Difference between revisions of "Tzold"

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|name=Zauner, Thomas
|status=PhD student
== Research Overview ==
[[Image:bent.jpg |thumb|200px|right| Sandstone is a very common natural porous medium. ©wikipedia]]
The general field of my research is the '''computational investigations of natural porous media'''. A typical example of such a natural porous medium is sandstone.
It consists of very small consolidated grains that form a solid backbone but,
due to the space between individual grains, is permeable for many fluids.
Insight into physical transport phenomena of natural porous media,
such as flow rates, trapping behavior and prediction
of effective transport coefficients, has always been of great practical
interest for the oil and gas industry and has currently drawn  public
attention in the context of CO<sub>2</sub> sequestration.
Porous materials are also used for  many industrial
applications, for example in filtration processes, as
catalyst in chemical reactions or building materials with specially
physical properties.
The scientific problems that I address in my work are:
*''' Developing algorithms that can generate realistic  and macroscopic computer models for granular porous media'''. These models will be made of many hundred millions of individual grains whose positions, orientations and sizes  must fulfill certain correlations and restrictions.  The associated large computational demand requires highly efficient parallelized computer algorithms.
* '''Identifying and evaluating numerical methods that allow accurate and predictive calculations of physical properties of porous media'''. These calculations typically require numerically solving partial differential equations within a chosen discretization scheme and at a specific resolution or order of accuracy.
== Realistic computer models for granular porous media ==
In the reconstruction procedure we use a dense packing of spheres is created. The packing must fulfill given restrictions such as density, overlap, size distribution and others. The spheres are later substituted by more complex geometrical
objects determined by the shapes of the grains used in the
specific model. One option is to use polyhedrons as grain shapes.
The resulting model then is a continuum model in the sense that the
geometry is defined by a points in the continuum and  polyhedrons with analytical defined shapes, sizes and orientations. An example of such a model for Fountainebleau sandstone is shown in image 1. Such a continuous computer model can then be discretized at any desired resolution, see image 2,  for further analysis and computer simulations.
[[Image:all.png |thumb|400px|left| Picture 1: Three dimensional rendering of a model for Fontainebleau sandstone. The model contains over 1.2 million quartz grains. Each grain is modeled as a polyhedron. A crosssection is shown in orange.]]
[[Image:muCT_ani.gif |thumb|300px|right|Picture 2: Two dimensional crosssections of the discretized model.The sidelength of the crosssection is L  and the resolution a. The porespace is black and the grains are gray. A the highest resolution  narrow channel are solved by more than 20 nodes. ]]
<br>  </br>
== Flow Simulations  ==
A porous mediums '''permeability''' is an example of a
physical transport parameter. It describes the mediums ability to
transmit fluid flow through it.  Using '''Darcy's law''' the permeability
of a porous medium can be calculated from the velocity and
corresponding pressure field on the porescale. These fields
are solutions of hydrodynamic partial differential
equations describing fluid flow on the porescale. Many different
numerical methods that  solve different hydrodynamic  equations
can be used to obtain the velocity and pressure field.
Possibilities are '''Navier-Stokes simulations''' and  '''Lattice-Boltzmann simulations'''. Our  Lattice-Boltzmann implementation, for example,  numerically solves the Boltzmann equation using  a '''transient explicit finite-difference scheme'''. The  simulation is ran until a stationary solution has been reached. From this stationary solution the hydrodynamic fields can be calculated.
Simulations in stochastic geometries often require very large system sizes to obtain representative solutions. In our investigations, typical sizes of the  discretized system are in the range 1024³-4096³ voxel.
[[Image:poreflow1.jpg|thumb|550px|center| Very small subvolume (128³ voxel) of a sandstone at a resolution 5µm. The porespace-matrix interface is shown as a mesh. The velocity  magnitude in lattice units, as calculated by a Lattice-Boltzmann simulation, is shown within the porespace. Areas of slow flow  are blue, fast flow is shown in red. An empty porespace indicates areas where the fluid is at rest. It can be seen that only a small portion of the porespace contributes to the mass transport. [[Media:poremovie.avi]] ]]
== Publications ==
[1]  A. Narvaez, T. Zauner, F. Raischel, R. Hilfer, J. Harting, “Quantitative analysis of numerical estimates for the permeability  of porous media from lattice-Boltzmann simulations”, Journal of Statistical Mechanics, P11026, 2010, [http://www.icp.uni-stuttgart.de/~zauner/publications/LB_JStat08.pdf Preprint]
[2] S. Grottel, G. Reina, T. Zauner, R. Hilfer, T. Ertl, "Particle-based Rendering for Porous Media", SIGRAD, 2010, [http://www.icp.uni-stuttgart.de/~zauner/publications/sigrad_2010.pdf Preprint]
[3] J. Harting, T. Zauner, R. Weeber, and R. Hilfer
Numerical modeling of fluid flow in porous media and in driven colloidal suspensions
in High Performance Computing in Science and Engineering '08, edited by W. Nagel, D. Kröner, M. Resch, Springer ,2008. [http://www.icp.uni-stuttgart.de/~zauner/publications/HPC08.pdf Preprint]

Revision as of 12:54, 2 March 2011