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ahenkes1

[GNA] Post-Buckling of arch plate in Optistruct

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Hello

 

I want to analyse the post buckling behaviour of an arched plate (SHELL Elements) with GNA (Geometric nonlinear analysis, implicit). The model is attached. In another forum (RADIOSS) a similar case was presented, with an pdf file attached, discribing a similar problem :

 

I am not able to reproduce the results (should be look like this:

A3-1-600x379.png

I tried different parameters for shell thickness, force size, starting load increment size and solver options (Arc, RIKS,...). Sometimes I get nothing at all, sometimes only results up to point A (s. picture above). How can I get post buckling results?

 

Thank you

PlateTest.fem

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Yes, I choose Optistruct as the solver (I think he uses a coupling with RADIOSS). I managed to get closer to the benchmarke when using FORCE as convergence criteria and as method for LINE SEARCH. However, I cant get the area between B and D. It would be usefull to know how to plot correctly, than I could send you my outcomes at this moment.

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Hi,

 

I have several questions concerning the solver deck you send:

 

1) No buckling occures? I could increase the load, but anyways, I want to get the deflection of the arched plate from the benchmark (post buckling behaviour including area B-D). The model set up for a general GNA is known.

2) Why using NLOAD in this case? Its static anyways.

3) Why including EIGRL in GNA? It isnt used?

----------------------------------------------------------------------------------------

4) How to plot Load time steps over Displacement (Y-X) in Hypergraph?

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As I pointed out, it was just a similar problem. I am used to Optistruct and want to use it, as Optistruct should be capable of solving such a problem (it is a non dynamic behaviour I think, because of that no need for RADIOSS?).

 

There are different sites presenting this, as it is a rather common benchmark:

https://enterfea.com/problems-with-nonlinear-analysis-convergence-read-this/

 

https://www.comsol.com/blogs/buckling-structures-suddenly-collapse/

 

https://www.youtube.com/watch?v=JS7dgba2qLc

 

Similar load path:

 

https://www.researchgate.net/post/Arc_length_method_for_non_linear_buckling_Nonlin-FEM_in_ANSYS_Is_there_any_way_I_can_continue_the_Simulation_beyond_the_critical_point

 

And here a different Video with snap-back also:

 

https://www.youtube.com/watch?v=o5Nu5GF_zZk

----------------------

 

I want to go through the whole deflection path with the model I attached in the original post. Normaly, the RIKS ARC LENGHT method should be able to get all points .... as pointed out before, with 1mm shell thickness I only get up to point A....

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I think I got an update, see files attached. I think it could be the solution, but the post processing isnt working as I imagine:

 

1) also I solved 1700+ time steps, I only get a view (they are actually ordered by deflection size) to e.g. animate the model behaviour (The time steps solved go ++, than --, than ++ again, as supposed, but the time steps in the drope down menu from HyperView are only from 0 to ++, so around 180).

2) again, how to plot time steps (the actual one solved, not the sorted, censored ones) against displacement? (For validation and comparison)

PlateTest.h3d

PlateTest.out

PlateTest.stat

PlateTest.res

PlateTest_rad_s1_0001.out

PlateTest.fem

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Another thing, I was using the geometric nonlinear analysis load step, which indeed uses RADIOSS. I will try the Nonlinear quasi static loadstep with large Displacement and report back. 

 

The post process problem exists anyways, so it would be kind to get help with that. 

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Hello,

 

Know, using NLSTAT, I dont get the expected results. I attached the concerning files. I am not able to plot Load vs Displacement (I cant choose Nodes for either Load or Displacement using h3d, for .res I cant choose Loads as Y reference). Therefore I cant realy say, whether my results are right (as in the Benchmark). The solver doesnt converge at a specific increment, therefore I think he cant go through the whole deflection cuve).

 

Could you look at the results and try to get a Load vs Displacement graph?

PlateTest.out

PlateTest.h3d

PlateTest.res

PlateTest.fem

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"TSTEPNL        7     500     0.0                       1        UPW"

  *** ERROR # 1000 *** in the input data:
  Incorrect data in field # 4.

 

This error I get, no Idea how to go on

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