Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions

[Ulf Schiller]

Hi Markus,

this looks like a bug. I haven't touched the code in a while and after a
brief look at the master I think the coupling needs to be revisited.
There's a MPI call somewhere in the velocity calculation which is
inefficient and defies the locality of the algorithm. I couldn't spot
anything in particular which might cause your problem, and I don't have
time right now, sorry. I'll try to come back to this in the afternoon or
over the weekend.

Cheers,
Ulf

On 28/11/14 11:07, Wink, Markus wrote:
> Hello everybody,
> 
>  
> 
>  
> 
> I remember spotting something like this in one of the older versions of
> the master, but I tried to find it and could not reproduce the bug with
> the latest version, which one are you using?
> 
> -       I am using version 3.3.0, so the latest I guess
> 
>  
> 
>  
> 
> Yes, looks like something is at odds with the periodicity here. Can you
> plot the z-velocity over x-position? That may point towards what is
> going wrong.
> 
>  
> 
> -          Attached you will find the z-velocity as a function of the
> x-position (by accident I named it y-position). The velocity of the
> particle looks awkward when it gets close to the boundary (marked with a
> black line). I furthermore performed a simulation, where I checked the
> interpolated velocities of the fluid at the origin of the particle. The
> v_z component of the fluid looks also awkward close to the periodic
> boundary. Even if I don’t put particles in the fluid, I get a strange
> velocity of the fluid close to the periodic boundary. I was wondering,
> if the periodic boundary condition for the LB fluid has some bug. I
> played around a bit with the variable tau, but it still shows that
> strange behavior close to the boundary.
> 
> 
> Does anyone has a clue where this could come from?
> 
>  
> 
> Attached I put some graphs of the velocity and the forces acting on the
> particle as a function of the position in the channel as well as the
> interpolated velocities of the fluid. Maybe that helps people spotting
> the error.
> 
>  
> 
> Thanks in advance.
> 
> Greetings
> 
>  
> 
> Markus
> 
>  
> 
>  
> 
> *Von:address@hidden
> [mailto:address@hidden
> *Im Auftrag von *Joost de Graaf
> *Gesendet:* Montag, 24. November 2014 21:25
> *An:* Ulf Schiller
> *Cc:* address@hidden
> *Betreff:* Re: [ESPResSo-users] Particle in Fluid, periodic boundary
> conditions
> 
>  
> 
> Dear Markus,
> 
> I remember spotting something like this in one of the older versions of
> the master, but I tried to find it and could not reproduce the bug with
> the latest version, which one are you using?
> 
> KR, Joost
> 
>  
> 
> On 24 November 2014 at 19:35, Ulf Schiller <address@hidden
> <mailto:address@hidden>> wrote:
> 
> Hi Markus,
> 
> On 24/11/14 18:12, Wink, Markus wrote:
>> can explain it to me? It seems, that the periodic boundary condition in
>> the LB Fluid doesn’t work. If I remove the fluid I don’t see that.
> 
> Yes, looks like something is at odds with the periodicity here. Can you
> plot the z-velocity over x-position? That may point towards what is
> going wrong.
> 
> Cheers,
> Ulf
> 
> --
> Dr Ulf D Schiller
> Centre for Computational Science
> University College London
> 20 Gordon Street
> London WC1H 0AJ
> United Kingdom
> 
>  
> 


-- 
Dr Ulf D Schiller
Centre for Computational Science
University College London
20 Gordon Street
London WC1H 0AJ
United Kingdom

Phone: +44 (0)20 7679 5300