[MOAB-dev] Representation of spectral meshes, opinions wanted

[Lorenzo Botti]

Option 5 is very very close to what I consider an agglomerated element, with a strong restriction on the element shape in this case. Actually I store agglomerated elements as entity sets. Some time ago I submitted a patch to partition such agglomerated elements meshes based on an arbitrary tag associated to each set.
I can resubmit it if someone is interested.

It would be interesting to have the ability to generate high order spectral elements starting from block structured meshes. Is it possible to do such a thing using the structured mesh MOAB interface?

Regarding the spectral meshes storage I have to say I use nodes only to define the domain discretization, then I use modal basis functions for the discrete spaces. For lagrangian elements I don't need a tag for dofs storage since the dofs are the nodes coordinates themselves. I'm interested in considering other possibilities like splines, nurbs... In this context I think that the ability to easily obtain all (low and high order) nodes for each side is important, so option 2 I guess. This also allows to easily get the nodes required to define a high order serendipity element.

Thanks for the opportunity to share ideas. 
Best regards.
Lorenzo




Tim Tautges <tautges at mcs.anl.gov> wrote:

>Aha, right, forgot to mention the current solution, which is to construct fine mesh from GLL points in each element. 
>Your option 5 would be to do that then link those elements to coarse elements somehow.  Would probably be easiest using 
>a tag with start/end of a coarse element's refined elements.  This would also work for h-refined meshes.
>
>- tim
>
>On 10/31/2012 12:07 PM, Iulian Grindeanu wrote:
>>
>>
>> ------------------------------------------------------------------------------------------------------------------------
>>
>>     Hi all,
>>         We're now supporting with MOAB two different applications that use spectral meshes (Nek5000, an ANL CFD code, and
>>     HOMME, an SNL/NCAR climate code).  As is usually the case, we not only have to represent these meshes in MOAB, but
>>     support meshes of those types in tools working on MOAB (viz, partitioning, etc).  Spectral meshes are challenging
>>     because there are many ways to represent and order them, with applications typically using a lexicographic ordering and
>>     mesh-based tools preferring something more akin to higher-order element ordering.
>>         I've written the attached document that describes the problem, along with a few possible options for representation
>>     of these meshes.  I'd welcome comments if you have them.  Thanks.
>>
>>     - tim
>>
>> Hello,
>> There is another option, which is actually close to what we do now in Homme meshes: store the "finer" mesh, formed by
>> spectral points, in a
>> very regular grid, on each "coarse" element. And maybe have a method to group the "finer elements" on each "coarse"
>> (spectral ) element.
>>
>> It is much more expensive for 3d (homme is basically 2d manifold), so maybe it is not worth mentioning. The only
>> advantage to this (5th) option is that is probably the easiest in terms of development, and we could even use the
>> existing visu tools. (actually, there is a visit plugin to display nek meshes directly, using this concept)
>>
>> All other options will need some working on the visu side.
>>
>> Iulian
>>
>>     --
>>     ================================================================
>>     "You will keep in perfect peace him whose mind is
>>         steadfast, because he trusts in you."               Isaiah 26:3
>>
>>                    Tim Tautges            Argonne National Laboratory
>>                (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>>        phone (gvoice): (608) 354-1459      1500 Engineering Dr.
>>                   fax: (608) 263-4499      Madison, WI 53706
>>
>>
>
>-- 
>================================================================
>"You will keep in perfect peace him whose mind is
>   steadfast, because he trusts in you."               Isaiah 26:3
>
>              Tim Tautges            Argonne National Laboratory
>          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>  phone (gvoice): (608) 354-1459      1500 Engineering Dr.
>             fax: (608) 263-4499      Madison, WI 53706
>