Coordinate System CORD2R vs CORD3R Difference?
Hello,
What is the difference between CORD2R and CORD3R? What are their properties?
If I reference joints to a specific coordinate system what would the difference be with CORD2R and CORD3R?
Thank you!
Answers

Hi,
the difference is in the creation process and in their behavior:
 the CORD2R is created by axis direction and its position is fixed in space
 the CORD3R is created by node reference and its position is moving according to the movement of the reference nodes
<?xml version="1.0" encoding="UTF8"?>
from Optistruct User's guide:
Coordinate Systems
In geometric nonlinear analysis there are moving and fixed coordinate systems. Rectangular
coordinate systems that are defined thru grid points (CORD1R, CORD3R) are moving with the
deformations of the model. Systems defined in terms of point coordinates (CORD2R,
CORD4R) are fixed.
The behavior of loads depends on the coordinate system referenced. If the loads FORCE,
MOMENT are desired to be follower forces, a CID that references a moving coordinate system
(CORD1R, CORD3R) must be defined. Otherwise these loads are not following the
deformation. PLOAD always follows the deformations.0 
Thank you for your response!
This was extremely helpful!_)
0