Regional thin layer unit modeling and parameter identification method for bolted connection cylindrical shell structure

Abstract

The invention discloses a regional thin layer unit modeling and parameter identification method for a bolt connection cylindrical shell structure, and relates to the field of structural engineering and finite element analysis, and the method comprises the following steps: firstly, dividing a single bolt connection contact region into a contact main region and a contact auxiliary region, and equivalently replacing a bolt connection structure with a regional thin layer unit; carrying out parameter design on a thin layer unit material in the contact area, and carrying out finite element model establishment and simulation analysis on the whole; and finally, carrying out a modal test on a test piece of the bolt connection cylindrical shell structure, and carrying out reverse optimization identification on linear material parameters of the thin layer unit by utilizing a test result. According to the method, the genetic optimization algorithm is utilized to iterate the linear parameters meeting the target function, the parameters are substituted into the thin layer unit model for simulation analysis, through comparison with the test result, the accurate linear parameter identification value is obtained, and the simulation modal shape of the linear parameter identification value is matched with the test modal shape.

Description

Technical Field

[0001] The invention relates to the fields of structural engineering and finite element analysis, and in particular to a method for modeling and identifying parameters of a sub-region thin-layer unit of a bolt-connected column shell structure. Background Art

[0002] As a typical connection structure, bolted column-shell structure is widely used in aerospace and other engineering fields due to its simple structure, convenient loading and unloading, and excellent sealing performance. Due to the existence of the connection structure, the continuity and consistency of the overall structure are destroyed, and there are complex dynamic characteristics at the joint surface, which are often accompanied by nonlinear characteristics such as energy dissipation, stiffness softening, and local damping changes. As the weak point of the overall structure, in order to improve the safety and reliability of the bolted column-shell structure, it is necessary to efficiently and accurately establish its dynamic model, analyze its nonlinear dynamic characteristics, and study the influence of related parameters.

[0003] Aiming at the research demand on the nonlinear vibration characteristics and mechanism of bolted cylindrical shell structures, the present invention proposes a dynamic modeling and parameter identification method of bolted cylindrical shell structures based on nonlinear thin-layer elements on the basis of connection stiffness characteristics analysis, providing a feasible and more efficient dynamic analysis model. Summary of the invention

[0004] In the finite element simulation analysis of bolted column-shell structures, traditional modeling methods often cannot accurately simulate the real behavior of the bolted connection part, resulting in a large deviation between the simulation results and the dynamic characteristics of the actual structure. In addition, the material parameter settings of the bolted connection area are complex, and there is a lack of effective parameter identification methods, which limits the accuracy and practicality of the model. Therefore, the present invention provides a method for modeling and parameter identification of a sub-region thin-layer unit for a bolted column-shell structure. The technical solution adopted by the present invention to solve its technical problems is as follows:

[0005] A method for regional thin-layer unit modeling and parameter identification of a bolt-connected cylindrical shell structure includes the following steps:

[0006] Step 1: According to the results of the stiffness analysis of the bolted cylindrical shell structure, the thin layer element area is divided into the main contact area and the secondary contact area;

[0007] Step 2: Through theoretical analysis of structural stiffness, set initial values ​​for the material parameters of the thin layer area after the area division in step 1;

[0008] Step 3: Use the parameters set in step 2 to establish a thin layer unit model, and then establish a 3D model of the bolted column shell structure according to the actual size;

[0009] Step 4: Mesh the 3D model of the bolted column shell structure established in step 3 to determine the meshed bolted connection structure model;

[0010] Step 5: Set constraint boundary conditions and load boundary conditions for the bolt connection structure model after meshing in step 4;

[0011] Step 6: Create an APDL parameterized command stream for the model set in step 5 to perform simulation calculations;

[0012] Step 7: Perform a hammer modal test on the machined test piece to obtain the modal vibration shape and natural frequency of the bolted column shell structure;

[0013] Step 8: Compare and analyze the modal test results with the simulation data, and optimize and identify the linear parameters of the thin layer element material;

[0014] Step 9: Substitute the optimized and identified parameter values ​​into the parametric simulation model, perform the same simulation calculation as step 6, and compare and analyze with the modal test results of the test piece to verify the accuracy and effectiveness of the simulation model.

[0015] Furthermore, the step 1 is specifically as follows: define thin layer area 1 as the main area for bolt tightening, i.e., the main contact area; define thin layer area 2 as the area remaining after removing the main contact area, i.e., the secondary contact area; and select an appropriate thin layer unit thickness according to the microscopic morphology structure of the surface of the micro-convex body on the metal surface.

[0016] Further, the step 2 is specifically as follows: the material of the contact main area is established with transverse isotropy, and the elastic modulus E in the z direction of the contact main area is b Depend on Calculate, where E maj or is the elastic modulus of the main contact area, K a is the normal equivalent stiffness of the series connection, k BS is the screw stiffness, h is the thickness of the thin layer element, A major The contact area of ​​the main contact area, the elastic modulus E in the x or y direction a Depend on Calculate, where A r is the actual contact area, A a is the nominal contact area, E′ is the comprehensive elastic modulus, al is the area of ​​the maximum contact point, D is the fractal dimension of the rough surface, ψ is the domain expansion coefficient of the micro-contact size distribution, and the shear modulus G in the xz plane is b Depend on

[0017] Calculate, where K τis the tangential contact stiffness of a single microscopic protrusion, and the density ρ is calculated by dividing the removed mass by the volume of the thin layer unit;

[0018] The material of the contact sub-region is set to be isotropic, and the normal stiffness of the contact sub-region is equal to the normal contact stiffness of the contact sub-region in the theoretical calculation, and the density is the same as that of region 1.

[0019] Furthermore, the step 3 is specifically as follows: the finite element simulation process is simplified, the bolts and nuts are simulated as cylinders, and the details of the threads are ignored. The structure mainly includes upper and lower flanges, bolts and nuts.

[0020] Furthermore, the step 5 specifically includes: applying a full fixed constraint to the bottom end surface, and connecting the thin layer unit with the upper and lower flange surfaces by using a node coupling method.

[0021] Furthermore, the step 6 is specifically as follows: establishing an APDL parameterized command stream and importing it into APDL for simulation calculation. At the same time, it is observed through the simulation results that the vibration mode changes of the overall structure are mainly concentrated on the circumferential wave number changes of the upper cylindrical shell.

[0022] Furthermore, the step 7 is specifically as follows: the structural dimensions of the test piece are the same as the finite element simulation model, the fixed constraint conditions of the bottom end face in the simulation analysis are simulated, a bottom end face fixture is designed, the test piece is fixed on the workbench, the measurement points are arranged evenly around the circumference, two reference points are fixed, and the test is performed by a moving hammer method.

[0023] Furthermore, the step 8 is specifically as follows: performing vibration mode matching of the same-order modes to ensure the consistency of vibration modes of each order of modes involved in the identification process, and clarifying the parameter values ​​to be identified, mainly including the horizontal elastic modulus E of the thin layer region 1 a , elastic modulus E in the horizontal normal direction b , shear modulus G in the xz plane b A total of 6 parameters, including the central angle β, the elastic modulus E2 of the thin layer area 2, and the thickness h of the entire thin layer unit, are used to iteratively optimize and identify the material parameters through the response surface optimization module and the Latin hypercube sampling method combined with the genetic algorithm.

[0024] Furthermore, step 9 is specifically as follows: substituting the optimized identified parameter values ​​into the parametric simulation model for simulation calculation and comparative analysis with the modal test of the test piece. The vibration mode of the thin-layer unit model after identification can correspond to the modal test result, and at the same time, the error of its natural frequency value is significantly reduced, and the errors of the first 5 orders are all within 5%.

[0025] The advantage of the present invention is that the modeling method can significantly improve the efficiency and accuracy of the simulation analysis of the bolted cylindrical shell structure. By comparing and analyzing the simulation results with the modal test results, the accuracy and effectiveness of the model are verified, and the errors of the first five natural frequency values ​​are all within 5%, which meets the requirements of practical engineering problems. In addition, the present invention also provides an effective material parameter identification method, so that the model can better reflect the dynamic characteristics of the actual structure, and improve the reliability and economy of the structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic diagram of a stress cloud diagram of a contact surface of a bolt connection structure provided by an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of thin layer area division provided by an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of a finite element simulation provided by an embodiment of the present invention;

[0030] FIG4( a ) is a schematic diagram of a three-dimensional model of a bolted column shell structure provided in an embodiment of the present invention;

[0031] FIG4( b ) is a schematic diagram of a special fixture for bolt-connecting a column shell structure provided by an embodiment of the present invention;

[0032] Figure 5 A schematic diagram of a modal testing system provided by an embodiment of the present invention;

[0033] FIG6( a ) is a schematic diagram of measurement point distribution of an actual structure provided by an embodiment of the present invention;

[0034] FIG6( b ) is a schematic diagram of the distribution of measurement points in the modal testing software provided in an embodiment of the present invention;

[0035] Figure 7 A parameter identification flow chart provided for an embodiment of the present invention;

[0036] Figure 8 The figure is a flow chart of an embodiment of the present invention.

[0037] Fig. 9 The natural frequency value results and vibration mode of the thin layer unit model provided by the embodiment of the present invention;

[0038] Fig.10 The natural frequency of the overall structure connected by six bolts provided in the embodiment of the present invention;

[0039] Table 1 shows the initial values ​​of the thin layer unit material parameters provided by the embodiment of the present invention;

[0040] Table 2 is the thin layer unit parameter identification result provided by the embodiment of the present invention;

[0041] Table 3 is a comparison of the first five natural frequency values ​​of the thin layer unit model provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. The present invention provides a thread simplified modeling method based on a regional thin layer element method, comprising the following steps:

[0043] Step 1: According to the results of the stiffness analysis of the bolted cylindrical shell structure, the thin layer element area is divided into the main contact area and the secondary contact area;

[0044] According to Figure 1 The stress cloud diagram of the bolt connection shown in the figure shows that the contact stress is concentrated in the bolt clamping area. The area of ​​the clamping area is a fan-shaped area, and the center angle is about 4°. Therefore, the thin layer unit is divided into regions as follows: Figure 2 As shown, firstly, thin layer region 1 is defined as the main bolt compression region, i.e., the main contact region, and thin layer region 2 is defined as the remaining region after removing the main contact region, i.e., the secondary contact region, and the center angle of thin layer region 1 is 4°; according to the microscopic morphology of the surface layer of the micro-convex body on the metal surface, the thickness of the micro-convex body fluctuates around 0.5mm, so the thickness of the thin layer unit can be taken as 1mm;

[0045] Step 2: Through theoretical analysis of structural stiffness, set initial values ​​for the material parameters of the thin layer area after the area division in step 1;

[0046] The material of thin layer region 1 is established with transverse isotropy. The elastic constants of transverse isotropic materials are reduced to 6, namely the elastic modulus Ea of the thin layer unit in the direction of each isotropic axis x (or y), the elastic modulus E of the thin layer unit in the direction of the symmetry axis z b , Poisson's ratio μ of the material in the horizontal direction (x-y plane) a , Poisson's ratio μ between the horizontal direction (x-y plane) and the vertical direction (z direction) ab , Poisson's ratio μ between the vertical direction (z direction) and the horizontal direction (x-y plane) of the material ba , the shear modulus G of the thin layer element in the xz plane b , the shear modulus G of the thin layer element in the xy plane a7 parameters, whose matrix form is

[0047]

[0048] Among them, ε x , ε y , ε z Represent the normal strain in the xyz direction, γ yz , γ zx , γ xy are the shear strains on the yz, zx, and xy planes, σ x , σ y , σ z are the normal stresses in the x, y, and z directions, τ yz , τ zx , τ xy are the shear stresses on the yz, zx, and xy planes respectively.

[0049] The elastic modulus of the thin layer element in the direction of the symmetry axis z is Among them, K a is the normal equivalent stiffness of the series connection, in N / M; k BS is the screw stiffness, in N / M; h is the thickness of the thin layer unit, in mm; the elastic modulus of the thin layer unit in the x (or y) direction of each isotropic axis is Where A r is the actual contact area, A a is the nominal contact area; the shear modulus of the thin layer element in the xz plane is where k τ is the tangential contact stiffness of a single microscopic protrusion, in N / m; the density ρ is calculated by dividing the removed mass by the volume of the thin layer unit;

[0050] For the contact sub-region, that is, the thin layer region 2, since its load is negligible compared with the contact main region, it is considered to be set as an isotropic material. At the same time, the normal stiffness of the thin layer region 2 is equal to the normal contact stiffness of the contact sub-region in the theoretical calculation, and the density is the same as that of region 1. The elastic modulus of the thin layer region 2 is obtained as follows: Among them, K n-minor is the normal stiffness A of the secondary contact area minor is the contact area of ​​the secondary contact region, and the initial values ​​of the parameters are shown in Table 1;

[0051] Table 1

[0052]

[0053] Step 3: Use the parameters set in step 2 to establish a thin layer unit model, and then establish a 3D model of the bolted column shell structure according to the actual size; the solid structure uses SOLID185 units.

[0054] Considering the size model of the actual structure, the following is established: Figure 3 The specific dimensions shown are: the outer diameter of the upper cylindrical shell is 300mm, the height is 100mm, the outer diameter of the flange is 340mm, and the thickness is 5mm; the outer diameter of the lower cylindrical shell is 300mm, the height is 100mm, the outer diameter of the upper flange is 340mm, and the thickness is 5mm; the outer diameter of the lower flange is 360mm, and the thickness is 10mm; the wall thickness of the upper and lower cylindrical shells is both 2mm.

[0055] Step 4: Mesh the 3D model of the bolted column shell structure established in step 3 to determine the meshed bolted connection structure model;

[0056] The model is meshed, the thin layer unit type is solid unit SOLID186, the total number of units is 7548, and the number of nodes is 45288.

[0057] Step 5: Set constraint boundary conditions and load boundary conditions for the bolt connection structure model after meshing in step 4;

[0058] The thin layer element is connected to the upper and lower flange surfaces by using the node coupling method, and a full fixed constraint is applied to the bottom end surface;

[0059] Step 6: Create an APDL parameterized command stream for the model set in step 5 to perform simulation calculations;

[0060] According to the above conditions, an APDL parameterized command flow is established and imported into APDL for simulation calculation. The results are as follows: Fig. 9 At the same time, it is observed through the simulation results that the vibration mode changes of the overall structure are mainly concentrated on the changes in the circumferential wave number of the upper cylindrical shell. Based on this finding, the vibration mode order of the thin layer unit model is defined as f n , where n represents the annular wave number of the upper cylindrical shell. This definition helps to distinguish and identify different vibration mode changes.

[0061] Step 7: Perform a hammer modal test on the machined test piece to obtain the modal vibration shape and natural frequency of the bolted column shell structure;

[0062] The test piece is a bolt-connected cylindrical shell structure assembly as shown in Figure 4(a). The specific structural dimensions are the same as the finite element simulation model. The material is Q235 and the bolts are M8 high-strength bolts. In order to simulate the fixed constraint conditions of the bottom end face in the simulation analysis, a bottom end face fixture is designed as shown in Figure 4(b). The test piece is fixed on the workbench for modal testing. The principle is as follows Figure 5. 168 measuring points were set, 24 measuring points were arranged circumferentially, and a layer of measuring points was set every 20 mm from the top of the upper cylindrical shell, for a total of 5 layers. One layer was set every 30 mm and one layer was set every 60 mm from the bottom of the lower cylindrical shell. There were 7 layers of structural design measuring points, for a total of 168 measuring points. The distribution of structural measuring points is shown in Figure 6(a) and Figure 6(b). Two reference points were fixed (that is, two sensors were fixed, the position of reference point 1 was measuring point 1; the position of reference point 2 was measuring point 109), and the test was carried out in a moving hammer manner. Setting of boundary conditions: The bottom surface of the structure was fixed to achieve the boundary condition of one end being free and the other end being fixed. A tightening torque of 15 N·m was applied to the 6 uniformly distributed bolts. Modal testing was carried out using the excitation method of a moving hammer, and the data was processed using the DASP-V11 modal testing software of the Oriental Institute to obtain the results as shown below. Fig.10 shown.

[0063] Step 8: Combine the modal test results with the simulation data to identify the linear parameters of the thin layer element material;

[0064] Before optimizing the design, the consistency of the modal vibration modes involved in the identification process must be ensured. The parameter values ​​that need to be identified are mainly the horizontal elastic modulus E of the thin layer area 1. a , elastic modulus E in the horizontal normal direction b , shear modulus G in the xz plane b There are 6 parameters in total, including the central angle β, the elastic modulus E2 of the thin layer area 2, and the thickness h of the entire thin layer unit. Taking into account the vibration mode of the overall structure, the circumferential wave number of the upper cylindrical shell increases with the increase of the natural frequency value. It is planned to involve the first 4 vibration modes of the thin layer unit model in the analysis process of the optimization design. The specific parameter identification process is as follows: Figure 7 shown.

[0065] Step 9: Verify the accuracy and effectiveness of the model by comparing the simulation results with the modal test results, and perform necessary parameter optimization;

[0066] Taking the above analysis into consideration, the above parameters are optimized and identified by combining APDL parameterized command flow modeling with the response surface optimization module of Workbench. First, the Latin hypercube sampling method is used to obtain 200 sets of simulation samples within the above initial value variation range, and finite element simulation calculations are performed to obtain the corresponding target value data. The response surface model is established using the optimization module of Workbench, and the material parameters are iteratively optimized and identified by combining the genetic algorithm as shown below. At the same time, the trend chart of the influence of different parameters on the target value can be obtained. Subsequent analysis mainly considers the E b , and the parameters of E2. At the same time, the identification values ​​shown in Table 2 were obtained.

[0067] Table 2

[0068]

[0069] Step 10: Substitute the optimized and identified parameter values ​​into the parametric simulation model, perform simulation calculations, and compare and analyze them with the experimental results to verify the accuracy and effectiveness of the model.

[0070] The optimized and identified parameter values ​​are substituted into the parametric simulation model for simulation calculation and compared with the test results as shown in Table 3. By comparison, it can be found that the vibration mode of the thin-layer unit model after identification can correspond to the modal test results, and the error of its natural frequency value is significantly reduced, and the errors of the first 5 orders are all within 5%.

[0071] Table 3

[0072]

[0073]

[0074] Through the above specific implementation methods, the present invention can achieve accurate modeling and simulation analysis of bolt-connected column shell structures, and provide reliable data support for engineering design.

[0075] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above implementations are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and change the above embodiments within the scope of the present invention.

Claims

1. A method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure, characterized in that: The following steps are involved: Step 1: According to the results of the stiffness analysis of the bolted cylindrical shell structure, the thin layer element area is divided into the main contact area and the secondary contact area; Step 2: Through theoretical analysis of structural stiffness, set initial values ​​for the material parameters of the thin layer area after the area division in step 1; Step 3: Use the parameters set in step 2 to establish a thin layer unit model, and then establish a 3D model of the bolted column shell structure according to the actual size; Step 4: Mesh the 3D model of the bolted column shell structure established in step 3 to determine the meshed bolted connection structure model; Step 5: Set constraint boundary conditions and load boundary conditions for the bolt connection structure model after meshing in step 4; Step 6: Create an APDL parameterized command stream for the model set in step 5 to perform simulation calculations; Step 7: Perform a hammer modal test on the machined test piece to obtain the modal vibration shape and natural frequency of the bolted column shell structure; Step 8: Compare and analyze the modal test results with the simulation data, and optimize and identify the linear parameters of the thin layer element material; Step 9: Substitute the optimized and identified parameter values ​​into the parametric simulation model, perform the same simulation calculation as step 6, and compare and analyze with the modal test results of the test piece to verify the accuracy and effectiveness of the simulation model.

2. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: Specifically, step 1 is as follows: thin layer region 1 is defined as the main bolt compression region, i.e., the main contact region; thin layer region 2 is defined as the remaining region after removing the main contact region, i.e., the secondary contact region; and appropriate thin layer unit thickness is selected according to the surface microscopic morphology of the metal surface micro-convex body.

3. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 2 is specifically as follows: the material of the contact main area is established with transverse isotropy, and the elastic modulus E in the z direction of the contact main area b Depend on Calculate, where E major is the elastic modulus of the main contact area, K a is the normal equivalent stiffness of the series connection, k BS is the screw stiffness, h is the thickness of the thin layer element, A major The contact area of ​​the main contact area, the elastic modulus E in the x or y direction a Depend on Calculate, where A r is the actual contact area, A a is the nominal contact area, E′ is the comprehensive elastic modulus, al is the area of ​​the maximum contact point, D is the fractal dimension of the rough surface, ψ is the domain expansion coefficient of the micro-contact size distribution, and the shear modulus G in the xz plane is b Depend on Calculate, where K τ is the tangential contact stiffness of a single microscopic protrusion, and the density ρ is calculated by dividing the removed mass by the volume of the thin layer unit; The material of the contact sub-region is set to be isotropic, and the normal stiffness of the contact sub-region is equal to the normal contact stiffness of the contact sub-region in the theoretical calculation, and the density is the same as that of region 1.

4. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 3 is specifically as follows: the finite element simulation process is simplified, the bolts and nuts are simulated as cylinders, and the details of the threads are ignored. The structure mainly includes upper and lower flanges, bolts and nuts.

5. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 5 specifically includes: applying a full fixed constraint to the bottom end surface, and connecting the thin layer unit with the upper and lower flange surfaces by using a node coupling method.

6. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 6 is specifically as follows: establishing an APDL parameterized command stream and importing it into APDL for simulation calculation. At the same time, it is observed through the simulation results that the vibration mode changes of the overall structure are mainly concentrated on the changes in the circumferential wave number of the upper cylindrical shell.

7. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 7 is specifically as follows: the structural dimensions of the test piece are the same as the finite element simulation model, the fixed constraint conditions of the bottom end face are simulated and analyzed, a bottom end face fixture is designed, the test piece is fixed on the workbench, the measurement points are arranged evenly around the circumference, two reference points are fixed, and the test is performed by a moving hammer method.

8. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1 is characterized in that: The step 8 is specifically as follows: matching the vibration modes of the same order modes to ensure the consistency of the vibration modes of each order mode involved in the identification process, and clarifying the parameter values ​​to be identified, mainly including the horizontal elastic modulus E of the thin layer area 1. a , elastic modulus E in the horizontal normal direction b , shear modulus G in the xz plane b A total of 6 parameters, including the central angle β, the elastic modulus E2 of the thin layer area 2, and the thickness h of the entire thin layer unit, are used to iteratively optimize and identify the material parameters through the response surface optimization module and the Latin hypercube sampling method combined with the genetic algorithm.

9. The method for regional thin-layer unit modeling and parameter identification of a bolted cylindrical shell structure according to claim 1, characterized in that: The step 9 is specifically as follows: substituting the optimized identified parameter values ​​into the parametric simulation model for simulation calculation and performing comparative analysis with the modal test of the test piece. The vibration mode of the thin-layer unit model after identification can correspond to the modal test result, and at the same time, the error of its natural frequency value is significantly reduced, and the errors of the first 5 orders are all within 5%.

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