[Dune] globalRefine and ALUGRID_SIMPLEX

[Dragan Vidovic]

Hi Andreas,

Thank you for you reply. Alu does not needs to know that I started
with cubes in order to divide each of the tetrahedra into eight
similar ones. It just needs to divide each edge in two, each face in
four, and connect nodes right. I think it fails in the last step: it
connects the nodes in a wrong way. This is difficult to see because it
looks all right from the outside, but four of the 48 tetrahedra in my
final grid have cell centres at z=0.5, which means that they are not
similar to the big tetrahedra that they were made from.

Cheers,

Dragan


On Mon, Mar 8, 2010 at 2:53 PM, Andreas Dedner
<dedner at mathematik.uni-freiburg.de> wrote:
> Hi,
> the grids will always be different.
> DGF transforms cubes to simplicies by a dividing them into 6
> tetrahedrons. Whereas globalrefine should actually divide each
> each tetra! into 8 similar ones, e.g.,
> your first DGF+globalrefine = 6*8=48 tetras
>     second DGF             = 8*8=64 tetras
> alu does not know that you started with cubes so it can not remove
> the "make6" step, reine for cubes and then repeat the make6 algorithm
> again.
> Andreas
>
> Dragan Vidovic wrote:
>>
>> Dear all,
>>
>> I would like to draw your attention to the way the globalRefine
>> function works with ALUGRID_SIMPLEX in 3d. I define a simple unit cube
>> in a dgf file
>>
>> DGF
>> Interval
>> 0 0 0  % first corner
>> 1 1 1  % second corner
>> 1 1 1  % 1 cells in x and 1 in y direction
>>
>> and I do globalRefine(Dune::DGFGridInfo<GridType>::refineStepsForHalf())
>> in the code. I would expect the result to be as if my dgf file was
>>
>> DGF
>> Interval
>> 0 0 0  % first corner
>> 1 1 1  % second corner
>> 2 2 2  % 2 cells in x and 2 in y direction
>>
>> but it is not. Actually, in the grid made by globalRefine, four cells
>> stretch from the bottom to the top of the cube, which means that the
>> new cells were not made by simply dividing the old cells into eight
>> similar cells. This reduces the grid quality, and I believe it was not
>> intended.
>>
>> I must admit that my installation is somewhat older - I'm using a SVN
>> version of Dune from 13. of November 2009, and Alugrid 1.1.14.
>>
>> Cheers,
>>
>> Dragan
>>
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