## 3 Experimental Results
### Dimensionality Reduction Preprocessing of Time Domain and Frequency Domain Feature Parameters  
The fluctuation signal is divided into two stages, which are the normal operation stage from 0 to 80 months, and the stage of the gearbox operation fault from 80 to 100 months, and the vibration acceleration amplitude increases sharply. The time domain and frequency domain characteristic parameters of the vibration signals in the two stages are calculated, respectively. The intraclass distance and interclass distance of the characteristic parameters in the time domain and frequency domain in the normal operation state and fault state are calculated, and the distance evaluation factor value of the characteristic parameters is calculated based on it, and the results are shown in Tables 8 and 9. According to the structural analysis of the lubricating oil system, the fault tree of the lubricating oil system is constructed. The reliability data in this paper are mainly from simulation results, including normal operation (N state), repair state (I state), damage state (D state), and deactivated state (C state) [33]. However, the upgrade process of faults during the operation of the equipment cannot be ignored; therefore, the transition rate of faults from state I to state D (\(\lambda 2=\lambda 4\)) and from state N to state I (\(\lambda 1=\lambda 5=\lambda 6\)) are \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time Domain Characteristic Parameters** & **Normal** & **Failure** & **Distance Evaluation Factor** \\ \hline \multirow{3}{*}{Standard deviation} & 4.5861 & 7.3958 & \multirow{3}{*}{5.9720} \\  & 4.0433 & 9.3157 & \\  & 3.3452 & 10.0678 & \\ \hline \multirow{3}{*}{variance} & 19.1380 & 61.2737 & \multirow{3}{*}{4.7736} \\  & 15.5499 & 82.5962 & \\  & 13.8262 & 93.7664 & \\ \hline \multirow{3}{*}{Peak value} & 10.6474 & 16.2266 & \multirow{3}{*}{2.4520} \\  & 9.4719 & 17.1758 & \\  & 10.9320 & 26.7617 & \\ \hline \multirow{3}{*}{Absolute mean} & 3.5267 & 6.9092 & \multirow{3}{*}{6.0793} \\  & 3.0921 & 7.9261 & \\  & 2.6026 & 7.4857 & \\  & 4.1820 & 7.7753 & \\ \hline \multirow{3}{*}{Root mean square} & 4.4395 & 8.9834 & \multirow{3}{*}{5.3709} \\  & 3.3413 & 9.8353 & \\ \hline \multirow{3}{*}{Mean value} & 0.3744 & \(-\)0.8398 & \multirow{3}{*}{0.4749} \\  & 0.4586 & 0.2229 & \\  & 0.3371 & 0.3990 & \\ \hline \multirow{3}{*}{skewness} & 0.3320 & 0.0470 & \multirow{3}{*}{0.4627} \\  & 0.4397 & \(-\)0.4461 & \\  & 0.5806 & 0.3872 & \\ \hline \multirow{3}{*}{kurtosis} & 1.8478 & 1.7644 & \multirow{3}{*}{0.3190} \\  & 2.4754 & 2.1138 & \\  & 2.5793 & 3.2862 & \\ \hline \multirow{3}{*}{Maximum value} & 10.8732 & 16.5552 & \multirow{3}{*}{2.5717} \\  & 9.3770 & 17.0674 & \\  & 11.0391 & 26.9376 & \\ \hline \multirow{3}{*}{Minimum value} & \(-\)0.1742 & 0.5286 & \multirow{3}{*}{1.0862} \\  & 0.0057 & 0.6916 & \\ \cline{1-1}  & 0.5071 & 0.6590 & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Each time domain characteristic parameter value and distance evaluation factor under different running conditions. assumed to be equal in this paper. In addition, the data in IEEE STD-493 contain only two states: normal operation and equipment failure [34]; therefore, this kind of equipment is considered as binary nodes in this paper, that is, there are only normal states (N states) and faulty states (C states). When the multi-state device is in state I and D, the probability of its child node being in state C is obtained by judgment, and the relevant values are shown in Table 10. The signals of each part are shown in Table 5.The fault tree is shown in Figure 7.  
In this paper, Genie Bayesian software (GeNie 2.3 academic) is applied to model this system. According to the construction principle of the DBN structure, the fault tree of the ship oil system is transformed into a DBN, and the conditional probability table of each node in the DBN can be output. During DBN inference, the time interval \(\Delta t\) is set to 1 day (24 h). The ship sails 29% of the time per year, or about 106 days.