how can i simulate rolling friction?

Hi Jacob,

For the 2nd point, you may want to have a look at the paper from Plassiard: http://www.springerlink.com/content/16688jw766197204/ (I can send it to you if you cannot download it).

For the 1st point, I cannot help... I though that combining 2 constitutive laws was possible but, actually, I never tried...

Luc

Hello,

Once you have identified the contact law you need (assuming it is indeed Law2_ScGeom_MindlinPhys_Mindlin() ), you have first to use the good functors.

Here, Ip2_FrictMat_FrictMat_MindlinCapillaryPhys() has two major drawbacks :
- it uses material data of "FrictMat" type, whereas you want to use CohFrictMat..
- it computes interaction data of MindlinCapillaryPhys(), while your law needs MindlinPhys..

Thanks to inheritance your script did not crash, but it is not surprising that something went wrong (in your case nothing changed apparently)

Second, we were /are quite many to perform simulations with rolling stifness. Many of us, I think, did computations inspired by the work (on SDEC) of Jean Patrick Plassiard, you should find references in the "yade bibliography". For what I am concerned you can find the parameters values I used in Table 1 of reference "Duriez2011". However, linking these values with the rounded feature of the grains is a task too difficult for me...

Thanks for the fast answers.

@Luc: download successful ...

@jduriez:

>Here, Ip2_FrictMat_FrictMat_MindlinCapillaryPhys() has two major drawbacks :
>- it uses material data of "FrictMat" type, whereas you want to use CohFrictMat..
>- it computes interaction data of MindlinCapillaryPhys(), while your law needs MindlinPhys..

MindlinCapillaryPhys and MindlinPhys are working equal, when Law2_ScGeom_CapillaryPhys_Capillarity is not active.

>However, linking these values with the rounded feature of the grains is a task too difficult for me...

What do you mean with that?

For further explanations:
I perform pour cone tests to get the natural repose angle (ca. 30 degree for well rounded sand). While increasing friction parameter I can get 24-25 degree as maximum repose angle, so I thought including rolling friction will help me getting the right repose angle to verify my model ...

1) Yes it should be possible Everything looks correct.
The fact that it has no effect is probably only due to your constitutive parameters.

If you really type [Ip2_FrictMat_FrictMat_MindlinCapillaryPhys()] in your script, then clearly there is no rolling friction (inspect parameters of this functor and default values, you will see).
Else, open inspector and check the values of moment in interactions, you will see if they are really zero or just very small.

Note that it is useless (even if harmless) to define a cohesive material. A FrictMat should be enough.

@chiara:

Thanks, will

...
#define material:
id_SphereMat=O.materials.append(FrictMat(young=young_modulus,poisson=poisson_ratio,density=rho_p,frictionAngle=angle))
...
 InteractionLoop(
  ...
  [Ip2_FrictMat_FrictMat_MindlinCapillaryPhys(krot=roll_stiff)],
  [Law2_ScGeom_MindlinPhys_Mindlin(includeMoment=True)]
  ),

work in my case?

On 6 Jun 2012, at 15:10, Christian Jakob wrote:

> Question #199585 on Yade changed:
> https://answers.launchpad.net/yade/+question/199585
>
> Christian Jakob posted a new comment:
> @chiara:
>
> Thanks, will
>
> ...
> #define material:
> id_SphereMat=O.materials.append(FrictMat(young=young_modulus,poisson=poisson_ratio,density=rho_p,frictionAngle=angle))
> ...
> InteractionLoop(
> ...
> [Ip2_FrictMat_FrictMat_MindlinCapillaryPhys(krot=roll_stiff)],
> [Law2_ScGeom_MindlinPhys_Mindlin(includeMoment=True)]
> ),
>
> work in my case?
It should, indeed. Mind that you can also define eta parameter if you want to set a maximum plastic moment.
Chiara

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>>However, linking these values with the rounded feature of the grains is a task too difficult for me...

>What do you mean with that?

I meant that I can not point a "good" value of the rolling stifness, only from the information that the sand is "well rounded" (as you asked)

ok, thanks everybody!

Thanks Chiara Modenese, that solved my question.

I am trying to add a rolling physics using
Ip2_MomentMat_MomentMat_MomentPhys
Law2_SCG_MomentPhys_CohesionlessMomentRotation

However, rolling parameters have no effect to the macroscopic response too, like u.

- either you did not set parameters in right syntax (like i did)
-> send the part(s) of your code to see if it is correct

- or parameters are set to a value, where you do not "see" any effect
-> send the values you set

- or everything is ok, but rolling parameters have no big effect in your case ... (see also the paper luc proposed to read -> #1)
-> simulation inspection may help ...

Hi Jakob, as you would like to use rolling resistance, u have at least 4 DOFs ( 1 normal, 2 shear and 1 roll),

so which Ig (Interaction Geometry) do u use, ScGeom or ScGeom6D?

ScGeom is enough in that case. ScGeom6D is needed for bending and twisting at the contact point, not for rolling resistance.

Someone should explain the the difference in documentation ...

https://yade-dem.org/doc/yade.wrapper.html?highlight=updaterotations#yade.wrapper.Ig2_Sphere_Sphere_ScGeom6D

The answer to "which Ig" to use is: "the one imposed by the contact law".
Different laws have rolling friction, some will use 3Dof, others will
use 6Dof.
Allthough I admit one easily gets lost in the many contact laws (I
removed some of them last week, btw), I don't see something missing in
the documentation on this precise question.
Feel free to suggest something to add if I overlooked.

Something missing, however, is a table summarizing the features of all
the laws.

Bruno

On 06/07/12 08:35, Christian Jakob wrote:
> https://yade-
> dem.org/doc/yade.wrapper.html?highlight=updaterotations#yade.wrapper.Ig2_Sphere_Sphere_ScGeom6D

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