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A robust computational framework for the mixture-energy-consistent six-equation two-phase model with instantaneous mechanical relaxation terms
No full textWe present a robust computational framework for the numerical solution of a hyperbolic 6-equation single-velocity two-phase system. The system's main interest is that, when combined with instantaneous mechanical relaxation, it recovers the solution of the 5-equation model of Kapila. Several numerical methods based on this strategy have been developed over the years. However, neither the 5- nor 6-equation model admits a complete set of jump conditions because they involve non-conservative products. Different discretizations of these terms in the 6-equation model exist. The precise impact of these discretizations on the numerical solutions of the 5-equation model, in particular for shocks, is still an open question to which this work provides new insights. We consider the phasic total energies as prognostic variables to naturally enforce discrete conservation of total energy and compare the accuracy and robustness of different discretizations for the hyperbolic operator. Namely, we discuss the construction of an HLLC approximate Riemann solver in relation to jump conditions. We then compare an HLLC wave-propagation scheme which includes the non-conservative terms, with Rusanov and HLLC solvers for the conservative part in combination with suitable approaches for the non-conservative terms. We show that some approaches for the discretization of non-conservative terms fit within the framework of path-conservative schemes for hyperbolic problems. We then analyze the use of various numerical strategies on several relevant test cases, showing both the impact of the theoretical shortcomings of the models as well as the importance of the choice of a robust framework for the global numerical strategy
Joint optical-digital design strategy for adaptive optics systems: application to wavelength selection for satellite imaging
No full textInternational audienceAdaptive optics can be used to mitigate the effects of atmospheric turbulence on imaging systems, but the correction is only partial, and deconvolution is often required to improve the resolution. This results in entire optical/digital systems, which are traditionally designed sequentially, i.e. , the adaptive optics system is optimised first, and the restoration algorithms are designed a second time. Studies on optical/digital systems have shown that jointly optimizing the whole system is a better alternative. We propose to extend these co-design strategies to the design of an adaptive optics-assisted imaging system. We derive a simple criterion that takes into account the source properties and the entire optical/ digital system performance. To illustrate its interest, we use it to optimize the wavelength distribution between the wavefront sensor and the imaging camera. In addition, we explore the potential of using multiple imaging channels operating at different wavelengths as a means of making an imaging system robust to turbulence strength and source magnitude variations. Later, any parameter of the optical/digital system, if not the entire system itself, could be optimized this way
What We Can Learn From the Sensor-to-Plasma Coupling Resistance Measurements in the Earth Ionosphere
No full textInternational audienceMeasurements of electric potentials and currents in the Earth’s ionosphere are primarily influenced by the thermal plasma properties and the intensity of photoelectron emission from sunlit spacecraft surfaces. These measurements can be significantly affected by a plasma sheath that forms around the satellite to neutralize surface electric charging in contact with the ambient plasma. In the ionosphere, this sheath typically ranges from a few to several tens of centimeters in thickness and contains plasma that slightly differ from the surrounding undisturbed environment. Therefore, accurately characterizing the electrical properties of the sheath is essential for reliable data interpretation. In this study, we analyze ion plasma and electric field measurements taken at an altitude of 700 km by the Centre National d’Etudes Spatiales (CNES) detection of electro-magnetic emissions transmitted from earthquake region (DEMETER) microsatellite. The data were collected during specific orbital passes when onboard instruments operated in calibration mode. During these sequences, electric currents were intentionally injected from the electric field sensors into the surrounding plasma, enabling estimation of the sensor-to-plasma coupling resistance across the sheath. Plasma parameters obtained by fitting the resistance–current curve with a standard orbital-motion-limited (OML) model are compared with those derived from the ion instrument on the same spacecraft. The dataset confirms the consistency of plasma measurements performed by the two instruments
Modélisation hiérarchique et optimisation d'architectures de systèmes : Revue comparative et cadre unifié
No full textInternational audienceSimulation-based problems involving mixed-variable inputs frequently feature domains that are hierarchical, conditional, heterogeneous, or tree-structured. These characteristics pose challenges for data representation, modeling, and optimization. This paper reviews extensive literature on these structured input spaces and proposes a unified framework that generalizes existing approaches. In this framework, input variables may be continuous, integer, or categorical. A variable is described as meta if its value governs the presence of other decreed variables, enabling the modeling of conditional and hierarchical structures. We further introduce the concept of partially-decreed variables, whose activation depends on contextual conditions. To capture these inter-variable hierarchical relationships, we introduce design space graphs, combining principles from feature modeling and graph theory. This allows the definition of general hierarchical domains suitable for describing complex system architectures. The framework supports the use of surrogate models over such domains and integrates hierarchical kernels and distances for efficient modeling and optimization. The proposed methods are implemented in the open-source Surrogate Modeling Toolbox (SMT 2.0), and their capabilities are demonstrated through applications in Bayesian optimization for complex system design, including a case study in green aircraft architecture.Les problèmes basés sur la simulation à variables mixtes présentent fréquemment des domaines hiérarchiques, conditionnels, hétérogènes ou arborescents, ce qui complique la représentation des données, la modélisation et l’optimisation. Cet article dresse un panorama exhaustif de la littérature sur ces espaces d’entrée structurés, puis propose un cadre unifié généralisant les approches existantes. Dans ce cadre, les variables d’entrée, continues, entières ou catégorielles, peuvent être qualifiées de « méta » lorsqu’elles régissent la présence d’autres variables décrétées, autorisant ainsi la modélisation de dépendances conditionnelles et hiérarchiques. Nous introduisons également les « variables partiellement décrétées », dont l’activation dépend de contextes spécifiques. Pour formaliser ces relations, nous définissons des graphes d’espace de conception (design space graphs) combinant notions de feature modeling et théorie des graphes, capables de décrire des architectures systèmes complexes. Le cadre prend en charge des modèles de substitution (surrogate models) adaptés à ces domaines, et intègre des distances hiérarchiques ainsi que des noyaux dédiés pour optimiser efficacité et précision. Les méthodes proposées sont implémentées dans la boîte à outils libre Surrogate Modeling Toolbox (SMT 2.0) et validées via des applications d’optimisation bayésienne, notamment une étude de cas portant sur l’architecture d’avions écologiques
Interferences within a certifiable design methodology for high-performance multi-core platforms
No full textInternational audienceThe adoption of high-performance multi-core platforms in avionics and automotive systems introduces significant challenges in ensuring predictable execution, primarily due to shared resource interferences. Many existing approaches study interference from a single angle—for example, through hardware-level analysis or by monitoring software execution. However, no single abstraction level is sufficient on its own. Hardware behavior, program structure, and system configuration all interact, and a complete view is needed to understand where interferences come from and how to reduce them.In this paper, we present a methodology that brings together several tools that operate at different abstraction levels. At the lowest level, PHYLOG provides a formal model of the hardware and identifies possible interference channels using micro-architectural transactions. At the program level, machine learning analysis locates the exact parts of the code that are most sensitive to shared-resource contention. At the compilation level, MLIR-based transformations use this information to reshape memory access patterns and reduce pressure on shared resources. Finally, at the system level, Linux cgroups enforce static execution constraints to prevent highly interfering tasks from running together. The goal of our approach is to reduce memory interference and improve the system's predictability, thereby easing the certification process of multi-core systems in safety-critical domains
Benchmark for two-dimensional large scale coherent structures in partially magnetized E × B plasmas—community collaboration & lessons learned
No full textInternational audienceAbstract Low-temperature plasmas (LTPs) are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of LTP codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized E × B Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development
Enhancing Multi-Fidelity Bayesian Optimization for Mixed-Variable, Multi-Objective Multi-Disciplinary Drone Design Optimization
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Creation of manufacturing cost estimation surrogate models for application in a cross-organizational design workflow
No full textInternational audienceEstimating manufacturing cost is a crucial step in evaluating the value of an aircraft design. However, this estimation is often performed only after the design and optimization phases are completed. In this paper, cost estimation is captured in surrogate models, making it available early in the design process. Using surrogate models for cost estimation also addresses intellectual property and complexity challenges. The use case presented in this paper focuses on a seaplane wing. The surrogate models are built using results from a Design of Experiments approach. To obtain these results, a knowledge-based engineering tool is employed to model the seaplane wing, and an open-source cost model is used to estimate the cost. The surrogate model itself is created using a Gaussian process model. Its sensitivity is analyzed, revealing that some design variables can be omitted while maintaining good model quality. Finally, the surrogate model is prepared for integration into a cross-organizational design workflow for the seaplane wing. The developed surrogate model proves useful in addressing intellectual property and complexity issues
Étude numérique d'un système de jet vectorisés par effet coanda pour l'injection d'air dans le jeu d'un compresseur
No full textInternational audienceThe operating range of compressors is limited by the outbreak of flow instabilities with a highly negative impact on performance. Active control such as air tip injection delays the onset of stall. Previous research [1] indicates that optimal performance is achieved when the air injection is tangential to the casing with a relative blowing yaw angle closely matching the blade stagger angle. As the relative blowing yaw angle changes with the operating point, the study focuses on the development of a device which can adjust its blowing angle using two co-flow jets and the Coandă effect. An extensive numerical parametric study is conducted involving various geometries. To fasten and ease the meshing process, a mesh adaptation technique is employed. A first bi-dimensional case is examined to validate the method on a Coandă-based co-flow jet vectorization. Subsequently, a three dimensional actuator geometry is analysed, accounting the constraints of a compressor. A validation of the method on the bi-dimensional case is presented and the effect of massflow ratios and radius of curvature are examined. Numerical results on the actuator geometry demonstrate the ability of the actuator to deflect a jet with an angle up to 15 degrees, while staying attached to the casing.La plage de fonctionnement des compresseurs est limitée par l’apparition d’instabilités d’écoulement ayant un impact très négatif sur les performances. Le contrôle actif, comme l’injection d’air en tête d’aube, permet de retarder l’apparition du pompage. Des études précédentes ont montré que les meilleures performances sont obtenues lorsque l’injection d’air est tangentielle au carter, avec un certain angle de soufflage relatif en lacet. Comme cet angle de soufflage relatif varie selon le point de fonctionnement, l’étude se concentre sur le développement d’un dispositif capable d’ajuster son angle de soufflage en utilisant deux jets co-courants et l’effet Coandă
Simulations numériques haute fidélité de l'écoulement et du bruit d'un jet double flux installé sous un empennage en T
No full textInternational audienceThe aerodynamic field and the acoustic signature of a mixed-stream coaxial jet, representative of a low-bypass ratio engine and installed on a T-tail configuration typical of business jets is investigated numerically. The nozzle diameter is 80 mm and the jet velocity is 280 m/s (M=0.9) for both streams, leading to a Reynolds number Re_D = 1.5 × 1e6. The time-accurate flows fields are simulated with a Wall Modelled LES approach (ZDES mode 3) and are used to reconstruct radiated noise with the Ffowcs Williams and Hawkings integral formulation. The full T-tail region is included in the aerodynamic simulation to account for scattering effects. A very good match with the experimental flow and noise data is found but the important numerical dissipation that occurs during the propagation of the sound waves towards the tailplane restricts the prediction to low- and medium-frequencies in this direction. The jet is found to be far enough from the fuselage and horizontal tailplane not to be impacted by their presence; this property is used to model the acoustic radiation towards the tailplane from an isolated jet configuration that matches the wall pressure levels and spatial coherence up to the high frequencies.Cette étude porte sur l’écoulement et la signature acoustique d’un jet coaxial issu d’une tuyère à flux mélangés, représentatif d’un moteur à faible taux de dilution, installé sous un empennage en T et caractéristique d’un avion d’affaire. Le diamètre de la tuyère est de 80 mm et la vitesse du jet est de 280 m/s (M=0,9) pour les deux flux, ce qui correspond à un nombre de Reynolds Re_D = 1,5 × 1e6. L'écoulement instationnaire est simulé avec une approche LES avec loi de paroi (ZDES mode 3) et est utilisé pour reconstruire le bruit rayonné avec la formulation intégrale de Ffowcs Williams et Hawkings. Toute la région de l'empennage en T est incluse dans la simulation aérodynamique pour tenir compte des effets de réfraction et de diffraction lors de propagation acoustique. On constate une très bonne correspondance avec les données expérimentales pour l'écoulement et le bruit, mais la dissipation numérique importante des ondes acoustiques pendant leur propagation vers l'empennage limite la prévision aux basses et moyennes fréquences dans cette direction. Le jet est suffisamment éloigné du fuselage et de l'empennage pour ne pas être affecté par leur présence ; cette propriété est utilisée pour modéliser le rayonnement acoustique vers l'empennage à partir d'une configuration de jet isolée. Les niveaux de pression à la paroi et la cohérence spatiale simulés reproduitent les mesures jusqu'aux hautes fréquences