Hi Max, you should first check if the problem is the linear solver by switching to a direct solver. If you use Dumux 2.x, that's setting a SET_TYPE_PROP(YourTypeTag, LinearSolver, UMFPackBackend<TypeTag>); in the problem file, for 3.0 you have to change the corresponding line in the main file.
Let us know how this changes things and we can decide what to do next. Concerning the other issue about only one affected element, I'd proceed as you and use a graded mesh to check if it spreads over more elements once it's fine enough. Kind regards Bernd On Thu, Mar 7, 2019 at 7:53 PM +0100, "Maximilian Johannes Lueftner" <[email protected]<mailto:[email protected]>> wrote: Dear DuMuX experts, i have adapted the simulation from the test folder „dumux/test/porousmediumflow/mpnc/implicit/thermalnonequilibrium" . I used the YASPGrid for 1D with grading: struct Grid { using type = Dune::YaspGrid<1, Dune::TensorProductCoordinates >; }; With 800 Elements (400 in the porous domain and 400 in the outflow) and with 1600 Elements it works fin, but with more than 2000 Elements I get the following error message: Solve: M deltax^k = rNewton: Caught exception: "FMatrixError [luDecomposition:/.../dumux/dune-common/dune/common/densematrix.hh:909]: matrix is singular" If I try it with grading I receive the following error message: Solve: M deltax^k = rNewton: Caught exception: "NumericalProblem [solveLinearSystem:/.../dumux/nonlinear/newtonsolver.hh:354]: Linear solver did not converge" Could you please help me to solve this problem? I tried it myself several times but was not successful until now. I suspect that an even finer grid is needed, since only in the last element of the porous area does the temperature of the vapor increase dramatically. Or does this behavior have a different reason? When the heat flow is doubled, however, superheated steam is still calculated only in the last element. Thank you in advance and best regards, Max _______________________________________________ Dumux mailing list [email protected] https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
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