Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A inflação consegue dar conta de uma série de problemas do Modelo padrão da Cosmologia, preservando ainda o sucesso do modelo do Big Bang. Na sua versão mais simples, a inflação é controlada por um campo escalar, o ínflaton, que faz com que o universo se expanda exponencialmente. Após, o ínflaton decai e ocorre o reaquecimento do universo. Contudo, alguns autores apontam a existência de uma fase intermediária, chamada de pré-aquecimento. O decaimento do ínflaton possui uma rica dinâmica não-linear. No primeiro estágio, a ressonância paramétrica promove o crescimento exponencial de alguns modos do ínflaton. Isto altera a dinâmica do modo homogêneo do ínflaton, promovendo uma reestruturação das cartas de ressonâncias da equação de movimento dos modos perturbativos. Desta forma, ocorre a transferência de energia para estes modos, até que o universo termaliza. Esta transferência de energia é típica de um sistema turbulento. Por se tratar de uma evolução não-linear, torna-se conveniente a implementação computacional de métodos numéricos. Neste contexto, os métodos espectrais têm se mostrado uma excelente ferramenta para estudar este tipo de sistema. Esta dissertação apresenta os resultados do esquema numérico desenvolvido para o modelo com potencial quártico, que será a base para os demais estudos a serem desenvolvidos. Como mostrado, este esquema é extremamente preciso e eficiente. / Inflation can resolve a few problems of the Standard Model of Cosmology, while still preserving the successful from Big Bang model. In the simplest version, inflation is driven by a scalar field, the inflaton, which causes the universe to expand exponentially fast. Afterwards, the inflaton decays and reheating of the universe occurs. However, some authors suggest the existence of an intermediate phase, called preheating. The decay of the inflaton has a rich non-linear dynamics. In the first stage, the parametric resonance produces exponential growth in some modes. This changes the homogeneous inflaton dynamics, producing a restructuring the resonance charts of the equation of motion of the perturbative modes. Therefore, there is energy transfer to other modes, until the universe thermalize. This energy transfer is typical of a turbulent system. Since the evolution is non-linear, a implementation computational of numerical methods is convenient. In this context, spectral methods have proven to be an excellent tool for studying this kind of system. This thesis presents the results of the numerical scheme developed for the model with the quartic potential, that will be the basis for other studies to be undertaken. As shown, this scheme has proven to be extremely accurate and efficient.

Made available in DSpace on 2014-12-17T14:58:16Z (GMT). No. of bitstreams: 1 RudsonSL_DISSERT.pdf: 2711682 bytes, checksum: 322c3d4fe0f471064164ab72367f6ce8 (MD5) Previous issue date: 2012-09-14 / Due to the increasing need to promote the use of resources that support the environment and the clean industry, the science has developed in the area of natural resource use as well as enhanced use of the renewable energy sources. Considering also the great need for clean water and wide availability of salt or brackish water, added to the great solar energy potential in northeastern of the Brazil, it was developed a solar distiller whose main difference is its system of pre-solar heating also. From experimental adjustments, the system was developed by the use of a cylindrical solar concentrator coupled to a conventional distiller. The system is designed such that attempt to facilitate the process termination trap to ensure constant movement of the fluid mass and thus enable higher temperatures to the system and thus fetch a higher amount of distillate collected. In a stage of the experiment were used a forced circulation to try to further increase the amount of energy exchange system. To develop the study were set up four settings for comparison in which one was only distiller simple as basic parameter, the second proposed configuration were with the coupling of the concentration triggered manually every 30 minutes to monitor the sun, the third configuration occurred with automatic triggering of a timer, and the fourth configuration was also used a pumping system that tried to improve the circulation of the fluid. With the comparative analysis of the results showed a gain in the amount of distillate system, especially in the forced model / Devido ? crescente necessidade de promover o uso de recursos que favore?am o ambiente e a ind?stria limpa, a ci?ncia tem desenvolvido-se na ?rea da utiliza??o de recursos naturais visando uma melhor utiliza??o de fontes de energias renov?veis. Tendo em vista tamb?m a grande necessidade de ?gua pot?vel e a grande disponibilidade de ?gua salgada ou salobra, agregado ao grande potencial energ?tico solar da regi?o nordeste do Brasil, foi desenvolvido um destilador solar cuja principal diferen?a ? o seu sistema de pr?aquecimento tamb?m solar. A partir de adapta??es experimentais, o sistema foi desenvolvido atrav?s da utiliza??o de um concentrador solar cil?ndrico acoplado a um destilador convencional para promover troca de calor consider?vel e ac?mulo de energia. O sistema foi desenvolvido de tal maneira que tente favorecer o processo de termossif?o para garantir o movimento constante da massa de fluido, e assim permitir temperaturas mais elevadas para o sistema e, consequentemente, buscar uma maior quantidade de destilado recolhido. Em uma das fases do experimento buscou-se uma circula??o for?ada para tentar aumentar mais a quantidade de troca de energia do sistema. Para o desenvolvimento do trabalho montou-se quatro configura??es de compara??o em que uma teve apenas o destilador simples como par?metro b?sico, a segunda configura??o prop?s o acoplamento do concentrador acionado manualmente a cada 30 minutos para o acompanhamento do sol, a terceira configura??o ocorreu com o acionamento autom?tico por um temporizador, e na quarta configura??o usouse tamb?m um sistema de bombeamento que tentasse melhorar a circula??o do fluido. Com a an?lise comparativa dos resultados observou-se um ganho da quantidade de destilado do sistema, principalmente no modelo com circula??o for?ada

This thesis deals with the study of influence of preheating/reheating by TIG arc method in the laser welding process of Domex 700 MC fine-grained steel through the evaluation of laser-welds properties, respectively properties of welds made by laser-TIG hybrid technology. The main part of this thesis is experiment, in which Domex 700 MC plates 3 mm thick were welded – first using laser itself, then using laser with arc preheating and finally using laser with arc reheating. The variable parameter during the processes preheating or reheating was distance of TIG tungsten electrode and laser beam (DLA = 1 mm, 2 mm and 4 mm). The criterion for the assessment of welds properties thus produced was tensile strength verified by the tensile test. For a more detailed study of the laser-welds properties, a macrostructure / weld microstructure analysis and a Vickers hardness test were performed.

In this thesis is studied the influence of arc TIG preheating during laser welding of 2 mm Hardox 450 material sheets. This material achieves its good mechanical properties by processes of heat treatment. That causes problems during welding because of heat degradation. Experimental sheets were welded within various configurations of welding parameters and positions of TIG nozzle. Testing specimens were cut out by laser and were used for tension testing, Vickers hardness testing and metallographical testing (macro and microstructure). The results of using the second heat source are: wider heat affected zone, smoother transitions among its zones, reduction of toughness and hardness, finer grain structure and occurring ferritic microstructure. This hybrid technology, combination of laser welding and TIG preheating, is very productive creating joints with greatly good quality. The thesis also contains a comparison with common MAG welding method.

Thesis is focused on analyzing the influence of preheating process parameters using electric arc from TIG torch during laser welding on weld properties of stainless steel and carbon steel with higher strength. In this thesis experiment was done in which metal sheets 3 mm thick from X12Cr13 and S355 steels were welded. Welding was done first with using only laser, then laser with TIG preheating and lastly laser with preheated material by induction heater. When TIG preheating was used than set welding current was changed on the power source. The welds were subsequently evaluated based on macrostructure, microstructure and Vickers hardness test.

This thesis deals with the usage of arc preheating for welding high strength boron enhanced steel 22MnB5 using hybrid technology known as laserTIG and also its impact on the final weld compared to welds welded by only the laser or the arc method. During the experiment I welded five sheets of the above mentioned steel 1,3 or 1,9 milimeters wide. Except for the welds fabricated by the laser and the TIG method was the only variable the electric current of the arc (I = 20, 40, or 60 A). Welds welded this way were compared based on strength limits measured by the tensile tests. Additionally were they compared according to the metalographic survey and the progress of weld hardness, calculated using the Vickers hardness test.

For TIG welding of transformer fame is important enough weld root fusion, however exposed surfaces must remain unaffected. Three types of test were made to determine properties of welds under different conditions. Tests were macroscopic inspection, tensile test and fracture test. Next was economic evaluation of different methods. Best results were for single layer weld with pre-heated material.

The thesis is focused on the study of the use of electric arc preheating, in this case source WIG, during laser welding of steel with a higher carbon content, specifically for this work steel 1.1191 thickness 2 mm. Based on the calculation of the carbon equivalent, the preheating was determined to 208 °C. The welding parameters were selected on the basis of the first experiments. In the experimental section, the samples were welded with laser with preheating using a source WIG, which were then made to a tensile test, Vickers microhardness, macrostructure and microstructure. By using a second heat source, the heat-affected area of the samples was expanded. Samples that cracked in the middle of the weld during the tensile test were heat influenced by cutting samples. The remaining samples was broken in the base material, thus the weld produced was of good quality. Combination of laser welding with WIG electric arc preheating is a very productive method over conventional methods and one of the few pre-heating solutions for laser welding. These are the initial experiments for the use of the WIG arc for preheating in laser welding, to be followed by further research, mainly for the automotive industry.

This investigation aims to understand and improve the deposition quality and rates of cold spray for additive manufacturing in a way that is economically sound and without the detrimental temperature effects seen in traditional metallic additive manufacturing processes. It focuses on materials that are desired by the additive manufacturing community and built upon the current knowledge in cold spray. This thesis is presented as a collection of published, or soon to be published, manuscripts accompanied by an introduction, literature review, and conclusion. The effect of a non-spherical particle morphology was the first objective investigated. Titanium has been shown repeatedly to require pure helium at very high temperatures and pressures to get dense coatings, however, the unique coral-like morphology resulting from the Armstrong Process was revealed as a key to successful deposition with nitrogen. Using low pressure cold spray, under conditions that would be considered mild, a deposition efficiency of 100% and a porosity of nearly 0% was achieved. This is a promising approach for cold spray as a method for additive manufacturing of titanium parts. The low powder cost and the advantages of additive manufacturing could allow for a substantial cost savings in titanium part production when compared to traditional manufacturing methods. With these cost saving advantages, additive manufacturing of titanium using Armstrong process powder and CS could lead to a paradigm shift of titanium production, allowing titanium to enter markets that under traditional methods would be far too expensive. Unfortunately, this unique powder morphology was not available in other materials. To address the low deposition efficiency of the other metals of interest, such as aluminum and stainless steel, the concept of mixing the propellant gas was introduced in the second objective. Considering the relative costs of gases, powder, electricity, and labour, the second paper focuses on the concept of optimizing the amount of helium to produce the minimum component cost. It was found that for the specific stainless steel and aluminum alloy powders discussed, costs could be reduced by 44% and 59%, respectively, using the gas mixing system. However, no cost saving was found for the most inexpensive of the powders, pure aluminum. For gas mixing to be effective, the cost of helium must be offset by the cost of the powders. Therefore, low-cost powders, such as pure aluminum, results in pure nitrogen as the least expensive option. This however doesn’t address the low deposition efficiency that is preventing its adoption in cold spray additive manufacturing. The third objective addresses just this, an improvement in deposition efficiency without the introduction of expensive helium. In this study, aluminum particles were preheated using a novel particle preheater that does not clog. This resulted in a deposition efficiency increase of 260% with a minimal increase in electrical costs. These three objectives, while studied and published separately, all relate to the purpose of this work to improve the process economics without detrimental temperature effects. These findings have been (or will be) published in international peer reviewed journals to add to the collective knowledge.

This report deals with the mathematical model of the transient behaviour of an existing ethane dehydrogenation furnace which is composed of two main sections: a preheating convection section and a radiant-heated section. The correlation of pressure drop with time has been found from the available data. The fractional carbon deposition and the multiplier coefficient of a pressure drop equation have been determined by the direct search optimization technique of Hooke and Jeeves. An optimal policy for the cyclic operation of the furnace was determined by considering plant temperature profile and hydrocarbon/ steam ration as parameters for maximizing average ethylene produced per day. The effect of temperature profile on the distribution of carbon deposited along the reactor was also predicted and discussed. / Thesis / Master of Engineering (ME)