# Weak Fault Feature Extraction and Enhancement of Wind Turbine Bearing Based on OCYCBD and SVDD
## 5 Experiment Verification
### Experimental Signal Analysis and Result Comparison  
Figure 8 displays the waveform of experimental signal as well as its spectra. There exists obvious impact phenomenon in the waveform, while the interval between adjacent impacts isn't the reciprocal of any fault feature frequency. The frequency components are mainly concentrated below 2500 Hz and there exists broad resonant band in the frequency spectrum. However, the spectral line related to bearing defect can't be found in the low frequency region. The traditional envelope spectrum analysis is also executed, but there exist a large number of unknown spectral lines except for feature frequency component in the envelope spectrum. Then the presented method is applied for analyzing this experimental signal. Firstly, the precise influencing parameters of CYCBD need to be selected. During the process of parameter optimization, the fast spectral coherence is calculated as shown in Figure 9a to determinate the search center of cyclic frequency, from which we can find the energy distribution is largest when cyclic frequency is 114.7 Hz (the red block indicated by green arrow), then the search center \(a^{M}\) is confirmed to perform more elaborate search process. As the cyclic frequency resolution of fast spectral coherence \(\Delta f=1.572\) Hz, then the search scope is set as \([a^{d},a^{E}]=[\)floor (114.7\(-\)1.572), ceil(114.7 + 1.572)\(]=[\)113 Hz, 117 Hz\(]\) with search step size of 0.05 Hz. The MFWEE values corresponding to different cyclic frequencies within the search scope are illustrated in Figure 9b. And the optimal parameter \(a^{o}=115.7\) Hz can be automatically confirmed in terms of MFWEE minimum value. Then the filter length parameter is further optimized on the basis of \(a=a^{o}\), and the search scope is set as [20,200] with search step size of 1. The FWEE indicators of deconvolution signals, which are obtained by CYCBD with different filter lengths and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of Balls** & **Diameter of Balls (mm)** & **Pitch Diameter (mm)** & **Contact Angle (\({}^{o}\))** \\ \hline
9 & 7.94 & 39.04 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Structure parameters of SKF6205 bearing. Figure 7: The experimental site: (**a**) The structure of experimental platform; (**b**) The roller fault bearing; (**c**) The installed PCB acceleration sensors; (**d**) The data acquisition system. optimal cyclic frequency \(a^{o}=115.7\), are shown in 9c. And the optimal filter length parameter \(L^{o}=117\) can also be chosen according to FWEE minimum value. Then the optimal parameters \(a^{o}=115.7\) and \(L^{o}=117\) are substituted into CYCBD to recover the fault source from the original signal, and the acquired deconvolution signal is displayed in Figure 9d. Secondly, FWEO operation is further carried out to gain the instantaneous energy signal of deconvolution result, in which the impulsive phenomenon is amplified to a certain extent. Thirdly, SVDD is performed on the instantaneous energy signal to get rid of the influence of interference components. And the fitting error minimum principle is applied to adaptively select the effective singular value order during denoising process. In order to present the result more clearly, Figure 9e only displays the former 150 singular value orders and the corresponding fitting error values. As marked in this figure, the 24 th singular value order is considered as the diacritical location of the available and the useless singular values. Therefore, the former 24 singular values except for the first one are adopted to construct the purified instantaneous energy signal. Finally, after performing spectrum analysis on the denoised instantaneous energy signal, the enhanced energy spectrum of deconvolution signal is obtained. In Figure 9f, the fault related spectral lines \(fe\sim 8 fe\) with obvious peaks are able to be presented distinctly. Thus, we can determinate that there exists local flaw in the ball, and this conclusion is consistent to the actual condition.