As simulações de escoamentos em torno de geometrias de aplicações industriais (geometrias complexas), como por exemplo configurações de aeronaves com hipersustentadores defletidos, apresentam uma vasta gama de estruturas vorticais (complexidade do escoamento). A importância das interações entre as estruturas é grande para a correta previsão da dinâmica das estruturas vorticais presentes no escoamento, uma vez que estas interações ditam as características do processo de transferência de energia cinética turbulenta. Vale ressaltar que no processo de transferência de energia cinética turbulenta não temos uma única direção e sim a possibilidade de duas direções, que representam o processo de cascata direta ou clássica (a transferência de energia cinética turbulenta se dá das maiores estruturas vorticais para as menores - forward scatter ) e a cascata indireta (a transferência de energia cinética turbulenta que se dá das menores estruturas vorticais para as maiores - backscatter ). O balanço entre estes dois processos, direto e indireto, resulta na dominância do processo direto, ou seja, o processo dominante de transferência de energia se dá das maiores estruturas vorticais para as menores. Entretanto, ambos os processos devem estar presentes na solução numérica, para que esta seja capaz de prever de forma correta a dinâmica (interações entre estruturas vorticais de tamanhos variados) presente no escoamento. Os modelos convencionais utilizados no tratamento da turbulência (ou fechamento da turbulência), sejam do tipo RANS (Reynolds Average Navier Stokes ) ou do tipo LES (Large Eddy Simulation) apresentam limitações teóricas (modelo não é capaz de representar as interações entre todas as escalas presentes no escoamento) e práticas (necessidade de discretização espacial que aumenta significativamente o custo computacional). No caso dos modelos LES a malha nas proximidades de paredes sólidas deveriam ser extremamente refinadas, o que resulta em praticamente resolver todas as escalas, para representar os efeitos da cascata direta (forward scatter ) e da cascata indireta (backscatter ) de energia cinética turbulenta. Isto ocorre em decorrência do caráter dissipativo dos modelos submalha utilizadas nas formulações LES. Por este motivo, o presente trabalho tem por objetivo desenvolver uma metodologia para solução do escoamento turbulento que seja capaz de apresentar os processos de cascata direta e cascata indireta sem a necessidade de malhas extremamente refinadas. Para tanto, iremos utilizar as equações Navier-Stokes escritas em função das flutuações (flutuações resolvidas), sendo esta formulação baseada nos trabalhos de Morris et al. [1997], Labourasse e Sagaut [2002] e Batten et al. [2004b]. As equações são obtidas por meio da divisão dos campos em uma média temporal, flutuações resolvidas e flutuações submalha. Sendo a média temporal, obtida previamente por meio de uma solução RANS do escoamento, que no nosso caso é obtida com o modelo RANS SA-QCR2013 proposto por Mani et al. [2013]. As flutuações resolvidas são o resultado da solução numérica das equações obtidas com a discretização espacial dada pela malha utilizada. Por fim as flutuações submalha são introduzidas via modelo de Billson [2004] (modelo de sintetização ou reconstrução da turbulência). Esta formulação foi aplicada para solução do escoamento em um canal formado por paredes paralelas com Re? = 395 e Re? = 1000. Estes números de Reynolds foram escolhidos por existirem resultados obtidos via DNS ou até mesmo resultados experimentais disponíveis na literatura, os resultados são enconstrados em Moser et al. [1999], del Álamo et al. [2004] e Schultz e Flack [2013]. Os resultados obtidos com o modelo proposto mostraram que a cascata inversa (backscatter ) está presente em todas as regiões da camada limite (subcamada laminar, buffer layer e logarítmica) do canal, onde o pico de transferência ocorre, para os números de Reynolds avaliados, na região da buffer layer. Este comportamento foi observado nos resultados gerados por todas as malhas avaliadas, a diferenças entre as malhas está no refinamento na região próxima às paredes sólidas. O refinamento da malha na direção da altura do canal (normal às paredes sólidas) faz com que o balanço entre as taxas de dissipação de energia cinética turbulenta passe a indicar a dominância da cascata direta no processo de transferência de energia. Nas malhas menos refinadas na região próxima à parede temos o domínio da cascata indireta no processo de transferência de energia cinética turbulenta. A introdução das flutuações submalha via modelo de sintetização da turbulência leva a uma tendência de inverter o domínio da cascata inversa (backscatter ) nas malhas menos refinadas. Os resultados obtidos com a metodologia NLDE com flutuações turbulentas submalha introduzidas por meio de modelo de sintetização turbulenta apresentam boa concordância com os respectivos resultados obtidos via DNS e ou experimentais. / Simulations of flows around industrial geometries (complex geometries), such as configurations of aircraft with deployed high-lift surface, present a wide range of vortical structures (flow complexity). The importance of the interactions between the structures is great for the correct prediction of the dynamics of the vortical structures present in the flow since these interactions dictate the characteristics of the turbulent kinetic energy transfer process. It is noteworthy that in the process of transferring turbulent kinetic energy we do not have a single direction but the possibility of two directions, which represent the direct cascade or classical cascade process (the transfer of turbulent kinetic energy occurs from the large eddy to small eddy - the forward scatter) and the reverse cascade (the transfer of turbulent kinetic energy occurs from small eddy to the large eddy - backscatter). The net balance between these two processes, direct and reverse, results in the predominance of the direct process, that is, the dominant process of energy transfer occurs from the largest eddy to the smaller ones. However, both processes must be present in a numerical solution, so that it is able to predict correctly the dynamics (interactions between vortical structures of varying sizes) present in the flow. The conventional models used in turbulence treatment (or turbulence closure), whether of the RANS (Reynolds Average Navier Stokes) type or the LES (Large Eddy Simulation) type have theoretical limitations (model is not able to represent the interactions between the scales present in the flow) and practices (needs spatial discretization that signifcantly increases the computational cost). In the case of LES models, the mesh close to solid walls should be extremely refined, which results in practically resolving all scales to represent the effects of the forward scatter and the backscatter of turbulent kinetic energy. This is due to the dissipative character of the sub-grid models used in the LES formulations. For this reason, the present research effort aims to develop a methodology for solving turbulent flow, that is able to present both energy transfer process, forward scatter and backscatter without the need of extremely refined meshes. For this, we will use the Navier-Stokes equations written in function of the fluctuations (resolved fluctuations), being this formulation based on the works of Morris et al. [1997], Labourasse e Sagaut [2002] and Batten et al. [2004b]. The equations are obtained by dividing the fields into an average time, resolved fluctuations and sub-grid fluctuations. The time-averaged, obtained previously by means of a RANS solution of the flow, which in our case is obtained with the model RANS SA-QCR2013 proposed by Mani et al. [2013]. The resolved fluctuations are the result of the numerical solution of the equations obtained with the spatial discretization given by the mesh used. Finally, the sub-grid turbulence fluctuations are introduced via the model of Billson [2004] (model for synthesizing or reconstructing turbulence). This formulation was applied to solve of the flow in a channel formed by parallel walls at Re? = 395 and Re? = 1000. The reason to choose those Reynolds number is related to the fact that there are results obtained via DNS or even experimental results available in the literature, one can found those results in Moser et al. [1999], del Álamo et al. [2004] and Schultz e Flack [2013]. The results obtained with the proposed model showed that the backscatter is present in all regions of the boundary layer (lamellar layer, buffer layer, and log-layer) of the channel, where the transfer peak occurs, for the evaluated Reynolds numbers, in the region of the buffer layer. This behavior was observed in the results generated by all meshes evaluated, the differences between the meshes are in the refinement in the region near the solid walls. The refinement of the mesh in the direction of the channel height (normal to the solid walls) causes the balance between the rates of dissipation of turbulent kinetic energy to indicate the dominance of the direct cascade in the energy transfer process. In the less refined meshes in the region near the wall, we have the domain of the indirect cascade in the process of transfer of turbulent kinetic energy. The introduction of the sub-grid fluctuations via the turbulence synthesizing model leads to a tendency to invert the reverse cascade domain (backscatter) in the solutions obtained with the coarsest grid. The results obtained with the NLDE turbulence, in which we use a synthetic turbulence model to introduce subgrid turbulent fluctuations, show good agreement with DNS results and or experimental results.

"July, 2003" / Includes bibliographical references (leaves 177-183) / xxii, 183 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, School of Chemistry and Physics, Discipline of Physics and Mathematical Physics, 2004

This paper offers a comprehensive and integrative overview of all empirical data available from the open literature on the in-tunnel radiowave-communication channel's power loss characteristics, as a function of the tunnel's cross-sectional shape, cross-sectional size, longitudinal shape, wall materials, presence or absence of vehicular/human traffic, and presence/absence of branches. These data were originally presented in about 50 papers in various journals, conferences, and books.

This paper offers a comprehensive and integrative overview of all empirical data available from the open literature on the in-tunnel radiowave-communication channel's power loss characteristics, as a function of the tunnel's cross-sectional shape, cross-sectional size, longitudinal shape, wall materials, presence or absence of vehicular/human traffic, and presence/absence of branches. These data were originally presented in about 50 papers in various journals, conferences, and books.

<p>Landminor är ett stort problem både under och efter krigstid. De metoder som används för att detektera minor har inte ändrats mycket sedan 1940-talet. Forskning med mål att utvärdera olika elektro-optiska sensorer och metoder som skulle kunna användas för att skapa mer effektiv min-detektion genomförs på FOI. Försök som har gjorts med data från bland annat laser-radar och IR-sensorer har gett intressanta resultat.</p><p>I det här examensarbetet utvärderades olika fenomen och egenskaper i laser-radar- och IR-data. De testade egenskaperna var intensitet, IR, ytlikhet och höjd.</p><p>En metod som segmenterar intressanta objekt och bakgrundsdata utformades och implementerades. Metoden använde sig av expectation-maximization-skattning och ett minimum message length-kriterium. Ett scatter separability-kriterium användes för att bestämma kvalitén på de olika egenskaperna och på den resulterande segmenteringen.</p><p>Data insamlad under en mätkampanj av FOI användes för att testa metoden. Resultatet visade bland annat att ytlikhetsmåttet gav en bra segmentering för stora objekt med släta ytor, men var sämre för små objekt med skrovliga ytor. Vid jämförelse med en manuellt skapad mål-mask visade det sig att metoden klarade av att välja ut egenskaper som i många fall gav en godkänd segmentering.</p> / <p>Land mines are a huge problem in conflict time and after. Methods used to detect mines have not changed much since the 1940's. Research aiming to evaluate output from different electro-optical sensors and develop methods for more efficient mine detection is performed at FOI. Early experiments with laser radar sensors show promising results, as do analysis of data from infrared sensors.</p><p>In this thesis, an evaluation is made of features found in laser radar- and in infrared -sensor data. The tested features are intensity, infrared, a surfaceness feature extracted from the laser radar data and height above an estimated ground plane.</p><p>A method for segmenting interesting objects from background data using theexpectation-maximization algorithm and a minimum message length criterion is designed and implemented. A scatter separability criterion is utilized to determine the quality of the features and the resulting segmentation.</p><p>The method is tested on real data from a field trial performed by FOI. The results show that the surfaceness feature supports the segmentation of larger object with smooth surfaces but gives no contribution to small object with irregular surfaces. The method produces a decent result of selecting contributing features for different neighbourhoods of a scene. A comparison with a manually created target mask of the neighbourhood and the segmented components show that in most cases a high percentage separation of mine data and background data is possible.</p>

Landminor är ett stort problem både under och efter krigstid. De metoder som används för att detektera minor har inte ändrats mycket sedan 1940-talet. Forskning med mål att utvärdera olika elektro-optiska sensorer och metoder som skulle kunna användas för att skapa mer effektiv min-detektion genomförs på FOI. Försök som har gjorts med data från bland annat laser-radar och IR-sensorer har gett intressanta resultat. I det här examensarbetet utvärderades olika fenomen och egenskaper i laser-radar- och IR-data. De testade egenskaperna var intensitet, IR, ytlikhet och höjd. En metod som segmenterar intressanta objekt och bakgrundsdata utformades och implementerades. Metoden använde sig av expectation-maximization-skattning och ett minimum message length-kriterium. Ett scatter separability-kriterium användes för att bestämma kvalitén på de olika egenskaperna och på den resulterande segmenteringen. Data insamlad under en mätkampanj av FOI användes för att testa metoden. Resultatet visade bland annat att ytlikhetsmåttet gav en bra segmentering för stora objekt med släta ytor, men var sämre för små objekt med skrovliga ytor. Vid jämförelse med en manuellt skapad mål-mask visade det sig att metoden klarade av att välja ut egenskaper som i många fall gav en godkänd segmentering. / Land mines are a huge problem in conflict time and after. Methods used to detect mines have not changed much since the 1940's. Research aiming to evaluate output from different electro-optical sensors and develop methods for more efficient mine detection is performed at FOI. Early experiments with laser radar sensors show promising results, as do analysis of data from infrared sensors. In this thesis, an evaluation is made of features found in laser radar- and in infrared -sensor data. The tested features are intensity, infrared, a surfaceness feature extracted from the laser radar data and height above an estimated ground plane. A method for segmenting interesting objects from background data using theexpectation-maximization algorithm and a minimum message length criterion is designed and implemented. A scatter separability criterion is utilized to determine the quality of the features and the resulting segmentation. The method is tested on real data from a field trial performed by FOI. The results show that the surfaceness feature supports the segmentation of larger object with smooth surfaces but gives no contribution to small object with irregular surfaces. The method produces a decent result of selecting contributing features for different neighbourhoods of a scene. A comparison with a manually created target mask of the neighbourhood and the segmented components show that in most cases a high percentage separation of mine data and background data is possible.

By examining continuous data from the Poker Flat Incoherent Scatter Radar (PFISR) in Poker Flat, Alaska, short-lived enhancements in the F-region ion temperature, or "Tᵢ spikes", were discovered in the evening while the radar was on the equatorward edge of the high latitude convection region. These enhancements were several hundred Kelvin above the background temperature, would last less than 15 minutes and were preceded by sharp depletions in plasma density (of roughly one half). Though they were mostly detected in the summer, 25 events throughout a whole year of data were identi ed in which the spike occurred within 1.5 hours of the density drop. By examining the location of PFISR at the time of the enhancements, as well as the conditions under which these spikes occurred, it was concluded that these enhancements were the result of electric elds increasing the frictional heating between ions and neutrals. By then examining geophysical data, it was found that these events were temporal and related to changes in magnetic indices. One possible explanation for the observations is that the electric eld is at its strongest near the plasmapause during substorms. Another more likely possibility is that during substorms the region of sunward ion convection expands into a region in the evening side where the neutral gas moves in a direction opposite to the ions, thereby enhancing the frictional heating rate.

X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method. A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries. Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude. The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.

X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method. A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries. Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude. The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.

Made available in DSpace on 2014-06-11T19:22:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-04-18Bitstream added on 2014-06-13T18:08:30Z : No. of bitstreams: 1 taglialenha_sls_dr_ilha.pdf: 776756 bytes, checksum: ee3e13f4456bb0d2f6f5faaf48d8309f (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O Problema de Planejamento da Expansão de Sistemas de Transmissão de Energia Elétrica consiste em se escolher, entre um conjunto pré-definido de circuitos candidatos, aqueles que devem ser incorporados ao sistema de forma a minimizar os custos de investimento e operação ao e atender a demanda de energia futura ao longo de um horizonte de planejamento com confiabilidade, assumindo como conhecido o plano de geração. É considerado um problema muito complexo e difícil por se tratar de um problema não linear inteiro misto, não convexo, multimodal e altamente combinatório. Este problema tem sido solucionado usando técnicas clássicas como Decomposição ao de Benders e Branch and Bound, assim como também algoritmos heurísticos e metaheurísticas obtendo diversos resultados, mais com uma série de problemas como, por exemplo, alto esforço computacional e problemas de convergência. Neste trabalho apresentam-se duas novas técnicas de solução para o problema, a saber, as metaheurísticas Busca em Vizinhança Variável e a Busca Dispersa. A Busca em Vizinhança Variável é uma técnica baseada em trocas de estruturas de vizinhança dentro de um algoritmo de busca local, e a metaheurística Busca Dispersa, um método evolutivo que combina sistematicamente conjuntos de soluções para se obter solucões melhores. Essas técnicas de solução oferecem novas alternativas de solução que oferecem solução aos problemas encontrados com outros métodos, como é um baixo esforço computacional é uma melhor convergência, sendo este o principal aporte do trabalho. Os algoritmos são apresentados sistematicamente, explicando os seus algoritmos e a forma como são adaptados para resolver o problema do planejamento da expansão de sistemas de transmissão considerando-se a modelagem matemática conhecida com o modelo de transporte e o modelo DC. São realizados testes com os sistemas... / Electric Energy Transmission Network Expansion Problem consist in choose among a set of pre-defined circuits candidates, who must be incorporated into the system so as to minimize the investment costs and operation and meet the future energy demand over a planning horizon with reliability, assuming the generation plan is known. It is a very complex and difficult problem because it is non linear, non convex, multimodal and highly combinatorial. This problem has been solved using traditional techniques such as Benders decomposition and Branch and Bound, as well as heuristic algorithms and metaheuristics getting different results, but with a series of problems such as high computational effort and convergence problems. This paper tests out two new techniques for solving the problem as are the metaheuristics Variable Neighborhood Search and Scatter Search. The Variable Neighborhood Search is a technique based on trading structures within a neighborhood of a local search algorithm, and the Scatter Search metaheuristic is a method which combines systematically sets of solutions in an evolutionary way to achieve better solutions. These solution techniques offer new alternatives to solve the problems encountered with other methods, such as a low computational effort and better convergence, which is the main contribution of this work. The techniques are presented systematically, explaining their algorithms and the way they are adapted to solve the network expansion planning problem based on the mathematical model known as the transportation model and the DC model. They are tested with the systems Southern Brazilian with 46 buses and the IEEE 24 buses system, results are compared with those obtained with other metaheuristics, obtaining excellent results with a best performance both in processing speed as in computational effort.