[ESPResSo-users] constant velocity field in "object in fluid"

[gianmarco]

Hello everyone,

I'm writing this messsage because I'm trying to reproduce a fluid 
constant velocity field within the package "object in fluid". To do 
this, I created a fluid at rest, therefore by setting the parameter 
"ext_force_density" to a zero 3d vector. To impose a constant velocity 
field I inserted a wall on the top of the simulation  box, with the command


walls=[None]*1

wall_shape = shapes.Wall(normal=[1, 0, 0], dist=Lz)

walls[0]=lbboundaries.LBBoundary(shape=wall_shape, 
velocity=np.array([vcell,0.0,0.0]))

system.lbboundaries.add(wall[0])


where vcell is a parameter representing the boundary velocity. The 
resulting effect is that a mesh inserted in the fluid "feels" the effect 
of the velocity field, i. e. it moves at constant velocity. However, the 
configuration files produced with the command

lbf.print_vtk_velocity("fluid_%04i.vtk" %i)

show a uniform and constant velocity field, equal to zero. Does anyone 
know how to fix this problem?


Thank you in advance for you response.

Best regards

GL