Setting up an accretion disk simulation in Astrobear 2.0

Modules and Files

These directions assume that you are able to compile a problem, in case you have never compiled AstroBEAR check the page ​How to Build AstroBEAR 2.0

In order to set up a simple accretion disk simulation proceed to select the BasicDisk problem in the modules folder, this can be done by typing the following commands in the astrobear root directory:

cd modules
ln -s BasicDisk Problem

After compilation, you need to be able to run the AstroBEAR executable, a tutorial for this procedure can be found at ​How to Run AstroBEAR 2.0 page.

Warning: It is good practice to delete profile.data from the problem folder before executing AstroBEAR for the first time, failure to do so will likely result in execution errors.

Getting familiar with the module

After checking that the disk module compiles and runs without any issues, you can examine the chombo files created by the first run of this module.

If you have no experience on visualization tools, the page ​VisIt Basics is a good resource to learn the basics of it.

The following image is a density plot of the disk at time t=0, a log scale has been applied to the perpendicular and parallel slices.

Different elements can be recognized in the image above:

• GxBounds: the boundaries of the plot, namely the physical boundaries of the simulation
• Radius: the radius of the disk
• Height: the height of the disk
• Ambient: the blue portion of the plot, it represents the area around the disk
• PointGravity: a point mass located at the center of the disk

Initial Conditions

Now you can proceed to examine problem.data contained in the BasicDisk folder. The default problem.data file contains an array of field that can be changed depending on the user's needs, let's analyze some of them

ddensity=1d0	disk density
adensity=0.001d0	ambient density
dtemp=1d4	disk temperature
atemp=6d6	ambient temperature
radius=2e10	disk radius
height=5e9	disk height
mass=.6d-1	central particle mass

Sometimes it can be useful to change the size of the physical boundaries of the simulation, this can be done by modifying the section below contained in global.data

GxBounds          = -10.d0,         ! Problem boundaries in computational units.
                    -10.d0,         ! format: (xlower, ylower, zlower, xupper, yupper, zupper)
                    -10.d0,         ! For 2D problems, set zlower and zupper to 0.d0.
                     10.d0,
                     10.d0,
                     10.d0

Scales

Softening

Fixed grid to AMR

Mach Number

MHD and Solvers