Hi Sebastian, I think what you described is correct. I could not see why it did not work out. But I recommend reading Timo's dissertation. Also, for the implementation, you can check out my code for the implicit scheme <https://github.com/OpenIFEM/OpenIFEM/blob/master/source/insim.cpp#L56> and explicit-implicit scheme <https://github.com/OpenIFEM/OpenIFEM/blob/master/source/insimex.cpp#L42>.
Best, Jie On Thu, Nov 1, 2018 at 5:58 PM SebG <seb_gl...@gmx.de> wrote: > Dear Jie, dear deai.ii user, > > I am working on the Cahouet-Chabbard preconditioner in context > buoyancy-driven flow problems. Somehow my preconditioner does not work > quite well. The number of iterations depends on the time step, which should > not be the case. With more than 50 iterations it is also quite large. I > would like to ask if you or someone else could provide some details of your > implementation or give tips. > > The velocity block of the system matrix is given by: > alpha / timestep * M + gamma * c * K . > M, K are the velocity mass and stiffness matrix. The scalars alpha and > gamma are related to the time discretization and c is a dimensionless > parameter. If I am not wrong, the Cahouet-Chabbard Schur complement > approximation is given by > S^-1 = alpha / timestep * K_p^-1 + gamma * c * M_p^-1 . > > I am assembling the pressure stiffness and pressure mass matrix > explicitly. However my problem is a pure Dirichlet problem w.r.t. the > velocity, which in contrast mean that preconditioner is using Neumann BCs. > Therefore, I am constraining one pressure dof, which regularizes the > pressure laplace matrix. This approach is discussed in another thread > <https://groups.google.com/forum/#!msg/dealii/HBQD_WXuNOs/w0A56WAf2WcJ>. > For this reason I have two ConstraintMatrix object one for the system > matrix and one for the preconditioner. > > I also attached my code which is based step-32 but in serial. > > Best wishes, > Sebastian > > Am Freitag, 20. Oktober 2017 09:36:07 UTC-7 schrieb Jie Cheng: >> >> Hi Martin and Wolfgang >> >> Thank you very much for the helpful comments and references. I'll start >> to read the works you mentioned. >> >> >>> Jie -- I think this would be a very interesting program for others as >>> well. >>> Would you be interested in contributing it to the code gallery? >>> >> >> I'd love to contribute after I work it out! >> >> Jie >> > -- > 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 a topic in the > Google Groups "deal.II User Group" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/dealii/41VjIh5dzng/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > dealii+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- 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.
