Interpolation Function Help

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Erin  Koksal

Erin Koksal

July 18, 2011 1:33pm UTC

Interpolation Function Help

Good Morning,

I'm having trouble using COMSOL's interpolation function, and I was hoping someone might be able to help. I'm trying to load data from a tab-delimited text file. I've followed the instructions in the COMSOL user guide on interpolation functions, however I get the following error when I click "plot":

"Internal error in mesh initialization.
-Plot: previewplot1 (Surface)
-Function: int1"

Additionally, when I try to solve the model I get the following error message:

"-Feature: Compile Equations: Stationary (sol1/st1)
-Error: Internal error in mesh initialization."

When I disable the interpolation function, COMSOL successfully solves the model.

The input data used for the interpolation function was a velocity distribution exported from a previous solution surface. It has the following structure:

% x y z myfun1
0.005164328 0.094835672 0.2 0.098519135
0.015894103 0.087647192 0.2 0.511590803
0.015569986 0.095339275 0.2 0.22689919
0.006197193 0.083275657 0.2 0.312314232
0.005469283 0.016082383 0.2 0.2672031
0.004733427 0.004733427 0.2 0.081290304
0.012546053 0.01240331 0.2 0.43510989
0.015707096 0.004896326 0.2 0.232560416
0.027164381 0.094602393 0.2 0.368319369
etc.

A very simple flow model demonstrating the problem is attached, along with an excel version of the data I'm using. I'm a new COMSOL user, and any advice would be greatly appreciated.

Thank You!

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Yoann  Many

Yoann Many

July 19, 2011 7:32am UTC in response to Erin Koksal

Re: Interpolation Function Help

Had the same issue with an imported data .txt file, and it has 2 parameters while yours seems to have three of them. The only thing I figured was to reduce the number of parameters to 1, and no more error messages.... But I guess in your case it's quite out of the question.....
sorry I can't help you

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Lichun  Wang

Lichun Wang

August 14, 2012 7:33pm UTC in response to Erin Koksal

Re: Interpolation Function Help

Me toooo! Once I used interpolation function with three arguments, it will pop out the error message. Hope someone expert will answer this question soon.

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Nagi Elabbasi

Nagi Elabbasi
Certified Consultant
Veryst Engineering

August 15, 2012 6:37pm UTC in response to Lichun Wang

Re: Interpolation Function Help

One of your variables always has the same value of 0.2. It seems that this is not acceptable for COMSOL. If you change some numbers to say 0.3 it works. Alternatively you can remove that variable completely from the function.

Nagi Elabbasi
Veryst Engineering

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Magnus Ringh

Magnus Ringh
COMSOL Employee
Sweden

August 16, 2012 12:38pm UTC in response to Nagi Elabbasi

Re: Interpolation Function Help

Hi,

As Nagi explains above, an interpolation function of three arguments does not work well when one of them is a constant value (it is a degenerated case). Perhaps you want to treat this as function of two variables (arguments), neglecting the values in the third column. You can then import it without having to modify the data file but specifying, in the settings window for Interpolation, that there are 2 arguments, and, under Functions, that the position in the file for the function values is 2. That means that COMSOL treats columns 1 and 2 as the argument values, and the second of the following columns (that is, column 4) as the column with the associated function values. Column 3 is then not used.

In this particular case the data is in an Excel file, which the Interpolation function does not support in a general way, but you can save it as text file, which is a supported data format. Furthermore, the values in the file seem to use a decimal comma rather than a decimal point. Replacing commas with points in the text file it is possible to import it as described above and plot the interpolation function as a surface plot.

Best regards,
Magnus Ringh, COMSOL

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Xu Gong

Xu Gong

October 10, 2012 11:02pm UTC in response to Nagi Elabbasi

Re: Interpolation Function Help

Hi, Nagi:
I have a question for the interpolation function, can you help me? Thanks.
My function has two arguments p and e instead of coordinates x and y, and the form is:

G=f(p,e)

So, I create the spreadsheet as:
% p e G
1e6 0.5 2e6
2e6 0.6 3e6
etc...

But the COMSOL always assume to be coordinates as argument. How to fix this problem?


Thanks a lot.


Xu

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Xu Gong

Xu Gong

October 10, 2012 11:05pm UTC in response to Magnus Ringh

Re: Interpolation Function Help

Hi, Magnus:
I have a question for the interpolation function, can you help me? Thanks.
My function has two arguments p and e instead of coordinates x and y, and the form is:

G=f(p,e)

So, I create the spreadsheet as:
% p e G
1e6 0.5 2e6
2e6 0.6 3e6
etc...

But the COMSOL always assume to be coordinates as argument. How to fix this problem?


Thanks a lot.


Xu

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Jeff Hiller

Jeff Hiller
COMSOL Employee
USA
Moderator

October 11, 2012 12:49pm UTC in response to Xu Gong

Re: Interpolation Function Help

Hello Xu,
The Discussion Forum is primarily meant for customers to assist each other. To request support from COMSOL support personnel, please email support@comsol.com.

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Francesco Travascio

Francesco Travascio

May 23, 2013 6:43pm UTC in response to Jeff Hiller

Re: Interpolation Function Help

Hi,

I have a quick question on the interpolation functions used a boundary conditions.

I am working on a 3D model with PDE weak form. I need to introduce a boundary condition for a weak contribution that is tabulated in a file. This is

f=f(t) meaning that the only input argument is the time.

I have a text file built in this way:

% t force
0 1
0.1 3
0.3 7

etc.,

When I introduce this function as boundary condition I receive the following error message:


Failed to evaluate variable Jacobian
- Variable: int1
-Geometry: 1
-Boundary: 4 8
-Feature: Time-Dependent Solver 1 (sol/t1)
-Error: Failed to evaluate variable Jacobian


can anybody help me?

thanks

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