# porosity

Hi everyone,

When I calculate the porosity, does Vs simply add up all the balls or subtract out the overlap of the balls?

Thanks,

James

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Chareyre
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2019-01-25
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2019-01-25
2019-01-25
 Bruno Chareyre (bruno-chareyre) said on 2019-01-24: #1

Hi,
It is taking Vs as a constant regardless of interactions.
Bruno

 jamespaul (jamespauljames) said on 2019-01-24: #2

Thanks Bruno,

Since particles overlap whenever they collide, what does this porosity really mean?

James

 jamespaul (jamespauljames) said on 2019-01-24: #3

Hi,Bruno,

If I want to measure some particles that overlap, how do I write code?

Thanks,

James

 Bruno Chareyre (bruno-chareyre) said on 2019-01-24: #4

> Since particles overlap whenever they collide

I don't think so. I would think they deform, instead.

> what does this porosity really mean?

That's more a question for people including some overlaping volume in the porosity calculation. :)

Bruno

 Bruno Chareyre (bruno-chareyre) said on 2019-01-24: #5
 jamespaul (jamespauljames) said on 2019-01-24: #6

> I would think they deform, instead.

Are the particles deformed rather than overlapping?Doesn't the discrete element method always overlap?

James

 Bruno Chareyre (bruno-chareyre) said on 2019-01-24: #7

DEM is crunching numbers rather independently of the conceptual models we have in mind.
There is no overlap in my conceptual model. I don't need that concept. In yade documentation we refer to normal displacement or normal strain usually. There is no overlap in classical contact mechanics either.
B

 jamespaul (jamespauljames) said on 2019-01-24: #9

I am sorry for my lack of knowledge in physics and modeling.However, if there is no deformation or overlap between the particles, how can the force between the particles be calculated?

James

 jamespaul (jamespauljames) said on 2019-01-24: #10

There's this passage

false
if there is no geometrical overlap, and the interaction will stillremain potential-only

true
if there is geometrical overlap; the functor will have created an IGeom in such case.

So I think there's overlap between the particles, right?I'm lost.

James

 Bruno Chareyre (bruno-chareyre) said on 2019-01-24: #11

"there is no geometrical overlap" is misleading IMO.
Should be replaced by "distance is larger than R1+R2".

> if there is no deformation or overlap between the particles, how can the force between the particles be calculated?

I never claimed there was no deformation.
See [1] as an example of force computation between two spheres.

Bruno

 jamespaul (jamespauljames) said on 2019-01-25: #12

I may not be making myself clear.I mean the force between the particles must be due to deformation.After I read the documentation,I think that yade, when it comes to calculating forces, should be determined by how much overlap there is.I'm sorry to have wasted so much of your time.

James

 Jérôme Duriez (jduriez) said on 2019-01-25: #13

Hi,

Jamespaul: this actually was recently discussed on yade-dev [*] after a previous similar question (see question id in [*])
As you will see (if you go through all of [*]..), the way we see things may not be uniform, even among yade-devs.

Maybe you can just keep in mind that YADE (DEM in general) computes contact forces according to relative displacements.

Whether you see the normal relative displacement as
- an overlap,
- or as a relative displacement between the centers' of the particles (particles that would somewhat deform to comply with this relative displacement without any overlap, but we do not care/neglect these bodies' strains)

may be just up to you, and will only affect the way you will present things in the scientific publications we wish you to obtain with YADE.

Jérôme

 Chareyre (bruno-chareyre-9) said on 2019-01-25: #14

Yes.
The volume change in this deformation is neglected in the porosity
calculation. Vs=constant.
What is unclear to me is why you think the intersected volume of
overlapping spheres would be related to the actual volume change of
deformable non-overlapping particles.
Bruno

Le ven. 25 janv. 2019 03:27, jamespaul <email address hidden>
a écrit :

> Question #678055 on Yade changed:
>
> jamespaul posted a new comment:
> I may not be making myself clear.I mean the force between the particles
> must be due to deformation.After I read the documentation,I think that
> yade, when it comes to calculating forces, should be determined by how
> much overlap there is.I'm sorry to have wasted so much of your time.
>
> James
>
> --
>
> _______________________________________________
> Post to : <email address hidden>
>
>

 jamespaul (jamespauljames) said on 2019-01-25: #15

Thanks Chareyre, that solved my question.

 jamespaul (jamespauljames) said on 2019-01-25: #16

Thanks Bruno and Jérôme so much