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Using non-linear CBUSH elements in transient dynamic response (SOL 601,129)


Dear NX Nastran Experts,


I am trying to model the ground impact test (drop test) of a stiff box that features an internal structure which is connected to the box via spring-damper elements. I am using SOL 601,129 in NX 10.2. The spring-dampers are modelled with (four) CBUSH elements between (four) pairs of coincident nodes. The imapct is modelled with CGAP elements that have a initial gap opening.  As long as I use a single stiffness value for the CBUSH elements (linear stiffness), I get results which make sense. However, when I use a nonlinear force-deflection table (with PBUSHT) for the CBUSH elements, the results do not make sense: the final deflection (after dynamic effects have disappeared) of the spring-suspended structure is far too big. Has somebody of  you used nonlinear CBUSH elements (with coincident nodes) in SOL601,129? Are there any pitfalls with nonlinear CBUSH type elements and SOL601,129? Appreciate your help on this topic! thank you, Markus