Propelling storage box lightweight design method based on variable thickness topological optimization

Abstract

The invention discloses a propulsion storage tank lightweight design method based on variable thickness topological optimization, which is characterized in that topological optimization is carried out on a storage tank wall plate structure, the weight is reduced while the design requirement is met, and the lightweight of a micro propulsion storage tank is realized. According to the topological optimization process of the inner wall face of the storage box, the wall thickness, stress, inherent materials and the like serve as boundary conditions, the stress distribution state is optimized by optimizing structural characteristics, and meanwhile the process of structural weight reduction is achieved. Compared with the prior art, optimization of the stress distribution state of the storage tank and lightweight design of the structure of the storage tank are achieved at the same time; the universality is high, and the method can be used in the design of regular containers or special-shaped pressure-bearing containers; the coincidence with the 3D printing technology is high, and the design redundancy in the structural design under the limitation of the traditional 3D printing technology is effectively reduced; the operation is simple, and the practicability is high.

Description

Technical Field

[0001] The invention belongs to the technical field of structural design of micro-nano satellite micro-propulsion systems, and specifically relates to a lightweight design method for a propulsion tank based on variable thickness topology optimization. Background Art

[0002] With the development of technology and the deepening of space exploration, higher requirements are placed on the micro-propulsion system of micro-nano satellites. While ensuring the good performance of the structure, the goal of spacecraft structural design is to reduce redundant mass and improve material utilization through structural optimization design in a limited space, thereby increasing payload and reducing costs. As a key structure of micro-nano satellites, the micro-propulsion tank accounts for a large proportion of the total weight of micro-nano satellites and is the main lightweight design component. In order to achieve the goal of further reducing stress and reducing the weight of the tank, it is necessary to optimize the tank.

[0003] There are many existing lightweight design methods: designing weight-reducing holes on the original structure to reduce weight by reducing the structure; replacing lightweight materials to directly reduce the weight of the design body from an overall perspective; filling reinforcing materials to replace part of the design body with lightweight materials; using lightweight materials to design supporting structures based on the original structure, thereby reducing the wall thickness of the original structure, etc. However, all of the above methods have their limitations.

[0004] The optimization of structural strength mainly includes topology optimization, shape optimization, size optimization and morphology optimization. Topology optimization is to find the force transmission path in the design space to obtain the optimal material distribution, geometry optimization is to optimize the cross-sectional dimensions of each component in a given structure, shape optimization is to adjust the shape of the internal and external boundaries of the structure to improve the structural performance, and morphology optimization is to improve the performance by changing the position and shape of the stiffeners on the thin shell structure.

[0005] Traditional tank processing methods have complex product structures, many types of processing sequences, high production and assembly costs, and long production cycles. Additive manufacturing technology can quickly and accurately manufacture parts with complex shapes on a single device, solving many problems in forming parts with complex structures made of difficult-to-process materials. In recent years, it has been widely used in the forming and manufacturing of complex structural parts in the aerospace field at home and abroad. Summary of the invention

[0006] The purpose of the present invention is to provide a lightweight design method for a propulsion tank based on variable thickness topological optimization, which can reduce the weight while meeting the design requirements by topologically optimizing the tank wall structure, thereby realizing lightweighting of a micro-propulsion tank. The topological optimization process of the inner wall of the tank is to optimize the stress distribution state by optimizing the structural characteristics, while realizing the process of reducing the weight of the structure.

[0007] The technical solution to realize the present invention is: a lightweight design method of a propulsion tank based on variable thickness topology optimization, the steps are as follows:

[0008] S1: tank before design morphology optimization.

[0009] S2: Define the structural optimization design domain, perform topological optimization design on the internal wall of the tank based on the variable thickness topological optimization design method, and check the stress distribution state and quality parameters before and after the tank morphology optimization to confirm whether the design requirements of optimizing the stress distribution state and reducing the system quality are met at the same time.

[0010] S3: The stress distribution cloud diagram of the tank before and after topology optimization is used to determine whether the mass and stress distribution state of the tank are optimized.

[0011] Compared with the prior art, the present invention has the following significant advantages:

[0012] (1) The topology optimization design method of the present invention effectively extracts the target features, separates the design domain from the non-design domain, realizes independent processing of the design domain, reduces the impact on the structural function, and realizes the optimization of the stress distribution state of the tank and the lightweight design of the tank structure.

[0013] (2) The topology optimization design method described in the present invention is highly universal and can be used in the design of regular containers or special-shaped pressure vessels.

[0014] (3) The design domain and design parameters of the topology optimization design method described in the present invention are autonomously adjustable, which can highly meet the process requirements of 3D printing and effectively reduce the design redundancy in structural design under the limitations of traditional 3D printing processes.

[0015] (4) The topology optimization design method described in the present invention is simple to operate and highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The figure is a flow chart of the topology optimization design of the tank based on morphology optimization.

[0017] Figure 2 3D modeling of the front tank for topology optimization (example).

[0018] Figure 3 Schematic diagram of the design domain for topology optimization.

[0019] Figure 4 To extract the target features (inner wall surface) and mesh division.

[0020] Figure 5 It is the target feature (inner wall) after variable thickness topology optimization.

[0021] Figure 6 The tank structure after integrating the topology optimization results.

[0022] Figure 7 This is the tank mesh division diagram after topology optimization.

[0023] Figure 8 This is the stress distribution cloud diagram of the tank before topology optimization.

[0024] Fig. 9 This is the stress distribution cloud diagram of the tank after topology optimization. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; "connection" can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] The following will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention in combination with this design example.

[0029] Combination Figure 1 The lightweight design method of a propulsion tank based on variable thickness topology optimization described in the present invention comprises the following steps:

[0030] S1: tank before design morphology optimization.

[0031] S1.1: Calculate the tank volume before shape optimization:

[0032] The volume of the propellant tank before morphology optimization is determined by the speed increment ΔV and the filling rate required for the mission, and the required amount of propellant is determined by the ideal rocket equation:

[0033]

[0034] Where Δm is the propellant consumption, m0 is the initial total mass of the satellite, and I sp is the specific impulse and g is the acceleration due to gravity.

[0035] According to the design indicators, the required amount of propellant is calculated, and the minimum volume of the propellant tank is further obtained.

[0036] The volume of the surge tank is determined based on the nozzle design and the maximum single propellant consumption requirements during the mission.

[0037] S1.2: Design of appearance structure and mechanical interface:

[0038] According to the space limitations on the satellite and the system function requirements, the interface form between the structural system and the layout of components such as sensors required to meet the propulsion system functions and the corresponding interface form are confirmed. Finally, the structural constraints and mechanical interface constraints of the propulsion tank are confirmed to complete the tank shape structure design.

[0039] S1.3: Calculate wall thickness and assess strength:

[0040] Structural strength is the most important performance indicator of the propulsion tank and the basis for ensuring product functions. Mises equivalent stress is usually used to determine whether the structure has failed. Since the propulsion tank and the connecting parts are sealed by the extrusion effect of the sealing surface or the sealing ring, it should be ensured that the system does not have elastic failure, that is, the maximum stress value of the structure should be less than the yield strength of the material.

[0041] Therefore, the calculation of wall thickness has the following design constraints:

[0042]

[0043] Where P is the pressure on the inner wall of the tank; δ ni is the surface normal stress of the microelement on the inner surface of the tank with the inside of the cavity as the positive direction; σ1, σ2, σ3 are the principal stresses in the three directions of the microelement respectively; σ s It is the yield strength of the tank structural material and is the maximum stress value under conditions that ensure the tank does not fail.

[0044] S1.4: Perform three-dimensional modeling:

[0045] Combination Figure 2 Based on the volume of the surge tank, the tank's external structure, and the maximum stress value under the condition that the tank does not fail, a three-dimensional model of the tank structure is built, and the edges are blunted to verify whether the tank volume meets the design requirements.

[0046] S1.5: Calculate the tank mass and stress distribution before shape optimization:

[0047] Use the modeling software to read out the tank volume parameter V1, and the tank mass M1 before optimization is:

[0048] M1=ρV1

[0049] Where ρ is the tank density, and V1 is the tank volume before morphology optimization.

[0050] Static pressure simulation of the tank, combined with Figure 8 , and obtain the stress cloud diagram of the tank before morphology optimization.

[0051] Go to step S2.

[0052] S2: Combination Figure 3 , clarify the structural optimization design domain, and carry out topological optimization design on the internal wall of the tank based on the variable thickness topological optimization design method. Also, check the stress distribution state and quality parameters before and after the tank morphology optimization to confirm whether the design requirements of optimizing the stress distribution state and reducing the system quality are met at the same time.

[0053] S2.1: Topology optimization of tank with variable wall thickness:

[0054] When performing variable wall thickness topology optimization design on the tank before shape optimization, the target design domain is clearly used as the design variable, and the structures outside the design domain, such as the tank shape, remain unchanged. When the tank is working on orbit, it is filled with gas-liquid mixed propellant. In a microgravity environment, the propellant is in a suspended state in the tank, so the tank only bears a constant pressure along the normal direction of the inner wall.

[0055] When the inner wall of the tank is subjected to constant pressure, the stress value on the structure is unevenly distributed. A small stress value indicates that there is structural material redundancy. By calculating the stress value of each point on the tank by pressure and removing the excess material, the variable thickness topological optimization design of the tank can be realized. The tank before morphology optimization is the tank before variable thickness topological optimization (hereinafter referred to as the tank before topological optimization).

[0056] The relationship between pressure and stress is as follows:

[0057]

[0058] Where P is the pressure on the inner wall of the tank; δ ni is the surface normal stress of the microelement on the inner surface of the tank with the inside of the cavity as the positive direction; l i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the x-axis, m i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the y-axis, n i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the z-axis, δ xi , δ yi , δ zi are respectively the normal stress on the microelement surface of the tank inner surface, τ yxi , τ zxi , τ xyi are the shear stress values ​​of the microelement surface on the inner surface of the tank, δ i is the surface stress of the microelement on the inner surface of the tank.

[0059] The three solutions σ of the system of equations 1i , σ 2i , σ 3i , which are the three principal stresses on the microelement.

[0060] The tank is divided into hexahedral meshes, and topological optimization is performed on the hexahedral meshes to be filled. Based on the boundary conditions of the structure and the load distribution state, the topological optimization algorithm, convergence criteria and constraints are confirmed.

[0061] The mathematical model of topology optimization based on the minimum strain energy criterion can be described as follows:

[0062] find:ρ=[ρ1,ρ2,…,ρ i ,…,ρ n ] T

[0063] minimize:

[0064] subject to:KU(ρ)=F

[0065]

[0066] 0≤ρ min ≤ρ i ≤ρ max ≤1

[0067] s0≤t′≤t0

[0068]

[0069] Among them, the objective function C represents the structural strain energy, and the minimum strain energy is taken as the optimization target, that is, the maximum stiffness; U(ρ) represents the node displacement vector, which is obtained by solving the finite element equilibrium equation KU(ρ)=F, K represents the overall stiffness matrix, and F represents the overall force matrix; n represents the number of discrete hexahedral elements in the topology optimization design domain, and ρ is the normalized density field of each hexahedral element; V* represents the volume limit of the material in the topology optimization design domain, v1, v2, ..., v i , ..., v n is the volume vector of each hexahedral unit, ρmin and ρ max They represent the lower and upper limits of the density field of the hexahedral unit, ρ i Represents the average value of the hexahedral unit density field; t′ represents the wall thickness of the target design domain after topology optimization, t0 represents the wall thickness of the target design domain, and the result of the design domain after topology optimization design should be within the range of the design domain; σ1, σ2, and σ3 are the principal stresses in the three directions of the microelement, which are calculated by the relationship between pressure and stress. T represents transposition, σ s Represents the yield strength of the material.

[0070] Combination Figure 4 , extract the target features of the tank designed in S1, perform topological optimization on the target features, merge the topological optimization results, and combine them. Figure 5 , 6 , and the tank after topology optimization based on variable thickness is obtained (hereinafter referred to as the tank after topology optimization).

[0071] S2.2: Calculate the tank mass and stress distribution after topology optimization:

[0072] The volume parameters are calculated to obtain the volume V2 of the tank after topology optimization, and the mass M2 of the tank after topology optimization is calculated as:

[0073] M2=ρV2

[0074] Where ρ represents the density of the additively manufactured material.

[0075] Combination Figure 7 , static pressure simulation of the stress distribution state of the tank after topology optimization, combined with Fig. 9 , and obtain the stress cloud map after topology optimization.

[0076] Go to step S3.

[0077] S3: The stress distribution cloud diagram of the tank before and after topology optimization is used to determine whether the mass and stress distribution state of the tank are optimized.

[0078] Example

[0079] Combination Figure 1 The present invention will be further described in detail below by taking a certain liquefied gas type micro-propulsion tank as an example in conjunction with the accompanying drawings.

[0080] The design requires hexafluoropropane (R236fa) as the propellant (specific impulse I sp =36s), providing a velocity increment of 30m / s (ΔV=30m / s) for a 40Kg satellite (m0=40kg), the designed filling duty cycle is 65% (liquid propellant occupies 35% of the tank volume), and the operating temperature range of the propulsion system is 20-30℃.

[0081] S1: tank before design morphology optimization.

[0082] S1.1: Calculate the tank volume before shape optimization:

[0083] By formula It can be calculated that the amount of propellant △m = 3.09Kg, the design safety margin is 1.1, then at least 3.4Kg of propellant is needed, and the final design propellant filling amount is 3.5Kg. The density of hexafluoropropane at 20℃ is 1376.7049Kg / m 3 , and finally confirmed that the tank capacity is at least 3.95L.

[0084] According to the nozzle flow parameters and the maximum single propellant consumption for attitude and orbit control, the volume of the surge tank is determined to be no less than 1.5L.

[0085] S1.2: Determine envelope size and interface parameters:

[0086] According to the mission requirements, it was determined that there were 8 fixed interfaces on the tank for the structural system and 19 sealing interfaces for connecting internal components of the system such as pressure sensors and pipelines.

[0087] S1.3: Wall thickness calculation and strength assessment:

[0088] According to the operating temperature range of the propulsion system, the maximum pressure of the cavity is determined to be 0.32MPa. With a design safety margin of 2.5, the tank design pressure P = 0.8MPa, that is, the normal stress of each microelement on the inner wall of the tank is ni =0.8MPa. The propulsion tank is formed by 3D printing and machining, with AlSi10Mg as the printing material. The yield strength after molding can reach 210MPa. The following design constraints can be determined:

[0089]

[0090] Calculation shows that the tank wall thickness is not less than 3mm.

[0091] S1.4. Tank modeling:

[0092] Combination Figure 2 According to the volume of the surge tank, the tank's external structure and the maximum stress value under the condition that the tank does not fail, the tank is 3D modeled, and the wall thickness of mechanical interfaces such as threaded connections is thickened to ensure the reliability of threaded connections.

[0093] S1.5: Calculate the tank mass and stress distribution before shape optimization:

[0094] The final calculated tank mass before topology optimization is: M1 = ρV1 = 3.19Kg

[0095] Combination Figure 8 , the maximum stress value of the tank before topology optimization was obtained by ABAQUS simulation, which was 227.1MPa.

[0096] Go to step S2.

[0097] S2: Combination Figure 3 , clarify the structural optimization design domain, and carry out topology optimization design on the internal wall of the tank based on the variable thickness topology optimization design method. Also, check the stress distribution state and quality parameters of the tank before and after topology optimization to confirm whether the design requirements of optimizing the stress distribution state and reducing the system quality are met at the same time.

[0098] S2.1: Topology optimization of the tank before topology optimization:

[0099] The design domain range of the variable thickness topology optimization of the tank before topology optimization is the 1.5mm wall thickness area inside the tank, and the other areas maintain the original structural characteristics unchanged, that is, the shape of the tank does not change after topology optimization, and the wall thickness should be greater than 1.5mm.

[0100] Combination Figure 4 and Figure 5 , use AltairInspire to extract the target design features of the tank, that is, extract the internal shell of the tank (thin-wall feature) and use it as the topology optimization design target.

[0101] Import the design goal into ABAQUS and clarify the mathematical expressions of the design response, objective function, and constraint conditions of the topology optimization process:

[0102] find:ρ=[ρ1, p2,...,ρ i , .., ρ n ] T

[0103] minimize:

[0104] subject to:KU(ρ)=F

[0105] subject to:

[0106] subject to:0≤ρ min ≤ρ i ≤ρ max ≤1

[0107] subject to:0≤t′≤1.5

[0108] subject to:

[0109] The extracted target features are solved using the TOSCA solver in ABAQUS. A design pressure value of 0.8 MPa is applied to the target, and the topology optimization domain is preset to 1.5 mm (the maximum change height is 1.5 mm). This can then intelligently generate the inner wall features after topology optimization.

[0110] Combination Figure 6 , Magics is used to integrate the design features after topology optimization with the original structure to obtain the tank structure after structural topology optimization design.

[0111] S2.2: Calculate the mass and stress distribution of the tank:

[0112] Combination Figure 7 The mass of the tank that has completed the variable thickness topology optimization is calculated, and the stress distribution state of the tank after topology optimization is analyzed through simulation.

[0113] The final calculated tank mass before topology optimization is: M2 = ρV2 = 2.95Kg

[0114] Combination Fig. 9 , the maximum stress value of the tank is 198.9MPa obtained by ABAQUS simulation.

[0115] S3: The stress distribution cloud diagram of the tank before and after topology optimization is used to determine whether the mass and stress distribution state of the tank are optimized.

[0116] The comparison of parameters before and after tank topology optimization design is as follows:

[0117] Before topology optimization After topology optimization Tank quality 3.19Kg 2.95Kg Maximum stress 227.1MPa 198.9MPa

[0118] By comparison, it can be confirmed that the mass and maximum stress of the tank are optimized. It can be considered that the lightweight design of the tank is successfully achieved by using the variable thickness topology optimization method.

Claims

1. A lightweight design method for a propulsion tank based on variable thickness topology optimization, characterized in that: Here are the steps: S1: tank before design morphology optimization; S2: Define the structural optimization design domain, perform topological optimization design on the internal wall of the tank based on the variable thickness topological optimization design method, and check the stress distribution state and quality parameters before and after the tank morphology optimization to confirm whether the design requirements of optimizing the stress distribution state and reducing the system quality are met at the same time; S3: The stress distribution cloud diagram of the tank before and after topology optimization is used to determine whether the mass and stress distribution state of the tank are optimized.

2. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 1 is characterized in that: In S1, the tank is designed before morphology optimization, as follows: S1.1: Calculate the tank volume before shape optimization; S1.2: Design the appearance structure and mechanical interface; S1.3: Calculate wall thickness and evaluate strength; S1.4: Perform three-dimensional modeling: S1.5: Calculate the tank mass and stress distribution before shape optimization.

3. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 2 is characterized in that: In S1.1, the tank volume before shape optimization is calculated as follows: The volume of the propellant tank before morphology optimization is determined by the speed increment ΔV and the filling rate required for the mission, and the required amount of propellant is determined by the ideal rocket equation: Where Δm is the propellant consumption, m0 is the initial total mass of the satellite, and I sp is the specific impulse, g is the acceleration due to gravity; According to the design indicators, the required amount of propellant is calculated, and the minimum volume of the propellant tank is further obtained; The volume of the surge tank is determined based on the nozzle design and the maximum single propellant consumption requirements during the mission.

4. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 3 is characterized in that: In S1.2, the design of the external structure and mechanical interface is as follows: According to the space limitations on the satellite and the system function requirements, the interface form between the structural system and the layout of components such as sensors required to meet the propulsion system functions and the corresponding interface form are confirmed. Finally, the structural constraints and mechanical interface constraints of the propulsion tank are confirmed to complete the tank shape structure design.

5. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 4 is characterized in that: S1.3: Calculate wall thickness and assess strength: Since the propulsion tank and the connecting parts are sealed by the extrusion effect of the sealing surface or the sealing ring, it should be ensured that the system does not have elastic failure, that is, the maximum stress value of the structure should be less than the yield strength of the material; The calculation of wall thickness has the following design constraints: Where P is the pressure on the inner wall of the tank; δ ni is the surface normal stress of the microelement on the inner surface of the tank with the inside of the cavity as the positive direction; σ1, σ2, and σ3 are the principal stresses in the three directions of the microelement respectively; σ s It is the yield strength of the tank structural material and is the maximum stress value under conditions that ensure the tank does not fail.

6. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 5 is characterized in that: In S1.4, three-dimensional modeling is performed as follows: Based on the volume of the surge tank, the tank's external structure and the maximum stress value under the condition that the tank does not fail, a three-dimensional model of the tank structure is constructed and the edges are blunted to verify whether the tank volume meets the design requirements.

7. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 6 is characterized in that: In S1.5, the tank mass and stress distribution before shape optimization are calculated as follows: According to the tank volume parameter V1, the tank mass M1 before optimization is: M1=ρV1 In the formula, ρ is the tank density, V1 is the tank volume before morphology optimization; The static pressure simulation of the tank is carried out to obtain the stress cloud diagram of the tank before morphology optimization.

8. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 7 is characterized in that: In S2, the structural optimization design domain is clarified, and the internal wall of the tank is topologically optimized based on the variable thickness topological optimization design method. The stress distribution state and quality parameters of the tank before and after the optimization are checked to confirm whether the design requirements of optimizing the stress distribution state and reducing the system quality are met at the same time. The details are as follows: S2.1: Carry out tank variable wall thickness topology optimization; S2.2: Calculate the mass and stress distribution of the tank after topology optimization.

9. The method for lightweight design of a propulsion tank based on variable thickness topology optimization according to claim 8, characterized in that: In S2.1, the tank variable wall thickness topology optimization is performed as follows: When performing variable wall thickness topology optimization design on the tank before morphology optimization, the target design domain is clearly used as the design variable. When the tank is working on orbit, it is filled with gas-liquid mixed propellant. In a microgravity environment, the propellant is in a suspended state in the tank, so the tank is only subjected to a constant pressure along the normal direction of the inner wall. When the inner wall of the tank is subjected to constant pressure, the stress value on the structure is unevenly distributed. A small stress value indicates that there is redundancy in the structural material. By calculating the stress value of each point on the tank through pressure and removing the excess material, the variable thickness topology optimization design of the tank can be realized. The tank before morphology optimization is the tank before variable thickness topology optimization: The relationship between pressure and stress is as follows: Where P is the pressure on the inner wall of the tank; δ ni is the surface normal stress of the microelement on the inner surface of the tank with the inside of the cavity as the positive direction; l i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the x-axis, m i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the y-axis, n i is the surface normal vector of the microelement on the inner surface of the tank Cosine of the angle with the z-axis, δ xi , δ yi , δ zi are respectively the normal stress on the microelement surface of the tank inner surface, τ yxi , τ zxi , τ xyi are the shear stress values ​​of the microelement surface on the inner surface of the tank, δ i is the surface stress of the microelement on the inner surface of the tank; The three solutions σ of the system of equations 1i , σ 2i , σ 3i , which are the three principal stresses on the microelement; Divide the tank into hexahedral meshes and perform topological optimization on the hexahedral meshes to be filled. Based on the boundary conditions of the structure and the load distribution state, confirm the algorithm, convergence criteria and constraints of the topological optimization. The mathematical model of topology optimization based on the minimum strain energy criterion can be described as follows: find: p = [p1, p2,…, p i ,…,r n ] T subject to:KU(ρ)=F 0≤ρ min ≤ρ i ≤ρ max ≤1 s0≤t'≤t0 Among them, the objective function C represents the structural strain energy, and the minimum strain energy is the optimization target, that is, the maximum stiffness; U(ρ) represents the node displacement vector, which is obtained by solving the finite element equilibrium equation KU(ρ)=F, K represents the overall stiffness matrix, and F represents the overall force matrix; n represents the number of discrete hexahedral elements in the topology optimization design domain, and ρ is the normalized density field of each hexahedral element; V * represents the volume limit of the material in the topology optimization design domain, v1,v2,…,v i ,…,v n is the volume vector of each hexahedral unit, ρ min and ρ max They represent the lower and upper limits of the density field of the hexahedral unit, ρ i Represents the average value of the hexahedral unit density field; t' represents the wall thickness of the target design domain after topology optimization, t0 represents the wall thickness of the target design domain, and the result of the design domain after topology optimization design should be within the range of the design domain; σ1, σ2, σ3 are the principal stresses in the three directions of the microelement, which are calculated by the relationship between pressure and stress, T represents transposition, σ s Indicates the yield strength of the material; The target features of the tank designed in S1 are extracted, topology optimization is performed on the target features, and the topology optimization results are merged to obtain the tank after variable thickness topology optimization.

10. The lightweight design method of propulsion tank based on variable thickness topology optimization according to claim 9 is characterized in that: In S2.2, the mass and stress distribution of the tank after topology optimization are calculated as follows: The volume parameters are calculated to obtain the volume V2 of the tank after topology optimization, and the mass M2 of the tank after topology optimization is calculated as: M2=ρV2 Where ρ represents the density of the additive manufacturing material; The static pressure simulation is performed on the stress distribution state of the tank after topology optimization to obtain the stress cloud map after topology optimization.

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