yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

>
> Hello Bruno,
> I am a little bit confused about the periodic. In NewtownIntegrator we
> update the velocities and _then_ we integrate the positions. This is exactly
> the way of Cundall (I am checking the equations right now) except that he
> chooses to update positions and not velocities (defining a strain rate
> instead of a gradient of velocity which we said is fine but not in the
> general case). I understand that the reason why Cundall updates the relative
> velocities at contact (btw, according to his paper this is not meant to be
> only for the shear direction) before going for the computation of contact
> forces is that he was not updating the velocities at the level of the
> integration. So my guess is: why do we need to update the relative
> velocities if that has already been done in NewtonIntegrator? That would
> have made sense if updating positions and not velocities. Bruno, you said
> there was a problem using periodic ScGeom before the last changes. Where you
> testing with homothetic=1? Because I think that case you would have needed
> to update velocities (which is not a problem in Dem3dofGeom).
>
>>
>> I have been looking at molecular dynamics (sorry for my lack of knowledge
in this field) and I see that "shift2" as well as the "shift" introduced
recently by Bruno for the velocities, are independent by the way we update
displacements (or velocities) in NewtonIntegrator. If I have got it right,
this shift has to deal with the periodicity (though I will reread carefully
the part of the code where this is computed). This shift is not described in
Cundall paper, that is why I got confused.
Btw, why do you choose to update the cell in Scene?

cheers.
Chiara

>
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