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−  {{Person
 
−  name=Zauner, Thomas
 
−  status=PhD student
 
−  phone=67652
 
−  room=202
 
−  email=Thomas.Zauner
 
−  category=hilfer
 
−  }}
 
   
− 
 
− 
 
−  == Research Overview ==
 
−  [[Image:bent.jpg thumb200pxright 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 thumb400pxleft 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 thumb300pxrightPicture 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 '''NavierStokes simulations''' and '''LatticeBoltzmann simulations'''. Our LatticeBoltzmann implementation, for example, numerically solves the Boltzmann equation using a '''transient explicit finitedifference 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 1024³4096³ voxel.
 
− 
 
−  [[Image:poreflow1.jpgthumb550pxcenter Very small subvolume (128³ voxel) of a sandstone at a resolution 5µm. The porespacematrix interface is shown as a mesh. The velocity magnitude in lattice units, as calculated by a LatticeBoltzmann 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 latticeBoltzmann simulations”, Journal of Statistical Mechanics, P11026, 2010, [http://www.icp.unistuttgart.de/~zauner/publications/LB_JStat08.pdf Preprint]
 
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− 
 
−  [2] S. Grottel, G. Reina, T. Zauner, R. Hilfer, T. Ertl, "Particlebased Rendering for Porous Media", SIGRAD, 2010, [http://www.icp.unistuttgart.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.unistuttgart.de/~zauner/publications/HPC08.pdf Preprint]
 