Amélioration et accélération de l'Optique Physique Itérative pour le calcul de SER de cavités complexes

This thesis dissertation deals with the computation of the Radar Cross Section (RCS) of complex-shaped open-ended cavities whose dimensions are large compared to the wavelength. Many methods have been developed for such a calculation and IPO (Iterative Physical Optics) has been chosen for its interesting trade-off between the accuracy and the computation time. It is an asymptotic method based on an iterative resolution of the electromagnetic fields integral equations by Physical Optics. The thesis works aim at improving IPO, in terms of both accuracy and computation time.The first original contribution of the thesis concerns a detailed study of the shadowing phenomenon, which has a significant impact on the accuracy. The method, called physical shadowing, has been developed, based on fields integral equations applied to coupled objects, and the shadow radiation of Physical Optics. The method has been tested and compared to classical approaches for open surfaces and open-ended cavities.The second original contribution concerns the acceleration of IPO, based on a technique of matrix compression. First, IPO has been written into a matrix formulation, which allows to apply the ACA (Adaptive Cross Approximation) algorithm, and its recompressed version R-ACA, to compress the interactions matrices of IPO. Moreover, the computation time has been reduced by applying the S-IPO, consisting in separating the cavity in sub-sections where IPO is applied. The simulations has shown a reduction of the computation time and the memory requirements.Ce manuscrit est consacré au calcul de la Surface Equivalente Radar (SER) de cavités de formes complexes dont les dimensions sont grandes devant la longueur d'onde. De nombreuses méthodes ont été développées pour un tel calcul, et l'IPO (Iterative Physical Optics) a été retenue pour son compromis intéressant entre précision et temps de calcul. Il s'agit d'une méthode asymptotique basée sur la résolution itérative des équations intégrales des champs électromagnétiques par l'Optique Physique. Les travaux de cette thèse ont pour but d'améliorer l'IPO, en termes de précision et de temps de calcul.La première contribution originale de cette thèse repose sur une étude détaillée du phénomène d'ombrage, qui a un impact important sur la précision du calcul. La méthode d'ombrage physique a alors été développée, basée sur les équations intégrales des champs pour des objets couplés, et sur le rayonnement en zone d'ombre avec l'Optique Physique. Elle a été testée et comparée aux approches classiques pour des cavités et des surfaces ouvertes.La seconde contribution originale de cette thèse repose sur l'accélération de l'IPO, basée sur une technique de compression matricielle. Le formalisme matriciel de la méthode IPO a alors été établi et optimisé, et l'algorithme de compression ACA (Adaptive Cross Approximation) ainsi que sa version recompressée R-ACA, ont alors été appliqués aux matrices d'interactions impliquées dans l'IPO. De plus, le calcul a pu être accéléré par l'application de la S-IPO, qui consiste à découper une cavité en tronçons pour y appliquer l'IPO. Les nombreuses simulations ont montré un gain en temps de calcul et une réduction de l'occupation mémoire

Improvement of shadowing with iterative physical optics for radiation pattern of mounted antennas

International audienceModeling interactions between antennas and structures is an important challenge for systems carrying antennas such as aircrafts, satellites, frigates. This paper focuses on the electromagnetic field propagated by an antenna interacting with a structure that includes effects of shadowing and multiple reflections. In such a case, several method can be used, and Iterative Physical Optics (IPO) is an asymptotic method based on Physical Optics (PO), which has shown good results in calculation of electromagnetic diffraction in open-ended cavities. In IPO, different techniques can be used to take into account shadowing effects. First method, classically used, is a geometrical way of considering shadowing, based on ray bouncing. A more recent method uses a physical approach, based on shadow radiation (around forward direction) with PO approximation. The idea of this paper is to use IPO method to determine electromagnetic field from a structure including an antenna on a large complex platform, comparing different ways of considering shadowing effect

Optimisation de la méthode IPO par compression ACA pour des calculs de SER de cavités

National audienceCet article s’intéresse au calcul de la Surface Equivalente Radar (SER) de cavités, pour lequel différentes techniques existent, notamment la méthode IPO (Iterative Physical Optics), basée sur l’OP (Optique Physique). Une compression numérique novatrice a été ajoutée à l’IPO afin d’optimiser les performances de la méthode en termes de stockage mémoire, de complexité et donc de temps de calcul

Low Computational cost method for scattering of large cavities based on ACA compression of Iterative Physical Optics

International audienceThis paper is about Radar Cross Section(RCS) calculation of large cavities. For such targets,Iterative Physical Optics (IPO) is a method knownto provide a good trade-o between complexity andaccuracy. In this article, a numerical compressionis applied to interaction matrices of IPO betweencoupled surfaces. The compression is made by usingthe algebraic Adaptive Cross Approximation (ACA)technique, which is known to provide a good com-pression and acceleration when used with dense ma-trices involved in rigorous numerical methods. It isalso improved by a recompression (RACA). Resultsshow that this technique highly compresses the IPOmatrices, without damaging the RCS prediction byIPO

An overview of recent advances on Iterative Physical Optics

International audienceThe Radar Cross Section (RCS) of electrically large targets including cavities (such as jet engine inlets) remains a challenging problem in electromagnetic modeling. Rigorous methods are known to provide a good accuracy, since only the approximation due to meshing is considered. Nevertheless, these methods are difficult to use for targets much greater than the wavelength due to the computation time and memory requirements. For electrically large targets, High Frequency asymptotic methods can be used, among which Iterative Physical Optics (IPO) is very efficient. IPO is an asymptotic numerical method based on Physical Optics (PO). This method, first introduced in 1995 by Obelleiro et al, is known to provide a good trade-off between complexity and accuracy.Since 1995, several improvements were published. More recently, some improvements were made to the IPO method by the help of fast numerical techniques, generally inherited from advances made for rigorous methods.Given all these previous studies, the IPO method can be implemented into very various forms depending on the desired application.Thus, the goal of this paper is to provide a complete overview of the recent improvements on Iterative Physical Optics. The advantages and drawbacks of each specific form and acceleration of IPO will be discussed in order to give some advices on the choice of the best IPO form for a given problem

Amélioration de la méthode IPO par le rayonnement en zone d'ombre de l'optique physique

National audienceCe papier s'intéresse particulièrement à la prédiction de la Surface Equivalente Radar (SER) dans des cavités de type manche à air d'aéronefs, pour laquelle différentes techniques existent, notamment la méthode IPO ("Iterative Physical Optics"), basée sur l'OP (Optique Physique). Une technique novatrice appelée ombrage physique (par le fait qu'elle utilise une approche physique pour l'ombrage, au lieu d'une technique géométrique, utilisée classiquement dans l'OP) est introduite. Cette technique de modélisation de l'ombrage, basée sur l'utilisation de l'approximation de l'OP en zone d'ombre, permet une amélioration de la méthode IPO. La méthode est présentée, en comparaison avec la technique déjà utilisée, et des résultats de simulation mettant en évidence l'apport de l'ombrage physique sont montrés

Optimized Iterative Physical Optics for EM Scattering from Large Structures

International audienceThe modelization of electromagnetic interactionsbetween antennas and structures is an important challenge forsystems carrying antennas such as aircrafts, satellites, frigates.This problem deals with electromagnetic scattering from largestructures with shadowing effect and multiple scattering. Asimilar problem is the Radar Cross Section computation oflarge cavities. For both cases, several methods can be used, andIterative Physical Optics (IPO) is an asymptotic method basedon Physical Optics (PO), which has shown good results for suchkind of problems. In IPO, several techniques can be used totake into account shadowing effects. The geometrical shadowing,based on ray tracing, is classically used. But a recent method hasbeen proposed and is based on a physical approach: the shadowradiation (around forward direction) with PO approximation.Moreover, the IPO method can be optimized by applying analgebraic compression, the Adaptive Cross Approximation, of theinteraction matrices of IPO between coupled surfaces. Resultsshow that IPO matrices can be highly compressed, withoutdegrading the accuracy

Using Physical Optics shadow radiation to improve shadowing in Iterative Physical Optics

International audiencePredicting aircraft ducts Radar Cross Section (RCS) is an interesting challenge. In order to calculate electromagnetic scattering in such open-ended cavities, several methods have been developed: some rigorous methods, and some asymptotic ones. Iterative Physical Optics (IPO) is an asymptotic method based on Physical Optics (PO), which has shown good results. This paper shows an improvement of IPO method for calculation of electromagnetic scattering by cavities, by using a physical approach (and not a geometrical technique as in classical PO method) to take into account shadowing effects. The method, called physical shadowing, is based on using shadow radiation (around forward direction) with PO approximation in the magnetic field integral equation applied to two coupled objects

Optimisation de l’optique physique itérative pour le calcul de rayonnement d’antennes sur porteur

International audienceCet article concerne le calcul de rayonnementd’antenne sur porteur par la méthode IPO (Iterative PhysicalOptics) optimisée. L’IPO, basée sur l’Optique Physique(OP) est une méthode asymptotique couramment utiliséepour le calcul de SER (Surface Equivalente Radar).Il est proposé ici de l’utiliser pour calculer les interactionsentre une antenne et son porteur puis le rayonnement del’ensemble. De plus, une optimisation novatrice est apportéeau calcul : l’application d’une compression numériqueafin de réduire le stockage mémoire, la complexité et doncle temps de calcul

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