Fig. 1. Testing equipment

Fig. 2. Time-domain waveforms of the flywheel acoustic signals

Fig. 3. 3D waterfall diagram of the flywheel acoustic signals under acceleration

Fig. 4. Flow chart of the identification process for the flywheel during the high-energy frictional period

Fig. 5. Time-frequency diagram of the flywheel high-energy friction acoustic data

Fig. 6. Frequency band energy curve of the flywheel high-energy frictional acoustic data

Fig. 7. Detailed variations diagram of the frequency band energy curve of the flywheel high-energy frictional acoustic data within a specific time interval

Fig. 8. Result of Gaussian smoothing processing

Fig. 9. Histogram of the calculation results for the data indices of the flywheel in high-energy friction periods

Fig. 10. Flow chart of flywheel fault diagnosis