Exporting mesh generated by iso2mesh to COMSOL and simulating fluid flow

[SNorouzi]

Hello everyone,

First of all I need to thank Dr. Fang for developing magnificent iso2mesh toolbox. It helped me too much.
I was wondering if anyone has experience with COMSOL software (As I realized most of group members are
working with FLUENT for their simulations)?
For some reasons I am using COMSOL to simulate coupled free and porous medium flow. I have a segmented
image of a sphere pack (200*200*200), It was meshed by iso2mesh (one snapshot attached) and exported to COMSOL as .mphtxt (thanks to Donghyeon Kim for his script).
I encountered some difficulties in assigning boundary conditions in COMSOL and need help!

Sorry if it is off topic, but i was thinking here I could get some help.

Any input is highly appreciated.
Regards,
Saeid

[Qianqian Fang]

in the latest release, you can find a function, savemphtxt(),
contributed by Donghyeon Kim, with this function, you should
be able to export iso2mesh meshes to use in COMSOL.

You can find the related discussions in this thread:

https://groups.google.com/group/iso2mesh-users/browse_thread/thread/9f42554d2d0aa940/f54d08c6cf8cff60?hl=en&lnk=gst&q=comsol#f54d08c6cf8cff60

Qianqian

Any input is highly appreciated.
Regards,
Saeid

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[SNorouzi]

Dear Dr. Fang,

Thanks for your reply,
I had seen this thread before. Since I didn't have Matlab Livelink I did not use the function "savemesh2comsol.m" written by Sanket Jain and instead i used another function written by Kim (called savemphtxt.m). Basically COMSOL tries to generate a geometry from imported mesh and let you select the boundaries or domains. However in my case when I export my mesh to COMSOL, COMSOL recognize it as a mesh but can not make  a geometry out of it and as a result I can not select any boundary to assign conditions on it.
I tried a commercial software called Simpleware and generated mesh and exported to COMSOL. In this case COMSOL was happy and I could select boundaries.
If you find a way to get around this problem in iso2mesh, please let me know.

Thanks and regards,

[SNorouzi]

Dear Yvonka,

Thanks for your reply. Of course it is not late and I really appreciate your help.

Best regards,

saeid

On Friday, May 24, 2013 5:03:51 PM UTC+2, j.h.v...@student.tue.nl wrote:

Dear SNorouzi,

Perhaps this reply is a bit late, but I was having the exact same problem you were having and I found a solution, which, in the end, was disappointingly simple, so I decided to give you the solution I found anyway.

The problem I was experiencing when using savemphtxt.m was that I could import the mesh into comsol nicely, and it would show it, but it would not recognise it in the geometry as a domain, so I could add no source
or material or anything to my object. I didn't want to use a commercial solution, so I took a look at the code of savemphtxt, and I found the error.

At some point in the code you will find these lines:

for i = 1:n_face
    fprintf(fp,'0 0\n');
end

Here the up/down information of the mesh is printed, but for comsol 4.3a at least this is not correct. Change this to the following:

for i = 1:n_face
    fprintf(fp,'0 1\n');
end

This resolved the problem for me, and I could add a source to the domain and a material and comsol was happy as a clam.

I hope this helps some other people with the same problems. Respect for iso2mesh, I really love the package!

Yvonka

Op vrijdag 8 februari 2013 02:24:24 UTC+1 schreef SNorouzi het volgende: