An Extended Operational Modal Analysis Method Enabling the Separation of Whirling Direction Information in Rotating Machinery (Full Operational Modal Analysis Method)

Abstract Operational Modal Analysis (OMA) has recently been applied to the condition monitoring of rotating machinery. However, only one previous report has addressed the application of OMA to rotating machinery with the capability of separating whirling direction information, and this approach requires an excitation signal. In this study, a novel OMA method, referred to as Full OMA, has been developed to separate whirling direction information without the need for an excitation signal. To achieve this, signal data in both the x and y directions are acquired, and their auto-correlation and cross-correlation functions are calculated and combined as complex numbers. Spectral analysis of these functions yields a pseudo Full Frequency Response Function (FRF), from which modal parameters for each whirling direction can be estimated. The validity and usefulness of the proposed Full OMA method have been confirmed through both theoretical analysis and experimental validation. This Full OMA method enables the accurate estimation of vibration characteristics for each whirling direction, even when the forward and backward natural frequencies are in close proximity. Consequently, the proposed Full OMA method is highly effective for monitoring and diagnosing rotating machinery.