This is more a question for Vaclav or Jan, but here are my two cents: There is no simple definition of stiffness in the general case. The definition you find in periEngines is based on the implicit assumptions that there is no strong heterogeneity of the displacement field, and that rotations of particles are negligible, which can happen if you have more than ~10 contacts per particle (it was the case in Vaclav's PhD). For e.g. Cundall law or HM, it doesn't apply.
I don't know precise references but I think the main points of the derivation are, with the assumptions mentioned above: 1- relative displacement at contact is du=epsilon*dl, with dl the distance between centers 2- forces increments are df = dun*kn+dus*ks 3- average df's somehow to get a dsigma (they could be averaged using Love Weber stress, but I think there is a different averaging currently) 4- derive dsigma/depsilon = stiffness Bruno On 04/04/11 16:54, Chiara Modenese wrote: > Hi there, > > Do you have any reference which shows the formula for the stiffness > tensor? I see that in the PeriIsoCompressor.*pp there is a vector > called stiff, is this correct? > > Cheers. > Chiara > > > _______________________________________________ > Mailing list: https://launchpad.net/~yade-dev > Post to : [email protected] > Unsubscribe : https://launchpad.net/~yade-dev > More help : https://help.launchpad.net/ListHelp
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