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Grounded CBUSH Element (Nastran) for Model Boundary Conditions

thread727-492307

Grounded CBUSH Element (Nastran) for Model Boundary Conditions

Grounded CBUSH Element (Nastran) for Model Boundary Conditions

(OP)
Hi, I'm trying to understand the use of CBUSH elements with PBUSH properties for grounded constraints on a model. Normally I'd use displacement constraints in the 6 DOFs to constrain my model, but I recently came across "grounded bush" elements. In Hypermesh, these elements are classified as 1D CBUSHs applied at a single node and assigned the PBUSH property card. By single node, I mean the element itself is created using a single node, not two coincident nodes.

How do these "grounded" elements constrain a model? I understand that the PBUSH property card allows for the application of various stiffnesses in the 6 DOFs, but I don't see how a model can be free of rigid body motion without hard displacement constraints?

Thanks!

RE: Grounded CBUSH Element (Nastran) for Model Boundary Conditions

Request to post Nastran related questions in- forum825: Nastran. This is general FEA forum for general queries on FEA.

Search entire eng-tips.com/Nastran forum with "CBUSH", may be the question is already posted.

RE: Grounded CBUSH Element (Nastran) for Model Boundary Conditions

According to Nastran’s documentation, CBUSH element is generalized spring and damper. When you leave the definition of the second connection point blank, a grounded spring and damper are used. That’s how it works internally. PBUSH is just a generalized spring and damper property - it’s used to specify the spring stiffness and damping coefficient.

RE: Grounded CBUSH Element (Nastran) for Model Boundary Conditions

Yes it's just a convenient shortcut. Functionally identical to an spc with 6dof constraint on one of the cbush nodes.

RE: Grounded CBUSH Element (Nastran) for Model Boundary Conditions

why would you not constrain the node in question ?

Or is the CBUSH creating a finite stiffness constraint ?

another day in paradise, or is paradise one day closer ?

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