yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 7 May 2010 13:31, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

>
>> Ok, can I change something in Shop for the dt/2 shift or should I save
>> velocities and accelerations and then interpolate?
>>
>>
> You can change in shop.
>
I changed in shop the kinetic as

ret+=.5*(b->state->mass*(b->state->vel+b->state->accel*dt/2).SquaredLength()+(b->state->angVel+b->state->angAccel*dt/2).Dot(diagMult(b->state->inertia,(b->state->angVel+b->state->angAccel*dt/2))));

I tried the sample example with the two balls and the time step estimated by
PWave. I attach the figure.
Now I suppose that if the kinetic energy is computed correctly (is it?) the
problem relies on the elastic energy. You said yourself that the total
energy is "approximately" constant. Is this approximation due to the
numerical scheme, is not it? If so the time step plays a role also on the
total energy, no?



> Another note : your remark on different dt for different problems is
> correct. PWave and GSTS both consider a dense packing.
> If you have problems where fast collisions between particles matter, there
> is another constraint on dt. In short, particles must not go through each
> other in only one time-step. It results in a definition of dt based on size
> of particles and incident velocities only, disregarding mass and stiffness.
>
>
>
> Bruno
>
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Attachment: kinetic_corrected.doc
Description: MS-Word document