[FLASH-USERS] refinement problems with FLASH 4.2

[Christoph Federrath]

Hi Thomas,

then I still think this is simply because those z velocities are so close to zero in the slice that you are showing that you basically plot noise around zero in the center. If this were the exact z=0 plane, v_z should be zero, but since you seem to set z on a cell center that is just above the disk, you see noise with some negative v_z caused by infall onto the disk, but just at 1/2*Delta_x above the disk. Can you confirm the slice position at z = + 0.5*Delta_x at the highest level of AMR? This is so close to v_z = 0 that what you see appears basically as noise around v_z = 0.

Kind regards,

Christoph



________________________________
Dr. Christoph Federrath
Monash Centre for Astrophysics,
School of Mathematical Sciences,
Monash University,
Clayton, VIC 3800, Australia
+61 3 9905 9760
http://www.ita.uni-heidelberg.de/~chfeder/index.shtml?lang=en


Am 21.05.2014 um 09:54 schrieb Thomas Peters:

> Dear Kevin, Christoph and John,
> 
> this is not a plotting issue, I can see these jumps using yt as well. Also, I don't think this is noise since the maximum velz value is only a factor of 10 smaller than the maxmimum velx value (in magnitude). The slices are not centered around zero but on the cell with the highest density. I am using the default paramesh library and hydro solver of the setup in FLASH 4.2.0.
> 
> Best regards,
> Thomas
> 
> 
> Am 2014-05-21 18:43, schrieb John ZuHone:
>> Thomas,
>> I would also suggest looking at the dataset in yt:
>> http://yt-project.org [2]
>> A python script that would get you going with looking at slices is:
>> from yt.mods import *
>> ds = load(your_filename)
>> slc = SlicePlot(ds, "z", ["velx", "vely", "velz"])
>> slc.annotate_grids()
>> slc.save()
>> you can find more examples here:
>> http://yt-project.org/docs/2.6/cookbook/simple_plots.html [3]
>> On May 21, 2014, at 11:58 AM, Christoph Federrath
>> <christoph.federrath at monash.edu> wrote:
>>> Hi Thomas, Hi Kevin,
>>> I don't think it's the refinement criterion. There shouldn't be big
>>> jumps and I don't think there are. Isn't it that you simply plot
>>> values very close to zero in velz? This is basically a slice in the
>>> mid plane of the disk, which should actually have zero velocity in z
>>> direction, because everything is symmetric in z direction? Thus, the
>>> velocity in the z=0 plane should be zero and what you are plotting
>>> is basically numerical noise around zero values?
>>> I'm also wondering whether this particular plotting issue might have
>>> something to do with the way xflash interpolates values? Have you
>>> tried using visit and making the same cut in z? Definitely, the velz
>>> axis you are showing is funny and seems skewed to negative values,
>>> but they are all quite small compared to sound speed. If this is
>>> really a cut at exactly z=0, then the z velocity should be zero.
>>> What paramesh lib (implementation) are you using? And what hydro/MHD
>>> solver are you using? Is this in the latest FLASH4.2.1?
>>> Kind regards,
>>> Christoph
>>> ________________________________
>>> Dr. Christoph Federrath
>>> Monash Centre for Astrophysics,
>>> School of Mathematical Sciences,
>>> Monash University,
>>> Clayton, VIC 3800, Australia
>>> +61 3 9905 9760
>>> http://www.ita.uni-heidelberg.de/~chfeder/index.shtml?lang=en [1]
>>> Am 21.05.2014 um 08:47 schrieb Kevin Olson:
>>> Hi Thomas,
>>> This is due to the fact that the Sink particle test uses only a
>>> Jeans criterion based refinement test. This does nothing to detect
>>> shocks and other discontinuities in the flow. I think you will find
>>> that if you turn on the standard FLASH refinement criterion plus the
>>> Jeans length criterion, you problem will go away...but at the cost
>>> of having many more refinements.
>>> Also, the problem you are running is basically that of a collapsing
>>> cloud and the regions where you are seeing large errors probably
>>> don't have a large impact on the overall solution you are looking
>>> for since those regions probably don't have a very high density.
>>> Hope this helps.
>>> Kevin Olson
>>> On May 21, 2014, at 11:18 AM, Thomas Peters wrote:
>>> Dear FLASH users,
>>> I am having some problems with the grid refinement in FLASH 4.2. I
>>> have attached some slices of a simulation run with the standard
>>> setup SinkRotatingCloudCore. The only thing I modified was to set
>>> lrefine_max to a larger number in order to get more refinement
>>> levels.
>>> The attached z-slices show very strong jumps in velz at refinement
>>> boundaries, while velx and vely remain smooth. However, velx has
>>> jumps in x-slices and vely has jumps in y-slices as well.
>>> Has anyone seen such a problem before and knows how to get rid of
>>> it?
>>> Thanks for your help,
>>> Thomas
>> <BB_hdf5_plt_cnt_blk_velz0142.png><BB_hdf5_plt_cnt_velx0142.png><BB_hdf5_plt_cnt_vely0142.png><BB_hdf5_plt_cnt_velz0142.png>
>> Links:
>> ------
>> [1] http://www.ita.uni-heidelberg.de/~chfeder/index.shtml?lang=en
>> [2] http://yt-project.org
>> [3] http://yt-project.org/docs/2.6/cookbook/simple_plots.html