[lammps-users] fix srd and fix addforce


I would like to look at particle alignment during flow. After looking at a few examples, I thought to combine the fix srd (in.srd.mixture example) with fix addforce (Poiseuille flow example) in a system containing some atom_style spheres. Thinking this might be a “cheap” way to simulate the fluid. But there was no directional flow.

Pretty positive this is the wrong way to do this so are there some other fixes or methods I should look over?


Just had a quick look at the fix srd docs and it appears that the only way you could impose a flow would be to change the fix srd c++ code (i.e. add a keyword and then change the velocities of the SRD particles).
This is consistent with the examples: note that the time integration fix is only applied to the “big” particles, so fix srd does all updates of the “small” particles internally.


Thanks Axel

I was hoping it would be something easier than having to change the code since fix viscosity will change the flow of the fix srd particles. I’m not familiar enough with the LAMMPS c++ code to modify it so I will try to find another method.

I am considering using a pair_style dpd and using “neigh_modify exclude type” so that the dpd particles would ignore each other but still have some random motion and collide with the “big” or rigid particles. I’m still reading/thinking about this so I’m not sure if it will work :slight_smile:


Ok, nevermind about using pair_style dpd and using neigh_modify exclude type…this does not give any random perturbations. Using the Langevin thermostat gives some random fluctuations. So that might work.