yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Thank you Boon for this summary!

It sounds perfectly in line with what we have in mind.

>                             deltaUi = deltaUi + eij xi dt
>           where eij is the strain rate of the space, and xi is the 
> particle coordinate
This is done in NewtonsIntegrator if proportionalStrain=1.
>     * The relative approach of velocity of two particles (used to
>       compute force increments) is found by summing their relative
>       real velocities and a velocity related to the strain rate of the
>       periodic space:             
>                         Vi (rel) = Vi (real) + eij(S)zi(diff)
This velocity is defined if proportionalStrain=2. However, there is 
still a small problem in this case (see the comment in NewtonIntegrator).
> The equations for servo-control to keep stress constant is :
>        volumetricstrainrate = volumetricstrainrate + 
> G(desiredMeanStress - measuredMeanStress)
> where G is the 'gain' of the servo control.  No expressions are given 
> to G.  I don't really understand.
In previous discussions, we said that G could be dt/mass_of_the_cell. 
Cundall perhaps just used numerical experiments to find a suitable value 
in his case.

> **
> e1 (rate)= (2/3)shearStrainRate + volumetricStrainRate/3
> e2 (rate) = -(1/3)shearStrainRate + volumetricStrainRate/3
> e3 (rate) = -(1/3)shearStrainRate + volumetricStrainRate/3
As I see it, Cundall didn't tackle the case of arbitrary deformations, 
which is the point of the current discussions, especially those related 
to vectors and matrices representations.

Best wishes.

Bruno






>               
>
>
> > Date: Wed, 23 Dec 2009 13:48:51 +0100
> > From: bruno.chareyre@xxxxxxxxxxx
> > To: yade-dev@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Yade-dev] periodic cell
> >
> > Hi,
> >
> > I'm still not sure how to make everything consistent with all the
> > vectors and matrices representing strain, shear, refSize, _size, Hsize,
> > etc. It is more a question of maths than implementation, in some 
> cases I
> > don't know how to define the vector representation properly.
> >
> > I'll focus on periodic compressors for now (strain control using mass),
> > I see most of the integration is/can be done here. We can decide later
> > what needs to be kept in Cell or not.
> >
> > Bruno
> >
> >
> >
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