D3PLOT 22.1

FIX_NODE Fixing a Node Position Despite Displacements

In some circumstances a model may move a long way between successive states, and it can be inconvenient to have it progressively disappearing off the screen.

This figure shows a few frames during the assembly of an animation of a dummy sled test analysis.

In these tests the sled is pulled backwards to mimic the deceleration during a crash, and it moves off the screen as a consequence. So a simple translation to bring it back to the undeformed position will suffice.

This second figure shows what happens when a node in the dummy's pelvis is fixed using FIX_NODE.

The FIX_NODE facility allows you to specify a node that remains fixed at its undeformed position, regardless of any displacements that may occur. This is implemented by finding the displacement vector of the node at each complete state, and subtracting that vector from the coordinates of every node in the model. In the example above one would fix a node on the sled, which would then appear to be fixed in space, and simply see dummy motion within it.

(If a rotation as well as a translation is required you can use SHIFT_DEFORMED instead: see SHIFT_DEFORMED Translating and rotating a model back to its undeformed position .)

This figure shows the FIX_NODE control panel in its default state: no node is fixed.

To fix a node PICK it, or type in its label. Once defined this mode can be switched on or off.

FIX_NODE applies a model space offset to what is drawn: it is a translation of the model, updated for each state.

(It is not the same as VIEW, CN (Centre on node) which is a purely graphical transformation that sets the viewing centre for rotations.)

Note 1:	FIX_NODE (which applies a translation) and SHIFT_DEFORMED (which applies both a rotation and a translation) are mutually exclusive: you can only have one or the other active at one time.
Note 2:	The node used in FIX_NODE (which affects the graphical displacements) is the same as that used as a single REFERENCE_NODE (which affects the contoured and reported values). They may be used separately or together.
Note 3:	FIX_NODE can be used at the same time as "explosion" vectors and magnified displacements: see Note 3 in Notes on explosion vectors for the order of application.

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