[FLASH-USERS] refinement problems with FLASH 4.2

[Christoph Federrath]

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


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>
>