A stress distribution reinforcing method for a multi-unit structure of a full-gas ring net cabinet gas tank

Abstract

The application discloses a kind of full inflation ring network cabinet gas tank multi-unit structure stress distribution strengthening method, belong to electric power equipment technical field, obtain gas tank geometric parameter by high-precision three-dimensional scanning, adopt hexahedron main guide grid to construct finite element model, realize the sequential coupling calculation of pressure field, temperature field and structure field;Based on stress gradient method and equivalent stress threshold method, automatically identify stress concentration area, adopt variable density method to carry out topological optimization, determine the optimal strengthening area range and form;Through the measures such as additional strengthening rib plate, setting transition fillet and optimizing unit bulkhead layout, stress transmission path is improved in coordination, and fatigue life is improved in combination with welding process optimization and heat treatment process;On the premise of guaranteeing structural strength and rigidity, realize that gas tank overall weight is significantly reduced, the maximum equivalent stress does not exceed material allowable stress safety threshold, stress distribution uniformity is significantly improved, solve the reliability problem caused by gas tank structure stress concentration under the action of multi-physical field coupling.

Description

Technical Field

[0001] This invention belongs to the field of power equipment technology, specifically relating to a method for strengthening the stress distribution of a multi-unit structure in a fully inflatable ring main unit. Background Technology

[0002] As the core infrastructure for energy transmission and distribution in modern society, the safe and stable operation of the power system is crucial to national economic and social development. Ring main units (RNBs), as key equipment in distribution networks for segmenting, connecting, and isolating power lines, play a vital role in ensuring power supply reliability and improving power quality. Fully gas-insulated RNBs, due to their excellent insulation performance, compact structure, and good environmental adaptability, have been widely used in urban power grid upgrades, industrial power distribution, and new energy integration. The gas tank, as the core pressure-bearing and insulation component of the fully gas-insulated RNB, typically integrates multiple electrical functional units to achieve diverse power distribution schemes.

[0003] The stress distribution design of the multi-unit structure inside the gas box is a key factor affecting the safe operation and service life of the fully inflatable ring main unit. In practical engineering applications, the gas box, when inflated, must withstand the internal gas pressure load, while also coping with the coupling effects of multiple physical fields such as temperature changes, short-circuit electrodynamics, and mechanical vibration. The integrated layout of the multi-functional units results in a highly non-uniform stress field distribution inside the gas box, which can easily lead to shell fatigue damage or even sealing failure in stress concentration areas. Furthermore, existing gas box structural design methods are often based on empirical formulas or simplified mechanical models, lacking precise analysis and optimization methods for stress distribution patterns, making it difficult to fundamentally eliminate stress concentration phenomena.

[0004] In existing technologies, stress optimization of multi-unit gas box structures mainly relies on passive reinforcement methods such as increasing wall thickness or adding stiffeners. These methods not only increase equipment weight and manufacturing costs but also have limited effect on improving stress distribution uniformity, making it difficult to meet the stringent structural reliability requirements of fully inflatable ring main units in high-capacity, high-parameter applications. Therefore, it is urgent to research a scientific and effective method for strengthening the stress distribution of multi-unit gas box structures in fully inflatable ring main units to achieve refined design and improved reliability of the gas box structure. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for strengthening the stress distribution of a multi-unit structure of a fully inflatable ring main unit air box, which addresses the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for strengthening the stress distribution of a multi-unit structure in a fully inflatable ring main unit includes the following steps: Step 1: Obtain the geometric parameters and operating condition information of the multi-unit structure of the air box: Use a high-precision three-dimensional scanning device to perform a full-range scan of the multi-unit structure of the air box, obtain the geometric dimensions, wall thickness distribution, unit partition position and sealing structure parameters of the air box shell, and collect the rated working air pressure, temperature change range, short-circuit electrodynamic amplitude and vibration frequency operating condition data of the air box. Step 2: Establish a multi-element finite element analysis model of the gas box: Based on the geometric parameters, construct a three-dimensional finite element model of the gas box using the hexahedral dominant mesh generation method, refine the local mesh in the stress concentration sensitive area, and define the gas pressure load, temperature load, electromagnetic load, and constraint boundary conditions. Step 3: Calculate the stress distribution under multi-physics coupling: The pressure field, temperature field and structural field are calculated sequentially using the sequential coupling method. Finite element analysis software is used to numerically simulate the stress distribution of the air box under the multi-physics coupling of inflation pressure, temperature cycle, short-circuit electrodynamics and mechanical vibration, and obtain the stress field distribution cloud map of the air box shell and unit partition and the stress time history curve of key nodes. Step 4: Identify stress concentration areas and assess structural safety: Based on the stress distribution calculation results, automatically identify stress concentration areas and mark their location, shape and severity, and compare the material yield strength and fatigue limit to assess structural safety. Step 5: Develop and implement a structural reinforcement scheme: Based on the identification results and safety assessment conclusions of the stress concentration areas, use topology optimization to determine the range and shape of the structural reinforcement areas, improve the stress transmission path by adjusting the wall thickness distribution, adding transition fillets and optimizing the unit partition layout, and conduct process feasibility analysis and cost assessment. Step 6: Verify the effect of stress distribution improvement in the optimized structure: Perform multiphysics coupled stress analysis on the air box structure after the reinforcement scheme is implemented, and compare the stress distribution uniformity and maximum equivalent stress value before and after optimization to verify the effectiveness of the structural reinforcement scheme.

[0007] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the fully inflatable ring network cabinet air box of the present invention, the high-precision three-dimensional scanning equipment in step 1 includes a composite scanning system combining a structure light scanner and a laser triangulation instrument. The scanning accuracy of the structure light scanner is a preset accuracy value, and the scanning accuracy of the laser triangulation instrument is higher than that of the structure light scanner. The sampling points with a point cloud density of not less than a preset density are used for complex curved surface areas.

[0008] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the fully inflatable ring network cabinet air box of the present invention, in step 2, the finite element model adopts a hexahedral-dominated hybrid mesh strategy, the unit size of the standard area is a preset first size, the unit size of the stress concentration sensitive area is densified to a preset second size, the mesh quality distortion coefficient is controlled above a preset distortion threshold, and the total number of model nodes is not less than the preset number of nodes.

[0009] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the gas box of the fully inflatable ring network cabinet of the present invention, the boundary conditions set in step 2 include the gas pressure range inside the gas box being a preset pressure range, the ambient temperature cycle range being a preset temperature range, the short-circuit electrodynamic peak value being determined based on the rated short-circuit withstand current, the frequency range of the vibration load being a preset frequency range, and the acceleration amplitude not exceeding a preset acceleration threshold.

[0010] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the gas box of the fully inflatable ring network cabinet of the present invention, the multi-physics field coupling calculation in step 3 adopts a sequential coupling strategy. The first step is to perform steady-state analysis of the gas pressure field to obtain the internal pressure distribution. The second step is to perform temperature field analysis to obtain the thermal stress distribution. The third step is to apply the results of the first two steps as body loads to the structural field for stress and strain calculation. The coupling iteration convergence accuracy is set to a preset convergence accuracy, and the residual displacement does not exceed a preset displacement threshold.

[0011] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the fully inflatable ring main unit air box of the present invention, the automatic identification of stress concentration areas in step 4 adopts a combination of stress gradient method and equivalent stress threshold method. Areas where the Von Mises equivalent stress exceeds a preset proportional threshold of the material yield strength are designated as dangerous areas, and areas where the stress non-uniformity coefficient exceeds a preset non-uniformity threshold are designated as areas requiring optimization. The formula for calculating the stress non-uniformity coefficient is as follows: ; in, The stress distribution uniformity coefficient is... The equivalent stress of the i-th element is... This is the average equivalent stress. The total number of units; the recognition results are displayed through a 3D visualization system and reviewed and confirmed by engineers.

[0012] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the air box of the fully inflatable ring network cabinet of the present invention, the topology optimization in step 5 adopts the variable density method, the optimization objective is set as minimizing the structural flexibility, the constraint condition is that the volume fraction is not higher than the preset volume ratio threshold of the original structure, and the minimum member size constraint is set as the preset minimum size to avoid the appearance of small structures that cannot be processed, the number of iterations is not less than the preset number of iterations, and the convergence accuracy is the preset optimization convergence accuracy. The optimization mathematical model for minimizing the structural flexibility is as follows: ; ; ; in, For structural flexibility, and Let be the stress and strain of the i-th element, respectively. To optimize the volume of the structure, For the original structural volume, For volume fraction constraints, It represents the minimum relative density.

[0013] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the air box of the fully inflatable ring main unit of the present invention, the implementation of the structural reinforcement scheme in step 5 includes adding reinforcing ribs in the stress concentration area. The thickness of the reinforcing ribs is between 1.5 and 3.0 times the thickness of the air box wall, and the height is 5 to 6 times the thickness of the air box wall. For air boxes with a wall thickness of 2.5mm-3.0mm, the corresponding actual height range is 10mm to 18mm. At the same time, transition rounded corners are set in all sharp corner areas to eliminate geometric stress concentration sources, and the radius of the rounded corners is not less than 1.2 times the thickness of the air box wall.

[0014] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the fully inflatable ring main unit air box of the present invention, step 5 also includes welding process optimization, welding positions avoiding stress concentration areas, and the weld type can adopt segmented spot welding or continuous full welding according to the stress level and structural requirements. The specific process parameters and stress influence analysis are as follows: (1) Segmented spot welding method: Applicable to areas where the equivalent stress is less than 50% of the material yield strength or where the rib size is small, i.e., the length is less than 100mm and the height is less than 15mm. The spot welding spacing is uniformly set to 30mm to 50mm, and the number of spot welds for each rib is not less than 4. The distance between the end welding position and the edge of the rib is not less than 5mm and not more than 10mm. The diameter of the spot weld nugget is not less than 1.2 times the thickness of the rib, and the shear strength of a single spot weld is not less than 70% of the shear strength of the rib base material. Finite element simulation analysis shows that the segmented spot welding method produces local stress concentration at the edge of the weld point, with a stress concentration factor of about 2.0 to 2.5. Under the rated working air pressure of 0.14MPa and temperature cyclic load, the peak equivalent stress in the spot welding area is 25% to 35% higher than that in the base material area, and the overall stress field uniformity coefficient deteriorates by about 5% to 8%. The peak value of the residual stress after spot welding is about 20% to 30% of the yield strength of the base material.

[0015] (2) Continuous full welding method: Applicable to areas where the equivalent stress exceeds 60% of the material's yield strength or where airtightness needs to be ensured; the weld leg height is not less than 0.8 times the thickness of the gas box wall, the weld is continuous and uninterrupted, and the starting and ending positions are not less than 10mm from the end of the rib plate; Finite element simulation analysis shows that the continuous full welding method generates a continuous welding residual stress field, and the peak value of the residual tensile stress along the weld direction can reach 60% to 80% of the yield strength of the base material; Under the combined action of rated working gas pressure 0.14MPa and short-circuit electrodynamic load, the peak equivalent stress in the full welding area is 15% to 20% higher than that in the base material area, but the stress transmission path is smoother, and the overall stress field uniformity coefficient is improved by about 10% to 15%. After the full welding is completed, stress relief heat treatment must be performed. The heating temperature is 60% to 80% of the material annealing temperature, that is, 180℃ to 240℃ for aluminum alloy 6061-T6, and the holding time is not less than 2 hours, and then cooled to room temperature with the furnace.

[0016] (3) Simulation verification of welding methods: A local finite element sub-model with dimensions of 50mm×50mm was established, including spot welding and full welding, with the mesh refined to 0.5mm. Simulation results show that for high-stress areas with equivalent stress exceeding 200MPa, continuous full welding combined with heat treatment can control the maximum equivalent stress below 160MPa after welding, which is about 18% lower than that of spot welding. For medium-low stress areas with equivalent stress below 150MPa, segmented spot welding can meet the strength requirements, and the welding deformation is reduced by about 40% compared to full welding.

[0017] As a further preferred embodiment of the stress distribution enhancement method for the multi-unit structure of the air box of the fully inflatable ring network cabinet of the present invention, step 6 also includes lightweight design verification of the multi-unit structure of the air box. Under the premise of ensuring structural strength and stiffness, the optimal material distribution scheme is determined by combining topology optimization and morphology optimization. Finally, the overall weight of the air box is reduced by no less than the preset weight reduction ratio, and the stress distribution uniformity coefficient is improved by no less than the preset uniformity improvement ratio. The formula for calculating the structural safety margin factor is as follows: ; Where η is the safety margin coefficient, σ_max is the maximum equivalent stress in the hazardous area, and σ_allow is the allowable stress of the material; The formula for calculating the maximum equivalent stress reduction ratio is as follows: ; Where σ_max(before) and σ_max(after) are the maximum equivalent stress before and after optimization, respectively; The formula for calculating the overall weight reduction percentage of the air box is as follows: ; Where W_before and W_after are the weights of the air box before and after optimization, respectively.

[0018] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects: 1. This invention achieves precise analysis of multi-physics coupling: By acquiring the geometric parameters of the air box through high-precision three-dimensional scanning, and constructing a finite element model using hexahedral dominant mesh generation, it realizes the sequential coupling calculation of pressure field, temperature field, and structural field, breaking through the accuracy limitations of traditional empirical formulas and simplified mechanical models, and significantly improving the accuracy of stress calculation; Based on the automatic identification algorithm combining the stress gradient method and the equivalent stress threshold method, it can quickly and accurately locate the position, shape, and severity of stress concentration areas, and the identification efficiency is greatly improved compared with manual judgment, providing reliable data support for subsequent optimization design; 2. This invention employs a variable density method for structural topology optimization, minimizing structural flexibility by using a volume fraction not exceeding a preset constraint threshold. This determines a scientifically reasonable range and shape of the reinforcement area, avoiding the blindness of setting the position of the reinforcing ribs based on experience in traditional methods. Through the synergistic effect of multiple measures such as adding reinforcing ribs, setting transition fillets, and optimizing the layout of unit partitions, the stress transmission path inside the gas box is systematically improved, the maximum equivalent stress is significantly reduced, and the uniformity of stress distribution is significantly improved. 3. Under rated pressure and standard temperature conditions, the optimized air box structure of this invention does not exceed the safety threshold of the allowable stress of the material under rated pressure and standard temperature conditions. It still meets the strength requirements under extreme conditions, and the structural safety margin is significantly improved. Through a design method that combines topology optimization and morphology optimization, the overall weight of the air box is significantly reduced while ensuring structural strength, which effectively reduces the weight of the equipment and manufacturing cost. At the same time, the optimization of welding process and the implementation of heat treatment process further improve the fatigue life and long-term reliability of the structure. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall technical solution architecture of the stress distribution enhancement method for the multi-unit structure of the fully inflatable ring network cabinet air box proposed in this invention. Figure 2 This is a schematic diagram of the core principle framework for stress distribution calculation under multi-physics coupling in this invention; Figure 3 This is a flowchart illustrating the main process framework for establishing the finite element analysis model of the multi-unit structure of the air box in this invention. Figure 4 This is a flowchart illustrating the logical process of automatic identification of stress concentration areas and structural safety assessment in this invention. Figure 5 This is a schematic diagram of the multi-level interaction relationship and data flow in the formulation and implementation of the structural reinforcement scheme in this invention; Figure 6 This is a schematic diagram comparing the improvement effect of structural stress distribution before and after optimization and the technical effect of lightweight design verification in this invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings: The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0021] like Figures 1 to 6 As shown in Example 1: To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0022] This embodiment fully describes a method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit. The method covers a complete technical process from geometric parameter acquisition, finite element model establishment, multiphysics coupling analysis, stress concentration identification, structural optimization design to effect verification. The following provides a detailed technical description of each step.

[0023] Step 1: Obtain the geometric parameters and operating condition information of the multi-unit air box structure: In step 1, a high-precision three-dimensional scanning device is used to perform an all-round scan of the multi-unit structure of the air box to obtain key parameters such as the geometric dimensions, wall thickness distribution, unit partition position and sealing structure of the air box shell. At the same time, operating condition data such as the rated working air pressure, temperature change range, short-circuit electrodynamic amplitude and vibration frequency of the air box are collected.

[0024] Specifically, the 3D scanning equipment uses a composite scanning system combining a structured light scanner and a laser triangulation instrument. The structured light scanner has a scanning accuracy of 0.05 mm and a point spacing of 0.1 mm, enabling high-density point cloud data acquisition of the outer surface of the gas box shell. The laser triangulation instrument has a scanning accuracy of 0.02 mm and is used for fine scanning of complex geometric features such as gas box sealing grooves and chamfered areas. The scanning equipment's measurement range covers the entire shape of the gas box, with a measurement volume of 2000 mm long, 1500 mm wide, and 1800 mm high, which can completely cover the external dimensions of a standard fully inflatable ring main unit gas box.

[0025] When performing encrypted scanning on complex curved surfaces, the point cloud density should be no less than 10,000 points / cm² to ensure the integrity of feature point acquisition in areas with drastic curvature changes. During the scanning process, the device moves along a preset path with a step size of 0.5mm to continuously scan the surface of the gas box shell. The overlap rate between adjacent scanning paths should be no less than 30% to ensure the accuracy and reliability of point cloud stitching.

[0026] After scanning, the collected multi-view point cloud data is imported into point cloud processing software for preprocessing. The preprocessing process includes: outlier removal using a filtering algorithm based on point distance statistics to remove noise points whose average distance from neighboring points exceeds three standard deviations; point cloud registration using an iterative nearest-point algorithm with a convergence threshold of 0.001 mm, performing at least 50 iterations; and point cloud fusion using a weighted average algorithm to fuse points in overlapping areas. Finally, a triangular mesh model of the complete outer surface of the gas box is generated, with at least 500,000 vertices and at least 1,000,000 triangular faces.

[0027] When acquiring geometric parameters, key dimensions of the air box are precisely measured using professional measuring instruments. Wall thickness distribution is measured using an ultrasonic thickness gauge with an accuracy of 0.01 mm. At least 200 measuring points are evenly distributed on the surface of the air box shell, arranged in a grid pattern with a spacing of 50 mm along the shell surface. Measurement data is automatically recorded and stored in the measurement database. The location of the unit partitions is determined by setting positioning reference points at the partition connections, measuring the three-dimensional coordinates between these reference points, and calculating the spatial positioning parameters of the partitions. The sealing structure is inspected using a sealing groove cross-sectional profile measurement method. By measuring parameters such as the depth, width, and chamfer radius of the sealing groove, and combining this with the standard specifications of the O-ring, the mating dimensions of the sealing structure are determined.

[0028] Simultaneously, the surface roughness and geometric features of the gas tank shell were recorded for subsequent stress concentration sensitivity analysis. Surface roughness was measured using a contact profilometer, with measurement parameters including Ra (arithmetic mean roughness) and Rz (ten-point mean roughness). The measurement sampling length was 12.5 mm, and the evaluation length was 62.5 mm. Geometric features included concave and convex areas, transition areas, and edge positions on the shell surface. Feature lines were automatically extracted from point cloud data, and a feature parameter table was established.

[0029] Operating condition data were collected as follows: Rated working air pressure data was obtained from the air box design technical documents, with a standard value of 0.12MPa to 0.15MPa (gauge pressure). The maximum allowable working air pressure of the air box design was 0.2MPa. Temperature variation range data was determined based on the actual operating environment of the air box, with a standard operating temperature range of -25℃ to +45℃ and an extreme storage temperature range of -40℃ to +85℃. Short-circuit electrodynamic amplitude was calculated based on the rated short-circuit withstand current, with a standard rated short-circuit withstand current of 20kA (4 seconds) or 25kA (1 second). The peak value of the short-circuit electrodynamic force was determined using electromagnetic field finite element analysis software. Vibration frequency data was obtained through on-site testing of the air box. The frequency range of the vibration load was 5Hz to 500Hz, and the acceleration amplitude did not exceed 10g (98m / s²).

[0030] Step 2: Establish a finite element analysis model of the multi-element structure of the air box: In step 2, based on the geometric parameters, a three-dimensional finite element model of the gas box is constructed using the hexahedral dominant mesh generation method. Local mesh refinement is implemented in the stress concentration sensitive area, and gas pressure load, temperature load, electromagnetic load, and constraint boundary conditions are defined.

[0031] The finite element model is established by first importing the triangular mesh model obtained in step 1 into the finite element preprocessing software. After importing the model, geometric cleanup operations are performed, including: merging duplicate vertices with a distance less than 0.5 mm; repairing broken facets with gaps less than 2 mm; deleting degenerate triangles (minimum interior angle less than 10°) and remeshing them; and eliminating feature overlap and self-intersection problems. After geometric cleanup, a mid-surface extraction operation is performed on the model to convert the shell geometry model into a neutral layer shell element model, which facilitates subsequent mesh generation and element attribute definition.

[0032] The mesh generation employs a hybrid meshing strategy dominated by hexahedrons. The element size for the standard region is set to 5mm, and hexahedron elements are used for mapping mesh generation to ensure mesh regularity and computational accuracy. In stress-concentration sensitive areas (including shell corners, partition joints, sealing groove edges, and near openings), the element size is refined to 1.25mm. Local refinement techniques are used to achieve mesh transition, with the transition zone length not less than three times the element size difference. A gradient transition algorithm is used, with the mesh size increasing or decreasing geometrically along the transition direction, and the transition ratio controlled within 1.2.

[0033] When complex geometric regions cannot be meshed using hexahedral elements, second-order tetrahedral elements are used for filling. The minimum element size in the filled region is no less than 2.5 mm to ensure smooth mesh transitions. Mesh quality control indicators include: Jacobian Ratio above 0.7, Aspect Ratio below 5.0, and mesh skew within 60°. The final model should have no fewer than 500,000 nodes and 200,000 elements, with hexahedral elements accounting for no less than 60%.

[0034] Regarding element type selection, shell elements are used to simulate the gas box shell and partition plates. Nine integration points are set in the thickness direction of the shell elements to accurately capture bending stress. The connection between the shell and partition plates adopts a common-node connection method, with the node coordinates of the connection area completely overlapping to ensure coordinated and continuous displacement and rotation. The sealing structure is simulated using contact elements. The contact stiffness is calculated and determined based on the elastic modulus and compression of the sealing ring, and the friction coefficient is set to 0.2.

[0035] The boundary conditions are set as follows: A gas pressure load is applied to the inner surface of the gas box shell, with a load value ranging from 0.12 MPa to 0.15 MPa of the rated working gas pressure, and the load direction is perpendicular to the inner surface of the shell. The temperature load is determined based on the temperature field analysis results, with an ambient temperature cycling range of -40℃ to +85℃ and a temperature change rate set to 5℃ / min, simulating the thermal shock effect when the gas box is transferred from a low-temperature environment to a high-temperature environment. A short-circuit electrodynamic load is applied to the conductor mounting location, with the load distribution calculated based on the conductor cross-sectional area and short-circuit current, and the peak load direction along the conductor axis. A vibration load is applied to the gas box mounting feet, and the frequency distribution characteristics of the vibration load are described using the power spectral density function (PSD), with a frequency range of 5 Hz to 500 Hz.

[0036] The boundary conditions are set to fully constrain the mounting flange surface of the gas box, including translational and rotational degrees of freedom. For the symmetrical analysis case of the gas box, the nodes on the symmetry plane can be set to satisfy the symmetry constraint conditions, and the normal displacement and normal rotation angle of the symmetry plane can be zero. After the boundary conditions are defined, the model is checked to confirm that the loads and constraints are applied correctly and that no boundary conditions are omitted or incorrectly applied.

[0037] Step 3: Perform stress distribution calculations under multiphysics coupling. In step 3, the pressure field, temperature field and structural field are calculated sequentially using a sequential coupling method. Finite element analysis software is used to numerically simulate the stress distribution of the gas box under the coupling of multiple physical fields such as inflation pressure, temperature cycle, short-circuit electrodynamics and mechanical vibration, and to obtain the stress field distribution cloud map of the gas box shell and unit partition and the stress time history curve of key nodes.

[0038] Multiphysics coupling calculations employ a sequential coupling strategy, decomposing complex multiphysics problems into several single-physics problems for sequential solution. The coupling effect between these physics fields is achieved through data transfer. The first step involves a steady-state analysis of the gas pressure field. The gas inside the tank is set to SF6 insulating gas or dry air, with a pressure ranging from 0.12 MPa to 0.15 MPa. The pressure distribution inside the tank is calculated using a fluid dynamics analysis module. The pressure field analysis utilizes a steady-state solver, with a set convergence accuracy of [value missing]. The distribution of the pressure field inside the air box is calculated to obtain the structural response under internal pressure load.

[0039] The second step involves temperature field analysis, using the pressure field analysis results as the boundary conditions. The temperature field analysis considers convective heat transfer of the SF6 gas inside the gas tank and thermal conduction of the shell material, employing a fluid-structure interaction analysis method. The ambient temperature boundary condition is set as a temperature cyclic load, with a temperature range from -40℃ to +85℃ and a temperature change rate of 5℃ / min, simulating the temperature change process under actual operating conditions. The relationship curves between the material's thermophysical parameters (thermal conductivity, specific heat capacity, and coefficient of thermal expansion) and temperature are determined through fitting experimental data. The temperature field analysis outputs temperature distribution cloud maps of the gas tank shell and internal components.

[0040] The third step involves applying the results of the first two steps as volume loads to the structural field for stress and strain calculations. In the structural field analysis, the internal pressure distribution calculated from the gas pressure field is applied as a surface load to the inner surface of the shell, while the temperature distribution calculated from the temperature field is applied as a volume load to the entire model. When applying the loads, both synchronous and asynchronous loading of the temperature and pressure fields need to be considered. The synchronous loading condition simulates the stress state of the gas box under the simultaneous action of rated operating pressure and maximum operating temperature; the asynchronous loading condition simulates the stress peak moment caused by the lag in temperature changes during temperature cycling.

[0041] For short-circuit electrodynamic loads, a transient dynamic analysis method is employed. The duration of the short-circuit current is set to 1 to 4 seconds, and the peak load is determined based on the rated short-circuit withstand current. The short-circuit electrodynamic load is applied to the conductor mounting location, with the load direction along the conductor axis. The relationship between the load magnitude and time is described by a damped oscillation function. The integration time step for the transient analysis is set to 0.001 seconds to ensure that the stress response at the peak load moment is captured.

[0042] For the vibration load, a random vibration analysis method is used, and the load spectrum is described by the acceleration power spectral density function. The vibration load is applied to the mounting feet of the air box, with a frequency range of 5Hz to 500Hz and an acceleration amplitude not exceeding 10g. The calculation results of the random vibration analysis are the statistical characteristic values ​​of the response, including the root mean square stress, peak stress equivalent value, etc.

[0043] The convergence accuracy of the coupled iteration is set to The residual displacement is kept below 0.001 mm to ensure the convergence and accuracy of the calculation results. After the calculation is completed, the stress field distribution cloud map of the gas box shell and unit partition is extracted, including the Von Mises equivalent stress distribution, principal stress distribution, and maximum shear stress distribution. The stress time history curves of key nodes are extracted, including the center point of the stress concentration area, the characteristic point of the corner area, and the main node at the partition connection.

[0044] Step 4: Identify stress concentration areas and assess structural safety: In step 4, based on the stress distribution calculation results, stress concentration areas are automatically identified and their location, shape and severity are marked, and structural safety is assessed by comparing the material yield strength and fatigue limit.

[0045] Automatic identification of stress concentration regions employs a combination of the stress gradient method and the equivalent stress threshold method. The stress gradient method identifies regions based on the stress difference between adjacent elements in the calculation results. The stress gradient of element i is calculated as the difference between the stress value of adjacent element j and the stress value of element i, divided by the distance between element i and element j. A stress gradient threshold is set; when the stress gradient of an element exceeds the threshold, that element is marked as a stress gradient concentration region. The threshold setting is determined based on material properties; for aluminum alloy materials commonly used in fully inflatable ring mains cabinet gas boxes (such as 6061-T6), the stress gradient threshold is 50 MPa / mm.

[0046] The equivalent stress threshold rule defines a critical area as the region where the Von Mises equivalent stress exceeds a preset proportional threshold of the material's yield strength. For material 6061-T6, the yield strength is 275 MPa, and with a safety factor of 1.5, the allowable stress is 183 MPa. Setting the proportional threshold to 0.8, when the Von Mises equivalent stress exceeds 220 MPa (0.8 times the yield strength), the region is deemed a critical area, requiring structural reinforcement design.

[0047] Meanwhile, regions where the stress non-uniformity coefficient exceeds a preset non-uniformity threshold are designated as regions requiring optimization. The stress non-uniformity coefficient is defined as the ratio of the element stress value to the average stress value of the region. When the stress non-uniformity coefficient of a certain region exceeds 1.5, it is determined that there is a stress non-uniformity problem in that region, and the stress transmission path needs to be improved through structural optimization.

[0048] The automatic identification results are displayed through a 3D visualization system. The display includes: a stress distribution cloud map, which visually displays the stress distribution using color gradients; stress concentration area markers, which highlight the identified stress concentration areas; and a stress time history curve, displaying the stress change history of key nodes in a timeline format. The interactive functions of the 3D visualization system allow engineers to switch perspectives, view sections, and perform annotation and measurement operations, facilitating the review and confirmation of the identification results. During review, engineers can correct the automatic identification results based on practical engineering experience, adding or deleting marked areas to ensure the accuracy and completeness of the identification results.

[0049] The structural safety assessment is conducted according to the following procedure. First, the strength of the identified hazardous areas is checked, the ratio of the maximum equivalent stress in the hazardous area to the allowable stress of the material is calculated, and the structure is assessed to determine whether it meets the strength requirements.

[0050] The calculation formula is as follows: ; in, For safety margin coefficient, The maximum equivalent stress in the danger zone. Let be the allowable stress of the material. When When the structure meets the requirements, its strength is sufficient; when At one time, the structural strength is sufficient but the safety margin is low, requiring attention; when If the structural strength does not meet the requirements, structural reinforcement is necessary.

[0051] Secondly, a fatigue life assessment of the gas box structure is performed. Based on the statistical characteristics of temperature cyclic loads and vibration loads, the fatigue damage degree of the structure is calculated using Miner's linear fatigue cumulative damage theory. The number of temperature cyclic load cycles is determined according to the gas box's design life, which is 30 years. The annual temperature cycle count is determined based on the operating environment, generally ranging from 50 to 200 cycles. The equivalent cycle count of vibration loads is calculated based on the power spectral density integral. The fatigue limit is described using the SN curve, and the SN curve parameters are determined by fitting material fatigue test data. The calculated fatigue damage degree should be less than 1.0 to ensure that the structure will not experience fatigue failure within its design life.

[0052] Step 5: Develop and implement a structural reinforcement plan: In step 5, based on the identification results and safety assessment conclusions of the stress concentration area, the range and shape of the structural reinforcement area are determined by the topology optimization method. The stress transmission path is improved by adjusting the wall thickness distribution, adding transition fillets and optimizing the unit partition layout. A process feasibility analysis and cost assessment are also conducted.

[0053] Topology optimization employs the variable density method, with the optimization objective set as minimizing structural flexibility. The basic principle of the variable density method is to introduce a relative density variable. (Values ​​range from 0 to 1), with relative density as the design variable for optimization calculations. The optimization mathematical model is expressed as follows:

[0054] ; ; ; in, This refers to structural flexibility (strain energy). and Let be the stress and strain of the i-th element, respectively. To optimize the volume of the structure, For the original structural volume, Volume fraction constraint (set to 0.6 to 0.8). The minimum relative density is set to 0.01 to 0.05.

[0055] The constraints include volume fraction constraints and minimum member size constraints. The volume fraction constraint is set to be no more than 0.7 of the original structure's volume, meaning the optimized structure's volume does not exceed 70% of the original volume. The minimum member size constraint is set to 3mm to avoid the creation of unmanufacturable small structures; this constraint is implemented using sensitivity filtering techniques. The number of optimization iterations is set to be no less than 100, with a convergence accuracy of [missing value]. .

[0056] After topology optimization, the range and shape of the structural reinforcement region are determined based on the optimization results. Elements with a relative density greater than 0.5 are extracted as material retention regions, and elements with a relative density less than 0.2 are extracted as material removal regions. The boundary of the material retention region is the recommended stiffener outline. The design of the stiffener needs to meet structural strength requirements while also considering manufacturability and material economy.

[0057] The structural reinforcement scheme includes the following specific measures: Reinforcing ribs are added to stress concentration areas. The thickness of the reinforcing ribs is 1.5 to 3 times the gas box wall thickness, and the height is 5 to 6 times the gas box wall thickness. For gas boxes with a wall thickness of 2.5mm to 3.0mm, the corresponding actual height range is 10mm to 18mm. Simultaneously, transition fillets are provided in all sharp corner areas to eliminate geometric stress concentration sources. The fillet radius is not less than 1.2 times the gas box wall thickness. For sharp corner areas with a stress concentration factor greater than 2.0, the fillet radius is increased to 2 to 3 times the wall thickness. The transition fillets are machined using CNC milling, and the surface roughness Ra of the fillets does not exceed 3.2μm.

[0058] The connection between the reinforcing rib and the air box shell can be achieved by segmented spot welding or continuous full welding. The specific choice is determined by comprehensively considering the stress level in the stress concentration area, the rib size, and the air box wall thickness. (1) Segmented spot welding method: Applicable to areas where the equivalent stress is less than 50% of the material yield strength or where the rib size is small (length less than 100mm, height less than 15mm). The spot welding spacing is uniformly set to 30mm to 50mm, and the number of spot welds for each rib is not less than 4. The distance between the end welding position and the edge of the rib is not less than 5mm and not more than 10mm. The diameter of the spot weld nugget is not less than 1.2 times the thickness of the rib, and the shear strength of a single spot weld is not less than 70% of the shear strength of the rib base material. Finite element simulation analysis shows that the segmented spot welding method generates local stress concentration at the edge of the weld point, with a stress concentration factor of approximately 2.0 to 2.5. Under the rated working pressure of 0.14MPa and temperature cyclic load, the peak equivalent stress in the spot welding area is 25% to 35% higher than that in the base material area, and the overall stress field uniformity coefficient deteriorates by approximately 5% to 8%. The peak value of the residual stress after spot welding is approximately 20% to 30% of the yield strength of the base material.

[0059] (2) Continuous full welding method: Applicable to areas where the equivalent stress exceeds 60% of the material's yield strength or where airtightness needs to be ensured. The weld leg height should be no less than 0.8 times the thickness of the gas box wall, the weld should be continuous and uninterrupted, and the starting and ending positions should be no less than 10mm from the end of the rib plate. Finite element simulation analysis shows that the continuous full welding method generates a continuous welding residual stress field, and the peak value of the residual tensile stress along the weld direction can reach 60% to 80% of the yield strength of the base material; under the combined action of rated working gas pressure 0.14MPa and short-circuit electrodynamic load, the peak equivalent stress in the full welding area is 15% to 20% higher than that in the base material area, but the stress transmission path is smoother, and the overall stress field uniformity coefficient is improved by about 10% to 15%. After the full welding is completed, stress relief heat treatment must be performed. The heating temperature is 60% to 80% of the material annealing temperature (180℃ to 240℃ for aluminum alloy 6061-T6), the holding time is no less than 2 hours, and the furnace is cooled to room temperature.

[0060] (3) Simulation verification of welding methods: A local finite element sub-model (50mm×50mm, mesh refined to 0.5mm) was established, including both spot welding and full welding methods. Simulation results show that for high-stress areas with equivalent stress exceeding 200MPa, continuous full welding combined with heat treatment can control the maximum equivalent stress below 160MPa after welding, which is about 18% lower than that of spot welding. For medium-low stress areas with equivalent stress below 150MPa, segmented spot welding can meet the strength requirements, and the welding deformation is reduced by about 40% compared to full welding.

[0061] When optimizing the unit partition layout, the position and spacing of the partitions are adjusted based on the stress distribution calculation results. The principle for adjusting the partition position is to place the partitions in areas with lower stress levels and avoid the partitions passing through areas of stress concentration. The optimization of the partition spacing is determined based on the shell span calculation, with a standard spacing of 0.4 to 0.6 times the shell span. The optimization of the partition thickness is determined based on the load borne by the partition, with the ratio of partition thickness to shell thickness controlled between 1.0 and 2.0.

[0062] The process feasibility analysis includes casting process assessment, welding process assessment, and machining process assessment. The casting process assessment checks the draft angle (not less than 3°) and wall thickness uniformity of the reinforcing ribs (wall thickness ratio between adjacent areas not exceeding 2:1). The welding process assessment checks the weldability of the reinforcing ribs to the shell and the rationality of the weld arrangement. The machining process assessment checks the machining difficulty and accuracy assurance measures for the transition fillets.

[0063] Cost assessment includes material costs, processing costs, and assembly costs. Material costs are calculated based on the optimized structural volume and material density. Processing costs are estimated based on the type of processing technology and processing time. Assembly costs are estimated based on the complexity of the assembly process and assembly time. The total cost is compared with the cost of the original solution to ensure the economic viability of the optimized solution.

[0064] Step 6: Verify the effect of the optimized structure on stress distribution improvement: In step 6, a multiphysics coupled stress analysis is performed again on the air box structure after the reinforcement scheme is implemented. The stress distribution uniformity and maximum equivalent stress value before and after optimization are compared to verify the effectiveness of the structural reinforcement scheme.

[0065] The verification process includes four stages: remodeling, reanalysis, result comparison, and effect evaluation. In the remodeling stage, the optimized structural geometry is updated in the finite element model, the mesh is re-generated, and the same boundary conditions and loads are applied. In the reanalysis stage, multiphysics coupled stress calculations are performed according to the method in step 3 to obtain the stress distribution results of the optimized structure.

[0066] The results comparison employed quantitative analysis methods. The comparison indicators included maximum equivalent stress, stress distribution uniformity coefficient, and structural safety margin. The formula for calculating the maximum equivalent stress is as follows:

[0067] ; in, and These represent the maximum equivalent stress before and after optimization. The maximum equivalent stress after optimization should be reduced by no less than 15%.

[0068] The stress distribution uniformity coefficient is defined as the ratio of the standard deviation of structural stress to the mean stress, and the calculation formula is as follows: ; in, The stress distribution uniformity coefficient is... The equivalent stress of the i-th element is... This is the average equivalent stress. This represents the total number of elements. The optimized stress distribution uniformity coefficient should improve by at least 15%.

[0069] The structural safety margin comparison verifies whether the optimized structure meets the strength requirements. The ratio of the maximum equivalent stress to the allowable stress of the material in the optimized structure is calculated, ensuring that this ratio is less than 1.0 and the safety margin factor is greater than 1.2.

[0070] The effectiveness evaluation also includes verifying the weight reduction effect. The actual weight of the optimized air box is measured, and the weight reduction percentage is calculated.

[0071] ; in, and The figures show the weight of the gas tank before and after optimization. While ensuring structural strength and rigidity, the overall weight of the gas tank should be reduced by no less than 10%.

[0072] In this embodiment, the complete application process of the stress distribution enhancement method for the multi-unit structure of the gas box of a fully inflatable ring main unit is as follows. A standard fully inflatable ring main unit gas box of model XGN-12 / 630-25 is selected as the analysis object. The gas box shell is made of 6061-T6 aluminum alloy, with a nominal thickness of 4mm. The gas box's external dimensions are 1200mm in length, 800mm in width, and 600mm in height, and it contains three electrical unit compartments.

[0073] In step 1, an ATOS Core 200 optical scanner was used to perform a 3D scan of the gas box, with a scanning accuracy of 0.05 mm and a point cloud density of 12,000 points / cm². The wall thickness distribution of the gas box shell was measured, and the normal wall thickness was 2.5 mm. Solid reinforcing ribs were 10-15 mm thick, and bent reinforcing ribs were 15-20 mm thick. The operating conditions were set as follows: rated working air pressure of 0.14 MPa, operating temperature range of -25℃ to +45℃, short-circuit withstand current of 25 kA (1 second), and vibration frequency range of 10 Hz to 200 Hz.

[0074] In step 2, a finite element model of the gas box is established, with a total of 658,000 nodes and 286,000 elements, of which hexahedral elements account for 67%. The boundary conditions are set as follows: the gas box mounting flange is fully constrained, the internal gas pressure is 0.14 MPa, the temperature cycle is -25℃ to +45℃, and the peak short-circuit electrodynamic force is calculated to be 12.8 kN / m based on 25 kA.

[0075] In step 3, multiphysics coupling analysis is performed, and the coupling convergence accuracy is... The residual displacement is 0.0008 mm. The calculated maximum equivalent stress is 248 MPa, located in the corner region of the shell; the stress distribution uniformity coefficient is 0.42.

[0076] In step 4, three stress concentration areas were automatically identified: the first was located at the connection between the shell side plate and the partition, with a Von Mises equivalent stress of 232 MPa; the second was located at the bottom corner of the shell, with a Von Mises equivalent stress of 248 MPa; and the third was located at the intersection of the partition and the sealing groove, with a Von Mises equivalent stress of 218 MPa. The safety margin factor was 1.11, which is lower than the design requirement of 1.5.

[0077] In step 5, topology optimization is used to determine the reinforcement scheme: triangular reinforcing ribs are added to the corner areas of the shell, and transverse reinforcing ribs are added to the partition connection areas.

[0078] In step 6, a new coupling analysis was performed on the optimized structure. The maximum equivalent stress was reduced to 168 MPa, a decrease of 32.3%. The stress distribution uniformity coefficient was reduced to 0.28, an improvement of 33.3%. The safety margin factor was increased to 1.64, meeting the design requirements. The overall weight of the gas box was reduced from 48.6 kg to 41.2 kg, a reduction of 15.2%.

[0079] The above verification results show that the stress distribution strengthening method for the multi-unit structure of the fully inflatable ring network cabinet air box provided in this embodiment can effectively identify stress concentration areas, scientifically formulate structural strengthening schemes, significantly improve stress distribution, enhance structural safety margin, and achieve the goal of lightweighting.

[0080] Example 2: To meet the structural reinforcement requirements of fully inflatable ring main unit gas boxes for different specifications and application scenarios, this embodiment provides a variant of the parametrically driven method for strengthening the stress distribution of multi-unit structures in the gas box. This scheme maintains the core methodological flow while optimizing key technical aspects through parametric adaptation and process optimization.

[0081] The method also includes the following steps: acquiring the geometric parameters and operating condition information of the air box, establishing a finite element analysis model, performing multiphysics coupled stress analysis, identifying stress concentration areas and assessing safety, formulating and implementing a structural reinforcement scheme, and verifying the optimization effect. The main differences between this embodiment and Embodiment 1 are as follows.

[0082] In step 1, a composite measurement scheme combining a handheld laser scanner and an articulated measuring machine is adopted for large air boxes (external dimensions exceeding 1500mm). The handheld laser scanner is the FARO Edge series, with a scanning accuracy of 0.025mm and a scanning rate of 1,200,000 points / second, suitable for efficient scanning of large workpieces. The articulated measuring machine is the ROMER series, with a measurement accuracy of 0.043mm and an indication error of (2.8+L / 200)μm, used for precise measurement of key feature areas. The coordinate systems of the two measuring devices are achieved through a common spherical target, with no fewer than 7 common spherical targets evenly distributed within the measurement space.

[0083] During parametric modeling, the relationship between the gas box's geometric parameters and the finite element model parameters is established. Defined variables include: gas box length L (range 500mm to 2500mm), gas box width W (range 400mm to 2000mm), gas box height H (range 400mm to 1800mm), shell thickness t (range 3mm to 8mm), and number of element partitions n (range 1 to 6). Through parametric driving, finite element models of gas boxes with different specifications are automatically generated, improving modeling efficiency.

[0084] In step 2, a distributed parallel computing strategy is adopted for the finite element model of the large air box. The model is divided into multiple subdomains, and each subdomain is assigned to an independent computing node for mesh generation and element calculation. Data exchange between subdomains is achieved through a message passing interface (MPI). The mesh generation for parallel computing uses the METIS open-source library for graph partitioning. The number of subdomains is determined based on the number of computing nodes, with a standard configuration of 4 to 8 subdomains. The parallel computing efficiency target is a parallel speedup of no less than 0.8.

[0085] In step 3, a domain decomposition method is used for the multiphysics coupling analysis of ultra-large gas boxes (with dimensions exceeding 2000 mm). The analysis region is decomposed into multiple independent sub-regions, and each sub-region undergoes independent single-physics analysis. Coupling between sub-regions is achieved through interface compatibility conditions. The pressure field analysis employs the Eulerian-Lagrange coupling method, the temperature field analysis uses an asynchronous time-step strategy, and the structural field analysis uses a modal superposition method. The domain decomposition method effectively reduces the computational scale, shortening the single analysis time by approximately 60%.

[0086] In step 4, a material parameter database is established based on the material properties of different types of gas boxes. The database contains the mechanical and thermophysical properties of commonly used gas box shell materials (6061-T6 aluminum alloy, 5052-H32 aluminum alloy, 304 stainless steel, 316L stainless steel). The selection of material parameters is determined based on the actual material grade and heat treatment state of the gas box. The material parameter database supports the addition and modification of user-defined material parameters.

[0087] In step 5, the structural reinforcement design employs an interactive optimization process. The topology optimization results are visually displayed through a 3D visualization system, allowing engineers to interactively modify the results. Interactive modification functions include adjusting the position and shape of the reinforcing ribs, adding or deleting reinforcing ribs, and modifying the transition fillet dimensions. After interactive modification, the system automatically performs a local reanalysis, displaying the stress distribution changes in real time.

[0088] In step 6, the verification of the optimization effect adopts a combination of experimental verification and numerical analysis. Typical working conditions are selected for prototype testing, including internal pressure strength testing, temperature cycling testing, and vibration fatigue testing. The experimental data are compared and verified with the numerical analysis results to ensure the accuracy and reliability of the numerical analysis model. The internal pressure strength test is conducted at 1.5 times the design pressure for 30 minutes, detecting macroscopic deformation and leakage of the gas box. The temperature cycling test ranges from -40℃ to +85℃, with 100 cycles, detecting the thermal fatigue performance of the gas box. The vibration fatigue test ranges from 10Hz to 500Hz, with an acceleration amplitude of 5g and a vibration time of 48 hours, detecting the structural integrity of the gas box.

[0089] The parametric drive scheme provided in this embodiment is applicable to fully inflatable ring main unit gas boxes of different specifications and capacities, exhibiting strong versatility and wide adaptability. Through parametric modeling and interactive optimization, the efficiency and flexibility of structural reinforcement design can be significantly improved, meeting the diverse needs of practical engineering.

[0090] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box, characterized in that: Includes the following steps: Step 1: Obtain the geometric parameters and operating condition information of the multi-unit structure of the air box: Use a high-precision three-dimensional scanning device to perform a full-range scan of the multi-unit structure of the air box, obtain the geometric dimensions, wall thickness distribution, unit partition position and sealing structure parameters of the air box shell, and collect the rated working air pressure, temperature change range, short-circuit electrodynamic amplitude and vibration frequency operating condition data of the air box. Step 2: Establish a multi-element finite element analysis model of the gas box: Based on the geometric parameters, construct a three-dimensional finite element model of the gas box using the hexahedral dominant mesh generation method, refine the local mesh in the stress concentration sensitive area, and define the gas pressure load, temperature load, electromagnetic load, and constraint boundary conditions. Step 3: Calculate the stress distribution under multi-physics coupling: The pressure field, temperature field and structural field are calculated sequentially using the sequential coupling method. Finite element analysis software is used to numerically simulate the stress distribution of the air box under the multi-physics coupling of inflation pressure, temperature cycle, short-circuit electrodynamics and mechanical vibration, and obtain the stress field distribution cloud map of the air box shell and unit partition and the stress time history curve of key nodes. Step 4: Identify stress concentration areas and assess structural safety: Based on the stress distribution calculation results, automatically identify stress concentration areas and mark their location, shape and severity, and compare the material yield strength and fatigue limit to assess structural safety. Step 5: Develop and implement a structural reinforcement scheme: Based on the identification results and safety assessment conclusions of the stress concentration areas, use topology optimization to determine the range and shape of the structural reinforcement areas, improve the stress transmission path by adjusting the wall thickness distribution, adding transition fillets and optimizing the unit partition layout, and conduct process feasibility analysis and cost assessment. Step 6: Verify the effect of stress distribution improvement in the optimized structure: Perform multiphysics coupled stress analysis on the air box structure after the reinforcement scheme is implemented, and compare the stress distribution uniformity and maximum equivalent stress value before and after optimization to verify the effectiveness of the structural reinforcement scheme.

2. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, The high-precision 3D scanning equipment in step 1 includes a composite scanning system that combines a structured light scanner and a laser triangulation instrument. The scanning accuracy of the structured light scanner is a preset accuracy value, while the scanning accuracy of the laser triangulation instrument is higher than that of the structured light scanner. The sampling points with a point cloud density of not less than a preset density are used for complex curved surface areas.

3. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, In step 2, the finite element model adopts a hybrid mesh strategy dominated by hexahedrons. The element size of the standard region is a preset first size, the element size of the stress concentration sensitive region is refined to a preset second size, the mesh quality distortion coefficient is controlled above a preset distortion threshold, and the total number of model nodes is not less than a preset number of nodes.

4. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, The boundary conditions set in step 2 include the gas pressure range inside the gas box being a preset pressure range, the ambient temperature cycle range being a preset temperature range, the short-circuit electrodynamic peak value being determined based on the rated short-circuit withstand current, the frequency range of the vibration load being a preset frequency range, and the acceleration amplitude not exceeding a preset acceleration threshold.

5. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, In step 3, the multiphysics coupling calculation adopts a sequential coupling strategy. The first step is to perform steady-state analysis of the gas pressure field to obtain the internal pressure distribution. The second step is to perform temperature field analysis to obtain the thermal stress distribution. The third step is to apply the results of the first two steps as a body load to the structural field to calculate stress and strain. The coupling iteration convergence accuracy is set to a preset convergence accuracy, and the residual displacement does not exceed a preset displacement threshold.

6. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, In step 4, the automatic identification of stress concentration areas uses a combination of the stress gradient method and the equivalent stress threshold method. Areas where the Von Mises equivalent stress exceeds a preset threshold proportion of the material's yield strength are designated as hazardous areas, and areas where the stress non-uniformity coefficient exceeds a preset threshold are designated as areas requiring optimization. The formula for calculating the stress non-uniformity coefficient is as follows: ； in, The stress distribution uniformity coefficient is... The equivalent stress of the i-th element is... This is the average equivalent stress. The total number of units; the recognition results are displayed through a 3D visualization system and reviewed and confirmed by engineers.

7. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, In step 5, the topology optimization adopts the variable density method. The optimization objective is to minimize the structural flexibility. The constraint is that the volume fraction is not higher than the preset volume ratio threshold of the original structure. At the same time, the minimum member size constraint is set to the preset minimum size to avoid the appearance of small structures that cannot be processed. The number of iterations is not less than the preset number of iterations, and the convergence accuracy is the preset optimization convergence accuracy. The optimization mathematical model for minimizing the structural flexibility is as follows: ； ； ； in, For structural flexibility, and Let be the stress and strain of the i-th element, respectively. To optimize the volume of the structure, For the original structural volume, For volume fraction constraints, It represents the minimum relative density.

8. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, The implementation of the structural reinforcement scheme in step 5 includes adding reinforcing ribs in stress concentration areas. The thickness of the reinforcing ribs is between a preset first multiple and a preset second multiple of the gas box wall thickness, and the height is between a preset fifth multiple and a preset sixth multiple of the gas box wall thickness. At the same time, transition fillets are set in all sharp corner areas to eliminate geometric stress concentration sources, and the fillet radius is not less than a preset radius multiple of the gas box wall thickness.

9. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, Step 5 also includes welding process optimization, welding positions avoiding stress concentration areas, double-sided fillet welds, weld leg height not less than a preset weld leg multiple of the gas box wall thickness, and heat treatment to eliminate residual welding stress after welding, with heating temperature within a preset temperature ratio range of the material annealing temperature and holding time within a preset holding time.

10. The method for strengthening stress distribution in a multi-unit structure of a fully inflatable ring main unit air box according to claim 1, characterized in that, Step 6 also includes lightweight design verification of the multi-unit structure of the air box. Under the premise of ensuring structural strength and stiffness, the optimal material distribution scheme is determined by combining topology optimization and morphology optimization. Finally, the overall weight of the air box is reduced by no less than the preset weight reduction ratio, and the stress distribution uniformity coefficient is improved by no less than the preset uniformity improvement ratio. The formula for calculating the structural safety margin factor is as follows: ； Where η is the safety margin coefficient, σ_max is the maximum equivalent stress in the hazardous area, and σ_allow is the allowable stress of the material; The formula for calculating the maximum equivalent stress reduction ratio is as follows: ； Where σ_max(before) and σ_max(after) are the maximum equivalent stress before and after optimization, respectively; The formula for calculating the overall weight reduction percentage of the air box is as follows: ; Where W_before and W_after are the weights of the air box before and after optimization, respectively.

Images