abstract: A numerical model for design of the geomembrane elements of waste containment systems has been validated by laboratory testing. Due to the absence of any instrumented case histories of seismic performance of geomembrane liner systems, a large scale centrifuge test of a model geomembrane-lined landfill subject to seismic loading was conducted at the University of California at Davis Centrifuge Test facility as part of National Science Foundation Network for Earthquake the Engineering Simulation Research (NEESR) program. Data collected in the large scale centrifuge test included waste settlement, liner strains and earthquake accelerations at various locations throughout the model. This data on landfill and liner seismic performance has been supplemented with additional laboratory and small scale centrifuge tests to determine the parameters required for the numerical model, including strength and stiffness of the model materials, interface shear strengths, and interface stiffness. The numerical model explicitly assesses the forces and strains in the geomembrane elements of a containment system to subject to both static and seismic loads the computer code FLACTM, a finite difference program for non-linear analysis of continua. The model employs a beam element with zero moment of inertia and with interface elements on both sides to model to represent the geomembrane elements in the liner system. The model also includes non-linear constitutive models for the stress-strain behavior of geomembrane beam elements and an elastic-perfectly plastic model for the load-displacement behavior of the beam interfaces. Parametric studies are conducted with the validated numerical model to develop recommendations for landfill design, construction, and construction quality assurance. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2017

Ground-Penetrating Radar (GPR) is a popular non-destructive geophysical technique with a wide range of diverse applications. Civil engineering, hydrogeophysics, forensic, glacier geology, human detection and borehole geology are some of the fields in which GPR has been applied with successful or promising results. One of the most mainstream applications of GPR is landmine detection. A lot of methods have been suggested over the years to assist the landmine detection issue. Metal detectors, trained rats or dogs, chemical methods and electrical resistivity tomography are –amongst others– some of the suggested techniques. The non-destructive nature of GPR makes it an attractive choice for a problem such as demining in which contact to the ground is not allowed. The main advantage of GPR is its ability to detect both metallic and non-metallic targets. Furthermore, GPR can provide an insight regarding the nature of the target (e.g. size, burial depth, type). From the above, it is evident that GPR can potentially reduce the false alarms emerging from small metallic objects (e.g. bullets, wires, etc.) usually encountered in battle-fields and industrialised areas. Combining the robustness of the metal detector with the resolution of GPR results in a reliable and efficient detection framework which has been successfully applied in Cambodia and Afghanistan. Despite the promising, and in some cases impressive results, aspects of GPR can be further improved in an effort to optimise GPR’s performance and decrease its limitations. The validation of a GPR system is usually achieved through the so called Receiver Operation Characteristics (ROC) which depicts the probability of detection with respect to the false alarm rate. ROC is a highly nonlinear function which is sensitive to the environment as well as to the antenna unit. Landmines are typically small objects, often less than 10 cm diameter, which are shallow buried, usually in less than 10 cm depth, and sometimes almost exposed. In order for the landmines to be resolved, high frequency antennas are essential. The latter are sensitive to soil’s inhomogeneities, rough surface, water puddles, vegetation and so on. Apart from that, the near field nature of the problem makes the antenna unit part of the medium which contributes to the unwanted clutter. The above, outlines the multi-parametric nature of the problem for which no straightforward approach has yet to be proposed. Numerical modelling is a practical and solid approach to understand the physical behaviour of a system. In the case of GPR for landmine detection, numerical modelling can be a practical tool for designing and optimising antennas in synthetic but nonetheless realistic conditions. Apart from that, evaluation of a processing method only to a specific environment is not a robust approach and does not provide any evidence for its wider inclusivity and limitations. However, evaluation in different conditions can become costly and unpractical. Numerical modelling can tackle this problem by providing data for a wide range of scenarios. An extensive database of simulated responses, apart from being a practical testbed, can be also employed as a training set for machine learning. A multi-variable problem like demining, in order to be addressed using machine learning, requires a large amount of data. These must equally include all possible different scenarios i.e. different landmines, in different media with stochastically varied properties and topography. Additionally, different heights of the antenna and different depths of the landmines must also be examined. Numerical modelling seems to be a practical approach to achieve an equally distributed and coherent dataset like the one briefly described above. Numerical modelling of GPR for landmine detection has been applied in the past using generic antennas in simplified and clinical scenarios. This approach can be used in an educational context just to provide a rough estimation of GPR’s performance. In the present thesis a realistic numerical scheme is suggested in which, simplifications are kept to a minimum. The numerical solver, employed in the suggested numerical scheme, is the Finite- Difference Time-Domain (FDTD) method. Both the dispersive properties and the Absorbing Boundary Condition (ABC) are implemented through novel and accurate techniques. In particular, a novel method which implements an inclusive susceptibility function is suggested and it is shown that surpasses the performance of the previous approaches while retaining their computational efficiency. Furthermore, Perfectly Matched Layer (PML) and more specifically Convolutional Perfectly Matched Layer (CPML) is implemented through a novel time-synchronised scheme which it is proven to be more accurate compared to the traditional CPML with no additional computational requirements. An accurate numerical solver, although essential, is not the only requirement for a realistic numerical framework. Accurate implementation of the geometry and the dielectric properties of the simulated model is highly important, especially when it comes to high-frequency near-field scenarios such as GPR for landmine detection. In the suggested numerical scheme, both the soil’s properties as well as the rough surface are simulated using fractal correlated noise. It is shown, that fractals can sufficiently represent Earth’s topography and give rise to semi-variograms often encountered in real soils. Regarding the dielectric properties of the soils, a semi-analytic function is employed which relates soil’s dielectric properties to its sand fraction, clay fraction, sand density, bulk density and water volumetric fraction. Subsequently, the semi-analytic function is approximated using a Debye function that can be easily implemented to FDTD. Vegetation is also implemented to the model using a novel method which simulates the geometry of vegetation through a stochastic process. The experimentally-derived dielectric properties of vegetation are approximated –similarly to soil’s dielectric properties– with a Debye expansion. The antenna units tested in the numerical scheme are two bow-tie antennas based on commercially available transducers. Regarding the targets, three landmines are chosen, namely, PMN, PMA-1 and TS-50. Dummy landmines are used in order to obtain their geometrical characteristics and comparison between measured and numerically evaluated traces are used to tune the dielectric properties of the modelled landmines. Lastly, water puddles are realistically implemented in the model in an effort to realistically simulate high-saturated scenarios. The proposed numerical scheme has been employed in order to test and evaluate widely used post-processing methods. The results clearly illustrate that post-processing methods are sensitive to the antenna unit as well as the medium. This highlights the importance of an accurate numerical scheme as a testbed for evaluating different GPR systems and post-processing approaches in wide range of scenarios. Using an equivalent 2D numerical scheme –restricted to 2D due to computational constrains– preliminary results are given regarding the effectiveness of Artificial Neural Network (ANN) subject to an adequate and equally distributed database. The results are promising, showing that ANN can be successfully employed for detection as well as classification using only a single trace as input. A basic requirement to do so is a representative training set. This can be synthetically generated using a realistic numerical framework. The above, provide solid arguments for further expanding the proposed machine learning scheme to the more computationally demanding 3D case.

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Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2012. / Submitted by Alaíde Gonçalves dos Santos (alaide@unb.br) on 2013-01-25T12:20:01Z No. of bitstreams: 1 2012_LeandroCarisioFernandes.pdf: 11244387 bytes, checksum: 56968dbdb42928aca7dfd8945faf01cd (MD5) / Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2013-02-01T12:59:34Z (GMT) No. of bitstreams: 1 2012_LeandroCarisioFernandes.pdf: 11244387 bytes, checksum: 56968dbdb42928aca7dfd8945faf01cd (MD5) / Made available in DSpace on 2013-02-01T12:59:34Z (GMT). No. of bitstreams: 1 2012_LeandroCarisioFernandes.pdf: 11244387 bytes, checksum: 56968dbdb42928aca7dfd8945faf01cd (MD5) / A demanda por serviços de comunicações móveis cresce ano após ano. A implantação de sistema que ofereça esse tipo de serviço requer mecanismos de predição de cobertura de sinal, a fim de otimizar parâmetros usados na fase de planejamento. E importante considerar que, em um enlace de comunicação via rádio, a propagação do sinal não ocorre em situações ideais, na maioria das vezes. A quantidade de fenômenos que influenciam a propagação do sinal é proporcional a complexidade do ambiente. Em regra, em áreas urbanas existe um número maior de obstáculos do que em localidades rurais, o que torna mais complicado estimar a perda de propagação em cidades e metrópoles. Melhorar a estimativa da perda de propagação pode assegurar mais qualidade ao serviço oferecido por operadoras de telecomunicações. Este trabalho mostra como o ambiente urbano pode ser considerado no cálculo da perda de propagação em duas faixas de freqüência. Para a faixa de 900 MHz, são propostos métodos que analisam situações em que a altura da antena transmissora é menor do que a altura média das construções. Os resultados demonstram uma melhora signicativa quando comparados com aqueles obtidos por meio do modelo COST-Walfisch-Ikegami. Em ondas médias, na faixa de 1MHz, propõe-se uma correção da Recomendação ITU-R P.368 de forma a se incluir informações sobre a densidade de área ocupada por construções na localização do receptor. Os valores estimados do campo elétrico estão mais próximos dos dados de medidas do que os obtidos usando-se apenas a recomendação do ITU. O estudo da propagação em ambientes indoor também e um problema de grande interesse prático. Nesse caso, devido a complexidade do ambiente, o uso de equações analíticas torna-se impraticável. Uma forma de contornar essa restrição e usando métodos numéricos. Nesse sentido, será mostrado também como problemas de propagação em ambientes indoor podem ser analisados via métodos numéricos. _______________________________________________________________________________________ ABSTRACT / The demand for mobile communications services grows year after year. Path loss prediction models are necessary to deploy any system that o ers this service. In a wireless communication link, the propagation of the signal occurs mostly over a non line of sight path. The more complex the environment, the greater the number of phenomena that a ect the propagation of the signal. In urban areas, the number of obstacles is greater than in rural areas, and therefore it is more di cult to estimate the path loss in those sites. However, improve estimates of path loss in urban environment can also improve the quality of service o ered by telecommunications operators. Thus, this thesis shows how the urban environment can be considered to calculate the path loss in two frequency bands. Two path loss models are proposed at 900 MHz, when transmitting antenna is lower than the average height of the buildings. The results show a signi cant improvement when compared with COST-Wal sch-Ikegami model. For medium waves, at 1 MHz, a correction of Recommendation ITU-R P.368 is proposed to include information of area occupied by buildings in the receiver's location. The estimated values of the electric fi eld are better than those obtained using the Recommendation ITU-R P.368. Propagation in indoor environments is also a problem with practical interest. Due to the complexity of the environment, the use of analytical equation is impractical. Numerical methods solve this limitation. Thus, it will be shown how to analyse indoor environments using numerical methods.

Orientador: Sergio Persio Ravagnani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-16T22:22:20Z (GMT). No. of bitstreams: 1 Armellini_VictorAntoniodeDeus_M.pdf: 4894836 bytes, checksum: 94bbcb586bf0955c10788e44b96533de (MD5) Previous issue date: 2010 / Resumo: A emissão de dióxido de carbono (CO2) na atmosfera, quando realizada em larga escala, é considerada como a mais séria causa de problemas ambientais a nível mundial. Devido à atual conscientização mundial em torno do assunto, as indústrias responsáveis estão reduzindo a emissão mediante a captura do gás, normalmente realizada através da absorção do poluente em solventes específicos. Os equipamentos mais comuns, que permitem o contato entre o gás e o solvente, são as colunas de borbulhamento, spray ou recheio. Porém, seu uso apresenta desvantagens que comprometem sua operação, tais como, formação de espuma e dispersão das fases. Frente às desvantagens existentes nos equipamentos convencionais, foram desenvolvidos os módulos de membrana, considerados equipamentos mais adequados para o contato e captura do CO2 pelos solventes. Devido à ausência de trabalhos em condições operacionais mais realistas utilizando módulos de membrana, o presente estudo buscou realizar a modelagem e simulação do processo de absorção de CO2 em módulos de membrana, utilizando como solventes o 2-amino-2-metil-1-propanol (AMP), dietanolamina (DEA) e metildietanolamina (MDEA). A modelagem matemática foi concebida através da adaptação das equações de balanço de massa, capazes de representar numericamente o processo em estudo. Com a intenção de resolver numericamente as equações foi aplicado o método das diferenças finitas de Crank-Nicholson, por fim, buscou-se a implementação de um algoritmo computacional, baseado em linguagem Fortran, para resolver o problema e simular o processo de absorção química de CO2 em módulos de membrana. Inicialmente as simulações foram conduzidas com o intuito de avaliar a estabilidade do método numérico adotado, quanto ao processo em estudo. Após a constatação da estabilidade do método proposto, foi conduzido um estudo para determinar a quantidade ideal de pontos a serem utilizados na discretização. Os resultados obtidos através da simulação tem um comportamento condizente com valores previstos pela teoria. Finalmente, o processo de absorção foi simulado utilizando AMP, DEA e MDEA, onde se verificou que as maiores taxas de absorção de CO2 foram obtidas com o uso de AMP como solvente reativo / Abstract: The emission of carbon dioxide (CO2), when performed on a large scale, is considered the most serious cause of environmental problems worldwide. Due to the current global awareness around the subject, the industries are responsible for reducing emissions by capturing the gas, usually performed by absorption of the pollutant by specific solvents. The most common equipment, which allow contact between gas and solvent are the bubble, spray or fixed bed columns. However, its use has disadvantages that undermine its operation, such as foam formation and phase dispersion. Due the disadvantages existing in conventional equipment, were developed membrane modules, considered the most appropriate equipment for the contact and capture of CO2 by solvents. Due to lack of work in more realistic operating conditions using membrane modules, this study sought to do the modeling and simulation of the process of absorption of CO2 in membrane modules, using the solvent as 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA) and metildietanolamina (MDEA). The mathematical model was designed by adjusting the balance equations of mass, capable to represent numerically the process under study. To solve numerically the equations was applied the method of finite difference Crank-Nicholson, finally, we sought to implement an algorithm based on Fortran, to solve the problem and simulate the process of chemical absorption of CO2 into modules membrane. Initially the simulations were conducted in order to assess the stability of the numerical method adopted. After verifying the stability of the proposed method, we designed a study to determine the ideal amount of points to be used in the discretization. Soon after, the validity of the simulator was verified by comparing its results with values predicted by theory. Finally, the absorption process was simulated using AMP, DEA and MDEA, and the highest rates of CO2 absorption were calculated, with the use of AMP as a reactive solvent / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

Orientador: Hugo Enrique Hernandez Figueroa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T08:31:54Z (GMT). No. of bitstreams: 1 Ambrosio_LeonardoAndre_M.pdf: 2415252 bytes, checksum: c4357386bcd33e0676d894544a47c85e (MD5) Previous issue date: 2005 / Resumo: Este trabalho apresenta um modelo numérico baseado no método das diferenças finitas no domínio do tempo, com objetivo de analisar as características da taxa de absorção específica, SAR, na cabeça humana, mediante um modelamento quiral das equações de Maxwell. A formulação é expressa em termos dos campos polarizados elétrico e magnético, permitindo investigar possíveis variações de SAR na cabeça humana, para diferentes valores de quiralidade, através de algoritmos simples. Tais algoritmos tornam possíveis a análise das diversas características da SAR em estruturas bidimensionais, representando secções transversais da cabeça humana, discretizada em seus tecidos de volumes significativos. Uma verificação foi feita calculando se a estabilidade numérica e simulando uma fonte pontual em um meio quiral. As influências da impedância equivalente da antena e da distância entre a antena e a cabeça humana foram investigadas, para diferentes valores quirais, bem como é feita a análise da SAR local média e sua variação percentual para os valores quirais escolhidos. Cinco cortes transversais foram analisados, com o objetivo de verificar características e comportamentos globais de SAR, evitando assim que variações locais fossem assumidas como um efeito global / Abstract: This work shows a numerical model based on the finite-difference time-domain method, with the aim of analysing the characteristics of the Specific Absorption Rate, SAR, in a human-head, through a quiral modeling of Mawell¿s equations. The formulation is expressed in terms of the electric and magnetic wave-fields, allowing to investigate possible changes in SAR, inside the human head, for different values of chirality, using simple algorithms. Such algorithms, make the analysis of the several characteristics of SAR in bidimensional structures representing the transversal layers of the human head, discretized in its tissues possessing significant volumes. A verification was made by calculating the numerical punctual stability and by simulating a punctual source in a chiral medium. The influences of the equivalent impedances of the antenna and of the distance between the antenna and the human head are analysed, for different chiral values, as well as an analysis of the average local SAR and its percentual variation for chosen chiral values. Five transversal layers were analysed, with the aim of verifying global characteristics and behaviors of SAR, avoiding that local variations were assumed as a global effect / Mestrado / Telecomunicações / Mestre em Engenharia Elétrica

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Orientador: Joerg Schleicher / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-08T08:06:07Z (GMT). No. of bitstreams: 1 Carvalho_RafaelAleixode_M.pdf: 679174 bytes, checksum: 087a9c376b3ab246bf6fe8cd05ae5d41 (MD5) Previous issue date: 2007 / Resumo: As equações da onda imagem para os problemas de remigração na profundidade eno tempo em meios elipticamente anisotrópicos são equações diferenciais parciais de segunda ordem similares a equação da onda acústica. A variável de propagação é a velocidade vertical ou a elipticidade do meio. Essas equações são deduzidas a partir das propriedades cinemáticas da remigração em meios anisotrópicos. O objetivo é propiciar a construção de imagens do subsolo que correspondam a diferentes velocidades verticais e/ou diferentes graus de anisotropia do meio diretamente de uma imagem migrada. ?Painéis de anisotropia? podem ser obtidos de maneira completamente análoga aos painéis de velocidade para a análise de velocidade de migração. Um exemplo numérico mostra a validade desta teoria / Abstract: The image-wave equations for the problems of depth and time remigration in elliptically anisotropic media are second-order partial differential equations similar to the acoustic wave equation. The propagation variable is the vertical velocity or the medium ellipticity. These differential equations are derived from the kinematic properties of anisotropic remigration. The objective is to enable the construction of subsurface images that correspond to different vertical velocity and/or different degrees of medium anisotropy directly from a single migrated image. In this way, ?anisotropy panels? can be obtained in a completely analogous way to velocity panels for a migration velocity analysis. A simple numerical example demonstrates the validity of the theory / Mestrado / Mestre em Matemática Aplicada

Submitted by Almir Azevedo (barbio1313@gmail.com) on 2014-05-09T16:42:31Z No. of bitstreams: 0 / Made available in DSpace on 2014-05-09T16:42:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2013 / Empregando a equação de difusão de nêutrons em estado estacionário multidimensional para simular o fluxo de nêutrons em reatores refrigerados água, e fazendo uso do Método de Diferenças Finitas, o presente trabalho tem por objetivo apresentar um estudo sobre o comportamento da distribuição de potência num reator tipo PWR, considerando a intensidade e a migração dos picos de potência à medida que ocorre a inserção das barras de controle no núcleo. Além disso, tomando como ponto de partida a distribuição axial de potência ao longo da vareta de maior fluxo de calor, realiza-se a análise térmica dessa vareta e do canal refrigerante associado. Para tal é empregado o código Fuel_Rod_3D, que usa o Método dos Elementos Finitos para modelar uma vareta combustível e seu canal refrigerante, possibilitando a simulação do comportamento termohidráulico de uma única vareta discretizada em três dimensões, considerando o fluxo de calor a partir do interior da pastilha combustível, passando pelo "gap" e pelo revestimento até alcançar o fluido refrigerante / This Work aims to present a study about the power distribution behavior in a PWR type reactor, considering both intensity and migration of power peaks due to insertion of control rods into the core. Employing the multidimensional steady-state neutron diffusion equation in order to simulate the neutron flux, and using the Finite Difference Method. Furthermore, based on the axial power distribution on the largest heat flux rod, is carried out thermal analysis of this rod and associated coolant channel. For this purpose is employed the Fuel_Rod_3D code, it uses the Finite Element Method to model the fuel rod and the associated coolant channel, allowing the thermohydraulics simulation of a single rod discretized in three dimensions, considering the heat flux from the pellet, crossing the gap and the cladding until it reaches the coolant.