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[Janek Kozicki <janek_listy@xxxxx>]

Hello,

As you already know, there are currently two main entities used to
store data about simulation:

Body
  |-PhysicalParameters (to be splitted into PhysicalParameters and State)
  |-GeometricalModel
  |-InteractingGeometry
  \-BoundingVolume

Interaction
  |-InteractionPhysics
  \-InteractionGeometry

I have however came to conclusion that a third entity must be added.
Examples of this entity exist currently inside yade, but they are all
implemented as some kind of hack and a note in the code that "something
must be done with it", those are:

FEMTetrahedron - it is a weird kind of Body, because it seems to be an
interaction from DEM point of view, but it seems to be a Body from FEM
point of view. It is currently implemented as Body, but we had a feeling
that it should be "cleaned up" and reimplemented as Interaction. It is
however noticeable that:
- this entity uses four Body elements as its nodes.
- Those Body elements (nodes) can change their position, so the
  whole FEMTetrahedron is also deformable.
- the nodes _cannot_ be inside FEMTetrahedron because each node is used
  by many FEMTetrahedrons

LatticeBeam - at first we thought that maybe it's an interaction between
two nodes (each node is a Body), but it isn't in fact - because the real
interaction is between one LatticeBeam and another LatticeBeam (through
angular springs), also it is noticaeable:
- this entity uses two Body elements as its nodes
- those nodes can change position, so LatticeBeam is deformable
- each node is used by many LatticeBeams, so they cannot be stored
  inside LatticeBeam

The problem is - how to name it?


I have read OOFEM manual (an opensource FEM program), and there Body is
called DOF, while this new entity (that uses many DOFs as nodes) is
called Element.

Of course thinking that Body is a DOF (Degree Of Freedom), or that DOF
is a Body is totally wrong - we have here two overlapping science
domains (DEM vs. FEM), and it just happens that the smallest primitive in
simulation of FEM is called DOF, while the smallest primitive in DEM
simulation is called Body.

(Also please note that LatticeBeam element from my PhD is _not_ a FEM
element, it is just a very sphisticated DEM element)

I was thinking about renaming Body to Primitive, and adding this new
entity under the name Element. But I'm not sure about that. I'd like to
know your opinion.



this new Element should at least contain following:

Element
  |- list of bodies' id numbers that it is using
  |
  |- since it's deformable (nodes can move independently) it should
  |  contain some stiffness model, or deformability model
  .
  ... possibly something more.


-- 
Janek Kozicki                                                         |
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