Step 4: Validation

The validation step provides tools to verify the extracted modal parameters through visualization, cross-checking, and comparison with measured data. A thorough validation ensures that the identified modes are physically meaningful and accurately represent the structure's dynamic behavior.

3D Mode Shape Animation

The primary validation tool is the animated 3D mode shape display. Each extracted mode is visualized as a deformed geometry, oscillating at the mode's natural frequency.

Animation Controls

Control	Shortcut	Description
Play / Pause	`Space`	Start or pause the mode shape animation.
Speed	`+` / `-`	Increase or decrease the animation speed. Range: 0.1x to 10x real time.
Scale	`Ctrl+Up` / `Ctrl+Down`	Increase or decrease the deformation amplitude scale factor.
Phase	`Left` / `Right`	Step through individual phase frames (when paused).
Reset View	`Home`	Reset camera to the default orientation.

Displacement Color Mapping

The deformed geometry is color-coded by displacement magnitude:

Color	Meaning
Blue	Minimum displacement (nodal region).
Green	Intermediate displacement.
Yellow	Moderate displacement.
Red	Maximum displacement (anti-nodal region).

The color scale range is set automatically based on the maximum modal displacement, or it can be fixed manually via the Color Scale settings.

Layout Presets

The validation workspace supports multi-viewport layouts for side-by-side mode comparison:

Preset	Viewports	Use Case
1 x 1	1	Single mode, detailed inspection.
1 x 2	2	Compare two modes side by side.
2 x 2	4	Four modes for quick overview.
2 x 3	6	Six modes for dense comparison.
3 x 3	9	Nine modes for full modal survey review.

Assigning Modes to Viewports

Select a layout preset from the Layout dropdown in the toolbar.
Drag a mode from the selected modes table and drop it onto a viewport.
The viewport immediately shows the animated mode shape with frequency and damping labels.
To replace a mode, drag a different mode onto the same viewport.
To clear a viewport, right-click > Clear Viewport.

Camera Synchronization

When comparing multiple modes, enable Camera Sync (toolbar toggle or Ctrl+L) to lock all viewport cameras together. Orbiting, panning, or zooming in one viewport applies the same transformation to all others, ensuring consistent viewing angles.

MAC Matrix

The Modal Assurance Criterion (MAC) matrix quantifies the correlation between mode shapes. It is displayed as a 3D bar chart where each bar height represents the MAC value between two modes.

MAC(i,j) = |{φ_i}^H {φ_j}|² / ( {φ_i}^H{φ_i} · {φ_j}^H{φ_j} )

Interpretation

MAC Value	Interpretation
0.9 – 1.0	Mode shapes are highly correlated. On the diagonal, this is expected. Off-diagonal, it indicates possible duplicate modes or insufficient spatial resolution.
0.1 – 0.9	Partial correlation. Off-diagonal values in this range may indicate closely spaced modes with spatial coupling.
0.0 – 0.1	Mode shapes are independent. This is the desired result for off-diagonal elements.

Tip: A well-identified modal model should have diagonal MAC values close to 1.0 and off-diagonal values below 0.1. If two modes have a high off-diagonal MAC (>0.5), consider whether they are actually the same mode selected at two different model orders.

Auto-MAC vs Cross-MAC

Auto-MAC: Compares the extracted mode shapes against themselves. Used to check mode orthogonality and detect duplicates.
Cross-MAC: Compares extracted modes against a reference set (e.g., from a previous test or an FE model). Used for model correlation.

FRF Comparison (Measured vs Synthesized)

The FRF synthesis tool reconstructs the FRF from the identified modal parameters and overlays it with the original measured FRF. Good agreement validates the completeness and accuracy of the modal model.

How to Use

Select an FRF channel from the dropdown (or click a DOF on the geometry).
The measured FRF is shown in blue and the synthesized FRF in red.
The residual (difference) is shown in gray at the bottom of the plot.
Toggle between Magnitude, Phase, Real, and Imaginary views.

What to Look For

Good fit at resonances: Peaks in the synthesized FRF should match the measured FRF in both frequency and amplitude.
Anti-resonances: The synthesized FRF should reproduce anti-resonance dips, especially for driving-point FRFs.
Residual magnitude: Small residuals across the frequency range indicate a complete modal model.
Missing modes: Large residuals at specific frequencies suggest modes that were not selected.

Important: If the synthesized FRF deviates significantly from the measured FRF in a frequency region, return to the stabilization diagram and check for unselected stable poles in that region.

Export Options

The validation results can be exported in multiple formats for reporting and downstream analysis:

Format	Content	Use Case
AVI Video	Animated mode shape recording with color mapping and labels.	Presentations, reports.
PNG Image	High-resolution screenshot of the current viewport(s).	Technical reports, publications.
Excel (.xlsx)	Modal parameters table (frequency, damping, MPC, Quality Score) and MAC matrix values.	Data exchange, tabular comparison.
UFF Type 55	Mode shape data in Universal File Format.	Import into other modal analysis packages (ME'scope, FEMtools, ANSYS).
HTML Report	Self-contained HTML report with embedded images, tables, and MAC chart.	Stakeholder distribution, archiving.

Exporting

Click Export in the toolbar.
Select the desired format(s) from the export dialog.
Choose the output folder and filename.
For AVI export, configure resolution (720p, 1080p, 4K) and frame rate (15, 30, 60 fps).
Click Export to generate the files.

Tip: The HTML report format is ideal for sharing results with colleagues who do not have V-Listen installed. It includes interactive tables and static images of all validated mode shapes.

Validation Workflow Summary

Animate each selected mode and verify that the mode shape is physically plausible.
Check the MAC matrix for diagonal dominance (no duplicate modes).
Compare measured vs synthesized FRFs for at least 3–5 representative DOFs.
If issues are found, return to mode selection and adjust.
Export results in the required formats.