Nastran-Specific Solid Mesh Characteristics (Splitting Pyramid Elements)

The default solid mesh type in Simulation Mechanical is a hex-dominant hybrid mesh consisting of 8-node bricks, 6-node wedges, 5-node pyramids, and 4-node tetrahedra. Nastran solvers typically do not directly support pyramid elements. Depending upon the particular Nastran version, each pyramid must either be represented as a degenerate CHEXA brick element or must be split into two tetrahedral elements.

When you run a simulation using the Autodesk Nastran solver, all pyramid elements within the solid mesh are automatically split into tetrahedra before the solver is called. This is true whether the Default Processor is set to Nastran or you use the Run with Nastran ribbon command.

Note: This pyramid-splitting operation is only performed for Nastran solutions within Simulation Mechanical. If you export an unsolved model to a Nastran file, the pyramids are represented as degenerate CHEXA elements in the resulting Nastran deck.