2010/4/3 Václav Šmilauer <[email protected]> > Hi folks (Bruno), > > where exactly does come the damping formulation we use in Yade? I > thought it was Cundall's damping (I don't have fulltexts of his papers, > sorry), but Hentz in his thesis reports formula from Cundall's book > "Analytical and Computational Methods in Engineering Rock Mechanics", > which is supposedly like this (3.21, pg. 71): > > Δa=-λ|a|(v/|v|) (*) > > (a=acceleration, v=velocity, λ=damping coeff. I write a=F/m instead of F > as he does) > > In Yade, we damp per-component, > > Δaᵢ=-λaᵢsgn(Fᵢvᵢ'), (**) > > where vᵢ'=(vᵢ+½(aᵢΔt)), approximate of velocity between this and next > timestep. > > I understand that in (*) you have to compute 1 square root, have to make > sure that |v|>0 etc, making (**) more efficient, but also less obvious > (it is not invariant to coordinate system rotation, for instance :-|) > > In short, can I get some references for what we use? >
A reference for this global damping can be found in PFC3d manual (chapter Theory and background) where they propose: Fdi=-λ|Fi|sgn(vi) (***) so basically the same as in Yade (**). The two formulations act exactly in the same manner (they oppose the motion), I suppose that is just a matter of efficiency to choose the (**) equivalent to (***). Chiara > > Cheers, Vaclav > > > _______________________________________________ > Mailing list: > https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev> > Post to : [email protected] > Unsubscribe : > https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev> > More help : https://help.launchpad.net/ListHelp >
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