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z and r are simply coordinates. They do not depend on one another. If you compute something that has an actual dependence on a coordinate, then you may then be able to compute its derivative with respect to that coordinate. {Note: You may be able to get some useful help here if you are willing to explain the physical nature of the problem you are trying to solve, which presumably led you to this question.}

Dear Mr. Koslover,

Yes, of course I can explain the problem. It is the one described in another forum thread in which you have already answered me :) : volume 2D axi model

My idea, since I am not able to calculate the volume of a hole with axisymmetric 2D geometry, is to use the line integral to calculate the volume by applying the Divergence Theorem or Gauss's Theorem. This theorem can be rewritten mathematically for cylindrical coordinates (2D axisymmetric model) if the COMSOL integral operator can only be applied to line integrals the theorem is rewritten as follows (I omit the mathematical development):

In this volume calculation, dS is the arc differential, and z(r) is the cylindrical coordinate as a function of radius for the curve that is shaded blue in the attached pic.

Can I know the "z" coordinate as a function of "r" for a given boundary in COMSOL ?

Thank you very much for your attention again,

Kind Regards, Andres

Hello Andres,

You're on the right track! See my post in your other thread: https://www.comsol.com/forum/thread/317481/how-to-calculate-the-volume-of-a-hole-inside-an-axisymmetric-2d-domain?last=2022-12-14T18:20:44Z

Best,

Jeff

Hello Andres,

You're on the right track! See my post in your other thread: https://www.comsol.com/forum/thread/317481/how-to-calculate-the-volume-of-a-hole-inside-an-axisymmetric-2d-domain?last=2022-12-14T18:20:44Z

Best,

Jeff

Thank you very much Jeff!

Best, Andres