Clicking the Optimize # DOF button on the main GA form will bring up the Optimize Number of DOF form, shown in Figure 13. This form allows the user to study the effects of iteratively removing the least important DOF/triax from the initial set to examine the trend in the TAM's cost and any other result metric (Pseudo-Orthogonality, Cross-Orthogonality, XMAC, or frequency comparison). The purpose of this form is to allow the user to quickly identify those DOF that contribute the least to the quality of the TAM in order to eliminate those DOF from the accelerometer set. If GA results exist when the Optimize # DOF button is clicked then the GA set will be the initial set. If no GA results exist, the user is required to import a DOF set using the Import ASET button at the bottom of the form.
By default the form will plot the cost sensitivity of reducing the initial DOF set down to two-thirds of its initial size by iteratively removing the least important individual DOF. The importance of each DOF/triax is calculated using the rank calculation as described in Viewing Results. The user can change the Min DOF entry and can also use this algorithm to iteratively remove triaxial locations if the Optmize Triaxs? checkbox is selected. Optimizing the number of triaxes requires that the input DOF set selected triaxes.
With the desired parameters set, the next step is to click the Calc DOF Sensitivity button to generate the blue curve in the axis. Each datapoint in this curve is created by iteratively calculating the rank (importance) of each individual DOF/triax and removing the DOF/triax with the lowest rank and calculating the cost of the resulting TAM. The cost is based on the target modes, weighting, and cost function specified in the main GA form and uses all FEM configurations that are loaded to the main GA form. The ranking process is repeated until the number in the Min DOF field is reached. For large models with a large number of starting DOF this may take a few minutes.
For the blue curve shown in Figure 13 there is very little change in the cost down to 55 DOF. To examine the TAM metrics of this DOF set the Select NDOF button is clicked, which brings up a set of crosshairs to let the user select the desired DOF set from the axis. Once a set is selected, a red box is placed on the plot and the items in the Results panel becomes active. These buttons allow the user to plot the TAM metrics previously described in Viewing Results. To select a different DOF set simply click Select NDOF again and pick a different value from the axis.
The Export ASET and Export XML buttons on the bottom-left of the form write Nastran ASET cards and XML reports of the selected DOF, providing the same functionality available from the main GA form in the Export menu option.