How to set the wall boundary conditions for van der Waals forces?

MFiX
1

Hello everyone:
I used the mfix-dem 22.2.2 to simulate effect of van der Waals forces on particle flow.
And i want to know how to apply the van der Waals force to the left ,right, bottom and top walls while ignoring the effects on the front and back walls.

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the case is uploaded as below:
testws.zip (76.4 KB)

2

Cohesion is a global setting, it applies to all or none of the walls. You can modify the source code mfix/model/des/calc_collision_wall_mod.f, Line 238. You have access to the BC ID of a STL facet on Line 235. Use it to modify the conditional statement on Line 238 to only apply cohesion for the BC IDs you want.

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3

hi jeff, thanks for your reply, but i have no idea how to modify the code…
the case is uploaded, can you use the example of modifying the bottom surface to illustrate?

4

I encourage you to spend a little time on this. Come back if you get stuck and someone on the forum may be able to help you.

5

Hi jeff，i wonder if it is right to set the front and back wall to be the cyclic boundary, while set the left and right wall to be the no-slip wall?

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6

You only have one particle along the depth of the bed. You could run this in 2D, this would eliminate the front and back walls. If you want to use cyclic BC in the z-direction, I would increase the depth in the z-direction, if this makes sense for the simulation you are trying to conduct.

7

thanks jeff. Folled with your advice, I set the model to be a 2D, and the results tend to be good.

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however, the bottom of the fluidized bed does not appear to have van der Waals forces.
What should I do if I want to generate van der Waals force at the bottom?
the mfix-dem-22.2.2 is used in the model. and it isinconvenient to upgrading mfix.
the source code mfix/model/des/calc_collision_wall_mod.fin mfix-22.2.2, looks like below:
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and the case is uploaded as below:
test-123-14th-2d.zip (57.4 MB)
and I really need your further help.

8

You have an inlet at the bottom, you won’t have any wall/particle cohesive force there (same for the top outlet).

9

so, what should i do to make the wall/particle cohesive force applied at the bottom?

10

There is no wall at the bottom, it is in inlet, therefore you cannot have and should not want to have wall/particle cohesion at the bottom.

11

yes, there is no bottom in reality, however, I do need to set up a virtual wall at the bottom to implement van der Waals forces.
Is there a way to achieve it?