yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Václav Šmilauer a écrit :
> Hi Bruno,
>
> I was reading code of GSTS trying to write down what it computes. Do you
> have some paper for reference?
>
>   
The one in ASCE is explaining that in details.

> 1. Concerning per-body stiffness, we have diagonal terms of the
> stiffness matrix Kii=(kn-kt)*ni²+kt. If I understand right, the
> "rotational stiffness matrix" are non-diagonal terms of K,
No. Think to K as a 6x6 matrix with one line per DOF. 
Taking the diagonal means you ignore cross-dependency (e.g. a rotation 
of the body generating a force, or a displacement on X giving a force on Y).

> Now, e.g. in  http://www.fisica.ufc.br/hans/p/256.pdf (please swallow
> the fact that they use (1), that is not important now) eq. (16) gives
> local rigidity proportional to
>
>   (Kn N ⊗ N)+(Kt T^T T)
>
> where N and T are projection tensors defined in (5).
>
> Now, I am not able to make up my mind whether these two definitions are
> equivalent (neglecting the difference kn vs. Kn). Can you enlighten me
> on that?
>
>   
Isn't it exactly the same?

> 2. If I see correctly, computation of timestep from rotational stiffness
> is mathematically incorrect; e.g. line 39:
>   
>   dtx = sdec->inertia.X()/Rstiffness.X();
>
> as it mixes up inertia.X() in local frame and Rstiffness.X() in global
> frame. For spherical particles, that makes no difference, of course.
>
>   
You are right.

Bruno