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This study reports the geometries and electronic energies of n-octane's unique conformations using perturbation methods that best mimic CCSD(T) results. In total, the fully optimised minima of n-butane (2 conformations), n-pentane (4 conformations), n-hexane (12 conformations) and n-octane (96 conformations) were investigated at several different theory levels and basis sets. We find that DF-MP2.5/aug-cc-pVTZ is in very good agreement with the more expensive CCSD(T) results. At this level, we can clearly confirm the 96 stable minima which were previously found using a reparameterised density functional theory (DFT). Excellent agreement was found between their DFT results and our DF-MP2.5 perturbation results. Subsequent Gibbs free energy calculations, using scaled MP2/aug-cc-pVTZ zero-point vibrational energy and frequencies, indicate a significant temperature dependency of the relative energies, with a change in the predicted global minimum. The results of this work will be important for future computational investigations of fuel-related octane reactions and for optimisation of molecular force fields (e.g. lipids).
A traditional way to teach bachelor students in electrical engineering is organized such that theoretical knowledge is predominant in the first year while applications and practical experiences are reserved for later stages of their education. In this contribution, we want to introduce a reverse approach: In a freshmen course at Bonn-Rhein-Sieg University of Applied Science, students gain hands-on experience with resistances, condensers and other active parts, like transistors or relays from the very first day. We present how the combination of practical experience directly linked with theoretical knowledge enhances students' learning. It promotes deeper understanding of the theory and a better transfer between theory and practice. This teaching approach is adapted to address two main goals: First, to give practical experience to first-semester students as a basis for further laboratory and working situations. Second, to create a deeper and more sustainable understanding of physics by directly observing the effects that are described in formulas. The key to success is to find an efficient solution to carry out this approach with the given spatial and financial resources-which means, to do it in the lecture hall with very few material resources. To show that this innovative teaching concept really enhances the competencies of the students, an innovative evaluation approach was used where the students have to reflect upon their competencies before and after the course.
In this contribution we briefly recap the general concept of the BRSU Race Academy. We then concentrate on and demonstrate how practical projects can be set up and executed within this framework. We discuss what is needed to train the members of the Race Academy properly and how the faculty advisor could change his course of action during the projects. The feedback and the results of such projects have been extremely positive so far: The Race Academy members have been perceived as role models to their peers, and an efficient peer-group atmosphere could be set up that facilitated learning. With their experience, solid user knowledge and the close contact to several industrial partners, a productive, authentic and practical working atmosphere has been established. We will give examples of how to use our new teaching approach to surpass the qualities of classes held in the traditional way. Furthermore, it is shown that the technical understanding is improved, as well as the personal experience to work with and integrate into a professional team.
In this contribution we present the concept for creating an “International Chair” position at a German University of Applied Sciences and our experiences in its first implementation. Our primary goal was to increase the diversity of the university’s teaching personalities and enrich student education by including content, methods, examples and experiences from other cultures. This gives students an international and intercultural learning experience that is otherwise only acquired through studying abroad. We conclude that the International Chair is a valuable and powerful university tool for increasing international exposure to the departments, their staff and students.
Wo Laborexperimente zu aufwendig, zu teuer, zu langsam oder zu gefährlich oder Stoffeigenschaften gar nicht erst experimentell zugänglich sind, können Computersimulationen von Atomen und Molekülen diese ersetzen oder ergänzen. Sie ermöglichen dadurch Reduktion von Kosten, Entwicklungszeit und Materialeinsatz. Die für diese Simulationen benötigten Molekülmodelle beinhalten zahlreiche Parameter, die der Simulant einstellen oder auswählen muss. Eine passende Parametrierung ist nur bei entsprechenden Kenntnissen über die Auswirkungen der Parameter auf die zu berechnenden Größen und Eigenschaften möglich. Eine Gruppe von Standardparametern in molekularen Simulationen sind die Partialladungen der einzelnen Atome innerhalb eines Moleküls. Die räumliche Ladungsverteilung innerhalb des Moleküls wird durch Punktladungen auf den Atomzentren angenähert. Für diese Annäherung existieren diverse Ansätze für verschiedene Molekülklassen und Anwendungen. In diesem Teilprojekt des Promotionsvorhabens wurde systematisch der Einfluss der Wahl des Partialladungssatzes auf potentielle Energien und ausgewählte makroskopische Eigenschaften aus Molekulardynamik-Simulationen evaluiert. Es konnte gezeigt werden, dass insbesondere bei stark polaren Molekülen die Auswahl des geeigneten Partialladungssatzes entscheidenden Einfluss auf die Simulationsergebnisse hat und daher nicht naiv, sondern nur ganz gezielt getroffen werden darf.
Ressourceneffiziente Optimierung von Hohlkörpern aus Kunststoff mittels Multiskalensimulation
(2017)
Die mechanischen Eigenschaften von extrusionsblasgeformten Kunststoffhohlkörpern hängen wesentlich von den vom Verarbeitungsprozess beeinflussten Materialeigenschaften ab. Ziel der dargestellten Untersuchung ist, prozessabhängige Materialkennwerte in Simulationsprogrammen zu berücksichtigen und damit deren Vorhersagegenauigkeit zu erhöhen. Hierzu ist die Schaffung einer Schnittstelle zwischen Prozess- und Bauteilsimulation notwendig. Darüber hinaus wird vorgestellt, wie Simulationen auf Mikroebene (molekulardynamische Simulationen) genutzt werden können, um Materialkennwerte ohne die Durchführung eines Realexperiments zu ermitteln.
Formula Student is known worldwide as a design contest for engineering students, in which they train technical skills and engineering thinking by developing and manufacturing a single-seated race car every year. The efficient transfer of highly specialized and professional knowledge about physics and manufacturing has to be ensured every year, as the members turn into alumni. This requires much more than only technical skills.
In this contribution, we want to present how the Bonn-Rhine-Sieg University of Applied Sciences supports its Formula Student team in order to foster and exploit its great potentials with a systematic approach, under the supervision of its team faculty advisor. We show how senior students learn how to teach their fellow students in their highly specialized skills in a so called “Race Academy”. This aims at the evolution of teaching content, and the art of teaching itself, by systematically involving peers in the teaching process.
The lattice Boltzmann method is a simulation technique in computational fluid dynamics. In its standard formulation, it is restricted to regular computation grids, second-order spatial accuracy, and a unity Courant-Friedrichs-Lewy (CFL) number. This paper advances the standard lattice Boltzmann method by introducing a semi-Lagrangian streaming step. The proposed method allows significantly larger time steps, unstructured grids, and higher-order accurate representations of the solution to be used. The appealing properties of the approach are demonstrated in simulations of a two-dimensional Taylor-Green vortex, doubly periodic shear layers, and a three-dimensional Taylor-Green vortex.
Ressourceneffiziente Optimierung von Hohlkörpern aus Kunststoff mittels Multiskalensimulation
(2017)
Gleichlaufgelenke als Teil der Antriebswellen (Seitenwellen und Längswellen) sind in allen maßgeblichen Triebstrangkonfigurationen im direkten Leistungsfluss angeordnet. Ihre Hauptfunktion ist die Übertragung einer Antriebsleistung unter Ermöglichung von Abbeugung und Axialverschiebung. Dieser Beitrag soll einen Überblick zu den wesentlichen, auf dem heutigen Markt verbreiteten Bauweisen und ihren jeweiligen Einsatzgebieten geben. Besonders berücksichtigt werden hierbei neue Gelenkkonzepte, die sich aufgrund ihrer besonderen Gestaltung durch deutlich höhere Wirkungsgrade auszeichnen. Der Einfluss auf den Energieverbrauch soll quantifiziert werden, hierzu wird ein neuartiger Berechnungsansatz vorgestellt, der eine einfache Abschätzung des Einflusses von Wirkungsgradverbesserungen auf den Energieverbrauch für verschiedener Antriebskonzepte (ICE / Hybrid / E-Fahrzeuge) erlaubt.
A central goal of molecular simulations is to predict physical or chemical properties such that costly and elaborate experiments can be minimized. The reliable generation of molecular models is a critical issue to do so. Hence, striving for semiautomated and fully automated parameterization of entire force fields for molecular simulations, the authors developed several modular program packages in recent years. The programs run with limited user interactions and can be executed in parallel on modern computer clusters. Various interlinked resolutions of molecular modeling are addressed: For intramolecular interactions, a force-field optimization package named Wolf2Pack has been developed that transfers knowledge gained from quantum mechanics to Newtonian-based molecular models. For intermolecular interactions, especially Lennard–Jones parameters, a modular optimization toolkit of programs and scripts has been created combining global and local optimization algorithms. Global optimization is performed by a tool named CoSMoS, while local optimization is done by the gradient-based optimization workflow named GROW or by a derivative-free method called SpaGrOW. The overall goal of all program packages is to realize an easy, efficient, and user-friendly development of reliable force-field parameters in a reasonable time. The various tools are needed and interlinked since different stages of the optimization process demand different courses of action. In this paper, the conception of all programs involved is presented and how they communicate with each other.
Molecular simulations are an important tool in the study of aqueous salt solutions. To predict the physical properties accurately and reliably, the molecular models must be tailored to reproduce experimental data. In this work, a combination of recent global and local optimization tools is used to derive force fields for MgCl2 (aq) and CaCl2 (aq). The molecular models for the ions are based on a Lennard-Jones (LJ) potential with a superimposed point charge. The LJ parameters are adjusted to reproduce the bulk density and shear viscosity of the different solutions at 1 bar and temperatures of 293.15, 303.15, and 318.15 K. It is shown that the σ-value of chloride consistently has the strongest influence on the system properties. The optimized force field for MgCl2 (aq) provides both properties in good agreement with the experimental data over a wide range of salt concentrations. For CaCl2 (aq), a compromise was made between the bulk density and shear viscosity, since reproducing the two properties requires two different choices of the LJ parameters. This is demonstrated by studying metamodels of the simulated data, which are generated to visualize the correlation between the parameters and observables by using projection plots. Consequently, in order to derive a transferable force field, an error of ∼3% on the bulk density has to be tolerated to yield the shear viscosity in satisfactory agreement with experimental data.
The paper describes methods for calculating chemical equilibria based on a constrained Gibbs free energy minimization. The methods allow the treatment of multicomponent systems with multiple phases, including gaseous phases, condensed phases, and stoichiometric phases. A special aspect is the detection and treatment of miscibility gaps. The underlying mathematical problem is described in detail together with the algorithmic approach for its solution. Results are presented for some test cases, including the computation of phase diagrams for ternary systems.
Transition point prediction in a multicomponent lattice Boltzmann model: Forcing scheme dependencies
(2018)
Pseudopotential-based lattice Boltzmann models are widely used for numerical simulations of multiphase flows. In the special case of multicomponent systems, the overall dynamics are characterized by the conservation equations for mass and momentum as well as an additional advection diffusion equation for each component. In the present study, we investigate how the latter is affected by the forcing scheme, i.e., by the way the underlying interparticle forces are incorporated into the lattice Boltzmann equation. By comparing two model formulations for pure multicomponent systems, namely the standard model [X. Shan and G. D. Doolen, J. Stat. Phys. 81, 379 (1995)] and the explicit forcing model [M. L. Porter et al., Phys. Rev. E 86, 036701 (2012)], we reveal that the diffusion characteristics drastically change. We derive a generalized, potential function-dependent expression for the transition point from the miscible to the immiscible regime and demonstrate that it is shifted between the models. The theoretical predictions for both the transition point and the mutual diffusion coefficient are validated in simulations of static droplets and decaying sinusoidal concentration waves, respectively. To show the universality of our analysis, two common and one new potential function are investigated. As the shift in the diffusion characteristics directly affects the interfacial properties, we additionally show that phenomena related to the interfacial tension such as the modeling of contact angles are influenced as well.
On the basis of the worldwide efforts to reduce CO2 and pollutant emissions, automobile manufacturers are being induced to pursue the development of more efficient vehicles with greater vigour. It is precisely the increased requirements for high-efficiency power transmission components that will allow suppliers of drivetrain components and systems as GKN to achieve a better position on the market by offering a drive technology with optimized efficiency levels.
