Propagation dans des guides d'ondes irréguliers : approximation unidirectionnelle pour une application à l'acoustique urbaine

Modéliser la propagation acoustique dans une rue représente un coût numérique élevé. Pour réduire le temps de calcul, nous proposons d'effectuer une approximation one-way. Par le biais d'un changement de coordonnées appliqué à l'équation parabolique standard, il est possible de modéliser des guides d'ondes dont la géométrie varie continument. Le modèle obtenu est comparé avec une solution de référence ce qui permet de mettre en avant la bonne modélisation du champ de pression pour des irrégularités variant lentement devant la longueur d'onde

On the approximation of total absorption of the street open ceiling at low frequencies

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Réfrigérateur thermoacoustique "compact" (modélisation, conception, évaluation)

La conception et réalisation de nouveaux réfrigérateurs thermoacoustiques de petites dimensions et à faible coût a compté parmi les axes d études dans ce domaine ces dernières années. Le développement de ces systèmes repose essentiellement sur la réduction d échelle des réfrigérateurs classiques et l usage de sources piézoélectriques. Mais la demande de systèmes miniaturisés pour l évacuation de la chaleur des composants microélectroniques ouvre la voie à de nouvelles études en vue de leur modélisation et de leur conception. C est ainsi que le travail effectué sur ce sujet comporte trois volets : -i- Etude analytique de sources piézoélectriques couplées aux résonateurs thermoacoustiques, faisant usage d une description améliorée du système piézoélectriques et de sa charge acoustique, qui a révélé des comportements non prévus, -ii- Présentation par extension des résultats analytiques de la littérature, d une méthode qui permet de mieux identifier les paramètres influant sur le comportement du cœur des systèmes thermoacoustiques en vue de son optimisation de fonctionnement (ici le maximum du gradient de température dans le stack), -iii- Conception et réalisation sur la base des résultats théoriques mentionnés ci-dessus, d un réfrigérateur thermoacoustique compact, et étude expérimentale confirmant en première approche les résultats théoriques. Les résultats de ces travaux et les idées qu ils ont portées permettent d ores et déjà d énoncer les exigences essentielles qu il convient de satisfaire dans la réalisation de ce nouveau type de réfrigérateur thermoacoustique compact, réalisation par technique MEMS pour le cœur du système et faisant usage de transducteurs piézoélectriques.In recent years, there has been a strong motivation for designing new thermoacoustic refrigerators involvong smaller dimensions and lower power consumption. Attempts to develop practical devices have been concentrated on both reducing th escale of the classical refrigerators and adapting piezoelectric sources. But the need for providing advances in modelling and designing miniaturized systems arises when dealing with the heat transfert from microelectronic components. Therefore, the aim of the work done on this subject is threefold : -i- To invistigate analytically the behaviour of the coupling between piezoelectric sources and thermoacoustic resonators, using a revisited description for the acoustically loaded piezoelectric system which conveys significant improvements and new (unexpected) results, -ii- To derive a method, extending analytical results available in the literature, to identify more deeply the parameters which govern the optimal behaviour of the core of the thermoacoustic systems (here the highest temperature gradient allowed in the stack), -iii- To design a miniaturized compact thermoacoustic refrigerator using the theoretical results obtained from the method mentioned above, and to show agreements and discrepancies between theoretical and experimental results. Requirements that have to be taken into account in the design of new kind of miniaturized compact thermoacoustic refrigerators (using MEMS techniques for the core and adapted piezoelectric transducers) can be adressed from results obtained and the ideas conveyed in this work.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

Higher Order Padé Approximation for the Parabolic Equation in a Varying Cross-Section Waveguide

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Bremmer series for the multimodal sound propagation in inhomogeneous waveguides

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Coarse-grid computation of the one-way propagation of coupled modes in a varying cross-section waveguide

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Switching perspective: Comparing ground-level and bird’s-eye views for bees navigating clutter

Sonntag A, Sauzet O, Lihoreau M, Egelhaaf M, Bertrand O. Switching perspective: Comparing ground-level and bird’s-eye views for bees navigating clutter. bioRxiv. 2023.**Abstract** Animals navigating in three dimensions encounter different perspectives of their world, often transitioning from bird’s eye views at higher altitudes to frog’s-eye views closer to the ground. How they integrate this information to pinpoint a goal location is virtually unknown. Here we tested the ability of bumblebees to use both types of views when homing in a cluttered environment. While prior research emphasised ground-level cues, recent evidence suggests bees incorporate bird’s-eye perspectives at higher altitudes for long-distance navigation. This raises the question of whether bird’s-eye views also aid local homing, especially in environments where nest entrances are concealed by undergrowth. Our combined modelling and experimental approach examined various views for goal location in cluttered settings. Whereas, bird’s-eye views performed best in simulations of current snapshot homing models, behavioural experiments revealed that bumblebees predominantly relied on frog’s eye views when pinpointing nest entrances in cluttered environments. These findings reveal the limitations of snapshot-homing models and suggest that bumblebees use a mix of navigational tools to successfully find their way home in cluttered environments. This is not only relevant for understanding bee movements, but also for other animals and humans navigating in 3D as well as the development of technologies inspired by natural systems, such as autonomous flying robots. **Significance statement** Navigation in three dimensions is essential for animals especially for those that swim or fly, like fish, birds, or bees. Moving at different altitudes relative to the destination, animals undergo a range of perspectives, transitioning from aerial, bird’s eye views to goal-level perspectives as they approach their goal. We investigated if bumblebees utilise both perspectives when homing in cluttered environments. While past studies focused on ground-level cues, recent findings suggest bees incorporate bird’s-eye views for long-distance navigation. Our study explores whether these views also aid local homing, particularly for visually concealed goals. The results challenge existing models, revealing that bumblebees employ a combination of navigational strategies in cluttered settings, impacting our understanding of 3D navigation in animals and technology development. </p

Navigation by Honey Bees

International audienceNavigation by honey bees refers to the cognitive and behavioral mechanisms bees of the genus Apis use to move between a location and one or multiple goals. These involve the evaluation and integration of direction and distance cues as well as the learning of specific places. For honey bees, goals can be as diverse as the colony nest, a foraging site, a new nesting site, or an open-air mating area

"Estimating long-term representative spl in complex environments using a coupling method based on acoustic (mw-wape) and micrometeorological (submeso) numerical predictions "

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