I am using Laminar flow mode of COMSOL coupled with Transport of Diluted Species.
After I get results exported to excel format, I observe some negative concentration values appearing, which is weird.
I saw some people commenting and asking about this issue, but couldn't quite find the actual solution they came up with.
If anyone who has experienced same problem, and figured out the way to prevent it, I would highly appreciate your help!
Hi Amanzhol,
I would first check if you have negative concentration values in COMSOL. Maybe you got this values just in Excel through interpolation by exporting it from COMSOL?
If you get negative concentration in your COMSOL Model, there are two options:
1. Your physical model is not correct. Check if you have consistent initial and boundary conditions.
2. Your mesh is too coarse and you use shape functions from higher order (second or third). In this case you should refine the mesh.
Hopefully it helps!
Best regards,
Antoni Artinov
Hi,
Check this blog, 'Avoiding negative concentrations', following the link below;
https://www.comsol.com/support/knowledgebase/952/
Well there are some problems especially at the start of diffusion simulation.
You can avoid this by using the "segregated solver" and add an extra node of limit and use "comp1.c 0" with out apostrophes in the variable.
Be sure u have correct boundary parameters. If u are solving the decreasing concentration simulation phenomena then stop your simulation when negative concentration appears by using "comp1.minop1(comp1.c)>=0" in the stop condition.
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