kan a écrit : > Hey, guys, > > I have a problem to get the critical timestep, could you please give > me hand? > if I need to calculate the critical time step for each time steps, how > can I calculate it? > From papers, I found that equation is: > critical_time_step=2*sqrt(mass/k), > > my questions are: > 1. is the mass the particle mass? Its the generalized mass. i.e. one mass for each degree of liberty : actual mass for 3 translation axis, and inertia matrix for the 3 rotation axis. Its a bit difficult to uncouple rotational degrees of liberty because corresponding "mass" is a matrix... Cundall proposed to use diagonal terms as an approximation, its what I did in GlobalStiffnessTimestepper.
> 2. k here is kn or ks or some other value else? Again generalized stiffness : a matrix including translational and rotational stiffnesses (taking into account all contacts on bodies). And again I used the diagonal terms to associate a scalar stiffness to each degree of liberty. > 3. I need to calculate all the critical_time_step for each particle, > and then use the mininum one, right? yes > > and I hear that in the past, the critical_time_step need to calculated > at each timestep, then why and how? Contact created/deleted = stiffness changed. > if I do it at the beginning and get the mininum critical_time_step, > and then keep it as the critical time step for the overall simulation, > will it work? No, unless you set big security margin, which would mean a waste of time. Bruno -- _______________ Chareyre Bruno Maitre de conference Institut National Polytechnique de Grenoble Laboratoire 3S (Soils Solids Structures) - bureau E145 BP 53 - 38041, Grenoble cedex 9 - France Tél : 33 4 56 52 86 21 Fax : 33 4 76 82 70 43 ________________ _______________________________________________ Yade-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/yade-users
