Perforated cylindrical shell reinforcement structure optimization design method

Abstract

The invention discloses an optimization design method for a perforated cylindrical shell reinforced structure. The problems that a traditional vertical rib structure is large in material consumption, the complex load bearing capacity is weak, and local failure is caused by hole periphery stress concentration are solved. The method specifically comprises the following steps: establishing a preliminary model of the cylindrical shell with holes and performing simulation analysis; taking the skin as a design area, and setting flexibility minimization, volume fraction and symmetric constraint to carry out topological optimization; the optimization model is simplified into a structure capable of being manufactured through post-processing, secondary ribs are arranged between the main ribs to prevent the skin from buckling, and the hole periphery area is thickened and reinforced; and finally, verifying the strength and modal performance of the optimized model through simulation. The weight is remarkably reduced while the structural strength is guaranteed, the complex load bearing capacity is enhanced through cooperation of the primary ribs and the secondary ribs, stress concentration is effectively restrained through hole periphery reinforcement, and the method is suitable for light-weight high-strength structural design such as aerospace.

Description

Technical Field

[0001] The present invention relates to the field of rib structure design of cylindrical shells, and particularly to an optimization design method for the stiffened structure of an open-hole cylindrical shell. Background Art

[0002] With the continuous development of aerospace technology, the cylindrical shell structure has been widely used in the cabin structures of various aircraft. The traditional cylindrical shell structure adopts a structure with an outer skin and inner ribs, and the rib part uses orthogonal straight ribs. However, with the further improvement of the performance requirements of aircraft, the problem that the traditional rib structure is difficult to bear complex loads has become increasingly prominent. At the same time, it is difficult to reduce weight while meeting the structural strength in the traditional structure, and the manufacturing cost is relatively high; in the traditional design, the surface of the skin is relatively flat, and it is difficult to arrange the internal ribs when there are holes on the surface.

[0003] Topology optimization is a mathematical method for optimizing the material distribution within a given region according to the given load conditions, constraints, and performance indicators; it mainly relies on the finite element method, that is, discretizing the material in the optimization space into a finite number of elements, determining the retention or removal of elements in the design space according to the algorithm, and the remaining elements constitute the final topology scheme. Topology optimization can find the best distribution scheme in the design space with uniformly distributed materials, and has an important guiding role in the structural optimization design. Summary of the Invention

[0004] The present invention proposes an optimization design method for the stiffened structure of an open-hole cylindrical shell, which solves the problems of large material consumption, weak ability to bear complex loads, and local failure caused by stress concentration around the holes in the traditional vertical rib structure.

[0005] The technical solution for realizing the present invention is as follows: an optimization design method for the stiffened structure of an open-hole cylindrical shell, and the steps are as follows:

[0006] Step 1: According to the structural and dimensional requirements, establish a preliminary model of the cylindrical shell, determine the thicknesses of the skin and ribs, as well as the positions and sizes of the holes.

[0007] Step 2: According to the established preliminary model, draw a finite element mesh, and use finite element analysis software to perform a preliminary simulation on the preliminary model to view the deformation amount, stress magnitude, and mode of the preliminary model under the working conditions; verify the rationality of the preliminary model.

[0008] Step 3: Perform topology optimization on the preliminary model, select the skin and rib structures as the design regions, set the constraint conditions and the optimization objective function according to the optimization objectives; at the same time, add manufacturing constraints to make the model after topology optimization easier to manufacture.

[0009] Step 4: Analyze the topology optimized model, redesign the rib structure according to the topology optimized model in the modeling software, and arrange secondary ribs between adjacent rib structures to further improve its anti-buckling ability; perform special treatment on the part around the hole to reduce stress concentration.

[0010] Step 5: Draw the finite element mesh based on the topology optimized model and use finite element analysis software for simulation verification; ensure that the stress and modal frequency of the optimized model are within the allowable range.

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

[0012] (1) The design is based on the topological optimization method, which greatly reduces the structural weight while ensuring the structural strength. The optimized ribs are staggered and diagonal, which significantly enhance the ability to bear complex loads compared with traditional orthogonal straight ribs.

[0013] (2) The structure of main reinforcement and secondary reinforcement is adopted, which takes into account both weight reduction and strength while effectively preventing local buckling failure of the skin.

[0014] (3) Special treatment was carried out for the cylindrical shell structure with a hole. Considering the local failure caused by the stress concentration around the hole, the hole was reinforced with ribs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a simplified flow chart of the optimization design method of the reinforced structure of a cylindrical shell with a hole.

[0016] Figure 2 It is a schematic diagram of the cylindrical shell skin structure and hole positions.

[0017] Figure 3 This is a schematic diagram of the preliminary rib model established.

[0018] Figure 4 It is a schematic diagram of the rib model after topology optimization.

[0019] Figure 5 It is a schematic diagram of the hole perimeter reinforcement structure scheme. DETAILED DESCRIPTION

[0020] 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.

[0021] The following will further introduce the specific implementation methods, as well as the technical difficulties and inventive points of this invention, in combination with this design example.

[0022] Combined with Figures 1 to 5 , an optimization design method for a stiffened structure of an open-hole cylindrical shell is as follows:

[0023] Step 1: According to the structural and dimensional requirements, establish a preliminary model of the cylindrical shell, determine the thickness of the skin and ribs, as well as the position and size of the holes.

[0024] According to the design requirements, establish a preliminary model of the cylindrical shell. The cylindrical shell adopts a skin-stiffener structure, that is, the circumferential outer wall of the cylindrical shell is covered with a skin, and a rib structure is provided inside the skin.

[0025] Among them, the skin thickness is 1.5 mm, and several hole positions are periodically and evenly arranged in the lower section of the skin. Its specific structure is as Figure 2 shown.

[0026] To prevent the skin from buckling and failing under load due to being too thin, a rib structure is used to strengthen the inside of the skin. The rib structure is an orthogonal straight rib, and its structure is as Figure 3 shown.

[0027] Step 2: According to the established preliminary model, draw a finite element mesh, and use finite element analysis software to conduct a preliminary simulation on the preliminary model to view the deformation amount, stress magnitude, and mode of the preliminary model under the working conditions. Verify the rationality of the preliminary model.

[0028] In the hypermesh software, establish a shell element mesh according to the preliminary model. To balance the accuracy and speed of simulation and optimization, it is necessary to control the number of finite element meshes. Generally, the element size is controlled to be 3 - 5 times the structural thickness; stress concentration is likely to occur around the hole structure, and usually the element size is 1 - 2 times the structural thickness; the aspect ratio of the element should be less than 5:1 to avoid generating deformed elements and making the simulation results inaccurate.

[0029] According to the design requirements, apply axial and radial forces to the preliminary model in hypermesh. The material is selected as aluminum alloy, and conduct a simulation on it to view the deformation amount, stress magnitude, and mode of the preliminary model. Ensure that the deformation amount does not exceed 0.5% of the diameter of the cylindrical shell, the stress is within the allowable stress range of the aluminum alloy material, and the first-order modal frequency is higher than 100 Hz.

[0030] Step 3: Conduct topology optimization on the preliminary model. Select the skin and rib structures as the design areas, set the constraint conditions and optimization objective functions according to the optimization objectives; at the same time, add manufacturing constraints to make the model after topology optimization easier to manufacture.

[0031] According to the design requirements, the skin and rib structure is set as the design area. Topological optimization is carried out on the preliminary model in HyperMesh software. To ensure the structural stiffness, the minimum compliance response is added; to achieve the weight reduction effect and make the optimized ribs more obvious at the same time, the volume fraction response is set to 0.3; the maximum displacement constraint is added as 0.005 m; according to the number of hole positions, symmetry constraints are added to make the optimized ribs arranged periodically on the circumference; at the same time, to avoid the "checkerboard" phenomenon, member size constraints are added, and the maximum member size is set to 0.03 m.

[0032] Step 4: Analyze the model after topological optimization. Redesign the rib structure according to the model after topological optimization in the modeling software, and arrange smaller secondary ribs between adjacent rib structures to further improve its buckling resistance; perform special treatment on the part around the hole to reduce the stress concentration phenomenon.

[0033] Redesign the rib structure according to the model after topological optimization in SolidWorks software. It is noted that the longitudinal vertical ribs in the preliminary model show an oblique trend after topological optimization. Such oblique ribs can carry axial and radial loads simultaneously, effectively improving the structural strength. The distance between the main ribs after topological optimization is relatively large, which may cause buckling failure of the skin. Therefore, it is necessary to arrange smaller secondary ribs between the main ribs to further strengthen the structural strength. The width and thickness of the secondary ribs are both 2 / 3 of the main ribs. The rib model after topological optimization is as Figure 4 shown.

[0034] It is noted that there is a stress concentration phenomenon around the hole. Therefore, additional reinforcement is required. In the present invention, the method of local thickening is used to improve its structural strength, as Figure 5 shown. Arrange the main rib position around the hole, and thicken the ribs in the area around the hole to complete the wrapping of the hole circumference to reduce the stress concentration at the hole position.

[0035] After calculation, it is found that the inclination angle θ of the rib after topological optimization satisfies the following relational expression:

[0036]

[0037] In the formula, θ is the inclination angle of the rib, F1 is the axial force, F2 is the shear force, M is the bending moment, and D is the outer diameter of the cylindrical shell.

[0038] Step 5: Draw a finite element mesh according to the model after topological optimization, and use finite element analysis software for simulation verification. Ensure that the stress and modal frequency of the optimized design model are within the allowable range.

[0039] Use the hypermesh software to establish the shell element mesh of the topology-optimized model, apply the same loads as the preliminary model, and conduct finite element analysis. Analyze the deformation, stress, and modal frequency of the topology-optimized model.

[0040] Compare the analysis results of the models before and after optimization, calculate the mass difference before and after optimization, and check the weight reduction effect of the optimization. Check the stress and modal frequency of the optimized model to ensure that the results after optimization are not much different from those before optimization and are within the allowable range of the material.

[0041] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the design of a reinforced structure of a cylindrical shell with a hole, characterized in that: Here are the steps: Step 1: According to the structural and dimensional requirements, establish a preliminary model of the cylindrical shell, determine the thickness of the skin and ribs, and the location and size of the holes; Step 2: Draw the finite element mesh based on the established preliminary model, and use the finite element analysis software to perform preliminary simulation on the preliminary model to check the deformation, stress magnitude and mode of the preliminary model under working conditions; verify the rationality of the preliminary model; Step 3: Topology optimization is performed on the preliminary model. The skin and rib structure are selected as the design area. According to the optimization goal, constraints and optimization objective functions are set. At the same time, manufacturing constraints are added to make the topology optimized model easier to manufacture. Step 4: Analyze the topology optimized model, redesign the rib structure based on the topology optimized model in the modeling software, and arrange secondary ribs between adjacent rib structures to further improve their anti-buckling capacity; perform special treatment on the part around the hole to reduce stress concentration; Step 5: Draw the finite element mesh based on the topology optimized model and use finite element analysis software for simulation verification; ensure that the stress and modal frequency of the optimized model are within the allowable range.

2. The method for optimizing the reinforced structure of a perforated cylindrical shell according to claim 1, characterized in that: In step 1, according to the structural and dimensional requirements, a preliminary model of the cylindrical shell is established to determine the thickness of the skin and ribs, as well as the location and size of the holes, as follows: According to the design requirements, a preliminary model of the cylindrical shell is established. The cylindrical shell adopts a skin-reinforced structure; that is, the circumferential outer wall of the cylindrical shell is covered with a skin, a rib structure is provided on the inner side of the skin, and a number of holes are periodically and evenly arranged in the lower section of the skin.

3. The method for optimizing the reinforced structure of a perforated cylindrical shell according to claim 2, characterized in that: The reinforcement structure is orthogonal straight reinforcement.

4. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 3, characterized in that: In step 2, based on the established preliminary model, a finite element mesh is drawn, and the preliminary model is simulated using finite element analysis software to check the deformation, stress magnitude, and mode of the preliminary model under working conditions; the rationality of the preliminary model is verified, as follows: In the hypermesh software, a shell unit mesh is established based on the preliminary model, and the unit size is controlled to be 3-5 times the thickness of the structure; stress concentration is prone to occur around the hole structure, so the unit size is set to 1-2 times the thickness of the structure, and the aspect ratio of the unit should be less than 5:

1.

5. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 4, characterized in that: According to the design requirements, axial and radial forces are applied to the preliminary model in hypermesh. Aluminum alloy is selected as the material, and simulation is performed to check the deformation, stress and mode of the preliminary model. It is ensured that the deformation does not exceed 0.5% of the diameter of the cylindrical shell, the stress is within the allowable stress range of the aluminum alloy material, and the first-order modal frequency is higher than 100 Hz.

6. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 5, characterized in that: In step 3, the preliminary model is topologically optimized, the skin and rib structure are selected as the design area, and the constraints and optimization objective function are set according to the optimization goal. At the same time, manufacturing constraints are added to make the topologically optimized model easier to manufacture, as follows: The skin and rib structure were selected as the design area; the preliminary model was topologically optimized in the hypermesh software; to ensure the structural stiffness, the minimum flexibility response was added; to achieve the weight reduction effect and make the optimized ribs more obvious, the volume fraction response was set to 0.3; the maximum displacement constraint was added to 0.005m; symmetry constraints were added according to the number of holes so that the optimized ribs were periodically arranged on the circumference; at the same time, to avoid the "chessboard" phenomenon, member size constraints were added and the maximum member size was set to 0.03m.

7. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 6, characterized in that: In step 4, the topology optimized model is analyzed, the rib structure is redesigned in the modeling software according to the topology optimized model, and secondary ribs are arranged between adjacent rib structures to further improve their anti-buckling capacity, as follows: In SolidWorks software, the rib structure is redesigned according to the topologically optimized model. The longitudinal vertical ribs in the preliminary model show an oblique trend after topological optimization. Such oblique ribs can bear both axial and radial loads at the same time. The rib inclination angle θ satisfies the following relationship: In the formula, θ is the inclination angle of the rib, F1 is the axial force, F2 is the shear force, M is the bending moment, and D is the outer diameter of the cylindrical shell; The rib structure after topological optimization is used as the primary rib, and secondary ribs are arranged between the primary ribs to further enhance the structural strength. The width and thickness of the secondary ribs are both 2 / 3 of the primary ribs.

8. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 7, characterized in that: In step 4, special treatment is performed on the part around the hole to reduce stress concentration, as follows: The main ribs are arranged around the hole, and the ribs in the area around the hole are thickened to complete the covering of the hole to reduce stress concentration at the hole position.

9. The method for optimizing the design of the reinforced structure of a perforated cylindrical shell according to claim 8, characterized in that: In step 5, according to the topology optimized model, the finite element mesh is drawn, and the finite element analysis software is used for simulation verification to ensure that the stress and modal frequency of the optimized model are within the allowable range, as follows: Hypermesh software is used to establish the shell unit mesh of the topology optimized model, and the same load as the preliminary model is applied to perform finite element analysis to analyze the deformation, stress and modal frequency of the topology optimized model.

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