Die vorliegende Arbeit umfasst im ersten Teil eine Literaturrecherche zu Aquifer Storage and Recovery (ASR) im Allgemeinen und den Einfluss physikalisch-chemischer Prozesse auf ASR. Aus dieser konnte abgeleitet werden, dass durch standortbedingte Untergrundeigenschaften stark unterschiedliche physikalische und chemische Prozesse ablaufen und eine eindeutige Vorhersage zum Verhalten und zur Effizienz von ASR an einem neuen oder bereits genutzten Standort ohne spezifische Informationen nicht möglich ist. Des Weiteren wurde eine Literaturstudie zum Einfluss der transversalen Dispersivität, als Maß für die Vermischung von transportierten Stoffen quer zu einer (natürlichen) Fließrichtung, auf den (reaktiven) Transport durchgeführt. Letztlich wurde im Rahmen einer betreuten Masterarbeit (M. Sc. Chang Liu) eine Bewertung aus der Literatur entnommener transversaler Dispersivitäten durchgeführt. In den weiteren Teilen der Arbeit wurden Fallstudien mit unterschiedlichen Fragestellungen für die Planung und den Betrieb von künstlichen Grundwasseranreicherungen und speziell ASR numerisch modelliert und bewertet. Zuerst wurden numerische Simulationen zum konservativen Transport am Testfeld „Lauswiesen“, Tübingen, Baden-Württemberg durchgeführt. Diese beinhalteten über Direct-Push(DP)-Erkundungsmethoden gewonnene Informationen zur Untergrundstruktur. Die Ergebnisse zeigen, dass zur Vorhersage des standortspezifischen Transports in den „Lauswiesen“ und für vergleichbare hydraulische Situationen, auch in Hinsicht auf ASR, deterministische hydrogeologische Einheiten und ihre situationsgerechte Berücksichtigung in numerischen Modellen höchst relevant sind. Aufbauend auf den genannten Ergebnissen wurde eine Masterarbeit durch Herrn M. Sc. Tsegaye Abera Sereche durchgeführt. Diese Masterarbeit zeigte für diesen Fall erneut die hohe Relevanz deterministischer Strukturen gegenüber kleinskaligen, dreidimensionalen Heterogenitäten für ASR. Weiterführende numerische Simulationen zu einem möglichen ASR-Feldtest am Standort „Lauswiesen“ ergaben, dass dieser unter den gegebenen Untergrundbedingungen nur bei Abweichungen von einem vertretbaren Konzept für einen Ein-Brunnen-Test, z. B. bei sehr großen Infiltrationsmengen, oder durch Umwandlung in einen Zwei-Brunnen-Test durchführbar ist. Während dieser Arbeit wurden gemeinsame Forschungsarbeiten mit dem Kansas Geological Survey, Kansas, USA durchgeführt, welche die Bewertung der Verwendbarkeit von DP-Brunnen als alternative Infiltrationsmethode zu Oberflächenmethoden beinhalteten. Als Teil der gemeinsamen Arbeiten wurde im Rahmen der vorliegenden Arbeit eine synthetisierte, numerische Bewertung der neuen DP-Infiltrationsbrunnen sowie einen Vergleich mit einer herkömmlichen Oberflächeninfiltrationsmethode übernommen. Im Einklang mit der Zielstellung der Arbeit wurde ebenfalls eine numerische Bewertung natürlicher und anthropogener Heterogenitäten auf die Infiltration durchgeführt. Aus den Ergebnissen konnten für die neue Infiltrationsmethode signifikante Vorteile abgeleitet werden. Weitere numerische Modellierungen wurden durchgeführt, um die wesentlichen Ergebnisse auf einen Feldstandort in der Südlichen Steiermark, Österreich, anzuwenden, welcher: a) bereits ein horizontales Versickerungssystem besitzt, b) weitere Systeme erhalten soll und c) letztlich eine besondere Herausforderung für vertikale Versickerungssysteme darstellt. Die Modellierung des vorhandenen Systems zeigt die hohe Komplexität der Infiltrationsprozesse. Jedoch konnten hydraulische Parameter bestätigt und in weitere planerische Simulationen zu Verwendung von DP-basierten Infiltrationsbrunnen eingefügt werden. Diese zeigen, dass ein Brunnenfeld am Standort auf relativ geringem Raum installiert werden kann. Zusätzlich zeigt ein Feldversuch an einem weiteren Standort (Pirna, Sachsen), dass hohe Infiltrationsraten unter Nutzung von DP-Brunnen möglich sind. / The works presented in the thesis include in the first part a literature research on Aquifer Storage and Recovery (ASR) in general and the impacts of different physico-chemical processes on ASR. This research concludes that site-specific subsurface conditions lead to varying physical and chemical processes and that a conclusive prediction of function and efficiency of ASR at any site, in-operation or new site design, is not possible without site-specific information. Additionally, a literature study was conducted that focused on the impacts of transverse dispersivity, as a measure for mixing of transported species perpendicular to the (natural) flow direction, on (reactive) transport. Finally, evaluation of transverse dispersivity data available in the literature was performed, which included a supervision of a master thesis (of M. Sc. Chang Liu). Numerical simulations of case studies for different questions of planning and operation of artificial recharge systems and more specifically ASR were realized for the other parts of the thesis. The first evaluated case was the “Lauswiesen” test site, Tübingen, Baden-Wuerttemberg. This study used new insights into the subsurface structure gained by Direct-Push(DP) exploration methods. The results obtained show that for further works at the site and for comparable hydraulic conditions, also in the view of ASR, deterministic hydrogeological subunits and their consideration in numerical models are critical for prediction of site-specific transport. Based on the previous findings, a master thesis was conducted by M. Sc. Tsegaye Abera Sereche. The master thesis yet again revealed for this case the high relevance of deterministic subunits compared to small-scale, three-dimensional heterogeneities for ASR. Further, numerical simulations of a possible ASR field test at “Lauswiesen” site showed that under the prevailing subsurface conditions, a field test can only be realized when the set-up of a single-well-test is impracticably changed, by e.g. very high infiltration volumes, or by transformation into a two-well-test. During the thesis joint research works were performed with the Kansas Geological Survey, Kansas, USA, which contained the evaluation of the applicability of DP wells as an alternative to surface infiltration methods. As part of the joint work, this thesis presents a synthesized numerical evaluation of the new DP well infiltration as well as a comparison to a common surface infiltration system. Furthermore, in accordance with the main objective of the work, numerical evaluation of natural and anthropogenic heterogeneities was performed. The results concluded the advantages for the DP wells for infiltration process. Further numerical models were implemented to convey the important results to a field site at Southern Styria, Austria, where: a) an existing infiltration system is already in operation, b) further infiltration systems are planned and c) the subsurface conditions are rather challenging for vertical infiltration systems. Modeling of the existent system revealed the high complexity of the infiltration processes. However, hydraulic parameters could be verified and included into planning simulations for DP-based infiltration wells. The findings show, that a well field can be installed at a comparably small land. Additionally, a field test at a further test site (Pirna, Sachsen) indicates that high infiltrations rates are possible when DP wells are used.

<p><a>Direct chill (DC) casting is the main production method for wrought aluminum alloys. In this semi-continuous process, significant heat is extracted through a narrow, solidified shell by impinging water jets. A combination of rapid cooling and inoculation of the liquid metal with heterogenous nucleation sites (grain refiner) produces the proper conditions for equiaxed solidification. As equiaxed grains nucleate and grow in the slurry, they are transported by natural convection until their eventual coalescence into a rigid mush. The preferential accumulation of these solute-depleted grains in localized regions of the casting can lead to long range composition differences known as macrosegregation. Because macrosegregation cannot be mitigated by subsequent processing, it is critical to understand and prevent its development during casting. </a></p> <p>Numerical models are often used to gain insight into the interplay of the different transport phenomena that cause macrosegregation. The formation of mobile equiaxed grains creates a multiphase system with many moving interfaces, causing several modeling challenges. In principle, a model could be formulated in terms of local instantaneous variables describing the evolution of these interfaces, however the associated computational cost prohibits its extension to the length scale of industrial castings. For this reason, macroscopic transport equations are mathematically formulated using volume averaging methods. Two different volume-averaged model formulations can be distinguished in the solidification literature. The first approach is the multiphase formulation, which solves separate sets of governing equations for each phase that are coupled using microscale interfacial balances. While this approach retains closure models to describe the behavior of the sub-grid interfaces, these interfacial models introduce significant uncertainty that is propagated through the model. The second approach is the mixture formulation, which solves a single set of governing equations for the mixture and utilizes more pragmatic closure relationships. While this approach significantly reduces the complexity and computational cost of the model, previous formulations have oversimplified the microscale transport. Recognizing the advantages and disadvantages of both formulations, a mixture model is rigorously derived, retaining appropriate relationships for the grain structure and microsegregation behavior in equiaxed solidification </p> <p>Implementation of this model into a 3-D finite volume method (FVM) code using a co-located grid is discussed along with appropriate treatment of the discontinuous body forces and phase mass fluxes across the interface between the slurry and rigid mush. More specifically, body forces in the momentum equation are treated at the face-centers of a control volume to prevent erroneous velocity oscillations near this interface, and a diffuse phase flux method is proposed to reduce the sensitivity of composition predictions to the numerical grid. The proposed methods are verified across a wide range of conditions present in equiaxed solidification. </p> <p>This model is then used to investigate the role of grain motion on macrosegregation development in equiaxed solidification, specifically in horizontal and vertical DC casting. In horizontal DC casting, the casting axis is perpendicular to gravity and there is a tendency for grains to accumulate along the bottom of the ingot. Feeding liquid metal through a constrained inlet near the bottom suspends grains in the slurry, both reducing the overall macrosegregation and improving the macrosegregation symmetry in the ingot. In vertical DC casting, the casting axis is parallel to gravity and there is a tendency for grains to accumulate in the center of the ingot. It is determined by a combination of simulations in the current work and previous experimental results that a strong localized jet at the centerline can suspend grains in the slurry and reduce negative centerline segregation. The change in segregation is attributed to a combination of reducing the accumulation of solute-depleted grains near the centerline and thinning the rigid mush where solidification shrinkage pulls enriched liquid away from the centerline. The strong localized jet also causes significant refinement and homogenization of the grain structure, which improves the mechanical properties of the ingot. These studies indicate that it is beneficial for DC casting practices to move towards agitated or stirred melts, and away from conventional practices which promote thermal stratification and localized accumulation of equiaxed grains.</p>

Résumé L’accumulation de sédiments sur le fond des égouts à faible pente est une contrainte au bon fonctionnement hydraulique et à la gestion des réseaux d’assainissement unitaire. Le recours à la chasse hydraulique est alors une pratique envisagée par les gestionnaires de réseau pour le nettoyage des canaux souterrains. Les processus de transport sédimentaire dans les réseaux d’assainissement unitaire est rendu complexe en raison du jeu de nombreux phénomènes tels que la variabilité de l’étendue granulométrique des sédiments et la cohésion. La thèse présente les résultats expérimentaux et numériques obtenus avant et après une chasse hydraulique réalisée dans le réseau unitaire parisien. Une campagne de mesures a permis d’acquérir des données hydro-sédimentaires à haute résolution, permettant de caractériser et quantifier les processus d’érosion, de transport et de sédimentation agissant sous l’effet de la chasse hydraulique, du reste performante dans le nettoyage du réseau étudié. Deux modèles de transport sédimentaire comportant un modèle simple en condition de transport uniforme, et un modèle plus complexe impliquant le transport non-uniforme ont été développés afin de mettre en place un outil prédictif des mouvements des particules solides pendant le phénomène de chasse. Les deux modèles ont été capables d’évaluer à différents niveaux de précision l’efficacité de la chasse hydraulique en termes de transport sédimentaire. La comparaison des résultats issus des deux modèles permet de déterminer les avantages et les contraintes de chacun, révélant ainsi l’importance de prendre en compte l’hétérogénéité texturale des dépôts dans l’analyse de l’érosion, du transport et de la sédimentation des particules solides sous l’effet des chasses hydrauliques. De plus, une analyse de sensibilité de la gamme d’application de certains paramètres d’entrée du modèle de transport non-uniforme des sédiments a été réalisée. Les résultats ont confirmé le bon fonctionnement du modèle. / Sediment accumulation on the invert of sewer channels has been recognized as one of the important sources of problems for the management of sewer networks.In the two most recent decades, flushing has been put forward as one of the most common methods of sewer cleaning, to limit sediment accumulation especially in large trunk sewers.Sewer sediment transport processes are not fully understood yet, due to numerous unknown variables and difficult measuring conditions. The current research aimed firstly to setup a field experimental campaign to obtain high-quality data. This data allowed understanding of the processes associated with flushing operation in sewers. In addition, this study aimed to model the flushing processes properly in order to set-up an adequate and practical numerical tool able to predict sediment removal of flushing in the sewer network of Paris. To this purpose, two models were used: (i) a simple model for uniform sediment transport, which is the most common used approach; and (ii) a more complex model for non-uniform sediment transport of mixtures. A comparative analysis was carried out to highlight advantages and drawbacks of either. Overall, the results pointed out that the numerical modelling is able to reproduce faithfully hydrodynamics and sediment transport during flushing operations. In fact, both models enabled evaluation of flush behaviour and associated sediment transport. However, despite its higher complexity and computational burden, the latter model provides better insight into the prediction of the removal effectiveness of flushes

Rock masses may present remarked geostatic stress anisotropy and anisotropic material properties; thus, the tunnel alignment with the geostatic principal stress directions and with the axes of material anisotropy is unlikely. Nevertheless, tunnel design often neglects those misalignments and; yet, the misalignment effects were unknown. In this doctoral research, tunnels under complex anisotropic conditions were modelled analytically and numerically with 3D nonlinear Finite Element Method (FEM). When the tunnel misaligns with the geostatic principal stress directions, anti-symmetric axial displacements and shear stresses are induced around the tunnel. Analytical solutions for misaligned shallow and deep tunnels in isotropic elastic ground are provided. The analytical solutions were validated with 3D FEM analyses. Near the face, the anti-symmetric axial displacements are partially constrained by the tunnel face, producing asymmetric radial displacements and stresses. The asymmetric radial displacements at the face can be divided into a rigid body displacement of the tunnel cross-section and anti-symmetric radial displacements. Those asymmetries may affect the rock-support interaction and the plastic zone developed around the tunnel. In anisotropic rock masses, the tunnel misalignment with the axes of material anisotropy also produces anti-symmetric axial displacements and stresses around the tunnel. It occurs because when the tunnel is not aligned with the principal material directions, the in-plane stresses are coupled with the axial displacements (i.e. the compliance matrix is fully populated). Thus, tunnels in anisotropic rock mass not aligned with the geostatic principal stresses and with the axes of material anisotropy are substantially more complex than tunnels not aligned with the principal stress directions in isotropic rock mass. An analytical solution for misaligned tunnels in anisotropic rock mass is provided. It was observed that the relative orientation of the geostatic principal stresses with respect to the axes of material anisotropy plays an important role. The axial displacements produced by far-field axial shear stresses and by the rock mass anisotropy may compensate each other; thus, axial and radial displacements around the tunnel are reduced. On the other hand, those anti-symmetric axial displacements may be amplified; thus, the ground deformations are increased. Asymmetric radial and axial deformations, and asymmetric spalling of the tunnel walls are commonly observed on tunnels in anisotropic rock masses. The tunnel misalignment with the geostatic principal stress directions and with the axes of material anisotropy could be associated with those phenomena that, so far, are not well comprehended

No description available.

[pt] O conhecimento do comportamento mecânico das rochas é fundamental para o desenvolvimento dos estudos de estabilidade voltados à construção de poços de petróleo. Neste sentido, a estimativa de suas propriedades mecânicas e a determinação do campo de tensões atuante são necessários para compreender as deformações às quais estão sujeitas. De modo a avaliar os efeitos da perfuração no comportamento mecânico das rochas, foram construídos modelos numéricos das litologias comumente descritas no pré-sal de um campo da bacia de Santos em duas etapas. Em um primeiro momento, foi idealizado um estudo de retroanálise de poço a fim de estabelecer a metodologia a ser aplicada neste trabalho. Os resultados numéricos obtidos nesta etapa reproduziram de maneira satisfatória os dados constatados em campo e, desta forma, foi possível validar a técnica utilizada. Em um segundo momento, foram construídos os modelos numéricos de litologias previstas em um poço sintético para um teste cego, tomando por base tanto as propriedades mecânicas estimadas das rochas quanto o estado de tensões in situ determinado em poços de correlação. Por último, os resultados obtidos neste teste foram comparados aos dados reais de um poço da área, de modo que foi possível corroborar a metodologia aplicada neste estudo pela coerência entre os dados numéricos e os constatados em campo. Desta forma, foi possível avaliar o comportamento mecânico das rochas no intervalo do pré-sal de poços correlacionáveis e estimar possíveis problemas geomecânicos a serem encontrados durante a etapa de perfuração. / [en] The modeling of rock mechanical behavior is essential to develop wellbore stability studies. In that sense, estimating rock mechanical properties and the in situ stress field are required tasks to understand the resulting deformations. In order to evaluate drilling effects on rock mechanical behavior, numerical models were constructed to represent the most commonly described rocks in the pre-salt session of an oil field located in Santos basin. Firstly, the author introduced the wellbore retro-analysis methodology proposed for this study. The technique was validated against real wellbore data with a fairly good match. Thereafter, a test model was conducted on a synthetic stratigraphy considering the typical occurrence of pre-salt rocks and the expected in situ stress field, as determined by correlated wellbores data. The numerical results of this test were compared to the data acquired in a local oil well and seemed to provide a reasonable fit, corroborating the applied technique. It was possible to evaluate typical pre-salt rock mechanical behavior by using correlation wellbores and still predict possible wellbore geomechanical problems during the drilling phase.

Samples from 13 different sites along the south coast of West Java yield 7 candidate paleo-tsunami sands, which may represent 4 different paleo-tsunami events. Ages obtained from one deposit may document a tsunami and coastal subsidence from an earthquake in 1,053 AD. The tsunami deposit from this event is preserved in an uplifted marine terrace exposed at Panto Cape, Banten Province. We speculated that the terrace has been uplifted about 4.6 m to the present height of 2 m above sea level, since the 1053 AD event at a rate of 4.8 mm/a. This uplift is strong evidence that strain is accumulating at the Java Trench and enough has already accumulated to generate a megathrust earthquake event.Numerical models using ComMIT of possible megathrust earthquake scenarios were constructed using the 2004 Sumatra earthquake, 30-m fault slip, and the 2011 Japan earthquake as proxies. These three scenarios yield earthquakes of Mw 9.3, 9.5 and 8.9, respectively. The worst case scenario is used to estimate the extent of tsunami inundation of the SW coast of Java, which totals 643 km2. The total number of people who inhabit the inundation area is around 451,000. Some coastal configurations cause a no escape situation where the modeled tsunami arrives in less than 20 minutes, which is not enough time for those near the coast to escape far enough inland or to a sufficient elevation to avoid the tsunami. These areas include the coastlines of Sukabumi, Cianjur and west Garut Regencies and the Pameungpeuk area.

Samples from 13 different sites along the south coast of West Java yield 7 candidate paleo-tsunami sands, which may represent 4 different paleo-tsunami events. Ages obtained from one deposit may document a tsunami and coastal subsidence from an earthquake in 1,053 AD. The tsunami deposit from this event is preserved in an uplifted marine terrace exposed at Panto Cape, Banten Province. We speculated that the terrace has been uplifted about 4.6 m to the present height of 2 m above sea level, since the 1053 AD event at a rate of 4.8 mm/a. This uplift is strong evidence that strain is accumulating at the Java Trench and enough has already accumulated to generate a megathrust earthquake event.Numerical models using ComMIT of possible megathrust earthquake scenarios were constructed using the 2004 Sumatra earthquake, 30-m fault slip, and the 2011 Japan earthquake as proxies. These three scenarios yield earthquakes of Mw 9.3, 9.5 and 8.9, respectively. The worst case scenario is used to estimate the extent of tsunami inundation of the SW coast of Java, which totals 643 km2. The total number of people who inhabit the inundation area is around 451,000. Some coastal configurations cause a no escape situation where the modeled tsunami arrives in less than 20 minutes, which is not enough time for those near the coast to escape far enough inland or to a sufficient elevation to avoid the tsunami. These areas include the coastlines of Sukabumi, Cianjur and west Garut Regencies and the Pameungpeuk area.

Recent geodynamic modeling studies suggest that the geometry of structural landforms in the Ouachita Mountains (OM) has been influenced by the reactivation of a weak scar in the mantle-lithosphere during intracontinental orogenesis. As deformation on one-plate planets such as Mars can be considered intracontinental, and impact cratering deeply scarred the Martian lithosphere, we hypothesize that structural geometries on Mars may also reflect heterogenous networks of lithospheric scarring. To investigate this hypothesis, we model the pre-erosional fold structure of the Maumelle Chaotic Zone in the OM to compare fault and fold geometries with that of the seismically-imaged mantle-lithosphere scar. We then numerically model deformation within the Martian crust and mantle-lithosphere in the presence of scarring to understand tectonic reactivation on one-plate planets. We find that structural geometries in the OM are consistent with a subsurface scar, and tectonic landforms on the surface of Mars may indeed reflect deformation generated by a network of lithospheric heterogeneity.

No description available.