On KB there is an example page showing how to create structures with surface roughness. The structure group that has been used to create the rough wire can be easily modified to create a rough cone. The resulting cone, even though not perfect, can be a simple solution to people who want to use a cone in their simulation with some surface roughness.
usr_surface_roughness_cone.fsp (1.3 MB)
The concept behind getting the cone from the wire is very simple. In the structure group, the wire is made up of thin slices stacked on top of each other. In order to create a cone, we simply change the radius of these slices linearly as we move from the base to the tip of the cone. The result is as if we have pinched the top of the wire to change it into a cone.
A couple of things to remember,
i) Since we are squeezing the top of the wire to make the cone, the correlation length does become smaller at the top of the cone. This can be seen as if we zoom on the top slice of the cone and compare it with the bottom slice
ii) Another thing to note here is that the radius of the top slice needs to be larger compared to the amplitude of the roughness otherwise the polygon (slices) at the top will be very ill-behaved.