[Users] Problem with CarpetRegrid2/AMR

[Erik Schnetter]

Hal

Thanks for taking the discussion to the list.

Looking at your pictures again, I see one large problem I didn't
realise before: your domain is periodic, but the grid structure is
not. It would be the task of CarpetRegrid2 to ensure that the grid
structure is also periodic, but this is not implemented yet; hence the
periodicity thorn cannot fill in the boundary points of the fine grid.

I suggest to switch to reflecting boundary conditions to test this,
and/or to use a larger domain so that there is no refinement near the
domain boundary.

It is straightforward to implement periodicity in the grid structure
-- one needs to take the current grid structure, shift it in the 26
directions, and take the logical union of all 27 grid structures. This
will then be automatically clipped. The most complex part is
calculating by how much to shift.

-erik

PS: You say "first picture" etc., but I think my email client shows
the attachment in a different order. I would rather specify
attachments via file names, and rename files accordingly. For my, chi
on level 1 is the 5th image, visit0007.png.

On Tue, Aug 30, 2011 at 3:37 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> I am trying to setup a simple simulation using CarpetRegrid2's AMR
> capability. As Erik has already pointed out to me (off list), the
> adaptive-refinement triggering code is still under development.
> Nevertheless, I would really like to get it working.
>
> In my current test case, I am using Kranc to solve a Klein-Gordon
> equation (with a non-linear potential). With the provided initial
> conditions, the system has an expanding bubble. This works well when
> refinement is turned off. To be clear, the evolution equation is:
>
> evolCalc =
> {
>        Name -> "SFBubble_Evolve",
>        Schedule -> {"in MoL_CalcRHS"},
>        Where -> Interior,
>        Shorthands -> {},
>        Equations -> {
>                dot[chi]        -> chiM,
>                dot[chiM]       -> PD[chi,li,lj] Euc[ui,uj] - Vchi[chi]
>        }
> };
>
> where Vchi[chi_] := V'[chi] (V is the potential). The AMR level_mask is
> set by:
>
> lvlmskSet =
> {
>        Name -> "SFBubble_SetLevelMask",
>        Schedule -> {"AT preregrid"},
>        Where -> Interior,
>        Shorthands -> { adchix, adchiy, adchiz },
>        Equations ->
>        {
>                adchix -> fabs[dx PD[chi,1]],
>                adchiy -> fabs[dy PD[chi,2]],
>                adchiz -> fabs[dz PD[chi,3]],
>
>                "level_mask" -> (
>                        Max[
>                                adchix, adchiy, adchiz
>                        ]/dchimax
>                ) /. Max[a_, b_, c_] -> fmax[a, fmax[b, c]]
>        }
> };
>
> (in words: the value of chi should not change by more than dchimax over
> the length of one grid cell)
>
> I am using the Periodic thorn to provide periodic boundary conditions.
>
> I've attached six pictures. They are at t = 0, the first level 1
> intermediate time step, and the first coarse time step. The first three
> pictures are the value of chi on a slice through the middle of the box.
> The second three pictures are the value of level_mask. As can be seen in
> the second chi image, the interpolation into the refined region seems to
> be incorrect. The "boundary" seems to have appeared in the middle of the
> block. I have also attached the block descriptions. Is there something I
> could be doing incorrectly which would cause this? Otherwise, does
> anyone have any ideas on where to look for the problem?
>
> I am using the trunk version as of this morning.
>
> Thank you in advance,
> Hal
>
> --
> Hal Finkel
> Postdoctoral Appointee
> Leadership Computing Facility
> Argonne National Laboratory
>
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>
>



-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/