On Mon, 11 Jul 2011, Ataollah Mesgarnejad wrote: > Can anyone please instruct me on elements and FE types that I can > use for second order problems? As part of my code solves biharmonic > equation. I get the warning:
Any FE type will give you second derivatives, but the results will only be L2 integrable for the CLOUGH and HERMITE (i.e. our C1) elements. Try to do a fourth-order problem with anything else we have and you'll need to use a discontinuous or semi-discontinuous formulation. > WARNING: Second derivatives are not currently correctly calculated on > non-affine elements! > > when I try to run my code on some of my meshes. The HERMITE elements are very restrictive: they basically require your elements to be parallelograms in 2D or parallelepipeds in 3D. For any other element, the restriction is that the master->physical element mapping has to be an affine map: (x,y,z) = A * (xi,eta,zeta) + b for some tensor A and vector b. For quad/hex elements that boils down to parallelograms/parallelepipeds again; for triangles and tets anything with all straight edges will work. We'd love to get a patch implementing more flexible C1 quad/hex elements, and/or a patch which calculates the second derivative terms we currently neglect on non-affine elements, but generally anyone who would benefit from such features is wise and/or lazy enough to switch to straight-edged tri/tet meshes instead. --- Roy ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2d-c2 _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
