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

From: Stefan Kesselheim
Subject: Re: [ESPResSo-users] terminal velocity for LB fluid
Date: Fri, 27 Sep 2013 09:26:43 +0200

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 :-).

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