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A reasonable material hardening model (MHM) should be determined for the accurate prediction of welding residual stresses (WRS) in numerical simulation. The present study methodically investigated the impact of material laws on the simulated residual stresses in ultra-high strength steel S960 weldments. Furthermore, mechanical tensile tests were performed to obtain the stress-strain curves and welding experiments were carried out to determine thermomechanical results for validation. The numerical and experimental results express that the amount of strain hardening for ultra-high strength steel S960 is very low at room temperature (RT) and high temperatures, while that is non-ignorable at medium temperatures such as from 200 to 500 °C here. The applied material plasticity model has almost no influence on the computed longitudinal residual stress in numerical simulation of S960 steel. Nevertheless, the predicted magnitude of transverse residual stress could be slightly affected by the employed MHM. For ultra-high strength steel S960, the perfect-plastic (non-hardening) model can accurately predict WRS, which is recommended to use in numerical simulation.

Lamb waves occur in thin-walled structures in two wave modes, the symmetric and antisymmetric mode. Their oscillation on the structures‘ surfaces is either in phase (symmetric) or shifted by a phase angle of π (antisymmetric). In this work, a method is developed to compare the surfaces‘ oscillation phase relation. It is based on the evaluation of time signals regarding the instantaneous phase angle using the continuous wavelet transformation and as a comparative method the short-time Fourier transformation. For this purpose, numerical simulations utilizing the finite element method provide time signals from the top and bottom surface of different thin-walled structures. They differ with respect to their material settings and laminate configurations. The numerically obtained time signals are evaluated by the developed methods. The occurring oscillation phase differences on the top and bottom surface are studied and both methods are compared. Subsequently, the oscillation phase is evaluated experimentally for the wave propagation in a fiber metal laminate. It is shown that the method based on the continuous wavelet transformation is suitable for the evaluation of oscillation phase relations in time signals. Additionally, it is proven that fiber metal laminates show only two phase relations which indicates the occurrence of Lamb waves.

Channel and spatial attention mechanisms have proven to provide an evident performance boost of deep convolution neural networks. Most existing methods focus on one or run them parallel (series), neglecting the collaboration between the two attentions. In order to better establish the feature interaction between the two types of attentions, a plug-and-play attention module is proposed, which is termed as ‘CAT’—activating the Collaboration between spatial and channel Attentions based on learned Traits. Specifically, traits are represented as trainable coefficients (i.e. colla-factors) to adaptively combine contributions of different attention modules to fit different image hierarchies and tasks better. Moreover, the global entropy pooling is proposed apart from global average pooling and global maximum pooling (GMP) operators, which is an effective component in suppressing noise signals by measuring the information disorder of feature maps. A three-way pooling operation is introduced into attention modules and the adaptive mechanism is applied to fuse their outcomes. Extensive experiments on MS COCO, Pascal-VOC, Cifar-100, and ImageNet show that our CAT outperforms the existing state-of-the-art attention mechanisms in object detection, instance segmentation, and image classification. The model and code will be released soon.

This study reassesses the optimum matrix composition of Co-Re-Cr-based alloys for strengthening by MC-type carbides. It is found that the composition of Co-15Re-5Cr is ideally suited for this purpose as it allows the solution of the carbide-forming elements such as Ta, Ti, Hf, and C within a matrix consisting entirely of fcc-phase (typically at 1450 °C), having a high solubility for these elements, while precipitation heat treatment (typically at 900-1100 °C) occurs in a hcp-Co matrix, displaying a much lower solubility. In the case of the monocarbides TiC and HfC, this was investigated and achieved for the first time in Co-Re-based alloys. TaC and TiC emerged as suitable particles in Co-Re-Cr alloys for creep applications due to a large population of nano-sized particle precipitation, which is not the case for the mainly coarse HfC. Both Co-15Re-5Cr-xTa-xC and Co-15Re-5Cr-xTi-xC exhibit a formerly unknown maximum solubility close to x = 1.8 at.%. Therefore, further research on the particle-strengthening effect and the governing creep mechanisms of carbide-strengthened Co-Re-Cr alloys should focus on alloys with the following compositions: Co-15Re-5Cr-1.8Ta-1.8C and Co-15Re-5Cr-1.8Ti-1.8C.

Present work investigates the potential of a long-range commercial blended wing body configuration powered by hydrogen combustion engines with future airframe and propulsion technologies. Future technologies include advanced materials, load alleviation techniques, boundary layer ingestion, and ultra-high bypass ratio engines. The hydrogen combustion configuration was compared to the configuration powered by kerosene with respect to geometric properties, performance characteristics, energy demand, equivalent CO2 emissions, and Direct Operating Costs. In addition, technology sensitivity studies were performed to assess the potential influence of each technology on the configuration. A multi-fidelity sizing methodology using low- and mid-fidelity methods for rapid configuration sizing was created to assess the configuration and perform robust analyses and multi-disciplinary optimizations. To assess potential uncertainties of the fidelity of aerodynamic analysis tools, high-fidelity aerodynamic analysis and optimization framework MACHAero was used for additional verification. Comparison of hydrogen and kerosene blended wing body aircraft showed a potential reduction of equivalent CO2 emission by 15% and 81% for blue and green hydrogen compared to the kerosene blended wing body and by 44% and 88% with respect to a conventional B777-300ER aircraft. Advancements in future technologies also significantly affect the geometric layout of aircraft. Boundary layer ingestion and ultra-high bypass ratio engines demonstrated the highest potential for fuel reduction, although both technologies conflict with each other. However, operating costs of hydrogen aircraft could establish a significant problem if pessimistic and base hydrogen price scenarios are achieved for blue and green hydrogen respectively. Finally, configurational problems featured by classical blended wing body aircraft are magnified for the hydrogen case due to the significant volume requirements to store hydrogen fuel.

Adhesive bonding has become increasingly popular in the manufacturing industry due to its many advantages. However, the need to completely fill the joint gap with adhesive for optimum force transfer remains a significant challenge. To ensure full gap filling and therefore joint integrity, safety critical applications often require the adhesive to flow beyond the bonded edges. Due to inadequate design of this process, the adhesive volume that escapes is often more than 30–50% of the adhesive volume. This current practice represents a suboptimal way of proceeding, which the current paper may mitigate. As a result, excessive amounts of adhesive are typically applied due to the lack of suitable models for predicting the flow and final distribution of the adhesive, including the excess amount. This limitation has hindered progress in adhesive bonding technology, and urgent action is needed to address this issue. This paper offers a solution to the significant challenge of predicting adhesive flow and distribution in manufacturing applications. The authors have developed and validated a model that allows the simulation of these complex processes. The paper goes further to present initial application patterns aimed at minimising adhesive waste while ensuring the full filling of the overlap. To achieve this, the authors employ a procedure that involves an advanced reverse squeeze flow simulation to derive an optimal application pattern from a simple initial design. It turns out that a wide range of different final distributions can be produced by a variety of initial star-shaped forms. This paper represents a significant contribution to adhesive bonding technology for anyone interested in manufacturing efficiency.

Im Rahmen dieser Arbeit werden zwei Projekte vorgestellt, in denen Magnetfelddaten komponentenweise ausgewertet werden. Dabei steht die Verarbeitung der Messdaten im Vordergrund. Ein System aus zwei Fluxgate-Magnetometern für komponentenweise Gradientenmessungen wird für einen Multikopter als Trägersystem in der oberflächennahen Aeromagnetik entwickelt. Es wird eine Kalibriermethode vorgestellt, die keinen dedizierten Kalibrierflug benötigt sondern direkt auf Messflüge angewandt werden kann. Mit einer IMU werden die Daten in das geographische Koordinatensystem überführt. Damit ist die komponentenweise Auswertung der Gradienten zwischen den Sensoren möglich. Verschiedene Störeinflüsse wie die magnetische Anomalie des Trägersystems sowie ein rotationsbedingtes Störsignal in den Magnetometern werden untersucht und mögliche Korrekturen erarbeitet. Mit einer auf Gradientendaten beruhenden Dipol-Inversion werden Messungen mit bekannten Störkörpern analysiert. Dabei wird untersucht, welche Vor- und Nachteile die Messung und Auswertung von Gradienten in der oberflächennahen Aeromagnetik hat. Die vorgestellte In-Flight-Kalibrierung bildet die Grundlage für ein neues Kalibrierverfahren für vektorielle Bohrlochmessungen. Das Verfahren beruht auf der Differenzbildung zwischen mehreren Messungen und wird auf Daten aus dem COSC-2 Projekt angewandt. Im Vergleich mit herkömmlichen Kalibriermethoden zeigt sich, dass die Streuung zwischen den Messungen bei den mit der neuen Methode kalibrierten Daten geringer ist als bei mit herkömmlichen Verfahren kalibrierten Daten. Anhand der Bohrlochmessungen sowie Messungen an Bohrkernen wird ein Modell der Magnetisierung in der Umgebung der Bohrung entwickelt. Dabei wird ein neuer Versuchsaufbau vorgestellt, mit dem Bohrkernsegmente von 1 m Länge hochgenau vermessen werden können. Der Aufbau ist so konzipiert, dass auch in einer gestörten Umgebung gemessen werden kann. Die wesentliche Gemeinsamkeit der vorgestellten Projekte ist die komponentenweise Auswertung der Magnetikdaten. Ein besonderer Aspekt ist dabei die Kalibrierung. Die vorgestellten Methoden können direkt auf Messdaten angewandt werden um daraus die Kalibrierparameter zu bestimmen. Die erreichte Qualität ist dabei mit der Qualität dedizierter Kalibriermessungen vergleichbar. Somit kann nicht nur auf dedizierte Kalibriermessungen verzichtet werden, sondern es können auch nachträglich Messdaten beliebiger Sonden ausgewertet werden, die nicht für weitere Messungen verfügbar sind., In the context of this work, two projects are presented in which magnetic field data are evaluated component by component. The focus is on the processing of the measurement data. A system consisting of two fluxgate magnetometers for component-wise gradient measurements is developed for a multicopter as a carrier system in near-surface aeromagnetics. A calibration method is presented that does not require a dedicated calibration flight but can be applied directly to measurement flights. With an IMU, the data are reoriented into the geographic coordinate system. This allows for the component-wise evaluation of the gradients between the sensors. Various interferences such as the magnetic anomaly of the carrier system as well as a rotation-related noise signal in the magnetometers are investigated and possible corrections are devised. Measurements with known test objects are analysed with a dipole inversion based on gradient data. The advantages and disadvantages of measuring and evaluating gradients in near-surface aeromagnetics are examined. The presented in-flight calibration forms the basis for a new calibration procedure for vectorial borehole measurements. The method is based on the difference formation between several measurements and is applied to data from the COSC-2 project. A comparison with conventional calibration methods shows that the scatter between measurements is lower for data calibrated with the new method than for data calibrated with conventional methods. Based on the borehole measurements as well as measurements on drill cores, a model of the magnetisation in the vicinity of the borehole is developed. A new experimental setup is presented, with which drill core segments of 1 m length can be measured with high precision. The setup is designed in such a way that measurements can also be taken in a disturbed environment. The main common feature of the projects presented is the component-by-component evaluation of the magnetic data. A special aspect is the calibration. The methods presented can be applied directly to measurement data in order to determine the calibration parameters. The achieved quality is comparable to the quality of dedicated calibration measurements. Thus, not only can dedicated calibration measurements be dispensed with, but measurement data of any probes that are not available for further measurements can also be evaluated subsequently.

Despite numerous research on new active materials for anodes, graphite remains the most commonly used material in Li-ion batteries. The spherical shape of the graphite particles has proven to be beneficial for application in electric vehicles, especially for fast charging. So far, the spheroidization of natural flake graphite is conducted by a rigid and inefficient cascade process. In this work, a scalable classifier system was used for spheroidization, and it was demonstrated that a spheroidization time of 15 min is sufficient to improve material properties and enhance electrochemical performance while maintaining high process yields of 55%. Insights into the influence of the morphology on the intrinsic and structural properties of the graphite particles and manufactured electrodes are provided. Spheroidization creates a more efficient pore network in the coating layer while reducing the internal resistance and increasing the surface area of the particles by a factor of 1.8. We demonstrate that the spherical shape improves the discharge rate capability by 1.8, and the specific charge capacity could be enhanced by more than 237% at a C-rate of 3. An additional carbon coating could significantly decrease the specific surface area and increase the specific capacity at high C-rates.

A number of major fire incidents in recent decades, particularly in tunnels and indoor car parks, have increased the awareness among construction designers towards the potential susceptibility of concrete to fire-induced explosive spalling. In some fields of application, this violent breaking-off of concrete layers may reduce the fire resistance time of fire-exposed construction elements. The mechanisms causing explosive spalling are not yet fully understood and discussed controversially among scientists. In cement production, a steadily increasing proportion of the market volume is constituted by cement types with several main constituents. In these types of cement, Portland cement clinker is replaced by granulated blast furnace slag, lime stone, fly ash or other inorganic materials. Fire tests of concrete specimens presented in a previous publication and the present paper have shown that the type of cement may have a marked influence on the susceptibility of concrete to explosive spalling. The main objectives of this thesis were therefore to: - determine the way in which the physical and chemical properties of the hardened cement paste influence the spalling propensity of heated concrete; and in this manner - contribute to a better understanding of the mechanisms causing explosive spalling. A particular focus was placed on the way in which the moisture present in the concrete pores promotes spalling. Three common characteristics of those concretes that were found to have an increased susceptibility of spalling were identified. For each of the three common characteristics, a corresponding hypothesis describing its possible contribution to the fire-induced concrete spalling was proposed. Each of the three hypotheses in turn was verified through a dedicated experimental programme. The evaluation of the experiments showed that explosive spalling was caused by the following principal mechanisms: • In the concretes that showed explosive spalling in the corresponding tests, the interfacial transition zone (ITZ) between the aggregate particles and the hardened cement paste was only weakly developed, and hence there was no pronounced interfacial porosity. Consequently, the differences in thermal strain between the expanding aggregates and the shrinking cement paste caused relevant tensile stresses in the cement paste. • Due to their pore size distribution, the concretes that showed explosive spalling had a comparably high moisture content. The moisture in the concrete pores caused an increase in the thermal gradients in the heated specimens. Beyond that, pressure from trapped water vapour enhanced the local stresses at the contact areas between the aggregate particles and the hardened cement paste. Eventually, this resulted in the formation of fracture planes and the spalling of near-surface concrete layers. The tests carried out confirmed that explosive spalling can be reliably prevented through the addition of polypropylene fibres to the concrete mix. Based on the results of the experimental programme, further potential ways to mitigate spalling are proposed., Einige größere Brandereignisse der letzten Jahrzehnte, insbesondere solche in Tunneln und Parkhäusern, haben das Bewusstsein von Planern bezüglich der möglichen Neigung von Beton zu explosiven Abplatzungen im Brandfall erhöht. In bestimmten Anwendungsbereichen können diese die Feuerwiderstandsdauer brandbeanspruchter Bauteile verkürzen. Welche Mechanis-men für die explosiven Abplatzungen verantwortlich sind, wird unter Wissenschaftlern kontro-vers diskutiert. In der Zementproduktion entfällt ein stetig wachsender Anteil des Marktvolumens auf Zemente mit mehreren Hauptbestandteilen. Bei diesen Zementarten wird Portlandzementklinker durch Hüttensand, ungebrannten Kalkstein, Flugasche oder andere anorganische Stoffe ersetzt. In einer früheren Veröffentlichung und der vorliegenden Arbeit beschriebene Brandversuche an Betonprobekörpern haben gezeigt, dass die Zementart einen deutlichen Einfluss auf die Nei-gung von Beton zu explosiven Abplatzungen haben kann. Das Hauptziel dieser Dissertation war es daher - zu bestimmen, in welcher Weise die physikalischen und chemischen Eigenschaften des Zementsteins die Neigung von erhitztem Beton zum Abplatzen beeinflussen; und auf diese Weise - zu einem besseren Verständnis der Mechanismen beizutragen, die explosive Betonab-platzungen verursachen. In diesem Zusammenhang wurde ein besonderes Augenmerk auf die Frage gelegt, auf welche Weise die in den Betonporen vorhandene Baustofffeuchte Betonabplatzungen begünstigt. Drei gemeinsame Merkmale wurden für diejenigen Betone identifiziert, die eine erhöhte Anfällig-keit für Abplatzungen aufwiesen. Für jedes dieser drei Merkmale wurde eine entsprechende Hypothese hinsichtlich seines möglichen Beitrags zum Betonabplatzen im Brandfall aufgestellt. Jede der drei Hypothesen wurde wiederum durch ein entsprechendes Versuchsprogramm über-prüft. Als Ergebnis der Untersuchungen wurden die folgenden Hauptmechanismen identifiziert, durch die Abplatzungen ausgelöst werden: • Bei den Betonen, bei denen Abplatzungen auftraten, war die Übergangszone (ITZ) zwi-schen Gesteinskörnung und Zementstein nur schwach ausgebildet. Im Bereich um die Gesteinskörner lag somit keine ausgeprägte Porosität vor. Als Folge verursachten die Unterschiede der thermischen Dehnung zwischen der sich ausdehnenden Gesteinskör-nung und dem schwindenden Zementstein maßgebliche Zugspannungen im Zement-stein. • Die Betone, bei denen Abplatzungen auftraten, hatten zu Beginn der Versuche aufgrund ihrer Porengrößenverteilung einen vergleichsweise hohen Feuchtegehalt. Die Feuchte in den Betonporen verursachte eine Erhöhung der Temperaturgradienten in den erhitzten Probekörpern. Darüber hinaus verstärkte der Druck des eingeschlossenen Wasser-dampfs die lokalen Spannungen an den Kontaktflächen zwischen Gesteinskörnung und Zementstein. Dies führte schließlich zur Bildung von Bruchflächen und zum Abplatzen der oberflächennahen Betonschicht. Die durchgeführten Versuche bestätigten, dass explosive Abplatzungen durch die Zugabe von Polypropylenfasern zur Betonmischung zuverlässig verhindert werden können. Basierend auf den Ergebnissen des Versuchsprogramms werden weitere Möglichkeiten zur Vermeidung von Abplatzungen vorgeschlagen.

Due to digitalization, robots are increasingly finding their way into public and private areas. Vacuum cleaning robots, lawn mowing robots, toy robots, and other assistive robots enter our daily lives and become more and more popular. Robots are utilized for health care services such as monitoring, motor skills, or cognitive support. As a next step, robots will no longer only serve as assistants responsible for physical and assistive tasks. They obtain a social component taking care of the psychological well-being of their users. Entertainment and educational purposes are addressed by providing social interactions and conversations. Thereby, robots are going to be seen as a friend or companion and shall be fully integrated as part of the family. Even if this scenario sounds exaggerated, the potential of robots can be demonstrated by such a scenario. A robot is supposed to simplify our everyday life in various ways soon. Thereby, it is indispensable for the robot to collect a large amount of personal information. This involves a residential map for autonomous movement, appointments for reminders, a connection to other smart home technologies, and login accounts to other services such as music streaming or social media. Furthermore, even more sensitive information about the users, their lives are collected when considering the robot as a friend and interaction partner. The robot needs to know about hobbies, habits, and preferences to be capable of companionship provision. This large amount of private and sensitive information about the users and their environment needs to be protected. To ensure this, two aspects are of essential importance. The first part considers data protection from a developer’s perspective. A privacy-respecting development is addressed by providing a privacy-centered framework introducing methodologies for risk identification and analysis. This involves security protection against threats and attackers as well as privacy protection against misuse by companies and service providers. Thereby, the focus is on two understandable and easy to apply methodologies due to the interdisciplinarity of robotics. It is not only relevant for the developers but also for e.g., psychologists, ethicists, lawyers, and users as privacy is an essential aspect for trust and acceptance towards social robots. Specifically users are of central interest as they have to cope with the robot. Therefore, the second part addresses the importance of user involvement in the development process. User should not only provide needs and requirements. Rather they need to be made aware and sensitized of these potential risks. Often it is not transparent for users when and which kind of data is collected, and the purpose of data collection. More importantly, what risks are associated with certain sensors. To control personal data, the users need to understand how the robotic system works and how they can protect themselves and their data. In order to increase understanding and acceptance, co-determination is an integral part of robotic development., Durch die Digitalisierung finden Roboter in öffentlichen und privaten Bereichen zuneh- mend ihren Einzug. Staubsaugroboter und andere Assistenzroboter werden im Alltag immer beliebter. Auch in der Gesundheitsfürsorge, z.B. zur Förderung motorischer Fähig- keiten oder zur kognitiven Unterstützung sollen Roboter in Zukunft eingesetzt werden. Bald dienen Roboter nicht mehr nur als Assistenten, die für unterstützende Aufgaben zuständig sind. Sie erhalten darüber hinaus eine soziale Komponente, die sich zusätzlich um das psychische Wohlbefinden der Benutzenden kümmert. Dabei geht es vor allem um die soziale Interaktionen. Die Roboter sollen als Freund oder sogar als Teil der Familie angesehen werden. Auch wenn sich dies übertrieben anhört, lässt sich das Potenzial demonstrieren, dass ein Roboter unseren Alltag auf vielfältige Weise vereinfachen soll. Dabei ist es unabdingbar, dass der Roboter eine große Menge an persönlichen Informationen sammelt. Dazu gehören z.B. der Wohnungs-Grundriss für die autonome Fortbewegung, eine Verbindung zu Smart-Home-Technologien und Anmeldedaten für Dienste wie Musikstreaming. Noch sensiblere Informationen werden über die Nutzenden gesammelt, wenn der Roboter als Freund betrachtet wird. Der Roboter muss über Hobbys, Gewohnheiten und Vorlieben Bescheid wissen, um eine sinnvolle Konversation führen zu können. Diese große Menge an privaten Informationen über die Nutzenden, also solche vertraulichen Daten, gilt es zu schützen. Um dies zu gewährleisten, sind zwei Aspekte von wesentlicher Bedeutung. \\ Der erste Teil betrachtet den Datenschutz aus der Entwicklungsperspektive. Privatsphäre soll als ein wesentlicher Bestandteil in den Entwicklungsprozess eingebunden werden. Dafür wird ein datenschutzzentriertes Konzept vorgestellt, welches zur Risikoidentifizier- ung und -analyse dient. Dabei geht es sowohl um den Schutz vor Bedrohungen als auch um den Schutz vor Zweckentfremdung. Der Schwerpunkt liegt auf verständlichen und einfach anwendbaren Methoden. Diese sind für die Entwickelnden, für andere Fachdisziplinen und Nutzende relevant, da die Privatsphäre ein wesentlicher Aspekt für die Akzeptanz gegenüber sozialen Robotern ist. Der zweite Teil befasst sich mit der Einbeziehung der Nutzenden während Entwicklungsprozesses. Diese sollen nicht nur Bedürfnisse und Anforderungen einbringen. Vielmehr müssen sie bezüglich der möglichen Risiken sensibilisiert werden. Oft ist es für die Nutzenden nicht nachvollziehbar, wann und welche Art von Daten erhoben werden und welchem Zweck die Datenerhebung dient. Wichtig ist, den Zusammenhang von Risiken, Sensoren und Funktionalität zu erfassen. Um über die Nutzung persönlicher Daten bestimmen zu können, müssen künftigen Nutzende verstehen, wie sie sich und ihre Daten schützen. Aus diesem Grund ist die Einbeziehung der Nutzenden ein wesentlicher Bestandteil der Roboterentwicklung.

The current work experimentally determined how the initial resistance and gauge factor in additively manufactured piezoresistive sensors are affected by the material, design, and process parameters. This was achieved through the tensile testing of sensors manufactured with different infill angles, layer heights, and sensor thicknesses using two conductive polymer composites. Linear regression models were then used to analyze which of the input parameters had significant effects on the sensor properties and which interaction effects existed. The findings demonstrated that the initial resistance in both materials was strongly dependent on the sensor geometry, decreasing as the cross-sectional area was increased. The resistance was also significantly influenced by the layer height and the infill angle, with the best variants achieving a resistance that was, on average, 22.3% to 66.5% lower than less-favorable combinations, depending on the material. The gauge factor was most significantly affected by the infill angle and, depending on the material, by the layer height. Of particular interest was the finding that increasing in the infill angle resulted in an increase in the sensitivity that outweighed the associated increase in the initial resistance, thereby improving the gauge factor by 30.7% to 114.6%, depending on the material.

The 5th European sCO2 Conference in 2023 focusses on supercritical carbon europe dioxide for energy systems. Conference Topics Heat Exchanger Turbomachines and Cycles sCO2 Applications and Energy Systems sCO2 Experiments and Loops Fluid and Material Aspects, Conference Proceedings of the European sCO2 Conference

For prospective applications of the sixth generation of mobile systems, the terahertz communication attracts increasing attention. The wireless channel and its characterization with regard to multipath propagation plays a fundamental role for the development of efficient algorithms and the system design. The published data contain extracted multipath components from two different time-domain channel sounders in the following scenarios: data center, industrial environment, aircraft cabin, shopping mall, and conference room. The multipath components are defined by amplitude, delay, angle of arrival. Additionally, the angle of departure is provided for the data center and the aircraft scenarios. Für zukünftige Anwendungen der Sechste Generation von Mobilfunksystemen kommt der Terahertz-Kommunikation mehr und mehr Bedeutung zu. Der Funkkanal und seine Charakterisierung in Hinblick auf Mehrwegeausbreitung spielen bei der Entwicklung von effizienten Algorithmen und Systemen eine entscheidende Rolle. Die publizierten Forschungsdaten enthalten extrahierte Mehrwegekomponenten, die mit zwei verschiedenen Channel Soundern in den folgenden Umgebungen gemessen wurden: Im Rechenzentrum, in einer industriellen Umgebung, in einer Flugzeugkabine, in einer Einkaufsgalerie und in einem Besprechungsraum. Die Mehrwegekomponenten sind durch die Amplitude, die Verzögerung und den Empfangswinkel definiert. Für das Rechenzentrum und die Flugzeugkabine wird zusätzlich der Sendewinkel angegeben.

To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication.

This thesis is devoted to investigation of new materials with ferroic and multiferroic properties by the means of Raman spectroscopy.The first discussed compound is chloromenite Cu9O2(SeO3)4Cl6. The crystal structure of the compound contains copper in five different coordination, which leads to a complicated magnetic structure. The chloromenite exhibits long range magnetic ordering at TN = 37 K and a polar ordering at TE = 270 K. The Raman study reveals signs of both magnetic and electric phase transitions: spin-phonon coupling below TN, and a symmetry lowering for T < TE. Rearrangement of magnetic subsystem below 20 K and an additional lattice instability in the temperature range 90 – 120 K is first discovered using Raman spectroscopy. In the mixed halide compound Fe(Te1.5Se0.5)O5Cl iron ions in the high-spin state form weakly coupled dimers showing the regime of short-range correlations at TM= 70 K and long-range magnetic order at TN = 22 K. Magnetic excitations revealed by the Raman study allow to determine the energy of magnetic interaction. A serious contradiction between the screening effect of metallic electrons and dielectric polarization has been recently overcome in LiOsO3. In the presented work we studied the isostructural compound LiReO3. The phonon anomalies point to the phase transition at T=175 K with a crossover regime down to temperatures as low as 140 K. The hysteresis in the temperature evolution of ReO6 related modes i contrast to an abrupt softening and damping of Li vibrations in the ferroelectric phase speak in favour of a decoupling of polar degrees of freedom and itinerant electrons. Creation of low dimensional magnetic structures is not the only possible effect of lone electron pair cations of p-elements. Features of the electronic structure cause a structural transition to a non-centrosymmetric state, which contributes to the manifestation of such actual physical properties as ferroelectricity, piezoelectricity, and optical activity like second-harmonic generation. Two new second-harmonic generation active iodates K3Sc(IO3)6 and KSc(IO3)3Cl, are discussed in this thesis. The large anharmonicity in the optical response of both compounds is confirmed by an anomalous temperature dependence of optical phonon energies as well as their enhanced Raman scattering intensities. The latter corresponds to a very large electronic polarizability., Die vorliegende Dissertation widmet sich der Untersuchung neuer Materialien mit ferroischen und multiferroischen Eigenschaften mittels Raman-Spektroskopie. Die erste diskutierte Verbindung ist Chloromenit Cu9O2(SeO3)4Cl6. Die Kristallstruktur der Verbindung enthält Kupfer in fünf verschiedenen Koordinationen, was zu einer komplizierten magnetischen Struktur führt. Chloromenit weist eine magneti-sche Fernordnung bei TN = 37 K und eine polare Ordnung bei TE = 270 K auf. Die Untersuchung mit der Raman-Methode ermöglicht die Untersuchung für magnetische und elektrische Phasenübergänge: Unterhalb von TN eine Spin-Phonon-Kopplung und für T < TE eine Symmetrieerniedrigung. Mit Hilfe der Raman-Spektroskopie wurden erstmals eine Neuordnung des magnetischen Subsystems bei Temperaturen unter 20 K und darüber hinaus eine Gitterinstabilität im Temperaturbereich von 90 – 120 K entdeckt. In der gemischten Halogenidverbindung Fe(Te1.5Se0.5)O5Cl bilden Eisenionen im High-Spin- Zustand schwach gekoppelte Dimere mit dem Überwiegen von Korrelationen kurzer Reichweite bei TM = 70 K und einer magnetischen Fernordnung bei TN = 22 K. Magnetische Anregungen, entdeckt durch die Raman Methode, ermöglicht die Bestimmung von Energie der magnetischen Wechselwirkung. Kürzlich wurde ein gravierender Widerspruch zwischen der Abschirmwirkung metallischer Elektronen und der dielektrischen Polarisation bei LiOsO3 überwunden. In vorliegender Arbeit wurde die isostrukturelle Verbindung LiReO3 untersucht. Die Phononenanomalien deuten auf einen Phasenübergang bei T = 175 K hin, wobei die Anomalien bis zu einer Tiefsttemperatur von T = 140 K auftreten. Die Hysterese der Temperaturentwicklung von auf ReO6 bezogene Moden – im Gegensatz zu einer abrupten Abschwächung und Dämpfung von Li-Schwingungen in der ferroelektrischen Phase – spricht für eine Entkopplung polarer Freiheitsgrade und itineranter Elektronen. Merkmale der elektronischen Struktur bewirken einen strukturellen Übergang in einen nicht zentrosymmetrischen Zustand, der zu einer Manifestation physikalischer Eigenschaften wie Ferroelektrizität und optischer Aktivität. Zwei neue, frequenzverdoppelnde Jodate werden diskutiert: K3Sc(IO3)6 und KSc(IO3)3Cl. Die große Anharmonizität in der optischen Reaktion der beiden Verbindungen wird durch eine anomale Temperaturabhängigkeit von optischen Phononenenergien sowie ihre vergrößerten Intensitäten bei der Raman-Streuung bestätigt.

Industrial processes are responsible for the largest share of greenhouse gas emissions worldwide. Therefore, improving the energy efficiency of industrial processes is necessary from an environmental and economic point of view. In the production environment, conditions must be ensured, particularly regarding temperature, humidity, and air quality. These tasks are performed by Heating, Ventilation, and Air Conditioning (HVAC) systems. HVAC systems are usually planned based on extreme static values to counter uncertainties during the dynamic operating phase. This planning approach often leads to the over-dimensioning of HVAC systems. There is, therefore, still considerable potential in the production environment to improve the energy efficiency of HVAC systems in the planning and operating phase. The main research objective of this thesis is to improve the planning and operation of HVAC systems in production environments by finding suitable compromise solutions between production conditions and energy demand as well as environmental impact. To this end, the technical background of the planning and operation of HVAC systems is first presented. The technical background includes a general classification of HVAC systems in the production environment, the explanation of system elements, and the economic, social, and environmental impacts of HVAC systems. The three main target dimensions of air quality, thermal comfort, and energy demand are identified in this context. The influence of Industry 4.0 and the relevance of a cyber-physical system approach is also presented. Subsequently, the research field is further narrowed down. Here, a distinction is made between general research contributions for the building sector and contributions specific to production environments. A total of nineteen research contributions, ten general and nine specific, are evaluated in detail based on five overarching evaluation criteria using an evaluation matrix. The evaluation shows a need for further research for an approach that addresses compromise solutions of the three mentioned target dimensions during the planning and operation phase of HVAC systems in production environments. In the conceptual part of the paper, relevant actors are first identified, and objectives and requirements are derived. At the concept's core is a cyber-physical system approach that covers data acquisition from the production environment, data processing, modelling and simulation, decision support, and automatic control. HVAC systems, production processes, users, building zones, the building envelope, and the weather are key system elements and influencing factors. These system elements and influencing factors must be considered for planning and operational improvement and explained in detail. Finally, four solution modules for decision support and automatic control are presented. Subsequently, the developed concept is implemented prototypically and applied in three exemplary use cases. In the first use case, an HVAC system's increase in operating and energy efficiency for managing a dry room in battery cell production is considered, whereby theoretically, up to 37 % of energy can be saved. In the second use case, monitoring and operational improvement are assessed using the example of incremental production. The monitoring is carried out employing a zone-resolved, dashboard-based visualisation. The fine dust concentration is used to determine the extent to which the airflow rate through HVAC systems must be increased to reduce the fine dust concentration and improve the air quality. In the third use case, the planning of dry rooms for battery cell production is considered. A total of 60 locations worldwide are considered, and the necessary energy demands and environmental impacts of dry room operation are determined. Dry rooms should be avoided in warm and humid regions, especially around the equator. In addition, if there are several dry rooms, the air supply should be provided by one decentralized HVAC system per room. However, the cooling and supply of the HVAC systems should be centralized as far as possible. Finally, there is a summary and evaluation of the work based on the previously defined evaluation criteria. In addition, a detailed outlook is given concerning other possible research topics., Industrielle Prozesse sind weltweit für den größten Anteil an Treibhausgasemissionen verantwortlich. Daher ist die Verbesserung der Energieeffizienz von industriellen Prozessen sowohl aus umwelt- als auch ökonomischen Gesichtspunkten notwendig. Im Produktionsumfeld müssen die Produktionsbedingungen insbesondere in Bezug auf Temperatur, Feuchtigkeit und Luftqualität gewährleistet werden. Diese Aufgaben wird durch raumlufttechnische Anlagen (RLT-Anlagen) gewährleistet. RLT-Anlagen werden üblicherweise basierend auf statischen Extremwerten geplant, um Unsicherheiten während der sehr dynamischen Betriebsphase zu begegnen. Dies führt oftmals zu einer Überdimensionierung von RLT-Anlagen. Es gibt daher im Produktionsumfeld noch erhebliche Potentiale die Energieeffizienz von RLT-Anlagen in der Planungs- und Betriebsphase zu verbessern. Das Hauptforschungsziel dieser Arbeit besteht darin, die Planung und den Betrieb von RLT-Anlagen in Produktionsumgebungen zu verbessern, indem geeignete Kompromisslösungen zwischen den Produktionsbedingungen und dem Energiebedarf sowie den Umweltauswirkungen gefunden werden. Hierzu wird zunächst der technische Hintergrund zur Planung und Betrieb von RLT-Anlagen dargelegt. Dies umfasst eine allgemeine Einordung von RLT-Anlagen in die Produktionsumgebung, die Erläuterung von Systemelementen und der ökonomischen, sozialen und umweltbezogenen Auswirkungen von RLT-Anlagen. In diesem Zusammenhang werden die drei wesentlichen Zieldimensionen der Luftqualität, des thermischen Komforts und des Energiebedarfs identifiziert. Der Einfluss von Industrie 4.0 und die Relevanz eines cyber-physischen Systemansatzes wird ebenfalls dargestellt. Anschließend wird das Forschungsfeld weiter eingegrenzt. Hierbei wird zwischen allgemeinen Forschungsbeiträgen für den Gebäudebereich und Beiträgen spezifisch für Produktionsumgebungen unterschieden. Insgesamt werden neunzehn Forschungsbeiträge, zehn allgemeine und neun spezifische, anhand von fünf übergeordneten Evaluationskriterien im Detail anhand einer Evaluationsmatrix ausgewertet. Aus der Evaluation geht hervor, dass es weiteren Forschungsbedarf für einen Ansatz gibt, der Kompromisslösungen der drei genannten Zieldimensionen während der Planungs- und Betriebsphase von RLT-Anlagen im Produktionsumfeld adressiert. Im Konzeptteil der Arbeit werden zunächst relevante Akteure identifiziert sowie Ziele und Anforderungen abgeleitet. Im Kern des Konzepts steht ein cyber-physischer Systemansatz, der die Datenakquise aus dem Produktionsumfeld, die Datenverarbeitung, Modellierung sowie Simulation und die Entscheidungsunterstützung sowie automatische Regelung abdeckt. Als wesentliche Systemelemente und Einflussfaktoren werden RLT-Anlagen, Produktionsprozesse, Nutzer, Gebäudezonen sowie Gebäudehülle und das Wetter herausgestellt. Diese Systemelemente und Einflussfaktoren müssen zur Planungs- und Betriebsverbesserung berücksichtigt werden und werden detailliert erläutert. Abschließend werden vier Lösungsbausteine zur Entscheidungsunterstützung sowie automatischen Regelung dargelegt. Im Anschluss wird das entwickelte Konzept prototypisch implementiert und in drei beispielhaften Anwendungsfällen angewendet. Im ersten Anwendungsfall wird die Betriebs- bzw. Energieeffizienzsteigerung einer RLT-Anlage zum Betrieb eines Trockenraums in der Batteriezellproduktion betrachtet, wobei theoretisch bis zu 37 % Energie eingespart werden kann. Im zweiten Anwendungsfall wird ein Monitoring und eine Betriebsverbesserung am Beispiel einer inkrementellen Fertigung betrachtet. Das Monitoring erfolgt mittels einer zonenaufgelösten, dashboardbasierten Visualisierung. Anhand der Feinstaubkonzentration wird bestimmt inwiefern der Luftvolumenstrom durch RLT-Anlagen erhöht werden muss, um die Feinstaubkonzentration zu senken und die Luftqualität zu verbessern. Im dritten Anwendungsfall wird die Planung von Trockenräumen zur Batteriezellproduktion betrachtet. Es werden insgesamt bis zu 60 Orten auf der Welt betrachtet und nötige Energiebedarfe sowie Umweltauswirkungen des Trockenraumbetriebs bestimmt. Es zeigt sich, dass Trockenräume in besonders warmen und feuchten Regionen, insbesondere um den Äquator, vermieden werden sollten. Zudem sollte bei mehreren Trockenräumen die Luftversorgung durch eine dezentrale RLT-Anlagen je Raum erfolgen. Die Kälteerzeugung sowie Versorgung der RLT-Anlagen sollte jedoch möglichst zentral erfolgen. Abschließend erfolgt eine kurze Zusammenfassung sowie Evaluation der Arbeit anhand der vorab definierten Evaluationskriterien. Darüber hinaus wird ein ausführlicher Ausblick hinsichtlich weiterer möglicher Forschungsthemen gegeben., Schriftenreihe des Instituts für Werkzeugmaschinen und Fertigungstechnik, vol. 2023

Vakuumbasierte Handhabung wird in einer Vielzahl unterschiedlicher Anwendungsbereiche eingesetzt, beispielsweise zur roboterbasierten Handhabung von Karosserieblechen in Presswerken oder zur Handhabung von Versandkartons in der Intralogistik. Aufgrund der verlustbehafteten Energiewandlungskette in der vakuumbasierten Handhabung ist der wirtschaftliche Umgang mit der Druckluft von hoher Priorität. Eine Herausforderung hierbei liegt in der Vielzahl von Unsicherheiten und äußeren Störeinflüssen. Industriell etablierte Auslegungsansätze begegnen diesen Einflüssen mit der Überdimensionierung mittels Sicherheitsfaktoren, beispielsweise durch die Bereitstellung einer erhöhten Haltekraft. Dies steht einer wirtschaftlichen Druckluftnutzung für die vakuumbasierte Handhabung jedoch entgegen. Eine zentrale Herausforderung besteht darin, die Haltekraft des Greifsystems mit dem Ziel einer hohen Prozesssicherheit und eines geringen Druckluftverbrauchs angemessen zu dimensionieren. Der methodische Kern der vorliegenden Dissertation liegt daher in der modellbasierten Greifsystemauslegung, mit Fokus auf der Blechhandhabung. Im Einzelnen wurden Methoden zur Greifpunktoptimierung und Greifsystemdimensionierung erarbeitet. Das Ziel der Greifpunktoptimierung ist, die an den einzelnen Greifpunkten erreichbare Haltekraft zu maximieren. Auf Basis einer vorgegebenen Robotertrajektorie wird anschließend überprüft, ob die Haltekraft ausreichend für einen stabilen Handhabungsprozess (ohne Bauteilverlust) ist. Im Rahmen der Greifsystemdimensionierung werden abschließend Saugeranzahl und -baugröße sowie die Regelparameter des Vakuumejektors dimensioniert, um den Energieaufwand zur Bereitstellung der erforderlichen Haltekraft zu minimieren. Als Kern dieser Auslegungsmethoden wurden im Rahmen dieser Dissertation drei Vorhersagemodelle erarbeitet. Das methodische Vorgehen für die Modellbildung basiert auf der Abstraktion von konkreten industrielle Bauteilen zu repräsentativen Prüfobjekten mit primitiven Oberflächengeometrien, sowie der Abstraktion industrieller Pick and Place Bewegungen auf die wesentlichen Lastfälle am Greifer-Objekt-Interface (Normal- und Querbelastung, wobei in dieser Arbeit ausschließlich die Normalbelastung betrachtet wurde). Auf Grundlage dieser Abstraktionsschritte wurde eine experimentelle Prüfmethode entwickelt, mit der die Versuchsdaten zur Parametrierung der Vorhersagemodelle aufgenommen wurden. Das methodische Vorgehen der Modellbildung lässt sich auf beliebige weitere Sauger-Objekt-Paarungen übertragen und somit eine breite Anwendbarkeit ermöglichen. Als Gegenentwurf zur Modellierung physikalischer Wirkzusammenhänge an der Sauger-Objekt-Grenzfläche für die Greifsystemauslegung wurde im Rahmen der vorliegenden Arbeit eine Prozessauslegungsmethode basierend auf Maschinellem Lernen erarbeitet und anhand des Beispiels der Kartonhandhabung experimentell untersucht. Basierend auf dem Deep Q-Learning, einer modellfreien Methode des Reinforcement Learning, wurde ein selbstständig lernendes Software-Agentensystem implementiert. Es wurde gezeigt, dass dieses System nach wenigen Hundert Versuchsiterationen in der Lage dazu ist, den Versorgungsdruck des Vakuumejektors so einzustellen, dass der Druckluftverbrauch um bis zu 70% reduziert werden konnte. Die Effizienzsteigerung in der vakuumbasierten Handhabung erfordert allgemein anwendbare und effiziente Auslegungsmethoden mit dem Ziel der Minimierung des Druckluftbedarfs. Die erarbeiteten modellbasierten und modellfreien Methoden liefern für die informierte Auslegung von vakuumbasierten Greifsystemen und den zugehörigen Prozessparametern einen wesentlichen Beitrag., Vacuum-based handling is used in a variety of different applications, for example for robot-based handling of car body panels in press shops or for handling shipping cartons in intralogistics. Due to the lossy energy conversion chain in vacuum-based handling, the economical use of compressed air is a high priority. One challenge here is the multitude of uncertainties and external disturbances. Industrially established design approaches counter these influences with oversizing using safety factors, for example by providing an increased holding force. However, this stands in the way of economical use of compressed air for vacuum-based handling. A central challenge is to appropriately dimension the holding force of the gripping system with the goal of high process reliability and low compressed air consumption. The methodological core of this dissertation therefore lies in model-based gripping system design with a focus on sheet metal handling. In detail, methods for gripping point optimization and gripping system dimensioning were developed. The goal of gripping point optimization is to maximize the holding force achievable at each gripping point. Based on a given robot trajectory, it is then evaluated if the holding force is sufficient for a stable handling process (without losing the grasp object). Finally, as part of the gripping system dimensioning, the number and size of the suction cups and the control parameters of the vacuum ejector are dimensioned in order to minimize the energy required to provide the necessary holding force. As the core of these design methods, three prediction models were developed within the scope of this dissertation. The methodological approach for model building is based on the abstraction of concrete industrial components to representative test objects with primitive surface geometries, as well as the abstraction of industrial pick and place movements to the essential load cases at the gripper-object interface (normal and transversal load, whereas in this thesis only the normal load was considered). Based on these abstraction steps, an experimental test method was developed to record the test data for parameterization of the prediction models. The methodological approach to model building can be applied to any other gripper-object pairings, thus enabling broad applicability. As an alternative to the modeling of physical cause-effect relationships at the gripper-object interface for gripping system design, a process design method based on machine learning was developed in the present work and experimentally investigated using the example of carton handling. Based on Deep Q-Learning, a model-free reinforcement learning method, a self-learning software agent system was implemented. It was shown that after a few hundred test iterations, this system is capable of variably adjusting the supply pressure of the vacuum ejector over time in such a way that compressed air consumption can be reduced by up to 70%. Increasing efficiency in vacuum-based handling requires generally applicable and efficient design methods with the goal of minimizing compressed air consumption. The developed model-based and model-free methods provide a significant contribution for the informed design of vacuum-based gripping systems and the associated process parameters.

Additive manufacturing with steel offers new opportunities for the construction sector. In particular, direct energy deposition (DED) processes such as Wire Arc Additive Manufacturing (WAAM or DED-Arc), are able to create large structures with a high degree of geometric freedom, like force-flow-optimized steel nodes and frameworks, as well as truss structures. By using high-strength steel, manufacturing times can be shortened because less material has to be applied. In order to enable the usage of WAAM components in the construction industry, profound knowledge of the material behavior is necessary. Based on reliable process parameters, extensive experimental and numerical investigations are carried out to characterize the influence of layer orientation and overhang angle on the mechanical parameters of WAAM high-strength low-alloy steel (HSLA) walls. The results have been compared to HSLA steel sheet material. It is shown that comparable characteristics exist for Young’s modulus E, yield strength Rp,0.2 and tensile strength Rm with regard to civil engineering applications. The influence of the loading direction on the material level is similar. Only the yield strength shows a slight dependence on the layer orientation for WAAM walls (difference 4.5%). The overhang angle has no influence on the material parameters.

Electrolyte filling and wetting is a quality-critical and cost-intensive process step of battery cell production. Due to the importance of this process, a steadily increasing number of publications is emerging for its different influences and factors. We conducted a systematic literature review to identify common parameters that influence wetting behavior in experimental settings, specifically focusing on material, processes, and experimental measurement methods but excluding simulation studies. We reduced the initially found 544 records systematically to 39 fully labeled articles. Our profound analysis guided by attributed labelings revealed current research gaps such as the lack of a holistic view on measurement methods for filling and wetting, underrepresented studies relevant to series production, as well as the negligence of research targeting the transferability of results from the material to the cell level, while also examining the measured variables’ interactions. After comparatively illustrating and discussing implications of our findings, we also discussed limitations of our contribution and suggested ideas for potential further research topics.

To achieve high efficiency and low degradation of a polymer electrolyte fuel cell (PEMFC), it is necessary to maintain an appropriate level of humidification in the fuel cell membrane. Thus, membrane humidifiers are typically used in PEMFC systems. Parameter studies are important to evaluate membrane humidifiers under various operating conditions to reduce the amount of physical tests. However, simulative studies are computationally expensive when using detailed models. To reduce the computational cost, surrogate models are set up. In our study, a 3D computational fluid dynamics (CFD) model of a hollow fibre membrane humidifier is presented and validated using measurement data. Based on the results of the validated CFD model, a surrogate model of the humidifier is constructed using proper orthogonal decomposition (POD) in combination with different interpolation methods. To evaluate the surrogate models, their results are compared against reference solutions from the CFD model. Our results show that a Halton design combined with a thin-plate-spline interpolation results in the most accurate surrogate humidifier model. Its normalised mean absolute error for 18 test points when predicting the water mass fraction in the membrane humidifier is 0.58%. Furthermore, it is demonstrated that the solutions of the POD model can be used to initialise CFD calculations and thus accelerate the calculation of steady state CFD solutions.

Monopiles are the preferred foundation for offshore wind turbines in Europe. These large-diameter pipe piles transfer predominantly horizontal loads to the soil by means of lateral bedding. The piles are commonly installed by impact driving. Vibratory driving as alternative installation method has advantages regarding installation time, fatigue and environmental aspects. However, the experiences with this installation technique for offshore foundations are limited. There are concerns regarding the influences on the load-bearing behaviour. To close this gap, comparing scale model tests were carried out with impact and vibratory driven pipe piles. During the installation of the model piles, forces and motions were measured at the pile head and radial stresses were measured in the soil. Soil stress developments known from impact driven piles were also witnessed in certain cases of vibratory installation. In such cases, a specific 'vibratory driving mode' could be identified from the pile head motion. After end of driving, increased soil stresses remained especially near the pile toe ('installation effect'). During subsequent cyclic loading, the load-displacement behaviour of the first cycle, the displacement accumulation as well as lateral stiffness over cycle count and the further development of soil stresses were analysed. Different lateral behaviour depending on the installation parameters could be identified. The 'certain' vibrated piles mentioned above showed similar lateral behaviour as impact driven piles while other vibrated piles behaved softer. Due to changes of loading direction, a back-accumulation of pile head displacement together with re-arrangements of soil stresses could be witnessed. The increased soil stresses near the pile toe observed at certain piles largely remained after cyclic loading. For the static lateral calculation of monopile foundations, a one-dimensional bedded beam (Winkler foundation) on nonlinear springs (p-y curves) is commonly used. A modified p-y approach considering the soil stresses due to pile installation effects was developed and shows good agreement with the first loading cycle of each model test. For offshore cases, the influence of increased soil stresses near the pile toe on the static lateral behaviour was predicted as well. The activation of lateral bedding below the point of zero displacement ('toe kick') is decisive for this behaviour. For the lower displacement accumulation during cyclic loading in case of increased soil stresses, a possible explanation could be found as well., Monopfahlgründungen stellen die Vorzugsvariante bei Gründung von Offshore-Windenergieanlagen dar. Diese Stahlrohrpfähle großen Durchmessers tragen die vornehmlich horizontalen Lasten durch laterale Bettung in den Baugrund ab. Die Installation der Pfähle erfolgt mittels Schlagrammung. Die Vibrationsrammung als alternatives Einbringverfahren hat Vorteile hinsichtlich Installationszeit, Stahlermüdung und Umwelteinwirkungen. Die Erfahrungen mit dem Verfahren für Offshore-Gründungspfähle sind jedoch begrenzt und Bedenken bestehen insbesondere hinsichtlich er Auswirkungen auf das Tragverhalten. Um diese Lücke zu schließen wurden vergleichende Modellversuche mit geschlagenen und vibrierten Rohrpfählen durchgeführt. Während der Installation der Modellpfähle wurden die am Pfahlkopf angreifenden Kräfte und resultierenden Bewegungen sowie die radial auf den Pfahl wirkenden Spannungen im Boden gemessen. Von geschlagenen Pfählen bekannte Spannungsentwicklungen im Boden wurden auch bei vibrierten Pfählen gemessen, bei denen anhand der Pfahlbewegungen ein bestimmter 'Vibrationsmodus' identifiziert werden konnte. Nach Ende der Pfahlinstallation blieben insbesondere im Bereich des Pfahlfußes erhöhte Bodenspannungen erhalten ('Installationseffekt'). Für die anschließende zyklisch laterale Belastung wurden das Last-Verformungsverhalten des ersten Belastungszyklus, die Verformungsakkumulation und die Entwicklung der Systemsteifigkeit infolge zyklischer Belastung sowie die weitere Entwicklung der Bodenspannungen ausgewertet. Ein unterschiedliches laterales Verhalten konnte in Abhängigkeit der gewählten Installationsparameter festgestellt werden. Die o.g. 'bestimmten' vibrierten Pfähle zeigten dabei ein ähnliches Verhalten wie geschlagene Pfähle, während andere vibrierte Pfähle sich 'weicher' verhielten. Infolge mehrerer Richtungswechsel der zyklisch lateralen Belastung konnten ein Rückgang der zuvor akkumulierten Verformungen und gelichzeitig Spannungslagerungen im Boden festgestellt werden. Die bei bestimmten Pfählen auftretenden erhöhten Bodenspannungen im Bereich des Pfahlfußes blieben auch nach der zyklischen Belastung weitestgehend erhalten. Die statische laterale Berechnung von Monopfahlgründungen erfolgt i.d.R. als eindimensionaler, gebetteter Balken (Winkler-Balken) mit nichtlinearen Federkennlinien (p-y-Kurven). Ein modifizierter p-y-Ansatz zur Berücksichtigung der Bodenspannungen infolge der Pfahlinstallation wurde entwickelt und zeigt gute Übereinstimmungen mit dem jeweils ersten Belastungszyklus der Modellversuche. Auch für Monopfahlgründungen im Offshore-Maßstab wurde ein Einfluss erhöhter Bodenspannungen im Bereich des Pfahlfußes auf das statisch laterale Tragverhalten prognostiziert. Die Aktivierung lateraler Widerstände unter dem Nulldurchgang der Biegelinie des Pfahls ('toe kick') ist hierfür entscheidend. Für die geringeren Verformungen infolge zyklischer Belastung bei erhöhten Bodenspannungen konnte ebenfalls ein Erklärungsansatz gefunden werden., Mitteilung des Instituts für Geomechanik und Geotechnik, vol. 112

The reconstruction of Mercury's internal magnetic field enables us to take a look into the inner heart of Mercury. In view of the BepiColombo mission, Mercury's magnetosphere is simulated using a hybrid plasma code, and the multipoles of the internal magnetic field are estimated from the virtual spacecraft data using three distinct reconstruction methods: the truncated singular value decomposition, the Tikhonov regularization and Capon's minimum variance projection. The study shows that a precise determination of Mercury's internal field beyond the octupole up to the dotriacontapole is possible and that Capon's method provides the same high performance as the Tikhonov regularization, which is superior to the performance of the truncated singular value decomposition.

Dynamic analysis of three-dimensional structures is common practice in industry to optimize products and in research to gain insights on the influence of parameters. The complexity differs based on the linearity or nonlinearity of the underlying problem, the type of excitation, e.g., forced or self-excitation, and the number of degrees of freedom that need to be examined. Reduced order models and optimized numerical methods are used to optimize the time and computational power needed to gain a certain insight. This article focusses on a specific class of problems where the modes of the structure do not or do not significantly change through the (damping) device or force that is added to the structure. Herein, lumped mass models are commonly used for analysis of the dynamic response of the system. In the article, it is highlighted that lumped mass models can give quantitative insight but modally reduced models allow a direct optimization of the problems with respect to the physical degree of freedom that, for example, is subject to self-excitation or dampened. The benefit of modal minimal models and its limitations are shown and discussed for different linear and nonlinear dynamic problems.

Viscosity shifts the flow features of a liquid and affects the consistency of a product, which is a primary factor in demonstrating forces that should be overcome when fluids are transported in pipelines or employed in lubrication. In carbon-based materials, due to their extensive use in industry, finding the simple and reliable equations that can predict the rheological behavior is essential. In this research, the rheological nature of graphene/aqueous nanofluid was examined. Fourier transform infrared spectroscopy, dynamic light scattering, energy-dispersive X-ray spectroscopy, and X-ray powder diffraction were used for analyzing the phase and structure. Transmission electron microscopy and field emission scanning electron microscopy were also employed for micro and nano structural-study. Moreover, nanofluid stability was examined via zeta-potential measurement. Results showed that nanofluid has non-Newtonian nature, the same as the power-law form. Further, from 25 to 50°C, at 12.23 s−1, viscosity decreased by 56.9, 54.9, and 38.5% for 1.0, 2.0, and 3.5 mg/mL nanofluids, respectively. From 25 to 50°C, at 122.3 s−1, viscosity decreased by 42.5, 42.3, and 33.3% for 1.0, 2.0, and 3.5 mg/mL nanofluids, respectively. Besides, to determine the viscosity of nanofluid in varied temperatures and mass concentrations, an artificial neural network via R 2 = 0.999 was applied. Finally, the simple and reliable equations that can predict the rheological behavior of graphene/water nanofluid are calculated.

New aerodynamic aircraft concepts enable the storage of volumetric liquid hydrogen (LH2). Additionally, the low temperatures of LH2 allow technologies such as the superconductivity of electrical components. An increased power density of the onboard wiring harness and the electrical machine can be expected. Nevertheless, the power electronic drive inverter has to deliver high power and high switching frequencies ( fPWMs ) under challenging conditions. Therefore, knowledge of the electric behaviour of different semiconductor materials under cryogenic temperatures is essential to answer the question: “Are modern power electronics a technology enabler or a system bottleneck?” This publication shows a comprehensive novelty study for cryogenic power electronics based on experimental-driven semiconductor investigations, mission profile-based considerations, requirement analyses of superconducting electrical machines, and studies of the cooling concepts. All aspects are discussed within one interdisciplinary publication. A cryogenic system cannot be considered without a feasible cooling concept. Different semiconductor structures based on various materials (silicon (Si), silicon carbide (SiC) and gallium nitride (GaN)) are evaluated for their suitability. The collected data and the literature review draw a technology feasibility studies supported by detailed cooling system analyses and superconducting electrical machine requirements. The power demand and high fPWM lead to a SiC non-cryogenic inverter approach. Due to the detailed cooling system assessment, a loss reduction is achieved by optimising the junction temperature ( TJ ) under various load cases (LCs) out of the mission profile.

Recent research efforts have highlighted the potential of hybrid composites in the context of additive manufacturing. The use of hybrid composites can lead to an enhanced adaptability of the mechanical properties to the specific loading case. Furthermore, the hybridization of multiple fiber materials can result in positive hybrid effects such as increased stiffness or strength. In contrast to the literature, where only the interply and intrayarn approach has been experimentally validated, this study presents a new intraply approach, which is experimentally and numerically investigated. Three different types of tensile specimens were tested. The non-hybrid tensile specimens were reinforced with contour-based fiber strands of carbon and glass. In addition, hybrid tensile specimens were manufactured using an intraply approach with alternating carbon and glass fiber strands in a layer plane. In addition to experimental testing, a finite element model was developed to better understand the failure modes of the hybrid and non-hybrid specimens. The failure was estimated using the Hashin and Tsai–Wu failure criteria. The specimens showed similar strengths but greatly different stiffnesses based on the experimental results. The hybrid specimens demonstrated a significant positive hybrid effect in terms of stiffness. Using FEA, the failure load and fracture locations of the specimens were determined with good accuracy. Microstructural investigations of the fracture surfaces showed notable evidence of delamination between the different fiber strands of the hybrid specimens. In addition to delamination, strong debonding was particularly evident in all specimen types.

The thesis illustrates the Life-Cycle Cost Analysis of road bridges equipped with Structural Health Monitoring systems (defined LCCA-SHM) framework developed in the research project. LCCA-SHM framework is designed as a support tool for the infrastructures management. The main intent of the research is to promote the implementation in the common practice of the alert devices to develop the realization of smart structures capable to timely predict the structural damages and to impose the most cost and safety effective operation and maintenance planning based on the collected data., Die Dissertation veranschaulicht die Lebenszykluskostenanalyse von Straßenbrücken, die mit Structural Health Monitoring-Systemen (definiert als LCCA-SHM) ausgestattet sind, die im Rahmen des Forschungsprojekts entwickelt wurden. Der LCCA-SHM-Rahmen ist als Hilfsmittel für das Infrastrukturmanagement konzipiert. Das Hauptziel der Forschung ist es, die Implementierung von Warngeräten in die gängige Praxis zu fördern, um die Realisierung von intelligenten Strukturen zu entwickeln, die in der Lage sind, strukturelle Schäden rechtzeitig vorherzusagen und die kosten- und sicherheitseffektivste Betriebs- und Instandhaltungsplanung auf der Grundlage der gesammelten Daten vorzuschreiben.Die Dissertation veranschaulicht die Lebenszykluskostenanalyse von Straßenbrücken, die mit Structural Health Monitoring-Systemen (definiert als LCCA-SHM) ausgestattet sind, die im Rahmen des Forschungsprojekts entwickelt wurden. Der LCCA-SHM-Rahmen ist als Hilfsmittel für das Infrastrukturmanagement konzipiert. Das Hauptziel der Forschung ist es, die Implementierung von Warngeräten in die gängige Praxis zu fördern, um die Realisierung von intelligenten Strukturen zu entwickeln, die in der Lage sind, strukturelle Schäden rechtzeitig vorherzusagen und die kosten- und sicherheitseffektivste Betriebs- und Instandhaltungsplanung auf der Grundlage der gesammelten Daten vorzuschreiben.

An ion chromatography technique with conductivity detection was selected as an analytical tool for the simultaneous indirect determination of sodium sulfate, potassium sulfate, and magnesium sulfate via their respective cations. The method was developed and validated for the quantitative assay of the inorganic salts under study in oral pharmaceutical dosage forms. Chromatographic separation was achieved on a Dionex®IonPac® CS16 column (250 × 5 mm) column using the gradient elution method. A mobile phase-A consisting of methane sulfonic acid (6.7%, v/v) in Milli-Q water, which is used together with Milli-Q water, was used as a mobile Phase-B. The flow rate was 1.2 mL/min. The retention times of sodium, potassium, and magnesium as sulfates were 7.8, 12.8, and 16.2 min, respectively. The method was validated according to ICH guidelines and showed good linearity and accuracy results within concentration ranges of 80.0–240.0, 20.0–60.0, and 4.5–13.5 ppm for sodium, potassium, and magnesium as sulfates, respectively. The relative standard deviation results for intra- and inter-day precision were less than 1.0%. The method was applied successfully for determination of the analytes under study in their mixed pharmaceutical oral solution and found suitable for their routine and stability analysis.

To improve the performance of lead-free piezoelectric composites, the functionalization of the filler particles has been suggested as a successful strategy in several recent reports. The details of the functionalization process, however, are not clear, nor is its influence on the dielectric properties of the composites. This study reports a systematic investigation of the functionalization process parameters of barium titanate nanoparticles (BTONP) with 3-(trimethoxysilyl)propyl methacrylate (TMSPM) used as a linker to an acrylate-based matrix polymer. Functionalization process temperature, time, functionalization agent ratio, solvent, and catalyst influence on the functionalization degree were measured by thermogravimetric analysis (TGA), elemental analysis, and Fourier-transform infrared (FTIR) spectroscopy. Elevated temperature and average functionalization time led to the highest functionalization degree in the form of a TMSPM monolayer on the particle surface. Three solvents, with and without catalysts, were investigated and two types of functionalized BTONP were selected for composite manufacturing. To this end, the functionalized particles were used to manufacture 10 vol.% BTONP/photopolymer UV light-curable composite suspensions. After solidification of the suspensions by exposure to UV light, the microstructure and dielectric properties of the resulting composites were investigated. It was seen that functionalization improves the dispersion of particles, increases suspension viscosity, and decreases the curing depth and dielectric properties.

The most precise measurement tools of humankind are equipped with ultra-stable lasers. State-of-the-art laser stabilization techniques are based on external cavities, that are limited by noise originated in the coatings of the cavity mirrors. Microstructured mirror coatings (so-called meta-mirrors) are a promising technology to overcome the limitations of coating noise and therewith pave the way towards next-generation ultra-stable lasers. We present experimental realization of a 12,000-finesse optical cavity based on one low-noise meta-mirror. The use of the mirrors studied here in cryogenic silicon cavities represents an order of magnitude reduction in the current limiting mirror noise, such that the stability limit due to fundamental noise can be reduced to 5 × 10−18.

Hard carbon (HC) was successfully synthesized using a bio-waste precursor from Musa acuminata fiber (MaF) as an eco-friendly option through the pyrolysis process at 500 °C. Further, it was activated using the chemical activating agents, NaOH and ZnCl2, at 900 °C, named Na–MaFDHC and Zn–MaFDHC. The MaFDHCs are employed as anode materials for emerging sodium-ion batteries (NIBs). The nitrogen (N2) adsorption and desorption studies and HRTEM images resulted that the MaFDHCs have a mesoporous nature. The surface area and pore diameter of the carbon materials are increased significantly after the treatment with activating agents, which are important factors for anodes of NIBs. The electrochemical performance of the MaFDHCs depends on the activation agent. Zn–MaFDHC with a higher surface area showed better results, yielding a charge capacity of about 114 mAh g−1 at a 1C rate.

Nanoparticle–polymer hybrids are becoming increasingly important because seemingly contrasting properties, such as mechanical stability and high elasticity, can be combined into one material. In particular, hybrids made of self-assembled polymers are of growing interest since they exhibit high structural precision and diversity and the subsequent reorganization of the nanoparticles is possible. In this work, we show, for the first time, how hybrids of silica nanoparticles and self-assembled vesicles of polystyrene-block-polyacrylic acid can be prepared using the simple and inexpensive method of co-precipitation, highlighting in particular the challenges of using silica instead of other previously well-researched materials, such as gold. The aim was to investigate the influence of the type of modification and the particle size of the silica nanoparticles on the encapsulation and structure of the polymer vesicles. For this purpose, we first needed to adjust the surface properties of the nanoparticles, which we achieved with a two-step modification procedure using APTES and carboxylic acids of different chain lengths. We found that silica nanoparticles modified only with APTES could be successfully encapsulated, while those modified with APTES and decanoic acid resulted in vesicle agglomeration and poor encapsulation due to their strong hydrophobicity. In contrast, no negative effects were observed when different particle sizes (20 nm and 45 nm) were examined.

Future V2X applications rely on the exchange of large sensor data samples and are subject to stringent safety and timing constraints. Due to the lossy nature of the wireless radio channel, data exchange of such larger samples has to be protected by a real-time capable reliability mechanism in order to recover from critical data loss in time. However, state-of-the-art V2X technologies so far are primarily designed for exchanging single packet data, which ignores the challenges of reliable transfer of larger data objects. The recently proposed DDSbased W2RP protocol, addresses such issues. Its effectiveness has been extensively tested and proven in an OMNeT++ simulation environment. In this work we developed a proof-of-concept implementation based on the open-source DDS implementation Fast DDS that can be used to validate the W2RP simulative results in a real-world environment. First experiments showed that the reliable exchange of large samples is possible by using W2RP., Publications Institute of Computer and Network Engineering

Folding wingtips are in the focus of research for their potential to counteract the challenges posed by high aspect ratio wings, such as airport conformity and increased wing root bending moment. Existing concepts for in-flight folding and morphing wingtips either enable passive load alleviation by adding free-flapping aeroelastic hinges to the wingtips or allow for advanced flight control and mission adaptability by actively deflecting the wingtips. In contrast, actuated adaptive wingtips combine the functionalities of passive and active in-flight folding wingtips by using a stiffness-adaptive aeroelastic hinge that is actively adjustable in flight. The objective of this paper is the aeroelastic analysis of a wing equipped with an adaptive-stiffness hinge. While the structural design of the wingtip actuator based on pressure-actuated cellular structures (PACS) was developed in a previous study, in this study the authors verify the concept of actuated adaptive wingtips through aeroelastic analysis. The aeroelastic model consists of a reduced beam structure coupled with the vortex lattice method. In the structural model, the PACS-based adaptive-stiffness hinge is implemented as an equivalent beam element and a pair of counteracting moments. This study shows that the investigated PACS actuator, which is structurally designed from glass-fiber reinforced plastic, is capable of bearing the loads acting on the wingtips of a Cessna Citation X. The adaptive-stiffness hinge, positioned between 86.7% and 91.2% of the semi-span, reduces the wing root bending moment by up to 7.8% in a 2.5 g maneuver load case, while keeping the wing straight in cruise. A further increase in load alleviation potential can be achieved in the future by extending the actuator’s operating envelope and thus increasing its load-bearing capacity so that the actuator can be positioned more inboard. The functional verification of the actuated adaptive wingtip concept by means of aeroelastic analysis forms the basis for the manufacturing and testing of a functional prototype., AIAA SCITECH 2023 Forum, 2023-0825

Polycrystalline diamond compact (PDC) bits with multiple fixed cutters drill through deep formations and are used in oil and gas, geothermal, and mining industry. The bit-rock interaction excites drill string vibrations, which need to be mitigated to improve drilling performance. A velocity-weakening characteristic of the bit torque can cause severe self-excited high-frequency torsional oscillations (HFTO) of the bottom hole assembly (BHA). The dependency on velocity can be attributed to rate-sensitive rock cutting forces at each cutter. The purpose of this paper is to model the rate effect of cutting forces and determine influencing factors in the single-PDC cutting process. In this paper, a modified bonded-particle model (discrete element method, DEM) for rock in deep drilling environments is applied to the pressurized cutting process. Potential modification strategies considering rate indicators at different scales are compared and discussed to reproduce rate dependency in the particle contact model. Two specific models, incorporating cutting-speed-dependent bond strength or grain elastoplasticity, are implemented and verified. The relationship between rate-sensitive cutting forces and the causal rock failure mechanisms is then clarified by interpreting the results from a continuum perspective. Moreover, the influences of axial force and cutter wear state on the rate dependency are investigated. In cutting simulations at a constant depth of cut and various cutting speeds, both models result in rate-dependent cutting forces in good qualitative agreement with rock experiments: Significant hardening is reflected in the axial force component. The modification of contact models combined with a macroscopic rate indicator (i.e. cutting speed) has proven to be a feasible and effective way to reproduce the rate effects in the cutting simulations. In subsequent simulations with constant axial force, the steady-state tangential force decreases as the cutting speed increases, matching the reduction of torque on the bit with increasing RPM. Rate dependency intensifies at higher axial forces or with dull cutters, which agrees with laboratory full-scale bit tests in the literature. This study proposes a practical approach to integrating observed rate effects of downhole rock cutting processes into numerical rock models. The results enhance our understanding of the rock cutting process and have positive implications for the improvement of the cutter design against undesirable rate effects.

Modern composite materials for lightweight designs in aerospace, automotive and mechanical engineering consist of multiple constituents which induce macroscopic properties by means of their microstructure and characteristics. This introduces a multiscale problem of inferring quantities of interest on the macroscale by means of microscopic entities. To this end, computational homogenization algorithms, such as Fast Fourier Transform based methods (FFT), aim toward the calculation of effective material properties from a given microstructure, which can be utilized by numerical methods like the finite element method (FEM) to resolve effects on structural levels. Moreover, these microstructures can be obtained explicitly using μCT-scans. Several problems arise in this context. First, the number of micrographs available in real-world engineering applications is typically limited. Second, the computational effort for numerical homogenization becomes infeasible, as soon as multiple runs are needed, which is the case in e.g., uncertainty quantification. To overcome these difficulties, an end-to-end machine learning framework for multiscale simulations in the context of uncertain continuum micromechanics is presented. Starting with a small number of μCT-scans, a chain of algorithms utilizing machine learning approaches like generative adversarial networks (GAN) and convolutional neural networks (CNN) is used to obtain uncertain homogenized material properties. Here, GANs are trained on the micrographs to obtain synthetic microstructures with the same topological and mechanical properties as the original ones. The GAN can then produce an unlimited amount of unique microstructures, from which a CNN based supervised neural network can be trained. By providing material parameters of the microscopic constituents, strain states and the microstructures as well as the related homogenized properties, the network learns homogenization. The obtained trained neural network can then be used as a very efficient and precise homogenization surrogate. The surrogate is embedded in a pseudospectral polynomial chaos expansion to obtain uncertain homogenized quantities, where even Monte Carlo simulations can be efficiently carried out for a large number of simulations on a single workstation. The framework is very flexible and allows to consider a broad family of multi-phase materials. Additionally it is shown, that artificial neural networks are able to solve micromechanical problems directly without the need of data, using a technique called physics informed neural networks (PINN). Several problems arise in the context of heterogeneous materials with high phase contrasts. Adaptive methods and domain composition are used to overcome this problem. The PINN is able to resolve highly inhomogeneous displacement and stress fields inside a real-world microstructure., Moderne Verbundwerkstoffe für Leichtbaukonstruktionen in der Luft-, und Raumfahrt, dem Automobilbau sowie dem Maschinenbau bestehen aus mehreren Konstituierenden, welche makroskopische Eigenschaften durch ihre Mikrostruktur und Charakteristiken induzieren. Dies führt zu einem Mehrskalenproblem, bei welchem Zielgrößen auf der Makroebene durch Mikrogrößen vorhergesagt werden sollen. Hierzu werden computergestützte Homogenisierungsalgorithmen, wie Fouriertransformationsbasierte Methoden, eingesetzt, welche effektive Eigenschaften der Mikrostruktur berechnen, in numerische Methoden, wie der finiten Elemente Methode, eingebettet, um Struktureffekte abbilden zu können. Die Mikrostrukturen können explizit durch μCT-Scans ermittelt werden. Hierbei treten mehrere Probleme auf. Erstens ist die Anzahl der verfügbaren Mikroabbildungen in Ingenieursanwendungen beschränkt. Zweitens wird der Rechenaufwand unüberwindbar, sobald eine Vielzahl an Evaluationen von Nöten sind, wie es z.B. der Fall ist, wenn Unsicherheiten quantifizert werden sollen. Um diese Problematiken zu überwinden, wird in dieser Arbeit ein End-zu-End Framework auf Grundlage von maschinellem Lernens für die Anwendung in der Kontinuumsmechanik mit Unsicherheiten, präsentiert. Angefangen mit einer kleinen Anzahl von μCT-Scans, wird eine Verkettung von Algorithmen, wie generative neuronale Netze (GAN) und Faltungsnetze (CNN), benutzt, um homogenisierte Eigenschaften unter dem Einfluss von Unsicherheiten zu bestimmen. Hier wird ein GAN auf Mikroabbildungen trainiert, um synthetische Mikrostrukturen mit den gleichen topologischen und mechanischen Eigenschaften der Originale zu erstellen. Danach kann das GAN eine unendliche Anzahl von einzigartigen Mikrostrukturen erstellen, mit deren Hilfe ein CNN überwacht traniert werden kann. Indem sowohl die Materialparameter, die Dehnungszustände und Mikrostrukturen als auch die homogenisierten Eigenschaften benutzt werden, lernt das Netzwerk die Homogenisierung. Das erhaltene, tranierte neuronale Netz kann dann als effizientes und genaues Ersatzmodell für die Homogenisierung verwendet werden. Das Ersatzmodell wird dann in eine pseudospektrale polynominelle Chaosexpanion eingebettet, um unsichere homogenisierte Eigenschaften zu erhalten, wobei sogar eine Vielzahl von Monte Carlo Simulationen effektiv auf einer einzelnen Workstation durchgeführt werden können. Das Framework ist sehr flexibel und auf eine breite Familie an Multiphasenmaterialen anwendbar. Zusätzlich wird gezeigt, dass künstliche neuronale Netze in der Lage sind, mikromechanische Problemstellungen ohne das Vorhandensein von Daten zu lösen, indem die Technik der physikinformierten neuronalen Netze (PINN) angewandt wird. Mehrere Probleme entstehen hierbei im Kontext von heterogenen Materialien mit hohem Phasenkontrast. Adaptive methoden und Domänendekomposition werden angewendet um diese Probleme zu beheben. Das PINN ist dann in der Lage, hochgradig inhomogene Verschiebungs- und Spannungsfelder in realen Mikrostrukturen zu lösen.

In der vorliegenden Arbeit wurde eine Methodik entwickelt, um bestehende und zukünftige Niederspannungsnetze für Deutschland adäquat zu modellieren. Den Referenzrahmen bildet das Jahr 2019, während als Zukunftsszenario das Jahr 2030 gewählt wurde. Es zeichneten sich jeweils drei verschiedene Netzmodelle zur repräsentativen Nachbildung für die nordöstliche und südwestliche Region ab, die sich in die Strukturklassen Land, Übergang und (Vor-)Stadt einteilen lassen. Anhand einer umfangreichen Literaturrecherche zum prognostizierten Technologieaufkommen von Photovoltaik-Anlagen, Heimspeichern, Wärmepumpen und privater Ladeinfrastruktur für Elektrofahrzeuge konnten drei unterschiedlich ambitionierte Technologieentwicklungspfade für das Zieljahr 2030 hergeleitet werden. Zusammen mit der Ableitung technologieabhängiger Durchdringungsraten können die derzeitigen und zukünftigen repräsentativen Niederspannungsnetze für Deutschland modelliert werden. Die Vorstellung der Anlagenmodellierung ermöglicht zudem, die Auswirkungen einer zunehmenden Sektorenkopplung netztechnisch bewerten zu können.

Low-temperature polymer electrolyte fuel cell systems (FCSs) need to reject large amounts of low temperature heat. Often a mobile FCS’s cooling capacity limits the FCS power output. Cryogenic hydrogen is typically utilized as a direct heat sink using heat exchangers (HXs), even though HXs destroy most hydrogen exergy. This paper investigates synergies between FCS thermal management and cryogenic hydrogen exergy utilization in terms of their benchmark performance: the FCS coolant circuit supplies heat at coolant temperature level to a so named reversible cryogenic exergy utilization system (rCEUS) comprised of thermodynamically ideal heat engine processes. The rCEUS converts this heat partly to electrical energy (the value of which equals the hydrogen exergy) and rejects remaining heat to hydrogen to heat it to coolant temperature. The rCEUS output power is used to support the FCS, so the FCS rejects less heat and a significant fraction of this heat is utilized by the rCEUS. As a result, significantly less heat has to be transferred to ambient and the fuel demand decreases. In this paper, three hydrogen storage options are compared: liquid hydrogen, subcooled liquid hydrogen and cryo-compressed hydrogen. Different para- and orthohydrogen compositions are evaluated. For typical FCS operating points, rejected FCS heat to ambient is reducible by 40–67%. FCS power demand is reducible by 14–31%. FCS rejected heat to ambient reduction is 4.5–8 times larger than that of conventional HXs. Calculations are based on hydrogen’s lower heating value.

The pan-European power grid is experiencing an increasing penetration of Variable Renewable Energy (VRE). The fluctuating and non-dispatchable nature of VRE hinders them in providing the Ancillary Service (AS) needed for the reliability and stability of the grid. Therefore, Energy Storage Systems (ESS) are needed along the VRE. Among the different ESS, a particularly viable and reliable option is Pumped Hydro Storage (PHS), given its cost-effective implementation and considerable lifespan, in comparison to other technologies. Traditional PHS plants with Francis turbines operate at a high head difference. However, not all regions have the necessary topology to make these plants cost-effective and efficient. Therefore, the ALPHEUS project will introduce low-head PHS for regions with a relatively flat topography. In this paper, a grid-forming controlled converter coupled with low-head PHS that can contribute to the grid stability is introduced, emphasising its ability to provide different AS, especially frequency control, through the provision of fast Frequency Containment Reserve (fFCR) as well as synthetic system inertia. This paper is an extended version of the paper “The Contribution of Low-head Pumped Hydro Storage to a successful Energy Transition”, which was presented at the 19th Wind Integration Workshop 2020.

In this thesis, the simulation of macroscopic bone tissue is studied in a probabilistic framework, where special emphasis is given to how to model and generate random material tensors that are symmetric and positive definite (SPD). The goal of this thesis is to discuss and propose a novel procedure—known as the fully controlled stochastic material modelling approach—for modelling random second-order SPD material tensors that extends the capability of the existing, random scaling-only, procedure by parametrizing/controlling the directional uncertainty, given that a specific class of material invariance for the entire random ensemble is prescribed. In addition, a scenario of fluctuating material symmetry around the Fréchet mean of random SPD tensors is developed, in which the mean tensor belongs to a higher order of material symmetry, whereas each realisation belongs to a lower order. Another focus of this thesis is on using a variance reduction technique known as the multilevel Monte Carlo method (MLMC) to efficiently assess the impact of material uncertainty on system response by determining statistics like mean and variance. As the convergence of the classical MLMC algorithm strongly depends on the solution magnitude, a novel scale-invariant version of the multilevel Monte Carlo procedure—called the scale-invariant multilevel Monte Carlo method (SMLMC)—is proposed. Finally, a 2D and 3D model of steady-state heat conduction in a human proximal femur is investigated as an example, with a spatially constant random thermal conductivity tensor. Furthermore, the random elastic tensor/matrix field of a 2D linear elastic material model is simulated., In dieser Arbeit wird die Simulation von makroskopischem Knochengewebe in einem probabilistischen Rahmen untersucht, wobei ein besonderer Schwerpunkt auf der Modellierung und Erzeugung von zufälligen Materialtensoren liegt, die symmetrisch und positiv definit sind (SPD). Ziel dieser Arbeit ist es, ein neuartiges Verfahren - bekannt als vollständig kontrollierter stochastischer Materialmodellierungsansatz - für die Modellierung zufälliger SPD- Materialtensoren zweiter Ordnung zu diskutieren und vorzuschlagen, das die Möglichkeiten des bestehenden, nur auf Zufallsskalierung basierenden Verfahrens durch Parametrisierung/Kontrolle der Richtungsunsicherheit erweitert, da eine bestimmte Klasse von Materialinvarianz für das gesamte Zufallsensemble vorgeschrieben ist. Darüber hinaus wird ein Szenario fluktuierender materieller Symmetrie um den Fréchet-Mittelwert zufälliger SPD- Tensoren entwickelt, bei dem der mittlere Tensor zu einer höheren Ordnung der materiellen Symmetrie gehört, während jede Realisation zu einer niedrigeren Ordnung gehört. Ein weiterer Schwerpunkt dieser Arbeit ist die Verwendung einer Varianzreduzierungstechnik, die als Multilevel-Monte-Carlo-Methode (MLMC) bekannt ist, um den Einfluss der Materialunsicherheit auf die Systemreaktion durch die Bestimmung von Statistiken wie Mittelwert und Varianz effizient zu bewerten. Da die Konvergenz des klassischen MLMC-Algorithmus stark von der Lösungsgröße abhängt, wird eine neuartige skaleninvariante Version des Multilevel-Monte-Carlo-Verfahrens - die skaleninvariante Multilevel-Monte- Carlo-Methode (SMLMC) - vorgeschlagen. Schließlich wird als Beispiel ein 2D- und 3D-Modell der station ̈aren Wärmeleitung in einem menschlichen proximalen Oberschenkelknochen mit einem räumlich konstanten zufälligen Wärmeleitfähigkeitstensor untersucht. Darüber hinaus wird das zufällige elastische Tensor/Matrixfeld eines linear- elastischen 2D-Materialmodells simuliert.

Lithium–sulfur batteries (LSBs) that utilize sulfur and lithium (Li) metal as electrode materials are highly attractive for transportation applications due to their high theoretical gravimetric energy density. However, two major challenges currently impede the commercialization of LSB, which are the formation of Li dendrites and polysulfide shuttling. To mitigate these two effects, a protective film or artificial solid–electrolyte interface (SEI) can be applied directly to the Li-metal surface. Herein, the preparation of freestanding polyethylene oxide (PEO)-based films using tape casting as a scalable coating technique is presented. Moreover, the films are applied directly to the Li surface via a solvent-free method. To demonstrate the suitability of the developed PEO-based films, the long-term cycling performance of the lithium–sulfur cells is discussed. It is shown that the cells with the Li-metal surface protected by PEO-based films achieve better stability and reproducibility, reaching ≈400 mA h g S−1 after 250 cycles compared to ≈200 mA h g S−1 after 250 cycles for the bare Li-metal electrode. An extensive postmortem analysis of the Li-metal electrode surface with scanning electron microscopy is additionally shown, revealing that the PEO-based artificial SEIs form uniformly with a low level of defect layers at the interface with the Li-metal electrode, which indicates the creation of a stable SEI.

Wind shear at low altitudes represents a potential hazard to landing aircraft. Based on two wind lidar data sets of one year, the occurrence of low-level jets (LLJs), the vertical wind shear and the rotation of the wind direction were analysed. The lidar system was located at the sites of Braunschweig in the North German Plain, Germany, and Clausthal-Zellerfeld in the low mountain range Harz, Germany. The observed wind shear gradients between the altitude of 40 m and the altitude of the maximum wind speed was in the range of −0.23 s−1 to +0.20 s−1. The rotation of the wind direction with altitude occurred both in clockwise and anticlockwise direction. The ratio of clockwise versus anticlockwise occurrence of directional shear was 4:1 for Braunschweig and 3:1 for Clausthal-Zellerfeld. The observed wind shear gradients were compared to values for hazard potential of different levels for a typical aircraft. Although the LLJ was not hazardous for manned aircraft in any observed case, the awareness of LLJ helps to reduce the pilot’s workload and possible pilot-introduced oscillations caused as a result of the wind shear and aircraft characteristics. In contrast to manned aviation, the value of changes in wind speed and direction during LLJ conditions can cause significant risks for unmanned aerial system operations with less than 25 kg of take-off weight. This is a result of the lower airspeed-wind-speed ratio and the flight control and flight planning.

The objective of the contribution is to understand the fatigue bond behaviour of brass-coated high-strength micro steel fibres embedded in ultra-high performance concrete (UHPC). The study contains experimental pullout tests with variating parameters like load amplitude, fibre orientation, and fibre-embedded length. The test results show that fibres are generally pulled out of the concrete under monotonic loading and rupture partly under cyclic tensile loading. The maximum tensile stress per fibre is approximately 1176 N/mm2, which is approximately one third of the fibre tensile strength (3576 N/mm2). The load-displacement curves under monotonic loading were transformed into a bond stress-slip relationship, which includes the effect of fibre orientation. The highest bond stress occurs for an orientation of 30° by approximately 10 N/mm2. Under cyclic loading, no rupture occurs for fibres with an orientation of 90° within 100,000 load changes. Established S/N-curves of 30°- and 45°-inclined fibres do not show fatigue resistance of more than 1,000,000 load cycles for each tested load amplitude. For the simulation of fibre pullout tests with three-dimensional FEM, a model was developed that describes the local debonding between micro steel fibre and the UHPC-matrix and captures the elastic and inelastic stress-deformation behaviour of the interface using plasticity theory and a damage formulation. The model for the bond zone includes transverse pressure-independent composite mechanisms, such as adhesion and micro-interlocking and transverse pressure-induced static and sliding friction. This allows one to represent the interaction of the coupled structures with the bond zone. The progressive cracking in the contact zone and associated effects on the fibre load-bearing capacity are the decisive factors concerning the failure of the bond zone. With the developed model, it is possible to make detailed statements regarding the stress-deformation state along the fibre length. The fatigue process of the fibre-matrix bond with respect to cyclic loading is presented and analysed in the paper.

Die Hochwasser- oder Flutereignisse aufgrund von Starkregen im Juli 2021 haben in Deutschland und angrenzenden Ländern ein bis dato nicht bekanntes Ausmaß an Todesopfern und Verlusten hinterlassen. Es ist wichtig aus solchen Ereignissen zu lernen, um künftig besser auf solche Situationen vorbereitet zu sein. Dieser Sammelband beinhaltet Erfahrungsberichte und Betrachtungen von Studierenden und Mitarbeiter:innen des Instituts für Rettungsingenieurwesen und Gefahrenabwehr (IRG), der TH Köln, sowie weiteren Personen, die im Bereich Gefahrenabwehr, Bevölkerungs- Katastrophen-, Zivilschutz tätig sind, oder sich mit Themen wie Naturgefahren und Katastrophenrisikomanagement befassen. Viele Studierende sind gleichzeitig in Organisationen der Feuerwehr, des Rettungsdiensts oder anderer Hilfsorganisationen neben dem Studium tätig, wie auch viele Alumni des IRG. Aber auch jene, die nicht operativ tätig sind, haben wichtige Beobachtungen durch Kontakte oder sogar eigene Schäden machen können. In einem ersten Austausch unter Studierenden des IRG Anfang August 2021 wurde festgestellt, wie wertvoll ein neutraler Austausch ist, und eine Offenlegung von Erfahrungen, Kritik und Lösungsideen, ohne Personen oder einzelne Organisationen allein dabei zu kritisieren. Da es mitunter an solchen Austauschmöglichkeiten zwischen den Organisationen der Gefahrenabwehr fehlt, soll dieser Sammelband eine solche Möglichkeit bieten. Um der Bandbreite an unterschiedlichen Hintergründen gerecht zu werden und vor allem im Sinne der Sache, um möglichst viele auch verschiedene Erfahrungen und Perspektiven zu sammeln, oder diese zu bestätigen, finden sich in diesem Sammelband Beiträge unterschiedlicher Länge und Sprache. Eine offene Bewertung auch aus unterschiedlichen Sichtweisen ist sehr wertvoll, um ein ganzheitlicheres Bild der ganzen Lage zu erhalten. Zum damaligen Zeitpunkt in den ersten Monaten nach dem Hochwasser beherrschten Themen wie Koordination der Einsatzkräfte, Verfügbarkeit und Ausfall technischer Ausrüstung aber auch Verpflegung, kritische Infrastruktur, Alarmierung und Warnung den Austausch. Inhaltlich ist dieser Sammelband ebenfalls bewusst nicht eingegrenzt, damit eine große Bandbreite an Aspekten dokumentiert werden kann. Aufgrund der inhaltlichen Auslegung der Lehre und Forschung am IRG werden bestimmte Themenbereiche wie etwa Einsatzorganisationen, Stabsarbeit, Frühwarnung, kritische Infrastruktur, verwundbare Personengruppen etc. häufiger behandelt als andere Themen. Es werden auch Beiträge aus laufenden Forschungsprojekten u.a. zu kritischer Infrastruktur, Notwasserversorgung, Integration von Einsatzkräften eingebunden. Die Ergebnisse einer Umfrage zur Zufriedenheit der Einsatzkräfte werden dargestellt und diskutiert. Für alle diese Themen dient jedoch hauptsächlich die Grundidee eine Klammer; was kann man im relativ neutralen Rahmen einer Hochschule äußern, und der Gesellschaft durch solch eine Dokumentation an die Hand geben, um die Erfahrungen zu dokumentieren und eine Diskussion anzuregen, was man daraus lernen könnte. Eine Hochschule kann nur einen Rahmen z.B. für Ideen, Wissenstransfer oder Technologien bieten. Aber alle, die daran mitarbeiten, als Studierende, Mitarbeiter:innen oder kooperierende Partner:innen, sind gleichzeitig Teil der Gesellschaft, die sich nicht alltäglich mit Krisen und Katastrophen dieses Ausmaßes befassen muss. Laut einer Definition von Katastrophen zeichnen sich diese durch ihren Überraschungseffekt, oder durch die Über-wältigung der Fähigkeiten Einzelner oder ganzer Gemeinden aus. Es gibt wenige, die sich damit langfristig planerisch befassen, weil solche Ereignisse zum Glück relativ selten lokal vorkommen. Oft steht man vor einem Rechtfertigungsproblem, weil in unserer Hochleistungsgesellschaft im Alltag wie auch in Katastrophen alles perfekt funktionieren soll. Aber es gibt den Spruch „There is no glory in prevention“ auch deswegen, weil tägliche Unfälle und Beinahestörfälle nahezu unbemerkt von ehrenamtlichen sowie hauptberuflichen Einsatzkräften bewältigt werden. Hier hat leider wieder eine Flutkatastrophe gezeigt, wo die Grenzen der Vorbereitung und in der Bewältigung liegen. Für den Wiederaufbau und das Lernen für die Vorbereitung auf andere Ereignisse und Katastrophen ist es daher wichtig, Lehren zu ziehen, diese zu dokumentieren und der Öffentlichkeit zur Verfügung zu stellen., Integrative Risk and Security Research; 1/2022

In this thesis, a novel approach is developed for visco-plasticity and nonlinear dynamics problems. In particular, variational equations are elaborated following the Helligner-Reissner principle, so that both stress and displacement fields appear as unknown fields in the weak form. Three novel finite elements are developed. The first finite element is formulated for the axisymmetric problem, in which the stress field is approximated by low-order polynomials such as linear functions. This approach yields accurate solutions specifically in incompressible and stiff problems. In addition, a membrane and plate bending finite element are newly designed by discretizing the stress field using the lowest order Raviart-Thomas vector space RT0 This approach guarantees the continuity of the stress field over an entire discrete domain, which is a significant advantage in the numerical method, especially for the wave propagation problems. The developments are carried out for the viscoplastic constitutive behavior of materials, where the corresponding evolution equations are obtained by appealing to the principle of maximum dissipation. To solve the dynamic equilibrium equations, energy conserving and decaying schemes are formulated correspondingly. The energy conserving scheme is unconditional stable, since it can preserve the total energy of a given system under a free vibration, while the decaying scheme can dissipate higher frequency vibration modes. The last part of this thesis presents procedures for upscaling of the visco-plastic material behavior. Specifically, the upscaling is performed by stochastic identification method via Baysian updating using the Gauss-Markov-Kalman filter for assimilation of important material properties in the elastic and inelastic regimes., In dieser Arbeit wird ein neuartiger Ansatz für Viskoplastizitäts- und nichtlineare Dynamikprobleme entwickelt. Insbesondere werden Variationsgleichungen nach dem Helligner-Reissner-Prinzip aufgestellt, so dass sowohl Spannungs- als auch Verschiebungsfelder als unbekannte Felder in schwacher Form erscheinen. Drei neuartige finite Elemente werden entwickelt. Das erste finite Element wird für das axialsymmetrische Problem formuliert, bei dem das Spannungsfeld durch Polynome niedriger Ordnung wie lineare Funktionen angenähert wird. Dieser Ansatz liefert genaue Lösungen speziell bei inkompressiblen und steifen Problemen. Darüber hinaus wird ein finites Element mit Membran- und Plattenbiegung neu entworfen, indem das Spannungsfeld unter Verwendung des Raviart-Thomas-Vektorraums RT0 niedrigster Ordnung diskretisiert wird. Dieser Ansatz garantiert die Kontinuität des Spannungsfeldes über eine gesamte diskrete Domäne, was insbesondere bei Wellenausbreitungsproblemen ein wesentlicher Vorteil der numerischen Methode ist. Die Entwicklungen erfolgen für das viskos-plastische Materialverhalten, wobei die entsprechenden Evolutionsgleichungen unter Berufung auf das Prinzip der maximalen Dissipation erhalten werden. Um die dynamischen Gleichgewichtsgleichungen zu lösen, werden entsprechende Energieerhaltungs- und -zerfallsschemata formuliert. Das energieerhaltende Schema ist bedingungslos stabil, da es die Gesamtenergie eines gegebenen Systems unter einer freien Schwingung erhalten kann, während das abklingende Schema höherfrequente Schwingungsmoden zerstreuen kann. Im letzten Teil dieser Arbeit werden Verfahren zum Upscaling des viskoplastischen Materialverhaltens vorgestellt. Konkret erfolgt die Hochskalierung durch stochastische Identifikationsverfahren mittels des Baysian Update unter Verwendung des Gauss-Markov-Kalman-Filters zur Assimilation wichtiger Materialeigenschaften im elastischen und inelastischen Bereich.

Hybridlaminate aus faserverstärktem Kunststoff (FVK) und Metall bieten aufgrund der unterschiedlichen Steifigkeiten der Werkstoffe, in Kombination mit dem lageweisen Aufbau eines Laminats ein großes Potential für die Variation der Federsteifigkeit von Blattfedern. Die Herausforderung bei der Entwicklung einer Blattfeder, basierend auf einem Hybridlaminat, liegt in der Vorauslegung des variierenden Lagenaufbaus aus FVK und Metall. Das Ziel dieser Arbeit ist die Entwicklung eines empirischen Prognosemodells zur gezielten Variation der Federsteifigkeit von Hybridlaminaten durch den Lagenaufbau. Der Lösungsweg zu diesem Ziel zeigt die systematische Herleitung des empirischen Prognosemodells auf. Für die Herleitung dieses Prognosemodells werden die signifikanten Einflussparameter und Wechselwirkungseffekte zwischen dem Lagenaufbau und den fertigungsbedingten Einflussgrößen aus dem Herstellungsverfahren bestimmt. Weitere Teilschritte zur Zielerreichung dieser Arbeit behandeln die Ausarbeitung einer angepassten Fertigungsstrategie zur Herstellung von Hybridlaminaten im Vakuuminfusionsverfahren und die Reduzierung des Versuchsumfangs für die Ermittlung der Messdaten für das empirische Prognosemodell. Im letzten Schritt wird die Validierung des Prognosemodells an einem praxisnahen Fallbeispiel durchgeführt. Für die Validierung werden numerische Modelle auf Grundlage eines dreidimensionalen Modellierungsansatzes aufgebaut und hinsichtlich ihrer Prognosegüte mit dem empirischen Prognosemodell verglichen. Die Ergebnisse dieser Arbeit zeigen die erfolgreiche Prognose der Federsteifigkeit von hybriden Blattfedern durch das empirische Modell. Die resultierenden Abweichungen zwischen der prognostizierten und der gemessenen Federsteifigkeit der Hybridlaminate liegt dabei unter 10 %. Weiterhin ist ein neues methodisches Vorgehen zur Kodierung von Versuchsplänen für Hybridlaminate aufgezeigt und eine neue Methode zur Reduzierung des Versuchsumfangs um 65 % erarbeitet worden., Hybrid laminates consisting of fibre-reinforced plastic (FRP) and metal have a great potential for varying the spring stiffness of leaf springs due to the different stiffnesses of materials in combination with the layer structure of a laminate. The main challenge in the development of a leaf spring based on a hybrid laminate is to anticipate the varying layer structure of FRP and metal. The aim of this work is the development of an empirical prognosis model for a specific variation of the spring stiffness of hybrid laminates through the layer structure. The approach is to achieve this goal by systematically deriving an empirical prognosis model. For the derivation of this prognosis model, the significant influencing parameters and interaction effects between the layer structure and the production-related influencing factors from the manufacturing process are determined. Further steps to achieve the objective of this work include the development of an adapted manufacturing strategy for the production of hybrid laminates in the vacuum infusion process and the reduction of the scope of experiments for the determination of the measurement data used in the prognosis model. In a final step, the validation of the prognosis model is carried out by means of a practical case study. For the validation, numerical models are built based on a three-dimensional modelling approach and compared with the empirical prognosis model with regard to their prognosis quality. The results of this work show the successful prognosis of the spring stiffness of hybrid leaf springs by the empirical model. The resulting deviations between the predicted and the measured spring stiffness of the hybrid laminates are less than 10 %. Furthermore, a new methodical procedure for the coding of experimental designs of hybrid laminates has been demonstrated and a new method for reducing the scope of experiments by 65 % has been developed., Schriftenreihe des Instituts für Werkzeugmaschinen und Fertigungstechnik, vol. 2022

To cope with the exponential increase in internet services and corresponding data traffic, especially data centers and access networks require new high data rate transmission methods with low cost, very small package and low energy consumption. In this paper, we demonstrate a filterless, agnostic Nyquist wavelength division multiplexing (ANy-WDM) transmission system based on cascaded ring modulators and a comb source. The single ring modulator acts as a filter, filtering one of the n WDM lines, generated by the comb. The same ring modulator modulates k time division multiplexed (TDM) channels on the single wavelength. Since each WDM channel, consisting of k time domain channels, has a rectangular bandwidth, the aggregated symbol rate of the superchannel modulated by this system corresponds to the optical bandwidth of all n WDM channels together. The approach is very simple and compact. Since no optical filters, delay lines or other special photonics or high bandwidth electronics is needed, an integration into any photonics platform is straightforward. Thus, the proposed method might enable very compact, ultra-high data rate transmission devices for future data centers and access networks.

The air-management system of a proton exchange membrane fuel cell (PEMFC) is responsible for supplying the fuel cell stack with ambient air at appropriate conditions. The compressor of the air-management system can be partly driven by utilizing the fuel cell exhaust gas in a turbine. The fuel cell exhaust is partially or fully saturated with water vapor. When the exhaust gas is expanded in the turbine, supersaturation occurs. This leads to the nucleation of droplets and their subsequent growth by condensation. This study provides an overview and understanding of the various phenomena caused by condensation and liquid water in the turbine of a PEMFC air-management system. The basis for this work is previously published numerical simulations that focused on individual aspects of the above phenomena. The present work revisits these results and puts them in context to provide a comprehensive understanding. Important phenomena are the effects of condensation on turbine performance through phase change losses, release of latent heat and thermal throttling. In addition, the released latent heat offers a power potential for downstream turbine stages. Through these effects, condensation can also impact the entire air-management system. However, condensation may occur unevenly, causing a circumferential asymmetry of the turbine outflow. Liquid water in the turbine can lead to droplet erosion, corrosion, and water-induced damage. In summary, it is essential to consider condensation and liquid water when developing turbines for PEMFC air-management systems.

Recently, the use of prismatic cells in electric vehicles has increased significantly. Unlike the cylindrical or pouch format, the prismatic cell format has not been sufficiently investigated. In this study, quasi-static mechanical tests are performed on prismatic cells. The tests include a cylindrical and a hemispherical impactor that mechanically load the cells in all three spatial directions. In both in-plane directions, a cell stack consisting of three cells is tested to capture the influence and loading of the outer cells of a cell stack. It is found out that, in the in-plane tests, short-circuiting occurs first in the outer cells and subsequently in the middle cell, which is targeted by the impactor. This result can also be supported by computed tomography scans. The results illustrate that, when evaluating the crash safety of battery cells, several cells should always be tested in order to capture the different loading of the cells.