Visualization of Magneto-rotational instability and turbulent angular momentum transport (Reloaded)

Table of Contents

Introduction

This project, led by by Fausto Cattaneo, University of Chicago, used a previous allotment of 2 million processor-hours to study the forces that help newly born stars and black holes increase in size. In space, gases and other matter often form swirling disks around attracting central objects such as newly formed stars. The presence of magnetic fields can cause the disks to become unstable and develop turbulence, thereby causing the disk material to fall onto the central object. This run at NERSC was used to set up initial conditions for a larger scale simulations. The Visualization Group assisted this project in generating High-quality visualizations of data produced in these runs. Based on these initial results, the project continues to carry out large-scale simulations to test theories on how turbulence can develop in such disks.

The visualization group continues to work with the researchers to visualize the results of their simulations. We use VisIt, which was initially developed at LLNL and now serves as one of main deployment vehicles for state-of-the-art production-quality visualization algorithms by the Visualization and Anautics Center for Enabling Technologies. Our recent work focused on defining an appropriate file format suitable for exchanging the results of these larger-scale simulations and using VisIt for parallel voume rendering.

Data Exchange

To facilitate data exchange with Incite 4 researchers, we developed an HDF5-based file format for their data and a corresponding VisIt database plugin. Simulations are performed on a mesh specified in cylindrical coordinates, which the plugin converts into a Cartesian representation at load time. Furthermore, the plugin automatically splits the data into as many blocks along the z-axis as there are processors used by VisIt, supporting VisIt's parallel operation on these data sets.

First Light

As a first step we generated volume rendered images of the azimuthal magnetic field (bt) and the magnetic energy (em), i.e., the square root of sum of squares of the radial, azimuthal and axial components, using various transfer functions. Figures 1-6 show the initial results.

Figure 1: First Attempt for bt and em.
Figure 2: Reverse background and revised transfer function for bt and em.
Figure 3: Cranking up the number of samples to 3500 Samples per ray for bt and em using the same transfer function as in Figure 2.
Figure 4: 5000 Samples per ray for bt and em, still the same transfer functions as in Figures 2 and 3.
Figure 5: 2000 and 3500 Samples per ray for fh with a slightliy different transfer function.
VisIt session file VisIt session file
Figure 6: 2000 and 3500 Samples per ray for fm with a sliughtly different transfer function.
VisIt session file

3D Visualization

After seeing these preliminary results, we were asked to generate visualizations for another variable (vtd). Again, we experimented with different transfer functions (Figures 7 - 9) until we settled on a final transfer function and rendered a movie for several time steps in the simulations. Since the volume rendered image contains large opaque regions, we decided to "cut out" a quarter of the cylinder to make the center region of the simulation visible.

Figure 7: Two different transfer functions for vtd. Clipped quarter of volume. 2000 samples per ray.
VisIt session file VisIt session file
Figure 8: Two more transfer functions for vtd. Clipped quarter of volume. 2000 samples per ray.
VisIt session file VisIt session file
Figure 9: (Left) Yet another transfer function for vtd. Clipped quarter of volume (using index select). 2000 samples per ray. (Right) Redone version of Figure 8 (right) with fixed transfer function min and max to help with movie generation.
VisIt session file VisIt session file
[Partial MPEG movie][Partial MPEG-4 AVI movie] [Partial MPEG movie][Partial MPEG-4 AVI movie]
Figure 10: Redone version of Figure 8 (left) with fixed transfer function min and max to help with movie generation.
VisIt session file
[Full MPEG movie][Full MPEG-4 AVI movie]

Source Code

References