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Numerically robust local continuum damage models with softening response via convex relaxation
No full textContinuum damage mechanics is characterized by mesh-dependent results unless specific countermeasures are taken. The most popular remedies involve introducing either nonlocality via filtering or a gradient extension for the damage variable(s). Such approaches have their limitations, e.g., they are hard to integrate into conventional finite-element codes, involve parameters that are non-trivial to determine experimentally and are incompatible with a scale transition that is both physically and mathematically sensible. The work at hand considers an alternative route to obtain mesh-independent damage models, namely via convex relaxation. Such convex damage models were considered before, but they are usually not capable of representing softening behavior. Schwarz et al. (Continuum Mech. Thermodyn., 33, pp. 69–95, 2021) proposed such a strategy by considering the convex envelope of a rate-limited simple damage model, i.e., an isotropic damage model without tension-compression anisotropy at small strains. However, they were not able to compute the envelope explicitly and provided an approximation only. In the work at hand, we introduce a number of conditions on the damage-degradation function which permit us to compute the convex envelope analytically for a large class of damage-degradation functions used in small-strain isotropic damage models. Interestingly, the obtained models involve a one-dimensional damaged microstructure, i.e., damage distributions emerge naturally. The resulting model is structurally simple and purely local, i.e., gradient-free, thermodynamically consistent and readily integrated into standard finite-element codes via traditional user subroutines. We discuss the computational and solid mechanical aspects of the ensuing model and demonstrate its numerical robustness via dedicated computational experiments. We also show that the model permits to be homogenized by considering a representative volume element study for an industrial-scale fiber-reinforced composite
Processes of Thermal Treatment on Hazelnuts Investigated by NMR and MRI
No full textNMR and MRI provide a variety of customizable methods for process monitoring. A selection was applied to monitor structural and compositional changes in hazelnuts during thermal treatment, with particular focus on the roasting and aging behavior of hazelnut oil. Hazelnuts contain a high oil fraction stored in subcellular oleosomes, whose stability is crucial for product quality and shelf life. Thermal stress can alter these microscopic oil-containing structures, affecting oil mobility and oxidative stability. In situ MRI measurements were combined with pulsed field gradient stimulated echo (PFG-STE) NMR diffusion experiments to investigate structural changes across multiple length scales. MRI detected mesostructural alterations in the hazelnut matrix from ~50 μm to several millimeters, corresponding to features above the cellular level. At roasting temperatures below 150°C, only minor structural changes occurred, whereas at 200°C, pronounced void formation and cellular collapse were observed. A dedicated experimental setup enabled in situ measurements during roasting under controlled temperature, allowing spatially resolved monitoring of oil redistribution in coarse nut structure. Complementary PFG-STE NMR diffusion measurements provided insight into the microstructure (100 nm–10 μm), revealing subcellular structural changes and oil mobility. These results showed that oleosomes were largely destroyed already at 100°C. Furthermore, NMR spectroscopy demonstrated temperature-dependent oxidation kinetics of unsaturated fatty acids in hazelnut oil on a molecular level, with clear formation of oxidation products upon heating, whereas ambient storage caused only minor chemical changes. The combined use of MRI and NMR enables quasi-nondestructive, in situ monitoring of molecular, microstructural, and mesostructural transformations in hazelnuts and their oil under controlled thermal processing conditions
Higher-Order QCD Corrections to Meson Mixing and Decays
No full textIn dieser Dissertation werden Korrekturen der nächst-zu-nächst-zu-führenden Ordnung in der perturbativen Quantenchromodynamik für die Mischung und die Zerfälle von Hadronen, die Bottom-Quarks beinhalten, berechnet. Für die Mischung von -Mesonen wird der absorptive Teil des nicht-diagonalen Elements der Zerfallsmatrix, , berechnet. Der Fokus der Analyse der Zerfälle liegt auf den Lebensdauerverhältnissen der - und -Mesonen sowie der entsprechenden Baryonen und . Die Rechnung liefert Matching-Koeffizienten für die und Übergangsoperatoren der führenden Ordnung in der Heavy-Quark-Entwicklung. Hierfür werden Zweischleifenamplituden für die Übergangsoperatoren berechnet, während die andere Seite des Matchings Dreischleifenkorrekturen zu Diagrammen umfasst, die in der Effektivfeldtheorie ausgewertet werden. Für die Berechnung werden allgemeine Projektoren für Spinorstrukturen mit bis zu elf -Matrizen auf zwei Spinlinien konstruiert, die für Zweipunktfunktionen mit vier externen Fermionen anwendbar sind. Darüber hinaus ist das hier entwickelte Renormierungsverfahren, welches die Fierz-Symmetrie erhält und Subtilitäten im Zusammenhang mit Massen-unterdrückten Korrekturen berücksichtigt, auch für weitere Prozesse anwendbar.
Die perturbativen Korrekturen werden ferner zur Ableitung theoretischer Vorhersagen für Mischungsobservablen und Lebensdauerverhältnisse verwendet. Für die -Mesonmischung werden die bislang präzisesten Berechnungen von und sowohl für das - als auch für das -System dargelegt. Zudem lassen sich aus den perturbativen Matching-Koeffizienten in Kombination mit Messungen von und strenge Einschränkungen für die Spitze des Cabibbo-Kobayashi-Maskawa-Unitaritätsdreiecks aufstellen. Die Relevanz von für Physik jenseits des Standardmodells wird außerdem anhand der Diskussion neuer Physik im chromoelektrischen Vertex hervorgehoben. Für die Lebensdauerverhältnisse werden die Vorhersagen für und auf die nächst-zu-nächst-zu-führende Ordnung aktualisiert. Die theoretischen Vorhersagen stimmen innerhalb der Unsicherheiten mit den aktuellen Messungen überein, was das Standardmodell und die Gültigkeit der Heavy-Quark-Entwicklung bestätigt
Teaching Concept of a Modeling Approach for the Analysis of Embodiment Function Relations for Product Engineering
No full textThe Extended Contact and Channel Approach (Extended C&C²-Approach) is a framework for analyzing and modelling of Embodiment Function Relations (EFR) in product engineering. Despite its potential, many students and professionals face challenges in understanding and applying its core principles and extensions. This paper presents and evaluates a modular training concept integrating short theory inputs, collaborative active-learning modules, and guided practice within the Live-Lab IP24/25 – Integrated Product Development. Results from a mixed-methods evaluation demonstrate that while foundational concepts are effectively taught, challenges remain in teaching advanced topics like the Designation Guideline and Functional Delimitation. This paper presents a validated instructional framework that connects the Extended C&C² modeling process to specific learning objectives and long-term behavioral outcomes. This framework supplements existing engineering education formats by explicitly focusing on EFR-oriented modeling proficiency. Limitations include a single-institution sample and limited statistical power, suggesting future multi-site comparative studies
Study design for human acuity in symbol recognition
No full textTo date, there are no adequate quality parameters for see-through displays based on augmented and virtual reality especially for future automotive applications available. Recent approaches define detected stimuli in sinusoidal grids by their size, spatial and temporal frequency contrast sensitivity, luminance and eccentricity. The approach in this work is to know the background luminance and the display luminance distribution in order to define the contrast local rather than global for displays. This approach is based on the assumption that the ambient luminance distribution has a major influence on human visual acuity and its parameters. Therefore, a quantitative study concept is proposed based on a case study and the derivation of the relevant parameters.
By means of the described investigations it is possible to define the operating range of the optical human-machine interaction and the relevant optical parameters in head-up displays
Non-Equilibrium Liquid Hydrogen Tank Modeling When Thermal Insulation Fails
No full textThe failure of liquid hydrogen (LH2) tank thermal insulation can lead to excessive heating of the stored hydrogen, causing it to boil and triggering safety mechanisms such as a pressure relief valve or a burst disc to prevent catastrophic vessel failure. This study investigates the boil-off behavior inside LH2 tanks using lumped parameter modeling. A non-equilibrium storage tank equipped with a pressure relief valve or burst disc is modeled, accounting for convection and different boiling regimes, flash evaporation during pressure drop when rupture activated. The model is validated against NASA and BMW experimental data. Furthermore, the study analyzes the LH2 tank under various thermal scenarios, including normal operation, loss of vacuum due to air ingress or ice formation, and an engulfing fire scenario combined with vacuum failure. The findings provide critical insights and methodologies for the safety evaluation and robust design of cryogenic hydrogen tank
Control and Power Management of Hybrid Energy Storage Systems
No full textThe increasing integration of renewable energy sources and the electrification of transportation have significantly raised the demand for efficient and reliable energy storage systems. Among the various technologies available, Lithium-ion Battery Energy Storage Systems (BESS) have become the most widely adopted solution due to their high energy density and maturity. However, BESS alone faces several challenges when subjected to applications that involve rapid power fluctuations, high-frequency cycling, and frequent charge/discharge events. These operational conditions accelerate battery aging, reduce cycle life, and increase the levelized cost of storage over time. This limitation has motivated the development of alternative system architectures, which aim to offload the high-frequency and transient power demands from the battery to a complementary storage device.
A promising approach to overcome these limitations is the use of Hybrid Energy Storage Systems (HESS), which combine complementary storage technologies, typically a high-energy BESS with a high-power storage element such as a Supercapacitor Energy Storage System (SCES) or a Flywheel Energy Storage System (FESS). The HESS configuration enables the power demand to be split: slow, energy-intensive components are allocated to the battery, while the auxiliary storage handles fast transients and high ramp-rate events. This decoupling not only enhances the performance and responsiveness of the storage system but also mitigates the aging mechanisms of the battery by reducing the stress caused by rapid power variations.
While the HESS architecture offers clear advantages over standalone battery systems, its effective operation requires sophisticated control and power management strategies. The fundamental challenge lies in dynamically coordinating two or more storage components with vastly different characteristics, such as response time, energy capacity, efficiency, and degradation behaviour, under highly variable power demands. Ensuring that each component operates within its safe limits, while jointly fulfilling system-level performance objectives (e.g., minimizing losses, extending lifespan, and maintaining power quality), requires real-time, intelligent control and management systems.
In particular, the power-splitting strategy between the BESS and the auxiliary storage must not only respond to the instantaneous power profile but also consider long-term state variables, such as the State of Charge (SoC) of each unit and the battery\u27s ramp rate limitations. Traditional rule-based or low-pass filter methods often fail to provide adequate flexibility or adaptability under dynamic conditions. Therefore, control of HESS is not just technically challenging; it is essential for unlocking the full potential of hybrid storage systems.
This thesis addresses these challenges by proposing advanced control and estimation strategies for hybrid energy storage systems. In particular, it explores methods for effective power management, accurate SoC estimation, and mitigation of battery aging under dynamic operating conditions. The work examines how HESSs can be controlled more effectively and demonstrates that carefully managing the various storage components can enhance the system\u27s efficiency and longevity. The findings help to better understand how HESS behaves in practice and provide useful guidance for designing hybrid storage systems that perform effectively in real-world applications
Elucidating Rate-Determining Steps of Surface-Catalyzed Reactions Exhibiting Isothermal Rate Multiplicity
No full textMicrokinetic models of surface-catalyzed reactions may admit multiple steady-state solutions of species balances in the absence of both mass and heat transfer limitations. As a result, the rate(s) of reactant consumption or product formation exhibit multiple rate states, a situation commonly called isothermal rate multiplicity. Established metrics for identifying the rate-determining (or rate-limiting) step of a reaction mechanism include reversibility, sensitivity, and degree of rate control. For reactions exhibiting rate multiplicity, these metrics indicate that disparate states (branches) in plots of rate versus the reactant concentration have rates that are limited by different steps in the catalytic mechanism. During competitive adsorption, high or “ignited” rate branches are controlled by adsorption of the reacting species requiring fewer active sites than that of a second reacting species that blocks the adsorption of the former. Low or “extinguished” branches are limited by the adsorption of the latter species, requiring more sites than the former. Reversibility, sensitivity, degree of rate control, and ultimately the rate-determining step of a sequence within the region of multiplicity are determined not only by the operating condition but also by the initial state of the catalyst surface. It is shown that despite also being multivalued, sensitivities and degrees of rate control sum to unity across stable and unstable steady-state branches. Thermodynamic degrees of rate control can also be used to estimate multivalued surface coverages along all branches, thereby demonstrating consistency with previously derived mathematical relationships. Pt-catalyzed carbon monoxide oxidation case studies show that the rate-determining step changes from CO to O adsorption depending on whether the system resides on ignited or extinguished branches, respectively. Analogously, Pt–Pd-catalyzed methane oxidation is controlled by either O or CH adsorption depending on whether the system resides on the ignited or extinguished rate branches
In situ mechanical foaming in fused filament fabrication
No full textIn the context of lightweight design and functional integration, the generation of foamed structures in additive manufacturing represents a key technological objective. Conventional foaming methods often rely on chemical blowing agents or physical foaming in downstream processes such as autoclaves, which require complex process chains and high energy input. To address these limitations, this work presents a first feasibility demonstration of a process-integrated mechanical foaming approach for material extrusion, ensuring continuous production in an in-line foaming process. A modular nozzle was developed, in which carbon dioxide is injected into the polymer melt under high pressure during extrusion. Gas enters the melt through a porous medium embedded in the nozzle, enabling controlled gas transfer while preventing melt backflow. This mechanism facilitates mechanical foaming within the nozzle itself, eliminating the need for separate process stages. Systematic material screening showed that metallic porous media with submicron pore diameters provide sufficient resistance to melt intrusion while allowing stable gas injection. Extrusion trials with polylactic acid confirmed that the resulting foam morphology depends on the gas-to-melt mass flow ratio, yielding uniform microcellular structures with porosities up to 25 % and mean pore diameters around 100 µm. The presented results demonstrate that stable foam extrusion based on mechanical foaming through in-nozzle gas injection is feasible, and they establish the foundation for further investigations aimed at process refinement towards finer microcellular structures and fully additively manufactured foamed components