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[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

> I am only applying an initial velocity to one particle, hence the 
> total energy of the system is only given by (kinetic + potential elastic).
> Look at the two attached figures. The first one (dt_crit) is the 
> result obtained using the critical time step computed by Pwave in 
> Yade. The second one (dt_Econst) is obtained decreasing the time step 
> to get the total energy constant.
I don't think it is an effect of the timestep, but mostly an effect of 
the dt/2 shift (smaller with smaller dt). I mean : energy WILL be 
constant even with the larger dt if you correct this shift (check in the 
previous ods file I sent).

> Now I see that the time step influences the solution in terms of 
> energy and this is just a very little example (so it does not really 
> quantify anything). However, I have one consideration: does this mean 
> that we are mainly dealing with non conservative systems in our dem 
> simulations? Is this the right way to compute the total energy?
Your way is correct. IMO, energy will be approximately constant if you 
correct the dt/2 shift in kinE. Without this correction, energy will 
still be constant in all quasi-static processes.

Cheers.

Bruno