# Research on Collision Warning Method for Ship-Bridge Based on Safety Potential Field
## 2 Description and Early Warning Framework of the Safety Potential Field in the Bridge Area
### Ship-Bridge Collision Prevention Warning Framework  
There are four main factors affecting the safety of ship navigation in bridge areas: human, ship, environment and management. Human factors mainly include the crew's driving skills, the negligence of a lookout, etc.; ship-related factors mainly include the ship's movement status; environmental factors mainly include the channel conditions and external environment; and management factors mainly include the lack of maintenance of waterways and bridges and the inadequacy of emergency plans.  
Ships navigating in the bridge area are affected by multiple risk sources, while the interaction between the factors also affects the navigation safety of ships. In inland river navigation, as the management factors are not easy to quantify, the bridge area is considered to be in good management condition for this study, and only the human, ship and environmental risk factors are quantified into specific values. Additionally, the current potential field strength is judged in terms of its safety range by setting the safety thresholds in advance and by assessing whether there is a danger of collision with the bridge.  
The safety potential field corresponding to the above factors can be divided into four types: potential field, kinetic field, boundary field, and behavioural field. Static risk elements in the bridge area generate potential fields, moving objects and navigable vessels in the bridge area generate kinetic fields, and the channel bank walls and navigation markers generate boundary fields. Factors affecting the safe behaviour of drivers are considered to be behavioural fields. The specific classifications are shown in Table 1.  
Based on the specific characteristics of the risk elements in bridge-area waters, the bridge area can be divided into corresponding safety fields as a whole. However, in the bridge-area waters, the effects of wind currents and other solid forces on ships cannot be ignored. In order to combine the solid force with the virtual force, this paper applies the Kalman filter algorithm to predict the state of the ship, and the solid force acting on the hull will be corrected to adjust the position, speed and other states of the ship.  
The kinetic energy field after correcting the ship state is vectorially superimposed with other safety fields to obtain the total safety potential field. By analysing the spatial distribution pairs of the total safety potential field, the risk of ship collision in the bridge-area waters can be quantitatively assessed, and then early warning can be carried out according to the specific field strength. The framework of this study is shown in Figure 1. In Figure 1, the dashed-line represents the different modules that make up the bridge warning, where blue represents the same warning level, green represents each small module, orange represents an explanation of some of the small modules, and purple represents a highlight in this article.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Bridge Area Risk Element** & **Elemental Characteristics** & \begin{tabular}{c} **Corresponding Safety** \\ **Potential Field** \\ \end{tabular} \\ \hline Navigation officers (persons) & \begin{tabular}{c} Physical quality \\ Mental quality \\ Ship navigation skills \\ \end{tabular} & Behavioural field \\ \hline Ship & \begin{tabular}{c} Ship speed \\ Ship navigation direction \\ \end{tabular} & Kinetic energy field \\ \hline Environment & \begin{tabular}{c} Channel boundary \\ Channel width, depth, etc. \\ Bridge piers, stationary \\ ships, quay \\ Traffic flow conditions \\ Channel floating debris \\ \end{tabular} & Boundary energy field \\ \hline Management & \
\begin{tabular}{c} Damaged or unclear \\ navigational aids \\ Emergency plan, team \\ coordination \\ \end{tabular} &
\begin{tabular}{c} Boundary energy field \\ Behavioural field \\ \(\ldots\) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 1: Risk elements and corresponding safety fields in the waters of the bridge area.