21549 research outputs found
Sort by
Improving damping capabilities of composites structures by electroactive films containing piezoelectric and conductive fillers
Get PDFIn this paper, a passive vibration damping concept based on multifunctional materials was studied for thermoplastic composite structures. The synergy between piezoelectric and conductive particles brings a new contribution of energy dissipation based on the local transduction-dissipation phenomenon. While piezoelectric fillers ensure the conversion of mechanical energy into electrical energy (transduction), conductive particles locally dissipate the electric charges created avoiding saturation in the vicinity of piezoelectric particles. Here, the concept has been studied at material and structure scales for laboratory and preindustrial samples in order to bring solid proof of the damping concept. For this purpose, piezoelectric and electrically conductive particles were dispersed into engineering thermoplastics polyamide 12 and poly ether ketone ketone. Damping films were obtained by hot press and embedded in a composite sandwich beam and carbon fiber reinforced polymer (CFRP)-aluminum panels. Dynamic mechanical analysis and vibration tests were performed on bulk nanocomposite samples and in composite sandwich beams. The study of hysteresis loops and frequency response function showed strong nonlinear effects and vibration amplitude decrease up to 50%. Tests on CFRP-aluminum panels highlighted the structural damping increase demonstrating the potential capacity of this multifunctional material for energy dissipation in typical aerospace structures
Simulation and evaluation of sustainable climate trajectories for aviation
Get PDFIn 2019, aviation was responsible for 2.6% of world CO2 emissions as well as additional climate impacts such as
contrails. Like all industrial sectors, the aviation sector must implement measures to reduce its climate impact.
This paper focuses on the simulation and evaluation of climate scenarios for air transport. For this purpose, a
specific tool (CAST for “Climate and Aviation - Sustainable Trajectories”) has been developed at ISAE-SUPAERO.
This tool follows a methodology for the assessment of climate impacts adapted to aviation. Firstly, models for the
main levers of action, such as air traffic, aircraft energy consumption and energy decarbonization, are provided using trend projections from historical data or assumptions from the literature. Second, the evaluation of scenarios is based on aviation carbon budgets, which are also extended to non-CO2 effects using the concept of
GWP*. Several scenario analyses are performed in this paper using CAST allowing different conclusions to be
drawn. For instance, the modelling of the scenarios based on the more recent ATAG (Air Transport Action Group)
commitments shows that aviation would consume 6.5% of the world carbon budget for +1.5 ◦C. Some illustrative
scenarios are also proposed. By allocating 2.6% of the world carbon budget to aviation, it is shown that air
transport is compatible with a +2 ◦C trajectory when the annual growth rate of air traffic varies between +1.8%
and +2.9%, depending on the technological improvements considered. However, using the same methodology
for a +1.5 ◦C trajectory shows that a drastic decrease in air traffic is necessary. Lastly, analyses including non-
CO2 effects emphasize the importance of implementing specific strategies for mitigating contrails
Pilotage optimal des utilités industrielles : méthodologie et processus décisionnel reposant sur le formalisme ERTN
Get PDFLongtemps considérée comme un objectif secondaire, la gestion optimale des utilités (énergie, eau, etc.) sur les sites industriels est désormais un enjeu économique et environnemental majeur. Outre la dynamique importante du marché des combustibles et les quotas d’émissions de CO2, les sites industriels doivent faire face à de nombreuses contraintes d’ordre technique, organisationnel et réglementaire. Dans le même temps, les exploitants cherchent à tirer profit des opportunités de valorisation économique des flux énergétiques co-produits proposées par le marché. Des outils logiciels qualifiés de Systèmes de Management de l'Energie (SME) sont proposés aux industriels pour faciliter la gestion de ces systèmes multifactoriels. Actuellement, la plupart des applications disponibles sur le marché proposent essentiellement des fonctions de suivi en temps-réel (visualisation, évaluation d’indicateurs de performance). S’il s’agit d’une première étape, la variabilité des besoins et les contraintes opérationnelles des équipements ont fait naître le besoin d’anticiper et de planifier la production des utilités pour optimiser la performance industrielle. Inclure un outil d’optimisation des flux au sein des SME de nouvelle génération permet de proposer de véritables solutions d'aide à la décision pour le pilotage et le contrôle de performance des systèmes industriels. L’introduction d’une telle fonction nécessite la mise en place d’un « jumeau numérique » de l’unité considérée. Du point de vue des développeurs de solutions, un des enjeux est de disposer d’outils de modélisation des processus de production, généraux et flexibles, qui leur permettent de réduire les temps de développement des applications tierces. C’est précisément dans cet objectif que ces travaux de thèse ont été menés. Si le modèle exécutable au cœur de l’application s’appuie sur une formulation de Programmation Linéaire Mixte (PLM), un des principes fondateurs de ces travaux est de proposer aux développeurs un modèle graphique formel de description de tout système de production. Ce niveau d’abstraction fait l’interface entre la représentation « métier » et le modèle exécutable et évite en grande partie la réécriture des équations fondamentales communes à tout processus industriel. Cette approche conceptuelle qui se veut la plus générique possible, est mise en œuvre grâce au formalisme Extended Resource-Task Network (ERTN) Sur le plan pratique, ces concepts ont été intégrés à des composants logiciels permettant le prototypage rapide et le développement d’applications dédiées au pilotage et à l’analyse de la performance des systèmes énergétiques. La pertinence et l’applicabilité des outils développés dans cette thèse ont été prouvées par leur mise en application sur différentes unités industrielles réelles, dont la centrale d’utilités d'un site de pétrochimie-raffinage en France. Ce site, dont la partie production d'utilités est composée de plus de 50 équipements de production, possède aussi la plus grande unité française de cogénération (d'une puissance de 250 mégawatts électriques
Effect of size, concentration, and nature of fillers on crystallinity, thermal, and mechanical properties of polyetheretherketone composites
Get PDFPolyetheretherketone (PEEK) composites exhibit high stiffness, chemical stability, and heat resistance and they are therefore employed in applications under severe operating environments. This work aims to provide insight into the effect of the size, concentration, and type of fillers on the thermal and mechanical properties of PEEK. A total of 32 composites are used to highlight the influence of nature (lamellae, such as boron nitride and graphite and silicon carbide and alumina), size (nano and micrometric), and content (2.5, 5, 7.5, and 10 vol%) of fillers. The melting temperature and lamellar thickness did not change regardless of the nature of the filler. The thermomechanical analysis demonstrates that lamellar fillers form a percolating network and contribute significantly to the enhancement of the storage modulus. The increase in the storage modulus is proportional to the filler content, and it is more pronounced for micro composites. As expected, the percolating network is formed at lower concentrations for lamellar fillers than for spherical ones. The highest conductivity is achieved with graphite at 0.823 W/(m·K), which is twice that of PEEK for 10 vol%. Moreover, the use of micrometric fillers results in thermal conductivity enhancement attributed to the higher amount of efficient hot zones for heat transfer
Dissipative Shallow Water Equations: a port-Hamiltonian formulation
Get PDFThe dissipative Shallow Water Equations (DSWEs) are investigated as port-Hamiltonian systems. Dissipation models of different types are considered: either as nonlinear
bounded operators, or as linear unbounded operators involving a classical diffusion term in 1D, or the vectorial Laplacian in 2D. In order to recast the dissipative SWE into the framework of pHs with dissipation, a physically meaningful factorization of the vectorial Laplacian is being
used, which nicely separates the divergent and the rotational components of the velocity field.
Finally, the structure-preserving numerical scheme provided by the Partitioned Finite Element Method (PFEM) is applied to the nonlinear bounded dissipative fluid models. For the linear unbounded cases, a change of variables is highlighted, to transform the DSWEs into a new pHs
with a polynomial structure, which proves more suitable for numerics
Pegasus Project Technical Report
Get PDFThis paper is a theoretical study about the implementation of a Global Navigation Satellite System around the Moon. The objective of the study is to investigate from the feasibility to the implementation of such a system within the framework of a broader project which aims to see humans activities back on the Moon in the next decade. In that order, the system is complying with technical specifications as defined by a client. The rationale behind the system is that to reach a satisfying level of performance - and therefore meet the client’s requirements - a constellation of twenty-one satellites spread out on three orbits around the Moon at a constant semi-major axis of 10,000 [km] is needed. The constellation is named after the Greek divinity Pegasus and in reference to the star constellation. Each orbit is set at an 80 [◦] inclination and respectively spaced at 120 [◦] from one another with regard to their Right Ascension of Ascending Node. There are seven satellites per orbit. Every Pegasus’s satellites carry on-board four atomic clocks, three Emergency Broadcast System antennas, two Tracking, Telecommand and Control antennas and one navigation antenna. Maneuvers for station-keeping and end-of-life are ensured by four 1500 [W] hall effect thrusters mounted on two robotic arms with six degrees of freedom. 150 [kg] of Xenon will be used as propellant so that the mission can be carried out for at least ten years. A Pegasus satellite has a dry mass of 711.04 [kg] and a wet mass of 860.64 [kg]. Regarding the service provided on the lunar surface and its low orbit, the Pegasus constellation guarantees a 100% GNSS and Emergency broadcast availability with a 6.80 [m] global precision at 3σ and a 33 [ns] time precision. All the subsystems are powered by a 50 [V] Power Conditioning Unit and 165 [Wh/kg] Li-on battery which will be recharged by 15 [m2] of solar panels and used during eclipses. The overall dimensions of one Pegasus spacecraft are 2.34 [m] × 1.480[m] × 1.284[m]. One full orbital plane of the constellation can be launched by one Ariane 64, which guarantees its implementation with only three launches, fulfilling a deployment time span inferior to a year
Exposition orale à l'argent colloïdal en condition de fonction barrière digestive intègre puis fragilisée : quels impacts croisés sur l'épithélium, le mucus et le microbiote intestinal?
Get PDFL’argent colloïdal, défini comme une suspension de particules d’argent, majoritairement de taille nanométrique (<100 nm), dans un liquide, est une catégorie de produits disponibles dans le commerce et vendu pour les bienfaits annoncés pour la peau mais également pour une meilleure santé digestive. En effet, Il est connu pour ses propriétés antimicrobiennes, spécifiques à l’argent sous forme de nanoparticules (AgNP) et/ou sous forme ionique (Ag+), via des mécanismes tels que la déstabilisation de la membrane cellulaire ou encore la production d’espèces réactives de l’oxygène. L’intérêt des nanoparticules réside dans les propriétés mécaniques, physico-chimiques ou biologiques uniques que leur confèrent leurs dimensions réduites. Toutefois, les dangers liés à l’usage de l’argent colloïdal pour l’organisme sont encore peu documentés et représentent une inquiétude croissante en santé publique. Les données sur l’ingestion d’argent colloïdal et son impact sur la fonction barrière de l’intestin, première surface d’exposition par voie orale, sont manquantes. A ce jour, les études menées sur les effets de l’argent ionique (sous forme AgNO3 principalement) ou nanoparticulaire (nanoparticules modèles synthétisées en conditions de laboratoire) sur l’épithélium, le mucus et le microbiote intestinal sont parcellaires, contradictoires, et ne prennent pas en considération les interrelations entre ces différents acteurs. Par ailleurs, les études de la littérature ont systématiquement été réalisées en condition de fonction barrière de l’intestin intègre. Or, une condition de barrière fragilisée, provoquée notamment par un stress psychologique chronique, peut être retrouvée pour une partie de la population générale. Ces personnes peuvent être d’autant plus sensibles aux bénéfices santé annoncés sur le bien-être intestinal. Nos travaux portent, pour la première fois, sur l’évaluation des conséquences d’une exposition répétée à deux produits d’argent colloïdal disponibles sur le marché à des doses « réalistes », tant sur des modèles cellulaires in vitro mimant l’épithélium intestinal, que in vivo lors d’une exposition orale sub-chronique de 28 jours chez la souris mâle adulte en condition de fonction barrière intestinale intègre ou fragilisée par l’induction d’un stress psychologique chronique. Une composition distincte entre les deux produits a été mise en évidence en termes de ratio AgNP/Ag+, conduisant à des différences de toxicité observées à la fois in vitro et in vivo. Ces travaux montrent pour la première fois les effets sur la fonction barrière intestinale de produits commercialisés et directement consommés par l’Homme, au cours d’une exposition répétée, et soulignent l’importance de considérer la composition exacte de ces produits et la prise en considération de l’action conjointe du stress chimique et du stress psychologique
Pilot-Scale Lanthanide Precipitation from Sulfate-Based Spent Ni-MH Battery Leachates: Thermodynamic-Based Choice of Operating Conditions
Get PDFAccess to critical metals required for high-performance technologies, particularly, the light rare earth elements (REEs = La, Ce, Nd, Pr), has become a major challenge for import-dependent economies such as the European Union. In this regard, the recycling of spent nickel metal hydride (Ni-MH) batteries by hydrometallurgical processes can serve as an attractive secondary source of REEs. In such processes, precipitation of REEs from pregnant leach solutions (PLS) in sulfate media using Na2SO4 is often reported. However, little consideration is given as to whether and how sodium ions influence the precipitation efficiency and selectivity. This work focuses on a better understanding of the precipitation process by coupling pilot-scale (2 L) experiments on industrially sourced PLS containing 50 g/L of Ni and 17 g/L of REEs, with thermodynamic modeling, to assess the influence of temperature (25 °C < T < 60 °C) and the Na/REEs molar ratio (0.8:1 < Na/REEs < 3.2:1). Equilibria calculations were performed using OLI Systems Inc. software whose database covers rare earth sulfate compound properties and an accurate description of the aqueous electrolytes. Highly selective precipitation was obtained at 60 °C and for a Na/REEs molar ratio of 4:1. A lanthanide-alkali solid solution was identified by multianalytical characterization
Effect of the presence of solid particles, on the vanadyl sulfate (VOSO4) oxidation current
Get PDFThis study considers the effect of mechanical stirring of V(IV) solutions and of the presence of solid suspensions on the VO(aq)2+ oxidation current measured on a graphite electrode, with the objective of a better understanding of the electrochemical reactions taking place in a vanadium redox flow battery (VRFB). Our research question was to determine whether the presence of different kind of solid particles (inert glass spheres, VOSO4 powder and nanometric ketjen black (KB)) could be beneficial to the electrochemical performances of the VRFB. The experimental method consisted in measuring the anodic limiting current of a VOSO4-H2SO4-H2O solution on a rotating graphite cylinder, by linear sweep voltammetry. In the absence of solid particles, we show that the mass transfer coefficient dependence against the angular velocity of both the electrode and an additional stirrer obey to a power law (k = f(ωγ)) with an exponent γ found to be lower than the theoretical value. The beneficial effect on the mass transfer of VO2+ at the interface observed with low fraction of inert glass particles dramatically disappears as the spheres fraction increases. This is attributed to the decrease of the available free volume for the diffusion. When the solid consists of VOSO4 particles, the anodic current decreases as the mass fraction of the solid increases, which demonstrates the absence of any significant beneficial effect of the dissolution of the VOSO4 grains in the diffusion layer. Conversely, an important increase (~ 40%) of the oxidation current is observed when KB particles were introduced at low fractions (0.15%) in the bulk, thanks to the electronic percolation created by the KB. However, this beneficial effect disappears for higher mass fraction of both vanadium or KB solid particles, because of the destruction of the aggregates enabling the electron to be driven into the bulk
Space-Time Plasma-Steering Source: Control of Microwave Plasmas in Overmoded Cavities
Get PDFRecently, space-time plasma-steering source has been proposed as an innovative microwave plasma source to meet the challenge of controlling plasmas in overmoded cavities. This concept has been successfully demonstrated experimentally, allowing the space-time control of nanosecond microwave plasmas on initiators. This paper gives insights into the path that shall be taken to reach full space-time control of plasmas in overmoded cavities. To that end, a key criterion, namely the “plasma-steering criterion,” is introduced and verified with a numerical model. This criterion must be respected for an accurate space-time control of plasmas in overmoded cavities. The usefulness of the plasma density (depending on its value with respect to the critical plasma density) on the plasma-control capabilities is also highlighted