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How to get rid of negative values of concentration?

Posted 27 juin 2012, 14:49 UTC−4 Porous Media Flow Version 4.3 2 Replies

Simin Akbariyeh
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I'm working on a vapor intrusion model in which the contaminant is moving in soil. The simulation is time dependent and I have used Darcy's law and solute transport in order to apply governing equations. After computing the model, I have negative values for concentration somewhere, that they are not ignorable. This problem is more sensible for last time steps (about one year). I don't know how to solve this. Is there any problem with my boundary conditions or mesh size?

If anyone can help me I will really appreciate it.

Simin
2 Replies Last Post 27 juin 2012, 16:54 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 juin 2012, 15:04 UTC−4
Hi

for me un-physical diffusion equation variables are mostly related to mesh density, material diffusivity and time stepping issues, these are linked.

But I have seen several "tricks" on the Forum how to help the solver to come over such errors. Even if I wonder how correct the results are (at least locally) when using these tricks, instead of checking the above three variables. try a search, one response was here

www.comsol.eu/community/forums/general/thread/29200/#p81519

--
Good luck
Ivar
Hi for me un-physical diffusion equation variables are mostly related to mesh density, material diffusivity and time stepping issues, these are linked. But I have seen several "tricks" on the Forum how to help the solver to come over such errors. Even if I wonder how correct the results are (at least locally) when using these tricks, instead of checking the above three variables. try a search, one response was here http://www.comsol.eu/community/forums/general/thread/29200/#p81519 -- Good luck Ivar
Simin Akbariyeh
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Posted: 1 decade ago 27 juin 2012, 16:54 UTC−4
Thank you very much, that works. Now I just need to make sure about the reliability of data.

Thanks a lot again
Thank you very much, that works. Now I just need to make sure about the reliability of data. Thanks a lot again

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