×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

shell theory and shell elements ?

shell theory and shell elements ?

shell theory and shell elements ?

(OP)
Hi all,
just a precision for me.

Is there a limit ratio between legth and thickness to be applied in theory of shell ?

Which ratio for part ?

Is there a ratio for elements too or is it applied for parts and after we can mesh the part with very small elements ?

Thx

caviac

RE: shell theory and shell elements ?

(OP)
Some people tell me that just the part has to follow the shell theory and you can mesh your part with small elements.

Others say that part and elements have to respect the shell theory criteria (length/thickness ratio)

Just to be clear... ;)

RE: shell theory and shell elements ?

Your first sentence in the second post is the correct one.
If you mesh a shell with smaller and smaller elements, you'll approach the analytical solution of shell theory (more correctly: of the particular shell theory that's implemented by the elements you use) that can be obtained for some geometries.

prex

http://www.xcalcs.com
Online tools for structural design

RE: shell theory and shell elements ?

I presume that you are interested in obtaining a complete solution where bending is prevalant.  To obtain an estimate of the required mesh size, examine the solution of bending in a cylindrical shell of revolution.

The key parameter is the characteristic length and is defined as  beta L = L(1- nu**2)**1/4  / (a h)**1/2, where L is the length of the shell, nu is Poisson's ratio, a is the radius and h is the thickness.  If you examine the bending from an applied moment, the first zero cross over point ocurrs at x=PI/4.  So to acquire the full benefit of bending in an element, beta x < PI/4. As bending diminishes, the element size can increase.  Usually membrane forces do not require such a small element size.

Element distribution in the circumfrental direction is generally based upon the Fourier harmonics of the loads being applied.  The higher the harmonic, the closer the element distribution will be required in the circumferental direction.  Of course, the assumed isoparametric displacements being used in the FE will also have an effect on the accuracy of the solution.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources