Import NASTRAN File: Grid Points

Description

NASTRAN uses GRDSET to specify:

Default grid point single-point constraints.
Default coordinate system in which grid point positions are defined.
Default local coordinate system for grid points. The local coordinate system for a grid point is used for restraints, offsets and displacements).
Straus7 uses these values as defaults when importing GRID entries.

NASTRAN uses GRID to create a grid point at a given position. A single-point constraint, a position coordinate system, and a constraint coordinate system may also be specified. If any of these values are not specified, the default values found in GRDSET are used instead.

Creating nodes

Straus7 creates a new node at the given position. If a position coordinate system has been specified on this GRID entry, or on a global GRDSET entry, the position is transformed into global coordinates.

New Straus7 nodes are numbered sequentially (starting at 1), whereas grid points in the NASTRAN file can be arbitrarily numbered (as long as all IDs are unique). The NASTRAN ID number will be assigned as a node ID attribute in Straus7.
Node restraints

If this GRID entry (or a global GRDSET entry) specifies a single-point constraint, Straus7 applies this restraint to this node for each freedom case.
Local coordinate systems

GRID and GRDSET entries can specify a local coordinate system for a grid point, using the CD field (this is quite separate to the coordinate system CP in which the node position is defined). Local coordinate systems are used in conjunction with displacements, degrees of freedom, constraints and solution vectors.

If a local coordinate system has been specified for a node:
- Any restraints created for that node by Straus7 (when importing GRID, GRDSET, SPC, SPCD or SPC1 entries) will reference that system rather than the global XYZ system.
- Any beam offsets (specified on CBEAM and CBAR entries) acting at that node will be given as components in that system. Straus7 will transform the offset vectors into the components in the global XYZ system, before posting them as components in the principal axis system of the beam.
- The DoF for any constraint equations referencing that node will be defined according to the local coordinate system.