53 research outputs found

    Modélisation de sols irréguliers par une impédance effective dans des codes de propagation acoustique

    Get PDF
    L’impact acoustique d’installations industrielles ou de transport sur l’environnement est fréquemment évalué en utilisant des méthodes d’ingénierie simplifiées. Afin de valider ces méthodes, il est nécessaire de disposer de résultats numériques de référence pour des situations réalistes de propagation en milieu extérieur. Ces situations incluent une variabilité géométrique des frontières du milieu (topographie, discontinuités dues à des obstacles, rugosité du sol), qui est souvent mal caractérisée (incertitudes de mesure) et connue uniquement de manière statistique. L’objectif de ce travail est d’implémenter des modèles d’impédance effective tenant compte de la rugosité du sol dans des codes de référence de propagation acoustique, notamment dans le domaine temporel. L’utilisation de ces modèles d’impédance effective permet de ne pas avoir à mailler les irrégularités du sol et ainsi de réduire le coût des calculs. On s’intéresse aux modèles d’impédance effective proposés par Attenborough, dans lesquels la rugosité est considérée à travers des petits diffuseurs de géométrique simple (demi-cylindres, demi-ellipses, triangles isocèles) disposés de manière régulière ou aléatoire le long du chemin de propagation. Des modèles d’impédance effective définis à partir de spectres de rugosité sont également étudiés. Des résultats de calculs utilisant ces modèles d'impédance dans des codes de calculs temporels de référence (TLM et FDTD) sont présentés

    Time-domain numerical modeling of acoustical propagation in the presence of boundary irregularities

    No full text
    International audienceNumerical reference models are necessary to validate engineering methods used for acoustical predictions in realistic situations. These situations include irregular geometries and characteristics that are not accurately known. This can be due to the complexity of the propagation medium, space and time variability of its physical properties, measurements uncertainties, etc. The objective of this work is to compute sound propagation through such complex media using two numerical methods. The first one is based on the resolution of the Linearized Euler Equations with high order finite difference schemes (FDTD). The second one is based on a discrete representation of the Huygens principle using nodes and transmission lines (TLM). The required improvements of the numerical codes are exposed. First examples of numerical studies dealing with irregular geometries and impedance ground properties are presented

    Age-specific olfactory attraction between Western honey bee drones (Apis mellifera) and its chemical basis.

    No full text
    During the mating season, drones (males) of the Western honey bee (Apis mellifera) form congregations numbering thousands high in the air. Virgin queens arrive at these congregations after they have formed and mate on the fly with 15-20 drones. To explain the formation of drone congregations, a drone-produced aggregation pheromone has been proposed many years ago but due to the low accessibility of natural mating sites in bees, its study has progressed slowly. Recently, we used a walking simulator in controlled laboratory conditions to show that drones are indeed attracted by groups of other drones. Since these previous experiments were carried out with drones captured when flying out of the hive, it is currently unclear if this olfactory attraction behaviour is related to the drones' sexual maturity (usually reached between 9 and 12 days) and may thus be indicative of a possible role in congregation formation, or if it is observed at any age and may represent in-hive aggregation. We thus assessed here the dependency of drone olfactory attraction on their age. First, we performed behavioural experiments in the walking simulator to measure olfactory preferences of drones in three age groups from 2-3 to 12-15 days. Then, we performed chemical analyses in the same age groups to evaluate whether chemical substances produced by the drones may explain age differences in olfactory attraction. We show that honey bee drones are attracted by conspecifics of the same age when they are sexually mature (12-15 days old) but not when they are younger (2-3 and 7-8 days old). In parallel, our data show that drones' chemical profile changes with age, including its most volatile fraction. These results are discussed in the context of drone mutual attraction both within the hive and at drone congregations

    Modelling of random ground roughness by an effective impedance and application to time-domain methods

    No full text
    International audienceNatural grounds can exhibit small scale geometric irregularities, compared to the acoustic wavelength, known as ground roughness. This roughness has a noticeable effect on sound pressure levels and produces a surface wave. In the context of prediction methods improvement for outdoor sound propagation, using an effective impedance appears to be an useful approach to model the effects of surface roughness. Two time-domain numerical methods are considered: finite difference schemes (FDTD), and the transmission line modeling (TLM) method. An effective impedance model for random ground roughness defined by a roughness spectrum, called the SPM model, is exposed. The efficiency of this model for taking into account the mean effects of random roughness on sound pressure levels and for modeling the roughness-induced surface wave is shown, by comparing with results of TLM simulations of propagation above random rough grounds. The direct implementation of the SPM model as a boundary condition in both TLM and FDTD methods is then studied. This approach allows the modeling of ground roughness effects in numerical methods without having to mesh finely the ground roughness profile, allowing easier and faster computations, and more accurate predictions for future impact studies in environmental acoustics

    UNE APPROCHE FONCTIONNELLE EN VISION PROTHETIQUE : ETUDE PRELIMINAIRE DANS LE CONTEXTE DE LA MOBILITE

    No full text
    International audienceCes travaux s'inscrivent dans le cadre plus général de la réalisation d'une prothèse visuelle destinée aux personnes atteintes de cécité tardive due par exemple à une maladie dégénérative de la rétine comme la rétinite pigmentaire. Les études consacrées au contenu informationnel de la vision prothétique proposent en général une diminution de la résolution des images issues d'une camera. En contraste à cela, nous proposons une approche fonctionnelle originale de la vision prothétique spécifique aux besoins en mobilité, conçue en collaboration avec des rééducateurs spécialisés. Nous proposons de montrer le fort intérêt que représente l'utilisation d'informations 3D de la scène observée. Pour évaluer nos propositions, un dispositif de simulation de vision prothétique a été développé et les résultats des premiers tests effectués apportent des preuves de la pertinence des représentations de l'environnement fournies. Mots-clefs: prothèse visuelle; mobilité; interface homme-machine; simulation de vision prothétique; approche fonctionnelle ; informations 3D

    A New Methodology to Predict the Magnetic Shielding Effectiveness of Enclosures at Low Frequency in the Near Field

    No full text
    International audienceIn this paper, a methodology to calculate the shielding effectiveness (SE) of enclosures with slots at low frequency in the near magnetic field is presented. This modeling technique is based on the magnetic moments and the transmission line (TL) approach and makes specific assumptions. It is applied to a slot of small size relative to the dimensions of the enclosure. The slot is electrically short. This technique is validated in the case of a real enclosure with numerical simulations and experimental data. This method is dedicated to the case of mechatronics boxes using in electric and hybrid vehicles (EHVs), it allows obtaining the results with sufficient accuracy precision for dimensioning a magnetic shielding in a short time
    • …
    corecore