Research Project D01

The long-term goal of this project is to develop new visualization techniques to support the projects of the CRC in understanding flow, transport and deformation phenomena occurring at interfaces in and around porous media. This requires the integrated visual analysis of processes captured across multiple fields to relate different quantities, analyze simulation ensembles, and compare simulations against experiments. The interactive exploration of large and heterogeneous volumes of data is achieved by efficiently using parallel architectures as well as insitu data aggregation. To bridge the gap between the techniques used by domain scientists and the approaches available from visualization research, we intend to continue developing visualization approaches for specific projects, and combine them into a flexible porous media visualization framework.

Volume Rendering

For the visualization of time-dependent volume data and as a basis for visualization tools developed later in the project, we implemented a free and open source volume renderer. This is a universal tool for the visualization of 3D scalar data and has already been used to visualize profiles at fluid-fluid and fluid-solid interfaces.

Spatio-temporal contours for time-dependent aggregation

Introducing a contour visualization that indicates spatial outlines of continuous processes, we allow aggregating dynamic fields from spatio-temporal processes to provide an overview and support interactive exploration. This aggregation of all time steps in one visualization enables us to efficiently analyze processes in the data. The visualization can be combined with volume rendering for context. To finally obtain a temporally dense representation that still maintains shape information, we convolve a noise texture along shape outlines at every time step, thus conveying shape changes over time.

Bubble extraction and comparative visualization

We investigated the influence of sequestrating bubbles on the seismic characteristics of porous rock formations based on micro-CT data of liquid CO2 filled sandstone. To this end, we developed an automatic technique that extracts emerged bubbles and their surrounding structure. To analyze how the structure of the porous medium affects the occurrence and shape of formed bubbles, we automatically classify and relate them in terms of morphology and geometric features. The results are visualized using 3D volume rendering and coordinated views. Bubbles are then clustered by similarity and are either visualized side-by-side or in a single view for comparison.

Stream surfaces for flow analysis

Extracting and visualizing stream surfaces between different flow regions and illustrating transport mechanisms with animated renderings, we investigated the behavior of single-phase flow in microfluidic structures. This includes the experimental recording of flow profiles, and a comparison between measured and simulated behavior.

Abstract visualization of displacement in porous media

For the investigation of a series of two-phase flow displacement experiments, we developed a visual analysis approach with the goal of better understanding the involved processes and relating them to the experiment parameter space. With a novel node-link diagram based representation, we temporally aggregate the propagation of the displacing fluid through the porous medium, yielding the usage rate. The two-dimensional parameter space can be analyzed using a small multiples representation of these diagrams. Transport graphs also enable to quantify the relation between displacement and pore-space characteristics, such as pore throat width.

Applied parameter space exploration

Our visual analysis method for a coalbed-methane production model allows to analyze the results of multiple simulation runs in several coordinated views. Rather than visualizing the data concurrently in space, we represent them as high-dimensional vectors in the parameter space of the underlying model. The influence of model parameters can be explored via dimensionality reduction and clustering techniques, while investigating the results in a combined view of scatter plots, line plots, and parallel coordinate plots.

Visual analysis of parameter spaces

To deal with large numbers of simulations or experiments and especially high-dimensional parameter spaces, we developed a generic approach to scalable visual analyses. We cluster ensemble data from simulations in computational fluid dynamics and thermodynamics, and relate them to their position in parameter space. Employing glyphs in a novel and intuitive visual representation, we show the transition between homogeneous regions in parameter space.

High performance visualization

High performance visualization covers approaches from maintaining interactivity for medium-size data sets to being able to process large-scale data sets at all. Here, we first focused on the analysis of large spatio-temporal data and on interactivity. For the Pretty Porous exhibition, we developed an interactive demonstrator for the investigation of geothermal energy sites. Through touch input, visitors could interactively modify the properties of two sets of injection and extraction wells, and explore the underground heat transport at geothermal energy sites. The underlying Polynomial Chaos Expansion (PCE) model is evaluated dynamically on the GPU. This allows to compute the temperatures in each cell of the domain on the graphics accelerator hardware and to visualize the results with interactive frame rates.

In situ coupling for visualization

Further, we have worked on an in situ visualization approach that makes use of preCICE to ingest the simulation data. Our current software prototype is coupled to a DuMux solver for fractures in porous media benchmark scenarios, providing a uniform way to visualize the results of arbitrary solvers that implement these benchmark cases.