yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

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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-- 
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Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
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