[FLASH-USERS] Numerical Effects in Spherical Coordinates UPDATE

[Michiel Bustraan]

Dear all,


I recently had some trouble with numerical effects in a spherical shock wave simulation.

I was getting some strange numerical fluctuations, and was uncertain of the cause.


It was suggested to me to use FLASH's Grid_MarkRefineDerefine to force an initial refinement as opposed to introducing random temperature fluctuations.


After some experimentation with this, I seem to have found a reasonable solution, as well as a better idea of the problem.

Still, there is something strange about some of my results.


I added an INRADIUS refinement criteria at 5 levels of refinement, out to a radius of 1e15 cm.

With just 5 AMR levels in the simulations, this meant that the simulation effectively did not refine at all.

In this case, the results were fine (image: 5layer_15d), though there were some small bumps due to the low resolution.


Now, I wanted to add additional levels of refinement, which is where things get interesting?.

I ran two simulations: the first was just with an extra level of refinement on top of the 5 layer INRADIUS, while the second also added a 6 layer INRADIUS up to 2e14 cm.

This meant that the second simulation would not have any additional refinement (or derefinement) until the shock reached past 2e14 cm.


The results are shown as 6layer_15d and 6layer_INRADIUS_15d, respectively.

While the 6 layer simulation with the additional INRADIUS refinement looks good, even beyond the boundary of 2e14, the simulation where I just added an extra level of refinement looks terrible.


Based on this, I think refining and derefining in early stages of the simulation causes the problem. The density waves in the image occur at early times and then just propagate.

Any simulation that does not allow refinement at early times shows good results.


While I consider my problem largely solved, I would still wonder why the refinement causes these large pressure waves to occur.

The outward motion of the matter leaves a minimum temperature region behind, as well as a steep pressure gradient, so that might be part of it.


Kind Regards,

Michiel Bustraan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20170407/62279abc/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 5layer_15d.png
Type: image/png
Size: 26963 bytes
Desc: 5layer_15d.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20170407/62279abc/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 6layer_15d.png
Type: image/png
Size: 37914 bytes
Desc: 6layer_15d.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20170407/62279abc/attachment-0001.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 6layer_INRADIUS_15d.png
Type: image/png
Size: 26053 bytes
Desc: 6layer_INRADIUS_15d.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20170407/62279abc/attachment-0002.png>