Multi-Objective structural optimization of repairs of blisk blades

Modern manufacturing technologies offer multiple options to extend the service life of expensive jet engine components through repairs. In this context, the repair processes of blade-integrated disks (blisks) are of particular interest, as the complex design makes replacement of this part very costly. However, currently, repairs of blisks are mainly done manually and repair design decisions still rely on the expertise of maintenance technicians. From a scientific perspective, these subjective, experience-based decisions are a major drawback, as today’s computational methods allow for systematic analysis and evaluation of design alternatives. The present doctoral thesis contributes to the decision-making process related to the repair of blisk blades by blending and patching by providing an engineering optimization framework and simulation routines for structural assessment of different repair designs. First, an object-oriented optimization framework is developed that is ideally suited to address engineering optimization problems such as blisk repair optimization. The design of the software architecture is chosen to achieve a high degree of flexibility and modularity. In particular, the framework provides a unified interface for global and local derivative-free optimization algorithms and custom engineering optimization problems. Thereby, optimization of single- as well as multi-objective problems is supported. The broad applicability of the framework in engineering optimization is demonstrated using examples from wind energy research. Furthermore, the optimization framework forms a suitable environment for structural multi-objective optimization of blend and patch repairs. The second part of this thesis is devoted to the application of the optimization framework to blend repairs of a compressor blisk. The geometry of the removed blade part and the resulting blend is parameterized by three geometric design variables. The two objectives of the optimization correspond to two modal criteria, because especially the vibration behavior of blades is affected by this kind of geometric modification. To check if frequency requirements are harmed by the repair the first objective reflects the deviation of the natural frequencies of the repaired blade to the natural frequencies of the nominal blade. The second objective considers resonance conditions by evaluating the proximity of natural frequencies to excitation frequencies. Pareto optimal repair designs are found by solving the derived optimization problem using appropriate structural mechanics models of a blade sector and employing the developed optimization framework. By analyzing the optimal blend shapes for two different damage patterns, it is shown that the characteristics of Pareto frontiers, like the occurrence of discontinuities, are damage-specific. Therefore, it is concluded that design decisions on blend repairs have to be made on a case-by-case basis. The third part of this thesis is concerned with the multi-objective optimization of patch repairs. While blend repairs change the blade geometry, patch repairs restore the original blade contour. In terms of structural integrity, the most significant modification due to patching is hence associated with the welding process to join patch and blade. The remaining residual stresses, affect the strength of the repaired blade, are therefore the most critical aspect of patch repairs. Utilizing the engineering optimization framework and the parametric simulation model, a multi-objective optimization problem is solved considering the length of the weld and the fatigue strength of the repaired blade. In addition to fatigue strength properties, the weld length is selected as an optimization goal, since the manufacturing effort of the high-tech repair is of practical importance. Pareto optimal repair designs are presented for a damage pattern at the leading edge. The optimization results are further complemented by subsequent thermal and mechanical simulations of the welding and heat treatment process. Different patch geometries are classified from the Pareto optimal solutions. Depending on the preferences in terms of weld length and the High-Cycle Fatigue strength of different load cases, short or long patches are to be used. In addition, the results show that some potential patch designs are not optimal in any case, and therefore can be completely excluded. Finally, the benefits of the unified interface of the engineering optimization framework are emphasized. Different optimization settings of a patch repair optimization are presented and compared utilizing the hypervolume metric. Concluding remarks on the potential of computational methods for improved repair design and an outlook on future maintenance of blisks complete this work.DFG/SFB 871/119 193 472./E

Inclusion of tetramethylpyrazine in channels of the organic zeolite 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine

2,4,6-tris(4-bromophenoxy)-1,3,5-triazine (BrPOT) features a channel size (11-12Å) allowing the inclusion of large guest molecules such as tetramethylpyrazine (TMPZ). TMPZ forms π-stacks (d: 3.5Å) along channels of BrPOT and shows rotational disorder for methyl positions. Co-inclusions of I2 resulted in a doped state where I2 molecules are oriented perpendicular to the channel axis with positional disorder as well. The particular orientation of I2 molecules is evident from the observed dichrois

How to prevent technostress at the digital workplace: a Delphi study

Technostress is a rising issue in the changing world of digital work. Technostress can cause severe adverse outcomes for individuals and organizations. Thus, organizations face the moral, legal, and economic responsibility to prevent employees’ excessive technostress. As technostress develops over time, it is crucial to prevent it throughout the process of its emergence instead of only reacting after adverse outcomes occur. Contextualizing the Theory of Preventive Stress management to technostress, we synthesize and advance existing knowledge on inhibiting technostress. We develop a set of 24 technostress prevention measures from technostress inhibitor literature, other technostress literature, and based on qualitative and quantitative contributions from a Delphi study. Based on expert feedback, we characterize each measure and, where possible, assess its relevance in addressing specific technostressors. Our paper contributes to research by transferring the Theory of Preventive Stress Management into the context of technostress and presenting specific measures to prevent technostress. This offers a complementary view to technostress inhibitors by expanding the theoretical grounding and adding a time perspective through the implementation of primary, secondary, and tertiary prevention measures. For practice, we offer a comprehensive and applicable overview of measures organizations can implement to prevent technostress

DNA binds to a specific site of the adhesive blood-protein von Willebrand factor guided by electrostatic interactions.

Neutrophils release their intracellular content, DNA included, into the bloodstream to form neutrophil extracellular traps (NETs) that confine and kill circulating pathogens. The mechanosensitive adhesive blood protein, von Willebrand Factor (vWF), interacts with the extracellular DNA of NETs to potentially immobilize them during inflammatory and coagulatory conditions. Here, we elucidate the previously unknown molecular mechanism governing the DNA-vWF interaction by integrating atomistic, coarse-grained, and Brownian dynamics simulations, with thermophoresis, gel electrophoresis, fluorescence correlation spectroscopy (FCS), and microfluidic experiments. We demonstrate that, independently of its nucleotide sequence, double-stranded DNA binds to a specific helix of the vWF A1 domain, via three arginines. This interaction is attenuated by increasing the ionic strength. Our FCS and microfluidic measurements also highlight the key role shear-stress has in enabling this interaction. Our simulations attribute the previously-observed platelet-recruitment reduction and heparin-size modulation, upon establishment of DNA-vWF interactions, to indirect steric hindrance and partial overlap of the binding sites, respectively. Overall, we suggest electrostatics-guiding DNA to a specific protein binding site-as the main driving force defining DNA-vWF recognition. The molecular picture of a key shear-mediated DNA-protein interaction is provided here and it constitutes the basis for understanding NETs-mediated immune and hemostatic responses

Evaluation des Nightingale Projekts anhand der von den MentorInnen verfassten Monatsberichte des Jahrgangs 2016/17

In der vorliegenden Arbeit geht es um die Evaluation eines Mentoringprogrammes, welches Kinder mit Migrationshintergrund fördern soll. Mentoring ist ein Konzept, bei dem eine erfahrene Person (Mentor/in) eine weniger erfahrene Person (Mentee) unterstützt und in ihrer Entwicklung begleitet. Zur Evaluation des Nightingale Projekts wurden die monatlichen Berichte der Mentor/innen herangezogen und mithilfe eines Kategoriensystems analysiert, welches mit der Methode der qualitativen Inhaltsanalyse erstellt wurde. Die monatlichen Berichte beinhalten die durchgeführten Aktivitäten, sowie die dabei auftretenden Gefühle, Herausforderungen, von den Mentor/innen eingesetzte pädagogische Strategien, die Beziehung zwischen Mentor/in und Mentee, auftretende sprachliche Aspekte, Stärken und Schwächen der Mentees und Informationen zu ihren Bezugspersonen. Untersucht wurden Einflussfaktoren auf die Inhalte der Monatsberichte. Es wurden Unterschiede in einzelnen Kategorien festgestellt, aufgrund des Geschlechts der Mentees in Kombination mit deren Erstsprache, sowie in Kombination mit der Studienrichtung der Mentor/innen. Zudem wurden für vereinzelte Kategorien Unterschiede über den zeitlichen Verlauf des Projekts hinweg festgestellt (Beginn, Mitte & Ende des Projekts). Außerdem wurden Zusammenhänge zwischen den Darstellungen der Mentor/innen und der Sprachentwicklung der Mentees festgestellt. Die in der vorliegenden Arbeit gefundenen Ergebnisse decken sich in einigen Bereichen mit bisherigen Ergebnissen und Erfahrungen zum Nightingale Projekt. Auch bisherige Funde, welche gewinnbringende Effekte von Mentoringprogrammen für Mentees und Mentor/innen berichten, konnten indirekt bestätigt werden durch die häufige Erwähnung von positiven Gefühlen der Mentees und Mentor/innen sowie durch die häufige Erwähnung der Kategorie positive Bewertungen der Treffen in den monatlichen Berichten.This thesis is evaluating a mentoring program, which is supposed to support children who have immigration backgrounds. Mentoring consists of an experienced person (mentor) who is supporting a younger, inexperienced person (mentee) and is helping them develop in various aspects of their life. In order to evaluate the Nightingale project, monthly submitted reports, which were written by the mentors, were used. They were analyzed with a system of categories, which have been established with the help of qualitative content analysis. The monthly reports consist of the activities that the mentors did with their mentees, the feelings that come up during their meetings, as well as occurring challenges, pedagogic strategies that the mentors are using, the relationship between mentor and mentee, linguistic aspects, strengths and weaknesses of the mentees and information regarding their families. Part of the analysis were factors that could influence the monthly reports. Differences in various categories were found due to the combination of the mentees´ gender and their first language, as well as, the combination of the mentees ´gender and the mentors´ field of study. Furthermore, for some categories differences were found, depending on the time the report was written (beginning, middle or end of the project). Furthermore, correlations were found between the mentors’ depiction in their reports and the mentees language development. The results that were found in this thesis, are consistent with previous results and experiences regarding the Nightingale project. Moreover, this thesis supports the belief, that mentoring is beneficial to mentees, as well as, mentors, as also found according to previous studies. This opinion is supported by the high number of mentioned positive feelings and positive evaluations of the meetings within the monthly reports

Rotational disorder of bis(mesitylene)vanadium in channels of a triazine inclusion compound

Electron paramagnetic resonance (EPR) was applied to study rotational disorder of bis(mesitylene)vanadium (VBM, S = \ubd) in channels of 2,4,6-tris(4-Br-phenoxy)-1,3,5-triazine. To ensure a magnetically dilute system, decamethylbis(cyclopentadienyl)ruthenium was used as a main guest to fill the channels. X-ray diffraction confirmed inclusion formation, resulting in an incommensurate host\u2013guest system. EPR spectra were measured using prismatic single crystals oriented to have Bo either parallel to the channel axis c or at any angle in between c and the perpendicular direction. Temperature-dependent spectra were recorded down to 80 K. The analysis revealed two types of paramagnetic guest entities, i.e. VBM (I) and VBM (II). Both showed dynamical effects due to a reorientational motion. VBM (I) is confined to show a molecular axis z distributed around c by a small angle (\ub1 1.25\ub0), whereas for VBM (II) the distribution is completely disordered. The reorientational motions are frozen at low temperature giving for VBM (II) a powder-like EPR spectrum. Analysing EPR intensities allowed us to conclude that the ratio of (I)/(II) species is of the order of 1.5