It is defined using three optimization parameters (OPT_PARAM):
MODETRACKING = <on/off>, <node_group>
MODENUMBERS = <number_modes>
MODETRACK_REFERENCE = INITIAL | PREVIOUS
Mode tracking is activated using the optimization parameter MODETRACKING= ON.
The second item in MODETRACKING defines the node group that is used for
the mode tracking. The node group can improve performance when the node group is small.
If no node group is defined all nodes in the model will be applied as default. This is
reasonable for small- to medium-sized finite element models. By default the mode
tracking applies for 5 modes. This can be changed by the item MODENUMBERS =
<number_modes>. This number should not be set too high otherwise the
CPU-time might have a significant increase.
Using the parameter MODETRACK_REFERENCE for the Modal Assurance Criterion (MAC)
allows the user to define the reference modes applied when tracking the modes during the
optimization iterations. If the parameter MODETRACK_REFERENCE is set to
INITIAL, the reference modes are set to be the modes of the initial
optimization iteration throughout the entire optimization history. If the parameter
MODETRACK_REFERENCE is set to PREVIOUS, the
reference modes are always set to be the modes of the previous optimization
iteration.
Typically, setting MODETRACK_REFERENCE to INITIAL is the most
consistent comparison in the mode tracking. However, some initial modes might change
significantly or completely disappear during the optimization iterations and, thus, the
INITIAL comparison might fail. When the INITIAL
setting for MODETRACK_REFERENCE is failing, the only option is to apply
PREVIOUS even though the comparison might not be as consistent as
INITIAL.