VT-960 Visual OMA™
The Visual OMA™ package combines all of the features of a Visual Modal™ package with the features of the VES-4700 Operational Modal Analysis option. For cases where the excitation forces cannot be measured and output-only responses can be acquired, modal parameters can still be extracted from a set of specially processed Cross Spectra or ODS FRFs.
The Operational Modal Analysis option adds special windowing and other features to a Visual Modal™ package, thus providing a complete set of tools for extracting modal parameters from measurements made in any type of testing environment.
Modal parameter estimation (curve fitting) is done in three steps; 1) count the number of modes using a Mode Indicator function, 2) estimate the modal frequency & damping for each mode, 3) estimate a modal residue (a mode shape component) for each mode & each measurement.
VT-960 Visual OMA™
Visual OMA™ Features:
- Deconvolution window. When this window is applied to a set of Cross Spectra or ODS FRFs, operational modal parameters can be extracted from them using FRF-based curve fitting methods
- Mode shape scaling. A modal model (a scaled set of mode shapes) can be created from a set of output-only operational mode shapes
- Mode Indicators for counting modes. Either a Complex Mode Indicator Function (CMIF) or a Multivariate Mode Indicator Function (MMIF) can be calculated, and all resonance peaks are counted above a scrollable noise threshold
- Frequency & damping curve fitting. Either the Local or the Global MDOF Orthogonal Polynomial method can be used, with extra polynomial terms to compensate for out-of-band modes
- Residue curve fitting. Either the MDOF Orthogonal Polynomial method or the SDOF Peak cursor method can be used
- Quick Fit. Automatically executes all three curve fitting steps with minimal user interaction
- Frequency & damping estimates are graphically indicated on the Mode Indicator graph
- A curve fit function is synthesized and overlaid on each measurement to graphically confirm each curve fit
- Selected measurements and frequency bands can be used to improve modal parameter estimates
- All modal parameter estimates and curve fitting functions are saved with each measurement
- FRFs can be synthesized using modal parameters
- Modal Assurance Criterion (MAC). A bar graph and spreadsheet of the MAC values between all mode shape pairs. If MAC = 1, two shapes are the same. If MAC < 0.9 two shapes are different.
- Shape Difference Indicator (SDI). A bar graph and spreadsheet of the SDI values between all mode shape pairs. If SDI = 1, two shapes have the same values. If SDI < 0.9 two shapes have different values
- Modal Participation. Displays the Real part, Imaginary part, and Magnitude of the modal participation factors that result when a set of shapes is curve fit to another set of shapes.
- Modal parameters can be imported & exported using the Universal File Format (UFF)
- Mode shapes can be imported from Ansys, Emerson Process Management (CSI), FEMAP, LMS, I-DEAS, NASTRAN, Ono Sokki, Rockwell Automation Emonitor, Spectral Dynamics Star disk files
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Operational Modal Analysis
This video illustrates the curve fitting capabilities of the Operational Modal Analysis Option in ME’scopeVES. To simulate an OMA, a “round trip” is performed using a modal model. The MIMO Simulator in the Acquisition window is used to “excite” the modal model of the structure with a random force. Acceleration Cross spectra are then “acquired” and curve fit to recover the modes of the modal model.
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