A Method for Identifying the Failure Mechanism and Dynamically Assessing the Operational Risk of 66kV Transmission Tower Structures

Abstract

This invention discloses a method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers. The method includes: measuring the mechanical properties of tower connection nodes, corroded tower materials, old tower materials, and bolts; collecting on-site data on wind speed, air temperature, strain, and tilt; establishing a mechanical-physical model combining data-driven analysis and finite element theory based on the measured data; using this model for strength verification, modal analysis, and damage evolution analysis to identify the structural failure mechanism; simulating and displaying the stress state of various parts of the tower in real time on a terminal system, and dynamically assessing the operational risk using the CRITIC method; and obtaining tower reinforcement technical measures based on the assessment results using a multi-objective global optimization method. This invention achieves visualized and quantitative assessment of operational risk and proposes scientifically reasonable reinforcement schemes based on global optimization, effectively preventing tower collapse accidents and ensuring the safe and stable operation of the power grid.

Description

Technical Field

[0001] This invention belongs to the field of power transmission line structural safety monitoring and assessment technology, specifically involving a method for identifying the structural damage mechanism of 66kV power transmission towers and dynamically assessing operational risks. Background Technology

[0002] The power transmission network is a complex system composed of power lines and transmission towers. Given the large-scale transmission of electricity in my country, many transmission lines must traverse regions with extreme geological conditions. The operation of the transmission network is affected not only by internal system factors but also by external environmental factors, such as natural disasters like wind loads, snow, and earthquakes, as well as geological disasters like landslides, mudslides, collapses, and ground subsidence. These factors pose serious threats to the safe operation of transmission lines. Transmission towers are crucial equipment in overhead transmission lines; years of load have caused cumulative damage to their structures, creating serious safety hazards. As a major lifeline project, damage to transmission tower structures can lead to the paralysis of the power supply system and even fires, resulting in significant economic losses and directly impacting national production and construction as well as people's lives. Transmission towers play an extremely important role in power energy transmission. Their mechanical properties and structural strength directly affect the safe and economical operation of the entire power system. Therefore, in-depth research on the safe operation of transmission towers in the line system, especially the overall stability and local load-bearing capacity of the towers themselves, is of great scientific research significance and practical application value.

[0003] Existing 66kV transmission towers in operation suffer from problems such as aging, flimsy structures, and insufficient strength in some components, resulting in severely inadequate load-bearing capacity. Under extreme weather conditions such as strong winds and icing, they are highly susceptible to collapse, seriously threatening the safe and stable operation of the power grid. To improve the safety and reliability of these towers, it is urgent to conduct in-depth research on their failure mechanisms. Based on this research, an effective method for assessing the safety operation risks of 66kV transmission towers needs to be developed to monitor their health status and operational risks in real time. Then, based on the results, effective reinforcement measures can be implemented to ensure the normal operation of 66kV transmission lines under different operating conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying the structural failure mechanism and dynamically assessing the operational risks of 66kV transmission towers, which can support the construction, operation and maintenance of 66kV transmission towers and prevent serious accidents such as tower collapse. At the same time, by using the proposed risk assessment system and reinforcement technology measures, the operation and maintenance costs of transmission lines can be significantly reduced, manpower can be saved, operation and maintenance efficiency can be improved, and equipment management level can be enhanced.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for identifying the structural failure mechanism and dynamically assessing the operational risk of a 66kV transmission tower, comprising the following steps: Step 1: Measure the mechanical properties of the connection nodes, corroded tower materials, old tower materials, and bolts of the 66kV transmission tower, including elastic modulus, allowable stress, bending and shear resistance, and collect on-site data on wind speed, temperature, strain, and tilt in the area where the tower is located. Step 2: Based on the field data obtained in Step 1, establish a mechanical and physical model of the 66kV transmission tower based on data-driven and finite element theory. Step 3: Using the aforementioned mechanical and physical model, identify the structural failure mechanism of the tower, including strength verification, modal analysis, and damage evolution analysis; Step four: Using the aforementioned mechanical and physical model, the stress state of each part of the 66kV transmission tower is simulated and displayed in real time on the terminal system, and the CRITIC method is used to assess the tower's operational risks. Step 5: Based on the evaluation results, obtain tower reinforcement technical measures using a multi-objective global optimization method.

[0006] Furthermore, the strength verification in step three adopts the fourth strength theory, using von Mises stress to verify the strength and stability of the tower. The strength judgment condition calculation expression is as follows:

[0007] In the formula: , , These are the principal stresses in three directions; The equivalent stress according to the fourth strength theory; This represents the allowable stress of the material.

[0008] Furthermore, the modal analysis in step three specifically includes: Neglecting damping, the equations of motion for the structural system simplify to: ; Let {x} = {u} cos (ωt), where, For the nodal acceleration vector, Let {u} be the nodal displacement vector; both {u} and ω are unknowns and Substituting into the above equation, we get:

[0009] Where ω is the natural frequency of the structure, ω 2 These are its corresponding eigenvalues, and {u}, as the characteristic vector, mainly represents the selected mode shape in modal analysis. formula The necessary and sufficient condition for a solution to have a non-zero solution is: There are n roots ω1, ω2 ω n , will ω i Substituting into the above equation in sequence, we get:

[0010] in The structural mass matrix, This is the overall stiffness matrix.

[0011] Furthermore, the damage evolution analysis in step three uses Lemaitre's damage evolution law to describe the plastic damage behavior of the 66kV transmission tower. The evolution law of the damage variable D is as follows:

[0012] in, For the rate of evolution of damage variables, Let P be the damage dissipation potential function, P be the cumulative plastic strain, and Y be the damage energy dissipation rate. For cumulative plastic strain rate; for generalized force dual to damage variable D;

[0013] in Here, E represents the Cauchy stress tensor component, and E represents the elastic modulus. σ is the Poisson's ratio of the material; σ is the Cauchy stress; σ H σ is the first invariant of the mean stress, i.e., the stress tensor. eq Von Mises equivalent stress: ;R υ It is a triaxial stress function, expressed as: ,and It is the equivalent stress after damage; The structural damage dissipation of a 66kV transmission tower can be expressed by the potential function as follows:

[0014] Where S0 is a material constant related to the damage energy dissipation intensity; The criteria for the onset of structural damage in 66kV transmission towers are as follows:

[0015] Where k0 is the plastic deformation threshold value required for damage, when the accumulated plastic strain reaches k0 and At that time, the damage begins to evolve, which can be further simplified to: .

[0016] Furthermore, the mechanical and physical model in step two is established using the finite element method. When a static wind load is applied, the static wind load acting on the transmission tower is calculated using the following formula:

[0017] in, This represents the standard value of wind load on the tower. This is the component shape coefficient. This is the wind pressure height variation coefficient. This is the wind load increase factor after the component is covered with ice. The calculated value is the projected area of ​​the component subjected to wind pressure. This is the adjustment factor for wind load on the tower. This is the benchmark wind pressure standard value.

[0018] Furthermore, the reference wind pressure standard value Determine using the following formula:

[0019] V represents the wind speed at a reference height of 10m.

[0020] Furthermore, the strength check in step three also includes calculating the slenderness ratio of the member and the strength stress of the main bending member. The slenderness ratio of the member is calculated using the following formula:

[0021] in, Where r is the component length and r is the component's radius of gyration. It is permissible to use the length-to-slenderness ratio; The formula for calculating the strength stress of the main member under bending is as follows:

[0022] Where N is the tensile or compressive force (N) within the calculated component segment range; A n The net cross-sectional area of ​​the component (mm²) 2 ); m is the component strength reduction factor; M x M y W represents the bending moments about the x-axis and y-axis at the same cross-section; x W y The section modulus is given about the x-axis and y-axis.

[0023] Furthermore, the strength check in step three also includes the stability calculation of the main material in the bending moment plane, and the calculation formula is as follows:

[0024]

[0025] in, m is the stability coefficient of an axially compressed member. N The coefficient for reducing the stability strength of the compression member is given by: A, E, M, and W. The gross cross-sectional area of ​​the member is given by: M, N × m; N, W, and W. The modulus of elasticity of the cross-section where the bending moment occurs. EX Let λ be a parameter, where λ is a parameter. x Let be the slenderness ratio of the component about the x-axis.

[0026] Furthermore, in step two, when establishing the mechanical physical model, a consistent multi-scale model is adopted, and the interface coupling between different scale models is achieved using constraint equations, which are expressed as follows:

[0027] Where U(I) is the term of degree of freedom; Coefficient(I) is the coefficient of the degree of freedom term U(I); and n is the number of the term in the equation.

[0028] Furthermore, the multi-objective global optimization method in step five adopts the filling function algorithm and transforms the multi-objective problem into a single-objective problem by scalarizing the multi-objective problem, so as to obtain the reinforcement technology measures for 66kV towers.

[0029] The beneficial effects of this invention are as follows: 1. This invention provides a method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers, offering significant technical advantages. Firstly, this method establishes a refined mechanical-physical model based on data-driven principles and finite element theory by measuring the mechanical properties of connection nodes, corroded tower materials, aged tower materials, and bolts in the field, combined with field data such as wind speed, air temperature, strain, and tilt. Compared to traditional methods, this model fully considers the actual material properties of weak components such as aged and corroded structures and the characteristics of node loosening, significantly improving the model's computational accuracy and engineering applicability. Based on this model, it is possible to accurately identify the strength failure, modal characteristics, and damage evolution patterns of the tower under different operating conditions such as strong winds and icing, providing a reliable theoretical basis and technical support for revealing the failure mechanism of 66kV transmission towers.

[0030] 2. This invention enables dynamic assessment and visualization of the operational risks of 66kV transmission towers. Utilizing the established mechanical-physical model and a terminal system, it can simulate and display the stress state of various parts of the tower in real time, and employs the CRITIC objective weighting method to quantitatively assess the tower's operational risks. This method effectively extracts information about the tower's structural state by analyzing the comparative strength of different assessment schemes within the same indicator and the correlation between indicators, solving the problems of information redundancy and strong subjectivity in traditional methods. Maintenance personnel can intuitively grasp the tower's health status and real-time risk level through the terminal system, significantly improving the efficiency and intelligence level of transmission line operation and maintenance, and providing an efficient decision support tool for timely detection of safety hazards and prevention of tower collapse accidents.

[0031] 3. This invention also proposes a tower reinforcement technology based on a multi-objective global optimization method. Based on the risk assessment results, a filling function algorithm is used, and scalarization is applied to transform the multi-objective optimization problem into a single-objective problem, thereby obtaining the globally optimal reinforcement scheme. This method overcomes the limitations of traditional reinforcement measures that only target locally weak components. It can scientifically and rationally formulate a comprehensive reinforcement strategy from the overall perspective of the tower foundation, tower legs, tower body, and tower head, including angle steel cladding, adding prestressed cables, parallel components, and bolt hole reinforcement. Using the reinforcement measures proposed in this invention can significantly improve the structural safety and stability of 66kV transmission towers under extreme weather conditions, effectively extend the service life of aging towers, and reduce the total life-cycle operation and maintenance costs, thus having significant engineering application value for ensuring the safe and stable operation of the power grid. Attached Figure Description

[0032] Figure 1 This is a flowchart of the modal analysis of the 66kV transmission tower of the present invention; Figure 2 This is the overall technical approach of the present invention; Figure 3 This is a diagram illustrating the automated algorithm for the tower model of the present invention; Figure 4 This is a schematic diagram of the equilateral angle steel of the present invention; Figure 5 This is a diagram showing the connection between different scale models of the present invention; Figure 6 This is a diagram of the 66kV transmission tower operation status assessment project of this invention. Detailed Implementation

[0033] Current research on the safety and stability of 66kV transmission towers, both domestically and internationally, mainly focuses on using image recognition and vibration acceleration monitoring to conduct condition monitoring. While a considerable amount of monitoring data has been obtained, the analysis and processing of this data are insufficient. There is a lack of in-depth research into the precise mapping relationship between state parameters such as tower acceleration, dynamic strain, and image information and the load-bearing capacity of various structural components of the tower. The understanding of the tower failure mechanism is inadequate, and the risk to safe tower operation cannot be monitored in real time. Furthermore, the scientific validity, rationality, and effectiveness of existing reinforcement technologies for addressing safety hazards in towers still need improvement. Therefore, this invention proposes a study on the failure mechanism and reinforcement technologies of 66kV transmission towers, providing technical support for improving the safety and stability of tower structures.

[0034] The finite element method (FEM) is a modern computational method that has rapidly developed with the advancement of electronic computers. This invention uses this method to model and calculate the mechanical properties of a 66kV transmission tower, thereby understanding the failure mechanism and damage patterns of the tower. The FEM divides the closed field containing the continuous function represented by partial differential equations into finite small regions. Each small region is replaced by a selected approximate function, thus discretizing the function across the entire field. This yields a set of approximate algebraic equations. By simultaneously solving these equations, the approximate value of the function in the field is obtained. The finer the region division, the more accurate the calculation results.

[0035] The mechanical property analysis process of a 66kV transmission tower based on ANSYS software includes preprocessing, load application and solution, and postprocessing. The main task of preprocessing is to establish a finite element model of the 66kV transmission tower using the software's preprocessing module. This is the beginning of the analysis and includes six basic steps: analysis preparation, setting element type, setting real constants, defining material properties, model creation, and element mesh generation. The main task of load application and solution is to perform calculations on the 66kV transmission tower using the software's analysis and calculation module. The steps include applying load conditions, applying boundary conditions, and solving. The main task of postprocessing is to analyze the data and graphics obtained from the mechanical calculations of the 66kV transmission tower using the software's postprocessing module, such as deformation, stress, internal forces, and reactions. It displays iso-displacement diagrams, iso-stress diagrams, etc., in various ways through a graphical interface.

[0036] During the operation of 66kV transmission towers, the towers may experience structural failure due to excessive local stress caused by the combined effects of various external loads and internal stresses. Therefore, it is necessary to analyze the stress and deformation under various conditions to ensure sufficient strength and safety. The failure modes of materials can generally be classified into two types: brittle fracture and plastic yielding. Most transmission towers are made of steel, which exhibits plastic yielding upon failure. Currently, strength theories can be broadly categorized into four types: maximum tensile stress theory, maximum tensile strain theory, maximum shear stress theory, and distortion energy density theory. Among these, the maximum tensile stress and tensile strain theories are less commonly used in practical engineering because their experimental results do not meet the requirements of most material properties. However, the maximum shear stress and distortion energy density theories are consistent with experimental results for most plastic materials. Therefore, this invention utilizes these theories to conduct a mechanical analysis of 66kV transmission towers.

[0037] 66kV transmission towers have a large number of members, and the structural relationships between these members are complex. Furthermore, the nodes are rigidly connected, meaning the members experience combined stresses in multiple directions. The stress at a structural point cannot be fully represented by the conventional unidirectional stress. To accurately characterize the tower's stress state, the von Mises stress method is used to check its strength and stability. This stress method equates the stress on a material under complex conditions to stress under a unidirectional state. It follows the fourth strength theory of materials mechanics, namely the distortion energy density theory. This theory states that regardless of the stress state, yielding is primarily caused by distortion energy density, and that yielding failure occurs when the distortion energy density at the critical point reaches the distortion energy density required for unidirectional tensile yielding. Based on the fourth strength theory, the strength judgment conditions for the tower and its mast are calculated as follows: (1) In the formula: , , These are the principal stresses in three directions; The equivalent stress according to the fourth strength theory; This represents the allowable stress of the material.

[0038] To analyze the dynamic characteristics of a 66kV transmission tower, modal analysis is required, mainly including natural frequencies and corresponding mode shape analysis. This invention employs the finite element method for modal analysis, and seven modal extraction methods are used: Block Lanczos method, Subspace iteration method, PowerDynamic method, Unsymmetric method, Reduced method or condensed method, Damping method, and QR damping method.

[0039] Block Lanczos: This method uses a set of eigenvectors to iteratively calculate the Lanczos algorithm. Its internal program enforces the use of a sparse matrix direct solver (SPARSE), making it suitable for solving symmetric and asymmetric matrices, especially for nonlinear analysis of nondeterministic matrices. This method offers high accuracy and speed, particularly when the system's frequency range is known. By specifying the frequency range, this method can provide a fast and accurate solution, with the solution speed being the same for both high and low frequencies, saving significant time.

[0040] Subspace Iteration Method: The default solver for this method is the Jacobian Conjugate Gradient (JCG) method. This method uses the complete [M] and [K] matrices for iterative solution and is suitable for solving symmetric, asymmetric, complex, deterministic, and non-deterministic matrices. It can be used in static, modal, and transient analyses. The computational accuracy is the same as the block Lanczos method, but the speed is relatively slower. This method is suitable for situations where the master degrees of freedom cannot be selected, especially for solving eigenvalues ​​of large symmetric matrices.

[0041] Power Dynamics: This method uses a lumped mass matrix and is often used to solve larger models (more than 100,000 degrees of freedom). It is mainly used to understand the mode shape of a structure by solving a few modes.

[0042] Unsymmetric method: Similar to the subspace iterative method, this method uses the global matrix for iterative solution and employs the Lanczos algorithm. If the system is non-conservative, this method can obtain complex eigenvalues ​​and complex eigenvectors. This method is mainly used in acoustic or fluid-structure interaction analysis.

[0043] Reduced methods, also known as condensed methods, calculate the eigenvalues ​​and eigenvectors of the iterative matrix using the system's master degrees of freedom. This method can generate an accurate [K] matrix, but only an approximate [M] matrix, leading to some quality loss during iteration. Therefore, although this method is fast, its accuracy is lower than that of the block Lanczos method or the subspace iteration method. The accuracy of its calculation results is affected by the number and location of the selected master degrees of freedom.

[0044] Damping method: In structural engineering, the effect of damping must be considered. The damping method is mainly used to solve problems where the damping cannot be ignored, such as rotor dynamics problems. This method uses the Lanczos algorithm and can obtain complex eigenvalues ​​and complex eigenvectors. However, the calculation speed is relatively slow and may miss high-end frequencies.

[0045] QR Damping Method: This method employs both the Hessenberg algorithm and the Lanczos algorithm. It can effectively extract modal solutions for highly damped systems. When using this method, a sufficient number of fundamental frequency modes should be extracted to ensure the accuracy of the calculation results. This method is suitable for solving proportionally damped and non-proportionally damped systems, but not for critically damped or overdamped systems.

[0046] Modal analysis of 66kV transmission towers essentially involves solving for their eigenvalues ​​and eigenvectors. According to the structural mechanics of transmission towers, the equations of motion for the structural system are: (2) Where [M], [C], and [K] are the structural mass matrix, damping matrix, and overall stiffness matrix, respectively; {F(t)} is the external load vector; {x}, , Let be the displacement, velocity, and acceleration vectors of the nodes, respectively. When the structure is not subjected to external forces and damping is neglected, the above equation simplifies to: (3) Let {x} = {u}cos(ωt), where {u} and ω are both unknowns and Substituting into the above equation, we get: (4) Where ω is the natural frequency of the structure, ω 2 It is its corresponding eigenvalue, and {u}, as the characteristic vector, is mainly represented by the selected mode shape in the modal analysis process.

[0047] The necessary and sufficient condition for formula (4) to have a nonzero solution is: There are n roots ω1, ω2, ω n , will ω i Substituting into the above equation in sequence, we get: (5) The eigenvalues ​​ω that satisfy the above equation i and the corresponding non-zero eigenvector solution {u i} represents the natural frequency and mode shape of the 66kV transmission tower structure, respectively.

[0048] This invention proposes to use ANSYS finite element analysis software to perform modal analysis on 66kV transmission towers. The software can perform modal analysis on undamped and damped 66kV transmission tower structures, as well as prestressed modal analysis. The modal analysis must specify the elastic modulus (or some form of stiffness) and material density of the 66kV transmission tower structure to provide the stiffness and mass required for the structural analysis. For the 66kV transmission tower studied in this invention, modal analysis of an undamped structure is adopted.

[0049] The damage evolution of a 66kV transmission tower structure is an irreversible process of energy dissipation, accompanied by the conversion of heat and mechanical energy. From a thermodynamic perspective, the damage variable of the transmission tower structure is a change from one internal state variable to another, which must satisfy the basic laws of thermodynamics: 1) The first law of thermodynamics, the law of conservation of energy, which is the conservation property in the process of energy transfer and transformation in all thermodynamic systems; 2) The second law of thermodynamics, which gives the directionality of energy transfer and transformation in all thermodynamic systems. For damage, it is accompanied by energy dissipation and is an irreversible thermodynamic process.

[0050] For 66kV transmission tower metal materials, under load, the connecting components in the high stress zone will undergo plastic deformation accompanied by damage evolution, i.e., ductile damage of the material. This paper adopts the Lemaitre damage evolution law to describe the plastic damage behavior of 66kV transmission towers. The Lemaitre model is a material damage model established within a thermodynamic framework, which is suitable for describing the damage evolution of tough materials such as metals in 66kV transmission towers during plastic deformation.

[0051] The evolution law of damage variable D during the plastic evolution of 66kV transmission towers can be written as the partial derivative of the damage dissipation potential function with respect to the damage energy dissipation rate: (6) in, Y is the cumulative plastic strain rate; Y is the damage energy dissipation rate (the generalized force dual to the damage variable D).

[0052] (7) Where E is the elastic modulus; υ is the Poisson's ratio of the material; σ is the Cauchy stress; σ H σ is the first invariant of the mean stress, i.e., the stress tensor. eq Von Mises equivalent stress: ;R υ It is a triaxial stress function, expressed as: ,and It is the equivalent stress after damage.

[0053] The structural damage dissipation of a 66kV transmission tower can be expressed by the potential function as follows: (8) Where S0 is a material constant related to the damage energy dissipation intensity.

[0054] The criteria for the onset of structural damage in 66kV transmission towers are as follows: (9) Where k0 is the plastic deformation threshold value required for damage, when the accumulated plastic strain reaches k0 and At that time, the damage begins to evolve, which can be further simplified to: (10) According to the Prandtl-Reuss flow law, the total strain in the plastic stage of a 66kV transmission tower is considered to be the superposition of elastic strain and plastic stage strain. In the elastic stage, the strain still obeys the generalized Hooke law, while the strain in the plastic part is determined by the deviatoric stress tensor in an incremental form.

[0055] (11) Among them, ε, ε e ε p These are the strain, elastic strain, and plastic strain tensors, respectively.

[0056] Based on the structural strain equivalence principle of 66kV transmission towers, the tower damage material (D...) 0) The strain generated under effective stress is equivalent to the strain occurring when the same material is undamaged (D = 0). In the plastic stage of a 66kV transmission tower, the plastic damage constitutive equation of the material is: (12) Among them, D e This is the elastic stress-strain matrix.

[0057] This invention proposes to use the CRITIC method to assess the risk of 66kV transmission towers. The CRITIC method is an objective weighting method. Its basic idea is to establish the objective weights of different indicators based on the comparative strength between different assessment schemes within the same indicator and the correlation or conflict between assessment indicators. The comparative strength of different assessment schemes is represented by the standard deviation; the larger the standard deviation, the greater the difference in values ​​between the schemes. The correlation or conflict between assessment indicators is determined by correlation analysis; if the correlation coefficient between two indicators is large, the information content conflict between the two indicators is low. Therefore, the CRITIC method can reflect the correlation and variability among 66kV transmission tower data, effectively extracting information from the indicators and solving the information redundancy problem caused by the correlation between different indicators. For the same 66kV transmission tower material, the larger the standard deviation of its stress response change, the greater the amount of information about the tower's structural state. For different tower materials of the same tower, there must be a certain correlation between the mechanical responses of similar main members, and the greater the spatial distance, the smaller the correlation. Therefore, as indicators, they are more conflicting, and increasing their weight can retain more information about the tower material's state.

[0058] The reliability of 66kV transmission towers mainly depends on the reliability of the tower materials with the highest utilization rate. The utilization rate of these materials is related to their bending condition and stress level. Therefore, by analyzing various indicators of the tower materials under wind conditions and comprehensively considering the impact of different materials on the tower's condition, the wind-induced condition and risks of the monitored towers can be assessed. Example

[0059] The overall technical approach of this invention is as follows: Figure 2 As shown. Compared with existing research, the innovation of the technical approach of this invention lies in: (1) Traditional methods do not utilize the actual characteristic data of transmission towers, that is, they do not consider the real characteristics of weak components such as old and corroded materials and loose connection nodes, and usually do not measure the field data such as wind speed, temperature, strain, and tilt of the tower, resulting in low accuracy of the proposed tower model and difficulty in obtaining the failure mechanism of transmission towers under different operating conditions such as strong winds and icing. This invention aims to establish a refined mechanical and physical model of 66kV transmission towers based on data-driven and finite element theory by measuring the material characteristics of weak components such as old and corroded materials and the loose characteristics of connection nodes, and based on the field data such as wind speed, temperature, strain, and tilt measured by existing 66kV transmission line monitoring devices, so as to accurately characterize the characteristics of 66kV transmission towers under different operating conditions such as strong winds and icing, thereby providing support for the derivation of the failure mechanism of 66kV transmission towers.

[0060] (2) Existing research has not proposed a real-time operation status characterization system and risk assessment system for transmission towers serving the operation and maintenance of transmission lines. However, this invention intends to use the proposed 66kV transmission tower mechanical and physical model based on data-driven and finite element theory to simulate and display the precise stress state of each part of the 66kV transmission tower in real time in the terminal system. Then, the operation risk of the 66kV transmission tower can be assessed in real time in the terminal system, laying a theoretical and technical foundation for the transmission line operation and maintenance department to monitor the status of the 66kV transmission tower and ensure its safe operation.

[0061] (3) Traditional reinforcement measures for transmission towers generally target only the weak components that have been identified, without proposing more scientific and reasonable global reinforcement measures from a holistic perspective. Consequently, it is difficult to ensure the safety of transmission towers under different operating conditions such as strong winds and icing. This invention aims to use a multi-objective non-dominated genetic algorithm to globally optimize 66kV transmission towers under different conditions based on the proposed 66kV transmission tower health visualization and operational risk quantification system. This will ensure that the tower foundation, tower legs, tower body, and tower head all meet the strength safety requirements, thereby proposing more reliable and reasonable reinforcement measures to achieve safe and stable operation of 66kV transmission towers under different operating conditions such as strong winds and icing.

[0062] In the analysis of 66kV transmission towers based on structural stability theory, this invention establishes an accurate analytical model of the 66kV transmission tower using the finite element analysis method, following the four steps below: ① A mechanical testing machine with a maximum loading capacity greater than or equal to 250kN was selected to measure the mechanical properties of transmission tower connection nodes, corroded tower materials, old tower materials, and bolts, including elastic modulus, allowable stress, bending resistance, and shear capacity. This provides accurate material property parameters for the construction of the transmission tower model and ensures the accuracy of the calculation results. Based on the structural drawings of the transmission tower, the spatial position equations of the main materials along the straight line were calculated, the spatial heights of key points within each tower section were listed, and the material properties and geometric sections of each member were listed and defined. ② Utilize the spatial linear equation of the main material and the spatial height of relevant key points, and leverage the symmetry of the structure itself to establish each key point, so that as the height increases, the key point numbering increases continuously and regularly; for the crossbeam members, generate key points separately according to the drawings to establish the model. ③ Leveraging the advantages of APDL parametric modeling, key points for section positioning are defined through parameter control, arrays, and loop statements. The key points of the members are connected by referencing their positions, and relevant attributes are assigned and meshes are generated, making the spatial position of the angle steel more consistent with reality. ④ Adjust the degrees of freedom of some structures according to the drawings, including releasing degrees of freedom and adding constraints; apply constraints to the tower legs to the numerical model to complete the preprocessing.

[0063] The flowchart of the finite element modeling algorithm used in this invention is as follows: Figure 3 As shown, h is the baseline tower height, hc is the subsequent design tower height, lc is the member control parameter, and kc is the key point control parameter. The initial values ​​of control parameters lc and kc are both 0. The values ​​are adjusted during the modeling process by varying the h and hc parameters of the tower structure, so that the key point numbering shows a continuously increasing pattern, which facilitates the later establishment of members and unit division.

[0064] Following the above modeling process, by controlling the relevant parameters, it is possible to flexibly establish structural models of different types of high-altitude transmission towers, which have good portability and convenience. Furthermore, for complex structural models, the APDL language is more suitable for model adjustment and analysis, so as to facilitate further in-depth research on the structure.

[0065] As a tall, outdoor building system, transmission tower structures are subjected to complex external loads. Based on the nature of the loads, they can be categorized into accidental loads, variable loads, and permanent loads. Seismic loads, line break loads, and installation loads are considered accidental loads; wind loads and icing loads are considered variable loads; and the self-weight of the tower components, conductors, ground wires, hardware, and insulators constitutes a permanent load. Due to the combined effects of various loads and localized extreme weather conditions, tower collapse accidents exhibit a certain degree of diversity.

[0066] The application of static wind load on 66kV transmission towers is mainly divided into two parts: 1) the wind load acting on the transmission line, which can be calculated according to the specifications and applied to the conductor and ground wire suspension points of the crossarm; 2) the wind load acting on the tower members, which can be calculated in sections according to the specifications based on the maximum wind speed in the area where the transmission tower is located and applied to the transmission tower.

[0067] According to DL / T5154-2012 "Technical Specification for Design of Overhead Transmission Line Towers", the wind load on transmission lines is calculated using the following formula: (13) (14) Among them, W x Standard value of horizontal wind load perpendicular to the conductor and ground wire (kN); α is the wind pressure non-uniformity coefficient; W0 is the standard value of reference wind pressure (kN / m). 2 ), determined according to formula (13); V is the wind speed at a reference height of 10m; μ z The wind pressure height variation coefficient; μ sc For conductors or ground wires: μ should be used when the wire diameter is less than 17.0 mm or when icy (regardless of wire diameter). sc All are 1.2, wire diameter is greater than or equal to 1.7 mm, μsc It should be 1.1; β c For 500kV and 750kV line conductors and ground wires, the wind load adjustment factor is β; for 110kV lines, β is... c Calculate using 1.0; For conductors or ground wires, the outer diameter or the calculated radius when icing occurs is used. For split conductors, the sum of the outer diameters of all sub-conductors (m) is used. p θ is the horizontal span of the tower (m); B1 is the wind load amplification factor for ice accumulation on conductors, ground wires and insulator strings, which is 1.1, 1.2, 1.3 and 1.5~2.0 for ice areas of 5.0mm, 10.0mm, 15.0mm and 20.0mm and above, respectively; θ is the angle (°) between the wind direction and the direction of the conductor or ground wire.

[0068] According to the provisions of DL / T 5154-2012 "Technical Specification for Design of Overhead Transmission Line Towers", the static wind load acting on the transmission tower is calculated according to formula (15): (15) Among them: W s The standard value of wind load on the tower (kN); μ s The component shape coefficient is calculated as 1.31 + η, where η is the load reduction coefficient on the leeward side of the tower; B2 is the wind load increase coefficient after icing, with 1.1 for 5.0mm icing, 1.2 for 10.0mm icing, 1.6 for 15.0mm icing, 1.8 for 20.0mm icing, and 2.0~2.5 for icing above 20.0mm; A s The calculated wind pressure projection area of ​​the component is given without considering the inclination of the tower's windward side. Using the fill factor φ = As / A (the ratio of the component's wind pressure projection area As to its outline area A), the windward area As is obtained by multiplying the fill factor by the outline area. Based on practical engineering experience, the tower head area has a denser component arrangement, so a value of 0.3 is used for calculation, while the tower body area has a sparser arrangement, generally using a value of 0.2. β z For tower wind load adjustment coefficients, when the total height of the structure does not exceed 60m, the same coefficient is applied to the structural height.

[0069] According to the current design specifications DL / T5154-2012 "Technical Specifications for Design of Overhead Transmission Line Tower Structures", GB50545-2010 "Design Specifications for 110kV~750kV Overhead Transmission Lines", and GB50017-2020 "Code for Design of Steel Structures", when the transmission tower structure is subjected to external loads, the main members mainly bear the combined action of axial pressure and bending moment. These members may have insufficient local stiffness, strength, and instability, which may lead to the failure of the transmission tower structure. Therefore, structural bearing capacity analysis is required.

[0070] The design specification for transmission towers, DL / T5154-2012 "Technical Regulations for Structural Design of Overhead Transmission Line Towers", adopts the method of limiting the slenderness ratio of components to ensure the stiffness of the components. The slenderness ratio of the components is calculated according to the following formula. (16) Where l0 is the component length and r is the component's radius of gyration. It is possible to use the ratio of length to slenderness.

[0071] The formula for calculating the strength stress of the main member under bending is as follows: (17) Where N is the tensile or compressive force (N) within the calculated component segment range; A n The net cross-sectional area of ​​the component (mm²) 2 ); m is the strength reduction factor for the member, taken as 0.85 for tension members and 0.70 for compression members; M x M y W represents the bending moments about the x-axis and y-axis at the same cross-section; x W y The section modulus is given about the x-axis and y-axis.

[0072] The formula for calculating the stability of the main material in the bending moment plane is: (18) (19) Where φ is the stability coefficient of the axially compressed member; m N is the reduction factor for the stability strength of the compression member; A is the gross cross-sectional area of ​​the member; M is the maximum bending moment (N×m) within the calculated member segment; W is the section modulus of the section where the bending moment occurs; N EX Let λ be a parameter, where λ is a parameter. x Let x be the slenderness ratio of the component about the x-axis. A schematic diagram of an equilateral angle steel is shown below. Figure 4 As shown, B is the side width and t is the side thickness.

[0073] For 66kV transmission towers, vibration instability is more likely to occur under dynamic external load excitation. Modal analysis is the basis of dynamic characteristic analysis. The research object of this invention is 66kV transmission towers. The influence of the connection form between the transmission tower and the conductor is ignored. The results of modal analysis are independent of external load and only related to the structure itself. The purpose of structural dynamic characteristic analysis is mainly to find the weak links in the structure itself and provide a certain reference for subsequent structural reinforcement.

[0074] To develop a risk assessment method for the operational status of 66kV transmission towers, it is necessary to understand the performance degradation mechanism and the evolution trajectory of the state characteristic vector throughout the entire life cycle. This invention establishes a consistent multi-scale model of the 66kV transmission tower structure and performs performance degradation and damage analysis throughout its entire life cycle to understand its performance decay law. A data-physical fusion time series prediction model for the tower's operational status is then established, leading to the development of a tower risk assessment system. This system enables real-time profiling and visualization of the tower's health status, accurately quantifying and assessing the operational risk of the tower. Compared to traditional single-scale models, the multi-scale approach considers not only the macroscopic performance of the structure but also local model information, more accurately determining the boundary conditions of the local model. Furthermore, it considers the synergistic effect of both during the analysis of the tower's service life, accurately achieving damage identification and simulation of the failure process of transmission tower materials.

[0075] Multi-scale modeling and damage analysis of transmission tower structures. In the simulation of multi-scale interface connections in transmission towers, the key is to consider the connections between various elements and the interface connections between models of different scales, i.e., the coupling between different scales. Interface coupling problems may involve connections between elements of different dimensions, such as beam elements and solid elements, shell elements and solid elements, etc. Different element models use different mechanical simplifications and assumptions, so appropriate connection methods need to be adopted between models of different precision to ensure that the force balance and deformation coordination of different types of elements on both sides of the interface are achieved without changing them, while avoiding excessive constraints on the model. When different types of elements have the same degree of freedom, shared nodes can be used to achieve connection; when different types of elements have different degrees of freedom, constraint equations need to be established to ensure the coordination of displacement and rotation between nodes. Connections between models of different scales are as follows: Figure 5 As shown.

[0076] Typically, the constraint equations for interface coupling are expressed as follows: (20) Where U(I) is the term of degree of freedom; Coefficient(I) is the coefficient of the degree of freedom term U(I); and n is the number of the term in the equation.

[0077] After the overall beam element model and the local microscopic solid model of the power transmission tower structure are established, the two are coupled into a multi-scale model using the interface coupling method. In ANSYS software, there are various ways to connect beam elements and solid elements across scales.

[0078] ① Interface constraint equation method Based on the connection characteristics of the nodes, the relationship between the degrees of freedom of the beam element nodes and the solid element nodes is established, namely the rotational degrees of freedom and displacement degrees of freedom of the nodes. For three-dimensional elements, six constraint equations are required.

[0079] ② Pseudo-beam method The pseudo-beam method involves creating "false beam elements" and inserting them into solid elements for a certain length. This length must span one solid element, meaning the pseudo-beam element should be connected to at least two nodes of the solid element. The bending stiffness of the pseudo-beam can be set to infinity or approximately 1E4 times the stiffness of the actual beam element.

[0080] ③ MPC184 method This method utilizes the ANSYS MPC184 element, which can be configured as a rigid rod, rigid beam, spherical constraint, universal joint, rotary hinge, and other motion joints. When the MPC184 element is used as a rigid beam, the geometric entity and the beam line share key points, forming an effect similar to the "rigid arm" in structural mechanics.

[0081] ④ Rigid Domain Method This method generates rigid lines by selecting master and slave nodes and applying constraint equations. Rigid lines with common nodes are then connected to form rigid surfaces or rigid bodies. The use of rigid domains eliminates the need for shared relationships between nodes, making it widely applicable.

[0082] By using a consistent multi-scale model and damage analysis of 66kV transmission tower structures, the performance degradation and damage patterns throughout the entire life cycle were obtained. A data-physical fusion time-series prediction model for tower operation status and a method for assessing tower operation status and risk were established. Furthermore, a transmission tower risk assessment system was developed to accurately quantify and assess tower operation risk. The invention for 66kV transmission tower operation status assessment is as follows: Figure 6 As shown.

[0083] In summary, based on the failure mechanism and operational risk assessment results of 66kV transmission towers, this invention proposes technical measures for tower reinforcement using a multi-objective global optimization method. Current global optimization methods mainly include gradient-based deterministic global optimization algorithms and intuitive or empirical stochastic global optimization algorithms. Deterministic global optimization algorithms include Filled Function Algorithms and Tunneling Function Algorithms, while stochastic global optimization algorithms include Genetic Algorithms and Simulated Annealing, etc. The main idea behind using auxiliary functions such as Filled Functions and Tunneling Functions is to minimize the function, moving from the current local minimum to a point with a smaller function value. The Filled Function method was first proposed by Ge Renfu and used to solve for the global minimum of multi-peaked functions; later, Zhang Liansheng and other scholars improved it. The basic idea of ​​the filling function method is to construct a filling function at the current local minimum and minimize it, so that the current point moves from the local minimum of the original objective function to a point smaller than the current objective function value. Compared with other global optimization algorithms, the filling function method has the advantage of being relatively simple in concept and easier to construct, and is also easier to implement and verify numerically. Therefore, this invention uses the filling function method to achieve global optimization of 66kV steel towers. The method of scalarizing multi-objective problems is used to achieve multi-objective optimization of 66kV steel towers. The basic idea is to use appropriate parameters to scalarize the multi-objective problem, transforming it into a single-objective problem. Specifically, this involves optimizing the multi-objective function by summing or multiplying by evaluation coefficients, then transforming it into a single-objective problem, which is then solved using a single-objective problem algorithm. Through the above research, a 66kV steel tower reinforcement technology based on a multi-objective global optimization method is obtained. For special structures of transmission lines, the following three methods are mainly used: 1) Reinforce the original towers; 2) Build new angle steel towers using the original foundations; 3) Build new towers at new sites; 4) Add auxiliary rods to some members to reduce the calculated length of the main material and avoid local instability of the components; 5) Increase the cross-sectional size of the structure and attach and install the reinforcement components by means of bolt drilling, welding and other methods. The reinforcement positions are mostly the tower legs and the middle of the tower body.Specific measures include: using welding technology to cover angle steel with existing main materials to achieve integrated strength enhancement and reinforcement of transmission towers; adopting different reinforcement measures for different parts of the poles and different material forms, such as adding prestressed cables, parallel components, removing bolts and replacing diagonal members, and auxiliary materials; studying the reinforcement method of bolt hole reinforcement of the main material of angle steel towers based on the structural characteristics of angle steel transmission towers, and continuously welding around the reinforcing angle steel to form a closed structure for reinforcement; and for old transmission towers, connecting the reinforcing components to the original support leg components by bolted cross-shaped connectors on the tower legs.

[0084] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for identifying the structural failure mechanism and dynamically assessing the operational risk of a 66kV transmission tower, characterized in that, Includes the following steps: Step 1: Measure the mechanical properties of the connection nodes, corroded tower materials, old tower materials, and bolts of the 66kV transmission tower, including elastic modulus, allowable stress, bending and shear resistance, and collect on-site data on wind speed, temperature, strain, and tilt in the area where the tower is located. Step 2: Based on the field data obtained in Step 1, establish a mechanical and physical model of the 66kV transmission tower based on data-driven and finite element theory. Step 3: Using the aforementioned mechanical and physical model, identify the structural failure mechanism of the tower, including strength verification, modal analysis, and damage evolution analysis; Step four: Using the aforementioned mechanical and physical model, the stress state of each part of the 66kV transmission tower is simulated and displayed in real time on the terminal system, and the CRITIC method is used to assess the tower's operational risks. Step 5: Based on the evaluation results, obtain tower reinforcement technical measures using a multi-objective global optimization method.

2. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The strength verification in step three adopts the fourth strength theory, using von Mises stress to verify the strength and stability of the tower. The formula for calculating the strength judgment condition is as follows: ； In the formula: , , These are the principal stresses in three directions; The equivalent stress according to the fourth strength theory; This represents the allowable stress of the material.

3. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The modal analysis in step three specifically involves: Neglecting damping, the equations of motion for the structural system simplify to: ; Let {x} = {u} cos (ωt), where, For the nodal acceleration vector, Let {u} be the nodal displacement vector; both {u} and ω are unknowns and Substituting into the above equation, we get: ； Where ω is the natural frequency of the structure, ω 2 These are its corresponding eigenvalues, and {u}, as the characteristic vector, is represented by the selected mode shape in the modal analysis process. formula The necessary and sufficient condition for a solution to have a non-zero solution is: There are n roots ω1, ω2 ω n , will ω i Substituting into the above equation in sequence, we get: ； in The structural mass matrix, This is the overall stiffness matrix.

4. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The damage evolution analysis in step three uses Lemaitre's damage evolution law to describe the plastic damage behavior of 66kV transmission towers. The evolution law of damage variable D is as follows: ； in, For the rate of evolution of damage variables, Let P be the damage dissipation potential function, P be the cumulative plastic strain, and Y be the damage energy dissipation rate. For cumulative plastic strain rate; for generalized force dual to damage variable D; ； in Here, E represents the Cauchy stress tensor component, and E represents the elastic modulus. σ is the Poisson's ratio of the material; σ is the Cauchy stress; σ H σ is the first invariant of the mean stress, i.e., the stress tensor. eq Von Mises equivalent stress: ;R υ It is a triaxial stress function, expressed as: ,and It is the equivalent stress after damage; The structural damage dissipation of a 66kV transmission tower can be expressed by the potential function as follows: ； Where S0 is a material constant related to the damage energy dissipation intensity; The criteria for the onset of structural damage in 66kV transmission towers are as follows: ； Where k0 is the plastic deformation threshold value required for damage, when the accumulated plastic strain reaches k0 and At that time, the damage begins to evolve, which simplifies to: 。 5. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The mechanical and physical model in step two is established using the finite element method. When applying static wind load, the static wind load acting on the transmission tower is calculated according to the following formula: ； in, This represents the standard value of wind load on the tower. This is the component shape coefficient. This is the coefficient of wind pressure height variation. This is the wind load increase factor after the component is covered with ice. The calculated value is the projected area of ​​the component subjected to wind pressure. This is the adjustment factor for wind load on the tower. This is the benchmark wind pressure standard value.

6. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The reference wind pressure standard value Determine using the following formula: ； V represents the wind speed at a reference height of 10m.

7. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The strength check in step three also includes calculating the slenderness ratio of the member and the strength stress of the main bending member. The slenderness ratio of the member is calculated using the following formula: ； in, Where r is the component length and r is the component's radius of gyration. It is permissible to use the length-to-slenderness ratio; The formula for calculating the strength stress of the main member under bending is as follows: ； Where N is the tensile or compressive force value within the calculated component segment; A n is the net cross-sectional area of ​​the component; m is the strength reduction factor of the component; M x M y W represents the bending moments about the x-axis and y-axis at the same cross-section; x W y The section modulus is given about the x-axis and y-axis.

8. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The strength check in step three also includes the stability calculation of the main material in the bending moment plane, and the calculation formula is as follows: ； ； in, m is the stability coefficient of an axially compressed member. N The coefficient for reducing the stability strength of the compression member is given by: A is the gross cross-sectional area of ​​the member; E is the modulus of elasticity; M is the maximum bending moment within the calculated member segment; N is the tensile or compressive force within the calculated member segment; W is the section modulus of the section where the bending moment occurs; N EX Let λ be a parameter, where λ is a parameter. x Let be the slenderness ratio of the component about the x-axis.

9. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, In step two, when establishing the mechanical physical model, a consistent multi-scale model is adopted. The interface coupling between models of different scales is achieved using constraint equations, which are expressed as follows: ； Where U(I) is the term of degree of freedom; Coefficient(I) is the coefficient of the degree of freedom term U(I); and n is the number of the term in the equation.

10. The method for identifying the structural failure mechanism and dynamically assessing the operational risk of 66kV transmission towers according to claim 1, characterized in that, The multi-objective global optimization method in step five adopts the filling function algorithm and transforms the multi-objective problem into a single-objective problem by scalarizing the multi-objective problem, so as to obtain the reinforcement technology measures for 66kV towers.

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