25.03.2010 14:29, chiara modeneseт: > Hi Sergei, > > I think that the global damping (the one at the contact level) as it > is now implemented in Yade (class ViscoelastiPM) is wrong in the shear > direction. > > At the moment we do the following (I only refer to the shear direction): > > First we rotate Fs_tot(old); > Then: > deltaFelastic=ks*deltaUs; > Fvisc=cs*deltaVrel_n;
May be deltaVrel_s here? > Fs_tot(new)=deltaFelastic+Fvisc+Fs_tot(old); > > Then we check Mohr-Coulomb on Fs_tot(new); > > The wrong thing (I suppose) is that we store Fs_tot including the > viscous component and then we go for the next step. Instead we should > only store the elastic part and then add the viscous part if we pass > the Mohr-Coulomb criterion (Bruno was right in pointing this out). So, if no moving then no viscous friction... I agree, of course... > Otherwise the final effect is that we are not dissipating energy but > only changing the amplitude and the frequency of the oscillation. I > did a comparison between the analytical solution, Yade code and what I > coded for the shear direction (I took a simple example to do that). I > attach the comparison. Very good! > If you think in the normal direction we do exactly the same. We work > out the normal elastic force as: > > Fn_tot_elastic=kn*Un_tot; > Fvisc=cn*deltaVrel_n; > Fn_tot=Fn_tot_elastic-Fvisc; (minus or plus depending on how we work > out the relative velocity) > > Next step we get a new Fn_tot_elastic that does not include the > hystory of the viscous force, and then we simply add the incremental > current viscous force. > > This is a total formulation but we could use the incremental one also > for the normal part (as in Bruno's notes). So you see that in the > normal direction there is no history of the viscous force. And this is > correct, in fact Un_tot (as well as Us_tot) includes the damping > effect since it is a result of the motion. > > I wrote a new class that adjusts the implementation of the damping in > the shear direction as explained above. Should I commit it? Or would > you prefer to modify your existing one (ViscoelasticPM)? If you agree > with me, of course. > Any comments would be appreciated. > I can modify ViscoelasticPM class. Please, add your test scripts (analytical solution and so on...) into scripts/test directory. Thanks for you very deep insight work! == Best regards, Sergei D. _______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : [email protected] Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp
