Discussion Forum

Hi

COMSOL has thousands of internal variables, if you use a few physics modules so often its quite simple to hit an already used name, and sometimes you may get trouble and strange results, without specially any warnings, because COMSOL allows you to change internal variables, therefore it could be correct that you change some internal variable, COMSOL cannot tell.

My way around is to :
a) use names with some length and/or some special termination or prefix as"my_var_"
b) check the names by defining a dummy Parameter and equate it to the name, if some values or units pop up, there is a good chance that the variable is already defined, but this last trick is not sufficient, it will only work with active variables once the model is set up and you have at least run an "get initial conditions" ideally solved the model once.
c) do the same (or ignore b and directly go to c) in the Definitions Variable, define a dummy variable and equate it to the name I want to use, again if some units pop up there is a good chance that its already defined as an internal variable. If the variable is flagged red probably its a genuine name at least until you load a new physics with more variables.
d) one must also refer to the scope of the variables, dependent variables are defined "globally" such as (u,v,w) but most physics variable are tagged with the specific physics prefix i.e. such as "solid.freq" : internal "solid" physics - eigenfrequency variable.

To get a view of the many variables under the hood, activate the equation view and study the equations therein (set in the preferences)

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Good luck
Ivar

Hi,

I think the problem might be that you call the interpolation function without arguments. You should call it using something like

Q_t(x,y)

depending on the number of arguments of the function and the geometry dimension.

Best regards,
Magnus Ringh, COMSOL

Hello, thank you both for replies. I tried renaming the variable to something specific (Heater41) as Ivar suggested. Still no luck. I then tried Heater41(t), which also did not work. Could it be something with the input file itself?

The first 10 rows of the input file looks like this:
0.00, 0.00
3.02, 0.00
6.05, 0.00
9.07, 0.00
12.01, 0.00
15.03, 0.00
18.06, 0.00
21.08, 0.00
24.02, 0.00
27.04, 0.00
and there are about 200000 more rows (mostly zeros- this heater doesn't come on often). Or could it be that the time step isn't constant? I can't imagine it's the file itself. Like I said, COMSOL does recognize the data when I plot it.

Hi Ryan,

That should work. Could you post a simple example file (MPH-file) and the input file? Otherwise, it's hard to say what the problem is.

Best regards,
Magnus Ringh, COMSOL

Hi

could this be the same issue reported some months ago (22 oct 2015) also on the Forum, about COMSOL's way of plot resampling and loss of visual data (although if I remember all data was used internally) ?

Because there was quite some differences in peak values and visual read out of plotted values for a long input file
see
www.comsol.eu/community/forums/general/thread/93111

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Good luck
Ivar

Hi Ryan,

Interesting model! I tested it in COMSOL Multiphysics version 5.2 (our current version), and it runs without errors. I can see now that you tagged this posting with version 4.3b. A lot has happened since that version, so I strongly recommend that you update to the latest version.

However, I also tested this model in version 4.3b, and it worked for me in that version, too.

Best regards,
Magnus Ringh, COMSOL

Hi

could this be the same issue reported some months ago (22 oct 2015) also on the Forum, about COMSOL's way of plot resampling and loss of visual data (although if I remember all data was used internally) ?

Because there was quite some differences in peak values and visual read out of plotted values for a long input file
see
www.comsol.eu/community/forums/general/thread/93111

--
Good luck
Ivar

With this issue, this user was able to import the spreadsheet and use it, but she just had different results than what she expected. I am able to import the spreadsheet, but I am unable to call the function later. It's close though. It does sound like I have the same format in my spreadsheet, with one column of time, and one column of data.

Hi Ryan,

Interesting model! I tested it in COMSOL Multiphysics version 5.2 (our current version), and it runs without errors. I can see now that you tagged this posting with version 4.3b. A lot has happened since that version, so I strongly recommend that you update to the latest version.

However, I also tested this model in version 4.3b, and it worked for me in that version, too.

Best regards,
Magnus Ringh, COMSOL

Interesting. Can you walk me through what you did, if you changed anything from the file I gave you? I feel like I'm missing one tiny thing.

Hi Ryan,

I opened the MPH-file and re-solved. I also discarded the interpolation data and reimported it from the data you sent (saved from the M-file as a plain text file) and re-solved again. I did not change any other settings. If you still cannot get it to work, I recommend that you contact your local COMSOL office for technical support.

Best regards,
Magnus Ringh, COMSOL