yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 2 June 2010 17:06, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

> Hi Chiara,
>
> I didn't take time to reply as it would need a long discussion. Keep
> looking into MD litterature and you should find questions to your answers,
> be it in a formalism that is excessively complex.
> I don't agree with your equations below (giving Cundall way). I don't think
> anybody ever wrote equation (1). There is a very BIG difference between
> vel=... and vel+=...; Cundall is using vel=... where vel is the mean field
> velocity.
>

What do you mean as mean field velocity ?
To report exactly from his paper what he wrote in terms of displacement
increment :

delta_u = delta_u(real_vel) + gradVel*pos*dt;

where :
delta_u(real_vel) = vel*dt; (vel is from the real particle velocity, hence =
a*dt)

So the increment of velocity I guess would be given by :

delta_v = vel + gradVel*pos;

That is why I was writing in my previous post :

vel+=vel+gradVel*pos; (I was only missing the vel given by a*dt, but I
thought it was implicit)

Is this wrong ?
IICR, you were writing the same thing in a previous post in this thread,
like:
if (homotheticCellResize>1) state->vel+=scene->cell->velGrad*state->vel*dt;

and now you say that equation
vel+=velGrad*vel*dt   (1)
is wrong. Does not look exactly the same you wrote ?

cheers. Chiara