What is FRF-based Curve Fitting?

FRF-based curve fitting is a process of matching a parametric model of an FRF An FRF (Frequency Response Function) is a cross-channel frequency domain function that defines the dynamic properties of a structure between an excitation Force and the Response caused by that force. An FRF is defined as the ratio (Response DFT / Force DFT). The FRF is a special case of a Transfer Function, where the response is the numerator (Output) and the force is the denominator (Input). (in a least squared error sense) to a set of experimental FRF data.

• The unknown parameters of the parametric model are modal frequency, damping & residues (mode shape components)

• The outcome of curve fitting is a set of modal parameters (frequency, damping & mode shape) for each mode that is identified in the frequency span of the experimental data.

After curve fitting is completed, mode shapes are stored into a Shape Table from which they can be displayed in animation on a 3D model of the test article.

Curve Fitting Steps

1. Determine the Number of Modes in a frequency band of measurement data

2. Estimate modal Frequency & Damping for all modes in the frequency band

3. Estimate modal Residues (mode shape components) for each mode and each measurement