O objetivo deste trabalho é o estudo de métodos multigrid para a solução de equações elípticas na esfera, discretizadas em malhas esféricas geodésicas icosaédricas. Malhas esféricas geradas a partir de sólidos platônicos receberam crescente atenção ao longo da última década, por serem razoavelmente uniformes e não apresentarem concentração de pontos em torno dos pólos como as tradicionais malhas latitude-longitude. Em especial, as malhas geodésicas icosaédricas (geradas a partir de um icosaedro inscrito na esfera com suas faces projetadas na superfície) têm sido adotadas no desenvolvimento de diversos modelos atmosféricos. Nestes é comum a necessidade de resolução de equações do tipo Poisson como parte do método de integração, motivando o nosso trabalho. Adotamos uma discretização do operador de Laplace baseada em volumes finitos. Para tal escrevemos o laplaciano como o divergente do gradiente. O divergente é discretizado com base nos fluxos nos pontos médios das arestas das células computacionais (com o auxílio do teorema da divergência de Gauss) e no uso de diferenças centradas para aproximar as derivadas nesses pontos médios. Validamos a discretização para o operador de Laplace resolvendo uma equação de Poisson através dos métodos iterativos de Jacobi e Gauss-Seidel. Estes sabidamente não são eficientes computacionalmente, devido ao grande e crescente número de iterações necessárias para atingir a convergência ao refinar a malha. Uma alternativa muito eficiente para a resolução de equações elípticas é a métodologia multigrid. Investigamos alguns métodos multigrid propostos na literatura para a solução destas equações na malha esférica geodésica icosaédrica. A partir desse estudo, utilizando também como referência a Análise Local de Fourier para a equação de Poisson em malhas hexagonais uniformes, como uma aproximação para malhas geodésicas icosaédricas, escolhemos um algoritmo multigrid para implementação. Testamos algumas opções para as componentes do esquema multigrid. Obtivemos taxas de convergência muito boas com V(1,1) ciclos com relaxação por Gauss-Seidel, restrição full weighting e interpolação linear. / This work is dedicated to the numerical solution of elliptic equations on the sphere, discretized on geodesic icosahedral grids. Spherical meshes generated from projections of platonic solids received considerable attention in the last decade, once they are almost isotropic and do not present a concentration of grid points around the poles, as traditional latitude-longitude grids. In particular, the geodesic icosahedral spherical grids have been adopted in the development of several atmospheric models. In these models, the necessity to solve Poisson type equations is very common, providing a motivation for our present work. We have employed a discretization of the Laplace operator based on finite volumes. We write the Laplacian as the divergent of the gradient operator and use Gauss theorem to derive the discretization of the operator. We integrate the fluxes along the cell borders and approximate them through finite-differences. We first validated the discretization solving Poisson\'s equation with a simple (and very innefficient) Jacobi-Relaxation and Gauss-Seidel. We then investigated the use of multigrid type schemes for the solution of this equation. We have analysed some schemes proposed in the literature, also using an idealized Local Fourier Analysis on hexagonal (planar) grids to estimate the behaviour of the schemes on the icosaedral grids. We have implemented and tested a multigrid method, comparing the performance with different relaxation schemes and transfer operators. We have obtained a very efficient method employing V(1,1) cycles with Gauss-Seidel relaxation, and full-weighting and linear interpolation as transfer-operators.

Energy poverty and lack of access to electricity is a global problem which is recognised in the sustainable development goal 7. Today 1.2 billion people live without access to electricity and most of them are situated in Sub-Saharan Africa where biomass still constitutes the main source of energy. Rural areas are unproportionally affected by this throughout SSA since grid-extension has been slow and most rural dwellers are not connected to any form of electricity grid. Extending the grid to more isolated rural areas may however be economically and politically infeasible which is why off-grid solutions is an attractive solution to close the energy poverty gap. Off-grid solar energy has during recent years been increasingly promoted as viable solution to provide clean, affordable and accessible energy to rural households in SSA. While there is extensive research available on the economic feasibility and socioeconomic impacts of off-grid solar energy, there has been limited research with explicit focus on how livelihoods of rural households in SSA have been impacted from a sustainable livelihood perspective. This case study on Tanzania argues that the sustainable livelihoods perspective is crucial in getting a holistic understanding of how off-grid solar energy has impacted rural households in SSA. Through qualitative interviews with a number of households, businesses and social services in three rural villages located in the Tanga region, this study found that off-grid solar energy overall seemed to have a positive impact on the communities and the livelihoods of individual households. However, some concerns are also raised with the sustainability of off-grid solar energy. While it has great recognised potential and direct impact, some key challenges were identified as issue of energy security for the household and concerns of economic feasibility in the solar energy sector.

Direct numerical simulations, where both the large and small scales in the flow are fully resolved, provide an excellent instrument to validate multiphase flow processes and also further our understanding of it. Three multiphase systems are studied using a finite difference/front-tracking method developed for direct numerical simulations of time-dependent system¬¬s. The purpose of these studies is to demonstrate the benefit in developing accurate sub-grid models that can be coupled with the direct numerical simulations to reduce the computational time. The primary reason to use the models is that the systems under consideration are sufficiently large that resolving the smallest scales is impractical. The processes that are examined are: (1) droplet motion and impact (2) nucleate boiling and (3) convective mass transfer. For droplet impact on solid walls and thin liquid films, the splash characteristics are studied. The collision of a fluid drop with a wall is examined and a multiscale approach is developed to compute the flow in the film between the drop and the wall. By using a semi-analytical model for the flow in the film we capture the evolution of films thinner than the grid spacing reasonably well. In the nucleate boiling simulations, the growth of a single vapor from a nucleation site and its associated dynamics are studied. The challenge here is the accurate representation of the nucleation site and the small-scale motion near the wall. To capture the evaporation of the microlayer left behind as the base of the bubble expands we use a semi-analytical model that is solved concurrently with the rest of the simulations. The heat transfer from the heated wall, the evolution of the bubble size and the departure diameter are evaluated and compared with the existing numerical results. The mass transfer near the interface, without fully resolving the layer by refining the grid is accommodated by using a boundary layer approximation to capture it. The behavior of the concentration profile is taken to be self-similar. A collection of potential profiles is tested and the accuracy of each of these models is compared with the full simulations.

Research efforts on the development of autonomous vehicles date back to the 1920s and recent announcements indicate that those cars are close to becoming commercially available. However, the most successful prototypes that are currently being demonstrated rely on an expensive set of sensors. This study investigates the use of an affordable vision system as a planner for the Robocart, an autonomous golf cart prototype developed by the Wireless Innovation Laboratory at WPI. The proposed approach relies on a stereo vision system composed of a pair of Raspberry Pi computers, each one equipped with a Camera Module. They are connected to a server and their clocks are synchronized using the Precision Time Protocol (PTP). The server uses timestamps to obtain a pair of simultaneously captured images. Images are processed to generate a disparity map using stereo matching and points in this map are reprojected to the 3D world as a point cloud. Then, an occupancy grid is built and used as input for an A* graph search that finds a collision-free path for the robot. Due to the non-holonomic constraints of a car-like robot, a Pure Pursuit algorithm is used as the control method to guide the robot along the computed path. The cameras are also used by a Visual Odometry algorithm that tracks points on a sequence of images to estimate the position and orientation of the vehicle. The algorithms were implemented using the C++ language and the open source library OpenCV. Tests in a controlled environment show promising results and the interfaces between the server and the Robocart have been defined, so that the proposed method can be used on the golf cart as soon as the mechanical systems are fully functional.

The present study utilizes the ultrasonic travel time technique to diagnose grid generated turbulence. Ultrasonic flow metering technology relies on the measurement and computation of small perturbations in the travel time of acoustic ultrasonic waves through the dynamic medium. The statistics of the travel time variations of ultrasonic waves that are caused by turbulence probably affect the performance of ultrasonic flow meters. Motivation for the study stems from the large travel time variations observed in typical ultrasonic flow and circulation meters. Turbulent flow data was collected downstream of a grid introduced in a uniform flow in the wind tunnel using ultrasonic techniques. Grid turbulence is well defined in literature, and is nearly homogeneous and isotropic. The experimental investigation was performed under well-controlled laboratory conditions. The grid mesh sizes varied from 0.25-0.5in, and flow velocities from 0-20m/s. The ultrasonic transducers were of 100 kHz working frequency; and all of the data was collected with them oriented perpendicular to the mean flow. Path lengths were increased from 2-10in; and the data acquisition and control system featured a very high speed data acquisition card with an analog to digital converter that enabled excellent resolution of ultrasonic signals. Experimental data was validated by comparison to other studies. The work aims to investigate the influence of the grid-generated turbulent flow on acoustic wave propagation, in terms of the variance of the travel time. The effect of turbulence on acoustic wave propagation was observed. The experimental data was used to compute average travel times, acoustic travel time variances, and standard deviation amplitude fluctuations. The data was collected in the region estimated to be homogeneous and isotropic. Average travel time data support the assumption that only the large (as compared to the wavelength ) turbulent inhomogeneities influence acoustic wave propagation. Variance data confirm the presence of a non-linear trend in the acoustic travel times with increasing path length. Amplitude fluctuations data confirm a correlation between areas of caustic formation and large amplitude fluctuations.

This work investigates numerically the process of Teflon ablation using a finite-volume discretization, implicit time integration and a domain decomposition method in three-dimensions. The interest in Teflon stems from its use in Pulsed Plasma Thrusters and in thermal protection systems for reentry vehicles. The ablation of Teflon is a complex process that involves phase transition, a receding external boundary where the heat flux is applied, an interface between a crystalline and amorphous (gel) phase and a depolymerization reaction which happens on and beneath the ablating surface. The mathematical model used in this work is based on a two-phase model that accounts for the amorphous and crystalline phases as well as the depolymerization of Teflon in the form of an Arrhenius reaction equation. The model accounts also for temperature-dependent material properties, for unsteady heat inputs and boundary conditions in 3D. The model is implemented in 3D domains of arbitrary geometry with a finite volume discretization on unstructured grids. The numerical solution of the transient reaction-diffusion equation coupled with the Arrhenius-based ablation model advances in time using implicit Crank-Nicolson scheme. For each time step the implicit time advancing is decomposed into multiple sub-problems by a domain decomposition method. Each of the sub-problems is solved in parallel by Newton-Krylov non-linear solver. After each implicit time-advancing step, the rate of ablation and the fraction of depolymerized material are updated explicitly with the Arrhenius-based ablation model. After the computation, the surface of ablation front and the melting surface are recovered from the scalar field of fraction of depolymerized material and the fraction of melted material by post-processing. The code is verified against analytical solutions for the heat diffusion problem and the Stefan problem. The code is validated against experimental data of Teflon ablation. The verification and validation demonstrates the ability of the numerical method in simulating three dimensional ablation of Teflon.

Made available in DSpace on 2015-03-05T13:59:42Z (GMT). No. of bitstreams: 0 Previous issue date: 29 / Hewlett-Packard Brasil Ltda / A implantação e a configuração de aplicações em grades computacionais são tarefas exaustivas e sujeitas a erros, ainda representando elo fraco do ciclo de vida de aplicações desta natureza. Para lidar com o problema, este trabalho propõe AGrADC, uma arquitetura para instanciação sob demanda de aplicações em grades que incorpora características da Computação Autônoma.Esta arquitetura instrumenta o processo de desenvolvimento de aplicações para grades computacionais, oferecendo ferramentas para definir (a) um fluxo de implantação, respeitando pendências entre componentes que compõem a aplicação, (b) parâmentros de configuração e (c) ações a serem executadas diante de situações adversas tais como falhas. O resultado desse processo, materializado na forma de um conjunto de descrições, é repassado a um motor de instanciação, que passa utonomamente conduzir e gerenciar o processo de implantação e configuração / Deployment and configuration of grid computing applications are eshaustive and error-prone tasks, representing a weak link of the lifecycle of grid applications. To adress the problem, this work proposes AGrADC, an arquitecture to instantiate grid applications on demand, which incorporates features from the Autonomic Computing paradigm. This architecture improves the grid applications development process, providing tools to define (a) a deployment flow, respecting dependencies among components that comprise the application, (b) configuration paramenters and (c) actions to be executed when adverse situations like faults arise. The result of this process, materialized in the form of a set of descriptions, is delivered to an istantiation engine, which starts to autonomously conduct and manage the deployment and configuration process.

Medically Unexplained Symptoms (MUS) are bodily symptoms for which no organic cause has been identified, and which result in significant levels of psychological distress and functional impairment. MUS are thought to be highly prevalent in primary care settings, and have considerable costs to society. Despite evidence of overlapping psychological and physical presentations, MUS are not well understood or treated in culture that predominantly views the body through the lenses of dualism and mechanistic reductionism. An alternative 'interactive' view of the body as playing a more dynamic role is elaborated through George Kelly's (1955) Personal Construct Psychology. The author draws upon Lin & Payne's (2014) 'frozen construing' theory, and empirical literature on relationships between identity and MUS, to suggest that for people with MUS, the symptomatic body is distressing because the person is struggling to integrate its meaning with their identity. It is hypothesized that embodied processes, that may actually protect the self (and others who share a construct system with that person) from events which threaten to dramatically alter how the self is construed, are difficult to understand because of their preverbal nature. Hence symptoms, and the body itself, are dissociated from the person's more elaborated verbal self-constructions. Several hypotheses relating to this suggestion were tested using a modified form of the repertory grid technique that was designed to explore construct systems of both mind and body, for self and others. Twenty participants with MUS, recruited from the community, completed the repertory grid interviews and measures of depression, anxiety and symptom severity, which were correlated with relevant repertory grid indices to test hypotheses. Findings indicated that symptom constructs, contrary to expectations, were well integrated into participants' construct systems. The alleviation of psychological distress was significantly associated with increased perceived distance between the self in general and the self when symptoms are worst (a relationship which appeared to be independent of severity of symptoms), providing evidence of a process of dissociation that protected the current self from assimilating the undesirable characteristics that were associated with the symptom. The way in which the self when symptoms are worst is construed appeared to influence levels of distress, with more predictive power than several other indices. The study also found evidence for some participants of hypothesized relationships between desired aspects of the current self and symptoms, that would imply that symptom disappearance would actually threaten a desirable aspect of how the self is construed. Content analysis of these constructs revealed (as predicted) that such desirable aspects of self tended to relate to being responsible and sensitive to the needs of others, and were elaborated through bodily constructs in a way that suggested that they were not well integrated with the primary ways that these participants made sense of their identity. For these particular participants, discrepancies between the ideals that they had for themselves, and how they would like to be seen by others, were associated with increased depression. Several participants were identified whose constructions of self and others were dominated by constructs relating to both mental and physical strength and weakness. These participants appeared to be struggling to find coherent meaning for themselves as the result of symptoms, which were regarded as invalidating a pre-symptom construal of themselves as being 'strong'. There seemed to be a continuum of being a 'body for others' on the one hand, a previously 'strong person' on the other, and a person who is 'strong for others' in the middle. Implications for clinical practice are discussed. Although the findings of the current study are limited by a small sample size, it appears that exploring the meaning of the body in the construction of self helps to elaborate the meaning of the body and symptoms in a verbal, expressible form. This process is likely to be helpful to those who struggle to find meanings for their symptoms both in their own construct systems and in a society that objectifies the body.

We present a novel dimensionally split Cartesian cut cell method to compute inviscid, viscous and turbulent flows around rigid geometries. On a cut cell mesh, the existence of arbitrarily small boundary cells severely restricts the stable time step for an explicit numerical scheme. We solve this `small cell problem' when computing solutions for hyperbolic conservation laws by combining wave speed and geometric information to develop a novel stabilised cut cell flux. The convergence and stability of the developed technique are proved for the one-dimensional linear advection equation, while its multi-dimensional numerical performance is investigated through the computation of solutions to a number of test problems for the linear advection and Euler equations. This work was recently published in the Journal of Computational Physics (Gokhale et al., 2018). Subsequently, we develop the method further to be able to compute solutions for the compressible Navier-Stokes equations. The method is globally second order accurate in the L1 norm, fully conservative, and allows the use of time steps determined by the regular grid spacing. We provide a full description of the three-dimensional implementation of the method and evaluate its numerical performance by computing solutions to a wide range of test problems ranging from the nearly incompressible to the highly compressible flow regimes. This work was recently published in the Journal of Computational Physics (Gokhale et al., 2018). It is the first presentation of a dimensionally split cut cell method for the compressible Navier-Stokes equations in the literature. Finally, we also present an extension of the cut cell method to solve high Reynolds number turbulent automotive flows using a wall-modelled Large Eddy Simulation (WMLES) approach. A full description is provided of the coupling between the (implicit) LES solution and an equilibrium wall function on the cut cell mesh. The combined methodology is used to compute results for the turbulent flow over a square cylinder, and for flow over the SAE Notchback and DrivAer reference automotive geometries. We intend to publish the promising results as part of a future publication, which would be the first assessment of a WMLES Cartesian cut cell approach for computing automotive flows to be presented in the literature.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-26T16:05:56Z No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) / Made available in DSpace on 2015-10-26T16:05:56Z (GMT). No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) Previous issue date: 2015-02 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os sistemas fotovoltaicos conectados à rede tem como finalidade a conversão da energia solar em energia elétrica. No Brasil, recentemente foi dado o primeiro passo efetivo com a publicação pela ANEEL da Resolução Normativa n° 482. Esta resolução, publicada em 17 de abril de 2012, possibilita à um consumidor doméstico e comercial possuir um sistema de microgeração de energia (hidráulica, solar, eólica, biomassa ou cogeração qualificada) conectado à rede elétrica e fazer compensação de energia. Neste trabalho foi instalado em caráter experimental, no Laboratório de Energias Renováveis da Unisinos, um sistema fotovoltaico conectado à rede com uso de um modelo de microinversor, e buscou-se por meio desta instalação e do monitoramento, analisar o comportamento elétrico e energético do sistema. O sistema é composto por um módulo monocristalino LG255S1C de 255 Wp conectado a um microinversor ENPHASE M215 de 215 W. O período de monitoramento foi de 1° de agosto até 20 de dezembro de 2014. Uma central de aquisição de dados Agilent HP 34970A foi empregada para coletar dados de irradiância no plano do gerador fotovoltaico, corrente e tensão na entrada e saída do microinversor, temperatura de uma célula FV no centro do módulo fotovoltaico e temperatura no dissipador do microinversor. Também foi utilizado como medidor o analisador de energia Fluke 43B, que coleta os dados de potência ativa, potência reativa e potência aparente injetada na rede elétrica pelo sistema. Índices de qualidade de energia como a distorção harmônica total de corrente e fator de deslocamento também foram medidos. A eficiência média diária máxima, considerando a incerteza, medida no microinversor empregado foi de 95,18 % e é semelhante aos valores de eficiência média diária dos microinversores de primeira e segunda geração. O sistema fotovoltaico monitorado com o uso do microinversor atingiu o valor máximo de desempenho global de 0,93. A produção de energia máxima diária em corrente alternada foi de 1,49 kWh. Estima-se, levando em consideração este valor, que a produção mensal pode ser de até 44,7 kWh. Isto significa uma redução de 58 % no consumo de energia em uma residência, levando em consideração o custo de disponibilidade e o sistema instalado em uma residência com consumo médio mensal da região nordeste que é de 120 kWh. / Photovoltaic grid-connected systems aims the conversion of solar energy into electrical energy. In Brazil, was recently given the first effective step with the publication by ANEEL Normative Resolution No. 482. This resolution published on 17 th April, 2012, enables domestic and commercial consumers have an energy microgeneration system (hydro, solar, wind, biomass or qualified cogeneration) connected to mains power and make compensation. In this work was mounted on an experimental character, in the Renewable Energy Laboratory of Unisinos, a photovoltaic grid-connected system that uses a microinverter model, and through this installation and monitoring, analyse the electrical and energetical behavior of the system. The system consists of a 255 Wp LG255S1C monocrystalline module, connected to a 215 W ENPHASE M215 microinverter. The monitoring period was 1 st August to 20 th December, 2014. A central acquisition of Agilent HP 34970A data was used to collect data irradiance in the plane of the PV array, current and voltage at the input and output of microinverter, temperature of a PV cell in the center of the PV module and the microinverter sink. It was also used as a measuring the energy analyzer Fluke 43B, which collects the data of active power, reactive power and apparent power injected into the grid by the system. Power quality indices as the total harmonic current distortion and displacement factor were also measured. The maximum daily average efficiency, considering the uncertainty, measured on the employed microinverter was 95.18 % and is similar than the daily average efficiency values of microinverters of first and second generation. The photovoltaic system monitored using the microinverter peaked overall performance of 0.93. The production maximum daily energy into alternating current was 1.49 kWh. It is estimated taking into account the value that the monthly production can achieved 44.7 kWh. This means a reduction of 58 % in the consumption of a residence considering the availability cost and that the system is installed in a residence with the northest comsumption whose the average monthly consumption is 120.00 kWh.