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Interpolation function of dependent variables

Posted Mar 12, 2010, 9:40 a.m. EST 3 Replies

Shao-Ling Wu
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Hi,

I have been trying to solve a problem which requires interpolation functions or look-up tables. I know we can import data files by adding functions into COMSOL. I have tried that, and it worked. The interpolation functions were dependent on spatial coordinates (r and z).

Now I need to solve a similar problem, but in which case the interpolation functions are dependent on "dependent variables".

For example, I am solving concentration (c) and potential (V) in an electrochemical system. I have a parameter "f" which is a function of concentration and potential, i.e., f=f(c,V). This parameter is used in one of my boundary conditions. I cannot find an explicit expression for "f" in terms of c and V. However, I can make a look-up table for "f".

So this is what I did.
I defined "f" in Options --> Functions, and it is interpolated from an external .txt file. In the text file, the two variables are c and V.
The results do not look correct.

Can COMSOL support an interpolation function dependent on dependent variables?
or Is there any other method to solve it?

Thank you very much!

3 Replies Last Post Jul 23, 2010, 12:00 p.m. EDT
COMSOL Moderator

Hello Shao-Ling Wu

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Jie Xiang
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Posted: 1 decade ago Jul 22, 2010, 11:22 a.m. EDT
Hi, Shao-Ling,

I also tried to use interpolation function and met a problem. Can you give me some suggestion?

I am trying to interpolate spatial-varying material data. The interpolation functions were dependent on spatial coordinates (r)

In Comsol Multiphysics user guide, the spatial arguments are x,y,z.

My question is:
How can we use r (r=sqrt(x^2+y^2)) as the spatial arguments?


Hi, Shao-Ling, I also tried to use interpolation function and met a problem. Can you give me some suggestion? I am trying to interpolate spatial-varying material data. The interpolation functions were dependent on spatial coordinates (r) In Comsol Multiphysics user guide, the spatial arguments are x,y,z. My question is: How can we use r (r=sqrt(x^2+y^2)) as the spatial arguments?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jul 22, 2010, 4:35 p.m. EDT
Hi

define a global variable r = sqrt(x^2+y^2) and use "r" thereafter, check the doc for global variables

--
Good luck
Ivar
Hi define a global variable r = sqrt(x^2+y^2) and use "r" thereafter, check the doc for global variables -- Good luck Ivar
Jie Xiang
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Posted: 1 decade ago Jul 23, 2010, 12:00 p.m. EDT
Hi, Ivar,

Thanks very much for your reply. I followed your sugestion,define a global variable r = sqrt(x^2+y^2), and also define a global interpolation ep_r(r). However, it still did not work. It seems that Comsol has not recognized this variable r in the interpolation ep_r(r). Maybe I did not understand your comments " use "r" thereafter ".

Can you explain more about this?

The attached mph file is my model.

Thanks in advance
Hi, Ivar, Thanks very much for your reply. I followed your sugestion,define a global variable r = sqrt(x^2+y^2), and also define a global interpolation ep_r(r). However, it still did not work. It seems that Comsol has not recognized this variable r in the interpolation ep_r(r). Maybe I did not understand your comments " use "r" thereafter ". Can you explain more about this? The attached mph file is my model. Thanks in advance

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