where lies the shell?

[qsk6060]

hi to everybody.

This is my first post.
Question: a cylinder, 5in inner diameter, 0.1in thick.
I want to mesh it with a shell.
How should I model the cylinder?
A cylindrical surface 5in diameter, or a cylindrical surface
5+2*0.1= 5.2in diameter?
How chooses the program in which direction grows the thicknes of the shell?

Thanks!

edu

 

[Drej]

Model the "mid-surface" of the cylinder i.e. the diameter of the cylinder will be (5 + 0.1) inches. Once you specify the thickness of the shell (0.1 inches) you will be modelling the exact dimensions of your cylinder.


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[qsk6060]

I still have doubts.
For example in the VM6 problem of the Verification Manual, there is cylinder with rext=4.953 and t=0.094, and the problem wasn't solved taking into account a radius r-t/2.
Is this because the value of the thickness is too small?

Thanks Drej!

 

[TGS4]

In cases such as this, I think that Drej and I would agree that you should be doing some hand-calcs first in order to satisfy your "doubts". In your particular case, I would suggest that you run both the "thin-shell" equations a la "Timoshenko" and the "Lame" equations are well. Then, once you have satisfied yourself with the hand calc (and only then) should you attempt to run your FE calcs.

 

[Drej]

Forget that problem and deal with the real world. VM6 doesn't explicitly state that the radius "r" is to the outer, centre or inner radius of the cylinder. It's just not clear from the notes. I've done this many, many, many, many times before using the mid-surface of the geometry but, as mentioned, do a test FE model on a simple closed form cylinder problem (see Roark for example problems on closed form solutions, or google it) to satisfy yourself.


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[ansysfreak]

Hi all

You always need to make hand-calcs so you know in what direction your result ought to be. Also you will need it for your report.
Always give an explination why Ansys gives a certain result solution. And yes thats the difficult part.

H.Adams

Garry