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How to divide a solution by another solution

Posted May 2, 2012, 4:11 p.m. EDT Fluid & Heat, Porous Media Flow, Results & Visualization, Studies & Solvers Version 4.2a 4 Replies

Evan Earnest
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Greetings all, I am solving Darcy's Law and Solute Transport in a 2D rectangular model domain (using Comsol 4.2). I would like to normalize the solution by a known solution. This would basically entail dividing my solution by another solution.

More detailed explanation:

I am calculating groundwater solute concentrations using the solute transport model for 2 scenarios: one is an isotropic hydraulic conductivity (Darcy's Law), and the second is an anisotropic hydraulic conductivity. I would like to divide the anisotropic results by the isotropic results for visualization on a surface plot. Can anybody provide an explanation for how to divide a solution by another solution?

Thanks for your help!

E.J.E.H.

4 Replies Last Post May 4, 2012, 3:19 p.m. EDT
Francois Gregoire
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Posted: 1 decade ago May 2, 2012, 4:31 p.m. EDT
It can be automated in 'Comsol with Matlab':
1. Run a first loop of your base case
2. Extract data from your base case with mpheval
3. Run a second loop of your modified case
4. Extract data again with mpheval, of course you assign different names to extracted variables. If the mesh hasn't changed, all dependent variables values will be stored in the same order.
5. divide the 2 sets of data as you wish

For the looping and extracting procedure, look here : www.comsol.com/community/forums/general/thread/8840/
It can be automated in 'Comsol with Matlab': 1. Run a first loop of your base case 2. Extract data from your base case with mpheval 3. Run a second loop of your modified case 4. Extract data again with mpheval, of course you assign different names to extracted variables. If the mesh hasn't changed, all dependent variables values will be stored in the same order. 5. divide the 2 sets of data as you wish For the looping and extracting procedure, look here : http://www.comsol.com/community/forums/general/thread/8840/
Evan Earnest
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Posted: 1 decade ago May 4, 2012, 3:05 p.m. EDT
Thanks, but I am hoping to find a way to do this in the COMSOL GUI. It seems like if you have two study's it shouldn't be difficult to do some simple algebra of the two solutions...

Thanks, but I am hoping to find a way to do this in the COMSOL GUI. It seems like if you have two study's it shouldn't be difficult to do some simple algebra of the two solutions...
Evan Earnest
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Posted: 1 decade ago May 4, 2012, 3:18 p.m. EDT
Once I have a solution in MATLAB and have exported it as a txt, how do I import it into COMSOL for visualization? I do not have the Comsol-Matlab license, so I have to do things piecemeal...

Once I have a solution in MATLAB and have exported it as a txt, how do I import it into COMSOL for visualization? I do not have the Comsol-Matlab license, so I have to do things piecemeal...
Alexander Kuznetsov
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Posted: 1 decade ago May 4, 2012, 3:19 p.m. EDT
In Results-Data Sets you can choose Join to combine two solutions. There are options to add, subtract or multiply the solutions. Unfortunately, you can't divide them. But maybe difference will work for you?
In Results-Data Sets you can choose Join to combine two solutions. There are options to add, subtract or multiply the solutions. Unfortunately, you can't divide them. But maybe difference will work for you?

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