Wood drying is essential for preparation of this natural resource for practical applications.Most drying models confirm that the tortuosity of the moisture transport path, associated with high wood density or low moisture permeability, is an important control parameter during the diffusion-controlled drying process. Drying systems, such as kilns, control the external environment in order to manipulate moisture diffusion and transport mechanisms; however they are powerless to manipulate wood density or permeability. Controlled application of microwave energy has been shown to selectively rupture the wood structure creating radial pathways in the wood through which moisture may readily move. New analytical equations that describe simultaneous heat and moisture transport during microwave heating have been derived and validated. These new equations assume that the microwave fields decay exponentially with distance inside the irradiated material and enforce a boundary condition, which allows convective heat transfer at the inter-facial boundary between the moist dielectric material and the air. They demonstrate the importance of applying the theory of simultaneous heat and moisture movement to microwave heating. In this theory a set of synchronised heat and moisture waves propagate through the material with velocities that are vastly different from those predicted by the constant vapour concentration thermal diffusivity of the material. They also correctly predict the “S” shaped temperature versus electric field strength curves discussed by other authors.(For complete abstract open document)

An efficient solution method for evaluating radiative transport in a foam layer is a valuable tool for predicting the properties of the layer. Two different solution methods have been investigated. First, a reverse Monte Carlo (RMC) simulation has been developed. In the RMC simulation photon bundles are traced backwards from a detector to the source where they were emitted. The RMC method takes advantage of time reflection symmetry, allowing the photons to be traced backwards in the same manner they are tracked in a standard forward Monte Carlo scheme. Second, a reduced order model based on the singular value decomposition (ROM) has been developed. ROM uses solutions of the reflectance-time profiles found for specific values of the governing parameters to form a solution basis that can be used to generate the profile for any arbitrary values of the parameter set. The governing parameters that were used in this study include the foam layer thickness, the asymmetry parameter, and the scattering coefficient. Layer thicknesses between 4 cm and 20 cm were considered. Values of the asymmetry parameter varied between 0.2 and .08, while the scattering coefficient ranged from 2800 m-1 to 14000 m-1. Ten blind test cases with parameters chosen randomly from these ranges were run and compared to an established forward Monte Carlo (FMC) solution to determine the accuracy and efficiency of both methods. For both RMC and ROM methods the agreement with FMC is good. The average difference in areas under the curves relative to the FMC curve for the ten cases of RMC is 7.1% and for ROM is 7.6%. One of the ten cases causes ROM to extrapolate outside of its data set. If this case is excluded the average error for the remaining nine cases is 5.3%. While the efficiency of RMC for this case is not much greater than that of FMC, it is advantageous in that a solution over a specified time range can be found, as opposed to the FMC where the entire profile must be found. ROM is a very efficient solution method. After a library of solutions is developed, a separated solution with different parameters can be found essentially in real-time. Because of the efficiency of this ROM it is a very promising solution technique for property analysis using inverse methods.

Dans de nombreuses études micrométéorologiques, les modèles numériques prenant en compte les bâtiments considèrent généralement l'atmosphère comme neutre. Néanmoins, les transferts radiatifs urbains jouent un rôle important en raison de leur influence sur le bilan énergétique. Afin de prendre en compte le rayonnement atmosphérique et les effets thermiques des bâtiments dans les simulations de l'écoulement atmosphérique et la dispersion des polluants en milieux urbains, nous avons développé un modèle de rayonnement atmosphérique tridimensionnel (3D), dans le module atmosphérique du code de mécanique des fluides Code_Saturne. Le schéma radiatif a été précédemment validé avec des cas idéalisés, en utilisant dans un premier temps, un champ constant de vent 3D. Dans ce travail, le couplage des schémas radiatifs et thermiques avec le modèle dynamique est évalué. L'objectif de la première partie est de valider le couplage complet avec les mesures de la campagne de mesure américaine ‘Mock Urban Setting Test' (MUST) sur des géométries simples. La deuxième partie traite deux approches différentes pour modéliser les échanges radiatifs en milieu urbain avec une comparaison entre Code_Saturne et SOLENE. La troisième partie utilise le couplage complet pour montrer l'apport du modèle de transfert radiatif sur l'écoulement de l'air dans des conditions de faible vitesse du vent dans une canopée 3D. Dans la dernière partie, nous utilisons le couplage dynamique-radiatif pour simuler un environnement urbain réel et valider le modèle avec les données expérimentales de la campagne ‘Canopy and Aerosol Particle Interactions in Toulouse Urban Layer' (CAPITOUL) / In many micrometeorological studies, building resolving models usually assumea neutral atmosphere. Nevertheless, urban radiative transfers play an important role because of their influence on the energy budget. In order to take into account atmospheric radiation and the thermal effects of the buildings in simulations of atmospheric flow and pollutant dispersion in urban areas, we have developed a three-dimensional (3D) atmospheric radiative scheme, in the atmospheric module of the Computational Fluid Dynamics model Code_Saturne. The radiative scheme was previously validated with idealized cases, using as a first step, a constant 3D wind field. In this work, the full coupling of the radiative and thermal schemes with the dynamical model is evaluated. The aim of the first part is to validate the full coupling with the measurements of the simple geometry from the ‘Mock Urban Setting Test' (MUST) experiment. The second part discusses two different approaches to model the radiative exchanges in urban area with a comparison between Code_Saturne and SOLENE. The third part applies the full coupling scheme to show the contribution of the radiative transfer model on the airflow pattern in low wind speed conditions in a 3D urban canopy. In the last part we use the radiative-dynamics coupling to simulate a real urban environment and validate the modeling approach with field measurements from the ‘Canopy and Aerosol Particle Interactions in Toulouse Urban Layer' (CAPITOUL)

Cette thèse est consacrée à la mise en place d'un système hyperfréquence dédié à l'imagerie du proche sous-sol. L'analyse de l'onde mesurée après interaction de l'onde incidente avec le milieu permet de remonter aux propriétés électromagnétiques de la structure illuminée. Ici, nous choisissons d'utiliser une seule fréquence en s'appuyant sur une configuration multistatique pour garantir une meilleure diversité de l'information.L'imagerie quantitative exige un calibrage minutieux des données mesurées après correction des erreurs expérimentales. Un calibrage a été donc proposé, basé sur la mesure du diagramme de rayonnement de chaque antenne. Celles-ci sont modélisées quantitativement en champ proche grâce à une combinaison de fils sources adéquatement optimisée. Ce calibrage, rapide et simple, ne nécessite pas d'objets de calibrage supplémentaires. Il a été d'abord testé dans le cas de la diffraction par des objets 2D en espace libre, puis dans le cas d'objets faiblement enfouis. Les champs calibrés servent de données d'entrée à des algorithmes d'inversion. En terme de localisation, les résultats obtenus sont très satisfaisants. Quant à la caractérisation, la configuration stratifiée apparaît bien moins propice que la configuration en espace libre, de part la faible quantité d'information disponible. Des changements ont été apportés à la configuration (différentes antennes avec ou sans orientation) dans l'optique d'améliorer le rapport signal à bruit. Bien que les reconstructions des permittivité soient encore perfectibles, les premiers résultats sont intéressants d'autant plus que les algorithmes n'exploitent aucune information a-priori sur la cible. / This thesis is devoted to the development of a microwave system dedicated to subsurface imaging applications. The analysis of the measured wave after the interaction with the medium allows to retrieve the electromagnetic properties of the probed structure. Here, we choose a single frequency operating mode combined with a multistatic configuration in order to improve the information diversity.Quantitative imaging requires a high-precision calibration of the measured data even after a careful correction of experimental errors. Thus, a calibration method is proposed, exploiting the measurement in free-space of the radiation pattern of each antenna. These patterns are quantitatively modeled thanks to an optimized linear combination of elementary sources positioned on the antenna's aperture. This simple and efficient calibration avoids additional measurements with calibration objects. This method provides successful results in a 2D free space scattering problem, as well as in the shallowly buried targets case.The calibrated data serve as inputs to inversion algorithms. As localization is concerned, very satisfactory detection results are obtained. Regarding the characterization aspects, the results indicate that the stratified configuration is less suitable than the free space configuration, due to its lack of spatial information. In order to improve the signal-to-noise ratio, some amendments are made to the experimental configuration (different antennas with or without orientation). Although the permittivity reconstructions are perfectible, the first results are promising especially since no a-priori on the targets has been inserted in the inversion algorithm so far.

In many micrometeorological studies, building resolving models usually assumea neutral atmosphere. Nevertheless, urban radiative transfers play an important role because of their influence on the energy budget. In order to take into account atmospheric radiation and the thermal effects of the buildings in simulations of atmospheric flow and pollutant dispersion in urban areas, we have developed a three-dimensional (3D) atmospheric radiative scheme, in the atmospheric module of the Computational Fluid Dynamics model Code_Saturne. The radiative scheme was previously validated with idealized cases, using as a first step, a constant 3D wind field. In this work, the full coupling of the radiative and thermal schemes with the dynamical model is evaluated. The aim of the first part is to validate the full coupling with the measurements of the simple geometry from the 'Mock Urban Setting Test' (MUST) experiment. The second part discusses two different approaches to model the radiative exchanges in urban area with a comparison between Code_Saturne and SOLENE. The third part applies the full coupling scheme to show the contribution of the radiative transfer model on the airflow pattern in low wind speed conditions in a 3D urban canopy. In the last part we use the radiative-dynamics coupling to simulate a real urban environment and validate the modeling approach with field measurements from the 'Canopy and Aerosol Particle Interactions in Toulouse Urban Layer' (CAPITOUL)