UDF - Temperature boundary condition for a pipe bundle
 

I am analyzing a 2D domain consisting a pipe bundle. I have written a UDF that
provides variable boundary temperature with y-coordinate. It works nice when
the boundary is one pipe (circle) only, but fails when applied to a pipe bundle. The cause is that UDF counts y-coordinates concerning the bundle center, not the each circle center.

Is there a way to determine the y-coordinates concerning each pipe (circle) center?

Thank you in advance.