Node and Element Definition

FEMGEN will generate a finite element mesh of nodes and geometric element types. These geometric element types are related to the NASTRAN element names via an element variant number. The element variant mappings may be displayed by using the FEMGEN command 'UTILITY TABULATE FE NASTRAN', and these mappings are shown in table 2.1. Element variants are assigned using the command 'MESHING TYPES part ELTYPE variantno'. The variant number is optional and the default is 1.

'GRID' or 'RINGAX' cards are generated for all nodes in the model. Nodal coordinates are output in the global cartesian system, regardless of the system in which the model was defined in FEMGEN.

Element definition cards e.g. 'CTRIA3' are generated for all elements in the model. The jacobian (or sense) of all elements is checked by the interface and corrected where necessary. The interface also re-numbers the elements according to the NASTRAN conventions. For models where one or more nodes lie outside the X-Y plane, the interface will not perform a jacobian check on TR3, TR6, QU4, QU8 and QU9 elements.

Eltype NASTRAN Element Variants

BE2 1 = BAR 2 = CONROD 3 = ---- 4 = ROD

5 = TUBE 6 = CONEAX 7 = DAMP2 8 = ELAS2

9 = RBAR 10 = RBE2 11 = RROD 12 = BEAM

TR3 1 = TRIA3-PS 2 = TRIA3-PE 3 = TRIA3-SH 4 = TRIAR-PS

5 = TRIAR-PE 6 = TRIAR-SH

QU4 1 = QUAD4-PS 2 = QUAD4-PE 3 = QUAD4-SH 4 = QUADR-PS

5 = QUADR-PE 6 = QUADR-SH 7 = SHEAR

TR6 1 = TRIA6-PS 2 = TRIA6-PE 3 = TRIA6-SH 4 = TRIAX6

QU8 1 = QUAD8-PS 2 = QUAD8-PE 3 = QUAD8-SH

PE6 1 = PENTA

HE8 1 = HEXA 2 = HEXA1 3 = HEXA2

PE15 1 = PENTA

HE16 1 = HEXA

HE20 1 = HEXA 2 = HEX20

P-EL 1 = CONM2 2 = NODE-GEN

 

Note that some element types have plane stress ('-PS'), plane strain ('-PE'), and shell ('-SH') variants. These three character extensions are removed by the interface program and used to control the assignment of materials on PSHELL cards in order to define the desired element sub-type (plane stress, plane strain, and shell).

BEAM elements (BE2 variant 12) will generate NASTRAN CBEAM cards with warping degrees of freedom except when the physical property attached to the BEAM elements has a torsional stiffness (J) equal to 0.