Importing Nastran Mesh Input Files

Typical file extensions for Nastran mesh input files are .dat and .bdf, although the oSP3D Nastran mesh import interface accepts all file extensions and does not distinguish between them. As described in [11], the input file must consist of sections arranged in the following order:

  • Nastran Statement

  • File Management Statements

  • Executive Control Statements

  • CEND

  • Case Control statements

  • BEGIN BULK

  • Bulk Data Entries

  • ENDDATA

While the first two sections are optional, the subsequent sections are all required, even if they do not contain an entry. The oSP3D Nastran mesh import interface checks for the existence of all required sections, informing you on the debug log level if any are missing. During this check, all the content until the required BEGIN BULK delimiter is skipped. The definition of the finite element mesh must then be given in the required Bulk Data Entries section.

Compared to the MSC.Nastran syntax in [11] and[12], only some of its syntax elements is supported. The following list of limitations is not exhaustive:

  • More than 80 characters per line are not supported.

  • System cell 363 as well as STRICTUAI are ignored. This, the free-field format is not automatically continued by terminating the parent with a comma. Instead, it is clipped. Again, more than 80 characters per line are not supported.

  • Comments may be inserted in any of the parts of the input file. They are identified by a dollar sign $ in any column.

  • oSP3D supports input in sorted order only. Therefore, continuation pointers are not resolved nor even checked at all. The Nastran mesh input interface takes only continuation entries into account, assuming an immediately following line not starting either with a delimiter or a keyword definition is a continuation line.

  • The Nastran IFPSTAR is ignored, so all entries in free-field format are limited to 8 characters. However, as implemented, a keyword followed by a * character activates the automatic conversion of the free-field format to the large field format. This is not part of the MSC.NASTRAN format specification.

  • Replication is not supported.

  • The Nastran mesh input interface supports the small, large, and free-field formats. The MSGMESH format is not supported.

  • Integer data types may contain decimal points.

  • Real data types may be written in C syntax only. While the following real numbers are legal to the MSC.Nastran format specification, they cause an error in the oSP3D Nastran mesh import interface

    • 0.7+1

    • .70+1

    • 70.-1

  • While not clearly documented in [12], the Nastran input interface assumes that the first field of any supported format is always left-justified.

Due to the Nastran mesh input interface limitations, each passed Nastran mesh file must contain a non-empty Bulk Data Entries section that defines either a valid finite element mesh or supported load bulk data. This definition can be given only with the bulk data entries in the following table. All other bulk data entries are ignored.

EntryShort Description
CHEXASix-Sided Solid Element
CPENTAFive-Sided Solid Element
CQUADFully Nonlinear Surface Strain Element
CQUAD4Quadrilateral Surface Element
CQUAD8Curved Quadrilateral Surface Element
CQUADRQuadrilateral Surface Element
CQUADXFully Nonlinear Axisymmetric Surface Element
CTETRAFour-Sided Solid Element
CTRIA3Triangular Surface Element
CTRIA6Curved Triangular Surface Element
CTRIARTriangular Surface Element
CTRIAXFully Nonlinear Axisymmetric Surface Element
GRIDDefines the geometry
PLPLANEFully Nonlinear Hyperelastic Surface Element
PLSOLIDFully Nonlinear Hyperelastic Solid Element
PSHELLSurface Element Property
PSOLIDProperties of Solid Elements
TEMPGrid Point Temperature

For the entries PSHELL, PSOLID, and TEMP, these bulk data entry comments are applicable:

  • The Nastran mesh input interface parses and validates the property bulk data entries but does not fully import them.

  • With the exception of the property identifier, properties are not imported into oSP3D.

  • Providing section definition is not obligatory because the Nastran mesh import interface creates oSP3D-compatible section definitions.

Note:  The oSP3D installation includes a simple Nastran input file: nastran.bdf. For more information, see Input File Examples.