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[Paul Pircher <question694146@xxxxxxxxxxxxxxxxxxxxx>]

Question #694146 on Yade changed:
https://answers.launchpad.net/yade/+question/694146

    Status: Expired => Open

Paul Pircher is still having a problem:
Hi Jan, 
thanks for your reply. Same as you I reply kinda late so no worries about that.
I read through your suggestions and tried several (new) approaches and extended my code versions in order to be able to formulate new questions. 
But first let me answer to your points:

Q: what is "bed of particles"? spherical particles?
A: Yes the bed of particles consists of clumped spherical particles. 

Q: You can create cohesive packing of overlapping spheres. The overlapping would make the surface smoother than distinct spheres, but not perfectly flat
A: It seems like I don't have to deal with the geometrical roughness since the approach with PFacets (from the paper I linked) builds a flat surface. Nevertheless, thanks for the suggestion!

Q: have a look at DeformableElement stuff [1]. I have no experience with it, but sounds relevant to your problem.
A: I had a first look at it and it seemed to be completely different to my approach so far. Therefore, I remained in modelling my elastic cuboid with Nodes, GridConnections and PFacets. Further down I explain my current modelling status.

Q: Also, as PFacets are present, something like PTetrahedron would solve your problem.
A: I just had a 2-minute search for PTetrahedron, but I did not find any information for that in the documentation or launchpad. Would you mind linking me something that explains your suggestion?

Q: Theoretically yes. But I doubt it is currently implemented.
A: Yes, I thought so, but right now it does not seem to be relevant.

My current modelling status:

General: I tried to model a simple beam that is fixed on one end and
free on the other. That should lead to a bend beam like in [1] that can
be compared to the analytic version. The only force acting on the beam
is its own weight. What I exactly mean is shown in [1] in the section
“Beam deflection tables” for a cantilever with uniform distributed load.

I followed the approach of the papers [2] and [3] in two different ways.
For the first one, I developed my own algorithms for creating my beam. First, all the nodes a created with given distance in between them. Then a grid is built up connecting them, but at first only a cuboid grid. This means that the complete beam is a big grid of little cubes. So, there are no cross-connections implemented yet that would divide the grid areas into triangles for putting PFacets in there. 
In the next step I developed code for implementing cross-connections on the surfaces of the beam (so not inside) and creating PFacets in between them. 
That leads to a beam, that has a smooth surface thanks to the PFacets and still has a grid structure inside (without PFacets, only grid connections). 
According to my ideas that should lead to a simple but solid structure. 
Right now, it only leads to an error message as follows:
<WARNING> InteractionLoop:135 virtual void yade::InteractionLoop::action(): IGeomFunctor returned false on existing interaction!
Segmentation fault (core dumped)
I did not research that error yet, but if someone has an idea where I might want to start looking for details, I would not mind. 
Furthermore, I do not have a publishable code yet as it is not well commented, fuzzy and my comments are in german. I will upload the script if that error proceeds to exist.

For the second approach I designed a meshed beam in the software “gmsh”,
meshed it there, exported it as a .mesh-file and imported it to yade via
the gmshPFacet()-function. It works smoothly and leads to a fully
working simulation. The only issue I have is that even if I create a 3D-
mesh in gmsh, it will only form a surface-structure in yade. That means
it will break it down to a 2D-surface mesh again.

For comparison, I plottet the deflection of the beam at the very end. Not surprisingly it does not lead to the same deflection as the analytical version, neither the mass nor mass-distribution is correct. Though these two points are other problems. 
Right now, I am focusing to get my scripts to work and the beam to behave like it is supposed to be. Without PFacets on the surface the beam shows completely wrong mechanical behaviour that would not be acceptable. Furthermore, it only works for small forces and small deflections as for higher density or higher gravity (the two ways of increasing the load on the beam that I tried) the surface breaks down and/or starts to buckle. That is the reason why I want to have a volume grid/mesh with connections on the inside of the beam to prevent surface crashes and being able to load it with higher forces. 
Hopefully, I will be able to collect some picture of the simulation soon. Together with a code sample I could image that I would be easier to understand what I am doing. I still wanted to answer “in time” and before holidays. 
Best regards!

[1] https://mechanicalc.com/reference/beam-analysis
[2] https://www.researchgate.net/publication/282996677_A_general_method_for_modelling_deformable_structures_in_DEM
[3] https://doi.org/10.1016/j.geotexmem.2015.07.015

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