Optimization method for shell design of underground intelligent cable traction device

Abstract

The present invention relates to the technical field of shell design optimization, and discloses a shell design optimization method for an underground intelligent cable traction device, the optimization method steps of which include: S1, constructing a traction device shell model; S2, determining a reasonable grid division method; S3, performing overall structural topological optimization on the traction device shell model based on a control optimization method; S4, performing shape adjustment and parameter optimization on the corner details of the traction device shell based on the material elastic-plastic deformation theory; the method realizes the optimized design of the traction device shell structure by constructing an initial model, determining a reasonable grid division method, performing topological optimization based on a control optimization method, and adjusting device details based on the material elastic-plastic deformation theory. The optimized shell structure has better rigidity and strength, can effectively resist the complex environment in the pipeline, and ensure the stable operation of the traction device.

Description

Technical Field

[0001] The invention relates to the technical field of shell design optimization, and in particular to a shell design optimization method for an underground intelligent cable traction device. Background Art

[0002] The underground intelligent cable traction device is a device that integrates intelligent control, power transmission and mechanical traction functions. It is mainly used to pull the cable from one end to the other and complete the cable laying task in underground pipelines, tunnels or other complex environments.

[0003] However, the shell design of the existing underground intelligent cable traction device still has certain shortcomings and cannot complete the work well. The applicant searched and found that the "A method and device for preventing body sheet metal fracture and failure based on finite element analysis" disclosed in its application number "202211537441.6" uses topological structure optimization design to design the body shell, but lacks parameter optimization, and numerical instability is usually prone to occur in the conventional topological optimization process, which leads to inaccurate optimization results or poor manufacturability, and unstable checkerboard phenomena and grayscale unit phenomena will appear; after another search by the applicant, the "Transformer shell design method and transformer shell based on multi-condition topological optimization" disclosed in its application number "202310282322.9" adopts the SIMP optimization method to further optimize the design of the shell, but the sensitivity function of zero in its method may cause too many units to be deleted prematurely during the iteration process, thereby affecting the overall optimization result.

[0004] Therefore, it is necessary to further solve the above-mentioned problems, and the applicant has proposed a shell design optimization method for an underground intelligent cable traction device. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a shell design optimization method for an underground intelligent cable traction device, which solves the problems raised by the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The shell design optimization method of the underground intelligent cable traction device includes the following steps:

[0008] S1. Construct a traction device shell model: Most underground pipelines are hollow cylinders, so the cylinder is selected as the main structure of the traction device shell. Hemispherical structures are set at both ends of the traction device shell to facilitate the placement of smart devices. In the actual construction process, the traction device shell is subject to the tension of the traction rope, so U-shaped rings are set at both ends of the hemispherical structure as a structure for hanging the traction rope;

[0009] S2. Determine a reasonable grid division method;

[0010] S3. Perform overall structural topology optimization on the traction device shell model based on the control optimization method;

[0011] S4. Based on the elastic-plastic deformation theory of materials, shape adjustment and parameter optimization are performed on the corner details of the traction device shell;

[0012] The specific steps of step S2 are as follows:

[0013] S21. At the front end of the traction device housing along the direction of movement of the pipeline axis, that is, the first contact surface of the traction device housing in the forward direction with the water flow in the pipeline, the burrs on the inner wall of the pipeline, and the debris in the pipeline is the front end surface of the traction device housing. This area is subject to large resistance and complex force conditions. The boundary layer refers to the area where the fluid flow interacts with the solid surface. The boundary layer thickness is determined according to the model size. The boundary layer thickness is usually set to 1% to 5% of the local characteristic length, and then 5 to 10 layers of fine boundary layer grids are generated. The area other than the boundary layer at the front end is meshed with high-density tetrahedral units;

[0014] S22. Define the widest surface of the traction device housing parallel to the pipeline axis as the side surface of the traction device housing. When the traction device housing is placed on a horizontal plane, the side area is the only surface in contact with the ground. The underground pipeline is a narrow cylindrical pipeline. The outer wall of the side surface of the traction device housing is easily squeezed by the inner pipe wall when it moves in the pipeline. Compared with the front face, the side surface has a regular shape. By scanning and stretching the discretized basic unit shape, a mesh is obtained. The force condition of the side surface is relatively simple compared with the front face, and the mesh density is moderate.

[0015] S23, define the rear end of the traction device housing along the moving direction of the pipeline axis, the area that is free from resistance due to the front end of the traction device housing blocking the accumulated water and foreign matter is the tail end area, the front end face is taken as the front face, when observing the traction device housing in the front view, this area is completely covered, this part of the area is small in force, and has little effect on the simulation results, use the mapping method to map the surface boundary to the two-dimensional parameter space, perform mesh division in the two-dimensional parameter space, and then reversely map the division result to the physical space to form the surface mesh of the tail end of the traction device, the force condition of the tail end is simple, and the mesh density is low;

[0016] S24. Divide the traction device shell into a front obstruction area, a side pressure area, and a tail low resistance area. Set the grid cells in the front obstruction area except the boundary layer to high density, the grid cells in the side pressure area to medium density, and the grid cells in the tail low resistance area to low density. The unit lengths of these density levels are described by the relationship of geometric series. The length of the grid cell in the high density area is , the length of the medium density area grid unit is set to , the length of the grid cell in the low-density area is set to ,in is the transition ratio, and the volume of the front area of ​​the known model is , the volume of the side area , the volume of the tail region and the total number of grids , according to the formula: , the excess ratio can be calculated The value of can effectively and reasonably allocate the number of grids to the three areas.

[0017] As a further solution of the present invention: the specific steps of step S3 are as follows:

[0018] S31. Based on the mesh division in step S2, a finite element analysis is performed on the traction device housing. In the finite element analysis, a horizontal load of 150,000 N is applied to the U-shaped ring part of the traction device housing, a vertical load of 5,000 N is applied to the side of the traction device housing, and a fixed constraint with zero displacement is applied to the tail end of the traction device housing, so as to simulate the working condition of the traction device housing in the underground pipeline being subjected to the pulling force of the traction rope, and the node load vector F and the displacement vector U are obtained through the finite element analysis;

[0019] S32. Define initial parameters and initial grid cell relative density =0.5, controller proportional gain =7.5, integral gain , derivative gain , the initial value of the Lagrange multiplier =1;

[0020] S33. The goal of topology optimization is set to minimize the overall flexibility of the traction device housing, which is expressed by the following formula:

[0021]

[0022] F=KU

[0023] Where f(x) is the flexibility function, F is the node load vector of the traction device shell under specific working conditions, U is the displacement vector, and K is the structural stiffness matrix;

[0024] The SIMP penalty interpolation function is used to correct the solid isotropic material of the traction device shell. The stiffness matrix of a certain unit It is expressed as follows:

[0025]

[0026] in The Young's modulus of the mesh element is equal to The stiffness matrix of is the Young's modulus of the traction device shell material, P is the introduced penalty factor, is the Young's modulus of the ith grid unit, and the conventional interpolation model is , adding infinitesimal terms to the general interpolation model To optimize the interpolation model, after optimization, the Young's modulus of the i-th unit is expressed by the following formula:

[0027]

[0028] The sensitivity function formula is:

[0029]

[0030] Differentiating the objective function gives the following system response formula:

[0031] ;

[0032] S34. The expression of topology optimization constraint is as follows:

[0033]

[0034] in is a constraint function, which is based on the mass of the traction device shell structure and quality score Defined by quality score =0.7, that is, the mass of the traction device shell after topology optimization is 70% of the mass of the traction device shell without optimization. and are the density and mass of the traction device shell respectively. In this model, =4440kg / m³, =1.99kg, is the volume of the ith grid cell, is the relative density of the grid unit, when When 1 is taken, the grid unit is solid. Take 0 to indicate that the unit has no material.

[0035] The set point is calculated according to the following formula and error signal :

[0036]

[0037] ;

[0038] S35. Use the PID controller to obtain the new grid cell density. The formula is as follows:

[0039]

[0040]

[0041] .

[0042] As a further solution of the present invention: according to step S3, it is determined whether the constraint condition is satisfied. ,when It is considered that the constraints are met. When the constraints are not met, according to the formula Update the Lagrange multiplier, where To satisfy h( )=0.

[0043] As a further solution of the present invention: according to step S3, it is judged whether the optimization result converges, and the specific judgment formula is as follows:

[0044]

[0045] If the convergence condition is met, the iteration stops and the grid cell density is ,If the convergence condition is not met, the process returns to step S33 to re-calculate the system response again.

[0046] As a further solution of the present invention: the specific steps of step S4 are as follows:

[0047] S41. Use the von-mises yield criterion as a criterion for determining whether plastic strain occurs in a material.

[0048] The formula for this criterion is as follows:

[0049]

[0050] in , , are the first principal stress, the second principal stress and the third principal stress respectively. is the yield strength of the traction device housing material;

[0051] S42. Use the hardening function as the isotropic hardening model of the device in the simulation. The hardening function is the stress-strain relationship function in the plastic strain region of the material, which can be calculated according to the formula Find, among which is the total material strain, is the material yield strength. The stress-strain curve of the material can be obtained through testing. ;

[0052] S43. Based on the hardening model and yield criterion, the topology optimized structure is simulated and analyzed, the simulation results are checked, and the parameters of the weak structure are adjusted using the parameter scanning function. Through simulation analysis, it is found that there is a stress singularity phenomenon at the connection between the U-shaped ring and the hemispherical structure of the original model, and plastic strain is prone to occur after being stressed, so the corners are rounded, and simulations with different fillet radii are performed through parameter scanning. The optimal fillet radius is determined through simulation results.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows: the optimization method adopts a reasonable grid division method, which can effectively solve the occurrence of the checkerboard phenomenon, and introduces the SIMP penalty interpolation function in the topology optimization process to correct the solid isotropic material of the traction device shell, and at the same time optimizes the regularization scheme of the traction device shell, adopts a continuation strategy to ensure the stability of the preliminary solution, and optimizes the value of the penalty factor P in subsequent iterations, which can solve the problem of local optimal solution to a certain extent, making the optimization result clearer and solving the occurrence of grayscale unit phenomenon. At the same time, the sensitivity function is introduced to verify the SIMP penalty interpolation function, so that the sensitivity function of the optimized interpolation model is always not equal to zero, which solves the problem that the sensitivity function is zero and too many units are deleted prematurely during the iteration process, thereby affecting the optimization result. Finally, based on the elastic-plastic deformation theory of the material, the details of the corners of the traction device are further adjusted and optimized, which is convenient for fine-tuning the parameters for simulation, thereby ensuring the accuracy of the optimization. The optimized shell structure has better stiffness and strength, can effectively resist the complex environment in the pipeline, and ensure the stable operation of the traction device. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of the structure of the topologically optimized front traction device housing model of the present invention;

[0055] Figure 2 This is a schematic diagram of the structure of the traction device housing model obtained through reasonable finite element analysis mesh division of the present invention;

[0056] Figure 3 It is a schematic diagram of the structure of the traction device housing model of conventional grid division of the present invention;

[0057] Figure 4 It is a flow chart of the algorithm for topological optimization of the traction device shell model based on the control optimization method in the present invention;

[0058] Figure 5 It is a schematic diagram of the structure of the conventionally optimized housing model of the traction device of the present invention;

[0059] Figure 6 It is a schematic diagram of the structure of the traction device shell model after topology optimization of the present invention. DETAILED DESCRIPTION

[0060] 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.

[0061] Example

[0062] See also Figure 1-6 The present invention provides a shell design optimization method for an underground intelligent cable traction device, and the specific steps of the optimization method are as follows:

[0063] Step 1: Build a traction device shell model based on specific project requirements and the specific underground pipeline environment

[0064] Most underground pipelines are hollow cylinders, so the cylinder is selected as the main structure of the traction device shell. Hemispherical structures are set at both ends of the traction device shell to facilitate the placement of smart devices. During the actual construction process, the traction device shell will be subjected to the tension of the traction rope, so U-shaped rings are set at both ends of the hemispherical structure as a structure for hanging the traction rope.

[0065] Step 2: Determine a reasonable finite element analysis meshing method based on the underground pipeline environment

[0066] (1) At the front end of the traction device housing along the direction of movement of the pipeline axis, that is, the first contact surface of the traction device housing in the forward direction with the water flow in the pipeline, the burrs on the inner wall of the pipeline, and the debris in the pipeline is the front end surface of the traction device housing. This area is subject to large resistance and complex force conditions. The boundary layer refers to the area where the fluid flow interacts with the solid surface. The boundary layer thickness is determined according to the model size. The boundary layer thickness is usually set to 1% to 5% of the local characteristic length. Then, 5 to 10 layers of fine boundary layer grids are generated. The area other than the boundary layer at the front end is meshed with high-density tetrahedral units. For example, Figure 1 In the traction device shell model shown, the local characteristic length of the front end is the shell thickness, i.e. 8 mm, the boundary layer thickness is set to 5%*8mm=0.4mm, and 5 boundary layers are set;

[0067] (2) Define the widest surface of the traction device housing parallel to the pipeline axis as the side of the traction device housing. When the traction device housing is placed on a horizontal plane, the side area is the only surface in contact with the ground. The underground pipeline is a narrow cylindrical pipeline. The outer wall of the side of the traction device housing is easily squeezed by the inner pipe wall when it moves in the pipeline. Compared with the front face, the side shape is regular. The mesh is obtained by scanning and stretching the discretized basic unit shape. The force condition of the side is relatively simple compared with the front face, and the mesh density is moderate.

[0068] (3) Define the rear end of the traction device housing along the direction of movement of the pipeline axis. The area that is free from resistance because the front end of the traction device housing blocks accumulated water and foreign matter is the tail end area. The front face is the front face. When observing the traction device housing in the front view, this area is completely covered. This part of the area is subject to small force and has little impact on the simulation results. Use the mapping method to map the surface boundary to the two-dimensional parameter space, perform mesh division in the two-dimensional parameter space, and then reversely map the division result to the physical space to form the surface mesh of the tail end of the traction device. The force condition of the tail end is simple and the mesh density is low.

[0069] (4) The traction device shell is divided into the front obstruction area, the side pressure area and the tail low resistance area. The grid cells in the front obstruction area except the boundary layer are set to high density, the grid cells in the side pressure area are set to medium density, and the grid cells in the tail low resistance area are set to low density. The unit lengths of these density levels are described by the relationship of geometric series. The length of the grid cell in the high density area is , the length of the grid cell in the medium density area is set to , the length of the grid cell in the low-density area is set to ,in is the transition ratio, and the volume of the front area of ​​the known model is , the volume of the side area , the volume of the tail region and the total number of grids , according to the formula: , the excess ratio can be calculated The value of effectively allocates the number of grids to the three areas reasonably. The grid division is shown in Table 1 below:

[0070]

[0071] It can be seen from Table 1 that the calculation time of meshing after reasonable finite element analysis is reduced compared with conventional meshing under the same equipment, thereby improving the calculation efficiency. At the same time, the total elastic strain energy of meshing after reasonable finite element analysis is smaller than that of conventional meshing. The minimum total elastic strain energy can minimize the displacement caused by the applied load, achieve the purpose of minimum flexibility, and improve the accuracy of the simulation.

[0072] Step 3: Optimize the overall structural topology of the traction device shell model based on the control optimization method

[0073] (1) Based on the mesh division in step 2, a finite element analysis is performed on the traction device shell. In the finite element analysis, a horizontal load of 150,000 N is applied to the U-shaped ring part of the traction device shell, a vertical load of 5,000 N is applied to the side of the traction device shell, and a fixed constraint with zero displacement is applied to the tail end of the traction device shell to simulate the working condition of the traction device shell in the underground pipeline being subjected to the tension of the traction rope. The node load vector F and the displacement vector U are obtained through finite element analysis;

[0074] (2) Define initial parameters and initial grid cell relative density =0.5, controller proportional gain =7.5, integral gain , derivative gain , the initial value of the Lagrange multiplier =1;

[0075] (3) The goal of topology optimization is set to minimize the overall flexibility of the traction device shell, which can be expressed as follows:

[0076]

[0077] F=KU

[0078] Where f(x) is the flexibility function, F is the node load vector of the traction device shell under specific working conditions, U is the displacement vector, and K is the structural stiffness matrix;

[0079] The SIMP penalty interpolation function is used to correct the solid isotropic material of the traction device shell. The stiffness matrix of a certain unit It is expressed as follows:

[0080]

[0081] in The Young's modulus of the mesh element is equal to The stiffness matrix of It is the Young's modulus of the traction device shell material. The traction device shell material is Ti-6Al-4V. The Young's modulus Take 109GPa, P is the penalty factor introduced. When the value of P is greater than 1, the number of intermediate density grid cells can be reduced. is the Young's modulus of the ith grid unit, and the conventional interpolation model is , adding infinitesimal terms to the general interpolation model To optimize the interpolation model, after optimization, the Young's modulus of the i-th unit is expressed by the following formula:

[0082]

[0083] The sensitivity function formula is:

[0084]

[0085] The sensitivity function is the response of the objective function to a small change in the design variable. Units with a sensitivity function of 0 have no effect on the objective function. The optimization algorithm tends to delete these units as early as possible to reduce material usage and achieve lightweight design. However, this will cause too many units to be deleted in the early stages of the design, thereby destroying the integrity of the overall structure or causing local stress concentration. The optimized model has This,sensitivity function is always different from zero, which can solve the problem of,deleting too many units too early;

[0086] Differentiating the objective function gives the following system response formula:

[0087] ;

[0088] (4) The expression of topology optimization constraint is as follows:

[0089]

[0090] in is a constraint function, which is based on the mass of the traction device shell structure and quality score Defined by quality score =0.7, that is, the mass of the traction device shell after topology optimization is 70% of the mass of the traction device shell without optimization. and are the density and mass of the traction device shell respectively. In this model, =4440kg / m³, =1.99kg, is the volume of the ith grid cell, is the relative density of the grid unit, when When 1 is taken, the grid unit is solid. Take 0 as the unit has no material, and calculate the set point according to the following formula and error signal :

[0091]

[0092] ;

[0093] (5) Use the PID controller to obtain the new grid cell density, the formula is as follows:

[0094]

[0095]

[0096] ;

[0097] (6) Determine whether the constraints are met ,when It is considered that the constraints are met. When the constraints are not met, according to the formula Update the Lagrange multiplier, where To satisfy h( )=0;

[0098] (7) Determine whether the optimization result converges. The specific judgment formula is as follows:

[0099]

[0100] If the convergence condition is met, the iteration stops and the grid cell density is ,If the convergence condition is not met, the process returns to step S33 to re-calculate the system response again.

[0101] Step 4: Based on the elastic-plastic deformation theory of materials, shape adjustment and parameter optimization of the corner details of the traction device shell are carried out

[0102] (1) Use the von-mises yield criterion as a criterion for determining whether plastic strain occurs in a material.

[0103] The formula for this criterion is:

[0104]

[0105] in , , are the first principal stress, the second principal stress and the third principal stress respectively. is the yield strength of the traction device shell material. Here, the yield strength of TC4 material is 861MPa. If the value on the right side of the equation is greater than the yield strength , it is judged that the material has undergone plastic strain, and the structural strength and corrosion resistance of the plastic strain will be affected and it will not be able to continue to be used;

[0106] (2) Use the hardening function as the isotropic hardening model of the device in the simulation. The hardening function is the stress-strain relationship function in the plastic strain region of the material, which can be calculated according to the formula Find, among which is the total material strain, is the material yield strength. The stress-strain curve of the material can be obtained through testing. ;

[0107] (3) Based on the hardening model and yield criterion, the topology optimized structure is simulated and analyzed. The simulation results are checked and the parameters of the weak structure are adjusted using the parameter scanning function. Through simulation analysis, it is found that there is a stress singularity at the connection between the U-shaped ring and the hemispherical structure of the original model. Plastic strain is prone to occur after being subjected to force. Therefore, fillet treatment is performed at this location. Different fillet radii are simulated through parameter scanning, and the optimal fillet radius is determined through simulation results.

[0108] In summary, this optimization method adopts a reasonable grid division method, which can effectively solve the occurrence of the checkerboard phenomenon, and introduces the SIMP penalty interpolation function in the topology optimization process to correct the solid isotropic material. At the same time, the regularization scheme of the traction device shell model is optimized, and the continuation strategy is adopted to ensure the stability of the preliminary solution. The value of the penalty factor P is optimized in subsequent iterations, which can solve the problem of local optimal solution to a certain extent, making the optimization result clearer and solving the grayscale unit phenomenon. Secondly, the sensitivity function is introduced to solve the problem that the sensitivity function is zero, which may lead to premature deletion of too many units in the iteration process, thereby affecting the optimization results. Finally, based on the material elastic-plastic deformation theory, the shape adjustment and parameter optimization of the corner details of the traction device shell are carried out, and the weak position of the model under force is analyzed to facilitate the fine-tuning simulation of the parameters, thereby ensuring the accuracy of the optimization. The optimized shell structure has better stiffness and strength, can effectively resist the complex environment in the pipeline, and ensure the stable operation of the traction device. It should also be noted that in the appendix of the manual Figure 5 And the instruction manual Figure 6 The highlighted red part of the structure contributes most to the overall strength of the device. After optimization, the thickness of this part remains unchanged. The silver area not highlighted in the figure becomes thinner after optimization, so that the overall structure meets the set mass constraint condition, that is, the mass after optimization is 70% of the mass before optimization, as shown in the attached manual. Figure 5 And the instruction manual Figure 6 By comparison, it can be seen that the topology optimization method used in this method has fewer intermediate density units in the optimized model and a clearer and more reasonable structure than the conventional method.

[0109] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A shell design optimization method for an underground intelligent cable traction device, characterized in that: The optimization method steps include: S1. Construct a traction device shell model: Most underground pipelines are hollow cylinders, so the cylinder is selected as the main structure of the traction device shell. Hemispherical structures are set at both ends of the traction device shell to facilitate the placement of smart devices. In the actual construction process, the traction device shell is subject to the tension of the traction rope, so U-shaped rings are set at both ends of the hemispherical structure as a structure for hanging the traction rope; S2. Determine a reasonable grid division method; S3. Perform overall structural topology optimization on the traction device shell model based on the control optimization method; S4. Based on the elastic-plastic deformation theory of materials, shape adjustment and parameter optimization are performed on the corner details of the traction device shell; The specific steps of step S2 are as follows: S21. At the front end of the traction device housing along the direction of movement of the pipeline axis, that is, the first contact surface of the traction device housing in the forward direction with the water flow in the pipeline, the burrs on the inner wall of the pipeline, and the debris in the pipeline is the front end surface of the traction device housing. This area is subject to large resistance and complex force conditions. The boundary layer refers to the area where the fluid flow interacts with the solid surface. The boundary layer thickness is determined according to the model size. The boundary layer thickness is usually set to 1% to 5% of the local characteristic length, and then 5 to 10 layers of fine boundary layer grids are generated. The area other than the boundary layer at the front end is meshed with high-density tetrahedral units; S22. Define the widest surface of the traction device housing parallel to the pipeline axis as the side surface of the traction device housing. When the traction device housing is placed on a horizontal plane, the side area is the only surface in contact with the ground. The underground pipeline is a narrow cylindrical pipeline. The outer wall of the side surface of the traction device housing is easily squeezed by the inner pipe wall when it moves in the pipeline. Compared with the front face, the side surface has a regular shape. By scanning and stretching the discretized basic unit shape, a mesh is obtained. The force condition of the side surface is relatively simple compared with the front face, and the mesh density is moderate. S23, define the rear end of the traction device housing along the moving direction of the pipeline axis, the area that is free from resistance due to the front end of the traction device housing blocking the accumulated water and foreign matter is the tail end area, the front end face is taken as the front face, when observing the traction device housing in the front view, this area is completely covered, this part of the area is small in force, and has little effect on the simulation results, use the mapping method to map the surface boundary to the two-dimensional parameter space, perform mesh division in the two-dimensional parameter space, and then reversely map the division result to the physical space to form the surface mesh of the tail end of the traction device, the force condition of the tail end is simple, and the mesh density is low; S24. Divide the traction device shell into a front obstruction area, a side pressure area, and a tail low resistance area. Set the grid cells in the front obstruction area except the boundary layer to high density, the grid cells in the side pressure area to medium density, and the grid cells in the tail low resistance area to low density. The unit lengths of these density levels are described by the relationship of geometric series. The length of the grid cell in the high density area is , the length of the grid cell in the medium density area is set to , the length of the grid cell in the low-density area is set to ,in is the transition ratio, and the volume of the front area of ​​the known model is , the volume of the side area , the volume of the tail region and the total number of grids , according to the formula: , the excess ratio can be calculated The value of can effectively and reasonably allocate the number of grids to the three areas.

2. The shell design optimization method of the underground intelligent cable traction device according to claim 1 is characterized in that: The specific steps of step S3 are as follows: S31. Based on the mesh division in step S2, a finite element analysis is performed on the traction device housing. In the finite element analysis, a horizontal load of 150,000 N is applied to the U-shaped ring part of the traction device housing, a vertical load of 5,000 N is applied to the side of the traction device housing, and a fixed constraint with zero displacement is applied to the tail end of the traction device housing, so as to simulate the working condition that the traction device housing in the underground pipeline is subjected to the pulling force of the traction rope and the pressure on the pipe wall side, and the node load vector F and the displacement vector U are obtained through the finite element analysis; S32. Define initial parameters and initial grid cell relative density =0.5, controller proportional gain =7.5, integral gain , derivative gain , the initial value of the Lagrange multiplier =1; S33. The goal of topology optimization is set to minimize the overall flexibility of the traction device housing, which is expressed by the following formula: F=KU Where f(x) is the flexibility function, F is the node load vector of the traction device shell under specific working conditions, U is the displacement vector, and K is the structural stiffness matrix; The SIMP penalty interpolation function is used to correct the solid isotropic material of the traction device shell. The stiffness matrix of a certain unit It is expressed as follows: in The Young's modulus of the mesh element is equal to The stiffness matrix of is the Young's modulus of the traction device shell material, P is the introduced penalty factor, is the Young's modulus of the ith grid unit. The Young's modulus of the ith unit is expressed by the following formula: The sensitivity function formula is: Differentiating the objective function gives the following system response formula: ； S34. The expression of topology optimization constraint is as follows: in is a constraint function, which is based on the mass of the traction device shell structure and quality score Defined by quality score =0.7, that is, the mass of the traction device shell after topology optimization is 70% of the mass of the traction device shell without optimization. and are the density and mass of the traction device shell respectively. In this model, =4440kg / m³, =1.99kg, is the volume of the ith grid cell, is the relative density of the grid unit, when When it is 1, the grid unit is solid. Take 0 as the unit has no material, and calculate the set point according to the following formula and error signal : ； S35. Use the PID controller to obtain the new grid cell density. The formula is as follows: 。 3. The shell design optimization method of the underground intelligent cable traction device according to claim 2 is characterized in that: According to step S3, determine whether the constraint condition is met ,when It is considered that the constraints are met. When the constraints are not met, according to the formula Update the Lagrange multiplier, where To satisfy h( )=0.

4. The shell design optimization method of the underground intelligent cable traction device according to claim 3 is characterized in that: According to step S3, it is determined whether the optimization result has converged. The specific determination formula is as follows: If the convergence condition is met, the iteration stops and the grid cell density is ,If the convergence condition is not met, the process returns to step S33 to re-calculate the system response again.

5. The shell design optimization method of the underground intelligent cable traction device according to claim 4 is characterized in that: The specific steps of step S4 are as follows: S41. Use the von-mises yield criterion as a criterion for determining whether plastic strain occurs in a material. The formula for this criterion is as follows: in , , are the first principal stress, the second principal stress and the third principal stress respectively. is the yield strength of the traction device housing material; S42. Use the hardening function as the isotropic hardening model of the device in the simulation. The hardening function is the stress-strain relationship function in the plastic strain region of the material, which can be calculated according to the formula Find, among which is the total material strain, is the material yield strength. The stress-strain curve of the material can be obtained through testing. ; S43. Based on the hardening model and yield criterion, the topology optimized structure is simulated and analyzed, the simulation results are checked, and the parameters of the weak structure are adjusted using the parameter scanning function. Through simulation analysis, it is found that there is a stress singularity phenomenon at the connection between the U-shaped ring and the hemispherical structure of the original model, and plastic strain is prone to occur after being stressed, so the corners are rounded, and simulations with different fillet radii are performed through parameter scanning. The optimal fillet radius is determined through simulation results.

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