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Posted:
6 years ago
2018年7月3日 GMT-4 05:16
I have to add, that the model basically works. I only changed one little thing from the working model: a rotation was added.
I have to add, that the model basically works. I only changed one little thing from the working model: a rotation was added.
Henrik Sönnerlind
COMSOL Employee
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Posted:
6 years ago
2018年7月4日 GMT-4 02:12
Updated:
6 years ago
2018年7月4日 GMT-4 05:28
Hi Jan,
This indicates that the system matrix is ill-conditioned. There can be many underlying reasons, ranging from the actual physical properties of the problem you are solving to erroneous boundary conditions or material properties.
If the solver for the 'innermost' problem (the linear solver) in your iterations reports this kind of problem, the 'outer' nonlinear solver will not accept the solution as converged, even though its own criteria are fulfilled.
You can force the nonlinear solver to accept the solutions nevertheless. Change the settings in the 'Error' section in the 'Direct' node in the solver sequence. This is usually safe in a nonlinear problem, since a 'bad' solution will give extra iterations. Your graph indicates that there are no large residuals, so suppressing the check on the solution from the linear solver seems OK.
Regards,
Henrik
-------------------
Henrik Sönnerlind
COMSOL
Hi Jan,
This indicates that the system matrix is ill-conditioned. There can be many underlying reasons, ranging from the actual physical properties of the problem you are solving to erroneous boundary conditions or material properties.
If the solver for the 'innermost' problem (the linear solver) in your iterations reports this kind of problem, the 'outer' nonlinear solver will not accept the solution as converged, even though its own criteria are fulfilled.
You can force the nonlinear solver to accept the solutions nevertheless. Change the settings in the 'Error' section in the 'Direct' node in the solver sequence. This is usually safe in a nonlinear problem, since a 'bad' solution will give extra iterations. Your graph indicates that there are no large residuals, so suppressing the check on the solution from the linear solver seems OK.
Regards,
Henrik
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Posted:
6 years ago
2018年7月4日 GMT-4 05:24
Updated:
6 years ago
2018年7月4日 GMT-4 05:30
Hi Henrik,
thank you very much for your reply.
I am testing the model without the Error check right now.
Regards,
Jan
Hi Henrik,
thank you very much for your reply.
I am testing the model without the Error check right now.
Regards,
Jan
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Posted:
6 years ago
2018年7月5日 GMT-4 07:25
Hi again,
I tried Henriks tip with the Error check and the model does solve for a few time steps now (see the attached plot of the Convergence). Unfortunately, after some succesfull time steps, the nonlinear solver fails to converge.
I checked if the dependent variables show questionable behaviour. They look very smooth and not suspicious. From my point of view, the results look physically correct, but the solver says otherwise...
Kind regards,
Jan
Hi again,
I tried Henriks tip with the Error check and the model does solve for a few time steps now (see the attached plot of the Convergence). Unfortunately, after some succesfull time steps, the nonlinear solver fails to converge.
I checked if the dependent variables show questionable behaviour. They look very smooth and not suspicious. From my point of view, the results look physically correct, but the solver says otherwise...
Kind regards,
Jan