A health assessment method for offshore wind turbine jacket based on strain energy equivalence

Abstract

The present application relates to offshore wind turbine jacket structure field, specifically relates to a kind of offshore wind turbine guide pipe frame health assessment method based on strain energy equivalence, including obtaining crack propagation state and local strain energy equivalent degradation data;Strain energy equivalent degradation conversion database is established;Local degradation area is embedded based on strain energy change Whole guide pipe frame model;Divide degradation process;Build evaluation system, obtain corresponding health state according to the score of each health index;Build judgment matrix, obtain static reference weight vector;Establish evaluation model, obtain dynamic weight that changes with structural damage process, degradation stage and environmental condition change, carry out multi-factor comprehensive dynamic evaluation to offshore wind turbine guide pipe frame structure.Local strain energy equivalent degradation, overall structure stress displacement response, inherent frequency change, degradation stage and sea state parameter are uniformly included in health assessment process, and continuous analysis process from local damage to overall health grade and leading risk is established.

Description

Technical Field

[0001] This invention relates to the field of health monitoring, safety assessment and operation and maintenance decision-making technology for offshore wind turbine jacket structures, specifically to a method for health assessment of offshore wind turbine jacket structures based on strain energy equivalence. Background Technology

[0002] The jacket-type support structure, composed of main pipes, diagonal braces, cross braces, and numerous welded pipe joints, features high overall rigidity, a clear load-bearing path, and a wide applicable water depth range, making it a commonly used foundation structure for medium-deep-water offshore wind turbines. Under the combined effects of long-term wind, wave, current, and turbine operating loads, stress concentration easily occurs at weld toes, pipe joint intersections, and geometric abrupt changes, gradually leading to fatigue cracks. The continued propagation of these cracks weakens the rigidity and load-bearing capacity of local pipe joints, alters the load transfer path between adjacent members, and consequently affects the overall jacket's stress, displacement, stability, and operational safety.

[0003] Existing research on cracks at pipe nodes in jacket structures largely focuses on crack propagation paths, stress intensity factors, fatigue life, and prediction of local structural performance degradation. By combining finite element analysis (FEM) software with fracture analysis software, crack states and local performance parameters at different crack lengths can be obtained; surrogate models or regression models can also be used to rapidly predict crack length and local performance parameters. However, these methods typically focus on local pipe nodes, and the resulting crack length, strain energy, or stiffness degradation results are difficult to directly translate into the overall health status and maintenance decisions of the jacket structure.

[0004] If a real crack is directly created in the finite element model of the overall jacket, a high-density mesh needs to be generated for the crack tip region, and repeated calculations are required under multiple crack states and various sea conditions. This can easily lead to a large model size, low computational efficiency, and difficulty in convergence. If the structural state is judged solely based on crack length or the amount of single local stiffness degradation, it is difficult to comprehensively reflect the overall stress redistribution, displacement growth, stability, and resonance risks caused by local damage.

[0005] Furthermore, traditional analytic hierarchy process (AHP) typically employs fixed weights, maintaining the relative importance of each health indicator throughout the assessment. However, the dominant risks to offshore wind turbine jackets shift with crack propagation and sea state changes: in the early stages of crack propagation, fatigue accumulation is predominant; in the middle stages, strength risks gradually become more prominent; and in the later stages, stability and resonance risks may increase rapidly. Fixed-weight methods struggle to track these dynamic changes, easily leading to an underestimation of critical risks in the later stages of damage or under severe sea conditions.

[0006] Therefore, for the health assessment of offshore wind turbine jackets under crack propagation conditions, a method is needed that can characterize the stiffness degradation of local pipe nodes in an equivalent manner using strain energy, map local degradation parameters to the overall jacket model, and dynamically adjust the assessment weights according to the structural damage state, degradation stage, and changes in the marine environment, so as to achieve continuous analysis from local crack propagation and overall structural response to comprehensive health level and dominant risk. Summary of the Invention

[0007] To address the problems in existing technologies, such as the difficulty in directly applying local crack analysis results to overall jacket health assessment, the high computational cost of explicit crack overall models, and the inability of fixed-weight health assessments to reflect risk transfer, the present invention aims to provide a strain energy equivalence-based offshore wind turbine jacket health assessment method. This method uses the equivalent strain energy degradation caused by crack propagation at key pipe nodes as input, constructs a local strain energy equivalent degradation database, maps local degradation information to the overall jacket model, and combines overall structural response, marine environmental parameters, degradation stage sensitivity coefficients, and dynamic weights of multiple indicators to assess health status.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a method for health assessment of offshore wind turbine jackets based on strain energy equivalence, comprising the following steps: Step 1: Obtain crack propagation state and local strain energy equivalent degradation data to form a strain energy equivalent degradation source database, which will serve as the input data source for subsequent overall jacket health assessment; Step 2: Convert local strain energy degradation parameters into global model degradation mapping parameters, establish a strain energy equivalent degradation transformation database, and unify the parameters required for local strain energy degradation, global response sensitivity and health assessment to provide a parameter interface for dynamic health assessment. Step 3: Embed the localized degradation region based on strain energy changes into the overall jacket model, and connect different element types in the overall model using a constraint method that can continuously transmit force, shear force, and bending moment; Step 4: Solve the overall structural response under different crack states, construct the performance degradation sequence, identify the degradation stage, and classify the degradation process according to the rate of structural performance decline and the characteristics of stress and displacement response changes; Step 5: Construct an assessment system that includes five primary health indicators: fatigue, resonance, environment, strength, and stability. Stiffness degradation, frequency clearance, wave parameters, maximum stress, and maximum displacement are used as quantitative parameters for the indicator layer. Based on the scores of each health indicator, the corresponding health status is obtained. Step 6: Construct a judgment matrix for the five indicators using the nine-level scaling method, and perform column normalization and row mean calculation on the judgment matrix to obtain the static benchmark weight vector; Step 7: Establish a stage-damage-environment coupled dynamic variable weight assessment model, and obtain normalized dynamic weights for comprehensive assessment after normalization. By repeating the process at each crack propagation increment step, obtain dynamic weights that change with the structural damage process, degradation stage and environmental conditions. Perform multi-factor comprehensive dynamic assessment of offshore wind turbine jacket structures under crack propagation.

[0009] The above-mentioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, step 1 includes: Step 1-1: Select the key KK pipe node or other welded pipe node in the offshore wind turbine jacket structure as the research object of local performance degradation, and obtain the crack location, crack length, crack propagation cycle number and local structural response data in the crack-free state and multiple representative crack length states; Steps 1-2: Under the same boundary conditions and load levels, the structural performance of local tube nodes is characterized using the structural equivalent strain energy, based on the crack length as... a Equivalent performance parameters of local strain energy K ( a Structural performance parameters in the crack-free state K 0 yields the local structural stiffness retention coefficient or ( a ) and damage variables D ( a ), , ; Steps 1-3: Based on the results obtained under the discrete crack state K ( a Construct a continuous mapping relationship between crack length and local structural performance degradation, so that the corresponding local stiffness retention coefficient and damage variable can be obtained for any crack length; Steps 1-4: Generate a strain energy equivalent degradation source database by combining crack length, number of cycles, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall maximum stress, overall maximum displacement, and degradation stage labels. This database will serve as the input data source for subsequent overall jacket health assessment.

[0010] The above-mentioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, step 2 includes: Step 2-1: Based on the correspondence between structural stiffness and elastic modulus in elasticity, the strain energy of local pipe nodes is equivalently degraded into changes in equivalent material parameters in local areas. Step 2-2: Based on the principle of equivalence in continuous damage mechanics, the crack length is... a Corresponding damage variables D ( a Convert to the equivalent elastic modulus of the local regionE eff ( a ): ,in, E 0 represents the elastic modulus under healthy conditions; Steps 2-3: Establish a strain energy equivalent degradation transformation database containing crack length, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall response change, and degradation stage label. This database unifies the local strain energy degradation, overall response sensitivity, and parameters required for health assessment, providing a parameter interface for subsequent dynamic health assessment.

[0011] In the above-mentioned method for health assessment of offshore wind turbine jackets based on strain energy equivalence, in step 2-1, the axial stiffness of the axially stressed member can be expressed as: ,in, A For the cross-sectional area, L It is the length; for bending members, their bending stiffness is related to the material's elastic modulus and the moment of inertia of the cross section, expressed as: Where E is the elastic modulus and I is the interfacial moment of inertia.

[0012] The above-mentioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, step 3 includes: Step 3-1: Establish a finite element model of the overall structure of the offshore wind turbine, in which the jacket is represented by beam elements, the tower and deck by shell elements, and the upper rotor, nacelle and other components are equivalent to lumped mass; Step 3-2: In the overall model, determine the local degradation mapping region based on the actual geometric range of the key pipe nodes, the equivalent variable energy density change of the local model, and the unit partitioning of the overall model. Step 3-3: Based on the current crack length, call the local degradation state database and retrieve the elastic modulus of the node degradation region under healthy conditions. E 0 is replaced with the equivalent elastic modulus E eff ( a The material properties, quality properties, and boundary conditions of the remaining areas remain unchanged, forming an overall jacket degradation model corresponding to different crack states; Steps 3-4: Shell-solid coupling constraints are used between the tower shell unit and the top solid mass block, and beam-type multi-point constraints are used between the lower jacket beam unit and the tower shell unit, so that force, shear force and bending moment can be continuously transmitted between different unit types.

[0013] In the aforementioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, in step 3-2, when the strain energy change rate of a local unit or sub-region exceeds a preset threshold, the local unit or sub-region is included in the degradation mapping region. The degradation region is determined jointly by the energy change caused by local damage and the engineering geometric boundary. Where e is the index of a finite element or sub-region in the local pipe node model. This represents the degenerate region in the overall model under the current crack state. This represents the change in energy equivalent to that of a single unit. The equivalent change energy under the no-damage condition, The threshold for determining the degradation region.

[0014] The above-mentioned method for health assessment of offshore wind turbine jackets based on strain energy equivalence, step 4 includes: Step 4-1: Perform modal analysis on the overall jacket degradation model corresponding to each crack state to obtain the structure's natural frequencies and mode shapes. Perform static or dynamic response analysis under marine environmental loads to obtain the maximum equivalent stress at key locations of the structure. s max ( a and the overall maximum displacement u max ( a ); Step 4-2: Sort the equivalent performance parameters of local strain energy, stiffness retention coefficient, maximum stress, maximum displacement and natural frequency gap during crack propagation according to crack length or load cycle number to form a structural performance degradation sequence composed of local degradation and overall response. Step 4-3: Use Savitzky-Golay filtering to smooth the structural performance degradation sequence, reducing the impact of numerical fluctuations and local errors on trend identification; Step 4-4: Using the global optimal piecewise fitting method, the boundary points between the two degradation stages are determined based on the sum of the piecewise fitting errors. The performance degradation of the jacket structure is divided into a safe period, a warning period, and a dangerous period. A direct link is established between the structural degradation stages and the subsequent weight adjustments of health indicators. During the safe period, the structural response changes slowly. During the warning period, the degradation rates of stress, displacement, and stiffness increase significantly. During the dangerous period, the structural response changes drastically and gradually approaches the bearing or stability limit.

[0015] In the aforementioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, step 5 uses fatigue indices to reflect the strain energy equivalence degradation caused by localized cracks, strength and stability indices to reflect the overall model response, and resonance and environmental indices to reflect external sea state excitation. Fatigue index The fatigue health score is used to calibrate the stiffness degradation caused by crack propagation. ,in, K max Represents the equivalent performance parameters of local strain energy K ( a The maximum value in the reference data. K min Represents the equivalent performance parameters of local strain energy K ( a The minimum value in the reference data; Resonance Indicator Where δ represents the first natural frequency of the structure. f s With wave spectrum dominant frequency f w The relative frequency gap between them ; Environmental indicators are assessed through environmental adaptability scoring. S E This indicates that the current significant wave height is used. H s Design reference wave height H d ratio Perform calibration. ; Strength indicators S S The strength health score at the current crack length is used to calibrate the overall structure based on the maximum stress under different crack states. ,in, s min Indicates the reference stress in a good condition. s max Indicates the critical state reference stress; Stable indicators S ST The stability and health score is used to calibrate the overall structure based on the maximum displacement under different crack states. ,in, u min Indicates the reference displacement in the intact state. u ma x This represents the reference displacement for the critical state.

[0016] The above-mentioned method for assessing the health of offshore wind turbine jackets based on strain energy equivalence, step 6 includes: Step 6-1: Construct fatigue using the nine-level scaling method W F Resonance W R ,environment WE ,strength W S and stability W ST The AHP judgment matrix for five indicators, where the matrix elements represent the relative importance between any two indicators; Step 6-2: Perform column normalization and row mean calculation on the judgment matrix to obtain the static benchmark weight vector. W static =[ W F , W R , W E , W S , W ST ] T Calculate the consistency ratio CR , ,in, CI Indicators of consistency , RI This represents the random consistency index. l max This represents the largest eigenvalue, and n represents the order of the judgment matrix; Step 6-3: When CR When the value is less than 0.1, the judgment matrix satisfies the consistency requirement; when... CR When the consistency requirement is not met, consistency optimization is performed using the upper triangular elements of the judgment matrix as optimization variables to obtain a static benchmark weight vector.

[0017] The above-mentioned method for health assessment of offshore wind turbine jackets based on strain energy equivalence, step 7 includes: Step 7-1: Establish a damage-driven dynamic weighted module. For the three indicators of fatigue, strength, and stability, based on the current health score... S i Penalty amplification of its static baseline weights, damage-driven temporary weights Represented as: ,in, The static baseline weights for this indicator are determined using traditional AHP. Indicates the penalty factor. q s Indicates the sensitivity coefficient for the degradation stage; Step 7-2: Establish an environment-driven dynamic weighting module, with temporary weights for environmental indicators. Adjustments based on significant wave height: ,in, Represents the static weights of the environment. Indicates the environmental incentive coefficient. Indicates the characteristic wave height and ratio used in the structural design. The relative severity of the current sea state has been normalized; Step 7-3: Based on frequency deviation d Adjusting the temporary weight of the resonance index ,when d Less than d th When, a quadratic amplification function is used to increase the weight of the resonance index; when d Not less than d th At that time, the resonance index weights remain at a static benchmark value: ,in, Static weights representing the risk of resonance. Indicates the risk incentive coefficient. This indicates a pre-set safety threshold for frequency deviation; Step 7-4: Combine the damage-driven weights and environment-driven weights into a temporary dynamic weight vector. And perform normalization: ,in, i , j Index of five indicators; For the first i Temporary weights; For the first j Temporary weights; For the normalized first i Item dynamic weight; Step 7-5: After normalization, the normalized dynamic weights used for comprehensive evaluation are obtained. By repeating this process at each crack propagation increment step, dynamic weights that change with the structural damage process, degradation stage, and environmental conditions are obtained. Multi-factor comprehensive dynamic evaluation of offshore wind turbine jacket structures under crack propagation is then performed.

[0018] The beneficial effects of this invention's method for health assessment of offshore wind turbine jackets based on strain energy equivalence are as follows: It uniformly characterizes the local performance degradation caused by crack propagation in key pipe nodes using strain energy equivalence, and constructs a database containing crack states, strain energy equivalence degradation parameters, overall response changes, and degradation stage labels, transforming local strain energy degradation results into overall health assessment inputs. By integrating local strain energy equivalence degradation, overall structural stress-displacement response, natural frequency changes, degradation stages, and sea state parameters into the health assessment process, a continuous analysis process from local damage to overall health level and dominant risk is established. Through joint analysis of overall natural frequency, maximum stress, and maximum displacement, the impact of local damage that is difficult to detect in a timely manner relying solely on overall natural frequency is identified. Furthermore, through degradation curve smoothing and globally optimal piecewise fitting, the structural performance evolution is divided into safe periods, warning periods, and dangerous periods, and the stage sensitivity coefficient is directly input into the dynamic weight calculation. Five health indicators—fatigue, resonance, environment, strength, and stability—are constructed, and a stage-damage-environment coupled dynamic weighting mechanism is designed to enable the indicator weights to be automatically adjusted according to crack propagation, degradation stages, and sea state changes. At the same time, it avoids the underestimation of extreme stress, displacement, stiffness, or resonance risks by simple comprehensive scoring, providing a quantitative basis for predictive maintenance and operation and maintenance decisions for offshore wind turbine jackets. Attached Figure Description

[0019] Figure 1 This is the overall process for catheter health assessment based on strain energy equivalence in this embodiment of the invention; Figure 2 This is a multi-unit hybrid modeling strategy for the overall structure of offshore wind turbines in this embodiment of the invention; Figure 3 Comparison of strain energy equivalent natural frequency results of the front guide frame structure in the embodiments of the present invention; Figure 4 This is a comparison of the natural frequency results of the jacket structure after strain energy equivalence in the embodiments of the present invention; Figure 5 This is the analysis result of the jacket under the degraded state at the equivalent degradation point of strain energy in the embodiments of the present invention; Figure 6 This is the analysis result of the duct stent under the degraded state of the duct stent displacement response in the embodiments of the present invention; Figure 7 This is the analysis result of the duct stent stress response under the degraded state in the embodiments of the present invention; Figure 8 This is a three-stage degradation curve of the duct stent structure performance in an embodiment of the present invention; Figure 9 This is the AHP hierarchical structure for the structural health assessment of offshore wind turbine jackets in this embodiment of the invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the following detailed embodiments and appendices are provided. Figure 1 -Appendix Figure 9 The technical solution of the present invention will be described.

[0021] Example 1 like Figure 1 As shown, a method for health assessment of offshore wind turbine jackets based on strain energy equivalence is characterized by the following steps.

[0022] Step 1: Obtain crack propagation state and local strain energy equivalent degradation data to form a strain energy equivalent degradation source database, which serves as the input data source for subsequent overall jacket health assessment.

[0023] Specifically, it includes: S1.1 Select key KK pipe nodes or other welded pipe nodes in the offshore wind turbine jacket structure as the research object of local performance degradation, and obtain crack location, crack length, crack propagation cycle number and local structural response data in the crack-free state and multiple representative crack length states.

[0024] S1.2 Under the same boundary conditions and load levels, the structural performance of local tube nodes is characterized by the structural equivalent strain energy. Let the crack length be... a The equivalent performance parameters of local strain energy are as follows: K ( a The structural performance parameters in the crack-free state are: K If the coefficient is 0, then the local structural stiffness retention coefficient is... or ( a ) and damage variables D ( a They are represented as follows: , .

[0025] S1.3, Based on the results obtained under the discrete crack state K ( a A continuous mapping relationship between crack length and local structural performance degradation is established so that the corresponding local stiffness retention coefficient and damage variable can be obtained for any crack length.

[0026] S1.4. The crack length, number of cycles, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall maximum stress, overall maximum displacement, and degradation stage labels are used to form a strain energy equivalent degradation source database, which serves as the input data source for subsequent overall jacket health assessment.

[0027] Step 2: Convert local strain energy degradation parameters into global model degradation mapping parameters, establish a strain energy equivalent degradation transformation database, and unify the parameters required for local strain energy degradation, global response sensitivity, and health assessment to provide a parameter interface for dynamic health assessment.

[0028] The specific steps include: S2.1. Based on the correspondence between structural stiffness and elastic modulus in elasticity mechanics, the strain energy of local pipe nodes is equivalently degraded into changes in equivalent material parameters in a local region. For axially stressed members, the axial stiffness can be expressed as: In the formula, E is the elastic modulus. A For the cross-sectional area, L It is the length.

[0029] S2.2 For bending members, their bending stiffness is related to the material's elastic modulus and the moment of inertia of the cross section, as expressed as: In the formula, I is the interface moment of inertia, which is related to the cross-sectional shape of the structure.

[0030] S2.3. Based on the principle of equivalence in continuous damage mechanics, the crack length is... a Corresponding damage variables D ( a Convert to the equivalent elastic modulus of the local region E eff ( a ): In the formula, E 0 represents the elastic modulus under healthy conditions. This equivalent elastic modulus is not used to re-describe the local fracture behavior at the crack tip, but rather serves as an equivalent parameter for the locally degraded region in the overall jacket model, used to evaluate the impact of local degradation on the overall structural response and health status.

[0031] S2.4. Establish a strain energy equivalent degradation transformation database that includes crack length, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall response change, and degradation stage labels. This database does not only store equivalent material parameters, but also organizes local strain energy degradation, overall response sensitivity, and parameters required for health assessment in a unified manner, providing a parameter interface for subsequent dynamic health assessment.

[0032] The strain energy equivalent degradation database does not only store the equivalent elastic modulus, but also records the crack state, the degree of local strain energy degradation, the change in the overall structural response, and the degradation stage label. The equivalent elastic modulus in the database is only used as an intermediate parameter for updating the overall finite element model, and is ultimately used to drive the calibration of overall health indicators and the determination of dominant risks.

[0033] Step 3: Embed the localized degradation region based on strain energy change into the overall jacket model, and connect different element types in the overall model using a constraint method that can continuously transmit force, shear force and bending moment.

[0034] The specific steps include: S3.1 Establish a finite element model of the overall structure of the offshore wind turbine, in which the jacket is represented by beam elements, the tower and deck by shell elements, and the upper rotor, nacelle and other components are equivalent to solid mass blocks or concentrated mass.

[0035] S3.2. In the overall model, the local degradation mapping region is determined jointly based on the actual geometric range of the key pipe nodes, the equivalent energy density change of the local model, and the unit partitioning of the overall model. Preferably, when the strain energy change rate of a local unit or sub-region exceeds a preset threshold, it is included in the degradation mapping region, so that the degradation region is no longer determined solely by a fixed geometric range, but jointly determined by the energy change caused by local damage and the engineering geometric boundary.

[0036] In the formula, e is the index of a finite element or sub-region in the local tube node model. This represents the degenerate region in the overall model under the current crack state. This represents the change in energy equivalent to that of a single unit. The equivalent change energy under the no-damage condition, The threshold for determining the degradation region.

[0037] S3.3. Based on the current crack length, call the local degradation state database and set the initial elastic modulus of the nodal degradation region. E 0 is replaced with the equivalent elastic modulus E eff ( a The material properties, quality properties, and boundary conditions of the remaining areas remain unchanged, thus forming an overall jacket degradation model corresponding to different crack states.

[0038] S3.4 In the overall model, different element types are connected by constraints that can continuously transmit force, shear force and bending moment; the tower shell element and the top solid mass block are connected by shell-solid coupling constraints, and the lower jacket beam element and the tower shell element are connected by beam-type multi-point constraints.

[0039] Step 4: Solve the overall structural response under different crack states, construct the performance degradation sequence, identify the degradation stage, and classify the degradation process according to the rate of structural performance decline and the characteristics of stress and displacement response changes.

[0040] The specific steps include: S4.1. Perform modal analysis on the overall jacket degradation model corresponding to each crack state to obtain the structure's natural frequencies and mode shapes. Simultaneously, conduct static or dynamic response analysis under marine environmental loads to obtain the maximum equivalent stress at key structural locations. s max ( a and the overall maximum displacement u max ( a ).

[0041] S4.2. The equivalent performance parameters of local strain energy, stiffness retention coefficient, maximum stress, maximum displacement and natural frequency gap during crack propagation are sorted according to crack length or load cycle number to form a structural performance degradation sequence composed of local degradation and overall response.

[0042] S4.3. The Savitzky-Golay filter is used to smooth the structural performance degradation sequence in order to reduce the impact of numerical fluctuations and local errors on trend identification.

[0043] S4.4. Employing a globally optimal piecewise fitting method, with the goal of minimizing the sum of fitting errors across all pieces, the boundary points between the two degradation stages are automatically determined, dividing the performance degradation of the jacket structure into a safe period, a warning period, and a critical period. During the safe period, the structural response changes relatively slowly; during the warning period, the rates of stress, displacement, and stiffness degradation accelerate significantly; during the critical period, the structural response changes drastically and gradually approaches the bearing or stability limit. Furthermore, stage sensitivity coefficients are assigned to the safe period, the warning period, and the critical period respectively. q 1. q 2 and q 3, and q 1< q 2< q 3. Used for subsequent dynamic weight calculation. The stage sensitivity coefficient satisfies... q s ∈{ q 1, q 2, q 3}, and q 1< q 2< q 3; among which q 1 corresponds to the safe period. q 2 corresponds to the warning period. q 3 corresponds to the critical period. This coefficient is used to establish a direct link between the structural degradation stage and subsequent weight adjustments of health indicators.

[0044] Step 5: Construct an assessment system that includes five primary health indicators: fatigue, resonance, environment, strength, and stability. Stiffness degradation, frequency clearance, wave parameters, maximum stress, and maximum displacement are used as quantitative parameters for the indicator layer. Based on the scores of each health indicator, the corresponding health status is obtained.

[0045] The specific steps include: S5.1 Construct an evaluation system comprising five primary health indicators: fatigue, resonance, environment, strength, and stability. Stiffness degradation, frequency clearance, wave parameters, maximum stress, and maximum displacement are used as quantitative parameters for the indicator layer, respectively. Among them, the fatigue indicator reflects the equivalent degradation of strain energy caused by local cracks, the strength and stability indicators reflect the overall model response, and the resonance and environmental indicators reflect external sea state excitation.

[0046] S5.2 Fatigue Index S F The calibration is based on the stiffness degradation caused by crack propagation, represented by a fatigue health score. Let the local structural performance corresponding to the current crack length be... K ( a Local strain energy equivalent performance parameters K ( a The maximum and minimum values ​​in the reference data are respectively K max and K min ,but .

[0047] S5.3, Resonance Index Based on the first-order natural frequency of the structure f s With wave spectrum dominant frequency f w The relative frequency gap δ between them is calibrated: In the formula, .

[0048] S5.4 Environmental indicators are assessed through environmental adaptability scoring. S E This indicates that the current significant wave height is used. H s Design reference wave height H d ratio Perform calibration. .

[0049] S5.5, Strength Index S S The strength health score at the current crack length is used to calibrate the overall structure based on the maximum stress under different crack states. Let the reference stress for the intact state be... smin The critical state reference stress is s max The strength health score at the current crack length is: .

[0050] S5.6, Stability Indicators S ST The stability and health score is used to calibrate the overall structure based on the maximum displacement under different crack states. Let the reference displacement for the intact state be... u min The critical state reference displacement is u ma x The stable health score is: .

[0051] S5.7 Limit each health score to the range of [0,1], where a higher score indicates a better health status.

[0052] Step 6: Construct a judgment matrix for the five indicators using the nine-level scaling method, normalize the columns and calculate the row mean of the judgment matrix to obtain the static benchmark weight vector.

[0053] The specific steps include: S6.1. A nine-level scaling method is used to construct the AHP judgment matrix for five indicators: fatigue, resonance, environment, strength and stability. The matrix elements are used to represent the relative importance between any two indicators.

[0054] S6.2. Perform column normalization and row mean calculation on the judgment matrix to obtain the static benchmark weight vector. W static =[ W F , W R , W E , W S , W ST ] T , W static It is a unified static benchmark weight for five indicators. The damage-driven module calls one of them. W F , W S , W ST Environment-driven module call W E Resonance drive module call W R and through the largest eigenvalue lmax , represents the consistency index CI and the random consistency index RI calculate the consistency ratio CR : , , n represents the order of the judgment matrix, and this embodiment includes 5 health indicators, so n = 5.

[0055] S6.3, when CR is less than 0.1, the judgment matrix meets the consistency requirement; when CR the consistency requirement is not satisfied, consistency optimization is performed with the upper triangular elements of the judgment matrix as optimization variables to obtain a static benchmark weight vector. The judgment matrix satisfies the reciprocal relationship, so it is only necessary to optimize the upper triangular elements with i<j; the lower triangular elements are automatically determined by the reciprocal relationship. The optimization objective is not to directly optimize the weight, but to make the modified judgment matrix satisfy CR<0.10 while retaining the original expert judgment as much as possible; then the static benchmark weight vector is calculated from the modified matrix.

[0056] Step 7: Establish a stage-damage-environment coupled dynamic weight evaluation model, obtain normalized dynamic weights for comprehensive evaluation after normalization, obtain dynamic weights that change with the structural damage process, degradation stage and environmental conditions by repeating execution on each crack growth increment step, and perform multi-factor comprehensive dynamic evaluation on the jacket structure of an offshore wind turbine under crack propagation.

[0057] The specific steps include: S7.1, establish a damage-driven dynamic weight module. For the three indicators of fatigue, strength and stability, according to the current health score S i , perform punitive amplification on its static benchmark weight, and the damage-driven temporary weight is expressed as: , in the formula, is the static benchmark weight of the indicator determined by the traditional AHP, which reflects its average importance in the long term, is a penalty factor greater than 0, which reflects the sensitivity of the weight to performance deterioration. q s is the degradation stage sensitivity coefficient, and the safety period, early warning period and danger period correspond to q 1, q 2 and q 3, and q 1< q 2< q 3, so that the same health score decrease produces different weight amplification effects in different degradation stages.

[0058] S7.2 Establish an environment-driven dynamic weighting module. Temporary weights for environmental indicators. Adjustments based on significant wave height: In the formula, It is the static weight of the environment. It is the environmental incentive coefficient. It is the characteristic wave height used in the structural design. (Ratio) The relative severity of the current sea state has been normalized.

[0059] S7.3, Temporary Weight of Resonance Index Based on frequency deviation d Make adjustments when d Less than the safety threshold d th When, a quadratic amplification function is used to increase the weight of the resonance index; when d Not less than d th At that time, the resonance index weights remain at a static benchmark value: In the formula, It is the static weight of resonance risk. It is the risk incentive coefficient. It is a pre-set safety threshold for frequency deviation. When The weights are amplified in a quadratic form, which allows for a keen detection of critical changes in resonance risk.

[0060] S7.4 Combine the damage-driven weights and environment-driven weights into a temporary dynamic weight vector. And perform normalization: In the formula, step 5 first obtains three health scores. , , Step S7.1 uses these scores as inputs to the damage-driven variable weighting. In the formula, i only takes... , , . , , These represent the temporary weights of the three damage-driving factors: fatigue, strength, and stability. i , j The index consists of five indicators. For the first i Temporary weights, For the first j Temporary weights, For the normalized first i Item dynamic weight.

[0061] S7.5. After normalization, the final normalized dynamic weights used for comprehensive evaluation are obtained. By repeating this process at each crack propagation increment step, the dynamic weights that change with the structural damage process, degradation stage, and environmental conditions can be obtained, thereby enabling a multi-factor comprehensive dynamic evaluation of the offshore wind turbine jacket structure under crack propagation.

[0062] The method described in this embodiment uses the equivalent strain energy change caused by crack propagation at key pipe nodes as a characterization quantity for local performance degradation, and establishes a strain energy equivalent degradation database. The degradation parameters in the database are then converted into local degradation mapping parameters recognizable by the overall jacket model, used to update the overall structural model and calculate the overall response. The equivalent material parameters are only used for local degradation mapping in the overall health assessment and are not used to describe crack tip fracture behavior, nor are they the same as the constitutive performance degradation of steel caused by corrosion fatigue. Instead of directly embedding the crack-containing microscopic model into the overall jacket model, or constitutively fitting the steel material performance degradation, the method transforms the local strain energy degradation results into inputs for the overall health assessment. Through degradation stage sensitivity coefficients, damage-environment dual-drive weights, and hard threshold coverage rules, the method outputs a comprehensive health index, health level, and dominant risk.

[0063] Example 2 This embodiment provides a detailed description of the method in Embodiment 1.

[0064] A method for health assessment of offshore wind turbine jackets based on strain energy equivalence includes the following implementation steps.

[0065] The first step is to obtain the crack propagation state and equivalent degradation data of local strain energy of key KK pipe nodes. KK pipe nodes with high stress levels under wave loads in offshore wind turbine jackets are selected as the research object. Equivalent strain energy, stress intensity factor, and crack propagation cycle number under different crack lengths are obtained through numerical simulation of local crack propagation. To ensure that the local model can reasonably reflect the boundary constraints of the overall model, a local model of the key KK node is established by splitting the overall model and reconstructing the local model. The stress results at corresponding locations in the local model and the overall model are compared. The error of the local multi-scale model is 4.67%, which meets the requirements for obtaining local strain energy degradation data. It should be noted that this local crack analysis is used to form the front-end degradation data for health assessment. The overall health assessment process of this invention does not directly embed the crack-containing micro-model into the overall jacket model.

[0066] Local structural performance parameters were obtained by converting the equivalent strain energy of the structure, and the stiffness retention coefficient and damage variables were calculated based on the ratio between the crack-free state and the cracked state. The average error between the theoretical stiffness degradation model and the numerical simulation results was approximately 1.2%, with a maximum error not exceeding 2.5%, indicating that the obtained local structural performance degradation data can be used as the front-end input for overall health assessment. The above error data is used to illustrate the reliability of the input degradation data and is not used to prove the calculation accuracy of the actual crack-embedded model.

[0067] The second step is to calculate the equivalent elastic modulus of the locally degraded region based on the principle of continuous damage mechanics equivalence. In this embodiment, six representative crack states during crack propagation are selected, with crack lengths of 0 mm, 15 mm, 45 mm, 76 mm, 107 mm, and 152 mm, respectively. The corresponding structural performance parameters and equivalent elastic moduli are shown in Table 1.

[0068] Table 1: Representative Crack State Parameters .

[0069] As shown in Table 1, the changes in local structural performance parameters and equivalent elastic modulus are relatively small in the early stages of crack propagation; however, the rate of decrease in equivalent elastic modulus accelerates significantly as the crack length progresses into the middle and later stages. Based on the actual geometric dimensions of the key KK nodes and the distribution of local strain energy, a local degradation mapping region is determined in the overall jacket finite element model, and the equivalent elastic modulus in Table 1 is assigned to this region, thereby constructing an overall degradation model corresponding to the six crack states. The equivalent elastic modulus mentioned here is a substitute parameter for the overall model of local structural degradation, and not a parameter for the constitutive performance degradation of the steel material.

[0070] The third step is to establish a multi-element hybrid finite element model of the overall offshore wind turbine. The lower jacket structure uses beam elements, the tower and deck use shell elements, and the upper rotor and nacelle structures are simplified using solid mass blocks or equivalent masses. Shell-solid coupling constraints are used between the tower shell elements and the top mass blocks, and MPC-beam constraints are used between the lower jacket beam elements and the tower shell elements, ensuring continuous transmission of force, shear force, and bending moment between different element types. The calculation results for the first ten natural frequencies of the overall model are shown in Table 2.

[0071] Table 2: Calculation Results of the First Ten Natural Frequencies of the Overall Model .

[0072] After replacing the KK node with strain energy equivalent material, the first-order natural frequencies of the overall jacket structure before and after damage were compared. The results show that, under the local damage level considered in this embodiment, the first-order natural frequencies before and after material equivalent replacement are both approximately 0.30827 Hz, and the local node stiffness degradation did not cause a significant observable change in the overall first-order frequency. This indicates that relying solely on changes in the overall natural frequency may be insufficient to promptly identify local crack damage; a comprehensive analysis combining overall stress, displacement, local strain energy equivalent degradation indices, and degradation stage determination is necessary.

[0073] The fourth step involves conducting stress and displacement response analyses on the overall model corresponding to the six crack states. The analysis results show that as the performance of the critical KK node continues to deteriorate, both the maximum stress and maximum displacement of the jacket structure exhibit a monotonically increasing trend, and show a significant acceleration characteristic in the later stages of crack propagation. Local node degradation weakens the overall structural load-bearing capacity and redistributes the original load to adjacent components, thus creating new stress hotspots.

[0074] The structural performance degradation curve was smoothed using Savitzky-Golay filtering, and then two boundary points were automatically determined using a globally optimal three-segment linear fitting method. Based on the rate of structural performance degradation and the characteristics of stress and displacement response changes, the degradation process was divided into three stages: the first stage is the safe period, characterized by relatively minor local damage and slow overall response changes; the second stage is the warning period, where structural stiffness decreases and the rates of stress and displacement increase accelerate significantly; and the third stage is the critical period, where the structure is highly sensitive to damage increments and gradually approaches its bearing or stability limits. The results of these three stages were further converted into stage sensitivity coefficients q1, q2, and q3, which were then used in subsequent dynamic weight amplification calculations.

[0075] The fifth step is to construct a health assessment index system for the jacket structure. The target layer represents the health status of the offshore wind turbine jacket structure under crack propagation conditions; the criterion layer includes five indicators: fatigue, resonance, environment, strength, and stability; the index layer uses strain energy equivalent stiffness degradation, frequency gap, significant wave height, maximum stress, and maximum displacement for quantification. Each indicator is normalized and calibrated according to the formula, ensuring that its score range is between 0 and 1.

[0076] The AHP judgment matrix used in this embodiment is shown in Table 3.

[0077] Table 3: AHP Judgment Matrix Element Table .

[0078] Step 6: Normalization of the judgment matrix, calculation of static weights, and consistency check are performed to obtain reliable static benchmark weights. After normalizing the judgment matrix and calculating its eigenvectors, the static benchmark weights for the five indicators—fatigue, resonance, environment, strength, and stability—are 0.42, 0.26, 0.10, 0.16, and 0.06, respectively. The largest eigenvalue of the judgment matrix is ​​5.0682, the consistency index (CI) is 0.01705, and the consistency ratio (CR) is 0.0152, which is lower than 0.10, indicating that the judgment matrix has good consistency.

[0079] Step 7: Establish a stage-damage-environment coupled dynamic weighted assessment model. Based on this static weight, dynamic adjustments are made according to the current damage and degradation stage and sea state. The fatigue, strength, and stability indicators adopt stage-damage driven weights, and the static weights are penalized by amplifying the static weights based on the degree of decline in health score and the sensitivity coefficient of degradation stage. The environmental indicator weight is adjusted according to the ratio of significant wave height to design wave height. The resonance indicator weight is adjusted according to the proximity between the structure's first-order natural frequency and the dominant frequency of the wave spectrum. After normalizing the five temporary dynamic weights, they are weighted and summed with the five health scores to obtain the comprehensive health index (CHI).

[0080] To verify the effectiveness of the health assessment method of this invention, the NREL 5 MW jacket-type offshore wind turbine in the coastal waters of eastern Guangdong in the northern South China Sea was used as the implementation object. The design wave height was 8 m, the dominant wave frequency was 0.16 Hz, the yield stress of the structural material was 355 MPa, and the initial natural frequency of the structure was 0.308 Hz. The crack propagation was set from 0 mm to a critical length of 152 mm, and divided into 80 assessment steps.

[0081] The assessment results show that in the initial stage of crack propagation, within the range of 0 to 40 mm, the Comprehensive Health Index (CHI) remains above 0.85, indicating that the structure is in a safe operating range, with the risk contribution mainly coming from fatigue indicators. When the crack propagates to the range of 40 to 100 mm, the CHI rapidly decreases from 0.85 to 0.55, and the structure enters the close monitoring level. At a crack length of approximately 65 mm, the dominant risk factor changes from fatigue to structural strength. When the crack length enters the range of 100 to 152 mm, the CHI drops below 0.4, and the structure enters the shutdown and maintenance level, with the dominant risk further shifting to stability or resonance instability risk.

[0082] The above results are consistent with the structural performance degradation pattern in the overall finite element analysis: in the early stage of crack propagation, the structural stiffness degrades slowly, and the stress and displacement changes are small; in the middle stage, the stiffness degradation rate accelerates, and the maximum stress increases significantly; in the later stage, the structural performance deteriorates rapidly, and stability and resonance risks become the main threats. This embodiment illustrates that the present invention can transform local strain energy equivalent degradation information into overall health assessment results and can identify the stage transitions of dominant risks during crack propagation.

[0083] The above embodiments are merely illustrative of the structural concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for health assessment of offshore wind turbine jackets based on strain energy equivalence, characterized in that, Includes the following steps: Step 1: Obtain crack propagation state and local strain energy equivalent degradation data to form a strain energy equivalent degradation source database, which will serve as the input data source for subsequent overall jacket health assessment; Step 2: Convert local strain energy degradation parameters into global model degradation mapping parameters, establish a strain energy equivalent degradation transformation database, and unify the parameters required for local strain energy degradation, global response sensitivity and health assessment to provide a parameter interface for dynamic health assessment. Step 3: Embed the localized degradation region based on strain energy changes into the overall jacket model, and connect different element types in the overall model using a constraint method that can continuously transmit force, shear force, and bending moment; Step 4: Solve the overall structural response under different crack states, construct the performance degradation sequence, identify the degradation stage, and classify the degradation process according to the rate of structural performance decline and the characteristics of stress and displacement response changes; Step 5: Construct an assessment system that includes five primary health indicators: fatigue, resonance, environment, strength, and stability. Stiffness degradation, frequency clearance, wave parameters, maximum stress, and maximum displacement are used as quantitative parameters for the indicator layer. Based on the scores of each health indicator, the corresponding health status is obtained. Step 6: Construct a judgment matrix for the five indicators using the nine-level scaling method, and perform column normalization and row mean calculation on the judgment matrix to obtain the static benchmark weight vector; Step 7: Establish a stage-damage-environment coupled dynamic variable weight assessment model, and obtain normalized dynamic weights for comprehensive assessment after normalization. By repeating the process at each crack propagation increment step, obtain dynamic weights that change with the structural damage process, degradation stage and environmental conditions. Perform multi-factor comprehensive dynamic assessment of offshore wind turbine jacket structures under crack propagation.

2. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 1, characterized in that, Step 1 includes: Step 1-1: Select the key KK pipe node or other welded pipe node in the offshore wind turbine jacket structure as the research object of local performance degradation, and obtain the crack location, crack length, crack propagation cycle number and local structural response data in the crack-free state and multiple representative crack length states; Steps 1-2: Under the same boundary conditions and load levels, the structural performance of local tube nodes is characterized using the structural equivalent strain energy, based on the crack length as... a Equivalent performance parameters of local strain energy K ( a Structural performance parameters in the crack-free state K 0 yields the local structural stiffness retention coefficient η ( a ) and damage variables D ( a ), , ; Steps 1-3: Based on the results obtained under the discrete crack state K ( a Construct a continuous mapping relationship between crack length and local structural performance degradation, so that the corresponding local stiffness retention coefficient and damage variable can be obtained for any crack length; Steps 1-4: Generate a strain energy equivalent degradation source database by combining crack length, number of cycles, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall maximum stress, overall maximum displacement, and degradation stage labels. This database will serve as the input data source for subsequent overall jacket health assessment.

3. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 2, characterized in that, Step 2 includes: Step 2-1: Based on the correspondence between structural stiffness and elastic modulus in elasticity, the strain energy of local pipe nodes is equivalently degraded into changes in equivalent material parameters in local areas. Step 2-2: Based on the principle of equivalence in continuous damage mechanics, the crack length is... a Corresponding damage variables D ( a Convert to the equivalent elastic modulus of the local region E eff ( a ): ,in, E 0 represents the elastic modulus under healthy conditions; Steps 2-3: Establish a strain energy equivalent degradation transformation database containing crack length, local strain energy equivalent performance parameters, stiffness retention coefficient, damage variable, equivalent elastic modulus, overall response change, and degradation stage label. This database unifies the local strain energy degradation, overall response sensitivity, and parameters required for health assessment, providing a parameter interface for subsequent dynamic health assessment.

4. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 3, characterized in that, In step 2-1, for axially stressed components, the axial stiffness can be expressed as: ,in, A For the cross-sectional area, L It is the length; for bending members, their bending stiffness is related to the material's elastic modulus and the moment of inertia of the cross section, expressed as: Where E is the elastic modulus and I is the interfacial moment of inertia.

5. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 3, characterized in that, Step 3 includes: Step 3-1: Establish a finite element model of the overall structure of the offshore wind turbine, in which the jacket is represented by beam elements, the tower and deck by shell elements, and the upper rotor, nacelle and other components are equivalent to lumped mass; Step 3-2: In the overall model, determine the local degradation mapping region based on the actual geometric range of the key pipe nodes, the equivalent variable energy density change of the local model, and the unit partitioning of the overall model. Step 3-3: Based on the current crack length, call the local degradation state database and retrieve the elastic modulus of the node degradation region under healthy conditions. E 0 is replaced with the equivalent elastic modulus E eff ( a The material properties, quality properties, and boundary conditions of the remaining areas remain unchanged, forming an overall jacket degradation model corresponding to different crack states; Steps 3-4: Shell-solid coupling constraints are used between the tower shell unit and the top solid mass block, and beam-type multi-point constraints are used between the lower jacket beam unit and the tower shell unit, so that force, shear force and bending moment can be continuously transmitted between different unit types.

6. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 5, characterized in that, In step 3-2, when the strain energy change rate of a local unit or sub-region exceeds a preset threshold, the local unit or sub-region is included in the degradation mapping region. The degradation region is determined by the energy change caused by local damage and the engineering geometric boundary. Where e is the index of a finite element or sub-region in the local pipe node model. This represents the degenerate region in the overall model under the current crack state. This represents the change in energy equivalent to that of a single unit. The equivalent change energy under the no-damage condition, The threshold for determining the degradation region.

7. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 5, characterized in that, Step 4 includes: Step 4-1: Perform modal analysis on the overall jacket degradation model corresponding to each crack state to obtain the structure's natural frequencies and mode shapes. Perform static or dynamic response analysis under marine environmental loads to obtain the maximum equivalent stress at key locations of the structure. σ max ( a and the overall maximum displacement u max ( a ); Step 4-2: Sort the equivalent performance parameters of local strain energy, stiffness retention coefficient, maximum stress, maximum displacement and natural frequency gap during crack propagation according to crack length or load cycle number to form a structural performance degradation sequence composed of local degradation and overall response. Step 4-3: Use Savitzky-Golay filtering to smooth the structural performance degradation sequence, reducing the impact of numerical fluctuations and local errors on trend identification; Step 4-4: Using the global optimal piecewise fitting method, the boundary points between the two degradation stages are determined based on the sum of the piecewise fitting errors. The performance degradation of the jacket structure is divided into a safe period, a warning period, and a dangerous period. A direct link is established between the structural degradation stages and the subsequent weight adjustments of health indicators. During the safe period, the structural response changes slowly. During the warning period, the degradation rates of stress, displacement, and stiffness increase significantly. During the dangerous period, the structural response changes drastically and gradually approaches the bearing or stability limit.

8. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 7, characterized in that, In step 5, fatigue indices reflect the equivalent degradation of strain energy caused by localized cracks, strength and stability indices reflect the overall model response, and resonance and environmental indices reflect external sea state excitation. Fatigue index The fatigue health score is used to calibrate the stiffness degradation caused by crack propagation. ,in, K max Represents the equivalent performance parameters of local strain energy K ( a The maximum value in the reference data. K min Represents the equivalent performance parameters of local strain energy K ( a The minimum value in the reference data; Resonance Indicator Where δ represents the first natural frequency of the structure. f s With wave spectrum dominant frequency f w The relative frequency gap between them ; Environmental indicators are assessed through environmental adaptability scoring. S E This indicates that the current significant wave height is used. H s Design reference wave height H d ratio Perform calibration. ; Strength indicators S S The strength health score at the current crack length is used to calibrate the overall structure based on the maximum stress under different crack states. ,in, σ min Indicates the reference stress in a good condition. σ max Indicates the critical state reference stress; Stable indicators S ST The stability and health score is used to calibrate the overall structure based on the maximum displacement under different crack states. ,in, u min Indicates the reference displacement in the intact state. u ma x This represents the reference displacement for the critical state.

9. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 8, characterized in that, Step 6 includes: Step 6-1: Construct fatigue using the nine-level scaling method W F Resonance W R ,environment W E ,strength W S and stability W ST The AHP judgment matrix for five indicators, where the matrix elements represent the relative importance between any two indicators; Step 6-2: Perform column normalization and row mean calculation on the judgment matrix to obtain the static benchmark weight vector. W static =[ W F , W R , W E , W S , W ST ] T Calculate the consistency ratio CR , ,in, CI Indicators of consistency , RI This represents the random consistency index. λ max This represents the largest eigenvalue, and n represents the order of the judgment matrix; Step 6-3: When CR When the value is less than 0.1, the judgment matrix satisfies the consistency requirement; when... CR When the consistency requirement is not met, consistency optimization is performed using the upper triangular elements of the judgment matrix as optimization variables to obtain a static benchmark weight vector.

10. The method for health assessment of offshore wind turbine jackets based on strain energy equivalence according to claim 9, characterized in that, Step 7 includes: Step 7-1: Establish a damage-driven dynamic weighted module. For the three indicators of fatigue, strength, and stability, based on the current health score... S i Penalty amplification of its static baseline weights, damage-driven temporary weights Represented as: ,in, The static baseline weights for this indicator are determined using traditional AHP. Indicates the penalty factor. q s Indicates the sensitivity coefficient for the degradation stage; Step 7-2: Establish an environment-driven dynamic weighting module, with temporary weights for environmental indicators. Adjustments based on significant wave height: ,in, Represents the static weights of the environment. Indicates the environmental incentive coefficient. Indicates the characteristic wave height and ratio used in the structural design. The relative severity of the current sea state has been normalized; Step 7-3: Based on frequency deviation δ Adjusting the temporary weight of the resonance index ,when δ Less than δ th When, a quadratic amplification function is used to increase the weight of the resonance index; when δ Not less than δ th At that time, the resonance index weights remain at a static benchmark value: ,in, Static weights representing the risk of resonance. Indicates the risk incentive coefficient. This indicates a pre-set safety threshold for frequency deviation; Step 7-4: Combine the damage-driven weights and environment-driven weights into a temporary dynamic weight vector. And perform normalization: ,in, i , j Index of five indicators; For the first i Temporary weights; For the first j Temporary weights; For the normalized first i Item dynamic weight; Step 7-5: After normalization, the normalized dynamic weights used for comprehensive evaluation are obtained. By repeating this process at each crack propagation increment step, dynamic weights that change with the structural damage process, degradation stage, and environmental conditions are obtained. Multi-factor comprehensive dynamic evaluation of offshore wind turbine jacket structures under crack propagation is then performed.

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