Re: [Yade-dev] triaxial test with membrane

[Janek Kozicki]

Thank you for your help!

I have done something, still not perfect, but starts to work ;-)
See videos:

  http://geo.hmg.inpg.fr/~janek/membrane/

Spheres are behaving erratically now, because the acting forces are
not radial, but orthogonal. I will fix that soon also.

I will commit that as soon as I will catch up with Vaclav's changes
in HEAD, because I was working in bzr2284.

I am making this membrane compression to cooperate with Bruno's
"classical" triaxial test. Curently I do this by hand in .xml, but
I want to get this to work in python:

- run TriaxialCompression until it gets compacted.
- stop simulation
- perform jinx stuff with engines, namely: set MembraneCompressor.active=true
- start simulation again (now TriaxialCompression engine will
  continue without even noticing that his walls are not longer walls, but
  a membrane).

How to stop simulation in python when TriaxialCompressionEngine is
changing state?


best regards
-- 
Janek Kozicki   http://janek.kozicki.pl/  |

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Re: [Yade-dev] triaxial test with membrane

[chiara modenese]

On 7 June 2010 07:13, Luc Sibille  wrote:

> Hi,
>
> It is just to give some details about strain localization. I don't think
> you need a menbrane to obtain shear band, it has already been found in a
> rigid cubical box with the DEM, and experimentally on sand with the
> apparatus TRITRI in lab. 3S-R. Experimentally they found that the shear band
> was reflected on the rigid boundaries.
>

> About periodic boundaries, I think I have already seen shear band with
> periodic boundaries, but shear band are somehow constraint since they have
> to verify the periodicity.
>
If it is true that shear bands might be a natural phenomenon, then also with
a PBC it is possible to see them. But I think you are right, Luc, that the
constraint due to the periodicity could be a "problem". At least it would be
almost impossible a study of the inclination of the bands, which would be
inevitably affected by the periodicity.

Janek, may I ask you how is your membrane going? I am just very curious, it
would be much more than interesting to have it in Yade.
thanks, Chiara

>
> Best,
>
> Luc
>
> Janek Kozicki a écrit :
>
>  Hi,
>>
>> I'm thinking about implementing membrane in triaxial test, in order
>> to be able to see localization due to internal shearing.
>>
>> questions:
>> 1) was it done already by someone, and I missed this?
>>
>> 2) it is maybe not necessary, because periodic boundaries also allow
>> to see localization due to shearing? (I doubt that, because the shift
>> on one side is on different height than the shift on right side).
>>
>> I would do this in following way: detect which spheres are on the
>> outer boundary (so they are touching the membrane), and push them
>> inside with some force.
>>
>> To detect spheres that touch the membrane I will do a Delaunay
>> triangulation of whole sample, with extra four points added. Each of
>> those four points is on the exterior of the sample and is a
>> "membrane point". Any sphere that gets connected through Delaunay
>> with this point must be lying on the boundary and is in contact with
>> membrane.
>>
>> do you have any comments on that?
>>
>> I suppose that eigen has Delaunay triangulation. Previously I was
>> using wm3 for that.
>>
>>
> --
> Luc Sibille
>
> Université de Nantes - Laboratoire GeM UMR CNRS
>
> IUT de Saint Nazaire
> 58, rue Michel-Ange - BP 420
> 44606 Saint-Nazaire Cedex, France
>
> Tel: +33 (0)2 40 17 81 78
>
>
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Re: [Yade-dev] triaxial test with membrane

[Bruno Chareyre]

1) was it done already by someone, and I missed this?

  
Membranes have been fully implemented for a while, as minkowsky sums of 
triangulated surface and sphere, in... SDEC!
The most complex part to implement in Yade is you have to track when 
interactions are going from body-facet1 to body-facet2, in order to 
guarantee the continuity of the force.
If you want to try and implement that in Yade, I'm sure colleagues will 
be glad to provide their SDEC code.



2) it is maybe not necessary, because periodic boundaries also allow
to see localization due to shearing? (I doubt that, because the shift
on one side is on different height than the shift on right side).

  

Not sure.

To detect spheres that touch the membrane I will do a Delaunay
triangulation of whole sample, with extra four points added. Each of
those four points is on the exterior of the sample and is a
"membrane point". Any sphere that gets connected through Delaunay
with this point must be lying on the boundary and is in contact with
membrane.
  
This is already implemented in Yade, with weighted "radical" Delaunay. 
See e.g. volumicContactLaw or TesselationWrapper::addBoundingPlanes, 
where bounding planes are spheres of very big radius far away from the 
packing (distance=radius).



I suppose that eigen has Delaunay triangulation.

No, eigen is only for basic linear algebra, but you can use CGAL.

http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_3/Chapter_main.html
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_3_ref/Chapter_intro.html

Bruno


--
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Associate Professor
Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : 33 4 56 52 86 21
Fax : 33 4 76 82 70 43



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Re: [Yade-dev] triaxial test with membrane

[Janek Kozicki]

Bruno Chareyre said: (by the date of Fri, 04 Jun 2010 21:21:56 +0200)

> > To detect spheres that touch the membrane I will do a Delaunay
> > triangulation of whole sample, with extra four points added.
> >   
> This is already implemented in Yade, with weighted "radical" Delaunay. 
> See e.g. volumicContactLaw or TesselationWrapper::addBoundingPlanes, 
> where bounding planes are spheres of very big radius far away from the 
> packing (distance=radius).
> 
> > I suppose that eigen has Delaunay triangulation.
> No, eigen is only for basic linear algebra, but you can use CGAL.
> 
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_3/Chapter_main.html
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_3_ref/Chapter_intro.html

so it is good that I have asked :) Thanks for the pointers, after I
read that I will have more questions. I want to go in this direction,
instead of doing minkowski sum.

I wonder how we could later merge that with your whole triaxial test.

A reminder - my goal here is to obtain an inclined localization due to
shearing.

-- 
Janek Kozicki   http://janek.kozicki.pl/  |

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Re: [Yade-dev] triaxial test with membrane

[Luc Sibille]

Hi,

It is just to give some details about strain localization. I don't think 
you need a menbrane to obtain shear band, it has already been found in a 
rigid cubical box with the DEM, and experimentally on sand with the 
apparatus TRITRI in lab. 3S-R. Experimentally they found that the shear 
band was reflected on the rigid boundaries.


About periodic boundaries, I think I have already seen shear band with 
periodic boundaries, but shear band are somehow constraint since they 
have to verify the periodicity.


Best,

Luc

Janek Kozicki a écrit :

Hi,

I'm thinking about implementing membrane in triaxial test, in order
to be able to see localization due to internal shearing.

questions:
1) was it done already by someone, and I missed this?

2) it is maybe not necessary, because periodic boundaries also allow
to see localization due to shearing? (I doubt that, because the shift
on one side is on different height than the shift on right side).

I would do this in following way: detect which spheres are on the
outer boundary (so they are touching the membrane), and push them
inside with some force.

To detect spheres that touch the membrane I will do a Delaunay
triangulation of whole sample, with extra four points added. Each of
those four points is on the exterior of the sample and is a
"membrane point". Any sphere that gets connected through Delaunay
with this point must be lying on the boundary and is in contact with
membrane.

do you have any comments on that?

I suppose that eigen has Delaunay triangulation. Previously I was
using wm3 for that.



--
Luc Sibille

Université de Nantes - Laboratoire GeM UMR CNRS

IUT de Saint Nazaire
58, rue Michel-Ange - BP 420
44606 Saint-Nazaire Cedex, France

Tel: +33 (0)2 40 17 81 78

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