Ok, thanks! Will try. ______________________________ Anton Gladkyy
2010/3/25 chiara modenese <[email protected]> > > > On 25 March 2010 11:57, Anton Gladky <[email protected]> wrote: > >> Hi, Chiara! >> >> Recently I have got some problems with damping in shear directions, but I >> don't know the reason. >> >> When my RockPM had only normal forces, it worked normally. When I added >> shear forces, bodies started to "hang" in the air. If I reduce dampingCoef, >> it become better, but too low dampingCoef brings other problems. >> >> I use only NewtonIntegrator for damping purposes, so I have to check it >> there. >> > > Hi Anton, > > the local damping (alias the one defined used in NewtonIntegrator law) is > working properly in the shear direction as well as in the normal. This time > I have not properly checked with a closed solution (it is a little bit more > complicated than with viscous damping) but numerically I get the expected > behavior (so I see an energy dissipation and a tendency to an equilibrium > position). > I do not know about your specific problem, maybe you can try to use the > viscous damp and see what happens (but wait till Sergei will have updated > his class). > > cheers, Chiara > > ______________________________ >> >> Anton Gladkyy >> >> >> 2010/3/25 chiara modenese <[email protected]> >> >>> 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; >>> 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). 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. >>> 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. >>> >>> Cheers, Chiara >>> >>> >>> _______________________________________________ >>> 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 >>> >>> >> > > _______________________________________________ > 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 > >
_______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : [email protected] Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp
