Fatigue analysis method for offshore wind power supporting structure

Abstract

The invention discloses a fatigue analysis method for an offshore wind power support structure, which comprises the following steps: acquiring fatigue test data of steel, performing S-N curve autonomous fitting based on the fatigue test data, performing finite element analysis, and acquiring a stress response time history of a node to be analyzed; and statistical processing and average stress correction are carried out on the stress response time history based on a rain flow counting method, and a fatigue damage prediction value of the offshore wind power support structure is obtained based on a Palmron-Miner rule. According to the method, the influence of the machining process conditions of the structural material on the fatigue performance is comprehensively considered, and the problem that the obtained fatigue damage predicted value of the offshore wind power supporting structure and the actual fatigue damage have deviation can be effectively solved.

Description

Technical Field

[0001] This application relates to the field of offshore wind power technology, and in particular to a fatigue analysis method for offshore wind power support structures. Background Technology

[0002] Offshore wind power is an important component of the global energy transition towards low carbon emissions. However, offshore wind turbine structures are subjected to the coupled effects of multiple dynamic loads from wind, waves, and currents over long periods, leading to complex fatigue damage risks on structural materials throughout their service life. Therefore, fatigue analysis of offshore wind turbine structures is of great significance for the development and construction of offshore wind power projects.

[0003] In existing technologies, general fatigue damage analysis methods are typically used to obtain wind-induced fatigue damage and wave-induced fatigue damage of monopile structures, and the fatigue damage of monopile structures is obtained by linear superposition. However, this method does not comprehensively consider the influence of the processing conditions of structural materials on fatigue performance, resulting in a large deviation between the theoretical fatigue damage and the actual fatigue damage. Moreover, there is currently no fatigue analysis method for offshore wind power structures that comprehensively considers the influence of the processing conditions of structural materials on fatigue performance. Summary of the Invention

[0004] The purpose of this application is to provide a fatigue analysis method for offshore wind power support structures, aiming to solve the problem of large deviation between theoretical fatigue damage and actual fatigue damage in offshore wind power monopile structures.

[0005] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0006] This application provides a fatigue analysis method for an offshore wind turbine support structure made of steel, comprising the following steps:

[0007] Obtain fatigue test data for the steel;

[0008] Based on the fatigue test data, perform autonomous fitting of the SN curve;

[0009] Finite element analysis was performed on the offshore wind power support structure to obtain the stress response time history of the nodes to be analyzed.

[0010] The stress response time history was statistically processed and the average stress was corrected based on the rainflow counting method.

[0011] The fatigue damage prediction value of the offshore wind power support structure is obtained based on the Palmgren-Miner rule.

[0012] In some embodiments of this application, the step of performing autonomous fitting of the SN curve based on the fatigue test data of the steel includes establishing a relationship expression between the number of cyclic loading N and the loading stress amplitude σ based on a linear mathematical model, and determining the optimal estimate of the average SN curve of the total sample of the fatigue test data.

[0013] In some embodiments of this application, the method includes establishing a relationship between the number of cyclic loading N and the loading stress amplitude σ based on a linear mathematical model, and the relationship expression is as follows:

[0014] x = b - ay;

[0015] In the formula, x = logN;

[0016] Where x is the fatigue life variable, a and b are the material parameters to be fitted, and y is the loading stress amplitude corresponding to a specific value of x.

[0017] In some embodiments of this application, the determination of the optimal estimate of the average SN curve of the total sample of the fatigue test data is determined by the following expression:

[0018]

[0019] In the formula,

[0020]

[0021] Where, x i Let y be the i-th pair of fatigue life variables in a set of fatigue test data. i Let be the applied stress amplitude corresponding to the i-th pair of fatigue life variables, and k be the number of fatigue life variables recorded in a set of fatigue test data.

[0022] In some embodiments of this application, the statistical processing and average stress correction of the stress response time history based on the rainflow counting method includes converting the stress time history into usable stress cycle information, wherein the stress cycle information includes stress amplitude, average stress, and the number of cycles corresponding to the stress amplitude and the average stress.

[0023] In some embodiments of this application, the average stress correction is performed on the obtained stress amplitudes using a Goodman curve, wherein the Goodman curve is expressed as follows:

[0024]

[0025] Where, σ e σ is the stress cycle amplitude under equivalent zero mean stress. m For the mean stress, σu This represents the ultimate tensile strength of the steel.

[0026] In some embodiments of this application, the fatigue damage prediction value of the offshore wind power support structure is obtained based on the Palmgren-Miner rule, and the fatigue damage prediction value D is calculated by the following formula:

[0027]

[0028] Where, n i N represents the number of stress cycles in the i-th group. i The constant amplitude stress amplitude σ i The number of cycles required for fatigue failure to occur under certain conditions.

[0029] In some embodiments of this application, the offshore wind power support structure experiences fatigue failure when the fatigue damage prediction value D equals 1.

[0030] In some embodiments of this application, obtaining fatigue test data of steel includes determining and evaluating the type of steel, designing fatigue tests based on the type of steel, and fabricating standard test specimens.

[0031] In some embodiments of this application, obtaining fatigue test data of steel further includes:

[0032] Multiple equally spaced stress range levels are obtained under a given stress ratio R;

[0033] The loading stress level of the fatigue test is determined such that the fatigue life range includes a difference of at least three orders of magnitude.

[0034] An axial cyclic load is applied to the specimen until the specimen experiences fatigue fracture or the number of cycles reaches a preset number. The number of cycles N and the loading stress amplitude σ at which the specimen experiences fatigue fracture or reaches the preset number of cycles are obtained.

[0035] This application has the following beneficial effects:

[0036] This application provides a fatigue analysis method for offshore wind power support structures. Based on fatigue test data of steel under different processing conditions, the method includes acquiring fatigue test data of the steel and performing autonomous fitting of the SN curve based on the fatigue test data. Furthermore, it performs finite element analysis of the offshore wind power structure to obtain the stress response time history of the analyzed nodes. The method also performs statistical processing and average stress correction on the stress response time history based on the rainflow counting method, and obtains the predicted fatigue damage value of the offshore wind power support structure based on the Palmgern-Miner rule. This application comprehensively considers the influence of the processing conditions of the structural materials on fatigue performance, effectively solving the problem of deviation between the obtained predicted fatigue damage value and the actual fatigue damage of the offshore wind power support structure. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the fatigue analysis method for offshore wind power support structures in the embodiments of this application;

[0038] Figure 2 This is a geometrical schematic diagram of a standard round bar specimen in an embodiment of this application;

[0039] Figure 3 This is an example of an SN curve fitted based on fatigue test data in this application embodiment;

[0040] Figure 4 This is a schematic diagram of the finite element model of the offshore wind power monopile support structure in the embodiments of this application;

[0041] Figure 5 This is a time history diagram of the stress at the offshore wind power node to be tested in the embodiments of this application. Detailed Implementation

[0042] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification.

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the accompanying drawings and embodiments. To enable those skilled in the art to better understand the solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0044] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, article, or apparatus that comprises a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element; for example, a process, method, system, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0045] It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0046] In the embodiments of this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design; rather, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0047] Offshore wind turbine monopile structures are subjected to harsh environmental conditions involving multiple dynamic loads such as wind, waves, currents, and sea ice over long periods. This leads to complex fatigue damage risks on the structural materials throughout their service life. Furthermore, the processing and heat treatment conditions of the structural materials significantly influence their fatigue performance. Therefore, comprehensive fatigue analysis of offshore wind turbine structures is of great importance for the development and construction of offshore wind power projects.

[0048] In existing technologies, general fatigue damage analysis methods are typically used to obtain wind-induced and wave-induced fatigue damage of monopile structures, and the fatigue damage of the monopile structure is obtained through linear superposition. However, this method does not comprehensively consider the influence of the processing conditions of the structural materials on fatigue performance. For example, it does not comprehensively consider the impact of different heat treatment processes or rolling directions on the fatigue performance of the same grade of steel, resulting in a large deviation between the obtained theoretical fatigue damage and the actual fatigue damage. Therefore, there is an urgent need to provide a fatigue analysis method for offshore wind turbine support structures that comprehensively considers the influence of the processing conditions of the structural materials on fatigue performance.

[0049] To address the aforementioned problems in the prior art, this application provides a fatigue analysis method for offshore wind power support structures. For example... Figure 1 As shown, Figure 1 This is a schematic flowchart of a fatigue analysis method for an offshore wind power support structure in some embodiments of this application. In some embodiments, the fatigue analysis method for the offshore wind power support structure, which is made of steel, includes the following steps S100-S500:

[0050] Step S100: Obtain fatigue test data of steel.

[0051] This application's embodiment describes a fatigue analysis method for offshore wind power support structures based on fatigue test data of steel monopile. In step S100, fatigue test data of steel under different processing conditions is acquired, and fatigue analysis is performed based on this data. It is understood that these different processing conditions can refer to different heat treatment processes for the same grade of monopile steel, or different rolling directions for the same grade of monopile steel.

[0052] To address the aforementioned problems in the prior art, the inventors of this application propose a fatigue analysis method for offshore wind turbine support structures based on fatigue test data of steel materials under different processing conditions. This method comprehensively considers the impact of processing conditions on the fatigue performance of monopile support structure materials. The embodiments of this application extend the applicability of material fatigue test data from ideal laboratory conditions to the complex load application environment of actual offshore wind turbines. This solves the problem in related prior art where insufficient material-operating-condition compatibility leads to overly critical fatigue damage assessment results for offshore wind turbine support structures, providing important reference value for the structural optimization design and operation and maintenance of offshore wind power.

[0053] In step S100, fatigue test data of the steel is obtained, specifically including the following steps S101-S102:

[0054] Step S101: Determine the type of steel to be evaluated, design fatigue tests based on the type of steel, and prepare standard test specimens.

[0055] In step S101, in order to ensure the objectivity of the obtained fatigue test data of steel materials, the type of steel material is determined through preliminary evaluation, and fatigue tests are designed based on the steel material; and standard test specimens for fatigue tests are made by processing the raw materials into standard round bar specimens that meet the requirements of industry standards.

[0056] In step S101, the standard specimen used in the fatigue test can be a standard round bar specimen or a dumbbell-shaped plate specimen, or other standard specimens, to obtain the relationship between the fatigue loading stress amplitude and fatigue life of the steel.

[0057] Step S102: Obtain multiple equally spaced stress range levels under a determined stress ratio R;

[0058] Determine the loading stress level for fatigue testing so that the fatigue life range includes a difference of at least three orders of magnitude.

[0059] An axial cyclic load is applied to the specimen until fatigue fracture occurs or the preset number of cycles is reached. The number of cycles N and the loading stress amplitude σ at which fatigue fracture occurs or the preset number of cycles is reached are obtained.

[0060] In step S102, given a determined stress ratio R, at least a plurality of equally spaced stress range levels are obtained, each stress level including at least a plurality of test specimens. In this embodiment, fitting a set of material-based SN curves requires at least 30 specimens, i.e., given a determined stress ratio R (typically -1), at least 5 equally spaced stress range levels are obtained, with at least 6 specimens tested at each stress level.

[0061] Simultaneously, given the stress levels applied in the fatigue tests, it is ensured that the fatigue life range covers a difference of at least three orders of magnitude. In this step, the lowest load level can be selected as 60% of the steel's yield strength, corresponding to the stress level at the material's fatigue limit; the highest load level can be selected as 80% of the steel's yield strength, corresponding to the stress level at which the material will exhibit plastic strain. The specific stress level values ​​can be fine-tuned based on the preliminary fatigue life test results of actual steel, and will not be elaborated further here.

[0062] Through fatigue test design, axial cyclic loads are applied to standard specimens on a material fatigue testing machine until the specimens experience fatigue fracture or the preset number of cycles is reached. The number of cycles N and the applied stress amplitude σ are recorded for each standard specimen at the point of fatigue fracture or reaching the preset number of cycles. In this step, the number of axial cyclic loads applied to the standard specimens until fatigue fracture or reaching the preset number of cycles can be between 1,000,000 and 2,000,000.

[0063] Step S200: Perform autonomous fitting of SN curve based on fatigue test data.

[0064] In existing technologies, the general SN curve for steel is usually used directly without taking into account the impact of different heat treatment processes or rolling directions on the fatigue performance of the same grade of steel. Furthermore, the SN curve under fixed stress ratio conditions is directly used without establishing a real-time stress ratio influence correction mechanism. The fatigue damage prediction results obtained under complex load conditions are biased towards danger. Moreover, the standard SN curve obtained by existing technologies in an environment with a mean stress of 0 is difficult to apply to the fatigue assessment of actual engineering structures under high mean stress.

[0065] Based on the aforementioned technical issues, in step S200, the SN curve is autonomously fitted based on the aforementioned fatigue test data. This allows the average stress correction for stress cycles in this embodiment to effectively extend the applicable scenarios of the material fatigue test data from an ideal laboratory environment to the complex load application environment of offshore wind turbines, making the test results more universal and practical.

[0066] In step S200, the SN curve is automatically fitted based on the fatigue test data. Specifically, this includes establishing a relationship between the number of cyclic loading N and the loading stress amplitude σ based on a linear mathematical model, and determining the optimal estimate of the average SN curve of the total sample of fatigue test data.

[0067] Based on a linear mathematical model, the relationship between the number of cyclic loading times N and the loading stress amplitude σ is expressed as follows:

[0068] x = b - ay;

[0069] In the formula, x = logN;

[0070] Where x is the fatigue life variable, a and b are the material parameters to be fitted, and y is the loading stress amplitude corresponding to a specific value of x.

[0071] The optimal estimate of the average SN curve for the total sample of fatigue test data is determined by the following expression:

[0072]

[0073] In the formula,

[0074]

[0075] Where, x i Let y be the i-th pair of fatigue life variables in a set of fatigue test data. i Let be the applied stress amplitude corresponding to the i-th pair of fatigue life variables, and k be the number of fatigue life variables recorded in a set of fatigue test data.

[0076] Step S300: Perform finite element analysis on the offshore wind power support structure to obtain the stress response time history of the nodes to be analyzed.

[0077] In step S300, the offshore wind turbine geometry is evaluated and analyzed, and finite element modeling and meshing are performed using shell or solid elements at the principal scale, taking into account material mechanical properties, boundary conditions, and the actual operating environment and loads. Finite element analysis is then conducted on the offshore wind turbine support structure, and the stress response time history at the analyzed nodes is obtained.

[0078] Step S400: Perform statistical processing and mean stress correction on the stress response time history based on the rainflow counting method.

[0079] In step S400, the stress response time history is statistically processed and the mean stress is corrected based on the rainflow counting method. Specifically, the stress time history is converted into usable stress cycle information, which includes stress amplitude, mean stress, and the number of cycles corresponding to stress amplitude and mean stress.

[0080] It also includes using Goodman curves to perform average stress correction on the obtained stress amplitudes. The Goodman curve is expressed as follows:

[0081]

[0082] Where, σ e σ is the stress cycle amplitude under equivalent zero mean stress. m For the mean stress, σ u This represents the ultimate tensile strength of the steel.

[0083] By using Goodman curves to correct the average stress of each obtained stress amplitude, and in the fatigue analysis stage, based on the actual stress time history data of the offshore wind turbine support structure, the average stress under each stress cycle is statistically calculated using the rainflow counting method. By introducing Goodman diagrams, adaptive average stress correction for different working conditions is completed, realizing dynamic calibration of stress amplitude under complex load conditions, and fatigue damage analysis is performed based on the linear fatigue damage accumulation law. This extends the applicability of the SN curve fitted in the laboratory under constant stress ratio conditions to random load conditions with dynamic changes in stress ratio in actual working conditions.

[0084] Step S500: Obtain the fatigue damage prediction value of the offshore wind power support structure based on the Palmgren-Miner rule.

[0085] In step S500, the fatigue damage prediction value of the offshore wind turbine support structure is obtained based on the Palmgren-Miner rule, and the fatigue damage prediction value D is calculated by the following formula:

[0086]

[0087] Where, n i N represents the number of stress cycles in the i-th group. i The constant amplitude stress amplitude σ i The number of cycles required for fatigue failure to occur under certain conditions.

[0088] In step S500, this embodiment of the application combines the obtained modified stress cycle amplitude, cycle technology and SN curve, and uses the Palmgren-Miner rule to predict fatigue damage of the offshore wind power support structure. When the fatigue damage prediction value D is equal to or greater than 1, the offshore wind power support structure fails due to fatigue.

[0089] This application provides a fatigue analysis method for offshore wind power support structures. Based on fatigue test data of steel under different processing conditions, combined with the obtained corrected stress cycle amplitude, cycle technology and SN curve, and using the Palmgern-Miner rule to predict fatigue damage of offshore wind power support structures, this method comprehensively considers the influence of the processing conditions of structural materials on fatigue performance, and can effectively solve the problem of deviation between the obtained fatigue damage prediction value and the actual fatigue damage of offshore wind power support structures.

[0090] In order to objectively evaluate the technical effects of the embodiments of this application, the present application will be described in detail below through specific embodiments. However, the embodiments of this application are not limited to the following specific embodiments, and appropriate modifications can be made within the scope of unchanged main rights.

[0091] This embodiment provides a fatigue analysis method for offshore wind turbine support structures, based on material fatigue test data of the target steel under different rolling directions. In this embodiment, the offshore wind turbine support structure is made of Q355D steel, and the steel material properties required for the design fatigue test and subsequent fatigue analysis summary are shown in Table 1.

[0092] Table 1. Material Properties of Q355D Steel

[0093]

[0094] The Q355D steel was fabricated into standard round bar specimens conforming to industry standards, such as... Figure 2 As shown, Figure 2 This is a geometric schematic diagram of the standard round bar specimen in this embodiment, that is, according to Figure 2Standard round bar specimens were prepared along the rolling direction of the steel plate and perpendicular to the rolling direction, as shown in the diagram, to ensure the objectivity of the fatigue test data of the steel specimens obtained.

[0095] In this embodiment, the rolling direction of Q355D steel is taken into consideration, and based on the preliminary test results, the lowest load level is set to the steel yield strength σ. y When the load was between 60% and 70%, the number of loading cycles for the specimen exceeded the preset stop loading cycle of 2,000,000.

[0096] The test scheme used in this embodiment adjusts the lowest level load to 70% of the steel's yield strength and re-divides the other load levels at equal intervals; the final material fatigue test stress amplitude is divided into 70.0% σ. y 72.5% σ y 75.0% σ y 77.5% σ y 80.0% σ y Eight specimens were tested for each stress level and corresponding sampling direction, i.e., 40 specimens were tested along the rolling direction and 40 specimens were tested perpendicular to the rolling direction. In this embodiment, the fatigue test loading frequency was 15 Hz.

[0097] Using the provided SN curve fitting method, the optimal estimate of the average SN curve of the total sample of material fatigue test data was determined, and the SN curves of Q355D steel in different rolling directions were fitted. The parameters of the fitted SN curves are shown in Table 2.

[0098] Table 2 SN curve parameters for Q355D steel

[0099]

[0100] The obtained SN curve is plotted on a logarithmic coordinate system, such as... Figure 3 As shown, Figure 3 This is the SN curve plot based on fatigue test data fitted in this embodiment.

[0101] A finite element model of a monopile support structure for an offshore wind power plant was established and meshed, as follows: Figure 4 As shown, Figure 4 This is a schematic diagram of the finite element model of the offshore wind turbine monopile support structure in this embodiment. The finite element model is divided into 1548 shell elements, containing 1560 nodes, and node 569 is selected for fatigue analysis in this embodiment. Fixed constraints are set at the bottom of the structure, and a concentrated load along the horizontal direction is applied to the top of the tower. The relationship between the applied load and the first principal stress of the node under test is obtained, thereby converting the external load time history curve into a stress time history curve, as shown below. Figure 5 As shown, Figure 5 This is a time history diagram of the stress at the offshore wind power node to be tested in this embodiment.

[0102] The stress time history of the test node of the monopile support structure is statistically processed based on the rainflow counting method, and then converted into usable stress cycles, including stress amplitude, average stress, and the number of cycles corresponding to stress amplitude and average stress.

[0103] The determined SN curve was corrected for mean stress using the Goodman curve.

[0104] Combining the obtained corrected stress cycle amplitude, cycle count, and SN curve, the design fatigue factor is set to 6. Based on the Palmgren-Miner rule, fatigue damage prediction is performed on the test nodes of the offshore wind turbine monopile support structure. For all stress amplitudes below the fatigue limit of the SN curve, the corresponding fatigue damage is set to 0.

[0105] In this embodiment, fatigue damage results at the test nodes of offshore wind power monopile support structures along different steel plate rolling directions are obtained, as shown in Table 3. At the same time, the fatigue damage calculation results of the SN curve fitted by the test data without using the average stress correction described in this invention are also listed in Table 3 for comparison.

[0106] Table 3. Fatigue damage at key nodes of monopile foundation for 222MW offshore wind turbines

[0107]

[0108]

[0109] As can be seen from Table 3 above, based on the fatigue analysis method provided in this application, the actual SN curves of steel in different rolling directions were obtained through experiments for fatigue analysis. The difference in fatigue damage calculation results along different rolling directions is close to 4 times.

[0110] However, existing technologies do not consider the influence of the steel rolling direction on the fatigue performance of materials. They only select a specific or general SN curve for analysis of specific steel or structures, which may lead to overly conservative or dangerous prediction results caused by the material processing and laying direction. The obtained fatigue damage results have a large deviation from the actual fatigue damage.

[0111] Moreover, combined Figure 5As shown in Table 3, the actual load time history of offshore wind power is not a constant average stress, which makes it difficult to directly apply the SN curves obtained in the laboratory environment under a specific average stress. However, the average stress correction for stress cycles in the fatigue analysis method provided in this application can effectively extend the applicable scenarios of material fatigue test data from the ideal laboratory environment to the complex load application environment of offshore wind turbines, making the test results more universal and practical.

[0112] It should be noted that although the above implementation only shows fatigue analysis of Q355D steel and offshore wind turbine monopile support structures with different rolling directions, in actual implementation, this step can also consider the influence of different steel processing techniques on the material's fatigue performance, such as the use of heat treatment processes. This step can also be used for fatigue analysis of offshore wind turbines with different steel materials and foundation types.

[0113] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. All embodiments obtained by any modifications, alterations or equivalent substitutions made by those skilled in the art without departing from the technical concept of this application shall fall within the scope of protection of the claims of this application.

Claims

1. A fatigue analysis method for an offshore wind turbine support structure, wherein the offshore wind turbine support structure is made of steel, characterized in that, Includes the following steps: Obtain fatigue test data for the steel; Based on the fatigue test data, perform autonomous fitting of the SN curve; Finite element analysis was performed on the offshore wind power support structure to obtain the stress response time history of the nodes to be analyzed. The stress response time history was statistically processed and the average stress was corrected based on the rainflow counting method. The fatigue damage prediction value of the offshore wind power support structure is obtained based on the Palmgren-Miner rule.

2. The fatigue analysis method for offshore wind power support structures according to claim 1, characterized in that, The automatic fitting of the SN curve based on the fatigue test data of the steel includes establishing a relationship expression between the number of cyclic loading N and the loading stress amplitude σ based on a linear mathematical model, and determining the optimal estimate of the average SN curve of the total sample of the fatigue test data.

3. The fatigue analysis method for offshore wind power support structures according to claim 2, characterized in that, The relationship between the number of cyclic loading N and the loading stress amplitude σ is established based on a linear mathematical model, and the expression of the relationship is as follows: x = b - ay; In the formula, x = logN; Where x is the fatigue life variable, a and b are the material parameters to be fitted, and y is the loading stress amplitude corresponding to a specific value of x.

4. The fatigue analysis method for offshore wind power support structures according to claim 3, characterized in that, The optimal estimate of the average SN curve for the total sample of the fatigue test data is determined by the following expression: In the formula, Where, x i Let y be the i-th pair of fatigue life variables in a set of fatigue test data. i Let be the applied stress amplitude corresponding to the i-th pair of fatigue life variables, and k be the number of fatigue life variables recorded in a set of fatigue test data.

5. The fatigue analysis method for offshore wind power support structures according to claim 1, characterized in that, The statistical processing and average stress correction of the stress response time history based on the rainflow counting method includes converting the stress time history into usable stress cycle information, which includes stress amplitude, average stress, and the number of cycles corresponding to the stress amplitude and the average stress.

6. The fatigue analysis method for offshore wind power support structures according to claim 5, characterized in that, This includes applying an average stress correction to each of the obtained stress amplitudes using a Goodman curve, which is expressed as follows: Where, σ e σ is the stress cycle amplitude under equivalent zero mean stress. m For the mean stress, σ u This represents the ultimate tensile strength of the steel.

7. The fatigue analysis method for offshore wind power support structures according to claim 1, characterized in that, The fatigue damage prediction value of the offshore wind power support structure is obtained based on the Palmgren-Miner rule, and the fatigue damage prediction value D is calculated by the following formula: Where, n i N represents the number of stress cycles in the i-th group. i The constant amplitude stress amplitude σ i The number of cycles required for fatigue failure to occur under certain conditions.

8. The fatigue analysis method for offshore wind power support structures according to claim 7, characterized in that, When the fatigue damage prediction value D equals 1, the offshore wind power support structure experiences fatigue failure.

9. The fatigue analysis method for offshore wind power support structures according to claim 1, characterized in that, The process of obtaining fatigue test data of steel under different processing conditions includes determining and evaluating the type of steel, designing fatigue tests based on the type of steel, and preparing standard test specimens.

10. The fatigue analysis method for offshore wind power support structures according to claim 9, characterized in that, Also includes: Multiple equally spaced stress range levels are obtained under a given stress ratio R; The loading stress level of the fatigue test is determined such that the fatigue life range includes a difference of at least three orders of magnitude. An axial cyclic load is applied to the specimen until the specimen experiences fatigue fracture or the number of cycles reaches a preset number. The number of cycles N and the loading stress amplitude σ at which the specimen experiences fatigue fracture or reaches the preset number of cycles are obtained.

Images