I am using LAMMPS to deform a box of granular particles. The simulation
runs fine and I get the desired velocity profile (0 at bottom, highest at
the top) when only fix deform is used. However, when I add forces on some
particles using fix addforce, the velocity of all the layers increase. The
strain rate remains the same, however in the end the bottom most layer has
a velocity of about 100.
I can not figure out why this is happening. Kindly help.
I am using LAMMPS to deform a box of granular particles. The simulation
runs fine and I get the desired velocity profile (0 at bottom, highest at
the top) when only fix deform is used. However, when I add forces on some
particles using fix addforce, the velocity of all the layers increase. The
strain rate remains the same, however in the end the bottom most layer has
a velocity of about 100.
I can not figure out why this is happening. Kindly help.
this is far too vague a description to give any substantial kind of help.
if you add a force, you change the dynamics of the system, so why should it
*not* affect the velocities of atoms?
But if that is the only difference between inputs, it is very likely that your forcing is adding a force on the center of mass of the collection of granules. And as you indicated, fix deform only works to impose a strain rate, which is a Galilean invariant (it won’t do anything to slow down your forcing). As long as you continue to force the center of mass (supply a net force in a particular direction), your collection will continue to accelerate.