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

[Owen Hickey]

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:
http://lists.gnu.org/archive/html/espressomd-devel/2014-01/msg00015.html

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: http://cell-in-fluid.fri.uniza.sk
>
>
>