Em uma aeronave, dispositivos de hiper-sustentação à altos ângulos de ataque promovem a formação de esteiras. Tais esteiras influenciam o desempenho aerodinâmico. A esteira do eslate, por exemplo, afeta o ponto de transição do elemento principal da asa e é a fonte de ruído mais importante na estrutura do avião. Devido a geração de sustentação estas esteiras são assimétricas. Corpos imersos em escoamento cisalhante também produzem esteiras assimétricas, com importantes aplicações para a indústria petrolífera. Existem aspectos de tais escoamentos que precisam de investigação. Por exemplo, não há consenso sobre se pode ou não a assimetria suprimir desprendimento de vórtice ou como afeta o desprendimento da frequência. Na verdade, existe uma aparente discrepância entre os resultados encontrados na literatura. O objetivo do presente trabalho é contribuir para esta questão. A idéia foi investigar a influência da assimetria em um perfil de esteira bidimensional sob desenvolvimento temporal. O perfil da esteira assimétrica foi obtido por uma combinação entre um perfil de uma esteira gaussiana e um perfil tangente hiperbólico da camada de mistura. Foi desenvolvido uma análise bidimensional (2D) da teoria de estabilidade linear para o perfil. O trabalho também incluiu simulações numéricas diretas (DNS) bidimensionais da evolução da perturbação usando formulação característica das equações compressíveis de Navier-Stokes na forma não-conservativa. Os resultados mostraram que a assimetria reduz o frequência de desprendimento para a faixa investigada do parâmetro de assimetria 0 \'< OU =\' K \'< OU =\' 0,25. Para pequenos valores deste parâmetro os resultados mostraram que a assimetria promove a estabilidade. Efeitos do número de Mach na esteira assimétrica também foram investigados. Os resultados mostraram que o aumento do Ma reduziu a máxima taxa de amplificação e a banda instável. Além disso, os resultados da literatura foram reconciliados, levando-se em conta a variação do coeficiente de arrasto com a assimetria. Portanto, uma possível explicação para a controvérsia foi oferecido. / In an aircraft, high-lift devices operating at high angle of attack promote the formation wakes. Such wakes influence the aerodynamic performance. The slat wake, for example, affects the transition point of the wing main element and is the most important source of noise in the airframe. Owing to the generation of lift these wakes are asymmetries. Bodies immersed in a shear flow also produce asymmetric wakes, with important applications to the oil industry. There are aspects of such flows that need investigation. For instance, there is no consensus about whether or not the asymmetry can suppress vortex shedding or how it affects the shedding frequency. Indeed there is an apparent discrepancy between results found in literature. The aim of the present work was to contribute to this issue. The idea was to investigate the influence of asymmetry on a two-dimensional wake profile under temporal development. The asymmetric wake profile was obtained by a combination between a Gaussian wake profile and a hyperbolic tangent mixing layer profile. The bidimensional (2D) linear stability theory analysis of the profile was performed. The work also included 2D Direct Numerical Simulation (DNS) using the characteristic formulation of the compressible Navier-Stokes equations in non-conservative form. The results showed that the asymmetry reduces the shedding frequency for the range of 0 \'< OU =\' K \'< OU =\' 0,25 investigated. For small values of the asymmetric parameter the results showed that the asymmetry promotes stability. Effects of the number of Mach in asymmetric wake also were investigated. The results showed that the increase of Ma reduced the maximum rate amplification and the band unstable. Moreover, the results from literature were reconciled by taking into account the variation of the drag coefficient with the asymmetry. Therefore, a possible explanation for the controversy was offered.

Made available in DSpace on 2016-04-01T17:54:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-12-11. Added 1 bitstream(s) on 2016-04-01T18:00:36Z : No. of bitstreams: 1 000545779.pdf: 2757359 bytes, checksum: 9bbcad089c80aaed637169a9fce58845 (MD5) / Este trabalho consiste de três partes, na primeira fez - se o estudo da dinâmica de um oscilador com um grau de liberdade, em que uma massa é conectada a um elemento com memória de forma e um amortecedor, onde o sistema é excitado harmonicamente (sistema ideal). Uma solução analítica para o movimento estacionário do sistema é obtida através da análise de técnicas de perturbações, onde foi utilizado o método das múltiplas escalas. Por intermédio desta solução observa - se fenômenos não lineares através das curvas de resposta em freqüência. Além disso, obtém - se condições de estabilidade para o sistema e condições para a existência de bifurcação do tipo sela - nó. Na segunda parte apresenta - se o estudo do comportamento dinâmico não linear de um oscilador com memória de forma, excitado por uma fonte não ideal - um motor elétrico de corrente contínua, desbalanceado e com potência limitada. Toma - se, um problema cujo modelo matemático representa um sistema simplificado (com característica do motor no regime estacionário). Adota - se a formulação Lagrangeana para gerar as equações de movimento. Os resultados são obtidos através de integrações numéricas das equações de movimento sendo possíveis obter oscilações regulares e irregulares (caóticos), os quais dependem da escolha dos parâmetros do sistema. A solução analítica é obtida utilizando - se o método da média, onde é possível observar fenômenos intrínsecos a sistemas não ideais tais como dependência da freqüência de excitação com relação à amplitude de oscilação da coordenada de movimento do sistema (Efeito Sommerfeld). A terceira parte é dedicada à aplicação de uma técnica de controle linear ótimo para a supressão do movimento caótico tanto do sistema ideal quanto do sistema não ideal, via simulações numéricas. / This work concerns of three parts, in the first we will make the study of the dynamical of a single - degree of freedom oscillator, which consist of a mass connected to a shape memory element and a dashpot, where the system harmonically excited (ideal source). An analytical solution for the system stationary oscillations is obtained by perturbations method, where was used the method of multiple scales. Due to this solution one can observe nonlinear phenomena trough of frequency - response curves. Besides, conditions for the system stability and the existence of saddle - node bifurcations are also obtained. In the second part show the computational and analytical study of the nonlinear dynamic behavior of the SMA oscillator, excited by a non ideal source - an unbalanced direct current electric motor of limited power. A problem whose mathematical model represents a simplified system (the characteristic of the motor in stationary state). It adopts the Lagrange formularization to deducing the equations of motion. Regular and irregular (chaotic) behaviors depend of the physical parameters and can be observed when a numerical integration is performed. The analytical solution is obtained using the averaging method, where due to this solution on can observe typical non-ideal phenomena like the amplitude motion dependency to the frequency of the excitation (Sommerfeld effect). The third part is dedicated to the application and performance of the linear feedback control for the suppressing of the chaotic motion of an ideal and non ideal system, theses systems are numerical studied.

Em uma aeronave, dispositivos de hiper-sustentação à altos ângulos de ataque promovem a formação de esteiras. Tais esteiras influenciam o desempenho aerodinâmico. A esteira do eslate, por exemplo, afeta o ponto de transição do elemento principal da asa e é a fonte de ruído mais importante na estrutura do avião. Devido a geração de sustentação estas esteiras são assimétricas. Corpos imersos em escoamento cisalhante também produzem esteiras assimétricas, com importantes aplicações para a indústria petrolífera. Existem aspectos de tais escoamentos que precisam de investigação. Por exemplo, não há consenso sobre se pode ou não a assimetria suprimir desprendimento de vórtice ou como afeta o desprendimento da frequência. Na verdade, existe uma aparente discrepância entre os resultados encontrados na literatura. O objetivo do presente trabalho é contribuir para esta questão. A idéia foi investigar a influência da assimetria em um perfil de esteira bidimensional sob desenvolvimento temporal. O perfil da esteira assimétrica foi obtido por uma combinação entre um perfil de uma esteira gaussiana e um perfil tangente hiperbólico da camada de mistura. Foi desenvolvido uma análise bidimensional (2D) da teoria de estabilidade linear para o perfil. O trabalho também incluiu simulações numéricas diretas (DNS) bidimensionais da evolução da perturbação usando formulação característica das equações compressíveis de Navier-Stokes na forma não-conservativa. Os resultados mostraram que a assimetria reduz o frequência de desprendimento para a faixa investigada do parâmetro de assimetria 0 \'< OU =\' K \'< OU =\' 0,25. Para pequenos valores deste parâmetro os resultados mostraram que a assimetria promove a estabilidade. Efeitos do número de Mach na esteira assimétrica também foram investigados. Os resultados mostraram que o aumento do Ma reduziu a máxima taxa de amplificação e a banda instável. Além disso, os resultados da literatura foram reconciliados, levando-se em conta a variação do coeficiente de arrasto com a assimetria. Portanto, uma possível explicação para a controvérsia foi oferecido. / In an aircraft, high-lift devices operating at high angle of attack promote the formation wakes. Such wakes influence the aerodynamic performance. The slat wake, for example, affects the transition point of the wing main element and is the most important source of noise in the airframe. Owing to the generation of lift these wakes are asymmetries. Bodies immersed in a shear flow also produce asymmetric wakes, with important applications to the oil industry. There are aspects of such flows that need investigation. For instance, there is no consensus about whether or not the asymmetry can suppress vortex shedding or how it affects the shedding frequency. Indeed there is an apparent discrepancy between results found in literature. The aim of the present work was to contribute to this issue. The idea was to investigate the influence of asymmetry on a two-dimensional wake profile under temporal development. The asymmetric wake profile was obtained by a combination between a Gaussian wake profile and a hyperbolic tangent mixing layer profile. The bidimensional (2D) linear stability theory analysis of the profile was performed. The work also included 2D Direct Numerical Simulation (DNS) using the characteristic formulation of the compressible Navier-Stokes equations in non-conservative form. The results showed that the asymmetry reduces the shedding frequency for the range of 0 \'< OU =\' K \'< OU =\' 0,25 investigated. For small values of the asymmetric parameter the results showed that the asymmetry promotes stability. Effects of the number of Mach in asymmetric wake also were investigated. The results showed that the increase of Ma reduced the maximum rate amplification and the band unstable. Moreover, the results from literature were reconciled by taking into account the variation of the drag coefficient with the asymmetry. Therefore, a possible explanation for the controversy was offered.

Submitted by ANDRES FELIPE VASQUEZ TOCORA (anfvasquezto@unal.edu.co) on 2018-10-02T21:56:33Z No. of bitstreams: 1 thesis.pdf: 3832471 bytes, checksum: 13b65d2c4a9d5e2b2c7414dd2cdfba50 (MD5) / Rejected by Hellen Sayuri Sato null (hellen@ift.unesp.br), reason: Solicitamos que realize correções na submissão seguindo as orientações abaixo - Favor inserir a ficha catalográfica no pdf , logo após a página de rosto - No PDF está faltando as palavras-chave logo após o resumo e abstract on 2018-10-03T14:34:04Z (GMT) / Submitted by ANDRES FELIPE VASQUEZ TOCORA (anfvasquezto@unal.edu.co) on 2018-10-03T16:52:45Z No. of bitstreams: 1 Thesis.pdf: 4205198 bytes, checksum: 499748f6d69605fda811e56805ac4e12 (MD5) / Approved for entry into archive by Hellen Sayuri Sato null (hellen@ift.unesp.br) on 2018-10-03T17:32:51Z (GMT) No. of bitstreams: 1 vasqueztocora_af_me_ift.pdf: 4205198 bytes, checksum: 499748f6d69605fda811e56805ac4e12 (MD5) / Made available in DSpace on 2018-10-03T17:32:51Z (GMT). No. of bitstreams: 1 vasqueztocora_af_me_ift.pdf: 4205198 bytes, checksum: 499748f6d69605fda811e56805ac4e12 (MD5) Previous issue date: 2018-03-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The main goal of this dissertation is to show the enhancement of the cross-section for the double Higgs production through pair annihilation by including effective interactions and through the non-perturbative Sommerfeld effect. Bounds to some Wilson coefficients were obtained from such enhancement, this in the scenarios of the future e+ e− -colliders (FCC-ee, ILC, CLIC). In order to achieve this, some computational tools were implemented: FeynRules, FeynArts, FormCalc, and LoopTools. It is also shown the enhancement of the double Higgs production in 2HDM and MSSM, discussing the general framework of these two models. In addition, it is studied the threshold behavior of the cross-section for the double Higgs production when a hidden sector couples to the Higgs boson, yielding resonances below the threshold energy due to non-perturbative effects. We study the Sommerfeld effect in the double Higgs production in the scenario of e+ e− -colliders. The enhancement is discussed as generated from a hidden sector coupled to the Higgs boson. Below and above threshold enhancements are presented. Such analysis is of importance in the ILC project, which will operate up to the threshold energy √s = 250 GeV. The results has been achieved by the use of computational tools like FeynArts, FormCalc, and LoopTools. / O objetivo principal dessa dissertação é, mostrar o aprimoramento da seção de choque para a produção em dobro dos bósons de Higgs, por meio de aniquilação de pares, incluindo interações efetivas e através do efeito não perturbativo de Sommerfeld. De tais aprimoramentos, os limites para alguns coeficientes de Wilson foram obtidos, isso nos cenários de futuros aceleradores de e+e- (FCC-ee, ILC, CLIC). Para atingir estes resultados, algumas ferramentas computacionais foram implementadas: FeynRules, FeynArts, FormCalc e LoopTools. Também, é mostrado o aprimoramento da produção em dobro de bósons de Higgs no “2HDM” e “MSSM”, discutindo o marco geral desses dois modelos. Além disso, foi estudado o comportamento, perto do limite de produção, da seção de choque da produção em dobro dos bósons de Higgs, quando um setor escondido é acoplado ao Higgs, produzindo ressonâncias abaixo da energia limite de produção, devido à efeitos não perturbativos.

A study is undertaken of the numerical reconstruction of acoustic and electromagnetic (EM) localized waves (LWs). The latter are carrier-free ultra-wideband pulses characterized by large focusing depths and extended ranges of localization. Special emphasis is placed on finite energy LWs that can be generated by dynamic aperture antennas with independently addressable elements. The reconstruction techniques are based on Huygens and Rayleigh-Sommerfeld integral I and II representations, both in the time and frequency domains. In contradistinction to the Weyl representation,they lend themselves to the physical realization of space-time aperture sources capable of generating localized wave solutions propagating away from the aperture plane. A detailed comparison of the three reconstruction techniques has been carried out in connection with LW solutions to the scalar wave equation, especially with respect to their handling of acausal components incorporated in the aperture excitation fields. In addition, a study is presented of the characteristic properties of LWs propagating through dispersive media modeled by the Klein-Gordon equation. It is demonstrated that contrary to expectation, the depletion of the spectral components of the LW Klein-Gordon field may be slower than that associated with the free space scalar field. Previous work by Power et al. [73] is extended by studying the acoustic bistatic scattering of a modified power spectrum (MPS) pulse from rigid and compressible spheres. The analysis allows the extraction of the radius of a sphere from the backscattered data. Finally, a special class of electromagnetic (EM) LWs, referred to as azimuthally polarized X waves (APXWs), is derived and their reconstruction is addressed, both in the time and frequency domains. / Ph. D.

Focaliser l’énergie optique en un petit spot de diamètre beaucoup plus petit que la limite de diffraction a longtemps été un sujet très intéressant en photonique. Dans le domaine Térahertz (avec une longueur d’onde de l’ordre de 300 µm) ce défi est particulièrement important pour répondre à l’intérêt croissant de l’imagerie haute résolution et de la spectroscopie des matériaux d’une taille inférieure à l’échelle submillimétrique de la longueur d’onde en espace libre. Dans ma thèse, j’ai étudié le confinement des ondes de surface aux fréquences THz sur des structures métalliques de dimensions sous longueur d’onde. J’ai expérimentalement mesuré le confinement du champ électrique et calculé la relation de dispersion du mode de surface sur une structure métallique déposée sur un substrat diélectrique de faible permittivité. Ces mesures sont obtenues à l’aide d’un banc de mesures THz guidé, développé pendant ma thèse. La mesure est faite en champ proche par une sonde électro-optique micrométrique, librement positionnable. Ces résultats expérimentaux sont complétés par des simulations numériques, obtenues par le logiciel de simulation par éléments finis, Comsol Multiphysics. Les résultats expérimentaux montrent un confinement de λ/20 du mode EM de surface sur une ligne métallique rectangulaire de petites dimensions. / Focusing optical energy into a small spot diameter much smaller than the diffraction limit has long been a very interesting topic in photonics. In Terahertz (with a wavelength of about 300 microns) this challenge is particularly important to meet the growing interest in high-resolution imaging and spectroscopy of materials whose size is smaller than the wavelength in free space. In my thesis, I studied the confinement of surface waves at THz frequencies on metal structures with sub-wavelength dimensions . I experimentally measured the confinement of the electric field and calculated the dispersion relation of the surface mode on a metal structure deposited on a low permittivity dielectric substrate. These measurements are obtained using a guided-wave time domain spectroscopy set-up, developed during my PhD. The measurement is made by a near-field freely positionable electro-optical probe. These experimental results are supplemented by numerical simulations obtained by finite element analysis software Comsol Multiphysics. The experimental results show a confinement of λ/20 of the EM surface mode on a sub-wavelength dimension rectangular metal wire.

Motivée par le développement de diverses applications déployant des antennes près d'une interface, comme les systèmes militaires UGS, les réseaux corporels sans fil BAN et la surveillance environnementale impliquant des capteurs au sol, cette thèse porte sur la modélisation de la propagation des ondes électromagnétiques près d'une interface. Tout d'abord, la méthode classique de l'optique géométrique est confrontée à des formules approchées fournies par Norton et par Bannister. Cette étude met en évidence les cas où l'optique géométrique ne décrit pas correctement la propagation près de la surface. Pour une compréhension plus exhaustive, les fonctions de Green de ce type de propagation, présentées sous forme d'intégrales de Sommerfeld, sont évaluées à la lumière de la méthode de la plus grande pente. Cette évaluation permet d'extraire trois équations importantes pour la propagation près d'une interface. La première est la condition essentielle pour que la proximité au sol puisse profiter au bilan de liaison grâce à l'excitation d'une composante de l'onde diffractée qui se propage près de l'interface. Les deux autres identifient des distances critiques qui bornent le début et la fin de la zone présentant un affaiblissement de trajet amélioré. L'ensemble de ces trois équations permet d'évaluer le rôle de certains paramètres physiques, notamment les propriétés électromagnétiques du sol, la fréquence de travail et la hauteur des antennes. Cette thèse inclut également les pistes pratiques envisagées pour une démonstration de faisabilité de l'amélioration d'une liaison sans fil par la proximité des antennes à l'interface. La couverture du sol ayant une importance prépondérante, nous présentons des recherches préliminaires sur la réalisation et la caractérisation d'un matériau approprié pour ce type de propagation. Dans un axe de recherche parallèle, cette thèse évalue également l'exactitude et la pertinence d'une nouvelle formulation théorique pour la propagation près du sol. Cette formulation dite « de Schelkunoff » suscite des controverses dans la communauté scientifique / Motivated by the development of various applications deploying antennas near an interface, such as military systems (UGS), wireless body area networks (BAN) and environmental monitoring involving ground sensors, this thesis deals with the near-ground wave propagation modelling. First, the results of the geometrical optics are confronted with the approximations provided by Norton and Bannister. This study reveals the cases where geometrical optics does not correctly describe the wave propagation near the surface. For a more comprehensive understanding, Green's functions of this type of propagation, presented as Sommerfeld integrals, are evaluated using the steepest descent technique. This evaluation offers the possibility to extract three important equations for near-ground wave propagation. The first one presents the essential condition under which the link budget can benefit from the ground proximity through the excitation of a diffracted wave component propagating near the interface. The other two equations identify critical distances indicating the beginning and the end of the zone with an improved path loss. All these three equations highlight the role of certain physical parameters, in particular the electromagnetic properties of the ground, the working frequency and the heights of the antennas. This thesis also includes the practical solutions that can be considered to demonstrate the feasibility of improving a wireless link by the proximity of the antennas to the interface. Since floor coating is of major importance, we present preliminary research on the realisation and characterisation of a suitable material for this type of propagation. In a parallel research axis, this thesis also evaluates the accuracy and relevance of a new theoretical formulation for near-ground propagation. The "so-called Schelkunoff" formulation has become a controversial issue in the scientific community

Orientador: José Manoel Balthazar / Banca: Bento Rodrigues de Pontes Junior / Banca: Vicente Lopes Júnior / Resumo: Este trabalho consiste de três partes, na primeira fez - se o estudo da dinâmica de um oscilador com um grau de liberdade, em que uma massa é conectada a um elemento com memória de forma e um amortecedor, onde o sistema é excitado harmonicamente (sistema ideal). Uma solução analítica para o movimento estacionário do sistema é obtida através da análise de técnicas de perturbações, onde foi utilizado o método das múltiplas escalas. Por intermédio desta solução observa - se fenômenos não lineares através das curvas de resposta em freqüência. Além disso, obtém - se condições de estabilidade para o sistema e condições para a existência de bifurcação do tipo sela - nó. Na segunda parte apresenta - se o estudo do comportamento dinâmico não linear de um oscilador com memória de forma, excitado por uma fonte não ideal - um motor elétrico de corrente contínua, desbalanceado e com potência limitada. Toma - se, um problema cujo modelo matemático representa um sistema simplificado (com característica do motor no regime estacionário). Adota - se a formulação Lagrangeana para gerar as equações de movimento. Os resultados são obtidos através de integrações numéricas das equações de movimento sendo possíveis obter oscilações regulares e irregulares (caóticos), os quais dependem da escolha dos parâmetros do sistema. A solução analítica é obtida utilizando - se o método da média, onde é possível observar fenômenos intrínsecos a sistemas não ideais tais como dependência da freqüência de excitação com relação à amplitude de oscilação da coordenada de movimento do sistema (Efeito Sommerfeld). A terceira parte é dedicada à aplicação de uma técnica de controle linear ótimo para a supressão do movimento caótico tanto do sistema ideal quanto do sistema não ideal, via simulações numéricas. / Abstract: This work concerns of three parts, in the first we will make the study of the dynamical of a single - degree of freedom oscillator, which consist of a mass connected to a shape memory element and a dashpot, where the system harmonically excited (ideal source). An analytical solution for the system stationary oscillations is obtained by perturbations method, where was used the method of multiple scales. Due to this solution one can observe nonlinear phenomena trough of frequency - response curves. Besides, conditions for the system stability and the existence of saddle - node bifurcations are also obtained. In the second part show the computational and analytical study of the nonlinear dynamic behavior of the SMA oscillator, excited by a non ideal source - an unbalanced direct current electric motor of limited power. A problem whose mathematical model represents a simplified system (the characteristic of the motor in stationary state). It adopts the Lagrange formularization to deducing the equations of motion. Regular and irregular (chaotic) behaviors depend of the physical parameters and can be observed when a numerical integration is performed. The analytical solution is obtained using the averaging method, where due to this solution on can observe typical non-ideal phenomena like the amplitude motion dependency to the frequency of the excitation (Sommerfeld effect). The third part is dedicated to the application and performance of the linear feedback control for the suppressing of the chaotic motion of an ideal and non ideal system, theses systems are numerical studied. / Mestre

Terahertz waveguides are the focus of considerable research interest due to their potential for sensing, imaging and communications applications. Two of the most promising designs are the metal wire waveguide and the parallel-plate waveguide. The metal wire waveguide exhibits excellent low loss and low dispersion characteristics. However, the radiation is only weakly coupled to the wire and the beam extends a great distance from the waveguide, which can lead to high bending loss. In my research I show that this large beam extent also gives a high degree of flexibility in the geometry required to couple radiation into the waveguide or between waveguide sections. I also show that the traditional formalism of bending loss is incomplete, and that there is an optimum radius of curvature to reduce loss. The relationship between the beam extent and the radius of the wire presents the possibility of a tapered waveguide to confine the radiation as it propagates. I here present experimental data and simulations results to verify this subwavelength confinement at the tip of a tapered metal wire waveguide, which is of great interest for near-field imaging applications. The parallel-plate waveguide is another design frequently employed due to its low loss and low dispersion characteristics. Resonant structures may also be easily incorporated into the waveguide for sensing and filtering applications. One such structure is a single rectangular groove, which serves as a notch filter with a very narrow linewidth when the transverse-electric (TE) mode of the waveguide is excited, though its physical origin is poorly understood. In this work I present a detailed experimental and theoretical study of the rectangular resonant cavity in a TE-mode parallel-plate waveguide, particularly with respect to its potential as a microfluidic refractive index sensor. This study is extended to include the possibility of two grooves, in both coupled and non-coupled geometries, and their efficacy as multichannel or high-resolution single-channel microfluidic sensors.

Ce travail de thèse traite les domaines du rayonnement d'antennes basses fréquences et de la propagation du champ électromagnétique, en présence du sol et d'environnement réalistes. Des éléments qui diffèrent du cas canonique du sol plan homogène et infini sont considérés par le mot "réalistes". Les méthodes numériques classiques pour l'électromagnétisme, en particulier pour la modélisation du rayonnement d'antennes, sont plutôt adaptées à des fréquences au-delà des hautes fréquences et au rayonnement en espace libre. Deux axes de recherche ont été définis comme suit: les effets d'environnements situés en zone proche sur le rayonnement d'antennes filaires basses fréquences et l'étude de systèmes éloignés de la source par la création d'une méthode hybride. En ce qui concerne le rayonnement en zone proche, une méthode des différences finies dans le domaine temporel est utilisée. Celle-ci est lourde d'un point de vue des temps de calculs et de l'occupation de la mémoire, cependant elle est effective du fait du maillage volumique de la scène. Dans le cas de la propagation lointaine, la solution parfaite du rayonnement d'un dipôle infinitésimal électrique vertical au-dessus d'un sol plan homogène infini a été traitée par la création d'un algorithme adaptatif d'intégration numérique. Ce dernier permet d'obtenir les valeurs du champ électromagnétique dans tout l'espace avec une précision numérique contrôlée. Une technique originale d'hybridation a été réalisée entre l'algorithme d'intégration et la méthode des différences finies pour rendre compte efficacement des effets d'éléments lointains sur la propagation du champ. / This work is about the radiation of low frequency antennas and the propagation of the electromagnetic field, in the presence of soil and realistic environments. Elements that differ from the canonical case of homogeneous infinite and planar ground are considered by the word realistic. Conventional numerical methods for electromagnetism, in particular for modeling the radiation of antennas are rather suitable for frequencies beyond the high frequencies and in free space. Two research areas were defined as follows : the effects of environments located near the low frequency wire antennas and the study of systems far from the source through the creation of a hybrid method. Regarding the near-field radiation, a method of finite-difference in the time-domain is used. It needs a large computer memory size and long solution times, however it is effective because the entire scene is included in a volumetric mesh. In the case of field propagation, the radiation of a vertical electric current element above a homogeneous flat ground has been computed with the creation of an adaptive algorithm for numerical inte- gration. This allows to obtain the values of the electromagnetic field in the whole space with controlled numerical accuracy. An original technique of hybridization was performed between the integration algorithm and the method of finite differences to effectively observ the effects of distant elements on the field propagation.