query about granular moving wall


I am having some problem in setting the granular wall to move in the perpendicular direction to the plane of the granular wall.

For fix wall/gran/hooke command, there are only two types of movement possible, one is shear and another one is oscillatory.

I want to perform an uniaxial compression, where suppose y wall comes down with some velocity in the y direction.

I dont find any such fix…is there any way to get over the problem?

thanking you


fix wall/piston does this. If you want granular interactions though (soft spheres, damping, and friction), you will need to modify the code.

Motion of the wall in the perpendicular direction would have

to be added to fix wall/gran, similar to how it is with
fix wall/lj93 or fix wall/harmonic.


thanks a lot for your response steve…but with fix wall/gran there are only two keywords that can be appended one is shear and another one is wiggle…none of them gives the motion in the perpendicular direction…when i am trying to append vel keyword like the other wall styles, it is saying illegal fix style…can u plz have your say on this

even I have tried to use equal style variable command in place where i need to give the co-ordinate of the wall so that wall position gets updated or gets to move…that also dint work…your help is highly appreciated

I believe what Steve is saying is that the fix/gran would need to be altered, so that this is possible. He pointed you to fixes that do this for other types of particles, which you could use as an example of how to do it. Currently, it won’t work simply because it isn’t coded.

You could look at LIGGGHTS (a code built on top of LAMMPS), which has many more granular specific commands and the ability to simulate much more complex geometry.

okay Eric thanks a lot for your reply