Das Ziel dieser Arbeit ist die Untersuchung der Wasserhaushaltsprozesse und Stofftransportvorgänge innerhalb der grundwassergeprägten Talauenlandschaften von Tieflandeinzugsgebieten am Beispiel der im Nordostdeutschen Tiefland gelegenen Havel. Die Arbeiten in verschieden skaligen Teileinzugsgebieten der Havel beschäftigen sich dabei zum einen mit der experimentellen Untersuchung und vorrangig qualitativen Beschreibung der Wasserhaushaltsdynamik, zum anderen mit der Entwicklung eines zur quantitativen Analyse von Wasserhaushalts- und Stofftransportprozessen geeigneten Modells und der anschließenden Modellsimulation von Wasserhaushalt und Stickstoffmetabolik im Grundwasser sowie der Simulation von Landnutzungs- und Gewässerstrukturszenarien.<br><br> Für die experimentelle Untersuchung der Abflussbildung und der Wasserhaushaltsprozesse in den Talauenlandschaften des Haveleinzugsgebiets wurde Einzugsgebiet der &#8221;Unteren Havel Niederung&#8220; ein umfangreiches Messnetz installiert. Dabei wurden an mehreren Messstationen und Pegeln meteorologische Parameter, Bodenfeuchte sowie Grundwasserstände und Abflüsse beobachtet. Die Analyse der Messergebnisse führte zu einem verbesserten Verständnis von Wasserhaushaltsprozessen in der durch das oberflächennahe Grundwasser und die Oberflächengewässerdynamik beeinflussten Talauenzone. Darüber hinaus konnten durch die Implementierung der Messergebnisse konsistente Anfangs- und Randbedingungen für die Wasserhaushalts- und Grundwassermodellierung im Modellkonzept IWAN realisiert werden. Mit dem Modell IWAN (Integrated Modelling of Water Balance and Nutrient Dynamics) wurde ein Werkzeug geschaffen, welches die Berücksichtigung spezifischer hydrologischer Eigenschaften von Tieflandauen, wie z. B. den Einfluss des oberflächennahen Grundwassers bzw. der Dynamik von Oberflächenwasserständen auf den Wasserhaushalt, ermöglicht. Es basiert auf der Kopplung des deterministischen distribuierten hydrologischen Modells WASIM-ETH mit dem dreidimensionalen Finite-Differenzen-basierten Grundwassermodel MODFLOW. Die Modellierung der Stickstoffmetabolik im Grundwasser erfolgt durch das mit Grundwassermodell gekoppelte Stofftransportmodel MT3D. Zur modellbasierten Simulation des Wasserhaushalts der Tieflandauenlandschaften wurde das Modellkonzept IWAN für verschieden skalige Teileinzugsgebiete an der Havel für Simulationszeiträume von 2 Wochen bis zu 13 Jahren angewandt. Dabei wurden die Teilmodelle für Wasserhaushalts- und Grundwassermodellierung in zwei unterschiedlichen Teileinzugsgebieten der &#8221;Unteren Havel Niederung&#8220; kalibriert. Die anschließende Validierung erfolgte für das gesamte Einzugsgebiet der &#8221;Unteren Havel&#8220;. Die Unsicherheiten des Modellansatzes sowie die Anwendbarkeit des Modells im Untersuchungsraum wurden geprüft und die Limitierung der Übertragbarkeit auf andere grundwasserbeeinflusste Tieflandeinzugsgebiete analysiert. Die Ergebnisse der Wasserhaushaltssimulationen führen einerseits zum erweiterten Prozessverständnis des Wasserhaushalts in Flachlandeinzugsgebieten, andererseits ermöglichten sie durch die Quantifizierung einzelner Prozessgrößen die Beurteilung der Steuerungsfunktion einzelner Wasserhaushaltsprozesse. Auf der Basis lokaler Simulationsergebnisse sowie geomorphologischer und gewässermorphologischer Analysen wurde ein Algorithmus entwickelt, welcher die Abgrenzung des direkten Eigeneinzugsgebiets der Havel als Raum der direkten Interaktion zwischen Oberflächengewässer und umgebendem Einzugsgebiet beschreibt. Durch Simulation des Wasserhaushalts im Eigeneinzugsgebiet mit dem Modell IWAN konnten die Interaktionsprozesse zwischen Fluss und Talauenlandschaft quantitativ beschrieben werden. Dies ermöglichte eine Bewertung der Abflussanteile aus dem Eigeneinzugsgebiet sowie eine Quantifizierung der zeitlich variablen Retentionskapazität der Auenlandschaft während Hochwasserereignissen. Zur Abschätzung des Einflusses veränderter Landnutzung und angepassten Managements auf den Wasserhaushalt der Talaue wurden Szenarien entwickelt, welche Änderungen der Landnutzung sowie der Gewässergeometrie implizieren. Die Simulation des Wasserhaushalts unter jeweiligen Szenariobedingungen ermöglichte die detaillierte Analyse sich ändernder Randbedingungen auf den Gebietswasserhaushalt und auf die Austauschprozesse zwischen Grundwasser und Oberflächengewässer. Zur Untersuchung der Stickstoffmetabolik im Grundwasser der Talauenlandschaft wurde das im Modellkonzept IWAN integrierte Stofftransportmodell MT3D für das Eigeneinzugsgebiet der Havel angewandt. Dies ermöglichte eine Bilanzierung der aus dem Grundwasser des Eigeneinzugsgebiets stammenden Nitratfrachtanteile der Havel sowie von Nitratkonzentrationen im Grundwasser. Szenariensimulationen, welche verminderte Nitrateinträge aus der durchwurzelten Bodenzone annehmen, ermöglichten die Quantifizierung der Effizienz von Managementmaßnahmen und Landnutzungsänderungen in Hinblick auf die Minimierung von Einträgen in Grundwasser und Oberflächengewässer. / For a sustainable management of lowland river basins, a comprehensive knowledge about floodplain water balance and nutrient transport processes is required. This investigation aims to analyse water balance processes and nutrient dynamics and transport within the groundwater influenced floodplains of lowland areas. Thus, the investigation was focused on the Havel river catchment at the Northeast German Lowlands, which is a typical example of a lowland floodplain. Experimental investigations were performed at different spatial scales for qualitative analysis of water balance. The complex model IWAN was developed which enables the simulation and quantitative analysis of water balance and nutrient dynamics. Furthermore it allows the scenario based simulation and analysis of changing landuse management and boundary conditions.<br><br> For experimental investigation of runoff generation and water balance processes within the floodplains of the Havel river an extensive measurement campaign was installed at several testsites of the 198 km2 catchment of the &#8220;Lower Havel river basin&#8220;. These testsites include stations and gauges for the observation of meteorological parameters, soil moisture, groundwater depths and river runoff. Analysis of the observed data led to an improved understanding of water balance processes within the specific part of the floodplain which is influenced by the dynamics of the uppermost groundwater and by the surface water dynamics. Furthermore the implementation of the observed data within the model concept realised the consistent definition of time variable, spatial distributed initial and boundary conditions. The IWAN model was developed as a tool which implements the speci- fic hydrological characteristics of floodplains within the concept of modelling water balance and nutrient dynamics. It is based on the coupling of the distributed deterministic hydrological model WASIM-ETH with the three-dimensional finite difference based numerical groundwater model MODLFOW. Simulation of the metabolism of nitrogen within the groundwater passage was realised by the nutrient transport model MT3D which was coupled with the groundwater model. For model based simulation of the water balance within lowland river floodplains the IWAN model was applied for different scaled subcatchments of the Havel river with varying sizes from 2 to 1000 km2 and simulation periods from 2 weeks up to 13 years. Calibration of the model was performed for two different sized subcatchments of the &#8220;Lower Havel river basin&#8220;. The subsequent validation of the model focused on the entire &#8220;Lower Havel river basin&#8220;. Uncertainties of the model approach and the limited applicability and transferability for further groundwater influenced floodplain landscapes were analysed. The results of the water balance simulations led to an improved understanding of the processes and dynamics within floodplains. It furthermore enabled the quantification and impact analysis of certain processes and interactions. Based on local simulation results and on the analysis of surface and groundwater morphology an algorithm was developed which was used for delineation of the direct catchment of the Havel river. This direct catchment is specified as the part of the floodplain which is characterised by the direct interaction between river and adjacent catchment. Water balance simulations with the IWAN model in the direct catchment led to the quantification of interaction processes between river and floodplain. This enabled the assessment of the runoff fraction from the direct catchment during the ecologically sensitive low flow periods in summer and of the retention capacity of the floodplain during flood events. For the evaluation of the influences of alternative landuse management on the water balance within floodplains, complex scenarios were developed which implemented alterations of landuse or changes of surface water geometries and drainage structures. Simulation of water balances for each scenario allowed the detailed analysis of changing boundary conditions on the floodplain water balance and on the interaction processes between groundwater and river. Modelling nitrogen metabolism within the groundwater: For investigation of the nitrogen metabolism within the groundwater of floodplains the nutrient transport and dynamics model MT3D, which considers also interactions between groundwater and surface waters, was integrated in the IWAN concept. The model was applied for the simulation of nitrate dynamics within the direct catchment of the Havel river.With this approach, the nitrate loads between groundwater and river could be quantified. In addition, nitrate concentrations within the groundwater were analised in dependence of surface water dynamics. Scenario simulations, assuming a decrease of incoming nitrate loads from the root zone, caused by landuse techniques, led to the quantification of the efficiency of landuse changes and advanced management strategies to inhibit pollution of groundwater and surface waters.

La mayoría de las estructuras de hormigón armado se someten a solicitaciones combinadas de esfuerzos axiles, flexión, cortante y torsión. La fisuración del hormigón, plastificación de las armaduras y otros efectos no-lineales hacen que las secciones transversales de estos elementos presenten un comportamiento anisótropo que deriva en el acoplamiento de los esfuerzos normales y tangenciales. Es decir, esfuerzos normales o momentos flectores pueden producir deformaciones de corte y vice versa. Aunque en algunas ocaciones, esta interacción es considerada de forma simplificada en el dimensionamiento de estructuras, hasta el momento no se ha realizado un análisis profundo de los efectos acoplados en secciones de forma arbitraria bajo cargas 3D generales utilizando modelos de fibras.El objetivo principal de esta tesis es generalizar el análisis de secciones de hormigón armado mediante fibras, de forma que se pueda reproducir la res-puesta no-lineal acoplada frente a esfuerzos normales y tangenciales bajo solicitaciones tridimensionales generales. De igual forma, se pretende obtener, para los esfuerzos cortantes y torsión, la misma capacidad de representación de geometrías y combinación de materiales que ofrecen los modelos de fibras para esfuerzos de flexo-compresión.La primera problemática estriba en representar adecuadamente la cinemática de la sección transversal. Con la excepción de las deformaciones normales contenidas en el plano de la sección, no existe una teoría cinemática que a priori pueda dar la distribución del resto de deformaciones o tensiones en la sección, sin dejar de satisfacer las condiciones de equilibrio interno o continuidad entre las fibras que componen la misma.Por otra parte, para materiales anisótropos, como el hormigón fisurado, en general todos los esfuerzos internos pueden estar acoplados. Además, es preciso considerar la distorsión de la sección transversal para satisfacer el equilibrio entre fibras.El problema se aborda de forma general, considerando una sección de forma y materiales cualesquiera. Se parte del problema diferencial de equilibrio de un sólido con el que se ha podido deducir un sistema de equilibrio entre fibras (equilibrio a nivel sección). Se puede demostrar que éste es complementario al problema estándar de vigas. El sistema complementario permite recuperar información tridimensional que normalmente se pierde al resolver un problema de vigas.Posteriormente, se propone una solución interna del problema complementario, en la que el alabeo y la distorsión de la sección quedan expresados como una función de las deformaciones generalizadas de una viga: deformaciones axil y cortantes, curvaturas de flexión y torsión. No son necesarios grados de libertad adicionales a nivel estructura ni hipótesis a-priori sobre la forma de los campos de deformación o tensión interna.A partir de la formulación teórica, se desarrolla un modelo de elementos finitos plano de la sección transversal. El modelo está preparado para servir como respuesta constitutiva de cualquier tipo de elemento viga en sus puntos de integración. %Se evita así la necesidad de realizar un modelo de elementos sólidos de toda la barra para estudiar la respuesta frente a una combinación general de esfuerzos normales y tangenciales.Se implementan una serie de modelos constitutivos para distintos materiales. En particular, se implementa un modelo constitutivo triaxial para hormigón fisurado, considerando la anisotropía inducida por la fisuración e incluyendo la superficie de rotura según un criterio multiaxial.La formulación seccional es validada mediante varios casos de estudio teóricos y experimentales. La respuesta no-lineal acoplada bajo diversas combinaciones de esfuerzos normales y tangenciales es reproducida con precisión, lo cual queda patente tanto en las curvas esfuerzo-deformación obtenidas como en las matrices de rigidez seccionales.Finalmente, se recopilan las conclusiones derivadas de la presente investigación y seofren recomendaciones para futuros trabajos. / Most RC structures are subjected to combined normal and tangential forces, such as bending, axial load, shear and torsion. Concrete cracking, steel yielding and other material nonlinearities produce an anisotropic sectional response that results in a coupling between the effects of normal and shear forces, i.e. normal force or bending moments may produce shear strains and vice versa. Although this interaction is sometimes taken into account, in a simplified manner, in the design of RC structures, a deep analysis of the coupling effects of RC sections using fiber models has not yet been made for arbitrary shape sections under general 3D loading.The main objective of this thesis is to generalize the fiber-like sectional analysis of reinforced concrete elements, to make it capable of considering the coupled non-linear response under tangential and normal internal forces, from a general 3D loading.Similarly, it is desired to obtain, for torque and shear forces, the same capacity and versatility in reproducing complex geometry and materials combination that fiber-like sectional representations offers for bending and stretching.The first problematic lies in finding a proper representation of the section's kinematics under such general loading. Except for in-plane normal strains, there is no single kinematical theory capable of a-priori representing the correct distribution of the others strains or stresses satisfying, at the same time, inter-fiber equilibrium and continuity. On the other hand, for rather anisotropic materials, such as cracked concrete, all internal forces are, in general, coupled. It is also required that distortion is allowed for the section's kinematics in order to guarantee satisfaction of internal equilibrium.The problem is dealt in a general form considering arbitrary shaped sections and any material behaviour. Starting from the differential equilibrium of a solid, an inter-fiber equilibrium system (equilibrium at the sectional level) was deduced. This system, which is complementary to the standard equilibrium problem of a beam-column, allows to recuperate information of the three-dimensional problem that is generally lost when solving a beam problem.Further, a solution of the equilibrium at the sectional level is proposed in which the section's warping and distortion are posed as a function of the generalized beam-column strains (axial and shear strains, bending and torsion curvatures). No additional degrees of freedom are required at the structural level nor a-priori hypotheses on the distribution of the internal strains or stresses.After the theoretical formulation, a planar finite element model for cross-sectional analysis is developed. The model can be used as a constitutive law for general beam column elements at their integration points.A series of constitutive models have been implemented for several materials. In particular, a triaxial constitutive model for cracked concrete is implemented considering crackinduced anisotropy and a multiaxial failure criterion.The sectional formulation is validated by means of various theoretical and experimental case studies. Non-linear coupled response under normal and tangential internal forces is reproduced with accuracy, as can be seen both in the predicted internal force-strain curves and in the sectional stiffness matrixes.Finally, the conclusions drawn from the current research are summarized andrecomendations for future works are given.

In this study, hydrogeological modeling of the Somme river basin situated in the north of France was made with special emphasis on the stream-aquifer interaction. The coupled model developed at Ecole des Mines de Paris was used. Geographic Information Systems (GIS) tools were incorporated during all the stages of modeling process for both preparation of input data and visualization of the results of simulations. Initially, the process began with Digital Elevation Model (DEM) analysis. Afterwards, the surface and aquifer grids were generated by using nested grid generators and refinement was made on the stream network and subcatchment boundaries in order to increase the accuracy of numerical solution. In order to run the surface model, meteorological forcing, land use and soil type data were acquired. Surface model was used to partition the precipitation into evapotranspiration, infiltration and surface runoff components. A steady-state piezometric head distribution was computed by the groundwater model to serve as an initial condition to the coupled model. The flow in the unsaturated zone was simulated by using Nash cascade model. The unsteady groundwater and surface flow simulations were performed by taking into consideration the stream-aquifer interaction on a daily time step. The calibration and validation were realized by using the streamflow and piezometric head measurements distributed around the basin. The strong groundwater influence on the hydrology of the basin is well represented by the model. Comparisons of predicted flooded areas in year 2001 were made with other models and a satellite derived image. In the end, several sensitivity analyses were performed for several parameters concerning the groundwater flow.

L'objectif initial de cette thèse est d'apporter une solution à ce problème en proposant, premièrement, une approche cognitive basée sur le paradigme appelé Belief-Desire-Intention (BDI) pour représenter les processus de prise de décision des acteurs humains, et deuxièmement, une validation de cette approche dans le contexte d'un modèle complet de changement d'usage des sols dans lequel la plupart des facteurs cités ci-dessus sont également simulés. Le résultat de ce travail est une approche générique qui a été validée sur un modèle intégrant le changement d'usage des sols d'une région située dans le Delta du Mékong au Vietnam. Nos contributions principales sont les suivantes : Intégration d'une architecture BDI au sein d'une plateforme de modélisation à base d'agents (GAMA) ; Conception d'un cadre générique baptisé " Multi-Agent Based Land-Use Change " (MAB-LUC) permettant de modéliser et de simuler les changements d'usage des sols en prenant en compte les décisions des agriculteurs ; Proposition d'une solution permettant d'intégrer et d'évaluer les facteurs socio-économiques et environnementaux dans le cadre de la planification agraire et d'intégrer MAB-LUC dans le processus existant proposé par la FAO. Ce travail, au-delà du cas d'étude concernant le Delta du Mékong, a enfin été conçu de façon générique afin que la méthodologie utilisée puisse être généralisée à la modélisation de systèmes socio-écologiques où les facteurs humains doivent être représentés avec précision. / Integrated modeling approaches (multi-simulation, multimodeling, etc.) have proven challenging in practice. The first challenge deals with the technical aspects of coupling different computational or mathematical components. The second challenge lies in the alignment of the semantics of these components so that their integration does make sense, which is particularly critical in pluridisciplinary models. A number of approaches have been proposed in the last 20 years but none of them is really suitable to our context . We propose in this thesis an alternate approach, called co-modeling, which borrows concepts and tools from agent-based modeling, agent-oriented software engineering and multimodel ecologies. Simply speaking, a co-model can be defined as a multi-agent system of models and datasets. Each model or dataset is represented by one or several agents interacting with one another within the context of a larger representation of their — potentially dynamic — environment. The proposed approach does not aim at providing a general solution to the two challenges above, but at providing a framework in which modelers can easily implement their solution or test different coupling solutions. The proposed approach is fully implemented within the GAMA agent-based modeling platform. Its advantages are shown in terms of flexibility, composability and reusability in a number of case studies. The first case study is the dynamic coupling of equation-based and agent-based models to obtain “switching” models dynamically. The second one is the design of a complex integrated model where three formalisms and four modeling approaches have been successfully coupled.

[pt] A grande maioria dos problemas de estabilidade de poços de petróleo ocorre em trechos de folhelhos, rochas nas quais, uma especificação eficiente da pressão do fluido de perfuração requer previamente uma especificação correta da concentração salina e da temperatura. Todavia, para um dimensionamento adequado das características do fluido de perfuração necessárias à estabilidade do poço, é necessário o uso de modelos matemáticos que considerem um acoplamento adequado entre efeitos poroelásticos, químicos e térmicos. Entretanto, a complexidade matemática das equações de modelos acoplados normalmente leva à adoção de soluções numéricas, que consomem um tempo computacional muito grande e, por isso, esses modelos não são atrativos à aplicação na análise da estabilidade de poços. Este trabalho apresenta um modelo acoplado termo-químico-poroelástico representado por duas soluções, uma numérica, que utiliza o método dos elementos finitos, e outra analítica, baseada no método das transformadas de Laplace. Ao comparar ambas as soluções é demonstrado que a solução analítica consegue representar tão bem quanto à solução numérica os principais processos acoplados presentes durante a perfuração de folhelhos e que influenciam na sua estabilidade e, por esta razão, pode ser utilizada na análise de estabilidade de poços em folhelhos. Através de um estudo de caso, é verificado que um controle eficiente da estabilidade do poço é obtido especificando a pressão do fluido de perfuração em função da sua temperatura e concentração salina. Estes resultados também indicam as razões de alguns problemas não previstos por modelos desacoplados, e que quase sempre ocorrem durante a perfuração em folhelhos. / [en] Wellbore stability problems are most common when drilling through shales. In order to avoid such problems in this kind of rocks the solute concentration and temperature must be properly defined in the drilling fluid composition, which requires considering poroelastic, thermal and chemical effects in a coupled way. The equations complexity of coupled models usually results in numerical solutions that are very time consuming, thus, unattractive for stability analysis. In an opposite way, it is very difficult to develop closed- form solutions for coupled models. This work presents a thermochemoporoelastic model represented by a numerical solution based upon the finite element method and an analytical solution based upon the Laplace transform method. A comparison between the results of the numerical solution and analytical solution shows that the later can reproduce the coupled processes involved in the wellbore stability problem in shales as well as the former, and for this reason the closed-form solution can be applied as a practical tool in wellbore stability analysis. The analysis of a typical wellbore drilled through shales showed that an efficient control of wellbore stability can be obtained through an adequate specification of the drilling fluid pressure when taking in account its solute concentration and temperature. The model was also able to explain some problems not predicted by uncoupled models, but almost always seen while drilling through shales.

Cette thèse présente une contribution à l’étude des transferts d’eau au sein des piles à combustible de type PEMFC, un aspect clé de cette technologie. Une approche de simulation numérique est développée en couplant un modèle de type réseau de pores dans la couche de diffusion (DM), une approche mixte continue –réseau de pore dans la couche microporeuse (MPL) et une modélisation par compartiments dans la couche active. L’approche développée prend en compte les transferts couplés de chaleur et d’eau via notamment la modélisation des phénomènes de changement de phase dans la DM et la MPL (évaporation et condensation). Dans une première partie, nous étudions le cas où l’eau migre dans l’assemblage MPL-DM directement en phase liquide. L’impact de la variation de pression dans la phase gazeuse sur la distribution de la phase liquide est étudié. L’épaisseur optimale de la MPL est également étudiée. Dans une seconde partie, nous étudions des situations où l’eau se forme par condensation dans la couche de diffusion. Nous étudions tout d’abord l’impact des propriétés de la couche de diffusion et de la MPL sur le diagramme de condensation. Ensuite nous analysons l’impact de la formation de l’eau liquide sur la distribution de courant locale. Enfin, l’impact de la mouillabilité sur les figures de condensation est étudié. Cette dernière étude est vue comme un premier pas vers l’étude des mécanismes de dégradation dans le régime de condensation. / This thesis is a contribution to the study water transfers within PEM fuel cell, a key element of this technology. A numerical simulation tool is developed coupling a pore network model in the gas diffusion layer (DM), a mixed continuum – pore network approach in the microporous layer (MPL) and a model by compartments in the catalyst layer. The developed approach takes into account the coupled heat and water transfers through the modeling of phase change phenomena (evaporation – condensation) in the DM and in the MPL. In the first part, we study the case where water migrates into the MPL-DM assembly directly in liquid phase. The impact of gas pressure variation on liquid phase distribution is studied. The optimal thickness of MPL is studied too. In the second part we study situations where liquid water essentially formed by condensation in the diffusion layer. We first study the impact of DM and MPL properties on the condensation diagram. Then we analyze the impact of liquid water formation on the local current density distribution. Finally the impact of wettability modifications on the liquid water patterns is studied. This last study is considered as a first step toward the study of degradation mechanisms in the condensation regime.

Made available in DSpace on 2016-12-12T20:15:49Z (GMT). No. of bitstreams: 1 Willians Prants.pdf: 18721085 bytes, checksum: 3872eb4cc3f6155fd37e124cf75d4e35 (MD5) Previous issue date: 2012-07-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work we analyze the dynamics of two continuous time models: (i) the Rössler model, a model for the Lorenz system, composed by a set of three differential equations of first order, autonomous, and has only one nonlinearity and (ii) the model of two coupled chaotic Rössler oscillators, built by the linear coupling between two Rössler systems and controlled by two coupling parameters &#1028; e &#952;, which correspond to intensity and symmetry of the coupling. For the first model, we find analytically the equilibrium points and analyzed by the method of Routh-Hurwitz, their stability. We construct numerically the parameters space a × b, a × c and c × b identifying the regions of chaotic regime and detect typical periodic structures immersed in these regions. For the second model, we construct numerically the parameter space for the coupling parameters &#1028; e &#952;, and we find a periodic region immersed in chaos characterizing the effect of suppression of chaos. By analyzing the second largest Lyapunov exponent we detect a hiperchaotic region. For both models we use bifurcation diagrams to analyze the periodic structures and to determine the routes to chaos / Neste trabalho analisamos a dinâmica de dois modelos a tempo contínuo: (i) o modelo de Rössler, um modelo para o sistema de Lorenz, composto pelo conjunto de três equações diferenciais, de primeira ordem, autônomo e que apresenta apenas uma não-linearidade e (ii) o modelo de dois osciladores caóticos de Rössler acoplados, construído pelo acoplamento linear entre dois sistemas de Rössler e controlado por dois parâmetros de acoplamento &#1028; e &#952;, que correspondem a intensidade e simetria de acoplamento. Para o primeiro modelo, encontramos analiticamente os pontos de equilíbrio e analisamos, através do método de Routh-Hurwitz, suas estabilidades. Construímos numericamente os espaços de parâmetros a × b, a × c e c × b identificando as regiões de regime caótico e detectamos estruturas periódicas típicas imersas nessas regiões. Para o segundo modelo, construímos numericamente o espaço de parâmetros para os parâmetros de acoplamento &#1028; e &#952;, e encontramos uma região periódica imersa em caos, caracterizando o efeito de supressão de caos. Analisando o segundo maior expoente de Lyapunov detectamos uma larga região hipercaótica. Para ambos os modelos usamos diagramas de bifurcação para analisar as estruturas periódicas e determinar as rotas para o caos.

Uncertainty in rainfall forecasts affects the level of quality and assurance for decisions made to manage water resource-based systems. However, eliminating uncertainty in a complete manner could be difficult, decision-makers thus are challenged to make decisions in the light of uncertainty. This study provides statistical models as an approach to cope with uncertainty, including: a) a statistical method relying on a Gaussian mixture (GM) model to assist in better characterize uncertainty in climate model projections and evaluate their performance in matching observations; b) a stochastic model that incorporates the El Niño–Southern Oscillation (ENSO) cycle to narrow uncertainty in seasonal rainfall forecasts; and c) a statistical approach to determine to what extent drought events forecasted using ENSO information could be utilized in the water resources decision-making process. This study also investigates the relationship between calibration and lead time on the ability to narrow the interannual uncertainty of forecasts and the associated usefulness for decision making. These objectives are demonstrated for the northwest region of Costa Rica as a case study of a developing country in Central America. This region of Costa Rica is under an increasing risk of future water shortages due to climate change, increased demand, and high variability in the bimodal cycle of seasonal rainfall. First, the GM model is shown to be a suitable approach to compare and characterize long-term projections of climate models. The GM representation of seasonal cycles is then employed to construct detailed comparison tests for climate models with respect to observed rainfall data. Three verification metrics demonstrate that an acceptable degree of predictability can be obtained by incorporating ENSO information in reducing error and interannual variability in the forecast of seasonal rainfall. The predictability of multicategory rainfall forecasts in the late portion of the wet season surpasses that in the early portion of the wet season. Later, the value of drought forecast information for coping with uncertainty in making decisions on water management is determined by quantifying the reduction in expected losses relative to a perfect forecast. Both the discrimination ability and the relative economic value of drought-event forecasts are improved by the proposed forecast method, especially after calibration. Positive relative economic value is found only for a range of scenarios of the cost-loss ratio, which indicates that the proposed forecast could be used for specific cases. Otherwise, taking actions (no-actions) is preferred as the cost-loss ratio approaches zero (one). Overall, the approach of incorporating ENSO information into seasonal rainfall forecasts would provide useful value to the decision-making process - in particular at lead times of one year ahead.

The work presented in the thesis focuses on systematically documenting the multi scale nature of the temporal persistence and spatial coherence of tropical rainfall. There are three parts to the thesis: The first two parts utilize satellite-retrieved rainfall at multiple observational resolutions to characterize the space-time organization of rain; the third part assesses the ability of state-of-the-art coupled models to reproduce some of the observed features. In the first part of the study, which focuses on the temporal persistence of rain, we analyze the Tropical Rainfall Measurement Mission (TRMM) satellite-based observations to compare and contrast wet and dry spell characteristics over the tropics (30 S-30 N). Defining a wet (dry) spell as the number of consecutive rainy (nonrainy) days, we find that the distributions of wet spells (independent of spatial resolution) exhibit universality in the following sense. While both ocean and land regions with high seasonal rainfall accumulation (humid regions) show a predominance of 2-4 day wet spells, those regions with low seasonal rainfall accumulation (arid regions) exhibit a wet spell duration distribution that is essentially exponential in nature, with a peak at 1 day. The behaviour that we observed for wet spells is reversed for dry spell distributions. The total rainfall accumulated in each wet spell has also been analyzed, and we find that the major contribution to seasonal rainfall for arid regions comes from very short length wet spells; however, for humid regions, this contribution comes from wet spells of duration as long as 30 days. An exhaustive sensitivity study of factors that can potentially affect the wet and dry spell characteristics (e.g., resolution) shows that our findings are robust. We also explore the role of chance in determining the 2-4 day mode, as well as the inuence of organized convection in separating reality from chance. The second part deals with the spatial coherence of tropical rain. We take two different approaches, namely, a global and local view. The global view attempts to quantify the con-ventional view of rain, i.e., the dominance of the intertropical convergence zone (ITCZ), while the local view tries to answer the question: if it rains, how far is the influence felt in zonal and meridional directions? In both approaches, the classical e-folding length for spatial decorrelation is used as a measure of spatial coherence. The major finding in the global view approach is that, at short timescales of accumulation (daily to pentad to even monthly), rain over the Equator shows the most dominant zonal scale. It is only at larger timescales of accumulation (seasonal or annual) that the dominance of ITCZ around 7 N is evident. In addition, we also find a semi-log linearity between the spatial scales, seen from afar, and timescale of accumulation, with a break in linearity around typical synoptic timescales of 5-10 days. The local view quantifies the dominance of the zonal scale in the tropical ocean convergence zones, with an anisotropy value (ratio of zonal to meridional scales) of 3-4. Over land, on the other hand, the zonal and meridional scales are comparable in magnitude, suggesting that rain tends to be mostly isotropic over continental regions. This latter finding holds true, irrespective of the spatial and temporal resolutions at which rain is observed. Interestingly, the anisotropy over ocean, while invariant with spatial resolution, is found to be a function of temporal resolution: from a value of 3-4 at daily timescale, it decreases to around 1.5 at 3-hourly resolution, suggesting that perhaps rain fundamentally might be isotropic in nature at an event scale. The final part analyses a few models from the suite of Coupled Model Intercomparison Project (CMIP5) models, to evaluate their ability to reproduce some of these aforementioned features. For all the strong biases that models are known to have, some of the observed features are captured well by the models. Specifically, on the temporal persistence front, the observed 2-4 day mode of wet (dry) spells of rain over humid (arid) regions is also seen in models. The overestimation of longer duration wet spells appears to be the primary cause of a positive bias in the number of rainy days from the models. In general, the tendency of models to not stop raining results in lower and higher number of shorter and longer duration wet spells, respectively, and consequently an overall reduction in dry spells of all durations. On the spatial coherence front, the main finding from the global view approach is that the observed semi-log linearity of the zonal spatial scale of rainfall as a function of timescale of accumulation is strikingly well-reproduced by the models. Even more remarkable is that the models are able to mimic the break in this linearity around 5 days (typical synoptic scale). What the models fail to do prominently is the transition of the dominance of equatorial rain at smaller timescales of accumulation to the dominance of ITCZ at around 7 N at higher timescales of accumulation. Based on the local view approach, we find that, in general, even though the zonal and meridional scales are overestimated, the observed isotropy of continental rain is captured very well by the models. Over the oceans, the success is less prominent, especially with the core of the ITCZ showing much larger ratios than those observed. Thus, the models seem to be able to reproduce the anisotropy for the wrong reasons, and the proposed anisotropy ratio could be a useful metric in further diagnosis of climate models.

This paper deals with interaction of different physical phenomena in asynchronous motor. The first part of this work is devoted to computing of electrical ratios in asynchronous motor. By using the equivalent circuit in the shape of Gamma-circuit the equation for computing of currents, performances and losses of asynchronous motor are derived. The second part describes calculating of electromagnetic circuit and iron-core losses. In the next part there is the first part of associated model created which respects electric and electromagnetic ratios in the asynchronous motor. This model can be used for example to pursuance of variation of flux density caused by resizing load. In this model the unconventional way of computing the magnetizating inductance and resistance coresponding to iron-core losses is used. The next part deals with calculation of machine warming using the thermal network. In the last part there is a complete coupled model assembed which respects the interaction of electrical, electromagnetical and thermal ratios of induction machine.