# A Research on Fault Diagnosis of a USV Thruster Based on PCA and Entropy
## 3 Experimental Validation of Selected Fault Features
### Results of the Water-Tank Experiment  
The data obtained in the experiments under the normal condition and each fault condition of the thruster were classified into Case 1 and Case 2, according to the battery voltage, and the mean values and range of values for each data type are summarized in Table 2.  
Using the data outlined in Table 2, the vibration data are illustrated as a graph in Figure 6; evidently, the vibration value under all the fault conditions was higher than that under the normal condition. In addition, the current and RPM data are illustrated in Figure 7. As shown by the data in Table 2 and Figure 7, under the fault condition of breakage, the consumed current decreased and the RPM increased according to the severity of the fault. Furthermore, under the fault condition of entanglement, the consumed current increased and the RPM decreased with the increasing severity of the fault. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fault** & **Case** & **Battery Voltage (V)** & **Input Voltage (V)** & **Consumed Current (A)** & **RPM** & **Vibration (g)** \\ \hline \multirow{2}{*}{Normal} & Case 1 & 28.10 & 18.87 & 16.46 & 821 & \(-\)0.1231\(-\)0.1327 \\  & Case 2 & 28.76 & 19.21 & 17.03 & 843 & \(-\)0.1359\(-\)0.1487 \\ \hline \multirow{2}{*}{1 cm breakage} & Case 1 & 28.06 & 18.58 & 16.78 & 811 & \(-\)0.2103\(-\)0.2062 \\  & Case 2 & 28.65 & 19.11 & 17.43 & 829 & \(-\)0.2041\(-\)0.1995 \\ \hline \multirow{2}{*}{2 cm breakage} & Case 1 & 28.42 & 18.58 & 16.11 & 822 & \(-\)0.3053\(-\)0.3010 \\  & Case 2 & 28.55 & 18.77 & 16.58 & 835 & \(-\)0.2665\(-\)0.2751 \\ \hline \multirow{2}{*}{3 cm breakage} & Case 1 & 28.02 & 18.53 & 14.71 & 842 & \(-\)0.2290\(-\)0.2685 \\  & Case 2 & 28.48 & 18.74 & 15.13 & 850 & \(-\)0.2463\(-\)0.2774 \\ \hline \multirow{2}{*}{Thin rope} & Case 1 & 28.65 & 19.07 & 19.36 & 643 & \(-\)0.1738\(-\)0.1686 \\  & Case 2 & 28.33 & 18.71 & 22.66 & 752 & \(-\)0.2106\(-\)0.2307 \\ \hline \multirow{2}{*}{Thick rope} & Case 1 & 28.49 & 18.50 & 27.36 & 706 & \(-\)0.5724\(-\)0.5654 \\  & Case 2 & 28.22 & 18.13 & 30.61 & 658 & \(-\)0.4944\(-\)0.4510 \\ \hline \multirow{2}{*}{Net} & Case 1 & 28.43 & 18.36 & 28.23 & 692 & \(-\)0.2012\(-\)0.1951 \\  & Case 2 & 28.09 & 17.64 & 41.11 & 483 & \(-\)0.3771\(-\)0.3737 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Water-tank experiment results for normal and fault conditions. Figure 6: Vibration data for each condition. A more detailed analysis of the data change in Table 2 revealed that the magnitude of vibration generally increased under fault conditions. The increase was more pronounced under the conditions of 2 cm and 3 cm breakage compared to the condition of 1 cm breakage. There was no significant difference in the magnitude of vibration under the conditions of 2 cm and 3 cm breakage. However, under the breakage conditions, as the fault worsened, the consumed current slightly decreased, unlike the RPM, which increased slightly. This was attributed to a decrease in the diameter and area for pushing away the fluid. Under the fault condition of entanglement, the general trend indicated that the consumed current increased and the rotation speed decreased. The fault was more severe in the thick rope compared to the thin rope. Compared to the net condition, it was observed that the current consumption and RPM increased noticeably in the entanglement condition. In addition, the current value in the case of entanglement was higher when the net was involved than when the rope was involved because the net had a larger water-repellent surface area and was more flexible under the entanglement condition, resulting in a more significant change in the consumed current than in the vibration. Finally, it can be observed from the input voltage data in Table 2 that the input voltage also changed according to the battery voltage. Thus, through the analysis of changes in data according to the fault conditions, the selection of fault features in this study was validated.