A Design Method for Wings with Variable-Size and Variable-Density Lattice Structures Optimized for Heat Dissipation and Load Bearing

Abstract

The present invention provides a design method for a variable-size and variable-density lattice structure wing with optimized heat dissipation and load-bearing capabilities, which relates to the field of aerospace engineering technology and includes the following steps: S10: Perform variable cross-section design on the D-shaped unit to obtain a variable cross-section D-shaped unit, and use the variable cross-section D-shaped unit as the lattice unit configuration to fill the wing to form a skin lattice structure; the skin lattice structure of the wing includes a skin and a lattice filling area; S20: Adopt variable cell size design for the lattice unit to construct a variable-size lattice unit; S30: According to the stress field of the wing, adopt variable cell density design for the variable-size lattice unit to construct a variable-size and variable-density lattice unit; S40: Establish the wing configuration. The present invention uses a variable cross-section D-shaped unit as the lattice unit configuration, and adopts variable size and variable density designs to achieve deep coupling of the integrated design of heat dissipation and load-bearing performance. The application scenario can be flexibly adjusted to meet complex working conditions requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerospace engineering, and particularly relates to a design method for a variable-size and variable-density lattice structure wing with optimized heat dissipation and load-bearing capabilities. Background Art

[0002] Complex thin-walled structural components of high-speed UAV wings often adopt curved skins-lattice structures, which are widely used in aerospace products. Their design and manufacturing technologies have a direct impact on the quality, load-bearing, and heat dissipation performance of the products. When a high-speed UAV wing flies at Mach 3, its surface temperature reaches 350 °C. When the speed reaches 5-6 Mach, its surface temperature will be even higher. Even a wing made of titanium alloy material can hardly withstand such high temperatures. Moreover, during flight, it is subjected to multiple loads such as compression, bending, and torsion. To improve the ability of a high-speed UAV wing to cope with multi-field environments during high-speed flight and make it have lightweight, high load-bearing, and high heat dissipation performance, the generative design technology of complex curved skins-lattice structures based on additive manufacturing is particularly important.

[0003] In the prior art, first, in the research on the force, heat performance, and optimization design of minimal surface lattice structures at Nanjing University of Science and Technology, the research was based on the cooling wall panel of an engine combustion chamber, and a force and heat performance optimization design method for a lattice sandwich panel structure based on minimal surfaces was given. However, this method only uses lattice units with equal cross-sections. During the variable-size optimization process, the length of the lattice unit is set as a fixed value, that is, only the width and height of the lattice unit are optimized. This method has defects such as stress concentration in the node area of the lattice unit and structural failure defects. The focus of this research is limited to the performance of minimal surface structures and has not been extended to the design of more complex geometric shapes or heterogeneous structures, so the design flexibility is limited. And this research only targets the lattice plate structure of the engine combustion chamber in terms of material, and does not involve the titanium alloy structure of the aircraft wing, having defects such as poor high-temperature resistance, weak mechanical properties, and inconvenient processing. Second, in the research on the thermal-mechanical performance analysis and optimization of composite lattice sandwich structures under thermal loads at Harbin Institute of Technology, the distribution and geometric dimensions of the rods in the lattice core were optimized. This research mainly relies on the embedding of heat pipes. Although this method can improve the heat dissipation performance of composite materials, it lacks flexibility in complex multi-functional structures, especially for the design requirements of simultaneously optimizing load-bearing and heat dissipation are not perfect enough. And because the research object is a composite material structure, the design and embedding position of the heat pipe will limit the design freedom of the structure. Especially under complex working conditions, the heat dissipation and load-bearing performance cannot be flexibly adjusted. Therefore, the design flexibility of this research is limited, and there are also defects such as low heat dissipation efficiency, poor continuous cooling performance, and large structural influence. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention proposes a design method for a variable-size and variable-density lattice structure wing with optimized heat dissipation and load-bearing capacity. Taking a variable-section D-shaped unit as the lattice unit configuration, a skin lattice structure wing is constructed. Based on the high-strength titanium alloy TC4 wing material, variable-size and variable-density designs are adopted to achieve a deep coupling of the integrated design of heat dissipation and load-bearing performance, enabling the lattice structure to be flexibly adjusted according to the actual application scenario, meeting the requirements of complex working conditions, realizing precise control of the heat dissipation and load-bearing performance of the wing, making the wing have the properties of light weight, high heat dissipation and high load-bearing, and ensuring the improvement of the comprehensive performance of the wing; moreover, the present invention adopts cold flow heat dissipation, which has the advantages of high heat dissipation efficiency, continuous cooling and little influence on the structure.

[0005] To achieve the above object, a design method for a variable-size and variable-density lattice structure wing with optimized heat dissipation and load-bearing capacity of the present invention includes the following steps:

[0006] S10: Perform a variable-section design on the D-shaped unit to obtain a variable-section D-shaped unit. Taking the variable-section D-shaped unit as the lattice unit configuration, fill the wing to form a skin lattice structure; the skin lattice structure includes a skin and a lattice filling area;

[0007] S20: Adopt a cell variable-size design for the lattice unit to construct a variable-size lattice unit;

[0008] S30: The wing is made of titanium alloy TC4. According to the stress field of the wing, adopt a cell variable-density design for the variable-size lattice unit to construct a variable-size and variable-density lattice unit;

[0009] S40: Use the variable-size and variable-density lattice unit to fill the lattice filling area to establish the overall wing configuration.

[0010] Preferably, the S10 includes S101, S102 and S103, wherein,

[0011] S101: Add an auxiliary function based on the D-shaped implicit function of TPMS to establish an implicit function expression for the parallel connection of variable-section D-shaped units. Use the implicit function expression for the parallel connection of variable-section D-shaped units to model the D-shaped unit to obtain a variable-section D-shaped unit;

[0012] S102: Perform parameter definition and analysis on the variable-section D-shaped unit to establish a relationship function between the cross-section control coefficient and the strut cross-section radius of the variable-section D-shaped unit;

[0013] S103: According to the design requirements, by adjusting the value of the cross-section control coefficient , complete the parametric variable-section design of the D-shaped unit.

[0014] Preferably, in the step S101, the implicit function expression of the variable cross-section D-type unit in parallel is as follows:

[0015] ;

[0016] In the formula, is the implicit function of the variable cross-section D-type unit in parallel, is the unit vector of the three axes in the Cartesian coordinate system, ， ， ， , , are the coordinates in the Cartesian coordinate system, is the side length of the lattice unit, is the threshold value, is the cross-section control coefficient.

[0017] Preferably, in the step S102, the relationship function between the cross-section control coefficient and the strut cross-section radius of the variable cross-section D-type unit is as follows:

[0018] ;

[0019] In the formula, is the strut cross-section radius of the variable cross-section D-type unit.

[0020] Preferably, in the step S20, the variable cell size design is to set the cell size as a cell size with gradient gradual change.

[0021] Preferably, the step S20 includes S201, S202 and S203, where

[0022] S201: Determine the skin and lattice filling area of the wing. The skin is the non-design domain, and the lattice filling area is the design domain;

[0023] S202: Uniformly fill the lattice filling area with a single lattice unit;

[0024] S203: Determine the heated surface of the skin, and take the heated surface of the skin as the reference to perform gradient gradual change design on the cell size of the lattice filling area.

[0025] Preferably, the step S30 includes S301, S302 and S303, where

[0026] S301: Establish the threshold value in the D-type implicit function of TPMSThe corresponding relationship with the volume fraction of D-type units, and the equivalent elastic modulus of D-type units is calculated by the homogenization method; the equivalent elastic modulus is a polynomial interpolation model of the equivalent elastic matrix;

[0027] S302: Combine the topology optimization method of SIMP with the optimization criterion method, and optimize to obtain the grid cell density information of the lattice unit according to the stress field load of the corresponding wing;

[0028] S303: Construct the variable-size variable-density lattice unit according to the correspondence between the grid cell density information of the lattice unit obtained by optimization and the volume fraction of the lattice unit.

[0029] Preferably, the wing includes but is not limited to the wing of an unmanned aerial vehicle.

[0030] The beneficial effects of the present invention are:

[0031] The present invention uses a variable-section D-type unit as the lattice unit configuration to construct the skin lattice structure of the wing, improves the stress concentration phenomenon in the node area of the lattice unit, overcomes the discontinuity of the structure and the defect of extremely small size at an extremely small volume fraction of the skin lattice structure, improves the mechanical properties of the structure, and realizes the light weight, high heat dissipation and high load-bearing performance of the wing.

[0032] The present invention adopts the design of variable-cell-size wing to enable the wing surface temperature to be quickly transferred to the inside of the wing and carried away by the cold flow, realizing the high heat dissipation performance of the wing.

[0033] On the basis of considering heat dissipation factors, the present invention adopts the design of variable-cell-density wing based on the high-strength titanium alloy TC4 wing material and designs according to the stress field to realize the load bearing such as high compression, high bending and high torsion of the wing.

[0034] The present invention takes the cell size and cell density as two groups of design variables, takes the thermal control and load-bearing performance as two groups of optimization design objectives, conducts an integrated optimization design of thermal control - load-bearing for the wing with a variable-section lattice structure, establishes an overall wing configuration with excellent heat dissipation - load-bearing performance, and realizes the precise regulation of the heat dissipation - load-bearing performance of the wing.

[0035] The present invention provides strong support for the design of the complex thin-walled structure of the wing, improves the modeling and design quality of complex thin-walled structural parts, meets the design and manufacturing requirements of lightweight, high strength and high heat dissipation of complex thin-walled structural parts under additive manufacturing, and improves the thermal-mechanical properties of complex thin-walled structural parts and the ability to cope with complex working conditions.

[0036] According to the design requirements, based on the target design domain, boundary conditions, gradient size design conditions, and volume fraction, the present invention configures the D-type unit as a lattice unit after variable cross-section design, fills the wing to form a skin lattice structure, improves the stress concentration phenomenon in the node region of the original equal cross-section D-type unit, overcomes the discontinuity and extremely small size phenomenon of the skin lattice structure at an extremely small volume fraction, and improves the mechanical properties of the wing structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the flow chart of the design method of the variable-size variable-density lattice structure wing for heat dissipation and load-bearing optimization of the present invention Figure 1 ;

[0038] Figure 2 is the flow chart of the design method of the variable-size variable-density lattice structure wing for heat dissipation and load-bearing optimization of the present invention Figure 2 ;

[0039] Figure 3 is a schematic diagram of the x-z plane of the variable cross-section D-type unit; wherein,

[0040] (a) is the front view of the x-z plane of the variable cross-section D-type unit;

[0041] (b) is a schematic diagram of the strut parameters of the variable cross-section D-type unit;

[0042] (c) is Figure 3 an enlarged schematic diagram of the dashed box in (b);

[0043] Figure 4 is a schematic diagram of the relationship curve between the value of K and r and R;

[0044] Figure 5 is a schematic diagram of the shape of the D-type unit and the cross-sectional shape of the strut under different values of K; wherein,

[0045] (a) is a schematic diagram of the shape of the D-type unit and the cross-sectional shape of the strut when the value of K is 0.05;

[0046] (b) is a schematic diagram of the shape of the D-type unit and the cross-sectional shape of the strut when the value of K is 0.06;

[0047] (c) is a schematic diagram of the shape of the D-type unit and the cross-sectional shape of the strut when the value of K is 0.07;

[0048] Figure 6 is a schematic diagram of the wing lattice cross-section under different conditions of cell size and cell density design; wherein,

[0049] (a) is a schematic diagram of the wing lattice cross-section designed with equal cell size and uniform cell density;

[0050] (b) Schematic diagram of the wing lattice cross-section designed only with variable cell sizes;

[0051] (c) Schematic diagram of the wing lattice cross-section designed only with variable cell densities;

[0052] (d) Schematic diagram of the wing lattice cross-section constructed with variable-size and variable-density lattice units of the present invention;

[0053] Figure 7 Flowchart of the variable-density lattice structure design of the present invention;

[0054] Figure 8 Schematic diagram of the load-bearing situation of the wing of the present invention in the air flight state;

[0055] Figure 9 Schematic diagrams for the analysis of the wing under different static conditions; among them,

[0056] (a) Schematic diagram of the simplified load-bearing static analysis of the wing;

[0057] (b) Schematic diagram of the equivalent stress static analysis of the wing;

[0058] Figure 10 Schematic diagrams for the filling of different lattice cell sizes of the wing; among them,

[0059] (a) Schematic diagram of the filling of uniform lattice cell sizes of the wing;

[0060] (b) Schematic diagram of the filling of gradient lattice with variable cell sizes of the wing;

[0061] Figure 11 Schematic diagrams for the filling of different lattice units of the wing;

[0062] (a) Schematic diagram of the analysis of the density distribution of the lattice units of the wing;

[0063] (b) Schematic diagram of the filling of uniform lattice units of the wing;

[0064] (c) Schematic diagram of the filling of variable-size lattice units of the wing;

[0065] (d) Schematic diagram of the filling of variable-size and variable-density lattice units of the wing;

[0066] In the figure, q is the aerodynamic distributed load; Q is the mass force distributed load. Specific implementation manner

[0067] The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted again that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0068] Embodiment 1

[0069] As Figure 1 shown, a method for designing a variable-size and variable-density lattice structure wing with optimized heat dissipation and load-bearing of the present invention includes the following steps:

[0070] S10: Perform variable cross-section design on the D-type unit to obtain a variable cross-section D-type unit, use the variable cross-section D-type unit as the lattice unit configuration, and fill the wing to form a skin lattice structure; the skin lattice structure includes a skin and a lattice filling area;

[0071] S20: Adopt cell variable-size design for the lattice unit to construct a variable-size lattice unit;

[0072] S30: On the basis of considering heat dissipation factors, based on the wing made of titanium alloy TC4, according to the stress field of the wing, adopt cell variable-density design for the variable-size lattice unit to construct a variable-size and variable-density lattice unit;

[0073] S40: Use the variable-size and variable-density lattice unit to establish the overall wing configuration.

[0074] In this embodiment, the wing includes but is not limited to the wing of a high-speed unmanned aerial vehicle. In S10, the D-type unit (Diamond) is a basic building unit with relatively good comprehensive performance of heat dissipation and load-bearing of TPMS (Triply Periodic Minimal Surface). According to the design requirements, based on the target design domain, boundary conditions, gradient size design conditions and volume fraction, on the basis of considering heat dissipation factors, perform variable cross-section design on the D-type unit and then use it as the lattice unit for configuration, fill the wing to form a skin lattice structure, improve the stress concentration phenomenon in the node area of the original equal cross-section D-type unit, and improve the discontinuity and extremely small size phenomenon of the skin lattice structure at extremely small volume fractions, and improve the mechanical properties of the wing structure.

[0075] S10 includes three steps: S101, S102 and S103:

[0076] S101: Add an auxiliary function based on the D-type implicit function of TPMS, establish an expression of the parallel implicit function of the variable cross-section D-type unit, and perform modeling on the D-type unit to obtain a variable cross-section D-type unit.

[0077] The D-type implicit function expression of a conventional TPMS is as follows:

[0078] (1)

[0079] In the formula, are the unit vectors of the three axes in the Cartesian coordinate system, ， ， ， 、 、 are the coordinates in the Cartesian coordinate system, is the side length of the lattice unit, is the threshold.

[0080] The volume fraction of the D-type implicit function and the threshold are in the following relationship:

[0081] (2)

[0082] Where , when , discontinuity occurs in the lattice unit. When , the minimum volume fraction to maintain unit continuity is reached, which is 9.58% at this time. Such a volume fraction obviously does not meet the lightweight design requirements. To avoid the phenomenon of discontinuity and extremely small size of the lattice unit due to small volume fractions, an auxiliary function is added based on the above D-type implicit function of the TPMS, and an implicit function expression of the parallel connection of variable cross-section D-type units is established, so that on the premise of not changing the geometric topology configuration of the D-type unit, the isosurface of the function in the same period range is further indented, thereby improving the lightweight design ability of the D-type implicit function of the TPMS and effectively improving the mechanical properties of the lattice structure. Thus, the above implicit function expression of the parallel connection of variable cross-section D-type units is as follows:

[0083] (3)

[0084] In the formula, is a constant; to achieve the function of variable cross-section of the D-type unit, the value is set as a variable, and is defined as the cross-section control coefficient; is the implicit function of the parallel connection of variable cross-section D-type units; is the D-type implicit function of the TPMS; is the auxiliary function; are the unit vectors of the three axes in the Cartesian coordinate system; is the threshold.

[0085] Set auxiliary functions as follows:

[0086] (4)

[0087] Substitute expressions (1) and (4) into expression (3). To reduce complexity, let to obtain the implicit function expression for the parallel connection of variable cross-section D-shaped units as:

[0088] (5)

[0089] In the formula, is the implicit function of the parallel connection of variable cross-section D-shaped units, are the unit vectors of the three axes in the Cartesian coordinate system, ， ， ， 、 、 are the coordinates in the Cartesian coordinate system, is the side length of the lattice unit, is the threshold value, is the cross-section control coefficient.

[0090] S102: Refer to Figure 3 (a), Figure 3 (b) and Figure 3 (c) as shown, define and analyze the parameters of the variable cross-section D-shaped unit, and establish the relationship function between the cross-section control coefficient and the cross-sectional radius of the strut of the variable cross-section D-shaped unit. Specifically, Figure 3 (a), Figure 3 (b) and Figure 3 (c) are the front views of the variable cross-section D-shaped unit and its strut parameters, Figure 3 (c)is Figure 3 the enlarged schematic diagram of the AOFM unit in (b), where is the side length of the lattice unit, , is the pore width, B is the midpoint of AC section, E is the midpoint of GF, is the cross-sectional radius at the center of the strut of the variable cross-section D-shaped unit, is the cross-sectional radius at the edge of the strut of the variable cross-section D-shaped unit; it can be seen from the enlarged view of the strut of the D-shaped unit shown in Figure 3 (c) that on this plane, the strut of the D-shaped unit is in x - zThe angle between the planar strut and the horizontal plane is 45°. The cross-sectional radius of the variable cross-section D-shaped unit strut increases gradually from the center to both sides. The closer it is to the node, the relatively larger the cross-sectional radius of the variable cross-section D-shaped unit strut is, and the transition at the node is relatively smooth. This will enable the structure to have a better stress distribution at the nodes where stress concentration is likely to occur, thereby improving the load-bearing performance of the skin lattice structure. Since the surfaces of the variable cross-section D-shaped lattice units are all generated by the isosurfaces of implicit functions, and the D-shaped unit struts are x - z The angle between the planar strut and the horizontal plane is 45°, then in this plane z = x The distance between the two intersection points of the axis and the isosurface strut is the cross-sectional diameter of the variable cross-section D-shaped unit strut. According to the threshold of this relationship and the cross-section control coefficient and the variable cross-section D-shaped unit strut The cross-sectional radius at the position satisfies the following relationship:

[0091] (6)

[0092] In the formula, is the cross-sectional radius of the variable cross-section D-shaped unit strut at the position, is the side length of the lattice unit, is the cross-section control coefficient, is the threshold.

[0093] Now assume that the side length of the lattice unit is dimensionless 10 and the volume fraction is 10%. Define the cross-sectional radius of the variable cross-section D-shaped unit strut at this time as the normalized cross-sectional radius. Its value and the and relationship curve is as Figure 4 shown. It can be seen from Figure 4 that as the value gradually increases from 0 to 0.14, the value gradually increases, the value gradually decreases, and the values gradually approach. Therefore, the larger the value, the more the cross-sectional rod diameter change of the variable cross-section D-shaped lattice unit strut approaches that of an equal cross-section strut. Therefore, by adjusting the value, the cross-sectional size of the strut can be freely adjusted to meet the parametric design requirements of the variable cross-section D-shaped unit. According to the Figure 4 slope change in, as the value increases, the change range of the cross-sectional rod diameter of the strut is less and less affected by the value change, and the cross-sectional rod diameter of the strut The change range of the size gradually decreases and approaches that of a constant cross-section strut.

[0094] S103: Complete the parametric variable cross-section design of the D-type unit by adjusting the cross-section control coefficient according to the design requirements. Specifically, during the design process, set a reasonable value according to the comprehensive mechanical property requirements of the equivalent elastic modulus and equivalent yield strength to adjust the effect of the variable cross-section of the D-type unit, thereby improving the discontinuity and extremely small size phenomena of the structure at an extremely small volume fraction, optimizing the distribution of the strut cross-section sizes of the D-type unit, and further optimizing its stress distribution and enhancing the mechanical properties of the structure. As Figure 5 shown, it is the shapes of the D-type unit and the strut cross-section shapes under different values. It is obtained from the experiment that when the value is in the range of 0.05 - 0.07, the equivalent elastic modulus of the skin lattice structure gradually increases with the increase of the value. This is because as the cross-section radius at the center of the strut of the variable cross-section D-type unit increases, the stress at the center gradually diffuses to the edge, and the stress concentration at the center of the strut gradually decreases, reaching the peak when ; while with the increase of the value, the further increase of the cross-section of the strut at the center of the strut of the variable cross-section D-type unit causes the cross-section at the edge nodes to decrease, and its stress gradually diffuses to the node parts of the strut. Therefore, when the value is in the range of 0.07 - 0.09, it shows a decrease again; and the yield strength is that when the value is in the range of 0.05 - 0.08, it shows a relatively large increase with the value, and the yield strength reaches the peak when

[0095] . Its change trend does not completely coincide with that of the elastic modulus, indicating that the design of the variable cross-section D-type unit does not change the mechanical properties of the structure completely in the same way as homogeneous materials. When the change of the strut cross-section radius from the center to the edge is within a relatively small difference range, a greater enhancement of mechanical properties can be achieved.

[0096] In this embodiment, S20 is to perform a cell variable size design on the above lattice unit to quickly transfer the surface temperature of the wing to the inside of the wing and take it away by the cold flow, realizing the high heat dissipation performance of the wing. Specifically, Figure 2 and Figure 6As shown, the cell variable size design is the cell gradient size design, which is an optimized design for the thermal control performance of the wing thin-walled structure. It is a wing structure with excellent heat dissipation performance obtained by establishing a skin lattice structure formed by filling the wing with lattice units after variable cross-section and variable size. In this step, the cell variable size design is to set the cell size as a gradient-varying cell size. The cell size at the center of the wing is the largest, and the cells gradually become smaller along the gradient direction of the wing airfoil. The closer to the wing wall surface, the smaller the cells. In other words, the upper and lower skins of the wing are the heated surfaces, and the cell size in the area closer to the upper and lower skin walls is smaller. Conversely, the cell size in the area farther from the upper and lower skin walls is larger, and the cell sizes on the isogradient contour lines of the airfoil are the same. The cell size near the wing skin wall is small, and the cell density of the lattice structure is large, which is conducive to quickly transferring the heat on the wing surface to the central area inside the wing; the cell size in the central area of the wing is large, the cell density of the lattice structure is small, and the voids are large, which is conducive to the flow of cold fluid, accelerating the cold fluid flow rate, and can take away heat faster.

[0097] As Figure 6 shown in (a), the overall wing filled with a uniform lattice structure of a single lattice unit configuration, as Figure 6 shown in (b), the overall wing filled only with variable-size lattice units. By comparing the two, it can be seen that the cell size near the wing skin wall is small, making the local convective heat transfer more intense. The internal lattice structure absorbs a large amount of heat, which is conducive to quickly transferring the heat on the wing surface to the inside of the wing; the cell size in the central area of the wing far from the heated surface is large, and the voids are large, making the flow resistance smaller when the cooling medium flows into the lattice structure, which is conducive to the flow of cold fluid, accelerating the cold fluid flow rate, enabling the inside of the wing to fully exchange heat with the cooling medium in a high-temperature environment, and thus taking away the heat from the wing body to achieve the heat dissipation of the wing components. Therefore, the cell variable size design can better improve the heat dissipation performance of the wing.

[0098] S20 includes S201, S202, and S203, and the specific steps are as follows:

[0099] S201: The skin lattice structure of the wing includes the skin and the lattice filling area. Determine the skin and the lattice filling area of the wing. Among them, the skin is the non-design domain, and the lattice filling area is the design domain;

[0100] S202: Fill the lattice filling area with a single lattice unit with a uniform cell size. The filled cell size should ensure the minimum cell size under the condition of maintaining a small flow resistance after the coolant is introduced into the skin lattice structure. The cell size is set to ;

[0101] S203: Determine the heated surface of the skin. Using the heated surface of the skin as a reference, perform a gradient design on the cell size of the lattice filling area. That is, the cell size closer to the heated surface of the skin is closer to the set minimum cell size, and the cell size farther from the heated surface of the wing skin is closer to the maximum cell size. The minimum cell size of the gradient is , and the maximum cell size is , where and select appropriate values according to the gradient direction size. In the heat dissipation gradient design, the cell size will gradually change in different regions of the structure and should maintain a smooth transition. According to experience and select 5%-15% of the cell size in the gradient direction as appropriate values.

[0102] In this embodiment, in S30, on the basis of considering heat dissipation factors, after determining the cell size, based on the wing made of high-strength titanium alloy TC4 material, according to the load field of the wing's flight state in the air, perform a cell variable density design accordingly to achieve the load bearing of high compression, high bending and high torsion of the wing. Specifically, refer to Figure 6 (d) and Figure 6 (b) By comparison, the density of the cell itself corresponds to the load field. The greater the load, the greater the cell density, and the smaller the load, the smaller the cell density. The greater the cell density, the better the bearing performance. Therefore, the bearing performance of the wing structure is better, and lightweight can be achieved.

[0103] S30 includes S301, S302 and S303. Refer to Figure 7 shown as follows:

[0104] S301: Establish the correspondence between the threshold C in the D-type implicit function of TPMS and the volume fraction of the D-type unit. Use the homogenization method to calculate the equivalent elastic modulus of the D-type unit. In order to avoid the cumbersome homogenization calculation in the optimization process, establish a polynomial interpolation model of the equivalent elastic matrix;

[0105] S302: Combine the topology optimization method of SIMP (Solid Isotropic Material with Penalization) and OC (Optimality Criteria Method), and according to the stress field load of the corresponding wing, obtain the grid unit density information of the lattice unit; specifically, use the SIMP method to solve the variable density distribution problem of the material in the topology optimization combined with sensitivity analysis, optimize the distribution of the design variables, and use the OC optimization criterion method to update and iterate the density of the new cell structure unit.

[0106] S303: Based on the correspondence between the grid cell density information of the optimized lattice unit and the volume fraction of the lattice unit, construct a variable-size and variable-density lattice unit. If the result converges, output the cell structure with the average density size in the interval and construct a variable-density lattice structure. If the result does not converge, return to the SIMP method to solve the topology optimization process for re-analysis.

[0107] In this embodiment, in S40, the variable cell size design and the variable cell density design are used as two sets of design variables, and the thermal control and load-bearing performance are used as two sets of optimization design objectives to perform the integrated thermal control-load-bearing optimization design on the lightweight wing, establish an overall wing configuration with excellent heat dissipation-load-bearing performance, and achieve precise control of the heat dissipation and load-bearing performance of the wing.

[0108] Embodiment 2

[0109] See Figures 1 - 11 As shown, in this embodiment, the wing of a high-speed UAV is used as a design example. The skin of the wing is taken as the non-design domain and its original shape is maintained during the optimization process, while the lattice filling area is the design domain. The lattice filling area is filled with a variable-section D-shaped lattice as the lattice unit configuration. The aim is to implement a variable-size and variable-density lattice structure wing design method for the heat dissipation and load-bearing optimization of the skin lattice structure of the high-speed UAV wing and verify the effectiveness of its optimization design. In this embodiment, when the high-speed UAV is in service, it mainly bears two types of distributed loads, as Figure 8 shown, the load sources are respectively the mass force distribution load Q generated by the self-weight of the wing structure under the action of gravity and the aerodynamic distribution load q that maintains the lift during flight; and in order to maintain the lift, the aerodynamic distribution load q is generally greater than the mass force distribution load Q. Therefore, the loading condition of the wing is simplified as: the wing root is fixed and the distributed load pressure acts on the lower wing surface.

[0110] Through the simplified wing loading model, the static analysis of the wing model is carried out using Abaqus / CAE2022 software. Set its material as additively manufactured titanium alloy TC4, with a material density of 4.43 g / cm 3 , the elastic modulus of the material is 118 GPa, the Poisson's ratio is 0.3, its mesh size is set to 100 mm, and 72,476 C3D10 tetrahedral meshes are divided. Among them, according to the simplified wing loading model, its distributed load is set as Figure 9 (a) shown, the wing root part is set as a "fully fixed" constraint, and a uniform distributed load pressure of 1×10 -5 N / mm 2 is set on the lower wing surface, and the equivalent stress nephogram of the wing as shown in Figure 9 (b) is obtained. From Figure 9It can be obtained from (b) that, when looking at the wing from the wingspan direction, the stress value is greater closer to the wing root of the wing and smaller closer to the wing tip. And closer to the center of the wing root, the stress value is greater, while closer to the edge of the wing root, the stress value is smaller. Therefore, when filling the lattice units subsequently, lattice units with a larger volume fraction should be arranged near the center of the wing root, and lattice units with a smaller volume fraction should be arranged in areas with smaller stress values such as the wing tip.

[0111] During the flight of the wing, since the leading edge of the wing often first undergoes intense compression, friction, and viscous dissipation with the air when flying forward, the temperature load is often greater closer to the leading edge. As time goes by, the entire fuselage skin will be subjected to high-temperature loads. To reduce the complexity of the design, the temperature load of the wing is considered as: uniformly heated on the surface, and the temperature is higher closer to the fuselage skin. Since the surface heating condition of the wing is considered as uniform heating of the wing skin and the temperature is higher closer to the fuselage skin. Therefore, taking the skin as the reference, a gradient design of variable cell size for the variable cross-section D-shaped units filling the wing is carried out. Variable cross-section D-shaped units with a cell size of 300mm×300mm×300mm and a volume fraction of 15% are used for filling, and the result of its uniform filling of the variable cross-section D-shape is as Figure 10 (a) shown; the variable cell size design still uses the above-mentioned variable cross-section D-shaped lattice units. Different from the uniform filling, the lattice cell size of the original 300mm is offset by 30mm up and down, that is , the minimum cell size is set to 270mm×270mm×270mm, and the maximum cell size is set to 330mm×330mm×330mm. When filling the lattice, taking the wing skin as the gradient design reference, the closer to the wing skin, the closer to the minimum cell size, and vice versa, the lattice cell size farther away from the wing skin is closer to the maximum cell size. By filling the wing with gradient variable cell sizes in this way, the filling result as shown in Figure 10 (b) is obtained. Only the cell size is gradient-changed, and the volume fraction is still 15%, that is, the volume fraction remains unchanged.

[0112] After the gradient variable cell size design of the cell size, its active cooling performance should be improved to a certain extent, and the bearing performance is further optimized according to the variable density design method of the cell based on topology optimization. Among them, the optimization model uses the homogenization topology optimization theory for the variable density design of the cell, and the process of the variable density design of the topology optimization of the cell is as follows:

[0113] Step 1: Topology optimization design area

[0114] Divide the design domain and the non-design domain.

[0115] Step 2: Constraint conditions

[0116] Set the overall volume fraction percentage to be retained after optimization to 15%. Regarding the setting of the unit cell volume fraction, when the setting is too small, it is not conducive to the load-bearing and additive manufacturing in the low-stress area. When the unit cell volume fraction is too large, it will cause the coolant to not flow smoothly into the lattice structure. Therefore, the constraint range of the defined unit cell volume fraction is: the minimum unit volume fraction is not less than 5%, and the maximum unit volume fraction is not higher than 60%. The remaining constraint conditions are the same as those in the static analysis.

[0117] Step 3: Optimization objective

[0118] Set the optimization objective to maximize the stiffness, that is, solve by setting the compliance to the minimum.

[0119] Step 4: Solving and calculating

[0120] After completing all the settings, perform the solving and calculation to obtain Figure 11 (a) The unit density distribution diagram shown, where 9 density gradients are divided. The maximum value of the unit volume fraction is 52.66% and the minimum value is 5%. Based on the density distribution information solved by this topology optimization algorithm, model the variable-density lattice structure wing. Figure 11 (b), Figure 11 (c) and Figure 11 (d) are respectively the comparison diagrams of the wing filled with uniform lattice, the wing filled with lattice after variable-size design, and the wing filled with lattice after variable-size and variable-density design. For convenient display, the wing skin is hidden. Among them, Figure 11 (b) The wing filled with uniform lattice is directly filled with a variable-section D-shaped lattice structure with a volume fraction of 15% and a unit cell size of 300mm×300mm×300mm; while Figure 11 (c) The lattice structure wing with variable unit cell size is filled with lattice unit cells of the same volume fraction in the lattice filling area. The unit cell size continues the result of the unit cell size gradient design, that is, the minimum unit cell size is set to 270mm×270mm×270mm, and the maximum unit cell size is set to 330mm×330mm×330mm. And under the condition of the same overall volume fraction as the uniform filling, different-sized lattice units are used to fill the lattice filling area. When filling the lattice, the wing skin is used as the gradient design reference. The closer to the wing skin, the closer to the minimum unit cell size. On the contrary, the farther away from the wing skin, the closer the lattice unit cell size is to the maximum unit cell size; Figure 11(d) The results of the variable-size and variable-density design use lattice units with different volume fractions to fill the lattice filling area. Based on the results of the cell size gradient design, a variable-density cell design with variable cell volume fractions is carried out on this basis. Lattice units with different volume fractions are used to fill the lattice filling area. According to the structural force transmission path calculated by topology optimization, lattice units with a larger volume fraction are set in the areas with larger loads, while lattice units with a smaller volume fraction are set in the areas with smaller loads. That is, the active cooling performance of the wing structure is optimized by optimizing the cell size, and the load-bearing performance of the wing structure is optimized by optimizing the unit density distribution in different areas, so as to achieve the integrated design of thermal control and load-bearing.

[0121] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A design method for a variable-size, variable-density lattice structure wing with optimized heat dissipation load, characterized in that: The steps include: S10: Designing a variable cross-section of the D-type unit of the TPMS to obtain a variable cross-section D-type unit, using the variable cross-section D-type unit as a lattice unit configuration, filling the wing to form a skin lattice structure; the skin lattice structure includes a skin and a lattice filling area; The S10 includes S101, S102 and S103, wherein: S101: adding an auxiliary function based on the D-type implicit function of the TPMS, establishing a variable-section D-type unit parallel implicit function expression, and using the variable-section D-type unit parallel implicit function expression to model the D-type unit to obtain a variable-section D-type unit; In S101, the variable cross-section D-type unit parallel implicit function expression is: In the formula, is the parallel implicit function of the variable cross-section D-type unit, are the unit vectors of the three axes in the Cartesian coordinate system, X =2π x , Y =2π y , Z =2π z , x , y , z is the coordinate in the Cartesian coordinate system, L is the side length of the lattice unit, C is the threshold, and K is the cross-section control coefficient; S102: defining and analyzing parameters of the variable cross-section D-type unit, and establishing a relationship function between the cross-section control coefficient K and the cross-section radius of the support rod of the variable cross-section D-type unit; In S102, the relationship function between the cross-section control coefficient K and the cross-section radius of the support rod of the variable cross-section D-type unit is: In the formula, The support rod of the variable cross-section D-type unit x The radius of the cross section; S103: completing the parametric variable cross-section design of the D-type unit by adjusting the value of the cross-section control coefficient K according to the design requirements; S20: adopting a cell variable size design for the lattice unit to construct a variable size lattice unit; S30: The wing is made of titanium alloy TC4. According to the stress field of the wing, the variable-size lattice unit is designed with variable cell density to construct a variable-size and variable-density lattice unit. S40: Filling the lattice filling area with the variable size and variable density lattice units to establish an overall wing configuration.

2. The design method of a variable-size and variable-density lattice structure wing with optimized heat dissipation load according to claim 1 is characterized in that: In the S20, the cell variable size design is to set the cell size to a gradient cell size.

3. The design method of a variable-size and variable-density lattice structure wing with optimized heat dissipation load according to claim 2 is characterized in that: The S20 includes S201, S202 and S203, wherein: S201: Determine a skin and a lattice filling area of ​​a wing, wherein the skin is a non-design domain and the lattice filling area is a design domain; S202: Filling the dot matrix filling area with a uniform cell size using a single dot matrix unit; S203: Determine the heating surface of the skin, and use the heating surface of the skin as a reference to perform a gradient design on the cell size of the lattice filling area.

4. The design method of a variable-size and variable-density lattice structure wing with optimized heat dissipation load according to claim 1, characterized in that: The S30 includes S301, S302 and S303, wherein: S301: establishing a corresponding relationship between a threshold value C in a D-type implicit function of the TPMS and a volume fraction of a D-type unit, and calculating an equivalent elastic modulus of the D-type unit by a homogenization method; the equivalent elastic modulus is a polynomial interpolation model of an equivalent elastic matrix; S302: Utilizing a topology optimization method of SIMP combined with an optimization criterion method, and optimizing and acquiring grid unit density information of the lattice unit according to a stress field load of a corresponding wing; S303: constructing the variable-size and variable-density lattice unit according to the correspondence between the grid unit density information of the lattice unit obtained through optimization and the volume fraction of the lattice unit.

5. The design method of a variable-size and variable-density lattice structure wing with optimized heat dissipation load according to claim 1, characterized in that: The wing comprises a drone wing.

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