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it seems that y-direction is a direction normal to that plane of the beam (in the plane of the beam's profile).
lookup "Specifying Y Direction for Beams" in documentation.local y and z directions are in profile's plane.
There are actually three coordinate systems that are involved with beam sections.
1. Beam ACTION csys
2. Beam SHAPE csys
3. Beam Centroidal Principal csys
The BACsys (1), is always located on the curve that defines the beam. It's X axis is parallel to the beam curve, and the Y and Z axes are defined using the Beam definition dialog box in Mechanica.
The BSCsys (2), and the shape of the beam's cross section are related. Again, the X axis of this csys is parallel to the curve that defines the beam. The Y axis is represented by a 'Y" shape on the positive end of the icon representation. The Z axis is represented by by an arrow shape on its positive end.
Another way to think about the orientation is to consider a sweep feature. Sweeps have two basic parts; a trajectory, and a section.
The trajectory is like the beam definition, and the sections are similar for both the sweep and beam definition.
In the sweep, the trajectory's direction is analogous to the 'X' direction of the BSCsys. The section you sketch to define the shape you want to sweep is defined by a set of center lines, like a crosshair. The direction of the crosshairs's axes correspond to the Y and Z axes of the BSCsys in Mechanica.
So, having said all of that, the error message Mechanica is reporting should make more sense now. What it means, is that the section in your sweep would by 'flat', and wouldn't create any geometry. One easy fix is to rotate one direction 90 degrees, so that you can see the orientation of the beam after Mechanica creates the elements.
The final type of Coordinate system is the Beam Centroidal Principal Csys (3). It is located at the section's centroid. This is sometimes called the Principal Csys. For channel and 'L' shapes, it is located away from the BSCsys. For general sections, and the other standard sections, they are coincident.
I didn't mean to write a book, but I hope that adds some detail so you can run your analysis.
-tsl
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