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[Paul Pircher <question694146@xxxxxxxxxxxxxxxxxxxxx>]

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

Dear Yade community,

I am kinda new to Yade and I am still learning about all the possibilities that Yade offers to simulation complex material behaviour. However, it seems I want to try something that was not used a lot before (or I am bad in researching) and I need some guidance on how to proceed.

What is my application:

I want to simulate an elastic beam in Yade with the discrete element method.

What I found out so far: 

There are already examples for this like "fast bending beams" [1] which uses nodes and cylinderConnection together with high cohesion parameter values to simulate bending "sticks".
Other examples show the use of gridNodes and gridConnection like "simple_grid_falling" [2].
Furthermore there is a paper for deformable structures in yade aswell from the Particles2015 conference. [3]

What I want to achieve:

I want my elastic beam to be an actual cuboid with a cross-section of a rectangle and not a cylinder with spheres at the top and the bottom. 
To be more precise: The surface of the beam has to be (kind of) flat and edges and corners should be somewhat accurate.
This beam or cuboid is then loaded with a force and presses onto a bed of particles. 
The beam deformation and the particles displacement would be of interest.

Some ideas so far:

First thought: Coupling DEM with FEM, but this will consume way too much computational power (and time) that I don't have. Furthermore as I saw how fast these connection approaches could work in Yade I kind of want to stay in DEM solely.

I thought about building up my wanted beam with lots of gridNodes and gridConnections so it builds a 3D-mesh as commonly seen in finite element method simulations. 
However, I won't achieve a smooth surface without any grooves where spherical particles will be pushed into as soon as force is applied. This effect would highly influence the simulation outcome as friction becomes higher, because of this geometrical effect.

The actual questions:

A. Are there further methods in yade on simulating deformable bodies that could work for that application?

B. What is the actual difference between the cylinder-connection approach and the grid-connection approach if there is any?

C. Why is cohesion/the connections so important here? I know that the particles aren't bonded, but if they stick together because of cohesion why do I need a connection between them? Or vice-versa. Where does the actual stiffness of the beam-element come from? 

D. Is it possible to use boxes or cubes instead of spherical nodes and cylinders as connection? If yes, how? 


[1] https://yade-dem.org/doc/tutorial-more-examples-fast.html#reffastbendingbeams
[2] https://yade-dem.org/doc/tutorial-more-examples-fast.html#reffastsimple-grid-falling
[3] https://www.researchgate.net/publication/282996677_A_general_method_for_modelling_deformable_structures_in_DEM

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