> if the time step is ok without viscous damping, it will necessary be ok with > the damping. Actually not, or you are thinking of stiffness and viscosity in series? If they are in parallel, dt will have to be smaller.
> Anyway it's million times better than the so called Cundall damping which > must be proscribed (in my own opinion) when the inertial number is to high > (say > 10e-4 ?). If realistic dynamic is required in one's problem, then Cundall damping doesn't apply since it doesn't reflect true dynamics. If quasistatic problems are simulated, or if transient dynamics is not important (pluviation), then Cundall is better, since it is numerically more efficient and it doesn't change the timestep. > I don't know your topic, but if you want to dissipate a certain rate of > energy (defined as the ratio of energy = e_n^2) you could simply multiply the > force (even non-linear with respect to the overlap) by this rate during > unloading... > Think about it... If (1) viscosity is just a numerical trick to damp the equations of motion with elastic contacts, then it results in wrong dynamics exactly as with Cundall's damping (then better use Cundall). The same remark applies to multiplication of contact forces by an artificial dissipation rate. If (2) visco-elastic contacts are supposed to reflect the realistic behaviour, then there is a contact _viscosity_ resulting from material behaviour, and this viscosity will not be tweaked just to give a certain dissipation or over-relaxation. I was assuming (2) in this discussion, because if the question of time-step is solved for any user-defined viscosity, then it will also work for the special cases in (1) (e.g. viscosity=critical viscosity). It's better if we have dt determination in the most general case. Bruno _______________________________________________ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp