampling and gas chromatography for composition analysis. Measurement uncertainties were determined to be within 0.04 K for temperature, 0.008 MPa for pressure, and 0.100 for mole fractions for all systems. The measured data were successfully correlated using the direct method, primarily employing the Peng-Robinson equation of state 3 with the Mathias-Copeman alpha function 4 and Wong-Sandler mixing rules 5 incorporating the nonrandom two-liquid activity coefficient model 6 . The results showed that perfluorohexane exhibited strong high selectivity for CO₂ over CO. In contrast, C₂ H₆ and H 2 S displayed significant co-absorption with CO 2 at low pressures