Square membrane subjected to pressure. ERROR on dof 3.

[eng23bio]

Hi Everyone!

I am having some trouble using the membrane elements (elastic linear). I have a simple square subjected to pressure. The boundary conditions are that the four apex do not have displacements nor rotations. The error I get is too many attempts required although the time step is pretty small (and it should converge with 1, doesn't it?)
I get these warnings for a lot of nodes but i do not really understand it.

***WARNING: SOLVER PROBLEM. NUMERICAL SINGULARITY WHEN PROCESSING NODE
PART-2-1.7 D.O.F. 3. THIS NODE HAS NO STIFFNESS IN THE SPECIFIED
DIRECTION AND IS NOT COUPLED WITH THE REST OF THE MODEL.

Please find attached the .inp file.

Thank you very much for your help,amigos!!

 

[IceBreakerSours]

I have not looked at your model but numerical singularity error is an easy one: Some node(s) are allowed rigid body translation/rotation. Check your boundary conditions carefully.

[By the way, it is always a good idea to search in the forums or google before you create a new post.]

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

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

 

[eng23bio]

Hi IceBreakerSours,

I have checked the boundary conditions before submitting the question. The thing is that dof 3 cannot (to my understanding) have a singularity since its value is imposed, 0, as all the other dofs.

Any more ideas, anyone?

Thank you very much!

 

[IceBreakerSours]

Look at the .msg file; you'll know what DOF/node combination is giving you trouble.

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

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

 

[IceBreakerSours]

I looked at your INP. You are using the element incorrectly by applying an out-of-plane loading which explains the numerical singularities from the unconstrained nodes in the 3rd DOF. By the way, you can view the problematic nodes from the Create Display Group and Job Diagnostics menus available in the ABAQUS/Viewer - the post-processor. Of course, as I mentioned previously, these nodes are also enlisted in the .msg file.

Read the Analysis User's Manual (Membrane elements section 28.1.1 in ABAQUS v6.12) for more. If that particular type of loading is essential to the problem at hand, then you might consider shell elements. However, I recommend reading the manual before trying anything.

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

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

 

[eng23bio]

Thank you very much IceBreakerSours, the particular load I imposed (pressure) is essential since I am trying to model a textile structure. I will read carefully abaqus user's manual and try to solve the problem.

Once again thank you very much for your help.