Die Eisverhältnisse im Kaiser Wilhelm-Kanal

Vita.Inaug.-diss.--Kiel.Mode of access: Internet

Reactions with pions and vector mesons in the sector of odd intrinsic parity

The Wess-Zumino-Witten structure is supplemented by a simple vector-meson Lagrangian where the vector mesons are described by antisymmetric tensor fields. With the \rho-\omega-\pi{} coupling as the only parameter in the sector of odd intrinsic parity, i.e. without additional contact terms, one can achieve a proper description of the decay of an \omega-meson into three pions, the single- and double-virtual pion transition form factor and the three-pion production in electron-positron collisions

Analysis of irradiation processes for laser-induced periodic surface structures

The influence of errors on the irradiation process for laser-induced periodic surface structures (LIPSS) was studied theoretically with energy density simulations. Therefore an irradiation model has been extended by a selection of technical variations. The influence of errors has been found in a deviation from optimal conditions, by a shift or spread of accumulated fluence and a variation of local fluence, related to variations of the peak fluence and relative pulse intersection. The analysis of the irradiation process by energy density simulations, gives the possibility to perform realistic irradiation simulations and derive optimization strategies for the determination of irradiation parameters. This analysis is required for the application of LIPSS for surface functionalization. © 2013 The Authors

Influence of measurement uncertainty on machine learning results demonstrated for a smart gas sensor

Humans spend most of their lives indoors, so indoor air quality (IAQ) plays a key role in human health. Thus, human health is seriously threatened by indoor air pollution, which leads to 3.8 × 106 deaths annually, according to the World Health Organization (WHO). With the ongoing improvement in life quality, IAQ monitoring has become an important concern for researchers. However, in machine learning (ML), measurement uncertainty, which is critical in hazardous gas detection, is usually only estimated using cross-validation and is not directly addressed, and this will be the main focus of this paper. Gas concentration can be determined by using gas sensors in temperature-cycled operation (TCO) and ML on the measured logarithmic resistance of the sensor. This contribution focuses on formaldehyde as one of the most relevant carcinogenic gases indoors and on the sum of volatile organic compounds (VOCs), i.e., acetone, ethanol, formaldehyde, and toluene, measured in the data set as an indicator for IAQ. As gas concentrations are continuous quantities, regression must be used. Thus, a previously published uncertainty-aware automated ML toolbox (UA-AMLT) for classification is extended for regression by introducing an uncertainty-aware partial least squares regression (PLSR) algorithm. The uncertainty propagation of the UA-AMLT is based on the principles described in the Guide to the Expression of Uncertainty in Measurement (GUM) and its supplements. Two different use cases are considered for investigating the influence on ML results in this contribution, namely model training with raw data and with data that are manipulated by adding artificially generated white Gaussian or uniform noise to simulate increased data uncertainty, respectively. One of the benefits of this approach is to obtain a better understanding of where the overall system should be improved. This can be achieved by either improving the trained ML model or using a sensor with higher precision. Finally, an increase in robustness against random noise by training a model with noisy data is demonstrated

Ermüdungsbewertung sehr großer Schraubenverbindungen für Tragstrukturen von Windenergieanlagen

High-strength ‘System HV’ bolting assemblies with large bolt diameters of M36 and bigger are frequently used in ring-flange connections in steel support structures for on- and offshore wind turbines. At the bottom parts of the supporting steel towers the magnitude of the acting loads usually requires the application of very large bolt diameters M64 or M72. The bolts are subjected to high cyclic loads with considerable numbers of load cycles and variable amplitudes. Thus, for reduction of fatigue loads, preloading of bolts with high forces is mandatory. Reliable protection against corrosion is commonly achieved by hot-dip galvanizing. It is known that the zinc coating has an impact on the fatigue strength of structural steel components. Moreover, the high mean stress level affects the bolts’ fatigue behaviour and thus needs to be appropriately considered in experimental as well as analytical fatigue analyses. Fatigue testing of HV-bolts with large diameters under a representative mean stress level imposes challenges to the required testing equipment. Hence, S-N curves in applicable design standards, in particular EN 1993-1-9, are mostly validated on tests with smaller bolts and the influence of an increased diameter is yet to be verified. Moreover, the quantitative effect of hot-dip galvanizing on the fatigue strength of large-size HV-bolts is still under investigation. Analytical fatigue assessment procedures provide valuable potentials to supplement expensive experimental test series and to discretely investigate specific impact factors with relevance to the fatigue strength. However, to this end suitable assessment methodologies need to be adapted and validated for the application to HV-bolts with large diameters as well as for an appropriate consideration of the effect of hot-dip galvanizing. This dissertation presents comprehensive research work on the experimental and analytical fatigue assessment of large-size HV-bolts. The performed fatigue tests extend the range of the experimental validation of normative regulations to a bolt diameter of M64, representative for the upper end of bolt sizes applied in today’s modern wind turbine support structures. Thereby, the safe applicability of the relevant fatigue class FAT 50 of the Eurocode 3 is confirmed. The comparison of performed tests on hot-dip galvanized bolts of diameters M36 and M64, as well as further analytical analyses, indicate a minor impact of the bolt size in the considered large diameter range. The corresponding reduction function of the Eurocode 3 thus tends to overestimate the diameter related effect. Moreover, the results of tests with variable amplitude loading suggest a rather conservative hypothesis of damage accumulation, considered in the Eurocode. Regarding the discrepancy of fatigue strength between uncoated and hot-dip galvanized HV-bolts ambiguous results are obtained for bolt sizes M36 and M64. Thus, the results put into question a superior fatigue classification of uncoated, black large-size HV-bolts, as for instance suggested in the VDI Guideline 2230. The systematically elaborated analytical fatigue assessment methodology, specifically refined for the application to large size HV-bolts, yields calculations in good agreement with experimental results for different bolt sizes and loading conditions. Thereby, an introduced engineering model also enables the calculation of the fatigue life for hot-dip galvanized bolts.Hochfeste Schraubengarnituren des Systems HV mit Durchmessern M36 und größer kommen bevorzugt in Ringflanschverbindungen von Tragstrukturen von Windenergieanlagen zum Einsatz. Insbesondere an unteren Turmsektionen wird bedingt durch die auftretenden Belastungen häufig die Verwendung sehr großer Durchmesser M64 oder M72 erforderlich. Die HV-Schrauben sind hohen zyklischen Lasten mit variablen Amplituden ausgesetzt. Zur Begrenzung von Ermüdungsbeanspruchung werden die Schrauben daher auf hohe Vorspannungsniveaus angezogen. Ein zuverlässiger Schutz gegen Korrosion wird in der Regel durch Feuerverzinken sichergestellt. Es ist bekannt, dass die dabei thermisch hergestellte Zinkoberfläche die zyklische Beanspruchbarkeit stählerner Bauteile beeinträchtigt. Zudem hat auch das durch die Vorspannung erzeugte hohe Mittelspannungsniveau einen Einfluss auf die Ermüdungseigenschaften der Schrauben. Die Durchführung von Ermüdungsversuchen an großen HV-Garnituren, insbesondere unter repräsentativer Mittelspannung, ist mit hohen Anforderungen an die verwendete Prüfeinrichtung verbunden. Bemessungswöhlerlinien normativer Regelwerke, mit besonderer praktischer Relevanz der EN 1993-1-9, sind aus diesem Grund nur begrenzt für große Schraubendurchmesser validiert. Zudem ist der quantitative Einfluss der Feuerverzinkung auf die Ermüdungsfestigkeit hochfester großer Schrauben bislang nicht abschließend untersucht. Ergänzend zu kostspieligen Ermüdungsversuchen können mit analytischen Methoden spezifische ermüdungsrelevante Einflussfaktoren isoliert bewertet werden. Allerdings sind hierzu geeignete Verfahren noch für die Anwendung auf große HV-Garnituren anzupassen und zu validieren. Außerdem bedarf es einer geeigneten Möglichkeit zur Berücksichtigung des Einflusses der Feuerverzinkung. Diese Dissertation beinhaltet umfangreiche, systematische Untersuchungen zum Ermüdungsverhalten großer HV-Schraubengarnituren mit experimentellen und analytischen Methoden. Die durchgeführten Ermüdungsversuche erweitern die experimentelle Validierung normativer Regelwerke erstmalig bis zum Nenndurchmesser M64. Die Anwendbarkeit des relevanten Kerbfalls 50 aus dem Eurocode 3 kann dabei bestätigt werden. Der Vergleich der erzielten Versuchsergebnisse an feuerverzinkten HV-Garnituren mit Durchmessern M36 und M64 sowie weiterführende analytische Untersuchungen zeigen für diese Schraubengrößen einen geringen Einfluss des Durchmessers. Die im Eurocode 3 berücksichtigte durchmesserabhängige Reduzierung führt darum tendenziell zu einer Unterschätzung der Ermüdungsfestigkeit. Versuche mit variablen Amplituden deuten darüber hinaus darauf hin, dass die verwendete Hypothese zur Schädigungsakkumulation zu einer konservativen Bemessung führt. Bezüglich des Unterschieds der Ermüdungsfestigkeit bei unbeschichteten und feuerverzinkten Garnituren weisen die Versuche an M36 und M64 Schrauben uneinheitliche Ergebnisse auf, was eine mögliche Besserstellung schwarzer Schrauben in Frage stellt. Das für die Anwendung auf große HV-Schrauben weiterentwickelte analytische Bewertungsverfahren der Ermüdungsfestigkeit liefert Ergebnisse in guter Näherung mit Versuchen unterschiedlicher Durchmesser und Lastverhältnisse. Ein vorgeschlagenes Ingenieurmodell ermöglicht dabei ebenfalls die Ermüdungsberechnung feuerverzinkter Schrauben

Towards Friction Control using laser-induced periodic Surface Structures

This paper aims at contributing to the study of laser-induced periodic surface structures (LIPSS) and the description of their tribological properties in order to facilitate the knowledge for contact mechanical applications. To obtain laser parameters for LIPSS formation, we propose to execute two D2-Experiments. For the transfer of results from static experiments to areas of LIPSS we propose the discrete accumulation of fluences. Areas covered by homogeneously distributed LIPSS were machined. Friction force of these areas was measured using a tribometer in a ball on flat configuration. The friction force was found to be higher on the structured area than on the initial surface

Efficient vectorised Cuda kernels for high-order finite element flow solvers

In this work, we develop efficient kernels for elemental operators of matrix-free solvers of the Helmholtz equation, which are the core operations for more complete Navier-Stokes solvers. We consider straight-sided and deformed quadrilateral elements from unstructured high-order meshes. We investigate two types of efficient CUDA kernels for a range of polynomial orders; a first type which maps each elemental operation to a CUDA-thread, and a second that maps each element to a CUDA-block. Our results show that the first option is beneficial for small elements with low polynomial order, whereas the second option is beneficial for larger elements. For both options we show the importance of the right layout of data structures, and analyse the effect of utilising different memory spaces on the GPU

Erratiska basaltblock ur N. Tysklands och Danmarks diluvium

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Dynamic Uncertainty for Compensated Second-Order Systems

The compensation of LTI systems and the evaluation of the according uncertainty is of growing interest in metrology. Uncertainty evaluation in metrology ought to follow specific guidelines, and recently two corresponding uncertainty evaluation schemes have been proposed for FIR and IIR filtering. We employ these schemes to compare an FIR and an IIR approach for compensating a second-order LTI system which has relevance in metrology. Our results suggest that the FIR approach is superior in the sense that it yields significantly smaller uncertainties when real-time evaluation of uncertainties is desired