Operational modal analysis with cepstral methods and its application to washing machines

This study aims to extract the natural frequencies and mode shapes of washing machines during operation using only vibration responses. To ensure the quality and detect defects, selected mass-produced washing machines are evaluated based on their vibrational characteristics. This process involves conducting modal experiments in a stationary state and operating the products under various extreme conditions for prolonged periods to assess their condition. If the vibration characteristics and modal parameters of the structure can be concurrently verified during operation, it could significantly save time and cost. Therefore, this research utilizes Operational Modal Analysis (OMA) techniques to identify the structural modal parameters through vibration responses alone. Specifically, the operation of washing machines not only involves primary operating frequencies but also slight frequency variations during operation. These manifest in the frequency domain as the primary operating frequency, its harmonics, and sidebands. These components interfere with the application of conventional OMA techniques, necessitating their removal. For this purpose, cepstral techniques were applied as a preprocessing step before applying OMA techniques in this study, and the employed cepstral techniques were evaluated through the extracted modal parameter results.