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Experimental aeroelastic analysis of flexible rotating blades with optical laser vibrometer
No full textExperimental analysis of fluid-structure interactions on flexible rotating blades in real operational conditions is a useful tool to understand the behavior of the structure undergoing aeroelastic phenomena. Moreover, it represents a challenging task as well since external interference sources could alter the studied phenomena. For instances, the instrumentation to measure the dynamic deformations must consist of non-intrusive technical means without perturbing the systems. In this context, an experimental test bench is developed and it is presented with the equipped sensor for the aeroelastic analysis purpose. Modal analysis of the rotating flexible blades, through a scanning laser vibrometer equipped with a derotator system, has been held and aerodynamic performance measurements through the dynamic torque have been performed. Finally, experimental Campbell diagrams have been plotted to detect the potential modal coupling between bending and torsional frequencies within the interval of the operational rotating speed of the test bench
Comprehensive Characterization of Agricultural By-Products for Bio-Aggregate Based Concrete
Full text linkThe valorization of available agricultural by-products is important for the development of bio-aggregate based concretes as eco-friendly solutions for building materials. However, their diversity requires to assess their potential of use in vegetal concretes. This study aims to propose simple and relevant multi-physical characterization methods for plant aggregates. Basic and complementary characterizations were carried out on hemp shiv as a reference plant aggregate, and nine by-products available in the South-West part of France, i.e., oleaginous flax shiv, sunflower pith and bark, coriander straw, wheat straw, wheat chaff, corn shuck, miscanthus stem and vine shoot. The basic characterizations performed were those recommended by the TC-RILEM 236 BBM, i.e., particle size distribution, bulk density, water absorption and thermal conductivity. Complementary characterizations have also been proposed, taking into account the possible environment of the binder and the vegetal concrete manufacturing method. The additional tests developed or adapted from previous research assess the following properties: the content of water-soluble compounds at pH 7 and 12, the dry density of plant aggregates compacted in wet state, the real water absorption after compaction and the compression behavior of these compacted aggregates. This complete characterization highlights the distinct behavior of the different agroresources and allows to correlate these characteristics to the use properties of hardened composites
Fabrication of a pH microsensor for local pH measurement during chromium electrodeposition from a trivalent chromium-based electrolyte
Full text linkIn this work, the pH conditions during chromium electrodeposition are investigated using a home-made pH microsensor and scanning electrochemical microscopy (SECM). Few studies have focused on measuring local pH during metal electrodeposition and none has been conducted during chromium electrodeposition. The novelty of this work is the study of the local pH during chromium electrodeposition in very acidic (pH 1 mol·L−1). Along with several other determinants, pH is a key factor in achieving an even metallic deposit. pH buffers and complexing agents are often used for this purpose but in the vicinity of the electrode, at the electrode/electrolyte interface, strong variations are highly likely to occur. For this reason, a pH microelectrode has been developed to scan the pH gradient during the electrodeposition of chromium. This is based on an iridium oxide-modified microelectrode, since iridium oxide has been reported to be suitable for local pH sensing. The thermal treatment of iridium oxide (IrOx) has also been studied. The deposition of a Nafion layer on top of the oxide has also been shown to achieve good selectivity and good stability while maintaining a reasonable level of sensitivity. An optimized IrOx microelectrode was obtained and used as a SECM microelectrode to investigate the evolution of the pH at the electrode/electrolyte interface during electrodeposition. The results are promising and will enable us to further develop our understanding of chromium electrodeposition
The influence of gravity on granular impacts II. A gravity-scaled collision model for slow interactions
Full text linkSlow interactions on small body surfaces occur both naturally and through human intervention. The resettling of grains and boulders following a cratering event, as well as observations made during small body missions, can provide clues regarding the material properties and the physical evolution of a surface. In order to analyze such events, it is necessary to understand how gravity influences granular behavior. In this work, we study slow impacts into granular materials for different collision velocities and gravity levels. Our objectives are to develop a model that describes penetration depth in terms of the dimensionless Froude number and to use this model to understand the relationship between collision behavior, collision velocity, and gravity. We use the soft-sphere discrete element method to simulate impacts into glass beads under gravitational accelerations ranging from 9.81 m/s^2 to 0.001 m/s^2. We quantify collision behavior using the peak acceleration, the penetration depth, and the collision duration of the projectile, and we compare the collision behavior for impacts within a Froude number range of 0 to 10. The measured penetration depth and collision duration for low-velocity collisions are comparable when the impact parameters are scaled by the Froude number, and the presented model predicts the collision behavior well within the tested Froude number range. If the impact Froude number is low (0 < Fr < 1.5), the collision occurs in a regime that is dominated by a depth-dependent quasi-static friction force. If the impact Froude number is high enough (1.5 < Fr < 10), the collision enters a second regime that is dominated by inertial drag. The presented collision model can be used to constrain the properties of a granular surface material using the penetration depth measurement from a single impact event. If the projectile size, the collision velocity, the gravity level, and the final penetration depth are known and the material density is estimated, then the internal friction angle of the material can be deduced
Key Note Address at SCIFI-IT'2022
Full text linkLooking at novel technologies that step-by-step are coming into our lives, we can be impressed by the results, by the possibilities new products offer, and by the way they slowly change our lives as well. These networked technologies are often communicating continuously with other systems and have a certain degree of autonomy for taking decisions. Such “Cyber Physical Systems” (CPS), with sometimes the human in the loop, pose real challenges to industries. Looking from a systems design point of view, such new technologies tend to increase the complexity a designer or an engineer needs to manage. Characterised by multiplicity, by interdependence, by a certain degree of heterogeneity, with continuous interactions, and overall with a product or system behaviour that is difficult to predict, such systems, such systems are also difficult to validate. And, if it concerns safety-critical embedded systems, to get those systems certified.
Still, this is a road that is taken, and when looking for example at autonomous vehicles of autonomous drones, such technologies are being considered, so to be able to cover the stakeholder requirements, or more in general the expectations from our society. So, what to do about them… This presentation aims at analysing the challenges and to propose a methodology to support the design process. Starting from a new value-based approach to system design and engineering, research directions are suggested for the coming years, so to be able to prepare the future
Detailed Numerical Simulation of Multi-Dimensional Plasma Assisted Combustion
Full text linkInteraction between flames and plasmas are the guiding thread of this work. Nanosecond Repetitively Pulsed (NRP) discharges are non-thermal plasmas which have shown interesting features for combustion control. They can interact with flames not only through heat, but also chemically by producing active species. In this work, fully-coupled plasma assited combustion simulations are targeted. To achieve this goal, plasma discharge capabilities are built in the low temperature plasma code, AVIP. The corresponding numerical methods, as well as validation cases regarding each set of equations, are first presented. To simulate plasma discharges, the coupled drift-diffusion equations and the Poisson equation are considered. AVIP is coupled to the AVBP code which solves the reactive Navier-Stokes equations to describe combustion phenomena. In a second part, we start by constructing and validating a fully-detailed chemistry for methane-air mixtures in zero-dimensional reactors before reducing it for multi dimensional simulations. The multi-dimensional streamer simulation capabilities of the code are then assessed using simple chemistries. All the validated parts of the code come together in a fully detailed simulation of ignition using NRP discharges. We finish by discussing phenomenological models built upon the knowledge that we gained from fully-detailed simulations. In a last part, finally, attempt to solve the Poisson and generalized Poisson equations using neural networks, which have a potential for speedup compared to classical linear solvers, is carried out
Collage réversible au service de la démontabilité
Full text linkL’objectif principal est de développer un système adhésif structural ou semi-structural interfacial stimulable thermiquement et permettant un démontage propre des films de peinture secs développés par Corso Magenta. La formulation proposée mettra en jeu deux systèmes thermosensibles pouvant conduire à la démontabilité de pièces collées. Ces systèmes associent des réactions thermoréversibles pour la réversibilité du collage, au moussage par voie chimique du matériau pour la séparabilité des pièces assemblées. Aujourd’hui la «démontabilité» des structures collées est recherchée pour diverses raisons tels la récupération des substrats pour faciliter la réutilisation et le recyclage de ces ressources. Les pratiques actuelles de démontage pour une structure collée font appel à des actions mécaniques de raclage souvent associées à la dégradation thermique de l’adhésif. Il en résulte une diminution des propriétés intrinsèques des substrats. De plus les méthodes de démontage recherchées doivent être faciles et peu coûteuses avec une séparation nette des substrats sans résidu adhésif laissant au moins une surface propre. Le collage structural implique une transmission quasi-totale de l’effort d’un substrat à l’autre sur la durée de service, effort très souvent élevé dans nombres d’application tels que les transports. Cette exigence impose d’emblée que le procédé de «démontabilité» n’altère pas les propriétés du système adhésif d’origine sur sa durée de fonctionnement
Enabling Blockchain Services for IoE with Zk-Rollups
Full text linkThe Internet of Things includes all connected objects from small embedded systems with low computational power and storage capacities to efficient ones, as well as moving objects like drones and autonomous vehicles. The concept of Internet of Everything expands upon this idea by adding people, data and processing. The adoption of such systems is exploding and becoming ever more significant, bringing with it questions related to the security and the privacy of these objects. A natural solution to data integrity, confidentiality and single point of failure vulnerability is the use of blockchains. Blockchains can be used as an immutable data layer for storing information, avoiding single point of failure vulnerability via decentralization and providing strong security and cryptographic tools for IoE. However, the adoption of blockchain technology in such heterogeneous systems containing light devices presents several challenges and practical issues that need to be overcome. Indeed, most of the solutions proposed to adapt blockchains to devices with low resources confront difficulty in maintaining decentralization or security. The most interesting are probably the Layer 2 solutions, which build offchain systems strongly connected to the blockchain. Among these, zk-rollup is a promising new generation of Layer 2/off-chain schemes that can remove the last obstacles to blockchain adoption in IoT, or more generally, in IoE. By increasing the scalability and enabling rule customization while preserving the same security as the Layer 1 blockchain, zk-rollups overcome restrictions on the use of blockchains for IoE. Despite their promises illustrated by recent systems proposed by startups and private companies, very few scientific publications explaining or applying this barely-known technology have been published, especially for non-financial systems. In this context, the objective of our paper is to fill this gap for IoE systems in two steps. We first propose a synthetic review of recent proposals to improve scalability including onchain (consensus, blockchain organization, …) and offchain (sidechain, rollups) solutions and we demonstrate that zk-rollups are the most promising ones. In a second step, we focus on IoE by describing several interesting features (scalability, dynamicity, data management, …) that are illustrated with various general IoE use cases
Apprentissage automatique profond pour la modélisation de sous-maille en simulations aux grandes échelles de combustion prémélangée turbulente
Full text linkDans un siècle défini par le changement climatique et l'abondance de données, la combustion se dirige vers de nouvelles opportunités créées par la révolution numérique. Les simulations aux grandes échelles (Large Eddy Simulations, LES) de systèmes de combustion à échelle réelle deviennent réalisables, mais leur capacité prédictive se base sur la précision de modèles de sous-maille (Subgrid-Scale, SGS) qui tiennent compte de l'activité de combustion turbulent non résolue. L'apprentissage automatique profond (Deep Learning, DL) a récemment été utilisé pour entraîner des modèles SGS basés sur les données qui atteignent une excellente précision lors de tests a priori. Toutefois, il n'y a toujours presque pas d'applications de modèles DL SGS à des LES de systèmes de combustion industriels. Ces travaux s'intéressent à trois éléments qui doivent être étudiés pour permettre l'adoption du DL dans des LES de combustion turbulente prémélangée : l'évaluation de modèles DL sur des cas tests à haut Reynolds, l'assurance de leur capacité à généraliser au-delà de leur configuration d'entraînement, et l'implémentation d'une intégration efficace de modèles DL à des solveurs LES haute performance. Trois modèles DL incluant graduellement chacun de ces éléments sont développés. Ils sont basés sur des réseaux de neurones convolutionnels (Convolutional Neural Networks, CNNs) U-Nets entraînés sur des instantanés filtrés et déraffinés de simulations numériques directes. Premièrement, un modèle pour la densité totale de surface de flamme est entraîné sur la flamme de jet turbulente à haut Reynolds R2. Une excellente généralisation a priori à de plus hauts nombres de Reynolds et à des instantanés LES est observée, et des aperçus sur le fonctionnement interne du modèle sont proposés. Dans un second temps, un modèle CNN pour la variance SGS de la variable de progrès est entraîné sur une flamme plane turbulente statistiquement stationnaire. Avec une formulation Pfitzner du terme source et une fermeture beta densité de probabilité, il est capable de prédire a priori avec précision la variance SGS et le taux de réaction filtré sur la flamme de jet R2, démontrant ainsi sa capacité à généraliser à de nouvelles configurations. Troisièmement, la stratégie de couplage AVBP-DL est développée pour permettre à des modèles DL d'être interrogés par le solveur AVBP avec un surcoût de calcul négligeable. Enfin, le cas test d'explosion aérée et obstruée Masri est utilisé pour tester a posteriori un modèle CNN pour le facteur de plissement SGS entraîné sur la flamme plane turbulente statistiquement stationnaire. Le modèle prédit la bonne suppression maximale, mais ceci résulte d'une compensation entre un plissement excessif lors de la phase initiale laminaire et d'un plissement insuffisant durant l'étape critique de propagation turbulente. Plusieurs tentatives de correction de ce comportement sont ensuite explorées
Étude du vieillissement de pièces en matériaux composites à matrice organique de moteurs d’aéronefs et de ses conséquences sur leur réparation collée
Full text linkCe travail vise à étudier les conséquences du vieillissement hygrothermique sur la réparation collée de matériaux composites tissés 3D carbone/époxy, qui constituent les aubes fans du moteur CFM LEAP. Dans un contexte d’introduction massive de pièces en matériaux composites à matrice organique dans les moteurs d'avions, la maîtrise de leur réparation, notamment par collage, devient essentielle et prend de l'essor. L'optimisation de ces réparations collées est rendue possible par l'utilisation de traitements de surface, comme le traitement plasma atmosphérique dont l'intérêt a déjà été prouvé. Cependant, ces pièces en composite sont sensibles aux conditions climatiques dans lesquelles elles évoluent, notamment la chaleur et l'humidité, et subissent de ce fait des dégradations. La première étape de ce travail a permis de mettre en lumière les paramètres influençant la diffusion d'humidité via une étude statistique. Par la suite, l'analyse des effets vieillissement hygrothermique sur les matériaux composites tissés 3D a mis en évidence des altérations physico-chimiques, massiques et surfaciques, telles que la migration de particules, un lessivage de la matrice, ou l'apparition de fissures, ce qui va affecter l'efficacité des collages. L'utilisation du plasma atmosphérique sur le matériau vieilli a montré un effet désorbant sur les surfaces et des niveaux d'oxydation semblables à ceux des surfaces neuves traitées au plasma, ce qui pourrait permettre d'activer chimiquement la surface en vue d'un collage et de restaurer certaines de ses propriétés. La caractérisation mécanique via des tests d’adhérence des assemblages matériau composite vieilli/colle a montré une nette amélioration de la résistance mécanique suite à l’utilisation du traitement de surface par plasma