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Error in pressure drop simulation
Posted Mar 11, 2015, 9:51 a.m. EDT Fluid & Heat Version 5.0 1 Reply
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Hi!
I get the following error when trying to simulate the pressure drop in a long pipe with a lot of inlets (se attached model).
Failed to find a solution.
Segregated group 1
Matrix has zero on diagonal for the SSOR update submatrix in the Vanka algorithm.
In segregated group 1:
Returned solution is not converged.
The model has been working before but when i made a few changes it won't run anymore.
Thank you for your help!
I get the following error when trying to simulate the pressure drop in a long pipe with a lot of inlets (se attached model).
Failed to find a solution.
Segregated group 1
Matrix has zero on diagonal for the SSOR update submatrix in the Vanka algorithm.
In segregated group 1:
Returned solution is not converged.
The model has been working before but when i made a few changes it won't run anymore.
Thank you for your help!
Attachments:
1 Reply Last Post Mar 12, 2015, 10:57 a.m. EDT
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Posted:
10 years ago
Dear Olof,
For CFD models I generally advise the following steps (in that order):
- enable pseudo timestepping, this can stabilize your model (already enabled in your model)
- try to reset your solver (remove all, and rebuilt it). This can set up the problem in a proper way
- Use ramping, that is try with lower velocities / pressure differences first, and slowly increase them
- Simplify the physics. I notice that you use mass flux boundaries. COMSOL finds a single pressure for these inlets, so that the total flux is equal to the prescribed value. You could try to rewrite these to velocity inlets, to simplify the model.
- switch to a direct solver
You can also take a few steps back, and check which modification caused your model to stop converging. That is typically the section that you need to modify.
Best regards,
Frank
For CFD models I generally advise the following steps (in that order):
- enable pseudo timestepping, this can stabilize your model (already enabled in your model)
- try to reset your solver (remove all, and rebuilt it). This can set up the problem in a proper way
- Use ramping, that is try with lower velocities / pressure differences first, and slowly increase them
- Simplify the physics. I notice that you use mass flux boundaries. COMSOL finds a single pressure for these inlets, so that the total flux is equal to the prescribed value. You could try to rewrite these to velocity inlets, to simplify the model.
- switch to a direct solver
You can also take a few steps back, and check which modification caused your model to stop converging. That is typically the section that you need to modify.
Best regards,
Frank