Evolution of state and shape of viscoplastic formations

Estimations of expected deformation rates of viscoplastic formations, due to artificially induced changes of the natural stress field, are key issues related to underground storage of CO2 and the viability of boreholes. The objective of this thesis is to close the gap between the comprehension of the evolutions of state and shape of viscoplastic formations and practical requirements, and to better describe subcritical evolutions of viscoplastic formations

Efficient computation of quasiperiodic oscillations in nonlinear systems with fast rotating parts

We present a numerical method for the investigation of quasiperiodic oscillations in applications modeled by systems of ordinary differential equations. We focus on systems with parts that have a significant rotational speed. An important element of our approach is to change coordinates into a co-rotating frame. We show that this leads to a dramatic reduction of computational effort in the case that gravitational forces can be neglected. As a practical example we study a turbocharger model for which we give a thorough comparison of results for a model with and without gravitational forces

Vibrations in Nonlinear Rotordynamics - Modelling, Simulation, and Analysis

Mechanical vibrations of rotor-bearing systems are an ubiquitous problem in mechanical engineering and the prediction of response frequencies and amplitudes with the help of mathematical models is of major importance for the design of more efficient and reliable machinery. In the present work a model for the dynamics of fast rotating, elastic beams supported in hydrodynamic bearings is derived and its vibration behavior analyzed. Special focus is put on the influence of the nonlinear bearing reaction forces on the dynamics. The continuous rotor is modeled using Euler-Bernoulli beam theory under the inclusion of rotatory inertia and gyroscopic effects. For a general class of support functions the existence of weak solutions to the equations of motion is proved. The pressure distribution in the oil-lubricated simple journal bearings is modeled by the well known Reynolds’ equation. Its derivation from the Navier-Stokes equations by an asymptotic expansion in the film thickness is reviewed and new correction terms for fluid inertia effects are derived. Additional correction terms for the short bearing approximation to Reynolds’ equation are also derived by making additional assumptions on the bearings’ width-to-radius ratio. Furthermore, the pressure distribution and the bearing reaction forces are computed numerically in dependence of the position and the velocity of the rotor inside the bearings. The finite element method is applied to discretize the beam equation and the bearing forces are included into the model as point forces in the bearing nodes. While the classical lubrication theory leads to explicit equations of motion, the inertia corrections lead to implicit equations of motion for the rotor-bearing system. The model is evaluated by comparing numerical simulations with experimental results obtained for a passenger car turbocharger. For this example it is shown that the model equations describe the dynamics well, capturing most experimentally observed phenomena, such as unbalance oscillation and self-excited oil whirl. Some differences between model and experiment can be seen in the response frequency of the subharmonic oil whirl. The inertia corrections yield a small improvement compared to the classical models. A new phenomenological correction of the short bearing approximation based on the adaptation of the average circumferential lubricant velocity is proposed and shown to influence the whirl frequency ratio strongly. Continuation methods for periodic and quasiperiodic solutions are shown to be more efficient and are hence more appropriate tools for the examination of the vibration response behavior than direct numerical simulation. It is shown numerically, that the static gravity load can be neglected for higher rotational frequencies. Combined with a transformation to a co-rotating frame of coordinates this leads to a significant simplification, since the resulting ODE becomes autonomous, and the vibration response can be computed by the continuation of periodic orbits instead of invariant tori. This is applied successfully to study the parameter range where the inertia correction for the short bearing is valid. All in all, the presented model and its variations prove to be useful for future industrial application in the design of more efficient turbomachinery. Parts of the presented research are already actively used for turbocharger design by the Toyota Central Research and Development Laboratories

Infrared absorption of porous silicon layers and silicon particle films

Using TaC filaments for a hot-wire chemical vapor deposition (HWCVD) compact material (substrate temperatures 220°C) and porous, non-compact or void-rich layers (120°C) were produced in a silane-hydrogen atmosphere in the pressure range from 1 Pa to 30 Pa. For high pressures the adhesion of the layers was weak. In this case the thus pulverized silicon particles could be removed from the substrate by an ultrasonic process in an isopropanol bath. The suspension of these silicon particles was spread to form a continuous film, namely a "particle-film". The infrared (IR) spectra of the compact solid, the original porous layers and a series of temper stages of the particle-films are compared and discussed. The role of H and O atoms in the silicon network is investigated. Thus those structural properties, which may be found out by infrared tools, e.g. the bonding configurations of the Si related bonds of the said materials and some possible chemical reactions are explained

Improving Business Model Configuration through a Question-based Approach

In the competitive context of agile innovation cycles, it is necessary for companies to construct their business model leading them to a creative strategy innovation. There already are a number of methods to create business models, many of which are also implemented in software. However, these are often unstructured, unguided and static, resulting in diverse and heterogeneous business models. This complicates automated evaluation allowing recommendations. The aim is to develop a question-based tool yielding for comparable and, thus, analyzable business models based on a developed standardized taxonomy. The questions guiding through the configurator were derived from this taxonomy. A tool was developed implementing the question-based concept. User tests were conducted as part of an evaluation showing promising results concerning usability in addition to the already achieved standardization

Optimization and Augmentation for Data Parallel Contour Trees

Contour trees are used for topological data analysis in scientific visualization. While originally computed with serial algorithms, recent work has introduced a vector-parallel algorithm. However, this algorithm is relatively slow for fully augmented contour trees which are needed for many practical data analysis tasks. We therefore introduce a representation called the hyperstructure that enables efficient searches through the contour tree and use it to construct a fully augmented contour tree in data parallel, with performance on average 6 times faster than the state-of-the-art parallel algorithm in the TTK topological toolkit

Didaktische Referenzpunkte der wissenschaftlichen Weiterbildung. Studentische Arbeiten zwischen Forschungs- und Praxisorientierung

Der folgende Artikel geht der Frage der Ausgestaltung einer Didaktik wissenschaftlicher Weiterbildung nach. Unter Bezugnahme auf die Besonderheiten wissenschaftlicher Weiterbildung an der Hochschule wird das Oszillieren zwischen Forschungsorientierung und Praxisnotwendigkeiten als Kennzeichen hochschuldidaktischen Handelns in der wissenschaftlichen Weiterbildung festgestellt. Gefragt wird in einer empirischen Untersuchung zu didaktischen Referenzpunkten der wissenschaftlichen Weiterbildung welche Anforderungen an Abschlussarbeiten als Leistungsnachweise und Teil eines wissenschaftlichen Studiums gestellt werden. In der Diskussion der Ergebnisse bietet der Artikel Anlass zur Reflexion der didaktischen Gestaltung von Angeboten in der wissenschaftlichen Weiterbildung

The Wunderkammer from pre-Enlightenment to contemporary art

Robert Williams (Artist, University of Cumbria) took part in a panel discussion involving participants: Mark Dion (Artist, New York), Dirk Syndram (Director Grünes Gewölbe, Dresden), Matthias Flügge (Rektor HfBK Dresden), Robert Felfde (Art Historian, University of Hamburg), Rosamond Purcell (Artist), Ulrike Grossgarth (HfBK Dresden), Nadine Engel (Art Historian, Geneva), Donna Roberts (Art Historian, Helsinki), Jane Wildgoose (Artist), Stephan Köhler (Curator, Hamburg & West Africa), Verena Kuni (Scholar for Visual Culture, Frankfürt am Main), Helen Gregory (PhD Candidate, University of Western Ontario), Marion Endt-Jones (Art Historian, Manchester University), Nike Bätzner (Art Historian, Kunsthochschule, Halle), Gabriele Beßler (Curator, Stuttgart/Köln) and Sarah Wade (PhD Candidate, UCL)