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Institut für Wasserbau - IWS

Selected Topics and International Network Lectures (WS 2007/08)

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noch laufendeSS-2008WS-2007/08SS-2007WS-2006/07SS-2006WS-2005/06SS-2005WS-2004/05(vor WS-2004/05)

Donnerstag
29.05.2008
16:00 Uhr
Priv.-Doz./ Dr.-Ing./ Dipl.-Math. Ekkehard Holzbecher
Weierstrass Institute of Applied Analysis and Stochastics, Berlin

'Multiphysics Modeling' in Umwelttechnik und -wissenschaft

In vielen Bereichen der Umwelttechnik und -wissenschaft helfen Modelle heutzutage bei der Behandlung von Umweltproblemen: bei der Lokalisierung von Schadstoffen, der Vorhersage der Entwicklung einer Kontamination, beim Design und der Bewertung der Gefahrenabwehr, sowie bei Sanierungs- massnahmen. Bei der Simulation des Schadstofftransports spielt zumeist der Prozess der Advektion die wichtigste Rolle. Es ist daher in der Regel entscheidend, Strömung und Transport gleichermassen zu simulieren. Für solche Aufgabenstellungen bieten sich heutzutage 'Multiphysics'-Software-Pakete an, wie z.B. das Finite-Element Programm COMSOL Multiphysics. Im Vortrag wird die Arbeit mit diesen Ansätzen erläutert. Es werden Beispiele, vorwiegend aus dem Bereich Grundwasser, vorgestellt, die z.T. mit numerischen und z.T. mit analytischen Ansätzen gelöst werden.

Donnerstag
05.06.2008
16:00 Uhr
Christian Graf
DLR, Stuttgart

Modellbildung im Bereich PEFCs - ein 1+1-D-Ansatz

Aktuelle Tendenzen in der Brennstoffzellenforschung zielen darauf ab die ablaufenden Vorgänge und deren Zusammenspiel transparent zu machen. Da die gezielte Separation bei in situ Messungen nur mit Aufwand oder teilweise gar nicht möglich ist, rücken Modellbildung und Simulation in den Vordergrund.

Dieser Vortrag zeigt den aktuellen Stand der Modellbildung von PEFCs am DLR. Fokus ist ein 1+1-D-Modell, wobei die Transportvorgänge der Gase und Flüssigkeiten entlang der Stromrichtung auf nm-Skala innerhalb von Referenzporen modelliert sind. Des weiteren sind die elektrochemischen Vorgänge der Katalysatorschichten ortsaufgelöst implementiert. Der Vortrag stellt den Modellaufbau und dessen Umsetzung in MATLAB dar.

Donnerstag
12.06.2008
16:00 Uhr
Anozie Ebigbo
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung, Institut für Wasserbau, Uni Stuttgart

Microbial clogging in the subsurface - A one-phase flow model and issues involved in extension to two-phase flow

In the talk, a Darcy scale model capable of simulating microbial transport and accumulation in saturated porous media is presented. The modelled processes include biomass growth and decay, transfer processes between the bulk fluid and the solid and advective/dipsersive transport of bacteria with the bulk fluid.

The model is intended to be used in simulations of microbial clogging in an underground CO2 storage site and thus two fluid phases need to be accounted for. The extension from one-phase to two-phase flow is not straight-forward. The second part of the presentation focuses on the issues that need to be included in a two-phase model such as the estimation of surface areas, capillary pressure and relative permeabilities.

Donnerstag
26.06.2008
16:00 Uhr
Dr. Iryna Rybak
Institut für Angewandte Analysis und Numerische Simulation, Uni Stuttgart

Numerical upscaling for flows in heterogeneous porous media

Porous media are often highly heterogeneous. Solving porous media problems at the fine scale, which resolves all the heterogeneities, is computationally expensive due to the required memory and computational time. Upscaling techniques, such as homogenization, averaging, etc., have to be used to make solving multiscale problems possible.

Essential success was achieved during the last decades in the studies of problems with clearly separated fine and coarse scales (periodic microstructure, statistically homogeneous porous media). When the fine and the coarse scales can be decoupled, solving a multiscale problem reduces to one way two-stage procedure: i) solve fine scale “cell-problem” and use its solution to upscale the effective properties of the multiscale media; ii) solve coarse scale equations with the calculated effective coefficients. The separation of scales, however, is not always possible, and developing numerical upscaling techniques for such problems is the subject of this presentation.

We consider pressure equation, obtained by combining the continuity equation and Darcy's law, for steady state incompressible single-phase flow. Finite volume discretization (Multi-Point Flux Approximation) for this problem is developed in the case of jump discontinuities for the permeability. The effective properties of the media are calculated, two-grid method is discussed and the results from numerical experiments are presented.

Donnerstag
03.07.2008
16:00 Uhr
David Werner
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung, Institut für Wasserbau, Uni Stuttgart

Harmonic mean values of positive definite tensors: Motivation for developing a MPFA-scheme

User of UG and DUMUX-Codes often apply a generalized formula of harmonic means for permeablilities. This formula, originally derived for 1D-Codes, has some serious drawbacks in its simple generalization. I want to discuss this topic and present a different method for calculating a mean tensor. Starting with these thoughts on interpretation of weighted permeability tensors in the application of finite volume discretizations, I want to go on with a motivation for a certain multipoint flux approximation (MPFA) method.

Donnerstag
10.07.2008
16:00 Uhr
Irina Komarova, M.Sc.
Institut für Mechanik (Bauwesen), Uni Stuttgart

Carbon dioxide storage in the subsurface: A triphasic model and constitutive settings

Nowadays, the problem of reduction of the carbon dioxide (CO_2) concentration in the atmosphere is a relevant subject and an important field in research. Engineers and scientists are making important contributions in this topic. But there are still a lot of open questions in this field which should be solved. One way to solve this problem is to store the CO_2 in deep geological formations. For example, the possibility is to inject CO_2 into deep water-saturated aquifers, where the upward migration of CO_2 is blocked by a low impermeable cap rock layer.

Within the topic of CO_2 storage in an aquifer, a triphasic non-isothermal model within the continuum mechanical Theory of Porous Media will be discussed on the seminar. More precisely, the model with an elastic properties for the solid skeleton, incompressible fluid and compressible gas is currently under consideration. A part of the talk will be focused on the discussion about some constitutive relations, which are important for the investigated model. Finally, some numerical examples will be presented.