Question #214773 on Yade changed: https://answers.launchpad.net/yade/+question/214773
Jan Stránský proposed the following answer: Hello once more, my last answer is a bit complicated.. a very simple example came to my mind: imagine elastic contact of two bodies. According to bodies velocities before contact, kinetic energy conservation and momentum conservation you are able to evaluate velocities after the contact [1]. You don't care about contact forces at all. That's why the velocities / positions are the same / comparable The forces depends on material (material law) and stiffness. Therefore for different laws the forces are different. Now it should be clear Jan [1] http://en.wikipedia.org/wiki/Elastic_collision 2012/11/21 Jan Stránský <honzik.stran...@gmail.com> > Hello guys, > > thanks to Eugen for summary. Based on his answer (I did not checked the > scripts in detail myself): > > the free falling is the same for both contact laws (besause there is no > contact :-). > > Then there is a short contact impulse causing force acting on particles > causing their acceleration. The contact laws / parameters may be (and > according to the results they are) different, resulting in different > forces. With different forces the acceleration is also different. But under > assumption of low energy dissipation, the velocity before and after the > contact is the same for any contact law. The difference is the time of > actual contact (for stiffer law it is shorter). But in your simulation this > time is negligible compared to the total time of simulation, therefore you > do not see differences in velocities / positions (at least in the > beginning), although they are there. And also there may be some energy > dissipation in MindlinPhys, I don't know. > > Hope it helps you. > Jan > > > 2012/11/21 Eugen Kubowsky <question214...@answers.launchpad.net> > >> Question #214773 on Yade changed: >> https://answers.launchpad.net/yade/+question/214773 >> >> Status: Open => Answered >> >> Eugen Kubowsky proposed the following answer: >> Hi Guys, >> I think I know what confuses you. If I take a look at your python >> script, your simulation is a rather simple experiment. One sphere drops >> from a given height without any initial velocity to ground. Reaching ground >> it jumps up again but with less altitude - drops again and so on and so on. >> Looking at your graphs, we see, that positions as well as velocities are >> roughly the same for Cundall and Hertz at least for t <=0,45. >> But the graphs of forces are completely different. You have about 400N at >> Cundall and about 70N at Hertz. >> >> Thats why you're confused I guess: how can velocities and positions be >> roughly the same for that different forces. >> >> I'm sorry, but I cant help you with that. But maybe it helps someone to >> understand your problem. >> >> Greetings, kubeu >> >> -- >> You received this question notification because you are a member of >> yade-users, which is an answer contact for Yade. >> >> _______________________________________________ >> Mailing list: https://launchpad.net/~yade-users >> Post to : yade-users@lists.launchpad.net >> Unsubscribe : https://launchpad.net/~yade-users >> More help : https://help.launchpad.net/ListHelp >> > > -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. _______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : yade-users@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp
