yade-users team mailing list archive

[boon chiaweng <booncw@xxxxxxxxxxx>]

Hi Bruno,

Could you include the source of the paper (ISBN or link)?  Please.  I am interested too.


Yours,

Boon


> Date: Mon, 22 Feb 2010 09:16:15 +0100
> From: bruno.chareyre@xxxxxxxxxxx
> To: yade-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Yade-users] DEM equations, written down.
> 
> Václav Šmilauer a écrit :
> >>> (16) is supposed to update shear force F_s (vector):
> >>>
> >>> 	F_s=F_s+K_s*ΔX_s
> >>>
> >>> but this is not correct, since you add ΔX_s (which is in the _current_
> >>> contact plane) to F_s (which is shear force from the previous step, i.e.
> >>> in the _previous_ contact plane)!!
> >>>       
> >> I don't understand the problem. F_s and ΔX_s  are in the global 
> >> coordinate system, not in any contact plane.
> >>     
> >
> > Yes, they are in global coordinates, but, at the same time, current F_s
> > must be always perpendicular to current n (in global coords); otherwise,
> > we wouldn't call is F_s, right?
> >
> > Now, F_s from previous step is perpendicular to _previous_ n, while ΔX_s
> > is perpendicular to _current_ n. Summing these 2 together doesn't make
> > sense, since the sum not perpendicular to anything (neither current, nor
> > previous n).
> >
> >   
> Well, in the code you rotate F_s before summing dF_s : no problem.
> In a paper, you want to split the problems usually, and you comment on 
> the contact law disregarding the rest. But ok, the equations for 
> rotation should be explained somewhere.
> 
> The incremental approach is very common in the DEM litterature, but 
> usually not explained in details in papers (perhaps because it is so 
> common?). I'll send you a detailed paper in a separate mail. It is using 
> the same "approximate" rotation equations than yade, with 
> cross-product(oldN,newN), and then it defines the shear increment like 
> in (16).
> 
> Bruno
> 
> 
> 
> 
> 
> 
> 
> > v
> >
> >
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> 
> -- 
> _______________
> Bruno Chareyre
> Associate Professor
> Grenoble INP
> Lab. 3SR
> BP 53 - 38041, Grenoble cedex 9 - France
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> Fax : 33 4 76 82 70 43
> ________________
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