Universität Stuttgart
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Item Open Access Identifizierung neuer Proteine des Polyphosphat Granulumkomplexes von Ralstonia eutropha H16(2017) Tumlirsch, Tony; Jendrossek, Dieter (Prof. Dr.)Item Open Access Supercharacter theories for Sylow p-subgroups 3D4syl(q3), G2syl(q) and 2G2syl(32m+1)(2017) Sun, Yujiao; Dipper, Richard (Prof. Dr.)Item Open Access Zur Abschätzung der Lebensdauer von laufenden hochmodularen Faserseilen(Stuttgart : Institut für Fördertechnik und Logistik (IFT) der Universität Stuttgart, 2017) Novak, Gregor; Wehking, Karl-Heinz (Univ.-Prof. Dr.-Ing. Dr. h. c.)Die vorliegende Forschungsarbeit untersucht die Lebensdauer laufender hochmodularer Faserseile. Hierzu gehört das Aufstellen einer Abschätzungsmethode um eine statistisch relevante Aussage über die Lebensdauer eines hochmodularen Faserseiles beim Lauf über Seilscheiben zu treffen und die Untersuchung der Faktoren, die die Lebensdauer dieser laufenden hochmodularen Faserseile beeinflussen. Weiter wird eine neuartige Spulvorrichtung für laufende hochmodulare Faserseile vorgestellt, die einer durch Schrägzug oder Höhenspannung hervorgerufenen Verdrehung entgegenwirkt und eine Erhöhung der Seillebensdauer ermöglicht.Item Open Access High order large eddy simulation for the analysis of tonal noise generation via aeroacoustic feedback effects at a side mirror(2017) Frank, Hannes; Munz, Claus-Dieter (Prof. Dr.)In this work, the flow around a side mirror and the resulting tonal noise generation are investigated using highly accurate compressible large eddy simulations. Avoiding tonal noise, which can be perceived as disturbing whistling sound, is a crucial target in automotive aeroacoustics. However, the underlying mechanisms are not completely understood and can typically not be captured with state of the art computational aeroacoustics solvers used in industry. Acoustic feedback effects known from tonal airfoil self-noise are a possible cause at smooth mirror housings that exhibit laminar separation upstream of the trailing edge. Since this application demands high accuracy, a simulation code based on the high order discontinuous Galerkin spectral element method is employed. To enhance geometrical flexibility, it is augmented with an extension to non-conforming curved elements in three dimensions. In the first part of the investigation, the simulation framework is used to analyze an early development stage side mirror exhibiting tonal noise generation. Adopting the corresponding experimental configuration, the study considers an isolated side mirror mounted on the wind tunnel floor. The computational flow field is shown to agree remarkably well with the experimental one based on comparisons with static wall pressure, hotwire and PIV measurements. Discrete peaks are obtained in the computational acoustic spectrum, originating at the trailing edge of the mirror downstream of laminar separation. The identified tonal noise source regions match the experimental ones and quantitative agreement is achieved for one of the tonal peak frequencies. Perturbation simulations reveal global acoustic feedback instabilities selecting the same discrete frequencies observed in the developed flow. The feedback loop comprises convective disturbance growth in the separated shear layer, scattering at the trailing edge and reinforcement through receptivity to the emitted sound in the upstream boundary layer. In a second step, this mechanism is studied in more detail based on a specifically designed simplified two-dimensional model. A subdomain approach is introduced to exploit the two-dimensional shape and circumvent the computational cost associated with the bluff body wake of the model. Simulations of a range of free-stream velocities exhibit tonal frequencies varying similarly to the experimentally observed so-called 'ladder structure'. The tone frequencies are shown to evolve according to a theoretical feedback model based on linear stability theory. Finally, the efficacy of various modifications to the mirror contour to eliminate tonal noise generation is evaluated. The present work contributes to the understanding of tonal noise generation mechanisms and can guide future designs. Moreover, it corroborates the capacity of the present discontinuous Galerkin framework to accurately capture relevant but delicate aeroacoustic effects at complex geometries.Item Open Access Modeling of porous polymer membrane formation(2017) Hopp-Hirschler, Manuel; Nieken, Ulrich (Prof. Dr.-Ing.)Porous polymer membranes are used in several separation processes, e.g. in dialysis or in water purification. The morphology of the membrane affects the quality of separation, e.g. selectivity, as well as the mechanical stability of the membrane. To control the morphology of the membrane during the preparation process we first need to understand the mechanism that leads to different pore structures. It is desirable to use a numerical model to predict the pore type and detailed structure. Wet-casting is a very common preparation process for porous polymer membranes where a liquid precipitation agent is used. Herein, a polymer solution and a coagulation bath is brought into contact. After contact the polymer solution is driven into a miscibility gap and starts to phase separate into a polymer lean and a polymer rich phase. Starting from the contact area between polymer solution and coagulation bath a pore structure grows where the polymer rich phase leads to the pore matrix. Although the process is used frequently in the last decades, its mechanism is still not fully understood. Therefore, the motivation in this thesis is to bridge experimental observations from membrane science to theoretical physics where concepts exist to understand the formation of pore structures in porous polymer membranes.Item Open Access Modeling of various mixed traffic zones for evaluation of operating performance on urban rail-bound networks(2017) Liu, Di; Martin, Ullrich (Prof. Dr.-Ing.)Item Open Access Beitrag zur Untersuchung von hochfesten synthetischen Faserseilen unter hochdynamischer Beanspruchung(Stuttgart : Institut für Fördertechnik und Logistik (IFT) der Universität Stuttgart, 2017) Wehr, Martin; Wehking, Karl-Heinz (Prof. Dr.-Ing. Dr. h.c.)Item Open Access Lithium intercalation in bilayer graphene devices(2017) Kühne, Matthias; Smet, Jurgen H. (Dr.)The subject of this dissertation is the experimental investigation of Lithium intercalation in bilayer graphene devices. An on-chip electrochemical cell architecture is implemented, consisting of a solidified polymer electrolyte confined at and covering only a small part of the perimeter of a patterned bilayer graphene device. This allows the operation of bilayer graphene as a single-phase mixed (electronic and ionic) conductor. Magnetotransport techniques as well as Raman spectroscopy are deployed to reveal Li intercalation-induced changes in situ during repeated lithiation and delithiation cycles. In combination with a range of ex situ characterization methods, evidence for efficient Li diffusion between graphene sheets only is brought forward. From a numerical analysis of time-dependent in situ Hall measurements, Lithium diffusion in bilayer graphene is revealed be exceptionally fast.Item Open Access Hybrid model for proactive dispatching of railway operation under the consideration of random disturbances in dynamic circumstances(2017) Zhao, Weiting; Martin, Ullrich (Prof. Dr.-Ing.)With the increasing traffic demand and limited infrastructure expansion, railway networks are often operated close to the full capacity, especially in heavily used areas. As a result, the basic timetable is quite susceptible to the operational disturbances, and thereby the propagation and accumulation of delays significantly degrade the service level for customers. To solve this problem, extensive researches have been conducted by focusing on the predefined robust timetables and the real time dispatching algorithm development. However, it has been widely recognized that excessive robust timetables may deteriorate the operating capacity of the railway network and the addition of recovery time and buffer time can be hardly implemented in the congested area. Moreover, most of the conventional dispatching algorithms ignore the further potential random disturbances during the dispatching process, which yield non-implementable dispatching solutions and, as consequences, inferior punctuality and repetitive dispatching actions. To this end, this project aims to develop a new algorithm for real-world dispatching process with the consideration of risk-oriented random disturbances in dynamic circumstances. In the procedure of this project, an operational risk map will be firstly produced: by simulating considerable amount of disturbed timetables with random disturbances generated in a Monte-Carlo scheme and calculating the corresponding expected negative impacts (average total weighted waiting time among all the disturbances scenarios), different levels of operational risk will be assigned to each block section in the studied railway network. Within a rolling time horizon framework, conflicts are detected with the inclusion of risk-oriented random disturbances in each block section, and the near-optimal dispatching solutions are calculated by using Tabu search algorithm. Finally, three indicators including total weighted waiting time, the number of relative reordering and average absolute retiming, are chosen to testify the effectiveness and advantages of the proposed dispatching algorithm. The sensitivity analysis of dispatching-related parameters is conducted afterwards to investigate the most appropriate relevant parameters for the specific studied area. The proposed algorithms are expected to be capable of automatically producing near-optimal and robust dispatching solutions with sufficient punctuality achieved.Item Open Access Visual analytics of human mobility behavior(2017) Krüger, Robert; Ertl, Thomas (Prof. Dr.)Human mobility plays an important role in many domains of today’s society, such as security, logistics, transportation, urban planning, and geo-marketing. Both, government and industry thus have great interest in understanding mobility patterns and their driving social, economical, and environmental causes and effects. While stakeholders had to rely on manual traffic surveys for a long time, improvements in tracking technology made analyses based on large digital datasets possible. Recently, the omnipresence of mobile devices significantly increased the amounts of collected movement and context data. People are willing to reveal their position, but also further personal details such as visited places, observations, events, news, and sentiments in exchange for personalized services and social networking. This opens up new possibilities for many domains where a semantic mobility understanding is required but also raises major challenges. To reveal a holistic picture, heterogeneous datasets of different services with different resolution and format have to be fused and analyzed. However, social sensing data is vast, has varying scale, is unevenly distributed, and constantly updated. Especially content from social media services is often inconsistent, unreliable, and incomplete, which requires special treatment. Fully automatic mapping approaches are not trustworthy as they do not take into account these uncertainties. At the same time, manual approaches become insufficient with large amounts of data. Even when data is perfectly aligned, analysts cannot purely rely on existing techniques. Answering questions about reasons for movement requires a broader perspective that takes into account environmental and social context, the driving forces for human mobility behavior. Visual analytics is an emerging research field to tackle such challenges. It creates added value by combining the processing power and accuracy of machines with human capabilities to perceive information visually. Automatic means are used to fuse and aggregate data and to detect hidden patterns therein. Interactive visualizations allow to explore and query the data and to steer the automatic processes with domain knowledge. This increases trust in data, models, and results, which is especially important when critical decisions need to be made. The strengths of visual analytics have been shown to be particularly advantageous when problems and goals are underspecified and exploratory means are needed to discover yet unknown patterns. This thesis presents novel visual analytics approaches to derive meaning and reasons behind movement, by taking into account the aforementioned characteristics. The approaches are aligned in a holistic process model covering all steps from data retrieval, enrichment, exploration, and verification to externalization of gained knowledge for various fields of application such as electric mobility, event management, and law enforcement. It is shown how data from social media can not only be used to retrieve up-to-date movement information, but also to enrich movement trajectories from other sources with structured and unstructured information about places, events, transactions, and other observations. Through highly interactive visual interfaces analysts can bring in domain knowledge to deal with uncertainties during data fusion and to steer the subsequent semantic analysis. Exploratory and confirmatory analysis techniques are presented to create hypotheses, refine them, and find support in the data. Analysts can discover routines and abnormal behavior with assistance of automatic pattern detection methods to cope with the vast amounts of data. Spatial drill-down is supported by a set-based focus+context technique, while a more abstract visual query language allows to explicitly formulate, extract, and query for movement patterns. The approaches are applied in different scenarios and are integrated in a visual analytics system. Evaluation with experts and novice users, case studies, and comparisons to ground truth data reveal the need and effectiveness of the contributions. Overall, the thesis contributes a visual analytics process for human mobility behavior with novel semantic analysis approaches, ranging from global movements of many to local activities of a few people, for a wide range of application domains.