Skeg fin design method for improving ship course stability

Abstract

The invention relates to a skeg design method for improving ship course stability, which comprises the following steps of: determining the initial shape of a longitudinal section line of a skeg at a ship longitudinal midline plane, and correcting the initial shape of the longitudinal section line by taking the increase of the projection area of the lower side of a ship skeg part waterline under the hydrodynamic force constraint as a target, the curvature radius of the longitudinal section line of the corrected skeg at the longitudinal midline plane of the ship is increased, the whole skeg extends in the stern direction, a skeg curved surface is regenerated based on the longitudinal section line of the corrected skeg at the longitudinal midline plane of the ship, and the corrected skeg is obtained; the problem that the rudder area is enlarged and limited can be effectively solved, the fast performance of a ship is considered, the ship course stability is effectively improved, the ship course recovery capacity when the ship is subjected to external disturbance is improved, the yawing phenomenon of the ship in the sailing process is remarkably reduced, meanwhile, the skeg and the ship body are seamlessly fused, and the overall structural strength is guaranteed; the method is especially suitable for ships sailing in a complex water area environment, and has the advantages of improving maneuverability and safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of ship design, and particularly relates to a design method for a stern fin for improving the course stability of a ship. Background Art

[0002] In the modern shipping field, the course stability of a ship is not only directly related to navigation safety, but also has a profound impact on economic indicators such as transportation efficiency, energy consumption cost, etc. During the navigation process of a ship, it continuously faces the interference of complex environmental factors such as water flow, wind, and waves. Especially when sailing at high speed or encountering strong wind and rapid flow, if the course stability of the ship is poor, the hull will deviate from the predetermined course, which may lead to safety accidents such as collisions and groundings. Traditional ship course stability designs mostly adopt conventional single-stern fin line types, mainly by increasing the rudder area to improve the course control ability. However, this method has obvious drawbacks. The main problem is that the limited space layout at the stern of the ship and the established draft seriously limit the expansion of the rudder area. At the same time, an overly large rudder area will significantly increase the navigation resistance, increase the load on the steering gear, and raise the requirements for the structural strength of the ship's stern. It may be necessary to strengthen the structure, increasing the construction cost and the hull weight, resulting in a significant increase in the fuel consumption of the ship, which goes against the current development trend of energy conservation and emission reduction in the shipping industry. Therefore, it is necessary to develop a design method for a stern fin so as to improve the course stability of the ship while better maintaining the propulsion efficiency of the ship and having little impact on the fast performance.

[0003] The longitudinal sectional line, transverse sectional line, and three-dimensional schematic diagram of the conventional stern fin design in the prior art are as Figures 1 to 4 shown. In order to reduce the weight of the stern section and the increase in resistance caused by the increase in volume, a conventional transition section is used for the longitudinal section line of the stern fin. The initial shape 1 of the longitudinal section line of the stern fin at the longitudinal mid-plane of the ship, that is, the shape of the longitudinal section line at y = 0 of the ship's stern fin, is a fair curve from the stern to the fin end. The maximum curvature value is at the connection between the stern and the stern fin, and the curvature change of the part below the tail shaft outlet is relatively large. The bottom contour of the transverse section of the stern fin is as Figure 3 shown. The initial bottom contour 3 of the transverse section of the stern fin is relatively round. Although when ensuring certain main dimensions and displacement distribution of the ship, the additional resistance of the stern fin at the design speed is small, the course stability of the ship is insufficient, resulting in the ship's maneuverability still not meeting the requirements. Summary of the Invention

[0004] The present invention aims to solve at least one of the above technical problems to some extent. The present invention provides a design method for a stern fin for improving the course stability of a ship, which can effectively solve the problem of limited increase in the rudder area, take into account the fast performance of the ship, effectively improve the course stability of the ship, and ensure the overall structural strength.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] A method for designing a stern fin to improve the course stability of a ship, the method comprising:

[0007] Determine the initial shape of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship. With the goal of increasing the lateral projected area S below the waterline of the stern fin part of the hull under hydrodynamic constraints, correct the initial shape of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship, so that the radius of curvature of the longitudinal section of the corrected stern fin at the longitudinal mid-plane of the ship increases, and the whole extends towards the stern. Regenerate the stern fin surface based on the longitudinal section of the corrected stern fin at the longitudinal mid-plane of the ship to obtain the corrected stern fin.

[0008] In order to further ensure that the correction of the longitudinal section shape meets the hydrodynamic constraint conditions on the basis of the stern fin design for improving the course stability of the ship, in a preferred technical solution, the hydrodynamic constraint includes that the additional resistance of the corrected stern fin at the design speed does not exceed 1% of the total resistance of the ship.

[0009] Through the calculation and statistical analysis of ships including container ships and bulk carriers, the inventor found that due to the limitation of the propeller diameter and draft, the space is limited, and the lateral projected area below the waterline of the stern fin part of the hull cannot be set too large. In order to ensure the course stability, increase the lateral projected area, and further simplify the optimization of the change amount of the lateral projected area below the waterline of the stern fin part of the hull. In a preferred technical solution, the optimization method with the goal of increasing the lateral projected area below the waterline of the stern fin part of the hull under hydrodynamic constraints includes:

[0010] Parallel to the mid-plane along the ship length direction, equally divide the ship length into 20 station intervals through station lines. The second station line from the stern to the bow direction is counted as the S2 waterline, and determine the lateral projected area A0 of the longitudinal mid-section of the hull from the tail to the S2 waterline before correction;

[0011] Regenerate the stern fin surface based on the longitudinal section of the corrected stern fin at the longitudinal mid-plane of the ship, determine the lateral projected area A of the longitudinal mid-section of the hull from the tail to the S2 waterline after correction, and with the hydrodynamic constraint, take the maximum value of A being 1.0A0 - 1.05A0 as the optimization goal to optimize the shape of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship.

[0012] In a preferred technical solution, the correction of the initial shape of the longitudinal section is a continuous curvature curve.

[0013] In order to further optimize the shape of the longitudinal section and make the rapid performance not affected too much, in a preferred technical solution, the position of the maximum curvature value of the longitudinal section of the corrected stern fin at the longitudinal mid-plane of the ship is located at the front 1 / 3 of the longitudinal section, and the curvature of the rear 2 / 3 section gradually decreases to smoothly transition to the stern end point.

[0014] The side projection area of the skeg part of the hull below the waterline increases, and the wet area increases accordingly, and the increased part is concentrated in the middle and lower area in the height direction of the skeg. In order to reduce the resistance and meet the structural construction requirements at the same time, the bottom contour of the skeg cross-section can be further optimized. In the preferred technical solution, it includes determining and correcting the initial bottom contour of the skeg cross-section, obtaining the corrected bottom contour of the skeg cross-section, and regenerating the skeg surface based on the longitudinal section line of the corrected skeg at the longitudinal centerline of the ship and the corrected bottom contour of the skeg cross-section.

[0015] In a preferred technical solution, the bottom profile of the modified skeg fin cross section is a "V"-shaped structure.

[0016] Compared with the prior art, the beneficial effects of the present invention are at least:

[0017] (1) The present invention increases the side projection area of the waterline part of the longitudinal mid-section of the hull by adjusting the longitudinal section shape of the skeg at the longitudinal mid-line plane of the ship, i.e., y=0, thereby enhancing the hydrodynamic damping effect of the stern of the ship, effectively suppressing the yaw phenomenon caused by waves, side wind or rudder effect lag during navigation, and combining with the optimization of the longitudinal section shape of the skeg at y=0, improving the wake distribution, further taking into account the rapid performance of the ship, reducing the heading swing amplitude, so that the ship can still maintain a stable heading under complex sea conditions, and improving the ship's ability to restore the heading when subjected to external disturbances. The present invention is particularly suitable for ships sailing in complex water environments, and has the advantages of improving maneuverability and safety.

[0018] (2) The present invention regenerates the skeg surface based on the longitudinal section line of the modified skeg at the longitudinal centerline of the ship, so that the improved skeg design forms an integrated design, effectively solving the problem of limited increase in rudder area, improving the rudder effect response speed, and enabling the ship to restore a stable state more quickly during turning or emergency obstacle avoidance. At the same time, it is seamlessly integrated with the hull, so that the overall structural strength is fully guaranteed, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0020] Figure 1 It is a longitudinal section of a conventional skeg design hull in the prior art;

[0021] Figure 2 It is a partial enlarged view of the longitudinal section of the hull from the tail to the second station line of the conventional ship skeg design in the prior art;

[0022] Figure 3 It is a cross-section line diagram of a conventional skeg design hull in the prior art;

[0023] Figure 4is a three-dimensional schematic diagram of the conventional stern fin part of a hull in the prior art;

[0024] Figure 5 is a longitudinal sectional view of a hull with a stern fin design according to an embodiment of the present invention;

[0025] Figure 6 is a partial enlarged view of the tail of the longitudinal sectional view of the hull with a stern fin design according to an embodiment of the present invention to the second station line;

[0026] Figure 7 is a diagram for marking the position with the maximum curvature of the stern fin design according to an embodiment of the present invention;

[0027] Figure 8 is a sectional line diagram of the hull with a stern fin design according to an embodiment of the present invention;

[0028] Figure 9 is a three-dimensional schematic diagram of the stern fin part of a hull according to an embodiment of the present invention;

[0029] Figure 10 is a comparison diagram of the tail pressure distribution between Comparative Example 1 and Example 1;

[0030] Figure 11 is a comparison diagram of the tail velocity vectors between Comparative Example 1 and Example 1;

[0031] Figure 12 is a comparison schematic diagram of the longitudinal sectional views of the hulls with stern fin designs of Example 1, Comparative Example 2, and Comparative Example 3.

[0032] Markings in the figures: 1. Initial shape of the longitudinal section line of the stern fin at the longitudinal mid-plane of the ship; S. Lateral projected area of the part of the hull below the waterline of the stern fin; S2. Second station line from the stern to the bow direction; A0. Lateral projected area of the longitudinal mid-section of the hull from the tail to the waterline of S2 before correction; 2. Longitudinal section line of the corrected stern fin at the longitudinal mid-plane of the ship; A. Lateral projected area of the corrected longitudinal mid-section of the hull from the tail to the waterline of S2; 3. Initial bottom contour of the stern fin cross-section; 4. Corrected bottom contour of the stern fin cross-section; Figure 10 (a) represents the tail pressure distribution diagram of Comparative Example 1; Figure 10 (b) represents the tail pressure distribution diagram of Example 1;

[0033] Figure 11 (a) represents the tail velocity vector diagram of Comparative Example 1; Figure 11 (b) represents the tail velocity vector diagram of Example 1. Detailed implementation mode

[0034] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by terms such as "center", "longitudinal", "transverse", "length", "bottom", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0036] Regarding the problem in the prior art that improving stability depends on increasing the rudder area, but due to the limitations of the stern hull form and draft, the increase in the rudder area is restricted, and at the same time, it will increase resistance and reduce the fuel efficiency of the ship. The inventor adopts the strategy of using a stern fin design to improve the course stability of the ship. Due to the limitations of draft and propeller diameter, considering the basic requirements of the tip clearance, the course stability of the ship is mainly improved by increasing the lateral projected area below the waterline of the stern fin profile part, as Figures 1 to 8 shown, which is a preferred embodiment of the stern fin design method for improving the course stability of the ship according to the present invention. The method includes:

[0037] As Figures 1 to 4 shown, determine the initial shape 1 of the longitudinal section of the stern fin at the longitudinal midplane of the ship, with the goal of increasing the lateral projected area S of the part of the hull stern fin below the waterline under hydrodynamic constraints, as Figures 5 to 7 shown, correct the initial shape 1 of the longitudinal section of the stern fin at the longitudinal midplane of the ship, so that the curvature radius of the longitudinal section 2 of the corrected stern fin at the longitudinal midplane of the ship, that is, at y = 0, increases, and the whole extends towards the stern, as Figure 9 shown, regenerate the stern fin surface based on the longitudinal section 2 of the corrected stern fin at the longitudinal midplane of the ship to obtain the corrected stern fin.

[0038] The above method is a stern fin design method for improving the course stability of a ship by adjusting the shape of the longitudinal section of the stern fin at the longitudinal midplane of the ship, that is, at y = 0, to increase the lateral projected area of the waterline part of the longitudinal midsection of the hull, when the main dimensions and displacement distribution of the ship are fixed and the ship's maneuverability still does not meet the requirements. Compared with increasing the rudder area, it has at least the following advantages:

[0039] 1. Less restricted by space: Compared with the increased rudder area being easily restricted by the stern line shape and draft, the improved stern fin design is integrated with the ship. The stern fin can be flexibly designed according to the stern space and hydrodynamic requirements. Without changing the main structure and draft of the stern, it effectively utilizes the space behind the stern, increases the lateral projected area S below the waterline of the stern fin part of the hull, effectively solves the problem of limited increase in rudder area, enhances the hydrodynamic damping effect at the stern of the ship, effectively suppresses the yaw phenomenon caused by waves, crosswinds or lagging rudder effect during navigation, improves the response speed of the rudder effect, and enables the ship to quickly return to a stable state when turning or making an emergency obstacle avoidance.

[0040] 2. Capable of taking into account the ship's speed performance and effectively improving the ship's course stability: Compared with the increased rudder area that will significantly increase the hydrodynamic resistance of the ship and affect fuel efficiency, in the stern fin design, since the longitudinal section line 2 of the corrected stern fin at the longitudinal mid-plane of the ship has an increased radius of curvature at y = 0 and extends towards the stern as a whole, by optimizing the shape, under hydrodynamic constraints, increasing the lateral projected area of the stern fin, combined with optimizing the shape of the longitudinal section line of the stern fin at y = 0, changing the bending degree of the stern fin profile line, so that the increased part of the lateral projected area of the stern fin is concentrated in the middle and lower regions in the height direction of the stern fin, it can improve the wake distribution, reduce the amplitude of course swing, make the water flow more smoothly over the surface of the stern fin, enhance the stabilizing moment of the ship, effectively solve the problem of insufficient course stability due to limited increase in rudder area, while improving the course stability, the increase in ship resistance is relatively small, can better maintain the propulsion efficiency of the ship, reduce the operating cost, and enable the ship to maintain a stable course under complex sea conditions.

[0041] 3. Ensure the overall structural strength: Compared with the increased rudder area that will increase the load on the steering gear and raise the requirement for the structural strength of the ship's stern, and may require strengthening the structure, increasing the construction cost and the weight of the hull, the stern fin design has relatively low requirements for the structural strength of the ship. The stern fin is seamlessly integrated with the hull, without the need for large-scale strengthening of the hull structure, which helps to control the ship construction cost and keep the hull lightweight, and fully ensures the overall structural strength.

[0042] In order to further make the correction of the longitudinal section line shape meet the hydrodynamic constraint conditions on the basis of the stern fin design for improving the ship's course stability, further, the hydrodynamic constraints include that the additional resistance of the corrected stern fin at the design speed does not exceed 1% of the total resistance of the ship. For example, by performing CFD simulation calculations on the stern fin ship models before and after correction, calculating the additional resistance of the corrected stern fin at the design speed, and calculating the total resistance according to the frictional resistance and pressure resistance, the correction constraint is carried out with the preference of minimizing the increase in the total resistance after correction.

[0043] Through the calculation and statistical analysis of ships including container ships and bulk carriers, due to the limitations of propeller diameter and draft, and limited space, the lateral projected area S below the waterline of the stern fin part of the hull cannot be set too large. To ensure course stability, increase the lateral projected area, and further simplify the optimization of the lateral projected area S below the waterline of the stern fin part of the hull, that is, the change amount of S. Further, the optimization method with the goal of increasing the lateral projected area S below the waterline of the stern fin part of the hull under hydrodynamic constraints includes:

[0044] As Figure 2 shown, parallel to the midship plane along the ship length direction, divide the ship length into 20 station intervals equally by station lines. Each station line, that is, the transverse section line, is numbered in sequence from the stern to the bow direction. The second station line from the stern to the bow direction is counted as the S2 waterline. Determine the lateral projected area A0 of the longitudinal midship section of the hull from the stern to the S2 waterline before correction, and determine the initial shape 1 of the longitudinal section line of the stern fin at the longitudinal midline plane of the ship;

[0045] As Figure 6 shown, correct the initial shape of the longitudinal section line so that the radius of curvature at y = 0 of the longitudinal section line 2 of the stern fin at the longitudinal midline plane of the ship after correction increases, and the whole extends towards the stern direction. Based on the longitudinal section line 2 of the stern fin at the longitudinal midline plane of the ship after correction, regenerate the stern fin surface. Determine the lateral projected area A of the longitudinal midship section of the hull from the stern to the S2 waterline after correction. Under hydrodynamic constraints, with the maximum value of A being 1.0A0 to 1.05A0 as the optimization goal, optimize the shape of the longitudinal section line of the stern fin at the longitudinal midline plane of the ship. Through the calculation and statistical analysis of ships including container ships and bulk carriers, A being 1.0A0 to 1.05A0 is more suitable for improving course stability. Being too small will cause incomplete ship functions and unable to ensure stability.

[0046] To further optimize the hydrodynamic performance of the ship, reduce resistance, improve propulsion efficiency, and improve the maneuverability and stability of the ship. Further, the initial shape of the longitudinal section line is corrected to a continuous curvature curve. For example: use mathematical curves such as Bezier curves, or fairing algorithms such as the least squares method and curvature analysis method to correct the initial shape of the longitudinal section line to a continuous curvature curve.

[0047] To further optimize the shape of the longitudinal section line and make the fast performance not affected too much. Further, as Figure 7 shown, the position of the maximum curvature value of the longitudinal section line 2 of the stern fin at the longitudinal midline plane of the ship after correction is located at the front 1 / 3 of the longitudinal section line, and the curvature of the rear 2 / 3 section gradually decreases to smoothly transition to the stern end point to provide greater righting force, optimize the curvature distribution of the longitudinal section line, and achieve the best hydrodynamic performance, which can meet various constraint conditions of ship design while ensuring curvature continuity.

[0048] The side projection area S of the skeg part of the hull below the waterline increases, and the wet area increases accordingly, and the increased part is concentrated in the middle and lower area in the height direction of the skeg. In order to reduce the resistance and meet the structural construction requirements at the same time, the bottom contour of the skeg cross-section can be further optimized. Further, it includes determining and correcting the initial bottom contour 3 of the skeg cross-section to obtain the corrected bottom contour 4 of the skeg cross-section, and regenerating the skeg surface based on the longitudinal section line 2 of the corrected skeg at the longitudinal centerline of the ship and the corrected bottom contour 4 of the skeg cross-section. When the main dimensions and displacement distribution of the ship are guaranteed to be certain, if the maneuverability of the ship still does not meet the requirements, the stabilizing moment of the ship can be further improved by changing the curvature degree and contour shape of the skeg line, thereby improving the ability of the ship to restore its course when subjected to external disturbances. For example, Figure 3 The initial contour 3 of the bottom of the skeg cross section is relatively rounded, as shown in FIG. Figure 8 As shown, the bottom profile 4 of the modified skeg cross section is a "V"-shaped structure, and finally forms the following Figure 9 The three-dimensional structure of the skeg part shown in the figure, the "V"-shaped structure can make the water flow to the bottom of the ship more smoothly, reduce the possibility of vortex generation at the bilge, make the lower part of the stern relatively thin, have an advantage in drainage, and thus reduce the resistance of the ship when sailing, which has a positive impact on the speed performance of the ship.

[0049] For example: Comparative Example 1: Figures 1 to 4 Conventional skeg design as shown; Example 1: Figures 1 to 2 Determine the initial shape of the longitudinal section of the skeg at the longitudinal centerline of the ship 1; Figures 5 to 9 As shown in the figure, under the constraint that the additional resistance of the modified skeg at the design speed does not exceed 1% of the total resistance of the ship, the maximum curvature position of the longitudinal section line 2 of the modified skeg at the longitudinal centerline of the ship is located at the front 1 / 3 of the longitudinal section line, and the curvature of the rear 2 / 3 section gradually decreases to a smooth transition to the stern end point, and the bottom profile of the skeg cross-section is a "V" type structure, and A is 1.03A0.

[0050] The actual ship test and CFD simulation calculation were compared for Example 1 and Comparative Example 1. Two different skeg ship models were towed in still water to measure the resistance at a specific speed. The models of the two schemes were subjected to CFD simulation calculation. The calculation results are shown in Table 1 below:

[0051] Table 1. Comparison of CFD resistance calculation results

[0052]

[0053] Comparison of tail pressure distribution between Example 1 and Comparative Example 1 Figure 10 As shown, the tail velocity vector comparison between Example 1 and Comparative Example 1 is as follows: Figure 11As shown, the results show that the total resistance ratio of Example 1 increases by about 0.1% compared with that of Comparative Example 1. The additional resistance of the modified stern fin at the design speed does not exceed 1% of the total ship resistance. According to the prediction method of full-scale ship standards, the propulsion power of the new scheme increases by about 0.15% compared with the original scheme, indicating that the present invention can effectively solve the problem of limited increase in rudder area, improve the stability moment of the ship, enhance the ship's ability to restore its course when affected by external disturbances, take into account the fast performance of the ship, effectively improve the course stability of the ship, and ensure the overall structural strength.

[0054] On the premise that the lateral projected area S below the waterline of the stern fin part of the hull is the same, Example 1: As Figure 12 shown in ②; Comparative Example 2: The difference from Example 1 is that, as Figure 12 shown in ①, the position of the maximum curvature of the longitudinal section line 2 of the modified stern fin at the longitudinal mid-plane of the ship extends to the stern end point; Comparative Example 3: The difference from Example 1 is that, as Figure 12 shown in ③, the longitudinal section line 2 of the modified stern fin at the longitudinal mid-plane of the ship is in a right-angled shape; CFD simulation calculations are carried out for Example 1, Comparative Example 2, and Comparative Example 3, and the resistances of the three stern fin forms at a specific speed in still water are compared. The results show that the total resistance of Comparative Example 2 increases by about 0.15% compared with that of Comparative Example 1, and the total resistance of Comparative Example 2 increases by about 0.3% compared with that of Comparative Example 1. It can be seen that optimizing the curvature distribution of the longitudinal section line can further optimize the hydrodynamic performance and improve the course stability of the ship. It is preferable that the position of the maximum curvature of the longitudinal section line 2 of the modified stern fin at the longitudinal mid-plane of the ship is located at the front 1 / 3 of the longitudinal section line, and the curvature gradually decreases in the latter 2 / 3 section and smoothly transitions to the stern end point.

[0055] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method of a stern fin for improving the course stability of a ship, characterized in that The method includes: Determine the initial shape (1) of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship. With the goal of increasing the lateral projected area S below the waterline of the stern fin part of the hull under hydrodynamic constraints, correct the initial shape (1) of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship, so that the radius of curvature of the longitudinal section (2) of the corrected stern fin at the longitudinal mid-plane of the ship increases, and the whole extends towards the stern. Regenerate the stern fin surface based on the longitudinal section (2) of the corrected stern fin at the longitudinal mid-plane of the ship to obtain the corrected stern fin.

2. The design method of the stern fin for improving the course stability of a ship according to claim 1, characterized in that, The hydrodynamic constraint includes that the additional resistance of the corrected stern fin at the design speed does not exceed 1% of the total resistance of the ship.

3. The design method of the stern fin for improving the course stability of a ship according to claim 1 or 2, characterized in that, The optimization method with the goal of increasing the lateral projected area S below the waterline of the stern fin part of the hull under hydrodynamic constraints includes: Parallel to the mid-plane along the ship length direction, equally divide the ship length into 20 station intervals through station lines. Count the second station line from the stern to the bow direction as the S2 waterline, and determine the lateral projected area A0 of the longitudinal mid-section of the hull from the stern to the S2 waterline before correction. Regenerate the stern fin surface based on the longitudinal section (2) of the corrected stern fin at the longitudinal mid-plane of the ship, determine the lateral projected area A of the longitudinal mid-section of the hull from the stern to the S2 waterline after correction. With the hydrodynamic constraint, take the maximum value of A being 1.0A0 - 1.05A0 as the optimization goal to optimize the shape of the longitudinal section of the stern fin at the longitudinal mid-plane of the ship.

4. The design method of the stern fin for improving the course stability of a ship according to claim 3, characterized in that, The initial shape of the longitudinal section is corrected to a continuous curvature curve.

5. The design method of the stern fin for improving the course stability of a ship according to claim 4, characterized in that, The position of the maximum curvature of the longitudinal section (2) of the corrected stern fin at the longitudinal mid-plane of the ship is located at the front 1 / 3 of the longitudinal section (2), and the curvature of the rear 2 / 3 section gradually decreases and smoothly transitions to the stern end point.

6. The design method of the stern fin for improving the course stability of a ship according to claim 3, characterized in that, It includes determining and correcting the initial profile (3) of the bottom of the stern fin cross-section to obtain the corrected profile (4) of the bottom of the stern fin cross-section, and regenerating the stern fin surface based on the longitudinal section (2) of the corrected stern fin at the longitudinal mid-plane of the ship and the corrected profile (4) of the bottom of the stern fin cross-section.

7. The method for designing a stern fin for improving the course stability of a ship according to claim 6, characterized in that, The corrected profile (4) of the bottom of the stern fin cross-section is a "V" type structure.

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