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[Christian Jakob <1070744@xxxxxxxxxxxxxxxxxx>]

> I forgot to say: this is clearly not a bug report. Please use
launchpad consistently.

I know, but I like the possibility of sending attachments, as far as I
know this neither possible in launchpad questions nor in mail to yade-
dev ...

I tried to understand how to calculate torsional moments for clumps. Please have a look at the pictures in the attachment. There two clumps are shown and I do not understand how their torsional moments can be calculated. In the first picture there is box clumped with a "half sphere". In the second picture you can see a box inside a sphere, like I want to model my sand grains in future. How is torsional moment calculated in this cases?
Can this be simulated with RotationEngine already?

> For box-box interactions, there is a serious background in 3-DEC from
> itasca, where arbitray polyhedral shapes are modelized. It should apply
> to boxes.

Hm, I think in the case of cubids (boxes) it should be much easier, than
a general polyhedral shape.

> My only question is if it is really necessary to modelize angular
vertices instead of rounded shapes.

If I want to model rounded shapes, I could clump spheres, as it is
already possible in Yade ... but this is also a nice idea.

** Attachment added: "2 pictures of sphere-box clumps"
   https://bugs.launchpad.net/yade/+bug/1070744/+attachment/3412779/+files/clump-box-sphere.zip

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https://bugs.launchpad.net/bugs/1070744

Title:
  boxes with torsional moment

Status in Yet Another Dynamic Engine:
  Invalid

Bug description:
  Hi all,

  I thought about extending boxes ability by including torsional moment
  and box-box interactions. And I want to know from you, if this a good
  idea.

  The reason is the following: I want the model more realistic sand
  grains. I can create complex shapes by using clumps, but there are 2
  disadvantages. First, the number of spheres is getting too high, which
  corresponds to high calc. times. Second, by clumping just spheres,
  there are no real egdes, just rounded ones. To override this I want to
  create clumps consisting of one sphere and one or more boxes inside
  the sphere. Only the edges of the box are outside the sphere, so one
  can create an angular particle. With one box maximal eight edges can
  be created.

  For implementation, boxes must be extended by following abilities:

  - boxes can rotate (torsional moment must be implemented)

  - boxes can interact with each other (Ig2_Box_Box_ScGeom will be
  needed)

  - all interaction types must be handled:
   * box vertex - box plane interaction
   * box vertex - box edge interaction
   * box vertex - box vertex interaction
   * box vertex - sphere interaction ----- see figure below
   * box edge - box plane interaction
   * box edge - box edge interaction
   * box edge - sphere interaction
   * box plane - box plane interaction

  example box vertex - sphere interaction:

  ```````````````````````````******
  ````````````````````````*''''''''''''''''' *
  `````````````````````*'''''''sphere''''''*
  ```````````````````*'''''''''''''''''''''''''''''''''''*
  ################'''''''''''''''''''''''*
  ___________________*''''''''''#'''''''''''''''''''''''*
  _____________________*''''''#''''''''''''''''''''*
  ________box___________ *'#''''''''''''''' *
  _________________________#'******

  What do you think about this? I know it will be a lot of work, but in the end it will be a very big extension in possibilities of DEM simulations with yade (not just angular particles!).
  Are there other DEM codes, where something similar it is implemented?
  What about the details of implementation? Where do you see problems in coding?

  Christian.

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