Discussion Forum

Hi

you have the integration and extrusion coupling operators under the "Definition" node to do that, see the doc

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Good luck
Ivar

Hi Clinton

You have to use the projection integration operator: Model->Definitions->Model Couplings->General projection


Lars Gregersen
Comsol Denmark

I've never explored this feature. I've only ever used the "derived values" node for simpler postprocessing. I will give it a look. Thank you.

I am still having some trouble, so let me describe the problem in more detail, now that I've looked at the coupling functions...

I am trying to use general projection coupling to take a temperature distribution within a
cylinder from 3D to an axisymmtric 2D approximation. Mathematically, it is
expressed (in terms of cylindrical coordinates) as...

T2D(r,z)=int(T3D(r,theta,z),theta,0,2*pi)/(2*pi)

The model as it stands is in cartesian coordinates, so I defined
variables r=sqrt(x^2+y^2) and theta=atan2(x,y). I attempted to defined a
secondary, cylindrical coordinate system to remove the shortcomings of
these definitions (like atan2 not being unique from 0 to 2*pi), but the
coupling feature doesn't seem to allow for different systems.

As far as the interface for general projection, I do not quite understand
x-,y-, and z-expression fields. The source lists x,y,z, but destination
only lists x,y. Does that mean that the program integrates along whatever
is in the z-expression field, since it is not in the destination domain? I
have entered r into the x field, z into the y field, and theta into the z
field. I defined a variable T2D as the result of this projection. When I
graph T2D, the results do not make sense.

I believe that I am missing some things to do this correctly. Please
walk me through how to do this. Thank you.

Thanks again for the help.

I am still having some trouble, so let me describe the problem in more detail, now that I've looked at the coupling functions...

I am trying to use general projection coupling to take a temperature distribution within a
cylinder from 3D to an axisymmtric 2D approximation. Mathematically, it is
expressed (in terms of cylindrical coordinates) as...

T2D(r,z)=int(T3D(r,theta,z),theta,0,2*pi)/(2*pi)

The model as it stands is in cartesian coordinates, so I defined
variables r=sqrt(x^2+y^2) and theta=atan2(x,y). I attempted to defined a
secondary, cylindrical coordinate system to remove the shortcomings of
these definitions (like atan2 not being unique from 0 to 2*pi), but the
coupling feature doesn't seem to allow for different systems.

As far as the interface for general projection, I do not quite understand
x-,y-, and z-expression fields. The source lists x,y,z, but destination
only lists x,y. Does that mean that the program integrates along whatever
is in the z-expression field, since it is not in the destination domain? I
have entered r into the x field, z into the y field, and theta into the z
field. I defined a variable T2D as the result of this projection. When I
graph T2D, the results do not make sense.

I believe that I am missing some things to do this correctly. Please
walk me through how to do this. Thank you.

Thanks again for the help.

Hi

first of all normally the right hand rule angles are defined as thetaz = atan2(y,x) but that is also a question of convention. Then for me atan2 is unique, but if it is not from 0-2*pi its probably from -pi to pi

I didn neither niot find the extrusion and projection coupling operator very intuitive, and still need to carefully check each tim what I'm doing on a simple example, the variable names x,y,z can normall be replaced by your own equation a 3D to 2D means indeed integration over the missing 1D, it all depends on how you define this integration line

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Good luck
Ivar