Exporting elements to LS-DYNA for hex-pyramid mesh
Hello All,
Hypermesh Version 14
LS-dyna version 4.0.
1>>> I have to mesh a component as shown in figure 1 which consists of Hex and tet elements. I have completed the mesh and and exported to LS-dyna (Figure 3) . While zooming and panning in it, I see some edges as shown in figure 2 below. Is this a major issue?
2>> I have read somewhere that one should not connect Hex and tet mesh directly. It should be done by inserting pyramid elements. I have manually converted the tet elements in contact with the hex elements into pyramid elements. Checked for all connectivity by edges and faces. In hypermesh it seems ok but in LS dyna pyramid elements are not visible. Also the edges from the previous points are still visible.
Is there a solution to this. Can this be an version issue? i have attached a .hm file with pyramid elements as reference.
Thanks in advance.
Bharat
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
Answers
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- From point of view FEA, you can not connect TET to HEXA directly. You have to use PYRAMID between them.
- Default LS-DYNA template of Hypermesh can not (at least until release v14) export Pyramid elements for LS-DYNA. But you can do it by modifying this template
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Thanks Q.Nguyen-Dai for the reply.
These edges shown in LS dyna image are a point of concern? Can you please elaborate on it?
Also, how do we modify this template you are referring to?
Altair Forum User said:Default LS-DYNA template of Hypermesh can not (at least until release v14) export Pyramid elements for LS-DYNA. But you can do it by modifying this template
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Could you share Hypermesh model?
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Altair Forum User said:
Could you share Hypermesh model?
Can't share the entire model. Sorry About that.
But the region of concern is shared in my original comment.
thanks,
Bharat
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Your mesh is NOT valid!
Have a look at my modification: components 'my_3D(*)' :
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Thanks for the help,
But your version is 19 and I am using 14. Is there a way for backward compatibility?
Thanks
Bharat
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Sorry. Here's V14 model:
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thanks again.
Can you please elaborate on why my model was not valid? is it about the element quality index or something else?
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Altair Forum User said:
thanks again.
Can you please elaborate on why my model was not valid? is it about the element quality index or something else?
You can not connect TET elements to Quad faces. It's not valid from point of view of FEA.
You have to use Pyramid elements as in my model.
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I just tested LS-DYNA export under Hyperworks 2019.1, it's OK for Pyramid elements!
Check this key file:
And here's what I got with LS-PrePost:
So if you use Hypermesh 2019.* you not need to modify the template.
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Thanks for the help again.
Regarding the mesh validity, please check images for exploded elements from my original model shared (1.1.hm I have just organised elements as per their types now, also attached to this thread again). Hex elements (Green coloured) are connected to tetra elements (yellow coloured) by pyramids (purple coloured elements). Is this mesh still not valid?
Thanks
Bharat
Altair Forum User said:You can not connect TET elements to Quad faces. It's not valid from point of view of FEA.
You have to use Pyramid elements as in my model.
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
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If you use Pyramid between Hexa & Tet, it's OK.
In you model '1.1.hm' please check 'Tet collapse'!!! I see some bad elements.
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I agree on bad quality elements. Will have to modify them.
Thanks you so much for the help.
With regards,
Bharat
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