Most of diagnostic systems of rotating machinery that is currently in service use symptom based approach. The need for system fault localisation indicates demand for application of structural model based approach. Operational Modal Analysis (OMA) method might be used in such Structural Health Monitoring systems. OMA method permits to achieve modal parameters based on output only measurements performed during operation for actual excitation and boundary conditions and can be applied in case when application of controlled vibration excitation is unpractical, technically difficult or even impossible. The presented case study comprises 4 industrial examples of use of OMA method for diagnostic purpose in case of a big fan and a high power gearbox. These examples deal with: structural design and assembly validation, description of mutual forced influence of closely localised machines and decomposition of a polyharmonic vibration response signal into harmonic components.
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