X.B.4.3 Projected coordinate systems

The projected coordinate system is a local Cartesian coordinate system the definition of which depends on the type of element:

1.

For 0D elements, no coordinate system is build.

2.

For 1D and 3D elements, the Nastran element coordinate system is returned.

3.

For 2D elements, the projection makes sense. The coordinate system is build as follows:

(a)

The Z vector is the normal to the surface of the 2D element. For a CTRIA3, the vector Z is constant on the element. But for a CQUAD4 the nodes of which are not co-planar, the vector Z depends on the location on the element.

(b)

The direction vector is projected on a plane perpendicular to Z and defines direction X. Note that the direction vector is associated to a coordinate system which may be curvilinear.

Note that for 2D elements, the definition of projected coordinate system is more general that in Patran. Indeed, in Patran, only the vector X of the specified coordinate system is projected.