Дисертації з теми "Integral simulation"

This dissertation looks at exploiting the mathematics of vorticity dynamics and potential flow using integral equations to reformulate critical parts of fully dynamic fluid animation methods into surface based problems. These reformulations enable more efficient calculation and data-structures due to the reduction of the simulation domain to the two dimensional fluid surface, rather than its volume. We also introduce a surface compression and real-time playback method for continuous time-dependent iso-surfaces. This compression method further increases the impact of our highly efficient surface-based simulation methods.
Science, Faculty of
Computer Science, Department of
Graduate

The energy renovation of buildings is an essential action to achieve the European target of 20/20/20. However, the dynamics of the energy renovation are very slow and the development of urgent policy actions beyond the national energy efficiency action plans is needed. In that context, the main objective of the thesis is to develop a cost-effective analysis for the energy renovation of the main residential building typologies of Catalonia, considering three main criteria: thermal comfort, primary energy use and global costs. The main building typologies of Catalonia are analysed, comparing the current situation with the effect of different energy efficiency measures. Four building typologies are studied, each of them in different climates and locations, in order to evaluate the differences and the particularities of every one. The building model definition is an important task where all the methods and hypotheses to estimate the energy consumption are defined. In that sense, the objective of the building model definition is to go further to the previous studies, trying to improve the detail and the results of the simulation. The emphasis of the PhD is on the following aspects: the building characterization, including information from surveys and monitoring campaigns; the user behaviour and its interaction with the building, using stochastic occupancy profiles; the improvement of the implementation of passive strategies, as natural ventilation and the use of solar protections; and the thermal comfort of the users, as a criteria to choose the appropriate measures. A validation process of the building model is done to obtain reliable results. A pilot site is used to develop the validation of the model. A monitoring campaign has been done to characterize the pilot site and to implement the simulation model. The pilot site is a dwelling representative of one of the typologies analysed under the PhD. The validation of the model confirms that the hypotheses and methods included in the model are appropriate for the residential building simulation. Finally, the simulation process is defined in two-step evaluation: passive and active evaluation. The objective of the passive evaluation is to reduce, as much as possible, the thermal discomfort with the minimum initial investment cost of passive measures. This first step provides information to make a first selection of the appropriate passive measures in each building. In the second step where the passive and active measures are implemented in the building, the active evaluation wants to obtain the cost-effective measures, minimizing the primary energy use and the global costs. For concluding, the PhD provides technical and economic information to help to take decisions for the energy renovation of residential buildings in Catalonia.
La rehabilitació energètica dels edificis és una acció essencial per assolir els objectius Europeus 20/20/20. Malauradament, les dinàmiques de renovació energètica són molt lentes i requereixen de accions polítiques urgents emmarcades sota els plans d’acció nacional per l’eficiència energètica. En aquest context, el principal objectiu de la tesi es desenvolupar un anàlisis cost-efectiu per la renovació energètica dels principals edificis residencials de Catalunya, considerant tres criteris principals: confort tèrmic, energia primària i costos globals. Les principals tipologies d’edificis de Catalunya s’analitzen comparant la seva situació actual amb l’efecte de les diferents mesures d’eficiència energètica. S’han estudiat quatre tipologies d’edifici, cada una d’elles en diferents climes i localitzacions, per tal d’avaluar les diferencies i les particularitats de cada una d’elles. La definició dels models d’edifici és una tasca important on s’han de definir tots els mètodes i hipòtesis per estimar el consum energètic. En aquest sentit, l’objectiu de la definició del model d’edifici és anar mes enllà dels estudis previs, intentant millorar el detall i els resultats de la simulació. L’enfoc de la tesis es centra en els següents aspectes: la caracterització de l’edifici, incloent informació obtinguda d’enquestes i campanyes de monitorització; el comportament de l’usuari i la seva interacció amb l’edifici, fent servir perfils d’ocupació estocàstics; la millora en la implementació de estratègies passives, com ara la ventilació natural o les proteccions solars; i el confort tèrmic dels usuaris com a criteri per elegir els mesures adequades. S’ha realitzat la validació del model d’edifici per tal d’obtenir resultats fiables. S’ha utilitzat un habitatge pilot per realitzar la validació del model. S’ha realitzat una campanya de monitorització per tal de caracteritzar el pilot i poder implementar el model. L’habitatge pilot és un habitatge representatiu de una de les tipologies analitzades al PhD. La validació del model confirma que les hipòtesis i mètodes implementats al model son els adequats per la simulació d’edificis residencials. Per concloure, el procés de simulació s’ha definit en dos etapes d’avaluació: avaluació passiva i activa. L’objectiu de l’avaluació passiva és reduir lo màxim possible el desconfort tèrmic amb el mínim cost d’inversió inicial en mesures passives. Aquesta etapa proporciona informació per realitzar una primera selecció de les mesures passives adequades per cada edifici. A la segona etapa, on les mesures passives i actives s’implementen a l’edifici, l’avaluació passiva proporciona les mesures cost-efectives, minimitzant l’energia primària i els costos globals. Finalment, la tesi proporciona informació tècnica i econòmica per ajudar la presa de decisions per la renovació energètica dels edificis residencials de Catalunya.

Bauteile mit Rissen können mit Hilfe der Bruchmechanik bewertet werden. Da die Ermittlung der Rissspitzenbeanspruchung nicht immer analytisch gelingt, ist die Nutzung numerischer Verfahren von Vorteil. Nach einer kurzen Einführung in die Bruchmechanik wird an zwei Beispielen die Vorgehensweise diskutiert.

This thesis proposes an interactive software tool that can be used to compute complete sets of Proportional Integral Derivative (PID) Controllers from knowledge of the plant transfer function/frequency response data. This is based on research results and algorithms developed by Bhattacharyya and others. Until these research results were published, it was not known if a nominal system could be stabilized using PID Controllers, and current PID Controller designs are carried out using ad hoc tuning rules. By using simulations, engineers can best plan for and observe the stabilizing effect each of the variables has on system performance in a realistic environment. The software application developed calculates and optimizes complete stabilizing sets of PID Controllers for a rational Linear Time Invariant (LTI) system, and has been developed for analytical models of plants with and without time delay. Further, these PID Controller sets are optimized to project subsets simultaneously satisfying multiple performance index specifications. Sets of PID Controllers that stabilize a system are also calculated automatically from knowledge of the frequency response of the plant. It allows the user ease of design and the ability to customize the final solution while permitting full control over source parameters. This thesis includes an introduction to the algorithms that have been developed for plant stabilization, a complete description of the graphical user interface, the simulation of the algorithms performed using LabVIEW, and a summary of future work.

A new large eddy simulation (LES) code is developed and used to investigate non-local features of turbulent planetary boundary layers (PBLs). The LES code is based on filtered Navier-Stokes equations, which describe motions of incompressible, Boussinesq fluid at high Reynolds numbers. The code computes directly large-scale, non-universal turbulence in the PBL whereas small-scale, universal turbulence is parameterized by a dynamic mixed subgrid closure. The LES code is thoroughly tested against high quality laboratory and field data.

This study addresses non-local properties of turbulence which emphasis on the stable stratification. Its basic results are as follows. The flow stability in PBLs is generally caused by two mechanisms: the negative buoyancy force (in the stable density stratification) and the Coriolis force (in the rotating system). The latter stabilizes the flow if the earth’s vorticity and the turbulent vorticity are anti-parallel. The Coriolis force stability suppresses large-scale turbulence and makes large eddies asymmetric. The density stratification suppresses vertical scales of turbulence. Joint actions of the Coriolis and the buoyancy forces result in a more complex behavior of turbulence. Particularly, the layers of vigorous turbulence may appear in the course of development of low-level jets in baroclinic atmosphere.

Non-local effects determine integral measures of PBLs, first of all the PBL depth. This study clearly demonstrates its pronounced dependences on the Coriolis parameter, the Kazanski-Monin internal stability parameter, and newly introduced imposed-stability and baroclinicity parameters. An LES database is created and used to validate an advanced PBL-depth formulation. LES support the idea that PBLs interact with the stably stratified free flow through the radiation of gravity waves, excited by large turbulent eddies at the interface.

Despite the progress in structural biology over the last decades, it is still challenging to determine the structure of the transmembrane domains (TMDs) of integral membrane proteins. The work of this thesis has focused on two groups of integral membrane proteins: Toll-like receptors (TLRs) and polysaccharide co-polymerases (PCPs). TLRs are single transmembrane-spanning receptors responsible for recognizing a vast number of exogenous pathogens derived from bacteria, viruses and fungi. Upon ligand binding to the extracellular ectodomains (ECDs), TLRs dimerize and conformational changes are transmitted to the TMDs and intracellular domains to initiation of inflammatory signaling pathways. Overstimulation or dysregulation of the TLR-associated pathways can lead to a number of diseases including sepsis, cancer and rheumatoid arthritis. Although there is extensive structural information available for the dimeric extracellular and intracellular soluble domains, little is known about the TMD assemblies. Clarifying the structure of the TMDs, as it is described in this thesis, should help to further the understanding of the molecular mechanisms of signaling, and hence provide new starting points for therapeutic immunomodulation. Wzz is a PCP1 protein found in the bacterial inner membrane and is involved in the regulation of the O-antigen (Oag) chain length of lipopolysaccharides (LPSs), essential for the virulence of many gram-negative pathogens. All Wzz proteins are comprised of a large periplasmic domain, two transmembrane helices and a short cytosolic domain. Although several experimental oligomeric structures are available for the periplasmic domains of Wzz, the in vivo oligomerization state and transmembrane architecture of Wzz is unclear. Work towards a better understanding is described here and it may help to clarify the mechanism of Oag regulation, and in the future may contribute to new antimicrobial strategies. A multiscale simulation approach has been carried out to investigate the self-assembly of modelled TLR and Wzz TMDs within lipid membrane environments. Upon assembly, interfacial TMD arrangements were assessed to provide structural insights into key residues and motifs that may drive association. In addition, cryo-electron microscopy data for a novel dodecameric structure for Wzz were incorporated into this approach. The dynamics of various oligomers of the full-length Wzz within a lipid membrane environment were investigated via simulations. This work provided new insights into the role of TMDs in the activation and function of TLRs and led to the development of a new model for the mechanism of function of Wzz, as well as providing predictions on which oligomerization state is most likely to represent the in vivo state.

To get an improved understanding and knowledge of the processes and phenomena during the late phase of a core melt down accident the FOREVER-experiments (Failure of Reactor Vessel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. During the first series of experiments the Creep behaviour of the vessel is investigated. Due to the multi-axial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are on the one hand an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used for an optimized experimental procedure. Therefore a Finite Element model is developed on the basis of the multi-purpose commercial code ANSYS/Multiphysics®. Using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress for each element. Performing post-test calculations for the FOREVER-C2 experiment it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. A slight temperature increase during the creep deformation stage of the experiment for example could explain the creep behaviour which appears to be tertiary because of the accelerating creep strain rate. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

To get an improved understanding and knowledge of the processes and phenomena during the late phase of a core melt down accident the FOREVER-experiments (Failure of Reactor Vessel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. During the first series of experiments the Creep behaviour of the vessel is investigated. Due to the multi-axial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are on the one hand an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used for an optimized experimental procedure. Therefore a Finite Element model is developed on the basis of the multi-purpose commercial code ANSYS/Multiphysics®. Using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress for each element. Performing post-test calculations for the FOREVER-C2 experiment it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. A slight temperature increase during the creep deformation stage of the experiment for example could explain the creep behaviour which appears to be tertiary because of the accelerating creep strain rate. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

In the pursuit of excellence industrial companies are increasingly employing production system development to rationalize their processes. One such approach that has been employed to great extend in the automotive industry is that of introducing modularity to the product design. This shift from integral products to modular ones, is associated with a higher level of standardization of parts and processes. However, researchers are still mapping out this correlation. As the connection between modularity and the recorded effects is still up for discussion, still fewer studies have been made on how to most effectively adopt modularisation. This thesis is therefore a research that explores the relationship between product design and production from a perspective of production system development. It is a collaborative study conducted with a manufacturer of industrial robots that is preparing to transition from an integral product design to a modular one. The case study utilizes discrete – event simulation to model the impact of such a changeover in the production system. Not resulting in a step-by-step how-to guide, the study nevertheless shows that discrete – event simulation can prove to be a valuable asset both when analysing what-if scenarios and when pinpointing pre-emptive measures in order to mitigate any negative disruption such a transition might initially bring.

In this report we describe simulation of the surface current density on a PEC cylinder and the diffracted field for a line source above a finite PEC ground plane as a means to verify the Nero2D program. The results are compared with the exact solution and give acceptable errors. A terrain model for a communication link is studied in the report and we simulate the wave propagation for terrain with irregular shapes and different materials. The Nero2D program is based on the fast multipole method (FMM) to reduce computation time and memory. Gaussian sources are also studied to make the terrain model more realistic

Les raies gamma sont la signature de reactions nucleaires et d'autres processus a haute energie existant dans l'univers. Leur mesure et leur etude fournissent d'inestimables informations sur des problemes d'astrophysique des hautes energies comme l'acceleration de particules, la physique des objets tres compacts (trous noirs, quasars), ou encore la nucleosynthese. Pour observer les sources gamma astronomiques, on doit s'affranchir de l'atmosphere terrestre qui constitue un ecran opaque aux photons gamma. Malheureusement, les equipements spatiaux incorporant des detecteurs de rayonnements electromagnetiques a haute energie (rayons x et gamma) sont, a ces altitudes, exposes a des flux parasites intenses de rayonnements et de particules induits par le rayonnement cosmique primaire galactique. Que ce soit par leur impact direct ou par celui des rayonnements et des particules secondaires qu'ils engendrent dans leur voisinage immediat, ces flux parasites suscitent au sein des detecteurs un bruit de fond considerable qui en limite les performances. Ce travail de these entre dans le cadre de la mission integral projet d'astronomie gamma spatiale de l'agence spatiale europeenne destinee a l'observation des emissions x et gamma d'origine celeste. Integral est constitue de deux instruments principaux : un imageur ibis et un spectrometre germanium a haute resolution e/e = 1,6 10 3 a 1,3 mev, appele spi. Nous avons etudie la composante hadronique du bruit de fond de spi, constituee d'un spectre continu auquel se superposent des raies. Elle est due aux decroissances radioactives des noyaux residuels crees par les interactions des protons du rayonnement cosmique avec les materiaux constituant spi. Pour etudier tous les aspects nucleaires, des simulations monte-carlo ont ete realisees en utilisant le code de physique nucleaire tierce developpe au cea / dam. Ensuite avec le code geant du cern nous avons simule la reponse spectrale des detecteurs en germanium. Des techniques telles que la psd (pulse shape discrimination) et les signatures energetiques ont ete utilisees dans des bandes d'energie bien choisies afin de reduire le bruit de fond et ainsi ameliorer la sensibilite de spi. Avec la sensibilite de detection des raies fines estime dans cette etude, le spectrometre spi devrait pouvoir detecter de nombreuses raies gamma nucleaires emises dans les sites actifs de la galaxie.

Le but de cette thèse est de poser de nouvelles contraintes sur les différents mécanismes d'accélération de particules opérant au sein de la géométrie complexe de l'environnement d'une étoile à neutrons, c'est à dire dans la magnétosphère du pulsar, dans le jet, dans le plan équatorial ainsi qu'au choc terminal. Proche de la surface l'accélération est produite par l'entraînement du très fort champ magnétique par la rotation de l'étoile. Au delà du cylindre de lumière, les particules sont également accélérées dans le plan équatorial par reconnexions magnétiques. Ces processus ont pour principale signature observationnelle une émission puisée pouvant être observée dans tous les domaines de longueurs d'onde. Un des outils les plus puissants afin de contraindre ces mécanismes est l'étude de la polarisation suivant la phase de rotation. C'est dans cet esprit que nous avons utilisé le mode Compton d'IBIS à bord du satellite S\gammaS INTEGRAL. En effet ce dernier permet par la mesure de la distribution selon l'angle azimuthal de diffusion, des événements diffusés entre les deux plans détecteurs d'IBIS, de remonter à la direction et à la fraction de polarisation d'une source au delà de 200 keV. Une méthode d'analyse et de traitement de données a donc été développée dans ce but. La sensibilité atteinte permet de mesurer la polarisation de sources persistantes fortes ainsi que celle de sursauts S\gammaS. Cette méthode a été appliquée au pulsar du Crabe ainsi qu'a sa nébuleuse. Pour la première fois la polarisation d'une source a été mesurée dans le domaine S\gammaS entre 0. 2 et 0. 8 MeV. L'évolution de cette dernière avec la phase de rotation est en accord avec celle trouvée en optique dans les régions centrales, c'est à dire pour des régions S<0. 01S pc du pulsar. Dans le domaine non puisé l'angle de polarisation semble aligné le long de l'axe de rotation, ce qui suggère un rayonnement venant principalement du jet ou bien du point brillant proche du pulsar. Le fait qu'aucune polarisation ne soit observée juste après les pics en émission pourrait être la signature d'effets caustiques sur de grandes distances le long de la dernière ligne de champ ouverte dans la magnétosphère du pulsar. Dans ce cas le modèle du \textit{slot gap} pourrait être responsable de l'émission puisée et donc de la réaccélération de particules proche du pulsar. Afin de mieux contraindre les processus d'accélération par la polarisation il est alors nécessaire d'utiliser une configuration de champ magnétique la plus réaliste possible. Ce paramètre est en effet à la base de tous les modèles d'accélération et d'émission hautes énergies. Jusqu'à maintenant cette géométrie fut supposée dipolaire. C'est donc dans l'optique d'établir une configuration du champ E et B plus réaliste que les équations d'Einstein et de Maxwell furent résolues proche de la surface et dans le vide en utilisant la librairie LORENE. Cette librairie est basée sur les décompositions spectrales, méthode bien adaptée à la résolution des équations de type Poisson. La géométrie obtenue diffère légèrement de celle d'un dipôle classique pour de faibles rotations et les zones d'accélération sont elles localisées proche des calottes polaires. Il est maintenant nécessaire de poursuivre cette étude dans le cas d'une magnétosphère chargée. Dans la magnétosphère lointaine et plus particulièrement proche du choc terminal, les particules peuvent être réaccélérées par absorption d'ondes cyclotrons émises par les ions ainsi que par processus de Fermi relativiste. Des contraintes spectrales comme l'énergie maximum ou l'indice spectral de la distribution de particules permettent de contraindre de façon très efficace ces processus. Pour remonter à de telles informations et notamment à l'énergie maximum qui est en général de l'ordre de S10*{l4-15}S TeV, il est en général nécessaire d'utiliser les émissions synchrotron dans le domaine des X durs (>20 keV). Le champ magnétique doit dans ce cas être connu de manière très précise. C'est dans cet esprit que nous avons étudié les émissions au delà de 20 keV de PSR B1509-58. Ce pulsar produit une longue traine observée en X et au TeV, traine qui a été interprète comme étant du à un jet. Dans le domaine non puisée, de son émission, où la contribution du pulsar par rapport au vent qu il crée est minimum, 1'imageur IBIS détecta lui aussi entre 20 et 200 keV une source s'étendant dans la direction de ce jet et ayant un spectre coupé vers 160 keV. Le champ magnétique a été contraint à des valeurs comprises entre 2 et 3 nT en utilisant la variation de la longueur apparente du jet avec l'énergie entre 0. 1 et 100 keV. Dans ce champ les particules y rayonnant à 160 keV possèdent une énergie comprise entre 400 et 730 TeV. Pour des pulsars plus vieux, le vent relativiste est confiné par la pression du au déplacement de l'étoile dans le milieu interstellaire. La morphologie de ce dernier est alors modifiée et la simple hypothèse de vent sphérique utilisée dans le modèle standard de Kennel et Corroniti ou bien de jet cylindrique, s'évanouit alors au profit de 1'apparation d'un choc en étrave. C'est pourquoi un simple modèle MHD analytique des émissions synchrotrons d'un vent relativiste choqué de pulsar fut développé dans une telle géométrie. Ce modèle fut appliqué au cas de Geminga récemment observé avec XMM et Chandra. Dans cette géométrie l'amplification du champ magnétique le long de la discontinuité de contact permet d'expliquer les flux observés alors que l'énergie maximum nécessaire pour reproduire les observations est incompatible avec celle donnée par un processus de Fermi relativiste. L'énergie maximum de l'ordre de 400 TeV nécessite d'utiliser l'intégralité du potentiel dipolaire aux calottes polaires. Ce simple modèle montre également combien l'évaluation du champ magnétique est primordiale pour interpréter les données
The context of this thesis is to gain new constraints on the different particle accelerators that occur in the complex environment of neutron stars: in the pulsar magnetosphere, in the striped wind or wave zone outside the light cylinder, in the jets and equatorial wind, and at the wind terminal shock. Near the star, the accelerator is powered by the rotation of the intense magnetic field and can be probed by the pulsed radiation at all wavelengths. An additional powerful tool to investigate the magnetic geometry in the radiative zones, therefore the accelerator location, is polarimetry, especially at high photon energy. The shocked wind of the Crab nebula and a handful of other wind nebulae are known to host 1014-15 eV particles, but thé energy estimates are always subject to the uncertain evaluation of the local magnetic field strength. The famous spherical model of Kennel and Coroniti (1984) has been challenged by high-resolution X-ray and TeV images that show a growing wealth of jets and equatorial flows, confined by asymmetric pressure gradients in a supernova remnant or by interstellar bow shocks. An important tool to constrain both the magnetic field and primary particle energies is to image the synchrotron ageing of the population, but it requires a careful modelling of the magnetic field evolution in the wind flow. The current models and understanding of these different accelerators, the acceleration processes, and open questions have been reviewed in the first part of the thesis. In this context, the thesis work is three-fold: instrumental, observational, and theoretical. On board INTEGRAL, the IBIS imager provides images with 12' resolution from 17 keV to MeV energies where the SPI spectrometer takes over up, to 10 MeV, but with a reduced 2° resolution. The first part of the work provides a new method for using the double-layer IBIS imager as a Compton telescope with coded mask aperture. Its performance has been measured. The new concept takes advantage of the coded mask deconvolution for high resolution and background rejection to construct images with a 12' resolution, over a 29°x29° field of view, at the 0. 1-0. 4 Crab sensitivity level, in the 0. 2-1 MeV range. The Compton scattering information and the achieved sensitivity also open a new window for polarimetry in gamma rays. A method has been developed to extract the linear polarization properties and to check the instrument response for fake polarimetric signais in the various backgrounds and projection effects. The achieved sensitivity of 0. 3-1 Crab for polarized emission allows the study of bright sources and AGN flares, gamma-ray bursts and solar flares for the first time at high energy. The INTEGRAL data recorded for the Crab pulsar and nebula show good evidence for a high degree of polarization for both the pulsed and the unpulsed emissions in the 0. 2-0. 8 MeV band. The measured polarization closely follows the optical one from the central < 0. 01 pc region around the pulsar. The polarization orientation along the rotation axis is consistent with emission from the jet and bright knot, not with DC emission from the pulsar beams. No polarization has been detected on the trailing sides of the pulsed peaks. It could sign the caustic effects that characterize emission along a fair fraction of the last open field lines on the trailing sides of the pulsar magnetosphere. A dipolar magnetic field geometry is assumed in the magnetosphere and a split-monopole one outside, but they can be questioned for very intense stellar fields or very compact magnetospheres. As a first step to map this field in general relativity, Einstein and Maxwell equations have been solved near the pulsar, in vacuum, using the LORENE library to find the rotating star metric together with the associated magnetic and electric fields. This library is based on spectral methods well adapted for Poisson type equations. The resulting field geometry differs slightly from a dipole and the acceleration regions are closed to the polar caps. Studying the geometry in a charged magnetosphere with potential currents will be the next step. INTEGRAL synchrotron data above 30 keV is best suited to probe the most energetic wind particles and their ageing in the flow by comparison with lower-energy images. The wind from PSR B1509-58 powers a long X-ray jet and TeV tail. The unpulsed emission recorded by INTEGRAL-IBIS at 20-200 keV has been used to detect a slightly extended source along the jet axis, with a power-law spectrum up to 160 keV. The variation of the apparent jet length with energy from 0. 1 to 100 keV has been interpreted as synchrotron ageing in a simple cylindrical jet. This allows to constrain both the average jet magnetic field to 2 or 3 nT and the electron energies near the cut-off to 400-700 TeV. Many older wind nebulae are confined into a bow shock geometry by the ram pressure of their motion into the interstellar medium. This morphology modifies the MHD flow by providing an exit for the kinetic and magnetic energy and stationary conditions. Very hard synchrotron X-ray tails have been imaged around the nearby, 0. 3 Myr-old, Geminga pulsar. A first attempt at modelling the emission shows that Fermi acceleration at the wind terminal shock or at the bow shock cannot produce the required particle energies. As for the Crab, the particles must somehow tap the potential drop from the pulsar unipolar inductor. We also find that the particles are too few and/or the magnetic field to low to account for the observed X rays. The prediction falls short by 2 or 3 orders of magnitude. A simple analytical MHD model has been developed to show that the magnetic field advection toward the bow-shock contact discontinuity and the resulting amplification can explain the observed flux. Electron energies of 400 TeV are found. This 'toy model1 proves the importance of a careful modelling of the magnetic flow to interpret the data

Path integral Monte Carlo (PIMC) is a method suitable for quantum liquid simulations at finite temperature. We present in this thesis a study of PIMC dealing with the theory and algorithms related to it, and then two applications of PIMC to current research problems of quantum fluids in the Bolzmann regime.
The first part encompasses a study of the different ingredients of a PIMC code: action, sampling and physical property estimators. Particular attention has been paid to Li-Broughton's higher order approximation to the action. Regarding sampling, several collective movement methods have been derived, including the bisection algorithm, that has been thoroughly tested. We also include a study of estimators for different physical properties, such as, the energy (through the thermodynamic and virial estimators), the pair distribution function, the structure factor, and the momentum distribution.
In relation to the momentum distribution, we have developed a novel algorithm for its estimation, the trail method. It surmounts some of the problems exposed by previous approaches, such as the open chain method or McMillan's algorithm.
The Richardson extrapolation used within PIMC simulations, is another contribution of this thesis. Up until now, this extrapolation has not been used in this context. We present studies of the energy dependence on the number of "beads", along with the betterment provide by the Richardson extrapolation.
Inasmuch as our goal is to perform research of quantum liquids at finite temperature, we have produced a library of codes, written from scratch, that implement most of the features theoretically developed. The most elaborated parts of these codes are included in some of the appendixes.
The second part shows two different applications of the algorithms coded. We present results of a PIMC calculation of the momentum distribution of Ne and normal 4He at low temperatures. In the range of temperatures analysed, exchanges can be disregarded and both systems are considered Boltzmann quantum liquids. Their quantum character is well reflected in their momentum distributions witch show clear departures from the classical limit. The PIMC momentum distributions which show clear departures from the classical limit. The PIMC momentum distributions are sampled using the trail method. Kinetic energies of both systems, as a function of temperature and at a fixed density, are also reported.
Finally, the solid-liquid neon phase transition along the 35 K isotherm has been characterized.While thermodynamic properties of the solid phase are well known the behaviour of some properties, such as the energy or the dessity, during the trasition presen6 some uncertainties For example, experimental data for the place diagram, which determines solid and liquid boundaries, present sizeable differences. The temperature chosen is high enough so that Bose or Fermi statistics corrections are small, although the system is strongly quantum mechanical. The results obtained show a discontinuity in the kinetic energy during the transition.

In this thesis, simulations are performed to study the motion ofindividual cells in flow, focusing on the hydrodynamics of actively swimming cells likethe self-propelling microorganisms, and of passively advected objects like the red bloodcells. In particular, we develop numerical tools to address the locomotion ofmicroswimmers in viscoelastic fluids and complex geometries, as well as the motion ofdeformable capsules in micro-fluidic flows. For the active movement, the squirmer is used as our model microswimmer. The finiteelement method is employed to study the influence of the viscoelasticity of fluid on theperformance of locomotion. A boundary element method is implemented to study swimmingcells inside a tube. For the passive counterpart, the deformable capsule is chosen as the modelcell. An accelerated boundary integral method code is developed to solve thefluid-structure interaction, and a global spectral method is incorporated to handle theevolving cell surface and its corresponding membrane dynamics. We study the locomotion of a neutral squirmer with anemphasis on the change of swimming kinematics, energetics, and flowdisturbance from Newtonian to viscoelastic fluid. We also examine the dynamics of differentswimming gaits resulting in different patterns of polymer deformation, as well as theirinfluence on the swimming performance. We correlate the change of swimming speed withthe extensional viscosity and that of power consumption with the phase delay of viscoelasticfluids. Moreover, we utilise the boundary element method to simulate the swimming cells in astraight and torus-like bent tube, where the tube radius is a few times the cell radius. Weinvestigate the effect of tube confinement to the swimming speed and power consumption. Weanalyse the motions of squirmers with different gaits, which significantly affect thestability of the motion. Helical trajectories are produced for a neutralsquirmer swimming, in qualitative agreement with experimental observations, which can beexplained by hydrodynamic interactions alone. We perform simulations of a deformable capsule in micro-fluidic flows. We look atthe trajectory and deformation of a capsule through a channel/duct with a corner. Thevelocity of capsule displays an overshoot as passing around the corner, indicating apparentviscoelasticity induced by the interaction between the deformable membrane and viscousflow. A curved corner is found to deform the capsule less than the straight one. In addition, we propose a new cell sorting device based on the deformability of cells. Weintroduce carefully-designed geometric features into the flow to excite thehydrodynamic interactions between the cell and device. This interaction varies andclosely depends on the cell deformability, the resultant difference scatters the cellsonto different trajectories. Our high-fidelity computations show that the new strategy achievesa clear and robust separation of cells. We finally investigate the motion of capsule in awall-bounded oscillating shear flow, to understand the effect of physiological pulsation to thedeformation and lateral migration of cells. We observe the lateral migration velocity of a cellvaries non-monotonically with its deformability.

QC 20140313

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The teaching and learning of Differential and Integral Calculus, taken as fundamental in Exact Sciences courses, has been focused throughout time as a traditional methodological practice, based on definitions, theorems, properties, examples and exercises. This methodology has been contributing to a very high number of giving up and failure in such courses. One of the possibilities of trying to revert this, is the use of new computerized technologies as a didactic tool in Calculus courses. This work has aimed the creation and use of activities, all fundamented in cognition theories and in the main historical elements of Integral, to be developed in a computerized atmosphere. A qualitative type methodology has been chosen and it was based on a sequence of teaching and working in pairs in a computer lab. The choice of working in pairs is based on the fact that it leads to dialogues, changing of ideas and conclusions in a much more spontaneous way. The computer is used to give meaning to the concept of Integral. The different steps were created with the purpose of allowing students to develop the elements which would lead to such concept. During the activities students have used the computer in different steps.This use permitted the process of visualizing, simulating and deepening in the mathematical thought, some guesses and its contradictions or validations. The results of having had the sequence of teaching applied show that in a computerized atmosphere the teaching and learning are much more meaningful, contextualized and motivating for students as well as for teachers
O ensino e a aprendizagem de Cálculo Diferencial e Integral, considerado básico nos cursos da área de ciências exatas, tem sido, ao longo dos anos, focado numa prática metodológica tradicional baseada em: definições, teoremas, propriedades, exemplos e exercícios. A aplicação desta metodologia tem apresentado um índice muito alto de abandono e repetência. Uma das possibilidades de reverter este quadro é a utilização de novas tecnologias computacionais como ferramentas didáticas no curso Cálculo. Este trabalho tem como objetivo a elaboração e aplicação de uma seqüência de ensino baseada na fundamentação teórica e nos principais elementos históricos da Integral, implantada num ambiente computacional. Para atender a este objetivo , optou-se por uma metodologia do tipo qualitativa, baseada na realização de uma seqüência de ensino, trabalhando com duplas de estudantes em um ambiente computacional. A opção de trabalhar com duplas foi baseada no fato que esta dinâmica produz diálogos, troca de hipóteses e conclusões de forma mais espontânea. Nesta metodologia, o computador é utilizado para dar significação ao conceito de Integral. As várias etapas da seqüência foram elaboradas de modo que permitiram aos alunos construírem conceitos, que no final dela culminaram na significação do conceito de Integral. Na aplicação das atividades, o computador foi incorporado pelos estudantes em estágios diferentes. A sua utilização permitiu o surgimento do processo de visualização, a simulação, o aprofundamento do pensamento matemático, as conjecturas, as refutações e validações. Os resultados da aplicação da seqüência de ensino evidenciam que num ambiente computacional o ensino e aprendizagem passa a ser mais significativo, contextualizado e motivante, para os alunos e professores

Deux concepts très importants dans mes travaux sont ceux de la diffusion (mouvement aléatoire des particules) et de ceux de la transformée de Fourier. La diffusion des particules peut être décrite par l'équation de la diffusion, dont la solution fondamentale a un forme beaucoup plus complexe que sa transformée de Fourier. Tout d'abord, nous profitons de la forme spéciale de la transformée de Fourier (dans l'espace) de la fonction de Green de l'équation de diffusion pour formuler des méthodes numériques qui sont locales en temps pour la solution des équations avec mémoire. L'idée principale est que la solution sera calculée dans le domaine de Fourier, pour éviter d'évaluer les intégrales de convolution en temps portent la " mémoire ". Ce travail a été rendu possible par le développement d'une quadrature adaptée de l'intégrale de Fourier où un petit nombre de points dans la variable de Fourier était suffisant pour une bonne résolution du problème dans l'espace physique, sur un intervalle de temps important. En particulier, nous avons développé une méthode numérique pour simuler la diffusion dans des domaines non bornés avec sources et l'avons appliquée à la modélisation de la croissance des cristaux, à l'aide du modèle du champ de phase. Puis, afin d'étendre cette approche à des problèmes aux limites, nous avons abordé la question de l'évaluation des potentiels de simple couche et de double couche sur le bord du domaine. Enfin, nous avons généralisé l'idée de remplacer les intégrales de convolution en temps par une quadrature efficace dans le domaine de Fourier, aux intégrales et aux dérivés d'ordres fractionnaires, et obtenu une borne rigoureuse de l'erreur de quadrature. Nous avons aussi appliqué cette approche à une équation des ondes fractionnaire. En 2010, j'ai commencé à appliquer les outils numériques et analytiques à l'équation de Bloch-Torrey, dans le domaine de l'imagerie par résonance magnétique de la diffusion (IRMd) du cerveau. Ce travail a commencé dans le cadre d'une collaboration avec des physiciens d'IRM de Neurospin. Nous avons essayé d'expliquer la relation entre la géométrie cellulaire, la perméabilité membranaire et le signal d'IRMd obtenu. Certaines difficultés de la modélisation et de la simulation du signal d'IRMd au niveau de l'échelle de temps et de l'espace viennent de la physique et de la biologie d'IRMd du cerveau. Premièrement, pour des raisons biologiques et techniques, l'IRMd ne peut mesurer que des temps de diffusion compris entre une et cent millisecondes, correspondant à une distance de diffusion moyenne de 2,5 à 25 micromètres. Cette distance est moyennée sur toutes les molécules d'eau, et la distance de diffusion réelle peut être différente selon que la localisation, au début de la mesure, des molécules d'eau : dans les corps neuronaux, dans les neurites (dendrites et axones) ou dans l'espace extra-cellulaire. Deuxièmement, certaines caractéristiques de la matière grise du cerveau rendent l'analyse et la simulation très difficiles: \begin{enumerate} \item Les cellules sont géométriquement complexes. Les neurones ont un corps solide, mesurant 1 à 10 micromètres de diamètre auquel sont attachés de longues neurites (axones et dendrites) qui mesurent de l'ordre d'un micromètre de diamètre et de plusieurs centaines de micromètres de longueur. \item Les cellules ont une répartition très dense. Les corps neuronaux occupent 12\% du volume du cortex cérébral, les axones 34\%, les dendrites 35\%, l'espace extracellulaire 6\%, pour une largeur moyenne de 10 à 30 nanomètres. \item L'organisation cellulaire est complexe. Les cellules du cortex sont organisées en couches, avec des colonnes de cellules liant différentes couches. \item Les cellules sont perméables. En général, l'eau peut se déplacer entre les cellules et l'espace extracellulaire. \end{enumerate} La résolution d'IRMd est de l'ordre de 1 mm$^3$, ce qui signifie que chaque pixel de l'image affiche les caractéristiques de diffusion moyennées dans un volume de tissu (voxel) de 1 mm$^3$, ce qui est très grand devant les échelles spatiales cellulaires. Pour modéliser le signal de l'IMRd dans un voxel, il faut simuler l'aimantation à l'intérieur de ce voxel et calculer son intégrale au moment de l'écho. La distance de diffusion moyenne ne dépassant pas 25 micromètres, il suffit de faire le calcul dans un domaine légèrement plus grand qu'un voxel pour tenir compte de la diffusion de toutes les molécules d'eau qui auront " vu " ce voxel durant le temps de diffusion. De plus, si nous supposons que le voxel contient un environnement cellulaire qui ne varie pas beaucoup à dans le voxel, nous utilisons un domaine de calcul plus petit, celui-ci devra ne contenir qu'une " portion représentative " du tissu dans le voxel. Pour étudier le lien entre l'atténuation du signal d'IRMd et les propriétés géométriques du tissu, tels que le diamètre moyen des cellules et la fraction volumique cellulaire, nous avons généré, dans un premier temps, des domaines de calcul qui contiennent une configuration cellulaire à étudier. A terme, nous envisageons des simulations sur beaucoup de configurations pour obtenir des résultats statistiquement significatifs. Actuellement, nous construisons une seule configuration cellulaire et résolvons le problème forward et inverse associé. Le signal d'imagerie par résonance magnétique de diffusion dans le tissu biologique peut être considéré comme une sorte de " transformée de Fourier " de la fonction de densité de probabilité de déplacement de l'eau dans les milieux hétérogènes. L'aimantation des protons de l'eau en tissu biologique en présence d'impulsions du gradient de champ magnétique, peut être modélisée par une équation aux dérivées partielles (EDP), l'équation de Bloch-Torrey microscopique à compartiments multiples. Cette EDP peut être comprise comme l'attribution aux molécules d'eau en milieu hétérogène, d'une fréquence spatiale qui dépend de leurs positions. Le signal d'IRMd est l'intégrale de la solution de cette EDP au moment de l'écho. Nous avons résolu numériquement cette EDP en couplant une discrétisation spatiale cartésienne standard avec une discrétisation en temps adaptative (Runge-Kutta Chebyshev " RKC ") et nous avons étudié les caractéristiques de la diffusion d'un modèle de la matière grise du cerveau constitué de cellules cylindriques et sphériques dans l'espace extracellulaire. Puis, par homogénéisation, nous avons formulé un nouveau modèle macroscopique, sous forme d'un système d'équations aux dérivées ordinaires (EDO), pour le signal d'IRMd. Ensuite, nous avons montré par des simulations numériques que ce modèle d'EDO donne une bonne approximation du signal du modèle d'EDP complet pour des temps de diffusion relativement longs. Je mentionne aussi le travail de deux doctorants que je co-encadre actuellement. Dang Van Nguyen (soutenu par le projet SIMUDMRI, ANR COSINUS 2010-2013) a couplé une discrétisation d'éléments finis avec la méthode RKC pour obtenir une discrétisation plus précise des surfaces cellulaires. Il travaille sur l'analyse du signal de l'IRMd des neurones isolés. Huan Tuan Nguyen (soutenu par une bourse de l'École Doctorale " Sciences et Technologies de l'Information, des Télécommunications et des Systèmes " ED STITS, 2010-2013) travaille sur le problème inverse du modèle d'EDO. Enfin, j'envisage trois orientations futures de mes recherches dans l'IRMd. \begin{enumerate} \item En collaboration avec le centre Neurospin IRM, confronter les résultats numériques du modèle d'EDP avec les données expérimentales IRMd des ganglions (réseaux neuronaux) de l'Aplysie (limace de mer géante). \item Prendre en compte l'écoulement sanguin dans les micro-vaisseaux du cerveau, via un nouveau modèle d'EDP. \item Obtenir la formulation d'un nouveau modèle d'EDO valable aux temps de diffusion plus courts ou en présence des cellules plus grandes. \end{enumerate}

Apesar dos sistemas hidráulicos estarem entre os mais antigos meios de transmissão de energia usados pelo homem, atualmente vem recebendo muita atenção nas pesquisas científicas. A busca por maios controle da energia gerada impulsionou um aumento da utilização e aplicação e novas investigações tecnológicas de tais sistemas. Além da alta capacidade de controle e precisão, a sensibilidade, rigidez, força e potência conferem aos sistemas hidráulicos um conjunto completo de propriedades, permitindo sua ampla aplicação nos mais diferentes ramos. Porém a não linearidade da dinâmica de suas partes faz a modelagem dos sistemas hidráulicos ser complexa. Sabendo que a bomba é a parte mais importante do circuito hidráulico, este estudo apresenta um modelo matemático e a simulação computacional de uma bomba de palhetas auto-compensada por pressão com controle tipo integral. O modelo teórico está baseado na aplicação leis da física em quatro partes das bomba: Lei de Newton no carretel de válvulas e no conjunto dos pistões e o anel, e, Lei da Conservação da Massa nos volume de controle sob a pressão de operação Po e no volume sob a pressão interna da carcaça (pressão no servo cilindro), Pcc. O comportamento do sistema foi verificado com a aplicação de uma carga hidráulica proporcionada por um orifício com abertura instantânea (entrada tipo degrau). Dessa maneira a pressão de operação, saída do sistema, apresenta um pequeno transiente no início da simulação e rapidamente entra em regime. No momento no qual a carga hidráulica atua o transiente volta e em seguida entra em regime com o mesmo valor que apresentava antes da entrada degrau, comportamento específico de sistemas com controle tipo PI, proporcional e integral.
Despite the hydraulic systems are among the oldest means of energy transmission used by man, currently they are receiving special attention in scientific researchs. The search for greater control of energy generated spurred an increase in the use and application of technology and new research such systems. Besides high capacity of control and precision, sensitivity, stiffness, speed, strength, power hydraulic systems give a complete set of properties allowing their wide applications in many different areas. But the non-linearity of the dynamics of its parts is the modeling of hydraulic system is complex. Knowing that pumb is the most important part of the hydraulic circuits, this study presents a mathematical model and computer stimulation of a vane-type pump offset by pressure with integral control type. The theoretical model is based on the application laws of physics in four parts of the pumb: Newton\'s law of the spool valves and the coupling of the piston ring and with the Law of Conservation of Mass in volumes of controlling the pressure, and the Po inside if the carcass (pressure in the slave cylinder), Pcc. The behavior of the system was checked with the application of a hydraulic load (request) type entry step. Thus the pressure, leaving the system, presents a transient at the beginning of the simulation and quickly enter into arrangements. At the moment in which the hydraulic load transient operates the back and then enter into arrangements with the same value as presented before the step, specific behavior of systems with full control type.

Particle suspensions occur in many situations in nature and industry. In this master’s thesis, the motion of a single rigid spheroidal particle immersed in Stokes flow is studied numerically using a boundary integral method and a new specialized quadrature method known as quadrature by expansion (QBX). This method allows the spheroid to be massless or inertial, and placed in any kind of underlying Stokesian flow.   A parameter study of the QBX method is presented, together with validation cases for spheroids in linear shear flow and quadratic flow. The QBX method is able to compute the force and torque on the spheroid as well as the resulting rigid body motion with small errors in a short time, typically less than one second per time step on a regular desktop computer. Novel results are presented for the motion of an inertial spheroid in quadratic flow, where in contrast to linear shear flow the shear rate is not constant. It is found that particle inertia induces a translational drift towards regions in the fluid with higher shear rate.
Partikelsuspensioner förekommer i många sammanhang i naturen och industrin. I denna masteruppsats studeras rörelsen hos en enstaka stel sfäroidisk partikel i Stokesflöde numeriskt med hjälp av en randintegralmetod och en ny specialiserad kvadraturmetod som kallas quadrature by expansion (QBX). Metoden fungerar för masslösa eller tröga sfäroider, som kan placeras i ett godtyckligt underliggande Stokesflöde.   En parameterstudie av QBX-metoden presenteras, tillsammans med valideringsfall för sfäroider i linjärt skjuvflöde och kvadratiskt flöde. QBX-metoden kan beräkna kraften och momentet på sfäroiden samt den resulterande stelkroppsrörelsen med små fel på kort tid, typiskt mindre än en sekund per tidssteg på en vanlig persondator. Nya resultat presenteras för rörelsen hos en trög sfäroid i kvadratiskt flöde, där skjuvningen till skillnad från linjärt skjuvflöde inte är konstant. Det visar sig att partikeltröghet medför en drift i sidled mot områden i fluiden med högre skjuvning.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

El Método de los Momentos (MoM) ha sido ampliamente utilizado en las últimas décadas para la discretización y la solución de las formulaciones de ecuación integral que aparecen en muchos problemas electromagnéticos de antenas y dispersión. Las más utilizadas de dichas formulaciones son la Ecuación Integral de Campo Eléctrico (EFIE), la Ecuación Integral de Campo Magnético (MFIE) y la Ecuación Integral de Campo Combinada (CFIE), que no es más que una combinación lineal de las dos anteriores.
Las formulaciones MFIE y CFIE son válidas únicamente para objetos cerrados y necesitan tratar la integración de núcleos con singularidades de orden superior al de la EFIE. La falta de técnicas eficientes y precisas para el cálculo de dichas integrales singulares a llevado a imprecisiones en los resultados. Consecuentemente, su uso se ha visto restringido a propósitos puramente académicos, incluso cuando tienen una velocidad de convergencia muy superior cuando son resuelto iterativamente, debido a su excelente número de condicionamiento.
En general, la principal desventaja del MoM es el alto coste de su construcción, almacenamiento y solución teniendo en cuenta que es inevitablemente un sistema denso, que crece con el tamaño eléctrico del objeto a analizar. Por tanto, un gran número de métodos han sido desarrollados para su compresión y solución. Sin embargo, muchos de ellos son absolutamente dependientes del núcleo de la ecuación integral, necesitando de una reformulación completa para cada núcleo, en caso de que sea posible.
Esta tesis presenta nuevos enfoques o métodos para acelerar y incrementar la precisión de ecuaciones integrales discretizadas con el Método de los Momentos (MoM) en electromagnetismo computacional.
En primer lugar, un nuevo método iterativo rápido, el Multilevel Adaptive Cross Approximation (MLACA), ha sido desarrollado para acelerar la solución del sistema lineal del MoM. En la búsqueda por un esquema de propósito general, el MLACA es un método independiente del núcleo de la ecuación integral y es puramente algebraico. Mejora simultáneamente la eficiencia y la compresión con respecto a su versión mono-nivel, el ACA, ya existente. Por tanto, representa una excelente alternativa para la solución del sistema del MoM de problemas electromagnéticos de gran escala.
En segundo lugar, el Direct Evaluation Method, que ha provado ser la referencia principal en términos de eficiencia y precisión, es extendido para superar el cálculo del desafío que suponen las integrales hiper-singulares 4-D que aparecen en la formulación de Ecuación Integral de Campo Magnético (MFIE) así como en la de Ecuación Integral de Campo Combinada (CFIE). La máxima precisión asequible -precisión de máquina se obtiene en un tiempo más que razonable, sobrepasando a cualquier otra técnica existente en la bibliografía.
En tercer lugar, las integrales hiper-singulares mencionadas anteriormente se convierten en casi-singulares cuando los elementos discretizados están muy próximo pero sin llegar a tocarse. Se muestra como las reglas de integración tradicionales tampoco convergen adecuadamente en este caso y se propone una posible solución, basada en reglas de integración más sofisticadas, como la Double Exponential y la Gauss-Laguerre.
Finalmente, un esfuerzo en facilitar el uso de cualquier programa de simulación de antenas basado en el MoM ha llevado al desarrollo de un modelo matemático general de un puerto de excitación en el espacio discretizado. Con este nuevo modelo, ya no es necesaria la adaptación de los lados del mallado al puerto en cuestión.
The Method of Moments (MoM) has been widely used during the last decades for the discretization and the solution of integral equation formulations appearing in several electromagnetic antenna and scattering problems. The most utilized of these formulations are the Electric Field Integral Equation (EFIE), the Magnetic Field Integral Equation (MFIE) and the Combined Field Integral Equation (CFIE), which is a linear combination of the other two.
The MFIE and CFIE formulations are only valid for closed objects and need to deal with the integration of singular kernels with singularities of higher order than the EFIE. The lack of efficient and accurate techniques for the computation of these singular integrals has led to inaccuracies in the results. Consequently, their use has been mainly restricted to academic purposes, even having a much better convergence rate when solved iteratively, due to their excellent conditioning number.
In general, the main drawback of the MoM is the costly construction, storage and solution considering the unavoidable dense linear system, which grows with the electrical size of the object to analyze. Consequently, a wide range of fast methods have been developed for its compression and solution. Most of them, though, are absolutely dependent on the kernel of the integral equation, claiming for a complete re-formulation, if possible, for each new kernel.
This thesis dissertation presents new approaches to accelerate or increase the accuracy of integral equations discretized by the Method of Moments (MoM) in computational electromagnetics.
Firstly, a novel fast iterative solver, the Multilevel Adaptive Cross Approximation (MLACA), has been developed for accelerating the solution of the MoM linear system. In the quest for a general-purpose scheme, the MLACA is a method independent of the kernel of the integral equation and is purely algebraic. It improves both efficiency and compression rate with respect to the previously existing single-level version, the ACA. Therefore, it represents an excellent alternative for the solution of the MoM system of large-scale electromagnetic problems.
Secondly, the direct evaluation method, which has proved to be the main reference in terms of efficiency and accuracy, is extended to overcome the computation of the challenging 4-D hyper-singular integrals arising in the Magnetic Field Integral Equation (MFIE) and Combined Field Integral Equation (CFIE) formulations. The maximum affordable accuracy --machine precision-- is obtained in a more than reasonable computation time, surpassing any other existing technique in the literature.
Thirdly, the aforementioned hyper-singular integrals become near-singular when the discretized elements are very closely placed but not touching. It is shown how traditional integration rules fail to converge also in this case, and a possible solution based on more sophisticated integration rules, like the Double Exponential and the Gauss-Laguerre, is proposed.
Finally, an effort to facilitate the usability of any antenna simulation software based on the MoM has led to the development of a general mathematical model of an excitation port in the discretized space. With this new model, it is no longer necessary to adapt the mesh edges to the port.

Pastilhas de nitrato de potássio foram irradiadas no núcleo do reator de pesquisas IEA-R1m do Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, operando a 2 MW de potência, para determinar a secção de choque térmica e integral de ressonância da reação 41K(n,g)42K. O fluxo de nêutrons foi monitorado com folhas de liga ouro-alumínio. As atividades induzidas nos alvos foram determinadas por espectroscopia gama com detectores de germânio hiper puro. Os cálculos realizados se basearam no formalismo de Westcott. Foram realizadas simulações com o código MCNP (Monte Carlo N-Particle) para determinar a auto-blindagem e a depressão do fluxo de nêutrons nas pastilhas durante as irradiações e os fatores de correção da eficiência de detecção para fontes volumétricas, que leva em conta a absorção de raios gama nas mesmas. Foi efetuado um tratamento estatístico das incertezas envolvidas e determinadas as covariâncias entre os resultados, incluindo aquelas decorrentes das incertezas do padrão de referência (ouro). Os resultados obtidos foram comparados com os de outros autores. Foi testada a possibilidade de se observar o produto da reação 41K(n,g)42K(n,g)43K.
Pellets of potassium nitrate were irradiated in the IPEN/CNEN-SP (Instituto de Pesquisas Energeticas e Nucleares, Comissao de Energia Nuclear, Sao Paulo, SP) IEAR1m reactor core operating at 2 MW power in order to determine the 41K(n,g)42K reaction thermal cross-section and resonance integral. The neutron flux was monitored by Au-Al alloy foils, and the Westcott formalism was applied. Neutron self-shielding, flux depression and gamma-ray self-absorption in the relatively large samples, as well as the gamma-ray detection efficiency correction factor, were determined by simulation with MCNP code. The data reduction statistical methods included the determination of the covariances between the obtained results and the standard cross-sections used (Au). The results were compared to those already published. The observation of the consecutive neutron capture reaction leading to 43K was tried.

Etude du dispositif de régulation sur une portion de frontière d'une région ouverte oméga du plan : ce dispositif comprend un régulateur PID dont le signal de commande est une mesure de différence de température. Possibilité d'un réglage optimal du régulateur pour une perturbation connue de la température initiale. Simulation numérique bidimensionnelle du fonctionnement

Le principe du contrôle non destructif par Flux de Fuite Magnétique (FFM) consiste à magnétiser une pièce à contrôler par un champ magnétique intense et à détecter à l'aide d'un capteur magnétique les fuites des lignes de champ qui résultent de la présence d'un défaut dans la pièce. Les méthodes de contrôle FFM sont très employées notamment lors du processus de fabrication des tubes ferromagnétiques par la société Vallourec, le leader mondial des fabricants de tube. Dans le but d'améliorer les performances des systèmes de contrôle installés en usine, le CEA LIST et le centre de recherches de Vallourec (VRA) collaborent pour développer des outils de simulation rapides dédiés au contrôle virtuel des tubes ferromagnétiques. Le système expérimental existant concerne plus particulièrement la détection des défauts longitudinaux. Le problème de modélisation se pose en termes de modélisation d'un système électromagnétique à géométrie complexe en régime magnétostatique non-linéaire. Les courants de Foucault induits par le mouvement relatif entre la pièce et le circuit magnétique sont négligés. Dans ce contexte, une approche semi-analytique reposant sur le formalisme des équations intégrales (EI) a été choisie. Les travaux effectués dans cette thèse ont pour but de traiter des géométries complexes 3D mais limitées dans une première étape aux matériaux linéaires. Toutefois, le caractère non-linéaire de la relation liant l'induction magnétique et le champ magnétique dans un matériau ferromagnétique doit être envisageable lors du choix de la formulation du problème. Après une étude des paramètres influents du système expérimental existant, menée par des simulations par éléments finis, nous avons considéré deux stratégies de modélisation. La première consiste à proposer un schéma de résolution qui combine un module de calcul 2D et un module d'extension du 2D vers le 3D. Le manque de généralisation de cette première approche simplifiée nous a conduits à proposer une deuxième stratégie qui résout le problème complet de magnétostatique 3D. La formulation par équations intégrales porte sur une quantité scalaire auxiliaire : la densité surfacique de charges magnétiques. Afin de pouvoir résoudre à terme un problème 3D non-linéaire, le schéma numérique proposé considère deux hypothèses : la pièce ferromagnétique est divisée en un ensemble de cellules hexaédriques dans lesquelles la perméabilité magnétique est constante et les inconnues du problème, les densités surfaciques de charge sur les faces de chaque cellule sont projetées sur des fonctions de base d'ordre 0. Le calcul numérique des intégrales singulières s'effectue de manière analytique. Plusieurs résultats de simulation confirment la validité du modèle numérique présenté. Même si le modèle présente encore aujourd'hui quelques limitations notamment sur le manque de précision des calculs en présence de défaut, celui-ci donne satisfaction en absence de défaut. Diverses configurations géométriques ont été traitées grâce à l'emploi du mailleur libre Gmsh. Le travail réalisé débouche sur un modèle 3D linéaire intégrable dans un procédé itératif pour effectuer une simulation en régime non-linéaire. Les inconvénients liés au formalisme des équations intégrales sont aujourd'hui contournables grâce aux méthodes de compression de matrices. Ce modèle est un bon candidat pour servir d'outil de simulation pour le contrôle virtuel des matériaux plans ou cylindriques par flux de fuite.

The paper considers approximations of time-continuous epsilon-correlated random processes by interpolation of time-discrete Moving-Average processes. These approximations are helpful for Monte-Carlo simulations of the response of systems containing random parameters described by epsilon-correlated processes. The paper focuses on the approximation of stationary epsilon-correlated processes with a prescribed correlation function. Numerical results are presented.

Fluid mechanics of blood can be well approximated by a mixture model of a Newtonian fluid and deformable particles representing the red blood cells. Experimental and theoretical evidence suggests that the deformation and rheology of red blood cells is similar to that of phospholipid vesicles. Vesicles and red blood cells are both area preserving closed membranes that resist bending. Beyond red blood cells, vesicles can be used to investigate the behavior of cell membranes, intracellular organelles, and viral particles. Given the importance of vesicle flows, in this thesis we focus in efficient numerical methods for such problems: we present computationally scalable algorithms for the simulation of dilute suspension of deformable vesicles in two and three dimensions. Our method is based on the boundary integral formulation of Stokes flow. We present new schemes for simulating the three-dimensional hydrodynamic interactions of large number of vesicles with viscosity contrast. The algorithms incorporate a stable time-stepping scheme, high-order spatiotemporal discretizations, spectral preconditioners, and a reparametrization scheme capable of resolving extreme mesh distortions in dynamic simulations. The associated linear systems are solved in optimal time using spectral preconditioners. The highlights of our numerical scheme are that (i) the physics of vesicles is faithfully represented by using nonlinear solid mechanics to capture the deformations of each cell, (ii) the long-range, N-body, hydrodynamic interactions between vesicles are accurately resolved using the fast multipole method (FMM), and (iii) our time stepping scheme is unconditionally stable for the flow of single and multiple vesicles with viscosity contrast and its computational cost-per-simulation-unit-time is comparable to or less than that of an explicit scheme. We report scaling of our algorithms to simulations with millions of vesicles on thousands of computational cores.

Surface topography is, generally, composed of many length scales starting from its physical geometry, to its microscopic or atomic scales known by roughness. The spatial and geometrical evolution of the roughness topography of engineering surfaces avail comprehensive understanding, and interpretation of many physical and engineering problems such as friction, and wear mechanisms during the mechanical contact between adjoined surfaces. Obviously, the topography of rough surfaces is of random nature. It is composed of irregular hills/valleys being spatially correlated. The relation between their densities and their geometric properties are the fundamental topics that have been developed, in this research study, using the theory of random fields and the integral geometry.An appropriate random field model of a rough surface has been defined by the most significant parameters, whose changes influence the geometry of its excursion. The excursion sets were quantified by functions known as intrinsic volumes. These functions have many physical interpretations, in practice. It is possible by deriving their analytical formula to estimate the parameters of the random field model being applied on the surface, and for statistical analysis investigation of its excursion sets. These subjects have been essentially considered in this thesis. Firstly, the intrinsic volumes of the excursion sets of a class of mixture models defined by the linear combination of Gaussian and t random fields, then for the skew-t random fields are derived analytically. They have been compared and tested on surfaces generated by simulations. In the second stage, these random fields have been applied to real surfaces measured from the UHMWPE component, involved in application of total hip implant, before and after wear simulation process. The primary results showed that the skew-t random field is more adequate, and flexible for modelling the topographic roughness. Following these arguments, a statistical analysis approach, based on the skew-t random field, is then proposed. It aims at estimating, hierarchically, the significant levels including the real hills/valleys among the uncertain measurements. The evolution of the mean area of the hills/valleys and their levels enabled describing the functional behaviour of the UHMWPE surface over wear time, and indicating the predominant wear mechanisms.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
It is presented in this thesis, a proposal for solution of engineering problems in heat transfer area using the network simulation method (NSM - Network Simulation Method), which is to solve these problems by analogy between the thermal circuits and electrical circuits. It will be presented to validate the two-dimensional problem of heat conduction in a cylinder in which the solutions obtained by simulation with the solution analytically obtained via Technical Generalized Integral Transform will face (GITT). In the simulations makes up the body discretization study with the aim of establishing a correlation between the amount of cells (the mesh refinement) and the relationship between the radius of the size and length of the cylinder so that the problem solution of heat transfer in the body can be considered one-dimensional. A comparison will be made between the analytical response and obtained by simulation, varying the number of divisions and different relationships between beam dimensions and length of the cylinder. From the solution validated the proposed method, applying the work presented as a generic fabric prepared by the NSM and implementation PSPICE, which serves for solving many problems of heat conduction in a cylindrical geometry.
É apresentada neste trabalho de tese, uma proposta para solução de problemas de engenharia na área de transferência de calor utilizando o método de simulação de rede (NSM – Network Simulation Method), que consiste na resolução destes problemas pela analogia existente entre os circuitos térmicos e os circuitos elétricos. Nele será apresentada a validação do problema bidimensional de condução de calor em um cilindro, no qual, serão confrontadas as soluções obtidas por simulação com a solução obtida analiticamente via Técnica da Transformada Integral Generalizada (GITT). Nas simulações realizadas fazse a discretização do corpo em estudo, com o objetivo de se estabelecer uma correlação entre a quantidade de células (refinamento da malha) e a relação entre o tamanho do raio e comprimento do cilindro para que a solução do problema de transferência de calor no corpo possa ser considerada unidimensional. A comparação se dará entre a resposta analítica e a obtida por simulação, variando o número de divisões e as diferentes relações entre as dimensões raio e comprimento do cilindro. A partir da solução validada pela metodologia proposta, o trabalho apresenta como aplicação, uma malha genérica elaborada através do NSM e implementação no PSPICE, a qual serve para resolução de diversos problemas de condução de calor em geometria cilíndrica.

Simulators are important tools for wireless sensor network (sensornet) design and evaluation. However, existing simulators only support evaluations of protocols and software aspects of sensornet design. Thus they cannot accurately capture the significant impacts of various hardware designs on sensornet performance. To fill in the gap, we proposed SUNSHINE, a scalable hardware-software cross-domain simulator for sensornet applications. SUNSHINE is the first sensornet simulator that effectively supports joint evaluation and design of sensor hardware and software performance in a networked context. SUNSHINE captures the performance of network protocols, software and hardware through the integration of two modules: a network simulator TOSSIM [1] and hardware-software simulator P-Sim composed of an instruction-set simulator SimulAVR [2] and a hardware simulator GEZEL [3]. This thesis focuses on the integration of TOSSIM and P-Sim. It discusses the integration design considerations and explains how to address several integration challenges: time conversion, data conversion, and time synchronization. Some experiments are also given to demonstrate SUNSHINEâ s cross-domain simulation capability, showing SUNSHINE's strength by integrating simulators from different domains.
Master of Science

This thesis is concerned with the evaluation, in-situ, of the elastic strain energy release rate of cracks. This can define the criteria for crack propagation, and it is usually necessary to obtain this via calculation from the geometry and applied load. A new method is proposed, based on the conjoint use of digital image correlation to measure full-field displacements and finite element to extract the strain energy release rate of surface cracks. It has been extended to 3-D datasets with the use of digital volume correlation and tomographic imaging. A finite element model with imported full-field displacements measured by DIC/DVC acting as boundary conditions is solved and the J-integral is calculated. For linear elastic materials, modal contributions can be separated via the interaction integral. The method has been benchmarked using synthetic datasets to assess its sensitivity to noise and experimental uncertainties. It is very robust to experimental noise and can be used without knowledge of the specimen geometry and applied loads. The application of the method in 2-D is demonstrated in an analysis of experimental data for a mode I fatigue crack, introduced to an aluminium alloy compact tension specimen. Analysis of mixed-mode cracks in 2-D is shown on a PMMA sample with the Arcan geometry. In 3-D, static loading of a fatigue crack in nodular graphite cast iron is studied and the results from the method are compared with those obtained via a field-fitting approach. Diffraction analysis of polycrystalline materials can determine the full tensor of the elastic strains within them. Maps of elastic strains can thus be obtained typically using synchrotron X-rays or neutrons. A method is presented to calculate the elastic strain energy release rate of a crack from 2-D diffraction strain maps. The diffraction data is processed via a finite element approach to obtain the parameters required to calculate the $J$-integral. A validation is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of synchrotron X-ray diffraction strain maps of a propagating fatigue crack in a bainitic steel, before and after an overload. Finally, a complex case study of stable fracture propagation in polygranular isotropic nuclear graphite is presented. Synchrotron X-ray tomography and strain mapping by diffraction were combined with DVC and image analysis to extract the full-field displacements and elastic crystal strains. The displacement fields have been analysed using the developed methods to extract the critical strain energy release rate for crack propagation. Non-linear properties described the effect of microcracking on the elastic modulus in the fracture process zone. The analysis was verified by comparison of the predicted and measured elastic strain fields.

Les vésicules sont utilisées d'une manière extensive comme modèle pour comprendre les dynamiques et les déformations des globules rouges au niveau individuel, mais aussi concernant les phénomènes collectives et la rhéologie. La membrane de la vésicule résiste à la flexion mais pas au cisaillement, contrairement aux globules rouges, néanmoins elles partagent plusieurs propriétés dynamiques avec les globules rouges, comme le tank-treading (mouvement en chenille de char) et le tumbling (mouvement de bascule) sous écoulement de cisaillement, ou les formes parachutes et slippers (pantoufles) sous un écoulement de Poiseuille. Les globules rouges sont connus pour former des trains de cellules (clusters) dans la microcirculation attribués à la nature attractive des interactions hydrodynamiques. Nous avons étudié numériquement plusieurs types de problème comme:(i) les dynamiques de cellules isolées, (ii) le couplage hydrodynamique entre globules rouges (en utilisant les vésicules comme modèle) soumis à un écoulement de Poiseuille sous différent confinements; (iii) l'agrégation des globules rouges et la formation de rouleaux; et (iv) le rôle des macromolécules dans la formation de clusters sous écoulement. les résultats obtenus apportent un nouveau regard à la physique des objets déformables et sont transposables au cas de l'écoulement des globules rouges dans la microcirculation
Vesicles are extensively used as a model for understanding dynamicsand deformation of red blood cells at the individual level but also regarding collective phenomena and rheology. Vesicles' membranes withstand to bending butdo not have a shear resistance, unlike red blood cells, but they still share several dynamical properties with red blood cells, like tank-treading and tumbling under linear shear flow, or parachute and slipper shapes under Poiseuille flow. The red blood cells are known to form train of cells in the microcirculation attributed to attractive hydrodynamic interactions. We investigate numerically several kind of problems such as: (i) the dynamics of isolated cells; (ii) the hydrodynamic coupling between the red blood cells (by using vesicles as a model) subject to a Poiseuille flow under different confinements; (iii) the aggregation of red blood cells and formation of rouleaux; and (iv) the contribution of macromolecules in the formation of clusters under flow condition. The obtained results give a new insight into thephysics of deformable objects under confinement that are transposable to the flow of red blood cells in the microcirculation

De nombreux systèmes fluides dans les domaines de la biologie ou encore de la cosmétique sont limités par une interface dont les propriétés mécaniques régissent la stabilité. En particulier, les objets tels que des gouttes, vésicules ou polymersomes se déforment dans un écoulement simple et mènent à une grande richesse de dynamiques spatio-temporelles contrôlées par la nature des matériaux qui composent l'interface. Les travaux présentés concernent l'étude numérique de la déformation de ces objets dans un écoulement de Stokes, en particulier dans des situations où les viscosités de l'interface jouent un rôle important. Un code de calcul couplant intégrales de frontières et éléments finis a été utilisé afin de décrire la physique interfaciale et étudier leur comportement une fois plongés dans un écoulement. Ces travaux ont permis d'étudier l'influence des viscosités interfaciales sur la dynamique d'une goutte dans un écoulement extensionnel plan, leur influence sur sa dynamique de déformation et sur les conditions de rupture de celle-ci. Les études réalisées sur une vésicule fortement dégonflée et plongée dans un écoulement cisaillé ont caractérisé la bifurcation entre les deux familles de forme existantes dans ces conditions. Ces formes ayant une influence sur la dynamique de la vésicule dans l'écoulement, celle-ci a été étudiée dans le cadre d'un écoulement infini puis proche d'une paroi parallèle à l'écoulement. Enfin, de premiers résultats sur la dynamique d'un polymersome dans un écoulement cisaillé permettent de construire un diagramme de phase illustrant les différents comportement de cet objet en fonction de la viscosité de la membrane et du taux de cisaillement
There are many fluid systems in the biology, food industry, pharmacology or cosmestics fields that are bound by an interface which mechanical properties rule the system stability. Objects like droplets, vesicles or polymersomes change their shape in a simple flow which lead to a wealth of space and time dynamics. These properties are controlled by the nature of the interface material. The aim of this work is the numerical study of the deformation of droplets, vesicles and polymersomes in a Stokes flow, especially when the interfacial viscosities play an important role. A numerical computation code coupling boundary integrals and finite elements was used to describe the interfacial physics of these objects and study their behaviour when immerged in a flow. Multiple resolution strategies where developped to this end in order to optimize the numerical computation in the cas of an interface with viscosities.Using this work, the influence of interfacial viscosities on the dynamics of a droplet in an extensional flow is studied : in particular, their influence on the stretching dynamics of a droplet and its break up conditions was characterized. The study of a vesicle, droplet bounded by a lipid bilayer, strongly deflated and immerged in a shear flow detailed the bifurcation between two shape types existing for this system. These shapes have an influence on the vesicle dynamics under flow, which is studied for an unbounded flow and a near-wall flow. Finally, we show first results about the dynamics of a polymersome in a shear flow. We used them to build a phase diagram for the behaviour of this object depending on the membrane viscosity and the shear rate

L'alcool allylique est une molécule plate-forme intéressante en raison de sa large gamme d’applications. La Désoxydehydratation (DODH) du glycérol semble actuellement la méthode la plus compétitive pour synthétiser l'alcool allylique à partir de ressources renouvelables. Cependant, jusqu'à présent, cette réaction n'a été que peu étudiée en littérature. Le but de cette thèse était de développer un procédé de production intégré d'alcool allylique via DODH de glycérol en utilisant un alcool secondaire comme solvant-réducteur. Le développement du catalyseur a été réalisé en utilisant un catalyseur d'oxyde de rhénium supporté sur cérine. Ce dernier a été synthétisé via un processus de nanocasting en utilisant de la silice et du charbon actif comme agents structurants, donnant d'excellents rendements allant jusqu'à 86%, en utilisant un 2-hexanol ou MIBC comme donneur d'hydrogène et solvant. En ce qui concerne le développement du procédé, les données d'équilibre liquide vapeur isobare ont été déterminées pour les principaux systèmes binaires afin de modéliser la colonne de distillation. Les données expérimentales de VLE ont été ajustées avec succès en utilisant les modèles thermodynamique NRTL, UNIQUAC et Wilson. Enfin, la modélisation intégrée du procédé a été réalisée à partir des résultats expérimentaux et proposant différents scénarios en fonction du solvant utilisé. Toutes les stratégies proposées ont permis une purification d'alcool allylique de 99,99%. Dans tous les scénarios, le procédé MIBC s'est révélé être une faisable stratégie d’un point de vue technique, qui pourrait potentiellement servir de point de départ pour le développement d'un procédé DODH à grande échelle
Allyl Alcohol is an interesting platform molecule due to its broad range of applications. The Deoxydehydration (DODH) of glycerol seems currently the most competitive method to synthesize allyl alcohol from renewable sources. However, so far, this reaction has been only marginally investigated. The aim of this thesis was to develop an integrated production process of allyl alcohol via DODH of glycerol using a secondary alcohol as solvent-reductant. The catalyst development was carried out using ceria-supported rhenium oxide catalyst. Mesoporous ceria materials were synthetized via a nanocasting process using SiO2 and activated carbon as hard templates, giving excellent yields of up to 86%, using a 2-Hexanol or MIBC as a hydrogen donor and solvent. With respect to the process development, isobaric vapor liquid equilibrium data were determined for main binary systems in order to model the distillation column. The experimental VLE data was successfully fitted using NRTL, UNIQUAC and Wilson thermodynamic model. Finally, the integrated process modelling was carried out based on the experimental results and proposing different scenarios depending on the used solvent. All the proposed strategies allowed to obtain an allyl alcohol purity of 99.99%. In any scenario, the MIBC process proved to be a feasible strategy from a technical point of view, which could potentially be used as starting point for the development of a large scale DODH process

Le principe du contrôle par flux de fuite magnétique (Magnetic Flux Leakage MFL) consiste à aimanter la pièce à contrôler par un champ magnétique et à détecter à l'aide d'un capteur magnétique les fuites des lignes du champ qui résultent de la présence d'un défaut dans la pièce. Dans le but d'améliorer les performances d'un dispositif de détection, le CEA et la société Vallourec collaborent pour développer un modèle numérique dédié au contrôle virtuel des défauts longitudinaux dans les tubes ferromagnétiques. Le dispositif expérimental comprend un circuit magnétique tournant à une vitesse constante autour du tube qui défile. Dans le cadre de cette thèse, on débute le problème de la modélisation sans tenir compte des effets de la vitesse de rotation, il s'agit donc de résoudre un problème d'électromagnétisme en régime magnétostatique.Pour résoudre ce problème, on propose de comparer une approche semi-analytique basée sur le formalisme des équations intégrales (EI) et une approche purement numérique utilisant les éléments finis (EF).Dans la première partie de cette thèse, après avoir établi le formalisme théorique par EI, un premier modèle considérant des matériaux ferromagnétiques à perméabilité magnétique constante (régime linéaire) a été mis en œuvre en 2D. Ce modèle a été appliqué pour un exemple de système extrait de la littérature et validé numériquement par une comparaison des résultats EI/EF. Pour une meilleure détection, il est opportun de saturer magnétiquement la pièce. Le matériau ferromagnétique est alors caractérisé par une courbe B(H) non-linéaire. Par conséquent, la deuxième partie de la thèse a été consacrée à la mise en œuvre du modèle en régime non linéaire qui tient compte de cette caractéristique.Différentes méthodes de discrétisation ont été étudiées afin de réduire le nombre d'inconnues et le temps de calcul. L'originalité de la thèse réside dans l'utilisation des fonctions d'interpolation d'ordre élevé (polynôme de Legendre) pour une discrétisation des équations intégrales par une approche de type Galerkin. Les premiers essais de validation numérique de ce modèle ont été effectués sur un système MFL simplifié. Des premiers essais de validation expérimentale pour des données obtenues par EF ont été effectués en deux phases : La première a consisté à vérifier le distribution du champ magnétique pour un tube sain et en régime magnétostatique. La deuxième phase a consisté à calculer la réponse d'un défaut dans le tube ferromagnétique en tenant en compte les effets éventuels de la rotation du circuit magnétique par rapport au tube
The principle of the non destructive testing by magnetic flux leakage (MFL) is to magnetize the part to be inspected by a magnetic field and to detect a flaw thanks to magnetic leakage field lines due to the strong decreasing of the magnetic permeability in the flawed region. In order to improve the performance of detection, the CEA and the Vallourec society collaborate to develop a numerical model dedicated to the virtual NDT of longitudinal defects in ferromagnetic tubes. The experimental system includes a magnetic circuit rotating at a constant speed around the tube to be inspected. The modeling task is started without considering the effects of the rotational speed, so the magnetostatic regime is considered to solve the modeling problem. In the framework of this thesis, we propose to compare a semi-analytical approach based on the formalism of integral equations method (IEM) and a purely numerical approach using finite element method (FEM).In the first part of this thesis, the theoretical formalism was established. A first simple discretization scheme is been implemented in the linear regime considering a constant magnetic permeability. This first numerical model has been validated for a simplified MFL configuration extracted and modified from the literature.For better detection, it is wishable to magnetically saturate the piece under-test. The ferromagnetic material is then characterized by a B(H) curve. Therefore, the second part of the thesis was devoted to the implementation of the model in the non-linear regime that takes into account this non-linear characteristic. Different discretization schemes have been studied in order to reduce the number of unknowns and the computational time. The originality of the thesis lies in the use of basis function of high order (Legendre polynomials) associated to a Galerkin approach for the discretization of integral equations. The first numerical result has been validated on a simplified MFL system. The first results of the experimental validation based on simulated data obtain by FEM have been performed in two steps. The first one consists to verify the distribution of the magnetic field for a ferromagnetic tube without any defect and in the magnetostatic regime. The objective of the second one was to compute the response of the flaw and to evaluate the effects of the rotational speed of the magnetic circuit around the tube

Ce travail de these est consacre a l'application des methodes integrales aux frontieres a la simulation numerique des ecoulements non-lineaires a frontieres libres. Deux principales parties peuvent etre distinguees. L'une, est consacree au probleme de la progression en temps dans le cadre d'une approximation potentielle et plus precisement l'etablissement d'une procedure de suivi d'interfaces fondee sur des schemas explicites d'ordres eleves issus de developpements en serie de taylor. L'autre, propose une methode generale pour resoudre les equations de navier-stokes fondee sur une formulation entierement integrale. Basee sur la decomposition de helmholtz, notre demarche porte sur l'etablissement de conditions aux limites et de projection associees a l'equation de transport du tourbillon. Cette etude met en evidence les avantages d'une formulation integrale qui ne sont pas seulement theoriques et numeriques. Ils apportent en effet un eclairage sur la comprehension des phenomenes de la genese et la propagation de la vorticite.

La théorie spatiale des valeurs extrêmes permet de modéliser et prédire la fréquence d'évènements extrêmes ayant une étendue spatiale comme, par exemple, des pluies ou des températures extrêmes, ou encore de fortes concentrations de pollution atmosphérique. Elle s'adapte bien aux données temporelles, lorsque le phénomène spatial étudié est observé plusieurs fois dans le temps. Cependant, nous n'avons parfois pas accès à de telles données: seulement un ou quelques enregistrements sont disponibles. C'est le cas, par exemple, des études sur l'estimation des ressources minières ou sur l'évaluation de la pollution des sols et plus généralement de toute recherche dont l'objet d'étude varie très peu au cours du temps ou pour lequel le coût d'échantillonnage est trop élevé. Ce cas de figure est très peu abordé par la communauté des extrêmes. Au contraire, c'est un cadre d'analyse auquel la Géostatistique s'intéresse particulièrement. Les travaux réalisés au cours de cette thèse ont pour objectif d'établir des connexions mathématiques entre ces deux disciplines afin de mieux appréhender les évènements extrêmes, lorsque le phénomène spatial sous-jacent n'est observé qu'une seule fois.Nous nous intéressons, dans un premier temps, au concept de portée intégrale. Intrinsèquement lié aux propriétés d'ergodicité et de mélange, ce paramètre issu de la théorie géostatistique caractérise les fluctuations statistiques, à large échelle, d'un champ aléatoire stationnaire. Lorsque ce dernier est un champ max-stable, nous montrons que sa fonction coefficient extrémal (ECF) est fortement liée à la portée intégrale du champ des excès, au dessus d'un certain seuil, correspondant. Cette approche permet de retrouver et de compléter des résultats précédemment établis dans un contexte de risque spatialisé. Elle met également en évidence une nouvelle expression de la fonction coefficient extrémal qui dépend du variogramme du champ des excès.À partir de cette formule, nous proposons un nouvel estimateur non-paramétrique de l'ECF. Ses propriétés asymptotiques sont établies lorsqu'il est évalué à partir d'une unique réalisation, partiellement observée, d'un champ stationnaire max-stable. En particulier, lorsque le nombre d'observations se densifie en même temps que le champ d'observation grandit, et sous certaines hypothèses concernant la portée intégrale susmentionnée, nous montrons qu'il est consistent et asymptotiquement normal. Il est donc pertinent d'utiliser les outils géostatistiques pour enrichir l'analyse des valeurs extrêmes.Finalement, nous développons un nouvel algorithme permettant de simuler, en continu, des processus aléatoires tempête pour lesquels la fonction de forme est déterministe. Il se distingue donc de la plupart des algorithmes existants qui s'utilisent exclusivement lorsque le domaine de simulation est composé d'un nombre fini de points. À cet égard, il permet d'étudier plus facilement la géométrie des réalisations de tels processus. Cela est particulièrement intéressant quand la caractéristique géométrique étudiée mêle différentes échelles d'observation
Spatial extreme value theory helps model and predict the frequency of extreme events in a spatial context like, for instance, extreme precipitations, extreme temperatures. It is well adapted to time series. However, in some cases, such types of data cannot be accessed: only one or just a few records are made available. This is the case, for instance in soil contamination evaluation. This situation is rarely addressed in the spatial extremes community, contrary to Geostatistics,which typically deals with such issues. The aim of this thesis is to make some connections between both disciplines,in order to better handle the study of spatial extreme events, and especially their spatial dependence structure, when having only one set of spatial observations. A link is first established through the concept of integral range. It is a geostatistical parameter that characterizes the statistical fluctuations of a stationary random field at large scale. When the latter is max-stable, we show that its extremal coefficient function (ECF), which is a measure of spatial dependence, is closely related to the integral range of the corresponding exceedance field above a threshold. From this, we move toproposing a new nonparametric estimator of the ECF. Its asymptotic properties are derived when it is computed from a single and partially observed realization of a stationary max-stable random field. Specifically, under some assumptions on the aforementioned integral range, we prove that it is consistent and asymptotically normal. Finally, we develop a novel algorithm to perform exact simulations in a continuous domain of storm processes with deterministic shape function. It distinguishes itself from most existing procedures, which apply to simulation domains made of a finite number of points. Most part of the algorithm are designed to be parallelizable

Numerical simulations using a boundary integral method are used to model three inviscid fluid flows with surface tension. The problems considered are the motions of a free drop, the self-similarity in the shape of inviscid pinchoff, and the evolution of a finite jet. Various shapes of drops are studied, and their frequencies of oscillation are compared to result in the literature. Non-linear shapes are evolved, simulating a drop after ejection from a finite jet, which determines whether the drop holds together or forms satellites. Special numerical techniques are added to the code for free drops in order to model the pinchoff process. Evidence is found for a similarity solution for inviscid pinchoff which adopts a double-cone shape with one cone angle greater than 90°. A novel result is that the two cone angles are always about 18.1° and 112.8° independent of the initial conditions. The potential far from the pinchoff region in the numerical simulations is shown to match with certain scalings expected from a similarity solution. A model of a finite axisymmetric jet evolving from a fixed nozzle is used to simulate various conditions of drop ejection. Driven by a time-dependent backpressure, the jet forms a neck due to surface tension and pinches off. Various backpressure functions are imposed which cause different shapes of jets to emerge. The model is intended to simulate a drop-on-demand ink-jet printing process for which the optimum result is a fast, satellite-free drop that can be ejected repeatably.

Integral Membrane Proteins (IMPs) are an important and scientifically interesting class of protein which span the lipid bilayer surrounding cells, cell compartments and many viruses. Molecular Dynamics (MD) simulation has revealed intimate and often highly specific relationships between membrane lipids and IMPs critical to many metabolic and signalling pathways. Meanwhile, the use of Coarse-Grained (CG) MD techniques has extended capabilities of biomolecular simulation to larger proteins over longer time periods. Several tools and resources for biomolecular simulations of IMPs are presented here, as well as two MD studies of specific IMPs. The previously developed MemProtMD pipeline automates the setup of MD simulations of IMPs; major extensions to this are presented here with the MemProtMD database and web server, automating the analysis of IMP simulations. The results of this can be viewed using the MemProtMD web server, an interactive, searchable online resource containing data from simulations of over 3000 experimentally determined IMP structures in explicit lipid bilayers. Using data from analysis of the entire MemProtMD database, MemProtMetrics has been developed to automate identification and orientation of IMP structures from Protein DataBank (PDB) depositions. This is shown to effectively predict membrane protein orientations seen in MD simulations. A tool for identification and classification of membrane lipids is also described, and used to identify over 500 IMPs structures with resolved lipids. CGMD simulations have also been used to assess dependence on side-chain ionisation state of interactions between lipids and two IMPs observed in mass spectrometry experiments. The simulations reveal similar trends to those seen in experiments. Finally, using multi-scale simulations, and through the development of a novel method for altering membrane composition in MD simulations, lipid-specific scramblase activity was shown for a novel structure of the TMEM16K scramblase IMP.

Cette étude s’inscrit dans le domaine de la simulation électromagnétique des problèmes de grande taille tels que la diffraction d’ondes planes par de larges plateformes et le rayonnement d’antennes aéroportées. Elle consiste à développer une méthode combinant décomposition en sous-domaines et compression hiérarchique des équations intégrales de frontière. Pour cela, nous rappelons dans un premier temps les points importants de la méthode des équations intégrales de frontière et de leur compression hiérarchique par l’algorithme ACA (Adaptive Cross Approximation). Ensuite, nous présentons la formulation IE-DDM (Integral Equations – Domain Decomposition Method) obtenue à partir d’une représentation intégrale des sous-domaines. Les matrices résultant de la discrétisation de cette formulation sont stockées au format H-matrice (matricehiérarchique). Un solveur spécialement adapté à la résolution de la formulation IE-DDM et à sa représentation hiérarchique a été conçu. Cette étude met en évidence l’efficacité de la décomposition en sous-domaines en tant que préconditionneur des équations intégrales. De plus, la méthode développée est rapide pour la résolution des problèmes à incidences multiples ainsi que la résolution des problèmes basses fréquences

This thesis presents i-PI, a new path integral molecular dynamics code designed to capture nuclear quantum effects in ab initio electronic structure calculations of condensed phase systems. This software has an implementation of estimators used to calculate a wide range of static and dynamical properties and of state-of-the-art techniques used to increase the computational efficiency of path integral simulations. i-PI has been designed in a highly modular fashion, to ensure that it is as simple as possible to develop and implement new algorithms to keep up with the research frontier, and so that users can take maximum advantage of the numerous electronic structure programs which are freely available without needing to rewrite large amounts of code. Among the functionality of the i-PI code is a novel integrator for constant pressure dynamics, which is used to investigate the properties of liquid water at 750 K and 10 GPa, and efficient estimators for the calculation of single particle momentum distri- butions, which are used to study the properties of solid and liquid ammonia. These show respectively that i-PI can be used to make predictions about systems which are both difficult to study experimentally and highly non-classical in nature, and that it can illustrate the relative advantages and disadvantages of different theoretical methods and their ability to reproduce experimental data.