On Sun, Jun 1, 2008 at 10:51 PM, Derek Gaston <[EMAIL PROTECTED]> wrote: > So... I've been working with the NonlinearImplicit system... solving > jacobian free problems using Petsc SNES. Everything is going pretty > well (Ben's interface is great!)... but I've hit a bit of a snag on > the boundary conditions. I would really like to impose both Dirichlet > and Neumann conditions similarly... by integrating their residual > contributions over the boundary. So for instance for a Dirichlet > condition I have something like this: > > Intg_boundary( u - BC )
Hey Derek, Are you doing a penalty formulation for the Dirichlet BC? You'll need to multiply by a large penalty for this condition to be enforced. > and similarly for Neumann: > > Intg_boundary( grad_u - BC ) Here I don't think you subtract... you just replace du/dn with whatever the BC is (it may depend on u, it may be nonlinear) and then add that term to your weighted residual statement. -J > The trouble that I'm running into is that these residual contributions > seem to be too small... and are only very loosely satisfied by SNES. > For instance, solving u''=0 on [0,1]x[0,1] with u=0 at x=0 and u=1 at > x=1... I end up with u actually being .3333 at x=0 and .6666 at x=1. > Of course I can dial down the residual tolerances for snes... but this > only gets me so much closer. The other thing I've tried is to put a > multiplier in front of the boundary integral (like 1e7 or so)... this > ends up working well for satisfying the boundary conditions... but > then the interior residuals are swamped out... meaning they aren't > well resolved. > > So, I'm wondering if anyone has any better ideas? Is there a good way > to choose the correct multiplier? Am I going about the whole thing > incorrectly? > > Thanks for any help... > > Derek > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Libmesh-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/libmesh-users > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
