Import NASTRAN File: Static Loads

Description

NASTRAN uses FORCE, FORCE1 and FORCE2 to define a concentrated load at a grid point. Strand7 transforms the vector (if required), and applies this using a force attribute on the specified node, in the specified load case. A new load case is created if required.

NASTRAN uses GRAV to define a gravity load vector for a given load case. Strand7 transforms the vector (if required) and posts it as the global linear acceleration for the given case. A new load case is created if required.

NASTRAN uses MOMENT, MOMENT1 and MOMENT2 to define a moment at a grid point. Strand7 transforms the vector (if required), and applies this using a moment attribute on the specified node, in the specified load case. A new load case is created if required.

NASTRAN uses PLOAD to define a uniform static pressure load on a triangular or quadrilateral surface comprised of surface elements and/or the faces of solid elements.

NASTRAN uses PLOAD1 to define distributed and concentrated loads on various line element types (CBAR, CBEAM, CBEND).

If the load is concentrated (i.e., P1 and P2 are the same point):

• Load type is FX, FY, FZ: A point force is posted at P1 with one non-zero component in the appropriate X, Y or Z direction.
• Load type is FXE, FYE, FZE: A point force is posted at P1 with one non-zero component in the appropriate 1, 2 or 3 direction.
• Load type is MX, MY, MZ: A point moment is posted at P1 with one non-zero component in the appropriate X, Y or Z direction.
• Load type is MXE, MYE, MZE: A point moment is posted at P1 with one non-zero component in the appropriate 1, 2 or 3 direction.

If the load is uniformly or linearly distributed (i.e., P1 and P2 are not the same point):

• Load type is FX, FY, FZ: A uniform or linear distributed load is posted between P1 and P2 in the appropriate X, Y or Z direction.
• Load type is FXE, FYE, FZE: A uniform or linear distributed load is posted between P1 and P2 in the appropriate 1, 2 or 3 direction.
• Load type is MX, MY, MZ, MXE, MYE, MZE: The moment vector is transformed according to the beam local axis system and posted as a uniform or linear distributed moment.

If the load scale type is LEPR or FRPR, and the load is a distributed load in a global direction, the load is posted with Act On Projected Length turned on.

Strand7 and NASTRAN have different beam local axis system conventions and default beam positions. These differences are particularly important when there is an offset between the centroid of the cross section and the shear centre. NASTRAN applies beam loads along the shear centre of the element whilst Strand7 applies loads along the centroidal axis. Additional moment loads are added to the model to account for these offset where applicable.

The beam loads are created in the specified load case. A new load case is created if required.

NASTRAN uses PLOAD2 to define a normal pressure load on N surface elements. Strand7 posts this as a normal pressure on each of the N plate elements, in the specified load case. A new load case is created if required.

Strand7 also supports the alternate THRU format to specify a range of plate elements.

NASTRAN uses PLOAD4 to define pressure loads on various surface and solid element types (TRIA3, TRIA6, TRIAR, QUAD4, QUAD8, QUADR, TETRA, PENTA, HEXA).

If no direction vector is defined, Strand7 posts the load as a normal face pressure on the specified plate or brick surface. NASTRAN and Strand7 use the same sign conventions for normal pressures.

If a direction vector is defined, Strand7 posts the load as a global surface pressure on the specified plate or brick face. If a coordinate system is referenced, the direction is transformed before posting. When the coordinate system is cylindrical or spherical, the direction used is based on the orientation of the coordinate system at the centre of the plate or brick face.

When transforming from a cylindrical or spherical coordinate system, the direction is obtained at the centre of the plate or brick face.

When the pressure varies at different corners on the surface, Strand7 uses the average value of the corner pressures. The pressure is posted into the specified load case. A new load case is created if required.

Strand7 also supports the alternate THRU format to specify a range of plate elements.

NASTRAN uses PLOADX1 to define a surface traction on TRIAX6 axisymmetric surface element types. Strand7 posts this as a combination of plate edge pressure and plate edge shear on one edge of the corresponding Tri6 plate element. A new load case is created if required.

The applied attributes are calculated by:

1. Taking the average of the surface traction at each end of the edge.
2. Using the traction angle to calculate components tangential and normal to the edge.
3. Posting the tangential component as a plate edge shear, and the normal component as a plate edge pressure. If the edge is curved, this will only be an approximation, because these components will vary along the length of the edge.

NASTRAN uses RFORCE to define a centrifugal force field for a given load case. Strand7 transforms the angular velocity and acceleration vectors (if required), and posts them as the angular velocity and acceleration for the given case. The origin of rotation is also stored. A new load case is created if required.

NASTRAN uses TEMP to define the temperatures at N grid points for a given load case. Strand7 posts these values using fixed temperature attributes for the specified nodes, in the specified load case. A new load case is created if required.

NASTRAN uses TEMPD to define the default node temperatures for N load cases. Strand7 posts these values as the global temperatures for the specified load cases. Any new load cases are created if required.

NASTRAN uses TEMPRB to define a temperature field for one-dimensional elements for determination of thermal loading, temperature-dependent material properties or stress recovery. Strand7 does not support this attribute.

See Also

• NASTRAN File: Import