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[Raphaël Maurin <question238696@xxxxxxxxxxxxxxxxxxxxx>]

Question #238696 on Yade changed:
https://answers.launchpad.net/yade/+question/238696

Raphaël Maurin posted a new comment:
Hi all,

I implemented inside GlobalStiffnessTimeStepper a calculation of the time step which take into account the damping [1] based on the idea of Emanuele Catalano . 
Basically it evaluates the critical time step of the whole system considering the critical time step of the system with only springs on one side (dt_e), and with only viscous damping on the other side (dt_v). It then takes the minimum of the two critical time step with a safety coefficient (dt = n*min(dt_v,dt_e).  This method is equivalent to evaluate the minimal time step of the system considering that the elastic and viscous effect are decoupled, and to multiply it by a safety factor in order to take into account the coupling between the two. This is not completely rigorous but I am currently using it and I have no problem of stability.

It is for now possible to use it only with ViscElPhys ([2], linear
spring-dashpot), but it can probably easily be modified for any other
law with linear damping.

And to answer the other previous question, the introduction of damping
can effectively reduce the critical time step of the system when
considering interactions with strong importance of the damping with
respect to the stiffness. In my problem, I can see it at very low
restitution coefficient (e<0.1). The effect can be understood
considering that the damping introduce a new characteristic time step in
the problem, which is not in general bigger than the elastic one.

I hope the expanation is clear,.

Raphael

[1] https://github.com/yade/trunk/blob/master/pkg/dem/GlobalStiffnessTimeStepper.cpp
https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.GlobalStiffnessTimeStepper
viscEl option
[2] https://github.com/yade/trunk/blob/master/pkg/dem/ViscoelasticPM.hpp

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