Hello again gurus...
I just got some rather disappointing news about damping and
cosmos/M. "Composite material damping" specified when I use the
DAMP material property assigns the value of damping ratio for the
material. It isn't the damping coefficient, "c" that is in all the
structural dynamics books. That is a bummer. It means I can get
whatever response I want out of the simulation, not a prediction of
real life response. damping should depend on the mass and stiffness
of the system in the form of damping = 1/root(k*m) for a single
degree of freedom. So if I use a heavier mass, the response at
resonance should increase due to damping decreasing. That doesn't
happen unless I also decrease DAMP when I increase density. The
response turns out to be identical for increased density and DAMP
I know some rules of thumb for damping like more damping for denser
materials, etc. Please tell all of your rules of thumb you use to
change damping for a changing elastic modulus or density(or both).
I know that modal damping is a very difficult property to simulate
unless you can physically measure the system. But we wouldn't be
using FEA then, if we already had the system.