Source separation algorithms for the analysis of hyperspectral observations of very small interstellar dust particles

International audienceThe mid-infrared (mid-IR) spectrum of our galaxy is dominated by continuum and band emission due to carbonaceous very small dust particles amongst which are polycyclic aromatic hydrocarbon (PAH) molecules. Because they absorb the UV photons ofmassive stars and re-emit this energy in the infrared, IR spectro-imaging of extended interstellar (or circumstellar) regions is a powerful tool to diagnose the nature of these particles together with the local physical conditions. In this paper, we review how the applications of blind / bayesian source separation (BSS) methods applied to mid-IR hyperspectral data can help analyzing these data. We then discuss, in the light of simulations in progress, how BSS methods could be used to identify specific PAH molecules in the interstellar medium when applied to the hyper-spectral data of forthcoming IR telescopes (Herschel, SOFIA, SPICA)

Contrasting the Harmonic Balance and Linearized Methods for Oscillating-Flap Simulations

In the framework of unsteady aerodynamics, forced-harmonic-motion simulations can be used to compute unsteady loads. In this context, the present paper assesses two alternatives to the unsteady Reynolds-averaged Navier–Stokes approach, the linearized unsteady Reynolds-averaged Navier–Stokes equations method, and the harmonic balance approach. The test case is a NACA 64A006 airfoil with an oscillating ␣ap mounted at 75% of the chord. Emphasis is put on examining the performances of the methods in terms of accuracy and computational cost over a range of physical conditions. It is found that, for a subsonic ␣ow, the linearized unsteady Reynolds-averaged Navier–Stokes method is the most ef␣cient one. In the transonic regime, the linearized unsteady Reynolds-averaged Navier–Stokes method remains the fastest approach, but with limited accuracy around shocks, whereas a one- harmonic harmonic balance solution is in closer agreement with the unsteady Reynolds-averaged Navier–Stokes solution. In the case of separation in the transonic regime, the linearized unsteady Reynolds-averaged Navier–Stokes method fails to converge, whereas the harmonic balance remains robust and accurate

Implicit Hybrid mesh Method for the Computation of Rotorcraft Flows

No abstract available

Modelling directional sound radiation in Antares by the Ffowcs Williams and Hawkings acoustic analogy

Progress is made in the validation and use of a shareable, royalty-free, non-commercial Computational AeroAcoustics (CAA) post-processor for predicting the far-field noise radiated by acoustically active transonic flows. Building upon past validation tests of this Ffowcs Williams and Hawkings CAA post-processor, which is part of the Antares software suite, predictions are obtained of a single isothermal Mach 0.9 jet at a Reynolds number of approximately half million. A more challenging application to a dual-flux transonic isothermal jet issuing from two axisymmetric coaxial nozzles, with axially staggered nozzle exit planes, shows salient spectral roll-off rates and directivity patterns typical of this geometry, which represents an idealised turbofan engine exhaust configuration. This builds confidence in the application of this new tool to aeroacoustic research as well as to aircraft design

Implementing the Ffowcs Williams and Hawkings acoustic analogy in ANTARES

The aerodynamic noise radiating from an unsteady flow can be extracted by an acoustic analogy approach from time-resolved Computational Fluid Dynamic (CFD) simulations. For this purpose, a Ffowcs Williams and Hawkings (FW-H) post-processor is developed, based on an advanced time formulation. The method is coded in Python and embedded in Antares, which is a CFD companion software developed by Cerfacs, France. The availability in Antares of input and output data interfaces for structured and unstructured CFD geometries and solutions provides a good software development platform. The new post-processor is tested on a hierarchy of noise sources of increasing complexity, for which comparison is made with existing data. The radiating field from a simple monopole is considered first, with progression to a subsonic jet test case, for which acoustic data have been estimated by Bogey and Bailly (2006). CFD results obtained at Cerfacs (France), using a compressible Large Eddy Simulation (LES) on the same test case, provide the input to the acoustic analogy to estimate the far-field noise. The far-field noise predictions are compared to the acoustic results obtained with the CFD software elsA (Onera, France), that uses the same Ffowcs Williams and Hawkings acoustic analogy formulation and these are found in good agreement

A one year study to estimate maritime contributions to PM10 levels in a coastal area in northern France

International audienc

Projet TOSCA OSYNICO : Optimisation et SYNergie des données In situ et COuleur de l'eau pour l’étude de la dynamique biogéochimique des eaux côtières

National audienceLa mise en place de plusieurs réseaux nationaux d’observation in situ (e.g. SOMLIT, REPHY, COAST-HF,..) ainsi que les récents développements méthodologiques en terme d’observation spatiale dite « couleur de l’eau » à l’échelle nationale permettent désormais de suivre la dynamique des eaux côtières françaises à de multiples échelles spatiales ou temporelles. L’exploitation de ces informations terrain ou satellite, généralement effectuée de manière indépendante, doit cependant faire face à différentes limitations propres aux observations in situ (e.g. faible emprise spatiale : données localisées et nombre de stations limité au sein d’un même site ou le long du littoral) ou aux données satellitaires (e.g. incertitudes sur les produits, fréquence d’acquisition, couverture temporelle réduite). Le projet OSYNICO (TOSCA/CNES) a été défini dans ce contexte et a pour objectif général de démontrer l’avantage de la complémentarité des observations in situ et satellite pour 1) décrire les évolutions à long terme (évolution des signaux moyens et des oscillations saisonnières) des caractéristiques biogéochimiques des eaux côtières françaises (de l’échelle locale à l’échelle synoptique) 2) d’apprécier l’impact des évènements climatiques extrêmes sur ces écosystèmes côtiers. Les bases de données et outils/métriques mis en place dans le cadre du projet pour la comparaison des dynamiques observées pour des variables clés (e.g. Chla, MES, POC) via les observations in situ et couleur seront présentés. Un focus sera effectué sur les premiers résultats obtenus aux échelles saisonnières et interannuelles

Space Adaptive Methods/Meshing

This chapter describes space adaptive approaches developed by six TILDA partners for the application in scale-resolving simulations. They are designed to provide sufficient spatial resolution in regions where required and to allow a lower resolution elsewhere for efficiency reasons. Adaptation techniques considered include mesh (h-refinement), order refinement of the spatial discretization (p-refinement) or a combination of both (hp-refinement). Furthermore, near-wall local mesh refinement, refinement using feature-based indicators and indicators obtained from the Variational Multiscale Method are considered

Space Adaptive Methods/Meshing

This chapter describes space adaptive approaches developed by six TILDA partners for the application in scale-resolving simulations. They are designed to provide sufficient spatial resolution in regions where required and to allow a lower resolution elsewhere for efficiency reasons. Adaptation techniques considered include mesh (h-refinement), order refinement of the spatial discretization (p-refinement) or a combination of both (hp-refinement). Furthermore, near-wall local mesh refinement, refinement using feature-based indicators and indicators obtained from the Variational Multiscale Method are considered