Inclusion of attractive Van der Waals type particle-particle forces?

Hi Mark,

On 9 May 2011 15:21, Mark S. Bentley
<email address hidden>wrote:

> New question #156756 on Yade:
> https://answers.launchpad.net/yade/+question/156756
>
>
> I've been playing with YADE for a few days now, and think I have a handle
> on the basic way simulations are set up and run - but now I need to dig into
> the details to see if it's suitable for my application. Basically I want to
> model the behaviour of cohesive aggregates of fine particles under low
> gravity, and am trying to figure out if YADE is well suited for this.
>
> I see that the Hertz-Mindian law includes adhesive energy, but is this only
> for the "pull off" of particles? Does it include the attractive force
> between particles due to the Van der Waals forces prior to the onset of the
> repulsive "contact" region, for example?
>
No, it does not include that. It only considers the attraction between
particles as long as the contact physically exists. The need for distant
interactions really depends on the type and scale of the problem. From a
physical point of view, it is very difficult to deal with transition between
long-range interactions and contact body forces of both repulsive and
attractive origin. My personal suggestion is: make sure you understand
physics, limitations and assumptions behind the choice of your contact
model.

> Ideally I would like to model the purely attractive VdW forces down to a
> critical distance, and then include both attractive and
> repulsive/frictional/etc. forces thereafter (since the attractive forces
> drop of quickly I guess it's only a nearest neighbours problem, with a
> cut-off for larger distances anyway). Is this possible?
>
Yes, it is possible. Have a look at
https://yade-dem.org/doc/yade.wrapper.html?highlight=detection#yade.wrapper.Ig2_Sphere_Sphere_ScGeom.interactionDetectionFactor

HTH,
Chiara

Any thoughts or hints appreciated :)
>
> Thanks, Mark
>
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Hi Mark,

VdW forces are not implemented but I see no big obstacle to implement them.
It is close to the capillary force problem
(https://yade-dem.org/wiki/CapillaryTriaxialTest) in the sense that you
have additional forces that act between distant grains.
I recommend doing that in a separate engine, so that VdW forces will not
depend on a specific contact law (then you can switch between all
existing contact laws, linear or non-linear elasticity, contact moments,
etc.)

Bruno

VdW forces can also have an influence on the contact law itself. There are
different formulations around which consider the interplay between repulsive
and attractive forces at the contact. In physics, this interplay exists and
would change the contact stress distribution even. As I said, think first
about the assumptions you want to make. If you will like to consider the
superposition of adhesion to repulsive forces, then Bruno's suggestion can
work well. Otherwise, you should modify your contact law, I believe.

Chiara

On 9 May 2011 16:11, Chareyre <email address hidden> wrote:

> Question #156756 on Yade changed:
> https://answers.launchpad.net/yade/+question/156756
>
> Chareyre proposed the following answer:
> Hi Mark,
>
> VdW forces are not implemented but I see no big obstacle to implement them.
> It is close to the capillary force problem
> (https://yade-dem.org/wiki/CapillaryTriaxialTest) in the sense that you
> have additional forces that act between distant grains.
> I recommend doing that in a separate engine, so that VdW forces will not
> depend on a specific contact law (then you can switch between all
> existing contact laws, linear or non-linear elasticity, contact moments,
> etc.)
>
> Bruno
>
> --
> You received this question notification because you are a member of
> yade-users, which is an answer contact for Yade.
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users
> Post to : <email address hidden>
> Unsubscribe : https://launchpad.net/~yade-users
> More help : https://help.launchpad.net/ListHelp
>

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