openHSU (HSU Hamburg)
Not a member yet
7291 research outputs found
Sort by
Redundant multi-source multi-3-phase fuel cell propulsion architecture for electric aviation
No full textElectrification of aviation with fuel cells requires a redundant and fail-safe system design. To achieve this, multi-3phase systems can offer advantages through segmentation and redundancy. Fuel cell systems, directly coupled to the machine segments without additional batteries, enable additional increases in energy and power density. In this work, multi-source multi-3-phase propulsion system architectures are presented, tested and validated, which show advantages regarding the redundancy of propulsion systems. It is shown that the system is able to compensate multiple failing segments during partial loading.Vo
Acoustic applications of high-performance adaptive filters for FPGA platforms
No full textOne of the great challenges in modern society is the reduction of noise and vibration. High noise levels can occur in urban environments or industrial applications. Whether the goal is to protect humans from the negative effects of noise, enable communication in extreme environments, or acoustically disguise vehicles, traditional passive dampening is not always the best option. The concept of active noise and vibration control has been in existence for several decades, yet it has only been adopted on a widespread basis in certain applications, such as headphones. When larger acoustic volumes need to be controlled, active control systems with many components must be applied. In these systems, the computational effort of the algorithms, coupled with low latency requirements, presents a significant challenge. Hardware-based active noise control systems can be a solution due to their high level of parallel computing and low latency. In other areas of signal processing, they have already become the industry standard for the same reasons.
In this thesis, acoustic applications of adaptive filters implemented on Field Programmable Gate Arrays will be presented and evaluated. The developed systems in this work include well-known setups, such as Kundt’s Tube or an active headrest, for validation purposes. The more advanced solutions incorporate a helicopter headset with additional speech enhancement capabilities and active impedance control of an underwater surface. Additionally, an overview of the theoretical background is given, and state-of-the-art related work is discussed.
The results of the measurements show that hardware-based adaptive filters not only match their software counterparts, but they can enhance noise reduction performance. In the case of the helicopter headset, the additional computational headroom of the chosen platform is used to include Wiener filter-based speech enhancement. This system produces impressive results in the evaluated speech quality, in addition to the active noise reduction of the headset. Active control of underwater sound bears additional challenges when it comes to latency requirements due to the high speed of sound. The proposed hardware-based system in this thesis is capable of effectively minimizing reflected sound waves from an underwater surface. This outstanding feature could be used in future applications to conceal underwater vehicles from active sonar. Overall, the findings in this thesis provide compelling arguments for hardware-based adaptive filters for acoustic applicationsVo
Toward realistic multiscale simulations of nanoparticle injection devices used for single particle diffractive imaging
No full textSingle-particle diffractive imaging (SPI) is a powerful technique used in structural biology and nanoscience to determine the three-dimensional structure of individual nanoparticles, biomolecules, and viruses without the need for crystallization. By exposing freely flowing particles to ultrafast X-ray free-electron laser (XFEL) pulses, SPI captures diffraction patterns that can be reconstructed into high-resolution images. Efficient and accurate modeling and simulation of nanoparticle injection systems are essential for designing and optimizing injectors that deliver high-density, well-collimated particle streams – an important requirement for maximizing hit rates and image quality in SPI experiments. This thesis addresses these challenges by developing and optimizing multiscale simulation methodologies for nanoparticle injection devices, with a particular focus on aerodynamic lens systems (ALS) and its combination with cryogenically cooled buffer-gas cells (BGC).
A hybrid molecular-continuum simulation framework, integrating classic Computational Fluid Dynamics (CFD) based on the continuum assumption and the Direct Simulation Monte Carlo (DSMC) method based on the kinetic theory of gases, is employed to accurately capture the carrier gas flow and nanoparticle trajectories across diverse flow regimes. The approach improves the computational efficiency by selectively applying DSMC in regions where molecular-scale effects dominate, while using CFD for low Knudsen number regions. Comprehensive evaluations of drag force models from the literature including molecular drag formulations are conducted, along with the introduction of a relaxation-based correction for highly rarefied, low-speed flows, to enhance particle trajectory predictions, particularly in transitional and rarefied regimes.
The framework’s scalability and computational performance are assessed through detailed benchmarking, while sensitivity analyses on DSMC parameters such as particle number, grid size, and time step size further guide efficient model implementation. Key benchmark cases, including gas dynamic nozzles and re-entry vehicles, demonstrate the framework’s versatility in simulating internal and external flows.
The ALS configuration highlights the framework’s applicability to injector modeling, where the hybrid DSMC/CFD approach combined with improved drag models achieve excellent agreement with experimental data, outperforming conventional CFD. Further validation against measured beam widths and focus positions is carried out for BGC and combined BGC-ALS setups across different particle sizes and inlet pressures. This validated setup is then used to assess the injector performance, with emphasis on proteinsized nanoparticles, enabling an insightful evaluation of the focusing efficiency and beam quality under realistic SPI conditions. Notably, the BGC-ALS configuration, through cryogenic cooling, enhances the focusing of smaller particles by reducing thermal velocities and suppressing Brownian motion, thereby improving the beam collimation – ideal for SPI experiments.
By bridging gaps in current methodologies, validating simulation results against experimental data, and advancing drag force modeling techniques, this thesis establishes a robust foundation for optimizing SPI injector systems and paving the way for future innovations in nanoparticle injection technologies.Vo
Statistisch optimierte akustische Nahfeldholografie (SONAH) für die Ermittlung von Schallfeldgrößen auf der Oberfläche von Schallquellen
No full textDiese Studienarbeit behandelt die Anwendung der statistisch optimierten akustischen Nahfeldholografie (SONAH) zur inversen Rekonstruktion der Schallschnelle auf der Oberfläche eines Kolbenstrahlers in einer unendlich ausgedehnten schallharten Wand. Die Eingangsgrößen der Rekonstruktion des Schalldruckfeldes lieferte das Rayleigh-Integral. Das Schalldruckfeld wurde mit Hilfe des Rayleigh-Integral simuliert und mit Näherungslösungen im Fern- und Nahfeld validiert. Die Implementierung der SONAH erfolgte unter Verwendung ebener Wellenfunktionen und wurde durch Tests hinsichtlich ihrer Genauigkeit beurteilt. Erste Rekonstruktionsergebnisse zeigten realistische Druck- und Schnelleverteilungen, jedoch bestehen noch Abweichungen, deren Ursachen analysiert und in Hinblick auf eine spätere Anwendung bewertet wurden.Vo
Identifying children at risk
No full textDer dritte Teilartikel dieser Dissertation befindet sich aktuell im Review-Prozess und ist noch nicht veröffentlicht.This cumulative dissertation investigates how temperament and self-regulation contribute to the emergence of psychopathological symptoms in early childhood. Drawing on three empirical studies, it integrates psychometric, cross-sectional, and longitudinal perspectives.
The first study examines the structural relationship between effortful control and executive function, revealing that although the constructs are highly interrelated, they form empirically distinct factors. The second study analyses how reactive temperament traits (surgency, negative affectivity) and self-regulation (parent-rated and performance-based executive functions) predict ADHD, conduct problems, emotional symptoms, and peer problems in preschool-aged children. The findings highlight strong and consistent associations between surgency and ADHD, while the predictive value of negative affectivity diminishes when self-regulation is simultaneously considered. Parent-rated executive functioning deficits emerged as the strongest predictors across domains, whereas performance-based executive functioning was not significantly associated with symptoms. No significant moderation effects were found, supporting an additive rather than an interactive model. The third study uses a latent change score model to analyze intraindividual changes in reactive temperament between ages three and five. The results demonstrate that change in surgency and negative affectivity, but not trait levels, predict subsequent conduct and ADHD symptoms, emphasizing the developmental dynamics of temperament-related risk.
Together, the findings show that temperament and self-regulation are developmentally interrelated but distinct processes, and that changes in reactivity, more than static traits, represent a critical pathway to early externalizing psychopathology. The dissertation supports an integrative developmental model and provides implications for the early identification and targeted support of children at risk.Vo
