The NASTRAN Export feature is currently subject to the limitations listed below.
- General
The NASTRAN Export feature is only supported for stand-alone systems (Static Structural and Modal).
- Supported Elements Types
Only the following element types are supported: 14, 21, 154, 156, 170, 173, 174, 175, 177, 180, 181, 184, 185, 186, 187, 188, 201, 250, 281.
Not all features of the element types above are supported. Check the NASTRAN Export log file for messages about unsupported KEYOPT settings or element behaviors.
- Pyramid Elements
Not all NASTRAN versions support pyramid-shaped 3D solid elements. For this reason, the NASTRAN Export ignores pyramid elements in the Mechanical model by default. The menu does have an option to include pyramid-shaped elements in the export. If pyramid elements are present in the Mechanical model and this option is set to ignore them (left unchecked), there will be voids in the exported mesh in place of the pyramid elements.
- Element Properties
Element/Specification Limitation LINK180 This element Is exported as CROD elements with the torsional constant J equal to 0.1 x the cross-sectional area. COMBIN14 For this element: Body-to-ground preloaded springs are not supported.
The damping portion of the element contributes only damping coefficients to the structural damping matrix.
3D torsional elements are not supported.
Preloaded springs are exported as beams with end releases and a temperature load applied. New properties are created for these equivalent beams. The beam sections have orientation vectors that reference the displacement coordinate system of the end nodes; this may result in an improper orientation vector if the beam nodes reference the basic coordinate system and the model is rotated.
COMBI250 For this element: Assumes KEYOPT(1)=0, (lumped mass between nodes I and J).
Offsets are not supported.
Beam Sections For beam section specifications: Also review the Beam and Pipe Cross Sections documentation in the Mechanical APDL Structural Analysis Guide.Section offsets are assumed to be relative to the shear center of the beam.
'Hat' cross-sections assume average section thicknesses and bottom flange widths.
'Z' cross-sections assume average flange thicknesses and widths.
Tapered sections are not supported.
Warping constants, shear corrections, and shear relief are not supported.
Pre-integrated Shell Sections Pre-integrated shell sections do not support density. Shell Offsets Only user-defined offsets are supported ( and are not supported). - Connections
Remote Points: CTE is not supported for remote points or surface-based constraints.
- Distributed Mass
When scoped to a solid body, Distributed Mass applied to a/an:
Face of a solid body is not supported.
Edge of a solid body is not supported.
When scoped to a surface body, Distributed Mass applied to a/an:
Surface body must be applied to all faces of the surface body.
Edge of a surface body is not supported.
Surface body and also scoped to a layered section or thickness must be scoped to all faces of the surface bodies within the layered section.
Scoped to a line body, Distributed Mass must be scoped to:
All edges of the line body.
Every body that has the same cross-section assignment.
- Loading
For the SFE/SFEBLOCK commands:
Imaginary components of SFE loads are not supported.
Line pressures and forces defined on surface or solid body edges are not supported.
An SFE load scoped to a line body assumes the element coordinate system is aligned with the global coordinate system and the load is uniformly applied over the length of element.
For the BFE/BFEBLOCK commands: Temperatures applied with BFE/BFEBLOCK commands are only supported for shell element types SHELL181 and SHELL281.
Tabular force loading is only supported for Transient analyses. Otherwise, loads applied using tabular data or functions are not supported.
- Solution Options
Multiple load steps are not supported. Use the Time option in the NASTRAN Export menu to specify the time at which time-varying loads will be exported.