From: Roy Stogner <roystgnr@ic...>  20070911 04:53:08

On Tue, 11 Sep 2007, Shengli Xu wrote: > Hi, I use the mixed galerkin finite element to sovle darcy equation. > pressure is linear interpretation, velocity is quadratic interpretation¡£ The > domain is square. The result is correct when I apply noslip b.c on top and > bottom side, zero pressure on rightbottom corner, Ux=1.0 on left side. But > I can not get correct result if I apply noslip b.c on top and bottom side, > zero pressure on the right side, P=1 on the left side. Why can I get correct > result with this b.c.? Unless someone has seen a similar Darcyflow problem before (John?), which is a long shot, you're not likely to find someone who can answer this. If you've already got the problem boiled down to a simple benchmark, I'd try running it on a single square element and comparing the numerical linear system to what you can compute by hand. Doing so for even that bare minimum (22x22 in your case, I suppose) system can be tedious, but in the past it's been the only way I've been able to find one or two subtle bugs in application codes.  Roy 