NASTRAN SHELL ELEMENTS - VARIABLE THICKNESS SHEET METAL

[poornamviswa]

HI,

 I have a single Sheet metal of variable thickness ranges from 1.5 to 2 mm. when i go for applying thickness i found i have only one option t. How can i assign thickness for this kind of variable thickness sheet metal.

[Roelof.Feijen]

Hello @poornamviswa ,

If you look at the (nastran) definition of a shell element you will see there is no option to create a variable thickness.

One element that can have a variable thickness is the line element - beam type. It's called a tapered beam. Because I don't know anything about your model / analysis wishes,  I don't know if this solution is suitable for you.

[viktor_velichko]

Hi! Interest question. The possibility is inherent.
I found in the description of the card for the shell element, where for each element you can specify different thicknesses in the nodes (see in help CTRIA3, CTRIAR, CQUAD4 and CQUADR). But this, as I understand it, is unrealized, and I consider it unrealistic to set my thickness for each element in the nodes.

[John_Holtz · Accepted solution]

Hi @poornamviswa 

It is not clear to me if you mean that one face of your model varies in thickness (such as a uniform change from 1.5 mm at one end to 2 mm at another end), or if one face has a constant thickness (such as 1.5 mm) and another face has a different but constant thickness (such as 2 mm).

• If one face varies in thickness, then Viktor is correct. You would need to translate the GRID and CTRIA/CQUAD commands from the Nastran file to text, then use Excel to calculate the thickness of each corner of the shell based on the coordinates, and then translate the CTRIA/CQUAD commands back to the Nastran format. This requires a little bit of work, but it is straight forward to do. A program such as FNO Reader version 1.22 will translate the cards between the Nastran format to text and back to the Nastran format.
• If different faces are different thickness but constant thickness, then click the "Associated Geometry" checkbox and choose which faces the thickness applies to. For example, the bottom of a pan may be 2 mm thick, so select those faces for the Idealization and enter a thickness of 2 mm. The sides may be 1.5 mm thick, so create a new idealization, choose the faces for the sides, and enter a thickness of 1.5 mm.

[viktor_velichko]

John, you have added great options to this program and extensive documentation. Thanks!

[poornamviswa]

Thank you 

[poornamviswa]

Hi 

I want to do Transient thermal analysis for enclosed cabinet which contains pcb board stuff like that. I did with Solid elements it took almost 5 to 6 hrs to complete study . Even after simplifying geometry it took 3 hrs. 

My question is shall i consider shell elements for Transient thermal analysis. Can u help me on this. Iam wondering how to proceed with that