On 25 March 2010 14:13, Sergei D. <[email protected]> wrote: > 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? >
Oh yes. > > > 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... > Exactly. > > > 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. > I derived the analytical solution by hand (no script, I have just used excel to plot the results over time). Once your class is ready I will update/commit my test script so I can include your class in my example and plot shear displacements and so on to show it works. cheers, chiara > > Thanks for you very deep insight work! > > == > Best regards, > Sergei D. > > > > _______________________________________________ > Mailing list: > https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users> > Post to : [email protected] > Unsubscribe : > https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users> > More help : https://help.launchpad.net/ListHelp >
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