About the stress tensor in facet and wall

Asked by Xiaolong ZHAO on 2020-07-30

Hello, dear professors,
I recently use the 'utils.bodyStressTensor()' to obtain the stress tensors on each partcile. I found in the list, there were also the stress tensors for facets and walls. The stress tensors are the sum of the contact force of one partile divided by the its volume and is negative for compression. Since actually there is no volume in facets and walls, I want to know how these stress tenors are calculated ?
Thank you in advance!

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Jérôme Duriez
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Best Jérôme Duriez (jduriez) said : #1


The answer in C++ language is at [1].

In a maybe more human language, the interactions that carry the forces entering the stress expression are assumed to have a geom [2] component of GenericSpheresContact [3] (or child) type (if not, YADE would probably crash)

As such, there necessarily is a reference radius assigned to each interacting body, see refR* [4]. For wall or facets, the radius seems to be chosen as once or twice the sphere's one [5], hence the volume.

How much sense this makes might be a next question ;-)

[*] https://gitlab.com/yade-dev/trunk/-/blob/b87224b638ed162dd8865d097332286b4b2c9263/pkg/dem/Shop_02.cpp#L885, most recent version as of now
[2] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Interaction.geom
[3] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.GenericSpheresContact
[4] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.GenericSpheresContact.refR1 and refR2
[5] https://gitlab.com/yade-dev/trunk/-/blob/b87224b638ed162dd8865d097332286b4b2c9263/pkg/dem/Ig2_Facet_Sphere_ScGeom.cpp#L122 for Facet-Sphere and https://gitlab.com/yade-dev/trunk/-/blob/b87224b638ed162dd8865d097332286b4b2c9263/pkg/dem/Ig2_Facet_Sphere_ScGeom.cpp#L220 for Wall-Sphere

Xiaolong ZHAO (xiaolong1989) said : #2

Thanks Jérôme Duriez, that solved my question.