Meshes in 2D and 3D

[eltw77]

Hello everybody!

For 2D FE models ABAQUE generate meshes containing 3-nodes and 4-nodes elements. But for 3D combination of tetrahedral (pyramid), hexahedral (brick) and wedge elements can be found.

Why are 3 elements types needed for 3D meshes rather then just pyramid and bricks?

Why in 2D both triangular and quadrilateral elements are permitted?

Thanks for your help and clarification.

 

[StefCon]

Hi,
What do you mean by "needed"? I'd say that they are available. Next version of Abaqus will add (I think) a fourth element (pyramid) which is not the same as regular tet.

Hex have generally good performance and/or accuracy (many if's here)
Tets are easy to mesh (where hex are hard/impossible to use), for structures these should be second order (which can be a disadvantage)
Wedge is, I guess, to fill the gaps. I've done tests and concluded that they should mostly be avoided (same as first order tets for structural problems)
Pyramid elements lets you bridge tet meshes with hex meshes.

Both tria and quad 2D elements are allowed because there is no reason for them not to be. First order tria are not good in a way because they are too stiff. They do however mesh easily. Many times it is better to use a tria element here and there in order to avoid very ill-shaped quad elements.

Cheers!

 

[eltw77]

Thank you! I am new in FE stuff. By "needed" I meant that why they exist? If there is wedge option in abaqus that I thought it has to be good for something.

 

[StefCon]

Hello,
The wedge could be good for something, I just don't know what. A wedge can be split into two tets.

Since you are new, I suggest reading "Getting started with Abaqus" Link
I should have read it earlier than I did. It is really easy to read as well.

Cheers!

 

[rstupplebeen]

A wedge can be used to transition from a tet to a hex mesh.

Rob Stupplebeen
OptimalDevice.com/blog
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