# Research on Collision Warning Method for Ship-Bridge Based on Safety Potential Field
## 5 Simulation Experiments
### Bridge Area Early Warning Experiment  
In this section, the AIS data of the upstream bulk carrier Shengyuan 506 and the downstream multipurpose ship Shuiyu Huang 16, in the bridge area from 10:00 to 13:00 on 5 June 2024, are selected. The state of the two vessels in the bridge area is predicted every 30 s. Using the safety potential field model, the field strength prediction values for the upstream and downstream vessels at different times are calculated. Combining the risk early warning method proposed in Section 3.2, the dynamic changes of the potential field are analysed to determine the risk levels of the vessels and take corresponding early warning measures. Meanwhile, in order to more intuitively illustrate the relationship between field strength values and warning levels, the predicted field strength values and the actual safety potential field values corresponding to the AIS data are normalised so that they are both in the range of 0-1 in order to eliminate the differences in magnitude between the different features and so that the potential field values and the warning ranges can be compared on the same scale. Taking an upstream bulk carrier as an example, the vessel parameters are shown in Table 5. The field strength values and early warning levels at four moments during a vessel's upstream voyage--approaching the edge of the channel, sailing near the bridge abutment, directly in front of the bridge abutment, and passing the bridge abutment--are analysed. The specific early warning level analysis results are shown in Table 6.  
Figure 15a,b show the predicted and actual instantaneous risks of the vessel from time T1 to T2. At T1, the vessel's risk value is 0.3, with a warning level of 1. The predicted value for T2 is 0.79, while the actual value is 0.74, both with a warning level of 2, and the error is 0.05. Figure 15c,d display the predicted and actual instantaneous risks of the vessel from time T2 to T3. At T2, the vessel's risk value is 0.74, with a warning level of 2. The predicted value for T3 is 0.25, while the actual value is 0.21, both with a warning level of 2, and the error is 0.04. Figure 15e,f show the predicted and actual instantaneous risks of the vessel from time T3 to T4. At T3, the vessel's risk value is 0.21, with a warning level of 1. The predicted value for T4 is 0.20, while the actual value is 0.18, both with a warning level of 1, and the error is 0.02. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Time** & **Projected** & **Warning** & **AIS** & **Warning** & **Error** & **Range of Warning** \\
**Point** & **Value** & **Level** & **Value** & **Level** & **Level** \\ \hline T1 & - & Level 1 & 0.30 & Level 1 & - & Level 1 (0–0.50) \\ \hline T2 & 0.79 & Level 2 & 0.74 & Level 2 & 0.05 & Level 2 (0.51–0.80) \\ \hline T3 & 0.25 & Level 1 & 0.21 & Level 1 & 0.04 & Level 3 (0.81–1) \\ \hline T4 & 0.20 & Level 1 & 0.18 & Level 1 & 0.02 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Warning levels for different moments of prediction versus real AIS scenarios. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Ship Name & Shengyuan 506 \\ Length & 100 m \\ Width & 24 m \\ Draft & 11 m \\ Speed & 10 kn \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Parameters of the upstream bulk carrier. Taking a downstream multipurpose cargo ship as an example, the vessel parameters are shown in Table 7. The analysis focuses on the field strength values and warning levels at four moments during its downstream voyage: approaching the edge of the dock, sailing near the bridge abutment, directly in front of the bridge abutment, and passing the bridge abutment. The specific early warning level analysis results are shown in Table 8.  
Figure (a)a,b show the predicted and actual instantaneous risks of the vessel from time T1 to T2. At T1, the vessel's risk value is 0.71, with a warning level of 2. The predicted value for T2 is 0.91, while the actual value is 0.81, both with a warning level of 3, and the error is 0.1.