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Caractérisation acoustique d’un open fan à l’aide de modèles semi-analytiques et d’essais en soufflerie
No full textInternational audienceThis study investigates the ability of CFD coupled to semi-analytical methods to restitute the sound radiation from an open-fan designed by SAE (Safran Aircraft Engines) recently tested in S1-Modane wind tunnel. The acoustic predictions are restricted to sound sources located on the rotor blades and stator vanes. The tone noise is assessed using a source-mode integral formulation derived from the Ffowcs-Williams and Hawkings analogy written in the frequency domain and in which the harmonic loadings are issued from URANS calculations performed by SAE. A compact-source approach allowing quite fast calculations is also proposed. Broadband noise is estimated using analytical models derived from Amiet’s theory with RANSbased inputs. Calculations are focused on take-off condition (sideline point), without incidence angle. First results obtained for tone noise show a fairly good matching between fully non-compact and compact predictions and a reasonable agreement with measured sound directivities at BPF1 and BPF2, which should be presented during the Conference. Broadband noise assessment is still underway and present analyzes, at takeoff condition too, are devoted to a previous generic open fan from SAE. ONERA predictions (using in-house tools) are found to be very close to SAE ones (from own industrial tool), in terms of both power spectra and overall sound pressure level directivities, when using common RANS inputs.Cette étude évalue la capacité de la CFD couplée à des méthodes semi-analytiques à restituer le rayonnement sonore d'un open fan conçu par SAE (Safran Aircraft Engines) récemment testé dans la soufflerie S1-Modane. Les prévisions acoustiques sont restreintes aux sources sonores situées sur les pales du rotor et du stator. Le bruit tonal est évalué à l'aide d'une formulation intégrale en modes-sources dérivée de l'analogie de Ffowcs-Williams et Hawkings écrite dans le domaine fréquentiel et dans laquelle les harmoniques de charge sont issues de calculs URANS effectués par SAE. Une approche source compacte permettant des calculs plus rapides est également proposée. Le bruit large bande est estimé à l'aide de modèles analytiques dérivés de la théorie d'Amiet avec des entrées basées sur des données RANS. Les analyses sont menées en condition de décollage (take-off), sans angle d'incidence. Les premiers résultats obtenus pour le bruit tonal montrent une assez bonne concordance entre les prédictions entièrement non compactes et compactes et un accord raisonnable avec les directivités sonores mesurées aux BPF1 et BPF2, qui devraient être présentés lors de la conférence. L'évaluation du bruit à large bande est toujours en cours et les analyses actuelles, également en conditions de décollage, portent sur un open fan générique de SAE. Les prévisions de l'ONERA (utilisant des outils internes) se révèlent très proches de celles de SAE (issues de leur code industriel), tant en termes de spectres de puissance que de directivités en niveau global, lorsque des entrées RANS identiques sont utilisées
Modeling magnetopause location for 4D drift-resolved radiation belt codes: Salammbô model implementation
No full textInternational audienceWe present a new semi-analytical magnetopause location model specifically designed for 4D drift-resolved radiation belt modeling codes. We specifically designed this magnetopause location model for the 4D version of Salammbô, but it can be adaptable to similar codes. The model combines parameterization by the Kp index with a representation of the magnetopause in L∗ geomagnetic coordinates and magnetic local time (MLT). It is based on a 20-year dataset relying on computed magnetopause stand-off distances using a solar wind database and a relevant magnetopause model, then converted into L∗ geomagnetic coordinates for all dayside MLT. Through the statistical analysis of this dataset, the model was formulated and validated against a magnetopause crossing catalog. Its performance was benchmarked against the magnetopause location model previously developed for the 3D version of the Salammbô code. The results demonstrate an improvement in predicting the magnetopause position in L∗ across dayside MLT sectors, with enhanced accuracy in the dawn sector. These results highlight the model's ability to model the magnetopause location in L∗ across dayside MLT sectors. This advancement may be specifically useful for simulating magnetopause shadowing in ring current and radiation belt modeling codes
Symbolic regression modelling of the linear growth rates of stationary cross-flow instabilities
No full textInternational audienceAccurately predicting the growth rates of stationary cross-flow instabilities is crucial for understanding transition mechanisms in swept-wing configurations, which can significantly impact aerodynamic performance. This paper introduces a model for the prediction of cross-flow instability growth rates, focusing on both accuracy and ease of implementation. The proposed model consists of straightforward expressions involving key boundary layer quantities. Validation against established methods demonstrates that the new model achieves comparable or superior accuracy in predicting growth rates. Additionally, tests conducted on a three-dimensional (3-D) prolate spheroid show strong alignment with transition lines computed by means of exact linear stability. Overall, this model provides a practical and efficient alternative for accurately predicting cross-flow transitions in complex 3-D geometries, contributing to improved aerodynamic design and analysis
Blottner’s Coefficients and Prandtl Number for Charring Materials Atmospheric Entry Simulations
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Characterization of the long-lived light emission induced by a 1030 nm femtosecond laser filament in air and nitrogen flow
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High-order adaptive multi-domain time integration scheme for microscale lithium-ion batteries simulations
No full textInternational audienceWe investigate the modeling and simulation of ionic transport and charge conservation inlithium-ion batteries (LIBs) at the microscale. It is a multiphysics problem that involves a wide range oftime scales. The associated computational challenges motivate the investigation of numerical techniquesthat can decouple the time integration of the governing equations in the liquid electrolyte and the solidphase (active materials and current collectors). First, it is shown that semi-discretization in space of thenon-dimensionalized governing equations leads to a system of index-1 semi-explicit differential algebraicequations (DAEs). Then, a new generation of strategies for multi-domain integration is presented,enabling high-order adaptive coupling of both domains in time, with efficient and potentially differentdomain integrators. They reach a high level of flexibility for real applications, beyond the limitations ofmultirate methods. A simple 1D LIB half-cell code is implemented as a demonstrator of the new strategyfor the simulation of different modes of cell operation. The integration of the decoupled subsystems isperformed with high-order accurate implicit nonlinear solvers. The accuracy of the space discretizationis assessed by comparing the numerical results to the analytical solutions. Then, temporal convergencestudies demonstrate the accuracy of the new multi-domain coupling approach. Finally, the accuracy andcomputational efficiency of the adaptive coupling strategy are discussed in the light of the conditioningof the decoupled subproblems compared to the one of the fully-coupled problem. This new approachwill constitute a key ingredient for the high-fidelity 3D LIB simulations based on actual electrodemicrostructures
A Simple P+d Controller for Consensus of Euler-Lagrange Systems Over Directed Graphs
No full textInternational audienceThe state of the art in consensus control for multiagent Euler-Lagrange (EL) systems relies on one or several of the following assumptions: the graph is undirected or directed and strongly connected, the controller is centralized, knowledge of the inertia and Coriolis matrices is needed, the systems' trajectories are bounded. In this letter we show that a simple Proportional Derivative controller with gravity compensation, which does not rely on any of the previous hypotheses, achieves consensus for EL systems over connected acyclic directed graphs. The proof follows a cascaded-systems argument. Also, we provide some numerical simulations to illustrate the performance of the controller
Développement d'architectures de commande sûres pour un véhicule terrestre autonome
No full textThe increasing automation of ground transportation necessitates the development of safe and efficient control architectures for over-actuated autonomous vehicles. This thesis focuses on designing and implementing a decentralized hierarchical control architecture that integrates longitudinal, lateral, and yaw stability control to ensure optimal vehicle performance in various operating conditions. Specifically, it addresses the challenges of vehicle control allocation, actuator dynamics, and integration of longitudinal, lateral, and lateral stability control strategies.A key contribution of this thesis is the development of advanced control allocation techniques that consider actuator dynamics, including the Daisy Chaining Kalman Filter Control Allocation (DCKFCA) and the Enhanced Weighted Pseudo-Inverse with Reference Governor (EWPI-RG). These approaches improve vehicle response by effectively distributing control inputs across multiple actuators while accounting for actuator constraints and limitations. The proposed control strategies are validated through high-fidelity simulations using the IPG CarMaker environment, demonstrating their effectiveness in various driving scenarios, including lane-keeping, path tracking, and fault-tolerant controlThe thesis contributes to the development of safer autonomous vehicle systems by reducing the driver’s workload and ensuring robust performance under different operational conditions.L'automatisation croissante du transport terrestre nécessite le développement d'architectures de contrôle sûres et efficaces pour les véhicules autonomes suractionnés.Cette thèse porte sur la conception et la mise en œuvre d'architectures de contrôle hiérarchiques décentralisées intégrant le contrôle longitudinal, latéral et de stabilité en lacet afin d'assurer des performances optimales du véhicule dans diverses conditions de fonctionnement. Elle traite en particulier les défis liés à l'allocation de commande du véhicule, à la dynamique des actionneurs et à l'intégration des stratégies de contrôle longitudinal, latéral et de stabilité latérale.Une contribution clé de cette thèse est le développement de techniques avancées d'allocation de commande prenant en compte la dynamique des actionneurs, notamment l'Allocation de commande avec Filtrage de Kalman avec Daisy Chaining (DCKFCA) et une version améliorée de la pseudo-inverse pondérée avec Reference Governors (EWPI-RG). Ces approches améliorent la réponse du véhicule en répartissant efficacement les entrées de commande entre plusieurs actionneurs tout en tenant compte de leurs contraintes et limitations. Les architectures de contrôle proposées sont validées à l'aide de simulations haute fidélité dans l'environnement IPG CarMaker, démontrant leur efficacité dans divers scénarios de conduite, notamment le maintien de voie, le suivi de trajectoire et le contrôle tolérant aux défauts.Cette thèse contribue au développement de systèmes de véhicules autonomes plus sûrs en réduisant la charge de travail du conducteur et en garantissant des performances robustes dans différentes conditions opérationnelles
Characterization of atmospheric channel for free space optical communications
No full textInternational audienceIn order to accurately predict free space optical communication performance, knowledge of the refractive index structure parameter (Cn2) and wind profiles is of great interest.We present our approach to extract these parameters from Shack-Hartmann wavefront sensor (SHWFS) measurements collected by ONERA’s FEELINGS optical ground station. The approach is inspired by the Single Coupled Slopes and Intensities Detection and Ranging (SCO-SLIDAR) method [1] and relies on spatiotemporal covariances of wavefront slopes and intensities gathered by the SHWFS. It is first validated with the PICOLO/LISA turbulence emulator bench [2].References[1] N. Védrenne , V. Michau , C. Robert, and M. Conan. “Cn2 profile measurement from Shack Hartmann data”. In: Optics letters 32.18 (2007), pp. 2659 2661.[2] Robles, P., Petit, C., Velluet , T., Le Leuch , L., Montmerle Bonnefois , A., Paillier , L., Conan, M., Cassaing , F., Montri , J., Neichel , B., & Védrenne , N. (2023). “Emulating and characterizing strong turbulence conditions for space to ground optical links: The PICOLO bench”. Journal of Astronomical Telescopes, Instruments, and Systems, 9(04
Synthesis of Aldehyde Functional Polydimethylsiloxane as a New Precursor for Aliphatic Imine‐Based Self‐Healing PDMS
No full textInternational audienceThe development of a simple synthetic route to aldehyde functional poly(dimethylsiloxane) (PDMS) through oxidative C─C bond cleavage of terminal epoxide functions by periodic acid is presented first. Nuclear Magnetic Resonance (NMR) and Infrared spectroscopies revealed the full conversion of the PDMS terminal epoxides to aldehyde groups. This new aldehyde functional PDMS is then used to elaborate aliphatic self-healing materials through imine chemistry by reaction with an amine-terminated PDMS featuring urea moieties in its structure. The reactivity of the aldehyde terminated PDMS is investigated through the preparation of supramolecular networks formed by the hydrogen bonds of ureas. The incorporation of permanent chemical cross-linking points through reaction with a triisocyanate leads to the preparation of covalent adaptable networks (CANs). As a result, materials with a wide range of mechanical properties are obtained, depending on the composition and structure of the PDMS networks. Due to the presence of dynamic covalent imine bonds, the supramolecular networks show excellent scratch recovery at room temperature while the CANs retain their mechanical properties after two cycles of reshaping by heating