# Discussion Forum

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## inverse initializing model

Hi my Dear Friends,

I have a constant amount of liquid between a sphere and a flat plate in axisymmetric geometry. I want to insert some specific volume of liquid in comsol and find the height that it fills. I have V(z) = some expression for z. Now I want F-1 (V ) = z . This z is actually gap distance that I read on sphere. What can help me?
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Marjan

3 Replies Last Post Oct 11, 2012, 10:22 AM EDT
Posted: 5 years ago
Hi

I can propose, once you have drawn your geometry and defined some physics + loaded at least the initial conditions to populate the FEM matrices (and allow you to do postprocessing) then you can select the domain (2D-axi surface) you consider, and integrate it with a surface integration, while you turn on the "2D-axi volumetric function which simply, implicitely multiplies the operand by 2*pi*r the loop length. You can then add a bolean function to your operand defining the height, such as *(z<H) where H is your height, defined in the correct coordinate frame (with the correct z0 initial height).

If you need to use these variables in the solution (and not only the postprocessing) you need to define the integration in the top Definition node, and define the olume as a variable in the same Definitions but under Variables node

In V4.3 we have now a series of new functions/operators, check the help, so you can perhaps also define the integration directly

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Good luck
Ivar

Posted: 5 years ago
Hi Dear Ivar,

Thanks for your comment. I will try to define the bolean operator. I think it helps a lot. I need these variables in the solution (so I defined integrations in the top Definition node.

I am working in Max Planck institute for polymerforsschung and we have a network license so it takes a while until I can have access to comsol multiphysics version 4.3.a. I hope I can do that in version 4.3 :).

Viele Gruesse,
Marjan

Posted: 5 years ago
Hi

no problem, that was possible even back in 3.3 ;)

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Good luck
Ivar

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