Cyclostationarity and the cepstrum for operational modal analysis of mimo systems - Part I: Modal parameter identification

This paper presents a new technique for operational modal analysis (OMA) of multiple input multiple output (MIMO) systems excited by at least one cyclostationary input with a unique cyclic frequency. The technique is based on two signal separation steps; the cyclostationary properties of the input are exploited to estimate the cyclic spectral density, effectively reducing the system from a MIMO to a single input multiple output (SIMO) situation, and curve-fitted in the cepstrum domain, which allows for the separation of the input and transfer function. This technique is demonstrated using measurements taken on a steel beam test rig and a passenger rail vehicle. The performance of this technique is discussed and compared to traditional input/output modal analysis and an existing cepstrum-based OMA technique. It is shown that the technique is able to correctly identify modal parameters, but like other spectrum-based OMA techniques, long time records are required in order to obtain both smooth cyclic spectrum estimates and sufficient resolution for accurate damping estimates. The nature of the input may also inhibit its performance in the very low-frequency region. (c) 2006 Elsevier Ltd. All rights reserved.