Another vote for shells - this would be super handy...
Derek
On Fri, Feb 21, 2014 at 9:55 AM, David Knezevic
<dkneze...@seas.harvard.edu>wrote:
> I'd definitely be enthusiastic about getting support for shells in
> libMesh as well.
>
> David
>
>
>
> On 02/21/2014 11:20 AM, Paul T. Bauman wrote:
>
> Others may also be interested in this, but I have a keen interest. I'd be
> happy to look at the patch, but, even better, would be for you to open a
> pull request on GitHub (https://github.com/libMesh/libmesh) so that, if
> we decide to integrate the patch, we have a commit history of your
> development since it sounds like it's not a small patch.
>
> Best,
>
> Paul
>
>
> On Fri, Feb 21, 2014 at 8:53 AM, Roman Vetter <vette...@ethz.ch> wrote:
>
>> Dear libMesh devs,
>>
>> the roots of the finite element method lie in structural analysis and
>> the need to solve elasticity problems. Thin shells with a stretching and
>> a bending rigidity are an extremely important special case. The bending
>> term requires C1 finite elements which have been hard to construct for
>> arbitrary surface topologies until the subdivision surface paradigm
>> found its way to the FEM a few years ago (Int. J. Numer. Meth. Engng.
>> 47, 2039-2072 (2000), more than 300 citations!). Ever since, subdivision
>> surfaces are the way to go in thin shell finite element analysis, as they
>>
>> 1) require only the three nodal displacement dofs, no rotational or
>> other auxiliary dofs,
>> 2) require only one Gauss point per element (very efficient), although
>> more still work of course,
>> 3) greatly simplify the implementation of thin shells with arbitrary
>> topology.
>>
>> Still, they have not made it into most finite element packages, perhaps
>> because they somewhat deviate from conventional FE principles:
>>
>> a) the shape functions don't interpolate the mesh nodes, instead they
>> approximate them,
>> b) the solution on an element is determined not only by the nodal
>> solutions of its nodes, but also of nodal solutions at the neighboring
>> nodes
>> c) the number of shape functions per element depends on the mesh
>> connectivity,
>> d) the conventional h-refinement and p-refinement techniques can't be
>> applied
>> e) they require special treatment of boundaries and constraints.
>>
>> I have prepared a patch that adds the most popular, versatile and
>> widely-used type of subdivision surface elements to libMesh: Loop
>> subdivision surface elements. Everything is readily Doxygen-commented
>> like all of libMesh. I've also prepared a new example
>> (miscellaneous_ex11) showing how to use the new element on a loaded thin
>> elastic plate.
>>
>> This is a joint effort initiated by Norbert Stoop in 2008. The related
>> discussions can be looked up at:
>> http://sourceforge.net/mailarchive/message.php?msg_id=20778890
>> http://sourceforge.net/mailarchive/message.php?msg_id=20808509
>>
>> Why didn't I attach the patch already? I'd first like to know if you're
>> interested at all. Why wouldn't you, you're asking? Bear in mind the
>> unconventional nature of subdivision surface finite elements. (b)
>> requires a more general treatment of the number of shape functions in
>> DofMap, as it is no longer constant. (c) requires a new integer stored
>> in each Node instance, holding the node valence. (d) means some of the
>> nice features of libMesh like AMR won't work with the new element. (e)
>> means that libMesh's built-in boundary and constraint handling won't
>> work with the new element. Furthermore the new element supports only 2D
>> triangular meshes in 3D space, so it is a far cry from being as general
>> as other elements implemented in libMesh.
>>
>> Why would you be interested despite all this? First of all, subdivision
>> surfaces seem to be the future of two-dimensional C1 elements. They
>> would give libMesh an advantage over other FEM packages. Moreover,
>> recent advances in finite element research suggest that more new
>> elements of this general kind (isogeometric analysis) are on the way.
>> Some of them similarly generalize the way we traditionally think about
>> element shape functions and even work with less than one quadrature
>> point per element [sic!].
>>
>> This extension of libMesh adds five new source code files and modifies
>> 22 more (mostly small additions like enums etc.). I've tried to keep the
>> patch minimal. It has been in successful operation for a few years now
>> at our labs, and I think it's about time it's committed to the official
>> libMesh repository. It would make a great added value to libMesh for all
>> those who use it for thin shell analysis (and I know that there are a
>> few of them around). I'm happy to send you the patch and further
>> explanations on it if you're willing to give it a closer look.
>>
>> Best regards,
>> Roman
>>
>>
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