Dear Roy, On Mon, 19 Oct 2009, Roy Stogner wrote:
> On Mon, 19 Oct 2009, Tim Kroeger wrote: > >> Has there ever been the idea of implementing composite finite elements >> (CFE) into libMesh? How much work would that approximately be? > > There appears to be a slight overloading of the nomenclature here... > I'm used to "composite finite elements" being a synonym for > "macroelements" like the Clough-Tocher triangles, which were > practically the first thing I added to the library years ago. > > But you're referring to something libMesh doesn't have. I assume you > mean elements with subgrids, i.e. to build "handbook functions" for > discretizing problems with complex fine-scale constitutive fields? Well, actually I don't know what Clough-Tocher elements are, hence it is possible that they are exactly what I am meaning, although I don't think so. Let me explain in my own words what I mean: If a complicated geometry is involved in a problem (which can either mean that the computational domain has a complicated geometry or the boundary between subdomains has a complicated shape -- or both), an alternative to the usage of a grid that resolves these shapes sufficiently well is to use just a grid of uniform squares/cubes (on a larger domain, if necessary) and to modify the shape functions on those squares/cubes that intersect with the complicated boundary. That is, if there are eg. subdomains with different diffusion coefficients, the shape functions on squares/cubes that intersect with the boundary will include the required gradient jump conditions. Is this what Clough-Tocher elements are? >> This is a low-priority task; I would just like to see what you guys >> think. If CFEs would generally be welcome and you think there would >> be a sensible API for that, I'll keep that in my mind and perhaps some >> day put a student on this task. > > CFEs would definitely be welcome, since they ought to be able to fit > onto the FEBase API without changing the latter too much. The > tricky question is "how do you automatically solve the subproblem" > with them... You'd basically have to hot swap an entire new Mesh (and > corresponding DoF numbering and algebraic discretizations) in and out > from underneath the EquationSystems. Or you'd have to require the > user to have an FEMSystem or some other API that provides physics at a > non-global level. If I understand you correctly and if were're talking about the same thing, you are refering to the question how the library should know (and store) which cells would have to use modified shape functions and in which way they are modified. I currently don't know how other FEM libraries manage this, but I guess there is some solution. Best Regards, Tim -- Dr. Tim Kroeger [email protected] Phone +49-421-218-7710 [email protected] Fax +49-421-218-4236 Fraunhofer MEVIS, Institute for Medical Image Computing Universitaetsallee 29, 28359 Bremen, Germany ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
