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Problem with dynamic meshing in 2D

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Old   November 13, 2015, 17:02
Default Problem with dynamic meshing in 2D
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Bhargav Bharathan
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Hi,

I'm trying to simulate a boger slump test using Fluent. The boger is essentially a cylinder with open ends. It is placed on the floor and filled with a paste. It is then lifted slowly and the paste settles on the floor. I'm simulating this in 2D.

To explain the set up:
A - air (fluid)
B - paste (fluid)
C - PVC boger (solid)

1. I have the pressure inlet and outlet BC as shown.
2. I wrote a UDF for C to move in -X direction and it works.
3. Transient case.
4. Gravity on in +X direction.
5. (A, B): face sizing mesh + mapped face meshing (triangular)
6. (C): face sizing mesh + mapped face meshing (quad)
7. Laminar + Multiphase VOF models

I'm having troubles with the remeshing, smoothing and layering.

The problems I'm facing are:
8. There is a stretching of the mesh on one side and compression on the other side. There are no new layers of mesh being generated. The mesh stretches and at a point there is divergence due to high skewness.
9. The paste B is supposed to flow out through the gap after C moves. But this isn't happening either.

My one concern is when modelling and meshing (I used workbench modeller and ANSYS meshing), I created 3 different sketches, created surfaces from them.
I tried by selecting A, B, C and forming 1 single part. I tried without making the single part (current case) and selecting only A and B for 1 part, but I was facing bad meshes all around.
What is the best way to model this?

I have attached images of my setup.
10. The layering settings is default.

Any help is appreciated.

Thanks,

Bhargav
Attached Images
File Type: jpg Outline.jpg (42.0 KB, 24 views)
File Type: jpg mesh.JPG (149.9 KB, 30 views)
File Type: jpg dynamicmesh.JPG (38.5 KB, 20 views)
File Type: jpg smoothing.JPG (37.9 KB, 22 views)
File Type: jpg remeshing.JPG (35.3 KB, 19 views)
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Old   November 14, 2015, 20:18
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Ahmed Jalal
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I did somehow a similar problem.
For me it was enough to hook the SDOF UDF to the moving part iin your case "C" and that would be the only zone you need to create a dynamic Mesh for.
Also, I believe smoothing you can change it to Diffusion and set the diffusion factor to 0. Smoothing and remeshing should be sufficient ie no need for layering. Also, you need to check the Six DOF in your dynamic mesh.

Try it with these modifications and see if there is any difference.

Goodluck!
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Old   November 15, 2015, 11:39
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Bhargav Bharathan
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Hi,

Thanks for the ideas, they are things I have not tried till now. Will give it a go.
Just to confirm, the SDOF UDF looks a little bit like this right?

#include "udf.h"

DEFINE_SDOF_PROPERTIES(test_box, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 666.66;
prop[SDOF_IXX] = 129.6296;
prop[SDOF_IYY] = 111.1111;
prop[SDOF_IZZ] = 129.6296;

}

This is from a tutorial. If all I specify is the moment of inertia and mass and gravity. Where do I include the motion in -X direction? Or can I put it in this itself?


Thanks,

Bhargav
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Old   November 18, 2015, 12:58
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Bhargav Bharathan
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Hi,

Thanks for your help. I solved it, my UDF was correct. I had made an error in the modelling.

Works great now.

Bhargav
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