Universität Stuttgart
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Item Open Access Low-field chip-based Overhauser dynamic nuclear polarization platforms(2026) Yang, Qing; Anders, Jens (Prof. Dr.)Item Open Access Methodology to qualify batteries for safety-critical vehicle applications(2025) Conradt, Rafael; Birke, Kai Peter (Prof. Dr.-Ing.)Item Open Access PC-SAFT density functional theory in 3 dimensions : adsorption in ordered porous media and solvation free energies in non-polar solvents(Stuttgart : Universität Stuttgart, Institut für Technische Thermodynamik und Thermische Verfahrenstechnik, 2023) Eller, Johannes; Groß, Joachim (Prof. Dr.-Ing.)Item Open Access Modeling, testing and application of tuned liquid multi-column dampers for floating offshore wind turbines(2024) Yu, Wei; Cheng, Po Wen (Prof. Dr.)Item Open Access Bedload transport estimation in mountainous intermittent rivers and streams(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2023) Sadid, Najibullah; Wieprecht, Silke (Prof. Dr.-Ing.)Rivers and streams with the flow, sediment, and habitat seasonality are termed as intermittent rivers and streams (IRS). IRS are the main water bodies in arid and semi-arid regions of the world but are also found in the temperate and humid environment, where they are particularly draining headwater streams. Thus, a large part of headwater streams in the mountainous regions behave as intermittent water bodies, where the steep channel slope and a wide variety of sediment sizes add to their hydrosedimentological complexity. Bedload transport as an important sedimentological characteristic of mountainous IRS and essential for planning sediment management strategies, is far from being well understood. Often the knowledge of lowland perennial rivers is adapted to steep IRS, which may lead to an overestimation of bedload transport mainly due to the overestimation of near-bed flow characteristics. Despite the development of numerous methods for modifying near-bed flow parameters for steep IRS such as Double-averaging of Navier-Stokes equation and flow resistance methods modifications for steep IRS, their application is limited to small domains and laboratory conditions. In this research, the flow resistance, main determinant of near-bed flow characteristic is estimated using a regime channel approach. In this approach, the flow resistance is estimated on reach-scale based on the channel’s regime dimension, slope and bankfull discharge assuming an IRS is in regime state (equilibrium condition). A channel’s regime state represents a long-term average characteristic of a river and does not significantly change over time. A channel reach of a constant slope develops a certain flow resistance during its regime state development to resist the change imposed by bankfull discharge and maintain a specific regime geometry, slope, and sediment grain size. 2D- hydromorphological computer simulations are employed to simulate the development of channel regime state for several cases of initial geometries, slopes, and grain sizes by steering the flow resistance. This modifies the riverbed shear stress by the ratio of total flow resistance to grain resistance also known as relative flow resistance µ in order to account for flow energy dissipation on resistance sources such as macro-roughness elements (MRE), and bedforms. Alternatively, two cases of MRE as a main flow resistance inducer is built as non-erodible trapezoidal shapes (i) randomly distributed over the channel bed, and (ii) arranged in cascade bedforms are used in regime channel simulations. MRE protects the channel by reducing the exposed riverbed to erosion and changing the flow characteristics in their vicinity. Regime channel simulations are performed on artificial channels of initial slopes between 0.0% to 10% and initial dimensions of 5.5 m x 200 m and 16.5 m x 200 m resembling a fixed (laboratory) and an extended-width (natural wide channel) condition. Three channel slope combination cases representing a natural channel reach which can be composed of one or more constant slope stretch are also studied beside single slope channels. Steady state simulations are performed for six sediment grain size (GSD) sets, which cover a wide spectrum of naturally occurring sediment sizes. The simulation results show a power-law relationship between µ and regime channel slopes for all channel dimensions, reach combinations, GSD, initial slopes and with (R1) and without sediment feeding (R). The increase in relative flow resistance (µ) with regime channel slope is well reproduced in form of bedforms. Regime channels developed step-pool to cascade bedforms for steep slopes and plane- to riffle bed for gentle slopes channels. The relationship between µ and regime slope derived using regime channel simulation approach exhibits good agreement with some field measurement of flow resistance for mountainous rivers and streams. The approach is applied on two IRS case studies with observed data in Kabul River basin, Afghanistan to estimate bedload transport. The relative flow resistance resulted from models calibration showed good agreement with those derived from test channels regime development simulation. The outcome of channel regime simulation with presence of MRE as geometrical shapes produced a logarithmic-law with a horizontal asymptote relationship between MRE concentrations and channel regime slopes. Similar results are also reported from flume experiments that the ratio of drag to total shear stress increases rapidly when the MRE are sufficiently distant. Regime channels develop micro-channels around MRE, where the bulk of bedload transport occur. For MRE arrangements as cascades, the results show a power-law relationship between channel regime slope and step-pool dimensions λ = LD/DB. The results obtained are in good agreement with field measurement of naturally occurring and artificially built λ relationship with SR. Future studies can further enrich the validation of this approach by applying it to other study sites. Present modelling tools have their limitations when dealing with strong geometries which is often the case for mountain rivers, therefore, improvement in modelling techniques is required to flexibly deal with abrupt changes in riverbed geometry for instance when implementing MRE as main flow resistance inducer.Item Open Access Ganzheitliche Analyse und Optimierung der Systembelastungen schnell drehender Hochdruck-Radialventilatoren(Stuttgart : Institut für Konstruktionstechnik und Technisches Design, 2023) Recker, Stefan; Binz, Hansgeorg (Prof. Dr.-Ing.)Die Arbeit beschäftigt sich mit der umfassenden Untersuchung und Optimierung der Systembelastungen bei schnell drehenden Hochdruck-Radialventilatoren. Durch ein systematisches Vorgehen und gewonnene Erkenntnisse ermöglicht sie die Anwendung hoher Drehzahlen in Kombination mit der bewährten und kostengünstigen Blechbauweise von Laufrad und Gehäuse. Dies führt zu neuen Ventilatorentypen mit bisher nicht verfügbarer Effizienz und Betriebspunkten. Die herkömmlichen Blechbauweise-Ventilatoren sind meist ineffizient und bauen sehr groß, während Ventilatoren mit Freiformlaufrädern kompakter sind, aber teurer in der Herstellung. Die Arbeit schließt eine Marktlücke, indem sie schnell drehende Ventilatoren mit hoher Effizienz in kostengünstiger Blechbauweise untersucht. Die Studie analysiert und bewertet die auftretenden Belastungen im Ventilator, insbesondere die Lagerkräfte. Durch Lagerkraftmessungen und ein entwickeltes Vorauslegungsprogramm können effizient ausgelegte Ventilatoren hinsichtlich Lagerkräften und Lebensdauer vorhergesagt werden. Die Ergebnisse zeigen, dass die Wahl des Nennbetriebspunktes die lasttechnisch optimale Auslegungsdrehzahl beeinflusst, des Weiteren werden Maßnahmen zur Optimierung der Lebensdauern gefunden. Nach Festlegung der belastungsoptimalen Basisparameter erfolgt die Feingestaltung des Ventilators. Potenziell problematische Eigenfrequenzen werden analysiert und optimiert, um Resonanzen zu vermeiden. Die Arbeit betrachtet zudem den Fliehkrafteinfluss auf das hochbelastete Blechlaufrad mit Optimierungsmöglichkeiten durch den Einsatz von hochfesten Werkstoffen und Reduzierung von Kerbspannungen. Die vorgestellten Methoden und Optimierungsmöglichkeiten werden anhand zweier entwickelter Ventilatoren bewertet. Der direkte Vergleich mit anderen Herstellern bestätigt einen bis zu 30 % höheren Luftwirkungsgrad und kompakte, kostengünstige Blechbauweise. Die Arbeit schließt mit einem Leitfaden zur Analyse und Optimierung der Systemlasten.Item Open Access Coupling mechanisms of magnetic nanoparticles in polymeric environments(2026) Kreissl, Patrick; Holm, Christian (Prof. Dr.)Item Open Access Scalable traffic engineering heuristics for time-triggered communication in real-time networks(2026) Geppert, Heiko; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c.)Distributed safety-critical cyber-physical systems require real-time behavior. This means they must respond not just quickly, but in time, to new situations considering both, the task processing and network communication time. From a networking perspective, meticulous, time-driven traffic planning performed at the frame level is necessary to guarantee low end-to-end delay bounds and low latency. This involves carefully planning transmission operations along each time-critical frame's network path are carefully planned, including precise timing, to limit or even eliminate interference from cross-traffic and ensure timely delivery. Since modern real-time systems can consist of hundreds or thousands of devices - for example, large manufacturing plants or continental-sized power grids - the traffic planning must be highly scalable. Although there are many traffic planning approaches in the literature, there is a lack of very fast heuristics that can handle very large stream sets and networks quickly. This thesis investigates traffic planning heuristics and optimization techniques, focusing on different aspects of the traffic planning domain. The traffic planning consists of novel methods for conflict-graph-based scheduling and new heuristics for very large instances of traffic planning problem. The optimizations include multicast partitioning, which combines the benefits of multicast and unicast traffic plans, and load-balanced stream placement, which generates traffic plans that can accommodate additional streams joining the system later. We created prototype implementations and analyzed their performance in solving the traffic planning problem. Our traffic plans yielded a higher accumulated network throughput or admitted more streams while maintaining computation times ranging from sub-seconds to minutes, even for extremely large-scale problem instances. The traffic planning methods and optimization techniques presented in this thesis can be applied to modern real-time networking technologies, such as Time-Sensitive Networking and TTEthernet.Item Open Access Potentials and limitations of the a priori data-augmentation of turbulence closure models(2026) Mandler, Hannes; Weigand, Bernhard (Prof. Dr.-Ing. habil.)Turbulent flows occur in numerous technical applications. In some applications, turbulence is deliberately exploited to increase their efficiency. In others, the efficiency can be increased by suppressing turbulence to the greatest extent possible. The ability to accurately predict turbulent flows is, therefore, of immense importance. Nowadays, mainly numerical simulation methods are used for this purpose. As solving the Navier-Stokes equations would be far too costly for most applications of practical interest, the Reynolds-averaged Navier-Stokes equations are typically considered instead. However, their solution requires closure models to describe the influence of the turbulence on the mean flow. As a result of structural and parametric deficiencies of existing models, especially the popular eddy viscosity models, the accuracy of the predicted flow fields often no longer meets the current quality requirements. One way to address these deficiencies is to replace the empirical but often constant model coefficients by functions of the local mean flow field. Unlike the classical modeling approach, which seeks to derive such functional dependencies from theory and physical reasoning, leveraging machine learning instead allows for extracting the desired coefficient functions from publicly available DNS data. The models could, therefore, be calibrated for applications that are still simple but exceed the complexity of the traditional calibration cases, e.g., applications governed flow separation and reattachment. This thesis investigates the merits of this approach with respect to the accuracy of the flow field predictions and the possibility of developing more universal closure models. To this end, an a priori augmentation method for existing closure models was developed. A two-stage procedure was proposed to find appropriate functions for the closure coefficients. First, using the DNS data, the extended closure model is inverted to obtain the spatial distribution of the optimal coefficients for a particular training case. These allow the optimal structure of the constitutive equation to be determined in order to prevent any structural deficiencies. By subsequently solving a regression problem, functions represented by neural networks can be inferred that predict those optimal values of the coefficients as a function of the local mean flow state. Based on three examples, namely the flows through a plane channel, a plane channel with periodic hills, and a square duct, the data-augmented development of such model corrections was demonstrated. The errors in the prediction of the velocity field for the respective training cases could be reduced by up to 65%. The accuracy achieved with this method is typically unmatched even for significantly more complex existing closure models. In addition, it was proven that the extended models provide at least equivalent, but often more accurate predictions than the baseline model for a wide range of Reynolds numbers. The same applies to applications that differ geometrically, but not phenomenologically from the training case. However, if the test case was characterized by different flow phenomena than the training case, a sometimes considerable decrease in the predictive accuracy compared to the baseline model was observed. The obvious strategy of dealing with this loss of universality, i.e., deriving the coefficient functions from a more diverse training data set, proved to be ineffective. This is considered to be due to the complexity of the structure of the coefficient functions, which is limited for stability reasons and, hence, usually not sufficient to actually reflect the diversity of the training data. The method developed in this work for the data-driven augmentation of existing closure models is representative of a number of similar approaches that seek to improve flow field predictions via a more accurate description of the Reynolds stress tensor. In summary, such methods are suitable for developing highly specialized models that achieve the desired accuracy gains for a class of not too complex and phenomenologically similar flows. These two limitations could probably be remedied by CFD-integrated training and well-designed combinations of many such expert models.Item Open Access Der Architekt Bodo Rasch : sein Leben und Werk(2023) Stolz, Katharina; Philipp, Klaus Jan (Prof. Dr. phil. habil.)Die vorliegende Arbeit widmet sich monografisch dem architektonischen Autodidakten Bodo Rasch (1903-1995), der seit seinem Studium zum Agraringenieur in Hohenheim ab 1923 bis zu seinem Tod 1995 in Stuttgart lebte und der sich in der hiesigen Architekturszene sehr engagierte. Die Dissertationsschrift stellt nun erstmals die Person und das Œuvre Bodo Raschs, unabhängig von dessen älterem Bruder Heinz (1902-1996) vor und widmet sich mit dessen wissenschaftlicher Aufarbeitung und Kontextualisierung einem Forschungsdesiderat. Entgegen der vorherrschenden Fachmeinung war Bodo Rasch nach der Auflösung des mit seinem Bruder Heinz gemeinsam geführten Bauateliers nicht nur als Journalist und Herausgeber tätig. Vielmehr konnten durch die Aufarbeitung der Nachlassunterlagen bisher in der Fachliteratur unkorrekt beiden Brüdern zugeschriebene Projekte allein auf Bodo Rasch zurückgeführt werden, dazu gehören insbesondere die pneumatischen Konstruktionen und die Containerarchitektur. Durch die vorliegende Arbeit wird nun deutlich, dass sich Rasch auf zahlreichen unterschiedlichen architektonischen Gebieten engagierte und profiliere und wichtige Beiträge zu deren Entwicklung leistete, die bis dato keinen Niederschlag in der Fachliteratur fanden, wodurch ihm ein Platz in der Reihe der Vordenker und Wegbereiter bislang verwehrt blieb. Des Weiteren liefert die Arbeit auf der Basis der Monografie Raschs einen Beitrag zur historischen Erforschung der Netzwerke von Ingenieuren, Architekten und Planern der Stuttgarter Region, während und nach der Zeit der NS-Herrschaft.