08 Fakultät Mathematik und Physik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9

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Institute: search.filters.UBSInstitut.Institut für ComputerphysikSubject: search.filters.subject.620

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    Permeability estimation of regular porous structures : a benchmark for comparison of methods
    (2021) Wagner, Arndt; Eggenweiler, Elissa; Weinhardt, Felix; Trivedi, Zubin; Krach, David; Lohrmann, Christoph; Jain, Kartik; Karadimitriou, Nikolaos; Bringedal, Carina; Voland, Paul; Holm, Christian; Class, Holger; Steeb, Holger; Rybak, Iryna
    The intrinsic permeability is a crucial parameter to characterise and quantify fluid flow through porous media. However, this parameter is typically uncertain, even if the geometry of the pore structure is available. In this paper, we perform a comparative study of experimental, semi-analytical and numerical methods to calculate the permeability of a regular porous structure. In particular, we use the Kozeny-Carman relation, different homogenisation approaches (3D, 2D, very thin porous media and pseudo 2D/3D), pore-scale simulations (lattice Boltzmann method, Smoothed Particle Hydrodynamics and finite-element method) and pore-scale experiments (microfluidics). A conceptual design of a periodic porous structure with regularly positioned solid cylinders is set up as a benchmark problem and treated with all considered methods. The results are discussed with regard to the individual strengths and limitations of the used methods. The applicable homogenisation approaches as well as all considered pore-scale models prove their ability to predict the permeability of the benchmark problem. The underestimation obtained by the microfluidic experiments is analysed in detail using the lattice Boltzmann method, which makes it possible to quantify the influence of experimental setup restrictions.
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    Tuning electrode and separator sizes for enhanced performance of electrical double‐layer capacitors
    (2024) Paolini, Daniele; Antony, Lintymol; Seeta Rama Raju, Ganji; Kuzmak, Andrij; Verkholyak, Taras; Kondrat, Svyatoslav
    An electrical double‐layer capacitor (EDLC) comprises two porous electrodes sandwiching an electrolyte‐permeable separator, which prevents the electrodes from short‐circuiting. While previous studies have mainly focused on electrolyte and electrode properties of EDLCs, the device configuration in terms of electrode and separator sizes received less attention, with separators often simplistically modelled as infinitely large reservoirs of ions. Herein, we investigate how the relationship between electrode and separator thicknesses impacts EDLC charging. We find that the assumption of bulk reservoir holds only under specific conditions. Moreover, we identify a tradeoff between stored energy density and pressure variations within the separator, potentially jeopardizing the EDLC durability. We also explore the influence of ionic liquid additives on EDLC charging. While prior research has shown that trace amounts of uncharged additives with strong electrode affinity can significantly enhance energy storage, we observe this effect as negligible for electrodes and separators of comparable sizes. Instead, we show how to optimize EDLC performance by fine‐tuning the concentration of additives and separator‐to‐electrode size ratio to maximize stored energy density.
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    Entwurf eines integrierten Systems zur Visualisierung von Ergebnissen numerischer Berechnungsverfahren für massiv parallele Rechnerarchitekturen
    (2000) Schlageter, Hans-Ulrich; Rühle, Roland (Prof. Dr.-Ing.)
    In dieser Arbeit wird ein Visualisierungsprogrammsystem, bestehend aus parallelen und interaktiven Komponenten vorgestellt. Das Anwendungsgebiet der Software ist neben der numerischen Strömungsmechanik vor allem die Strukturmechanik. Das Programmsystem erlaubt es, zahlreiche unabhängige Software-Einheiten (Moduln) individuell zu gruppieren und zu benutzerspezifischen Anwendungen zusammenzubinden. Die Software-Einheiten umfassen Eingabe, Ausgabe, Import und Export von Daten ebenso wie eine Bandbreite an Visualisierungstechniken zum sequentiellen und parallelen Gebrauch. Als Beispiele seien Kontur- und Isoflächen, Stromlinien, die Verfolgung von Partikeln, Flächen und Kugeln genannt. Das Modulpaket läuft auf einer leistungsfähigen UNIX-Graphik-Workstation unter dem Application Visualization System (AVS) und erlaubt die Anbindung eines Parallelrechners der MIMD-Klasse als Back-End, zum einen, um Berechnungsaufwände umzuverteilen und zu minimieren (Lastenausgleich ) und zum anderen, um visuelle Ergebnisdaten aus einer laufenden parallelen CFD-Simulation heraus zu erhalten. Ein besonderer Fokus liegt auf dem Austausch von Daten und Anweisungen über das Netzwerk zwischen verschiedenen Prozessen der wichtigsten Komponenten des Systems. Der Datenaustausch wird direkt über eine neuentwickelte, auf den Sockets der Interprozeßkommunikation basierende Transmitter-Software abgewickelt, die Punkt-zu-Punkt-Verbindungen auf Anforderung anbietet, die nicht bereits im Vorhinein spezifiziert und aufgebaut werden müssen.
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    Renormalized charge and dielectric effects in colloidal interactions : a numerical solution of the nonlinear Poisson-Boltzmann equation for unknown boundary conditions
    (2023) Schlaich, Alexander; Tyagi, Sandeep; Kesselheim, Stefan; Sega, Marcello; Holm, Christian
    The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, introduced more than 70 years ago, is a hallmark of colloidal particle modeling. For highly charged particles in the dilute regime, it is often supplemented by Alexander’s prescription (Alexander et al. in J Chem Phys 80:5776, 1984) for using a renormalized charge. Here, we solve the problem of the interaction between two charged colloids at finite ionic strength, including dielectric mismatch effects, using an efficient numerical scheme to solve the nonlinear Poisson-Boltzmann (NPB) equation with unknown boundary conditions. Our results perfectly match the analytical predictions for the renormalized charge by Trizac and coworkers (Aubouy et al. in J Phys A 36:5835, 2003). Moreover, they allow us to reinterpret previous molecular dynamics (MD) simulation results by Kreer et al. (Phys Rev E 74:021401, 2006), rendering them now in agreement with the expected behavior. We furthermore find that the influence of polarization becomes important only when the Debye layers overlap significantly.