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

[Owen Hickey]

Hey Markus,

I used the test script from Iva and the erroneous dependence on the
grid spacing disappears. The new code still passes all of the LB tests
too. The new scaling also makes more sense, so we believe that this
fixes the problems with the grid spacing rescaling.

Sincerely,
Owen

On 31 July 2015 at 13:45, Wink, Markus <address@hidden> wrote:
> 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.
>
> Greetings
>
> Markus
>
> -----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 
> resolutions
>
> 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.ht
>> 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:
>>> http://cell-in-fluid.fri.uniza.sk
>>>
>>>
>>>
>