[FLASH-USERS] Refinement and Derefinement Criteria

[Klaus Weide]

On Wed, 23 Apr 2008, Robert Fisher wrote:

> Hi Seyit :
>
>  What criterion one chooses to refine an adaptive mesh depends crucially 
> upon what physics one is simulating, and what scientific questions one is 
> seeking to address. [...]
>
> On Wed, 23 Apr 2008, Seyit Hocuk wrote:
>> Flash, as I believe, refines automatically when you don't put lrefine_max 
>> equal to lrefine_min. With witch criteria can I play with the refinement 
>> and how can I say when to derefine. Basically I don't completely understand 
>> how refinement works and the user guide is not completely transparant about 
>> this. I assumed that delta_ref, delta_deref and the reference_density were 
>> exactly these parameters. I initially thought that when the density "rho" 
>> (or whatever parameter is set for refinement) at each block exceeds the 
>> reference density by amount of delta_ref (multiplied or added?) then it 
>> refines and when it is lower by an amount of delta_deref it derefines. 
>> However, changing these parameters has proven to have little effect for me.
>> 
>> Can anybody explain me how this works and what the formula's are if any?

In addition to Bob Fisher's remarks:

FLASH does have a default implementation of refinement/derefinement 
criteria.  This is described in the User's Guide; for FLASH 2.5, in
the Mesh chapter under "8.5 Adaptive mesh" (in particular,
"8.5.2 Algorithm").

Klaus