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Investigation of cooling efficiency and structural characteristics of supercritical CO2 jets for machining assistance
No full textInternational audienceIn a context of safer, more cost-effective, and environmentally friendly machining processes, supercritical carbon dioxide (scCO2) emerges as a promising alternative to conventional cutting fluids. However, a consolidated understanding of the optimal scCO2 jet parameters for machining and its impact on the tool and the material remains unavailable. This work intends to address the behavior of a free and impinged scCO2 jet structure and its geometrical evolution in function of the upstream jet conditions. The supersonic structure and parameters were analyzed under varying initial pressures and temperatures in both near and far fields. The obtained images showed the detailed jet structure and highlighted the presence of three different zones within the flow: laminar, transitional then turbulent. To investigate this behavior and to better understand the jet’s cooling ability in these different zones, an in-depth analysis of the jet’s complex structure was carried out using high-speed imaging combined with an optical imaging known as Schlieren
Microstructures à profil optique contrôlé par évaporation via un masque en demi-teintes
No full textOn présente une variante d’évaporation à masque d’ombrage utilisant des masques en demi-teintes réutilisables pour imposer un contrôle du flux de matière et donc de l’épaisseur locale. Comme illustré en Figure 1, on démontrera que l’utilisation de dépôts d’aluminium ou de composés organiques, en combinaison avec étapes de gravure ou d’implantation ionique, permettent de réaliser des structures présentant des variations graduelles d’épaisseur optique freeform à des échelles <100 µm
Reviewing experimental studies on chemical thermal energy storage in Cementitious composites: report of the RILEM TC 299-TES
No full textInternational audienceThermochemical energy storage (TCES) is a method of storing energy by using reversible chemical reactions to absorb and release heat. TCES materials generally possess the highest volumetric energy density and negligible heat losses during cyclic charging/discharging when compared with sensible and latent heat storage materials. The controllable charging/discharging processes in the TCES materials make them suitable for long-term or seasonal thermal energy storage, which can help improve the resilience of the existing energy system and built environment. In recent years, there has been a growing number of studies on the use of cementitious materials as low-cost and low-carbon thermochemical energy storage materials, including ettringite, calcium aluminate cements, and geopolymers. In this study, the state-of-the-art development using cementitious materials for thermo-chemical energy/heat storage applications is reviewed and systematically compared in terms of their compositions, energy storage operating conditions, and energy storage performance. Technical recommendations are proposed for standardised characterisation and testing protocols of these cementitious (composite) materials used for thermochemical heat storage. The current research challenges and future research needs in this field are also discussed
Superviz25-SQL: High-Quality Dataset to Empower Unsupervised SQL Injection Detection Systems
No full textInternational audienceThe digitalization of public and private services has led to more sophisticated and serious cybersecurity threats. Among them, SQL injection attacks leverage user inputs to remotely execute malicious actions on a database, such as data exfiltration and deletion, or privilege escalation. They are regularly classified as one of the most prominent threats to web services. Intrusion detection systems are widely used to detect such injection attacks and react to them, but it is difficult to assess their actual effectiveness and compare them because of a lack of high-quality datasets. Current SQL injection detection datasets lack diversity, are poorly documented, and the generated samples are not representative of real-world infrastructures. This article presents a new dataset Superviz25-SQ , whose design is structured around four quality dimensions: realism, diversity, benchmarking capabilities and the presence of good documentation. We examine the dataset diversity using lexical, syntactic and semantic metrics, and demonstrate that its size is sufficient to evaluate data-intensive detectors. Finally, we provide nine classical and state-of-the art SQL injection detection pipelines as baselines for future works
Expansion d'anneaux pré-entaillés pour l'étude de l'endommagement dynamique des métaux
No full textInternational audienceCette étude porte sur le développement d’un dispositif expérimental permettant de réaliser des essais de traction dynamique indirecte sur des éprouvettes entaillées à des vitesses de déformation d’environ 10s pour étudier l’endommagement dynamique des matériaux métalliques. Basé sur un dispositif existant nommé PIDRET, il consiste à soumettre des anneaux pré-entaillés à une expansion radiale dynamique et à observer les différentes phases de déformation et d’endommagement jusqu’à rupture. Le travail présenté ici concerne le pré-dimensionnement numérique de la géométrie des entailles et la validation expérimentale de l’expansion radiale dynamique d’anneau épais
Addressing viscosity-driven singularities: accurate development of thermo-elasto-visco-plastic constitutive models
No full textInternational audienceA novel analytical-mathematical formulation for the multi-physics thermo-elasto-visco-plastic (TEVP) behavior of materials with nonlinear combined hardening is proposed. New closed-form expressions for the incremental visco-plastic multiplier (IVPM) and the consistent tangent operator (CTO) were derived. Specifically, all stiffness, hardening, and viscous coefficients were treated as temperature-dependent, and their temperature derivatives were explicitly included in the analytical solution. A UMAT (User Material) subroutine was programmed and implemented to compute the IVPM, CTO, and isotropic, kinematic, and viscous stresses for TEVP modeling. Finite element (FE) models were created and compared for the Abaqus® built-in material model and the developed UMAT subroutine. The IVPM and CTO equations were successfully validated and the influence of the initial IVPM value on the accuracy of the results and the run time of simulations was examined for the first time. It was found that, in the Newton-Raphson method, the initial IVPM value must not only be nonzero to avoid singularity issues, but also be less than or equal to 10−8 to ensure accurate results. In addition, the initial IVPM value did not influence computational efficiency. Ultimately, based on a comparative study of analytical solutions, UMAT-driven simulations, and standard Abaqus simulations, the developed formulation enables accurate prediction of strains, stresses, and temperatures in TEVP problems, providing a solid foundation for modeling industrial manufacturing processes such as quenchin
Algèbre homotopique des feuilletages
No full textThere are two natural analogues of algebraic foliations in derived algebraic geometry, called partition Lie algebroids and infinitesimal derived foliations, and both make sense in general characteristics. We construct an equivalence between these two notions under some finiteness conditions. Our method is refining the PD Koszul duality by Brantner--Mathew, Brantner--Campos--Nuiten using the (completed) Hodge filtration.Il existe deux analogues naturels des feuilletages algébriques en géométrie algébrique dérivée, appelés algebroïdes de Lie à partition et feuilletages dérivés infinitésimaux, qui sont tous deux définis en caractéristique générale. Nous construisons une équivalence entre ces deux notions sous certaines conditions de finitude. Notre méthode consiste à raffiner la dualité de Koszul à puissances divisées de Brantner--Mathew, Brantner--Campos--Nuiten en utilisant la filtration de Hodge (complétée)
Safe and wind-aware synchronous path planning for a fleet of fixed-wing constant speed aircraft
No full textPath planning for multiple vehicles is a difficult task, but even more so for fixed-wing aircraft. When flying several of them, multiple constraints may apply: constant airspeed, to maintain optimal operational conditions; synchronous arrival to destination, to achieve formation flight; taking into account wind, for limiting deviation from plan, especially for smaller Unmanned Aerial Vehicles. We present a method to solve this problem based on enumerating variations of Dubins paths until a conflict-free solution is found. This provides a simple and parallelizable scheme that can be extended to handle sequencing tasks. We showcase different situations solved in simulation to illustrate the possible applications: transitions between formations, getting into formation and airport arrival sequencing
The optical analogy between a Lorentz-violating cosmos and a magneto-electric medium
No full textInternational audienceThe goal of our study is to investigate the effects of Lorentz symmetry violation by examining the behavior of photons within the framework of the Standard Model Extension (SME). We show that, from an optical point of view, the Lorentz-violating cosmos is analogous to a magneto-electric medium like the quantum vacuum in the presence of the magnetic and electric field. This analogy provides a formulation for exploring experimental evidence of Lorentz symmetry violation in the propagation of light in a vacuum, in particular in the case of a radiation background observed like the CMB
Automatic selection of inducing points in sparse Gaussian process for approximations of finite element analyses
No full textInternational audienceGaussian process regression (GPR) is a widely used regression model, but it has poor scalability. Sparse approximation methods improve scalability by using in- ducing points to approximate the GPR, but determining the optimal number and placement of these points is challenging. This article presents a method to esti- mate the necessary number of inducing points for accurate predictions of finite element method (FEM) analyses using approximate GPR. The approach lever- ages the proper orthogonal decomposition (POD) technique, using its modes to determine the inducing points. POD has previously been combined with GPR to provide computationally efficient predictions for the full solution field across un- seen variable combinations, treating spatial components separately via reduced basis functions. However, this work treats the spatial component as a variable within the GPR approximation, allowing continuous spatial predictions. This en- sures that the covariance in the spatial dimension is captured by a single GPR. The method is applied to simulations of a three-span, post-tensioned concrete girder bridge. Results demonstrate that the proposed method identifies a suf- ficient number of inducing points for approximate GPR to achieve predictive accuracy comparable to full GPR, but with half the training time. Furthermore, approximate GPR achieves accuracy similar to POD with GPR, while slightly reducing predictive variance in specific areas. This approach ensures computa- tional efficiency without significant loss in accuracy, making it a valuable tool for scalable regression in engineering applications