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solution does not converge when using more intensive mesh

Posted 20 mars 2013, 10:05 UTC−4 Version 4.3a 4 Replies

Leilei Hu
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Dear:

I am making a 2d model about laminar flow around a plane. When I use better mesh, the solution does not converge. It works quite well using not so intensive mesh. Can anybody explain this to me please?

Thank you very much !
4 Replies Last Post 21 mars 2013, 09:24 UTC−4
Dan Jia
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Posted: 1 decade ago 20 mars 2013, 11:17 UTC−4
I've ever met this problem before. What I did was to check the tolerance.
I've ever met this problem before. What I did was to check the tolerance.
Leilei Hu
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Posted: 1 decade ago 20 mars 2013, 13:28 UTC−4
The tolerence is fine. I think maybe it is caused by the geometry or something else. I have tried to smooth the corners in the geometry, it works a little bit, but didn't sole the problem completely.
The tolerence is fine. I think maybe it is caused by the geometry or something else. I have tried to smooth the corners in the geometry, it works a little bit, but didn't sole the problem completely.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 20 mars 2013, 15:43 UTC−4
Hi

without the model it's difficult for me to tell ;) Sometimes I have seen such issues when one forget to set up boundary mesh for the no-slip walls. Normally COMSOL does this by default, if "physics driven mesh" is selected (default) but if you make our own mesh, you must not forget to add some boundary layers to better resolve the "noslip" velocity change

What often also makes life tricky is to use reasonable initial conditions with some pressure drop and a realistic velocity profile, not only at inlet but all through, and if in time transient solving, running frat a stationary case to establish correct initial conditions to then ramp up or down th eflow in transient mode often helps too

--
Good luck
Ivar
Hi without the model it's difficult for me to tell ;) Sometimes I have seen such issues when one forget to set up boundary mesh for the no-slip walls. Normally COMSOL does this by default, if "physics driven mesh" is selected (default) but if you make our own mesh, you must not forget to add some boundary layers to better resolve the "noslip" velocity change What often also makes life tricky is to use reasonable initial conditions with some pressure drop and a realistic velocity profile, not only at inlet but all through, and if in time transient solving, running frat a stationary case to establish correct initial conditions to then ramp up or down th eflow in transient mode often helps too -- Good luck Ivar
Leilei Hu
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Posted: 1 decade ago 21 mars 2013, 09:24 UTC−4

Thank you very much for your advice. I really didn't set boundary layers in the model. I tried it today but the result was still not satisfactory. The attachment is my model. The mesh in this model is not intensive and it converges. If we make it more intensive, convergence problem will occur. I think it is quite a simple model. Could you help me find the problem, please?
Thank you very much for your advice. I really didn't set boundary layers in the model. I tried it today but the result was still not satisfactory. The attachment is my model. The mesh in this model is not intensive and it converges. If we make it more intensive, convergence problem will occur. I think it is quite a simple model. Could you help me find the problem, please?

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