This work deals with the one-dimensional Stefan problem with a general time- dependent boundary condition at the fixed boundary. The solution will be obtained using a discrete random walk method and the results will be compared qualitatively with analytical- and finite difference method solutions. A critical part has been to model the moving boundary with the random walk method. The results show that the random walk method is competitive in relation to the finite difference method and has its advantages in generality and low effort to implement. The finite difference method has, on the other hand, higher accuracy for the same computational time with the here chosen step lengths. For the random walk method to increase the accuracy, longer execution times are required, but since the method is generally easily adapted for parallel computing, it is possible to speed up. Regarding applications for the Stefan problem, there are a large range of examples such as climate models, the diffusion of lithium-ions in lithium-ion batteries and modelling steam chambers for oil extraction using steam assisted gravity drainage.

Modèle monodimensionnel de type Piston-Dispersion. Le terme de dispersion axiale englobe alors toutes les imperfections de l'écoulement : injection des fluides non homogène dans l’espace et étalée dans le temps, effet de parois, et enfin volumes morts derrière les obstacles noyés dans le tamis (poutres, conduites...) dans le cas des Lits Mobiles Simulés. Cette représentation, quoique très simpliste, s'avère généralement suffisante tant que l’étalement des fronts de concentration est d'abord induit par les limitations au transfert externe, interne (macro/microporeux) et par la thermodynamique du système. Par contre, lorsque l’adsorbant employé présente d’excellentes performances de transfert, une approche aussi simple s'avère extrêmement risquée. En effet, les phénomènes dispersifs associés à l’adsorbant (transfert et thermodynamique) et à l’hydrodynamique ont des contributions de même ordre de grandeur sur la dispersion des fronts de concentration. Dans ce cas, une description plus réaliste de l'écoulement est requise afin de mieux appréhender son effet sur les performances de séparation.Dans ce contexte, l’objectif de ce projet de thèse est de mettre en place une méthodologie pour prendre en compte ces phénomènes hydrodynamiques lors de l’extrapolation d’un procédé de séparation par adsorption. Pour cela, nous proposons une étude du couplage entre les phénomènes hydrodynamiques et le phénomène d’adsorption. / Hydrodynamics inside industrial Simulated Moving Bed (SMB) adsorption columns can be complex due to the presence of internal distribution devices, free flow chambers and heterogeneous injections. These have to be taken into account in SMB numerical models to scale-up purposes. In the present thesis, a CFD approach is adopted as an intermediate step to develop a 1D model simple enough to be used for cyclic SMB simulations while being able to represent realistic hydrodynamics. This model results from the interpretation of the moments of the fluid age distribution, transported by CFD according to the method developed by Liu and Tilton (2010) that allows to estimate the degree of mixing (Liu, 2011) of the adsorption columns. The resulting 1D model consists in the two examples provided by Zwietering (1959) of a completely segregated system and a maximum mixedness system. This model is able to reproduce the residence time distribution of the CFD model of an adsorption column, while being representative of the internal flow patterns. This results in a good representation of the coupling of adsorption and hydrodynamics by the 1D model. When integrated in a SMB simulator and compared to the traditionally used dispersed plug flow model, the new 1D model demonstrates that for most of the adsorption column geometries considered a detailed hydrodynamic description is mandatory. Such detailed hydrodynamic description is even more important when employing adsorbents with better mass transfer performances than those currently used for the p-xylene purification, which is expected in the upcoming years.

Simulações de escoamentos multifásicos são de grande interesse em aplicações práticas na indústria, em particular na indústria petrolífera, entre outras. Vários processos dependem do entendimento físico de escoamentos envolvendo iteração com partículas, sedimentação e separação de fluidos. Dos muitos métodos existentes para a simulação dos processos acima descritos, há um crescente interesse no aumento de precisão, o que levou ao desenvolvimento de estratégias que utilizam esquemas de elementos finitos discretizados em malhas dinâmicas e adaptativas, usando uma formulação ALE (do inglês, Arbitrary Lagrangian-Eulerian), juntamente com uma representação geométrica da interface. Neste sentido, este trabalho tem o objetivo de estudar e implementar estratégias robustas de controle e adaptação de malhas, em situações onde a malha dinâmica é sujeita a grandes deformações. Uma biblioteca de algoritmos e rotinas foi então desenvolvida para este fim, implementando técnicas de controle e otimização da qualidade dos elementos da malha, técnicas de adaptação da interface entre fluidos com esquemas de conservação de massa, técnicas de mudanças topológicas e preservação de propriedades materiais, além de uma comunicação facilitada destas rotinas com códigos de simulação numérica de escoamentos multifásicos existentes / Multiphase flow simulations are of great interest in practical applications, particularly in the oil industry. Several processes depend on understanding physical aspects of flows with particle interaction, sedimentation and fluid separation. Among the several existing methods to simulate the processes described above, theres a growing interest in achieving higher precision, which led to the development of strategies that use finite element discretization in adaptive, dynamic meshes, using the ALE formatulation along with a geometrical representation of the interface. In this context, this thesis aims to study and implement robust strategies for mesh adaptation, for cases where the dynamic mesh is subject to large deformations. A library of routines and algorithms was developed, implementing mesh elements control and quality optimization techniques, fluid interface adaptation techniques with a mass conservation scheme, topological modifications and material properties preservation techniques, and also a decoupled, simplified communication between these routines with existing multiphase flow numerical simulation code

O seguinte trabalho procura estudar problemas de fronteira móvel, conhecidos por problemas de Stefan, bem como aproximar suas soluções. Aplicações de problemas de Stefan encontram-se, por exemplo, na física termal de mudança de estados, presente em diversos fenômenos físicos e químicos naturais e na indústria. Devido a não-linearidade, a maior parte destes problemas não possuem solução analítica conhecida e uma técnica comum para se aproximar soluções é o método de balanceamento integral, inicialmente estudado por Goodman (1958). Este método e suas variações propõem perfis de aproximação no domínio da solução e resolvem uma versão integral da equação diferencial. O problema se resume a resolver uma equação diferencial ordinária no tempo envolvendo a profundidade de penetração do calor e o perfil de aproximação proposto. O trabalho estuda tais métodos para problemas termais clássicos em primeiro lugar, de modo que a extensão para problemas de Stefan seja natural. Refinamentos são apresentados, bem como uma técnica de subdivisão do espaço que resulta num esquema numérico. A técnica de imobilização e fronteira é desenvolvida e aplicada em diversos momentos, a fim de simplificar a utilização dos métodos integrais. / The current work aims to study moving boundary problems, known as Stefan problems, and approximate their solutions. Applications of Stefan problems are found in situations where there is change of physical state, present in several natural and industrial physical and chemical phenomena. Due to their inherent nonlinearity, most of these problems have no known analytic solution and a common technique to approximate solutions is the heat balance integral method, originally studied by Goodman (1958). This method and its variations propose an approximating profile and solve an integral version of the differential equation. The problem is reduced to solving an ordinary differential equation in time involving the depth of heat penetration and the proposed profile. This work studies such classic methods to thermal problems first, in a way that the extension to Stefan problems is natural. Refinements are presented, as well as a technique of subdividing the space domain which results in a numerical scheme. The technique of boundary immobilization is developed and applied at different times in order to simplify the use of these methods.

O declínio das capacidades motoras é inevitável ao longo do envelhecimento, porém, a curva desse declínio pode ser reduzida quando o exercício físico é utilizado como forma de intervenção. Em geral, envolvem a repetição de movimentos cíclicos e de baixa complexidade, com o objetivo de aumentar a eficiência fisiológica dos praticantes. Entretanto, há evidências que comprovam a plasticidade cerebral de animais, inclusive em animais idosos, que foram expostos a ambientes e experiências enriquecedoras. Estudos com humanos permitiram observar que os efeitos da aprendizagem de habilidades motoras estão associados a mudanças não apenas comportamentais, mas também nas estruturas cerebrais. Os resultados desses estudos têm sido discutidos em termos do esforço cognitivo relativo ao processo de aprendizagem e, em especial, das habilidades motoras complexas. Neste sentido, este estudo pretendeu verificar os efeitos de dois programas de exercícios físicos nas estruturas cerebrais e capacidades motoras de idosas. Mais especificamente, em uma situação experimental de ensino, foram aplicados dois programas de exercícios físicos, um voltado para a prática de habilidades motoras complexas e o outro voltado especificamente para a prática de movimentos de baixa complexidade (simples). Foram avaliados os efeitos desses programas sobre as estruturas cerebrais, por meio de ressonância magnética cerebral e, também, sobre as capacidades motoras, por meio de testes de capacidade funcional. Participaram do estudo 40 mulheres com idade média de 66,56 anos. Foram formados 3 grupos: Condicionamento Físico, Jogos e Controle. O programa de exercícios teve a duração de 14 semanas, com 3 sessões semanais. As avaliações ocorreram no início e no final dos programas nos 3 grupos. Os resultados revelaram que o grupo controle não apresentou mudanças significantes nas capacidades motoras nem em relação às estruturas cerebrais. O grupo Condicionamento Físico obteve melhora significante no desempenho dos testes de força de membros superiores, flexibilidade de membros inferiores e agilidade/equilíbrio dinâmico. Já o grupo Jogos demonstrou aumento significante no desempenho dos testes de flexibilidade de membros inferiores, agilidade/equilíbrio dinâmico e equilíbrio pé direito olho aberto. Entretanto, nenhum dos grupos, inclusive daqueles que praticaram exercícios físicos, apresentou mudanças significantes no que diz respeito às estruturas cerebrais. Concluiu-se que os programas de exercícios físicos foram parcialmente efetivos para a melhora das capacidades motoras, mas não promoveram alterações na estrutura cerebral / Although the diminishing in the motor abilities is inevitable along the aging process, the tendency of this decrease may be reduced when physical exercise is used as an intervention. These interventions, in general, include the repetition of movements which are cyclical and have low complexity, aiming to increase physiological efficiency of the practitioners. There are evidences of animal\'s brain plasticity, including elderly animals, which have been exposed to enriching environments and experiences. Studies with human beings have lead to the conclusion that the motor learning effects are associated to changes not only behavioral, but also in brain structure. The results of these studies have been discussed in terms of the cognitive effort related to the learning process and, specially, to the complex motor skills. Therefore this study aimed to verify the effects of two programs of physical exercises on the brain structure and motor capacities of elderly women. Specifically, in an experimental teaching condition, there have been developed two physical exercises programs: one oriented to the practice of complex motor skills; and the other directed to the practice of low complexity movements (simple). The effects of these programs in the brain structure have been evaluated through cerebral magnetic resonance and, also, in the motor capacities through functional capacities tests. Forty women with mean age of 66.56 years old have taken part of the study. There were three groups: Fitness, Games and Control. The exercises programs were developed during 14 weeks, with 3 sessions per week. The evaluations were in the beginning and in the end of the program. Results showed that the Control group has neither presented changes in their motor capacities nor related to their brain structures. The Fitness group significantly improved its performance in the tests for upper body strength, flexibility of the limbs and agility/ dynamic balance. The Games group demonstrated significant increase in the test for flexibility of the limbs, agility/dynamic balance and balance right foot open eye. Even though, none of the groups, including those which have practiced physical exercises, presented changes in their brain structures. In conclusion, the physical exercise programs have been partially effective for the improvement of the motor capacities, but have not brought changes in the brain structure

The aim of this study is to examine how notions of ageing, old age, life course and a good life is related to old peoples understanding of and their actions about their living situation. Notions, ideals and practices of home, ageing and old age are studied with ethnographic methods and analyzed with Sara Ahmeds phenomenological and queer theoretical tools ”the straight line” and ”orientation” to show how they relate to each other. The empirical material is based on 13 qualitative interviews with 15 persons who are more than 65 years old and live in different housing types in Sweden. The informants understanding of ageing and old age is one focus of the study, and the decision to move or not – and to where – is another. Even the experience of moving to a new place and the experience of elderly care in their home is described. The result shows that the decision of where to live and if, or when, it is necessary to move is often characterized by ambivalence during old age. It is related to two opposite norms about how to act during old age. Old people are expected to move as a preparation for negative changes in health, which follows a normative life course. At the same time, old people are expected to counteract their ageing by trying to stay in their home as long as possible. The event to move during old age can therefore be seen as a part in the process of becoming old. The opposite norms which old people have to relate to makes it difficult for old people to stay oriented. The study also shows that the feeling of home, the experiance of becoming old and orientation to norms affect each other.

<div>Unmanned Aerial Vehicle (UAV) technology is being increasingly used in a wide variety of applications ranging from remote sensing, to delivery, to security. As the number of UAVs increases, there is a growing need for UAV to UAV detection and tracking systems for both collision avoidance and coordination. Among possible solutions, autonamous “see-and-avoid” systems based on low-cost high-resolution video cameras offer the important advantages of light-weight and low power sensors. However, in order to be effective, camera based “see-and-avoid” systems will require sensitive, robust, and computationally efficient algorithms for UAV to UAV detect and tracking (U2U-D&T) from a moving camera.</div><div><br></div><div>In this thesis, we propose a general architecture for a highly accurate and computationally efficient U2U-D&T algorithms for detecting UAVs from a camera mounted on a moving UAV platform. The thesis contains three studies of U2U-D&T algorithms.<br></div><div><br></div><div>In the first study, we present a new approach to detect and track other UAVs from a single camera in our own UAV. Given the sequence of video frames, we estimate the background motion via perspective transformation model and then identify distinctive points in the background subtracted image to detect moving objects. We find spatio-temporal characteristics of each moving object through optical flow matching and then classify our targets which have very different motion compared with background. We also perform tracking based on Kalman filter to enforce the temporal consistency on our detection. The algorithm is tested on real videos from UAVs and results show that it is effective to detect and track small UAVs with limited computing resources.<br></div><div><br></div><div>In the second study, we present a new approach to detect and track UAVs from a single camera mounted on a different UAV. Initially, we estimate background motions via a perspective transformation model and then identify moving object candidates in the background subtracted image through deep learning classifier trained on manually labeled datasets. For each moving object candidates, we find spatio-temporal traits through optical flow matching and then prune them based on their motion patterns compared with the background. Kalman filter is applied on pruned moving objects to improve temporal consistency among the candidate detections. The algorithm was validated on video datasets taken from a UAV. Results demonstrate that our algorithm can effectively detect and track small UAVs with limited computing resources. </div><div><br></div><div>The system in the third study is based on a computationally efficient pipeline consisting of moving object detection from a motion stabilized image, classification with a hybrid neural network, followed by Kalmann tracking. The algorithm is validated using video data collected from multiple fixed-wing UAVs that is manually ground-truthed and publicly available. Results indicate that the proposed algorithm can be implemented on practical hardware and robustly achieves highly accurate detection and tracking of even distant and faint UAVs.<br></div>

Durante as últimas décadas, têm sido realizados vários estudos sobre a aplicação de veículos suspensos como em teleféricos, bondinhos, linhas de transporte e/ou montagem em indústrias, e robôs para finalidades diversas. Como veículos suspensos possuem comportamento de pêndulo, estão suscetíveis as ações de forças externas que geram oscilações e balanços indesejados no veículo que podem comprometer sua função e segurança. Um levantamento bibliográfico mostrou a deficiência de estudos de sistemas que mantenham a estabilidade física de veículos suspensos. Usando conceitos de conservação de energia e quantidade de movimento foi concebida a ideia de desmembrar o corpo do veículo suspenso em duas partes, uma massa fixa e uma massa móvel de atuação e estabilização da estrutura do veículo; dessa forma fazendo uso apenas de componentes internos ao veículo, uma vez que em sistemas suspensos é grande a dificuldade de aplicação de forças externas para correção de posicionamento. Neste trabalho foi desenvolvido um sistema ativo de autoestabilização para veículos suspensos capaz de amenizar os efeitos de forças externas que possam comprometer a atividade desempenhada pelo veículo. Para a autoestabilização foi montado um sistema de controle em malha fechada com sensor de detecção de inclinação (posição) e atuador com motor de corrente contínua para deslocar uma massa móvel dentro do robô suspenso, acionados por um microcontrolador embarcado. A eficiência do sistema foi comprovada com a montagem de um protótipo, onde uma programação baseada em controle proporcional e derivativo foi suficiente para garantir uma eficiente e rápida estabilização no robô quando sujeito a forças externas como atuação de ventos, por exemplo. / During the last decades, many researches and studies have been done about suspended vehicles such as chair lifts, cable cars, carrying and assemblies of parts in the industry, etc. Suspended vehicles behave like a pendulum and they are susceptible to the action of external forces which cause oscillations and unwanted swing at the vehicle that may affect function and security of the vehicle. For several applications it is important to keep the physical stability of suspended vehicles (or part of them), such as in autonomous robots for inspection. In suspended systems it is very difficult to apply external forces to correct its position due the swing; so, it is proposed a new stabilizing system for suspended vehicles based on the conservation of energy and quantity of motion. Using only internal components of the suspended vehicle, the mass of the system was separated in two parts: an active mobile part that stabilizes a fixed part such as the structure of the vehicle. In this work, it is described an active system for swing control on suspended vehicles, able to soften the effects of external forces that can dangerously damage the performance of the vehicle. An autonomous off-board microcontroller with feed-back program was assembled to stabilize the structure of the vehicle by using an inclination sensor attached to it. A DC motor is used to move the mobile part of the suspended vehicle to correct the equilibrium of the vehicles structure. The microcontroller program based on proportional-derivative control system was implemented and tests were performed on a prototype vehicle. A good performance of the system was obtained with an efficient and fast stabilization of the prototype structure under the action of external forces, such as wind forces.

In this thesis, a numerical method is developed for simulating non-isothermal multiphase flows, which are important in many technical applications such as crystal growth and welding. The method is based on the arbitrary Lagrangian Eulerian method of Li (2013). The interface is represented explicitly by mesh lines, and is tracked by an adaptive moving unstructured mesh. The $P2-P1d$ finite element method (FEM) is used for discretisation and the incompressible Navier-Stokes equations are solved by the uzawa method. Firstly, a thorough study is presented on the method's capability in numerically representing the force balance condition on the interface. An inaccurate representation of this condition induces the non-physical spurious currents, which degrade the simulation accuracy especially when the viscous damping is weak (small Ohnesorge number, $Oh$). For the example of a circular/spherical droplet, the interfacial tension and the associated pressure jump are exactly balanced numerically and thus the static Laplace solution exists in our method. The stability of this solution is examined numerically. The amplitude of the dimensionless spurious currents is found to be around $10^{−15}$ for $Oh \geq 10^{−3} $. Another benchmark test is the axisymmetric oscillation of a freesurface droplet/bubble. The simulation results are in good agreement with the analytical solution for $Oh = 10^{−3}$. This is by far the first successful simulation of droplet/bubble oscillation with such weak viscous damping and it demonstrates the ability of our method in simulating flows with strong capillary forces. Secondly, a numerical treatment of interface topology changes is incorporated into our method for studying problems with interface breakup. Thanks to the adaptive mesh generator, the thin region between the interface boundary and another boundary consists of one layer of elements. The interface topology change is performed once the minimum distance between the two boundaries falls below a pre-set scale $l_{breakup}$ . The numerical implementation is verified through two different examples: dripping faucet and droplet coalescence. Remarkably good agreement has been obtained with the experimental results. The simulation of the low Oh dripping problem shows both the accuracy and robustness of our method. The simulation of droplet coalescence demonstrates the great advantage of our method in solving problems with a large disparity in length scales. Finally, an FEM solver for temperature is developed and the non-isothermal effects are included in our method for the purpose of simulating non-isothermal multiphase flows. The modified method is validated to be accurate through three benchmark examples: natural convection in a cavity, thermocapillary convection of two layers, and droplet migration subject to a temperature gradient. Our method is then applied to investigate the liquid bridge breakup with thermocapillary effect. The non-isothermal liquid bridge breakup in the viscous and inertial regimes are studied. It has been found that the inertial regime breakup exhibits different pinchoff shapes as the Capillary number increases, and that the viscous regime breakup is accelerated by the thermocapillary motion.

Este trabalho teve como objetivo avaliar o uso do método das médias móveis na atomização de cádmio, crômio e chumbo utilizando filamento de tungstênio de 150 W (OSRAM) como atomizador eletrotérmico. Realizou-se um estudo sistemático da influência da altura de observação, da temperatura e taxa de aquecimento na atomização dos analitos e a viabilidade do uso do método das médias móveis no tratamento dos sinais transientes gerados na atomização. O estudo da influência da altura de observação foi realizado posicionado-se o filamento no centro (0 mm), 1 e 2 mm abaixo do feixe de radiação. A influência da temperatura e da taxa de aquecimento foi estudada utilizando temperaturas na etapa de atomização entre 1890 e 2780 °C. O método das médias móveis foi aplicado aos sinais transientes gerados na atomização, com o filamento posicionado no centro (0 mm), 1 e 2 mm e com temperatura de atomização entre 2060 e 2780 °C, utilizando fatores 0, 3, 5, 7 e 9. No estudo da temperatura e da taxa de aquecimento foram aplicadas ddps no software de controle na etapa de atomização entre 4 e 12 V. As soluções usadas no desenvolvimento deste trabalho foram preparadas em meio 0,1 % v/v HNO3. Utilizou-se como gás de proteção a mistura de 90% Ar+10 % H2. Para o cádmio, recomenda-se a utilização da altura de observação de 1 mm, para o chumbo recomenda-se 0 mm e para o crômio a altura recomendada é a de 2 mm. Os estudos comprovaram a dependência dos sinais de absorção atômica em altura de pico com a temperatura e a taxa de aquecimento. O cádmio foi o analito em que a taxa de aquecimento foi a menos crítica para a atomização, enquanto que o crômio foi o mais afetado pela variação da taxa de aquecimento. Não foi observada diferença significativa entre os sinais de cádmio com alturas de observação de 0 e 1 mm. Para o chumbo, a diferença entre os sinais com altura de observação de 0 e 1 mm foi constante em todas as taxas de aquecimento estudadas. A 2 mm a diferença entre os sinais aumentou com o aumento da taxa de aquecimento. Para o crômio, não ocorreu uma diferença significativa entre os sinais nas alturas de 1 e 2 mm com atomização até 2180 °C. Nos três analitos a sensibilidade aumentou com o aumento da taxa de aquecimento. O método das médias móveis permitiu a diminuição da variação dos sinais transientes do branco e do ruído. Para o cádmio, não ocorreu uma melhora no limite de detecção do método com a aplicação das médias móveis em nenhuma condição. Para o chumbo e crômio, ocorreu uma melhora no limite de detecção do método nas alturas de observação de 0 e 1 mm. O limite de detecção instrumental apresentou uma melhora significativa para os três elementos em todas as condições estudadas. / The aim of this paper was to evaluate the use of moving averages of cadmium, chromium and lead transient atomic absorption signals generated by 150 W (OSRAM) tungsten coil electrothermal atomizer. A systematic study dealing with the influence of observation height, temperature and heating rate on atomization was carried through in order to demonstrate the viability of moving averages in the treatment of the transient signals during the atomization step. The influence of observation height was carried out with the tungsten coil in the center (0 mm), at 1 and 2 mm below the radiation beam. The influence of atomization temperature and heating rate were evaluated between 1890 °C (3.3 K.ms-1) and 2780 °C (9,3 K.ms-1). The transient moving averages were obtained by using factors 0, 3, 5, 7 and 9, with the tungsten coil in the center (0 mm), 1 and 2 mm and with atomization between 2060 and 2780 °C. For obtaining different temperatures and heating rates, an appropriate power supply was used by applying 4 to 12 V (40 to 120 W) to the atomizer during atomization and a mixture 90% Ar+10% H2 was used as purge/atomization gas. Blanks and reference solutions were prepared in 0,1% v/v HNO3. Best results for cadmium were obtained at 1 mm. For lead it is recommended 0 mm and for chromium 2 mm. The studies had proven the dependence of peak height absorbance signals with temperature and heating rate. Cadmium was the analyte where the heating rate was to less critical for the atomization, whereas chromium was affected by the variation of the heating rate. Significant differences were not observed between cadmium signals with observation heights of 0 and 1 mm. For lead, the difference between the absorbance signals with observation heights of 0 and 1 mm were constant in all tested heating rates. At 2 mm the difference between signals increased by increasing the heating rates. For chromium, a significant difference was not noticed between peak height absorbance signals at 1 and 2 mm with up to 2180 °C. As expected, sensitivity increased for all three analytes by increasing the heating rate. The moving average is a powerful mathematical treatment for minimizing unpredictable fluctuations of the base line during the chosen time interval for measuring the transient absorbance signals. With the exception of Cd, where no improvements on the method detection limit were noticed, the application of the moving average for the lead and chromium showed 3 to 4 fold improvement in the LDmet at 0 and 1 mm observation heights, respectively. The LDinstr presented a significant improvement (3 to 6 fold) for the three analytes in all studied conditions.