On Sat, 6 Jan 2018, Renato Poli wrote:
Hi again, I am trying to close this issue here, but got into trouble again. Is there a common way to tie a dof against the derivative of other dofs.
Not really. For one thing, there's no such thing as a spatial derivative of a dof. You can get the spatial derivative of a variable at *some* places in a typical finite element solution, but not everywhere, and in particular not at the vertices (where your lowest-order C0 dofs will be located!).
My primary variables are 'pressure' and 'displacement' and I need to tie pressure to stress (C du/dx)? I can imagine using more dofs in the "constraint_row" (the element ones, which are summed together to get the derivative), but I am afraid of getting an unstable system.
You could get the dof coefficients corresponding to a du/dx (get dphi for each shape function at the point where you want a gradient evaluation, take the x component of each) and insert them into a constraint row, but this is not likely to be the most accurate way to solve your problem. Not sure what you're solving (contact? porous media flow?) but there's probably a formulation out there somewhere which enforces a pressure-strain relationship weakly rather than with point-by-point constraint equations. --- Roy ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
