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Post-processing Results

Posted Jun 2, 2011, 8:58 p.m. EDT Modeling Tools & Definitions, Results & Visualization, Studies & Solvers Version 4.1 2 Replies

Nikhil Shankar
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Hello everyone!

I am very new to the COMSOL interface.. so I could really use some help.

I'm solving 16 PDE's (Coefficient form PDEs) with 16 dependent variables over a spacial 1D domain of 27 finite elements. The total number of degrees of freedom solved for is 3216 and the solution was completed in about 2 minutes. Now I have 2 issues I am unable to figure out .

1. When I view my results I can only see the plot for 1 of the dependent variables over the distance 'x'. Where can I pick the other variables that I want a plot of?

2 (And this is a little more complex). While solving the 16 PDE's, I gave the value of the source term for each of the 16 equations as zero. Now what I need to do is run an iterative loop that will make the source term for each of the equations equal to a weighted sum of the dependent variables [i.e, the sum of (a constant for each variable times the variable itself)] and solve the whole bunch of equations again. This process has to be repeated till the solutions to the variables converge ( just say for 100 iterations)

I am given to understand that both of these can be done by postprocessing on COMSOL.
Am i right? Does anyone know how to do the stuff I have just explained?

Also : I have tried to explain the problem in a way that is easiest to understand. Please reply back with any doubts you may have about my question.

Thanks.

-Nikhil Shankar
2 Replies Last Post Jun 6, 2011, 1:09 p.m. EDT
Mikhail Titov
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Posted: 1 decade ago Jun 3, 2011, 3:20 p.m. EDT
1. When I view my results I can only see the plot for 1 of the dependent variables over the distance 'x'. Where can I pick the other variables that I want a plot of?

There should be an expression field of what to plot in your plot group. Check sub-nodes of your plot group.
2 (And this is a little more complex). While solving the 16 PDE's, I gave the value of the source term for each of the 16 equations as zero. Now what I need to do is run an iterative loop that will make the source term for each of the equations equal to a weighted sum of the dependent variables [i.e, the sum of (a constant for each variable times the variable itself)] and solve the whole bunch of equations again. This process has to be repeated till the solutions to the variables converge ( just say for 100 iterations)
I personally would use LiveLink and Matlab to extract all the stuff and rerun. I haven't ever used batch processing. I'm not sure if you can get away using it.
[QUOTE]1. When I view my results I can only see the plot for 1 of the dependent variables over the distance 'x'. Where can I pick the other variables that I want a plot of?[/QUOTE] There should be an expression field of what to plot in your plot group. Check sub-nodes of your plot group. [QUOTE]2 (And this is a little more complex). While solving the 16 PDE's, I gave the value of the source term for each of the 16 equations as zero. Now what I need to do is run an iterative loop that will make the source term for each of the equations equal to a weighted sum of the dependent variables [i.e, the sum of (a constant for each variable times the variable itself)] and solve the whole bunch of equations again. This process has to be repeated till the solutions to the variables converge ( just say for 100 iterations) [/QUOTE]I personally would use LiveLink and Matlab to extract all the stuff and rerun. I haven't ever used batch processing. I'm not sure if you can get away using it.
Nikhil Shankar
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Posted: 1 decade ago Jun 6, 2011, 1:09 p.m. EDT
Thanks for the reply Mikhail. Question 1 is solved.
As for question 2, I'm not sure how to do the whole livelink with matlab process.

But before I even try that, I'd like to know - How do you define algebraic equations on COMSOL?
I need to input a simple algebraic constraint equation that should should logically solve all my problems.

Thank you.

-Nikhil
Thanks for the reply Mikhail. Question 1 is solved. As for question 2, I'm not sure how to do the whole livelink with matlab process. But before I even try that, I'd like to know - How do you define algebraic equations on COMSOL? I need to input a simple algebraic constraint equation that should should logically solve all my problems. Thank you. -Nikhil

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