Hello Lammps Users,
I would like to apply a fixed force between two bodies but I also want to limit how fast the two bodies come into contact. I believe I can do so using a combination of fix aveforce to apply the force and fix viscous to apply drag.
The equation for the total force on the group is
Ftot = Fappled - gamma*velocity
If my logic is correct if you want to limit the maximum velocity you’d to set gamma value such that Ftot = 0 at vmax. Therefore:
gamma = Fapplied / vmax
(a good analogy here is a sky diver reaching terminal velocity)
That much I think makes sense.
To implement it I think I need to set the aveforce fix first the add the viscous term. Is that correct?
More or less as follows?
fix 2 topfix setforce 0.0 0.0 NULL
fix 22 topfix aveforce NULL NULL v_load
add load specific damping
desired velocity in real units = 0.0002 A/fs
gamma = target load / maximum velocity
variable gamma equal {load}/0.0002 fix damp topfix viscous {gamma}
Does this sound like a sane approach?
Thanks,
Dave