Some doubts about nonlinear analysis

[AnotherMike]

Hi Guys,

I don't know too much about analysis.
I have some questions about nonlinear analysis.

1. what kind of elements are available in Ansys or Abaqus(linear hex, second order hex, second order tet)?
2. what kind of elements are available in Ls-Dyna?
3. why some people prefer to use linear hex in nonlinear analysis?

Thanks.

 

[rstupplebeen]

Mike,

I'll speak to Abaqus and my experience. Abaqus has all of those element types and many more. For tets Abaqus has switched the default to second order because of their superiority in almost all situations. For hex elements it's usually more of a performance question. Second order elements require less elements but are more computationally intensive.

Rereading your post I also want to make it clear that linear elements are referring to the geometry not whether the are capable of non-linear analysis. The image below hopefully helps. Because of this I typically call them first or second order elements.

I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

https://sites.google.com/site/robertkstupplebeen/

 

[AnotherMike]

Hi Rob,

Thanks.
I recently read an old book about FEA.
There is a section about selecting elements.
The original words are: "Other more code dependent reasons to choose against the defaults are when an axisymmetric model cannot support anything but triangles or a nonlinear solution cannot support second order tetrahedrons".
This is not true for most current commercial codes , right?

And I also read some other material saying that "There are not second order elements in Ls-Dyna". This makes me feel confused.

 

[rstupplebeen]

Abaqus does have second order elements for solid and axisymmetric analysis. I'll let others with access to Ansys and Ls-Dyna manuals to answer for those. I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

https://sites.google.com/site/robertkstupplebeen/