2010/3/25 Bruno Chareyre <[email protected]> > > (As said, I never used that code; what I was driving at was to get >> comparison of critical timestep given by PWaveTimeStep and >> GlobalStiffnessTimeStepper.) >> >> >> >> > This is another interesting discussion I wish we could have when you were > here... > Actually, the relation between the two is relatively weak. > In short, they scale the same way, but the factor between them depends on > (always the same set) porosity, contact anisotropy, PSD,... > 8 contacts per grain or 4 contacts per grain really means different > critical timesteps for the explicit scheme. It is accounted for explicitely > in GlobalStiffness since it is a sum on all contacts (you will find a factor > sqrt(2) betwween the dt's), in PWave it is just ignored. > > The good point of global stiffness is it is dynamic (changing with packing > state), so it can really be as close as possible as the exact current > critical value. Even if GS gives dt only 10% higher than PWave (it is in > fact more based on what you put as default factor in dt=0.5*PWave), it is > worth using, since GS doesn't take more than 10% in cpu time. The weak point > is GS gives nothing when there is no contact, thats why I use both in > scripts now. PW gives an initial value, and GS adjusts it dynamicaly once > contacts are created. > > Bruno > > BTW, Bruno do you know if this method to get the timestep that varies with the global stiffness can be well applied also when we have a non linear relationship between forces and displacements at contact? As in the Hertz-Mindlin formulation, for instance. Do you think that in such a case the critical time step should change or should be taken differently than having a linear relationship?
Thanks for your opinion, Chiara > > >> >> > > > -- > _______________ > Bruno Chareyre > Associate Professor > Grenoble INP > Lab. 3SR > BP 53 - 38041, Grenoble cedex 9 - France > Tél : 33 4 56 52 86 21 > Fax : 33 4 76 82 70 43 > ________________ > > > > _______________________________________________ > 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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