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Experimental Investigation of the Effect of Small Off-Surface Vortex Generator on the Aerodynamic Performance of NACA0012 at Low Reynolds Number
No full textInternational audienceThis study experimentally investigates the aerodynamic performance enhancement of a NACA0012 aerofoil at a low Reynolds number of Re c = 2.6 × 10 4 through passive flow control. A micro cylinder rod (diameter d = 1.34% of chord length) was positioned upstream of the leading edge at varying distances (1 × d to 4 × d) to function as a vortex generator. Wind tunnel measurements, including hot-wire anemometry (HWA) for wake characterization and parietal oil stain visualization for flow structure assessment, were conducted to evaluate the control effectiveness. At low angles of attack (<10°), the rod suppressed the nonlinear lift variation characteristic of baseline low-Reynolds-number flows. For higher angles (>10°), optimal rod placement produced a significant increase in lift coefficient. The parietal oil stain visualization revealed that the rod injected freestream momentum into the boundary layer, delaying flow separation and reducing wake width, which correlated with measured drag reduction. This visualization technique provided clear evidence of separation point movement and boundary layer modification, demonstrating the rod's effecti veness as a passive control device
Net external moment expressed at the Body Center of Mass under perturbations during gait
No full textInternational audienceGait instability evaluation lacks consensus on the best parameter. Despite its understandability, the net external moment at the body center of mass (MBCoM) is poorly used. This study explores the impact of external perturbations on counter-rotation movements during gait using MBCoM. So far, eight asymptomatic participants walked on a dual-belt instrumented treadmill under controlled slip and trip perturbations. MBCoM maximum value was significantly affected on the anteroposterior and mediolateral axes. This may reflect compensatory strategies to maintain balance, as seen in older adults. While findings offer insights into dynamic equilibrium and counter-rotation, this ongoing study needs more participants to strengthen conclusions
Étude de l'effet de la formulation et du vieillissement des élastomères sur leur inflammabilité
No full textPolymer components (polychloroprene, EPDM) are used by Air Liquide for their sealing properties in its oxygen production, transportation, and distribution systems. However, the presence of these materials in contact with oxygen poses a flammability risk in the event of a critical heat source. Throughout their lifecycle, these materials undergo aging and their properties change, primarily due to oxidation. The research in this thesis characterizes this evolution using a laser-induced ignition test. Aging in air leads to an increase in ignition resistance. This phenomenon is explained by two mechanisms: the migration of flammable additives (e.g., plasticizers) out of the material, and the cross-linking of the polymer network. Conversely, aging under pressurized oxygen radically alters this behavior. It promotes chain scission, which decreases the polymer's ignition resistance. Indeed, the presence of shorter, more mobile chains facilitates the formation of a flammable, hydrocarbon-rich gas phase. To improve performance, fillers such as carbon black are added to the polymers. These play a crucial role in stabilizing the material against oxidation, particularly through functional groups on their surface that scavenge radicals and decompose hydroperoxides. Furthermore, carbon black reinforces the material's structure, which enhances its mechanical properties, sealing performance, and overall ignition resistance. Estimating the service life of these polymers is therefore highly dependent on the aging conditions and their chemical composition.. To refine these predictions, it is essential to further investigate the co-oxidation mechanisms of EPDM as a function of oxygen concentration and pressure.The objectives of this thesis are thus:- on the one hand, to understand and model the degradation of EPDM and HNBR based materials used by the industry, in particular by relying on model materials. To this end, a detailed study of the structural and microstructural modifications will be carried out by relying on traditional methods of ageing monitoring (Infrared spectroscopy, DMA analysis,...) and methods available at the industry (elemental analysis, analysis of volatiles emitted during ageing...).On the other hand, to apprehend the effect of ageing by studying the abatement of properties for materials presenting degradation thresholds corresponding to different degrees of ageing "in real conditions". This will lead us to study the resistance to combustion and the properties associated with it (conductivity and thermal capacity ...) and oxygen barrier properties. All this will allow us to derive structure-property relationships that are new in the field of polymers.Air Liquide utilise des solutions de production, de transport et de distribution d’oxygène qui intègrent des pièces en polymères (polychloroprène, EPDM) pour leurs propriétés d’étanchéité. Cependant, la présence de ces matériaux au contact de l’oxygène constitue un risque d'inflammation en cas de présence d'une source critique de chaleur. Au cours de leur cycle de vie, ces matériaux vieillissent et leurs propriétés évoluent, notamment par effet de l'oxydation. Les travaux de cette thèse caractérisent l'évolution de la résistance à l'inflammation via un test d'ignition par source laser. Le vieillissement sous air mène à une augmentation de la résistance à l’inflammation. Ce phénomène s'explique par deux mécanismes : la migration des additifs inflammables (ex: plastifiants) hors du matériau et une réticulation du réseau polymère qui le densifie. À l'inverse, le vieillissement sous pression d’oxygène modifie radicalement ce comportement. Il favorise les coupures de chaînes, ce qui diminue la résistance à l’inflammation du polymère. La présence de chaînes plus courtes et plus mobiles facilite en effet la création d’une phase gazeuse riche en hydrocarbures inflammables. Pour améliorer la performance, des charges comme le noir de carbone, sont ajoutées aux polymères. Celles-ci jouent un rôle crucial en stabilisant le matériau face à l’oxydation, notamment grâce aux groupements fonctionnels présents à leur surface qui piègent les radicaux et décomposent les hydroperoxydes. De plus, le noir de carbone renforce la structure du matériau, ce qui améliore ses propriétés mécaniques, ses performances d'étanchéité et sa résistance globale à l’inflammation. L'estimation de la durée de vie de ces polymères dépend donc fortement des conditions de vieillissement et de leur composition chimique. Pour affiner ces prévisions, il est essentiel d'étudier de manière plus approfondie les mécanismes de co-oxydation de l’EPDM en fonction des concentrations et des pressions en oxygène.Les objectifs de cette thèse sont donc:D'une part, de comprendre et modéliser la dégradation des matériaux base EPDM et HNBR employés par l'industriel, notamment en s'appuyant sur des matériaux modèles. A cette fin, une étude fine des modifications structurales et microstructurales sera effectuée en s'appuyant sur des méthodes classiques de suivi du vieillissement (spectroscopie InfraRouge, analyse DMA,…) et des méthodes disponibles chez l'industriel (analyse élémentaire, analyse des volatils émis lors du vieillissement…). D'autre part, d'appréhender l'effet du vieillissement en étudiant l'abattement des propriétés pour des matériaux présentant des seuils de dégradation correspondant à différents degrés de vieillissement "en conditions réelles". Ceci nous conduira notamment à étudier la résistance à la combustion et les propriétés qui y sont associées (conductivité et capacité thermique …) et propriétés barrières à l'oxygène. L'ensemble nous permettra de dériver des relations structure-propriétés inédites dans le domaine des polymères
Système énergétique hybride pour l'île d'Ouessant : Commande floue appliquée à la gestion des énergies renouvelables et de l'hydrogène
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Modélisation semi-analytique des pertes cuivres d'une inductance planar
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Conception d'ondes mécaniques localisées contrôlées : application à l'haptique
No full textConducted within the framework of the multidisciplinary HASAMé project, this work aims to overcome the limitations of current surface haptic technologies, particularly in terms of energy efficiency and the spatial precision of tactile effects. The central objective is to generate localized vibration, allowing users to perceive tactile feedback such as textures, buttons, or directional cues directly on touch interfaces.To achieve this, two confinement approaches are explored: passive and active. Passive confinement leverages the geometric and material properties of periodic structures—such as mechanical pillars—to create localized vibratory zones through wave attenuation and mode conversion. These structures are designed and analyzed using analytical models based on beam and plate theories, as well as finite element simulations, with experimental prototypes validating their effectiveness.Active confinement, on the other hand, is implemented using networks of piezoelectric actuators and sensors integrated into the surface. Control strategies are developed based on modal superposition and implemented in a rotating reference frame, enabling real-time shaping of the vibration field. This approach allows not only for confinement but also for the generation of traveling waves, which are essential for inducing directional shear forces perceived at the user's fingertip.A major contribution of this thesis is the introduction of a modeling framework based on electrical analogy, using Mason's equivalent circuit, where each section of the vibrating surface is represented as a three-port electrical cell. This methodology provides a flexible tool for analyzing and designing complex haptic systems with distributed control.Experimental results obtained using custom-designed electronic boards and laser vibrometry confirm theoretical predictions, demonstrating precise vibration confinement and effective control of tactile responses. Ultimately, this work provides a comprehensive framework—spanning modeling, control, experimental implementation, and user-centered evaluation—for the development of next-generation haptic interfaces. It paves the way for intelligent, responsive surfaces applicable to automotive controls, medical devices, and interactive consumer electronics.Réalisés dans le cadre du projet pluridisciplinaire HASAMé, ces travaux visent à dépasser les limitations des technologies haptiques de surface actuelles, notamment en d'efficacité énergétique et de limitation spatiale des effets tactiles. L'objectif central est de générer une vibration localisée, permettant à l'utilisateur de percevoir des retours tactiles tels que des textures, des boutons ou des indications directionnelles directement sur des interfaces tactiles.Pour ce faire, deux approches de confinement sont étudiées : passive et active. Le confinement passif exploite les propriétés géométriques et matérielles de structures périodiques — comme des piliers mécaniques — pour créer des zones vibratoires localisées via l'atténuation d'ondes et la conversion de modes. Ces structures sont conçues et analysées à l'aide de modèles analytiques basés sur les théories des poutres et des plaques, ainsi que de simulations par éléments finis, et des prototypes expérimentaux valident leur efficacité.Le confinement actif, quant à lui, est réalisé au moyen de réseaux d'actionneurs et de capteurs piézoélectriques intégrés à la surface. Des stratégies de contrôle sont développées par superposition modale et mises en œuvre dans un référentiel tournant, ce qui permet de façonner en temps réel le champ vibratoire. Cette approche autorise non seulement le confinement, mais aussi la génération d'ondes progressives, essentielles pour induire des forces de cisaillement directionnelles perçues au bout du doigt de l'utilisateur.Une contribution majeure de cette thèse est l'introduction d'un cadre de modélisation par analogie électrique fondé sur le circuit équivalent de Mason, qui considère chaque section de la surface vibrante comme une cellule électrique à trois ports. Cette méthodologie offre un outil flexible pour l'analyse et la conception de systèmes haptiques complexes à contrôle distribué.Les résultats expérimentaux obtenus à l'aide de cartes électroniques spécialement conçues et de vibrométrie laser confirment les prédictions théoriques, montrant un confinement précis des vibrations et un contrôle efficace des réponses tactiles. Au final, ces travaux fournissent un cadre global — couvrant la modélisation, le contrôle, la mise en œuvre expérimentale et l'évaluation centrée utilisateur — pour le développement d'interfaces haptiques de nouvelle génération. Ils ouvrent la voie à des surfaces intelligentes et réactives applicables aux commandes automobiles, aux dispositifs médicaux et à l'électronique grand public interactive
Robust PSO‐Optimized Power Control for Stand‐Alone Variable‐Speed DFIG Wind‐Based High Stability and Power Quality Enhancement: Hardware Investigation‐Based dSPACE1103
No full textInternational audienceWind energy conversion systems (WECSs) operating in stand‐alone mode are increasingly recognized as a promising solution for delivering reliable renewable electricity in remote areas. However, their performance is often hindered by sudden wind speed fluctuations and parameter variations, which can compromise both stability and power quality. To address these challenges, this article presents a hardware implementation study of a direct power control (DPC) strategy applied to a doubly fed induction generator (DFIG) in variable‐speed WECSs. The proposed approach introduces a robust integral–proportional (IP) regulator for the rotor‐side converter (RSC), with its gains optimally tuned using the particle swarm optimization (PSO) algorithm. Control is performed through the direct and quadrature axis components of the rotor current using a back‐to‐back alternating current–direct current–alternating current converter. The methodology involves both simulation and real‐time implementation using the dSPACE dS1103 board, with system validation under subsynchronous and supersynchronous operating conditions. A Bode‐plot analysis is employed to compare the stability margins and response times of conventional and PSO‐optimized control schemes. Both simulation and experimental results demonstrate that the proposed strategy ensures high stability, accurate reference tracking, and effective decoupling of active and reactive power, even under sudden wind speed variations. Moreover, it achieves superior dynamic responses, shorter settling times, and significantly reduced power errors, thereby confirming its suitability for enhancing the performance and reliability of stand‐alone wind energy systems
Investigating major head loss in additively manufactured sand molds during casting
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First principles investigation of Radio-oxidation mechanisms in polyethylene
No full textInternational audienceKinetic simulations of radio-oxidation in polymers follows schemes developed several decades ago; recent updates on the list of relevant mechanisms as well as corresponding rates are mostly indirectly extracted from experiment [1]. In this paper we describe some recent advances in the investigation of atomic scale mechanisms relevant for aliphatic polymer oxidation taking the example of polyethylene. Based on a polymer model manageable by first principles calulations, but stil containing the main features of a semi-crystalline polymer, we determine relevant energy barriers and we corroborate our findings with first principles molecular dynamics simulations. Our calculations are based on density functional theory with a van der Waals exchange-correlation functional and, in some cases, we resort to a hybrid functional for comparison.After verifying the main reactions involved in the standard basis coxidation scheme [1], in particular the formation and decomposition of hydroperoxides [2], we investigate several reactions involving alkoxy radicals, which can originate from bimolecular reactions between peroxy radicals [3]. The results clearly show the crucial role of this radical in the whole radio-oxidation kinetic path.Furthermore, we consider the radical scavenging capacities of phenolic antioxidants, taking butylated hydroxy-toluene (BHT) as a prototype. Using static and dynamic simulations, we highlight the fact that BHT can easily eliminate alkoxy radicals which trigger the initiation of radio-oxidation [4].[1] J. L. Bolland, G. Gee, Trans. Faraday Soc. 42, 236 (1946).[2] Y. Ahn, X. Colin, G. Roma, Polymers 13, 2143 (2021).[3] Y. Ahn, G. Roma, X. Colin, Macromol. 55, 8676 (2022).[4] Y. Ahn, G. Roma, X. Colin, J. Phys. Chem. B 128, 12258 (2024)
