SDOFit: Single Degree Of Freedom Modal Parameter Estimation Application User Guide

Introduction

As the name might imply, SDOFit™ is a single degree of freedom (SDOF) modal parameter estimation (or “curve-fitting”) IMAT™ application. The algorithm is a single-input, single-output, frequency domain, rational fraction polynomial model with generalized residuals. It will estimate the frequency and damping of modes in a narrow frequency band from a single frequency response function (FRF). The residuals are included in the model to account for the out-of-band modes. Although it is primarily intended as an SDOF method, it will allow more than one mode to be included in the model, as there are occasions that this approach will yield better results. The details of this method can be found in reference [1].

SDOFit is implemented as an AFPoly™ tool and the FRFs, coordinate traces, test display model (TDM), and test-analysis model (TAM) are sent from AFPoly into SDOFit. The FRF dataset will include the references and responses in the sieve defined in AFPoly Setup. The coordinate traces can be used for filtering the listed responses, the TDM is used for animating mode shapes, and the TAM is used for mode shape back-expansion. The results (poles, residue vectors, and participation factors) returned from SDOFit are incorporated into the AFPoly stability diagram.

The SDOFit process consists of three tasks. First an FRF from which to estimate modes is chosen and the frequency band around the mode of interest is selected. Next, the poles are computed and a stability diagram is generated, not by varying the number of modes, which would defeat the purpose of an SDOF method, but by varying the order of the residuals polynomial. Then the results are selected and returned to AFPoly.

This user guide will explain the SDOFit IMAT application procedures and features.

 

SDOFit, AFPoly and IMAT are trademarks of ATA Engineering, Inc. Other trade names are trademarks of their respective organizations.