• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 393
  • 188
  • 158
  • 50
  • 30
  • 21
  • 11
  • 10
  • 7
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • Tagged with
  • 1034
  • 136
  • 122
  • 114
  • 90
  • 85
  • 73
  • 71
  • 71
  • 64
  • 63
  • 61
  • 60
  • 58
  • 58
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
331

O semanário Bundas e o jornalismo econômico /

Taveira, Caroline Gonçalves. January 2014 (has links)
Orientador: Maximiliano Martin Vicente / Banca: Rozinaldo Antonio Miani / Banca: Murilo Cesar Soares / Resumo: Esta dissertação procura analisar as formas de exercício do jornalismo econômico, com o objetivo de mostrar como este pode se tornar compreensível a qualquer público leitor. Ao longo dos capítulos, dentre teorias e análises, buscamos denotar como a imprensa alternativa pode contribuir para facilitar a compreensão da informação econômica e deixá-la ao entendimento não só de pessoas envolvidas no universo econômico, como também àqueles leitores que não estão familiarizados com os jargões do jornalismo econômico. Mediante ao exposto, vimos no semanário Bundas, periódico considerado alternativo e que circulou no final dos anos de 1990, um meio que facilitou a leitura dos textos sobre economia. Partindo de um estudo textual, inspirado na Análise de Conteúdo de Bardin, o intuito do trabalho é mostrar que é possível realizar a prática do jornalismo econômico sob o ponto de vista alternativo, evidenciando que esses podem levar informação ao público leitor de maneira muito mais atrativa e compreensível do que os grandes veículos impressos / Abstract: This dissertation analyzes the ways of exercising economic journalism, aiming to show how this can become understandable to any readership. Throughout the chapters, among theories and analyzes, seek denote as the alternative media can help facilitate economic understanding information and leave it to the understanding not only of people involved in the economic universe, as well as those readers who are unfamiliar with the jargon economic journalism. By the above, we have seen in the weekly Bundas, considered alternate periodic and circulated in the late 1990s, a medium that facilitated the reading of the texts on economics. Starding from a textual study, inspired by the Content Analysis Bardin, the aim of the paper is to show that it is possible to perform the practice of economic journalism under the alternative point of view, showing that these can bring information to the public in a much more attractive way player and understandable than the big print media / Mestre
332

Desenvolvimento de um dispositivo para avaliação do transporte de combustíveis no meio subterrâneo. / Development of a device for evaluating fuel transport in the underground soil.

Manoel Paulo de Toledo 13 November 2012 (has links)
O presente trabalho teve o intuito de desenvolver um novo dispositivo para melhor conhecer a movimentação de combustíveis no meio subterrâneo, fundamental à definição de tecnologias para remediação de áreas contaminadas. Paralelamente, procurou-se verificar a viabilidade da utilização do dispositivo proposto como método simples, rápido e de baixo custo para investigação do fluxo do óleo diesel, da gasolina e do biodiesel no solo. Fabricou-se um microcanal em poli(dimetil)siloxano que reproduziu fielmente as dimensões e geometrias dos poros e canais do solo. Inicialmente, o microcanal foi saturado com ar; em seguida, injetou-se o combustível e sequencialmente, a água de tal forma a simular um derramamento de combustível no solo sucedido por uma precipitação. Cada operação foi gravada em vídeo ou fotografada, o que permitiu a visualização dos fenômenos que ocorriam no interior do canal. Os resultados obtidos mostraram a viabilidade do dispositivo proposto para o estudo da movimentação dos combustíveis no meio subterrâneo. Verificou-se que tanto a gasolina quanto o óleo diesel evaporam, sendo a primeira mais rapidamente do que o segundo. O experimento permitiu calcular a taxa de evaporação de gasolina no solo. O óleo diesel e o biodiesel ficaram retidos nos poros fechados e a eventual água da chuva que escoava pelo mesmo caminho que a fase gasosa (ar e no caso do óleo diesel, vapores) removia parcialmente esses combustíveis. / The present work had the aim of developing a new device for better understanding fuel motion in the underground soil a key issue for the definition of contaminated area remediation technologies. As a side goal one tried to verify the feasibility of using the proposed device as a simple, fast and inexpensive tool for the investigation of underground fuel flow in porous soil by means of laboratory experiments with it. A poly(dimethyl)siloxane microchannel reproducing exactly the dimensions and geometries of soil pores and channels has been fabricated. Initially the microchannel was saturated with air; then firstly fuel was injected and sequentially water in order to mimic soil contamination by fuel leakage followed by a rain fall. Each and every operation was video recorded or photographed what allowed the visualization of the phenomena occurring inside the microchannel. Results showed the viability of the proposed device for studying the transport of fuels in the underground soil. It has been verified that gasoline vaporizes as does diesel oil as well, the former quicker than the last. The experiment allowed calculating the evaporation rate of gasoline in the soil. It has been seen that diesel oil and biodiesel remained trapped in closed pores and the eventual rain water flowed through the gaseous phase way (air and in the case of diesel oil, vapor) partially removing them.
333

Estruturas relacionadas ao potencial de rebrotamento de duas espécies de Myrtaceae do Cerrado: análises morfoanatômicas e químicas / Structures related to sprouting potential of two Myrtaceae species of Cerrado: morphoanatomical and chemical analyses

Gabriela Santos da Silva 02 February 2018 (has links)
A área de Cerrado escolhida para o estudo está em regeneração na Estação Ecológica de Santa Bárbara, localizada no município de Águas de Santa Bárbara, SP. Nesta área o Pinus, que estava sob cultivo desde os anos 70, foi retirado em 2012 e, em 2014, foi realizada uma queimada. As espécies Eugenia dysenterica (Mart.) DC. e E. punicifolia (Kunth) DC. foram escolhidas devido ao elevado número de indivíduos que rebrotaram na área. O objetivo geral do projeto foi conduzir análises morfoanatômicas e químicas das estruturas relacionadas ao potencial de rebrotamento. Foram realizadas: a contagem das gemas subterrâneas nos primeiros 10 centímetros abaixo do nível do solo, as análises químicas das raízes e análises anatômicas na região terminal de ramos aéreos e no sistema subterrâneo. Nas duas espécies, além da gema apical dos ramos aéreos, nas três regiões nodais subsequentes, acima da gema axilar ocorre uma gema acessória. Em todas as gemas, observam-se estruturas de proteção, pois junto ao meristema apical caulinar (MAC) ocorrem coléteres e cristais. Além disso, o MAC é protegido por primórdios foliares com cavidades de óleo, muitos cristais e tricomas unicelulares não glandulares que possuem espessamento parietal em celulose e podem acumular compostos fenólicos. Nos sistemas subterrâneos, o número de gemas, localizadas preferencialmente nos primeiros cinco centímetros do solo, variou entre os três indivíduos da mesma espécie: E. dysenterica 162, 17 e 253, E. punicifolia 24, 40 e 109. Esta variação deveu-se ao grau de desenvolvimento das estruturas subterrâneas as quais certamente formaram-se antes do período da retirada do Pinus. O sistema subterrâneo das espécies é formado por um eixo lenhoso cuja porção superior é caulinar e emite vários ramos aéreos enquanto a porção inferior é constituída por uma raiz axial espessada que pode atingir até um metro de profundidade em E. dysenterica. Em E. punicifolia o sistema subterrâneo ocupa uma região mais superficial do solo e, assim como o caule, as raízes axial e adventícias são distribuídas num plano mais horizontal. O tecido de revestimento nas raízes de E. punicifolia e no caule e raízes de E. dysenterica, apresenta camadas alternadas de células de paredes suberizadas e de células com espessamentos parietais em pectina; no caule de E. punicifolia há esclereides que se alternam com as células suberizadas. Em E. punicifolia o espessamento resulta de divisões anticlinais e expansão tangencial das células do parênquima floemático. Há floema interno e parênquima medular nos caules subterrâneos de ambas as espécies. Compostos fenólicos e grãos de amido estão presentes nas células parenquimáticas de regiões mais espessadas dos caules e raízes. Os teores de carboidratos totais, hemicelulose, celulose e lignina não diferem significativamente nas duas espécies. No entanto, as concentrações de flavonoides totais e de compostos fenólicos totais foram superiores nas raízes de E. punicifolia. O grau de proteção das gemas aéreas, o elevado número de gemas e o acúmulo de compostos de reserva (amido) e de proteção (fenóis, flavonoides, lignina) nas estruturas subterrâneas podem ter favorecido o seu rebrotamento após a retirada do Pinus e a sua permanência das espécies na área. / The Cerrado area studied is under regeneration at the Estação Ecológica de Santa Bárbara, located in Águas de Santa Bárbara (São Paulo, Brazil). In this area, the Pinus, cultivated since the 1970s, was removed in 2012 and then, in 2014, the area was burnt. The species Eugenia dysenterica (Mart.) DC. and E. punicifolia (Kunth) DC. were studied due to their high resprouting after the burnt event. The aim was to carry out morphoanatomical and chemical analyses of the structures related to the resprouting capacity. The number of belowground buds was counted in the first 10 cm below the soil surface. The chemical analyses of the roots and anatomical analyses of the end portion of the aerial branches and the underground system were performed. Besides the apical bud, both species showed an accessory bud above the axillary one at the three subsequent nodal regions. In all studied buds, protection structures were observed, as colleters and crystals occur close to the shoot apical meristem (SAM). Moreover, SAM is protected by leaf primordia with oil cavities, many crystals and non-glandular unicellular trichomes. These trichomes present parietal cellulose thickening and are able to accumulate phenolic compounds. In underground systems, the number of buds, mostly in the first five centimeters below the soil surface, varied between individuals per species: E. dysenterica 162, 17 and 253; E. punicifolia 24, 40 and 109. This variation was caused by the development degree of the underground system, whose structures were certainly developed before Pinus removal. The underground system of the species display a woody axis, whose upper portion is a stem structure and produces several aerial branches. Its lower part is formed by an axial thickened root that can reach one metre deep in E. dysenterica. In E. punicifolia, the subterranean system occupies a more superficial region of the soil and, similar to the stem, the axial and adventitious roots are distributed in a more horizontal plane. The covering tissue of underground systems in E. punicifolia and E. dysenterica displays alternate layers of cells with suberized walls and pectin-thickened walls. In E. punicifolia stem, the covering tissue exhibits sclereids alternate with cells of suberized walls. The thickening in E. punicifolia is a result of anticlinal divisions and tangential expansion of phloematic parenchyma cells. Both species show internal phloem and medullary parenchyma in underground stems. Phenolic compounds and starch grains are present in parenchyma cells of thickened regions in stems and roots. The contents of total carbohydrates, hemicellulose, cellulose and lignin do not differ significantly in the two species. However, concentrations of total flavonoids and total phenolic compounds are higher in roots of E. punicifolia. The protection level of aerial buds, large number of underground buds, and accumulation of storage (starch) and protection (phenols, flavonoids, lignin) compounds in the underground structures may have favoured resprouting of the species after Pinus removal and their maintenance in the area.
334

Análise de dados de instrumentação de túneis do metrô de São Paulo: uma abordagem por redes neurais / Analysis of instrumentation data of São Paulo subway tunnels: a neural network approach

Ovídio Joaquim dos Santos Júnior 29 September 2006 (has links)
Atualmente, a escavação de túneis rasos em regiões densamente ocupadas requer medidas severas para reduzir riscos e possíveis influências em estruturas próximas. Um importante passo é a previsão dos efeitos da escavação, principalmente no que concerne à geração de recalques. As redes neurais artificiais (RNAs) aparecem como uma nova ferramenta para auxiliar o entendimento desses fenômenos. Isso porque a rede neural possui a capacidade de realizar generalizações, isto é, após a rede aprender características de uma categoria geral de dados baseada em uma série de exemplos daquela categoria, a rede pode apresentar respostas idênticas ou similares às respostas treinadas para entradas não treinadas. Nesse trabalho, realiza-se a aplicação de redes neurais artificiais para os dados das linhas 1 e 2 do metrô de São Paulo, onde se observa a influência de alguns parâmetros e a melhoria significativa de previsão da rede neural devido à utilização de algumas técnicas no tratamento e manuseio dos dados. Dentre as técnicas de tratamento de dados utilizadas destaca-se a adimensionalização dos dados por parâmetros da própria obra garantindo melhor estabilidade à rede e melhor capacidade de previsão. Análises de sensibilidade também são realizadas para contemplar o tipo de influência que cada parâmetro exerceu nos recalques obtidos. / Excavating shallow tunnels in densely occupied areas currently requires strict precautions to reduce risks and possible effects on nearby structures. Being able to predict excavation effects and particularly settlement - related effects is an important step forward in this respect. Artificial neural networks (ANNs) have emerged as a new tool for analyzing geotechnical problem. Longstanding problems have been solved and conventional solutions enhanced as the ability to generate more information grows and the understanding of obscure points is deepened. Neural networks have the ability to make generalizations: once a network has learned the characteristics of a general category of objects based on a series of examples from this category, it can provide identical or similar responses to trained responses for non-trained inputs. This study uses artificial neural networks to analyze data from São Paulo subway line 1 and 2 to observe the effects of certain parameters and notes significantly enhanced neural network predictive ability due to the use of certain data processing techniques. The study also sets out to show that the use of dimensionless data in training may upgrade the predictive ability of the model. Knowledge acquired was applied to further develop use of this technique for tunnel instrumentation.
335

Análise de ponto ótimo de realocação da alimentação primária para mineração em câmaras e pilares

Vincenzi, Ricardo Andre January 2015 (has links)
O método de lavra câmaras e pilares é muito utilizado em minas de carvão subterrâneo, principalmente nos estados de Santa Catarina e Paraná, onde todas as minas subterrâneas utilizam este método. Vale ressaltar, porém, que o método apresenta recuperações de lavra abaixo de 50%, dependendo do tamanho dos pilares, e a produtividade é altamente dependente de uma boa concatenação das operações unitárias. Entre os aspectos relacionados à eficiência produtiva, a distância de transporte é um item preponderante no desempenho do sistema. Devido à profundidade da lavra, há um aumento do tamanho dos pilares de sustentação da mina, e assim, surgem problemas relacionados ao incremento no tempo de ciclo de transporte dos equipamentos. O aumento da distância de transporte entre uma frente de lavra com material desmontado e o alimentador/britador primário, reduz o resultado da produção de um conjunto de equipamentos. Em mineração a céu aberto, este tipo de problema é resolvido com o aumento da frota de transporte, todavia, na mineração de carvão subterrânea, não é possível aumentar de forma irrestrita a quantia de máquinas em subsolo, pois impactaria diretamente na necessidade de incremento da vazão de ar, assim como, limitação de espaço para o tráfego de equipamentos. A aproximação da distância do ponto de descarga para um local adjacente às frentes de serviço é uma alternativa para solucionar a necessidade de incremento da frota de produção. No entanto, o ponto de mudança deve ser avaliado de forma consistente para determinar o momento mais adequado para que essa reaproximação proporcione um resultado ótimo. Este estudo buscou compreender esta etapa necessária ao processo produtivo, utilizando técnicas de regressão para analisar o impacto da distância de transporte na capacidade produtiva. O problema foi modelado e foram propostas alternativas que forneçam um sequenciamento de lavra capaz de amenizar os problemas decorrentes do aumento da distância de transporte das frentes de lavra aos respectivos pontos de descarga. Os resultados demonstraram que a distância de transporte tem influência direta na produção, mas não somente a distância máxima, mas também, uma distância mínima que deve ser respeitada para obter maior produtividade quando se tem a associação de equipamentos de produção. É possível concluir com este estudo que a distância de transporte tem impacto relevante e deve ser considerada, não tão somente no sequenciamento, mas também no dimensionamento da frota e consequente capacidade produtiva. / The room and pillar mining method is widely used in underground coal mines. Santa Catarina and Paraná where all underground mines use this method. Indeed, the method has mining recoveries below 50% and the productivity is highly dependent on a good concatenation of unit operations. Among the aspects related to production efficiency, the transport distance is an important item on system performance. Due to the depth of the mine, there is an increment in the size of the underground supporting pillars, and consequently, problems related to the increase in equipment cycle times. The increase of the transportation distance between mining faces and the primary crusher reduces the result of a set of production equipment. In open pit mining, this problem is solved by increasing the haulage fleet, however, in the underground coal mining, the number of machines cannot be increased indefinitely because it would impact directly on the need of increased air flow. Therefore, the approximation of the distance from the discharge point to an adjacent location from the mining faces is an alternative to address the need of increased production fleet. However, the relocation point must be evaluated consistently to determine the most appropriate time to get the most from this approach. The goal of the study was to understand this imperative step for the production process, using regression techniques to analyze the impact of transport distance in productive capacity. Based on the experimental design used in this study, alternative proposals provide a mining sequence able to mitigate the problems from increasing transportation distance from mining faces to their discharge points. The results show that the transport distance has directly influence on the production, and it is not limited to the maximum distance. Likewise, a minimum distance must be respected for higher productivity when you have the combination of production equipment. So, it is possible to conclude that the transport distance has a significant impact and must be considered not only during the sequencing, but also when determining the fleet size and consequent production capacity.
336

Análise de dados de instrumentação de túneis do metrô de São Paulo: uma abordagem por redes neurais / Analysis of instrumentation data of São Paulo subway tunnels: a neural network approach

Santos Júnior, Ovídio Joaquim dos 29 September 2006 (has links)
Atualmente, a escavação de túneis rasos em regiões densamente ocupadas requer medidas severas para reduzir riscos e possíveis influências em estruturas próximas. Um importante passo é a previsão dos efeitos da escavação, principalmente no que concerne à geração de recalques. As redes neurais artificiais (RNAs) aparecem como uma nova ferramenta para auxiliar o entendimento desses fenômenos. Isso porque a rede neural possui a capacidade de realizar generalizações, isto é, após a rede aprender características de uma categoria geral de dados baseada em uma série de exemplos daquela categoria, a rede pode apresentar respostas idênticas ou similares às respostas treinadas para entradas não treinadas. Nesse trabalho, realiza-se a aplicação de redes neurais artificiais para os dados das linhas 1 e 2 do metrô de São Paulo, onde se observa a influência de alguns parâmetros e a melhoria significativa de previsão da rede neural devido à utilização de algumas técnicas no tratamento e manuseio dos dados. Dentre as técnicas de tratamento de dados utilizadas destaca-se a adimensionalização dos dados por parâmetros da própria obra garantindo melhor estabilidade à rede e melhor capacidade de previsão. Análises de sensibilidade também são realizadas para contemplar o tipo de influência que cada parâmetro exerceu nos recalques obtidos. / Excavating shallow tunnels in densely occupied areas currently requires strict precautions to reduce risks and possible effects on nearby structures. Being able to predict excavation effects and particularly settlement - related effects is an important step forward in this respect. Artificial neural networks (ANNs) have emerged as a new tool for analyzing geotechnical problem. Longstanding problems have been solved and conventional solutions enhanced as the ability to generate more information grows and the understanding of obscure points is deepened. Neural networks have the ability to make generalizations: once a network has learned the characteristics of a general category of objects based on a series of examples from this category, it can provide identical or similar responses to trained responses for non-trained inputs. This study uses artificial neural networks to analyze data from São Paulo subway line 1 and 2 to observe the effects of certain parameters and notes significantly enhanced neural network predictive ability due to the use of certain data processing techniques. The study also sets out to show that the use of dimensionless data in training may upgrade the predictive ability of the model. Knowledge acquired was applied to further develop use of this technique for tunnel instrumentation.
337

INVESTIGATION OF THE EFFECTIVENESS OF AN INTEGRATED FLOODED-BED DUST SCRUBBER ON A LONGWALL SHEARER THROUGH LABORATORY TESTING AND CFD SIMULATION

Arya, Sampurna N. 01 January 2018 (has links)
Dust generation at an underground coal mine working face continues to be a health and safety issue. Prolonged exposure to high concentrations of airborne respirable dust can cause a debilitating and often fatal respiratory disease called Black Lung. In addition, the deposition of float dust in mine return airways poses a serious safety hazard if not sufficiently diluted with inert rock dust. A localized methane explosion can transition into a self-propagating dust explosion. Since dust is a byproduct of various mining activities, such as cutting and loading, crushing, and transportation, the dust-related issues cannot be totally eliminated. However, the adverse health effects and safety concerns can be minimized if a significant amount of the generated dust is removed from the ventilation air by a mechanical device, such as a dust scrubber. Over the last three decades, flooded-bed dust scrubbers integrated into continuous miners have been successfully applied for capturing and removing airborne dust generated at the working face. According to the National Institute for Occupational Safety and Health (NIOSH), a flooded-bed scrubber can achieve more than 90% capture and cleaning efficiencies under optimum conditions. Although flooded-bed scrubbers have proven useful in the vast majority of cases, they have not yet been successfully applied to a longwall face. In the United States, numerous attempts have been made to reduce dust concentration at a longwall face through the application of a scrubber; but, none were successfully implemented. Encouraged by the successful use of a flooded-bed scrubber system at continuous miner faces, this research revisits the flooded-bed scrubber concept for a longwall shearer. For this investigation, a full-scale physical model of a Joy 7LS longwall shearer, modified with an integrated flooded-bed dust scrubber, was designed and fabricated at the University of Kentucky. The scope of work for this research was limited to capturing and cleaning dust generated near the shearer headgate drum only. The mock-up was transported to, and assembled in, the full-scale longwall dust gallery at the NIOSH Pittsburgh Research Laboratory (PRL). Tests were conducted to examine: (1) the effect of the scrubber on headgate-drum dust reduction and (2) the combined effect of the scrubber and splitter sprays on headgate drum dust reduction. Analysis of test results for the scrubber-alone condition indicates a significant dust reduction of up to 57% in the return airway and 85% in the test gallery walkway, whereas the combination of scrubber and splitter-arm sprays shows dust reduction of up to 61% and 96% in the return and walkway, respectively. These results indicate that a flooded-bed scrubber integrated into a longwall shearer can be used as a viable technique to reduce a large portion of airborne dust at a longwall face. Subsequently, a Computational Fluid Dynamics (CFD) model of the longwall gallery and shearer was developed and validated using the results of the experimental study. The CFD simulation results are in good agreement with the experimental results with a maximum of 9.7% variation. This validated CFD model can be used in future research to predict the effects of modifications to the scrubber system, including modifications to the scrubber inlet, to optimize the scrubber design, and to evaluate the effectiveness of adding a tailgate drum dust scrubber.
338

Subsidence prediction and mine design for underground coal mining in the Collie Basin.

Misich, Ian J. January 1997 (has links)
The subsidence characteristics of the Collie Basin sediments have been investigated to provide site specific design criteria for the Wongawilli method of coal extraction. As historical coal extraction (bord and pillar) methods did not generally give rise to large scale subsidence, there were very few details on mining subsidence in the Collie Basin available to base any design methodology on. Consequently, the investigation was conducted on a Green fields basis. Firstly, the mechanisms involved in the development of mining subsidence needed to be investigated and identified. It was then necessary to determine the effects that mining subsidence would have on mine and ground mass (specifically aquitards) structures and surface features. Once these two areas of work were completed, design criteria were formulated to manage the effects of mining subsidence by controlling the critical mechanisms of subsidence development.The results from this study have greatly enhanced the level of understanding of the subsidence mechanisms involved, and allowed for the development of predictive models which can be used for the design of coal extraction by the panel/pillar mining method in the Collie Basin. Mine planning engineers can now use this design information to derive the most cost effective methods for the extraction of coal within the Collie Basin.
339

Corrosion of rock reinforcement in underground excavations

Hassell, Rhett Colin January 2008 (has links)
The effect of corrosion on the performance of rock support and reinforcement in Australian underground mines has not been widely researched and is generally not well understood. This is despite the number of safety concerns and operational difficulties created by corrosion in reducing the capacity and life expectancy of ground support. This thesis aims to investigate corrosion and relate how the environmental conditions in Australian underground hard rock mines impact on the service life of rock support and primarily rock reinforcement. Environmental characterisation of underground environments was completed at a number of mine sites located across Australia. This provided an improved understanding of the environmental conditions in Australian underground hard rock mines. Long-term testing on the impact of corrosion on the load bearing capacity of reinforcement and support under controlled experimental conditions was conducted in simulated underground environments. Rock reinforcement elements were examined in-situ by means of overcoring of the installed reinforcement and surrounding rock mass. Laboratory testing of the core determined changes in load transfer properties due to corrosion damage. These investigations provided an excellent understanding of the corrosion processes and mechanisms at work. Corrosion rates for a range of underground environments were established through the direct exposure and evaluation of metallic coupons in underground in-situ and simulated environments. / It was found that the study of corrosion is challenging due to the time required to gather meaningful data. In particular, the wide range of materials that comprise ground support systems means that it is impossible to examine all the possible combinations of variables and their potential influence on the observed levels of corrosion and measured corrosion rates. Despite these challenges, the systematic investigation has resulted in new corrosivity classifications for both groundwater and atmospheric driven corrosion processes for various reinforcement and support systems used in the Australian underground mining industry. Previous corrosivity classifications were not found applicable. Furthermore, these new corrosivity classifications are simpler than previous classifications and corrosion rates may be predicted from readily obtained measurements of ground water dissolved oxygen and atmospheric relative humidity. Different types of reinforcement and surface support systems have been rated with respect to their corrosion resistance and estimates have been made for the expected service life for various rates of corrosion.
340

Mathematical modelling of underground coal gasification

Perkins, Gregory Martin Parry, Materials Science & Engineering, Faculty of Science, UNSW January 2005 (has links)
Mathematical models were developed to understand cavity growth mechanisms, heat and mass transfer in combination with chemical reaction, and the factors which affect gas production from an underground coal gasifier. A model for coal gasification in a one-dimensional spatial domain was developed and validated through comparison with experimental measurements of the pyrolysis of large coal particles and cylindrical coal blocks. The effects of changes in operating conditions and coal properties on cavity growth were quantified. It was found that the operating conditions which have the greatest impact on cavity growth are: temperature, water influx, pressure and gas composition, while the coal properties which have the greatest impact are: the thermo-mechanical behaviour of the coal, the coal composition and the thickness of the ash layer. Comparison of the model results with estimates from field scale trials, indicate that the model predicts growth rates with magnitudes comparable to those observed. Model results with respect to the effect of ash content, water influx and pressure are in agreement with trends observed in field trials. A computational fluid dynamics model for simulating the combined transport phenomena and chemical reaction in an underground coal gasification cavity has been developed. Simulations of a two-dimensional axi-symmetric cavity partially filled with an inert ash bed have shown that when the oxidant is injected from the bottom of the cavity, the fluid flow in the void space is dominated by a single buoyancy force due to temperature gradients established by the combustion of volatiles produced from the gasification of carbon at the cavity walls. Simulations in which the oxidant was injected from the top of the cavity reveal a weak fluid circulation due to the absence of strong buoyancy forces, leading to poor gasification performance. A channel model of gas production from underground coal gasification was developed, which incorporates a zero-dimensional cavity growth model and mass transfer due to natural convection. A model sensitivity study is presented and model simulations elucidate the effects of operating conditions and coal properties on gas production.

Page generated in 0.0497 seconds