×
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

Buckling of pipe on nonlinear elastic foundation

Buckling of pipe on nonlinear elastic foundation

Buckling of pipe on nonlinear elastic foundation

(OP)
Hi,

I am trying to model axial buckling of a pipe buried in sand, in Abaqus. The pipe is modelled with 2D beamelements B21 and the sand is modelled with springelement SPRING1 attached to the beam in one end and the "ground" in the other. I have used about 100 springs along the 3 m long pipe and have given the springs a nonlinear behaviour by changing the input file. The analysis is static general with nonlinear geometry on and with a displacement at the end of the pipe.

The problem is however that the analysis will not go through with the nonlinear springs when the stiffenss in the spring is set to zero after 0.2 mm displacement upwards. Any ideas what to do?

I have also tried to modell with connector elements, but the same happends.

RE: Buckling of pipe on nonlinear elastic foundation

instead of stipulating zero stiffness can you just use a very small value which might make it numerically more stable?

RE: Buckling of pipe on nonlinear elastic foundation

(OP)
I have tried with a small stiffness after the breaking point at 0.2mm, but have only been able to use a stiffness down to 50% of the original stiffness (way to high). I have also tried to modell the springs force/displacement relation as a piecewise curve with decreasing stiffness, but it did not work.   

RE: Buckling of pipe on nonlinear elastic foundation

Taking a step back, once you've gone from a finite stiffness to zero you've competely rewritten the Jacobian.

It seems to me your options are

1) switch to a code that is specifically designed to handle weird changes in the system as it goes. Perhaps LS Dyna, certainly it would be possible in Open FEM, which runs in Matlab. Basically you'd write a new model out each time a grain of sand moves. Another option is ADAMS, which has a robust solver and has non linear beam elements.


2) hand analysis
 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

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