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Hi

read the doc about Model coupling operators (Define Model Couplings integration) then define a variable "Definition - variables" calling this integration operator.

Solve or update your solution

post process in a plot or in a derived variables node

You might be able to define the full equation of your variable in a Global derived Variable node, but to refer to the integration you are better off defining them as operator first, then solve (to update the model data set) then display the results. The derived variables makes tables that you can plot out with a simple icon click

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Good luck
Ivar

post process in a plot or in a derived variables node

You might be able to define the full equation of your variable in a Global derived Variable node, but to refer to the integration you are better off defining them as operator first, then solve (to update the model data set) then display the results. The derived variables makes tables that you can plot out with a simple icon click

Hi Ivar,
thanks for your reply; but I don't know what to do in the section "Results": practically, in the "surface integration" I wrote my equation:
1-exp(-1/((sigma0^m)*Veff)*((solid.sp1*(solid.sp1>0))^m+(solid.sp2*(solid.sp2>0))^m+(solid.sp3*(solid.sp3>0))^m)*Th_AsA)
But obviously, it solves an integral for this entire equation, and it's wrong, the surface integral is only:
((solid.sp1*(solid.sp1>0))^m+(solid.sp2*(solid.sp2>0))^m+(solid.sp3*(solid.sp3>0))^m)
Now, I tried to solve this integral with Results>Derived values>surf. integration and I was well about this; the problem is after:

1) How can I implement the remaining equation:
1-exp(-1/((sigma0^m)*Veff)*RES_INT*Th_AsA)

2) For the point 1), How can I call the results of "surface integration" as a variable (for instance RES_INT)?

Thank you again in advance, sorry for inexperience, it's one of my first approaches with Comsol!

Fabio

Hi

indeed if you have a complex equation that requires the integral of a value over a surface and its combined with other variables, or other integrations, you need to do it in steps:
1) define your integrals in the definition node and have them prepared by solving or updating your solution (the solver node is lower in the three than the Definition node so changing anything "above" requires updates below)
2) define a variable that refers to your integration (as this is also "above" the solver node finish this part before your resolve or update)
3) use the Derived variables global evaluation and refer to the variables or to a combination of variables (COMSOL's internal ones as well as yours) and / or to the intop1() operators fully defined with the required expressions for the integrands. Then plot the resulting table

Note often you do not really need the Definition Variables, but such variables might also be referred to in all the other line surface or volume plots, but not the derived variables tables items

An important thing is to distinguish the variables (yours and COMSOL's) that are global and those who are implicit field variables with an implicit dependence on the spatial coordinates (x,y,z or r) and/or time "t"

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Good luck
Ivar

Hi Ivar,
thank you so much for your help! Now it works! But now I should improve my model, and so to use a Time dependent study instead of a Stationary, and I would evaluate this equation for each time (at 0 s, 10 s, 20 s etc); I have seen that the evaluation of a Derived Values is "manually" (practically, I have to click the = icon to see the result); this is properly for a stationary study (only one solution after the study), but for a Time dependent, in that I have a new solution after each step, how can I make it?

Thank you again

Fabio

Hi

try it out, the derived variable nodes make lists for each time steps, these are the easy paces to make simple post processing. but you can also "define variables" (before you solve, or at least try a solver update F5) and refer to these in the plots. Most variables arein fact field variables depending on x,y,z and "t" when you have a time solver

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Good luck
Ivar

Yes, I have tried and works.
Thank you so much Ivar.

Regards

Fabio