Method for corrosion fatigue damage assessment and life prediction of offshore wind turbine structure considering wind turbine operation and performance degradation after damage and its application

Abstract

The application discloses a kind of offshore wind power corrosion fatigue damage assessment and life prediction method considering fan operation and damage performance degradation and application thereof.The method comprises the following steps: determining external load, calculating structure corresponding, establishing refined model, obtaining stress time history, calculating fatigue damage, determining corrosion distribution, adjusting material performance, and carrying out iterative calculation.The method can consider the operation effect of offshore wind turbine in service state, and the influence of material mechanical property degradation after corrosion fatigue damage.The application can be used for corrosion fatigue damage assessment of in-service offshore wind power structure, and can also be used for corrosion fatigue design of offshore wind power structure.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures, in particular to a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures considering the operation of wind turbines and performance degradation after damage, and application thereof. BACKGROUND

[0002] With the deepening of China's marine power strategy, offshore wind power has been developed profoundly. In service state, offshore wind power structures will bear long-term alternating loads such as wind load, wave and current load, wind turbine operation, and then accumulate fatigue damage. At the same time, the corrosion environment of offshore wind power structures is severe, and the corrosion problem is serious during the service of the structure. Meanwhile, there is a significant coupling effect between corrosion and fatigue, and the development of corrosion will further lead to the deterioration of the fatigue performance of the structure. In addition, the mechanical properties of the material will be degraded after corrosion fatigue damage, which will endanger the service safety of the structure. Therefore, a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures needs to be established. At present, the analysis method for offshore wind power structures does not consider the influence of wind turbine operation in service state and the coupling effect of corrosion fatigue, and does not consider the performance degradation after corrosion fatigue damage, which will lead to unsafe evaluation of the corrosion fatigue damage and service life of offshore wind power structures. Therefore, a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures considering the operation of wind turbines and performance degradation after damage needs to be established. SUMMARY

[0003] In order to overcome the shortcomings of the prior art, the present application provides a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures considering the operation of wind turbines and performance degradation after damage, and application thereof. The method can consider the operation of offshore wind turbine in service state and the influence of mechanical property degradation of the material after corrosion fatigue damage. The present application can be used for evaluating and predicting the corrosion fatigue damage and residual life of existing offshore wind power structures, and can also provide a reference for the design of offshore wind power structures with corrosion fatigue problems.

[0004] The present application provides a method for evaluating and predicting the corrosion fatigue damage and service life of offshore wind power structures considering the operation of wind turbines and performance degradation after damage. The method comprises:

[0005] (a) generating a wind field with a time length of dT according to the external load parameters of the service site and wind turbine information of offshore wind power, and establishing an offshore wind power model in OpenFAST software;

[0006] (b) based on OpenFAST, calculating the response of offshore wind power structure under the coupling effect of wind-wave-current-structure-turbine operation within dT1 time, and extracting the displacement and force boundary conditions at the top of the tower;

[0007] (c) Establish a refined finite element model of the structure in ABAQUS, input the boundary conditions extracted in step (b) at the top of the tower, and calculate the stress distribution of the offshore wind power structure in time dT1;

[0008] (d) According to the natural atmospheric corrosion test data or empirical formula, the development function law w(t) of the natural atmospheric corrosion degree of the steel structure steel in its service environment is established; according to the high-cycle fatigue test after corrosion or the empirical formula, a nonlinear damage evolution model of the steel under different corrosion degrees is established based on the continuum damage mechanics, the damage evolution model parameters C, β under each corrosion degree are calibrated, and the function relationship C(w), β(w) between the corrosion degree and the corrosion degree is established;

[0009] (e) According to the stress distribution characteristics, the fatigue vulnerable position is identified, the stress time history is extracted, and the corrosion fatigue damage D s1 is calculated in time dT1 by combining the rainflow counting method and the continuum mechanics;

[0010] (f) According to the corrosion fatigue damage D T , the corrosion degree w T distribution and the material performance degradation model after corrosion fatigue damage, the material parameters in OpenFAST are adjusted, and the service state structure response is recalculated;

[0011] (g) Repeat (a) to (e) until the corrosion fatigue damage D T =1, and the structure is corroded and fatigued. At this time, the total service time T is the corrosion fatigue life of the structure in the service environment considering the operation of the wind turbine and the performance degradation after damage.

[0012] According to the method of claim 1, in step (a), the wave flow and wind field characteristics are determined according to the service location of the offshore wind power structure;

[0013] According to a specific embodiment, in step (a), the wind field with a time length of dT can be generated by referring to the relevant requirements in the IEA specification, or can be obtained by measuring the data at the service location of the wind turbine;

[0014] According to a specific embodiment, in step (a), a model is established in OpenFAST according to the geometric size of the evaluated offshore wind power structure, and the wave flow and wind field with a time length of dT are applied according to the service location of the offshore wind power structure;

[0015] According to a specific embodiment, in step (a), the wind turbine parameters of the evaluated structure are set in the OpenFAST software, including the weight of the wind turbine, the position of the center of gravity, the rated power generation, and the operating state control system parameters;

[0016] According to a specific embodiment, in step (b), the response of the offshore wind power structure under the wind-wave-current-structure-turbine operation coupling in dT time is calculated based on OpenFAST to extract the time history curve L1 of the displacement and force boundary conditions at the top of the tower;

[0017] According to a specific embodiment, in step (c), a refined finite element model of the offshore wind power structure without the upper turbine is established in ABAQUS finite element software, and the boundary condition time history curve obtained in step (b) is input at the top of the tower to consider the effect of the upper structure on the tower top during service, so as to realize the consideration of the wind-wave-current-turbine operation in the refined finite element analysis;

[0018] According to a specific embodiment, in step (c), according to the finite element calculation results, the stress distribution cloud chart of the offshore wind power structure is obtained;

[0019] According to a specific embodiment, in step (d), according to the natural atmospheric corrosion test data or the empirical formula, the development function law w(t) of the natural atmospheric corrosion degree of the steel structure steel under its service environment is established;

[0020] According to a specific embodiment, in step (d), different corrosion degree steel specimens are obtained by natural corrosion, periodic immersion, salt spray, and electric corrosion, high cycle fatigue tests are carried out on different corrosion degree steel specimens, and according to the high cycle fatigue test results, a nonlinear damage evolution model of steel under different corrosion degrees is established based on continuous medium mechanics, and the damage evolution model parameters C(w), β(w) under each corrosion degree are calibrated. When the fatigue performance test of the steel specimen after corrosion cannot be carried out, the damage evolution model parameters C(w), β(w) under each corrosion degree can be obtained through existing research data or empirical formula;

[0021] wherein C(w), β(w) are obtained from formula (1) through the fatigue test data of the steel with corrosion degree w:

[0022]

[0023] According to a specific embodiment, in step (e), the fatigue vulnerable position is determined according to the construction category and the stress distribution, the stress time history at the position is extracted, and the stress amplitude sequence S1 is obtained through rain flow counting method;

[0024] The fatigue damage increment generated by a single load cycle is calculated by formula (2), wherein S max , S min is the maximum stress and minimum stress of each stress amplitude in S1, and N is the number corresponding to each stress amplitude:

[0025]

[0026] According to one specific embodiment, in the step (e), the fatigue damage D caused by the standard stress amplitude sequence in the service dT1 time is calculated s1 , the number n of dT1 is calculated in one year, and the damage dD1 = n·D is calculated in one year s1 , the process is repeated and the total fatigue damage D is accumulated T =∑dD i , the total service time T = ∑dT i , and the corrosion degree w T ;

[0027] wherein

[0028] According to one specific embodiment, in the step (f), the evolution law of the mechanical properties of the steel material with the fatigue damage degree D and the corrosion degree w is determined according to the mechanical property test of the steel material after corrosion fatigue damage or the empirical formula, including the elastic modulus E(D, w), the yield strength f y (D, w), and the ultimate strength f u (D, w);

[0029] According to one specific embodiment, in the step (f), the mechanical properties of the steel material when the total service time T is determined are determined according to D T and w T , and the material parameters are adjusted accordingly in the OpenFAST software;

[0030] According to one specific embodiment, in the step (g), the steps (a)-(e) are repeated to obtain L i , D si , dD i , and the total damage D T , when D T =1, the structure is corroded and damaged, and at this time, the total service time T is the corrosion fatigue life of the structure under the service environment considering the operation of the wind turbine and the performance degradation after damage;

[0031] The technical scheme of the present application has the following advantages: the method considers the time history of the offshore wind power guide pipe load under the action of the service state wind-wave flow-structure and the operation of the wind turbine, realizes the corrosion fatigue damage position identification and damage calculation by combining with the refined finite element model analysis, considers the performance degradation of the material after damage during the service period by combining with the material performance degradation model after damage, realizes the corrosion fatigue life prediction of the offshore wind power structure, and can be used for the residual corrosion fatigue life evaluation of the existing offshore wind power structure and the corrosion fatigue life design of the newly built offshore wind power structure. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1A flow chart of a method for offshore wind power structure corrosion fatigue damage assessment and life prediction considering wind turbine operation and performance degradation after damage;

[0033] Figure 2 A wind farm schematic diagram;

[0034] Figure 3 A wave flow height time history schematic diagram;

[0035] Figure 4 A schematic diagram of establishing an offshore wind power model in OpenFAST;

[0036] Figure 5 A wind turbine operation power schematic diagram;

[0037] Figure 6 A service state offshore wind power structure tower top displacement time history schematic diagram;

[0038] Figure 7 A service state offshore wind power structure tower top force boundary time history schematic diagram;

[0039] Figure 8 A schematic diagram of establishing a finite element of offshore wind power structure in ABAQUS;

[0040] Figure 9 A service state offshore wind power structure stress distribution schematic diagram;

[0041] Figure 10 A C(w), beta(w) calibration schematic diagram;

[0042] Figure 11 A C(w), beta(w) change with corrosion degree schematic diagram;

[0043] Figure 12 A rain flow counting method stress amplitude statistics schematic diagram;

[0044] Figure 13 A corrosion fatigue damage D development schematic diagram. DETAILED DESCRIPTION

[0045] The present application will be further described below in conjunction with the accompanying drawings.

[0046] The present application discloses a method for offshore wind power structure corrosion fatigue damage assessment and life prediction considering wind turbine operation and performance degradation after damage, and the specific flow chart is as follows Figure 1The first step is to generate a wind field with a time length of dT according to the offshore wind power service location and wind turbine information external load parameters, and to establish an offshore wind power model in OpenFAST software. The second step is to calculate the response of the offshore wind power structure within dT1 time under the action of wind-wave-current-structure-turbine operation coupling based on OpenFAST, and to extract the displacement and force boundary conditions at the top of the tower. The third step is to establish a refined finite element model of the structure in ABAQUS, input the boundary conditions extracted in step (b) at the top of the tower, and calculate the stress distribution of the offshore wind power structure within dT1 time. The fourth step is to establish the natural atmospheric corrosion degree development function law w(t) of the steel structure steel under its service environment according to the natural atmospheric corrosion test data or empirical formula. According to the high-cycle fatigue test after corrosion or empirical formula, a nonlinear damage evolution model of steel under different corrosion degrees is established based on continuum damage mechanics, the damage evolution model parameters C, β under each corrosion degree are calibrated, and the function relationship C(w), β(w) between them and the corrosion degree is established. The fifth step is to identify the fatigue vulnerable position according to the stress distribution characteristics, extract the stress time history at this position, and calculate the corrosion fatigue damage D s1 within dT1 time by combining the rainflow counting method with continuum mechanics. T The sixth step is to adjust the material parameters in OpenFAST according to the corrosion fatigue damage D T , the corrosion degree w T distribution, and the material performance degradation model after corrosion fatigue damage, and recalculate the service state structure response. The seventh step is to repeat (a)-(e) until the corrosion fatigue damage D T =1, and the structure is corroded and fatigued. At this time, the total service time T is the corrosion fatigue life of the structure in the service environment considering the operation of the wind turbine and the performance degradation after damage.

[0047] According to a specific embodiment, in step (a), the wind field and wave flow characteristics are determined according to the service location of the offshore wind power structure, the wind field time history is as shown in Figure 2 , and the wave flow height time history is as shown in Figure 3 .

[0048] According to the geometric size of the evaluated offshore wind power structure, a model is established in OpenFAST, as shown in Figure 4 , and the wave flow and wind field are applied.

[0049] According to the evaluated structure turbine parameters, the turbine weight, center of gravity position, rated power generation, and operating state control system parameters are set in OpenFAST software, and the rated output power of the wind turbine is as shown in Figure 5 .

[0050] Based on OpenFAST, the response of offshore wind turbine structures under the coupled effects of wind, wave, current, structure and wind turbine operation within dT time is calculated, and the time history curve L1 of the displacement and force boundary condition of the tower top is extracted. The time history curve of the tower top displacement boundary condition is as follows: Figure 6 As shown, the time history curve of the tower top force boundary condition is as follows Figure 7 As shown;

[0051] A refined finite element model of an offshore wind turbine structure without upper wind turbines is established in ABAQUS finite element software, such as Figure 8 As shown, by inputting the boundary condition time history curve obtained in step 2 at the top of the tower, the effect of the superstructure on the tower top during service is considered, so that the influence of wind, wave flow and wind turbine operation can be considered in the refined finite element analysis.

[0052] According to the finite element calculation results, the stress distribution cloud map of the offshore wind power structure is obtained, such as Figure 9 As shown;

[0053] Based on the natural atmospheric corrosion test data or empirical formula, establish the natural atmospheric corrosion degree development function law w(t) of the evaluated steel structure in its service environment;

[0054] According to the post-corrosion high-cycle fatigue test or empirical formula, based on the Continuum Damage Mechanics (CDM), a nonlinear damage evolution model of steel under different corrosion degrees is established, and the damage evolution model parameters C(w) and β(w) under each corrosion degree are calibrated, such as Figure 10 As shown, the evolution law of C(w),β(w) with the degree of corrosion is established, as shown in Figure 11 As shown;

[0055] According to a specific embodiment, in step (e), the fatigue vulnerable position is determined by combining the structural type and stress distribution, the stress time history at this location is extracted, and the stress amplitude sequence S1 is obtained by statistically calculating the rain flow counting method, such as Figure 12 As shown;

[0056] According to a specific embodiment, in step (e), the fatigue damage D generated by the standard stress amplitude sequence during the service time dT1 is calculated. s1 , calculate the number n of dT1 in one year, calculate the damage dD1 in one year = n·D s1 , repeat this process and accumulate the total fatigue damage D T =∑dD i , total service time T = ∑dT i And the degree of corrosion w T ;

[0057] in

[0058] According to the mechanical property test of steel after corrosion fatigue damage or empirical formula, the evolution law of the mechanical property of steel with fatigue damage degree D and corrosion degree w is determined, including elastic modulus E(D, w), yield strength f y (D, w), ultimate strength f u (D, w);

[0059] According to a specific embodiment, in step (f), the mechanical property of steel when the total service time T is determined is determined according to D T and w T , and the material parameters are adjusted in the OpenFAST software accordingly;

[0060] According to a specific embodiment, in step (g), steps (a)-(e) are repeated to obtain L i , D si , dD i , and total damage D T When D T = 1, the structure is corroded and fatigued, and at this time, the total service time T is the corrosion fatigue life of the structure under the service environment considering the operation of the wind turbine and the performance degradation after damage. Total damage D T develops as shown in Figure 13 ;

[0061] The method considers the offshore wind power guide pipe rack load time history under the action of wind-wave flow-structure and wind turbine operation in the service state, combines with the refined finite element model analysis, realizes the corrosion fatigue damage position identification and damage calculation, combines with the material performance degradation model after damage, considers the influence of material performance degradation after damage during service, realizes the corrosion fatigue life prediction of offshore wind power structure, and can be used for the remaining corrosion fatigue life evaluation of existing offshore wind power structure, and can be used for the corrosion fatigue life design of newly built offshore wind power structure.

Claims

1. A method for corrosion fatigue damage assessment and life prediction of offshore wind turbine structures considering wind turbine operation and performance degradation after damage, characterized by: The method takes into account the load history of offshore wind turbine jackets under the effects of wind, wave, current, structure and wind turbine operation in service, and combines refined finite element model analysis to achieve corrosion fatigue damage location identification and damage calculation. Combined with a post-damage material performance degradation model, it considers the impact of material performance degradation after damage during service, and achieves corrosion fatigue life prediction of offshore wind turbine structures. The method includes: (a) Generate a wind farm with a duration of dT based on the offshore wind power station service location and wind turbine information and external load parameters, and establish an offshore wind power model in OpenFAST software; (b) Calculate the response of offshore wind turbine structures within dT1 under the coupled effects of wind, wave flow, structure, and turbine operation using OpenFAST, and extract the displacement and force boundary conditions at the top of the tower. (c) Establish a refined finite element model of the structure in ABAQUS, input the boundary conditions extracted in step (b) at the top of the tower, and calculate the stress distribution of the offshore wind turbine structure within the time dT1; (d) Based on the natural atmospheric corrosion test data or empirical formula, the natural atmospheric corrosion degree development function law w(t) of the evaluated steel structure in its service environment is established; based on the high-cycle fatigue test after corrosion or empirical formula and the continuum medium damage mechanics, a nonlinear damage evolution model of steel under different corrosion degrees is established, the damage evolution model parameters C and β are calibrated under each corrosion degree, and the functional relationship C(w) and β(w) between them and the corrosion degree is established, where C(w) and β(w) are obtained from the fatigue test data of steel with corrosion degree w by formula (1): (e) Identify the fatigue-prone location based on stress distribution characteristics, extract the stress time history at this location, and calculate the corrosion fatigue damage D within dT1 time by combining the rain flow counting method with continuum mechanics. s1 , the corrosion degree w of each component in each region of the structure is determined based on the calculated time and the corrosion development model; the fatigue vulnerable position is determined in combination with the structural type and stress distribution, the stress time history at this location is extracted, and the stress amplitude sequence S1 is obtained by statistical analysis using the rain flow counting method; the fatigue damage increment caused by a single load cycle is calculated using formula (2): Among them S max , S min is the maximum stress and minimum stress of each stress amplitude in S1, N is the number of times each stress amplitude corresponds to; calculate the fatigue damage D generated by the standard stress amplitude sequence during the service time dT1 s1 , calculate the number n of dT1 included in one year, calculate the damage dD1 = n·D s1 , repeat this process and accumulate the total fatigue damage D T =∑dD i , total service time T = ∑dT i And the degree of corrosion w T ,in (f) According to the corrosion fatigue damage D T , corrosion degree w T Adjust the material parameters in OpenFAST based on the distribution of the material and the degradation model of the material performance after corrosion fatigue damage, and recalculate the structural response in service state; (g) Repeat (a) to (e) until corrosion fatigue damage D T =1, the structure suffers from corrosion fatigue damage. At this time, the total service time T is the corrosion fatigue life of the structure under the service environment, taking into account the operation of the wind turbine and the performance degradation after damage.

2. The method according to claim 1, wherein In step (a), wave and wind field characteristics are determined based on the location where the offshore wind turbine structure is in service; or Wherein, in step (a), obtaining the wind field with a duration of dT includes obtaining it by citing IEA specifications or obtaining it through measured data; or Wherein, in step (a), a model is established in OpenFAST according to the geometric dimensions of the offshore wind turbine structure to be assessed, and the wave current and wind field with a duration of dT determined according to the service location of the offshore wind turbine structure are applied; or In step (a), the wind turbine weight, center of gravity position, rated power generation and operating status control system parameters are set in the OpenFAST software according to the evaluated structural wind turbine parameters.

3. The method according to claim 1, wherein In step (b), the response of the offshore wind turbine structure under the coupled effects of wind, wave flow, structure and wind turbine operation within the time dT is calculated based on OpenFAST, and the time history curve L1 of the tower top displacement and force boundary condition is extracted.

4. The method according to claim 1, wherein In step (c), a refined finite element model of an offshore wind turbine structure without an upper wind turbine is established in ABAQUS finite element software. By inputting the boundary condition time history curve obtained in step (b) at the top of the tower, the effect of the upper structure on the tower top during service is considered, thereby taking into account the influence of wind, wave flow, and wind turbine operation in the refined finite element analysis. or Wherein, in step (c), a stress distribution cloud map of the offshore wind power structure is obtained based on the finite element calculation results.

5. The method according to claim 1, wherein In step (d), a natural atmospheric corrosion degree development function law w(t) of the assessed steel structure steel in its service environment is established based on natural atmospheric corrosion test data or empirical formula; or In step (d), steel specimens with different corrosion degrees are obtained through natural corrosion, periodic infiltration, salt spray, and energized corrosion. High-cycle fatigue tests are carried out on the steel specimens with different corrosion degrees. According to the results of the high-cycle fatigue tests, a nonlinear damage evolution model of steel under different corrosion degrees is established based on continuum mechanics, and the damage evolution model parameters C(w) and β(w) under each corrosion degree are calibrated. When fatigue performance tests of the corroded steel specimens cannot be carried out, the damage evolution model parameters C(w) and β(w) under each corrosion degree are obtained through existing research data or empirical formulas.

6. The method according to claim 1, wherein In step (e), the fatigue-vulnerable location is determined by combining the structural type and stress distribution, the stress time history at this location is extracted, and the stress amplitude sequence S1 is statistically obtained by the rainflow counting method; or Among them, in step (e), the fatigue damage D generated by the standard stress amplitude sequence during the service time dT1 is calculated s1 , calculate the number n of dT1 included in one year, calculate the damage dD1 = n·D s1 , repeat this process and accumulate the total fatigue damage D T =∑dD i , total service time T = ∑dT i And the degree of corrosion w T .

7. The method according to claim 1, wherein In step (f), the evolution law of the mechanical properties of the steel with the fatigue damage degree D and the corrosion degree w is determined based on the mechanical property test of the steel after corrosion fatigue damage or the empirical formula, including the elastic modulus E(D,w), the yield strength f y (D,w), ultimate strength f u (D,w); or Wherein, in step (f), according to D T and w T Determine the mechanical properties of the steel when the total service time T is determined, and adjust the material parameters accordingly in the OpenFAST software.

8. The method according to claim 1, wherein In step (g), repeat steps (a) to (e) to obtain L i , D si , dD i , and total damage D T , when D T =1, the structure suffers from corrosion fatigue damage. At this time, the total service time T is the corrosion fatigue life of the structure under the service environment, taking into account the operation of the wind turbine and the performance degradation after damage.

9. The method according to any one of claims 1 to 8, wherein the method takes into account the load history of the offshore wind turbine jacket under the influence of wind, wave, current, structure and wind turbine operation in the service state, combines with refined finite element model analysis to achieve corrosion fatigue damage location identification and damage calculation, combines with post-damage material performance degradation model to consider the impact of material performance degradation after damage during service, and realizes the prediction of corrosion fatigue life of offshore wind turbine structures.

10. A method according to any one of claims 1 to 8, wherein the method is used for residual corrosion fatigue life assessment of an existing offshore wind power structure, or for corrosion fatigue life design of a new offshore wind power structure.

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