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

[Owen Hickey]

Hey all,

This appears to fix the problematic scaling with agrid:
https://github.com/ohickey/espresso/tree/LB_scaling

Regards,
Owen

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:
> 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
>>
>>
>>