Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

How to get rid of negative values of concentration?

Posted Jun 27, 2012, 2:49 p.m. EDT Porous Media Flow Version 4.3 2 Replies

Simin Akbariyeh
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

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 Jun 27, 2012, 4:54 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 27, 2012, 3:04 p.m. EDT
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 27, 2012, 4:54 p.m. EDT
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

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content