non linear static does not converge optistruct (simple compression test)
Hello dear all
I am trying to perform a simple compression test using non linear static the goemetry is really simple. as far as i can see my problem might come from the contact. However, i am not an expert on this area, and i was wondering if can you guide me on how to solve the issue.
the error in the ouput is
*** ERROR # 4965 *** Maximum number of time increment cutbacks reached, analysis aborted.
but before that a warning quite curious also appears
*** WARNING # 3400 Singularity detected at following 1 DOFs. Possible reasons are: 1) insufficiently constrained model, 2) having rigid body mechanisms within the model, 3) extremely ill-conditioned rigid element sets, 4) extremely thin shells (as used for skinning) that have MID2/MID3, 5) gap elements with extremely high stiffness (KA, especially KT or MU). 6) extremely high Poisson's ratio in hyperelasticity material definition. Check the model and rerun the problem. (MECHCHECK may be used to find the rigid body modes. To do so, change the input to be an eigenvalue analysis and add MECHCHECK.) (WARNING: results obtained with MECHCHECK cannot be used because the model is changed internally.)
Look i did the same geometry using contact and and displacement before but using "linear static" and everything went right, even no warnings, then i changed to "non-linear static" also i added NLPARAM(LGDISP), NLOUT, and under parameter card (PARAM) i added EXPERTNL and HASHASSM.
During the running the iterations appear but it seems they are oscillating trying to converge after certain point the go back to the begging.
Can you guide me on this situation?
i attached the *.out file along with the *.hm file
finally i am using hyperworks 2022 and optistruct in windows 10
Thanks in advance
Best Answer
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Hi,
you could take a look at this blog to understand what can be helpful to you.
https://community.altair.com/community?id=community_blog&sys_id=538764ab1b3790d4a5f742eddc4bcba4
but I would review your boundary conditions, specially at the bottom of your structure, as it has onnly constraints in Z direction.
As you have a SLIDE contact in the top, there's no friction, and at the bottom, there's nothing holding your tube to slide in XY plane.
It would be good to constraint this movement in XY plane somehow, to avoid these convergence issues.
Imagine that you're supporting your tube over an ice platform. As soon as the solver starts loding your structure, any non-vertical loading will push your structure away. That's what the .out file is telling you.
0
Altair EmployeeAnswers
-
Hi,
you could take a look at this blog to understand what can be helpful to you.
https://community.altair.com/community?id=community_blog&sys_id=538764ab1b3790d4a5f742eddc4bcba4
but I would review your boundary conditions, specially at the bottom of your structure, as it has onnly constraints in Z direction.
As you have a SLIDE contact in the top, there's no friction, and at the bottom, there's nothing holding your tube to slide in XY plane.
It would be good to constraint this movement in XY plane somehow, to avoid these convergence issues.
Imagine that you're supporting your tube over an ice platform. As soon as the solver starts loding your structure, any non-vertical loading will push your structure away. That's what the .out file is telling you.
0