Re: [Yade-users] [Question #264174]: how is shear force related to poisson ratio?

2015-03-26 Thread Hongyang Alex Cheng
Question #264174 on Yade changed:
https://answers.launchpad.net/yade/+question/264174

Hongyang Alex Cheng proposed the following answer:
Hi, Shenyang

Like Bruno said. you should take a look at the functors you use. The
contact springs are defined by the law2 and the Ip2 functors. The meaning
of Young's modulus and poisson ratio varies from different set of law2 and
lp2 functors in use (see linear contact and mindlin contact for instance).
If you use the linear contact law changing poisson ratio will only affect
the shear stiffness. Note that adjusting material constants doesn't have
effect on existing contacts.

Alex

On Fri, Mar 27, 2015 at 10:41 AM, Shenyang Cai <
question264...@answers.launchpad.net> wrote:

> Question #264174 on Yade changed:
> https://answers.launchpad.net/yade/+question/264174
>
> Shenyang Cai posted a new comment:
> Hi Bruno,
>
> I'm still confused.  When two spheres are in contact, I suppose there
> must be a normal stifness and a shear stiffness(though it may equal
> zero) between them, regardless of the IPhys and Law functors.
>
> My idea is to change some parameters in the material class to enlarge
> the shear stiffness between the spheres. And I thought "poisson" is a
> factor. If changing "poisson" does not lead to the change of shear
> stiffness,  then what paremeters should I focus on to achieve my goal?
>
>
> Thanks!
> Shenyang
>
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Re: [Yade-users] [Question #264174]: how is shear force related to poisson ratio?

2015-03-26 Thread Shenyang Cai
Question #264174 on Yade changed:
https://answers.launchpad.net/yade/+question/264174

Shenyang Cai posted a new comment:
Hi Bruno,

I'm still confused.  When two spheres are in contact, I suppose there
must be a normal stifness and a shear stiffness(though it may equal
zero) between them, regardless of the IPhys and Law functors.

My idea is to change some parameters in the material class to enlarge
the shear stiffness between the spheres. And I thought "poisson" is a
factor. If changing "poisson" does not lead to the change of shear
stiffness,  then what paremeters should I focus on to achieve my goal?


Thanks!
Shenyang

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Re: [Yade-users] [Question #264142]: Law Functor

2015-03-26 Thread Felipe
Question #264142 on Yade changed:
https://answers.launchpad.net/yade/+question/264142

Felipe posted a new comment:
Hello Jerome,

Thank you for answering my question..

I'll read both tutorial. I also liked the link about others examples.

For the moment, you solved my questions.

Cheeres,

Felipe

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Re: [Yade-users] [Question #264142]: Law Functor

2015-03-26 Thread Felipe
Question #264142 on Yade changed:
https://answers.launchpad.net/yade/+question/264142

Status: Answered => Solved

Felipe confirmed that the question is solved:
Hello Jan,

Thank you again.

For sure, the next time I will try more specific in my questions.

For the moment, you solved my questions.

Thank you so much.

Cheeres,

Felipe

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Re: [Yade-users] [Question #264142]: Law Functor

2015-03-26 Thread Felipe
Question #264142 on Yade changed:
https://answers.launchpad.net/yade/+question/264142

Felipe confirmed that the question is solved:
Thanks Jan Stránský, that solved my question.

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Re: [Yade-users] [Question #263739]: isotropic compression at controled pressure

2015-03-26 Thread Bruno Chareyre
Question #263739 on Yade changed:
https://answers.launchpad.net/yade/+question/263739

Status: Open => Answered

Bruno Chareyre proposed the following answer:
>coupled with a small max_vel

No need I think. For very smooth evolutions select a large N (10e4 or
so), in which case "number" can be 1 (the number of iterations between
each change of the applied pressure). Depends how close to equilibrium
you want to be (it will need a bit of trial-error probably).

In my experience there is an overhead when writing:
for k in range(100):
   O.run(1,1)

which makes things slower compared to (for instance)
for k in range(10):
   O.run(10,1)

That would be the only reason to use larger stress steps with more
iterations between them.

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[Yade-users] [Question #264191]: Ig2_Facet_Sphere_ScGeom contact calculation

2015-03-26 Thread Dominik Boemer
New question #264191 on Yade:
https://answers.launchpad.net/yade/+question/264191

Hello everyone,

I am wondering how the contact between spheres and facets is handled (overlap 
calculation), if the normal projection of the sphere's center onto the facet is 
not located on this facet (edge/vertex contact; regularization)?  If you know 
how works this algorithm, I would appreciate to get a simple explanation before 
decrypting the code [1] during hours.

Thank you,
Dominik

[1] 
https://github.com/yade/trunk/blob/master/pkg/dem/Ig2_Facet_Sphere_ScGeom.cpp

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Re: [Yade-users] [Question #263739]: isotropic compression at controled pressure

2015-03-26 Thread Luc OGER
Question #263739 on Yade changed:
https://answers.launchpad.net/yade/+question/263739

Status: Answered => Open

Luc OGER is still having a problem:
thanks for the fast reply.

I don't want to reach quickly the isotropic goal as some local
reorganisaiton for the contacts between spheres is part of my studies,
indeed the particles are frictionless which allow rotations and sliding
during the slow compression process.

so I guess that this solution (copy from your answer) will be the good one 
coupled with a small max_vel if the change of the triaxgoal loop only occurs 
when it is reached ?: Number effect  is unclear for me in this example :
"If what you want is to increase the isotropic confinement progressively:
for k in range(N):
triax.goal1=triax.goal2=triax.goal3=isoP*float(k)/float(N)
   O.run(number,True)"

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Re: [Yade-users] [Question #263739]: isotropic compression at controled pressure

2015-03-26 Thread Bruno Chareyre
Question #263739 on Yade changed:
https://answers.launchpad.net/yade/+question/263739

Status: Open => Answered

Bruno Chareyre proposed the following answer:
Hello,
I don't understand exactly in which sense it is not what you expect. I suggest 
to forget max_vel, assign a very large value to it so that it does not 
interfere.

Trying to summarize what to do in your case (assuming
TriaxialStressCOntroller is labeled "triax"):

#stress control in all directions and for all boundaries independently
triax.stressMask = 7 
triax.internalCompaction=False

# if there is gravity, imposing the same stress at the top and bottom 
boundaries would lead to free fall... block the bottom wall:
triax.wall_bottom_activated=False

#define the target stresses to be applied, if it must be isotropic: 
triax.goal1=triax.goal2=triax.goal3=isoP
#then run
O.run()

This will reach the target isoP very quickly (a few iterations), in fact it 
could well result in a dynamic compaction at constant applied pressure 
(exception is if you impose a small max_vel).
If what you want is to increase the isotropic confinement progressively:
for k in range(N):
triax.goal1=triax.goal2=triax.goal3=isoP*float(k)/float(N)
   O.run(number,True)

The problem is the initial stress under gravity is not isotropic, for
superimposing an isotropic stress to the intitial anisotropic one,
better something like this:

#initialize with current stress
triax.goal1=triax.stress(0)[0]
triax.goal2=-triax.stress(3)[1]
triax.goal3=triax.stress(4)[2]
#and increase progressively
for k in range(N):
   triax.goal1+= isoP/float(N)
   triax.goal2+= isoP/float(N)
   triax.goal3+= isoP/float(N)
   O.run(number,True)

Bruno

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Re: [Yade-users] [Question #264057]: Simulating time-dependent behavior of geo-material in Yade

2015-03-26 Thread Fu zuoguang
Question #264057 on Yade changed:
https://answers.launchpad.net/yade/+question/264057

Status: Answered => Solved

Fu zuoguang confirmed that the question is solved:
Dear Prof. Chareyre,

Thanks all the same.

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Re: [Yade-users] [Question #263739]: isotropic compression at controled pressure

2015-03-26 Thread Luc OGER
Question #263739 on Yade changed:
https://answers.launchpad.net/yade/+question/263739

Status: Answered => Open

Luc OGER is still having a problem:
I made several tests to see if putting some max_vel solved my problem,
it seems that it is not what I was expected.

but to understand more my queston, I have to described what I was looking for :
I want to look at the consequence at the anisotropy linked to the gravity 
deposition process. So my first step is doing a packing from spheres 
distributed randmoly inside big vertical box , letting them settling down, (in 
order to get a quasi cubic dense packing) putting the top wall at the upper 
point of the packing and then doing an isotropic compression by pressure 
control on all the walls but one by one. 
Indeed, the top wall starts with zero pressure and has to move alone to reach 
some pressure similar to the mean values of the others before moving the other 
walls. Otherwise I will reorganise too much the structure before compressing.

i hope my description is clear enough for the understanding.

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Re: [Yade-users] [Question #264174]: how is shear force related to poisson ratio?

2015-03-26 Thread Chareyre
Question #264174 on Yade changed:
https://answers.launchpad.net/yade/+question/264174

Status: Open => Answered

Chareyre proposed the following answer:
Hi,
The parameters in Material classes cannot be "studied" because they are
only numbers with names, not well defined physical parameters (suprising
maybe).
Better start thinking the other way around: look what kind of contact
parameters the law functors are using, then how this contact parameters
are defined based on material parameters.
You will see that different functors lead to different interpretations
of what Material::poisson is.
For Ip2_FrictMat_FrictMat_FrictPhys+ Law2_ScGeom_FrictPhys_CundallStrack
the normal force is independent of Poisson, yes. It is the expected
behavior.
I hope it helps.
Bruno

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Re: [Yade-users] [Question #264142]: Law Functor

2015-03-26 Thread Jan Stránský
Question #264142 on Yade changed:
https://answers.launchpad.net/yade/+question/264142

Jan Stránský proposed the following answer:
Hi Felipe,

brief summary contact laws are at [1]. There is brief description,
publications and also names of example scripts you can look at. You can
also browse documentation [2], where are listed parameters you can use.
There are some derived from base classes which are not usually used (bases,
dict, updateAttrs) and some you can set/modify, specifically
for Law2_ScGeom_FrictPhys_CundallStrack [3]: neverErase, sphericalBodies.
Furthermore you can use some methods defined on this law, on the
example: elasticEnergy(), initPlasticDissipation(), plasticDissipation().
See examples for more details.

if you are new to Yade, I really recommend to read the introduction,
tutorial and user's manual, as cnatact law iteslf depends not only on law
functor, but also on used particle shapes, materials, igeom functors and
iphys functors..

cheers
Jan

PS: I am really not sure what "how you construct in ".py"" exactly means,
next time please be more specific to get answer earlier :-)

[1] https://yade-dem.org/wiki/ConstitutiveLaws#Constitutive_laws
[2] https://yade-dem.org/doc/yade.wrapper.html#constitutive-laws
[3]
https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Law2_ScGeom_FrictPhys_CundallStrack


2015-03-25 23:51 GMT+01:00 Felipe
:

> Question #264142 on Yade changed:
> https://answers.launchpad.net/yade/+question/264142
>
> Status: Answered => Open
>
> Felipe is still having a problem:
> Hey Jan,
>
> Thank you for answering my question.
>
> I'm really appreciate that.
>
> However, I would like to learn more specific about contact laws.
>
> If you have examples about it, could you send me to learn and also
> seeing how you construct in ".py"?
>
> Cheers,
>
> Felipe
>
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Re: [Yade-users] [Question #264057]: Simulating time-dependent behavior of geo-material in Yade

2015-03-26 Thread Chareyre
Question #264057 on Yade changed:
https://answers.launchpad.net/yade/+question/264057

Status: Open => Answered

Chareyre proposed the following answer:
Dear Fu Zuogang,
The paper is still "in preparation" unfortunately, it should be removed
from the web page. The contact law itslef is functional though.
Bruno

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