Tangential force acting on a tube by water


I have a tube with its axis in the z direction, and water molecules flowing past the tubes in the x direction. I am trying to measure the tangential force acting on the tube atoms by the water molecules using lammps.

The best way that I have come up with for now is to divide the tube atoms into strips, each strip having atoms with the same x and y coordinates. The atoms in each strip will then be assigned to a group. Then using compute group/group command, I compute the force in the x and y direction acting on each tube strip by the water molecules. Then using post processing, I will resolve the forces into the right tangential direction.

I am wondering if there is an easier way to do this? There will be a problem if I scale up my problem, since lammps limit the number of groups I can define.

Hoping for any advice please. Thanks!



If you can just use the total force on the tube atoms

(maybe because tube/tube interactions cancel out),

then you can use fix chunk/atom to sum/average

forces on any spatial binning defined by the

compute chunk/atom command.