Re: [ESPResSo-users] Lattice Boltzmann - Force Exerted on Object by Fluid

[Kai Szuttor]

Hi Esteban,

1. I can not give a exper answer here because I'm not familiar with the
   OIF implementation, but in principal you can get
   the total force on the object by summing up the forces you get with
   F_particle = -fric * (v_particle - v_fluid)
   where v_particle is the particle velocit and v_fluid is the fluid
   velocity at the position of the particle.
2. I can not reproduce your issue, I tested with the following minimal
   script:

import espressomd
import espressomd.lb                                                     
                                                                                
   
system = espressomd.System(box_l = [10.0, 10.0, 10.0])
system.time_step = 0.01 
system.cell_system.skin = 0.4
                                                      
lb_fluid = espressomd.lb.LBFluid(agrid=1.0, dens=1.0, visc=1.0, fric=1.0, 
tau=0.01)
system.actors.add(lb_fluid)
system.thermostat.set_lb(kT=1.0)

system.integrator.run(10)

I hope that helps.

Best,

Kai
print lb_fluid.get_interpolated_velocity([1.0, 2.3, 5.2])

On Mon, Jun 25, 2018 at 12:54:57PM +0000, Ongini  Esteban wrote:
>    Dear Espresso Developers,
>    I am currently implementing  a simulation using the LB in espresso along
>    with the OIF extension . I have two questions regarding the Lattice
>    Boltzmann code:
>     1. I was wondering if it is possible to output the force exerted on an
>        object by the fluid using the code ?
>     2. The second question is regarding how use
>        get_interpolated_velocity(pos) function? I have tried to implement
>        this however, I receive the following error message:  
>                'espressomd.lb.LBFluid' object has no attribute
>    'get_interpolated_velocity'   
>    Thank You,
>    Esteban

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