ON THE PROBLEM OF STOCHASTIC EXPERIMENTAL MODAL-ANALYSIS BASED ON MULTIPLE-EXCITATION MULTIPLE-RESPONSE DATA .2. THE MODAL-ANALYSIS APPROACH

In this part of the paper the stochastic multiple-excitation multiple-response experimental modal analysis problem is considered. The relationship between the actual structural and noise dynamics and their discrete special-form ARMAX-type representation is studied for each one of the vibration displacement, velocity and acceleration data cases, and a novel and effective modal analysis approach is introduced that, unlike previous schemes, is capable of operating on any one of these types of data records. By accounting for issues such as the required excitation signal type and stochastic model form, algorithmic instability occurrence and other well-known estimation difficulties, model structure estimation and model validation, as well as model reduction and analysis based on the dispersion analysis methodology introduced in the first part of the paper [1], the proposed approach not only overcomes the limitations and drawbacks of current schemes but also constitutes the first comprehensive procedure for stochastic multiple-excitation multiple-response experimental modal analysis. The effectiveness of the approach is demonstrated through numerical experiments with structural systems characterized by well-separated and closely spaced modes, and data records of various lengths and signal-to-noise ratios. Comparisons with the classical frequency domain method and the deterministic eigensystem realization algorithm are also made, and the approach is finally used for the experimental modal analysis of a three-span beam from laboratory data. © 1993 Journal of Sound and Vibration.