[yt-users] RAMSES MHD visualisation weirdness

Romain Teyssier romain.teyssier at gmail.com
Tue Feb 11 13:31:02 PST 2014


Hi all,

The RAMSES MHD output is indeed different than the hydro outputs.

What is stored is in order:
1- density
2- x-velocity
3- x-velocity
4- x-velocity
5- Left Bx field
6- Left By field
7- Left Bz field
8- Right Bx field
9- Right By field
10- Right Bz field
11- Thermal pressure
12 and beyond: Passive scalars


The left and right B fields means that in Ramses the magnetic field is face centred.
So for each cell, you have a left-face and right-face centred quantity.

Romain




On 11 Feb 2014, at 19:27, Sam Geen <samgeen at astro.ox.ac.uk> wrote:

> Hi Nathan,
> 
> Ah, thanks, you just gave me an idea - the MHD code (for some reason, I've no idea why) has 3 extra variables than NVAR, and the RAMSES frontend currently assumes that the output is reliably reporting the number of variables, so it could be getting confused. I'll try that tomorrow; you're right that this could be causing the visualisation to wig out. This could be a bug/feature that's worth changing in RAMSES itself as it's quite confusing, but since it's existed for a while now it might be simpler just to work around it in YT somehow.
> 
> I'll look at getting together some simple MHD test problems and making some outputs, too - there's at least one included with RAMSES so I'll try running that now and contact you once I'm done.
> 
> Sam
> 
> On 11/02/14 19:02, Nathan Goldbaum wrote:
>> Hi Sam,
>> 
>> Can you share the script you're using to make that plot?  In
>> particular I'd like to see the call you use to load the dataset, since
>> the number of fields you request and their order can matter a lot for
>> the RAMSES data format.
>> 
>> It would also be nice to have a public RAMSES MHD test dataset - there
>> doesn't appear to be one on yt-project.org. If you (or anyone else on
>> the list) has one to share, that should help in debugging RAMSES MHD
>> issues in the future. If so, contact me off-list and we can work out
>> how to share the data.
>> 
>> -Nathan
>> 
>> 
>> On Tue, Feb 11, 2014 at 7:58 AM, Sam Geen <samgeen at astro.ox.ac.uk> wrote:
>>> Hi,
>>> 
>>> I tried visualising a RAMSES MHD output in YT and got this weird effect:
>>> http://i.imgur.com/abjRorm.png (this happens for slices and projections)
>>> 
>>> Any idea what could be causing this? Nearly-identical non-MHD simulations
>>> seem to visualise fine, and it happened for every MHD output I've looked at.
>>> I can give more info if you like, although I'm not sure what diagnostics to
>>> check for, so pointers on how to hunt this down would be appreciated as
>>> well! It's entirely possible it's a bug/side-effect of the MHD solver,
>>> although I'm not sure what, and other visualisation routines (in
>>> IDL/Fortran) seem to work fine with some of the outputs I've tried on it.
>>> 
>>> Thanks,
>>> 
>>> Sam
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