yade-users team mailing list archive

[Václav Šmilauer <eudoxos@xxxxxxxx>]

> I am playing a little bit with the code to understand how thinks work
> in terms of energy. I started with a very simple example of two balls
> in normal contact.
> 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. 

Hi Chia, very nice plots. What were values of Δt in there two cases? Or
rather, what was the Δt_Econst/Δt_crit ratio? (PWave is only an
estimate; there is a section on that in my thesis)

What is also interesting that in both cases Etot has eventually the same
value.

> 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? I
> guess what happens in a system with many bodies (I am gonna try)..

Speaking of myself, I never measured the energy. Besides fear of never
getting constant total energy ;-) I was mostly using some fixed
particles, viscosity etc and didn't bother to compute energy
dissipation.

Doing this kind of studies might be tremendously useful, though. I am
sure it will reveal a whole pile of physically questionable things.

Best regards,

Vaclav