3.1. Analysis of the Force on the Steel Plate of the Ship Caused by the High-Pressure Water Jet
In order to effectively change the navigation direction of large-tonnage ships and avoid obstacles such as bridge piers, it is necessary to use high-intensity high-pressure water jets to spray and impact the hull. However, this operation method poses a risk of potential damage to the hull structure. Therefore, in this article, the transient structure and fluent modules in ANSYS 2023 R1 were utilized to perform a fluid–structure interaction analysis in order to assess whether the adopted high-pressure water jet would cause irreversible damage to the hull structure.
To ensure the reliability and broad applicability of the simulation results, the dimensions and strength grade of steel plates under the most unfavorable loading conditions, namely, general-strength structural steel with a length of 18 m, a width of 4.5 m, and a thickness of 0.05 m [
27], were selected as the object of this simulation study.
Hull structural steel is subdivided into two major categories based on its minimum yield point: general-strength structural steel and high-strength structural steel [
27]. Among them, general-strength structural steel is further classified into four quality grades, namely, A, B, C, and D, which reflect different manufacturing processes and are labeled as CCSA, CCSB, CCSD, and CCSE in the specifications (CCS stands for China Classification Society). The yield strengths of these steels all meet the minimum standard strength of 235 MPa for hull structural steel.
To better simulate the actual operating environment of ships, the outer steel plate of the ship was set to a four-sided fixed state in the static structural section. Additionally, to comprehensively assess the impact of high-pressure water jets on the steel plate, four high-pressure nozzles arranged side by side were set up, each with a diameter of 1 m. The nozzle openings were kept flush with the water surface, and the spacing between adjacent nozzles was set to 2 m. The flow rate of each nozzle was precisely controlled at 11.775 m/s, with a total flow rate of 45 m
3/s [
28], as shown in
Figure 5.
Based on the distance between the steel plate and the high-pressure water jet nozzle, three comparative cases were carefully set up, covering three different distances of 2 m, 4 m, and 8 m. Through detailed calculations and an in-depth analysis, the stress distribution and total deformation data of the steel plate at various distances were successfully obtained, as shown in
Figure 6. It was found that the maximum stress was primarily concentrated at the upper and lower ends of the steel plate, reaching a specific value of 93.2 MPa, as illustrated in
Figure 6a, whereas the deformation was primarily concentrated in the middle of the water jet, with a maximum deformation of approximately 1.07 cm, as shown in
Figure 6d.
As the distance between the steel plate and the nozzle increased, a significant decrease in both stress and deformation was observed. When the steel plate was placed 4 m away from the nozzle, the maximum stress value was significantly reduced to approximately 62.0 MPa, as shown in
Figure 6b; simultaneously, the maximum deformation also dropped to approximately 0.60 cm, as shown in
Figure 6e. When the distance between the steel plate and the nozzle further increased to 8 m, the maximum stress value continued to decrease to 34.3 MPa, while the maximum deformation remained minimal, only about 0.40 cm, as shown in
Figure 6c,f.
These simulation results indicate that by reasonably regulating the jet distance and flow rate of the high-pressure water jet, it is possible to change the ship’s course while protecting the pier, and without causing significant damage to the ship’s structure. This also suggests that the high-pressure water jet anti-collision method has the potential to become a new, safe, and effective ship navigation and pier protection strategy.
3.2. High-Pressure Water Jet Layout and Flow Field Analysis
In this paper, high-pressure nozzles were arranged around the impacted pier, specifically the left pier shown in
Figure 2c. The setup parameters of these nozzles strictly adhered to the standards established in detail in
Section 3.1. The aim was to ensure that the high-pressure water jets effectively deflect the ship’s course without causing any potential damage to the hull, thus safeguarding the safety and effectiveness of the entire system.
Given the specific scenario of the ship’s bow colliding with the pier at a 35° angle [
29], the precise impact of high-pressure water jet spraying angles on the deflection effect of ships was investigated. Three different spraying angles (0°, −35°, 35°) of water jets were set near the pier, as illustrated in
Figure 7. Among them, the 0° condition represented a high-pressure water jet spraying perpendicular to the river flow, where the impact of the vertical water jet would maximize the alteration of the river’s flow direction. The −35° condition signified that the high-pressure water jet sprays perpendicular to the river and deflects upstream by 35°, aligning with the ship’s impact direction. Theoretically, this condition would cause the ship to be affected by the high-pressure water jet the earliest. Conversely, the 35° condition involved the high-pressure water jet spraying perpendicular to the river and deflecting downstream by 35°, potentially subjecting the ship to a greater turning moment.
When the high-pressure water jet impacted the river channel, the original flow field structure underwent significant changes. Upon being subjected to the action of high-momentum fluid, the ship’s original navigation state altered, effectively averting the risk of direct collision between the ship and the bridge [
23]. Turbulence is a crucial consideration in waterways, especially when the lateral flow velocity exceeds 0.3 m/s, defining the turbulence width range, which significantly impacts the safe navigation of ships [
30]. Therefore, in this paper, a lateral flow velocity greater than 0.3 m/s is used as the criterion for determining the influence area of the high-pressure water jet.
Figure 8 shows the velocity contour and dynamic pressure contour of the high-pressure water jet under different conditions. The velocity contour clearly reveals that the dynamic pressure and flow velocity of the high-pressure water jet reach their maxima at the nozzle outlet. As the water jet expands outward, its velocity and dynamic pressure gradually decrease. The dynamic pressure contour exhibits a similar trend to the velocity contour, with high flow velocities and dynamic pressures concentrated in the central portion of the water jet coverage area, gradually decreasing from the center to the sides. Near the outlet, the maximum dynamic pressure can reach 99,571.4 Pa, and the water flow velocity attains approximately 14.8 m/s.
When ships under the three different conditions arrived at the same location, coordinate calculations revealed that the water jet coverage impact range is approximately 30 m long for the −35° condition, 33 m for the 0° condition, and the longest at about 38 m for the 35° condition. The width of the water jet is approximately 10 m for all conditions. Notably, the −35° condition, as an upstream scenario, exhibits a relatively shorter spreading distance of the high-pressure water jet when the ship reaches the same location. Conversely, the 35° condition, being a downstream scenario, demonstrates the farthest spreading distance due to the influence of the river’s flow velocity. This causes the tail end of the high-pressure water jet to bend downstream, thereby expanding the interference area of the water jet.
3.3. Analysis of Ship Yaw Trajectory under Different Working Conditions
In this paper, the navigation process of a large-tonnage ship approaching the impacted pier was simulated, focusing on the observation of the yaw trajectory of the ship under different working conditions. At the beginning of the experiment, the ship was placed 50 m away from the high-pressure jet nozzle and sailed towards the pier with a deviation angle of 35° and an initial speed of 2.7 m/s. Given the relatively low initial speed, a dragging force of 65 kN was applied to the ship to ensure a stable sailing speed throughout the experiment.
Three different conditions were set up for the experiment to simulate the sailing state of the ship.
Figure 9 details the trajectory curves of the ship’s center of gravity throughout the entire motion process. It can be seen from the figure that before the ship reaches the coverage area of the high-pressure water jet, its sailing trajectory will be deflected to a certain degree due to the influence of river currents. When the bow reaches the coverage area of the high-pressure water jet, the entire hull will deflect downstream by approximately 2.5 m.
Under the −35° working condition, the ship first came into contact with the impact area of the high-pressure water jet. At this time, the ship was located at the green dashed line scale of 50 m in
Figure 9. Since the hull had already deflected slightly, the impact direction of the high-pressure water jet formed a small angle with the ship’s forward direction. This small-angle jet impact further steers the ship, as shown in
Figure 10a. As the voyage continues, although the ship was still approaching the pier, the deflecting force of the water jet on the hull gradually increased under the continuous high-pressure water jet. This caused the ship to continue steering while its tendency to approach the pier gradually weakened and ultimately began to steer away from the pier. During this process, the minimum distance between the upper right side of the ship and the pier is approximately 8.75 m, as shown in
Figure 10d.
Under the 0° working condition, the ship began to be affected by the high-pressure water jet when it reached approximately 62.6 m on the blue dashed line scale in
Figure 9. Compared to the −35° working condition, the ship advanced an additional distance of approximately 12.6 m under this condition. During this part of the voyage, the high-pressure water jet hardly interfered with the ship’s sailing. Although the high-pressure water jet under the 0° working condition exerted a larger moment on the river water to steer it, the safe space left for the water jet to push away the ship was relatively smaller. When the ship reached the position shown in
Figure 10e, the minimum distance between its upper right side and the pier was approximately 5.14 m. Ultimately, the entire hull successfully cleared the impacted pier. However, when the stern passed through the jet nozzle, due to the strong effect of the high-pressure jet source, the bow deflected towards the left-side pier, as shown in
Figure 10h. Although the minimum distance between the ship and the pier decreased under this working condition, the ship could still successfully avoid the pier and achieve safe navigation.
Under the 35° working condition, the ship began to be affected by the high-pressure water jet when it reached approximately 66.2 m on the red dashed line scale in
Figure 9, as shown in
Figure 10c. Compared to the previous two working conditions, the ship was affected by the high-pressure water jet later under this condition, resulting in a smaller space for adjusting its sailing trajectory. After the bow passed through the coverage area of the high-pressure water jet, it arrived at the position shown in
Figure 10f. At this point, the minimum distance between the upper right side of the bow and the pier was approximately 2.6 m, which was more urgent compared to the previous two working conditions and posed a greater potential risk to the pier. However, thanks to the strong effect of the high-pressure water jet, the ship was still able to successfully avoid the pier and achieved safe navigation. The moment when the stern passed the pier is shown in
Figure 10i.
Through an analysis of the first three sets of working conditions, it can be seen that under the condition of maintaining the jetting speed of the high-pressure water jet at 14.8 m/s, ships can effectively and safely avoid the risk of collision with piers. However, during the testing of the 35° working condition, the navigation status of the ship was particularly dangerous, posing a significant potential risk to the pier.
To further clarify the minimum jetting intensity of the high-pressure water jet required to ensure the safety of the ship, the 35° working condition was taken as a benchmark and gradually reduced.
Figure 11 clearly shows that when the jetting speed was reduced to 10 m/s, although the minimum distance between the ship and the pier was only about 1.29 m when the ship approached the pier, posing a significant risk to the pier, thanks to the continuous action of the high-pressure water jet, the ship ultimately successfully completed an extreme turn, avoiding collision with the pier. It is worth noting that when the stern of the ship successfully passed the pier, although the bow continued to veer towards the right-side pier and continued to move forward, overall, the ship had safely sailed through the pier area.
Figure 12 details the trend of changes in the yaw angle of the ship under the action of the high-pressure water jet. As can be seen from the figure, due to the influence of the natural flow direction of the river, the bow had already deviated slightly by about 2° before contacting the high-pressure water jet. When the bow first touched the area impacted by the high-pressure water jet, it quickly veered to the left under the significant influence of the force moment generated by the water jet. Among them, the ship under the −35° working condition turned earlier than under other conditions. However, due to the small angle between the water jet and the hull, the turning moment acting on the ship was relatively small, resulting in a relatively gradual increase in its yaw angle. In contrast, under the 0° working condition, the impact direction of the high-pressure water jet was perpendicular to the flow direction, causing the maximum impact on the flow direction of the river water, leading to the most rapid increase in the yaw angle of the ship in this area. The accumulated yaw angle when exiting the area reached a maximum of 55°. As for the 35° working condition, although the ship was subjected to a large turning moment from the impact of the water jet, as the water jet was sprayed downstream, when the ship turned to a certain angle, the force moment of the water jet on the ship rapidly decreased, ultimately resulting in a yaw angle that was larger than under the −35° working condition but smaller than under the 0° working condition. In the working condition with a reduced jetting flow rate of the water jet, due to insufficient power of the water jet, the increase in the yaw angle of the ship was the slowest, and the final yaw angle was also the smallest.
Based on the experimental results of the four working conditions mentioned above, the following conclusions can be drawn: the high-pressure water jet collision avoidance method is practical and effective for large-tonnage ships. Under various working conditions, the ships exhibited significant lateral displacement and yawing, effectively correcting their off-course situations. After being influenced by the high-pressure water jet, the lateral displacement of the ships reached more than 22 m. Additionally, due to differences in the impact area and duration of the high-pressure water jet under different working conditions, the ship under the −35° working condition was first affected by the water jet and was affected for a longer duration, providing sufficient time for the ship to turn away from the pier. Under the 0° and 35° working conditions, although the force moment of the water jet on the ship was greater, due to the later timing of the impact, the ship had limited space and time to adjust its course. Although it ultimately succeeded in avoiding the pier, it was clearly very close to it, posing a certain risk of collision. This finding suggests that compared to the force moment of the water jet, the duration of its impact is more critical for collision avoidance effectiveness. When configuring the same high-pressure water jet, it is advisable to maximize the duration and range of the water jet’s impact on the ship to allow the ship to start turning and decelerating earlier.
It is worth mentioning that under the most unfavorable 35° working condition, when the jetting speed of the high-pressure water jet was reduced to about 10 m/s, the ship was still able to successfully avoid the pier. This finding indicates that there is still some room for optimization in the configuration of the high-pressure water jet. If a higher-power jetting device can be provided, it will be possible to protect the safety of piers while avoiding collisions with larger-tonnage ships.
When facing the emergency situation of large-tonnage ships losing control, relying solely on the ship’s own engine braking and rudder adjustment is often difficult to effectively avoid collisions. Therefore, from the perspective of the lateral displacement and yaw angle of the ship in this simulated experiment, the high-pressure water jet collision avoidance method has been proven as theoretically feasible. Through the impact of high-pressure water flow, it can provide a huge steering force for the uncontrolled ship, enabling it to completely avoid the pier and achieve “zero damage” between the ship and the bridge.
3.4. Impact of High-Pressure Water Jet on Ship Movement
When a ship encounters the instant impact of a high-pressure water jet, it will face the jet impact from the front or side depending on different working conditions. This impact will generate significant water waves at the bow position, further affecting the resistance of the hull. Ship resistance mainly includes wave-making resistance and viscous pressure resistance. Wave-making resistance originates from the water waves generated during hull propulsion, while viscous pressure resistance results from the viscosity of water molecules on the hull surface. The formation of these water waves undoubtedly increases the resistance of the ship, resulting in a significant reduction in ship speed, as shown in
Figure 13. Specifically, when the bow touched the area impacted by the high-pressure water jet, the ship speed decreased more significantly.
By comparing different working conditions, it was found that when the working condition was 35° and the flow rate was 10 m/s, the decrease in ship speed was relatively small, fluctuating only around 2.7 m/s. This may be because under this condition, the high-pressure water jet mainly impacts the side of the ship, and the flow rate of the water jet is relatively small. Therefore, the impact range of the water jet on the bow is relatively small, resulting in less wave-making resistance that can be almost ignored. However, when the water jet tilted upstream at an angle of −35°, the decrease in ship speed was the most significant, rapidly dropping from 2.55 m/s to approximately 1.7 m/s and remaining stable until the middle and tail sections of the ship passed through the area impacted by the high-pressure water jet, where the speed continued to decrease. This phenomenon further explains why, as mentioned in
Section 3.3, under this working condition, the ship can maintain a larger safety distance from the pier. This is mainly because, under this condition, the high-pressure water jet not only deflects the ship but also reduces its speed through the generation of reactive force, effectively preventing the ship from approaching the pier.
In addition, ships generate a series of waves, known as Kelvin waves, during navigation, which often leads to the phenomenon of ship pitching. The amplitude of pitching directly affects the stability of the ship’s movement and the comfort of passengers.
Figure 14 shows the variation curves of ship pitching under different working conditions. As can be seen from the figure, regardless of the working condition, when the ship’s center of gravity passed through the area impacted by the high-pressure water jet, its pitching amplitude decreased. Taking the −35° working condition as an example, before the ship’s center of gravity entered the area impacted by the high-pressure water jet, its pitching peak was 0.1°, the trough was −0.75°, and the difference between the peak and the trough was 0.85°, with a wavelength of approximately 10.5 m. However, when the ship’s center of gravity entered the water jet area (approximately within a range of 50 m), its pitching value decreased to −0.2°, the trough was −0.6°, and the difference between the peak and the trough reduced to 0.4°, while the wavelength remained approximately 10.5 m. This indicates that under the action of the high-pressure water jet, the peak pitching value of the ship decreases, but the period of the wavelength does not change significantly. Therefore, by interfering with ship navigation through high-pressure water jet spraying, it can not only effectively deflect the ship away from the pier, but the impact of the water jet on the stability of the ship’s movement and passenger comfort is relatively small.