yade-dev team mailing list archive

[Klaus Thoeni <klaus.thoeni@xxxxxxxxx>]

Hi all,

thanks for the active discussion. So I guess we just leave it as it is and use 
2 for boxes and facets if this is the usual assumption. No problem. And 
introducing r->infinity ignores the material properties of the facet, so I 
guess my suggestion was not the best one however mathematically correct ;-) 

Thanks again!

Klaus 

On Tue, 13 Dec 2011 10:10:08 PM Bruno Chareyre wrote:
> I have no explanation for the 2*refR other than that:
> - there was 2*refR in box-sphere interactions a while ago (I don't know
> why),
> - facet-sphere interactions inherited this 2* from box-sphere
> interactions (my assumption).
> 
> The thing is I changed that in box-sphere, and now refR of a box is the
> radius of the sphere. I can at least invoke symmetry to justify this.
> Infinite radius could be justified too, the problem is it would give
> contacts twice stiffer than the contacts between spheres, hence smaller
> timestep, without clear advantage.
> 
> Bruno
> 
> On 13/12/11 11:35, Klaus Thoeni wrote:
> > Everyone on holidays already?
> > 
> > Well I am still wondering why for the calculation of the stiffness of a
> > sphere and a facet the radius of the facet is assumed to be twice the
> > radius of the sphere. This is basically the value comming from
> > GenericSpheresContact. In my opinion it doesn't make sense. The facet
> > can be seen as a sphere with radius infinity. So if we take the harmonic
> > average (as it is done in
> > Ip2_FrictMat_FrictMat_FrictPhys ) considering e.g. rb->infinity the
> > stiffnesses become kn = 2*Ea*ra and ks = 2*Ea*ra*Va.
> > 
> > You agree? If so I could commit the changed code. Please let me know.
> > 
> > On Sun, 11 Dec 2011 06:38:35 PM Klaus Thoeni wrote:
> >> Hi Guys,
> >> 
> >> what value for refR does the GenericSpheresContact return for a facet?
> >> By introducing TRVAR2( Ra, Rb ) e.g. in
> >> Ip2_FrictMat_FrictMat_FrictPhys::go it seems if a sphere is
> >> intersecting with a facet the refR value for the facet is just 2*refR
> >> of the sphere. Is this true? And when yes, what's the reason? It's
> >> fundamental for kn and ks, isn't it?
> >> 
> >> Thanks,
> >> 
> >> Klaus
> >> 
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