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The Outer Space Inside Us: Ordinary Language and the Care for the Extraterrestrial Commons
No full textInternational audienc
Optimization of plasmonic metasurfaces: a homogenization-based design
No full textInternational audienceThis article deals with the optimization of resonant plasmonic metasurfaces through their surface-homogenized counterpart. The derivation of effective transition conditions that takes into account the spatially varying geometries is done using locally periodic surface homogenization. The resulting model reduces the numerical cost of simulating these metasurfaces, thus allowing to find their design using adjoint-based optimization methods. This new algorithm is presented in details, together with various numerical examples to asses its validity and compare its performance with the classical design based on local phase matching
A stochastic volume approach based on tailored Green’s functions for airfoil noise prediction at low Mach number
No full textInternational audienceThe presence of boundary surfaces in a turbulent flow can result in the enhancement of the radiated acoustic field especially for eddies close to any geometrical singularity. At low Mach number, the best suited prediction methods consist in using an acoustic analogy solved with an integral formulation. In the present study, we focus on the Lighthill's wave equation combined with a tailored Green's function and a new semi-analytical model for the turbulence statistics in the space-frequency domain to extend acoustic analogies to geometries of arbitrary shapes. To validate the model predictions for the leading edge noise and the trailing edge noise, a NACA 0012 airfoil at zero angle of attack is considered and predictions are compared to experimental data. The volume integral approach introduced in this study allows us to study the spatial distribution of the noise sources inside the turbulence volume. In addition, the direct noise radiation associated with the turbulent boundary layer is investigated
A hybridizable discontinuous Galerkin method with characteristic variables for Helmholtz problems
No full textInternational audienceA new hybridizable discontinuous Galerkin method, named the CHDG method, is proposed for solving time-harmonic scalar wave propagation problems. This method relies on a standard discontinuous Galerkin scheme with upwind numerical fluxes and high-order polynomial bases. Auxiliary unknowns corresponding to characteristic variables are defined at the interface between the elements, and the physical fields are eliminated to obtain a reduced system. The reduced system can be written as a fixed-point problem that can be solved with stationary iterative schemes. Numerical results with 2D benchmarks are presented to study the performance of the approach. Compared to the standard HDG approach, the properties of the reduced system are improved with CHDG, which is more suited for iterative solution procedures. The condition number of the reduced system is smaller with CHDG than with the standard HDG method. Iterative solution procedures with CGN or GMRES required smaller numbers of iterations with CHDG
Defense program quality‐cost‐delay optimization: architecture framework, a bridge between program management and system engineering
No full textInternational audienceAbstract Military program management and system engineering re quire the expression of costs and delay trade‐off with respect to system architecture. If architecture frameworks (AF) such as NATO (NAF) were designed to fill this common need, their current state is essentially descriptive. As it turns out, building defense systems architectures using those frameworks in a properly anticipated cost/delay budget envelope would require to have all system engineering already solved, because the architecture frameworks are designed to provide an explicit representation of the operational domain that can be used in analysis, for articulation of issues and requirements, as support to planning, and as a means of solution design and validation, among other things. Thus Quality‐Resource‐Time optimality in a regularly evolving environment cannot be represented in acceptable delay without automated optimization assistance. Our contribution in this article explores coupling architecture framework with operation research (OR) models to enable computer assisted design and evaluation of heterogeneous views in NATO Architecture Framework (NAF). Our illustrative example is a Linear Programming based bridge between program management and system engineering to anticipate optimal trade‐offs. This article presents promising results, with which we hope to show how OR and AF will be indivisible in architecture evaluation process
TRAJECTORY MONITORING FOR A DRONE USING INTERVAL ANALYSIS
No full textInternational audienceWhen modelizing a robot, uncertainties are bound to be taken into account. Uncertainties may appear because of approximations linked to the model. Sometimes uncertainties are unavoidable as they are linked to the sensors' accuracies, or inherent to the control of the robot. For instance, interval observers could be used for parameter estimation and state estimation. This paper proposes a method to consider all these uncertainties and to monitor the reliance of trajectories using interval analysis. The case study of this article is to monitor the trajectory of a holonomic drone controlled by its velocity, but the monitoring could be extended to more complex dynamic systems
A tribute to Professor Samir Zard
No full textInternational audienceProfessor Samir Z. Zard A tribute.This special issue of Arkivoc is dedicated to Professor Samir Z. Zard, on the occasion of his new status as Emeritus researcher and in recognition of his outstanding contribution to synthetic organic chemistry.Published on line 05-15-2023 Arkivoc 2024 (ii) 20231495 Six, Y
Free-Surface Effects on Two-Dimensional Hydrofoils by RANS-VOF Simulations
No full textInternational audienceFoiling yachts and crafts are both very sensitive to the flying height in terms of stability and performance, raising the scientific issue of the influence of the free-surface when the foil is at low submergence. This work presents numerical simulations of a 2D hydrofoil section NACA0012 at 5° angle of attack in the vicinity of the free-surface, for different values of the submergence depth, for a chord-based Froude number of 0.571 and a Reynolds number of 159,000. Unsteady-Reynolds Averaged Navier-Stokes (URANS) equations are solved with a mixture model to capture the free surface (Volume Of Fluid method), and using an automatic grid refinement. Verification of the numerical model and validation with data from the literature are presented. Deformation of the free surface and alteration of the hydrodynamic forces compared to the deep immersion case are observed for a submergence depth-to-chord ratio ℎ/c lower than 2. The foil drag increases up to more than three times the infinite-depth value at ℎ/c≈0.5. The lift force slightly increases until ℎ/c around 1, and then decreases sharply. For ℎ/c < 0.5, the pressure field around the foil is totally modified and the lift is swapped to downward. The study highlights the importance of considering the effect of finite submergence to compute foils’ hydrodynamic forces, for example to be used in Velocity Prediction Programs (VPP) of foiling crafts
Analyzing Data Efficiency and Performance of Machine Learning Algorithms for Assessing Low Back Pain Physical Rehabilitation Exercises,
No full textInternational audienc
Use of infrared thermography to model the effective stress ratio effect on fatigue crack growth in welded T-joints
No full textInternational audienceWelded joints constitute critical components in the high-cycle fatigue dimensioning of naval structures. In particular, the local geometry of the weld toe as well as the welding process induced residual stress strongly impact the fatigue properties. In that regard, such factors must be considered in a dedicated fatigue life forecast model, identified via an adapted experimental protocol. On the basis of X-ray stress analysis and in-situ crack growth monitoring by thermoelastic stress analysis, the present study introduces a linear elastic fracture mechanics model that considers the initial residual stress field in the vicinity of the weld toe