Take a look to the NX NASTRAN ELEMENT LIBRARY user manual, there you have all the information required to understand and know the nastran resources used by NX AdvSim.
CELASxx is a Scalar spring element that connect two degrees of freedom at two different grid point. They behave like simple extension/compression or rotational (e.g. clock) springs, carrying either force or moment loads. Forces result in translational (axial) displacement and moments result in rotational displacement. CELAS1 and CELAS2 are the only two types supported in NX AdvSim. You can define translational stiffness as well as rotational stiffness. EndA and EndB are the both ends of the element, each node in the case of a two-nodes CELAS2 element.
In addition to the CELAS elements, NX Nastran also includes the CBUSH element. The CBUSH is more convenient because it is capable of defining stiffness in all 6 degrees of freedom, whereas the CELAS elements allow you to define stiffness in only 1 degree of freedom per node that the element connects. A single CBUSH can accomplish the work of 6 CELAS elements. NX Advanced Simulation supports CELAS and CBUSH elements.
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