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[Kommentierung] § 19a Missbräuchliches Verhalten von Unternehmen mit überragender marktübergreifender Bedeutung für den Wettbewerb
No full textVo
Kinetisches Spritzen von Keramiken
No full textDiese Arbeit beschäftigt sich mit der Herstellung von keramischen Schichten mittels kinetischer Spritzverfahren. Als Modellsystem wurden die MAX Phasen Ti₃SiC₂, Ti₂AlC und Cr₂AlC, die sowohl keramische als auch metallische Eigenschaften aufweisen, in Partikelgrößen im Bereich von einigen zehn Mikrometern mittels Kaltgasspritzen aufgetragen. Hierfür wurden die Einflüsse von primären Spritzparametern wie Gastemperatur und -druck, sowie von sekundären Spritzparametern wie Substrattemperatur, Traversengeschwindigkeit und Phasenreinheit des Spritzpulvers untersucht, um so Informationen über die Voraussetzungen für die Schichtbildung zu gewinnen.
Die MAX Phasen Ti₃SiC₂ und Cr₂AlC wurden zusätzlich in Partikelgrößen von wenigen Mikrometern mittels Aerosolspritzen abgeschieden, um so generelle Einflüsse der Partikelgröße zu analysieren. Im Hinblick auf das rein keramische Verhalten und mögliche Anwendungspotenziale in der solaren Wasserstoffproduktion wurden des Weiteren die Halbleiter BiVO₄ und Fe₂O₃ mittels Aerosolspritzen als Schicht aufgetragen. Die Untersuchungen zur Ableitung von Randbedingungen für einen erfolgreichen Schichtaufbau umfassen dabei die Einflüsse der Partikelgröße, unterschiedlicher Gasarten, Spritzparameter und Substrattemperaturen.Vo
Investigation of cohesive particle deagglomeration in homogeneous isotropic turbulence using particle-resolved direct numerical simulation
No full textIn this study, agglomerate breakage in homogeneous isotropic turbulence is investigated using particle-resolved direct numerical simulations. Single agglomerates composed of 500 monodisperse spherical particles are considered, and their interaction with the turbulent flow is resolved through an immersed boundary method coupled with a soft-sphere discrete element model. A range of Reynolds numbers and cohesion levels is examined to assess their influence on the breakup behavior. Detailed insights into the underlying breakage mechanisms are provided through the analysis of local flow structures and fluid stresses. Strain-dominated regions are identified as the primary contributors to the onset and propagation of particle erosion. The benefits of the particle-resolved simulation framework in capturing these physical processes in detail are demonstrated. The predicted fragment size distributions and breakup modes are analyzed leading to the outcome that erosion-driven breakage is the dominating mechanism. The time evolution of the fragment number and the main agglomerate structure is quantified. The breakage rate is evaluated and its dependence on the modified adhesion number is established, showing a power-law decay that agrees with general trends reported in the literature. In addition, the analysis of the fragment ejection direction reveals a strong alignment with the local deformation plane spanned by the most extensional and compressive strain-rate eigenvectors, indicating that breakage results from the interplay between flow stretching and compression. The results contribute to the development of physics-informed breakup kernels for use in efficient but less-detailed simulation approaches, such as point-particle Euler–Lagrange predictions with agglomerates represented by effective spheres or Euler–Euler simulations.Vo
Accelerated development of multi-component alloys in discrete design space using Bayesian multi-objective optimisation
No full textThis is an open access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/).Bayesian optimisation (BO) protocols grounded in active learning (AL) principles have gained significant recognition for their ability to efficiently optimize black-box objective functions. This capability is critical for advancing autonomous and high-throughput materials design and discovery processes. However, the application of these protocols in materials science, particularly in the design of novel alloys with multiple targeted properties, remains constrained by computational complexity and the absence of reliable and robust acquisition functions for multiobjective optimisation. Recent advancements have demonstrated that expected hypervolume-based geometrical acquisition functions outperform other multiobjective optimisation algorithms, such as Thompson Sampling Efficient Multiobjective optimisation and pareto efficient global optimisation (parEGO), in both performance and speed. This study evaluates several leading multiobjective BO acquisition functions–namely, parallel expected hypervolume improvement (qEHVI), noisy qEHVI, parallel parEGO, and parallel noisy parEGO (qNparEGO)–in optimizing the physical properties of multi-component alloys. Our findings highlight the superior performance of the qEHVI acquisition function in identifying the optimal Pareto front across 1-, 2-, and 3-objective aluminum alloy optimisation problems, all within a constrained evaluation budget and reasonable computational cost. Furthermore, we explore the impact of various surrogate model optimisation methods from both computational cost and efficiency perspectives. Finally, we demonstrate the effectiveness of a pool-based AL protocol in expediting the discovery process by executing multiple computational and experimental campaigns in each iteration. This approach is particularly advantageous for deployment in massively parallel high-throughput synthesis facilities and advanced computing architectures.Vo
Multi-goal-oriented anisotropic error control and mesh adaptivity for time-dependent convection-dominated problems
No full textThis work is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).In this work, we present an anisotropic multi-goal error control based on the Dual Weighted Residual (DWR) method for time-dependent convection-diffusion-reaction (CDR) equations. This multi-goal oriented approach allows for an accurate and efficient error control with regard to several quantities of interest simultaneously. Using anisotropic interpolation and restriction operators, we obtain elementwise error indicators in space and time, where the spatial indicators are additionally separated with respect to the single directions. The directional error indicators quantify anisotropy of the solution with respect to the goals, and produce adaptive, anisotropic meshes that efficiently capture layers. To prevent spurious oscillations the streamline upwind Petrov-Galerkin (SUPG) method is applied to stabilize the underlying system in the case of high Péclet numbers. Numerical examples show efficiency and robustness of the proposed approach for several goal quantities using established benchmarks for convection-dominated transport.SMU
Modelling cyber-physical systems for fault diagnosis
No full textThis work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/Vo
Aktive intensitätsbasierte Minimierung der Schalltransmission durch ein teilgeöffnetes Fenster
No full textUrbanization and the resulting problems are a major challenge for a large part of the inhabitants of cities and furthermore for the planet. The population of many cities around the world such as Beijing, China or Hamburg, Germany have been steadily increasing for several years. In addition to increasing CO2 emissions through rising numbers of private transport, the increase of sound pollution in urban areas contributes to environmental pollution. High noise levels have been shown to have a negative impact on health, especially cardiovascular diseases.
As a conclusion, there are limit values to be observed in many countries in order to reduce noise, for example in the construction industry. In Hamburg there is a so-called ”Hafen-City-Clause”, which ensures that a noise level of 30dB(A) is not exceeded at night when the windows in bedrooms are partially open. Standard windows often do not achieve a sufficient reduction in sound transmission to be able to comply with this limit value.
The sound transmission can be minimized by the use of passive measures, but this is accompanied by a restriction of the ventilation through the partially open window. In order to enable unrestricted air circulation, active systems, so-called Active-Noise-Control (ANC) systems, can be used. These systems can be placed in the sound transmission path and reduce noise through destructive interference without restricting airflow of the window.
To design an effective active system it is necessary to examine the influence of sound transmission paths on transmitted noise. For further investigation of sound transmission, the complex geometry of a partially open window is simplified to a parameterizable two-dimensional gap.
The transmission of noise is calculated analytically in a first step with a substitute model, from which requirements for an active system are drawn. In order to get a deeper understanding of the influence of a sound path on sound transmission, the influence of parameters of a small gap in relation to the wavelength and the influence of a control signal of an anti-noise source on sound transmission are investigated.
As a result of the conducted analytical and numerical studies, an alternative approach of an algorithm for adaptive intensity-based noise reduction is introduced. In this approach, only sensors placed in the gap are used to reduce the transmission of sound. The presented approach is finally implemented in a rapid control prototyping system and the functionality is proven by an experiment.Vo
Lieferverweigerung, Zugangsbeschränkung, Kosten-Preis-Schere und Selbstbevorzugung
No full textIm europäischen Recht hat sich seit Bronner eine strenge Handhabung der Voraussetzungen für eine Lieferverweigerung (insbesondere: Unerlässlichkeit) entwickelt. Das führte dazu, dass andere Fallgruppen nach Möglichkeit von der Lieferverweigerung abgegrenzt wurden: die Kosten-Preis-Schere, die Selbstbevorzugung und zuletzt (im Leitlinienentwurf und Android Auto) die Zugangsbeschränkung. Der Beitrag weist auf die Diskontinuitäten und Fehlanreize hin, die durch diese künstliche Separierung erzeugt werden. Er plädiert dafür, in Anlehnung an die Rechtsprechung des Kartellsenats am BGH, Fälle der expliziten und impliziten Zugangsgewährung auf einem kontinuierlichen Spektrum anzuordnen und die Entscheidung von einer Gesamtwürdigung und umfassenden Abwägung aller beteiligten Interessen abhängig zu machen.Refusal to Supply, Access Restrictions, Margin Squeeze and Self-Preferencing: Birds of a Feather Flock Together
Since the Bronner decision, EU law has developed an overly strict approach to refusal to deal cases, requiring, in particular, indispensability. This motivated the Court to distinguish other categories of cases from refusals to deal: margin squeeze, self-referencing, and now (in the Commission draft guidelines and Android Auto) access restrictions. The article points to discontinuities and perverse incentives caused by the artificial separation of these categories of explicit or implicit refusals to deal. It suggests – as did AG Jacobs in para. 57 – a “careful balancing of conflicting considerations”, or, more precisely, a comprehensive balancing along the lines of the practice of the Cartel Senate at the German Federal Court of Justice. Whether or not access has already been granted is a relevant factor in this assessment, but should not result in a qualitatively different test.Vo
Node-level performance of adaptive resolution in ls1 mardyn
No full textIn this work we present a node-level performance analysis of an adaptive resolution scheme (AdResS) implemented in ls1 mardyn . This is relevant in simulations involving a very large number of particles or long timescales, because it lowers the computational effort required to calculate short-range interactions in molecular dynamics. An introduction to AdResS is given, together with an explanation of the coarsening technique used to obtain an effective potential for the coarse molecular model, i.e., the Iterative Boltzmann Inversion (IBI). This is accompanied by details of the implementation in our software package, as well as an algorithmic description of the IBI method and the simulation workflow used to generate results. This will be of interest for practitioners. Results are provided for a pure Lennard-Jones tetrahedral molecule coarsened to a single site, validated by verifying the correct reproduction of structural correlation functions, e.g. the radial distribution function. The performance analysis builds upon a literature-driven methodology, which provides a theoretical estimate for the speedup based on a reference simulation and the size of the full particle region. Additionally, a strong scaling study was performed at node level. In this sense, several configurations with vertical interfaces between the resolution regions are tested, where different resolution widths are benchmarked. A comparison between several linked cell traversal routines, which are provided in ls1 mardyn , was performed to showcase the effect of algorithmic aspects on the adaptive resolution simulation and on the estimated performance.Vo
Computational modeling of the FeTi hydrogenation
No full textInterstitial metal-hydrides can reversibly store sustainable energy in the form of hydrogen. Among these materials, the FeTi alloy has the advantage of operating under near-ambient temperature and pressure conditions, as well as exhibiting a generally lower cost of the raw materials compared with other intermetallics in the same class. These properties are associated with a high volumetric hydrogen storage capacity that surpasses even the storage of hydrogen in its molecular form. This translates into an economical advantage because the energy-intensive processes of pressurizing to extreme pressure levels or cooling to cryogenic temperatures are avoided.
Although this material has been extensively studied with experimental methods, the characterized properties of alloying elements, structural transformations, chemical stability of the phases, mechanical properties, macroscopic thermodynamics, just to mention a few, have not yet been systematically described in a multiscale model capable of yielding these properties and their mechanisms in a comprehensive integrated manner.
To establish a foundation for developing this digital twin, the hydrogenation process of the interstitial intermetallic FeTi metal-hydride is investigated computationally across various hierarchical levels. Three distinct theoretical approaches are utilized with the intention of integrating them into a comprehensive model that can quantitatively address questions in materials science based on precise properties across different material scales.
At the atomistic level, the properties of the FeTi-H system are studied with quantum mechanics within a high-throughput approach to analyze the equilibrium and non-equilibrium structures and their thermochemical and micromechanical properties. Computational thermodynamics is subsequently employed to wrap up these properties and integrate the chemical bulk equilibrium of the material in a macroscopic dependence with the external temperature and pressure engineering conditions. The atomistic and thermodynamic models are finally integrated into a thermokinetic mesoscale model capable of simulating the evolution of the properties when the material is subject to many different manipulated engineering conditions.
To guarantee successful integration of the different scale properties, the spatial microstructural evolution should yield good agreement with the lower-level properties. The last part of this thesis work thus demonstrate with simulations that these properties have been well integrated, utmostly providing a basis of a comprehensive multiscale computational model for FeTi hydrogenation.
The computational modeling of hydrogen storage in FeTi hydrides allows us to anticipate the evolution of the materials properties during their application, helping to develop new processes. In this context, this thesis work established a quantitatively integrated multiphysical multiscale model for simulation of the evolving hydrogenation phenomenon of the FeTi alloy. Ultimately, paving the path to the expansion of the model into a FeTi-based multi-component and multiphase mesoscale model.Interstitielle Metallhydride können nachhaltige Energie in Form von Wasserstoff reversibel speichern. Unter diesen Materialien zeichnet sich die FeTi-Legierung dadurch aus, dass sie unter nahezu Umgebungsbedingungen hinsichtlich Temperatur und Druck arbeiten kann und im Vergleich zu anderen intermetallischen Legierungen derselben Klasse allgemein geringere Rohstoffkosten aufweist. Diese vorteilhaften Eigenschaften sind auf die hohe volumetrische Wasserstoffspeicherkapazität zurückzuführen, die die Speicherung von molekularem Wasserstoff übertrifft. Dies bietet einen wirtschaftlichen Vorteil, da energieintensive Prozesse wie Kompression auf extreme Drücke oder Kühlung auf sehr niedrige Temperaturen von 20 K vermieden werden.
Trotz umfangreicher experimenteller Studien zu diesem Material wurden die Eigenschaften von Legierungselementen, Strukturtransformationen, Phasenstabilität, mechanischen Eigenschaften und makroskopischen Thermodynamiken, unter anderem, noch nicht systematisch in einem Mehrskalenmodell beschrieben, das diese Eigenschaften und deren Mechanismen umfassend integriert.
Um eine Grundlage für die Erstellung eines digitalen Zwillings zu entwickeln, untersucht diese Forschung computergestützt die Wasserstoffreaktion des interstitiellen intermetallischen FeTi-Metallhydrids auf verschiedenen hierarchischen Ebenen. Drei verschiedene theoretische Ansätze werden angewandt, um sie in ein umfassendes Modell zu integrieren, das materialwissenschaftliche Fragen durch die genaue Beschreibung von Eigenschaften über verschiedene Materialskalen hinweg quantitativ adressiert.
Auf atomarer Ebene werden die Eigenschaften des FeTi-H-Systems mit Hilfe der Quantenmechanik in einem Hochdurchsatzansatz untersucht, um die Gleichgewichts- und Nichtgleichgewichtsstrukturen sowie deren thermochemische und mikromechanische Eigenschaften zu analysieren. Diese Eigenschaften werden dann in ein makroskopisches computergestütztes thermodynamisches Modell integriert, das das chemische Gleichgewicht des Materials in Abhängigkeit von externen Temperatur- und Druckbedingungen beschreibt. Anschließend integriert ein thermokinetisches Mesoskalenmodell die atomaren und thermodynamischen Daten, um die Entwicklung der Materialeigenschaften unter verschiedenen ingenieurtechnischen Bedingungen zu simulieren.
Um eine erfolgreiche Integration der Eigenschaften über verschiedene Skalen hinweg zu gewährleisten, muss die räumliche Mikrostrukturevolution gut mit den Eigenschaften der unteren Ebenen übereinstimmen. Der letzte Teil dieser Dissertation zeigt anhand von Simulationen, dass diese Eigenschaften gut integriert wurden, und liefert letztlich die Grundlage für ein umfassendes Mehrskalenmodell für die Hydrierung von FeTi.
Durch Computermodellierung der Wasserstoffspeicherung in FeTi Hydriden kann man die Eigenschaften und die Entwicklung des Materials während seiner Anwendung antizipieren und neue Prozesse entwickeln. In diesem Kontext etabliert diese Dissertation ein quantitativ präzises, integriertes, multiphysikalisches Mehrskalenmodell zur Simulation der FeTi-Hydrierung. Dadurch wird der Weg für die Erweiterung auf Mehrkomponentensysteme geebnet.Vo