Select Poles Task

In the Select Poles task, the poles are selected from the stability diagram. The poles for the default residuals order are selected automatically when entering this task. The FRF synthesized for the selected residuals order is compared to the measured FRF to evaluate the estimated modal parameters. The FRF that is plotted is the function selected for parameter estimation and cannot be changed in this task. Information about the FRF dataset is displayed in the Info panel. Hovering the mouse pointer over AFU Name will show some additional information about the FRF dataset.

Stability Diagram – The stability diagram is generated by comparing the computed poles and vectors for successive residuals orders. If the difference in frequency is within the Frequency tolerance (as a percent difference), the Frequency is considered stable. If the difference in damping is within the Damping tolerance (as a percent difference), the Pole (frequency and damping) is considered stable. If the vectors associated with these two poles are within the Vector tolerance (as a MAC, or unity-length normalized vector inner-product), the Pole & Vector are considered stable. The vectors used for the stability comparison are the residues computed using the same generalized residuals polynomial.

If the number of modes is greater than one, the two poles that are closest in frequency are found and the same tolerance comparison described above is applied. Then these two poles are then removed from the sets of poles, and the process is repeated until all poles meeting the stability conditions are evaluated.

A marker for every computed pole will always be plotted. If the pole does not satisfy any of the stability criteria described above, the marker may indicate that the frequency is out-of-band, the damping is negative, or that it meets none of these criteria. The symbol and color of the pole markers for the stability conditions are set in the Plot Stability panel of the Preferences dialog.

Pole picking is activated by selecting Pick Poles from the axes context menu or by pushing the Pick Poles icon on the toolbar. Panning and pole picking are mutually exclusive, as only one can be active at a time, but switching directly between them is possible. Cursors cannot be added, deleted, or moved while peak picking or panning is active.

Poles are selected from the stability diagram using a cross-hairs cursor with an open area at the center. The currently highlighted pole marker is outlined in red. How close to a pole marker the cursor must be to highlight it is determined by the Pick Pole Cursor Tolerance, which set in the Preferences dialog. Information about the highlighted pole (residuals order, frequency, and damping) is displayed in the white frame at the lower right corner of the module. The highlighted pole is selected or deselected by clicking the left mouse button. Selecting any pole for a residuals order selects all poles for that order and deselects the other orders. The selected poles are added to the Poles List, and deselected poles are removed from the Poles List. The pole marker is filled if the pole is in the Poles List, and empty if it is not in the Poles List. If a selected pole is highlighted, pressing the middle mouse button will animate that mode shape if a TDM has been imported.

The FRF synthesized from a rational fraction polynomial model with generalized residuals is plotted with a thick solid line on the lower (magnitude or imaginary) and upper (phase or real) axes. The FRF synthesized from a rational fraction polynomial model that has been deconvolved from the generalized residual polynomial is plotted with a thick dashed line.[2] Sometimes the FRF synthesized with generalized residuals can have an arbitrary phase wrapping such that the phase is shifted by a multiple of 360 from the phase of the measured FRF. There are selections on the upper axes "Phase (deg)" y-label context menu to shift the phase of the synthesized FRF by ±360˚.

Poles List – The poles from the selected order are added to the Poles List, which is the table in the lower left side of the GUI listing the frequency and damping of the selected poles. The check boxes in the Poles List determine if a pole is returned in the results or sent to the animator. The rows of the Poles List can be selected with the mouse. Clicking in the Poles List and pressing Ctrl+A will select the entire list. The Animate button will send the mode shapes of the checked poles to the animator. If the Animate Back-Expanded Shapes check box is checked, then the shapes will be back-expanded when sent to the animator. A pole can be edited by selecting only one pole in the Poles List and pressing the Edit button. An input dialog GUI is presented, as shown below, to edit the frequency and damping values of the pole.

The Poles List has a context menu to check all or check none of the poles, list the checked poles in a table dialog, or to reset edited poles to the as-computed values. The frequency and damping of the checked the poles can be listed vertically or horizontally in a table dialog. Selected table cells can be copied with either Ctrl+C or by right-clicking on the table for a context menu. The contents of the copied cells can then be pasted as tab delimited text.

Plot Function – The only Plot Function is FRF. The colors of the measured (SDOFit MIF) and synthesized (SDOFit Synth) FRF plotted on the stability diagram are set in the Plot Stability panel of the Preferences dialog. The synthesized FRF and pole markers will be cleared from the plot whenever the stability tolerances are entered or a pole is edited. Push the Apply button to update the plot.

Stability – Enter the tolerance for stability criterion (Frequency, Damping, and Vector), as a percent.