Recent Submissions
Schaustücke : Einblicke in wissenschaftliche Sammlungen der Universität Stuttgart
(Stuttgart : Universität Stuttgart, 2025) Wiatrowski, Frank (Gestaltung; Engstler, Katja Stefanie (Gestaltung); Ceranski, Beate (Vorwort); Rambach, Christiane (Vorwort)
Die wissenschaftlichen Sammlungen der Universität zeugen von einer langen Lehr- und Forschungstradition. In Fakultäten und Instituten, in der Universitätsbibliothek und im Universitätsarchiv sind vielfältige Sammlungen beheimatet, zum Teil mit ungewöhnlichen oder gar einzigartigen Objekten. Die Broschüre gibt Einblicke in diese vielfach versteckte Welt der universitären Sammlungen in Stuttgart.
Proton exchange membrane-like alkaline water electrolysis using flow-engineered three-dimensional electrodes
(2024) Rocha, Fernando; Georgiadis, Christos; Van Droogenbroek, Kevin; Delmelle, Renaud; Pinon, Xavier; Pyka, Grzegorz; Kerckhofs, Greet; Egert, Franz; Razmjooei, Fatemeh; Ansar, Syed-Asif; Mitsushima, Shigenori; Proost, Joris
For high rate water electrolysers, minimising Ohmic losses through efficient gas bubble evacuation away from the active electrode is as important as minimising activation losses by improving the electrode’s electrocatalytic properties. In this work, by a combined experimental and computational fluid dynamics (CFD) approach, we identify the topological parameters of flow-engineered 3-D electrodes that direct their performance towards enhanced bubble evacuation. In particular, we show that integrating Ni-based foam electrodes into a laterally-graded bi-layer zero-gap cell configuration allows for alkaline water electrolysis to become Proton Exchange Membrane (PEM)-like, even when keeping a state-of-the-art Zirfon diaphragm. Detailed CFD simulations, explicitly taking into account the entire 3-D electrode and cell topology, show that under a forced uniform upstream electrolyte flow, such a graded structure induces a high lateral velocity component in the direction normal to and away from the diaphragm. This work is therefore an invitation to start considering PEM-like cell designs for alkaline water electrolysis as well, in particular the use of square or rectangular electrodes in flow-through type electrochemical cells.
Comparisons between upright and reclined seating positions in autonomous vehicles
(2022) Reinhard, René; Emmerich, Sebastian; Blumhofer, Benjamin; Kleer, Michael
In highly automated vehicles (SAE level 3 and up), the relinquishing of control allows its passengers to engage in non-driving-related tasks, including resting. Consequently, seat positions like a reclined seat may become more prevalent, which can in turn impact the passenger. The current study explored possible effects on comfort perceptions and the evaluation of the autonomous system in a driving simulator study. Here, 37 participants were seated on an off-the-shelf driver’s seat inside the RODOS driving simulator. They experienced three short driving scenarios that each included a swerving manoeuvre with noticeable lateral accelerations and yaw rotations in three different seating conditions: (1) an alert condition, with their hands on the steering wheel; (2) a hands free condition, where they were still seated upright, but were no longermonitoring the autonomous driving system; (3) a reclined seating condition, where they lay back in a reclined seat. They evaluated their experience with regard to overall comfort, the localisation of discomfort feelings, their trust in the autonomous driving system, and their perceived safety. Significant differences were found in comfort ratings and trust between the alert and hands free conditions, but not between the upright and reclined seating conditions.
Electronic moment tensor potentials include both electronic and vibrational degrees of freedom
(2024) Srinivasan, Prashanth; Demuriya, David; Grabowski, Blazej; Shapeev, Alexander
We present the electronic moment tensor potentials (eMTPs), a class of machine-learning interatomic models and a generalization of the classical MTPs, reproducing both the electronic and vibrational degrees of freedom, up to the accuracy of ab initio calculations. Following the original polynomial interpolation idea of the MTPs, the eMTPs are defined as polynomials of vibrational and electronic degrees of freedom, corrected to have a finite interatomic cutoff. Practically, an eMTP is constructed from the classical MTPs fitted to a training set, whose energies and forces are calculated with electronic temperatures corresponding to the Chebyshev nodes on a given temperature interval. The eMTP energy is hence a Chebyshev interpolation of the classical MTPs. Using the eMTP, one can obtain the temperature-dependent vibrational free energy including anharmonicity coming from phonon interactions, the electronic free energy coming from electron interactions, and the coupling of atomic vibrations and electronic excitations. Each of the contributions can be accessed individually using the proposed formalism. The performance of eMTPs is demonstrated for two refractory systems which have a significant electronic, vibrational and coupling contribution up to the melting point-unary Nb, and a disordered TaVCrW high-entropy alloy. Highly accurate thermodynamic and kinetic quantities can now be obtained just by using eMTPs, without any further ab initio calculations. The proposed construction to include the electronic degree of freedom can also be applied to other machine-learning models.
Uncertainty-biased molecular dynamics for learning uniformly accurate interatomic potentials
(2024) Zaverkin, Viktor; Holzmüller, David; Christiansen, Henrik; Errica, Federico; Alesiani, Francesco; Takamoto, Makoto; Niepert, Mathias; Kästner, Johannes
Efficiently creating a concise but comprehensive data set for training machine-learned interatomic potentials (MLIPs) is an under-explored problem. Active learning, which uses biased or unbiased molecular dynamics (MD) to generate candidate pools, aims to address this objective. Existing biased and unbiased MD-simulation methods, however, are prone to miss either rare events or extrapolative regions-areas of the configurational space where unreliable predictions are made. This work demonstrates that MD, when biased by the MLIP’s energy uncertainty, simultaneously captures extrapolative regions and rare events, which is crucial for developing uniformly accurate MLIPs. Furthermore, exploiting automatic differentiation, we enhance bias-forces-driven MD with the concept of bias stress. We employ calibrated gradient-based uncertainties to yield MLIPs with similar or, sometimes, better accuracy than ensemble-based methods at a lower computational cost. Finally, we apply uncertainty-biased MD to alanine dipeptide and MIL-53(Al), generating MLIPs that represent both configurational spaces more accurately than models trained with conventional MD.
Untersuchungen zur Auslegung und Gestaltung von zylindrischen Pressverbindungen mit elastisch-plastisch und vollplastisch beanspruchten Naben
(Stuttgart : Institut für Konstruktionstechnik und Technisches Design, 2025) Falter, Jan; Binz, Hansgeorg (Prof. Dr.-Ing.)
Aufgrund ihrer geometrischen Einfachheit und der damit verbundenen wirtschaftlichen Herstellung sind Pressverbindungen eine häufig in der Praxis eingesetzte Welle-Nabe-Verbindung. Infolge steigender Anforderungen an die Leistungsdichte von Maschinenelementen stößt die etablierte Auslegungsmethode von rein elastisch beanspruchten Pressverbindungen jedoch an ihre Grenzen, sodass andere Lösungsansätze erforderlich sind. Neben der elastischen Auslegung sind verschiedene Auslegungsmethoden für Pressverbindungen mit elastisch-plastisch beanspruchten Naben bekannt. Diese finden in der industriellen Praxis aufgrund verschiedener Defizite jedoch nur selten Anwendung, wobei insbesondere verlässliche Auslegungsgrenzen, Kenntnisse über versagenskritische Spannungen und eine experimentelle Absicherung fehlen.
Die vorliegende Arbeit stellt Auslegungs- und Prozessgrenzen für Pressverbindungen mit elastisch-plastisch und vollplastisch beanspruchten Naben bereit, um die Werkstoffausnutzung und die Leistungsdichte von Pressverbindungen zu steigern. Hierbei liegt der Fokus auf numerischen Untersuchungen zur Fugendrucksteigerung, zur Ermittlung von Auslegungsgrenzen und zur daraus resultierenden Nabenbeanspruchung. Zudem beinhaltet die Arbeit zahlreiche experimentelle Untersuchungen, die zur Validierung der numerischen Ergebnisse und der Ermittlung von Prozessgrenzen beim Fügen und Lösen der Pressverbindungen dienen. Zunächst wird der Aufbau geeigneter nichtlinearer Werkstoffmodelle beschrieben. Diese werden anschließend herangezogen, um die werkstoff- und geometrieabhängige Fugendrucksteigerung, die Nabenbeanspruchung und verschiedene Auslegungsgrenzen zu ermitteln. Darauf folgen numerische und experimentelle Untersuchungen zum Füge- und Lösevorgang. Dabei werden mithilfe von numerischen Berechnungen verschiedene Ansätze zur Geometrieoptimierung untersucht, die sowohl einen hohen und gleichmäßigen Fugendruck als auch ein sicheres Fügen ermöglichen. Die durchgeführten Experimente liefern wichtige Erkenntnisse zu Prozessgrenzen für das Fügen und Lösen der Pressverbindungen, zu geeigneten Schmierstoffen, zur Glättung der Rauheitsspitzen, zu Haft- und Gleitreibwerten und zum statischen Grenzdrehmoment. Die Arbeit endet mit einer Diskussion der Ergebnisse und Gestaltungsempfehlungen für zylindrische Pressverbindungen mit elastisch-plastisch und vollplastisch beanspruchten Naben.
Systematic investigation of oxymethylene ether combustion using electron and synchrotron radiation ionization mass spectrometry
(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2025) Gaiser, Nina; Aigner, Manfred (Prof. Dr.-Ing.)
Oxymethylene ethers (OMEs) are considered as sustainable alternatives or additives to conventional diesel fuels. They are characterized by their molecular structure CH3O-[CH2O]n-CH3 and can be produced through CO2-neutral processes. Having no direct C-C bonds, OME combustion shows a decrease in particulate matter emissions, such as soot, when compared to standard diesel blends, but they also show an increase in unregulated pollutants, such as aldehydes. The presented Ph.D. thesis systematically studies the oxidation behavior of OMEs with different chain lengths (OME0−5). Speciation data is measured using electron ionization molecular-beam mass spectrometry (EI-MBMS) with high mass resolution in an atmospheric flow reactor and low-pressure laminar flames. To obtain additional isomer-selective speciation analysis, double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy using vacuum ultraviolet (VUV) radiation at the Swiss Light Source is obtained. The combination of both spectroscopy methods provides a comprehensive understanding of OME oxidation processes and a more detailed overview of the species involved. Three consecutive experimental studies are presented in this Ph.D. thesis: Focusing on the impact of the OME chain length on the oxidation behavior, OME0−5 are investigated in atmospheric laminar flow reactors. Subsequently, the oxidation of OME2 and its branched isomer, trimethoxymethane, are compared to comprehend the structural influences on their oxidation behavior. Finally, high-temperature conditions are examined for OME0−4 using low-pressure laminar flames. Overall, oxygenated species are the dominant intermediates for all OMEs. The observed species pool is nearly independent of the OME’s chain length. Identification of significant isomers and detailed mole fraction profiles are provided for several oxygenated species such as methanol, formaldehyde, dimethyl ether, formic acid, methyl formate as well as for several hydrocarbons. Notably, the absence of typical soot precursors underscores OMEs’ potential for clean combustion. The reactivity of OMEs increases with longer chain lengths or branched structures, evidenced by changing peak temperatures of intermediates. The presence of ethanol as a key intermediate is remarkable and indicates unknown or underestimated reaction pathways. Comparison between the linear OME2 and its branched isomer, trimethoxymethane (TMM), reveals differences in the species pools illustrating the structural impacts on combustion and providing direct insights into the decomposition of the examined fuels. The experimental data on OMEn oxidation are compared with the DLR model Concise, revealing its accuracy while also suggesting areas for improvement. Based on this experimental study, enhancements are already implemented in DLR Concise and are highlighted in this Ph.D. thesis. Overall, the study highlights the benefits of combining two complementary diagnostic techniques to obtain a more comprehensive and detailed analysis. The experimental results of this systematic oxidation analysis of OMEs can be used to develop, validate, and optimize reaction models. This research supports the advancement of OMEs as replacements for crude-oil based diesel fuels, contributing to a more sustainable transportation sector.
Comparative analysis of zk-SNARK instantiations for ensuring ballot validity
(2025) Röhr, Felix
As e-voting schemes become increasingly prevalent, ensuring their security is essential. In many cases, Zero Knowledge Proofs (ZKPs) are used to allow users to prove the validity of their (encrypted) votes without revealing them. One class of ZKPs that can be used to prove (essentially) arbitrary valid statements are General Purpose ZKPs (GPZKPs) with Zero-Knowledge Succinct Non-interactive Arguments of Knowledge (zk-SNARKs) being one type of such. zk-SNARKs are a good choice for our use case since voters are usually resource constrained in practice and zk-SNARKs typically offer small proofs and efficient proof generation algorithms.
A typical form of encrypting ballots in e-voting schemes is Exponential ElGamal (EEG) encryption. The feasability of GPZKPs for showing validity of ballots that are component-wise encrypted using EEG ciphertexts in voting systems with arbitrary election types and ballot formats using Groth16-SNARKs has been shown by Huber et al. To demonstrate the versatility of GPZKPs, the authors implemented ballot validity relations for the different election types Single Vote, Multi-Vote, Line-Vote, Multi-Vote with Rules, the ranked election types Pointlist-Borda and Borda Tournament Style, Condorcet methods and Majority Judgment in libsnark and benchmarked their performance.
We extend on this research by implementing ballot validity relations for the same election types in Circom and generating the ZKPs using snarkjs. First, we follow the same approach as Huber et al. for our implementation, using EEG encryption instantiated with elliptic curves in Montgomery form for the encryption of individual ballot entries.
Then, as our main contribution, we introduce a novel variant of computing EEG ciphertexts: Precomputed Powers EEG (PPEEG). By providing some precomputed powers of group elements to the encryption, we reduce the computations needed for ZKPs of ballot validity. Additionally, we instantiate PPEEG encryption with elliptic curves in Twisted Edwards form rather than elliptic curves in Montgomery form, reducing the computational effort further.
Furthermore, we improve the performance of the election type specific computations in the ballot validity proofs for several election types, most notably for Condorcet methods. However, these improvements are negligible compared to the reduction of computational effort in the encryption part in most cases.
Compared to the results by Huber et. al, we reduce the computational effort for the ballot validity proofs accross all election types by 35% to 82% depending on the metric. Moreover, we can compute ballot validity proofs for ballots with up to 1000 votes on a standard PC which is sufficient for almost all real-world applications of any of the covered election types.
Generating 3D topiaries from base geometric shapes
(2025) Kemmler, Tobias
Virtual Reality (VR) is increasingly used to simulate real-world environments in immersive digital spaces. One notable application is VR tours, which enable users to explore historically and culturally significant sites-whether they still exist or have been lost-on demand. This thesis presents a method for generating topiaries based on arbitrarily complex 3D geometries. The system requires two primary inputs: a 3D model that defines the desired topiary shape, and an image of the leaf to be applied as surface detail. Leveraging Unreal Engine's Nanite technology, highly detailed leaf textures can be rendered with exceptional efficiency. This allows for the creation of topiaries that maintain visual fidelity even in performance-critical VR environments. The quality and performance of the generated results are evaluated through comparisons with real photographs and benchmark testing.
Investigating challenges in generalizing neural radiance fields with learned scene priors
(2025) Geiselhart, Jonas
This thesis investigates methods to generalize neural radiance fields across several different 3DScenes. Unlike prevailing approaches that emphasize more fine grained priors on ray or sample positions - often combined with classical 3D spatial (neural) processing, this work explores the use of implicit deep scene embeddings as prior to a generalized neural radiance field for scene rendering.
This work provides the theoretical groundwork for transitioning gradually from per scene retraining to a more perceiving network capable of extracting scene geometries by analyzing images and successfully building good latent representations.
In practical research the framework is implemented and analyzed. Here several key issues in the conceptualization are found and analyzed, that must be addressed in training process and model redesign.
Overall this thesis outlines a potential path toward scene-generalized NeRFs and highlights new issues that emerge through this shift in research focus.