yade-dev team mailing list archive

[Vincent Richefeu <richefeu@xxxxxxxxx>]

Hi,

Some comments (useful or not):
- If it's possible, try using velocity-Verlet integrator so that the the value of velocity is computed at time step (not mid-step)
- Time integration (trapezoidal rule) involves approximations. Vaclav is right in believing that this error accumulation should decrease when the time-step is decreased.

Should I suggest to perform the balance on a single contact by using a tiny time-step?

Other things come in my mind: 
- Are the angular rotations taking into account in the kinematic energy?
- Is the Cundall damping shut down?

Valclav, could you tell me which file has to be looked at?

ciao,
Vincent

Le 14 nov. 2010 à 00:26, chiara modenese a écrit :

> Hi Vaclav,
> 
> why not trying to calculate the velocities at the right time? I remember I was doing it and energy was conserved (without damping, either local or global). We just need to shift them by adding acc*dt/2 (btw, we need to _subtract_ this term in order to shift in the right way, as discussed with Bruno on the list). It is worth a try. However, reducing the time step should help, if we do not apply the shift.
> 
> Chiara
> PS nice idea to track energies in this way
> 
> 
> 2010/11/13 Václav Šmilauer <eu@xxxxxxxx>
> 
> I am not sure about the cause; two possible explanations come to mind (i) mid-step values of velocity vs. on-step accelerations etc. and (ii) without damping, many elastic collisions take place (their number increases if damping is small, as the system never goes to quasi-static state) and integration error accumulates (what contradicts this is that the precision would be increased with smaller dt, which is not the case, and also that the imprecision effects would cancel each other in average).
> 
> Could someone have a look at the code and suggest something?
> 
> Cheers, Vaclav
> 
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