Nonlinear and Non-stationary Vibration Analysis for Mechanical Fault Detection Using EMD-FFT Method

The Hilbert-Huang transform (HHT) is a powerful method for nonlinear and non-stationary vibrations analysis. This approach consists of two basic parts of empirical mode decomposition (EMD) and Hilbert spectral analysis (HSA). To achieve reliable results, Bedrosian and Nuttall theorems should be satisfied.Otherwise, the phase and amplitude functions are mixed together and consequently, the confidence of resultant frequencies are reduced. To prevent such an event, various methods entitled as improved Hilbert-Huang transforms have been proposed. Yet, another method is introduced in this paper that has ahigh ability to identify the mechanical defects easily. According to this method, the signal is decomposedto its intrinsic mode functions (IMFs) and then each of the IMF is analyzed by fast Fourier transform (FFT). Using the proposed method, which is called EMD-FFT, the mechanical defects of an electromotor have been detected in Kerman combined power plant. In addition, it is shown that theclassical FFT method is unable to detect all the defects because of nonlinear and non-stationaryproperties of the signals, and also use of the HHT method, regardless of satisfying the mentioned theorems, causes invalid results due to incorporation of phase and amplitude functions

Keywords:

Hilbert-Huang Transform , Fast Fourier Transform , Empirical Mode Decomposition , Bedrosian and Nuttall Theorems , Mechanical Fault Detection