Study On Safety Of Ship Navigation In The Waterway Of Bridge Area

To investigate the navigation safety of ships in bridge area,the navigation risk factors in bridge area were analyzed firstly.The probability of ship-bridge collision was studied,and then a navigation risk assessment model was established by means of field survey,theoretical research and mathematical model test.The design method which navigable bridge opening should cover the thalweg and the swing range of the deep channel which may form the new navigation channel was proposed.The calculation method of the effective navigable net width of skew bridge with forward and inclined layout of piers and bridge group based on the geometric relation was proposed.These models and methods were carried out in the design stage of Libu Yangtze River Bridge.The research contents and conclusions are as follows.1)Based on the analysis of the causes of the accident,the risk factors of the bridge area were determined,which are mainly bridge factors,environmental factors,ship factors and human factors.The bridge in bends and shoals,poor flow conditions and small navigable clearance are prone to accidents.In terms of environmental factors,the mismatch between bridge clearance and navigable channel caused by the change of waterway planning,navigation standards and ship enlargement as well as the impacts of poor natural conditions on ship navigation safety were analyzed.The ship and human factors also cause the navigation risks and bridge collision accidents.2)In order to simulate the influence of human factors,a mathematical model of ship maneuvering was established.Based on the simulation environment of Ship Simulator and the captain’s maneuvering experience,a ship maneuvering simulation experiment was carried out.The AASHTO model was improved on the basis of the experiments.A geometric probability model was proposed which takes the center position of ship track as the mean value and the sample calculation result of simulation as the variance.The concept of stopping probability was introduced.The probability of ship collision with Nanjing Yangtze River Bridge was calculated.The probability of the initial AASHTO was greatly bigger than the actual measured data.The accuracy between probability of improved AASHTO and actual measured one was in the range of 5%.3)Ten factors including navigable net width,navigable net height,bridge location,visibility,wind,current,human factors,VTS management,navigation aids and ship traffic flow were selected.Human factors were quantitative described by the probability of ship collision with bridge.Based on the theory of fuzzy mathematics,as well as expert advice,measured data and comparison of other investigation,a navigable risk assessment model was established.It solves the problem that the human factors are seldom considered and the quantification is insufficient in the navigable risk assessment in the bridge area.4)The bridge location is the most important factor in ship navigation risk assessment.The most significant risk in site selection is that the channel displacement caused by river bed evolution makes the ship navigation move from the navigable bridge opening to the non-navigable one.Taking the Jingzhou Yangtze River Bridge as an example,the influence of river bed evolution on navigation safety in the bridge area was studied.It is suggested that the navigable bridge opening should cover the thalweg and the swing range of the deep channel which may form the new navigation channel.The proposition has been applied to the design of Libu Yangtze River Bridge.5)The bridge navigation net width is another important factor in ship navigation risk assessment.Navigable net width should be determined comprehensively according to representative ship types,water flow conditions,ship track width and possible navigable area.The calculation method of the effective navigable net width of skew bridge with forward and inclined layout of piers and bridge group based on the geometric relation was proposed.It supports the construction of the skew bridge with poor location and ensures the navigation safety of the water area from the design prospect.The navigation risk assessment of Libu Yangtze River Bridge in the design stage was carried out.The results show that the first-class index of Libu Yangtze River Bridge for bridge factor in the water area is "low risk" and the comprehensive index is "low risk".