how to get across-wind "moment /force vs height of chimney" graph in fluent
 

hi guys i am working on flow around chimney using fluent.i did analysis but i don't know how to plot moment vs height graph? anyone working on the same?
i tried to calculate force by creating line on the the surface of chimney but got an error " force can only be calculated on edges or vertices"? is there any way to calculate force or moment?