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Scaler nonlinear continuum damage models for ceramic matrix composites with and without in plane ply anisotropy at room temperature
No full textInternational audienc
Exploration de l'émission infrarouge de particules d'alumine dans le panache d'un moteur de fusée : influence de la taille des particules et du modèle de rayonnement
No full textInternational audienceA numerical study reproducing experiments conducted by S&C Thermofluids Ltd. on a propulsion bench at the Kemble Engine Test Laboratory is presented. In experiments, gases were generated from heated compressed air undergoing a secondary combustion by fuel injection. Calibrated alumina particles were added to the hot gases to reproduce an aluminized plume. The mixture was expelled through a single convergent nozzle. Multiple tests were carried out, differing solely by the size of the introduced particles while maintaining a constant alumina mass flow rate. To characterize the particle infrared emission, CFD simulations of the plume were performed coupled with a radiative transfer code. A parametric study was focused on alumina particle size, exploring diameters ranging from 0.4 to 47 µm. The comparison reveals that increasing the diameter has little impact on plume radiation within the 0.4 and 15 µm range. However, a diameter increase between 15 and 47 µm, corresponding to the alumina oxide cap enlargement, results in a significant plume IR radiation enhancement. Multiple alumina absorption and refractive index models were compared, especially in the Short-Wave Infrared Range (SWIR), where particle radiation is predominant. Comparison shows that the imaginary part of the refractive index used, the absorption index, is of major significance on the SWIR signature
Surrogate Modeling for Robust Airfighters Radar Cross Section Predictions Under Uncertainty
No full textInternational audienceRadar Cross Section (RCS) prediction is essential for fighter aircraft design, but high-fidelity solvers like Maxwell3D are computationally expensive, especially when accounting for uncertainty in the incidence angle. In particular, a sharp RCS peak appears when looking at the front of the aircraft, potentially leading to overestimation if uncertainty is ignored. To overcome the cost of brute-force Monte Carlo sampling, we construct a surrogate model using an adaptively refined Polynomial Chaos Expansion (PCE). Our approach significantly reduces the number of high-fidelity solver evaluations while maintaining high accuracy in RCS prediction. Comparisons with Monte Carlo results confirm that, with a small Design of Experiments (DoE), our PCE model closely matches the reference distribution. Additionally, we show that a physics-driven adaptive refinement strategy outperforms naive optimization-based refinement
Advancements in Autonomous Space Robotics at ONERA : Control Frameworks and Co-Design Strategies for On-Orbit Servicing and Assembly
No full textInternational audienceSpace Manipulator Systems (SMS) are becoming key in space exploitation and exploration, offering a versatile range of solutions from space debris capture to structure assembly. However, recent missions involving manipulators aboard satellites and space structures must deal with lightweight and large ele- ments that exhibit flexible behaviors. Despite the challenges posed by flexible elements, enhancing the autonomy of SMS remains crucial to ensure their viability as solutions. For the pre-design of the SMS, path-planning applications, or controller design, there is a necessity for methods to assess the couplings between the manipulator, the SMS base, and any flexible elements manipulated by the manipulator or attached to the base. Moreover, recently proposed control strategies have demonstrated a keen interest in developing model-based controllers, which advantageously provide an efficient utilization of actua- tors and mitigation of internal disturbances within the system. The presentation focuses on recent research conducted at ONERA to design and validate control strate- gies for SMS performing On-Orbit Servicing (OOS) in the presence of flexible structures. These strate- gies are analyzed and validated across varying levels of detail and realism. The first part of the presentation addresses the derivation of kinematic and dynamic models for a free- floating SMS with a flexible body attached at the end of a kinematic chain, using a Lagrangian formal- ism. The second part presents ONERA’s real-time simulation platform, specifically developed to enable the rapid design, prototyping, and testing of model-based control solutions at fine time scales. The platform’s software and hardware architecture ensures high-fidelity modeling of space robot dynamics and flexible structures, integrating visual environment models for state observation, computer vision processing, virtual sensor data fusion, and full robot control. Finally, the presentation will demonstrate the platform’s value and versatility in addressing current challenges in space exploration and exploitation. Applications will include the On-Orbit deployment of large flexible space structures, co-design of assembly scenarios considering Guidance, Navigation, and Control (GNC) constraints, and strategies for the safe capture of tumbling target
Analyse et mise en œuvre d’une méthode de raffinement de maillage ciblé pour les écoulements fluides compressibles
No full textOver the past decades, numerical simulation in fluid mechanics has become an essential toolin both engineering and research. Mesh adaptationenables the computational effort to be focused whereit is most needed, whether through feature-based methods, which refine regions of strong variations in theflow field, or goal-oriented methods, which directly tar-get a given functional by solving the associated adjointproblem.This thesis builds on the work of Nguyen-Dinh et al.,who use the total derivative of the functional with respect to the mesh coordinates to relate sensitivity tolocal mesh refinement. A one-dimensional linear model problem was first studied in order to compare,both analytically and numerically, the criteria of Venditti–Darmofal and Nguyen-Dinh, leading to the pro-posal of an adapted bound to rigorously control thesensitivity of the functional to node displacement.The work then focused on the implementation of ametric-based targeted refinement strategy, applied tothe NACA0012 airfoil (inviscid flow) and subsequentlyto the RAE2822 configuration (viscous flow), usingunstructured meshes with anisotropic refinement. Fi-nally, a theoretical contribution was made on the characteristic equations of the direct and adjoint two-dimensional perfect-fluid systems, extending the results of Peter and D ´esid ´eri, with a concise derivation of the number of independent relations associated with the C+ and C− characteristics, and validationof the direct and adjoint characteristic equations on aninternal-flow configuration.Au cours des dernières décennies, la simulation numérique en mécanique des fluides s’est imposée comme un outil essentiel de l’ingénierie et de la recherche. L’adaptation de maillage permet déconcentrer l’effort de calcul là où il est nécessaire,qu’il s’agisse des méthodes feature-based, centrées sur les fortes variations du champ, ou des méthodes goal-oriented, qui ciblent directement une fonction d’intérêt via la résolution du problème adjoint associe.La thèse s’inscrit dans la continuité des travaux de Nguyen-Dinh et al., qui exploitent la dérivée totale de la fonction d’intérêt par rapport aux coordonnées du maillage volumique pour relier sensibilité et raffinement local. Un problème unidimensionnel linéaire a d’abord et étudié afin de comparer analytiquement et numériquement les critères de Venditti–Darmofal etde Nguyen-Dinh, menant à la proposition d’une borne adaptée pour contrôler rigoureusement la sensibilité au déplacement des nœuds.Le travail a ensuite porte sur la mise en œuvre d’un raffinement ciblé basé sur des métriques, applique aux profils NACA0012 ( écoulement de fluide parfait)puis RAE2822 ( écoulement de fluide visqueux), avec maillages non structures et raffinement anisotrope.Enfin, un apport théorique a ´et ´e propos ´e sur les caractéristiques des équations directes et adjointes de fluide parfait en prolongeant les travaux de Peter et Désidéri, avec une démonstration concise du nombre d’équations indépendantes sur les C+ et C− et la validation des équations caractéristiques directes et ad-jointes sur un cas d’écoulement interne
Separation Control Using Zero-Net-Mass Perturbations: Effect of the Duty Cycle
No full textInternational audienceThis study aims to investigate the influence of the duty cycle, DC, of zero-net-mass perturbations applied to active separation control. To that extent, a unique flow control apparatus producing alternating pulsed blowing and suction was implemented on an academic separated flow configuration. Three series of constant mass-flow coefficient perturbations were studied, for each of which values of the duty cycle ranged from 10 to 80 %. The results indicate that a better control efficiency is achieved for lower values of the duty cycle in terms of dimensions of the separation bubble and pressure distribution, at the cost of a higher fluctuating flow. The transient mechanisms involved in the periodic actuation were studied, highlighting the different timescales governing the controlled flow. The blowing phase was shown to be the main contributor to flow reattachment, whereas suction makes the flow more robust to separation
Additive manufacturing of fully metallic dual polarized leaky wave antenna array for polarimetric radar application
No full textInternational audiencePolarimetric radar provides additional information by analyzing the polarimetric state of the received backscattered wave with respect to the polarimetric state of the transmitted. One application for a polarimetric radar is to characterize natural environment as foliage for instance. Another specific application is the capability for the radar to separate the echoes from the near-nadir surface. As a well-known example, the SWOT mission for Surface Water and Ocean Topography, is based on a dual-polarized Ka-band interferometer with two reflectarray antennas. In our case, we focus on ocean monitoring applications as well. The polarimetric backscattered wave should provide information about the ocean and wind surface states. Consequently, we need a polarimetric radar antenna. In this communication, we describe a new polarimetric radar antenna design that is compact, efficient, and low-profile. First, a dual mode hollow square waveguide-based K-band leaky wave antenna (LWA) is proposed, with a focus on side lobe level reduction by tapering of the radiating apertures. This approach is then applied to a specific polarimetric radar system using the HOMARDS sensor. The antenna of this sensor, which consists of a triangular waveguide based dual polarized Ka-band LWA array, is described. The antenna concept is a monolithic entity formed of 4 LWA connected to an excitation structure made up of power dividers and orthomode transducers (OMTs). Finally, the continuation of this design through a biggest prototype is depicted. All the exhibited designs are printed by fully metallic additive manufacturing (AM) and is manufactured by the Swissto12 company. The full metal AM is a groundbreaking technology for future space microwave passive components. It flawlessly balances the tradeoff between high-performance components and small devices by printing complex geometries that are not possible with traditional manufacturing techniques. In our designs, the use of additive manufacturing allows for the monolithic printing of radiators and excitation structures with a very high level of compactness and very lightweight. The impact of AM on design choices is thoroughly discussed in the communication
Sound generation by entropy inhomogeneities in a thermally choked flow nozzle
No full textInternational audienceThe indirect entropy noise generation in a thermally choked flow nozzle, induced by the convection of 2D circular entropy spots, is investigated. Two configurations are examined: a thermal throat formed by non-uniform volumetric heat addition, and an equivalent isentropic nozzle with a geometric throat. Both are designed to produce the same steady Mach number distribution, in order to isolate the influence of heat addition on the acoustic response. The analysis combines two-dimensional CFD simulations with two asymptotic one-dimensional models: the quasi-steady (QSS) model, adapted for large spots, and the point-mass (PM) inertial model, for small spots. For the geometric-throat case, the CFD results show fair agreement with both the QSS and PM predictions in their respective asymptotic regimes. For the thermal-throat case, the QSS regime is reached for spots larger than 100 throat radius, which is a value lower than that of the geometric configuration. Then, the acoustic response exceeds QSS predictions (∼ 20%), which is certainly due to the invalidity of the assumption of no Mach fluctuations at the throat. In the small-spot limit, the PM model predicts the inertial regime with reasonable accuracy for both configurations, but at different spot radii. The thermal-throat case, however, deviates from the PM prediction, highlighting fundamental differences between heated and isentropic nozzles and the need to extend asymptotic models to non-isentropic base flows
Conception d'un double HMM pour la détection de signaux radar LPI
No full textInternational audienceDetecting Low Probability of Intercept radar signals in a passive and fully blind setting remains a major challenge in electronic warfare. In this paper, we introduce a Hidden Markov Models architecture, where the transition dynamics are explicitly designed from the physical properties of the signals rather than learned from data. This physically grounded modeling enables the system to handle a different modulation types, including both continuous and abruptly shifting frequencies, while preserving interpretability and eliminating the need for labeled data. The architecture can integrate multiple specialized HMMs, whose outputs are combined through a simple yet effective fusion mechanism. Extensive experiments over a wide SNR range show that our method matches the performance of modern deep learning detectors, while offering enhanced transparency and efficient frequency trajectory estimation
Response of a nonevaporating monodisperse spray in a uniform laminar gas flow to acoustic perturbations
No full textInternational audienceThis paper introduces a one-dimensional model for the response of a monodisperse nonevaporating spray injected into a laminar uniform gaseous stream when it is submitted to acoustic disturbances. The dynamics of both the continuous and dispersed phases of the spray are addressed using an Eulerian framework. Explicit analytical expressions are derived for the linearized balance equations governing particle velocity and particle number density responses to acoustic excitation in two scenarios: when particles are injected with the same velocity as the gaseous flow and when their injection velocities differ. It is shown that particle velocity disturbances can be decomposed into an evanescent convective wave and a propagating acoustic wave. The final amplitudes and phase lags of these waves with respect to acoustic disturbances depend on particle Stokes and flow Mach numbers. The expression for particle number density disturbances uncovers two distinct types of particle clustering. The first, termed acoustic particle clustering (APC), is controlled by the relative particle velocity fluctuations compared to the gas velocity fluctuations. The second, designated convective particle clustering (CPC), is linked to gas velocity fluctuations and operates independently of the acoustic particle velocity response. Particle clustering predominantly arises from CPC, whereas APC is only discernible at low Stokes numbers. The analysis further delves into the impact of differences between the particle injection velocity and gas mean velocity on the amplitude and phase lag of CPC wave. It is shown that the zone over which the particle velocity relaxes to the gas velocity fully controls CPC. Numerical simulations validate analytical predictions, with good agreement for relatively small Stokes numbers, and cases wherein the particle injection velocity exceeds the mean gas velocity. The expressions derived in this work represent a preliminary step toward modeling the acoustic response of spray flames