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Towards Improved Sonar Performance Using Environment-Informed Sparse Sub-Array Processing
No full textInternational audienceIn underwater acoustics, environmental fluctuations can lead to a loss of coherence in sonar arrays. Among the various approaches that can be considered to mitigate their effects, sub-array processing is a popular and intuitive one. However, it naturally results in sub-optimal performance. In this paper, we propose to enhance the approach in two ways. A first improvement is made by linking the parameters of the approach to those of the environment through a canonical correlation analysis. This leads in particular to an environment-informed calibration of the sub-arrays. A second improvement, more classical, is considered by using a sparse regularization on each sub-array processing. We show on real data the relevance of these choices and discuss the perspectives they open
Scattering in a partially open waveguide: the inverse problem
No full textInternational audienceIn this paper we consider an inverse scattering problem which consists in retrieving obstacles in a partially embedded waveguide in the acoustic case, the measurements being located on the accessible part of the structure. Such accessible part can be considered as a closed waveguide (with a finite cross section), while the embedded part can be considered as an open waveguide (with an infinite cross section). We propose an approximate model of the open waveguide by using Perfectly Matched Layers in order to simplify the resolution of the inverse problem, which is based on a modal formulation of the Linear Sampling Method. Some numerical results show the efficiency of our approach. This paper can be viewed as a continuation of the article [11], which was focused on the forward problem
Review of “Reduced-order modeling of geometrically nonlinear rotating structures using the direct parametrisation of invariant manifolds”
No full textThis is the Open Review of article “Reduced-order modeling of geometrically nonlinear rotating structures using the direct parametrisation of invariant manifolds” published in JTCAM with doi 10.46298/jtcam.1043
Does it work outside this benchmark? Introducing the rigid depth constructor tool
No full textInternational audienceA new framework called Rigid Depth Constructor (RDC) is proposed, allowing a user to create his own dataset for the validation of depth map estimation algorithms in the context of autonomous navigation. Compared to the existing tools that rely on high quality fixed Lidar sensor, RDC is usable in low-cost setups requiring only a camera and any (e.g. handheld, or UAV-carried) Lidar sensor, which implies more flexible-and much faster-scene scan. Furthermore, unlike photogrammetry tools that use sparse RGB views, it can be applied to smooth videos while remaining computationally tractable. The framework includes a test suite to get insightful information from the evaluated algorithm. As examples, validation videos made from UAV footage are provided to evaluate two depth prediction algorithms initially tested on in-car driving video datasets, which shows that the drone context is dramatically different. This supports the need to benchmark depth estimation algorithms on a dataset that fits one's particular context, which often means creating a brand new one. An open source implementation accompanies the paper, designed to be as user-friendly as possible, to make depth dataset creation possible even for small teams. The key contributions are the following: (1) a complete, open-source and almost fully automatic software application for creating validation datasets with densely annotated depth, adaptable to a wide variety of image, video and range data; (2) selection tools to adapt the dataset to specific validation needs, and conversion tools to other dataset formats; (3) as use case examples, two new real datasets, outdoor and indoor, readily usable in UAV navigation context are provided, and used a
An acoustic-transport splitting method for the barotropic Baer-Nunziato two-phase flow model
No full textInternational audienceThis work focuses on the numerical approximation of the barotropic Baer-Nunziato twophase flow model. The scheme relies on an operator splitting method corresponding to a separate treatment of fast propagation phenomena due to the acoustic waves on the one hand and slow propagation phenomena due to the fluid motion on the other. We propose to extend the implicit-explicit schemes developed in [7]. These methods enable the use of time steps that are no longer constrained by the sound velocity thanks to an implicit treatment of the acoustic waves, and maintain accuracy in the subsonic regime thanks to an explicit treatment of the material waves. In the present setting, a particular attention will be also given to the discretization of the non conservative terms in the Baer-Nunziato model. We prove that the proposed numerical strategy preserve positive values of the volume fractions and densities and we illustrate its behaviour with several relevant test cases.Ce travail porte sur l’approximation numérique du modèle de Baer-Nunziato barotrope. Le schéma se base sur une méthode de splitting correspondant à un traitement séparé des ondes acoustiques d’une part et des ondes matières d’autre part. Nous proposons d’´étendre les schémas implicites-explicites développés dans [7]. Ces méthodes permettent d’utiliser des pas de temps qui ne sont plus contraints par la vitesse du son grâce à un traitement implicite des ondes acoustiques, et de conserver une précision dans le régime subsonique grâce à un traitement explicite des ondes matières. Dans ce travail, une attention particulière sera également portée à la discrétisation des termes non conservatifs dans le modèle de Baer-Nunziato. Nous montrons que les méthodes numériques proposées préservent la positivité des densités et des fractions volumiques et nous illustrons leurs comportements à l’aide de plusieurs cas tests représentatifs des difficultés numériques liées à ce modèle
Le retard de Sanofi dans la course au vaccin contre la Covid- 19 : raisons technologiques, managériales et institutionnelles
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Assessment of the fracture properties of adhesively bonded joints submitted to fatigue loads using the Arcan fixture
No full textInternational audienceIn the present study, the crack propagation behavior under cyclic loading of an epoxy-based adhesive was investigated by the means of an Arcan device, in the mixed-mode plane I+II. The strain energy release rate (SERR) was calculated through an inverse identification method using a Finite Element (FE) modeling. The evolution of the cracked surfaces revealed three main stages during the tests. It was found that under fatigue loading, the crack propagated at a value of SERR per cycle lower than the values of the critical SERR calculated under monotonic loads. The evolutions of the crack propagation rate against the SERR are also provided to highlight the effects of the mixed-mode ratio on fatigue crack propagation