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

[Ulf Schiller]

On 09/27/2013 05:12 AM, Vincent Ustach wrote:
> Hi all,
>
> I am using the the sample script lb_fluid_coupling_gpu.tcl
>
> I have modified the script to print the velocity each time the script
> records for the average. I have also increased the integrations to 500
> steps per recording.
>
> When the force density ext_force $fdragx $fdragy $fdragz is removed from
> the fluid, the particle accelerates beyond the expected terminal
> velocity of 0.1, even beyond the allowance for effective friction having
> a lower value lower than the bare friction (Alrich & Dunweg 1999).
>
> Why is a terminal velocity not achieved?

Hi Vincent,

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.

Best,
Ulf

--
Dr. Ulf D. Schiller                        Building 04.16, Room 3006
Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
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