Category: ABRAVIBE Examples

This example compares the three currently available options to the frf2ptime command; ‘prony’, ‘lsce’, and ‘ptd’. It can serve as a reference for how to use these three options.

The example uses the same synthetic data for the Plexiglass plate that the Plexi Modal Example uses, but comes with the data to make it independent of the previous example.

The ABRAVIBE example ForcedResponse is illustrating the power of the digital filter forced response method for computing forced response developed by Kjell Ahlin and published in, among other references, “Noise and Vibration Analysis: Signal Analysis and Experimental Procedures,” by Anders Brandt. The method uses a modal superposition formulation using
a ramp invariant transform to formulate the forced response of each mode. Also see inside the ABRAVIBE command timefresp for references to original papers.

The example produces time data simulating a measurement of 35 displacement responses on a Plexiglass plate, when it is excited with four forces in the corners of the plate. Mode shapes and eigenfrequencies from a finite element model are used as a model for the plate.

This is an example of using ABRAVIBE for OMA. It uses synthesized data of the Plexiglas plate, and the modified Ibrahim Time Domain Method (MITD) which is virtually identical to the more known (Covariance-based) Stochastic Subspace Identification, SSI. MITD predated SSI by many years, however.

The ABRAVIBE example PlexiODS is an example using synthesized data
generated from a modal model of a Plexiglas plate (incidentally, by the
example called ForcedResponse) to illustrate operating deflection shapes
(ODS) analysis in ABRAVIBE. This is an advanced example including
multiple-reference ODS to be able to separate two close modes! The
example is divided into two parts, the first a single-reference technique
and the second an extended multi-reference technique.

The ABRAVIBE example PlexiModal is an example of using the ABRAVIBE
toolbox to do experimental modal analysis of a Plexiglass plate using measured data.

The example uses data measured using impact testing, and the
polyreference time domain (PTD) method with two references, to be able to
estimate the first two modes which are strongly coupled on this plate.
The example shows all involved steps such as importing and sorting data,
curve-fitting for poles and mode shapes, and evaluating the results with
a MAC matrix and animation of the modes.

This example is good to use as a template for all modal analysis tasks
with the ABRAVIBE toolbox; just replace the data imported, and the
geometry created before animation, to use the script for your modal
analysis tasks!

This is a complete example of finite element model verification and calibration (sometimes known as correlation).

The example uses a finite element model built in the free CALFEM toolbox and experimental modal analysis results of the Plexiglas plate used throughout ABRAVIBE as an example structure. The idea of this example is to be simple and illustrative, so that the techniques are not hidden by practical difficulties. The example includes verification of mode shapes using the MAC matrix and frequency tables, and calibration by adjusting the Young’s modulus to adjust the first bending mode of the FE model to fit the experimental data. You can download a paper from Sound and Vibration describing the example.