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


From: Ulf Schiller
Subject: Re: [ESPResSo-users] terminal velocity for LB fluid
Date: Fri, 27 Sep 2013 09:15:48 +0200
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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
Forschungszentrum J├╝lich, Germany          Fax:     +49 2461 61-3180

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