Re: [ESPResSo-users] terminal velocity for LB fluid

[Vincent Ustach]

These are all great answers, thanks everyone. It is definitely more of a physics question than a programming one.

Ulf,
My objective is to determine the constant g in the offset between the bare friction and effective friction of the system in reference to the above paper (Alrichs and Dunweg 1999, and again in Usta et al 2005). The velocity of a particle under an external force was measured and I can only assume a terminal velocity was somehow determined. 

Owen,

I think simulating flow between two plates could give the desired effect, as long as the system was large enough in the direction normal to the plates. I'm going to try it.

Stefan,

This is a very interesting point but I need to look into the implications of it to see if it satisfies the my problem. My hunch is that it does.

Best,

Vincent

--Vincent Ustach
  University of California, Davis

On Fri, Sep 27, 2013 at 12:26 AM, Stefan Kesselheim <address@hidden> wrote:

Hi Vincent,

On 27.09.2013, at 09:15, Ulf Schiller <address@hidden> wrote:

> I'm not sure I understand what exactly you are trying to do: Are you setting the external force of the particle to zero after some iterations? Then the momentum of the system at the time will be distributed until all perturbations have decayed and the particle and the fluid have the same speed (since kT=0). The total momentum of the system will be constant from the time you remove the force. This should be independent of the friction which just sets the time scale.

There is two forces in the script, the naming is just a bit stupid: drag[xyz] and fdrag[xyz]. The first is applied to the particle and the second is applied to the fluid. They exactly counterbalance each other so that the center of mass of the system remains at rest. If you switch of either of them (or alter one and not the other) the system will pick up speed in one direction and the center of mass will continuously accelerate.

I hope that one of the answers has helped you :-).
Cheers
Stefan