Learning Forum

[manuel.uruena]

I am modelling a hollow tube with shell elements for a stub column test.

I want to apply the loads/displacements to a central node at the top instead of to the edge of the tube.

The central node is the master node, and the nodes at the edge are the slave nodes.

When solving, I get the error "Specified degree of freedom constraint at unused node". I understand this is because the master node is not attached to any element.

How can I solve this error? I want the load/displacement applied to the master node to be transferred to the nodes at the edge of the tube.

[Erik Kostson]

Hi

Use RBE3 (small deflections only), or CERIG (small deflections only) or MPC184 elements (or MPC contacts to do the load transfer).

See the help manual for possible examples and explanation of these commands (the web should have quite a lot of info also).

Thank you

Erik

[manuel.uruena]

Dear ekostson I have tried both REB3 and CERIG, and either they both give me an error. I am using large deflections (NLGEO). I think the problem is not the coupling but the fact that the node is "unused".
Thanks

[Erik Kostson]

Hi

Since you are using large defections, you cannot use CERIG RBE3 (they are only for small deflections).

So you have to use MPC contact elements or MPC184 elements (a spider wheel is needed like you show in the CP image in your first post) for that see this helpful post on how to define them (mpc184 "spider" wheel).
All the best of luck

Erik