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Re: [ESPResSo-users] fluid-particle coupling in different LB resolutions

From: Wink, Markus
Subject: Re: [ESPResSo-users] fluid-particle coupling in different LB resolutions
Date: Fri, 31 Jul 2015 11:45:18 +0000

Helle everybody,

does the commit of Owen fix the problems mentioned below? I have seen, that the 
current master changed how the scaling is calculated. 



-----Ursprüngliche Nachricht-----
Von: address@hidden [mailto:address@hidden Im Auftrag von Owen Hickey
Gesendet: Freitag, 13. März 2015 10:15
An: Iveta Jancigova; Markus Gusenbauer
Cc: ESPResSo Users
Betreff: Re: [ESPResSo-users] fluid-particle coupling in different LB 

Hey all,

This appears to fix the problematic scaling with agrid:


On Thu, Mar 12, 2015 at 11:10 AM, Owen Hickey <address@hidden> wrote:
> Hey Iva and Markus,
> There is most likely a bug in Espresso when scaling the external force 
> and outputting the velocity with values of agrid that do not equal 1.
> There was a discussion some time ago and it definitely does seem like 
> something is wrong in the conversions:
> ml
> I hope that helps!
> Owen
> On Wed, Mar 11, 2015 at 8:07 PM, Iveta Jancigova 
> <address@hidden> wrote:
>> I realized I didn’t attach a simulation script to my question, so I’m 
>> attaching it now.
>> Please, let me know what could be the issue.
>> Thank you,
>> Iva
>>> On 11 Mar 2015, at 13:20, Iveta Jancigova <address@hidden> wrote:
>>> Hello,
>>> I want to ask about a strange behavior I encountered:
>>> When I put a single particle in the center of a channel 20x10x10 with fluid 
>>> (ext_force on fluid 0.0001 0 0, dens 1, visc 1) and look at the velocities 
>>> of the particle and fluid at the same position, I get the following:
>>> for grid=1:   v_fluid ~ 0.000728167   v_part ~ 0.000723167
>>> for grid=0.5:         v_fluid ~ 0.000737281   v_part ~ 0.00018307
>>> for grid=0.25:        v_fluid ~ 0.000738749   v_part ~ 4.58593E-05
>>> While the fluid velocity is roughly the same, the particle velocity seems 
>>> to decrease ~4 times when the grid size is halved.
>>> I have tried varying the friction parameter (even by orders of magnitude) 
>>> but it only made minimal difference. I suppose that is because the particle 
>>> is simply carried by the fluid.
>>> So my questions are: Is it possible there is an error in the coupling? Or 
>>> what can I do to get the proper velocity of the particle?
>>> Thank you,
>>> Iva Jancigova
>> ---------------------------------------------------------------------
>> -----
>> Iveta Jancigova, PhD student
>> Faculty of Management Science and Informatics University of Zilina, 
>> Slovakia cell-in-fluid research group: 

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