yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Bruno Chareyre a écrit :
>> Hmm... As me seems, prevVelocities is specific for leapfrog method.
>> For another integrator may be another implementation (Gear predictor-corrector as example...)
>>
> 
> Given that the kinematics (pos,vel) at time t depends on previous 
> kinematics. I don't see how an integrator could compute the motion 
> without previous velocity (the result would be independant on e.g. 
> initial velocities!).
> Yes, different schemes could need vel(t-2dt) instead of vel(t-dt) (or 
> both of them), but you always need a "previous" velocity.
> 
> Bruno
> 


Mmmmh...
Perhaps I missed your point. It may be true that some schemes don't need 
previousVel, and in fact it rings a bell for me :

Indeed, even in leap-frog, we could write

v(t+dt) = v(t) + acceleration*dt (in the code, it would read : v += 
acceleration*dt).

where v(t) is the previous velocity, but it's erased as soon as current 
velocity is computed.

This is how I write the second order finite difference scheme usually, 
and I'm still not sure that the equations in Yade are equivalent to this.

I will double-check that point as it could explain why we need unusually 
low timesteps...

Bruno






> _______________________________________________
> Yade-users mailing list
> Yade-users@xxxxxxxxxxxxxxxx
> https://lists.berlios.de/mailman/listinfo/yade-users
> 


_______________________________________________
Yade-users mailing list
Yade-users@xxxxxxxxxxxxxxxx
https://lists.berlios.de/mailman/listinfo/yade-users