Shape optimization error 339: The dependent d.o.f. is constrained by grid or spc data
Hi all,
I tried all day to get a shape optimization running, but I keep getting an error:
*** ERROR # 339 ***
The dependent d.o.f. is constrained by grid or spc data.
RBE3 element id = 25502.
grid id = 28613.
component = 1.
This does not happen when no RBE3 elements are used. I interpret this error message that a constrained node is also supposed to be optimized, but these nodes should be separated in this model. I'd be very grateful if someone could point me to my error.
Answers
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Hi,
RBE3 is used for load transfer and the load (but not constraints) can be applied on the dependent node.
In your case, the dependent node of the bottom RBE3 is constrained and this is causing the error.
As a workaround:
-stiff: change the bottom RBE3 to RBE2 (config edit)
-compliant: create cbush and connect one end with RBE3 and constrain the other end
For more info refer to:
https://community.altair.com/community?id=community_question&sys_id=465608f61b2bd0908017dc61ec4bcb4e0 -
Thank you very much, it works with RBE2 elements now. I wonder however why RBE3 elements cannot be used for a displacement constraint in this case as it runs without issues as a standard analysis or topology optimization.
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Glad to help.
RBE2 transmits the displacements and RBE3 transmits the loads (MPC Forces). Dependent and independent nodes are reversed in RBE2 and RBE3, therefore it is invalid to constrain the RBE3 master node, which is dependant on the deformation of the independent nodes. For more details refer to:
http://www.endurasim.com.au/wp-content/uploads/2015/02/EnDuraSim-Rigid-Elements.pdf
https://community.altair.com/community?id=community_question&sys_id=4a864c3a1b2bd0908017dc61ec4bcb420 -
Coming from other FEA/CFD packages and having used Hypermesh previously only as a preprocessor, I taught myself Optistruct on the fly. But I see that I have a lot of catching up to do. Thank you very much for the explanation and the links.
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