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Multipole-model approximation of the equivalent fluid model equations for porous media in the time domain
Full text linkMultipole-model approximation of the equivalent fluid model equations for porous media in the time domain
FAST-OAD-GA: an open-source extension for Overall Aircraft Design of General Aviation aircraft
Full text linkIn order to respond to the growing need for a reduced environmental footprint of the commercial aviation sector,
new aircraft architecture and propulsion technology have become a major focus in the aerospace research field.
In this context, many new projects featuring innovative configurations or powertrains, for which light aircraft are
under consideration as final products or as small scale test platforms for larger airplane, have taken shape. The
assessment of the feasibility of such concepts requires an Overall Aircraft Design (OAD) study at a preliminary
stage in order to rule out non-viable design choices and identify key features. Consequently, OAD tools play a
key role during the conceptual design phase as they allow to automatically carry out said studies and, using
their Multidisciplinary Design Analysis and Optimization capabilities, identify the most likely design. FASTOAD-
GA, an open-source extension of FAST-OAD completes the aircraft design techniques from FAST-OAD
with general aviation specific models to enable the preliminary sizing of aircraft regulated by the EASA CS-23.
This paper presents the FAST-OAD framework, its capabilities, the models added by FAST-OAD-GA for general
aviation aircraft sizing and the upcoming changes to model innovative architectures
Model-Checking of Space Systems Designed with TASTE/SDL
No full textModel-Based Software Engineering (MBSE) is a development approach aiming to build correct-by-construction systems, provided the use of clear, unambiguous and complete models to describe them along the design process. The approach is supported by several engineering tools, such as the TASTE toolset. TASTE is a pragmatic and mature open-source toolset supported by European Space Agency that enables and provides automation for most of the phases of software system development: (i) heterogeneous system design through several modelling and programming languages, (ii) code generation, build and deployment of the binary application(s), and (iii) validation through static analysis and simulation. One topic left open in TASTE is the formal verification of a system design with respect to specified properties. In this paper we describe our approach based on the IF model-checker to enable the formal verification of properties on TASTE designs, as well as the results obtained and lessons learned
Cognitive effects of prolonged continuous human-machine interaction: The case for mental state-based adaptive interfaces
Full text linkOperators of complex systems across multiple domains (e.g., aviation, automotive, and nuclear power industry) are required to perform their tasks over prolonged and continuous periods of time. Mental fatigue as well as reduced cognitive flexibility, attention, and situational awareness all result from prolonged continuous use, putting at risk the safety and efficiency of complex operations. Mental state-based adaptive systems may be a solution to this problem. These systems infer the current mental state of an operator based on a selection of metrics ranging from operator independent measures (e.g., weather and time of day), to behavioral (e.g., reaction time and lane deviation) as well as physiological markers (e.g., electroencephalography and cardiac activity). The interaction between operator and system may then be adapted in one of many ways to mitigate any detected degraded cognitive state, thereby ensuring continued safety and efficiency. Depending on the task at hand and its specific problems, possible adaptations -usually based on machine learning estimations- e.g., include modifications of information, presentation modality or stimuli salience, as well as task scheduling. Research on adaptive systems is at the interface of several domains, including neuroergonomics, human factors, and human-computer interaction in an applied and ecological context, necessitating careful consideration of each of the aforementioned aspects. This article provides an overview of some of the key questions and aspects to be considered by researchers for the design of mental state-based adaptive systems, while also promoting their application during prolonged continuous use to pave the way toward safer and more efficient human-machine interaction
Investigation of Lattice Boltzmann Methods applied to multiphase flows
Full text linkThe purpose of this thesis is the study of Lattice Boltzmann Methods (LBM), applied to multiphase flows. First, general principles of statistical physics and of Lattice Boltzmann Methods are introduced, followed by a historical review about Lattice Gas Automata. A state of the art of the multiphase flow simulation methods is then proposed, with a particular emphasize on diffuse interface methods. In particular, the phase field methods are introduced, and different methods allowing to numerically simulate surface tension are also presented. A second review concerning multiphase flow simulation in a Lattice Boltzmann framework is presented. More precisely, general principals are presented, and the four major methods, Color Gradient, Pseudo-Potential, Free Energy and HCZ, are successively presented. Lattice Boltzmann Methods advanced notions are then introduced, in particular, a Taylor expansion based method that allows to determine Lattice Boltzmann schemes equivalent macroscopic equation is described. A Gradient Color method theoretical study is proposed. First, an original reformulation of the algorithm allowing an improvement in computational efficiency is proposed. The Taylor expansion method is then applied to Gradient Color Method in order to determine the high order error induced by the numerical scheme. This expression allows to demonstrate how the degree of isotropy is essential to the scheme numerical stability. In particular, a numerical operator allowing to introduce an equation of states that differs from the athermal perfect gas equation is proposed. This operator efficiency is illustrated by being applied to academical testcases. The Taylor expansion method is also applied in order to show how the Color Gradient Method allows to solve an Allen-Cahn phase field equation. This theoretical result is then validated numerically. Finally, an original improved version of the Gradient Color Method is proposed. In this method, the efficient formulation and the isotropic Equation of State operator is used, and an original temporal correction term is proposed. This correction term improves the scheme numerical stability and allows to expands the method application range to higher density ratios. Finally, this method is validated through academical testcases
Optimisation pour l'ordonnancement et le spatial
Full text linkL’optimisation de processus complexes fait l’objet d’études en Recherche Opérationnelle et Optimisation Mathématique. Mes travaux en optimisation se sont concentrés sur deux types d’application : les problèmes d’ordonnancement et les problèmes issus du spatial. Parmi les problèmes d’ordonnancement, les problèmes cycliques correspondent à ceux pour lesquelles les tâches se répètent périodiquement. Ces problèmes ont été étudiés dans la littérature mais la plupart des travaux considèrent des paramètres déterministes. Pourtant, des incertitudes, comme la durée d’execution des tâches, peuvent survenir. Mes travaux sur l’ordonnancement cyclique visent à considérer ces incertitudes sous la forme d’un problème d'optimisation robuste bi-niveau. Une méthode de résolution basée sur une décomposition de Benders pour la version flexible du problème d'ordonnancement cyclique constitue une autre contribution dans ce domaine.
Concernant les problématiques du spatial, les technologies modernes posent de nouveaux problèmes d’optimisation que nous tentons de résoudre tels que l’optimisation du placement de faisceau d’un satellite de télécommunication. Pour résoudre ce problème, nous proposons un encadrement paramétrable de la norme euclidienne dans le plan
Simulation of multicomponent spray combustion in gas turbine engines
Full text linkLiquid fuels are the dominant source of energy from combustion and will continue to be so until the maturity of emerging technologies. During this transition phase the use of Sustainable Aviation Fuels (SAF) as blends or in totality inside existing infrastructure is an attractive option. The operational aspects of these new fuels inside the combustion chambers are not known in detail. Further, gas turbine engines operate under high pressure ratios and lean conditions to achieve emission targets making them susceptible to thermo-acoustic oscillations. Large Eddy Simulations (LES) have proven to be a successful tool in understanding fuel combustion processes. The focus of this thesis is on the modelling and simulation of complex multicomponent spray flame combustion in realistic systems. First step deals with the multi-component evaporation of the liquid fuel. Realistic fuels have hundreds of components each with their vapourisation characteristics. The Abramzon-Siringnano evaporation in the AVBP solver is extended to handle this complex compositional aspect of realistic fuels. Comparison of the implemented model with experimental and numerical studies show a good agreement and ability to capture the preferential evaporation characteristics of multicomponent fuels. Second, this multicomponent evaporation model is used in a canonical 1D laminar spray flame setup. A three-component jet fuel surrogate is coupled with Analytically Reduced Chemistry (ARC) to study the effects of droplet sizes, equivalence ratios and relative velocities on the spray flame structures. Correlations developed to estimate the spray flame speed agree with the numerical experiments indicating the correct physical parameters have been chosen to describe multicomponent spray flame propagation. Third part of the thesis deals with the simulations of swirled multicomponent spray flames in a large-scale LOTAR configuration. A three component description of conventional jet fuel and sustainable aviation fuel spray is coupled with turbulent combustion models and complex chemistry description to perform 3D-LES. The fuels composition effects on the overall vapour distribution and its effects on the spray flame structure indicate the role of preferential evaporation on flame stabilisation and combustion regimes. Finally, the forced response of the spray flame in the configuration is studied. The flame transfer function extracted using global chemistry agrees well with the experimental trends. Varying injection patterns to account for the effects of forcing on the droplet distribution shows a change in the flame response. The multicomponent spray flame response shows a strong role of composition and volatility of the fuel components
Dynamic crushing of wood-based sandwich composite tubes
Full text linkThe article presents the results of dynamic crushing of sandwich tubes that had skins made of carbon or glass fibers – with epoxy resin – and an I214 poplar ply core. By increasing the number of poplar plies from two to six, the absorbed energy is doubled, showing the significant contribution of the wood. The Specific Energy Absorption of sandwiches with carbon fiber skins oscillated between 49.4 J/g and 60 J/g while that with glass fiber skins varied from 35.4 to 43.3 J/g
Caractérisation du labneh Ambaris, un lait fermenté libanais, et exploration des communautés microbiennes impliquées dans sa réalisation
Full text linkLe labneh Ambaris est un lait fermenté libanais traditionnellement fabriqué avec du lait cru de chèvre dans des jarres spécifiques en terre cuite. Il est largement apprécié des consommateurs et représente une source de revenue non négligeable pour les producteurs. Nos modes de vie et l’industrialisation des procédés de fabrication questionnent sur le devenir des microorganismes endogènes qui structurent ce produit, patrimoine immatériel du Liban. Le premier objectif de cette thèse, menée dans des conditions réelles de fabrication, était de caractériser le labneh Ambaris en mettant l’accent sur les écosystèmes microbiens impliqués dans sa réalisation. Ainsi, une cartographie de ce lait fermenté, tant sur le plan physicochimique et microbiologique que sur le plan sensoriel a été établie. Les approches multidisciplinaires utilisées et notamment la « Next Generation Sequencing » nous ont fourni une vision globale du labneh Ambaris se présentant sous la forme d’un écosystème microbien complexe dont la biodiversité dépend des exploitations. Ce lait fermenté égoutté est acide (pH moyen de 3,4) et une matière sèche moyenne de 35%. Les espèces bactériennes et fongiques dominantes identifiées sont Lactobacillus kefiranofaciens, Lentilactobacillus kefiri, Lactiplantibacillus plantarum et Lactococcus lactis ainsi que Geotrichum candidum et Pichia kudriavzevii. Après construction d’un lexique sensoriel, le labneh Ambaris a été décrit comme ayant un goût acide accompagné d’une odeur et d’une saveur de chèvre. Par comparaison des profils microbiens des produits issus des laits crus et des laits pasteurisés, il semblerait que le lait ne soit pas le seul facteur déterminant de la diversité microbienne (ou du moins pas directement), suggérant des rôles de la flore résidente chez le producteur. Dans la troisième partie de cette thèse, les résultats ont confirmé que les espèces coeur identifiées s’installent précocement dans le produit et y persistent jusqu’à la fin de la maturation avec des abondances variables selon le stade de fermentation. Ils ont aussi suggéré qu’au démarrage de la fermentation, l’éventuelle contribution des flores résiduelles de la jarre, agissant comme starter, serait une piste à explorer. Par la suite, les flores semblent s’équilibrer de façon à évoluer similairement et indépendamment du contenant/ de l’âge du contenant. Les résultats de cette thèse constituent un point de départ et méritent d’être poursuivis pour mieux comprendre les rôles fonctionnels des espèces majoritaires, des facteurs biotiques et abiotiques qui régissent la biodiversité microbienne de ce produit, dans l’objectif de protéger et de valoriser le labneh Ambaris, et in fine de lui donner une place au sein de l'économie nationale et mondiale
A Reversible Jump MCMC to Improve State-Space Exploration in Gaussian Bayesian Blind Deconvolution
Full text linkIn this paper, we consider the problem of sampling posteriors in Bayesian blind deconvolution with Gaussian priors. In this framework, naive Gibbs samplers are known to have state-space exploration issues: samples are highly correlated, leading to poor mixing within and between modes of the posterior distributions. To enable a faster convergence, we present a Reversible Jump Markov chain Monte Carlo (RJMCMC) algorithm that proposes new states located in high-probability regions. We assume that the latter have been established in a preliminary stage. We show that the proposed RJMCMC deeply enhances state-space exploration, even in the case of strongly multimodal posteriors