Study on the effectiveness of navigation safety measures for Nanjing Yangtze River Bridge

Combined with navigation safety measures such as navigation mark adjustment, synchronous flash distribution, and real ship test adopted by Nanjing Yangtze River Bridge, theoretical analysis methods and data analysis are used to determine the safety evaluation risk index system, and an unascertained measure evaluation model based on entropy weight is constructed. Through the comparison of the effectiveness of the security measures analyzed by the questionnaire, the effectiveness of the bridge safety guarantee measures was evaluated; further suggestions on the optimization of relevant safety protection measures were proposed. The research results are of great significance for maintaining the safety of the bridge, the navigation order of the waters in the bridge area, protecting the navigation resources of the bridge area, and ensuring the navigation safety of the ship.


Introduction
Bridges play an irreplaceable role in promoting economic and social development. However, in the event of a bridge safety incident, the consequences will be unimaginable. Nowadays, more and more bridges are built in the same jurisdiction. It is especially important to carry out the necessary safety guarantees for the safety of the bridge and how to properly solve the problem of water traffic safety in the bridge section. Safety evaluation of the safety measures implemented by the bridge is carried out, and corresponding countermeasures are proposed in time. Through the analysis and evaluation of effectiveness, we can better understand and master the effectiveness of the safety and security measures implemented by the bridge, and provide scientific decision-making basis for the maritime management department to improve the navigation environment and traffic safety of the bridge section and the navigation management and control. And reference, thus having a certain practical value [1] .

Brief Introduction to Safety Measures for Navigation in Bridge Area
In order to ensure the safety of the bridge, the water management department has adopted the following navigation safety guarantee measures, as shown in Table  1 below. Guide the ship's driver to accurately identify the navigation bridge hole and reduce the drift of the ship. As shown in Figure 1 Navigation bridge hole setting buoy synchronous flash The navigation mark of the bridge area is more obvious, and the ship driver can correctly follow the navigation mark to guide the safe navigation through the bridge area. As shown in Figure 2 Lighting the navigation bridge hole Solved the problem that the crew "can't see clearly and unclear" about the bridge hole.
As shown in Figure 3. Intelligent early warning monitoring Improve the safe navigation ability of ships at night and effectively prevent ships from entering the non-navigate waters Carry out the 6-hole real ship test of the bridge Through the actual ship test data, the ship's navigation characteristics are analyzed, the navigation sign setting is optimized, the ship navigation method is simulated and simulated, navigation suggestions are provided, and the bridge navigation safety is guaranteed.

Safety Benefit Evaluation of Bridge Segment
Establish a safety assessment risk indicator system for this jurisdiction, including people, ships, bridges, environment, and management, with a total of 26 secondary evaluation indicators. The expert judgment method is used to construct the comparative judgment matrix of the evaluation index. The brainstorming method is used to determine the membership degree of each index. Finally, the center of gravity method is used to defuzzify and obtain the comprehensive evaluation score of each index [2] . Five fuzzy comments were expressed for the safety benefits, and finally the effectiveness of the bridge safety guarantee measures was judged.

Single indicator not determined calculation
The calculation of the single-index unascertained measure matrix uses the method of constructing the unascertained measure function, and is determined by the expert scoring method. According to the characteristics of the specific problem to be solved and the severity of the state change, the undetermined measure function can be connected by different curves such as a straight line and a quadratic curve [3] . Among them, the linear unascertained measure function is currently the most widely used. Its calculation formula is as follows: Among them, is the classification standard of each indicator, and is the evaluation level. From the calculation formula (1) (2), it can be concluded that the observation value of the index with respect to the index causes the object to be in the single-index unsure degree matrix of each evaluation level as follows:

Entropy weight method weight calculation
Entropy is a measure of the uncertainty of the state of the system. The index weight assignment method based on entropy weight is a combination of quantitative and qualitative methods, which expresses and processes human subjective judgments in quantitative form [4] . Calculate the measure value of the evaluation index according to the corresponding membership function to construct 1 2 l ( , , , ) The entropy is now: The weight is used as the weight vector of the attribute set U, that is, its entropy weight. Where H is the entropy value of the evaluation index; ij v is the proportion of the j-th evaluation object in the i-th indicator.

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According to the single-index unascertained degree ijk u and the index weight vector  ,the unascertained degree vector ij x of the evaluation object can be calculated, and the calculation formula is as follows: Then we call the vector 1 2 ( , , ) , T is a multi-indicator synthesis Measure vector.

Confidence recognition
Because the evaluation grades are ordered, it is not possible to adopt the maximum membership recognition criterion for the out-of-order division, and instead use the confidence recognition criterion.
Pre-set the confidence threshold  , then: From this formula, it is judged that the object i x belongs to the 0 k -th evaluation level and the confidence is higher than  .

Establishment of evaluation index system
According to the regulations of the ship's alignment system, combined with the natural environment and navigation environment of the waters of the bridge area, comprehensive consideration of various factors affecting the establishment of water efficiency indicators of the bridge area, and selection of ships, environment and management [5] as evaluation Indicators; as shown in Table 2. Bridge area water safety protection facilities First aid to improve the effect The effective grades of each evaluation index are divided into five levels: no effect, some effects, general effects, large effects, and large functions. They are represented by C1-C5, and the evaluation criteria corresponding to each level are shown in Table 3.

Determine evaluation indicator weights
The score of the evaluation is given to each indicator by the expert. The evaluation scores of the evaluation factors were counted, and the statistical results are shown in Table 4  First aid to improve the effect 0 0 6 10 64 The fuzzy evaluation is obtained by using the single index measure calculation method to determine the membership degree of the index, and the entropy weight of the second evaluation factor is calculated. The membership function is constructed as follows: membership degree = factor to get the corresponding questionnaire valid questionnaire/total effective questionnaire.
The measure values of the respective evaluation indexes can be calculated according to the constructed membership function, and the calculation results are shown in Table 5 below.   Table 6.

Single indicator unascertained degree calculation
The evaluation results were processed by the mean value analysis method to obtain the scores of the respective indexes, as shown in Table 7. From the definition of the single-index measure function, an image of the single-index unascertained function of each index risk assessment can be obtained, as shown in Figure 4. The values of the indicators in Table 7 are respectively taken into the single-index measure function, and the single-index evaluation matrix for the safety and effectiveness evaluation of the safeguard measures is calculated [6] . Taking the "improvement effect of dangerous goods ship accident" in the ship factor as an example, according to the score value of Table 7, Figure 5 and formula (1). (2) and the "normality" of the unascertained measure, it can be concluded that The single-index measure vector that separates the opposite traffic flow to reduce the effect on the situation is (0 0 0 0.675 0.325). The same method can be used to find the unascertained measure of other indicators.
According to the calculation, the unascertained measure evaluation matrix of the ship safety factor for safety and safety measures is:

Research conclusions and prospects
This paper takes the various security measures adopted by the Nanjing Yangtze River Bridge as the research object, and uses theoretical analysis methods and questionnaire survey data to evaluate the implementation effectiveness of the bridge navigation safety guarantee measures for the navigation environment of the bridge area of the Nanjing Yangtze River Bridge, and analyze the Nanjing Yangtze River. The safety benefits brought by the bridge in terms of ensuring the safety of the navigation of the ship, the smooth flow of the channel [8] , and the construction of the port are finally evaluated to evaluate the effectiveness of the safety measures for the navigation of the bridge; further recommendations for the optimization of relevant safety measures are proposed.
The research results are of great significance for maintaining the safety of other bridges, the navigation order of ships in the bridge area, protecting the navigation resources of the bridge area, and ensuring the navigation safety of the ships. It is of great significance to the development of the Yangtze River trunk shipping and the sustainable development of the port water transport economy. At the same time, it can provide suggestions for maritime affairs and related departments, which has certain practical significance for improving the safety of the bridge.