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Piotr Kasprzyk

Questions on NLGEOM

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Hello Everybody,

 

I've been struggling with NLGEOM analysis with CNTNLSUB since yesterday and I still don't understand a few things. What I want to do is to load a steel plate for 1 s and in the next step to unload it. I load the structure with one Force in Z direction NLOAD in the subcase 310. NLOAD activates TABLED1 where the basic linear function is defined x=0, y=0; x=1, y=1. In the next subcase 311 I use CNTNLSUB = YES, the same SPC and the same NLPARM. The nonly difference is that I do not define any load, since it should be the step, where the structure is being unloaded. Below you can find the plots I got and short descriptions of respective graphs.

 

On the Displacement - Force plot, you can see a discontinuity between the curve belonging to the SUBCASE 310 (loading) and SUBCASE 311 (unloading). What is more, the force increases in the second step despite the lack of any loading force. The force is being increased up to 8000 N, which is a doubled value of the load defined in the first step.

 

On the Time-Displacement plot the curve is continuos. However, the displacement is being increased till the end of the simulation (as expected based on the graph Displacement - Force).

 

The Time-Load graph shows discontinuity again. In the beginning of unloading step, the force seems to be 0 N and than in the next increment gets back immidiately to the value, as if it was being increased, according tothe linear function present in the loading step.

 

I would be grateful for some hints / tipps / explanation, where I make a mistake and if it is possible to create a proper loading - unloading time dependent simulation in two subcases with use of CNTNLSUB.

 

You can find my input-deck in the attachment.

1300_CNTNL_test_01_Disp_Force.png

1300_CNTNL_test_01_Time_Disp.png

1300_CNTNL_test_01_Time_Force.png

nlgeom_4060_H380LAD_0p6mm_1300_CNTNL_test_01.fem

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