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This paper is a short retrospective review of the predictive methods of turbulent flows in Computational Fluid Dynamics over the last 50 years since the first development of computers. The different schools of turbulence modeling are presented with the aim to guide both users and researchers involved in numerical simulation of turbulent flows.; Cet article est une courte rétrospective de synthèse des méthodes prédictibles des écoulements turbulents.Des simulations des écoulements sur ces 50 dernières années depuis les premiers développement des ordinateurs.Les différentes écoles de la modélisation des turbulences sont présentées dans le but de guider à la fois les utilisateurs et les chercheurs impliqués en simulation numérique des écoulements turbulents.

Aviation NOx emissions have not only an impact on global climate by changing ozone and methane levels but also contribute to deteriorate local air quality. In order to properly assess the co-benefit with air quality improvement and the trade-off with the climate change associated with CO2, it appears essential to better quantify the climate impact of aircraft NOx emissions. A new version of the LMDZ-INCA global model, including both tropospheric and stratospheric chemistry and the sulfate-nitrate-ammonium cycle, is applied to re-evaluate the impact of aircraft NOx and aerosol emissions on climate. The results confirm that the efficiency of NOx to produce ozone is very much dependent on the injection height. For the baseline simulation and reference scenario this efficiency is 6.6 TgO3/TgN. The efficiency increases with the background methane and NOx concentrations and with decreasing aircraft NOx emissions. The same findings translate to the associated ozone radiative forcing which exhibits a fairly constant value per ozone mass change of 3.4 mW/m2/TgO3. The methane lifetime variation is less sensitive to the aircraft NOx emission location than the ozone change. The change in CH4 mixing ratio itself represents 75 % of the total methane forcing. The indirect changes through long-term tropospheric ozone, stratospheric water vapour and methane oxidation to CO2 contribute for 19 %, 4 % and 1 %, respectively. The net NOx radiative forcing (O3 + CH4) is largely affected by the revised CH4 radiative forcing formula which increases the total CH4 negative forcing by 15 %. As a consequence, the ozone positive forcing and the methane negative forcing largely offset each other resulting in a slightly positive forcing for the present-day. However, in the future, the net forcing turns to negative due essentially to higher methane background concentrations. Additional radiative forcings involving particle formation arise from aircraft NOx emissions since the increased OH concentrations are responsible for an enhanced conversion of SO2 to sulfate particles. Aircraft NOx emissions also increase the formation of nitrate particles in the lower troposphere. However, in the upper-troposphere, increased sulfate concentrations favor the titration of ammonia leading to lower ammonium nitrate concentrations. The total forcing from sulfate and nitrate aerosols associated with NOx emissions is negative and is estimated to -3.0 mW/m2/TgN for the present-day. When these aerosol radiative forcings are considered, the total NOx forcing turns from a positive value to a negative value even for present-day conditions. Hence, total radiative forcing from aircraft emissions associated with changes in atmospheric chemistry and direct aerosols forcings is negative for both present-day and future (2050) conditions. NOx emissions only cause a negative forcing representing about 45 % of the total forcing. The negative forcing associated with sulfates largely dominates the effect of the other particles. The sulfate direct radiative forcing is estimated to be associated for about 50 % with the direct SO2 and SO4 aircraft emissions and for about 50 % with the increased conversion of SO2 to SO4 at higher OH concentrations, and hence related to the NOx emissions. The net effect of decreasing (resp. increasing) the flight altitude by 2000 ft (about 610 m) is to increase (resp. decrease) the total negative forcing by 57 % (resp. 65 %). The variation of the total forcing with flight altitude is dominated by the high sensitivity of the ozone positive forcing to the altitude of the perturbation. Several mitigation options involving flight aircraft operation and cruise altitude changes, traffic growth, engine technology, and fuel type, exist to reduce the climate impact of aircraft NOx emissions. However, the climate forcing of aircraft NOx emissions is likely to be small or even switch to negative (cooling) depending on atmospheric NOx or CH4 future background concentrations or when the NOx impact on sulfate and nitrate particles is considered. There remain large uncertainties on the NOx net impact on climate effect calculation. Nevertheless, the results suggest that reducing aircraft NOx emissions is primarily beneficial for improving air quality. For climate consideration, one option to reduce uncertainties in mitigation strategies might be to prioritize the reduction of CO2 aircraft emissions which have a well-established and long-term impact on climate, however this reduces the overall mitigation potential.

It is well known that acoustical factors explain only partly the human perception of aircraft noise. In order to truly understand annoyance ratings, acoustical and non-acoustical factors have to be taken into consideration, making it often complex to analyze studies that treat only one side of the issue. While field studies give a good insight of long-term annoyance in realistic living conditions, laboratory tests are commonly used as means to understand the impact of acoustic factors on noise annoyance and unpleasantness while usually smoothing inter individual differences. A French project (CIGALE) has set a goal of creating a frame of reference making it possible to include non-acoustical factors into laboratory studies. After an extensive field study and focus groups in the first part of the project resulting in six different profiles of residents, the second part comprises a vast laboratory test campaign in Toulouse and Paris region aiming at evaluating the impact of these profiles on the perception of two common acoustical factors in an ecological experimental setup. Overall more than 300 residents of the Toulouse Blagnac airport area and the Roissy Charles de Gaulle airport area participated in the CIGALE listening test. Participants were asked to read novels while seated in a listening room with a 3D audio simulation of an everyday soundscape. They were asked to rate their perception of four 15 minutes sequences randomly presented in which the number of aircraft flyovers and the maximum A-weighted sound level of each flyover were varied. Four different scales were used: task interference, mental effort, annoyance and comfort. The results support the hypothesis that profile type and noise sensitivity have an impact on annoyance ratings. The collected data also highlighted different response strategies regarding acoustical factors that need to be further investigated., Il est bien connu que les facteurs acoustiques n'expliquent qu'en partie la perception humaine du bruit des avions. Afin de bien comprendre une évaluation de gêne, les facteurs acoustiques et non acoustiques doivent être pris en compte, ce qui rend souvent complexe l'analyse d'études qui ne traitent qu'un aspect du problème. Alors que les études sur le terrain donnent un bon aperçu de la gêne à long terme dans des conditions de vie réalistes, les tests en laboratoire sont couramment utilisés pour comprendre l'impact des facteurs acoustiques sur la gêne et le désagrément liés au bruit, tout en atténuant généralement les différences interindividuelles. Un projet français (CIGALE) s'est fixé pour objectif de créer un référentiel permettant d'intégrer des facteurs non acoustiques dans les études en laboratoire. Après une vaste étude de terrain et des ateliers participatifs dans une première partie du projet aboutissant à six profils d'habitants différents, la seconde partie comprend une vaste campagne de tests en laboratoire à Toulouse et en région Parisienne visant à évaluer l'impact de ces profils sur la perception de deux facteurs acoustiques communs dans un montage expérimental écologique. Au total plus de 300 habitants de la région aéroportuaire de Toulouse Blagnac et de celle de Roissy Charles de Gaulle ont participé au test d'écoute CIGALE. Les participants ont été invités à lire des romans assis dans une salle d'écoute avec une simulation audio 3D d'un paysage sonore représentant une situation sonore rencontrée au quotidien. On leur a demandé d'évaluer leur perception de quatre séquences sonores de 15 minutes présentées au hasard dans lesquelles le nombre de survols d'aéronefs et le niveau sonore maximal de chaque survol étaient modifiés. Quatre échelles différentes ont été utilisées : l'interférence sur la tâche, l'effort mental, la gêne et le confort. Les résultats soutiennent l'hypothèse selon laquelle le type de profil et la sensibilité au bruit ont un impact sur les notations de gêne. Les données collectées ont également mis en évidence différentes stratégies de réponse concernant les facteurs acoustiques qui doivent être étudiées plus en détail.

The H2020 MINOTOR project focused on the study and the optimization of the ECRA thruster, an electric propulsion system for satellites. First, a 30 W prototype of this Electron Cyclotron Resonance Thruster (ECRT) is optimized. Then, a 200 W prototype is design based on these findings. The performances of both prototypes were assessed at two different facilities: at ONERA in France and at Justus Liebig University in Germany. Significant improvement of performances of both thrusters with the decrease of background pressure is presented. Total thrust efficiencies as high as 50% are measured at JLU, as well as erosion and lifetime assessment. The stability of the thruster for a constant point of operation was measured for one hundred hours of operation.

Nanocrystals’ (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm−2 and can be operated over a broad range of temperatures (130–300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W−1 or an external quantum efficiency of 500%) over a broadband spectral range.

Ice velocity observations available on-line or on-demand at intra-annual resolution still contain gaps, noise, and artifacts, especially in mountain areas. There is a need to fuse the available multi-temporal and multi-sensor velocity observations to be able to study intra-annual glacier dynamics. The proposed approach includes an inversion based on the temporal closure of displacement observation networks and a temporal interpolation. It reconstructs velocity time series between consecutive dates at a regular temporal sampling (called Regular Leap Frog (RLF) time series) inferred from all the velocity observations without a prori knowledge on the displacement behavior. The RLF time series can be reconstructed for different temporal sampling. Root Mean Square Error (RMSE) over stable areas and Velocity Vector Coherence (VVC) over fast moving areas are proposed to select a temporal sampling allowing a compromise between uncertainty and temporal resolution. This study focuses on the Fox glacier, in the Southern Alps of New Zealand. It shows that RMSE over stable areas is decreased from 78% for a temporal sampling of 5 days to 40% for a temporal sampling of 60 days. Thus, using this approach, we obtain a velocity time series with a complete temporal coverage and reduced uncertainty for a regular and optimal temporal sampling. The results highlight the large seasonal variability of the flow of Fox Glacier that fluctuates by more than 30% between spring and autumn.

Pulsed fluidic actuators play a central role in the fluid flow experimental control strategy to achieve better performances of aeronautic devices. In this paper, we demonstrate, through an experimental test bench, how the interpolatory-based Loewner Data-Driven Control (L-DDC) framework is an appropriate tool for accurately controlling the outflow velocity of this family of actuators. L-DDC combines the concept of ideal controller with the Loewner framework in a single data-driven rationale, appropriate to experimental users. The contributions of the paper are, first, to emphasise the simplicity and versatility of such a data-driven rationale in a constrained experimental setup, and second, to solve some practical fluid engineers concerns by detailing the complete workflow and key ingredients for successfully implementing a pulsed fluidic actuator controller from the data acquisition to the control implementation and validation stages., Comment: 20 pages, 7 figures

International audience; This paper deals with a new definition of the Radar Cross Section (RCS) suitable for surface wave propagation in the HF band. Indeed, it can be shown that the classical definition of the RCS is dependent on distance for this kind of propagation. Also, in simulation, with the classical definition, the power estimated on the receivers using the radar equation is inaccurate. This is an issue for the performance assessment of High Frequency Surface Wave Radars. Thanks to the analysis of different wave propagation models, the differences between the space wave propagation and surface wave propagation have been highlighted. The required modifications of the RCS can then be performed. The proposed new definition is explained and justified in the paper and has been successfully applied to the computation of the RCS of naval targets. In addition, the implementation of this normalization term into the radar equation, and conversely the gain, is discussed. It can be observed that the received power, determined with the definitions adjusted to the surface wave propagation, is accurate. The different obtained results are illustrated and commented.

International audience; This paper presents the development of an ontology for opinion mining in French corpora. Since ontology construction from scratch is expensive and time consuming, the model is built by adapting an existing ontology modeling appraisal categories in English. The construction method consists of two main steps: first, the ontology of appraisals is translated in French by using a conceptto-concept approach; then different adaptation strategies are implemented to improve the result of this translation. Adaptation strategies are based on text mining, weakly supervised methods and the use of WordNet to refine the model. The goal of the adaptation phase is to cope with limitations of concept-to-concept translation, to integrate concepts and relations from external corpora and resources, and to build a model that captures various features of opinions. The ontology was designed and build to incorporate linguistic and extra linguistic information on the description of opinions in French. The model was validated by using both expert insights to validate the relevance of concepts and relations and formal criteria to describe the ontology qualities for practical use.

Characterizing the boundary layer transition to turbulence around realistic hypersonic vehicles is a challenging task due to the numerous parameters that affect the process. To address this challenge, the cone-cylinder-flare (CCF) geometry has been designed to provide a flow topology that captures various transition mechanisms observed on reentry objects, such as absolute and convective instabilities, which are dependent on the free stream conditions. In this study, a global linear stability analysis is performed on the CCF model at Mach=6.0 to investigate and map the dominant instabilities at wind tunnel flow conditions. We examine optimal responses and forcings computed using resolvent analysis, as well as global modes originating from the recirculation bubble at the cylinder flare junction. The effects of bluntness are assessed through analyses of both blunt and sharp configurations. Our results shed light on the linear flow mechanisms that promote the transition to turbulence around such hypersonic objects., Comment: Conference paper

International audience; Large aperture periodically-poled Rb:KTP crystals designed for optical parametric amplifiers in 2 µm LIDAR systems were radiation hardness tested by exposure of proton beams at 10 MeV and 60 MeV energies. An irradiation dose of 55 Gy was used to commensurate the crystals' estimated exposure on board a mission in the low-Earth orbit. The irradiation effects were investigated by comparing optical transmission spectra and 2D effective nonlinearity mapping in a 2 µm OPO setup before and after irradiation. The results reveal that the periodically poled structure remained intact after irradiation, and the changes in the optical transmission and nonlinear properties were close to the measurement uncertainty. This investigation is essential for realizing efficient frequency converters for space applications, such as spaceborne active greenhouse gas monitoring LIDAR instruments or correlated photon-pair sources.

International audience; Context. Adaptive optics (AO) is a technique allowing for ground-based telescopes' angular resolution to be improved drastically. The wavefront sensor (WFS) is one of the key components of such systems, driving the fundamental performance limitations.Aims. In this paper, we focus on a specific class of WFS: the Fourier-filtering wavefront sensors (FFWFSs). This class is known for its extremely high sensitivity. However, a clear and comprehensive noise propagation model for any kind of FFWFS is lacking. Methods. Considering read-out noise and photon noise, we derived a simple and comprehensive model allowing us to understand how these noises propagate in the phase reconstruction in the linear framework.Results. This new noise propagation model works for any kind of FFWFS, and it allows one to revisit the fundamental sensitivity limit of these sensors. Furthermore, a new comparison between widely used FFWFSs is held. We focus on the two main FFWFS classes used: the Zernike WFS (ZWFS) and the pyramid WFS (PWFS), bringing new understanding of their behavior.; Contexte: L'optique adaptative (OA) est une technique permettant d'améliorer de façon drastique la résolution angulaire des télescopes terrestres. L'analyseur de surface d'onde (WFS pour WaveFront Sensing en anglais) est l'un des composants clés de ces systèmes, ce qui entraîne des limitations de performance fondamentales.Objectifs: Dans cet article, nous nous concentrons sur une classe spécifique de de WFS : les capteurs de front d'onde à filtrage de Fourier (FFWFS). Cette classe est connue pour sa sensibilité extrêmement élevée. Cependant, un modèle clair et complet de propagation du bruit pour tout type de FFWFS fait défaut.Méthodes: En considérant le bruit de lecture et le bruit photonique, nous dérivons un modèle simple et complet permettant de comprendre comment ces bruits se propagent dans la reconstruction de phase dans le cadre linéaire.Résultats: Ce nouveau modèle de propagation du bruit fonctionne pour tout type de FFWFS, et permet de revisiter la limite de sensibilité fondamentale de ces capteurs. De plus, une nouvelle comparaison entre les FFWFS les plus utilisés est effectuée. Nous nous concentrons sur les deux principales classes de FFWFS utilisées : le Zernike WFS (ZWFS) et le pyramid WFS (PWFS), apportant une nouvelle compréhension de leur comportement.

International audience; Optical parametric oscillators are versatile devices for generating a tunable coherent radiation from an incident laser beam. They rely on nonlinear frequency conversion to cover spectral ranges that are poorly or not covered by direct laser emission. This article presents a short overview of the optical parametric oscillators principles of operation, main implementations and related applications.

In this paper, we present the MESSII Dataset (Manipulator Experimental SyStem Identification and Interaction Dataset). This novel dataset aims at providing numerous sequences of movements of the KUKA iiwa manipulator, in order to evaluate methods for identification and estimation of the robot's dynamic parameters and signals, respectively. Different movements of the manipulator are provided, including trajectories moving one or multiple joints at the same time, trajectories that are specially designed for parameter identification, and trajectories including a payload attached at the end-effector of the manipulator. The information obtained from the propioceptive sensors of position and torque is presented. Furthermore, as physical Human-Robot Interaction (pHRI) is the main application of this robot, sequences with interaction with a person are provided to estimate the forces applied, where a force-torque sensor acts as the ground truth. The dataset can also be used in ROS to evaluate real-time methods as information is presented in rosbags files. Possible applications are given, highlighting the advantage of the dataset to help with state-of-the-art challenges, without the need of the real robot nor doing new and complex experiments. The dataset, as well as more information and tools, are publicly available in https://messii-dataset.enit.fr.

International audience; This work presents a study of the microstructure and mechanical properties of a TNM+ alloy (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, in at.%) densified by Spark Plasma Sintering (SPS), in comparison to the as-SPSed TNM alloy, which contains neither carbon nor silicon. Tensile tests at room temperature and 800 °C, as well as creep tests at 800 °C and 200 MPa, were performed. The microstructures and the fracture surfaces of deformed samples were studied by scanning and transmission electron microscopies, as well as by X-ray diffraction. The deformation mechanisms were investigated by means of in situ straining experiments and post-mortem analyses of deformed samples, both performed by transmission electron microscopy. Contrary to the TNM alloy, the as-SPSed microstructure of the TNM+ alloy does not contain β/βo phase due to the incorporation of carbon. At room temperature, the TNM+ alloy exhibits a yield stress of 520 MPa but a poor ductility of less than 0.1% of plastic strain. The incorporation of carbon and silicon leads to an increase in the creep resistance of the alloy at 800 °C. Despite the fact that iron inclusions are responsible for the premature failure of some samples during tensile tests, the TNM+ alloy is found to be able to deform plastically at room temperature by the glide of ordinary dislocations and by twinning.; Ce travail présente une étude de la microstructure et des propriétés mécaniques d'un alliage TNM+ (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, en at.%) densifié par Spark Plasma Sintering (SPS), en comparaison avec l'alliage TNM brut de SPS qui ne contient ni carbone ni silicium. Des essais de traction à température ambiante et 800°C ainsi que des essais de fluage à 800°C et 200 MPa ont été réalisés. Les microstructures et les surfaces de rupture des échantillons déformés ont été étudiées par microscopie électronique à balayage et à transmission, ainsi que par diffraction des rayons X. Les mécanismes de déformation ont été étudiés au moyen d'expériences de déformation in situ et d'analyses post-mortem d'échantillons déformés, toutes deux réalisées par microscopie électronique à transmission. Contrairement à l'alliage TNM, la microstructure brute de SPS de l'alliage TNM+ ne contient pas de phase bêta/bêta0 en raison de l'incorporation de carbone. Malgré le fait que les inclusions de fer soient responsables de la rupture prématurée de certains échantillons lors des essais de traction, l'alliage TNM+ est capable de se déformer plastiquement à température ambiante. L'incorporation de carbone et de silicium conduit à une augmentation de la résistance au fluage de l'alliage à 800°C.

International audience; The next generation of giant ground and space telescopes will have the light-collect-ing power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are opti-mized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ∕D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.; La prochaine génération de télescopes terrestres et spatiaux géants aura la capacité de collecter la lumière pour détecter et caractériser des exoplanètes terrestres potentiellement habitables en utilisant pour la première fois une imagerie à contraste élevée. Cela ne sera réalisable que si les performances des systèmes d'optique adaptative extrême (ExAO) des télescopes à miroir à segmentés géants (GSMT) sont optimisées à leur plein potentiel. Un composant clé d'un système ExAO est le senseur de front d'onde (WFS), qui mesure les aberrations de la turbulence atmosphérique. Un choix courant dans les instruments actuels et de prochaine génération est le senseur de front d'onde pyramidal (PWFS). Les systèmes ExAO nécessitent un échantillonnage spatial et temporel élevé des fronts d'onde pour optimiser les performances et en conséquence nécessitent des détecteurs de grande taille pour le WFS. Nous présentons une démonstration de banc d'essai en boucle fermée d'un capteur de front d'onde pyramidal à trois côtés (3PWFS) comme alternative au capteur conventionnel de front d'onde pyramidal à quatre côtés (4PWFS) pour les applications GSMT-ExAO sur l'optique adaptative complète innovante et l'instrument de test coronographe ( CACTUS). Le 3PWFS est moins sensible au bruit de lecture que le 4PWFS car il utilise moins de pixels détecteurs. Le 3PWFS a un avantages supplémentaire : une optique pyramidale à trois côtés de haute qualité est plus facile à fabriquer qu'une pyramide à quatre côtés. Nous décrivons la conception des deux composants du système CACTI, le simulateur d'optique adaptative et le banc d'essai PWFS qui comprend à la fois un 3PWFS et un 4PWFS. Nous détaillons le budget d'erreur du système CACTI, passons en revue ses procédures de fonctionnement et d'étalonnage, et discutons de son état actuel. Une expérience préliminaire a été réalisée sur CACTI pour étudier les performances de la 3PWFS à la 4PWFS dans différentes forces de turbulence en utilisant à la fois l'intensité brute et les méthodes de traitement du signal de la carte des pentes. Cette expérience a été répétée pour un rayon de modulation de 1,6 et 3,25 λ∕D. Nous avons constaté que les performances des deux capteurs de front d'onde sont comparables si les gains de boucle modale sont réglés.

International audience; One of the most promising solutions to access high power laser chains is to achieve a coherent combination of a large number of elementary lasers. To interfere constructively, these laser sources should be identical and operate under the same conditions. However, despite these efforts, differential delays appear in the course of time, which must be compensated for. While designing the required correction system, knowing the behavior of a laser as a function of the environmental conditions is not crucial, whereas having access to the differences in the behaviors of identical lasers is, leading to difficulties in modeling. The purpose of this paper is to illustrate how a large set of lasers can be simultaneously analyzed to estimate their variations and optimize a correction system. The X-Coherent Amplified Network laser relies on 61 fiber amplifiers, which are as identical as possible. This state of the art femtosecond digital laser therefore appears as an ideal candidate to study a large number of fiber lasers working under controlled conditions.; L'une des solutions les plus prometteuses pour accéder à des chaînes laser de haute puissance consiste à réaliser une combinaison cohérente d'un grand nombre de lasers élémentaires. Pour interférer de manière constructive, ces sources laser doivent être identiques et fonctionner dans les mêmes conditions. Cependant, malgré ces efforts, des retards différentiels apparaissent au cours du temps, qui doivent être compensés. Lors de la conception du système de correction requis, connaître le comportement d'un laser en fonction des conditions environnementales n'est pas crucial, alors qu'avoir accès aux différences de comportements de lasers identiques l'est, ce qui entraîne des difficultés de modélisation. Le but de cet article est d'illustrer comment un large ensemble de lasers peut être analysé simultanément pour estimer leurs variations et optimiser un système de correction. Le laser XCAN repose sur 61 amplificateurs à fibre, qui sont aussi identiques que possible. Ce laser "numérique" femtoseconde de pointe apparaît donc comme un candidat idéal pour étudier un grand nombre de lasers à fibre fonctionnant dans des conditions contrôlées.

International audience; Space lidar instruments for missions like AEOLUS or MERLIN require advanced high-power laser systems with according technical and financial effort. In order to increase the impact of such missions, it is advantageous to expand the versatility of their instruments. In the case of trace gas sensing, the ability to detect multiple trace gas species with the same instrument greatly enhances their value. Multi-species trace gas differential absorption lidar (DIAL) systems require absolute frequency referencing across large spectral bandwidths. While absorption cell based references need individual lasers at online and offline wavelengths for each species, a broadband mode locked laseroffering a frequency combcan provide the required frequency accuracy over the complete spectral range of the lidar instrument. In the frame of the LEMON project, we developed a combined design for an absolute frequency reference based on a wavemeter for coarse frequency determination (

The space mission MICROSCOPE dedicated to the test of the Equivalence Principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations ($a_{\rm A}$ and $a_{\rm B}$) of two test masses in terms of the E\"otv\"os parameter $\eta({\rm{A, B}}) = 2 \frac{a_{\rm A}- a_{\rm B}}{a_{\rm A}+ a_{\rm B}}$. No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 hours down to the limit of the statistical error which is smaller than $10^{-14}$ for $ \eta({\rm{Ti, Pt}})$. Accumulating data from all segments leads to $\eta({\rm{Ti, Pt}}) =[-1.5\pm{}2.3{\rm (stat)}\pm{}1.5{\rm (syst)}] \times{}10^{-15}$ showing no EP violation at the level of $2.7\times{}10^{-15}$ if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the E\"ot-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null E\"otv\"os parameter with a statistical uncertainty of $1.1\times{}10^{-15}$., Comment: Class. Quantum Grav. 39 204009

International audience; In the context of lightning strike impacting aeronautical fasteners, we investigate the in situ behaviour of fasteners subject to a current level of a few kA by using high-speed Xray phase-contrast imaging in a synchrotron facility. It reveals that the fastener erosion occurs in two time scales. On a microsecond timescale, hot particles are ejected from cavity walls of the Carbon fibre reinforced polymer due to sparking/arcing phenomena, whereas on a sub-millisecond time scale, the fastener wall is vaporized due to the electrical energy deposited in the arc-fastener interface. The experimental observations have been used as input for an electro-thermal model of electric contact. The estimated vaporised depth is in good agreement with the measured one. The nature of the internal damages has been confirmed by using X-ray phase tomography.

International audience; Chalcogenide glasses are increasingly being developed for photonic applications, particularly in the field of mid-infrared optical imaging. In this paper, we study the photosensitivity of one chalcogenide to direct femtosecond laser writing and its possible applications to micro-optics. Particular attention has been paid to the creation of phase changes and related refractive index variations. This chalcogenide glass was compared with two commercial heavy oxide glasses: Schott SF10 and Corning 9754. We observed different types of permanent modifications depending on the writing speed and the laser pulse energy. Index variations were measured at Δn>+0.055 in the chalcogenide glass while maintaining spectral transmission similar to the pristine materials before irradiation. This provides a good candidate to design optical components for infrared application and helps to unlock the potential of the femtosecond laser direct writing technique to implement at high writing speed and high index changes with low optical losses

International audience; The impact damage tolerance remains for laminated composite materials one of the critical step in the design of aeronautical structures. Due to couplings between the different involved damage mechanisms (transverse cracks, delamination, fibre failure), the determination of the damage scenarios is still very challenging considering only post-mortem controls, such as C-Scan or more recently CT-Scan. Therefore, the present study is dedicated to the real time measurement of the evolution of different damage mechanisms during low velocity / low energy impact tests using high-speed infrared thermography. Impact tests at different energy levels were conducted on a T700GC/M21 quasi-isotropic laminate in order to demonstrate for different damage scenarios of increasing complexity the contribution of this measurement technique and to extract valuable information in order to validate simulation. Various post-mortem observation techniques (SEM, C-scan and X-ray tomography) are used in this study to validate and/or determine the chronology of the various damage events identified with infrared thermography measurements. Finally the projected damaged areas have been estimated with IR-thermography at the end of impact tests, based on methodologies available in the literature, and compared with other classical postmortem measurement methods. This comparison highlights that the assessment of the extent of damage by IR thermography tends to overestimate the extent of damage.

International audience; MICROSCOPE is a space mission launched in 2016 that aims to test the validity of the Equivalence Principle (EP), the main postulate of General Relativity (GR), with a precision never reached before (Touboul et al. (2001)). EP states that two bodies of different compositions and masses fall with the same acceleration in the same gravitational field. In order to achieve this goal, MICROSCOPE's instrument is composed of two identical electrostatic differential accelerometers. MICROSCOPE will be the first lab to realize an experiment to test the EP in space which allows to break free from perturbations other than gravity. Those tests used to be presented in terms of the Eötvös ratio η. The first result published in December 2017 shows no evidence of violation higher than 1.3 × 10^−14 at 1 σ on η (Touboul et al. (2017)). This result was obtained with only 7% of the whole data, so the statistical uncertainty would be improved with the analysis of the complete data. During the experiment some thermal variations could disturb the estimation of the Eötvös parameter. In order to better estimate the thermal systematic effect, the thermal sensitivity has to be determined. To do so, thermal stimulus are induced on the instrument by means of dedicated heaters and the response in the measured acceleration is analysed. Two methods were applied for theses analysis and will be presented in this paper. The first one operates in the time domain and the second one in the frequency domain. Those methods allow us to obtain a thermal systematic of 8.6 × 10^−16 which represents an improvement by one order of magnitude with respect to the result of Touboul et al. (2017).; MICROSCOPE est une mission spatiale lancée en 2016 qui vise à tester la validité du principe d'équivalence (EP), le principal postulat de la relativité générale (GR), avec une précision jamais atteinte jusqu'à présent (Touboul et al. (2001)). Le PE stipule que deux corps de compositions et de masses différentes tombent avec la même accélération dans le même champ gravitationnel. Afin d'atteindre ce but, l'instrument de MICROSCOPE est composé de deux accéléromètres différentiels électrostatiques identiques. MICROSCOPE sera le premier laboratoire à réaliser une expérience pour tester le PE dans l'espace qui permet de s'affranchir des perturbations autres que la gravité. Ces tests étaient auparavant présentés en termes de rapport d'Eötvös η. Le premier résultat publié en décembre 2017 ne montre aucune preuve de violation supérieure à 1,3 × 10^-14 à 1 σ sur η (Touboul et al. (2017)). Ce résultat a été obtenu avec seulement 7% de l'ensemble des données, l'incertitude statistique serait donc améliorée avec l'analyse de l'ensemble des données. Pendant l'expérience, certaines variations thermiques pourraient perturber l'estimation du paramètre d'Eötvös. Afin de mieux estimer l'effet systématique thermique, la sensibilité thermique doit être déterminée. Pour ce faire, des stimuli thermiques sont induits sur l'instrument au moyen d'appareils de chauffage dédiés et la réponse dans l'accélération mesurée est analysée. Deux méthodes ont été appliquées pour ces analyses et seront présentées dans cet article. La première opère dans le domaine temporel et la seconde dans le domaine fréquentiel. Ces méthodes nous permettent d'obtenir une systématique thermique de 8.6 × 10^-16 ce qui représente une amélioration d'un ordre de grandeur par rapport au résultat de Touboul et al. (2017).

The Doppler signature of a man walking in a forested area analysed at L‐band is presented here. The aim is twofold: to assess the best time‐frequency distribution to characterise the activity; to highlight the similarity of the simulated data to the measured ones to validate the simulation tool. Indeed, the Doppler‐Time (DT) signal variation represents the main characteristic of Artificial Neural Networks (ANNs) for classification. The more accurately the DT characterises the activity, the higher the machine’s accuracy in classifying it. Besides, in the training data frame, reliable simulated models may supply the amount of data needed by ANN applications. Thus, a short‐time Fourier transform (STFT), a reassigned spectrogram (RE‐Spect), and a pseudo‐Wigner–Ville distribution have been applied to the measured and simulated data. The measurements have been performed using a bistatic radar working at 1 GHz. Then, the measurement setup has been replicated in simulation, and 3‐D human bodies walking in free space have been computed using physical optics. The results show that the STFT is the most suitable time‐frequency method for recognising and classifying the walk. Moreover, the simulated data are in agreement with the measured data, regardless of the chosen Cohen’s technique.

International audience; This article describes an experimental investigation into the heat fluxes generated by the combustion of AP/HTPB solid propellant samples inside 1-MPa pressurized combustion chambers. Fluxmeters developed at ONERA and recently improved were used to measure the local heat flux densities. Two kind of fluxmeters were used: total fluxmeters for which the convective and the radiative components are measured and radiative fluxmeters for which the convective component is suppressed by the use of a sapphire window mounted on top of the fluxmeter. Additionally, the flame was visualized by a narrow-band filtered IR camera which provided quantitative and spatially resolved radiance field. From the IR camera recordings, a radiative heat flux equivalent to that measured by the radiative fluxmeters was constructed by means of the integration over the fluxmeters' collection volumes of the spectrally equivalent radiance. A satisfactory agreement is thus found between the two radiative heat flux measurement methods.; Cet article décrit une étude expérimentale sur les flux de chaleur générés par la combustion d'échantillons de propergol solide AP/HTPB à l'intérieur de chambres de combustion pressurisées de 1-MPa. Des fluxmètres développés à l'ONERA et récemment améliorés ont été utilisés pour mesurer les densités locales de flux de chaleur. Deux types de fluxmètres ont été utilisés : les fluxmètres totaux pour lesquels les composantes convectives et radiatives sont mesurées et les fluxmètres radiatifs pour lesquels la composante convective est supprimée par l'utilisation d'une fenêtre en saphir montée sur le dessus du fluxmètre. En outre, la flamme a été visualisée par une caméra IR à bande étroite filtrée qui a fourni un champ de radiance quantitatif et spatialement résolu. À partir des enregistrements de la caméra IR, un flux de chaleur radiative équivalent à celui mesuré par les fluxmètres radiatifs a été construit par l'intégration de la radiance spectralement équivalente sur les volumes de collecte des fluxmètres. Un accord satisfaisant est donc trouvé entre les deux méthodes de mesure du flux de chaleur radiative.

International audience; The next generation of Extremely Large Telescope (24 to 39m diameter) will suffer from the so-called "pupil fragmentation" problem. Due to their pupil shape complexity (segmentation, large spiders ...), some differential pistons may appear between some isolated part of the full pupil during the observations. Although classical AO system will be able to correct for turbulence effects, they will be blind to this specific telescope induced perturbations. Hence, such differential piston, a.k.a petal modes, will prevent to reach the diffraction limit of the telescope and ultimately will represent the main limitation of AO-assisted observation with an ELT. In this work we analyse the spatial structure of these petal modes and how it affects the ability of a Pyramid Wavefront sensor to sense them. Then we propose a variation around the classical Pyramid concept for increasing the WFS sensitivity to this particular modes. Nevertheless, We show that one single WFS can not accurately and simultaneously measure turbulence and petal modes. We propose a double path wavefront sensor scheme to solve this problem. We show that such a scheme,associated to a spatial filtering of residual turbulence in the second WFS path dedicated to petal mode sensing, allows to fully measure and correct for both turbulence and fragmentation effects and will eventually restore the full capability and spatial resolution of the future ELT.; La prochaine génération de Télescope Extrêmement Large (de 24 a 39m de diamètre) souffrira du problème de fragmentation de la pupille. Du a la complexité de la pupille de ces télescopes (segmentation, grande araignée, ...) des différences de piston peuvent apparaître entre les fragments de la pupille. Les systèmes d'Optique adaptative (OA) censées corrigés l'effet de turbulence seront aveugles a ces perturbations induites par la structure du télescope. Ces effets de piston différentiels souvent nommés mode pétale nous empêcheront d'atteindre la limite de diffraction du télescope et peut représenter la limite des observations assistés par Optique Adaptatives. Dans ce travail nous étudions la structure spatial de ces modes pétales et comment cela affecte la capacité du senseur pyramide a le mesurer. Ensuite nous proposons une modification du senseur pyramide pour améliorer la sensibilité au mode pétale. Néanmoins, nous avons montré qu'un seul ne peut pas être efficace pour mesurer en même temps la turbulence et les modes pétales. Nous proposons un senseur a deux voies pour résoudre ce problème. Nous montrons aussi qu'un tel schéma, associé a un filtrage spatial des résidus de turbulence permet de mesurer plus complétement et corriger la turbulence et les effets de fragmentation et finalement permet de restaurer la capacité et résolution compléte des futurs ELT.

This paper proposes new algorithms for the metric learning problem. We start by noticing that several classical metric learning formulations from the literature can be viewed as modified covariance matrix estimation problems. Leveraging this point of view, a general approach, called Robust Geometric Metric Learning (RGML), is then studied. This method aims at simultaneously estimating the covariance matrix of each class while shrinking them towards their (unknown) barycenter. We focus on two specific costs functions: one associated with the Gaussian likelihood (RGML Gaussian), and one with Tyler's M -estimator (RGML Tyler). In both, the barycenter is defined with the Riemannian distance, which enjoys nice properties of geodesic convexity and affine invariance. The optimization is performed using the Riemannian geometry of symmetric positive definite matrices and its submanifold of unit determinant. Finally, the performance of RGML is asserted on real datasets. Strong performance is exhibited while being robust to mislabeled data., Published in EUSIPCO 2022. Best student paper award

International audience; This paper presents a new sequential method to calibrate a material model in the presence of significant material variability. Material variability is handled in the mixed-effects framework. In this approach, material variability is described by a probability distribution calibrated by maximizing a likelihood. Yet, when the number of model parameters or the computational time of a single run of the models increases (for multiaxial models for instance), the maximization of the likelihood of mixed-effects is more difficult to perform. Furthermore, the parameters do not have the same influence on the material model depending on the nature of the test. The proposed procedure enables to calibrate the model on multiple experiments. It relies on the definition of a sequence of calibration subproblems. Associated to the relevant experimental data, each subproblem allows to calibrate the joint distribution of a subset of the model parameters. The maximization of the attached likelihood is eased as the number of unknown parameters is reduced compared to full problem. The subproblems are solved sequentially. To ensure consistency of the global process, the research space for the distribution parameters already estimated with a previous calibration is restricted to a trust region. The proposed calibration process is applied to an orthotropic elastic model with laminates made from T700GC/M21 base ply material. The ability of the procedure to sequentially estimate the model parameters distribution is investigated. Its capability to ensure consistency throughout the calibration process is discussed. Results show that the proposed procedure is a promising methodology to handle the calibration of complex material models in the mixed-effects framework.

Super-Resolution (SR) is a technique that seeks to upscale the resolution of a set of measured signals. SR retrieves higher-frequency signal content by combining multiple lower resolution sampled data sets. SR is well known both in the temporal and spatial domains. It is widely used in imaging to reduce aliasing and enhance the resolution of coarsely sampled images.This paper applies the SR technique to the bi-dimensional wavefront reconstruction. In particular, we show how SR is intrinsically suited for tomographic multi WaveFront Sensor (WFS) AO systems revealing many of its advantages with minimal design effort. This paper provides a direct space and Fourier-optics description of the wavefront sensing operation and demonstrate how SR can be exploited through signal reconstruction, especially in the framework of Periodic Nonuniform Sampling. Both meta uniform and nonuniform sampling schemes are investigated. Then, the SR bi-dimensional model for a Shack Hartmann (SH) WFS is provided and the characteristics of the sensitivity function are analyzed. The SR concept is finally validated with numerical simulations of representative multi WFS SH AO systems. Our results show that combining several WFS samples in a SR framework grants access to a larger number of modes than the native one offered by a single WFS and that despite the fixed sub-aperture size across samples. Furthermore, we show that the associated noise propagation is not degraded under SR. Finally, the concept is extended to the signal produced by single Pyramid WFS. In conclusion, SR applied to wavefront reconstruction offers a new parameter space to explore as it decouples the size of the subaperture from the desired wavefront sampling resolution. By cutting short with old assumptions, new, more flexible and better performing AO designs become now possible., Astronomy & Astrophysics Section: 13. Astronomical instrumentation AA/2022/43954

Laboratory testbeds are an integral part of conducting research and developing technology for high-contrast imaging and extreme adaptive optics. There are a number of laboratory groups around the world that use and develop resources that are imminently required for their operations, such as software and hardware controls. The CAOTIC (Community of Adaptive OpTics and hIgh Contrast testbeds) project is aimed to be a platform for this community to connect, share information, and exchange resources in order to conduct more efficient research in astronomical instrumentation, while also encouraging best practices and strengthening cross-team connections. In these proceedings, we present the goals of the CAOTIC project, our new website, and we focus in particular on a new approach to teaching version control to scientists, which is a cornerstone of successful collaborations in astronomical instrumentation., 15 pages, 6 figures, 2 tables; SPIE proceedings Astronomical Telescopes + Instrumentation 2022, 12185-119

Ordinary Differential Equations are derived for the adjoint Euler equations firstly using the method of characteristics in 2D. For this system of partial-differential equations, the characteristic curves appear to be the streamtraces and the well-known C+ and C- curves of the theory applied to the flow. The differential equations satisfied along the streamtraces in 2D are then extended and demonstrated in 3D by linear combinations of the original adjoint equations. These findings extend their well-known counterparts for the direct system, and should serve analytical and possibly numerical studies of the perfect-flow model with respect to adjoint fields or sensitivity questions. Beside the analytical theory, the results are demonstrated by the numerical integration of the compatibility relationships for discrete 2D flow-fields and dual-consistent adjoint fields over a very fine grid about an airfoil., 22 pages, 7 figures

This work deals with recursive dynamic parameter identification in robotics and presents a new method applied to industrial manipulators based on the recursive instrumental variable. We construct the instrumental matrix by filtering the reference trajectory and its derivatives with the position closed-loop transfer function previously identified with standard today’s toolboxes, such as CAPTAIN. This implies that we no longer need to simulate the direct dynamic model and, therefore, to know the controller, and that we can build the instrumental matrix beforehand. Besides the closed-loop transfer function acting as a unitary gain at low frequencies, we can use the references directly if only low frequencies are excited. This approach, called Inverse Dynamic Identification Model Recursive Instrumental Variable (IDIM-RIV), is evaluated offline on the 7 degrees of freedom KUKA LBR iiwa R820 manipulator. The experimental validation suggests that IDIM-RIV is computationally cheaper than its en-bloc version, can identify 64 dynamic parameters, and presents good robustness against noise and algorithm initialization.

International audience; HARMONI is the first light visible and near-IR integral field spectrograph for the ELT covering a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes-SCAO and LTAO-or with no AO. The project is preparing for Final Design Reviews. The laser Tomographic AO (LTAO) system provides AO correction with very high sky-coverage thanks to two systems: the Laser Guide Star Sensors (LGSS) and the Natural Guide Star Sensors (NGSS). LGSS is dedicated to the analysis of the wavefront coming from 6 laser guide stars created by the ELT. It is made of 6 independent wavefront sensor (WFS) modules mounted on a rotator of 600mm diameter to stabilise the pupil onto the microlens array in front of the detector. The optical design accepts elongated spots of up to 16 arcsec with no truncation using a CMOS detector from SONY. We will present the final optical and mechanical design of the LGSS based on freeform lenses to minimize the numbers of optical components and to accommodate for the diversity of sodium layer configurations. We will focus on rotator design, illustrating how we will move 1 tons with 90" accuracy in restrictive environment. Finally, we will present the strategy to verify the system in HARMONI context. The main challenge for the verification being how to test an AO system without access to the deformable mirror, part of the ELT.

Context.The combination of large segmented space telescopes, coronagraphy, and wavefront control methods is a promising solution for producing a dark hole (DH) region in the coronagraphic image of an observed star in order to study planetary companions. The thermal and mechanical evolution of such a high-contrast instrumental setup leads to wavefront drifts that degrade the DH contrast during the observing time, thus limiting the ability to retrieve planetary signals.Aims.Lyot-style coronagraphs are starlight-suppression systems that remove the central part of the image for an unresolved observed star, that is, the point spread function, with an opaque focal plane mask (FPM). When implemented with a flat mirror containing an etched pinhole, the mask rejects part of the starlight through the pinhole which can be used to retrieve information about low-order aberrations.Methods.We propose an active control scheme using a Zernike wavefront sensor (ZWFS) to analyze the light rejected by the FPM, control low-order aberrations, and stabilize the DH contrast. We first present the concept formalism and then describe how we characterized the sensor behavior in simulations and in the laboratory. We performed experimental tests to validate a wavefront control loop using a ZWFS on the HiCAT testbed.Results.By controlling the first 11 Zernike modes, we show a decrease in the standard deviation of the wavefront error by a factor of up to 9 between open- and closed-loop operations using the ZWFS. In the presence of wavefront perturbations, we show the ability of this control loop to stabilize a DH contrast around 7 × 10−8with a standard deviation of 7 × 10−9.Conclusions.Active control with a ZWFS proves to be a promising solution in Lyot coronagraphs with an FPM-filtered beam for controlling and stabilizing low-order wavefront aberrations and DH contrast for exoplanet imaging with future space missions.

The impact of a temperature mesosphere inversion on the vertical propagation of gravity waves has been investigated using OH airglow images and ground-based Rayleigh lidar measurements carried out on December 2017 at the Haute-Provence Observatory (OHP, France, 44N). These measurements provide complementary information that allows the vertical propagation of gravity waves to be followed. An intense Mesospheric Inversion Layer (MIL) observed near 60 km with the lidar disappeared in the middle of the night offering a unique opportunity to evaluate its impact on gravity wave (GW) propagation observed above the inversion with airglow cameras. With these two instruments, a wave with 150 min period has been observed, and was also identified in meteorological analyses. The gravity waves potential energy vertical profile shows clearly the GW energy lost below the inversion altitude and a large increase of gravity waves energy above the inversion in OH airglow images with waves exhibiting higher frequency. The MIL are known to causes instabilities at its top part and this is probably the reason of enhanced gravity waves observed above., L'impact d'une inversion de température mésosphérique sur la propagation verticale des ondes de gravité a été étudié à l'aide d'images airglow et de mesures au sol par lidar Rayleigh effectuées en décembre 2017 à l'Observatoire de Haute-Provence (OHP, France, 44N). Ces mesures fournissent des informations complémentaires qui permettent de suivre la propagation verticale des ondes de gravité. Une intense couche d'inversion mésosphérique (MIL) située au voisinage de 60 km observée avec le lidar a disparu au milieu de la nuit offrant une opportunité unique d'évaluer son impact sur la propagation des ondes de gravité (GW) observées au-dessus de l'inversion avec les caméras airglow. Avec ces deux instruments, une onde avec une période de 150 min a été observée, et a également été identifiée dans les analyses météorologiques. Le profil vertical de l'énergie potentielle des ondes de gravité montre clairement la perte d'énergie des ondes de gravité en dessous de l'altitude de l'inversion et une forte augmentation de l'énergie des ondes de gravité au-dessus de l'inversion dans les images airglow avec des ondes de fréquence plus élevée. L'inversion mésosphérique est connue pour provoquer des instabilités dans sa partie supérieure et c'est probablement la raison de l'augmentation des ondes de gravité observées au-dessus.

In this article, we present a cryogenic spot scan bench in the 3-5 µm band currently under development in the ONERA MIRCOS platform. Initial tests have been carried out on a HgCdTe detector with a 30 µm pitch and improvements are underway to characterise smaller pixels., Dans cet article, nous présentons un banc de spot scan cryogénique dans la bande 3-5 µm actuellement en développement dans la plateforme MIRCOS de l'ONERA. Des premiers tests ont été réalisés sur un détecteur HgCdTe au pas de 30 µm et des améliorations sont en cours pour pouvoir caractériser de plus petits pixels.

We illustrate the benefits of Algorithmic Differentiation (AD) for the development of aerodynamic flow simulation software. In refining the architecture of the elsA CFD solver, developed jointly by ONERA and Safran, we consider AD as a key technology to cut development costs of some derivatives of interest, namely the tangent, adjoint, and Jacobian. We first recall the mathematical background of CFD applications which involve these derivatives. Then, we briefly present the software architecture of elsA (Cambier et al. [12]) and the design choices which give it its HPC capability while highlighting how these choices strongly constrain the applicability of AD. To meet our efficiency requirements, we select the Source-Transformation approach to AD through the Tapenade tool which is justified by a series of experiments and benchmarks. Finally, we present results on large scale configurations., On montre les bénéfices de la différentation algorithmique (AD) pour le développement de code de simulation aérodynamique. Lors de la réarchitecture du solveur CFD elsA, développé conjointement par l'ONERA, Airbus et Safran, on considère que l'AD est une technologie indispensable pour réduire les coûts de développement de certaines dérivées d'intérêt, i.e. les modes tangent, adjoint et jacobien. On rappelle le contexte mathématique qui rend central ces dérivées particulières. On présente brièvement l’architecture logicielle d’elsA et les choix de conception qui lui confèrent sa capacité HPC. On discute en quoi ces choix contraignent fortement l’applicabilité de l'AD. Pour répondre à nos exigences en matière d'efficacité, nous avons choisi l'approche Source-Transformation de AD et l'outil Tapenade, au regard d'une série d'expériences et de mesures que l'on présente ici. Enfin, les résultats de simulations plus ambitieuses réalisées récemment avec cette amélioration du logiciel elsA sont montrés.

International audience; The study of complex reactive flows met in aeronautical engines is an experimental challenge that requires the development of noninvasive and precise measurement techniques. Coherent anti-Stokes Raman scattering (CARS) is a standard spectroscopic technique used for temperature measurements, which provides unmatched reliability and accuracy at high repetition rate thanks to its recent adaptation to femtosecond temporal regime. This paper reports the first demonstration of hybrid fs/ps-CARS thermometry in a representative aeronautical combustor (ONERA MICADO test bench, Reynolds number ≈105). Single-shot N2 CARS spectra have been recorded at 1 kHz, allowing temperature follow up, statistical and frequency (0.1–500 Hz) analysis of CH4/air flame at 0.34-MPa total pressure. The achieved results demonstrate the ability of the technique to be applied in representative engines conditions and its maturity for semi-industrial applications.

International audience; We solve the full-consensus problem (in position and orientation) with connectivity maintenance for multiple nonholonomic vehicles in a leader-follower configuration. We rely on a polar-coordinates based model which is more natural for the problem setting. The proposed control law is smooth (in the domain of definition) time-invariant and uses only relative measurements, making it more suited for implementation. We establish asymptotic convergence to the consensus manifold as well as connectivity maintenance using the Lyapunov's first method and cascaded systems theory. In addition, we illustrate our theoretical contributions experimentally.

International audience; This study aims to numerically investigate the noise radiated by a reduced-scale rocket engine jet at lift-off conditions including a flame trench. An over-expanded Mach 3.1 hot jet entering a flame duct where it impinges on a deflector before being guided in a horizontal duct, is considered. The computation is performed with a two-way coupled approach on unstructured grids. This methodology relies on a large-eddy simulation of the jet and the acoustic near field, associated with a full Euler simulation of the acoustic far field. The aerodynamic and acoustic results are compared to a previous computation involving the Ffowcs Williams and Hawkings approach and show a better agreement with the measurements conducted at the MARTEL facility. A more careful analysis of the pressure field suggests that the noise is strongly influenced by the flame trench geometry. Nonlinear propagation effects, natively taken into account by the full Euler solver, are finally highlighted and discussed. Based on appropriate metrics, a good agreement with the experiment is obtained.; Cette étude vise à simuler le bruit généré par un jet de moteur-fusée à échelle réduite dans des conditions au décollage en présence d'un carneau. Un jet chaud sur-détendu à Mach 3.1 s'engouffre dans le carneau où il impacte un déflecteur avant d'être guidé dans un conduit horizontal. Le calcul est effectué par couplage fort sur des maillages non structurées. Cette méthodologie s'appuie sur une simulation aux grandes échelles du jet et du champ acoustique proche, associée à une simulation du champ acoustique lointain par résolution des équations d'Euler. Les résultats aérodynamiques et acoustiques sont comparés à un précédent calcul où l'acoustique avait été traitée par la méthode intégrale de Ffowcs Williams et Hawkings. Ils montrent un meilleur accord avec les mesures effectuées au banc MARTEL. Une analyse approfondie du champ de pression suggère que le bruit est fortement influencé par la géométrie du carneau. Enfin, les effets de propagation non- linéaire, pris en compte nativement par le solveur Euler, sont mis en évidence et discutés. Sur la base de métriques appropriés, un bon accord avec l'expérience est obtenu.

Millimeter wave (mmWave) generation using photonic techniques has so far been limited to the use of near-infrared lasers that are down-converted to the mmWave region. However, such methodologies do not currently benefit from a monolithic architecture and suffer from the quantum defect i.e. the difference in photon energies between the near-infrared and mmWave region, which can ultimately limit the conversion efficiency. Miniaturized terahertz (THz) quantum cascade lasers (QCLs) have inherent advantages in this respect: their low energy photons, ultrafast gain relaxation and high nonlinearities open up the possibility of innovatively integrating both laser action and mmWave generation in a single device. Here, we demonstrate intracavity mmWave generation within THz QCLs over the unprecedented range of 25 GHz to 500 GHz. Through ultrafast time resolved techniques, we highlight the importance of modal phases and that the process is a result of a giant second-order nonlinearity combined with a phase matched process between the THz and mmWave emission. Importantly, this work opens up the possibility of compact, low noise mmWave generation using modelocked THz frequency combs., Photonic solutions for generating free space millimeter radiation is a fast developing field that combines optoelectronics and RF domains but has many challenges. Here the authors present a quantum cascade laser (QCL) based solution for THz laser emission and millimeter wave generation in a single device.

International audience; In the context of an embedded structural health monitoring (SHM) system, two methods of transducer integration into the core of a laminate carbon fiber-reinforced polymer (CFRP) are tested: cutout and between two plies. This study focuses on the effect of integration methods on Lamb wave generation. For this purpose, plates with an embedded lead zirconate titanate (PZT) transducer are cured in an autoclave. The embedded PZT insulation, integrity, and ability to generate Lamb waves are checked with electromechanical impedance, X-rays, and laser Doppler vibrometry (LDV) measurements. Lamb wave dispersion curves are computed by LDV using two-dimensional fast Fourier transform (Bi-FFT) to study the quasi-antisymmetric mode (qA0) excitability in generation with the embedded PZT in the frequency range of 30 to 200 kHz. The embedded PZT is able to generate Lamb waves, which validate the integration procedure. The first minimum frequency of the embedded PZT shifts to lower frequencies and its amplitude is reduced compared to a surfacemounted PZT.

International audience; Shot peening of turbine disk engines is performed in the aerospace industry in order to enhance fatigue life. This surface enhancement method generates beneficial modifications like superficial compressive residual stresses that are known to delay crack initiation and propagation. In the same way, work hardening is also introduced at the surface of the part during shot peening and can have a significant influence on fatigue crack initiation. Taking this parameter into account in the fatigue design of parts, in addition to the residual stresses, is a real challenge to be the most predictive. One possibility for this is to be able to predict it during the modeling of the shot peening process. In the present work, various peening conditions are considered in order to be able to propose a model able to account for the influence of coverage and Almen intensity on residual stresses and work hardening. The studied material is Inconel 718, commonly used for aeronautical parts. The X-ray diffraction method is used to obtain the in-depth residual stress and work-hardening profiles. A three-dimensional numerical model is proposed to predict these quantities. Efforts are made to consider all recent advances in three-dimensional simulation of the process, in terms of coverage assessment, shot and treated part modeling. The numerical results are compared to the experimentally measured residual stresses and work hardening.

International audience; Background: Uncertainty quantifications are required for any measurement result to be meaningful. Objective: The present work aims at deriving and comparing a priori estimates of displacement uncertainties in T3-stereocorrelation for a setup to perform high temperature tests. Methods: Images acquired prior to the actual experiment (i.e., at room temperature) were registered using 3-noded triangular elements (T3-stereocorrelation) to determine displacement uncertainties for different positions of the experimental setup. Results: The displacement uncertainties were then compared to their a priori estimates. Conclusions: For the analyzed experiment, it is shown that noise floor estimates only differed by a factor 2 when compared to a posteriori measurements of standard displacement uncertainties.

International audience; An interval method based on Pontryagin's Minimum Principle is proposed to enclose the solutions of an optimal control problem with embedded bounded uncertainties. This method is used to compute an enclosure of all optimal trajectories of the problem, as well as open loop and closed loop enclosures meant to validate an optimal guidance algorithm on a concrete system with inaccurate knowledge of the parameters. The differences in geometry of these enclosures are exposed, and showcased on a simple system. These enclosures can guarantee that a given optimal control problem will yield a satisfactory trajectory for any realization of the uncertainties. Contrarily, the probability of failure may not be eliminated and the problem might need to be adjusted.

International audience; Reusable liquid-propellant rocket engines (LPREs) imply more demanding robustness requirements than expendable ones due to their extended capabilities. Therefore, the goal of this work was to develop a control loop adapted to all the operating phases of LPRE, including transients, and robust to internal parametric variations. Firstly, thermo-fluid-dynamic simulators representative of the gas-generator-cycle engines were built. These simulators were subsequently translated into nonlinear state-space models. Based on these models, the continuous subphase of the start-up transient is controlled to track precomputed reference trajectories. Beyond the start-up, throttling scenarios are managed with end-state-tracking algorithm. Model Predictive Control has been applied in a linearised manner with robustness considerations to both scenarios, in which a set of hard state and control constraints must be respected. Tracking of pressure (thrust) and mixture-ratio operating points within the design envelope is achieved in simulation while respecting constraints. Robustness to variations in the predominant parameters, to external state perturbations and to the possible impact of an observer on the loop, is demonstrated.

We present here a method for the quantitative prediction of the spectroscopic specular reflectivity line-shape in anisotropic layered media. The method is based on a 4 &times, 4 matrix formalism and on the simulation from the first principles (through density functional theory&mdash, DFT) of the anisotropic absorption cross-section. The approach was used to simulate the reflectivity at the oxygen K-edge of a 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) thin film on Au(111). The effect of film thickness, orientation of the molecules, and grazing incidence angle were considered. The simulation results were compared to the experiment, permitting us to derive information on the film geometry, thickness, and morphology, as well as the electronic structure.

International audience; Complex-chemistry direct numerical simulation (DNS) data obtained earlier from lean hydrogen-air flames associated with corrugated flame (case A), thin reaction zone (case B), and broken reaction zone (case C) regimes of turbulent burning are analysed to directly assess capabilities of the flamelet approach to predict mean concentrations of species in a premixed turbulent flame. The approach consists in averaging dependencies of mole fractions, reaction rates, temperature, and density on a single combustion progress variable c, which are all obtained from the unperturbed laminar flame. For this purpose, four alternative definitions of c are probed and two probability density functions (PDFs) are adopted, i.e. either an actual PDF extracted directly from the DNS data or a presumed β-function PDF obtained using the DNS data on the first two moments of the c(x, t)-field. Results show that the mean density and mean mole fractions of H2, O2, and H2O are well predicted using both PDFs for each c, although the predictive capabilities are little worse in case C. In cases A and B, the use of the actual PDF and the fuel-based c also offers an opportunity to well predict mean mole fractions of O and H, whereas the mean mole fraction of OH is slightly underestimated. In the highly turbulent case C, the same approach performs worse, but still appears to be acceptable for evaluating the mean radical concentrations. The use of the β-function PDFs or another combustion progress variable yields substantially worse results for these radicals. When compared to the mean mole fractions, the mean rate of product creation, i.e. the source term in the transport equation for the mean combustion progress variable, is worse predicted even for a quantity (species concentration or temperature) adopted to define c and using the actual PDF. Consequently, turbulent burning velocity is not predicted either.

At the nanoscale, materials exhibit unique properties that differ greatly from those of the bulk state. In the case of Ag$_{x}$Pt$_{1-x}$ nanoalloys, we aimed to study the solid-liquid transition of nanoparticles of different sizes and compositions. This system is particularly interesting since Pt has a high melting point (2041 K compare to 1035 K for Ag) which could keep the nanoparticle solid during different catalytic reactions at relatively high temperatures, such as we need in the growth of nanotubes. We performed atomic scale simulations using semi-empirical potential implemented in a Monte Carlo code at constant temperature and chemical composition in canonical ensemble. We observed that the melting temperature decreases with the size (pure systems and alloys) and the composition. We show that the melting systematically passes through an intermediate stage with a crystalline core (pure platinum or mixed PtAg depending on the composition) and a pure silver liquid skin, which strongly questions the idea of having a faceted solid particle in catalytic reactions for carbon nanotubes synthesis.

International audience; Le code MANTA a l’ambition de permettre la réalisation de simulations complexes en mécanique sur des supercalculateurs actuels et futurs tout en préservant les fondamentaux des codes développés au CEA : adaptabilité au problème posé, robustesse des algorithmes, pérennité des modèles et du code. On expose les principes de développement de ce code de nouvelle génération, et quelques exemples représentatifs de ses capacités actuelles sont également décrits.