Yade

Using expanding method to reach specific porosity doesn't work properly!

Asked by M.Meidani

Hi everyone,

I am using expanding method to create a pack with specific porosity.
I already used this method for another pack and it worked good, but in the new one after thousands of iterations, porosity converges to a specific value and after that the changes are very small! My target is 41% but it cannot get less that 53% in in the expanding step.
Do you have any idea about the reasons of this convergence?
Has anyone ever faced with this problem?

Thanks

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Fu zuoguang (zgfu1985) said : 		#1

Dear Meidani:

In my experience, the process of expanding method you said above strongly depends on two things, one is particle stiffness and the
other is specified confine pressure.

As you mentioned, after thousands of iterations, porosity changes are very small, I think it maybe beacause the particles you used in your running are too hard and the determined confine pressure that may actuate your sample to present the compressbility is not so high that the your sample is nearly stable before your target porosity is reached.

Decreasing the stiffnesses of particles or increasing the confine pressure before running may help you for your target.

Best wishes,
Fu

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Jérôme Duriez (jduriez) said : 		#2

Hi,

As for me, the ratio between confining pressure and particle stiffness mainly relates to the overlap between particles. Playing with it may indeed modify the porosity output, but because of biaised computations I'd say.
Indeed with "soft" particles (low stiffness / pressure ratio), the overall volume may shrink due to increasing overlaps, whereas the solid volume is constant (the sum of the spheres volume) => hence low porosity values as given by Yade.

However, this is kind of non-sense in my opinion because this overlap volumes are non physical, and not taken into account in the porosity Yade formula. Then you count twice the same solid volumes...

In the end, it is usually rather the friction angle that controls the porosity during sample preparation. As this belongs to the Yade questions greatest hits, you should hopefully find an answer in previous questions, e.g. https://answers.launchpad.net/yade/+question/270818

Jerome

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M.Meidani (masood-meidani) said : 		#4

Thanks Fu and Jerome for your responses.
I tried another simulation with higher confining pressure and lower stiffness. Still it converged to porosity more than my target!
I agree with Jerome about the effects of stiffness and confining pressure. But the problem is that changing friction angle doesn't help too! Because decreasing of friction angle to reach the target porosity is implemented in expanding method.
So it was the problem that I mentioned in my question. Even with friction angle equals to 0.5 porosity was not close to target value.

Thanks.

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Launchpad Janitor (janitor) said : 		#5

This question was expired because it remained in the 'Open' state without activity for the last 15 days.