Hi Roy, Thanks for the reply. On Wed, Mar 13, 2019 at 1:22 PM Stogner, Roy H <royst...@ices.utexas.edu> wrote:
> > On Wed, 13 Mar 2019, Renato Poli wrote: > > > In the same run (other timesteps), I also see DIVERGED_INDEFINITE_MAT. > > In many timesteps it converges. It happens sometimes... > > I am using LU preconditioners. > > Built-in PETSc LU? If so then you might try MUMPS or you might try > different dof ordering options; I've seen each of those fix LU > failures in the past. > How do I change the dof ordering options? I want to try this one before switching to MUMPS. > > I have a 2D circumference inside the domain (petroleum wellbore). > > I need to set a Neumann BC (total oil rate), but the pressure must be > constant in the circumference. > > That... sounds like it'll be well-defined even in the discrete case > (N-1 constraints for strong enforcement of that constant, 1 summed BC > for total flow rate) but it couldn't hurt to check what the matrix > conditioning looks like. > Agreed. > > > Similar to a distributed total force in a rigid plate - for mechanical > solvers. > > > > My approach: > > 1) select a DOF for the circumference. > > 2) tie all other DOFs in the circumference to this one with > "add_constrain_row". > > Darcy flow, using one LAGRANGE variable for pressure I assume? > Yes. > > > Can you see another way to do that? > > Add a SCALAR variable to use as a Lagrange multiplier? > This sounds like a much cleaner solution. I could not understand how to do that in libmesh so far. It is probably time to put some more effort here... I see I must add a Kp_alpha matrix. Do I need the Kalpha_p as well? My conditions are: p1=alpha , p2=alpha , p3=alpha , p4=alpha and so on. How the last equation looks like? I can imagine something like: p1 - p2 + p3 - p4 = 0 But that does not look right ... > > We don't have any examples corresponding to your case precisely but > systems_of_equations_ex3 and ex5 might be helpful. > --- > Roy > Thanks upfront, Renato _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
