Damping with spring foundation?

Hi everyone,

I'm analysing the effect of circular tapers (called Acoustic Black Holes) on beams when subjected to a point load. I wish to add a thin damping layer to these tapers but am unsure how exacly to go about it; I've tried spring foundation with loss factor damping of 0.1 but it doesn't seem to have any effect (same displacements with and without this). Looking at help, I can't see anything for just adding some good old standard damping to a geometry. Anyone know how to do that? Just a simple damping layer to the circular bits which you can see in the pic.

Thanks!