Why does the holding plate move unexpectedly in CNTNLSUB, even with SPCs applied?
I have a transient nonlinear analysis in OptiStruct with two subcases to analyze (subcase 2 is a CNTNLSUB relative to subcase 1). In the first subcase, a holding plate engages with the rubber teeth to geometrically position them in their final location, having in consideration their final stress state (which is important for the CNTNLSUB). Consequently, in subcase 2, a punch presses down on the top of the rubber, and the holding plate's purpose is to remain in place so the rubber can be pressed against it.
During subcase 1, the holding plate has an enforced displacement applied until it reaches its final position. The objective is for it to stay static and fixed in its six degrees of freedom in subcase 2.
However, when subcase 2 begins and the punch presses down on the rubber from above, the holding plate starts moving in the opposite direction, returning, gradually, to its initial position (before subcase 1).
The issue I’m facing is that I already have an SPC applied to the nodes of the holding plate in the SPC load collector associated with subcase 2, so this behavior doesn’t make sense. What could be causing this to happen? I’d appreciate any help!
P.S: I’ve attached a first video showing subcase 1 and a second video where the holding plate in subcase 2 can be seen moving (unexpectedly).
Answers
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Please verify the SPC applied to the holding plate in 2nd subcase. Have you done this by MODCHG?
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I've verified the SPC in the holding plate in 2nd subcase. I created an RBE2 all nodes from the holding plate and applying an SPC in the independent node. I didn't use the MODCHG property.
What could be the reasoning to use that property?
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Need the .fem file to see the setting. without checking it is difficult to suggest anything.
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Ok, here is the .fem file! Thank you!
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Hi,
Can you run the model by fixing the SPC and SPCD of the phase1 loading?
You need to have FIXED=F. For some reason I am not able to upload pic. Please try to edit and run.
Thanks
Rajashri
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Hello,
I'll try to do it to see if it works. Thank you, I'll keep you posted!0 -
Dear Rajashri,
I'm using v2023.1 and I can't find the option FIXED = F while editing SPC/SPCD cards. However, I found an option called "Retain Deformed Boundary". Is this the same option?
If YES, then I tried it in both SPC/SPCD and the run failed reaching the minimal time increment due to cutbacks. I tried to remove that option from the SPCD and kept it only in the SPC and the run is converging equally compared to when I didn't had that option activated. Is this okay?0 -
Yes, that is the one.
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Ok, thanks. What about what I described after?
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That's also yes, by using fixed=F, the motion of the holding plate will not be there in 2nd step. Else the motion will be converted into equivalent internal forces at the beginning of Subcase 2 and are ramped down gradually. Please try and see if this works for you.
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Alright, thank you! I'll try and see if it works.
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Sir, I tried to use the option FIXED on the SPCD Phase 1 - didn't work (the simulation can't process). I also tried to use that option on the SPC Phase 1 - didn't work (probably because it's not assigned to the Subcase 2). I'm going to try the option FIXED in the SPC Phase 2 (it's the only available option).
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Altair Employee