Doctor Scientiae / The management of the large volumes of solid wastes produced as coal combustion residue is of particular concern due to the presence of leachable metals and salts which may constitute a long term environmental risk and potential contamination of both surface and groundwater systems of the surrounding environment. In order to implement an efficient monitoring scheme and to assess the impact of the ash dump on the hydrologic system, a thorough knowledge on the migration of solutes fluxes in dry ash dumps as well as the controls on the transport of these solutes to the underlying groundwater system is required. The conventional methods which have been widely used for such applications are centred on extracting and analysing several samples from observation wells are drilled on the dump. This has however created a potentially hazardous situation as the installation of monitoring wells may result in the creation of new fluid pathways and results in further migration of leachates. Nevertheless, non–invasive characterization has often been useful in the determination of subsurface hydraulic properties and is a key step towards the solution of real-life problems in hydrology, hydrogeology and soil science. In contaminant transport non-invasive methods have often proved to be an efficient tool as compared to traditional drilling and sampling techniques which in most cases results in the creation of preferential flow paths and do not allow for the space and time resolution needed for the monitoring of hydrological and environmental processes. In this context, this study seeks to develop a generic conceptual model for the ash dump through the use of non-invasive geophysical techniques and numerical modelling techniques at the Tutuka Ash dump, Mpumalanga South Africa. Changes in electrical resistivity were used correlate changes in moisture contents during moisture and salt leachate ingression in ash dumps with a sufficient accuracy. A determination of the suitability of Archie‘s law to describe the relationship between electrical resistivity and solute transport ash medium was achieved through empirical laboratory experiments. Electrical resistivity tomography was then used as an appropriate tool for the elucidation of potential flow paths and brine dispersion in the ash dump. The flow rates through the ash dump were estimated by considering the rate of brine injection and the distance travelled by the brine plume over the time spanned in time lapse infiltration experiments. Additional geophysical profiles managed to show the lithostratigraphy of underlying hydro-geology, thereby ensuring that the knowledge of the geology can be established without the application of any intrusive methods. To ensure that development of the conceptual model of the unsaturated zone transport of the ash dump was developed with sufficient accuracy, numerical models were also used to describe solute transport in the vadose zone. The HYDRUS2D numerical package was used simulate the flux dynamics within the unsaturated zone of the coal ash medium, so as to develop a conceptual understanding of water flow and salt transport through the unsaturated zone of the coal ash medium. The results from the study suggested a conceptual solute transport model that consists of a two layers. The upper layer represented the unsaturated zone of the ash dump which was the source of any potential contaminant transport that could be of concern. The lower layer describe the underlying the subsurface environment to the ash dump which include the soil zone, the shallow aquifer and the deep fractured rock aquifer. To enable this conceptualisation, results from the numerical simulations and geophysical interpretations of the electrical resistivity profiles were the critical components for optimising the site-specific subsurface water flow and solute transport processes, as well as producing the most acceptable conceptualisation of the ash dump system that could be used in hazard assessment and mitigation against potential groundwater pollution. The conceptual models developed in this study proposed an explanation on impact of the ash dump to the hydro-geologic and the eco-hydrologic environment by proposing a scenario of contamination of the underling ash dump and the existing. In this regard, the study managed to provide important scenarios that may be necessary during mitigation procedures for both the ash dump and the wetland. Key words: non-invasive, coal ash, time lapse, electrical resistivity tomography, numerical models, HYDRUS2D, conceptual model.

Management of water quality is generally based on physically-based equations or hypotheses describing the behaviour of water bodies. In recent years models built on the basis of the availability of larger amounts of collected data are gaining popularity. This modelling approach can be called data driven modelling. Observational data represent specific knowledge, whereas a hypothesis represents a generalization of this knowledge that implies and characterizes all such observational data. Traditionally deterministic numerical models have been used for predicting flow and water quality processes in inland and coastal basins. These models generally take a long time to run and cannot be used as on-line decision support tools, thereby enabling imminent threats to public health risk and flooding etc. to be predicted. In contrast, Data driven models are data intensive and there are some limitations in this approach. The extrapolation capability of data driven methods are a matter of conjecture. Furthermore, the extensive data required for building a data driven model can be time and resource consuming or for the case predicting the impact of a future development then the data is unlikely to exist. The main objective of the study was to develop an integrated approach for rapid prediction of bathing water quality in estuarine and coastal waters. Faecal Coliforms (FC) were used as a water quality indicator and two of the most popular data mining techniques, namely, Genetic Programming (GP) and Artificial Neural Networks (ANNs) were used to predict the FC levels in a pilot basin. In order to provide enough data for training and testing the neural networks, a calibrated hydrodynamic and water quality model was used to generate input data for the neural networks. A novel non-linear data analysis technique, called the Gamma Test, was used to determine the data noise level and the number of data points required for developing smooth neural network models. Details are given of the data driven models, numerical models and the Gamma Test. Details are also given of a series experiments being undertaken to test data driven model performance for a different number of input parameters and time lags. The response time of the receiving water quality to the input boundary conditions obtained from the hydrodynamic model has been shown to be a useful knowledge for developing accurate and efficient neural networks. It is known that a natural phenomenon like bacterial decay is affected by a whole host of parameters which can not be captured accurately using solely the deterministic models. Therefore, the data-driven approach has been investigated using field survey data collected in Cardiff Bay to investigate the relationship between bacterial decay and other parameters. Both of the GP and ANN models gave similar, if not better, predictions of the field data in comparison with the deterministic model, with the added benefit of almost instant prediction of the bacterial levels for this recreational water body. The models have also been investigated using idealised and controlled laboratory data for the velocity distributions along compound channel reaches with idealised rods have located on the floodplain to replicate large vegetation (such as mangrove trees).

Numerous macroscale models of arteries have been developed, comprised of populations of discrete coupled Endothelial Cells (EC) and Smooth Muscle Cells (SMC) cells, an example of which is the model of Shaikh et al. (2012), which simulates the complex biochemical processes responsible for the observed propagating waves of Ca2+ observed in experiments. In a 'homogenised' model however, the length scale of each cell is assumed infinitely small while the population of cells are assumed infinitely large, so that the microscopic spatial dynamics of individual cells are unaccounted for. We wish to show in our study, our hypothesis that the homogenised modelling approach for a particular system can be used to replicate observations of the discrete modelling approach for the same system. We may do this by deriving a homogenised model based on Goldbeter et al. (1990), the simplest possible physiological system, and comparing its results with those of the discrete Shaikh et al. (2012), which have already been validated with experimental findings. We will then analyse the mathematical dynamics of our homogenised model to gain a better understanding of how its system parameters influence the behaviour of its solutions. All our homogenised models are essentially formulated as partial differential equations (PDE), specifically they are of type reaction diffusion PDEs. Therefore before we begin developing the homogenised Goldbeter et al. (1990), we will first analyse the Brusselator PDE with the goal that it will help us to understand reaction diffusion systems better. The Brusselator is a suitable preliminary study as it shares two common properties with reaction diffusion equations: oscillatory solutions and a diffusion term.

L’aménagement progressif du territoire conduit à l’exploitation de nouvelles zones, actuellement délaissées, car présentant des risques pour la sécurité des usagers. C’est notamment le cas des zones d’effondrements potentiels qui sont liées à la présence de cavités souterraines. Parmi les nombreuses solutions préventives, le renforcement géosynthétique permet de prévenir les risques d’effondrement localisés. Cette solution de renforcement est largement utilisée à la fois pour ses avantages économiques et environnementaux, que pour sa facilité et rapidité de mise en œuvre. Néanmoins, les méthodes de conception existantes des plateformes granulaires renforcées par géosynthétiques sont fondées sur diverses hypothèses simplificatrice et ne prennent pas en compte toute la complexité du problème. En effet, ces méthodes ne considèrent pas par exemple l’influence du mode d’ouverture de la cavité, le foisonnement du sol granulaire au droit de la cavité ou encore la distribution de charge sur le géosynthétique après ouverture de la cavité.La présente étude tente d’améliorer les méthodes de dimensionnement en analysant les mécanismes développés dans la plateforme granulaire renforcée sur la base d’une campagne expérimentale couplée à des modélisations numériques.Un dispositif expérimental a été développé pour simuler l’ouverture d’une cavité sous une plateforme renforcée par géosynthétique. Ce dispositif permet de simuler deux modes d’ouverture : une trappe qui s’abaisse ou une ouverture concentrique, pour différentes hauteurs de plateformes. Les mécanismes de renforcement sont étudiés en mesurant la déflexion du géosynthétique, le tassement en surface et la distribution de contrainte verticale qui s’applique du le géosynthétique. Un modèle numérique par éléments finis a été calibré sur les résultats expérimentaux puis utilisé pour analyser finement les mécanismes pour de nombreuses configurations.Cette étude expérimentale et numérique a permis d’améliorer la compréhension des mécanismes de transfert de charge et de foisonnement dans la zone effondrée et de valider expérimentalement l’influence du mode d’ouverture sur les mécanismes. Sur la base de ces résultats, des propositions sont formulées pour améliorer le dimensionnement des plateformes renforcées par géosynthétiques soumises à des effondrements localisés. / The progressive development of the territory leads to the exploitation of new areas, which are currently being abandoned because they come up risks to the safety of users. This is particularly the case for areas of potential collapse that are related to the presence of underground cavities. Among the many preventative solutions, geosynthetic reinforcement prevents localized collapse. This solution is widely used for both its economic and environmental benefits, as well as for its ease and speed of setting up. However, the existing design methods for granular platforms reinforced by geosynthetic are based on various simplifying assumptions and do not take the complexity of the problem into account. These methods do not consider, for example, the influence of how the cavity is opened, the expansion of granular soil above the cavity, or the stress distribution on the geosynthetic after opening the cavity.The present study tries to improve the design methods by analyzing mechanisms developed inside the reinforced granular platform on the basis of an experimental study coupled with numerical simulations.An experimental device was developed to simulate the opening of a cavity under a platform reinforced by geosynthetic. This device allows simulating two types of opening: a trapdoor or a concentric opening, for various heights of platforms. The mechanisms are studied by measuring the deflection of the geosynthetic, the settlement at the surface and the stress distribution applied of the geosynthetic. A finite element model was calibrated on the experimental results then used to analyze mechanisms finely for many configurations.This experimental and numerical study allows improving the understanding of the stress distribution, the soil expansion above the cavity and experimentally validated the influence of the opening mode on the mechanisms. Based on these results, proposals are formulated to improve the design of geosynthetic-reinforced platforms subject to localized collapse.

Este projeto apresenta a construção de um modelo numérico do Sistema Aqüífero Guarani pelo método de elementos finitos para auxiliar o gerenciamento de recursos hídricos subterrâneos na área do projeto piloto de Ribeirão Preto, localizada na região nordeste do Estado de São Paulo. Dados topográficos, hidrológicos e hidrogeológicos da região de interesse foram obtidos principalmente de mapas (impressos e digitais) e poços cadastrados junto a órgãos governamentais, em cooperação com o grupo coordenador do projeto piloto de Ribeirão Preto. Os dados levantados foram armazenados, processados e analisados utilizando ferramenta SIG, seguida da geração de mapas interpolados com características hidrogeológicas. Esses dados foram transferidos para o software de simulação SPA, onde se deu a construção da malha de elementos finitos e a atribuição dos parâmetros e condições de contorno ao modelo. Em seguida, foi feita uma análise de sensibilidade do modelo, e testadas algumas configurações de parâmetros hidrogeológicos e de taxas de recarga. O modelo apresentou bons resultados e desempenho, e, como parte de uma constante evolução, são propostas visitas de campo para verificação de dados para o seguimento desse projeto. / This work presents a numerical model for the Guarani Aquifer System management in the Ribeirão Preto pilot project area, located in the Northeast of São Paulo State. Topographical, hydrological and hydrogeological data of the region were obtained from printed and digital maps and well database recorded in governmental departments, in cooperation with the Ribeirão Preto coordinating group of the pilot project. The collected data were stored, processed and analyzed making use of GIS tool, followed by the generation of interpolated maps with hydrogeological parameters. These data were transferred to the SPA simulation software, which is based on the finite element method. After mesh construction, and attribution of parameters and boundary conditions, a sensitivity analysis of the model was performed. Different hydrogeological parameter configurations were tested. The model proved to represent the established conceptual model adequately. However base flow data and field visits are necessary, in order to improve the model representativity.

Understanding the behaviour of waves and their interaction with the coast is vital for marine engineers and maritime planners. As sea levels rise due to climate change, low-lying coastal areas and existing sea defences will become increasingly vulnerable to run-up and overtopping by large wave events. Accurate and effcient numerical models are essential tools for the assessment of such events and the impact they have on the coast so that effective coastal protection can be designed. This thesis presents a depth-integrated numerical solver with two horizontal dimensions for modelling waves in the coastal zone from intermediate depth to zero depth. Pre-breaking, the evolution of the water surface is calculated using the enhanced Boussinesq equation set of Madsen and Sorensen (1992). This equation set has improved dispersion characteristics over the classical Boussinesq equations, but with relatively few terms compared to models based on the Navier-Stokes equations, allowing for more effcient numerical modelling while maintaining suffcient accuracy. The equations are discretised using second-order finite differences and solved using the conjugate gradient method with fourth-order Runge-Kutta time stepping. Switching from the Boussinesq equation set to the shallow water equations allows shoaling waves to break, with the broken waves then propagating as bores. The shallow water equations are solved using a finite volume MUSCL-Hancock scheme with an HLLC approximate Riemann solver in order to resolve the behaviour of steep-fronted bores at the shore. The model incorporates a wetting and drying algorithm that models the moving wet/dry front. Waves are generated by a line of independently moving piston paddles, allowing full replication of laboratory experiments. A mapping technique is used in the region of the paddles to map the moving physical domain onto a fixed computational domain to facilitate the solution of the governing equations. Different aspects of the model are verified using standard benchmark tests. The complete model is then validated by comparing the numerical simulation of laboratory experiments with high quality experimental data from the UK Coastal Research Facility (UKCRF). The laboratory experiments simulated include the interaction of regular waves with sinusoidal and tri-cuspate beaches, and the interaction of both uni-directional and multi-directional focused wave groups with a plane beach. It is found that the model provides satisfactory wave phase resolution and reproduces most of the flow features of waves and currents in the shallow nearshore environment.

Este projeto apresenta a construção de um modelo numérico do Sistema Aqüífero Guarani pelo método de elementos finitos para auxiliar o gerenciamento de recursos hídricos subterrâneos na área do projeto piloto de Ribeirão Preto, localizada na região nordeste do Estado de São Paulo. Dados topográficos, hidrológicos e hidrogeológicos da região de interesse foram obtidos principalmente de mapas (impressos e digitais) e poços cadastrados junto a órgãos governamentais, em cooperação com o grupo coordenador do projeto piloto de Ribeirão Preto. Os dados levantados foram armazenados, processados e analisados utilizando ferramenta SIG, seguida da geração de mapas interpolados com características hidrogeológicas. Esses dados foram transferidos para o software de simulação SPA, onde se deu a construção da malha de elementos finitos e a atribuição dos parâmetros e condições de contorno ao modelo. Em seguida, foi feita uma análise de sensibilidade do modelo, e testadas algumas configurações de parâmetros hidrogeológicos e de taxas de recarga. O modelo apresentou bons resultados e desempenho, e, como parte de uma constante evolução, são propostas visitas de campo para verificação de dados para o seguimento desse projeto. / This work presents a numerical model for the Guarani Aquifer System management in the Ribeirão Preto pilot project area, located in the Northeast of São Paulo State. Topographical, hydrological and hydrogeological data of the region were obtained from printed and digital maps and well database recorded in governmental departments, in cooperation with the Ribeirão Preto coordinating group of the pilot project. The collected data were stored, processed and analyzed making use of GIS tool, followed by the generation of interpolated maps with hydrogeological parameters. These data were transferred to the SPA simulation software, which is based on the finite element method. After mesh construction, and attribution of parameters and boundary conditions, a sensitivity analysis of the model was performed. Different hydrogeological parameter configurations were tested. The model proved to represent the established conceptual model adequately. However base flow data and field visits are necessary, in order to improve the model representativity.

Thin layers (layers that are not resolvable in terms of GPR wavelengths) are very common in sedimentary deposits. To better understand ground penetrating radar (GPR) wave behavior in sequences of thin layers with contrasting electromagnetic parameters, 1D FDTD simulations are run for simple layer distributions. Laminated (mm-scale) sequences can produce reflected energy with 10-20% of the amplitude of reflections from equivalent isolated contacts. Amplitude spectra from laminae packages are shifted toward higher frequencies. Such spectral shifts in radar profiles may potentially be used as indicators of fine-scale laminations. A comparative study of GPR records and models generated from core data from Waites Island, South Carolina, a Holocene barrier island, suggest that magnetite-rich laminae contribute significantly to radar profiles, but that some features in the radar traces cannot be associated with lithologic changes seen in vibracores.

The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime. The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.

Excellent properties of Carbon Fiber Reinforced Polymer (CFRP) composites are usually obtained in the direction at which carbon fibers are embedded in the polymeric matrix material. The outstanding properties of this material such as high strength to weight ratio, high stiffness and high resistance to corrosion can be tailored to meet specific design applications. Despite their excellent mechanical properties, application of CFRPs has been limited to more lucrative sectors such as aerospace and automotive industries. This is mainly due to the high costs involved in manufacturing of this material. Machining, milling and drilling, is a critical part of finishing stage of manufacturing process. Milling and drilling of CFRP is complicated due to the inhomogeneous nature of the material and extreme abrasiveness of carbon fibers. This is why CFRP parts are usually made near net shape. However, no matter how close they are produced to the final shape, there still is an inevitable need for some post machining to obtain dimensional accuracies and tolerances. Problems such as fiber-matrix debonding, subsurface damage, rapid tool wear, matrix cracking, fiber pull-out, and delamination are usually expected to occur in machining CFRPs. These problems can affect the dimensional accuracy and performance of the CFRP part in its future application. To improve the efficiency of the machining processes, i.e. to reduce the costs and increase the surface quality, researchers began studying machining Fiber Reinforced Polymer (FRP) composites. Studies into FRPs can be divided in three realms; analytical, experimental and numerical. Analytical models are only good for a limited range [0° – 75°] of Fiber Orientations , to be found from now on as “FO” in this thesis. Experimental studies are expensive and time consuming. Also, a wide variety of controlling parameters exist in an experimental machining study; including cutting parameters such as depth of cut, cutting speed, FO, spindle speed, feed rate as well as tool geometry parameters such as rake angle, clearance angle, and tool edge/nose radius. Furthermore, the powdery dust created during machining is known to cause serious health hazards for the operator. Numerical models, on the other hand, offer the unique capability of studying the complex interaction between the tool and workpiece as well as chip formation mechanisms during the cut. Large number of contributing parameters can be included in the numerical model without wasting material. Three main objectives of numerical models are to predict principal cutting force, thrust force and post-machining subsurface damage. Knowing these, one can work on optimization of machining process by tool geometry and path design. Previous numerical studies mainly focus on the orthogonal cutting of FRP composites. Thus, the existing models in the literature are two-dimensional (2D) for the most part. The 2D finite element models assume plain stress or strain condition. Accordingly, the reported results cannot be reliable and extendable to real cutting situations such as drilling and milling, where oblique cutting of the material occurs. Most of the numerical studies to date claim to predict the principle cutting forces fairly acceptable, yet not for the whole range of fiber orientations. Predicted thrust forces, on the other hand, are generally not in good agreement with experimental results at all. Subsurface damage is reported by some experimental studies and again only for a limited FO range. To address the lack of reliable force and subsurface damage prediction model for the whole FO range, this thesis aims to develop a 3D finite element model, in hope of capturing out-of-plane displacements during stress formation in different material phases (Fiber, Matrix and the Interface bonding). ABAQUS software was chosen as the most commonly used finite element simulation tool in the literature. In present work a user-defined material subroutine (VUMAT) is developed to simulate behavior of carbon fibers during the cut. Carbon fibers are assumed to behave transversely isotropic with brittle (perfectly elastic) fracture. Epoxy matrix is simulated with elasto-plastic behavior. Ductile and shear damage models are also incorporated for the matrix. Surface-based cohesive zone technique in ABAQUS is used to simulate the behavior of the zero-thickness bonding layer. The tool is modeled as a rigid body. Mechanical properties were extracted from the literature. The obtained numerical results are compared to the experimental and numerical data in literature. The model is capable of capturing principal forces very well. Cutting force increases with FO from zero to 45° and then decreases up to 135°. The simulated thrust forces are still underestimated mainly due to the fiber elastic recovery effect. Also, the developed 3D model is shown to capture the subsurface damage generally by means of a predefined dimensionless state variable called, Contact Damage (CSDMG). This variable varies between zero to one. It is stored at each time step and can be called out at the end of the analysis. It was shown that depth of fiber-matrix debonding increases with increase in FO. / Graduate