yade-dev team mailing list archive

[Václav Šmilauer <eudoxos@xxxxxxxx>]

> 1) //! stretch ratio ?(n) 
> (http://en.wikipedia.org/wiki/Finite_strain_theory#Stretch_ratio)
> 
> This comment is wrong, the strectch ratio is |F.x|/|x|, which is a 
> function of non-diagonal terms. The values returned by getStretchRatio 
> are not stretchRatios, they have no clear meaning and are not invariants 
> of F.
> As mentionned before, out of diagonal terms have an effect on stretch 
> ratios (this is why I don't know how to work with _size without Hsize).
I will fix that. Actually the collider needs lengths of transformed
boundaries (i.e. lengths of Hsize column vectors), and it will also fix
the 1/cos(φ) term -- it will be the same algebraically, but the angle
will refer to true shew of the cell, regardless of (arbitrary) rotation.

I will do this today.

> 2) The stress update is not done at each step, this is a problem since 
> the size of the period will be controlled based on outdated values.
Where? In PeriTriaxController? Yes, but in the in-between steps, it is
estimated from stiffness value (which is perhaps computed wrongly, but
doesn't invalidate such approach by itself). Plus, you can control the
update interval manually and set it to 1 or 2 if unsure. (Remember the
strain-stress diagram I sent, with the saw-like shape as stiffness was
overestimated beween true stiffness updates?)
> 
> I think I'll commit to a branch, I have too many changes in view and I 
> don't want to mess with the trunk.
Plese commit to trunk, I don't mind if that code is broken temporarily.
At least you get testers (me) and no other people probably use that code
much.

Vaclav