A method for designing ship longitudinal skeletons based on design drawings

Abstract

This invention discloses a method for designing ship longitudinal girders based on design drawings, belonging to the field of ship structural design technology. The method includes: obtaining structural parameters from the ship design drawings; performing coupled buckling analysis of the faceplate and strip plate to calculate the critical buckling stress; iteratively optimizing the longitudinal girder section dimensions using a multi-objective genetic algorithm; generating an asymmetric longitudinal girder section with widened faceplates and curved web plates when the optimization results exceed the standard library; dynamically setting anti-rolling elbows according to the longitudinal girder inclination angle; and finally verifying the design through finite element analysis and outputting design drawings. This invention, by integrating precise analysis, intelligent optimization, and innovative configuration, solves the technical problem of balancing safety, lightweighting, and manufacturability in traditional longitudinal girder design methods, and can significantly improve the structural efficiency and design reliability of ship longitudinal girders.

Description

Technical Field

[0001] This invention belongs to the field of ship structural design technology, specifically relating to a method for designing ship longitudinal skeletons based on design drawings. Background Technology

[0002] The ship's hull structure is mainly composed of the outer plating and the internal skeletal system, among which the longitudinal skeleton (longitudinal ribs) is the key component that bears the overall longitudinal bending stress of the hull. The stability of the longitudinal ribs is directly related to the structural safety and load-bearing efficiency of the hull.

[0003] Traditional longitudinal frame design methods rely primarily on empirical formulas, code requirements, and standard profile libraries. Designers first calculate the required section modulus and moment of inertia according to the code, then select the smallest acceptable profile from the standard profile library (such as symmetrical bulb flats and angle steel). While simple, this method has several inherent drawbacks: First, its stability checks are typically based on simplified Euler formulas or independent plate buckling formulas, failing to adequately consider the coupled buckling effect between the longitudinal frame and its attached plates, as well as the elastic constraints provided by the transverse strong frame. This results in calculations that are either overly conservative, adding unnecessary structural weight, or insufficiently safe under certain complex stress states, posing potential risks. Second, the design process is often an open-loop "calculation-selection" model, lacking an effective feedback optimization mechanism, making it difficult to find the optimal balance between safety and economy (structural weight).

[0004] Furthermore, when standard profiles cannot meet the high load requirements of special areas (such as the sides and bottom of large ships), the traditional approach is to blindly select larger profiles or use composite sections, which often leads to low material utilization and a significant increase in structural weight. Meanwhile, for anti-tipping measures of longitudinal girders, standardized elbow plates are usually arranged at equal intervals, failing to be optimized according to the actual stress state and tilt angle of the longitudinal girders, which may result in poor support or material waste.

[0005] Therefore, there is an urgent need in this field for a systematic method for designing ship longitudinal skeletons that can perform precise coupled buckling analysis, automatically optimize cross-sectional dimensions, and generate non-standard high-efficiency cross-sections and their supporting processes, in order to overcome the limitations of traditional methods and achieve a balance between safety and economy. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a design method for ship longitudinal ribs based on design drawings, which solves the problem in the prior art that longitudinal ribs are prone to buckling of the panel or strip plate under compressive stress, leading to structural failure.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for designing the longitudinal skeleton of a ship based on design drawings, comprising the following steps: S1. Obtain the structural parameters of the side and bottom regions in the ship design drawings. The structural parameters include the longitudinal girder spacing, plate thickness, material yield strength, and design compressive stress value. Calculate the critical buckling stress of the longitudinal girder under compressive stress based on the structural parameters. The calculation of the critical buckling stress includes a coupled analysis of local buckling of the panel and overall buckling of the strip plate. S2. Adjust the longitudinal girder section dimension parameters through an iterative optimization algorithm. The longitudinal girder section dimension parameters include the panel width, web height, and web thickness, so that the critical buckling stress of the longitudinal girder is greater than 1.5 times the design compressive stress value and meets the ship structure weight constraint conditions. S3. When the optimized longitudinal section dimensions exceed the range of the standard profile library, an asymmetric longitudinal section design scheme is generated. The asymmetric longitudinal section includes a widened panel extending in the plate thickness direction and a web connection structure with an arc transition. Anti-rolling elbows are set at the intersection of the side longitudinals and the transverse strong frame. The installation angle of the anti-rolling elbows is dynamically adjusted according to the longitudinal inclination angle, and the ratio of the rib thickness to the longitudinal web thickness is 1.2-1.5. S4. Perform finite element verification on the optimized longitudinal rib arrangement, apply equivalent pressure load at the mid-span of the longitudinal rib and analyze the buckling mode. If the buckling safety factor is less than 2.0, return to step S2. S5. Output the final longitudinal rib design drawings, including detailed drawings of the side structure with the anti-rolling elbow plate positioning dimensions marked and the bottom longitudinal rib section drawing.

[0008] Furthermore, in step S2, the calculation of the critical buckling stress specifically includes: A1. Establish an equivalent orthotropic plate model of the longitudinal rib plate composite section, and use the energy method to solve for the buckling coefficient of the rib plate under compressive stress. The local buckling stress of the panel is calculated based on the lattice constraint conditions, taking into account the rotational constraint effect at the connection between the panel and the web. A2. By superimposing the buckling modes of the strip plate and the buckling modes of the panel plate using coupling equations, the critical buckling stress considering the interaction effect is obtained. : In the formula, For panel buckling stress, For the buckling stress of the plate, For panel width, The web height, is the modal coupling coefficient, with a value range of 0.8-1.2.

[0009] Furthermore, in step S2, the iterative optimization algorithm employs a multi-objective genetic algorithm, whose fitness function is defined as: In the formula, The critical buckling stress. To design compressive stress, For reference structural weight, To optimize structural weight, and The weighting coefficients are satisfied. ; Three types of constraints are set during the optimization process: geometric constraints include a panel width-to-thickness ratio of no more than 16 and a web height-to-thickness ratio of no more than 50; strength constraints require that the bending stress does not exceed 0.8 times the material yield strength; and process constraints require that the fillet radius at the connection between the panel and the web is no less than 3 times the plate thickness. The new longitudinal bone section dimensions generated in each iteration will synchronously update the section properties in the finite element model and automatically perform buckling analysis through the APDL command flow.

[0010] Furthermore, in step S3, the steps for generating the asymmetric longitudinal bone section design scheme include: B1. Determine the asymmetric expansion of the panel. : In the formula, For standard panel width, For the material's yield strength, To design compressive stress; B2. The web adopts a variable thickness design, with the thickness in the central region increased by 20% compared to the standard value, and the thickness in the edge region increased by 10% compared to the standard value. B3. A continuous transition curve is set at the connection between the panel and the web, and the radius of curvature of the transition curve is... satisfy , The thickness of the web is given, and the angle between the transition curve and the lower surface of the panel is given. Keep it within the range of 105°-120°; B4. Calculate the moment of inertia of the longitudinal section based on the asymmetric section characteristics, correct the bending section coefficient using the axis shifting formula, and perform local weakening compensation for the web opening area.

[0011] Furthermore, in step S3, the method for setting the anti-tilt elbow plate includes: C1. Based on the longitudinal bone inclination angle Determine the installation angle of the anti-tilt elbow plate Elbow plate height Take the height of the longitudinal sternite 1.2-1.5 times; C2. The connection between the elbow plate and the longitudinal web plate is a double-sided fillet weld, with weld leg dimensions... And not less than 4mm, Web thickness; C3. A 15mm wide bevel edge with a 30° bevel angle is set on the free edge of the elbow plate; elbow plate spacing. satisfy , The thickness of the plate is specified, and at least two anti-tilting elbow plates are set in each longitudinal bone span; the local stability of the longitudinal bone segment with anti-tilting elbow plates is checked, and the influence of the additional constraint provided by the elbow plates on the buckling waveform is considered, and the effective length coefficient in the Euler column buckling formula is modified.

[0012] Furthermore, in step A1, the specific process for calculating the local buckling stress of the panel includes: A11. Discretize the strip into four rectangular plate elements and establish the strain energy expression for each plate element; considering the rotational constraint of adjacent longitudinal ribs on the strip, introduce elastic support stiffness into the boundary conditions of the plate elements. ,in, For elastic modulus, For plate thickness, The distance between longitudinal bones; A12. Solve for the stationary value of the total potential energy of the system using the Ritz method to obtain the buckling coefficient. Implicit equation: In the formula, The aspect ratio of the grid is , Pi For the strip in Bending stiffness in the axial direction For the strip in Bending stiffness in the axial direction For torsional stiffness; A13. Based on the obtained buckling coefficient Calculate the critical elastic buckling pressure of a single plate under pressure. : In the formula, Poisson's ratio, This represents the width of the grid.

[0013] Furthermore, the implementation steps of the multi-objective genetic algorithm include: initializing the population size to 50, using real-number encoding for chromosomes, with each chromosome containing three genes: panel width, ventral height, and ventral thickness; employing a tournament selection strategy for selection, simulated binary crossover for crossover, and polynomial mutation for mutation; setting up a parallel computing architecture, using the MPI protocol to distribute finite element analysis tasks among multiple computing nodes; and considering both an improvement rate of less than 0.1% in the objective function and a constraint violation rate of less than [missing value]. After each iteration, an elite retention strategy is implemented, retaining the top 10% of individuals by fitness to directly enter the next generation; the Pareto front solution set is recorded during the optimization process, and a compromise solution is finally selected based on design preferences.

[0014] The beneficial effects of this invention are as follows: 1. Through closed-loop design based on precise analysis and optimization, the structural safety margin of the longitudinal ribs was significantly improved, and the buckling risk was reduced; the automated process replaced a large amount of tedious manual calculations and trial and error, shortening the design cycle from several weeks to several days; under the premise of ensuring safety, the optimal material distribution scheme was found through optimization, which effectively reduced the weight of the hull structure, thereby reducing construction costs and improving ship energy efficiency; the final finite element automatic verification process ensured the flawlessness of the design scheme and reduced the possibility of later modifications and construction rework. 2. Compared to traditional methods that analyze panels and strips in isolation, the calculation results of the coupled analysis model show extremely high agreement with the results of refined finite element analysis and experiments, with the error controllable within 5%. Accurate analysis avoids the use of excessively large profiles due to overly conservative estimations, providing a theoretical basis for structural lightweighting and shifting design decisions from "experience-dependent" to "data and model-driven." 3. The introduction of elastic supports greatly improves the consistency between the calculation model and the actual structure, and can be extended to consider more complex situations such as skeleton tilt and initial deformation. Attached Figure Description

[0015] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0016] like Figure 1 As shown, this invention discloses a method for designing the longitudinal skeleton of a ship based on design drawings, comprising the following steps: S1. Obtain the structural parameters of the side and bottom regions in the ship design drawings. The structural parameters include the longitudinal girder spacing, plate thickness, material yield strength, and design compressive stress value. Calculate the critical buckling stress of the longitudinal girder under compressive stress based on the structural parameters. The calculation of the critical buckling stress includes a coupled analysis of local buckling of the panel and overall buckling of the strip plate. S2. Adjust the longitudinal girder section dimension parameters through an iterative optimization algorithm. The longitudinal girder section dimension parameters include the panel width, web height, and web thickness, so that the critical buckling stress of the longitudinal girder is greater than 1.5 times the design compressive stress value and meets the ship structure weight constraint conditions. S3. When the optimized longitudinal section dimensions exceed the range of the standard profile library, an asymmetric longitudinal section design scheme is generated. The asymmetric longitudinal section includes a widened panel extending in the plate thickness direction and a web connection structure with an arc transition. Anti-rolling elbows are set at the intersection of the side longitudinals and the transverse strong frame. The installation angle of the anti-rolling elbows is dynamically adjusted according to the longitudinal inclination angle, and the ratio of the rib thickness to the longitudinal web thickness is 1.2-1.5. S4. Perform finite element verification on the optimized longitudinal rib arrangement, apply equivalent pressure load at the mid-span of the longitudinal rib and analyze the buckling mode. If the buckling safety factor is less than 2.0, return to step S2. S5. Output the final longitudinal rib design drawings, including detailed drawings of the side structure with the anti-rolling elbow plate positioning dimensions marked and the bottom longitudinal rib section drawing.

[0017] This implementation constructs a systematic longitudinal girder design process. First, key parameters for the hull and bottom regions are automatically extracted from the ship design database. Then, the core step is to perform precise buckling analysis, which goes beyond simple component stacking and considers the interaction between the panel and the strip. Based on the analysis results, an optimization algorithm automatically adjusts the longitudinal girder dimensions, forming an "analysis-optimization" closed loop. If the optimization results exceed the standard library range, the asymmetric section design module is activated. Simultaneously, the system intelligently generates a matching anti-rolling elbow plate design scheme based on the final longitudinal girder morphology. Finally, the design scheme is automatically verified using finite element software. If the verification fails, it is fed back to the optimization stage for recalculation until the optimal scheme that meets all safety and economic indicators is obtained.

[0018] Through closed-loop design based on precise analysis and optimization, the structural safety margin of the longitudinal ribs was significantly improved, and the buckling risk was reduced. Automated processes replaced a large amount of tedious manual calculations and trial and error, shortening the design cycle from weeks to days. While ensuring safety, the optimal material distribution was found through optimization, which effectively reduced the weight of the hull structure, thereby reducing construction costs and improving ship energy efficiency. The final automated finite element verification process ensured the flawlessness of the design scheme and reduced the possibility of later modifications and construction rework.

[0019] In one embodiment of the present invention, step S2, the calculation of the critical buckling stress specifically includes: A1. Establish an equivalent orthotropic plate model of the longitudinal rib plate composite section, and use the energy method to solve for the buckling coefficient of the rib plate under compressive stress. The local buckling stress of the panel is calculated based on the lattice constraint conditions, taking into account the rotational constraint effect at the connection between the panel and the web. A2. By superimposing the buckling modes of the strip plate and the buckling modes of the panel plate using coupling equations, the critical buckling stress considering the interaction effect is obtained. The coupling equation introduces the modal coupling coefficient. Its value ranges from 0.8 to 1.2, and its specific expression is: In the formula, For panel buckling stress, For the buckling stress of the plate, For panel width, The web height is the critical buckling stress. The purpose is to calculate the overall critical buckling stress of a stiffened plate (e.g., a hull lattice consisting of a face plate, web plate, and stiffeners). This means that the critical stress is taken as the smaller of the critical stresses of the panel and the web components. As a correction term, where, and It is sensitivity, indicating that the panel stress varies with the panel width. The rate of change of web stress with web height The rate of change.

[0020] The core of this implementation is to establish an accurate longitudinal rib-plate combination model. The plates between the longitudinal ribs are treated as continuous plates elastically supported by the ribs, and their buckling strength is calculated using the energy method. For the plate face, it is treated as a lath constrained by the web for local buckling analysis. The most crucial step is to use a model incorporating modal coupling coefficients... The mathematical equations of this method couple the overall buckling mode of the strip plate with the local buckling mode of the panel plate. This coefficient, calibrated based on extensive numerical simulations and experimental data, reflects the mutual weakening or strengthening effects between the two, thus yielding a critical buckling stress that more closely matches the actual stress state. Compared to traditional methods that analyze the panel and strip plate in isolation, the calculation results of the coupled analysis model show extremely high agreement with refined finite element analysis and experimental results, with errors controlled within 5%. This precise analysis avoids the use of excessively large profiles due to overly conservative estimations, providing a theoretical basis for structural lightweighting and shifting design decisions from "experience-dependent" to "data and model-driven."

[0021] In one embodiment of the present invention, in step S2, the iterative optimization algorithm employs a multi-objective genetic algorithm, and its fitness function is defined as: In the formula, The critical buckling stress. To design compressive stress, For reference structural weight, To optimize structural weight, and The weighting coefficients are satisfied. ; Three types of constraints are set during the optimization process: geometric constraints include a panel width-to-thickness ratio of no more than 16 and a web height-to-thickness ratio of no more than 50; strength constraints require that the bending stress does not exceed 0.8 times the material yield strength; and process constraints require that the fillet radius at the connection between the panel and the web is no less than 3 times the plate thickness. The new longitudinal bone section dimension parameters generated in each iteration will synchronously update the section properties in the finite element model and automatically perform buckling analysis through the APDL command flow.

[0022] This implementation transforms the longitudinal bone design problem into a mathematical optimization problem. The design variable is the cross-sectional dimensions of the longitudinal bone. The objective function is set as a weighted sum of safety and weight ratio. The optimization process is executed by an improved multi-objective genetic algorithm that simulates biological evolution, generating a new generation of design schemes through selection, crossover, and mutation. Each new scheme is checked for buckling strength and static strength using automatically invoked finite element software, and the calculation results are used to calculate the fitness of the scheme. Through iteration, the algorithm continuously eliminates inferior schemes, retains and proliferates superior schemes, and finally converges to one or a set of Pareto optimal solutions that are balanced in all aspects.

[0023] This implementation utilizes the global search capability of genetic algorithms to break out of local optima and find superior longitudinal bone sections that are difficult to discover using traditional methods. It can simultaneously provide multiple solutions with different focuses (such as lightest weight or highest safety factor) for designers to choose from based on project requirements. This frees designers from tedious repetitive calculations, allowing them to focus on higher-level design decisions and solution selection.

[0024] In one embodiment of the present invention, step S3, the step of generating the asymmetric longitudinal bone section design scheme includes: B1. Determine the asymmetric expansion of the panel. : In the formula, For standard panel width, The yield strength of the material; B2. The web adopts a variable thickness design, with the thickness in the central region increased by 20% compared to the standard value, and the thickness in the edge region increased by 10% compared to the standard value. B3. A continuous transition curve is set at the connection between the panel and the web, and the radius of curvature of the transition curve is... satisfy , The thickness of the web is given, and the angle between the transition curve and the lower surface of the panel is given. Keep it within the range of 105°-120°; B4. Calculate the moment of inertia of the longitudinal section based on the asymmetric section characteristics, correct the bending section coefficient using the axis shifting formula, and perform local weakening compensation for the web opening area.

[0025] When standard profiles cannot meet the requirements, this implementation proposes breaking the symmetry constraint. Based on the stress distribution, the panel is widened primarily towards the thickness direction (usually the outer side) where greater bending stress is experienced, which significantly improves the moment of inertia and bending resistance of the section. The web employs a variable thickness design, thickening in the middle where stress is higher and thinning at the ends to save weight. A large-radius arc transition is used at the connection between the panel and the web to smooth stress flow and avoid stress concentration. This design is essentially "material distribution on demand," placing material where it can best perform. This results in significantly higher stability and strength of the asymmetric section compared to standard symmetrical profiles at the same weight; a 10%-15% weight reduction can be achieved under the same performance requirements; the arc transition zone effectively reduces the stress concentration factor, improving the fatigue life of the structure under cyclic loading; and it provides a novel and efficient solution for special ship types or high-load areas.

[0026] In one embodiment of the present invention, the method for setting the anti-tilt elbow plate in step S3 includes: C1. Based on the longitudinal bone inclination angle Determine the installation angle of the anti-tilt elbow plate Elbow plate height Take the height of the longitudinal sternite 1.2-1.5 times; C2. The connection between the elbow plate and the longitudinal web plate is a double-sided fillet weld, with weld leg dimensions... And not less than 4mm, Web thickness; C3. A 15mm wide bevel edge with a 30° bevel angle is set on the free edge of the elbow plate; elbow plate spacing. satisfy , The thickness of the plate is specified, and at least two anti-tilting elbow plates are set in each longitudinal bone span; the local stability of the longitudinal bone segment with anti-tilting elbow plates is checked, and the influence of the additional constraint provided by the elbow plates on the buckling waveform is considered, and the effective length coefficient in the Euler column buckling formula is modified.

[0027] This embodiment features a refined design for the anti-tilting elbow plate. Its installation angle is not vertical or horizontal, but finely adjusted based on the actual tilt angle of the longitudinal bone, ensuring that the line of action of the supporting force passes through the shear center of the longitudinal bone section, providing the most effective lateral restraint. The elbow plate height is proportional to the longitudinal bone web height, ensuring sufficient restraint stiffness. The beveling of the free edge reduces weight and improves the welding and stress state in that area. The spacing specifications ensure effective intermediate support under multiple half-wave buckling modes that the longitudinal bone may experience. Dynamically adjusted angles and dimensions maximize the elbow plate's support efficiency for the longitudinal bone, effectively shortening the effective buckling length of the longitudinal bone to the expected value. The beveling design reduces weld length and welding heat input, lowering the resulting residual stress. The design rules provide clear guidance while retaining flexibility to adapt to different local structures.

[0028] In one embodiment of the present invention, the specific process of calculating the local buckling stress of the panel in step A1 includes: A11. Discretize the strip into four rectangular plate elements and establish the strain energy expression for each plate element; considering the rotational constraint of adjacent longitudinal ribs on the strip, introduce elastic support stiffness into the boundary conditions of the plate elements. ,in, For elastic modulus, For plate thickness, The distance between longitudinal bones; This indicates the ability of the longitudinal sternite to resist rotation of the ligament at its junction; The larger the value, the stronger the constraint and the closer it is to the fixed boundary. This indicates that there are no rotational constraints, i.e., it is a simply supported boundary. The expression for strain energy is: In the formula, For bending strain energy, The bending stiffness of the plate. , Poisson's ratio, Let be the area of ​​the plate element. The transverse deflection function represents the deflection at any point on the plane when the plate buckles or bends. Displacement in the direction perpendicular to the plate surface (z direction); For the board The degree of curvature in the direction, For the board The degree of curvature in the direction, The degree to which the plate surface undergoes saddle-shaped twisting. Represents the area of ​​a plate element. Integrate to accumulate the energy across all infinitesimal elements; Among them, elastic support stiffness is introduced into the boundary conditions of plate elements. The process is as follows: Strain energy not directly present in plate elements Instead of being added directly, it is introduced into the total potential energy of the system as an additional energy term. At the common boundary of two adjacent plate elements (that is, the boundary supported by the longitudinal bones), due to the elastic constraint of rotation, when the boundary rotates... At this time, the elastic support will generate a reaction torque. The boundary constraint energy generated by this constraint effect In the formula, For the boundary line to which elastic rotational constraints are applied, Deflection function Along the boundary normal direction The derivative; Then establish the total potential energy of the system. In the formula, Total number of board units This represents the total amount of the elastic constraint boundary. A12. Solve for the stationary value of the total potential energy of the system using the Ritz method to obtain the buckling coefficient. Implicit equation: In the formula, The aspect ratio of the grid is , Pi For the strip in Bending stiffness in the axial direction For the strip in Bending stiffness in the axial direction To increase torsional stiffness, ; A13. Based on the obtained buckling coefficient Calculate the critical elastic buckling pressure of a single plate under pressure. : In the formula, Poisson's ratio, Let be the width of the plate grid; where "plate grid" refers to a local area enclosed by stiffening ribs (including their face plates and webs) and strip plates, and the face plate is a boundary of this plate grid; where the buckling stress of the face plate is . and plate buckling stress According to the formula Please provide a solution.

[0029] This implementation is a concrete mathematical realization of the energy method. It discretizes a continuous strip plate into several rectangular plate elements. For each element, a strain energy expression is established under a micro-bending state. Crucially, instead of using simple or fixed supports at the element boundaries, an elastic support stiffness determined by the stiffness of adjacent longitudinal members is introduced. This more realistically reflects the actual structure. The total potential energy of the system is the sum of the strain energies of all elements. Applying the Ritz method, assuming the shape function of the buckling mode, and setting the first variation of the total potential energy to zero, an eigenvalue problem is derived. Solving this problem yields the accurate buckling coefficient and the corresponding critical stress. The analysis process first involves calculating the elastic buckling critical pressure of a single plate under pressure. Each plate segment separated by stiffeners is analyzed to ensure that it does not buckle locally before the overall structure; then, the critical buckling stress considering the interaction effects is calculated. The stability of the entire stiffened plate structure is analyzed by treating the panel, web, and the already verified slab as a whole.

[0030] This scheme greatly improves the consistency between the calculation model and the actual structure by introducing elastic supports, and can be extended to consider more complex situations such as skeleton tilt and initial deformation.

[0031] In one embodiment of the present invention, the implementation steps of the multi-objective genetic algorithm include: initializing the population size to 50, using real number encoding for chromosomes, with each chromosome containing three genes: panel width, ventral height, and ventral thickness; employing a tournament selection strategy for selection, simulated binary crossover for crossover, and polynomial mutation for mutation; setting up a parallel computing architecture, using the MPI protocol to distribute finite element analysis tasks among multiple computing nodes; and considering both an improvement rate of less than 0.1% in the objective function and a constraint violation rate of less than 0.1% for the convergence criterion. After each iteration, an elite retention strategy is implemented, retaining the top 10% of individuals by fitness to directly enter the next generation; the Pareto front solution set is recorded during the optimization process, and a compromise solution is finally selected based on design preferences.

[0032] This embodiment represents a deep customization of the genetic algorithm for engineering applications. Real-number encoding is more conducive to representing continuous design variables. Tournament selection ensures survival of the fittest. Simulated binary crossover and polynomial mutation generate diverse offspring based on the parent generation while maintaining good convergence. To address the time-consuming nature of finite element method computation, the MPI protocol is used for parallel computation, distributing individuals across multiple CPU cores for simultaneous analysis, significantly reducing the time per iteration. An elite retention strategy prevents the loss of superior individuals during evolution. Ultimately, the algorithm outputs a set of Pareto optimal solutions, meaning that among these solutions, no other solution can be found that is better on all objectives.

[0033] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for designing the longitudinal skeleton of a ship based on design drawings, characterized in that, Includes the following steps: S1. Obtain the structural parameters of the side and bottom regions in the ship design drawings. The structural parameters include the longitudinal girder spacing, plate thickness, material yield strength, and design compressive stress value. Calculate the critical buckling stress of the longitudinal girder under compressive stress based on the structural parameters. The calculation of the critical buckling stress includes a coupled analysis of local buckling of the panel and overall buckling of the strip plate. S2. Adjust the longitudinal girder section dimension parameters through an iterative optimization algorithm. The longitudinal girder section dimension parameters include the panel width, web height, and web thickness, so that the critical buckling stress of the longitudinal girder is greater than 1.5 times the design compressive stress value and meets the ship structure weight constraint conditions. S3. When the optimized longitudinal section dimensions exceed the range of the standard profile library, an asymmetric longitudinal section design scheme is generated. The asymmetric longitudinal section includes a widened panel extending in the plate thickness direction and a web connection structure with an arc transition. Anti-rolling elbows are set at the intersection of the side longitudinals and the transverse strong frame. The installation angle of the anti-rolling elbows is dynamically adjusted according to the longitudinal inclination angle, and the ratio of the rib thickness to the longitudinal web thickness is 1.2-1.

5. S4. Perform finite element verification on the optimized longitudinal rib arrangement, apply equivalent pressure load at the mid-span of the longitudinal rib and analyze the buckling mode. If the buckling safety factor is less than 2.0, return to step S2. S5. Output the final longitudinal rib design drawings, including detailed drawings of the side structure with the anti-rolling elbow plate positioning dimensions marked and the bottom longitudinal rib section drawing.

2. The method for designing ship longitudinal skeletons based on design drawings according to claim 1, characterized in that: In step S2, the calculation of the critical buckling stress specifically includes: A1. Establish an equivalent orthotropic plate model of the longitudinal rib plate composite section, and use the energy method to solve for the buckling coefficient of the rib plate under compressive stress. The local buckling stress of the panel is calculated based on the lattice constraint conditions, taking into account the rotational constraint effect at the connection between the panel and the web. A2. By superimposing the buckling modes of the strip plate and the buckling modes of the panel plate using coupling equations, the critical buckling stress considering the interaction effect is obtained. : In the formula, For panel buckling stress, For the buckling stress of the plate, For panel width, The web height, is the modal coupling coefficient, with a value range of 0.8-1.

2.

3. The method for designing ship longitudinal skeletons based on design drawings according to claim 2, characterized in that: In step S2, the iterative optimization algorithm employs a multi-objective genetic algorithm, whose fitness function is defined as: In the formula, The critical buckling stress. To design compressive stress, For reference structural weight, To optimize structural weight, and The weighting coefficients are satisfied. ; Three types of constraints are set during the optimization process: geometric constraints include a panel width-to-thickness ratio of no more than 16 and a web height-to-thickness ratio of no more than 50; strength constraints require that the bending stress does not exceed 0.8 times the material yield strength; and process constraints require that the fillet radius at the connection between the panel and the web is no less than 3 times the plate thickness. The new longitudinal bone section dimensions generated in each iteration will synchronously update the section properties in the finite element model and automatically perform buckling analysis through the APDL command flow.

4. The method for designing ship longitudinal skeletons based on design drawings according to claim 3, characterized in that: In step S3, the steps for generating the asymmetric longitudinal bone section design scheme include: B1. Determine the asymmetric expansion of the panel. : In the formula, For standard panel width, For the material's yield strength, To design compressive stress; B2. The web adopts a variable thickness design, with the thickness in the central region increased by 20% compared to the standard value, and the thickness in the edge region increased by 10% compared to the standard value. B3. A continuous transition curve is set at the connection between the panel and the web, and the radius of curvature of the transition curve is... satisfy , The thickness of the web is given, and the angle between the transition curve and the lower surface of the panel is given. Keep it within the range of 105°-120°; B4. Calculate the moment of inertia of the longitudinal section based on the asymmetric section characteristics, correct the bending section coefficient using the axis shifting formula, and perform local weakening compensation for the web opening area.

5. The method for designing ship longitudinal skeletons based on design drawings according to claim 4, characterized in that: In step S3, the method for setting the anti-tilt elbow plate includes: C1. Based on the longitudinal bone inclination angle Determine the installation angle of the anti-tilt elbow plate Elbow plate height Take the height of the longitudinal sternite 1.2-1.5 times; C2. The connection between the elbow plate and the longitudinal web plate is a double-sided fillet weld, with weld leg dimensions... And not less than 4mm, Web thickness; C3. A 15mm wide bevel edge with a 30° bevel angle is set on the free edge of the elbow plate; elbow plate spacing. satisfy , The thickness of the plate is specified, and at least two anti-tilting elbow plates are set in each longitudinal bone span; the local stability of the longitudinal bone segment with anti-tilting elbow plates is checked, and the influence of the additional constraint provided by the elbow plates on the buckling waveform is considered, and the effective length coefficient in the Euler column buckling formula is modified.

6. The method for designing ship longitudinal skeletons based on design drawings according to claim 5, characterized in that: In step A1, the specific process for calculating the local buckling stress of the panel includes: A11. Discretize the strip into four rectangular plate elements and establish the strain energy expression for each plate element; considering the rotational constraint of adjacent longitudinal ribs on the strip, introduce elastic support stiffness into the boundary conditions of the plate elements. ,in, For elastic modulus, For plate thickness, The distance between longitudinal bones; A12. Solve for the stationary value of the total potential energy of the system using the Ritz method to obtain the buckling coefficient. Implicit equation: In the formula, The aspect ratio of the grid is , Pi For the strip in Bending stiffness in the axial direction For the strip in Bending stiffness in the axial direction For torsional stiffness; A13. Based on the obtained buckling coefficient Calculate the critical elastic buckling pressure of a single plate under pressure. : In the formula, Poisson's ratio, This represents the width of the grid.

7. The method for designing ship longitudinal skeletons based on design drawings according to claim 6, characterized in that: The implementation steps of the multi-objective genetic algorithm include: initializing the population size to 50, using real-number encoding for chromosomes, with each chromosome containing three genes: panel width, ventral height, and ventral thickness; employing a tournament selection strategy for selection, simulated binary crossover for crossover, and polynomial mutation for mutation; setting up a parallel computing architecture, using the MPI protocol to distribute finite element analysis tasks among multiple computing nodes; and considering both an improvement rate of less than 0.1% in the objective function and a constraint violation rate of less than [missing value]. After each iteration, an elite retention strategy is implemented, retaining the top 10% of individuals by fitness to directly enter the next generation; the Pareto front solution set is recorded during the optimization process, and a compromise solution is finally selected based on design preferences.

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