[FLASH-USERS] refinement problems with FLASH 4.2

[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