High image fidelity in Magnetic Resonance Imaging (MRI) relies on precise magnetic field control of encoding gradient fields and background B0 magnetic fields. To ensure a high degree of accuracy in the spatial location of the proton spins and the resultant object geometry, conventional image encoding using linear gradient fields, as well as advanced techniques with non-linear encoding, requires field generating hardware capable of excellent field shaping capabilities and accuracy. Non-homogeneous B0 background fields in MR imaging cause faster relaxation, signal dropout, and geometry distortion, resulting in inferior image quality and reduced diagnostic accuracy. Besides manufacturing imperfections in the magnet and site conditions, the magnetic field inside the imaging object is not homogeneous due to the differences in geometries and magnetic properties of individual human tissues, which is recognized as the primary source of B0 variation in MRI. Considering the differences of B0 conditions across subjects, it is essential for MR imaging to utilize flexible B0 shimming techniques such as active shimming in order to produce a highly homogeneous B0 field. The control capability and optimized control strategy for these magnetic fields require the development of new hardware and methodologies. B0 background field generated by the magnet and the encoding gradient field from gradient coil are two critical pillars of MR imaging. Since the multi-coil array provides advanced shim capability and is proven to be capable of imaging encoding with a compact size, it is considered a perfect component as a combination of B0 shim coil and encoding gradient coil for an accessible head-only MR scanner. MR scanners like this type provide unique features that will enable researchers to develop new MRI methodologies and conduct research into the functionalities of the human brain through more natural human behaviors. Its clinical applications will be more accessible to the general population for disease screening and diagnosis due to its portability and low energy requirements. Since the multi-coil array has the advantage of smaller volume and wall thickness than the traditional gradient coil, its design and implementation is challenging because of its compact space, irregular curved shape of coil elements, mechanical reliability requirements during scan and good thermal control for long working periods. It was the challenges involved in the design and implementation of the multi-coil array that initiated the first project of my dissertation. In this project, we present 1) a novel molding method for the construction of resin-impregnated wire patterns with irregular curved shapes along with a microcontroller-driven motorized machine for automated coil construction, 2) the design and validation of a water-cooling system using multiple parallel pipes impregnated with thermal epoxy, 3) a quality-controlled procedure of building the multi-coil array employing the technique of vacuum resin infusion. A multi-coil array was fabricated successfully and evaluated in multiple sites and then integrated into the first-prototype of the accessible head-only MR scanner. The similar quality of experimental images from the fabricated multi-coil array compared to those from conventional gradient coils indicates that the multi-coil array can effectively shape fields for both image encoding and B0 shimming. Our lab has shown that multi-coil technology offers advanced shim capability when imaging the human brain, but it could potentially benefit the imaging of other organs like the heart. The MR imaging of the heart is subject to dark band artifacts or signal loss caused by B0 inhomogeneity, which can result in misinterpretation of lesions and a reduction in diagnostic accuracy. It has been demonstrated in a recent study that the use of multi-coil techniques can significantly reduce B0 inhomogeneity within the heart based on shim analysis using in vivo B0 maps. Multi-coil arrays are not a standard configuration in commercial scanners but are normally used for research, B0 shimming is typically implemented by using the commonly-installed spherical harmonic shim coils in the first, second, and potentially third orders. The development of multi-coil technology, more in-depth design of the coil structure and geometry as well as the optimal use of the current spherical harmonic shim technology require a thorough understanding of cardiac B0 conditions across subjects and at a population level. Since the in vivo cardiac B0 measurement is not a routine clinical protocol and dedicated in vivo measurement for a large sample size are extremely labor intensive and expensive, the lack of such B0 data is a long-standing problem, especially for the subject groups like pediatric or elderly patients who cannot undergo B0 map measurement with breath hold. This challenge could be resolved by the use of B0 simulation on the basis of structural images from different imaging modalities, assuming that the B0 distributions inside the human heart depends on the anatomical structures surrounding heart and across the entire body. The challenge and assumption led to my second project regarding B0 magnetic field simulation in the human heart. We proposed a novel B0 simulation approach based on chest-abdomen-pelvis structural CT images and validated it using in vivo acquired B0 maps in the heart from the same subjects. This B0 simulation approach was then applied to CT images from more than one thousand subjects and the resultant large set of simulated B0 maps were analyzed with different shim types for searching optimal shim solution based on popular spherical harmonic decomposition. The derived B0 conditions were also statistically analyzed for potential correlation and linear association with demographic parameters of these subjects for investigating potential population-based shim strategy. By the use of in vivo acquisition, we also investigated the B0 magnetic field variation across cardiac cycle and evaluated the impact of these variations on in vivo cardiac B0 shimming. The results of this study allow us to better understand the primary sources and characteristics of B0 distributions in the heart as well as pave the way for developing optimal B0 shim methods within heart in both subject-specific and population-based manners.

[pt] Simulações numéricas tendem a simplificar o comportamento de problemas reais, na maioria das vezes pela adoção de um modelo 2D para descrição da resposta hidráulico-mecânica de barragens de terra, escavações, fundações, etc., com base na maior facilidade da construção geométrica de malhas, rapidez de processamento, simplicidade na introdução das condições de contorno, menor dificuldade na obtenção dos parâmetros de engenharia, etc. Entretanto, para certos fenômenos como o fluxo através de barragem em vales estreitos ou no rebaixamento do lençol freático para execução de escavações para construção de fundações, os efeitos tridimensionais podem afetar consideravelmente os resultados obtidos com uma solução simplificada, seja em termos de vazão, cargas, gradientes hidráulicos ou fatores de segurança. Esta dissertação tem como objetivo principal analisar problemas de fluxo, na condição transiente e/ou permanente, considerando solos saturados e parcialmente saturados, em simulações 2D e 3D pelo método dos elementos finitos buscando destacar as principais diferenças entre as respostas obtidas, ressaltando as principais vantagens e dificuldades da realização de uma simulação 3D em relação a uma análise simplificada 2D. Os exemplos numéricos abordados neste trabalho se referem à barragem de terra Macusani, no Peru, à escavação realizada para construção das estruturas da Pequena Central Elétrica Canoa Quebrada - MT e ao rebaixamento do lençol freático para construção das fundações do shopping Brooklin na cidade de São Paulo - SP. / [en] Numerical simulations tend to simplify the behavior of real problems, mainly through the choice of 2D models to describe the hydromechanical responses of earth dams, excavations, foundations, etc., partly because it is easier to construct geometrical meshes, it is simpler to impose the required boundary conditions, the computer calculations are done more rapidly and the estimation of the engineering parameters, either through field or laboratory tests, are less difficulty than it would be if the problem was treated as a complete 3D case. However, for certain phenomena such as the flow of water through dams situated in narrow valleys or the water drawdown in excavations for construction of building foundations, 3D effects can considerably affect the results when compared to a simplified 2D solution, either in terms of quantity of flow, hydraulic heads and gradients, security factors, etc. The main goal of this dissertation is the analysis of flow problems, both in transient and permanent conditions, considering fully saturated or partially saturated soils, employing 2D and 3D numerical models based on the finite element method in order to highlight the main differences between the computed answers, emphasizing the advantages and difficulties of both approaches. The numerical examples studied in this work are the earth dam Macusani, situated in Peru, the excavation carried out for the construction of the structures in the small hydroelectric plant Canoa Quebrada - MT, and groundwater drawdown for the execution of the foundations of the Brooklin shopping mall, in the city of São Paulo - SP.

Au travers de l’ensemble de ces travaux, l’objectif principal consiste à valider la pertinence de la construction et de l’utilisation de modèles 3D géométriques ou paramétriques orientés BIM/hBIM pour des analyses numériques. Il s’agit notamment d’études structurales dans le cas de bâtiments historiques ainsi que la planification potentielle de travaux de restauration, rénovation énergétique et réhabilitation. Des travaux d’exploitation complémentaires des données et des nuages de points, pour la détection, la segmentation et l’extraction d’entités géométriques ont également été intégrés dans les travaux et la méthodologie proposée. Le processus de traitement des données, modélisation géométrique ou paramétrique et leur exploitation, proposé dans ces travaux, contribue à améliorer et mieux comprendre les contraintes et enjeux des différentes configurations et conditions liées aux cas d’études et aux contraintes spécifiques propres aux types de constructions. Les contributions proposées pour les différentes méthodes de modélisation géométriques et paramétriques à partir des nuages de points, sont abordées par la construction de modèles géométriques orientés BIM ou hBIM. De même, les processus de détection d’éléments surfaciques et d’extraction de données à partir de nuages de points mis en place sont présentés. La mise en application de ces méthodes de modélisation est systématiquement illustrée par différents cas d’étude, dont l’ensemble des travaux relatifs ont été effectués dans le cadre de cette thèse. Le but est dès lors de démontrer l’intérêt et la pertinence de ces méthodes numériques en fonction du contexte, des besoins et des études envisagées, par exemple avec la flèche de la cathédrale de Senlis (Oise) et le site de l’Hermitage (Oise). Des analyses numériques de type éléments finis permettent ensuite de valider la pertinence de telles démarches. / Throughout this work, the main objective is to validate the relevance of construction and use of geometric or parametric 3D models BIM or hBlM-oriented for numerical analyzes. These include structural studies in the case of historic buildings, as well as planning for restoration work, energy renovation and rehabilitation. Complementary data mining and use of point clouds for the detection, segmentation and extraction of geometric features have also been integrated into the work and proposed methodology. The process of data processing, geometric or parametric modeling and their exploitation, proposed in this work, contributes to improve and understand better the constraints and stakes of the different configurations and conditions related to the case studies and the specific constraints specific to the types of constructions. The contributions proposed for the different geometric and parametric modeling methods from point clouds are addressed by the construction of geometric models BIM or hBlM-oriented. Similarly, the process of surface detection, extraction of data and elements from point clouds are presented. The application of these modeling methods is systematically illustrated by different case studies, all of whose relative work has been carried out within the framework of this thesis. The goal is therefore to demonstrate the interest and relevance of these numerical methods according to the context, needs and studies envisaged, for example with the spire of the Senlis cathedral (Oise) and the Hermitage site (Oise). Numerical analyzes with finite element method are used to validate the relevance of these approaches.

In order to cope with system complexity and dynamic environments, modern industries are investing in a variety of sensor networks and data acquisition systems to increase information visibility. Multi-sensor systems bring the proliferation of high-dimensional functional Big Data that capture rich information on the evolving dynamics of natural and engineered processes. With spatially and temporally dense data readily available, there is an urgent need to develop advanced methodologies and associated tools that will enable and assist (i) the handling of the big data communicated by the contemporary complex systems, (ii) the extraction and identification of pertinent knowledge about the environmental and operational dynamics driving these systems, and (iii) the exploitation of the acquired knowledge for more enhanced design, analysis, monitoring, diagnostics and control. My methodological and theoretical research as well as a considerable portion of my applied and collaborative work in this dissertation aims at addressing high-dimensional functional big data communicated by the systems. An innovative contribution of my work is the establishment of a series of systematic methodologies to investigate the complex system informatics including multi-dimensional modeling, feature extraction and selection, model-based monitoring and root cause diagnostics. This study presents systematic methodologies to investigate spatiotemporal informatics of complex systems from multi-dimensional modeling and feature extraction to model-driven monitoring, fault identification and root cause diagnostics. In particular, we developed a multiscale adaptive basis function model to represent and characterize the high-dimensional nonlinear functional profiles, thereby reducing the large amount of data to a parsimonious set of variables (i.e., model parameters) while preserving the information. Furthermore, the complex interdependence structure among variables is identified by a novel self-organizing network algorithm, in which the homogeneous variables are clustered into sub-network communities. Then we minimize the redundancy of variables in each cluster and integrate the new set of clustered variables with predictive models to identify a sparse set of sensitive variables for process monitoring and fault diagnostics. We evaluated and validated our methodologies using real-world case studies that extract parameters from representation models of vectorcardiogram (VCG) signals for the diagnosis of myocardial infarctions. The proposed systematic methodologies are generally applicable for modeling, monitoring and diagnosis in many disciplines that involve a large number of highly-redundant variables extracted from the big data. The self-organizing approach was also innovatively developed to derive the steady geometric structure of a network from the recurrence-based adjacency matrix. As such, novel network-theoretic measures can be achieved based on actual node-to-node distances in the self-organized network topology.

Despite recent advances in statistics, artificial neural network theory, and machine learning, nonlinear function estimation in high-dimensional space remains a nontrivial problem. As the response surface becomes more complicated and the dimensions of the input data increase, the dreaded "curse of dimensionality" takes hold, rendering the best of function approximation methods ineffective. This thesis takes a novel approach to solving the high-dimensional function estimation problem. In this work, we propose and develop two distinct parametric projection pursuit learning networks with wide-ranging applicability. Included in this work is a discussion of the choice of basis functions used as well as a description of the optimization schemes utilized to find the parameters that enable each network to best approximate a response surface. The essence of these new modeling methodologies is to approximate functions via the superposition of a series of piecewise one-dimensional models that are fit to specific directions, called projection directions. The key to the effectiveness of each model lies in its ability to find efficient projections for reducing the dimensionality of the input space to best fit an underlying response surface. Moreover, each method is capable of effectively selecting appropriate projections from the input data in the presence of relatively high levels of noise. This is accomplished by rigorously examining the theoretical conditions for approximating each solution space and taking full advantage of the principles of optimization to construct a pair of algorithms, each capable of effectively modeling high-dimensional nonlinear response surfaces to a higher degree of accuracy than previously possible.

In this study, an appearance reconstruction method based on extraction of material re&amp / #64258 / ectance properties of a three-dimensional (3D) object from its twodimensional (2D) images is explained. One of the main advantages of this system is that the reconstructed object can be rendered in real-time with photorealistic quality in varying illumination conditions. Bidirectional Re&amp / #64258 / ectance Distribution Functions (BRDFs) are used in representing the re&amp / #64258 / ectance of the object. The re&amp / #64258 / ectance of the object is decomposed into di&amp / #64256 / use and specular components and each component is estimated seperately. While estimating the di&amp / #64256 / use components, illumination-invariant images of the object are computed from the input images, and a global texture of the object is extracted from these images by using surface particles. The specular re&amp / #64258 / ectance data are collected from the residual images obtained by taking di&amp / #64256 / erence between the input images and corresponding illumination-invariant images, and a Lafortune BRDF model is &amp / #64257 / tted to these data. At the rendering phase, the di&amp / #64256 / use and specular components are blended into each other to achieve a photorealistic appearance of the reconstructed object.

Quando ar escoa em regime transiente através do duto de admissão, câmaras e válvulas de um motor de combustão interna, alguns efeitos tais como atrito e forças inerciais têm influência direta sobre a eficiência volumétrica do sistema. O presente trabalho, intitulado “Estudo numérico do processo de admissão em um motor de combustão interna utilizando uma metodologia baseada na massa específica pré-condicionada para baixo número de Mach com comparação experimental”, estuda o processo de admissão em um motor de combustão interna simplificado e objetiva investigar o comportamento pulsante presente no duto de admissão e discutir as predições do escoamento através da válvula de admissão por meio da utilização inédita de uma metodologia numérica baseada na massa específica com précondicionamento para baixo número de Mach, incluindo a modelagem tridimensional do duto de admissão na simulação fluidodinâmica. O movimento da válvula de admissão origina números de Mach moderados durante sua abertura. Com o fechamento, o escoamento é restringido abruptamente e uma série de ondas de pressão se propaga através do fluido com baixo número de Mach. Embora a metodologia baseada na massa específica com précondicionamento para baixo número de Mach pareça atrativa, o estudo do escoamento em processos de admissão não tem sido realizado com a utilização desta metodologia, provavelmente por limitações impostas pela robustez e esforço computacional. De modo a verificar a solução numérica, os resultados são comparados a dados experimentais coletados em uma bancada de fluxo construída especificamente com este propósito. Os resultados numéricos mostram-se satisfatórios e diferentes aspectos do jato originado pelo movimento da válvula são expostos e discutidos. / When air flows unsteadily in an internal combustion engine through its inlet pipe, chambers and valves, some effects such as friction and inertial forces have direct influence on the volumetric efficiency of the system. The present work, titled “Numerical study of the intake process of an internal combustion engine using a low Mach preconditioned densitybased method with experimental comparison”, aims to investigate the pulsating phenomena present in an intake pipe of a simplified internal combustion engine and discuss the intake jet flow predictions through the inlet valve by means of the novel use of a low Mach preconditioned density-based method, including the three-dimensional modeling of the intake pipe in the fluid dynamic simulation. Inlet valve movement promotes moderate values of Mach numbers during its opening phase. After closing, the flow is abruptly restricted and a series of pressure waves propagate through the fluid at low Mach numbers. Although low Mach preconditioned density-based method seems to be very attractive in this case, the study of the intake flow process has not been performed using this method, probably due to robustness issues and simulation effort. In order to evaluate the numerical solution, these results are compared to experimental data collected from a flow test bench constructed specifically for this purpose. Numerical results were satisfactory for the amplitudes and the resonance frequencies in the air intake system and different aspects of the jet flow inside the cylinder are exposed and discussed.

La qualité des services écosystémiques qu'offrent les lacs est liée à la structure et au fonctionnement de leur écosystème. Protéger leur masse d'eau est devenu un objectif global qui requiert une meilleure compréhension de leur fonctionnement, un suivi et une évaluation de leur qualité. Expliquer les hétérogénéités spatio-temporelles des variables physico-chimiques et du phytoplancton est un problème récurrent rencontré en écologie et en hydrobiologie. Comprendre la dynamique de ces hétérogénéités est aussi un prérequis essentiel pour évaluer, protéger et restaurer objectivement les écosystèmes lacustres. En ce qui concerne la surveillance, les hétérogénéités spatio-temporelles introduisent des incertitudes sur la représentativité des mesures par rapport à l'entièreté de la masse d'eau qui est donc discutable et doit être vérifiée. En Europe, la directive cadre sur l'eau (DCE) initiée en 2000 définit un cadre pour la gestion et la protection des eaux. La classification des masses d'eau en fonction de leur état écologique est un point important dans l'implémentation de cette directive. Pour les lacs et les retenues, l'évaluation de cet état écologique est basée sur des paramètres biologiques, physico-chimiques et hydromorphologiques. Les indicateurs liés au phytoplancton et aux paramètres physico-chimiques sont calculés à partir de quatre prélèvements réalisés pendant la période d'activité biologique pour une année sur un plan de gestion de six ans. Dans ce contexte, la modélisation tridimensionnelle (3D) et la prise en compte des forçages qui conduisent aux hétérogénéités spatio-temporelles est une condition préalable nécessaire tant en limnologie appliquée que théorique. Cette thèse aborde la complexité du fonctionnement des lacs et la capacité des modèles 3D à reproduire leur fonctionnement. L'apport de la modélisation 3D est présenté i) pour la compréhension du fonctionnement de lacs de différentes tailles, ii) couplée aux observations satellitaires, pour l'étude de l'influence des forçages par le vent et de l'hydrodynamique sur l'abondance et la distribution spatiale de phytoplancton, iii) dans le cadre de la DCE, pour l'évaluation des incertitudes d'une évaluation de l'état écologique d'un plan d'eau. Pour cela, deux modèles 3D ont été créés et analysés, un pour le lac de Créteil (42~ha) et un autre pour le Léman (580~km$^2$). Celui du lac de Créteil a été validé à partir de données à hautes fréquences acquises en trois points du lac. Il reproduit correctement son hydrodynamique complexe, sa structure thermique, l'alternance entre les périodes de stratification et les épisodes de mélange, ainsi que les ondes internes. Le modèle du Léman a été validé en utilisant des données mensuelles et bimensuelles en deux stations de prélèvement du lac. Il reproduit aussi correctement son hydrodynamique et la variabilité saisonnière de paramètres physico-chimiques et biologiques. Les résultats des simulations mettent en avant les mécanismes physiques et hydrodynamiques responsables de l'apparition de sites où la biomasse de phytoplancton observée est plus élevée. Dans le cadre de la DCE, ces résultats montrent aussi une variabilité spatiale importante des sous-états écologiques basés sur les différents paramètres qui dépendent du choix des dates des campagnes de mesure et du point d'échantillonnage. Ces résultats ont aussi été utilisés pour estimer la représentativité d'une station de prélèvement. Les résultats de cette thèse i) confirment que le fonctionnement des plans d'eau de toute taille est complexe et que les processus physiques génèrent des hétérogénéités spatio-temporelles, ii) suggèrent que le vent et l'hydrodynamique influencent significativement l'abondance et la distribution spatiale du phytoplancton et que iii) ces hétérogénéités peuvent biaiser notre estimation du statut écologique des plans d'eau dans le cadre de la DCE / The quality of ecosystem services provided by lakes is related to the ecosystem structure and functioning. Protecting water bodies is therefore a global goal that requires a better understanding of their function, a monitoring and a water quality assessment. Explaining spatio-temporal heterogeneities of physico-chemical parameters and phytoplankton has been a recurrent ecological and hydrobiological issue. Understanding the dynamics of these heterogeneities is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. Moreover, three-dimensional (3D) and taking into account and drivers of these heterogeneities are essential prerequisites for theoretical and applied limnology. Concerning the monitoring, spatio-temporal heterogeneities are responsible of uncertainties on the representativeness of the data versus the whole lake which might be questionable and needs to be verified. In Europe, the Water Framework Directive (WFD) initiated in 2000 defines a framework for managing and protecting water bodies in Europe. The classification of water bodies into ecological status is a key issue for the implementation of that framework. For lakes and reservoirs, the assessment of this status is based on biological, physico-chemical and hydro-morphological indicators. Physico-chemical and phytoplankton indicators are calculated based on four observations at an unique sampling station over the growing season, this evaluation being assessed one year for a six-year management plan. In this context, this thesis focuses on the complexity of lakes functioning and the capability of three-dimensional (3D) models to reproduce their functioning. The contribution of 3D models is presented i) for understanding the functioning of lakes of different sizes, ii) coupled to satellite observations, for studying of the influence of wind forcing and hydrodynamics on phytoplankton abundance and spatial heterogeneities, iii) in the context of the WFD, for assessing uncertainties in the lake ecological status assessment. To do that, two 3D models have been created and analyzed, one for Lake Créteil (42 ha) and another for Lake Geneva (580 km2). Lake Créteil 3D model was validated by using high frequency data recorded at three stations. It reproduces well the complex hydrodynamic functioning of the lake, its thermal structure, the alternation between thermal stratification episodes and mixing events, and internal waves. Lake Geneva 3D model was validated by using monthly and bimonthly data at two stations. It reproduces also properly the hydrodynamic functioning of the lake and the seasonal variability of biological and physico-chemical parameters. Simulation results highlight physical and hydrodynamic mechanisms responsible for the occurrence of seasonal hot-spots in phytoplankton abundance. In the context of the WFD, simulation results show also a strong spatial variability of lake ecological status depending on the timing of the four sampling dates as well as the location of the sampling station. These results were also used to assess to representativeness of sampling stations. The results of this thesis suggest that i) the functioning of lakes of different sizes is complex and physical processes generates spatio-temporal heterogeneities, ii) wind and hydrodynamics influence the abundance and the spatial distribution of phytoplankton et iii) spatio-temporal heterogeneities can bias our evaluation of lake ecological status in the WFD

Quando ar escoa em regime transiente através do duto de admissão, câmaras e válvulas de um motor de combustão interna, alguns efeitos tais como atrito e forças inerciais têm influência direta sobre a eficiência volumétrica do sistema. O presente trabalho, intitulado “Estudo numérico do processo de admissão em um motor de combustão interna utilizando uma metodologia baseada na massa específica pré-condicionada para baixo número de Mach com comparação experimental”, estuda o processo de admissão em um motor de combustão interna simplificado e objetiva investigar o comportamento pulsante presente no duto de admissão e discutir as predições do escoamento através da válvula de admissão por meio da utilização inédita de uma metodologia numérica baseada na massa específica com précondicionamento para baixo número de Mach, incluindo a modelagem tridimensional do duto de admissão na simulação fluidodinâmica. O movimento da válvula de admissão origina números de Mach moderados durante sua abertura. Com o fechamento, o escoamento é restringido abruptamente e uma série de ondas de pressão se propaga através do fluido com baixo número de Mach. Embora a metodologia baseada na massa específica com précondicionamento para baixo número de Mach pareça atrativa, o estudo do escoamento em processos de admissão não tem sido realizado com a utilização desta metodologia, provavelmente por limitações impostas pela robustez e esforço computacional. De modo a verificar a solução numérica, os resultados são comparados a dados experimentais coletados em uma bancada de fluxo construída especificamente com este propósito. Os resultados numéricos mostram-se satisfatórios e diferentes aspectos do jato originado pelo movimento da válvula são expostos e discutidos. / When air flows unsteadily in an internal combustion engine through its inlet pipe, chambers and valves, some effects such as friction and inertial forces have direct influence on the volumetric efficiency of the system. The present work, titled “Numerical study of the intake process of an internal combustion engine using a low Mach preconditioned densitybased method with experimental comparison”, aims to investigate the pulsating phenomena present in an intake pipe of a simplified internal combustion engine and discuss the intake jet flow predictions through the inlet valve by means of the novel use of a low Mach preconditioned density-based method, including the three-dimensional modeling of the intake pipe in the fluid dynamic simulation. Inlet valve movement promotes moderate values of Mach numbers during its opening phase. After closing, the flow is abruptly restricted and a series of pressure waves propagate through the fluid at low Mach numbers. Although low Mach preconditioned density-based method seems to be very attractive in this case, the study of the intake flow process has not been performed using this method, probably due to robustness issues and simulation effort. In order to evaluate the numerical solution, these results are compared to experimental data collected from a flow test bench constructed specifically for this purpose. Numerical results were satisfactory for the amplitudes and the resonance frequencies in the air intake system and different aspects of the jet flow inside the cylinder are exposed and discussed.

Quando ar escoa em regime transiente através do duto de admissão, câmaras e válvulas de um motor de combustão interna, alguns efeitos tais como atrito e forças inerciais têm influência direta sobre a eficiência volumétrica do sistema. O presente trabalho, intitulado “Estudo numérico do processo de admissão em um motor de combustão interna utilizando uma metodologia baseada na massa específica pré-condicionada para baixo número de Mach com comparação experimental”, estuda o processo de admissão em um motor de combustão interna simplificado e objetiva investigar o comportamento pulsante presente no duto de admissão e discutir as predições do escoamento através da válvula de admissão por meio da utilização inédita de uma metodologia numérica baseada na massa específica com précondicionamento para baixo número de Mach, incluindo a modelagem tridimensional do duto de admissão na simulação fluidodinâmica. O movimento da válvula de admissão origina números de Mach moderados durante sua abertura. Com o fechamento, o escoamento é restringido abruptamente e uma série de ondas de pressão se propaga através do fluido com baixo número de Mach. Embora a metodologia baseada na massa específica com précondicionamento para baixo número de Mach pareça atrativa, o estudo do escoamento em processos de admissão não tem sido realizado com a utilização desta metodologia, provavelmente por limitações impostas pela robustez e esforço computacional. De modo a verificar a solução numérica, os resultados são comparados a dados experimentais coletados em uma bancada de fluxo construída especificamente com este propósito. Os resultados numéricos mostram-se satisfatórios e diferentes aspectos do jato originado pelo movimento da válvula são expostos e discutidos. / When air flows unsteadily in an internal combustion engine through its inlet pipe, chambers and valves, some effects such as friction and inertial forces have direct influence on the volumetric efficiency of the system. The present work, titled “Numerical study of the intake process of an internal combustion engine using a low Mach preconditioned densitybased method with experimental comparison”, aims to investigate the pulsating phenomena present in an intake pipe of a simplified internal combustion engine and discuss the intake jet flow predictions through the inlet valve by means of the novel use of a low Mach preconditioned density-based method, including the three-dimensional modeling of the intake pipe in the fluid dynamic simulation. Inlet valve movement promotes moderate values of Mach numbers during its opening phase. After closing, the flow is abruptly restricted and a series of pressure waves propagate through the fluid at low Mach numbers. Although low Mach preconditioned density-based method seems to be very attractive in this case, the study of the intake flow process has not been performed using this method, probably due to robustness issues and simulation effort. In order to evaluate the numerical solution, these results are compared to experimental data collected from a flow test bench constructed specifically for this purpose. Numerical results were satisfactory for the amplitudes and the resonance frequencies in the air intake system and different aspects of the jet flow inside the cylinder are exposed and discussed.