How to include thermal conduction effects across a RBE2 'spider' element in a NX Nastran heat transfer (SOL 153) analysis?
Solution
RBE2 'spider' elements do not support thermal conduction behaviour in a NX Nastran heat transfer (SOL 153) analysis - any such elements in the model are simply ignored and hence there is no heat transfer path across them.
However, if the model is created using the NX CAE/Simcenter interface, then defining a RBE2 'spider' element in the context of a '.fem' file where the analysis context is set to be NX Nastran heat transfer (SOL 153), the created element is described as a 'RBE2 (conductor)' element.
Although the RBE2 (conductor) element has been created in the normal manner, when the fea model is exported to NX Nastran for solution, the RBE2 (conductor) element is not exported as a normal RBE2 'spider' element but is instead converted into a number of Multi-Point Constraint Equations (MPC's).
Specifically, every individual leg of the RBE2 (conductor) element is exported as a single MPC equation with positive and negative unity coefficients for the two nodes. The result is that, when solved, the model behaves as if the RBE2 (conductor) element has infinite conductivity (i.e. it acts as a perfect conductor), and hence every node connected to it has the same temperature.
Of-course, the user could define the required MPC equations directly within NX CAE/Simcenter but this is likely to be more time consuming than defining an RBE2 (conductor) element and taking advantage of the software behaviour described above, especially if many such connections are required.
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