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hiranwale_bharat

Exporting elements to LS-DYNA for hex-pyramid mesh

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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

 

image.png

image.png

image.png

1.1.hm

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  1. From point of view FEA, you can not connect TET to HEXA directly. You have to use PYRAMID between them.
  2. 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?

3 minutes ago, Q.Nguyen-Dai 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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18 minutes ago, hiranwale_bharat 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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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

15 hours ago, Q.Nguyen-Dai 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.

 

image.png

image.png

1.1.hm

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