I am trying to apply an enforced rotation (on a hollow cylinder) on 3D solid hexa.
I used a RBE2 element to connect the inner diameter of the cylinder to a node in the middle of the cylinder.
I constrained the middle node on all translations (pinned) and used a enforced rotation on the middle node, but nothing happens, it doesnt rotate...
What am I doing wrong?
Solved! Go to Solution.
What you describe should return a fatal error: if your boundary conditions are limited to a pinned node your model is not sufficiently constrained, you need 6 fixed DOFs, and, equally important, if enforcing a rotation you first need to constrain the corresponding rotation DOF. In NASTRAN terms an SPCD is preceded by an SPC. FEMAP issues the following warning message if this isn't the case:
"Node XX, DOF Y is not constrained but has Enforced Displacement applied."
Last (but unlkely) check your RBE2: remember that 3D elements' nodes have no rotation, therefore limiting your RBE2 to rotation DOFs wouldn't work.
Hope this helps
Sorry for the partial information...
The middle node is constrained in all translations, the bottom and top of the cylinder are constrained so that they are free only to slide on their plane (to allow the rotation).
I am using sol 601 so constraining the rotation on the middle node is not necessary for my understanding.
Regarding your last point - in order to provide rotation I need to unconstrain the rotational DOFs?
But then I will have all DOFs free of constraint, what will cause rotation?
With Nastran, ANY node that has an enforced displacement or rotation has to have that degree of freedom constrained. This includes SOL601. So in your case, if the rotation is about the local Z axis, that node must have it's Z rotation constrained.
Thanks, I did constrained it and it did help.
This raises a question, when I used "displacement" load in advanced non-linear - It is not needed to constrain the displaced DOF, and everything works just fine, what is the difference between "displacement" load and the "enforced rotation" load in this matter?
Is the same, is a way of talking: in FEMAP "Displacement" under "Loads" is what we refer as "Enforced Displacement of Translation".
With Advanced NonLinear (SOL601) module you do not need to constrain the DOF where you prescribed an enforced displacement of translation or rotation because is not used the NX Nastran solver, but ADINA solver.
To clarify this better, with NX NASTRAN there are two methods available to you for specifying an enforced displacement at a component.
Grid points with an enforced displacement using the SPCD entry must also appear on an SPC or an SPC1 Bulk Data entry.
The SPCD method of enforcing a nonzero constraint is more efficient than using an SPC entry alone when you're using multiple subcases that specify different constraint conditions. Note also that when you use an SPCD entry, the displacement values entered on the SPC entry are ignored. The software only uses the SPCD values.