A load distribution optimization method and system for lattice skeleton design

Abstract

The application relates to the technical field of vehicle engineering, and particularly discloses a load distribution optimization method and system for a lattice frame design, which comprises the following steps: firstly, an initial three-dimensional design domain of the lattice frame is established, and a composite dynamic load working condition obtained based on multi-body dynamics simulation is applied; then, a material density distribution cloud picture is obtained through macroscopic topological optimization, a main force transmission path is identified and extracted, and the design domain is divided into a core bearing area, a transition area and a non-key area; in the non-key area and the transition area, a point array structure with gradient material properties is designed according to a stress state, and continuous change of the material properties is realized by adjusting the point array type, arrangement direction and control parameters; finally, performance verification and parameter iterative optimization are carried out on the overall structure containing the core bearing area and the point array filling area.

Description

Technical Field

[0001] This invention relates to the field of vehicle engineering technology, and more specifically to a method and system for optimizing load distribution in the design of a cargo box frame. Background Technology

[0002] As core equipment in modern logistics, the lightweight and reliable design of the frame structure of stake-mounted transport vehicles has always been a key research focus in the industry. Currently, mainstream stake-mounted vehicle frame designs primarily employ uniform cross-section design methods based on classical beam theory, or supplemented by topology optimization techniques based on a single typical working condition (such as pure bending or pure torsion). These methods, through the establishment of parametric models in computer-aided engineering software and the performance of static strength analysis and local morphology optimization, can achieve certain material savings under specific load conditions, forming the technological foundation widely adopted in the current industry.

[0003] Existing load distribution optimization methods for fence frame design cannot effectively cope with complex dynamic loads in actual operation, causing the optimized load distribution to completely fail under complex actual working conditions. Specifically, when a vehicle simultaneously experiences braking, turning, and bumps, the spatiotemporal coupling of multiple dynamic loads causes drastic changes in the stress distribution inside the frame. Load distribution schemes based on single-condition optimization cannot adapt to these changes, resulting in a significant deviation between the actual load distribution and the design expectations. Summary of the Invention

[0004] The purpose of this invention is to provide a load distribution optimization method and system for fence frame design to solve the problems mentioned above.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for optimizing load distribution in fence frame design includes the following steps:

[0007] S1: Establish the initial three-dimensional design domain of the fence skeleton, and apply composite dynamic load conditions to the initial three-dimensional design domain;

[0008] S2: Based on the composite dynamic load condition, perform macroscopic topology optimization on the initial three-dimensional design domain to obtain the material density distribution cloud map, and identify and extract the main force transmission path based on the material density distribution cloud map;

[0009] S3: Based on the material density distribution cloud map, the initial three-dimensional design domain is divided into a core load-bearing area, a transition area, and a non-critical area, where the core load-bearing area corresponds to the main force transmission path;

[0010] S4: Design lattice structures in non-critical and transitional areas, and adjust the lattice structure type, arrangement direction and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties.

[0011] S5: Based on the gradient material properties of the lattice filling area, the structural performance of the overall structure including the core bearing area and the lattice filling area is verified under composite dynamic load conditions. Based on the verification results, the control parameters of the lattice structure are iteratively optimized until the overall structure meets the preset performance indicators, and the final structural design of the fence skeleton is completed.

[0012] As a further aspect of the present invention: the establishment of an initial three-dimensional design domain for the fence skeleton, and the application of composite dynamic load conditions to the initial three-dimensional design domain, specifically includes:

[0013] A dynamic coupled load spectrum is constructed based on multibody dynamics simulation, which includes the coupling effect of road surface roughness, vehicle motion state and cargo inertia.

[0014] Load events with different phases and amplitudes are extracted from the dynamic coupled load spectrum, and the three load events of braking impact, cornering roll and vertical bump are superimposed in the time domain to generate a set of load boundary conditions for composite dynamic load conditions.

[0015] The set of load boundary conditions is mapped to the spatial location and structural surface corresponding to the initial three-dimensional design domain in the form of parametric load description, thus completing the application of composite dynamic load conditions.

[0016] As a further aspect of the present invention: the step of identifying and extracting the main force transmission path based on the material density distribution cloud map specifically includes:

[0017] A density gradient field is constructed based on the material density distribution cloud map. By tracking the continuity characteristics of gradient changes in the density gradient field, the bearing area with a density value higher than the first preset density threshold and spatial continuity in the material density distribution cloud map is identified.

[0018] The identified load-bearing areas are skeletonized, the center lines representing the main load transmission paths are extracted, and the center lines are topologically connected at the spatial intersections to form a preliminary force transmission path network.

[0019] Based on the composite dynamic load condition, the load transmission efficiency of the preliminary force transmission path network is analyzed, and the force transmission path with a load transmission efficiency higher than the second preset efficiency threshold is retained as the final main force transmission path, thus completing the accurate extraction of the main force transmission path.

[0020] As a further aspect of the present invention: the load transfer efficiency analysis of the preliminary force transmission path network based on composite dynamic load conditions specifically includes:

[0021] Under the combined dynamic load condition, an energy flow density field is constructed by calculating the energy flow density distribution of each path in the preliminary force transmission path network.

[0022] The relative importance of each path in the overall structure is determined by calculating the path load bearing ratio during the load transfer process based on the energy flow density field.

[0023] By analyzing the energy transmission continuity characteristics of each path in the dynamic load sequence and combining the path load bearing ratio data, a comprehensive evaluation system including path importance and energy transmission stability is established to complete the load transfer efficiency analysis of the preliminary force transmission path network.

[0024] As a further aspect of the present invention: the initial three-dimensional design domain is divided into a core bearing area, a transition area, and a non-critical area based on the material density distribution cloud map, specifically including:

[0025] Stress streamline distribution is generated based on material density distribution cloud map, and stress streamline density field is established by tracking the stress streamline density change characteristics around the main force transmission path.

[0026] Based on the gradient variation characteristics of the stress streamline density field, the first dynamic boundary between the core bearing area and the transition area is determined, and the second dynamic boundary between the transition area and the non-critical area is determined based on the contour distribution of the material density distribution cloud map.

[0027] By spatially coupling the first dynamic boundary and the second dynamic boundary, a three-dimensional partitioned structure is established, which includes a core bearing area, a transition area, and a non-critical area. The boundary of the core bearing area is consistent with the spatial orientation of the main force transmission path.

[0028] As a further aspect of the present invention: the adjustment of the lattice structure type, arrangement direction, and control parameters according to the stress state of each region specifically includes:

[0029] Based on the stress state of each region, the principal stress direction field and equivalent stress distribution are extracted, and the preferred orientation of the lattice structure is determined according to the streamline characteristics of the principal stress direction field.

[0030] A continuous variation function for the diameter of the lattice member is established based on the equivalent stress distribution, so that the diameter of the member increases continuously with the increase of the equivalent stress value;

[0031] Based on the stress invariant characteristics of each region under composite dynamic load conditions, a lattice structure type with corresponding mechanical properties is selected. In the transition zone, a lattice parameter with progressively changing characteristics is adopted to form a lattice-filled area with a continuous gradient material property distribution from the core load-bearing area to the non-critical area.

[0032] As a further aspect of the present invention: the continuous variation function of the diameter of the lattice member based on the equivalent stress distribution specifically includes:

[0033] The stress ratio parameter of each region is calculated based on the equivalent stress distribution. The stress ratio parameter is defined as the ratio of the local equivalent stress value to the reference stress.

[0034] A function for the continuous variation of bar diameter based on the hyperbolic tangent function is constructed, with the stress ratio parameter as the independent variable and the minimum and maximum bar diameters as boundary conditions.

[0035] By applying a continuous variation function for member diameter to the member diameter control of the lattice structure, the member diameter can achieve a smooth transition from the core load-bearing area to the non-critical area in the transition zone, and maintain a uniform distribution of the minimum member diameter in the non-critical area.

[0036] As a further aspect of the present invention: the formation of a continuous gradient material property distribution from the core bearing area to the non-critical area specifically includes:

[0037] Based on the stress analysis results under composite dynamic load conditions, the von Mises equivalent stress and deviatoric stress tensor invariants of each region are extracted as characteristic parameters.

[0038] Based on the numerical distribution range of the characteristic parameters, tetrahedral lattice structures are selected in the vicinity of the core bearing area, and body-centered cubic lattice structures are selected in the non-critical areas, establishing a correspondence between lattice structure types and stress invariant characteristics.

[0039] Within the transition zone, a continuous transition method using lattice structure types is adopted. The gradual transformation from tetrahedral lattice structure to body-centered cubic lattice structure is achieved through linear interpolation. Simultaneously, the continuous change in the diameter of the lattice rods forms a three-dimensional gradient distribution of material properties.

[0040] As a further aspect of the present invention: the iterative optimization of the control parameters of the lattice structure based on the verification results specifically includes:

[0041] Based on the structural performance verification results under composite dynamic load conditions, the von Mises equivalent stress distribution uniformity coefficient of the overall structure is calculated. The von Mises equivalent stress distribution uniformity coefficient is the ratio of the standard deviation to the average value of the equivalent stress values ​​at each location.

[0042] Based on the comparison between the von Mises equivalent stress distribution uniformity coefficient and the preset threshold, a lattice member diameter adjustment function is established. The von Mises equivalent stress distribution uniformity coefficient is constructed in a way that ensures the increase in member diameter in stress concentration areas is proportional to the stress reduction requirement.

[0043] Through multiple iterative optimizations, the uniformity coefficient of the von Mises equivalent stress distribution was made to meet the preset requirements, while maintaining a continuous transition of the displacement field between the lattice filling area and the core bearing area, thus completing the final optimization of the lattice structure control parameters.

[0044] A load distribution optimization system for fence frame design includes:

[0045] The design domain and load definition module is used to establish the initial three-dimensional design domain of the fence skeleton and apply composite dynamic load conditions to the initial three-dimensional design domain.

[0046] The macroscopic topology optimization and path extraction module performs macroscopic topology optimization on the initial three-dimensional design domain based on composite dynamic load conditions, obtains a material density distribution cloud map, and identifies and extracts the main force transmission path based on the material density distribution cloud map.

[0047] The multi-region dynamic partitioning module divides the initial three-dimensional design domain into a core load-bearing area, a transition area, and a non-critical area based on the material density distribution cloud map, where the core load-bearing area corresponds to the main force transmission path.

[0048] The gradient lattice design module is used to design lattice structures in non-critical and transitional areas. It adjusts the lattice structure type, arrangement direction, and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties.

[0049] The integrated verification and optimization module verifies the structural performance of the overall structure, including the core load-bearing area and the lattice filling area, under composite dynamic load conditions based on the gradient material properties of the lattice filling area. Based on the verification results, iteratively optimizes the control parameters of the lattice structure until the overall structure meets the preset performance indicators, thus completing the final structural design of the fence frame.

[0050] The beneficial effects of this invention are:

[0051] (1) Traditional homogeneous designs may suffer from latent instability due to the unpredictable migration of stress concentration areas under the coupled effects of various dynamic loads such as braking, turning, and bumps. This invention extracts composite dynamic loads from real road patterns for topology optimization, accurately identifies the main force transmission path, and designs lattice structures with gradient material properties in non-critical and transition areas. This allows the frame to automatically and continuously adjust the force flow distribution according to the real-time changing load path. This eliminates the risk of local failure caused by stress migration, enabling the fence frame to have reliability and safety under complex real road conditions.

[0052] (2) This invention uses topology optimization to precisely distribute materials in efficient force transmission paths to form the core load-bearing area, while introducing parametrically optimized lightweight lattice structures to fill low-stress areas. This "on-demand allocation" material usage strategy, combined with iterative optimization based on the von Mises stress uniformity coefficient, ensures optimal matching of structural performance. Ultimately, while maintaining or even improving the original structural stiffness and strength, the weight of the frame is reduced, directly improving the vehicle's load-bearing capacity and fuel economy, achieving a balance between lightweighting and high performance. Attached Figure Description

[0053] The invention will now be further described with reference to the accompanying drawings.

[0054] Figure 1 This is a flowchart of the method of the present invention;

[0055] Figure 2 This is a flowchart of the system in this invention. Detailed Implementation

[0056] 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Please see Figure 1 As shown, this invention is a load distribution optimization method for fence frame design, comprising the following steps:

[0058] S1: Establish the initial three-dimensional design domain of the fence skeleton, and apply composite dynamic load conditions to the initial three-dimensional design domain;

[0059] S2: Based on the composite dynamic load condition, perform macroscopic topology optimization on the initial three-dimensional design domain to obtain the material density distribution cloud map, and identify and extract the main force transmission path based on the material density distribution cloud map;

[0060] S3: Based on the material density distribution cloud map, the initial three-dimensional design domain is divided into a core load-bearing area, a transition area, and a non-critical area, where the core load-bearing area corresponds to the main force transmission path;

[0061] S4: Design lattice structures in non-critical and transitional areas, and adjust the lattice structure type, arrangement direction and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties.

[0062] S5: Based on the gradient material properties of the lattice filling area, the structural performance of the overall structure including the core bearing area and the lattice filling area is verified under composite dynamic load conditions. Based on the verification results, the control parameters of the lattice structure are iteratively optimized until the overall structure meets the preset performance indicators, and the final structural design of the fence skeleton is completed.

[0063] In S1, an initial three-dimensional design domain for the fence skeleton is established, and composite dynamic load conditions are applied to the initial three-dimensional design domain, specifically including:

[0064] A dynamic coupled load spectrum, incorporating road surface roughness, vehicle motion, and cargo inertial coupling, is constructed based on multibody dynamics simulation. Specifically, a multibody dynamics model is established, including the vehicle suspension system, frame, and cargo. By inputting standard road surface spectrum data, the dynamic response of the vehicle under different road conditions is simulated. In this model, road surface roughness is described using a graded highway spectrum, vehicle motion includes acceleration, velocity, and angular velocity parameters, and the cargo inertial coupling effect is characterized by calculating the additional torque generated by the shift of the cargo's center of gravity. Through this simulation process, a time-varying dynamic coupled load spectrum is obtained, which comprehensively records the time history data of forces and moments at each connection point.

[0065] It should be noted that "standard road surface spectrum data" is a statistical model established according to international standards (such as ISO 8608) to quantitatively describe the macroscopic smoothness of different grades of road surfaces. Its core is to characterize the random undulation height of the road surface that varies with space using the mathematical form of "displacement power spectral density". Therefore, in the simulation, it is no longer necessary to simulate specific potholes. Instead, the amplitude characteristics at different spatial frequencies (for example, Class A spectrum represents highways with high smoothness; Class C spectrum represents ordinary national roads with significantly increased unevenness) are used to reproduce the excitation input of real road conditions to vehicles. The model implementation process based on this data is as follows: First, in professional dynamics software (such as Adams and Simpack), a multibody dynamics system is established, including a suspension with stiffness and damping characteristics, an elastic frame, and cargo with mass and rotational inertia. Then, the selected standard road surface spectrum data is used as the excitation source input, and the dynamic differential equations of the system during the driving process are solved by numerical integration methods (such as the Runge-Kutta method), thereby calculating the vehicle's motion state (acceleration, angular velocity), and simultaneously solving for the additional torque generated by the inertial coupling of the cargo. Finally, by monitoring the force and torque responses at key connection points such as the vehicle and the frame, and the frame and the cargo, complete time history data is output, thus constructing the required "dynamic coupling load spectrum".

[0066] Load events with different phases and amplitudes are extracted from the dynamic coupled load spectrum. The three load events—braking impact, cornering roll, and vertical sway—are then superimposed in the time domain to generate a set of load boundary conditions for a composite dynamic load condition. Specifically, a peak detection algorithm is used to identify characteristic load events in the dynamic coupled load spectrum. This algorithm filters valid load events by setting amplitude and duration thresholds. For braking impact events, the period when longitudinal acceleration reaches its maximum value is extracted; for cornering roll events, the period when lateral acceleration continues to act is extracted; and for vertical sway events, the period when vertical acceleration fluctuates significantly is extracted. During the time-domain superposition process, a linear superposition method is used to combine the three load events along the time axis according to their actual phase relationship, generating a composite dynamic load condition containing multi-dimensional load components.

[0067] The set of load boundary conditions is mapped onto the spatial location and structural surface corresponding to the initial three-dimensional design domain in the form of parametric load descriptions, thus completing the application of composite dynamic load cases. In practice, the parametric load description is established using a functional relationship between spatial coordinates and load values, where the load values ​​are modified according to the geometric characteristics and stress properties of their location. For longitudinal beam structures of the skeleton, longitudinal inertial forces and bending moments are mainly mapped; for transverse support structures, transverse inertial forces and torsional loads are mainly mapped; for connection node regions, load components in multiple directions are mapped simultaneously. By establishing a load distribution function, the spatial distribution characteristics of composite dynamic load cases are accurately transferred to the corresponding locations in the three-dimensional design domain, ensuring the accuracy and rationality of load application.

[0068] In S2, macroscopic topology optimization is performed on the initial three-dimensional design domain based on composite dynamic load conditions to obtain a material density distribution cloud map. The main force transmission path is then identified and extracted based on this cloud map, specifically including:

[0069] A density gradient field is constructed based on a material density distribution cloud map. By tracking the continuity of gradient changes in the density gradient field, spatially continuous bearing regions with density values ​​higher than a first preset density threshold are identified in the material density distribution cloud map. Specifically, the density gradient field is calculated using the central difference method. The rate of density change of each grid point in the material density distribution cloud map along the direction of its adjacent grids is calculated to obtain the magnitude and direction of the density gradient. The first preset density threshold is set to 0.6, a value determined based on statistical analysis of multiple topology optimization results, which effectively distinguishes between primary and non-bearing regions. When identifying spatially continuous bearing regions, a region growing algorithm is used. Starting from any grid point with a density value higher than the threshold, the algorithm traces along the density gradient direction, merging adjacent grids with continuous gradient changes and density values ​​all higher than the threshold into the same bearing region. This process continues until all eligible grids are classified into the corresponding bearing regions.

[0070] The identified load-bearing areas are skeletonized to extract centerlines representing the main load transfer paths. These centerlines are then topologically connected at their spatial intersections to form a preliminary force transmission path network. Specifically, the skeletonization process employs an iterative refinement algorithm. This algorithm iteratively removes grid points from the load-bearing area boundaries through multiple iterations while maintaining the area's topology, until the area width is a single grid cell, thus obtaining the centerlines. After extracting the centerlines, the spatial distance between endpoints of different centerlines is determined, and endpoints with distances less than a set tolerance value are connected to form nodes. The centerlines between nodes constitute path segments, and all path segments are connected through nodes to form a preliminary force transmission path network. During this process, a tolerance value of 1.5 times the grid cell size is set to ensure that spatially similar paths can be correctly connected.

[0071] Load transfer efficiency analysis is performed on the preliminary force transmission path network based on composite dynamic load conditions. Force transmission paths with load transfer efficiencies exceeding a second preset efficiency threshold are retained as the final main force transmission paths. The specific process of load transfer efficiency analysis includes: under composite dynamic load conditions, calculating the energy flux density distribution of each path in the preliminary force transmission path network to construct an energy flux density field. The energy flux density is calculated based on the dot product of strain energy density and stress vector, reflecting the amount of energy transferred per unit area per unit time. Based on the energy flux density field, the path load-bearing ratio in the load transfer process is calculated. This ratio is determined by the ratio of the integral value of the energy flux density on the path to the total integral value of the energy flux density of the entire network. By analyzing the energy transfer continuity characteristics of each path in the dynamic load sequence, and combining the path load-bearing ratio data, a comprehensive evaluation system including path importance and energy transfer stability is established. Path importance is determined by the path load-bearing ratio, and energy transfer stability is characterized by the coefficient of variation of the energy flux density of the path in the dynamic load sequence. The second preset efficiency threshold is set as a path load-bearing ratio of not less than 15% and an energy flux density coefficient of variation not exceeding 0.25. This threshold is determined based on historical data and engineering experience. The force transmission path that meets the threshold condition is retained as the final main force transmission path, thus completing the accurate extraction of the main force transmission path.

[0072] In S3, the initial three-dimensional design domain is divided into a core load-bearing area, a transition area, and a non-critical area based on the material density distribution cloud map. The core load-bearing area corresponds to the main force transmission path, specifically including:

[0073] Stress streamline distribution is generated based on material density distribution cloud maps. A stress streamline density field is established by tracking the stress streamline density variation characteristics around the main force transmission path. Specifically, the stress streamline distribution is obtained by solving the principal stress direction field of the stress field. A fourth-order Runge-Kutta method is used for streamline tracking, with a tracking step size set to 0.5 times the grid cell size. When establishing the stress streamline density field, the number of stress streamlines passing through a unit area is counted around the main force transmission path. The statistical region uses a circular window with a radius of 3 grid cells. The stress streamline density value is determined by the ratio of the total streamline length to the window area within the statistical window. This calculation is performed at the centroid of the grid cell, and then an interpolation method is used to form a continuous stress streamline density field.

[0074] Based on the gradient variation characteristics of the stress streamline density field, the first dynamic boundary between the core load-bearing zone and the transition zone is determined. Simultaneously, the second dynamic boundary between the transition zone and non-critical zones is determined based on the contour distribution of the material density distribution cloud map. Specifically, the first dynamic boundary is determined using a region growing algorithm based on the gradient magnitude. Starting from the center of the main force transmission path, it expands along the direction of the decreasing gradient of the stress streamline density field. When the gradient magnitude drops to 20% of the peak gradient value, it is determined as the boundary of the core load-bearing zone. The second dynamic boundary is determined by extracting contour surfaces with a density value of 0.3 from the material density distribution cloud map. This density threshold is obtained based on statistical analysis of numerous topology optimization results and can effectively distinguish the main distribution areas of the structural material. During the determination of the two boundaries, cubic spline interpolation is used to smooth the discrete boundary points, ensuring the smooth continuity of the boundaries.

[0075] A three-dimensional partitioned structure, comprising a core bearing area, a transition area, and non-critical areas, is established through spatial coupling between the first and second dynamic boundaries. In specific implementation, the spatial coupling process employs Boolean operations. First, the area enclosed by the first dynamic boundary is defined as the core bearing area. Then, the area enclosed by the second dynamic boundary is subtracted from the core bearing area, and the resulting annular area is defined as the transition area. Finally, the initial three-dimensional design domain is subtracted from the area enclosed by the second dynamic boundary, and the remaining area is defined as the non-critical area. Throughout the partitioning process, the boundary of the core bearing area maintains consistency with the spatial orientation of the main force transmission path, achieved by constraining the distance between the boundary points of the core bearing area and the centerline of the main force transmission path to no more than five mesh elements. After partitioning, the boundaries of each area are smoothed using a Laplace smoothing algorithm for three iterations to ensure the smoothness and rationality of the partition boundaries.

[0076] In S4, lattice structures are designed in non-critical and transitional zones. The type, arrangement, and control parameters of the lattice structures are adjusted according to the stress state of each region to form lattice-filled regions with gradient material properties. Specifically, this includes:

[0077] Based on the stress state of each region, the principal stress direction field and equivalent stress distribution are extracted. The preferred orientation of the lattice structure is determined according to the streamline characteristics of the principal stress direction field. Specifically, the principal stress direction field is obtained by solving for the eigenvalues ​​and eigenvectors of the stress tensor using the Jacobi iteration method, with an iteration convergence tolerance set to 1e-6. The equivalent stress distribution is calculated using the von Mises stress formula, which integrates the influence of various stress components on material yield. When determining the preferred orientation of the lattice structure, the orientation of the main members is aligned with the first principal stress direction. When multiple principal stress directions exist, the priority alignment order is determined based on the relative magnitude of the principal stress values. For the transition zone, the orientation of the lattice structure is adjusted gradually, from the boundary of the core load-bearing zone to the boundary of the non-critical zone, with the adjustment angle not exceeding 45 degrees to ensure a smooth transition of mechanical properties.

[0078] A continuous variation function for the diameter of lattice members is established based on the equivalent stress distribution, causing the member diameter to continuously increase with the increase of the equivalent stress value. Specific implementation includes: calculating the stress ratio parameter for each region based on the equivalent stress distribution. This parameter is defined as the ratio of the local equivalent stress value to the reference stress, where the reference stress is taken as 50% of the material's yield strength, specifically 50 MPa. A continuous variation function for the member diameter based on the hyperbolic tangent function is constructed, with the expression: Member diameter = Minimum member diameter + (Maximum member diameter - Minimum member diameter) × (0.5 + 0.5 × tanh(stress ratio parameter / 0.8)). The minimum member diameter is set to 0.5 mm, and the maximum member diameter is set to 3 mm; these parameters are determined based on manufacturing process requirements and mechanical performance requirements. Applying the continuous variation function for member diameter control in the lattice structure achieves a smooth transition from the core load-bearing area to the non-critical area within the transition zone, while maintaining a uniform distribution of the minimum member diameter within the non-critical area.

[0079] Then, based on the stress invariant characteristics of each region under composite dynamic loading conditions, lattice structure types with corresponding mechanical properties are selected. In specific implementation, based on the stress analysis results under composite dynamic loading conditions, the von Mises equivalent stress and deviatoric stress tensor invariants of each region are extracted as characteristic parameters. The deviatoric stress tensor invariant is obtained by calculating the second invariant of the stress deviator, which reflects the shear characteristics of the stress state. Based on the numerical distribution range of the characteristic parameters, tetrahedral lattice structures are selected in the vicinity of the core load-bearing area, as these structures possess high stiffness and strength; body-centered cubic lattice structures are selected in non-critical areas, achieving maximum lightweighting while ensuring basic performance. A correspondence between lattice structure types and stress invariant characteristics is established: tetrahedral lattices are used when the von Mises equivalent stress is greater than 35 MPa and the second invariant of the deviatoric stress tensor is greater than 400 MPa², and body-centered cubic lattices are used when the von Mises equivalent stress is less than 15 MPa and the second invariant of the deviatoric stress tensor is less than 100 MPa².

[0080] Within the transition zone, a continuous transition of lattice structure types is adopted, using linear interpolation to achieve a gradual transformation from tetrahedral lattice structures to body-centered cubic lattice structures. Specifically, a control section is set every 2 millimeters within the transition zone. At each control section, the geometric features of both lattice structures are mixed according to positional weights. The positional weights are determined by the ratio of the distance from the section to the boundary of the core load-bearing area to the total width of the transition zone. When the ratio is 0, tetrahedral lattice is used exclusively; when the ratio is 1, body-centered cubic lattice is used exclusively; intermediate values ​​are calculated using linear interpolation. Simultaneously with the continuous transition of lattice structure types, a three-dimensional gradient distribution of material properties is formed within the transition zone by continuously varying the diameter of the lattice members. The variation in member diameter follows the aforementioned hyperbolic tangent function law, ensuring a smooth transition in stiffness performance.

[0081] In S5, based on the gradient material properties of the lattice filling region, the structural performance of the overall structure, including the core load-bearing region and the lattice filling region, is verified under composite dynamic load conditions. Based on the verification results, the control parameters of the lattice structure are iteratively optimized until the overall structure meets the preset performance indicators, completing the final structural design of the fence frame. Specifically, this includes:

[0082] Based on the structural performance verification results under composite dynamic loading conditions, the von Mises equivalent stress distribution uniformity coefficient of the overall structure was calculated. Specifically, monitoring points were evenly distributed across the overall structure, with each point spaced 5 mm apart, to collect the von Mises equivalent stress values ​​at each point under composite dynamic loading conditions. The von Mises equivalent stress distribution uniformity coefficient was calculated as follows: first, the arithmetic mean of the equivalent stress values ​​at all monitoring points was calculated; then, the standard deviation of these stress values ​​was calculated; finally, the standard deviation was divided by the mean to obtain the uniformity coefficient. This coefficient reflects the uniformity of the structural stress distribution; the smaller the coefficient value, the more uniform the stress distribution. During the calculation, monitoring points with stress values ​​less than 10% of the material's yield strength were excluded to avoid the influence of low-stress areas on the statistical results.

[0083] Based on the comparison between the von Mises equivalent stress distribution uniformity coefficient and a preset threshold, a lattice member diameter adjustment function is established. The preset threshold is set to 0.25, a value determined based on extensive engineering practice data, which effectively balances structural performance and lightweight requirements. The construction process of the lattice member diameter adjustment function is as follows: When the uniformity coefficient is greater than the preset threshold, regions with stress values ​​higher than 1.5 times the average value are identified as stress concentration areas. Within these regions, the adjustment range of the member diameter is proportional to the difference between the local stress value and the average stress value, with a proportionality coefficient of 0.001 mm / MPa. Simultaneously, for regions with stress values ​​lower than 0.8 times the average value, the member diameter is appropriately reduced to achieve further lightweighting, but the reduced member diameter must not be less than 0.5 mm below the minimum member diameter. The adjustment function ensures that the change in member diameter is continuous and smooth, avoiding abrupt changes in stiffness.

[0084] The uniformity coefficient of the von Mises equivalent stress distribution was optimized through multiple iterations to meet the preset requirements. In practice, the maximum number of iterations was set to 10, with each iteration including a complete structural performance verification and parameter adjustment process. In each iteration, the continuous transition of the displacement field between the lattice filling area and the core bearing area needed to be verified. The criterion for displacement continuity was that the displacement difference between boundary nodes of adjacent areas did not exceed 5% of the local displacement value. The iteration terminated when any of the following conditions were met: the uniformity coefficient dropped below 0.25, or the change in the uniformity coefficient over three consecutive iterations was less than 0.02, or the maximum number of iterations was reached. After iteration, the final lattice structure control parameters were recorded, including the distribution of member diameters, lattice structure types, and orientations in each area, completing the final structural design of the fence frame.

[0085] Please see Figure 2 As shown, a load distribution optimization system for fence frame design includes:

[0086] The design domain and load definition module is used to establish the initial three-dimensional design domain of the fence skeleton and apply composite dynamic load conditions to the initial three-dimensional design domain.

[0087] The macroscopic topology optimization and path extraction module performs macroscopic topology optimization on the initial three-dimensional design domain based on composite dynamic load conditions, obtains a material density distribution cloud map, and identifies and extracts the main force transmission path based on the material density distribution cloud map.

[0088] The multi-region dynamic partitioning module divides the initial three-dimensional design domain into a core load-bearing area, a transition area, and a non-critical area based on the material density distribution cloud map, where the core load-bearing area corresponds to the main force transmission path.

[0089] The gradient lattice design module is used to design lattice structures in non-critical and transitional areas. It adjusts the lattice structure type, arrangement direction, and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties.

[0090] The integrated verification and optimization module verifies the structural performance of the overall structure, including the core load-bearing area and the lattice filling area, under composite dynamic load conditions based on the gradient material properties of the lattice filling area. Based on the verification results, iteratively optimizes the control parameters of the lattice structure until the overall structure meets the preset performance indicators, thus completing the final structural design of the fence frame.

[0091] The working principle of this invention is as follows: By establishing an initial three-dimensional design domain and applying a composite dynamic load condition obtained from multibody dynamics simulation, macroscopic topology optimization is first performed to obtain a material density distribution cloud map and accurately identify and extract the main force transmission path. Subsequently, the design domain is divided into a core load-bearing area, a transition area, and a non-critical area based on the density distribution. In the non-critical area and the transition area, a lattice structure is adaptively designed according to the stress state of each region. By adjusting the lattice type, arrangement direction, and member diameter control parameters, a material property distribution with a continuous gradient change is formed. Finally, the overall structure, including the core load-bearing area and the lattice filling area, is subjected to performance verification and parameter iterative optimization to ensure that it meets the preset performance indicators under composite dynamic load.

[0092] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for optimizing load distribution in fence frame design, characterized in that, Includes the following steps: S1: Establish the initial three-dimensional design domain of the fence skeleton, and apply composite dynamic load conditions to the initial three-dimensional design domain; S2: Based on the composite dynamic load condition, perform macroscopic topology optimization on the initial three-dimensional design domain to obtain the material density distribution cloud map, and identify and extract the main force transmission path based on the material density distribution cloud map; S3: Based on the material density distribution cloud map, the initial three-dimensional design domain is divided into a core load-bearing area, a transition area, and a non-critical area, where the core load-bearing area corresponds to the main force transmission path; S4: Design lattice structures in non-critical and transitional areas, and adjust the lattice structure type, arrangement direction and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties. The adjustment of the lattice structure type, arrangement direction, and control parameters according to the stress state of each region specifically includes: Based on the stress state of each region, the principal stress direction field and equivalent stress distribution are extracted, and the preferred orientation of the lattice structure is determined according to the streamline characteristics of the principal stress direction field. A continuous variation function for the diameter of the lattice member is established based on the equivalent stress distribution, so that the diameter of the member increases continuously with the increase of the equivalent stress value; Based on the stress invariant characteristics of each region under composite dynamic load conditions, a lattice structure type with corresponding mechanical properties is selected. In the transition zone, a gradually changing lattice parameter is adopted to form a lattice filling zone with a continuous gradient material property distribution from the core load-bearing zone to the non-critical zone. The continuous variation function for the diameter of the lattice member based on the equivalent stress distribution specifically includes: The stress ratio parameter of each region is calculated based on the equivalent stress distribution. The stress ratio parameter is defined as the ratio of the local equivalent stress value to the reference stress. A function for the continuous variation of bar diameter based on the hyperbolic tangent function is constructed, with the stress ratio parameter as the independent variable and the minimum and maximum bar diameters as boundary conditions. The continuous variation function of member diameter is applied to the member diameter control of lattice structure, so that the member diameter can smoothly transition from the core load-bearing area to the non-critical area in the transition zone, and maintain the uniform distribution of minimum member diameter in the non-critical area. The formation of a continuous gradient material property distribution from the core bearing area to the non-critical area specifically includes: Based on the stress analysis results under composite dynamic load conditions, the von Mises equivalent stress and deviatoric stress tensor invariants of each region are extracted as characteristic parameters. Based on the numerical distribution range of the characteristic parameters, tetrahedral lattice structures are selected in the vicinity of the core bearing area, and body-centered cubic lattice structures are selected in the non-critical areas, establishing a correspondence between lattice structure types and stress invariant characteristics. In the transition zone, a continuous transition method of lattice structure type is adopted. The gradual transformation from tetrahedral lattice structure to body-centered cubic lattice structure is achieved through linear interpolation. At the same time, the continuous change of the diameter of the lattice rods forms a three-dimensional gradient distribution of material properties. S5: Based on the gradient material properties of the lattice filling area, the structural performance of the overall structure including the core bearing area and the lattice filling area is verified under composite dynamic load conditions. Based on the verification results, the control parameters of the lattice structure are iteratively optimized until the overall structure meets the preset performance indicators, and the final structural design of the fence skeleton is completed.

2. The load distribution optimization method for fence frame design according to claim 1, characterized in that, The establishment of the initial three-dimensional design domain for the fence skeleton, and the application of composite dynamic load conditions to the initial three-dimensional design domain, specifically includes: A dynamic coupled load spectrum is constructed based on multibody dynamics simulation, which includes the coupling effect of road surface roughness, vehicle motion state and cargo inertia. Load events with different phases and amplitudes are extracted from the dynamic coupled load spectrum, and the three load events of braking impact, cornering roll and vertical bump are superimposed in the time domain to generate a set of load boundary conditions for composite dynamic load conditions. The set of load boundary conditions is mapped to the spatial location and structural surface corresponding to the initial three-dimensional design domain in the form of parametric load description, thus completing the application of composite dynamic load conditions.

3. The load distribution optimization method for fence frame design according to claim 1, characterized in that, The process of identifying and extracting the main force transmission path based on the material density distribution cloud map specifically includes: A density gradient field is constructed based on the material density distribution cloud map. By tracking the continuity characteristics of gradient changes in the density gradient field, the bearing area with a density value higher than the first preset density threshold and spatial continuity in the material density distribution cloud map is identified. The identified load-bearing areas are skeletonized, the center lines representing the main load transmission paths are extracted, and the center lines are topologically connected at the spatial intersections to form a preliminary force transmission path network. Based on the composite dynamic load condition, the load transmission efficiency of the preliminary force transmission path network is analyzed, and the force transmission path with a load transmission efficiency higher than the second preset efficiency threshold is retained as the final main force transmission path, thus completing the accurate extraction of the main force transmission path.

4. The load distribution optimization method for fence frame design according to claim 3, characterized in that, The load transfer efficiency analysis of the preliminary force transmission path network based on composite dynamic load conditions specifically includes: Under the combined dynamic load condition, an energy flow density field is constructed by calculating the energy flow density distribution of each path in the preliminary force transmission path network. The relative importance of each path in the overall structure is determined by calculating the path load bearing ratio during the load transfer process based on the energy flow density field. By analyzing the energy transmission continuity characteristics of each path in the dynamic load sequence and combining the path load bearing ratio data, a comprehensive evaluation system including path importance and energy transmission stability is established to complete the load transfer efficiency analysis of the preliminary force transmission path network.

5. The load distribution optimization method for fence frame design according to claim 1, characterized in that, The material density distribution cloud map divides the initial three-dimensional design domain into a core load-bearing area, a transition area, and a non-critical area, specifically including: Stress streamline distribution is generated based on material density distribution cloud map, and stress streamline density field is established by tracking the stress streamline density change characteristics around the main force transmission path. Based on the gradient variation characteristics of the stress streamline density field, the first dynamic boundary between the core bearing area and the transition area is determined, and the second dynamic boundary between the transition area and the non-critical area is determined based on the contour distribution of the material density distribution cloud map. By spatially coupling the first dynamic boundary and the second dynamic boundary, a three-dimensional partitioned structure is established, which includes a core bearing area, a transition area, and a non-critical area. The boundary of the core bearing area is consistent with the spatial orientation of the main force transmission path.

6. The load distribution optimization method for fence frame design according to claim 1, characterized in that, The iterative optimization of the control parameters of the lattice structure based on the verification results specifically includes: Based on the structural performance verification results under composite dynamic load conditions, the von Mises equivalent stress distribution uniformity coefficient of the overall structure is calculated. The von Mises equivalent stress distribution uniformity coefficient is the ratio of the standard deviation to the average value of the equivalent stress values ​​at each location. Based on the comparison between the von Mises equivalent stress distribution uniformity coefficient and the preset threshold, a lattice member diameter adjustment function is established. The von Mises equivalent stress distribution uniformity coefficient is constructed in a way that ensures the increase in member diameter in stress concentration areas is proportional to the stress reduction requirement. Through multiple iterative optimizations, the uniformity coefficient of the von Mises equivalent stress distribution was made to meet the preset requirements, while maintaining a continuous transition of the displacement field between the lattice filling area and the core bearing area, thus completing the final optimization of the lattice structure control parameters.

7. A load distribution optimization system for fence frame design, characterized in that, A load distribution optimization method for fence frame design according to any one of claims 1-6 includes: The design domain and load definition module is used to establish the initial three-dimensional design domain of the fence skeleton and apply composite dynamic load conditions to the initial three-dimensional design domain. The macroscopic topology optimization and path extraction module performs macroscopic topology optimization on the initial three-dimensional design domain based on composite dynamic load conditions, obtains a material density distribution cloud map, and identifies and extracts the main force transmission path based on the material density distribution cloud map. The multi-region dynamic partitioning module divides the initial three-dimensional design domain into a core load-bearing area, a transition area, and a non-critical area based on the material density distribution cloud map, where the core load-bearing area corresponds to the main force transmission path. The gradient lattice design module is used to design lattice structures in non-critical and transitional areas. It adjusts the lattice structure type, arrangement direction, and control parameters according to the stress state of each area to form a lattice filling area with gradient material properties. The integrated verification and optimization module verifies the structural performance of the overall structure, including the core load-bearing area and the lattice filling area, under composite dynamic load conditions based on the gradient material properties of the lattice filling area. Based on the verification results, iteratively optimizes the control parameters of the lattice structure until the overall structure meets the preset performance indicators, thus completing the final structural design of the fence frame.

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