Shape optimization error 339: The dependent d.o.f. is constrained by grid or spc data

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:

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.

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://www.predictiveengineering.com/sites/default/files/predictive_engineering_white_paper_on_small_connection_elements-mpc_and_cbush_rev-1.pdf

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.