No description available.

Identifying tectonically active faults and quantifying rates of movement is a key challenge in the Earth Sciences, in addition to this the interactions between active faulting and the landscape, specifically involving the fluvial network, is a relatively new area of study. Previous work has highlighted the value of understanding how the fluvial network responds to active tectonics, showing that a comprehensive understanding of the dynamic relationship between fluvial geomorphology and active tectonics is an important next step in geological research. This study presents new information about the poorly constrained Quaternary tectonic history of the Gediz Graben, Turkey, providing the first quantification of rates of movement of the key fault array that presently controlling graben topography. The fluvial network has been investigated and the data has been used in order to add resolution to the tectonic history for the fault array, allowing for the quantification of post-linkage throw rates. The study then investigates the key controls on the behaviour of the fluvial network that cross the active topography building fault array in the Gediz Graben. This study shows that there has been a linkage event occurring between 0.6 – 1 Ma, involving the three segments of the graben bounding fault array. The pre- and post-linkage throw rates are then extrapolated using data derived from the fluvial network, showing a faulting enhancement factor of 3 at the centre of the fault array, with the throw rate at the centre of the array predicted to have increased from a pre-linkage rate of 0.6 ± 0.1 mm/yr to a rate of 2 ± 0.2 mm/yr. This research provides evidence that the fluvial network can be used in conjunction with other types of evidence to provide a greater resolution tectonic history. Using both digital data and field studies this research presents an examination of the factors that influence the behaviour of bedrock rivers undergoing perturbation due to tectonics. Factors such as drainage area, tectonic throw rates and lithology have been investigated and the complicated interactions of these variables with the fluvial system have been quantified. This study shows that the bedrock rivers are a significant source of information about tectonics, but further work is needed to resolve quantitatively how various factors influence how rivers adjust to tectonic perturbation, in a variety of tectonic situations, in order to enable river to be used as a primary tool for deriving information about tectonics.

No description available.

No description available.

<p>Topography is one of the primary drivers of physical processes in the rivers and floodplains. Advances in remote-sensing and survey techniques have provided high-resolution representation of the floodplains but information regarding the 3D representation of river channels (commonly known as river bathymetry) is sparsely available. Field surveys along an entire river network in a watershed remains infeasible and algorithms for estimating simple but effective characterization of river channel geometry are hindered by an incomplete understanding of the role of river bathymetry in surface and subsurface processes. </p> <p> The first objective of this dissertation develops an automated framework – System for Producing RIver Network Geometry (SPRING) for improving the geospatial descriptors of a river network. The tool takes as input the DEM and erroneous river centerline to produce spatially consistent river centerlines, banks, and an improved representation of river channel geometry. SPRING can process entire river networks and is not limited single reach applications. The proposed framework is flexible in terms of data requirements, resolution of output datasets and user preferences. It has a user-friendly graphic user interface (GUI) and is appropriate for large-scale applications since it requires minimal user input.</p> <p> A better understanding of the role of bathymetric characteristics in surface-subsurface hydrology and hydrodynamics can facilitate an efficient incorporation of river bathymetry in large river networks. The second objective explores the level of bathymetric detail required for accurately simulating surface and subsurface processes by developing four bathymetric representations using SPRING with reducing level of detail. These bathymetric configurations are simulated using a physically based tightly coupled hydrologic and hydrodynamic model to estimate surface and subsurface fluxes in the floodplains. Comparison of fluxes for the four bathymetric configurations show that the impact of river bathymetry extends beyond surface routing to surface water – groundwater interactions. Channel conveyance capacity and thalweg elevation are the most important characteristics controlling these interactions followed by channel side slope and channel asymmetry. </p> <p> The final objective aims to develop benchmarks for bathymetric characteristics for accurately simulating flooding related physical processes. The sensitivity of surface and subsurface fluxes to error in channel conveyance capacity is investigated across reaches with varying geomorphological characteristics. SPRING is used to create six bathymetric configurations with varying range of error in channel conveyance capacity (ranging from 25% to 300%). They are simulated using a tightly coupled physically distributed model for a flood event and the estimates of water surface elevation, infiltration and lateral seepage are compared. Results show that incorporating channel conveyance capacity with an error of within 25% significantly improves the estimates of surface and subsurface fluxes as compared to those not having any bathymetric correction. For certain reaches, such as those with high drainage area (>1000km²) or low sinuosity (< 1.25), errors of up to 100% in channel conveyance capacity can still improve H&H modeling.</p>

Alluvial river channels are self-formed by the sediment-laden flow that is supplied to them from upstream and the interactions between this flow and the materials forming the channel bed and banks. Thus, any changes in the volumes of solid and liquid discharge or the resistance of the boundary materials can produce adjustments in the form of river channels over time. These shifts may increase or decrease the capacity of a channel to contain flood flows. However, despite a wealth of studies on the average geometry of river channels across different scales and climatic regimes, there has not yet been a systematic assessment of the rates and controls of trends in channel form. Using a combination of USGS data, including manual field measurements and mean daily streamflow data at hundreds of stream gages, this work is the first attempt to quantify how trends in channel geometry develop over decadal timescales and how they contribute to shifts in flood hazard, in comparison with trends in streamflow. Findings reveal that two-thirds of all channel cross-sections studied exhibit significant trends in channel geometry. The majority of the investigated US river channels are eroding, with widening and deepening trends partially offset by decreases in average flow velocity. Rates of change are principally controlled by the channel size. Although large channels develop larger trends, changes are proportionally greater in small channels in percentage terms. A secondary major control is hydrology: rates of change in channel geometry are heightened by the variability and flashiness of flow regimes. Finally, results show that changing flood frequencies can only be accurately quantified when both hydrologic and geomorphic trends are accounted for, and that flood hazard is significantly increasing across the studied sites. These documented trends in channel geometry, hydraulics, and flood hazard have important implications for the management of alluvial channels, navigation, and riverside infrastructure.

Single-phase CFD calculations are already widely applied in nuclear industry for the thermal-hydraulic design optimization of fuel assemblies (FA). In contrast, two-phase CFD-applications are still in the state of development. The work presented in this thesis shows contributions towards the detailed two-phase modeling of boiling flows under swirl conditions in sub-channel geometries of pressurized water reactors (PWR) FAs, including a realistic description of the critical heat flux (CHF)-phenomena and identification of two-phase indicators characterizing CHF-phenomena. The numerical simulations were conducted with a 3-D CFD code (STAR CD) for various types of swirl generating components in FA. New insights regarding local void distribution in sub-channels under swirl conditions were obtained, which are relevant for CHF (“bubble pockets”). Furthermore, an enhanced wall partitioning model provides a more realistic description of the steep increase of the rod temperature due to CHF. Presented validation studies showed good agreement with the available experiments under PWR conditions for the radial void distributions at non-CHF conditions as well as for the CHF prediction. The results performed in this thesis show the incentives and chances of two-phase CFD applications for the development of thermal-hydraulically optimized PWR spacer grids with regard to heat transfer and improvement to the CHF behaviour. / Einphasige CFD Analysen stellen für typische thermohydraulische Fragestellungen aus dem Kernkraftwerksbereich bereits jetzt ein wichtiges Werkzeug für die Brennelement (BE)¬Auslegung dar. Die zweiphasige CFD-Modellierung befindet sich dagegen in der Entwicklungsphase. Die in dieser Dissertation präsentierten Arbeiten zeigen Fortschritte für die detaillierte zweiphasige Modellierung drallbehafteter Strömungen im Unterkanal eines BEs des Druckwasserreaktors (DWR) einschließlich der realistischen Beschreibung des kritischen Wärmestroms (CHF) sowie die Bestimmung zweiphasiger Indikatoren, welche das Auftreten von CHF-Phänomen beschreiben. Verschiedene drallerzeugende Komponenten im BE wurden mit dem 3-D CFD-Code STAR-CD modelliert. Es wurden neue Erkenntnisse zur lokalen Blasenverteilung in Unterkanälen unter Drallbedingungen gewonnen, die für CHF relevant sind (“bubble pockets”). Durch eine Modifikation des Wärmeübergangsmodells (heat partitioning model) wird der starke Anstieg der Stabtemperatur infolge CHF realistischer beschrieben. Die durchgeführten Validierungen zeigen eine gute Übereinstimmung mit verfügbaren Experimenten unter DWR-Bedingungen für die radialen Blasenverteilungen und für die Bestimmung von CHF. Die vorliegenden Ergebnisse dieser Dissertation verdeutlichen den Nutzen und die Möglichkeiten von zweiphasigen CFD-Anwendungen für die Entwicklung und die thermohydraulische Optimierung von DWR-Abstandshaltern bezüglich des Wärmeübergangs und der Verbesserung des CHF-Verhaltens. / Модели однофазовой среды в вычислительной гидродинамике (англ. CFD) являются уже сейчас важным инструментом для решения типичных термогидравлических задач в ядерной энергетике, например, при конструировании тепловыделяющих сборок (ТВС). Двухфазовое моделирование, в сравнении с однофазовым, находится на сегодняшний момент в стадии развития. Данная диссертация связана с совершенствованием двухфазовой модели в направлении улучшения детализации вихревого течения внутри ячейки ТВС в условиях работы двухконтурного ядерного реактора (тип PWR). Также в работе показана возможность более реалистичного описания феномена кризиса теплоотдачи и определения двухфазовых индикаторов, характеризующих критический тепловой поток (англ. CHF). Комплекс расчетов выполнен для различных интенсификаторов теплоотдачи, размещенных на дистанционирующих решетках TBC. Расчеты производились с помощью программного обеспечения STAR-CD, позволяющего моделировать трехмерные гидродинамические системы. Полученные новые данные о локальном распределении пузырьков в ячейках с вихревым течением дали важную информацию для идентификации критического теплового потока. Усовершенствование модели теплоотдачи на поверхности тепловыделяющего элемента (ТВЭЛ) позволило более реалистично описать резкое повышение температуры на поверхности ТВЭЛа при достижении критических условий. Полученные результаты численного моделирования для радиальных распределений пузырьков при нормальных условиях работы PWR и также для определения критического теплового потока показали хорошее совпадение с известными экспериментальными данными. Представленные в диссертации результаты показывают возможности применения двухфазовых CFD-расчётов для разработки и термогидравлической оптимизации дистанционирующих решеток с целью улучшения теплообмена и характеристик критического теплового потока в двухконтурном ядерном реакторе типа PWR.

Single-phase CFD calculations are already widely applied in nuclear industry for the thermal-hydraulic design optimization of fuel assemblies (FA). In contrast, two-phase CFD-applications are still in the state of development. The work presented in this thesis shows contributions towards the detailed two-phase modeling of boiling flows under swirl conditions in sub-channel geometries of pressurized water reactors (PWR) FAs, including a realistic description of the critical heat flux (CHF)-phenomena and identification of two-phase indicators characterizing CHF-phenomena. The numerical simulations were conducted with a 3-D CFD code (STAR CD) for various types of swirl generating components in FA. New insights regarding local void distribution in sub-channels under swirl conditions were obtained, which are relevant for CHF (“bubble pockets”). Furthermore, an enhanced wall partitioning model provides a more realistic description of the steep increase of the rod temperature due to CHF. Presented validation studies showed good agreement with the available experiments under PWR conditions for the radial void distributions at non-CHF conditions as well as for the CHF prediction. The results performed in this thesis show the incentives and chances of two-phase CFD applications for the development of thermal-hydraulically optimized PWR spacer grids with regard to heat transfer and improvement to the CHF behaviour. / Einphasige CFD Analysen stellen für typische thermohydraulische Fragestellungen aus dem Kernkraftwerksbereich bereits jetzt ein wichtiges Werkzeug für die Brennelement (BE)¬Auslegung dar. Die zweiphasige CFD-Modellierung befindet sich dagegen in der Entwicklungsphase. Die in dieser Dissertation präsentierten Arbeiten zeigen Fortschritte für die detaillierte zweiphasige Modellierung drallbehafteter Strömungen im Unterkanal eines BEs des Druckwasserreaktors (DWR) einschließlich der realistischen Beschreibung des kritischen Wärmestroms (CHF) sowie die Bestimmung zweiphasiger Indikatoren, welche das Auftreten von CHF-Phänomen beschreiben. Verschiedene drallerzeugende Komponenten im BE wurden mit dem 3-D CFD-Code STAR-CD modelliert. Es wurden neue Erkenntnisse zur lokalen Blasenverteilung in Unterkanälen unter Drallbedingungen gewonnen, die für CHF relevant sind (“bubble pockets”). Durch eine Modifikation des Wärmeübergangsmodells (heat partitioning model) wird der starke Anstieg der Stabtemperatur infolge CHF realistischer beschrieben. Die durchgeführten Validierungen zeigen eine gute Übereinstimmung mit verfügbaren Experimenten unter DWR-Bedingungen für die radialen Blasenverteilungen und für die Bestimmung von CHF. Die vorliegenden Ergebnisse dieser Dissertation verdeutlichen den Nutzen und die Möglichkeiten von zweiphasigen CFD-Anwendungen für die Entwicklung und die thermohydraulische Optimierung von DWR-Abstandshaltern bezüglich des Wärmeübergangs und der Verbesserung des CHF-Verhaltens. / Модели однофазовой среды в вычислительной гидродинамике (англ. CFD) являются уже сейчас важным инструментом для решения типичных термогидравлических задач в ядерной энергетике, например, при конструировании тепловыделяющих сборок (ТВС). Двухфазовое моделирование, в сравнении с однофазовым, находится на сегодняшний момент в стадии развития. Данная диссертация связана с совершенствованием двухфазовой модели в направлении улучшения детализации вихревого течения внутри ячейки ТВС в условиях работы двухконтурного ядерного реактора (тип PWR). Также в работе показана возможность более реалистичного описания феномена кризиса теплоотдачи и определения двухфазовых индикаторов, характеризующих критический тепловой поток (англ. CHF). Комплекс расчетов выполнен для различных интенсификаторов теплоотдачи, размещенных на дистанционирующих решетках TBC. Расчеты производились с помощью программного обеспечения STAR-CD, позволяющего моделировать трехмерные гидродинамические системы. Полученные новые данные о локальном распределении пузырьков в ячейках с вихревым течением дали важную информацию для идентификации критического теплового потока. Усовершенствование модели теплоотдачи на поверхности тепловыделяющего элемента (ТВЭЛ) позволило более реалистично описать резкое повышение температуры на поверхности ТВЭЛа при достижении критических условий. Полученные результаты численного моделирования для радиальных распределений пузырьков при нормальных условиях работы PWR и также для определения критического теплового потока показали хорошее совпадение с известными экспериментальными данными. Представленные в диссертации результаты показывают возможности применения двухфазовых CFD-расчётов для разработки и термогидравлической оптимизации дистанционирующих решеток с целью улучшения теплообмена и характеристик критического теплового потока в двухконтурном ядерном реакторе типа PWR.