User: BDF

This document is intended to be a reference guide for users.

Nodes

GRID

In NASTRAN, nodes can be in the global or a local coordinate frame (rectangular, cylindrical, spherical). Each node may reference a different coordinate frame \(cp\) for the reference coordinate frame (what the value is in the \(x_1, x_2\), and \(x_3\) fields) and for the analysis coordinate frame \(aid\).

Node Specific Variable Names:

Name	Description
xyz	Raw location <\(x_1, x_2, x_3\)> in the BDF
cp	reference coordinate system
cd	analysis coordinate system
Position	location in an arbitrary coordinate system
UpdatePosition	change the value of xyz and cp
resolveGrids	update all the positions of the grids to a common coordinate system in an more efficient way

Using the node object:

bdf = BDF()
bdf.readBDF(bdfName)
node = bdf.Node(nid)
node.Position()              % gets the position of the node in the global frame
node.Position(cid=0)         % same
node.Position(cid=1)         % gets the position of the node in a local frame

node.UpdatePosition(bdf,array([1.,2.,3.]),cid=3) % change the location of the node

bdf.resolveGrids(cid=0)      % change the xyz of all nodes to the same coordinate system as cid

bdf2 = BDF()
bdf2.readBDF(bdfNameAlt)
bdf.unresolveGrids(bdf2)     % change the coordinte system back to the coordinate system in bdf2

CORDx

A coordinate system may be defined by 3 points in any non-circular coordinate system or by 3 vectors.

Once cross-referenced a node may use it’s node.Position(cid) method to determine the position in any frame defined by a coordinate system.