Thesis (M.S.)--Michigan State University, 2006. / Includes bibliographical references (leaves 91-100). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.S.)--Michigan State University, 2006. / Includes bibliographical references (leaves 91-100).

Rock bolts have been extensively used as a support element in coal mines in the US for about 40 years. Longwall development and partial extraction room-and-pillar mining systems now rely heavily on fully-grouted roof bolts as the primary support with as needed inclined bolts, trusses, and cable bolts as secondary support. These two coal mining systems develop 3- and 4-way intersections during extraction processes. A study of Illinois (2004-2008) and US coal mines found that over 70% of roof falls occurred at intersections. It is therefore necessary to perform additional research in stress and displacement distributions around intersections and then design support systems to improve stability of intersections. This thesis research, in cooperation with a bolt supplier and NIOSH, analyses the stress and strain redistribution in and around intersections in typical lithologies in the Illinois Basin coal mines with the goal to develop a better understanding of failure initiation and propagation mechanisms with and without roof supports. Analyses were corroborated with field observations wherever possible. Non-linear continuum analyses using the Generalized Hoek-Brown failure criterion with rock mass properties is the foundation for these analyses. The first task (Task 1) toward these goals was to develop rock mass properties from available laboratory data using estimates of Geological Strength Index (GSI) for different lithologies. An important subtask was to perform an error analysis in estimates of rock mass properties assuming an amount of error in GSI estimates. Analyses and field observations were done for typical 4-way intersections at two mines in southern Illinois operating at depths of 150 m and 80 m, respectively in the No. 6 coal seam, which averages 1.8 m in thickness. Pre-mining horizontal stresses of 7.58 MPa and 4.13 MPa were applied in the E-W and N-S directions. These coal companies provided geologic logs and rock mechanics data for roof and floor strata. Rock mass engineering properties for different roof and floor lithologies were developed using estimated values of Geological Strength Index (GSI), and Hoek-Brown (H-B) rock mass failure parameters. A recent laboratory study provided normal and shear stiffness properties of the immediate roof interfaces within the bolting range of 1.8 m. MSHA-approved roof support plans were used for initial modeling. Short Encapsulation Pull Test (SEPT) data provided by bolt suppliers in the region were used to assign bolting system stiffness and strength parameters. Task 2 analyzed normal and shearing stresses and strains in and around mine intersections for typical pre-mining stress fields and then identified critical areas of failure initiation and progressive failure propagation. Failure initiation was hypothesized to occur for critical values of compressive (1 mm/m), tensile (0.5 mm/m), and shearing (0.5 mm/m) strains based on a review of laboratory stress-strain properties. This approach allows quantifying areas in and around an intersection where failures are likely to initiate with and without artificial supports. It computes three reinforcement factors with and without supports: reinforcement against tensile (RFT), compressive (RFC) and shearing (RFSS) strains. Task 3 assessed the performance of currently practiced roof support plans and identified where inadequacies exist and how they could be improved through spatial distribution of supports and their characteristics. Analyses were completed for two mines with one orientation of pre-mining horizontal stress field. The next logical step (Task 4) was to extend analyses in Task 3 to assess the effect of maximum compressive stress orientation in relation to entry direction (0o, 30o, 60o & 90o) and different cut sequences and their effect on changes in failure initiation and failure propagation mechanisms. Numerical analyses have shown that stress and strain distributions are significantly different when the cut sequence is included in models. For a horizontal stress ratio of two (2), the 60o orientation provided maximum stability. Separate models with all cuts excavated simultaneously corresponded well with the well-established NIOSH software AHSM and previous research. The effect of cut sequence combined with the directional effect of pre-mining stresses becomes evident from the dissimilar results. A separate statistical study was conducted on 211 SEPT test data provided by a roof support manufacturer and marketing company in the region. Goals were to analyze the database for grip factor (GF) and anchorage stiffness (AS) characteristics using histograms and frequency distributions and, perform regression analyses to relate GF and AS values on the basis of height above coal seam and bolt diameter. Results were used for one stochastic run with variable GF and AS values assigned to different bolts in a roof control plan. Results indicated Gamma distribution best fitted AS and GF data. It was thought that the reinforcement factor for such a bolting layout would be more realistic than assigning a single value of GF and AS to bolts in the model.

This research on Reusable Launchers was motivated by the need to reduce substantially the cost of space transportation. The specific objective was to explore the perception that launcher reusability is the key to achieving these major cost reductions. The exploration was achieved by undertaking a comparative system study on potentially feasible reusable launcher concepts, using a consistent set of design tools, a standard analysis methodology and a standard reference mission. To set the background for the research, the results of an extensive literature review are presented on the vehicle studies and technology developments that are engaged across the world on reusable launchers. Comprehensive vehicle studies appear to be engaged without justification for the choice of selected concepts in the absence of results from comparative system studies of reusable launchers. Technology developments also appear to be engaged without clear links to needs derived from vehicle system studies. The challenge of reusability is then addressed. Firstly, to set the performance and cost targets of reusable launchers, the capabilities of current expendable launchers are derived. Secondly, to establish the operational requirements for reusable launchers, the probable space transportation needs for the early 21st century are derived. Thirdly, the concepts and characteristics of reusable launchers are derived, allowing the selection, on a rationale basis, of a short-list of 13 potentially feasible reusable launcher concepts for analysis in the research. The performance equations of reusable launchers are then derived, leading to the preparation of the comparative analysis tools. The major work of the research, which comprises the performance analysis, technical feasibility assessment and cost analysis of each candidate vehicle, are then presented and compared. A set of acceptance requirements for performance, technical feasibility and operational costs of reusable launchers is then derived. The results of the comparative analysis for each candidate launcher are then measured against these requirements. The results of the comparative analysis show that only 2 of the 13 candidate reusable launcher concepts are able to meet all the acceptance requirements. These two acceptable vehicles are both rocket-propelled. They are, in order of preference: a single-stage-to-orbit, rocket-propelled, vertical launch and vertical landing vehicle; a two-stage-to-orbit, rocket-propelled, vertical launch and horizontal landing vehicle. The operational costs per launch for these two vehicles, based on a utilisation plan of 3 vehicles operating for 20 years at a launch rate of 12 launches per year, was calculated to be about 20% of the current costs of the European Ariane 44L expendable launcher. This warrants their further evaluation in a thorough feasibility study. The more complex, air-breathing propelled, horizontal launch and landing vehicles were found to be unable to meet the performance, technical feasibility and cost requirements; Several vehicles were found to be unable to deliver a positive payload mass to orbit; Several vehicles were found to have technology requirements that were deemed to be infeasible to achieve; Several vehicles were found to have operational costs ranging from equal to double that of the European Ariane 44L expendable launcher, which was adopted as a comparative reference vehicle. The contributions of this research to the advancement of knowledge on reusable launchers are: a clear identification of the performance capability limits of 13 plausible reusable launcher concepts; an analysis methodology for determining the performance capability limits for any reusable launcher concept; a clear identification of the reasons for the poor practical performance of air-breathing propulsion systems for Earth-to-orbit launchers, which results from their installed operational characteristics.

Made available in DSpace on 2014-10-09T12:37:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:18Z (GMT). No. of bitstreams: 1 05331.pdf: 854473 bytes, checksum: 5ebbe017fcb96df6aa5676f168b04c50 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:38:16Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:47Z (GMT). No. of bitstreams: 1 05660.pdf: 7392125 bytes, checksum: eb370b9192c312fd26fdb86ad9ed35bc (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

O estudo da dependencia espacial de variaveis do solo ou da planta, atraves da teoria das variaveis regionalizadas ou geoestatistica, permite a interpretacao e a projecao dos resultados com base na estrutura da sua variabilidade natural. Com o conhecimento das posicoes relativas das amostragens ou medidas feitas a campo, a variabilidade espacial passa a ser utilizada como um fator positivo identicando interacoes importantes nas conclusoes experimentais. O estudo da variabilidade de um solo, alem de caracterizar uma regiao, pode indicar o numero e a distribuicao de amostras a serem retiradas possibilitando ainda maior detalhamento da area e dos resultados. A base para a adocao dos procedimentos geoestatisticos e sua justicativa e o entendimento e o tratamento da variavel em questao. Para aplicacao desses procedimentos e fundamental a compreensao dos instrumentos e conceitosutilizados, tais como: semivariograma, autocorrelacao, hipotese de estacionaridade, efeito pepita, patamar, alcance, anisotropia, krigagem e outros. Desta maneira o presente trabalho apresenta e discute conceitos e metodos geoestatisticos, analisando o comportamento de dados reais de duas variaveis fisicas do solo: densidade do solo e umidade do solo nas tensoes da capacidade de campo e ponto de murcha permanente, de modo a avaliar a magnitude da variabilidade espacial, as caracteristicas qualitativas ligadas a estrutura do fenomeno natural que elas representam e a estrutura de correlacao existente entre valores tomados em dois pontos adjacentes no espaco. Para tanto, foram obtidas estimativas das estatisticas, gracos e mapas de dispersao e superficie que descrevessem espacial o comportamento da variavel em estudo. Os resultados demonstram a capacidade dos metodos em informar e ajudar a compreender o comportamento dos fenomenos fornecendo informacoes para o planejamento e analise estatistica futuras. / The study of the spatial dependence of parameters of soil or plant, through the theory of regionalized variables or geostatistics, can allow the interpretation and the projection of the results based on the structure of its natural variability. Knowing the relative positions of the samplings or field measures, the spatial variability can be used as a positive factor identifying important interactions in the experimental conclusions. The study of the soil variability, besides area characterization can indicate the number and the distribution of samples that should be removed and facilitate larger details of the area and the results. The adoption of geostatistical procedures and its justification is based on the understanding and the treatment of the cited variable. To apply these procedures it is important to know the instruments and concepts used, such as: semivariogram, autocorrelation, estationarity hypothesis, effect nugget, sill, range, anisotropy, kriging and others. Thereby this work presents and discusses geostatistical concepts and methods, analyzing the behavior of true data of two physical variables of the soil: density of the soil and soil-water content in the tensions of field capacity and point of permanent withered, to evaluate the magnitude of the spatial variability, the qualitative characteristics linked to the structure of the natural phenomenon that they represent and the structure of existent correlation among values taken in two adjacent points in the space. For such analysis statistics estimates, graphs and maps of dispersion and surface, that described spatially the behavior of the variable in study were obtained. The results demonstrate the capacity of the methods in informing and helping to understand the behavior of the phenomenons supplying information for the planning and future statistical analysis.

Made available in DSpace on 2014-10-09T12:37:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:18Z (GMT). No. of bitstreams: 1 05331.pdf: 854473 bytes, checksum: 5ebbe017fcb96df6aa5676f168b04c50 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:38:16Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:47Z (GMT). No. of bitstreams: 1 05660.pdf: 7392125 bytes, checksum: eb370b9192c312fd26fdb86ad9ed35bc (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP