×
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

Abaqus mesh analysis

Abaqus mesh analysis

Abaqus mesh analysis

(OP)
Hi everyone.

I am modelling a steel frame in Abaqus. The frame is modelled as a 3D-problem built by shell elements.
In the step-module i have chosen "buckle" as the type and eigensolver as Lanczos with 6-7 eigenvalues.
I should remind that i am a new user in Abaqus, few months of experience.
However, when i want to mesh the structure i am allways using the same types of elements. However, when i change the number of elements, that means changing the number in "approximate global size", it never seems to convergence. The eigenvalue changes alot if I for instances put 0.2 or 0.1 as the value of "approximate global size". It simply never converge to a stable value of the eigenvalue.

Is there something wrong with the model?
The way i mesh the structure?
Or is it simply impossible to a convergence analysis for this analysis?

Best regards
Kenan

RE: Abaqus mesh analysis

(OP)
Thanks for the answer IceBreakerSours.
Thats the thing that i dont understand.. because this anlaysis is giving me some eigenvalues..
Now, if I change the mesh.. For instances using, lets say 1000 elements in one analysis and 6000 elements in the second analysis, the resulting eigenvalues have a huge difference between them.. Also the deformed structure behaves strange... i have posted a picture of the structure deformed with the first positive eigenvalue in one analysis where i use a certain of elements.. and a picture of another analysis were i use even more elements (finer mesh).. as you can see from the result.. it is behaving very strange.. you have any idea of what is could cause this?

Picture of first analysis

Picture of second analysis with a fine mesh

RE: Abaqus mesh analysis

(OP)

RE: Abaqus mesh analysis

(OP)

RE: Abaqus mesh analysis

(OP)

First analysis
Link

Second analysis with a FINE mesh
Link

RE: Abaqus mesh analysis

I had suspected it but now I know that you do not know what you are doing. And that is fine, as long as you wish to learn.

So, you must go back to undergrad structural dynamics and differential equations texts to understand the concept of eigenvalues/eigenvectors. While you are reading up on it, visualize a rigid bar, a linked-chain, and a rope hanging from a ceiling with a pin joint at the ceiling.

Once you feel good about the concepts, open a book on practical finite element analysis and study the section on mesh convergence.

If you still have questions, feel free to continue the thread.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376
http://www.eng-tips.com/faqs.cfm?fid=1083

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