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1
Ho, Chau-man, and 何秋文. "Idealisation for mathematical modelling in geotechnical practice." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B45014280.
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2
Zhao, Qian, and 赵倩. "A thermomechanical approach to constitutive modeling of geomaterials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47166836.
Full textAbstract:
Modeling of the mechanical behavior of geomaterials is a fundamental yet very
difficult problem in geotechnical engineering. The difficulty lies in that the
engineering behavior of geomaterials is strongly nonlinear and anisotropic,
depending on confining pressure, void ratio, stress history, and drainage conditions.
A traditional approach to the modeling of geomaterials is to formulate empirical
equations to fit experimental data. Generally, this approach is not able to provide
physical insights into the diverse responses observed in the soil mechanics
laboratories. Another conventional approach is to make use of the classical
plasticity theory, established mainly for metals, to develop constitutive models for
geomaterials. While this approach is capable of shedding light on the mechanisms
involved, it has been recognized that such models may violate the basic laws of
physics.
The objective of this thesis is to apply a new approach to constructing constitutive
models for geomaterials, by making use of thermomechanical principles. The
essence of the new approach is that the constitutive behavior of geomaterials can be
completely determined once two thermomechanical potentials, i.e. the free energy
and dissipation rate functions, are specified. The yield function and flow rule in the
classical plasticity theory can be established from the two potentials, and the
models so derived satisfy the basic laws of physics automatically. In this thesis, the
theoretical framework for constructing thermomechanical models is introduced.
Several concepts in relation to plastic work, dissipated and stored energy are
discussed. Both the isotropic and anisotropic models are formulated and realized in
this framework and the generated predictions are compared with the test data of a
series of triaxial compression tests on sand. To address the important density- and
pressure-dependent behaviors of sand in the framework, a state-dependent
thermomechanical model is developed, by introducing the state parameter into the
dissipation rate function such that a unique set of model parameters is able to
predict the behaviors of sand for a wide variation of densities and pressures. Finally,
a thermomechanical model for predicting the complex unloading and reloading
behaviors of sand is developed by modifying the hardening laws, and the
performance of this model is investigated.published_or_final_version
Civil Engineering
Master
Master of Philosophy
3
Krantz, Robert Warren, and Robert Warren Krantz. "THE ODD-AXIS MODEL: ORTHORHOMBIC FAULT PATTERNS AND THREE-DIMENSIONAL STRAIN FIELDS." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/187542.
Full textAbstract:
Recent observations have highlighted the shortcomings of traditional thinking about faults and fault patterns. The slip model of faulting, developed by Ze'ev Reches, suggests that four sets of faults, arranged in orthorhombic symmetry about the principal strain axes, can accommodate general, three-dimensional strain. Classic conjugate faults are simply a special case of plane strain. Careful analysis of orthorhombic fault patterns and the tenets of the slip model has led to the development of a practical method for decoding the strain significance of fault systems developed in three-dimensional strain fields. The methods are implicit in a model here called the odd-axis model. This new model calls special attention to the odd axis: the one principal strain with sign opposite the other two, assuming a constant volume deformation. Odd-axis medel equations relate fault set geometry to principal strain magnitudes or ratios, the internal friction angle, φ, and the ratio of average fault slip to average spacing between faults of the same set, R. For systems where R < 0.1, the three principal strain ratios are given by tan²α, -sin²α, and -COS²α, where α is the strike of the fault set(s) measured in the plane perpendicular to the odd axis. The model also predicts slip vector orientations as functions of principal strain ratios and orientations. The kinematic implications of the odd-axis model are compatible with those of the slip model. In this first quantitative field test, both fault models are applied to the Chimney Rock array, a system of orthorhombic faults in the northern San Rafael Swell of central Utah. The odd-axis model uses fault plane and slip vector data from Chimney Rock to predict principal strain ratios (ε(y)/ε(x), ε(y)/ε(z), and ε(x)/ε(z)) of .20, -.16, and -.84. These compare extremely well with the observed values, based on fault separation measurements, of .17, -.15, and -.85. The value of ε(y)/ε(z) predicted by the slip model, -.16, matches exactly the value predicted by the odd-axis model and nearly matches the observed value, which is -.15. The success of the field test at Chimney Rock, and the conceptual agreement of both models, suggest that the new theory can accurately relate orthorhombic fault geometries and three-dimensional strain fields. Furthermore, the results underscore how important it is for geologists to recognize the sensitivity of fault geometry and kinematics to three-dimensional strain.
4
Camp, Nicholas Julian. "A model for the time dependent behaviour of rock joints." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/21138.
Full textAbstract:
This thesis is a theoretical investigation into the time-dependent behaviour of rock joints. Much of the research work that has been conducted to date in the area of finite element analysis has been involved with the development of special elements to deal with these discontinuities. A comprehensive literature survey is undertaken highlighting some of the significant contributions to the modelling of joints. It is then shown how internal variables can be used to model discontinuities in the rock mass. A finite element formulation is described resulting in a system of equations which can easily be adapted to cope with various constitutive behaviours on the discontinuities. In particular, a viscoplastic relationship; which uses a homogeneous, hyperbolic yield function is adopted. The viscoplastic relationship can be used for both time-dependent (creep) or quasi-static (elasto-plastic) problems. Time-dependent behaviour requires a time integration scheme and therefore a generalised explicit/implicit scheme is chosen. The resulting numerical algorithms are all implemented in the finite element program, NOSTRUM. Various examples are presented to illustrate certain features of both the formulation and the numerical algorithm. Jointed rock beams and a jointed infinite rock mass are modelled assuming plane strain conditions. Reasons are proposed to explain the predicted behaviour. The results of the analysis shows that the internal variable formulation successfully models time-dependent joint movements in a continuous media. The method gives good, qualitative results which agree with observations in deep level mines. It is recommended that quantitative mine observations be used to calibrate the model so that usable predictions of joint movement can be made. This would enable any new developments to be implemented in the model. Further work on implicit methods might allow greater modelling flexibility by reducing computer run times.
5
Biesiada, Veronica Catherine. "A Characterization of Structures Across the Hurricane Ridge Fault in the Southeastern Olympic Peninsula, WA, Hamma Hamma River Transect." PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/4883.
Full textAbstract:
The Olympic Mountains in northwestern Washington, USA are defined by the arcuate shape of the basaltic Crescent Formation (Fm.) that wraps a faulted and folded meta-sedimentary core. This area was developed through accretion and exhumation by subduction-related processes, but how this relates to the deformational history of the area is not fully understood. The region has been mapped geologically, however little focus has been placed on interpreting meso-scale structures. This study investigates structures along a transect where the Hamma Hamma River crosses the Hurricane Ridge Fault, which juxtaposes the meta-sedimentary core (west) and the basaltic Crescent Fm. (east). In the study area, the meta-sedimentary unit is characterized by outcrop scale folding with a calculated fold axis of 69-->342 and a penetrative foliation with a representative orientation of (178, 75). The folds and foliation are crosscut by two fracture populations with representative orientations of (115, 61) and (303, 76). The pillow basalts of the Crescent Fm. are near vertical, N-S striking beds that are cut by four fault groups. Fault Groups A and B have representative orientations of (304, 37) and (207, 59), respectively, and are associated with similarly oriented fracture populations. Fault Group C crosscuts Groups A and B and has a representative orientation of (031, 61). Fault Group D runs subparallel to the outcrop, cuts all other faults, and has a representative orientation of (087, 50). From an interpretation of this data, a deformation model is presented that proposes three distinct periods of deformation under three different states of stress. The first period was dominated by E-W or ENE-WSW oriented compression, followed by a period of N-S or NNW-SSE oriented compression, followed by vertical compression.
6
Wijns, Christopher P. "Exploring conceptual geodynamic models : numerical method and application to tectonics and fluid flow." University of Western Australia. School of Earth and Geographical Sciences, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0068.
Full textAbstract:
Geodynamic modelling, via computer simulations, offers an easily controllable method for investigating the behaviour of an Earth system and providing feedback to conceptual models of geological evolution. However, most available computer codes have been developed for engineering or hydrological applications, where strains are small and post-failure deformation is not studied. Such codes cannot simultaneously model large deformation and porous fluid flow. To remedy this situation in the face of tectonic modelling, a numerical approach was developed to incorporate porous fluid flow into an existing high-deformation code called Ellipsis. The resulting software, with these twin capabilities, simulates the evolution of highly deformed tectonic regimes where fluid flow is important, such as in mineral provinces. A realistic description of deformation depends on the accurate characterisation of material properties and the laws governing material behaviour. Aside from the development of appropriate physics, it can be a difficult task to find a set of model parameters, including material properties and initial geometries, that can reproduce some conceptual target. In this context, an interactive system for the rapid exploration of model parameter space, and for the evaluation of all model results, replaces the traditional but time-consuming approach of finding a result via trial and error. The visualisation of all solutions in such a search of parameter space, through simple graphical tools, adds a new degree of understanding to the effects of variations in the parameters, the importance of each parameter in controlling a solution, and the degree of coverage of the parameter space. Two final applications of the software code and interactive parameter search illustrate the power of numerical modelling within the feedback loop to field observations. In the first example, vertical rheological contrasts between the upper and lower crust, most easily related to thermal profiles and mineralogy, exert a greater control over the mode of crustal extension than any other parameters. A weak lower crust promotes large fault spacing with high displacements, often overriding initial close fault spacing, to lead eventually to metamorphic core complex formation. In the second case, specifically tied to the history of compressional orogenies in northern Nevada, exploration of model parameters shows that the natural reactivation of early normal faults in the Proterozoic basement, regardless of basement topography or rheological contrasts, would explain the subsequent elevation and gravitationally-induced thrusting of sedimentary layers over the Carlin gold trend, providing pathways and ponding sites for mineral-bearing fluids.
7
Burgess, Peter Mark. "A quantitative forward modelling analysis of the controls on passive rift-margin stratigraphy." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:1249833d-ef11-4327-bdbd-5d0c40faa29e.
Full textAbstract:
A quantitative forward model has been developed to investigate the controls on the deposition, erosion, and preservation of passive rift margin stratigraphy. The model includes thermal subsidence, variable absolute sealevel, flexural isostasy, subaerial and submarine deposition on fluvial and marine equilibrium profiles, and the facility to vary sediment supply through time. Results from the quantitative model can be used to reproduce elements of the sequence stratigraphic depositional model. Conducting sensitivity tests demonstrates that variables such as sediment supply and fluvial profile behaviour are likely to be of equal importance to thermal subsidence and eustasy in passive margin stratigraphy. Sensitivity tests with the quantitative model also demonstrate the problems associated with attempting to use a discretised stratigraphic model to investigate unforced cyclicty resulting from complex interactions in stratigraphic systems. Although the model appears capable of producing such unforced cyclical behaviour, this cyclicity is shown to be due to a numerical instability within the model which occurs with certain initial conditions and assumptions. The applicability of the model to observed stratigraphy is tested by comparing specific model output to patterns of stratigraphy from the North American Atlantic margin. The results from this test demonstrate that although the model is in many respects simplistic when compared to the complexities of natural systems, it is nevertheless capable of reproducing some of the basic elements of the observed stratigraphic patterns.
8
Linde, Tamara Causer. "Relational Database Analysis of Dated Prehistoric Shorelines to Establish Sand Partitioning in Late Holocene Barriers and Beach Plains of the Columbia River Littoral Cell, Washington and Oregon, USA." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1696.
Full textAbstract:
Studies of episodic shoreline accretion of the Columbia River Littoral Cell (CRLC) have been ongoing since 1964. In this study, the sediment volumes in the late Holocene barriers and beach plains are compiled and formatted in GIS compatible databases for the four sub-cells of the CRLC.
Initial evaluation involved the creation of a geodatabase of 160 dated retreat scarp positions, that were identified on across-shore GPR and borehole profiles. Ten primary timelines were identified throughout the CRLC (0-4700 ybp) and those were used to develop polygon cells. Elevation, distance measurements, and position information were all linked to the polygon through a centroid location within the geodatabase.
Once the geodatabase was completed, data was imported into MSAccessTM to create a relational database that would allow for examination of the littoral cell in its entirety or of the individual sub-cells. Within the database, sediment volumes, ages, accretion rates, sediment thicknesses, and timeline relationships were calculated and recorded.
Using the database, the accretion history of the Columbia River Littoral Cell was evaluated and this examination illustrated the complexity of the system. Northern littoral transport was shown to be an important factor in the development of the littoral cell as a whole. Total sediment volume in the littoral cell was calculated to be 1.74 x 109 m3, with a mean accretion rate of 1.90 x 104 m3/yr, which is significantly less than some previous studies. This is due to a more detailed analysis of the beach and foredune facies themselves. This is likely the result of the higher precision of beach and foredune surface information using LiDAR.
The database shows that the developmental history of the CRLC is dependent on temporal and spatial constraints that can be coupled with reverse modeling to predict shoreline erosion trends from impounded river sediments and potential global sea level rise. The North Beaches and Grayland Plains sub-cells have the greatest potential for future erosion; followed by the Clatsop Plains sub-cell.
9
Waibel, Michael Scott. "A Numerical Model Investigation of the Role of the Glacier Bed in Regulating Grounding Line Retreat of Thwaites Glacier, West Antarctica." Thesis, Portland State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10259298.
Full textAbstract:
I examine how two different realizations of bed morphology affect Thwaites Glacier response to ocean warming through the initiation of marine ice sheet instability and associated grounding line retreat. A state of the art numerical ice sheet model is used for this purpose. The bed configurations used are the 1-km resolution interpolated BEDMAP2 bed and a higher-resolution conditional simulation produced by John Goff at the University of Texas using the same underlying data. The model is forced using a slow ramp approach, where melt of ice on the floating side of the grounding line is increased over time, which gently nudges the glacier toward instability. Once an instability is initiated, the anomalous forcing is turned off, and further grounding line retreat is tracked.
Two model experiments are conducted. The first experiment examines the effect of different anomalous forcing magnitudes over the same bed. The second experiment compares the generation and progress of instabilities over different beds. Two fundamental conclusions emerge from these experiments. First, different bed geometries require different ocean forcings to generate a genuine instability, where ice dynamics lead to a positive feedback and grounding line retreat becomes unstable. Second, slightly different forcings produce different retreat rates, even after the anomalous forcing is shut off, because different forcing magnitudes produce different driving stresses at the time the instability is initiated. While variability in the retreat rate over time depends on bed topography, the rate itself is set by the magnitude of the forcing. This signals the importance of correct knowledge of both bed shape and ocean circulation under floating portions of Antarctic ice sheets. The experiments also imply that different ocean warming rates delivered by different global warming scenarios directly affects the rate of Antarctic contribution to sea level rise.
10
Hiester, Justin. "Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1022.
Full textAbstract:
Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes.
Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen.
11
Delaneze, Marcelo Elias [UNESP]. "Modelagem dinâmica espacial aplicada na avaliação das mudanças da cobertura da terra no entorno de dutos utilizando autômatos celulares: estudo de caso duto ORBEL." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/92738.
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A obtenção de informação sobre as condições da rede dutoviária representa papel primordial na operação dos dutos, não só com o propósito de manter a eficiência operacional, mas também, para a minimização dos riscos associados a possíveis acidentes, tanto decorrentes dos processos naturais quanto de causas antrópicas relacionadas ao uso e cobertura da terra. Neste sentido, o emprego de modelos matemáticos em estudos ambientais gera importantes contribuições científicas ao planejamento ordenado de uma área, uma vez que ajudam a entender o impacto das mudanças no uso e cobertura da terra e a prever alterações futuras nos ecossistemas. A área de estudo compreende porções dos municípios de Duque de Caxias, Belford Roxo e Nova Iguaçu e tem por objetivo realizar experimentos de mudanças da cobertura da terra em médio prazo (10 anos) para a faixa de dutos ORBEL. A modelagem realizada neste trabalho foi desenvolvida no software Dinamica-EGO, utilizando como entrada mapas classificados de cobertura da terra, obtidos através de imagens do satélite Landsat 5/TM, e variáveis espaciais para explicar as mudanças ocorridas na cobertura da terra. Para a calibração do modelo, utilizou-se o método de pesos de evidência, disponível no Dinamica-EGO, primeiramente categorizando-se os mapas de variáveis contínuas e, posteriormente, calculando-se os pesos de evidência. Valores positivos favorecem determinada transição, enquanto valores negativos indicam baixa probabilidade de transição, e valores próximos a zero não exercem efeito. A validação do modelo se deu pelo método de similaridade fuzzy, com decaimento exponencial. Os resultados mostram que, para os dois períodos analisados (1987-1998 e 1998-2010), a taxa de mudança para a transição “vegetação arbórea para outros” é bem maior do que para...
Reliable information about conditions of pipeline network represents a major role in the operation of pipelines, not only in order to maintain operational efficiency, but also to minimize the risks associated with possible accidents such as rupture of the ducts due to landslides or mudslides mass block, causing damage to humans and the environment. The use of mathematical models in environmental studies allows significant scientific contributions to the physical planning of an area, since they help to understand the impact of changes in land use and land cover and predict future trends of changes in ecosystems. The study area includes portions of the municipalities of Duque de Caxias, Nova Iguaçu, and Belford Roxo and aims to carry out experiments in land-cover changes in the medium-term (10 years) within the catchment area of ORBEL pipelines. The modeling performed in this work was developed using the software Dinamica-EGO, using as input classified land cover maps obtained from Landsat 5/TM satellite images as well as spatial variables to explain the observed changes in land cover. For the model calibration, we used the method of weights of evidence that is available at Dinamica-EGO. Initially, the maps of continuous variables were categorized according to discrete ranges, which were then employed for the calculation of the respective positive weights of evidence. Positive values foster certain transitions, while negative values indicate low probability of transition, and values close to zero have no effect on changes. Model validation was executed by means of the fuzzy similarity method using exponential decay. The results show that for the two study periods (1987-1998 and 1998-2010) the rate of change for the transition 'others to woody vegetation' is much higher than for the other transitions observed in the same... (Complete abstract click electronic access below)
12
Bienen, Britta. "Three-dimensional physical and numerical modelling of jack-up structures on sand." University of Western Australia. School of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0208.
Full textAbstract:
Mobile offshore jack-up drilling rigs are not custom-designed for a particular location but rated for typical operating characteristics, like water depths. They may be deployed at a number of different sites during their design life. Under the current guidelines, the jack-up is required to be assessed for its suitability for each new proposed location, assuming environmental loading conditions due to wind, waves and current corresponding to a 50-year return period storm applicable to the site. Traditionally, these assessments have been performed in two dimensions, simplifying the jack-up to a plane frame and the loading conditions to be in-plane with the rig's 'axis of symmetry'. This thesis introduces a computer program, named SOS_3D, for the fluid-structure-soil interaction analysis of jack-up response in three dimensions. Extensive experimental series have been performed to provide evidence for the generalisation of the foundationsoil interaction model to general six degree-of-freedom loading conditions and its applicability to load paths and stress levels relevant to jack-up spudcans. These experiments included (1) 1g single footing tests, (2) centrifuge single footing tests and (3) centrifuge model jack-up tests. The latter tests highlighted differences in response and mode of failure depending on the loading direction of the jack-up and re-iterated the importance of three-dimensional modelling. The numerical program SOS_3D introduced early in this thesis was shown to represent a useful tool for the prediction of jack-up behaviour under general combined loading in three dimensions. It provided reasonably good, conservative predictions of the experimentally measured jack-up behaviour.
13
Pokhrel, Pranav. "The Study of Temporal and Spatial Variability of Degree Day Factor of Snowmelt in Colorado." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849730/.
Full textAbstract:
Snowmelt is one of the major sources of surface water supply and ground-water recharge in high elevation areas and can also cause flooding in snow dominated watersheds. Direct estimation of daily snowmelt requires daily snow water equivalent (SWE) measurements that are not always available, especially in places without monitoring stations. There are two alternative approaches to modeling snowmelt without using direct measurements of SWE, temperature-based and energy-based models. Due to its simplicity, computational efficiency, and less input data requirement, the temperature-based method is commonly used than the energy-based method. In the temperature-index approach snowmelt is estimated as a linear function of average air temperature, and the slope of the linear function is called the degree-day factor (DDF). Hence, the DDF is an essential parameter for utilizing the temperature-based method to estimate snowmelt. Thereby, to analyze the spatial properties of DDF, 10 years DDF from the entire state of Colorado was calculated for this research. Likewise, to study the temporal properties, DDFs for 27 years from the White Yampa water basin and the Colorado Headwaters water basin were calculated.
As a part of the spatial analysis, the calculated DDFs were correlated with spatial variables (slope, aspect, latitude and elevation) and a spatial correlation graph was created to observe the possibility of predicting DDF. Also a multivariate regression model was prepared using these spatial variables to predict the DDF using spatial variables. Further, the DDFs calculated from Colorado headwaters and the White Yampa water basins were correlated for annual temporal variation, daily variation, variation with peak snow water equivalent and variation with important temporal cycles like accumulation period and melting period of snowmelt. The result obtained from this study showed that the variability of DDF is more dependent upon temporal factors compared to the spatial factors. Also, the results showed that predicting DDF is a difficult process and requires complex methods than simple linear models or multivariate models.
14
Delaneze, Marcelo Elias. "Modelagem dinâmica espacial aplicada na avaliação das mudanças da cobertura da terra no entorno de dutos utilizando autômatos celulares : estudo de caso duto ORBEL /." Rio Claro : [s.n.], 2011. http://hdl.handle.net/11449/92738.
Full textAbstract:
Orientador: Paulina Setti RiedelBanca: Cláudia Maria de Almeida
Banca: Maria Lúcia Marques
Resumo: A obtenção de informação sobre as condições da rede dutoviária representa papel primordial na operação dos dutos, não só com o propósito de manter a eficiência operacional, mas também, para a minimização dos riscos associados a possíveis acidentes, tanto decorrentes dos processos naturais quanto de causas antrópicas relacionadas ao uso e cobertura da terra. Neste sentido, o emprego de modelos matemáticos em estudos ambientais gera importantes contribuições científicas ao planejamento ordenado de uma área, uma vez que ajudam a entender o impacto das mudanças no uso e cobertura da terra e a prever alterações futuras nos ecossistemas. A área de estudo compreende porções dos municípios de Duque de Caxias, Belford Roxo e Nova Iguaçu e tem por objetivo realizar experimentos de mudanças da cobertura da terra em médio prazo (10 anos) para a faixa de dutos ORBEL. A modelagem realizada neste trabalho foi desenvolvida no software Dinamica-EGO, utilizando como entrada mapas classificados de cobertura da terra, obtidos através de imagens do satélite Landsat 5/TM, e variáveis espaciais para explicar as mudanças ocorridas na cobertura da terra. Para a calibração do modelo, utilizou-se o método de pesos de evidência, disponível no Dinamica-EGO, primeiramente categorizando-se os mapas de variáveis contínuas e, posteriormente, calculando-se os pesos de evidência. Valores positivos favorecem determinada transição, enquanto valores negativos indicam baixa probabilidade de transição, e valores próximos a zero não exercem efeito. A validação do modelo se deu pelo método de similaridade fuzzy, com decaimento exponencial. Os resultados mostram que, para os dois períodos analisados (1987-1998 e 1998-2010), a taxa de mudança para a transição "vegetação arbórea para outros" é bem maior do que para... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Reliable information about conditions of pipeline network represents a major role in the operation of pipelines, not only in order to maintain operational efficiency, but also to minimize the risks associated with possible accidents such as rupture of the ducts due to landslides or mudslides mass block, causing damage to humans and the environment. The use of mathematical models in environmental studies allows significant scientific contributions to the physical planning of an area, since they help to understand the impact of changes in land use and land cover and predict future trends of changes in ecosystems. The study area includes portions of the municipalities of Duque de Caxias, Nova Iguaçu, and Belford Roxo and aims to carry out experiments in land-cover changes in the medium-term (10 years) within the catchment area of ORBEL pipelines. The modeling performed in this work was developed using the software Dinamica-EGO, using as input classified land cover maps obtained from Landsat 5/TM satellite images as well as spatial variables to explain the observed changes in land cover. For the model calibration, we used the method of weights of evidence that is available at Dinamica-EGO. Initially, the maps of continuous variables were categorized according to discrete ranges, which were then employed for the calculation of the respective positive weights of evidence. Positive values foster certain transitions, while negative values indicate low probability of transition, and values close to zero have no effect on changes. Model validation was executed by means of the fuzzy similarity method using exponential decay. The results show that for the two study periods (1987-1998 and 1998-2010) the rate of change for the transition 'others to woody vegetation' is much higher than for the other transitions observed in the same... (Complete abstract click electronic access below)
Mestre
15
Thurley, Matthew J. (Matthew John) 1971. "Three dimensional data analysis for the separation and sizing of rock piles in mining." Monash University, Dept. of Electrical and Computer Systems, 2002. http://arrow.monash.edu.au/hdl/1959.1/7855.
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Levy, Nina Hannah. "Modelling multi-directional behaviour of piles using energy principles." University of Western Australia. Dept. of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0211.
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The loads applied to pile foundations installed offshore vary greatly from those encountered onshore, with more substantial lateral and torsional loads. For combined axial and lateral loading the current design practice involves applying an axial load to a deep foundation and assessing the pile behaviour and then considering a lateral load separately. For the problem of an altering directions of lateral loads (e.g. due to changes in the wind directions acting on offshore wind turbines) a clear design procedure is not available. There is thus a need for a clearly established methodology to effectively introduce the interaction between the four different loading directions (two lateral, one axial and one torsional). In this thesis, a model is presented that introduces a series of Winkler elasto-plastic elements coupled between the different directions via local interaction yield surfaces along the pile. The energy based method that is used allows the soil-pile system to be defined explicitly using two equations: the energy potential and the dissipation potential. One of the most interesting applications of this model is to piles subjected to a change in lateral loading direction, where the loading history can significantly influence the pile behaviour. This effect was verified by a series of experimental tests, undertaken using the Geotechnical Centrifuge at UWA. The same theory was then applied to cyclic loading in two dimensions, leading to some very useful conclusions regarding shakedown behaviour. A theoretically based relationship was applied to the local yielding behaviour for a pile subjected to a combination of lateral and axial loading, allowing predictions to be made of the influence of load inclination on the pile behaviour. The ability of this model to represent interaction between four degrees of freedom allows a more realistic approach to be taken to this problem than that considered in current design practice.
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Weatherford, Jonathan Michael. "Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2479.
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The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption.
A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components.
The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components.
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Zhang, Dongxiao. "Conditional stochastic analysis of solute transport in heterogeneous geologic media." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186553.
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This dissertation develops an analytical-numerical approach to deterministically predict the space-time evolution of concentrations in heterogeneous geologic media conditioned on measurements of hydraulic conductivities (transmissivities) and/or hydraulic heads. Based on the new conditional Eulerian-Lagrangian transport theory by Neuman, we solve the conditional transport problem analytically at early time, and express it in pseudo-Fickian form at late time. The stochastically derived deterministic pseudo-Fickian mean concentration equation involves a conditional, space-time dependent dispersion tensor. The latter not only depends on properties of the medium and the velocity but also on the available information, and can be evaluated numerically along mean "particle" trajectories. The transport equation lends itself to accurate solution by standard Galerkin finite elements on a relatively coarse grid. This approach allows computing without using Monte Carlo simulation and explicitly the following: Concentration variance/covariance (uncertainty), origin of detected contaminant and associated uncertainty, mass flow rate across a "compliance surface", cumulative mass release and travel time probability distribution across this surface, uncertainty associated with the latter, second spatial moment of conditional mean plume about its center of mass, conditional mean second spatial moment of actual plume about its center of mass, conditional co-variance of plume center of mass, and effect of non-Gaussian velocity distribution. This approach can also account for uncertainty in initial mass and/or concentration when predicting the future evolution of a plume, whereas almost all existing stochastic models of solute transport assume the initial state to be known with certainty. We illustrate this approach by considering deterministic and uncertain instantaneous point and nonpoint sources in a two-dimensional domain with a mildly fluctuating, statistically homogeneous, lognormal transmissivity field. We take the unconditional mean velocity to be uniform, but allow conditioning on log transmissivity and hydraulic head data. Conditioning renders the velocity field statistically nonhomogeneous with reduced variances and correlation scales, renders the predicted plume irregular and non-Gaussian, and generally reduces both predictive dispersion and uncertainty.
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Romanó, James Luigi. "Modelo numérico para determinação de zonas de perda de circulação de fluido de perfuração em poços de petróleo." Universidade Tecnológica Federal do Paraná, 2017. http://repositorio.utfpr.edu.br/jspui/handle/1/2631.
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Durante a perfuração de poços de petróleo, a determinação do perfil de temperaturas no poço é importante para tomada de decisões relativas ao processo de cimentação, para a seleção de revestimento do poço e equipamentos e, sobretudo, na identificação de zonas de influxo e perda de circulação. Neste trabalho é proposto um modelo matemático da transferência de calor em regime transitório do escoamento de fluido de perfuração em poços fraturados com perda de circulação. O poço é representado de maneira simplificada através de um cilindro anular concêntrico, cuja parede externa (interface poço-formação) apresenta uma ou mais fraturas discretas. Para a obtenção do modelo térmico é realizado um balanço de energia com foco nas trocas de calor entre a coluna de perfuração, região anular e formação rochosa. A característica principal do modelo proposto é a possibilidade de detecção da posição e número de fraturas a partir do perfil do gradiente térmico da região anular ao longo poço. Para tanto, com o código numérico, obtido via método dos volumes finitos, investiga-se a influência de parâmetros: da fratura (profundidade relativa, perda de circulação, número e distância entre fraturas), físicos (tempo de circulação) e do regime de escoamento (número de Reynolds e viscosidade dos fluidos de perfuração). As variáveis-resposta principais analisadas são a temperatura da região anular e o gradiente térmico. Como variáveis-resposta secundárias são utilizadas as evoluções térmicas da temperatura no fundo do poço e na saída da região anular. É constatado que o aumento da profundidade relativa ou número de fraturas diminui a temperatura do fundo do poço, sem causar variação significativa na temperatura de saída do anular. Para a variação da perda de circulação, o efeito na temperatura do fundo do poço é similar ao da variação do aumento da profundidade relativa da fratura, no entanto são observadas diferenças na temperatura de saída. Além disso, é verificado que, conforme se aumenta o número de fraturas distribuídas ao longo da profundidade do poço, a temperatura do poço tende ao caso de poço não fraturado. De maneira similar é evidenciada a tendência de que a diminuição na distância entre fraturas se aproxima dos resultados para um poço com uma única fratura. Finalmente, o aumento da perda de circulação facilita a detecção de fraturas devido a respectiva mudança na descontinuidade do perfil do gradiente térmico da região anular.During oil drilling operations, the wellbore temperature profile is used when selecting well casing materials, making cementation related decisions, and, most importantly, to identify loss zones. In this work, a transient heat transfer mathematical model for a fractured wellbore is proposed. The well has its geometry simplified to a concentric annular cylinder which has one or more discrete fracture in its external wall (wellformation interface). In order to obtain the thermal model an energy balance is used, focusing the heat transfer between the pipe, the annular region and the formation. The key characteristic of the model is the fracture detection through thermal gradient graphical analysis. The thermal gradient is an output of the solution of the discretized energy equation in the domains, obtained through the finite volume method. The following parameters are investigated: fracture depth, fracture number, fracture interference, loss circulation, circulation time, Reynolds number and drilling fluid viscosity. The analysis is done through the analysis of the annular region temperature profile and its gradient, along with the thermal evolution of both the bottomhole and outlet temperatures. It is verified that increasing the fracture relative depth or number decreases the bottomhole temperature, while having no significant impact in the outlet temperature. The same bottomhole temperature effect is noted when increasing loss rate, however outlet temperature changes are observed. In a similar way, when decreasing the distance between fractures, the temperature profile in the annular region trends to a wellbore with a single fracture. Finally, increasing loss rate favors fracture detection, since the discontinuity in the annular region thermal gradient profile is intensified.
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Zhang, You-Kuan. "A quasilinear theory of time-dependent nonlocal dispersion in geologic media." Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185039.
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A theory is presented which accounts for a particular aspect of nonlinearity caused by the deviation of plume "particles" from their mean trajectory in three-dimensional, statistically homogeneous but anisotropic porous media under an exponential covariance of log hydraulic conductivities. Quasilinear expressions for the time-dependent nonlocal dispersivity and spatial covariance tensors of ensemble mean concentration are derived, as a function of time, variance σᵧ² of log hydraulic conductivity, degree of anisotropy, and flow direction. One important difference between existing linear theories and the new quasilinear theory is that in the former transverse nonlocal dispersivities tend asymptotically to zero whereas in the latter they tend to nonzero Fickian asymptotes. Another important difference is that while all existing theories are nominally limited to situations where σᵧ² is less than 1, the quasilinear theory is expected to be less prone to error when this restriction is violated because it deals with the above nonlinearity without formally limiting σᵧ². The theory predicts a significant drop in dimensionless longitudinal dispersivity when σᵧ² is large as compared to the case where σᵧ² is small. As a consequence of this drop the real asymptotic longitudinal dispersivity, which varies in proportion to σᵧ² when σᵧ² is small, is predicted to vary as σᵧ when σᵧ² is large. The dimensionless transverse dispersivity also drops significantly at early dimensionless time when σᵧ² is large. At late time this dispersivity attains a maximum near σᵧ² = 1, varies asymptotically at a rate proportional to σᵧ² when σᵧ² is small, and appears inversely proportional to σᵧ when σᵧ² is large. The actual asymptotic transverse dispersivity varies in proportion to σᵧ⁴ when σᵧ² is small and appears proportional to σᵧ when σᵧ² is large. One of the most interesting findings is that when the mean seepage velocity vector μ is at an angle to the principal axes of statistical anisotropy, the orientation of longitudinal spread is generally offset from μ toward the direction of largest log hydraulic conductivity correlation scale. When local dispersion is active, a plume starts elongating parallel to μ. With time the long axis of the plume rotates toward the direction of largest correlation scale, then rotates back toward μ, and finally stabilizes asymptotically at a relatively small angle of deflection. Application of the theory to depth-averaged concentration data from the recent tracer experiment at Borden, Ontario, yields a consistent and improved fit without any need for parameter adjustment.
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Chauvet, Pierre. "Elements d'analyse structurale des fai-k a 1 dimension." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0070.
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L'information structurale d'une fai d'ordre k definie sur une maille reguliere monodimensionnelle est contenue dans ses accroissements d'ordre k+1. On cherche a etablir la relation entre les covariances d'accroissements (experiences) et la covariance generalisee (modele) et a l'utiliser dans les deux sens. Une tentative d'expliciter la covariance generalisee a l'aide du variogramme generalise s'est soldee par un echec
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Price, Matthew. "Investigating the initial condition of mantle models using data assimilation." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/96504/.
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Mantle convection models are computational models that utilise the equations defining the convective processes taking place in a terrestrial planet’s mantle. Mantle circulation models (MCMs) are a subclass of mantle convection models that constrain mantle flow by imposing a boundary condition that uses plate reconstructions. Time dependent assimilation of plate velocities generates structures within the mantle that have been shown to correspond with present day Earth observations. Inferences of past mantle structures in MCMs are however more difficult due to the lack of initial condition for models. Without access to an initial condition for MCMs, pseudo initial conditions are used in MCM studies. MCMs therefore contain some error due to this uncertainty in initial condition. This thesis addresses the uncertainties in MCMs caused by the lack of knowledge of the initial condition, and attempts to improve the initial condition for Earth models. Utilising perturbed twin experiments we show that assimilating plate reconstructions deters any chaotic growth over the assimilation period, minimising the influence of the initial condition at present day. We also investigate and utilise advanced assimilation techniques that constrain mantle flow back in time, using a method known as an adjoint. Running a series of synthetic test cases using the adjoint we determine its efficiencies and effectiveness at constraining initial condition estimates. We find the adjoint is an excellent method for reconstructing initial conditions. Using the adjoint, we conclude by running high resolution MCMs to construct initial conditions for differing viscosities, and compare these to the | iii standard method of obtaining an initial condition in MCM studies. We find that this yields mantle flow patterns markedly different from past studies, implying the adjoint can provide an alternate perspective for past mantle flow studies.
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Orr, Shlomo. "Stochastic approach to steady state flow in nonuniform geologic media." Diss., The University of Arizona, 1993. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1993_409_sip1_w.pdf&type=application/pdf.
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Geyer, Traver Adelina. "Dynamics and structural evolution of collapse calderas: A comparison between field evidence, analogue and mathematical models." Doctoral thesis, Universitat de Barcelona, 2007. http://hdl.handle.net/10803/1921.
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Collapse calderas are defined as the volcanic depression that result from the disruption of the geometry of the magma chamber roof due to down faulting during the course of an eruption. These structures have received considerable attention due to their link to Earth's ore deposits and geothermal energy resources, but also because large pyroclastic eruptions and associated caldera collapse structures represent one of the most catastrophic geologic events that have occurred on the Earth's surface in the Phanerozoic time and in the historical time.After several pioneering works, collapse calderas have been the subject of studies of diverse disciplines. However, some important aspects on caldera dynamics and structure remain poorly understood yet.
First, we have revised important works concerning field data about collapse calderas and summarized the most relevant aspects and results. We have created a database to record existing information about collapse calderas: Collapse Caldera DataBase (CCDB). After an exhaustive analysis of the included information we have observed two types of collapse caldera: type-A and type-B.
Experiments on caldera collapse modelling allow a qualitative study of the structural evolution of a caldera collapse process and suggest which of factors play a more relevant role. Analogue models have verified that caldera collapse formation is influenced by multiple aspects (e.g. regional tectonics). We have performed three types of semi-quantitative analyses of particular interest for volcanic hazard: the measurement of the erupted magma chamber volume fraction required to achieve each step of the collapse process, the estimation of the subsidence pattern and the study of the influence of the roof aspect ratio in the dimensions of the collapse parts at surface.
This work includes also a summary of the most important aspects concerning mathematical models of collapse calderas. In base of a mathematical analysis of the pressure evolution inside the chamber during volcanic cycles, we have defined two collapse caldera end-members: under- and overpressure calderas. We have (1) reproduced numerically some of the analogue experiments set out in this work; (2) studied the influence of the selected geometrical setting (e.g. axial symmetric or three-dimensional) in the obtained results and subsequent interpretations and (3) demonstrated that results obtained with mathematical models not strictly related to collapse caldera processes are also applicable to the study of collapse mechanisms and controlling factors.
Finally, we compare the different results obtained by the three distinct disciplines, in order to propose a genetic classification for collapse calderas and to describe the dynamic and structural evolution of the defined end-members. We distinguish between "Cordilleran type" and "Composite volcano type" calderas. Calderas related to the first group correspond to commonly rhyolitic or dacitic, large plate/piston or trap-door calderas formed from a sill-like overpressurized magma chamber in the presence of a regional extensive stress field and a large scale doming or underplating. These calderas tend to occur in areas of thick or thin continental crust and in evolved transitional thick crust. They are associated with C-type subduction zones and areas of continental rifting. "Composite volcano type" calderas occur at the culmination of a long eruptive cycle in composite volcanoes. They take place at the summit of a long-lived volcanic edifice, which has undergone various periods of magma chamber inflation and deflation and different eruptions. The caldera-forming eruption begins with overpressure inside the chamber that triggers, once overcome the tensile strength of the host rock, magma injection into the host rock and finally, an eruption. Calderas included in this group tend to be smaller and not too voluminous.
Concluding, the combination of field studies with experimental and theoretical/mathematical and modelling allows us to identify and quantify the main factors controlling collapse calderas.
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Yang, Xin-She. "Mathematical modelling of compaction and diagenesis in sedimentary basins." Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:0bdc6c43-4534-4f08-97e2-8a33d6b13e61.
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Sedimentary basins form when water-borne sediments in shallow seas are deposited over periods of millions of years. Sediments compact under their own weight, causing the expulsion of pore water. If this expulsion is sufficiently slow, overpressuring can result, a phenomenon which is of concern in oil drilling operations. The competition between pore water expulsion and burial is complicated by a variety of factors, which include diagenesis (clay dewatering), and different modes (elastic or viscous) of rheological deformation via compaction and pressure solution, which may also include hysteresis in the constitutive behaviours. This thesis is concerned with models which can describe the evolution of porosity and pore pressure in sedimentary basins. We begin by analysing the simplest case of poroelastic compaction which in a 1-D case results in a nonlinear diffusion equation, controlled principally by a dimensionless parameter lambda, which is the ratio of the hydraulic conductivity to the sedimentation rate. We provide analytic and numerical results for both large and small lambda in Chapter 3 and Chapter 4. We then put a more realistic rheological relation with hysteresis into the model and investigate its effects during loading and unloading in Chapter 5. A discontinuous porosity profile may occur if the unloaded system is reloaded. We pursue the model further by considering diagenesis as a dehydration model in Chapter 6, then we extend it to a more realistic dissolution-precipitation reaction-transport model in Chapter 7 by including most of the known physics and chemistry derived from experimental studies. We eventually derive a viscous compaction model for pressure solution in sedimentary basins in Chapter 8, and show how the model suggests radically different behaviours in the distinct limits of slow and fast compaction. When lambda << 1, compaction is limited to a basal boundary layer. When lambda >> 1, compaction occurs throughout the basin, and the basic equilibrium solution near the surface is a near parabolic profile of porosity. But it is only valid to a finite depth where the permeability has decreased sufficiently, and a transition occurs, marking a switch from a normally pressured environment to one with high pore pressures.
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Sancevero, Sergio Sacani. "Estudo de aplicação de metodos quantitativos em dados sismicos no processo de caracterização integrada de reservatorios." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287444.
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Orientador: Armando Zaupa RemacreTese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociencias
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Resumo: O processo de caracterização de reservatórios é atualmente uma das etapas mais importantes na exploração, desenvolvimento e produção de um campo. Porém, para que esse processo seja realizado da melhor forma possível é preciso se ter o conhecimento de determinados métodos, que integram as diferentes informações disponíveis. Desse modo, o objetivo principal dessa tese é estudar de forma criteriosa e quantitativa o processo de caracterização de reservatórios do ponto de vista dos dados sísmicos, avaliando antigos e novos métodos, e definindo novas metodologias que possam ser aplicadas de maneira decisiva neste processo. Para que esses métodos pudessem ser avaliados de maneira conclusiva foi utilizado nesta tese um modelo sintético que reproduzisse minimamente algumas características cruciais de determinados reservatórios como a complexa distribuição dos corpos de areia e a presença de corpos com espessura subsísmica que levassem ao limite as técnicas de modelagem tradicionais, proporcionando avaliar novos métodos. Assim, para caracterizar essas complexas feições, foram utilizados nesta tese dois meios principais de interpretação, primeiro a inversão sísmica dando um caráter preditivo ao dado sísmico e por fim a análise multiatributos, dando um caráter classificatório. No caso da inversão sísmica foram utilizados três métodos de obtenção da impedância acústica. Entre eles, foi a inversão geoestatística que demonstrou ser a mais eficiente das técnicas no que diz respeito à caracterização de reservatórios com espessura subsísmica e complexa distribuição dos corpos de areia. No caso dos atributos, pôde-se demonstrar que é necessário que sejam tratados com uma abordagem multivariada para que seja aproveitada a correlação entre eles e que por meio de técnicas de classificação e modelagem possa se decidir os mais relevantes para o processo. Neste caso 3 métodos de análise multivariada foram apresentados e testados, sendo que dois deles (ICA e MAF) de maneira inédita e que produziram resultados superiores àqueles alcançados quando a tradicional técnica de PCA é aplicada. Assim, com o que foi apresentado, pode-se concluir que o processo de caracterização é um estágio crucial para o desenvolvimento dos campos, mas não é fácil de ser realizado, a menos que os métodos e as técnicas envolvidas sejam conhecidas de maneira profunda. Só assim, é possível extrair o máximo de informações do dado sísmico, caracterizando o reservatório de forma quantitativa e integrada, otimizando sua produção e reduzindo os riscos e custos com a sua explotação
Abstract: The reservoir characterization process can be considered curretly the most important stage in the exploration, development and production of the oil field. However, this process is only carried out in the best way if the geologists, geophisicist and engineering has the knowledge of some definitive methods and techniques that integrated all information available about the field. Thus, the aim of this thesis is to study in a criterious and quantitative way the reservoirscharacterization process, analyzing the seismic data,by the evaluation of classic and novel methods, to defining new methodlogies that can be applied in decisive way into this process. So, for these methods could be evaluated in a conclusive way, were used in this thesis asynthetic reference model that reproduced some critical features of determined reservoirs, as the complex distribution of sand bodies and the subseismic thickness. These characteristics pushing to the limit the traditional modelling techniques. In this thesis to characterizze the complex features present in the reference model we used two interpretation techniques, first we analyze the seismic inversion that give a preditive character to the seismic data and after we study the multiattribute analysis that give a classificatory caracter to the seismic interpretation. For the seismic inversion, the stochastic or geostatistical inversion, that demonstrated to be the most efficient technique to characterized the complex and the subseismic features present in the model. About the seismic attributes it could be demonstrated that even so in some cases they represent the features of the model, are necessary that they are dealt with a multivariate approach, to used the advantage of the correlation between them. For the seismic attribute analysis, 3 methods of multivariate statistics analysis were used, two of them (ICA and MAF) for the first time in the reservoir characterization processo With the results we can proved that these 2 new methods improved the process of multiattribute anlysis prducing superior results when compare with the results obtained by the application of traditional PCA technique. With it was presented, can be concluded that the reservoir characterization process is a crucial stage and have some difficults to be accomplishment, unless the methods and the involved techniques are known deeply. Thus it is possible to extract the maximum informations from the datasets, characterizing the reservoir in a quantitative and integrated environmental, optimizing its production and reducing the risks and the costs with its explotation
Doutorado
Administração e Politica de Recursos Minerais
Doutor em Ciências
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Talebi, Hassan. "On the spatial modelling of mixed and constrained geospatial data." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2018. https://ro.ecu.edu.au/theses/2279.
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Spatial uncertainty modelling and prediction of a set of regionalized dependent variables from various sample spaces (e.g. continuous and categorical) is a common challenge for geoscience modellers and many geoscience applications such as evaluation of mineral resources, characterization of oil reservoirs or hydrology of groundwater. To consider the complex statistical and spatial relationships, categorical data such as rock types, soil types, alteration units, and continental crustal blocks should be modelled jointly with other continuous attributes (e.g. porosity, permeability, seismic velocity, mineral and geochemical compositions or pollutant concentration). These multivariate geospatial data normally have complex statistical and spatial relationships which should be honoured in the predicted models.
Continuous variables in the form of percentages, proportions, frequencies, and concentrations are compositional which means they are non-negative values representing some parts of a whole. Such data carry just relative information and the constant sum constraint forces at least one covariance to be negative and induces spurious statistical and spatial correlations. As a result, classical (geo)statistical techniques should not be implemented on the original compositional data. Several geostatistical techniques have been developed recently for the spatial modelling of compositional data. However, few of these consider the joint statistical and/or spatial relationships of regionalized compositional data with the other dependent categorical information.
This PhD thesis explores and introduces approaches to spatial modelling of regionalized compositional and categorical data. The first proposed approach is in the multiple-point geostatistics framework, where the direct sampling algorithm is developed for joint simulation of compositional and categorical data. The second proposed method is based on two-point geostatistics and is useful for the situation where a large and representative training image is not available or difficult to build. Approaches to geostatistical simulation of regionalized compositions consisting of several populations are explored and investigated. The multi-population characteristic is usually related to a dependent categorical variable (e.g. rock type, soil type, and land use). Finally, a hybrid predictive model based on the advanced geostatistical simulation techniques for compositional data and machine learning is introduced. Such a hybrid model has the ability to rank and select features internally, which is useful for geoscience process discovery analysis.
The proposed techniques were evaluated via several case studies and results supported their usefulness and applicability.
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Romary, Thomas. "INVERSION DES MODELES STOCHASTIQUES DE MILIEUX HETEROGENES." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00395528.
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La problématique du calage d'historique en ingénierie de réservoir, c'est-à-dire le calage des modèles géostatistiques aux données de production, est un problème inverse mal posé. Dans un cadre bayésien, sa résolution suppose l'inférence de la distribution de probabilité du modèle géostatistique conditionné aux données dynamiques, rendant compte à la fois de l'a priori géologique, exprimé dans le modèle géostatistique, et de l'adéquation aux données de production. Typiquement, la résolution de ce problème passe par la génération d'un ensemble de réalisations calées aux données, échantillon représentatif de cette distribution. Les modèles géostatistiques sont en général discrétisés sur des grilles de plusieurs centaines de milliers, voire des millions de blocs ; les approches classiques tentent de résoudre le problème inverse en considérant l'ensemble des blocs comme paramètres du modèle. Sa dimension est alors considérable et les méthodes d'échantillonnages deviennent impraticables sur un cas réel. Il convient alors de choisir une paramétrisation susceptible de réduire la dimension du problème. Dans la première partie de cette thèse, nous présentons une méthode de paramétrisation optimale des modèles géostatistiques basés sur les champs aléatoires gaussiens, à partir de leur décomposition de Karhunen-Loève (KL). Nous en décrivons les fondements théo- riques, puis, sur des applications aux modèles de champs aléatoires gaussiens courants en géostatistique, selon des critères d'abord statistiques puis hydrodynamiques, nous quantifions la réduction de la dimension du problème offerte par cette paramétrisation. Dans la seconde partie, nous présentons les principes des méthodes de Monte-Carlo par Chaînes de Markov (MCMC) et les défauts des méthodes classiques pour la résolution du problème inverse dans le cadre bayésien. Nous développons alors l'approche par chaînes de Markov en interaction dont nous exposons les avantages. Enfin, les résultats obtenus par l'emploi conjoint de ces deux méthodes sont présentés dans deux articles. Une approche différente, passant par l'emploi de méthodes d'analyse de sensibilité, est également décrite dans un troisième article.
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MOUSAVI, NADOSHANI SEYED SAEID. "Composition des lois élémentaires en hydrologie régionale : application à l'étude des régimes de crue." Grenoble 1, 1997. http://www.theses.fr/1997GRE10165.
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Un evenement hydrologique est souvent defini d'apres plusieurs variables aleatoires presentant un certain degre de liaison. L'etude probabiliste de cet evenement necessite alors la composition de lois de probabilite. Nous avons considere deux cas d'applications : 1) l'extrapolation de la distribution du debit de pointe et du debit seuil ; 2) l'estimation du quantile du debit de crue a l'aval d'une confluence. Nous avons teste plusieurs fonctions de deux variables : les modeles de farlie-gumbel-morgenstern, de farlie et hashino, en utilisant des echantillons sup-seuil. Pour ce dernier modele, nous utilisons le coefficient de correlation obtenu avec la totalite de l'information (evenements concomitants et non concomitants). Les performances des modeles de composition ont ete testees sur des donnees reelles, puis sur des donnees simulees a l'aide du modele de generation de pluies journalieres shypre, du modele pluie-debit gr4j et d'un modele de liaison spatiale des pluies. Nous avons enfin etudie les hydrogrammes d'apport a injecter dans un modele hydraulique, de facon a rester homogene en frequence sur tout le lineaire de la riviere.
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Taverna, Joël. "Modélisation mécanique des déformations de la lithosphère." Grenoble 1, 1998. http://www.theses.fr/1998GRE10084.
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Les objectifs de cette these sont de decrire les mecanismes de deformations de la lithosphere en regime compressif, et le controle impose par les parametres mecaniques sur la maniere dont le raccourcissement horizontal est accommode (par la formation de plis, de chevauchements, ou encore par epaississement homogene). Nous avons etudie la nature des instabilites susceptibles de se developper en utilisant des calculs analytiques bases sur la resolution des equations de navier-stokes ainsi que leur evolution pour des taux de deformation importants a partir de modeles analogiques et de calculs numeriques par la methode des elements finis. Les calculs analytiques ont permis de determiner l'influence des differents parametres mecaniques de la lithosphere sur le developpement d'instabilites. En domaine oceanique, le raccourcissement est essentiellement accommode par la formation de plis affectant l'ensemble de la lithosphere. Les parties fragiles de la lithosphere et les contrastes de densite controlent la croissance des instabilites. Deux series d'experiences analogiques ont ensuite permis de confirmer les resultats precedents et d'etudier l'evolution tridimensionnelle d'instabilites lithospheriques apres l'apparition de la fracturation. En domaine continental, le passe tectonique et les heterogeneites mecaniques qui en resultent joue un role essentiel pour l'initiation des plis. Les heterogeneites initiales peuvent favoriser l'apparition de failles aux depends des plis de grandes longueurs d'onde puis la subsidence des portions de lithosphere ainsi delimitees. Les structures ainsi formees s'apparentent a des bassins compressifs. Leur longueur d'onde reste cependant controlee en partie par celle des plis lithospheriques. Ces resultats ont ete completes par des calculs numeriques bases sur la methode des elements finis. Les plis ne se developpent qu'apres plastification complete des parties fragiles de la lithosphere oceanique ou continentale.
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Taha, Ammar. "Etude expérimentale et numérique de la contribution des eaux infiltrées à la formation des débits des crues en zone méditerranéenne : application à un versant du Real Collobrier." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10052.
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L'objectif de ce travail est de contribuer a la comprehension du fonctionnement hydrologique d'un bassin versant mediterraneen, notamment a l'occasion de ses crues. Il est compose d'un premier volet experimental destine a l'observation du comportement des eaux souterraines. Ce volet inclut des mesures de pression de l'eau dans le sol et de niveaux des nappes (fugitives ou perennes) sous un versant (ligne de plus grande pente perpendiculaire a la riviere), et une analyse approfondie des sols du versant: granulometries, conductivites hydrauliques in situ mesurees a l'aide de differents appareillages, mesures de la retention en eau des sols etc. Les proprietes hydrodynamiques des sols en place sont egalement decrites. Utilisant cette description hydrodynamique, on tente ensuite de modeliser le comportement du versant lorsqu'il est soumis a la pluie. La modelisation cherche a reproduire les infiltrations et les mouvements de nappes observes. Pour ce faire on developpe un modele d'infiltration et de montee de nappe dans une zone inclinee d'un sol multicouche. Pour resoudre l'equation de richards differentes methodes ont ete developpees. La meilleure, dans notre travail, s'avere etre celle qui utilise les differences finies avec un procede iteratif des directions alternees. Les resultats de la modelisation confirment qu'en cas de pluies importantes, une nappe peut s'elever relativement rapidement a proximite de la riviere et l'alimenter. Toutefois, les forts debits ne peuvent s'expliquer que par la saturation de l'ensemble du profil du sol qui engendre la montee de ces nappes et par les ecoulements de surface que ces aires saturees entrainent
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Hood, Julie A. "Fracture estimation in anisotropic media." Thesis, 1990. http://hdl.handle.net/10125/9834.
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Le, Calvez Joel Herve. "Physical modeling of normal faults and graben relays above salt." 2002. http://wwwlib.umi.com/cr/utexas/fullcit?p3114767.
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McQueen, Herbert William Scriven. "Geophysical inference of inplane stress in the lithosphere using numerical models." Phd thesis, 1986. http://hdl.handle.net/1885/140395.
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Philip, Zeno George. "Incorporating subcritical crack growth mechanics into natural fracture characterization for improved reservoir simulation." Thesis, 2003. http://hdl.handle.net/2152/860.
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Burbidge, David Ross. "The complex evolution of accretionary wedges and thrust belts : results from numerical experiments using the distinct element method." Phd thesis, 2000. http://hdl.handle.net/1885/148094.
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Shi, Mingjuan. "Characterizing heterogeneity in low-permeability strata and its control on fluid flow and solute transport by thermalhaline free convection." Thesis, 2005. http://repositories.lib.utexas.edu/bitstream/handle/2152/1724/shim98915.pdf.
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Stenhouse, Iona Rosslyn. "Diffusion modelling to constrain the duration of metamorphism." Phd thesis, 2013. http://hdl.handle.net/1885/155999.
Full textAbstract:
In this study the application of the garnet-ilmenite system to the diffusion modelling technique was investigated. Experiments were undertaken to accurately determine the rates of geochemical processes that are associated with the garnet-ilmenite system. The diffusion parameters of elements within ilmenite have been quantified and it was found that the diffusivity is relatively fast compared to garnet. Therefore in a garnet-ilmenite diffusion model ilmenite diffusivity can be treated as infinite. Additionally, experiments on garnet with an ilmenite thin film as a diffusant source provided further constraints on the rate of diffusion in garnet. Evidence of diffusion profiles preserved in garnet surrounding ilmenite inclusions in natural samples was obtained. Samples from the Barrovian metamorphic sequence showed possible diffusional features in Mn concentration profiles adjacent to ilmenite inclusions in garnet from sillimanite zone samples. However, it was also observed that analytical artefacts affected Ti concentration profiles up to 30 micrometers from the boundary. Further evidence was obtained from samples from the Ivrea-Verbano Zone in Italy. These samples preserved Mn and Mg diffusion profiles adjacent to ilmenite inclusions in garnet. However, in these samples retrograde reactions caused the ilmenite to be enriched in Mn compared to garnet, therefore, partitioning between garnet and ilmenite was incongruent. Nonetheless, this result shows that the garnet-ilmenite system can provide important information on the tectonometamorphic history of a terrane. The garnet-ilmenite system was used to place constraints on the duration of metamorphism. This duration was obtained using a simple forward model of the diffusional processes. From this, the duration of the thermal event associated with the emplacement of magma in the Ivrea-Verbano Zone was determined to be between 100 000 years to 1 Ma. Additionally, constraints on the duration of Buchan metamorphism in Scotland were obtained from argon diffusion modelling. The results from modelling were compared to apparent age spectra from cordierite grade samples that preserved detrital ages. This comparison allowed a constraint to be placed on the maximum duration these rocks could have endured and still preserve pre-Grampian ages. The results indicate that the peak conditions of the cordierite zone of the Buchan metamorphic sequence could not have endured longer than 100 000 years. Diffusion modelling to obtain timescales for thermal events provides insight into the tectonometamorphic history of a terrane. The results of this study have added to the mounting evidence that the duration of regional metamorphism is short (e.g. O'Brien and Vrana, 1995; O'Brien, 1997; Dachs and Proyer, 2002; Faryad and Chakraborty, 2005; Viete et al., 2011b; Viete et al., 2011a; Ague and Baxter, 2007; Camacho et al., 2009). However, there are large uncertainties on the diffusion parameters utilised in diffusion models. Therefore for diffusion modelling to provide better constraints on the duration of regional metamorphism accurate rates of diffusion must be determined.
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Tian, Xiaochuan. "Structural and Climatic Effects of Large-Scale Basaltic Magmatism: Constraints and Insights from Geodynamic Models." Thesis, 2021. https://doi.org/10.7916/d8-2dvc-e762.
Full textAbstract:
This thesis concerns the causes and consequences of magma emplacement in the Earth’slithosphere during the formation of Large Igneous Provinces (LIPs) and continental rifts. Motivated by geological, geophysical, geochemical and paleoclimate data, I formulate geodynamic models to address the following questions: (1) How were the massive volumes of subaerially erupted lava, described in multi-channel seismic data as seaward-dipping reflectors (SDRs), formed and what can SDRs tell us about the rifting processes? (2) What thermal and rheological conditions are required to produce the contrast in topography of the two youngest LIPs: namely that the Columbia Plateau sits ~0.7 km lower than the surrounding region while the Ethiopian Plateau is ~1.5 km higher than its surroundings? (3) Why does significant global warming occur a few hundred-thousand years prior to the main phase of eruptions of the Columbia River Basalts and the Deccan Traps?
The major results of my thesis are: (1) The first two-dimensional thermo-mechanical treatment of SDR formation shows how the lithosphere thickness affects the deformation in response to magmatic loads during volcanic margin formation. I provide a quantitative mapping between the shape of SDRs and the strength of the lithosphere and this mapping reveals weak continental margin lithosphere during the initial continental breakup. (2) Cold and strong crust results in slow lower crustal flow and a persistent high plateau like the Ethiopian Plateau. In contrast, a combination of three things can produce a low plateau like the Columbia Plateau. First, hot and weak lower crust flows fast in response to topographic and magmatic loads. Second, a significant fraction of the magma intruded in the crust freezes onto and becomes part of the strong upper crust. Finally, the bulk of the intrusions occur before the main phase of extrusion to explain the geometry of the Columbia River Basalt lava flows. (3) I argue that the major eruptions of continental flood basalts may require densification of the crust by intrusion of larger volumes of magma than are extruded. Simple models show that magma crystallization and release of CO² from such intrusions could produce global warming before the main phase of flood basalt eruptions on the observed timescale.
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Zhou, Shaohua. "Geophysical investigations on the formation mechanism of the Eromanga Baisn, Australia / by Shaohua Zhou." Thesis, 1991. http://hdl.handle.net/2440/19778.
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Zhou, Shaohua. "Geophysical investigations on the formation mechanism of the Eromanga Baisn, Australia / by Shaohua Zhou." 1991. http://hdl.handle.net/2440/19778.
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Bibliography : leaves 214-246.xiii, 246 leaves : ill., maps ; 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, Dept. of Geology and Geophysics, 1992
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Bye, Alan Russell. "The development and application of a 3D geotechnical model for mining optimisation Sandsloot open pit platinum mine South Africa." Thesis, 2003. http://hdl.handle.net/10413/4114.
Full textAbstract:
Detailed geological knowledge is often a major unknown factor in open pit mining and design, and
therefore poses a significant risk in the mining venture. As the knowledge of the geology improves
so the risk of unforeseen conditions reduces and therefore safety and productivity can be increased.
Historically, geotechnical methods and information have predominantly been used exclusively for
pit slope optimisation. This research documents the procedures and developments undertaken to
compile a comprehensive geotechnical database, and the application of the geotechnical data to
open pit mining, beneficiation and planning. The utilisation of the geotechnical information has
been enhanced through the novel development and application of a computerised, 3D geotechnical
model.
Sandsloot open pit was developed to extract the Platreef pyroxenite orebody, which is hosted within
the Northern Limb of the Bushveld Complex. Sandsloot is currently the world's largest open pit
exploiting Platinum Group Metals. Interaction of the basic magma with the footwall sediments of
the Transvaal Supergroup and varying degrees of assimilation has resulted in a unique suite of
hybrid rock types. These various rock types provide significant engineering geological challenges.
Geology and the detailed understanding of its properties are fundamental to the optimal design and
successful operation of any mine. Extensive fieldwork was conducted to collect geotechnical
information, both from exploration boreholes and in-pit mining faces. Over a 5-year period,
geotechnical data were collected from 29,213 m of exploration core and 6,873 m of exposed
mining faces. Extensive field and laboratory testing was undertaken in order to define the complete
set of geotechnical properties for each rock type in the Sandsloot mining area.
The geotechnical information relating to each borehole and facemap was stored in the Datamine®
software package. The information was collected in the form of rock mass rating (RMR), uniaxial
compressive strength (DCS), fracture frequency (FF/m) and rock quality designation (RQD). The
architecture of the database was developed along the principals used for generating an ore reserve
model.
One of the novel applications was the development of a computerized 3D, geotechnical model in
Datamine®. The geotechnical parameters, namely RMR, DCS, FF/m and RQD, were modelled for
each rock type, using geostatistics, to generate a 3D model. The data were interpolated between
exploration boreholes and exposed mining faces and the modelling was constrained using
wireframes separated by rock type. The result is a 3D model containing 15 m3 model blocks
populated with interpolated geotechnical information. The dimensions of the model blocks are
linked to the mining bench height of 15 m. The model can be queried to give predictions on rock
mass conditions for any planned mining area, as is the case with the ore reserve model, which
provides predictions on platinum grades.
The crux of the innovative research is the practical application of the 3D geotechnical model. This
was achieved through the development of both a fragmentation and a slope design model, which
read the interpolated geotechnical information. These models provided an engineering tool to optimise mining and milling perfonnance.
Rather than viewing the drill and blast department as an isolated cost centre and focussing on
minimising drill and blast costs, the application of the model concentrated on the fragmentation
requirements of the milling and mining business areas. Two hundred and thirty-eight blasts were
assessed to detennine the optimum fragmentation requirements for ore and waste. Based on the
study a mean fragmentation target of 150 mm was set for delivery to the crushing circuit and a
mean fragmentation of 230 mm was set for waste loading from the pit.
The mine operates autogenous mills, which are sensitive to the fragmentation profile delivered.
The harder zones occurring in the ore zone have a major impact on the plant's perfonnance. The
geotechnical parameters in the model were related to Lilly's Blastability Index, and in turn to
required explosive volumes and the associated drill and blast costs. Having defmed the
fragmentation targets, the Kuz-Ram equation was used in the fragmentation model to predict the
explosive volumes required to ensure consistent mining and milling perfonnance. The
geotechnical model is used to predict changes in geotechnical conditions and therefore the blasting
parameters can be adjusted in advance to ensure the milling and mining fragmentation
requirements are met. Through the application of the fragmentation model over an eighteen-month
period the loading and milling efficiencies improved by 8.5% and 8.8% respectively, resulting in
additional revenue ofR29 million for PPL.
Based on the mining rock mass rating (MRMR) values within the geotechnical model a stable slope
design model was created in order to calculate optimum inter-ramp angles. From a slope design
perspective the model was used to target data-deficient zones and highlight potentially weak rock
mass areas. As this can be viewed in 3D, the open pit slopes were designed to accommodate the
poor quality areas before they are excavated. It also follows that competent geotechnical zones can
be readily identified and the slope optimised accordingly.
Due to the detailed geotechnical infonnation being available in three dimensions, the open pit
slopes were designed based on a risk versus reward profile. As a significant geotechnical database
was available, more accurate and reliable designs were generated resulting in the overall slope
angle increasing by 3 degrees. This optimisation process will result in a revenue gain of R900
million over the life of the mine. The revenue and safety benefits associated with this design
methodology are substantial and have potential application to all open pit mining operations.
The research has enabled detailed geotechnical infonnation to be available in three dimensions.
This information can be readily accessed and interpreted, thus providing a powerful planning and
financial tool from which production optimisations, feasibility studies and planning initiatives can
be implemented. The development and application of a 3D geotechnical model has added a new
dimension to the constant strive for business improvement and reflects a novel and successful
approach towards the application of engineering geology at the Sandsloot mining operation.Thesis (Ph.D.)-University of Natal, Durban, 2003.
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Gai, Xiuli 1970. "A coupled geomechanics and reservoir flow model on parallel computers." Thesis, 2004. http://hdl.handle.net/2152/1187.
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Caritat, de Peruzzis Patrice de. "Aspects of sediment diagenesis : empirical investigation (Denison Trough, Queensland) and theoretical modelling." Phd thesis, 1990. http://hdl.handle.net/1885/140634.
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Rasmi, S. N. "Importance Of Lateral Flow In Groundwater Modeling : A Case Study Of Hard Rock Aquifer Of Gundal Sub Basin." Thesis, 2005. https://etd.iisc.ac.in/handle/2005/1492.
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Rasmi, S. N. "Importance Of Lateral Flow In Groundwater Modeling : A Case Study Of Hard Rock Aquifer Of Gundal Sub Basin." Thesis, 2005. http://etd.iisc.ernet.in/handle/2005/1492.
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Jaaback, Kathryn Margaret. "A two-dimensional hydrodynamic model for the St Lucia Estuary mouth." Thesis, 1993. http://hdl.handle.net/10413/5907.
Full textAbstract:
The reduced fresh water input into the St Lucia Estuary combined with the increase
of sediment in the St Lucia Lake System has necessitated the implementation of a
dredging programme. To ensure the effectiveness of the dredging programme, the
behaviour of the sediment under various flow and tidal conditions needs to be
determined.
To establish how sediment will move, it is necessary to understand the hydrodynamics
of the estuary. To achieve this, a hydrodynamic model which can be linked to a
sediment transport model needs to be developed. Various existing types of
hydrodynamic and sediment transport models are reviewed, to determine their
suitability for the above purpose. Results of the analysis indicate that a two-dimensional
hydrodynamic model is required.
The two-dimensional hydrodynamic model developed is based on the momentum and
continuity equations for an unsteady, non-uniform, free-surface flow for an
incompressible fluid. The two dimensions are in the horizontal plane and flow is
averaged over the depth. The equations are non-linear and are not decoupled, thus
a numerical technique was needed to solve them. An Alternating Direction Implicit
technique has been used. Boundary conditions in the modelled region were specified
as flow velocity at the upstream boundary, and water levels, relative to the Mean
Lake Level, at the downstream boundary.
Two short simulations using hypothetical data were run on a 80826 IBM compatible.
Results of the simulation indicate two areas where irregularities in the model output
are a consequence of the use of hypothetical data in defining the boundary conditions.
Recommendations for the collection of data in order to improve and calibrate the
model are discussed.Thesis (M.Sc.)-University of Natal, 1993.
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Ushendibaba, Mhaka. "Using electromagnetic methods to map and delineate high-grade harzburgite pods within the Ni-Cu mineralised Jacomynspan ultramafic sill, Northen Cape, South Africa." Thesis, 2016. http://hdl.handle.net/10539/21007.
Full textAbstract:
A dissertation submitted to the Faculty of Science,
University of the Witwatersrand, Johannesburg,
in fulfilment of the requirements for the degree of Master of Science.
Johannesburg, 2016.The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion.
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Braunmiller, Jochen. "Down-dip geometry and depth extent of normal faults in the Aegean-evidence from earthquakes." Thesis, 1991. http://hdl.handle.net/1957/29365.
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Spießl, Sabine Maria. "Development and evaluation of a reactive hybrid transport model (RUMT3D)." Doctoral thesis, 2004. http://hdl.handle.net/11858/00-1735-0000-0006-B309-D.
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