Hi Both, Thanks for your replies.
Daniel, the weak forms are as in the steps, but with Neumann ocnditions on boundaries other than the top. With the chosen spaces, I believe the problem is well-posed. Wolfgang, so that's exactly what I had done with MMS, and that was verified, so i assumed the way i was imposing it was correct. It then fails to get the correct value at the top. Initially, it's correct up to about 4 decimal places, then to 2, then to the unit value. I'm not sure why this would be happening when I am setting system_rhs and system_matrix to 0 each time and the only top boundary condition is as written above into the weak form. Doing std::cout of the value, it is inputting in the correct value, so not sure where the rest is coming from. I'd be grateful for any further suggestions...!! On Thursday, February 21, 2019 at 5:55:44 PM UTC+3, Wolfgang Bangerth wrote: > > > > I am trying to solve a system of equations that do this: > > Stokes to solve for v_r and p_r for one fluid (viscous rock), I use > these > > solutions on the RHS of a Darcy type equation solved like step-20 for > the > > pressure p_f in the fluid in the domain. Using the 3 solutions, I update > > another component (porosity - using a simple time dependent equation > like > > dphi/dt = rhs(pr-pf)) and put it back in the Stokes equation and so > on.... > > > > One of my conditions for the Darcy eqn is that for the top boundary, the > > pressure there equals pr found previously. > > > > Looking at the output, my values for p_f at the top boundary does not > equal > > the p_r just found. This is causing a massive issue as my porosity > equation > > needs pr-pf to be 0 (or at least very small) at the top boundary, and > this > > seems to be causing a real mess. I'm guessing because it's weakly > imposed, > > there might be issues. > > > > Does anyone have any suggestions on what to do for this? > > > > My base profile for the equations separately all work and have been > verified > > with MMS. With test values of the porosity, I have also verified that > the > > profiles separately give me what I expect (which then gives me pr-pf > monotonic > > at least, but with what is happening at the top, this bit is messed up). > > Jane -- the problem as you state it is too difficult to debug. Here's ho > to > approach this: > > * Pick a problem for which you know the exact solution. > * In the Stokes equation, in all of the places where you currently use the > Darcy solution, use the exact solution instead > * In the Darcy equation, in all of the places where you currently use the > Stokes solution, use the exact solution instead > > With this scheme, your iteration needs to converge in one step. If it > doesn't, > then you know where to look. If it does, revert the steps above one by one > until the problem stops working. > > I hope this helps! > Best > W. > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: bang...@colostate.edu > <javascript:> > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
