Re: complex boundaries

[Jean-Noël Grad]

Hi,

At the moment, 4.2.0 only supports basic shapes and metashapes (unions 
of basic shapes [1]). But in 4.3.0, it will be possible to provide a 3D 
bitmask numpy array to construct arbitrary geometries, as well as a 3D 
float numpy array to define the slip-velocity on individual nodes. In 
the attached pypresso script, a random landscape is generated with 
numpy.random.uniform and a smoothing kernel (lb_input_geometry.jpg), and 
it is forwarded to the walberla LB fluid class to define the boundary 
nodes, which are then visualized in the OpenGL visualizer 
(lb_espresso_visu.png). However the particles won't bounce off the LB 
boundary. To address that issue, one could for example derive normal 
vectors from the boundary surface to construct a 3D force field, which 
can then be used to repel particles via the field coupling feature [2].

We are still working on the 4.3.0 version of ESPResSo, though. You can 
try the development version by pulling the walberla branch locally [3]; 
the attached script should work on commit 9e6ddbb9c18f839450 (the 
`viridis` visualization option won't work).

Best,
JN

Links:
[1] 
https://espressomd.github.io/doc/espressomd.html#espressomd.shapes.Union
[2] 
https://espressomd.github.io/doc/espressomd.html#espressomd.constraints.ForceField
[3] https://github.com/espressomd/espresso/pull/2701

On 3/17/22 22:50, zzzaaalll@virgilio.it wrote:
> Hello everyone,
>
> I'm writing to you to ask if the last version of Espresso provides for 
> the possibility of inserting boundaries of arbitrary shape? Actually a 
> few years ago I obtained this result in the publication reported in the 
> link below by inserting a mesh kept fixed during the simulation (the 
> green mesh in fig. 4). However, the drawback of this method is that the 
> resulting boundaries didn't behave correctly with the Lattice-Boltzmann 
> fluid (the flow lines crossed the boundaries).
>
> Thank you in advance for your support.
>
> Best regards
>
> G
>
> link: 
> https://www.dropbox.com/s/ly3m8837pobcm51/lazzini_etal_2021.pdf?dl=0

mwe.py
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lb_input_geometry.jpg
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lb_espresso_visu.png
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