Ship type comprehensive optimization method

Abstract

The invention relates to the field of ship form optimization, in particular to a ship form comprehensive optimization method, which comprises the following steps: S1, setting constraint conditions; s2, designing a deformation control point and a deformation amplitude range thereof; s3, constructing a genetic algorithm and setting genetic algorithm parameters; s4, calculating still water resistance of the individuals and calculating fitness; s5, judging whether the maximum algebra of the genetic algorithm is reached or not; s6, selecting and copying individuals with high fitness; s7, carrying out crossover and variation on the individuals with high fitness, and returning to the step S4; s8, ending the genetic algorithm, and outputting no less than two still water resistance optimization schemes; s9, calculating the wave increase resistance of the still water resistance optimization scheme by using a slicing method; and S10, selecting a scheme which most meets the requirements of a ship owner as an optimal scheme, and calculating a corresponding optimal ship type through an FFD method. According to the method, the rapidity and seakeeping of the optimized ship are considered, and the calculation amount is reduced.

Description

Technical Field

[0001] The present invention relates to the field of ship type optimization, and in particular to a ship type comprehensive optimization method. Background Art

[0002] Nowadays, the research object of ship type optimization is no longer limited to a single performance, but the comprehensive optimization of multiple performances, and the optimized ship type obtained is also more practical, especially in terms of speed and seakeeping. SBD (Simulation Based Design) technology has opened up a new situation for ship type design and configuration innovation, and has achieved very significant drag reduction and energy saving effects. However, this method has two disadvantages. One is that the calculation amount is large because the static water resistance and seakeeping are calculated for all the generated optimization schemes at the same time. The other is that the generated ship type often cannot guarantee the optimization of static water resistance and seakeeping at the same time.

[0003] At present, the optimization of SBD requires the calculation of resistance and seakeeping for all generated ship type schemes at the same time, which results in excessive calculation and often only one of the rapidity and seakeeping is optimized, and the calculation is large. Summary of the invention

[0004] In order to solve the problems that the existing technology has too much calculation and cannot optimize both rapidity and seakeeping performance at the same time, the present invention proposes a ship type comprehensive optimization method to achieve both rapidity and seakeeping performance optimization and reduce the calculation amount.

[0005] The technical solution of the present invention is:

[0006] Step S1, setting constraints, wherein the constraints include ship size constraints, design draft and displacement volume constraints, structural draft and displacement volume constraints, and structural draft and stability constraints;

[0007] Step S2, designing deformation control points and deformation amplitude ranges: establishing a global coordinate system, constructing deformation regions at the bow and stern respectively, and taking the X, Y and Z directions as deformation directions respectively, setting deformation control points at the bow and stern and deformation amplitude ranges;

[0008] The deformation amplitude range of the bow control point in the Y direction is a negative value, that is, the bow width is reduced. According to the prompt of the CASES software, the reduction of the bow width can ensure that the bow waterline area is reduced;

[0009] Step S3, constructing a genetic algorithm, constructing an initial population that meets the conditions based on the constraint conditions set in steps S1 and S2, the global coordinate system, the deformation control points and their deformation amplitude range, and setting genetic algorithm parameters;

[0010] The genetic algorithm parameters include: population size, crossover rate, mutation rate, and maximum number of generations;

[0011] The population is composed of individuals with a population size, and the individuals are a set of the deformation control points and their deformation amplitude ranges;

[0012] Step S4: Calculate the still water resistance of the individuals, and calculate the fitness according to the still water resistance, including:

[0013] Step S401: Calculate the ship form corresponding to the individuals by the FFD method;

[0014] Step S402: Calculate the still water resistance according to the ship form;

[0015] Specifically, when calculating the still water resistance, the SST k - w model is used as the turbulence model, and the VOF method is used to solve the free surface;

[0016] In the VOF method, the finite volume method is used for the discretization method, the implicit Euler format is used for the time term, and the second - order upwind format is used for the convection term;

[0017] Step S403: Calculate the fitness of the individuals according to the calculated still water resistance of the individuals, and the fitness is negatively correlated with the still water resistance.

[0018] Step S5: Judge whether the maximum number of generations of the genetic algorithm has been reached. If the maximum number of generations has been reached, execute Step S8; otherwise, execute Step S6;

[0019] Step S6: Select and copy the individuals with high fitness;

[0020] Step S7: Cross and mutate the individuals with high fitness obtained in Step S6, and return to Step S4;

[0021] Step S8: End the genetic algorithm, output at least two individuals with the highest fitness and the corresponding still water resistance, and use the output individuals as the still water resistance optimization scheme;

[0022] Step S9: Calculate the wave - making resistance of the still water resistance optimization scheme output in Step S8 by the slicing method, including:

[0023] Step S901: Based on the ship form, use the STF slicing method to calculate the pitching and heaving, and based on the pitching and heaving, use the radiation energy method to calculate the ship motion - induced resistance;

[0024] Step S902: Based on the ship form, use the total reflection approximation formula to calculate the wave reflection - induced resistance;

[0025] Step S903: Sum the ship motion - induced resistance and the wave reflection - induced resistance to obtain the wave - making resistance.

[0026] Step S10: Select one solution that best meets the shipowner's requirements as the optimal solution based on the still water resistance and wave added resistance of the solution with the optimal still water resistance, and calculate the corresponding optimal ship form through the FFD method according to the optimal solution.

[0027] The present invention provides a comprehensive ship form optimization method, which realizes the consideration of optimizing the speed and seakeeping performance in ship form design and reduces the calculation amount. Specifically, by setting a group of deformation control points and their deformation amplitude ranges at the ship bow, the reduction of the waterplane area at the ship bow is ensured to optimize the seakeeping performance; the genetic algorithm is used to ensure the reduction of the still water resistance, that is, the speed is optimized; several solutions with the optimal speed are selected through the genetic algorithm, and only the wave added resistance of these solutions needs to be calculated to reflect the seakeeping performance, instead of calculating the wave added resistance for all solutions, thus reducing the calculation amount. Brief Description of the Drawings

[0028] Figure 1 It is a flowchart of the present invention.

[0029] Figure 2 It is a schematic diagram of the structural deformation area of an embodiment of the present invention.

[0030] Figure 3 It is a schematic diagram of the bow X-direction deformation points of an embodiment of the present invention.

[0031] Figure 4 It is a schematic diagram of the bow Y-direction deformation points of an embodiment of the present invention.

[0032] Figure 5 It is a schematic diagram of the bow Z-direction deformation points of an embodiment of the present invention.

[0033] Figure 6 It is a schematic diagram of the stern X-direction deformation points of an embodiment of the present invention.

[0034] Figure 7 It is a schematic diagram of the stern Y-direction deformation points of an embodiment of the present invention.

[0035] Figure 8 It is a schematic diagram of the stern Z-direction deformation points of an embodiment of the present invention.

[0036] Figure 9 It is a contour comparison diagram of the optimal ship form and the ship form to be optimized in an embodiment of the present invention. Detailed Embodiments

[0037] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0038] The present invention provides a comprehensive ship form optimization method, which combines the FFD geometric reconstruction method and the genetic algorithm, reduces the calculation amount of ship form optimization, and can optimize the speed and seakeeping performance of the ship form simultaneously.

[0039] The flow chart of the present invention is as Figure 1 shown, including:

[0040] Step S1, set constraint conditions, where the constraint conditions include ship size constraints, designed draft displacement volume constraints, structural draft displacement volume constraints, and structural draft metacentric height constraints.

[0041] In this embodiment, the dimensions of the ship to be optimized are: the length, width, and height of the ship are 172.8 m, 30.7 m, and 21.29 m respectively, and the displacement volumes at the designed draft and structural draft are 29309.7 m 3 、38218.37 m 3 , and the metacentric height at the structural draft is 14.39 m.

[0042] The constraint conditions that the ship needs to meet during the optimization process are as follows:

[0043] (1) Keep the length, width, and height of the ship unchanged;

[0044] (2) The displacement volume is not less than 28625.95 m3 at the designed draft of 8.5 m;

[0045] (3) The displacement volume is not less than 37545.61 m3 at the structural draft of 10.5 m;

[0046] (4) The metacentric height at the structural draft is not less than 14.30 m.

[0047] Step S2, construct a local coordinate system by the FFD (Free Form Deform) deformation method, construct control points at the bow and stern respectively, and set the control points, deformation directions, and deformation amplitude ranges for deformation.

[0048] The FFD free deformation technology breaks through the limitations of traditional methods when performing overall and local shape changes on the target object. The basic principle of this method is: first, create a parametric volume, embed the object to be deformed into this parametric volume through local coordinate transformation; second, define a control vertex grid on the parametric volume to make the parametric volume become a Bezier volume; finally, by moving the control points on the parametric volume, transfer the deformation of the parametric volume to the target object to be deformed.

[0049] Geometric reconstruction is mainly completed in the following four steps: constructing a local coordinate system, constructing control points, representing the points after deformation, and solving the linear equation. Here, the first two steps of geometric reconstruction are completed first.

[0050] Construct a local coordinate system. The origin of coordinates of the deformed area is located at the intersection of the mid-longitudinal section of the hull, the waterline plane, and Station 0. The positive direction of the X-axis points from the stern to the bow along the ship, the positive direction of the Y-axis points to the left side of the ship's hull along the mid-longitudinal section, and the positive direction of the Z-axis points to the deck direction along the waterline plane. The global coordinate system satisfies the right-hand rule.

[0051] The present invention selects the semi-parametric modeling method FFD to optimize the bow and stern of the ship simultaneously. When using FFD for parametric deformation, a certain area is deformed by selecting control points. The more concentrated the control points are in a region, the greater the deformation applied to that region.

[0052] A deformation frame is established at the bow and stern respectively. According to experience, a deformation frame with a length of 88m, a width of 15.35m, and a height of 21.25m is established at the bow, and a deformation frame with a length of 70m, a width of 15.35m, and a height of 21.25m is established at the stern, as Figure 2 shown.

[0053] Select the deformation control points in the X, Y, and Z directions of the bow and stern respectively.

[0054] The bow deformation frame has 4 columns in the ship length direction, 4 columns in the ship width direction, and 6 rows in the ship height direction. (For the setting of this ship type), the third row from bottom to top is at the design draft of 8.5m. When deforming the bow of the ship, the selection of control points is mainly based on the following points:

[0055] (1) Since the X-direction control points can affect the fullness of the bow geometry, 48 points in the second and third columns along the positive direction of the ship length are selected to deform the ship in the X direction, as Figure 3 shown;

[0056] (2) In addition to optimizing the calm water resistance of the ship, the present invention also needs to complete the optimization of its seakeeping performance. The wave-added resistance is mainly concentrated at the bow, and a smaller waterplane area helps to reduce the wave-added resistance; according to the display of the CASES software, a narrower bow width can ensure a smaller bow waterplane area. Therefore, 4 control points in the third row, that is, at the design draft of 8.5m, are selected to deform the ship in the Y direction, as Figure 4 shown. Considering the actual need to reduce the waterplane area, the value range of these 4 control points can only be negative and needs to have a greater impact on the hull;

[0057] (3) Considering that in order to obtain the optimal ship form as much as possible, the hull needs to be fully deformed, so it is still necessary to select the control points in the Z direction to change the positions of each station line. If the points at the bottom of the ship are selected as control points, excessive deformation will occur at the bottom of the ship and cannot meet the optimization requirements. Therefore, 8 points in the second row are selected to deform the ship in the Z direction, as Figure 5 shown.

[0058] The stern deformation frame has 5 columns in the ship length direction, 4 columns in the ship width direction, and 6 rows in the ship height direction. The third row from the bottom to the top is at the designed draft of 8.5 m. Since the hull lines at the stern are relatively complex, and it is found during the stern deformation process that if too many control points are selected at the stern to apply two-way deformation, it will cause excessive changes in the hull lines, especially at the fin, resulting in overlapping surfaces and making it impossible to complete the automated calculation. Therefore, the selection of control points at the stern is as follows:

[0059] (1) Select a total of 72 points in the second, third, and fourth columns along the positive ship length direction to perform X-direction deformation on the stern, as Figure 6 shown;

[0060] (2) For the Y-direction and Z-direction, not too much deformation is carried out. Therefore, 4 control points are selected for deformation in each of the two directions, as Figure 7 , Figure 8 shown.

[0061] When setting the change range of design variables, while each design variable causes obvious changes in the hull lines, it is also necessary to ensure that it will not cause excessive deformation of the hull. The change ranges of each design variable are shown in Table 1:

[0062] Table 1 Change ranges of design variables

[0063]

[0064] Among them, x, y, and z respectively correspond to the X-direction, Y-direction, and Z-direction deformations of the bow and stern.

[0065] Step S3, construct a genetic algorithm, and construct an initial population that meets the conditions based on the constraint conditions, the global coordinate system, the deformation control points, and their deformation amplitude ranges set in Step S1 - Step S2, and set the genetic algorithm parameters;

[0066] The genetic algorithm parameters include: population size, crossover rate, mutation rate, maximum number of generations;

[0067] The population is composed of individuals with the number of population size, and the individual is a set of the deformation control points and their deformation amplitude ranges;

[0068] Set the basic parameters of the genetic algorithm, as shown in Table 2.

[0069] Table 2 Set values of basic parameters of the genetic algorithm

[0070] Basic operating parameters Reasonable range Value taken in this embodiment Population size [20,100] 24 Crossover rate [0.4,0.99] 0.9 Mutation rate [0.0001,0.1] 0.01 Maximum number of generations According to the actual situation 10

[0071] According to the population size and the maximum number of generations, this embodiment will finally generate 240 optimization schemes.

[0072] Step S4, calculate the still water resistance of the individual, and calculate the fitness according to the still water resistance, including:

[0073] Step S401: Calculate the hull form corresponding to the individual by the FFD method.

[0074] Step S402: Calculate the still water resistance used to indicate the ship's speed performance. The numerical calculation software starccm+ is selected for the still water resistance calculation. The turbulence model used in the calculation is the SST k - w model, which is a variant form of the k - w model. It can not only ensure being unaffected by the free surface but also ensure the solution accuracy at the solid wall surface. The VOF (Volume of Fluid) method is used for the free surface solution. The discrete method in the present invention adopts the finite volume method, the time term adopts the implicit Euler format, and the convection term adopts the second - order upwind format, whose calculation accuracy is higher than the first - order.

[0075] Step S403: Calculate the fitness of the individual according to the still water resistance of the calculated individual. The fitness is negatively correlated with the still water resistance.

[0076] Step S5: Determine whether the maximum number of generations of the genetic algorithm has been reached. If the maximum number of generations has been reached, execute Step S8; otherwise, execute Step S6.

[0077] Step S6: Select and copy the individuals with high fitness.

[0078] Step S7: Cross and mutate the individuals with high fitness obtained in Step S6, and return to Step S4.

[0079] Individuals with high fitness have small still water resistance, that is, good speed performance. By using the genetic algorithm to select, cross, and mutate individuals with small still water resistance, the speed performance of the offspring can be guaranteed.

[0080] Step S8: End the genetic algorithm, output at least two individuals with the highest fitness and the corresponding still water resistance, and use the output individuals as the still water resistance optimization scheme.

[0081] Step S9: Calculate the wave - making resistance of the still water resistance optimization scheme output in Step S8 by the strip method to indicate the seakeeping performance of the ship, and determine the optimal hull form. The wave - making resistance consists of the ship motion - induced resistance and the wave reflection - induced resistance. The value of the wave - making resistance can be obtained by calculating and summing these two parts. Specifically, it includes:

[0082] Step S901: Based on the hull form, adopt the STF strip method to calculate the pitch and heave, and based on the pitch and heave, adopt the radiation energy method to calculate the ship motion - induced resistance.

[0083] Step S902: Based on the hull form, adopt the total reflection approximation formula to calculate the wave reflection - induced resistance.

[0084] Step S903: Sum up the increased resistance of the ship's motion and the increased resistance of wave reflection to obtain the wave - added resistance.

[0085] Step S10: Select one solution that best meets the shipowner's requirements as the optimal solution based on the still - water resistance and wave - added resistance of the solution with the optimal still - water resistance, and calculate the corresponding optimal ship form through the FFD method according to the optimal solution.

[0086] After processing by the genetic algorithm, solutions for optimizing the still - water resistance are obtained. Calculate the wave - added resistance of these solutions for optimizing the still - water resistance to obtain the optimal ship form, and the design variables are shown in Table 3.

[0087] Table 3 Values corresponding to the design variables of the optimal ship form

[0088] <![CDATA[x1]]> <![CDATA[y1]]> <![CDATA[z1]]> <![CDATA[x2]]> <![CDATA[y2]]> <![CDATA[z2]]> Optimal ship form -0.699 -0.816 -0.221 0.353 -0.096 0.240

[0089] Comparison of the profiles between the optimal ship form and the ship form to be optimized is as Figure 9 shown. In the figure, the red line represents the optimal ship form, and the black line represents the ship form to be optimized. The stern is on the left, the bow is on the right, and the curve numbers are the station numbers.

[0090] The calculation results of the still - water resistance and seakeeping performance of the optimal ship form and the ship form to be optimized are shown in Table 4 and Table 5 respectively.

[0091] Table 4 Comparison of the change in still - water resistance

[0092] Calculation result / N Change % Ship form to be optimized 60.14 － Optimal ship form 58.66 -2.46％

[0093] Table 5 Calculation results of seakeeping performance

[0094]

[0095] So far, the present invention has simultaneously ensured the speed and seakeeping performance of the ship. And compared with calculating the speed and seakeeping performance of all solutions in the prior art, the present invention only calculates the seakeeping performance for several solutions with good speed, reducing the computational amount required in the optimization process.

[0096] It should be noted that the above - described specific embodiments can enable those skilled in the art to understand the present invention - creation more comprehensively, but do not limit the present invention - creation in any way. Therefore, although this specification has described the present invention - creation in detail with reference to the drawings and embodiments, those skilled in the art should understand that the present invention - creation can still be modified or equivalently replaced. In short, all technical solutions and their improvements that do not depart from the spirit and scope of the present invention - creation should be covered by the protection scope of the patent of the present invention - creation.

Claims

1. A ship type comprehensive optimization method, characterized in that: include: Step S1, setting constraints, wherein the constraints include ship size constraints, design draft and displacement volume constraints, structural draft and displacement volume constraints, and structural draft and stability constraints; Step S2, designing deformation control points and deformation amplitude ranges: establishing a global coordinate system, constructing deformation regions at the bow and stern respectively, and taking the X, Y and Z directions as deformation directions respectively, setting deformation control points at the bow and stern and deformation amplitude ranges; The deformation amplitude range of the bow control point in the Y direction is a negative value, that is, the bow width is reduced. According to the prompt of the CASES software, the reduction of the bow width can ensure that the bow waterline area is reduced; Step S3, constructing a genetic algorithm, constructing an initial population that meets the conditions based on the constraint conditions set in steps S1 and S2, the global coordinate system, the deformation control points and their deformation amplitude range, and setting genetic algorithm parameters; The genetic algorithm parameters include: population size, crossover rate, mutation rate, and maximum number of generations; The group is composed of individuals of the population size, and the individual is a group of the deformation control points and their deformation amplitude ranges; Step S4, calculating the hydrostatic resistance of the individual, and calculating the fitness according to the hydrostatic resistance, wherein the fitness is negatively correlated with the hydrostatic resistance; Step S5, determining whether the maximum number of generations of the genetic algorithm has been reached, if so, executing step S8; otherwise, executing step S6; Step S6, selecting and copying individuals with high fitness; Step S7, crossover and mutation of the individuals with high fitness obtained in step S6, and return to step S4; Step S8, ending the genetic algorithm, outputting at least two individuals with the highest fitness and the corresponding hydrostatic resistances, and using the output individuals as a hydrostatic resistance optimization solution; Step S9, using the slicing method to calculate the wave resistance increase of the still water resistance optimization solution output in step S8; Step S10, according to the still water resistance and wave resistance increase of the solution with the best still water resistance, select a solution that best meets the needs of the ship owner as the best solution, and calculate the corresponding optimal ship type through the FFD method according to the best solution.

2. A ship type comprehensive optimization method according to claim 1, characterized in that: In step S4, the method for calculating the fitness is: Step S401, calculating the ship type corresponding to the individual by using the FFD method; Step S402, calculating the still water resistance according to the ship type; Step S403, calculating the fitness of the individual according to the calculated hydrostatic resistance of the individual, wherein the fitness is negatively correlated with the hydrostatic resistance.

3. A ship type comprehensive optimization method according to claim 2, characterized in that: The calculation of the hydrostatic resistance adopts the SST kw model as the turbulence model and the VOF method to solve the free liquid surface.

4. A ship type comprehensive optimization method according to claim 3, characterized in that: In the VOF method, the finite volume method is used as the discretization method, the implicit Euler format is used for the time term, and the second-order upwind format is used for the convection term.

5. A ship type comprehensive optimization method according to claim 1, characterized in that: In step S9, the method for calculating the wave resistance increase includes: Step S901, based on the ship type, using the STF slicing method, calculating the pitch and heave, and based on the pitch and heave, using the radiation energy method to calculate the increased resistance of the ship motion; Step S902, based on the ship type, using a total reflection approximation formula to calculate the wave reflection resistance increase; Step S903, summing the increased resistance due to ship motion and the increased resistance due to wave reflection to obtain the increased resistance due to wave.

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