It is a great challenge in the design of the PBMR to accurately predict gas flow and heat transfer in the reactor. Understanding the heat transfer at the core-reflector interface in particular is a very important aspect as the reactivity of the control rods housed in the reflectors is highly temperature dependent. It is also very important because the core-reflector interface is on the critical path for heat removal during accident conditions. PBMR has developed an OECD/NEA coupled neutronic/thermal-hydraulic benchmark to aid in the understanding of the different modelling approaches currently employed at PBMR. A comparison of THERMIX-KONVEK and DIREKT results showed large temperature differences at the core-reflector interfaces. Further investigation showed that these differences are as a result of the numerical methods used i.e. Cell-Centred (CC) vs. Vertex-Centered (VC). The present study extended this comparison to Star-CD (CC) and Flownex (VC) which are also used to simulate the reactor at PBMR. An ID MATLAB program that mimics the CC and VC numerical methods was verified against Star-CD and Flownex. This program was then used to model an ID version of the OECD/NEA benchmark. Results were compared with DIREKT and THERMIX-KONVEK. Although the results compared well, there were significant errors at the core-reflector interfaces. The findings of this study were that different numerical methods will predict different temperatures, heat fluxes and (temperature-dependent) sink terms. It was also shown that in addition to the differences resulting from numerical methods, differences were seen between Star-CD and DIREKT and Flownex and THERMIX-KONVEK in the region of the core-reflector boundary. In general, for complicated simulations like that of the pebble bed, the numerical basis of software used to simulate the problem needs to be understood for the problem to be correctly modelled. / Thesis (M.Sc. Engineering Sciences (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.

Thesis (Ph.D.) -- University of Western Sydney, 2001. / "Submitted in fulfilment of requirements for the degree of Doctor of Philosophy, School of Engineering and Industrial Design, University of Western Sydney" Includes bibliography.

[pt] A síntese de duplos refletores com um alimentador dielétrico é estudada sob as considerações da ótica geométrica. A análise ótica do problema leva a uma equação diferencial parcial não-linear de 2ª ordem do tipo Monge- Ampére. Soluções particulares desta equação, as geometrias Cassegrain e Gregoriana off-set, são apresentadas e estudadas. Estas são usadas como soluções iniciais no processo iterativo de síntese. / [en] The synthesis of offset dual reflectors with dieletric feed is studied under the assumptions of geometrical optics. The optical analysis leads to a nonlinear second- order partial differential equation of the Monge-Ampére type. Particular solutions described by offset Cassegrain or Gregorian configurations are presented. These are used as initial solutions in the iterative process of synthesis.

[pt] Este trabalho apresenta uma nova técnica para aproximação de uma superfície refletora definida numericamente, i.e., por pontos fornecidos pelo processo de síntese da antena. As limitações inerentes às técnicas usuais são aqui eliminadas pela utilização de Pseudo-Splines Quínticas que interpolam uma distribuição arbitrária de pontos por uma superfície suave, com derivadas primeiras e segundas contínuas, assegurando uma representação única para o domínio de interesse. O procedimento é, então, aplicado ao subrefletor modelado de uma antena Cassegrain, com subseqüente cálculo do campo eletromagnético espalhado, permitindo uma análise detalhada de sua aplicabilidade. Uma teoria assintótica uniforme de difração é, também, aqui desenvolvida de modo a acomodar o espalhamento de feixes Gaussianos, descritivos, em freqüências altas, do diagrama de irradiação de alimentadores comumente empregados em sistemas refletores, por superfícies condutoras, através do rastreamento do campo eletromagnético ao longo de raios no espaço complexo. A análise do problema canônico (difração por semi-plano) estabelece as particularidades do método e a comparação com a solução rigorosa existente comprova sua acurácia, permitindo a extensão a problemas tridimensionais vetorais. A teoria Complexa da Difração, assim formulada, é, então aplicada ao cálculo do campo espalhado por diferentes geometrias de antenas refletoras, ilustrando a versatilidade do método bem como suas limitações. / [en] In order to evaluate the electromagnetic field scattered by shaped reflector antennas, one has to fit a surface to a set of points furnished by a synthesis technique. A new method, capable of interpolating arbitrarily located data points by a smooth surface is here presented. The interpolating function, called Quintic Pseudo-Spline, has continuous first and seconde order derivatives and yields a unique representation for the entire domain. The method is tested on the shaped subreflector of a Cassegrain antenna providing a thorough investigation of its applicability. Also, an uniform asymptotic theory of diffraction is derived in order to analyse the scattering of Gaussin beams, descriptive of the high-frequency radiation pattern of feed horns commonly employed in reflector systems, by conducting surfaces with edges. The constraints inherent to usual methods of analysis are hereby avoided by tracking these beam-type fields along straight rays in a complex coordinate space. Investigation of the canonical problem of scattering of a Gaussian beam by a conducting half-plane establishes the characteristics of the complex ray diffraction process. Comparison of the results thus obtained with the rigorous solution reveals the accuracy of the proposed theory and permits its extension to the three-dimensional vector problem. The resulting Complex Theory of Diffraction is then applied to the evaluation of the scattered field for several reflector antenna geometries, illustrating the versatility of the method as well as its limitation.

[pt] Este trabalho analisa o efeito das estruturas de suporte do sub-refletor das antenas Cassegrain através da teoria de espalhamento por cilindros. São desenvolvidas expressões das densidades de correntes superficiais sobre cilindros de seção transversal qualquer e obtidas as componentes de campo espalhado. Com esses resultados analisa-se então o efeito que os estais provocam na redução do ganho e no aumento dos lobos secundários. Os resultados finais obtidos são então comparados com outras teorias aproximadas. / [en] This work presents a study on the effect of subreflector support members of Cassegrain antennas using the theory of scattering by cylinders structures. Expressions for the surface current densities on arbitrary cross section cylinders are developed, and the components for the scattered field are obtained. Using these results we analyse the effect of the struts on the gain reduction, and the rise of maximum side-lobe level. The final results aobtained are then compared to other approximate theories.

[pt] O projeto de antenas refletoras para a geração de feixes modelados envolve a construção de algoritmos baseados em métodos de análise eletromagnética associados a técnica de otimização. Em geral, estes algoritmos demandam considerável tempo de processamento computacional, impondo limites para sua utilização intensiva na exploração de diferentes conjuntos de especificações e na busca de soluções mais compactas. Neste trabalho, será considerada a síntese de antenas refletoras circularmente simétricas para a geração de feixes modelados circularmente simétricos. Em função das características de simetria da antena, simplificações serão introduzidas na formulação do problema, reduzindo substancialmente o tempo de processamento e viabilizando sua utilização intensiva. Para a análise eletromagnética da antena refletora serão consideradas as aproximações da Ótica Física (PO) e das correntes de franja (CF). Considerando alimentadores radiando um campo com dependência azimutal n=1, o algoritmo foi adaptado e aplicado no modelamento de antena refletora para atender as especificações do CBERS (China-Brazil Earth Resources Satellite). Para alimentadores com dependência azimutal n=0, foram considerados sistemas de antenas omnidirecionais de um e dois refletores para a geração de diagramas modelados no plano vertical. Para estes dois tipo de sistema, o algoritmo de modelamento foi utilizado para maximizar o diagrama em direção e para produzir diagramas com dependência do tipo cossecante ao quadrado no plano vertical. A validação da técnica de análise eletromagnética desenvolvida foi obtida comparando os resultados com os gerados via Métodos dos Momentos. / [en] The usual algorithms employed in the design of shaped reflector antennas for satellite applications embed an electromagnetic analysis method in an optimization technique. In general, these algorithms demand considerable computation time, limiting its intensive use in the study to explore different sets of specifications and to search for more compact geometries. In this work, it is considered the particular case of the shaping of circularly symmetric reflectors antennas for the generation of circularly symmetric radiation patterns. The use of the reflector surface properties simplifies the formulation of the electromagnetic scattering and substantially reduces the computer time involved in the optimization iteration. For the electromagnetic scattering, the algorithm employed here considers the approximations given by the Physical Optics and Fringe Currents methods. Firstly, the shaping algorithm was applied in the design of a single reflector antenna to comply with the specifications of the China-Brazil Earth Resources Satellite (CBERS). For this case, the feed radiation pattern was represented by model with azimuthal dependence n=1. As a second case, the shaping algorithm was applied in the design of single and dual reflector omnidirectional antennas. Theses antennas were feed by a TEM coaxial horn with azimuthal dependence n=1. For these two type of antenna configurations, the modelling algorithm was used to maximize the diagram in one direction or to produce radiation patterns with dependence of the type cosecant to the square in the vertical plan. A Methods of Moments electromagnetic analysis was used to validate the scattering fields yielded by the PO+Fringe currents approximations.

The following Master Thesis will talk about a C-PV prototype using bifacial PV technology, based on the Solarus Collector. The Solarus Collector consists in two PV cells built on a metallic receiver, where there are some water channels flowing through it, allowing to cool down the PV cells, thus increasing their efficiency. The collector also presents a reflector to provide irradiance to the back part of the receiver, where the other PV cells are located. The new prototype will present bifacial PV cells but not a metallic receiver. This construction aims to reduce the price of the receiver, but will not have a system to cool down the solar cells. This Master Thesis will be developed in the Solarus facilities, in collaboration with the Solarus members. In order to grasp an idea of this prototype, two main procedures will be done. Regarding the bifacial technology, a bifacial PV module will be measured under different conditions, depending on which sides can be illuminated or shaded. On the other hand, a thermodynamic simulation will be carried out on different geometries of the reflector and receiver, in order to figure out the evolution of the temperatures on the new prototype. This simulation will be done with a finite element method, widely known in this applications. The results will show several problems concerning this prototype. Although the measurements of the bifacial PV module will result beneficial and informative, the problem with the temperature will tend to back down this prototype. The lack of some system to cool down the bifacial cells will imply that the receiver could reach unacceptable temperatures. This hypothesis will be drawn under some specific conditions, so they will not be completely devastating to the idea of using bifacial cells, but perhaps a different approach should be used in case it is desired to continue this work.

Firewood has been used as fuel since the beginning of mankind resulted in health problems and deforestation. The solar cooking technology has been first developed in 1767 by Horace-Bénédict de Saussure but did not find development due to lack of reliability. Studies showed the necessity of having a backup facility. The primary goal of this study is to design a fully functional kitchen for National Park in Nairobi, Kenya. The kitchen will be serving up to 100 people daily. The study is done with five steps, the first step is literature and exploring of solar cooking products as well as backup facility products around the world. The second step is interviewing a local entrepreneur to get familiar with the parameters of a restaurant in Kenya. The third step is evaluating the solar cooking and backup facility to make an educated decision. The fourth step is integrating the systems into a functional kitchen. The fifth and last step is to analyse and discuss the results to draw conclusions. As a result, choosing Scheffler reflector as a solar cooker and backed up with a biogas plant would be the chosen solution. / Ved har använts som bränsle sedan mänsklighetens början som resulterade i hälsoproblem och avskogning. Solar-matlagningstekniken utvecklades först 1767 av Horace-Bénédict de Saussure men hittade ingen utveckling på grund av bristande tillförlitlighet. Studier visade nödvändigheten av att ha en reservfacilitetenhet. Det primära målet med denna studie är att designa ett fungerande kök för National Park i Nairobi, Kenya. Köket serverar upp till 100 personer dagligen.  Studien gjordes av fem steg, första är litteraturstudie och utforskning av produkter för sollagning samt reservfacilitet alternativ från hela världen. Andra steget är att intervjua en lokal entreprenör för att bekanta sig med parametrarna för att gestalta en restaurang i Kenya. Tredje steget är att utvärdera olika solkokare-enheter och reservfacilitetsenhet för att fatta ett välgrundat beslut. Fjärde steget är att integrera systemen i ett funktionellt kök. Femte och sista steget är att analysera och diskutera resultaten för att dra slutsatser. Som ett resultat skulle det vara den bästa lösningen att välja Scheffler reflector som solkokare och biogasanläggning som reservfacilitetsenhet.

The diploma thesis presents the usability of a new thermosetting material BMC for the construction of a car headlight. In the theoretical part there are described headlights, basic characteristics and properties of plastics focussing on polymer composite materials and material testing. The practical part deals with the processing of test samples for mechanical testing by compression moulding and also with the production of real samples of reflectors and carrier frames by injection moulding. The evaluation is based on comparison of the results of the performed tests of alternative material and the currently used BMC TETRADUR TD 492/2 in HELLA Autotechnik Nova s.r.o. Basic physical-mechanical properties such as strength, stiffness, toughness and hardness are tested and monitored. The reflectors and carrier frames are assembled into the headlight and then tested according to legal and customers´ requirements for climate and vibration resistance and photometry.

The diploma thesis deals with the production process of optical part of headlamp module produced by additive technology. The thesis contains the characteristics of headlamp, current manufacturing technology and description of additive manufacturng methods. The practical part is focused on the production of a reflector using 3D printing. The conclusion of the thesis is dedicated to the measuring of light output and its evaluation.