[FLASH-USERS] Possibility of restarting FLASH from a selected region

[Kevin Olson]

Dear Seyit,

Since you are using FLASH2.5, what I suggested before will not work 
since the version of PARAMESH that is used does not allow more than 10 
refinement levels.  Newer versions PARAMESH allow more refinement 
levels and are only supported in FLASH 3.x.

I don't think doing what you want to do will help with regards to the 
timestep problem.
You would still need to take smaller timesteps in your 'zoomed' in 
region.

Also, I and others have found the almost all the time computing done in 
FLASH is done on the finest meshes.  So, derefining the mesh in 
uninteresting regions of your simulation and keeping them shouldn't be 
a severe performance hit at all.

I am not that familiar with the details of ENZO, but from what I have 
seen I think it is a good code and if it does what you need, give it a 
shot!

Best,
Kevin Olson

On Mar 12, 2009, at 10:14 AM, Seyit Hocuk wrote:

> Dear Kevin,
>
> I am using FLASH 2.5 still. However, 50! levels? That's insane :).
> Refining is especially interesting (my opinion) if you do 
> structure/star formation where you have a core collapse and the 
> density, temperature and pressure increases thereby reducing the 
> timestep. In effect, for me, I can not go beyond level of ~10 
> refinement. However, starting from a smaller boxsize (in a specific 
> region) would make it possible to do the same resolution (say 10) and 
> result in a detailed image of that area. Of course, refining only this 
> selected region and adapting the mesh from 10-20, is more ideal 
> (boundary conditions and stuff), it is much more computer demanding 
> (even though the number of blocks do not seem increase much) and 
> impossible to achieve for me.
>
> I have the impression that other codes, like ENZO, can do this more 
> easily.
>
> Kind Regards,
> Seyit
>
>
>
> Kevin Olson wrote:
>> Dear Seyit,
>>
>> What version of FLASH are you using?  If you are using version 3.0 or 
>> above then you can refine up to 50 levels.
>>
>> I don't think FLASH supports specifically what you are asking for.  
>> You could try just keep the computational domain as it is, derefine 
>> in the regions where you are not interested and refine in the region 
>> where you are interested.  An advantage of doing this is that the 
>> original boundary conditions in your refined regions will be 
>> preserved.  A disadvantage is that the floating point computations 
>> may loose accuracy.
>>
>> Best,
>> Kevin Olson
>>
>> On Mar 12, 2009, at 9:15 AM, Seyit Hocuk wrote:
>>
>>> Hi Community,
>>>
>>> I was wondering if it is possible to start a new Flash simulation 
>>> from an end point of an older simulation by just selecting a part of 
>>> the data, perhaps by a child block/level. This would now be the top 
>>> block and act as the new initial conditions, forgetting everything 
>>> else. I hope I am being clear in this. This way we could go much 
>>> higher in resolution, without increasing the computational demands, 
>>> by zooming in on an area and restarting simulation from there.
>>>
>>> Thanks,
>>> Seyit
>>>
>>
>