yade-users team mailing list archive

[Anton Gladky <gladky.anton@xxxxxxxxx>]

Thanks, Vaclav, for the explanation. I needed to dive into the code for
that.
______________________________

Anton Gladkyy


2010/3/17 Václav Šmilauer <eudoxos@xxxxxxxx>

>
>
> >         not sure to understand your answer ;( What do you actually
> >         mean with "interaction" in this regard? Are you talking about
> >         the contact point? I would appreciate if you could say more.
> >         When I will have got it I will add documentation (since now to
> >         me it is still not clear).
>
> Interaction is (usually) positioned in space by its contact point and
> oriented by what we call normal (for spheres, unit vector from one
> sphere's center to center of the other one). Imagine now that spheres
> rotate around the contact point, without changing their mutual position;
> obviously, this should not change shearForce taken relative to the
> particles. However, shearForce is expressed in global coordinates,
> therefore it must be updated so that it "follows" the motion of spheres
> in global space.
>
> Global & local coordinates:
>
> If shearForce were expressed in interaction-local coordinates, it would
> not have to be updated; but unfortunately, 2 points (centers) in space
> only define direction (normal) and perpendicular plane (shear plane),
> but do not define orientation of the plane itself.
>
> In some FEM codes, you have to define reference point for beam elements
> (besides the two nodes that are connected by that element), so that it
> is possible to define local coordinate system, fixing orientation of the
> cross-section (shear plane, if you will).
>
> Since DEM happens in large strains (any motion is possible), any
> reference point could become aligned with the two centers, leading to
> loss of uniqueness of the local system. Therefore, we need to use global
> coordinates for shearForce.
>
> HTH, Vaclav
>
>
>
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> More help   : https://help.launchpad.net/ListHelp
>