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What a pain, but solved it - largely by trial and error. As always, once solved the answer looks obvious....

The trick is to remember (or in my case discover!!) that the source map needs to move the integration curves to vertical lines, and then if you have a surface in 3D what worked for me was to make it flat in the 3rd dimension of the image. So that means to integrate on curves r=a, then you need the destination map::

z, atan2(y,x), sqrt(x^2+y^2)

and the destination map then z and "blank". Bingo.... As I say, "obvious" once you know.

What seemed to cause a bit of grief was when surfaces overlapped (e.g. four sides of a cylinder), which I havent solved, but dont need to - I can project one quadrant at a time. And I needed to use tetrahedra in mesh.

Also, the Geometry to choose for the map was indeed the "Boundary" surface x^2+y^2=a^2, z=[0,L]

Not sure that anyone is really interested in seeing the answer, but just in case, I've also attached the file.

Sorry if this is a newbie question, but the documentation on projection coupling is incredibly confusing to me.

I have a 3D geometry in x,y,z and have a solution, p, boundary x^2+y^2=a^2 z=[0,L]

For a given z, I want to integrate p along the curved line of the cylinder r=a and project onto y=0, x=a.

What is the source map, what is the destination map. Heck, for that matter, what is the Geometric Entity to choose? (E.g. is it the edge x=a or the surface x^2+y^2=a^2).

Are there model examples to check out? I've tried doing a search of "Coupling' or "Projection", etc, then none of them give model examples that use the general projection.

Hi John,

It's incredible how you could make something out of the poor explanation in the documentation. I wonder if you needed the integral of only the exterior surface of your cylinder or the whole average on each "slice" of cylinder and then graph that average along the length. If that's the case, I'm looking to do exactly the same thing and I'm starting to give up :( Unfortunately I have version 4.2 and I can't open your model to understand what you did. It would help a lot to have a model or a better doc explaining that operator because I need it desperately. If you could help me I would very much appreciate. Thanks a lot!!!

Hi John,

I don't have a Subsurface Flow license, so I can't open yout model.
Is it possible to post the model again with removed physics (or solid)?
The problem is exactly what I am looking for...

Ralf

Hi Everybody,

I've got similar problem...

I'm trying to calculate the average temperature of a cylindrical hole as function of its own center position along z axis. In pratcice, I want to obtain something like this: <T>=f(z) where the average value of temperature <T> is calculated with an integral along a a circumference that has its own center positionated in the middle of hole. The highness and the position of this circumference is determinated by z coordinate.

I've tried "general projection module", named "genproj1", with this settings:
SOURCE MAP
x-epression: z
y-epression: atan2((y-y_inlet),(x-x_inlet))
z-epression: R

where: x-inlet, y-inlet are the x,y coordinates of hole axes and R is its radius.

DESTINATION MAP
x-expression: zperimeter
y-expression: "" (blank)

Then i've created a new variable in this way: Tm = genproj1(T) / P where P is hole perimeter.

I did several trials these days: one of these is to impose temperature in hole boundary in order to force Tm to assume my constraint value.

Unfortunately the rusults are unsatisfactory. Comsol gives me back a strange pattern of Tm: something like a sawtooth trend with teeth in correspondence of mesh lines.

Ah.. I'm forgetting to tell you that I've a sweep mesh converted in triangular mesh through the "Convert Module"

Any suggestion?