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Imported data from txt file as initial value

Posted 19 févr. 2020, 11:55 UTC−5 Heat Transfer & Phase Change Version 5.4 2 Replies

Tamer Tolba
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Dear all,

I will need to import a thermal data generated by an independent simulation program, as txt file, in COMSOL model. To train myself, I have created a simple 2D COMSOL model (Attached: Import_txt_data.mph) where I solved a thermal distribution in a solid. I exported the thermal data, i.e. the Temperature distribution, in a speard sheet as txt file (Attached: Edep_test_2D.txt). Now, I tried to "re-import" the solution data to the same model (after disabling the previous boundary conditions). To do that, I have created an "interpolation" function, which I passed it (with two arguments) to an "Initial Values 2" as boundary condition. If no other boundary conditions added, I expect that by solving the model as it is, it must result in a thermal distribution identical to the feeded/imported data, right? This is not the case?

Would you please check the attached model and guid me where could be moy mistake?

Regards, Tamer

2 Replies Last Post 20 févr. 2020, 09:07 UTC−5
Jeff Hiller COMSOL Employee

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Posted: 5 years ago 19 févr. 2020, 16:19 UTC−5
Updated: 5 years ago 19 févr. 2020, 17:25 UTC−5

Hello Tamer,

The Initial Values node is used to specify the initial conditions when solving time-dependent problems, or to provide an initial guess to the solver for stationary problems, so it does not do what you think it does.

If you want to practice using an Interpolation function, you could in postprocessing subtract the "re-imported" data from the solution (i.e. plot T-int1(x[1/m],y[1/m])), and you'll get zero within numerical accuracy.

Best,

Jeff

-------------------
Jeff Hiller
Hello Tamer, The Initial Values node is used to specify the initial conditions when solving time-dependent problems, or to provide an initial guess to the solver for stationary problems, so it does not do what you think it does. If you want to practice using an Interpolation function, you could in postprocessing subtract the "re-imported" data from the solution (i.e. plot T-int1(x[1/m],y[1/m])), and you'll get zero within numerical accuracy. Best, Jeff
Tamer Tolba
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Posted: 5 years ago 20 févr. 2020, 09:07 UTC−5

Hi Jeff,

At first, my problem is solved (thanks so much). I found that I was passing wrong arguments to the interpolition function when it was called at the "Initial Values" node ==> it must be int1(x[1/m], y[1/m])). Moreover, I changed the study case to Time dependent instead of the stationary solver. Now, for short time steps, I can see the development of the solution, and at time=0 s, the thermal distribution of the system is what I expected (identical to the distribution of the intital value.) As for what I thought, it was a wrong expectation/guess from me! For whatever reason that came to my mind at that time, I thought that if I put a closed/isolated system in some "thermal" intital condition (which is the imported T distribution from the txt file, in my case) it gonna stay stable, i.e. preserve its intital condition, forever. I forgot a very simple physics rule, that the "isolated" system will try to reach thermal equilibrium among its volume! So, solving for stationary case is not the right choice then!

Thanks once again, Tamer

Hi Jeff, At first, my problem is solved (thanks so much). I found that I was passing wrong arguments to the interpolition function when it was called at the "Initial Values" node ==> it must be int1(x[1/m], y[1/m])). Moreover, I changed the study case to Time dependent instead of the stationary solver. Now, for short time steps, I can see the development of the solution, and at time=0 s, the thermal distribution of the system is what I expected (identical to the distribution of the intital value.) As for what I thought, it was a wrong expectation/guess from me! For whatever reason that came to my mind at that time, I thought that if I put a closed/isolated system in some "thermal" intital condition (which is the imported T distribution from the txt file, in my case) it gonna stay stable, i.e. preserve its intital condition, forever. I forgot a very simple physics rule, that the "isolated" system will try to reach thermal equilibrium among its volume! So, solving for stationary case is not the right choice then! Thanks once again, Tamer

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