Rigid - nonrigid particle interaction

Hello all,

I am new to Lammps and I am working on a mesoscale simulation using granular and rigid packages. I use nonrigid atoms to model granular media (GM) and a rigid body, made out of small atoms, to represent an intruder of non-trivial geometry with the intention of manipulating the intruder within GM.

My question is about the contact relation between rigid and nonrigid bodies. The manual gives detailed information about the types of contact forces between individual atoms where I use atom_style sphere and gran/hertz/history as the pair_style. Does LAMMPS apply the same pair_style to solve for the interaction between the rigid body (of small particles) and the neighboring nonrigid granular particles? Also, does LAMMPS consider the full details of an intricate shaped rigid body when it is in contact with many neighboring nonrigid granular particles during calculation of the penetration depth and the resulting forces? Or does LAMMPS reduce the complexity of the rigid body geometry for such calculation purposes?

Thank you,

Yes. The fix rigid operation is completely independent from the force computation.

Same question, same answer. Plus fix rigid will also consider the impact of any torques on the constituent particles of a rigid body for the motion of the rigid body.

As a general rule: LAMMPS does what the documentation says it does. Nothing less, nothing more.

For rigid bodies the force computation is unchanged compared to non-rigid objects.
Fix rigid then will accumulate all the data from the constituent atoms and compute center of mass force and torques around the center of mass and then propagate the rigid body position and orientation accordingly. That will then be translated into atom positions and velocities for the atoms of the rigid body.

Hi Akohlmey,

Thanks for the response and clarification.