13 Zentrale Universitätseinrichtungen

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14

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Start date: 2008

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Now showing 1 - 10 of 333
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    A fully coupled thermomechanical 3D model for all phases of friction stir welding
    (2016) Hoßfeld, Max
    Although friction stir welding (FSW) has made its way to industrial application particularly in the last years, the FSW process, its influences and their strong interactions among themselves are still not thoroughly understood. The lack of understanding mainly arises from the adverse observability of the actual process with phenomena like material ow and deposition, large material deformations plus their complex thermo-mechanical interactions determining the weld formation and its mechanical properties. A validated numerical process model may be helpful for closing this gap as well as for an isolated assessment of individual influences and phenomena. Hereby such a model will be a valuable assistance for process and especially tool development. In this study a Coupled Eulerian-Lagrangian (CEL) approach with Abaqus V6.14 is used for modeling the whole FSW process within one continuous model. The resolution reached allows not only simulating the joining of two sheets into one and real tooling geometries but also burr and internal void formation. Results for temperature fields, surface and weld formation as well as process forces are shown and validated.
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    Exploring how personality affects perception of uncertainty visualization
    (2025) Aboulgadayel, Omar
    Interpreting uncertainty visualizations can be cognitively demanding, and individual differences, such as personality traits, may affect how people perceive such visualizations. While prior research has explored personality and cognitive load independently, few studies have investigated their combined influence on perception and decision-making in uncertainty visualizations. We conducted an experiment based on a wildfire evacuation task that compared textual and visual representations of uncertainty. Participants completed the NASA Task Load Index to assess perceived cognitive workload and a Big Five personality traits test to measure individual differences in personality. Consistent with prior findings, visual representations led to higher evacuation rates and faster decision times compared to textual representations. However, textual representations were associated with lower perceived cognitive workload. Personality traits significantly impacted decision-making behavior and perceived cognitive workload. Participants high in extraversion, neuroticism or openness were more likely to evacuate, while those high in agreeableness or conscientiousness were less likely to evacuate and tended to take more time to decide. Additionally, agreeableness and conscientiousness were positively correlated with perceived cognitive workload across all representations, whereas neuroticism and openness showed negative correlations, though only in certain representations. These findings offer new insights into how personality affects the perception and cognitive load in the context of uncertainty visualizations.
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    Computing power and model selection
    (2026) Formánek, Nico
    The relationship between computing power and model selection, following a scenario suggested by Humphreys (and others), is investigated. Against the worrisome conclusions of this scenario it is argued that using computing power to tune models has not been the only goal of science so far. Other reasons for model selection were always in play. It is discussed if modern computing methods, supplied with contemporary compute, make pursuing model selection on the grounds of error reduction alone more appealing. The conclusion is largely negative.
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    Influence of stirring pin geometry on weld appearance and microstructure in wire-based friction-stir additive manufacturing of EN AW-6063 aluminium
    (2025) Donaubauer, Stefan; Weihe, Stefan; Werz, Martin
    Additive manufacturing of metal components is predominantly based on fusion-welding processes involving melting and solidification. However, processing high-strength aluminium alloys presents challenges, including reduced mechanical properties and increased susceptibility to hot cracking. To address these issues, alternative solid-state processing methods for aluminium are being explored worldwide. One such method is wire-based friction-stir additive manufacturing, which builds on the principles of friction-stir welding. This study focused on assessing a range of pin tool designs to promote improved mixing between the filler material and substrate. The best results were achieved using a two-stirring-probe configuration, which was then employed to fabricate a multilayer wall made of EN AW-6063 aluminium alloy. The resulting structure showed significant grain refinement, with the deposited layers having an average grain size approximately four times smaller than that of the substrate, indicating dynamic recrystallisation. Tensile testing of the intermediate layer revealed a strength of 147 MPa and 10% elongation, corresponding to 77% of the filler wire strength. These findings highlight the potential of the W-FSAM process for producing near-net-shape, high-quality lightweight metal components with refined microstructures and reliable mechanical performance.
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    Die Klausur als Orakel? : Arbeitsergebnisse einer Klausurentwicklung in der Technischen Thermodynamik
    (Stuttgart : Universität Stuttgart, Zentrum für Lehre und Weiterbildung, 2018) Braun, Thorsten; Kröber, Edith
    Der Aufsatz stellt Zwischenergebnisse einer hochschuldidaktischen Kooperation mit dem Institut für Technische Thermodynamik und thermische Verfahrenstechnik (ITT) an der Universität Stuttgart vor. Es werden typische Schwachpunkte einer Klausur aus Perspektive einer Kompetenzmodellierung aufgezeigt und erläutert. Ziel ist es dabei, für Gütekriterien bei der Klausurgestaltung zu sensibilisieren und Ansatzpunkte aufzuzeigen, wie diese Kriterien umgesetzt werden können. Auch wenn die Ausführungen implizit auf eine Prüfungsmodellierung mittels Item Response Theory hinarbeiten, sind sie ohne Vorkenntnisse in der Testtheorie verständlich und umsetzbar.
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    Accelerated 2D visualization using adaptive resolution scaling and temporal reconstruction
    (2023) Becher, Michael; Heinemann, Moritz; Marmann, Thomas; Reina, Guido; Weiskopf, Daniel; Ertl, Thomas
    Data visualization relies on efficient rendering to allow users to interactively explore and understand their data. However, achieving interactive frame rates is often challenging, especially for high-resolution displays or large datasets. In computer graphics, several methods temporally reconstruct full-resolution images from multiple consecutive lower-resolution frames. Besides providing temporal image stability, they amortize the rendering costs over multiple frames and thus improve the minimum frame rate. We present a method that adopts this idea to accelerate 2D information visualization, without requiring any changes to the rendering itself. By exploiting properties of orthographic projection, our method significantly improves rendering performance while minimizing the loss of image quality during camera manipulation. For static scenes, it quickly converges to the full-resolution image. We discuss the characteristics and different modes of our method concerning rendering performance and image quality and the corresponding trade-offs. To improve ease of use, we provide automatic resolution scaling in our method to adapt to user-defined target frame rate. Finally, we present extensive rendering benchmarks to examine real-world performance for examples of parallel coordinates and scatterplot matrix visualizations, and discuss appropriate application scenarios and contraindications for usage.
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    Online visualization of German power plants and their production
    (2017) Ullah, Kazi Riaz
    Maps are used for centuries to visualize geographical or topological information and nowadays, with modern technology, we can create interactive maps that allow us to display and access additional information. Some of them have even become part of our daily life, such as, almost real-time traffic information. Furthermore, maps are often used to display data of population densities, temperatures and spatial distribution of geographical phenomenon. Fraunhofer Institute of Solar Energy ISE decided to build an interactive map that shows the locations of all power plants listed on the European Energy Exchange (EEX). Since July 2014, the Fraunhofer ISE has been providing interactive charts on electricity production and other related information about electricity and power generation in Germany. These charts became very popular and widely used by people from different professions, namely scientists, politicians, journalists as well as online/printed media. Due to the high popularity of these interactive energy charts, an interactive map has been added to the Energy Charts data visualization portal to make the framework more informative and interesting for users. The map has several search options and levels of detail for searching different power plant locations, technical data, and connectivity to the high voltage transmission lines. Furthermore, this new visualization framework is interconnected with the existing energy charts. The dynamic linking, brushing and filtering technique in both map and energy charts have enhanced the framework by an additional layer providing more visibility and information on the selected power plants.
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    Visualization and mesoscopic simulation in systems biology
    (2013) Falk, Martin Samuel; Ertl, Thomas (Prof. Dr.)
    A better understanding of the internal mechanisms and interplays within a single cell is key to the understanding of life. The focus of this thesis lies on the mechanism of cellular signal transduction, i.e. relaying a signal from outside the cell by different means of transport toward its target inside the cell. Besides experiments, understanding can also be achieved by numerical simulations of cellular behavior which require theoretical models to be designed and evaluated. This is where systems biology closely relates and depends on recent research results in computer science in order to deal with the modeling, the simulation, and the analysis of the computational results. Since a single cell can consist of billions of atoms, the simulation of intracellular processes requires a simplified, mesoscopic model. The simulation domain has to be three dimensional to consider the spatial, possibly asymmetric, intracellular architecture filled with individual particles representing signaling molecules. In contrast to continuous models defined by systems of partial differential equations, a particle-based model allows tracking individual molecules moving through the cell. The overall process of signal propagation usually requires between minutes and hours to complete, but the movement of molecules and the interactions between them have to be determined in the microsecond range. Hence, the computation of thousands of consecutive time steps is necessary, requiring several hours or even days of computational time for a non-parallel simulation. To speed up the simulation, the parallel hardware of current central processing units (CPUs) and graphics processing units (GPUs) can be employed. Finally, the resulting data has to be analyzed by domain experts and, therefore, has to be represented in meaningful ways. Typical prevalent analysis methods include the aggregation of the data in tables or simple 2D graph plots, sometimes 3D plots for continuous data. Despite the fact that techniques for interactive visualization of data in 3D are well-known, so far none of the methods have been applied to the biological context of single cell models and specialized visualizations fitted to the experts’ need are missing. Another issue is the hardware available to the domain experts that can be used for the task of visualizing the increasing amount of time-dependent data resulting from simulations. It is important that the visualization keeps up with the simulations to ensure that domain experts can still analyze their data sets. To deal with the massive amount of data to come, compute clusters will be necessary with specialized hardware dedicated to data visualization. It is, thus, important, to develop visualization algorithms for this dedicated hardware, which is currently available as GPU. In this thesis, the computational power of recent many-core architectures (CPUs and GPUs) is harnessed for both the simulation and the visualizations. Novel parallel algorithms are introduced to parallelize the spatio-temporal, mesoscopic particle simulation to fit the architectures of CPU and GPU in a similar way. Besides molecular diffusion, the simulation considers extracellular effects on the signal propagation as well as the import of molecules into the nucleus and a dynamic cytoskeleton. An extensive comparison between different configurations is performed leading to the conclusion that the usage of GPUs is not always beneficial. For the visual data analysis, novel interactive visualization techniques were developed to visualize the 3D simulation results. Existing glyph-based approaches are combined in a new way facilitating the visualization of the individual molecules in the interior of the cell as well as their trajectories. A novel implementation of the depth of field effect combined with additional depth cues and coloring aid the visual perception and reduce visual clutter. To obtain a continuous signal distribution from the discrete particles, techniques known from volume rendering are employed. The visualization of the underlying atomic structures provides new detailed insights and can be used for educational purposes besides showing the original data. A microscope-like visualization allows for the first time to generate images of synthetic data similar to images obtained in wet lab experiments. The simulation and the visualizations are merged into a prototypical framework, thereby supporting the domain expert during the different stages of model development, i.e. design, parallel simulation, and analysis. Although the proposed methods for both simulation and visualization were developed with the study of single-cell signal transduction processes in mind, they are also applicable to models consisting of several cells and other particle-based scenarios. Examples in this thesis include the diffusion of drugs into a tumor, the detection of protein cavities, and molecular dynamics data from laser ablation simulations, among others.