yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxxxxxx>]

On 24/11/14 18:55, Jerome Duriez wrote:
> Hi, regarding your remarks :
> ________________
>>
>> "returns the mean stress (> 0 in tension) existing in the sample, as
>> measured along boundary 'id', with 'id' between 0 and 5."
>
> Because:
> 1/ Stress "in the sample" is not the same thing, and
> 2 the good point of having the same sign everywhere is that we don't
> repeat the sign convention everywhere.
> ________________
>
> I do not understand 1/ : now, from my point of view, triax.stress(id)
> corresponds to "sigma(boundary id location).n" with sigma(boundary id
> location) the stress tensor for the sample media (including the
> boundaries), at the location of boundary "id". And "n" the outwards
> normal vector.
T=σn on the boundary, yes. The boundary is not inside, thus T or σ in
this equality are not average stresses "in the sample". It is the
average stress on a bounding surface.
Hence my suggestion: "returns the average stress on boundary 'id', with
'id' between 0 and 5."

>
> For 2/, you're obviously right, but in the current state, I think this
> sign convention is stated nowhere once for all in the doc... So, I
> fear that a very little percentage of yade users are aware there is
> one (and what is it)
Then the fix would be to add "we use the sign conventions of continuum
mechanics for strains and stresses" in the first lines of the doc, or at
least in the main doc of the triax engine itself (since the sign
convention is not only for the function triax.stress()).
We can't expect users to look for this general information in the
docstring of a specific function in a specific engine. Worst than
useless, specifying sign with such granularity suggests that the sign
may be different in another part of the code.

Bruno


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-- 
_______________
Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
Lab. 3SR
BP 53
38041 Grenoble cedex 9
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