Stratégie multi-méthodes dans le domaine temporel

International audienceDans cet article nous présentons une stratégie multi-méthodes pour la simulation de problèmes de CEM. Dans cette approche, nous utilisons des méthodes d'ordre élevé permettant de tenir compte de la courbure des géométries et de limiter les erreurs de dispersions et/ou de dissipation. Ces méthodes sont basées sur des schémas Galerkin Discontinu et différences finies utilisant une approximation spatiale d'ordre élevé. Enfin pour tenir compte des câbles dans les structures, nous utilisons une équation de ligne de transmission, dans le domaine temporel que nous couplons aux méthodes de calcul de champs 3D

New high order FDTD method to solve EMC problems

In electromagnetic compatibility (EMC) context, we are interested in developing new ac- curate methods to solve efficiently and accurately Maxwell’s equations in the time domain. Indeed, usual methods such as FDTD or FVTD present im- portant dissipative and/or dispersive errors which prevent to obtain a good numerical approximation of the physical solution for a given industrial scene unless we use a mesh with a very small cell size. To avoid this problem, schemes like the Discontinuous Galerkin (DG) method, based on higher order spa- tial approximations, have been introduced and stud- ied on unstructured meshes. However the cost of this kind of method can become prohibitive accord- ing to the mesh used. In this paper, we first present a higher order spatial approximation method on carte- sian meshes. It is based on a finite element ap- proach and recovers at the order 1 the well-known Yee’s schema. Next, to deal with EMC problem, a non-oriented thin wire formalism is proposed for this method. Finally, several examples are given to present the benefits of this new method by compar- ison with both Yee’s schema and DG approaches

Adaptive refinement and selection process through defect localization for reconstructing an inhomogeneous refraction index

We consider the iterative reconstruction of both the internal geometry and the values of an inhomogeneous acoustic refraction index through a piecewise constant approximation. In this context, we propose two enhancements intended to reduce the number of parameters to reconstruct, while preserving accuracy. This is achieved through the use of geometrical informations obtained from a previously developed defect localization method. The first enhancement consists in a preliminary selection of relevant parameters, while the second one is an adaptive refinement to enhance precision with a low number of parameters. Each of them is numerically illustrated

Determining the shape of defects in non-absorbing inhomogeneous media from far-field measurements

International audienceWe consider non-absorbing inhomogeneous media represented by some refraction index. We have developed a method to reconstruct, from far-field measurements, the shape of the areas where the actual index differs from a reference index. Following the principle of the Factorization Method, we present a fast reconstruction algorithm relying on far field measurements and near field values, easily computed from the reference index. Our reconstruction result is illustrated by several numerical test cases

Méthode FDTD d’ordre élevé pour la simulation électromagnétique dans le domaine temporel

International audienceDans ce papier, nous présentons une nouvelle méthode différences finies en ordre élevé (FDTDOE) pour résoudre les équations de Maxwell dans le domaine temporel sur maillage cartésien, et dans laquelle un formalisme de fil mince oblique a été introduit.Actuellement, la méthode temporelle la plus répandue pour effectuer des études numériques est basée sur le schéma de Yee (FDTD), qui peut présenter des erreurs importantes liées à la dispersion numérique du schéma.L’utilisation de la méthode FDTDOE permet de réduire considérablement ces erreurs de dispersion, et à précision égale, avec la méthode FDTD, nécessite moins de degrés de liberté, pour obtenir une solution similaire. Pour augmenter les performances de la méthode nous montrons aussi comment introduire des raffinements locaux dans le schéma. L’approche choisie pour l’introduction de ceux-ci permettra aussi de faire des couplages avec des méthodes de type Galerkin Discontinu (GD)

Interactive plant identification based on social image data

Speeding up the collection and integration of raw botanical observation data is a crucial step towards a sustainable development of agriculture and the conservation of biodiversity. Initiated in the context of a citizen sciences project, the main contribution of this paper is an innovative collaborative workflow focused on image-based plant identification as a mean to enlist new contributors and facilitate access to botanical data. Since 2010, hundreds of thousands of geo-tagged and dated plant photographs were collected and revised by hundreds of novice, amateur and expert botanists of a specialized social network. An image-based identification tool - available as both a web and a mobile application - is synchronized with that growing data and allows any user to query or enrich the system with new observations. An important originality is that it works with up to five different organs contrarily to previous approaches that mainly relied on the leaf. This allows querying the system at any period of the year and with complementary images composing a plant observation. Extensive experiments of the visual search engine as well as system-oriented and user-oriented evaluations of the application show that it is already very helpful to determine a plant among hundreds or thousands of species. At the time of writing, the whole framework covers about half of the plant species living in France (2200 species), which already makes it the widest existing automated identification tool (with its imperfections)