A reinforcement layout method for thin-walled structure of combined engine based on topology optimization

Abstract

The present invention discloses a reinforcement layout method for thin-walled composite engine structures based on topology optimization, comprising the following steps: S1, establishing a reinforcement region model; S2, establishing an analysis model; S3, partitioning the base structure into design and non-design domains, and identifying non-design points; S4, establishing an optimization model, and using finite element calculations based on the optimization model to determine the reinforcement layout results. This method addresses the complex and inefficient reinforcement layout design process for existing composite engine thin-walled components and test pieces subjected to thermal loads or coupled mechanical and thermal loads, as well as the difficulty in balancing manufacturing costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of engine reinforcement layout, and in particular relates to a reinforcement layout method for a combined engine thin-wall structure based on topology optimization. Background Art

[0002] Plate and shell structures are widely used in aviation, aerospace, and other fields. These thin-walled structures exhibit poor mechanical properties, such as stiffness, strength, buckling, and vibration. In practical applications, reinforced structures are often used to reduce weight. The shape, size, and layout of the reinforcements directly impact the weight and performance of the structure. The isolation section, square-to-circular section, and rocket section of the combined engine and its test piece are structural components of varying shapes. The isolation section is typically rectangular, the square-to-circular section is a transitional structure from square to circular, and the rocket section is cylindrical. During operation, they are subjected to varying degrees of high-temperature and high-pressure loads. These characteristics result in different stress distributions and deformation characteristics in each section, necessitating different structural designs to enhance their stiffness. Insufficient structural strength or excessive deformation in any particular area during operation or testing can potentially cause gas leakage, leading to test distortion or even inability to proceed. To meet the required stiffness without increasing manufacturing costs, reinforcements are typically added to the outer surfaces of thin-walled components. Reinforcement layout design for thin-walled parts can significantly reduce the weight of the structure, facilitate assembly and transportation, and has guiding significance for improving the structural thermodynamic properties of the combined engine and its test pieces, reducing material usage costs, and providing innovative structural forms.

[0003] Most reinforcement layout designs for thin-walled components are based on a single load, such as pressure or thermal loads. Topology optimization of reinforcement layouts involving thermal loads primarily focuses on simple flat structures subjected to a unidirectional temperature gradient. There is little research on complex thin-walled structures subjected to combined forces and thermal loads, such as the three-dimensional rectangular and circular-to-square structures found in modular engines. Previous rib layout approaches for these thin-walled structures often relied on designers' experience and structural analysis results to reinforce weak locations or increase wall thickness. Due to the complex structure of the engine combustion chamber and the coupled forces and thermal loads, this rib layout approach required multiple structural analyses and redesign iterations to control structural stress and deformation, resulting in low structural design efficiency. This design approach failed to consider the impact of rib layout on structural quality and mechanical properties from the outset, underutilizing the design guidance provided by topology optimization, and thus hindering manufacturing economics. Using topology optimization technology, within given loads, constraints, and design requirements, it can maximize material removal to achieve the optimal reinforcement layout, providing new insights into structural design. Summary of the Invention

[0004] The purpose of the present invention is to provide a reinforcement layout method for a thin-walled structure of a combined engine based on topology optimization, so as to solve the problems that the reinforcement layout design process of existing thin-walled parts of combined engines and their test pieces under thermal loads or thermal-mechanical coupling loads is complex, inefficient, and difficult to take into account the manufacturing cost.

[0005] The present invention adopts the following technical solution: a method for reinforcing the thin-wall structure of a combined engine based on topology optimization, comprising the following steps:

[0006] S1. Establish the reinforced area model:

[0007] Establishing a three-dimensional geometric model of the initial structure based on the engine flow channel profile, wherein the base structure and the reinforced area are divided and share topology, and the reinforced area is completely filled with solid material;

[0008] S2. Establishing an analysis model:

[0009] Meshing the three-dimensional geometric model, connecting the reinforcement area and the base area with common nodes, and defining the elastic modulus, Poisson's ratio and density of the material used in the three-dimensional geometric model; and then defining the degree of freedom constraints, temperature load and pressure load of the three-dimensional geometric model;

[0010] S3, partitioning the base structure into design domain and non-design domain, and identifying non-design points;

[0011] S4. Establish an optimization model, and obtain a reinforcement layout result based on the optimization model and using finite element calculation.

[0012] Furthermore, the specific content of step S3 is:

[0013] The finite elements of the base structure are defined as non-design domains, and the finite elements of the reinforcement area are defined as design domains; and the structural model of the design domain is partitioned along different surface normal directions;

[0014] Then, a surface normal direction constraint, a rib minimum width constraint, and a material usage constraint are applied to each of the design domains, corresponding to the height direction, width dimension, and volume ratio of the optimized rib, respectively;

[0015] Perform static analysis on the finite element model, identify stress concentrations and singular stress elements in the results, and create a set of elements that need to be optimized in the remaining areas of the model.

[0016] Furthermore, the specific content of establishing the optimization model in step S4 is:

[0017] The SIMP interpolation model is used to establish the design variable ρ iThe relationship between the elastic modulus of the corresponding unit is analyzed, and an optimization model is established based on the boundary conditions and load conditions. The topology optimization of the reinforced area is performed. The reinforcement distribution form is obtained based on the topology optimization cloud map results. The topology optimization results containing reinforcement strips are subjected to static analysis under the same load and boundary conditions to obtain their strength and stiffness results.

[0018] The optimization formula with the minimum maximum stress as the goal is:

[0019]

[0020] Among them, σ j is the equivalent stress of finite element j in the non-design domain, ρ is the design variable vector, F is the node equivalent load vector; U is the structural node displacement vector; K is the stiffness matrix; V(ρ) is the optimized volume, v i is the volume of unit i; V0 is the total volume of a given material; U s is the node displacement in the s domain within the design domain Ω, c is the displacement limit constant; ρ i is the design variable of finite element i, and its lower bound is ρ min and upper bound 1 represent holes and solid elements respectively, and ρ is generally taken min =0.001.

[0021] Furthermore, in step S2, when the material selected for the reinforcement area is different from that of the matrix structure, the elastic modulus, Poisson's ratio and density of the material selected for the reinforcement area and the matrix are defined respectively.

[0022] Furthermore, in step S2, the temperature load is a uniform temperature rise or includes a temperature gradient.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention considers the reinforcement topology optimization problem of the combined engine and its test piece under the combined action of high pressure and high temperature loads. Compared with the rib layout under a single load condition, it is more reasonable and conducive to improving the strength and stiffness of the thin-walled structure.

[0025] 2. The present invention optimizes the complex structure by partitioning it into different areas, ensuring that the ribs of the complex structure grow together along different height directions during a single optimization process, avoiding the problems of multiple optimizations and unreasonable rib generation, and simplifying the reinforcement layout design process. The method is applicable to the reinforcement topology optimization of various different types of structures.

[0026] 3. When thermal loads are involved, traditional structural optimization based on strain energy minimization will reduce strain energy while softening the structure, making it difficult to obtain a continuously reinforced structure. The present invention targets stress and limits displacement. The optimization process always takes strength and deformation into consideration. The continuous reinforcement form is beneficial to structural design.

[0027] 4. The present invention eliminates the need for static analysis and screening of multiple schemes during the design phase for the reinforcement of thin-walled structures of engines, thereby improving design efficiency. Furthermore, the optimized reinforcement form of the thin-walled structure is better, and a rib layout that takes into account both manufacturing costs can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of an optimization model according to Example 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the optimization results of Example 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of an optimization model according to Example 2 of the present invention;

[0031] Figure 4 This is a schematic diagram of the optimization results of Example 2 of the present invention;

[0032] Figure 5 This is a schematic diagram of an optimization model according to Example 3 of the present invention;

[0033] Figure 6 This is a schematic diagram of the optimization results of Example 3 of the present invention;

[0034] Figure 7 This is an iterative curve diagram of the optimization process of Example 2 of the present invention;

[0035] Figure 8 This is an iterative curve diagram of the optimization process of Example 3 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The present invention provides a reinforcement topology optimization method for a thin-walled component and a test component of a combined engine under mechanical and thermal coupling loads, comprising the following steps:

[0038] S1. Establishing a Reinforced Area Model: A three-dimensional geometric model of the initial structure is established based on the engine flow path profile. In the three-dimensional geometric model, the base structure and the reinforced area are divided and share topology to facilitate the subsequent definition of the design domain and the non-design domain. The reinforced area is completely filled with solid material. The initial structure refers to the three-dimensional geometric model including the design domain and the non-design domain established before optimization.

[0039] S2. Establish an analysis model: mesh the three-dimensional geometric model, connect the reinforced area and the base area with common nodes, and define the elastic modulus, Poisson's ratio and density of the material used in the three-dimensional geometric model; then define the degree of freedom constraints, temperature load and pressure load of the three-dimensional geometric model;

[0040] S3, partitioning the base structure into design domain and non-design domain, and identifying non-design points;

[0041] S4. Establish an optimization model, and obtain a reinforcement layout result based on the optimization model and using finite element calculation.

[0042] In some embodiments, the specific content of step S3 is: defining the finite element of the base structure as a non-design domain, and defining the finite element of the reinforced area as a design domain; partitioning the design domain, and naming each partition separately, and defining it as a different design domain; the partitioning principle is to partition the structural model of the design domain along different surface normals to control the growth direction of the ribs in each area during optimization.

[0043] Then, a surface normal direction constraint, a rib minimum width constraint, and a material usage constraint are applied to each of the design domains, corresponding to the height direction, width dimension, and volume ratio of the optimized rib, respectively;

[0044] Perform static analysis on the finite element model to identify stress concentration and stress singularity elements in the results. A collection of elements that need to be optimized in the remaining areas of the model is created so that these elements can be selected as the target elements for topology optimization. Static analysis is used to determine if there are areas of stress concentration and stress singularity in the results. If so, these areas are excluded during optimization to ensure stable optimization rather than excessive optimization in locations with excessive local stress. If there are no stress concentration and stress singularity elements, this step is skipped and only these two areas remain. The finite element model here is a computational model that has been meshed and loaded based on the 3D geometric model.

[0045] In some embodiments, the specific content of step S4 of establishing the optimization model is: using SIMP (Solid Isotropic Material with Penalization) interpolation model to establish the design variable ρ i The relationship between the elastic modulus of the corresponding unit is analyzed, and an optimization model is established based on the boundary conditions and load conditions. The topology optimization of the reinforced area is performed. The reinforcement distribution form is obtained based on the topology optimization cloud map results. The static analysis of the topology optimization results containing reinforcement strips is performed under the same load and boundary conditions to obtain its strength and stiffness results.

[0046] The optimization formula with the minimum maximum stress as the goal is:

[0047]

[0048] Among them, σ jis the equivalent stress of finite element j in the non-design domain, ρ is the design variable vector, F is the node equivalent load vector; U is the structural node displacement vector; K is the stiffness matrix; V(ρ) is the optimized volume, v i is the volume of unit i; V0 is the total volume of a given material; f is the volume fraction; U s is the node displacement in the s domain within the design domain Ω, c is the displacement limit constant; ρ i is the design variable of finite element i, and its lower bound is ρ min and upper bound 1 represent holes and solid elements respectively, and ρ is generally taken min =0.001.

[0049] In some embodiments, in step S2, when the material selected for the reinforcement area is different from that of the base structure, the elastic modulus, Poisson's ratio and density of the material selected for the reinforcement area and the base are defined respectively.

[0050] In some embodiments, in step S2 , the temperature load is a uniform temperature rise or includes a temperature gradient.

[0051] Example 1:

[0052] The base structure is a flat plate structure. The base plate is 500mm long and wide, 5mm thick, and the designed reinforcement height is 20mm. The base plate and the ribs are made of the same material, with an elastic modulus of E = 198Mpa, a Poisson's ratio μ = 0.3, and a thermal expansion coefficient of 1.76×10 -5 The reinforcement area is designed to be normal to the substrate surface, with a material usage of 40%. It is subjected to both compressive and thermal loads, resulting in a linear temperature distribution through the thickness: 100°C on the -Z surface and 60°C on the +Z surface. The compressive load is 1 MPa applied to the bottom surface of the plate. UG was used for modeling, and HyperWorks was used for finite element analysis.

[0053] 1. Build a 3D CAD model of the flat plate structure, determine the 500mm×500mm×5mm area as the non-design domain, and the 500mm×500mm×20mm area as the design domain. Divide the base plate and the reinforcement area and share the topology. Fill the reinforcement area with solid material.

[0054] 2. Divide the model into a grid with a grid size of 5 mm and define the model's elastic modulus, Poisson's ratio, and thermal expansion coefficient. Constrain the degrees of freedom of the two edges in the X direction of the substrate to dof1 = dof2 = dof3 = 0, and the degrees of freedom of the two edges in the Y direction to dof1 = dof2 = 0. Apply a linear temperature gradient from 100°C to 40°C along the Z axis of the structure.

[0055] 3. Based on the division of the design domain in step 1, the design domain finite element domain and the non-design domain finite element are partitioned according to their different locations and classified into different sets. The substrate finite element is defined as the non-design domain and named to distinguish it. The reinforced area finite element is defined as the design domain and named to distinguish it. The minimum width of the ribs formed by the design domain elements is limited to 15mm, the rib direction is the Z direction, and the volume fraction of the material amount is 30%, such as Figure 1 shown.

[0056] 4. According to the boundary conditions and loads, with the maximum stress minimized as the optimization goal, and volume and displacement as constraints, the following optimization formula is established. The rib layout result cloud diagram obtained by topology optimization is as follows: Figure 2 As shown, the dark area is the obtained rib layout.

[0057] from Figure 2 It can be seen from the figure that the optimization method of the present invention can be used to deal with the flat plate reinforcement design problem that is only subjected to thermal loads and can also achieve effective reinforcement effects.

[0058]

[0059] Example 2:

[0060] The base structure is quasi-rectangular. The base is 15 mm thick, 1340 mm long, and 375 mm wide. It is subject to an internal pressure of 0.25 MPa and a temperature difference of 720°C between the inner and outer surfaces. The base and ribs are made of the same material, with an elastic modulus E = 198 MPa, a Poisson's ratio μ = 0.3, and a thermal expansion coefficient of 1.76 × 10⁻⁵. The reinforcement layout is designed to minimize structural stress and deformation. The reinforcement area is normal to the base's outer surface, and the material content in the design area is 45%. UG was used for modeling, and HyperWorks was used for finite element analysis.

[0061] 1. The outer surface of the base structure is stretched 50mm along different normal directions to form a design domain. The corner transition positions are rounded with a radius of 50mm. The design domains with different normal directions are divided using the outer surface of the base plate and share the topology with the base structure. The reinforced design domain is filled with solid material.

[0062] 2. Based on symmetry, half of the model was taken and meshed with a mesh size of 18 mm. The elastic modulus, Poisson's ratio, and thermal expansion coefficient of the model were defined. The axial displacement of the gas inlet was constrained to 0. At the same time, the degrees of freedom along the surface expansion direction were released on both the inlet and outlet sides, and symmetry constraints were applied to the symmetry planes. A pressure of 0.22 MPa was applied to the inner surface elements of the model, and the temperature load was 750°C on the inner surface and 30°C on the outer surface. The node temperatures between the inner and outer surfaces were transitioned using linear interpolation. Static analysis of the finite element model was performed as needed. If the results showed stress concentration or stress singularity, the elements at these locations were excluded from the topology optimization model.

[0063] 3. Based on the division of the model in step 1, the design domain finite elements and non-design domain finite elements are partitioned according to their different locations and classified into different sets; the finite elements of the base structure are defined as the non-design domain and named to distinguish them; the finite elements of the reinforced area are defined as the design domain, and the design domain elements are partitioned into X, Y and Z directions according to the normal direction of the surface, and each design domain is named to distinguish them. The minimum width of the ribs formed by the design domain elements is limited to 35mm, and the rib directions of each design area are X, Y and Z directions respectively. The volume fraction of the material usage is 45%, as shown in the following example. Figure 3 As shown;

[0064] 4. Based on the boundary conditions and loads, the optimization model is established with the minimum maximum stress as the optimization goal and the volume and displacement as constraints. The optimization formula used for the above problem is as follows. The cloud diagram of the rib layout result obtained by topology optimization is as follows: Figure 4 As shown, the static analysis of the optimized model shows its strength and stiffness results as shown in Table 1, and the objective function iteration curve is shown in Figure 7 shown.

[0065]

[0066] Table 1 Comparison of mechanical properties parameters before and after optimization of the isolation segment

[0067]

[0068] Example 3:

[0069] Square to round transition structure. The base thickness is 15mm, the total length is 502.5mm, the total width is 368mm, and the outer diameter of the round end is 628mm. The structure is subjected to an internal pressure of 0.2Mpa and a temperature difference of 720℃ between the inner and outer surfaces. The base and ribs are made of the same material, with an elastic modulus E = 198Mpa, a Poisson's ratio μ = 0.3, and a thermal expansion coefficient of 1.76×10 -5The reinforcement layout was designed to minimize structural stress and reduce deformation. The reinforcement area was normal to the outer surface of the base, and the material usage in the design area was 40%. UG was used for modeling, and HyperWorks was used for finite element calculations.

[0070] 1. The outer surface of the base structure is stretched 50mm along different normal directions to form a design domain. The design domain is divided by the outer surface of the substrate and shares the topology with the base structure. The reinforcement design domain is filled with solid material.

[0071] 2. Based on symmetry, take one-fourth of the model and divide the model into a grid with a grid size of 10 mm. Define the elastic modulus, Poisson's ratio, and thermal expansion coefficient of the model. Constrain the axial displacement and rotational displacement of the gas inlet to 0. At the same time, release the degrees of freedom along the surface expansion direction on both the inlet and outlet sides, and apply symmetry constraints to the symmetry surface. Apply a pressure of 0.2 MPa to the inner surface elements of the model, and a temperature load of 740°C on the inner surface and 30°C on the outer surface. The node temperatures between the inner and outer surfaces are transitioned in the form of linear interpolation. Perform static analysis on the finite element model as needed. If the results show stress concentration or stress singularity, exclude the elements at these locations from the topology optimization model.

[0072] 3. Based on the division of the model in step 1, the design domain finite elements and the non-design domain finite elements are classified into two different sets according to their different locations; the finite elements of the base structure are defined as the non-design domain and named to distinguish them; the finite elements of the reinforced area are defined as the design domain and named to distinguish them. The minimum width of the ribs formed by the design domain elements is limited to 25 mm, the rib direction is radial, and the volume fraction of the material is 45%, such as Figure 5 As shown;

[0073] 4. Based on the boundary conditions and loads, the optimization model is established with the minimum maximum stress as the optimization goal and the volume and displacement as constraints. The optimization formula used for the above problem is as follows. The cloud diagram of the rib layout result obtained by topology optimization is as follows: Figure 6 As shown, the static analysis of the optimized model shows its strength and stiffness results as shown in Table 2, and the objective function iteration curve is shown in Figure 8 shown.

[0074]

[0075] Table 2 Comparison of mechanical properties of the isolation section before and after square-to-circular optimization

[0076] Equivalent stress / MPa x-direction (radial) displacement / mm Weight / kg Unreinforced model 112 3.0 26.8 Model before optimization 478 3.2 111.6 Optimized model 227 2.7 60.9

[0077] In summary, the reinforcement layout method of the combined engine thin-walled structure based on topology optimization of the present invention is used for the combined engine thin-walled structure. Compared with the original mechanism, the structural deformation is effectively reduced during the reinforcement design, and the structural thermal stress is significantly reduced compared with the design of increasing the thickness of the body. The reinforcement design method balances stress and deformation and reduces manufacturing costs.

[0078] Currently, the design of reinforcement for thin-walled composite engine structures primarily relies on multiple stiffness and strength analyses, combined with the designer's experience to determine reinforcement layout. However, the use of topology optimization techniques, particularly for studying reinforcement layout solutions under coupled mechanical and thermal loads, is relatively uncommon. This present invention provides a different approach for the reinforcement design of thin-walled composite engine structures.

[0079] This invention provides a reinforcement layout method for thin-walled composite engine structures based on topology optimization. This method addresses the reinforcement topology optimization of composite engines and their test specimens under combined high-pressure and high-temperature loads. Compared to single-load conditions, it achieves a more rational reinforcement layout and improves the strength and stiffness of thin-walled structures. By optimizing complex structural zoning, it simplifies the reinforcement layout design process and is applicable to reinforcement topology optimization for a wide range of different structures. When thermal loads are involved, conventional structural optimization focused on strain energy minimization results in a reduction in strain energy and a softening of the structure, making it difficult to achieve a continuous reinforcement structure. This invention targets stress and limits displacement, maintaining consideration of both strength and deformation during the optimization process. This continuous reinforcement pattern facilitates structural design. This invention eliminates the need for static analysis and screening of multiple design options during the design phase for thin-walled composite engine reinforcement, improving design efficiency. The optimized thin-walled structure reinforcement pattern offers a more optimal design, resulting in a rib layout that balances design performance with manufacturing economy. This method addresses the complex and inefficient reinforcement layout design process for existing composite engine thin-walled components and their test specimens under thermal or coupled mechanical and thermal loads, as well as the difficulty in balancing material costs.

Claims

1. A method for reinforcing the thin-wall structure of a combined engine based on topology optimization, characterized in that: The steps include: S1. Establish the reinforced area model: Establishing a three-dimensional geometric model of the initial structure based on the engine flow channel profile, wherein the base structure and the reinforced area are divided and share topology, and the reinforced area is completely filled with solid material; S2. Establishing an analysis model: Meshing the three-dimensional geometric model, connecting the reinforcement area and the base area with common nodes, and defining the elastic modulus, Poisson's ratio and density of the material used in the three-dimensional geometric model; and then defining the degree of freedom constraints, temperature load and pressure load of the three-dimensional geometric model; S3, partitioning the base structure into design domain and non-design domain, and identifying non-design points; S4. Establishing an optimization model, and obtaining a reinforcement layout result based on the optimization model and using finite element calculation; The specific contents of step S3 are as follows: The finite elements of the base structure are defined as non-design domains, and the finite elements of the reinforcement area are defined as design domains; and the structural model of the design domain is partitioned along different surface normal directions; Then, a surface normal direction constraint, a rib minimum width constraint, and a material usage constraint are applied to each of the design domains, corresponding to the height direction, width dimension, and volume ratio of the optimized rib, respectively; Perform static analysis on the finite element model, identify stress concentrations and singular stress elements in the results, and create a set of elements that need to be optimized in the remaining areas of the model.

2. The method for reinforcing and arranging thin-walled structures of a combined engine based on topology optimization according to claim 1, characterized in that: The specific content of the step S4 of establishing the optimization model is: The SIMP interpolation model is used to establish the design variable ρ i The relationship between the elastic modulus of the corresponding unit is analyzed, and an optimization model is established based on the boundary conditions and load conditions. The topology optimization of the reinforced area is performed. The reinforcement distribution form is obtained based on the topology optimization cloud map results. The topology optimization results containing reinforcement strips are subjected to static analysis under the same load and boundary conditions to obtain their strength and stiffness results. The optimization formula with the minimum maximum stress as the goal is: Among them, σ j is the equivalent stress of finite element j in the non-design domain, ρ is the design variable vector, F is the node equivalent load vector; U is the structural node displacement vector; K is the stiffness matrix; V(ρ) is the optimized volume, v i is the volume of unit i; V0 is the total volume of a given material; U s is the node displacement in the s domain within the design domain Ω, c is the displacement limit constant; ρ i is the design variable of finite element i, and its lower bound is ρ min and upper bound 1 represent holes and solid elements respectively, and ρ is generally taken min =0.

001.

3. The method for reinforcing and arranging thin-walled structures of a combined engine based on topology optimization according to claim 1, characterized in that: In step S2, when the material selected for the reinforcement area is different from that of the base structure, the elastic modulus, Poisson's ratio and density of the material selected for the reinforcement area and the base are defined respectively.

4. The method for reinforcing and arranging thin-walled structures of a combined engine based on topology optimization according to claim 1, characterized in that: In step S2, the temperature load is a uniform temperature rise or includes a temperature gradient.

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