Export NASTRAN File: Attributes

Description

Nodes Attributes

Restraints

Straus7 exports node restraints as SPC and SPCD entries in large-field format.

A node restraint is exported as follows:

If the restraint is fully fixed in at least one direction, an SPC entry is posted with a freedom set ID, node number and set of component numbers.
If the restraint has a fixed displacement in at least one direction, an SPCD entry is posted for each direction. Each SPCD entry is posted with the freedom set ID, node number, component number (1-6) and the enforced displacement value.

Straus7 restraints may reference a coordinate system other than the global XYZ system. NASTRAN does not store this information on an SPC or SPCD entry. Rather, NASTRAN references the coordinate system on the GRID entry of the parent node.

Forces

Straus7 posts node forces as FORCE entries in large-field format. Forces are always defined in the global coordinate system. Each FORCE entry is posted with the load case ID, node number, a force vector N1-N3, and a scale factor of 1.0.

Moments

Straus7 posts node moments as MOMENT entries in large-field format. Moments are always defined in the global coordinate system. Each MOMENT entry is posted with the load case ID, node number, a moment vector N1-N3, and a scale factor of 1.0.

Temperatures

Straus7 posts node temperatures as TEMP entries in large-field format. Each TEMP entry is posted with the load case ID, node number and temperature. No distinction is made between fixed, initial and tabular temperatures when exporting. Also, node temperature tables are lost.

Masses

Straus7 posts node translational and rotational masses as CONM2 entries in large-field format. Each CONM2 entry is posted with a node number and a unique global element ID number (because NASTRAN treats node mass as an element type). No mass offset or coordinate system is defined.

Node mass is exported as follows:

Translational mass

Posted as the mass value M. If mass varies with direction, the average of the X, Y and Z mass is posted.
Rotational mass

Posted as the mass moments of inertia I11, I22 and I33. The values I21, I31 and I32 are set to zero.

Beam Attributes

Beam Loads

Straus7 posts PLOAD1 entries for all beam load types: principal and global distributed loads, point forces and point moments. One PLOAD1 entry is posted for each non-zero component. For example, a global point force of (+60.0, 0.0, -20.0) is posted as two PLOAD1 entries. Each PLOAD1 entry is posted in large-field format, with a beam number and load case ID.

PLOAD1 entries are posted with the following load types:

Global distributed loads: FX, FY and FZ.
Global point forces: FX, FY and FZ.
Global moments: MX, MY and MZ.
Principal distributed loads: FXE, FYE and FZE.
Principal point forces: FZE, FYE and FZE.
Principal moments: MXE, MYE and MZE.

PLOAD1 entries are generally posted with a load scale of FR. This indicates that beam positions are given as fractional (rather than absolute) positions.

Length-projected global distributed loads are posted with a load scale of FRPR.

Straus7 defines distributed loads via an offset from each end, whereas NASTRAN defines distributed loads via two offsets from the first end.

Straus7 defines loads applied along the centroidal axis of the element, whereas NASTRAN defines loads applied along the shear centre of the element. For beams with a shear centre offset an additional moment load is added to account for this offset.

Plate Attributes

Normal Pressures

Straus7 posts normal plate pressures as PLOAD2 entries in large-field format. Each PLOAD2 entry is posted with a load case ID, plate number and pressure value. A positive value indicates a pressure in the direction of the plate normal (which is defined using the right hand rule with respect to the sequence of node connections).

Edge Loads

All plate edge pressure and shear loads are converted to an equivalent set of nodal loads and exported as NASTRAN FORCE entries. These pressure distributions are integrated over the area of the plate edge based on the plate thickness values entered at the property level.

Face Point Loads

Straus7 plate face point forces and moments are converted to an equivalent set of nodal loads and exported as NASTRAN FORCE entries.

Other Plate Loads

Straus7 combines any other plate face loads (global pressure and shear force), and posts them as a single PLOAD4 entry in large-field format. Each PLOAD4 entry is posted with a load case ID, plate number, a total load P1 and normalised direction vector N. Straus7 loads are constant over a given surface, so the loads P2, P3 and P4 are not required.

The total load vector is the vector sum of the global face load (LX, LY, LZ) and local shear force (Sx, Sy).

If the "projected area" flag is set, the exported pressure vector is scaled to account for the projected component of the plate area.

Point Loads

Straus7 plate face point forces and moments are converted to an equivalent set of nodal loads and exported as NASTRAN FORCE entries.

Brick Attributes

Brick Loads

Straus7 posts a PLOAD4 entry for each face that is loaded with global pressure, normal pressure or shear force. PLOAD4 entries are posted in large-field format. Each PLOAD4 entry is posted with a load case ID, plate number, a total load P1 and normalised direction vector N. Straus7 loads are constant over a given surface, so the loads P2, P3 and P4 are not required. The appropriate nodes required to uniquely define the face are also exported.

The total load vector on each face is the vector sum of the global face load (LX, LY, LZ), local face pressure (P) and local shear force (Sx, Sy).

If the "projected area" flag is set, the exported pressure vector is scaled to account for the projected component of the plate area.

Face Point Loads

Straus7 brick face point forces and moments are converted to an equivalent set of nodal loads and exported as NASTRAN FORCE entries.