## 5 Experimental Result and Analysis  
### Experimental Rig and Data Description  
The experiments were carried out on a Bently RK-4 rotor test bed as displayed in Figure 13a,b shows the structure diagram of the test bed. As can be seen from Figure 13, the test stand is an oil-fluid supporting rotor bearing system, which is mainly built with a motor, a shaft, two discs, several mounting blocks for probe and rub screw, two bearings and a speed regulating device. The test bed can be adopted for simulating some common rotor faults such as rubbing, imbalance and oil film instability failures (see [PERSON] et al. [35] and [PERSON] et al. [36]). During the experiments, a key phase senor was arranged near the rotating shaft to acquire the rotation speed information. Two sets of eddy current sensors which were installed on two mounting blocks were employed to collect the vibration signals of the shaft.  
Figure 13: (**a**) Bently RK4 rotor experimental rig; (**b**) its structure diagram.  
To verify the validity of the proposed method, four kinds of rotor fault types, which include normal state, rubbing, oil film whirl and imbalance fault were simulated using the experimental rig. Specifically speaking, a single disk was installed on the shaft for the normal, rubbing and imbalance rotor states simulation. Two bearings were symmetrically arranged on both sides of the disk. The first-order critical speed of the experimental rig is about 1890 rpm. As the working speed of many practical machines, such as the steam turbine, is above the first-order critical speed, the rotation speed of the normal state in this paper was set as 3000 rpm and the test rig was not subjected to any abnormal forces. Since the local rubbing fault is more common than the full rubbing fault, the rotor/stator local rubbing was simulated in the experiment. Figure 14 displays the schematic diagram of rubbing. A rub screw installed on a mounting block was adjusted to touch the shaft to simulate the rub process. The rotation speed for the rubbing sate simulation was kept as 1760 rpm. The rotor imbalance state was simulated by installing counterweight bolts on the disc. The counterweight is 1 g and the rotation speed of the imbalance was set as 1500 rpm. The occurrence of oil film whirl needs to satisfy two conditions: (1) the rotation speed is above a certain speed, which is usually the first-order critical speed; (2) the oil film force is instable. When simulating the oil film whirl state, the following equipment, i.e., oil pump assembly, oil lubricating system, rotor kit shaft with oil journal bearing and preload frame, were required to achieve the instable oil film force. The way this equipment was linked is shown in Figure 13b. Two disks were installed on the shaft for simulating the oil film whirl fault. The rotation speed increased from zero by adjusting the motor and light oil film whirl began to appear at the speed of 1800 rpm. The oil film whirl signal at the speed of 3000 rpm was collected for analysis. The corresponding rotation frequency of the normal, rubbing, oil film whirl and imbalance states can be calculated to 50 Hz, 29.33 Hz, 50 Hz and 25 Hz, respectively. The sampling frequency is 1280 Hz. To evaluate the classification accuracy of the proposed method, the vibration signal of each fault type was dived into 40 samples and the sampling number of each sample is 2048. Among the 40 samples of each rotor state, the former 20 samples were selected as the training sample sets and the other 20 samples were employed as the test sample sets.