Open combined deck weld joint arrangement and fatigue life collaborative topological optimization method

Abstract

The invention relates to the technical field of optimization design and fatigue life analysis, and discloses an open combined deck weld joint arrangement and fatigue life collaborative topological optimization method, which comprises the following steps of: establishing a finite element model of an open deck and performing statics analysis; material distribution is optimized by adopting a topological optimization technology, high and low density areas are distinguished, and welding seams are reasonably arranged at junctions; the optimization result is verified and iteratively adjusted; and carrying out fatigue analysis based on the optimization model, and carrying out secondary topological optimization by taking the fatigue life as a constraint condition. According to the technical scheme, the lightweight design of the open deck is achieved, meanwhile, the structural rigidity and strength are improved, the fatigue life is prolonged, material energy consumption is effectively reduced, and the method is suitable for optimal design of complex structures such as ships and ocean platforms and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of optimization design and fatigue life analysis, and in particular to a collaborative topological optimization method for weld arrangement and fatigue life of an open composite deck. Background Art

[0002] As the core load-bearing structure of ships, offshore platforms and large industrial equipment, open decks must meet multiple design requirements of high strength, lightweight and manufacturing feasibility. In actual applications, open decks often face challenges such as dynamic loads (such as wave impact, equipment vibration), local stress concentration and corrosive environment, which put higher demands on the durability and safety of the structure. Traditional design methods mainly rely on the experience of engineers to determine the opening position, reinforcement layout and weld setting through trial and error. Although empirical design can meet basic functional requirements, its limitations are significant: First, the experience-driven method is difficult to quantitatively evaluate the stress distribution under complex loads, which can easily lead to material redundancy or insufficient strength in local areas; second, the layout of welds is mostly based on process habits and lacks scientific basis, which may cause problems such as welding residual stress concentration and fatigue crack propagation, significantly reducing the life of the structure.

[0003] Topology optimization is a structural optimization method based on mathematics and computer technology, which aims to optimize the performance of the structure by rationally allocating materials or resources. Its core idea is to find the most suitable material distribution in the design space to achieve the optimal structural performance. Topology optimization usually does not focus on the specific geometric shape, but achieves the goal by adjusting the material distribution density of each unit in the design domain. In structural engineering, topology optimization helps to reduce material usage and improve the strength, stiffness, stability and durability of the structure. Topology optimization can not only achieve lightweight structures, but also optimize the design while ensuring structural strength and reduce unnecessary material waste. With the continuous improvement of computing power, the application of topology optimization in complex structural design has gradually deepened, especially in the fields of ships, aerospace, bridges and automobiles, and has achieved remarkable results.

[0004] Although existing topology optimization techniques can achieve efficient material distribution, the optimization results are mostly continuum structures, and the constraints of the welding process are not fully considered. Welds are a key process link in connecting structural components, and the impact of their layout on structural performance cannot be ignored. Unreasonable weld positions may lead to excessive stress and accelerate fatigue failure; while too many welds increase manufacturing costs and process complexity. In existing methods, weld layout often relies on simple rules (such as equal spacing) or empirical judgment, and fatigue optimization methods are mostly based on local stress correction or empirical formulas, resulting in large deviations between the optimization results and actual working conditions. This disconnect creates a gap between optimized design and actual manufacturing, making it difficult to achieve a balance between structural performance and process economy.

[0005] Therefore, there is an urgent need for a method that combines topology optimization with weld arrangement and fatigue life analysis to ensure structural performance and fatigue life, optimize material distribution to guide weld setting, achieve structural lightweighting, and improve deck reliability. Summary of the Invention

[0006] The present invention aims to address at least one of the technical problems existing in the related art. To this end, the present invention provides a method for collaborative topological optimization of weld layout and fatigue life for open composite decks. This method addresses the issues of weight redundancy, stress concentration, and high process costs caused by traditional design reliance on experience and irrational weld layout. By topologically optimizing the composite deck structure, rationally arranging plate thickness and weld distribution based on external pressure, and performing fatigue analysis with welds in mind, the method achieves lightweighting while ensuring fatigue life and structural strength.

[0007] A collaborative topology optimization method for weld arrangement and fatigue life of an open composite deck includes the following steps: S1, establish a finite element model of the open deck, set loads and boundary constraints on the model and perform static analysis to obtain stress and displacement distribution and model quality; S2, based on the static analysis results, defines the topology optimization objectives and constraints, and performs topology optimization to obtain the material density distribution; S3, distinguish the plate areas according to the density distribution and arrange the welds to generate a discretized geometric model; S4, applying the same loads and constraints as in step S1 to the model, performing static analysis, verifying the stress, displacement, and mass, and iteratively adjusting the optimization parameters according to the verification results until convergence, thereby obtaining the optimized model; In S5, the weld area is replaced with a plate of equivalent thickness, fatigue analysis is performed on the optimized model, and secondary topology optimization is performed based on fatigue life constraints to obtain the final optimized design.

[0008] Furthermore, a finite element model is established, meshing is performed using shell elements, and geometric dimensions, material properties, and initial thickness are defined; the geometric dimensions include length and width, and the material properties include elastic modulus, Poisson's ratio, and density.

[0009] Furthermore, the boundary constraints include fixed support constraints and multi-directional displacement constraints. The output forms of stress and displacement distribution are stress cloud map and displacement cloud map, which also include the maximum stress value and the maximum displacement value.

[0010] Furthermore, the topology optimization adopts the variable density method, the optimization objective is to minimize the flexibility, and the constraints include volume fraction and overall mass; The variable density method sets the penalty parameter so that the unit stiffness decreases faster when the density decreases, suppressing the intermediate density and making it approach zero.

[0011] Furthermore, topology optimization parameters include threshold filter value and base thickness to control material distribution and weld location; Set the threshold filter value, set the high-density area as thick plate, and the low-density area as thin plate, The welds are arranged at the junction of high and low density. The weld arrangement combines stress distribution and process accessibility to avoid areas of high stress concentration.

[0012] Furthermore, the verification in step S4 includes comparing the maximum stress, maximum displacement, and mass of the model before and after optimization, and adjusting the topology optimization parameters based on the comparison results; If not, adjust the topology optimization parameters and return to step S1 until the results converge.

[0013] Furthermore, the fatigue analysis is performed by treating the weld area as equivalent to a plate of equivalent thickness, and setting constraints based on the fatigue life results to perform secondary topology optimization. Fatigue analysis involves setting up stress-life curves and load cases.

[0014] Furthermore, the goal of the secondary topology optimization is to minimize mass, while imposing constraints that the fatigue life is not less than a preset value and the compliance is not higher than a preset value.

[0015] Furthermore, the fatigue life of plates of equivalent thickness is consistent with the fatigue life of plates with welds.

[0016] Furthermore, the method is suitable for optimizing the opening structures of ship decks, offshore platforms or bridge trusses.

[0017] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: (1) The present invention achieves a lightweight design of the open deck through topological optimization. At the same time, combined with the optimization of weld arrangement, it ensures that the strength and stiffness of the structure meet the design requirements. Under the premise of ensuring that the weight of the structure does not increase, the structural performance is significantly improved, the maximum stress is reduced, the structural stability is improved, and the material energy consumption is reduced.

[0018] (2) The method of the present invention is not only applicable to open decks, but can also be extended to the optimization design and weld arrangement of other complex structures (such as ship bulkheads, bridge trusses, etc.). It has wide applicability and can provide efficient and reliable optimization design solutions for various engineering structures.

[0019] (3) The weld area is equivalent to a thin plate of a specific thickness to simplify the analysis process and improve the accuracy of fatigue life prediction. Fatigue life constraints are introduced in topology optimization. The material distribution and weld layout are optimized through the variable density method to simultaneously improve the structural stiffness, strength and fatigue resistance.

[0020] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 A step diagram of an optimization method according to one embodiment of the present invention; Figure 2 A diagram showing a model of an opening deck in one embodiment of the present invention; Figure 3 for Figure 2 Stress cloud diagram obtained after static analysis of the model; Figure 4 for Figure 2 Displacement cloud diagram obtained after static analysis of the model; Figure 5 for Figure 2 Material density distribution cloud map after topology optimization of the model; Figure 6 Schematic diagram of weld arrangement after model topology optimization; Figure 7 The stress cloud obtained by static analysis of the optimized model; Figure 8 The displacement cloud obtained by static analysis of the optimized model; Figure 9 This is the conceptual model diagram of the weld equivalent substitution experiment; Figure 10 A schematic diagram showing the thickness of the weld seam of the optimized model. Figure 11 This is the result diagram of model fatigue analysis; Figure 12 This is the result diagram of the secondary topology optimization of the model; Figure 13 Final plate shape after model optimization and filtering. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0024] The specific structure and implementation process of this solution are described in detail below using an actual welding optimization design of a ship in which the inventor participated in designing as an example.

[0025] like Figure 1 As shown, the specific process of implementing this solution is shown.

[0026] Step 1: Create a finite element model of the open deck. Create a finite element model of the open deck in HyperMesh. The length is 32.9m, the width is 16.8m, the thickness of the deck opening joint is 5.5mm, and the thickness of the other plates is 3mm. The deck model is as follows: Figure 2 As shown. This size design fully takes into account the strength requirements and lightweight goals of the deck, and meets the engineering standards for open decks on large cruise ships. Shell elements are used to mesh the deck body in the deck model. Shell elements are four-node linear shell elements, suitable for simulating thin plate structures and can accurately calculate bending, shear, and in-plane stresses. To accurately capture the stress gradients at the edges of the openings and in the stiffener areas, the global element size is set to 0.01 meters (10 mm). This fine meshing enables the model to more realistically reflect the mechanical behavior of the deck, especially in sensitive areas of stress and deformation.

[0027] High-strength steel was selected for the deck, with specific material parameters including elastic modulus E = 210 GPa, Poisson's ratio γ = 0.3, and density ρ = 7850 kg / m³. This ensured the model accurately simulated the mechanical behavior of steel during calculations. Material properties were assigned using the Hypermesh material management module, ensuring consistent mechanical properties for each unit in the pipeline. Unit cross-sectional properties were defined using the property module, completing the model's parametric configuration.

[0028] Step 2: Set constraints and loads on the model. To meet the working condition requirements and simulate its stress conditions, set corresponding constraints on each side of the deck.

[0029] The constraints are applied as follows: The non-stressed end is separated by the transverse bulkhead and fixed restraints are applied to the elevator shaft wall at the non-stressed end; Apply y and z direction displacement constraints on the load-bearing end and the elevator shaft wall at the load-bearing end. Apply y and z direction displacement constraints on the upper and lower sides of the deck. Apply x, y, and z direction displacement constraints at the upper and lower ends of the large opening area.

[0030] Model structure diagram Figure 2 , the boundary condition settings are shown in Table 1.

[0031] Table 1: Model boundary constraints

[0032] The force from the transverse bulkhead on the deck is applied at BI and LD, and the magnitude is set to 30KN. The pressure from the elevator shaft is applied at JK, and the magnitude is set to 15KN.

[0033] Step 3: Perform static analysis on the model. After completing the boundary conditions and load settings for the deck, enter the static analysis phase. Create an analysis step, which defines the model's operating conditions throughout the calculation, ensuring that the calculation accurately simulates the effects of these load conditions on the open deck. In this analysis step, set up the statics solver to ensure accurate and convergent stress and displacement results for the deck under load.

[0034] Mises stress is an indicator to measure the strength of the deck structure under complex stress conditions. Under the action of external forces, various parts of the deck are subjected to external forces. The present invention obtains the Mises stress distribution of each unit through finite element analysis results, and pays special attention to the maximum stress value of the deck. The Mises stress results are visualized through Hyperview software to identify stress concentration areas and ensure that the key parts of the pipeline can meet the strength requirements. External forces will cause the overall displacement and local deformation of the open deck. Through the calculation results, the displacement changes of each node of the deck under the action of external forces are obtained. The obtained deck stress and displacement cloud map is as follows: Figure 3 and Figure 4 As shown in the figure, the maximum stress is 276.4 MPa, with the stress being higher at the middle opening connection of the deck. The maximum displacement is 7.745 mm, occurring at the load application end. Using the software's tools, the model's mass is directly calculated to be 9644.824 kg.

[0035] In the subsequent topology optimization phase, our goal was to improve the deck's structural strength without increasing its mass. Using HyperMesh, the system automatically calculated and output the deck's overall mass, which was used as a constraint in the optimization process. The key objective of topology optimization was to improve the deck's strength while maintaining its lightweight characteristics by optimizing material distribution. To achieve this goal, the optimization process also considered the optimal design of weld layout and material distribution to maximize structural performance.

[0036] Through this series of analysis and optimization, we can ensure that the deck meets strength requirements while maintaining its efficient quality performance, providing a solid foundation for subsequent engineering design.

[0037] Step 4: Define the topology optimization objectives and constraints, perform topology optimization, and extract the topology optimization results: Use the topology optimization interface of Optistruct and the variable density method to optimize the structural layout of the open deck.

[0038] Topology optimization technology can introduce specific constraints, such as mass limits and stiffness requirements, to more precisely tailor the optimization process to actual application needs. In this paper, a variable density method was used for deck topology optimization, resulting in the optimal material distribution and structural strength distribution for the open deck. The variable density method (SIMP) is one of the most common methods in topology optimization. In this method, the density of each element ranges from 0 to 1, with 0 representing no material used and 1 representing full material use. Through iterative optimization, the density of each element is gradually adjusted to achieve the optimal design.

[0039] First, multiple topology optimization responses were defined to ensure that the optimization objectives were aligned with the actual working conditions. These included: Compliance: Compliance is a measure of structural stiffness, and the optimization goal was to minimize compliance, that is, to minimize the overall deformation of the deck; Volume Fraction: This represents the ratio of the volume of the material in the deck to the total design volume, and is used to control the material distribution density; and Deck Mass: To ensure that the optimized structure meets lightweight requirements, a mass constraint was set.

[0040] In the topology optimization objective and constraints, set the following: Optimization objective: Minimize flexibility, that is, maximize the stiffness of the deck through optimized design.

[0041] Constraints: The overall mass of the deck is set to no more than 9644.8 kg to ensure that the optimized structure still meets the weight requirements.

[0042] Maximum number of iterations: Set the maximum number of iterations to 500 to ensure the convergence of the optimization process.

[0043] Base Thickness: Set the base thickness of the deck to 2.8mm as the minimum feasible thickness during the optimization process.

[0044] The calculation is performed through the topology optimization module of the software. The calculation formula for topology optimization is as follows: In the formula is the unit material density, x represents the position, and It is the elastic modulus of the material and the elastic modulus value actually used in the calculation; the exponent p is the penalty parameter, p>1. The role of the penalty parameter is to make the unit stiffness decrease faster when the density decreases, so that the intermediate density tends to zero, effectively suppressing the intermediate density.

[0045] represents the flexibility of the objective function, is the constraint condition in the i-th working condition, represents the load vector, is the overall stiffness matrix, is the displacement vector, Indicates the minimum relative density of the unit.

[0046] Step 5: After performing topology optimization, the material density distribution diagram is obtained as follows Figure 5 shown.

[0047] After obtaining the optimized density result, by selecting the appropriate threshold filter value Sk (initial threshold filter value S0, k is the number of modifications, k=0, 1, 2...), the basic thickness set during topology optimization is selected as 2.8mm, so: Where t is the plate thickness, is the unit material density, Sk is the threshold filter value of the current selection, S0=0.9.

[0048] Step 6: Generate a discretized geometric model based on the high-density areas acting as strong support structures, i.e., thickened plates. Welds are placed at the junctions with the low-density thin plates. Welds should be located along the centerline of the intersection of adjacent plates to maximize the strength of the connection. Based on the optimized stress distribution, topology optimization results, and stress contours, welds should be located away from areas of high stress concentration. High stress areas are often the most susceptible to fatigue crack propagation. Excessive welds can lead to excessive local stress and reduce the durability of the structure. Prioritize welds along the deck's primary load-bearing paths to enhance load-bearing capacity and overall structural strength. Welds that are too long or too short can affect the deck's performance, so adjustments are necessary based on specific operating conditions.

[0049] Through these design principles, the rationality and efficiency of weld layout are ensured. Model diagram after layout Figure 6 The optimization results are shown, where the dark gray area represents the thick plate part and the light gray area represents the thin plate part. The thickness variation shows the effectiveness of the optimized material distribution.

[0050] Step 7: Verify optimization results and iterations. To ensure the effectiveness of topology optimization and weld placement, a verification analysis is necessary to evaluate the performance of the optimized design. Static analysis of the optimized model is performed, comparing indicators such as maximum stress, displacement, and mass before and after optimization to verify that the optimized design meets structural requirements.

[0051] The optimized, discretized geometry was imported into Hypermesh. The weld locations were further configured using stress contours. Thickness attributes were assigned to the two plate regions: t1 = 5.5 mm for the thicker portion and t2 = 2.8 mm for the thinner portion. Static calculations were performed again, applying the same boundary constraints and external loads as the initial model. This calculation verified whether the deck structure, after topology optimization and weld placement, could meet the expected strength and deformation requirements under actual operating conditions.

[0052] Step 8: Compare the maximum stress and displacement obtained from the static analysis of the optimized model with those of the initial model. During the calculation process, the model's Mises stress and displacement contours are regenerated. Compare the maximum stress and displacement obtained from the static analysis of the optimized model with those of the initial model to examine quality changes and determine whether stress, displacement, and model quality exceed standards. If quality exceeds standards, stress and displacement decrease, reduce the topology parameters (base thickness T_base) or increase the threshold filter value. If quality is too low or stress and displacement exceed standards, increase the base thickness or decrease the threshold filter value. After changing the parameters, return to Step 5 and re-optimize and verify.

[0053] Step 9: Determine the convergence of the optimization results. If convergence occurs, the optimization is complete. Calculate the optimization target value and The absolute value of the error , as shown below: represents the flexibility of the objective function at the kth iteration, is the target value and The absolute value of the error is hour( is a minimum value close to zero) the result converges and the iterative calculation stops. Otherwise, set And return to step 3 to continue iterative solution.

[0054] The optimal distribution area and thickness of thick and thin plates after optimization convergence are obtained. The final plate thickness is t1 = 5.5 mm for thick plates and t2 = 2.8 mm for thin plates. Figure 7 and Figure 8As shown in Figure 3, the maximum stress of the optimized deck model is 159.4 MPa, the maximum displacement is 7.29 mm, and the overall mass is 9530.9 kg.

[0055] Compared to the initial model, the optimized deck showed significant improvements in: 1. Maximum stress reduction: The maximum stress of the original model was reduced from 248.7 MPa to 159.4 MPa, a decrease of approximately 36%. This indicates that topology optimization effectively reduced the stress concentration area on the deck and enhanced the strength of the structure.

[0056] 2. Reduction in maximum displacement: The maximum displacement is reduced from 8.578 mm in the original model to 7.29 mm, a decrease of approximately 1.29 mm, indicating that the structural stiffness of the optimized deck has been effectively improved.

[0057] 3. Mass reduction: The optimized deck mass is 9530.9 kg, which is lighter than the initial model’s 9644.8 kg, meeting the goal of lightweight design.

[0058] Step 10: By establishing a simple plate structure model, such as Figure 9 , set the thickness of the plate with the weld to T1, apply tension at both ends, and test its fatigue life; when the same parameters of the plate are subjected to the same tension, the plate thickness T2 is selected to make its fatigue life basically consistent with the fatigue life of the plate with the weld. The relationship between the two plate thicknesses can be approximated as: Therefore, the unit at the junction of the thick plate and the thin plate of the optimized model (i.e., the weld position) is separately created and the thickness is set to t0, t0 = 3.3 mm. The material mechanical properties remain unchanged. The schematic diagram of the weld part is as follows: Figure 10 .

[0059] Then set the fatigue analysis parameters, perform fatigue analysis on the thin plate area, import the deck model after dividing the weld area, create a fatigue analysis task, create a fatigue analysis condition, set the fatigue analysis parameters, the finite element analysis unit is MPa, set the stress-life curve (SN curve) through the material card, and complete the property setting, import the load curve, associate the condition with the load, submit the fatigue analysis calculation, and obtain the fatigue analysis calculation results as follows Figure 11 .

[0060] Step 11: Get the fatigue analysis results, the minimum fatigue life is 4.32×10 5Once the optimal weld position is determined, fatigue topology optimization is performed on the model. Open the Fatigue option in the Topology Optimization card, select Life, and set a fuzzy limit of fatigue life greater than or equal to 50,000 cycles. The optimization parameters are as follows: Select the thin plate structure as the topology optimization target, and optimize the responses including flexibility, volume fraction, and mass. Set the optimization constraint to minimize overall structural flexibility, the optimization objective to minimize mass, and the maximum number of iterations to 500 to ensure convergence of the optimization process.

[0061] Perform topology optimization and obtain the material density distribution diagram as shown below Figure 12 As shown, the final model after filtering low-density units is as follows Figure 13 As shown in the figure, the final shape of the plate is changed. The fatigue life, stress distribution and displacement distribution of the optimized model are compared and analyzed.

[0062] The minimum fatigue life of the optimized model is 4.101×10 5 times, the maximum displacement is 7.56mm, the maximum stress is 227MPA, the mass before optimization is 9442.295kg, and the mass after optimization is 8391.11kg.

[0063] Overall, topology optimization and weld placement significantly improved the deck's strength and stiffness. The optimized model not only met strength requirements, but also, through secondary fatigue topology optimization using fatigue analysis, effectively reduced overall mass while maintaining structural strength, ensuring fatigue life and achieving lightweight construction.

[0064] In summary, this paper proposes a topology optimization-based design method for weld layout optimization of open decks. This method aims to address the problems of traditional design methods, which rely on empirical evidence and suffer from irrational weld placement, resulting in excess weight, stress concentration, and high process costs. This method establishes a finite element model of the open deck, applies loads and constraints, and performs static analysis to obtain initial stress and displacement distributions. Subsequently, with the goal of minimizing structural flexibility, topology optimization is performed using the variable density method (SIMP) to obtain an optimal material distribution contour map. Thickened plate locations are determined based on high-density areas, generating a discretized geometric model. Welds are then placed at the junctions of low-density thin plates. The optimized model is then subjected to static analysis again to verify whether its stress, displacement, and mass meet design requirements. If not, the optimization is repeated by adjusting threshold filtering values ​​and topology parameters until the results converge. A weld equivalent surrogate model is introduced to perform fatigue analysis on the thin plate region to quantify fatigue life. Secondary topology optimization, combined with fatigue life constraints, achieves dual-objective optimization for lightweighting and durability. This method achieves lightweight design of open decks, significantly improves structural performance, reduces maximum stress, enhances stability, and reduces material energy consumption. It has wide applicability and can be extended to the optimized design and weld arrangement of complex structures such as ship bulkheads and bridge trusses.

[0065] It should be noted that the parameters in the specific implementation methods are specific parameters given based on the topology optimization of the specific ship mentioned in this application, and do not constitute a limitation on the technical solution to be protected. The specific parameters can be set according to the actual model and application scenario.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A collaborative topology optimization method for weld arrangement and fatigue life of open composite decks, characterized in that: The following steps are involved: S1, establish a finite element model of the open deck, set loads and boundary constraints on the model and perform static analysis to obtain stress and displacement distribution and model quality; S2, based on the static analysis results, defines the topology optimization objectives and constraints, and performs topology optimization to obtain the material density distribution; S3, distinguish the plate areas according to the density distribution and arrange the welds to generate a discretized geometric model; S4, applying the same loads and constraints as in step S1 to the model, performing static analysis, verifying the stress, displacement, and mass, and iteratively adjusting the optimization parameters according to the verification results until convergence, thereby obtaining the optimized model; In S5, the weld area is replaced with a plate of equivalent thickness, fatigue analysis is performed on the optimized model, and secondary topology optimization is performed based on fatigue life constraints to obtain the final optimized design.

2. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1 is characterized in that: The steps for establishing a finite element model are to use shell elements for meshing and define geometric dimensions, material properties and initial thickness; geometric dimensions include length and width, and material properties include elastic modulus, Poisson's ratio, and density.

3. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1 is characterized in that: The boundary constraints include fixed support constraints and multi-directional displacement constraints. The output forms of stress and displacement distribution are stress cloud map and displacement cloud map, which also include the maximum stress value and the maximum displacement value.

4. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1 is characterized in that: The topology optimization adopts the variable density method, the optimization goal is to minimize the flexibility, and the constraints include volume fraction and overall mass; The variable density method sets the penalty parameter so that the unit stiffness decreases faster when the density decreases, suppressing the intermediate density and making it approach zero.

5. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1 is characterized in that: Topology optimization parameters include threshold filter value and base thickness to control material distribution and weld location; Set the threshold filter value, set the high-density area as thick plate, and the low-density area as thin plate, The welds are arranged at the junction of high and low density. The weld arrangement combines stress distribution and process accessibility to avoid areas of high stress concentration.

6. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1 is characterized in that: The verification in step S4 includes comparing the maximum stress, maximum displacement, and mass of the model before and after optimization, and adjusting the topology optimization parameters based on the comparison results; If not, adjust the topology optimization parameters and return to step S1 until the results converge.

7. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1, characterized in that: The fatigue analysis is performed by treating the weld area as equivalent to a plate of equivalent thickness, and setting constraints based on the fatigue life results to perform secondary topology optimization. Fatigue analysis involves setting up stress-life curves and load cases.

8. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1, characterized in that: The goal of the secondary topology optimization is to minimize mass, while imposing constraints that the fatigue life is not less than a preset value and the compliance is not higher than a preset value.

9. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1, characterized in that: The fatigue life of plates of equivalent thickness is consistent with that of plates with welds.

10. The method for collaborative topology optimization of weld arrangement and fatigue life of open composite deck according to claim 1, characterized in that: Suitable for optimizing opening structures on ship decks, offshore platforms or bridge trusses.

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