Discussion Forum

Hi William

Well first of all check if the volume integration is not rather

intop(2*pi*r*Your_Variable) (or just Your_Variable=1 for the volume) in 2D-axi

you can also for postprocessing integrations (only) turn the automatic 2*pi*r multiplicant by selection in the "integration settings - Compute volume integration" "on"

Then you are easier out by defining an "Definition - Integration operand" and a "Definition - Variable"

My_Variable1 = intop1(2*pi*r*Your_Variable) on a given domain/boundary set
My_Variable2 = intop2(2*pi*r*Your_Variable) on another given domain/boundary set

Definition - Global Evaluation

with My_Variable1 / My_Variable2

By the way you have also the "Probes" that gives you feedback during the solving

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Lykke til
Ivar

Thanks!

I tried to define the following variable under Model:

mass = intop1(2*pi*r)

but the expression turns orange, and I don't know why. I try to do a Global Evaluation of the variable under Derived Values (Expression = mass), but get the following error:

Failed to evaluate variable
-Variable: mod1.mass
-Global scope:
Failed to evaluate expression.
-Expression: real(mod1.mass_tail)
Failed to evaluate expression.
-Expression: real(mod1.mass_tail)

Hi

Orange means check your units !

if you want the mass it's the sum over the "i" selected domains of the integration of solid.rho[kg/m^3] * dx*dy*dz

in 2D- axi a tripple integration is the double integration (over the section area) of 2*pi*r*solid.rho*dr*dz to get a mass =[kg] out

So if you add your "*solid.rho" to you integrand it should be fine

In general you should understand that the values you use in COMSOL are the mesh element items, all to be integrated of the elements hence *dx*dy*dz (in 3D). Just as most COMSOL variables are expressed as denisties in [Units/m^2] or [Units/m^3], all values to be integrate over the boundaries or domains to get the macro values we engineers are used to operate with

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Lykke til
Ivar

Thanks!

The problem got solved when I first defined a Model Coupling Integration for each of the domains, and then defined global equations for the two integrand operators.

Hi,

In a v4.2 mph file, I have two models (model 1 & model 2) each with a geometry. So there are 2 geometries (geom 1 & geom 2) in the same mph file. While postprocessing, I want to do subdomain integration of any 2 solutions, each from the respective geometries. But the data set for subdomain integration seems to accept solution set from any one geometry at a time and it shows error even if I specify geometry 2, e.g: "mod2.emw2.Ex" in the expression field. Can anybody help me in this respect, how solution from a different geometry can be specified in the expression field for subdomain integration ?

thanks