yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

>
>
>> 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; (1)
>>
>>
>> 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; (2)
>>
> Well, to get (2) I just followed the numerical scheme, delta_u is the
increment, I do not see why you want to derive it. Anyway, we get _exactly_
the same result at the end (for Cundall solution, I mean).

>
>>
> Heh, no! If you derive (1) vs. time, it will not give (2).
> First, divide (1) by dt to get instantaneous quantities :
>
> du/dt = vel = du_real/dt + gradVel*pos = v_real + gradvel*pos
> (v_real is not "real" at all, it is the velocity in the local coordinates
> of the corresponding cell, the real one is the sum)
>
> The time derivative gives :
>
> acceleration = acceleration_real + d(gradVel)/dt*pos + gradVel*d(pos)/dt
>
> first term : comming from contact forces
> second term : (grad-prevGrad)*pos (after integration on dt)
> third term : convective term.
>
> The third term blocks elastic waves. That is why I'm not sure which one is
> best. HCresize=1 (only first two terms) will gives periodic waves,
> HCresize=2 will stop them (I could confirm in simple 1D cases). For slow
> deformation, the convective term is negligeable and both gives the same.
>
mmh, this is interesting although atm I am not very familiar with this kind
of problems. Thank you for explanation.

Cheers.

Chiara
_______________________________________________

> Mailing list: https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> More help   : https://help.launchpad.net/ListHelp
>