Hey
I was just speaking to a visiting lecturer about LIGGGHTS and he said that he had an undergraduate using the code, and noticed something missing in the code to do with the correct calculation of the tangential history. He said it was a few months ago he was looking at it, so I was unsure as to if this may have been picked up and amended.
Basically if you have two particles which are colliding, which are in contact for period of time and one of the particles starts to slide around the other while in contact. The direction of the old tangential force considered in the history effect must also undergo a coordinate transformation in accordance with where the point of contact has moved. Similarly in the case where these two particles are rotating upon collision.
I wondered if you could give more detail as to how this tangential history force is updated, and if this effect has been included. He seemed to think many codes have missed this...
Jay
ckloss | Fri, 02/03/2012 - 15:58
Hi Jay,no we have not missed
Hi Jay,
no we have not missed this accidentially... Basically contact history is in the contact-local reference frame, so it has to be rotated along as the pair of contacting particles rotates relative to the fixed-space coordinate system. Some people do this by applying matrix rotation or quaternions, in LAMMPS/LIGGGHTS the rotatation is performed by cutting away the part of the shear history which is not in the tangential plane, so one could term this a very cheap "zero-order-rotation". Of course, explicitly performing the rotation is more accurate, but much more expensive.
This is basically the same topics for particle bonds, as discussed here: node/525
So, in a nutshell - there are different was, and it's open source - if you think your application requires a more accurate, feel free to do so - it should be pretty straight-forward to implement
Cheers, Christoph