×
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

How do you Insert a FEM buckling perturbation into a FEM cylinder?

How do you Insert a FEM buckling perturbation into a FEM cylinder?

How do you Insert a FEM buckling perturbation into a FEM cylinder?

(OP)
Hi Fellow engineers,

If you run a buckling analysis and you want to use the buckling mode. To introduce a small buckling perturbation. Where do you have to look at?

Eigenvalue and/or Eigenmodes? Is the (negative)frequency of any importance?

Thanks in advance.

RE: How do you Insert a FEM buckling perturbation into a FEM cylinder?

When you do an eigen buckling analysis, the usual procedure is linear static analysis (with pre stress effects on) followed by eigen buckling analysis. The preload*eigenvalue is the buckling load. Eigenvector is the buckling shape. You should not get negative eigenvalue in normal case. Maybe you reversed preload direction.

If you use ANSYS, they have a model update function to let you introduce a small perturbation to the structure.

RE: How do you Insert a FEM buckling perturbation into a FEM cylinder?

Buckling analysis of shells requires one to understand the program being used.  Artifically inducing an imperfection into an analysis package that only considers elastic buckling is worthless.  

You can examine the imperfection sensitivity using Kioter's method.  A complilation of programs to examine multi-modal interactions is presented in WRC Bull 313.  These show that the coupling of adjacent modes (m+n) and (m-n) can produce lower bounds than a single bifurcation mode.

There are several papers at http://www.volcano.net/~d.citerley  that examine the  responses of shells to various imperfection geometries.  I suggest that BuckTV examine these papers to gain a better appreciation as to what is involved.

RE: How do you Insert a FEM buckling perturbation into a FEM cylinder?

hi BuckTU,

i suggest u to work through linear petrubation step( under load option). Here u can introduce buckling petrubation.And give time steps according to test run (I hope u need to give more steps in ur case). And as analysis is done, if u want to check the buckling load..the eigen values give that. Or if u want to check the shapes of ur model, check the eigen vector.

good luck,
Krishi

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