# Research on a Ship Deflection Anti-Collision Method Based on a Water-Jet Interference Flow Field
## 1 Introduction  
With the development of the economy, the number and tonnage of inland navigation ships have increased over the years, and striking accidents of ships and bridges have frequently occurred. It has been pointed out by some scholars previously that at least one major ship-bridge striking accident with serious consequences occurred each year on average in the past [1; 2; 3; 4]. Since the major striking accident at the Sunshine Bridge in the United States in 1980 that attracted the attention of the world, bridge-striking prevention has developed rapidly [5]. However, there is still no striking prevention method that can actively intervene in the case of runaway ships to achieve the purpose of reducing and avoiding such traffic accidents. The existing bridge anti-striking measures are passive anti-striking devices and intelligent early warning systems [6]. Passive anti-striking devices reduce the impact force of the ship on the bridge through deformation and energy absorption. They mainly include anti-striking piles, artificial islands, rubber fenders, and anti-striking steel sleeves [7; 8; 9; 10]. As research becomes more advanced, more and more scholars are proposing the use of new materials to increase the crashworthiness of striking avoidance devicesand improve their effectiveness. The new prefabricated ultra-high-performance-concrete anti-striking device [11], rubberized concrete [12], fiber-reinforced polymer [13; 14; 15; 16; 17; 18], and the flexible and composite anti-striking devices [19; 20] are too costly, and their durability and application value need to be further explored. This kind of passive anti-striking device has a long construction period, and once a strike occurs, the maintenance and replacement cost is high, which also affects the navigation of the waterway and increases unnecessary risks and losses. For example, on 9 June 2020, a 3000-ton cargo ship hit the No. 18 main pier anti-striking buoy while passing through the Xijiang Bridge in Fengkai, Guangdong, causing damage to the anti-striking buoy, damage to the ship, and large economic losses as shown in Figure 1. By contrast, intelligent early warning systems find the ship's yaw through monitoring equipment and then warn dangerous ships through whistles, LEDs, or other warning methods [21; 22; 23]. [PERSON] (2018) explored a forward-looking infrared video surveillance system and investigated a ship safety navigation system based on GPS and wireless networking [24]. However, such \"powerless\" devices can only serve as a warning, cannot actively intervene in the case of out-of-control ships, and ultimately, they still need passive anti-striking devices to protect the bridge. It is necessary to actively intervene in out-of-control ships to avoid striking to fundamentally solve the problem of damage and replacement and maintenance of anti-striking devices, realize lossless protection of ship bridges, and improve bridge anti-striking systems. In this paper, an anti-striking method based on a water-jet interference flow field is proposed to actively intervene in the course of out-of-control ships to achieve the purpose of anti-striking as shown in Figure 2. This method divides the channel in the bridge area into a \"warning area\", an \"early warning area\", and an \"interference zone\" as shown in Figure 3 according to the water flow conditions and channel level of the bridge water areas where the bridge pier is located. A water-jet generator is installed in the interference zone, and a high-precision detector and water flow interference linkage system are deployed on the bridge to monitor the movement tracks in the bridge water areas through the detector. When a yaw ship enters the warning area, the yaw ship is warned by radio, whistle, and other means, and if the ship fails to adjust its course in time and enters the early warning area after the warning and still yaws, the water-jet generator is activated to change the flow of bridge water areas to form an interference zone.