Fluid Forces on a Circular Cylinder Moving Transversely in Cylindrical Confinement: Extension of the Fritz Model to Larger Amplitude Motions

International audienceThis paper is related to the fluid forces prediction on a rapidly moving circular cylinder in cylindrical confinement. The Fritz model, which mainly assumes infinitesimal motions of the inner cylinder in an inviscid fluid, is one of the simplest model available in the scientific literature and is often used by design engineers in the nuclear industry. In this paper, simple non-linear expressions of fluid forces are derived for the case of finite amplitude motions of the inner cylinder. Assuming a potential flow, advection term and geometrical deformations can be taken into account. The problem, formulated as a boundary-perturbation problem, is solved thanks to a regular expansion. The range of validity of the approximate analytical solution thus obtained is theoretically discussed. The results are also confronted to numerical simulations, which allows to emphasize some limits and advantages of the analytical approach

Contrôle optimal de la qualité de l’air dans une cavité bidimensionnelle par réduction de modèle

L’objectif à terme de la présente étude est d’agir sur l’écoulement pour contrôler la dispersion du polluant dans une pièce. L’utilisation des méthodes de réduction de modèle offre à cet égard des perspectives intéressantes. Le contrôle de la dynamique de l'écoulement est réalisé ici en jouant sur l’intensité du fluide injecté par les différentes entrées d’une cavité bidimensionnelle

Un modèle élasto-dynamique pour l’étude de la dynamique de coques immergées assujetties à une onde de choc de faible intensité

La dynamique transitoire de coques circulaires vides ou contenant un fluide, immergées dans un milieu fluide infini et assujetties à une onde de choc externe, est considérée ici. Un modèle élasto-dynamique est développé. L’approche est semi-analytique, et basée sur la transformation de Laplace en temps et des séries de Fourier associées à la méthode de séparation des variables en espace

Application of a two-step fluid-structure approach for the analysis of large deformations and linear vibrations of propeller blades with embedded viscoelastic material

In this paper, a simplified numerical approach is applied to the analysis of the linear vibrations of aluminum or composite marine propeller blades with embedded viscoelastic films, around a predeformed nonlinear state. This approach allows to evaluate in a sequential way the nonlinear deformation, induced by the generation of lift (propulsion phenomenon), and the acoustic power emitted (vibroacoustic phenomenon) of a non-cavitating flexible marine propeller blade. For a given incident flow, the deformation of an aluminum blade is much smaller than that of a composite blade. The composite blade’s deformation has a significant positive impact on lift generation whereas the deformation of the aluminum blade tends to reduce traction. The dynamic characteristics of the aluminum blade at rest and under the fluid induced static load are similar, while those of the composite blade are very different in these two cases. The simplified two-step approach proposed in this study is therefore useful to accurately assess the emitted sound power by the vibrating blades

Investigation of Numerical Hydrodynamic Performance of Deformable Hydrofoil (Applied on Blade Propeller)

The hydrofoil is a hydro-lifting surface that significantly contributes to marine transportation such as a boat, ship, and submarine for its movement and maneuverability. The existing hydrofoils are in fixed-shaped National Advisory Committee for Aeronautics (NACA) profiles, depending merely on the variation of Angle of Attack (AOA) such as rudder, hydroplane, and propeller blade. This research is concerned with the deformable hydrofoil that aims at modifying its NACA profile rather than its AOA. However, there is still a lack of knowledge about designing an appropriate deformable hydrofoil. Therefore, a numerical investigation of hydrodynamic characteristics for selected hydrofoils was conducted. After undergoing the 2D numerical analysis (potential flow method) at specific conditions, several NACA profiles were chosen based on the performance of NACA profiles. NACA 0017 was selected as the initial shape for this research before it deformed to the optimized NACA profiles, NACA 6417, 8417, and 9517. The 3D CFD simulations using the finite volume method to obtain hydrodynamic characteristics at 0 deg AOA with a constant flow rate. The mesh sensitivity and convergence study are carried out to get consistent, validated, and reliable results. The final CFD modeled for propeller VP 1304 for open water test numerically. The results found that the performance of symmetry hydrofoil NACA 0017 at maximum AOA is not the highest compared to the other deformed NACA profiles at 0 deg AOA. The numerical open water test showed that the error obtained on K.T., K.Q., and efficiency is less than 8% compared to the experimental results. It shows that the results were in good agreement, and the numerical CFD setting can be used for different deformed profiles in the future

Filtre SIW d'ordre 6 en bande C avec un couplage croisé. Analyse expérimentale du comportement thermique.

National audienceCet article présente un filtre SIW (Substrate Integrated Waveguide) d'ordre 6 en bande C réalisé sur un substrat d'alumine de permittivité 9.9. Un couplage croisé entre résonateurs non-adjacents est introduit afin d'améliorer les réjections; une contrainte indispensable pour les applications spatiales. La compatibilité avec les circuits planaires est assurée par l'intermédiaire d'une transition microruban spécifique. Des tests en température ont été réalisés afin d'évaluer le comportement du filtre dans un environnement spatial. Les résultats expérimentaux sont en accord avec les simulations

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707

Assistive Robotic arm control using point of gaze Estimation

RÉSUMÉ: Les avancées récentes de la robotique permettent aux personnes atteintes de troubles musculosquelettiques de s'équiper d'un bras robotique d'assistance pouvant être placé sur leur fauteuil motorisé. Il a été démontré que ces bras robotiques améliorent l'autonomie et l'habileté de ces personnes, notamment pour accomplir les tâches importantes du quotidien, telles que se nourrir seul. Cependant, certains problèmes perdurent, en particulier le fait que le temps pour accomplir les manoeuvres à l'aide d'un bras robotique reste encore élevé, en particulier pour les personnes atteintes de troubles musculo-squelettiques. Une des manoeuvres les plus longues est l'approche et la saisie d'un objet, car elle demande de contrôler 6 degrés de liberté à l'aide d'une manette commandant seulement 3 axes à la fois. Aussi, le contrôle à l'aide de manettes demande un haut niveau de dextérité, souvent difficile à atteindre par les utilisateurs ciblés. Pour résoudre ces problématiques, l'objectif de ce projet est de développer une solution de contrôle du bras robotique d'assistance à l'aide d'un système de suivi du regard de l'utilisateur. Pour ce faire, il est nécessaire de suivre les yeux de l'utilisateur et d'en déduire la direction du regard, de reconstruire la scène en face de l'utilisateur par stéréovision, d'y faire la correspondance entre la direction du regard et les objets présents dans la scène pour finalement planifier la trajectoire du bras robotique pour atteindre l'objet et le prendre. La solution finale détaillée dans cette thèse permet donc de faire l'approche et la prise d'objet automatique en estimant la direction du regard de l'utilisateur et en détectant les objets en face de ce dernier. Ce système n'est aucunement intrusif car il ne nécessite pas que le bénéficiaire porte un objet comme des lunettes. Il fonctionne en présence d'illumination du soleil, ce qui n'est pas le cas d'autres types de système. Il permet aussi de prendre des objets sans contrainte sur leur type et ne nécessite aucune calibration par utilisateur. Utilisant un modèle original d'estimation de la direction du regard et mettant en place un système de détection et sélection d'objets basé sur la détection de surface plane telle une table et de l'allure de l'objet par apprentissage profond en parallèle, le système permet de planifier une trajectoire automatiquement en évitant les collisions avec la scène. À la suite d'essais exécutés dans le contexte de cette thèse, il est possible de constater une réduction du temps pour accomplir une tâche de préhension d'un objet d'environ 72.0% pour un taux de succès de 90% , tout en obtenant un score de satisfaction élevé d'en moyenne 4.6 sur 5 selon un questionnaire complété par les participants. ABSTRACT: In recent years, advances in robotics allow people suffering from upper limb disabilities to equip their motorized wheelchair with an assistive robotic arm. These are generally controlled through a specialized joystick device using filters and calibrated specifically to the user's force and disability. These robotic arms have been proven to improve the autonomy of their users, especially to accomplish tasks of daily living such as eating. However, some issues still persist, such as that manipulating the robotic arm is still time intensive for the users, especially in the case of approaching and grasping an object, since it requires moving the robotic arm in 6 degrees of freedom using a joystick that typically provides only 3 axes of motion. Also, joystick controls are complicated and require a high degree of dexterity, which is often lacking in potential users. Furthermore, the learning curve for using this technology is steep and the adaptation time is often too long, which leads to low adoption rates for potential users. To mitigate these issues, this PhD project aims to develop a control system for assistive robotic arms using user point of gaze estimation and gazed-at object detection using computer vision. This implies that the developed system must estimate the gaze direction and origin of the user, reconstruct the scene in 3D in front of the user, detect objects in the scene and match the user's gaze to the best fitting object. The developed system must also be able to generate a valid and collision-free path to the object, leading to a grasping motion, thus being able to automatically approach and grasp an object that is gazed-at by the user. The system described in this thesis is non-intrusive since it does not require the user to wear any devices, instead relying on mounting points on the user's motorized wheelchair. It is also less sensitive to lighting conditions, working with direct sunlight which is not the case for most of the available gaze control systems in the literature. Furthermore, it allows the grasping of objects independent of their type, as long as it is found to fit inside the robot's gripper. The developed system uses a novel gaze estimation deep learning model and an object detection subsystem that uses both the detection of a flat surface such as a table and a deep learning segmentation model based on object classes in parallel, allowing for robust object detection. From the data collected through device trials performed in the context of this PhD thesis, the system has demonstrated a 72.0% reduction in the time to grasp varied objects over to the same tasks performed with a joystick, while keeping a high success rate of 90% and a high satisfaction score of 4.6 out of 5

Une méthode semi-analytique pour l'analyse de l'interaction entre une onde de choc et une coque élastique immergée. Application au pré-dimensionnement de coques de sous-marins

Le dimensionnement des structures immergées vis-à-vis des effets d'une explosion sous-marine constitue une exigence forte pour un constructeur de navires militaires. La présente étude s'intéresse à la description de l'interaction entre une coque élastique immergée et une onde acoustique se propageant dans le fluide. En utilisant un modèle linéaire pour le fluide et la structure, il est possible de proposer une description du problème couplé dont la résolution peut être conduite avec une méthode semi-analytique. Les inconnues du problème (pour le fluide : champ de pression incident, champ de pression réfléchi, champ de pression rayonné ; pour la structure : champ de déplacement radial et ortho radial) sont écrites sous la forme d'un développement en série de Fourier de la variable angulaire. L'évolution des différents champs est décrite dans le domaine de Laplace par transformation des équations temporelles du problème couplé. Une application est proposée ici au cas de deux coques couplées par un fluide. La méthode de calcul ainsi proposée est implantée dans un code de calcul MATLAB qui peut ainsi être utilisé en bureau d'études pour le pré-dimensionnement de coques de sous-marins