Average stress correction method for ultimate strength of butt weld of offshore wind turbine

Abstract

The invention discloses an average stress correction method for the ultimate strength of a butt weld of an offshore wind turbine. The average stress correction method comprises the following steps: step 1, determining welding process parameters and preparing a test piece for a tensile test; 2, quantifying the ultimate tensile property of the weld joint through a tensile test to eliminate the assumed deviation of the base metal; 3, establishing multi-scale data association from macrostructure analysis to local stress statistics; 4, the average stress is corrected based on the actually-measured weld joint ultimate tensile property, and an equivalent zero average stress amplitude is generated; and step 5, outputting a fatigue damage interval for preliminary design optimization of the welding area of the offshore wind turbine support structure.

Description

Technical Field

[0001] This invention belongs to the technical field of structural integrity assessment of welded joints in offshore wind power generation, and specifically relates to an average stress correction method for the ultimate strength of butt welds in offshore wind turbines. Background Technology

[0002] Offshore wind turbines are key equipment in the renewable energy sector, making significant contributions to the global supply of clean energy. However, their supporting structures contain numerous transverse and longitudinal butt welds. These welds, due to complex microscopic defects and material properties, result in high residual stress and unique stress distributions, significantly impacting the structure's fatigue life. Furthermore, the welded areas of offshore wind turbines are most susceptible to fatigue failure due to the cyclical effects of wind, waves, and currents in the harsh marine environment. The accuracy of fatigue life prediction directly affects structural safety and economic efficiency. Mean stress correction, as a core component of fatigue damage assessment, requires comprehensive consideration of the actual mechanical properties and load characteristics of the welded area. Traditional methods typically correct directly based on the ultimate strength of the base material. However, due to the influence of welding processes, residual stress, and microscopic defects, the mechanical properties of welds differ significantly from those of the base material, leading to correction results that easily deviate from reality. The finite element method (FEM) is one of the important tools for analyzing weld stress distribution. However, in the preliminary design stage of offshore wind turbines, performing detailed modeling of various weld geometries and microstructures to screen pre-design schemes would result in high computational costs and could also reduce the effectiveness of fatigue damage prediction due to unreasonable assumptions about residual stress distribution or material properties. Therefore, there is an urgent need for an efficient and reasonable mean stress correction method to meet the requirements of the preliminary design of offshore wind turbines.

[0003] In existing technologies, it is necessary to establish a refined finite element model that includes the geometric contour and micro-defects of the butt weld. For example, using solid elements or shell elements to simulate the weld structure leads to complex modeling and time-consuming calculations, making it difficult to meet the needs of efficient evaluation in the preliminary design stage. Traditional mean stress correction is based on the ultimate strength of the base material and does not consider the strength degradation or strengthening effect of the weld area caused by the welding process, resulting in deviations between the correction parameters and the actual weld performance. Furthermore, the correlation between the measured ultimate strength data of the weld area and the time history of the overall dynamic load of the structure has not been established, making it difficult to effectively predict fatigue damage under complex working conditions. Summary of the Invention

[0004] This application provides a method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines, comprising the following steps:

[0005] Step 1: Determine the welding process parameters and prepare the specimens for the tensile test;

[0006] Step 2: Quantify the ultimate tensile properties of the weld through tensile testing to eliminate biases in the assumptions about the base material.

[0007] Step 3: Establish multi-scale data correlation from macroscopic structural analysis to local stress statistics;

[0008] Step 4: Correct the mean stress based on the measured ultimate tensile properties of the weld to generate an equivalent zero mean stress amplitude.

[0009] Step 5: Output the fatigue damage range for preliminary design optimization of the welding area of ​​the offshore wind turbine support structure.

[0010] Based on the measured ultimate strength of butt welds, this application performs average stress correction on the fatigue stress cycle of the welded area of ​​the offshore wind turbine support structure, solving the problem of low computational efficiency caused by the reliance on complex and high-precision finite element analysis in the existing fatigue analysis of the welded area of ​​the offshore wind turbine support structure, and realizing efficient and reasonable prediction of weld fatigue damage in the preliminary design stage of offshore wind turbines.

[0011] The technical solution provided in this application also has the following technical features:

[0012] Preferably, in one embodiment of this application, in step one, the welding process parameters include parameters such as steel type, welding form, bevel form and size, welding wire grade, welding wire diameter, interpass temperature, filling speed, welding current, and arc voltage.

[0013] Preferably, in one embodiment of this application, in step one, butt welding of steel plates is performed according to the determined welding parameters, and specimens for axial tensile testing of the welded joint are prepared along the transverse and longitudinal positions of the weld.

[0014] Preferably, in one embodiment of this application, in step one, the transverse specimen is a plate-shaped tensile specimen, and the longitudinal tensile specimen is a full-weld round bar tensile specimen; for plates with a thickness of less than 20 mm, a full-thickness specimen should be used; the longitudinal round bar tensile specimen is a full-weld material specimen, and the diameter of the working section of the round bar is determined according to the actual weld shape, and its diameter ensures that the working section of the specimen is entirely composed of weld material.

[0015] Preferably, in one embodiment of this application, in step two, the ultimate tensile strength of the weld is determined: the ultimate tensile strength σ of the transverse specimen and the longitudinal specimen is finally measured. u Take the average value.

[0016] Preferably, in one embodiment of this application, step two, performing a tensile test on an electronic universal testing machine, includes the following steps:

[0017] Step 501: Select the test specimen, measure the characteristic geometric dimensions of the test section of the specimen with a vernier caliper and calculate the initial cross-sectional area S0 of the test section, and clamp the specimen;

[0018] Step 502: After moving the crossbeam of the testing machine to a suitable position via the control terminal on the gatepost, place the specimen into the fixture and then clamp the upper and lower clamps.

[0019] Step 503: Clear the existing test data records and set the corresponding loading speed to start this loading;

[0020] Step 504: After the specimen fractures, record the maximum load F applied during the tensile process. m The loading speed was kept constant during the test.

[0021] Step 505: Repeat steps 501-504 to complete the test of the next specimen, until all required test specimens have been tested. After compiling the experimental data, calculate the ultimate tensile strength σ for each specimen. u During each test, the loading rate and test parameter settings should be kept consistent.

[0022] Step 506, the ultimate tensile strength σ u The calculation formula is as follows:

[0023]

[0024] Step 507: The ultimate tensile strength σ of each transverse and longitudinal specimen is finally measured. u Take the average value to obtain the ultimate tensile strength of the weld representing the welding type.

[0025] Preferably, in one embodiment of this application, step three, establishing multi-scale data association, includes the following steps:

[0026] Step 301: Based on the analyzed support geometry and main dimensions of the offshore wind turbine, establish its structural finite element model and perform finite element analysis to obtain the stress response time history at the nodes to be analyzed of the offshore wind turbine.

[0027] Step 302: Calculate the stress concentration factor SCF at the welding position, and multiply the stress response time history obtained from the finite element analysis by the stress concentration factor SCF to obtain the stress response time history representing the weld area.

[0028] Step 303, the stress concentration factor SCF is calculated as follows:

[0029]

[0030] In the formula

[0031] δ0=0.05t

[0032] Where, δ m δ0 represents the actual non-parallelism of the butt plates, δ0 represents the inherent misalignment deviation of the butt weld, and t represents the plate thickness.

[0033] Preferably, in one embodiment of this application, step four, correcting the average stress, includes the following steps:

[0034] Step 401: Statistically process the processed stress time history based on the rainflow counting method to transform it into a stress cycle that can be used for fatigue analysis, including the actual stress amplitude δ. a The number of cycles n corresponding to each stress amplitude;

[0035] Step 402, based on the experimentally obtained ultimate tensile strength σ of the weld. u The obtained stress amplitudes are corrected by averaging the Goodman and Gerber curves so that the subsequent SN curves can be directly used for fatigue life prediction.

[0036] The Goodman curve formula is as follows:

[0037]

[0038] Where σ Goodman σ represents the stress cycle amplitude under the equivalent zero mean stress, corrected based on the Goodman curve. m The average stress;

[0039] The formula for the Gerber curve is as follows:

[0040]

[0041] Where σ Gerber The stress cycle amplitude is the equivalent zero average stress value based on the Gerber curve correction.

[0042] Preferably, in one embodiment of this application, in step five, σ Goodman With σ Gerber The corresponding number of cycles is used for fatigue analysis, where σ is the basis. Goodman The calculated fatigue damage is the upper limit of the fatigue damage value at the weld position, based on σ. Gerber The calculated fatigue damage is the lower limit of the fatigue damage value at the welding position; fatigue analysis is performed using the stress cycle amplitude after mean stress correction to determine the range of fatigue damage values ​​for the offshore wind turbine support structure, which is used for design scheme selection in the preliminary design stage.

[0043] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0044] 1. This application corrects the average stress by measuring the ultimate strength of the weld, which overcomes the deviation of traditional methods based on the strength of the base material, truly reflects the performance of the weld, avoids conservative or overly optimistic predictions caused by differences in welding processes, improves the accuracy of fatigue life prediction, and enhances structural safety.

[0045] 2. This application adopts a simplified finite element model and SCF, which eliminates the steps of complex weld modeling and transient dynamic analysis, avoids complex modeling and high-precision calculation, significantly reduces resource consumption and time costs, and meets the high-efficiency evaluation requirements of the preliminary design of offshore wind turbines.

[0046] 3. This application connects the measured data with the SCF calculation and SN curve recommended by industry standards, ensuring that the test results can be directly integrated into the existing design process methods. It is applicable to various offshore wind turbine foundation types, can take into account the influence of different welding processes, and enhances the flexibility of the structural design optimization process. Attached Figure Description

[0047] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0048] Figure 1 This is a flowchart illustrating the average stress correction method for the ultimate strength of butt welds in offshore wind turbines according to the present invention.

[0049] Figure 2 This is a geometrical diagram of a material specimen with weld seams and a diagram of sampling on a butt-welded steel plate.

[0050] Figure 3 A schematic diagram showing the V-groove shape and weld bead distribution for butt welding;

[0051] Figure 4 A schematic diagram of the geometric dimensions of the specimen for the ultimate tensile test.

[0052] Figure 5 This is the stress-time history of the welded joints to be tested on an offshore wind turbine. Detailed Implementation

[0053] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings. These embodiments are only for illustrating this application and are not intended to limit the invention.

[0054] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0055] In the description of this invention, 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 a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0057] like Figure 1 A method for correcting the mean stress of offshore wind turbines based on the ultimate tensile performance test of butt welds includes the following steps:

[0058] Step 1: Determine the type of steel used in the support structure of the offshore wind turbine to be evaluated, and design detailed parameters for butt welding of steel plates, including welding method, bevel type and size, welding wire grade, welding wire diameter, interpass temperature, filling speed, welding current, arc voltage, etc.

[0059] Step 2: Perform butt welding of steel plates according to the determined detailed welding parameters, and prepare specimens for axial tensile testing of the welded joint along the transverse and longitudinal positions of the weld.

[0060] Step 3, the transverse specimen is a plate-shaped tensile specimen, and the longitudinal tensile specimen is a full-weld round bar-shaped tensile specimen. The geometric diagram of the specimen and the sampling locations on the welded steel plate are shown below. Figure 2 As shown.

[0061] Step 4: For transverse plate thicknesses less than 20mm, full-thickness specimens shall be used; for longitudinal cylindrical tensile specimens, full-weld material specimens shall be used, and the diameter of the working section of the cylindrical bar shall be determined according to the actual weld shape, and its diameter shall ensure that the working section of the specimen is entirely composed of weld material.

[0062] Step 5: Perform a tensile test on an electronic universal testing machine. The specific steps are as follows:

[0063] Step 501: Select the test specimen, measure the characteristic geometric dimensions of the test section of the specimen with a vernier caliper and calculate the initial cross-sectional area S0 of the test section, and clamp the specimen.

[0064] Step 502: Move the crossbeam of the testing machine to a suitable position via the control terminal on the gatepost, then place the specimen into the fixture, and then clamp the upper and lower clamps.

[0065] Step 503: Clear the existing test data records and set the corresponding loading speed to start this loading.

[0066] Step 504: After the specimen fractures, record the maximum load F applied during the tensile process. m The loading speed was kept constant during the test.

[0067] Step 505: Repeat steps 501-504 to complete the test of the next specimen, until all required test specimens have been tested. After compiling the experimental data, calculate the ultimate tensile strength σ for each specimen. u During each test, the test parameters, such as the loading rate, should be kept consistent.

[0068] Step 506, the ultimate tensile strength σ u The calculation formula is as follows:

[0069]

[0070] Step 507: The ultimate tensile strength σ of each transverse and longitudinal specimen is finally measured. u Take the average value to obtain the ultimate tensile strength of the weld representing the welding type.

[0071] Step 6: Based on the analyzed support geometry and main dimensions of the offshore wind turbine, establish its structural finite element model and perform finite element analysis to obtain the stress response time history at the nodes to be analyzed of the offshore wind turbine.

[0072] Step 7: Calculate the stress concentration factor (SCF) at the welding position. Multiply the stress response time history obtained from the finite element analysis by the stress concentration factor (SCF) to obtain the stress response time history representing the weld area.

[0073] Step 8, the stress concentration factor SCF is calculated as follows:

[0074]

[0075] In the formula

[0076] δ0=0.05t

[0077] Where, δ m δ0 represents the actual non-parallelism of the butt plates, δ0 represents the inherent misalignment deviation of the butt weld, and t represents the plate thickness.

[0078] Step 9: Statistically process the processed stress time history using the rainflow counting method to transform it into stress cycles suitable for fatigue analysis, including the actual stress amplitude δ. a The number of cycles n corresponding to each stress amplitude.

[0079] Step 10, based on the experimentally obtained ultimate tensile strength σ of the weld. u The obtained stress amplitudes were corrected by averaging the stress using Goodman and Gerber curves so that the subsequent SN curves could be directly used for fatigue life prediction.

[0080] Step 11, the Goodman curve formula is as follows:

[0081]

[0082] Where σ Goodman σ represents the stress cycle amplitude under the equivalent zero mean stress, corrected based on the Goodman curve. m The average stress is given.

[0083] Step 12, the formula for the Gerber curve is as follows:

[0084]

[0085] Where σ Gerber The stress cycle amplitude under the equivalent zero mean stress after Gerber curve correction.

[0086] Step 13, σ after the above average stress correction process Goodman With σ Gerber The corresponding cycle number information can be used in fatigue analysis, where σ is the basis for this information. Goodman The calculated fatigue damage is generally the upper limit of the fatigue damage value at the weld location, based on σ. Gerber The calculated fatigue damage is generally the lower limit of the fatigue damage value at the weld location. Fatigue analysis using the stress cycle amplitude after mean stress correction can determine the approximate range of fatigue damage values ​​for offshore wind turbine support structures, providing data support for design scheme selection in the preliminary design stage.

[0087] This application proposes a method for correcting the average stress of the measured ultimate strength of butt welds. By conducting tensile tests on specimens with welds in the transverse and longitudinal directions, the ultimate tensile strength is measured, and this strength value is incorporated into the expression of the Goodman and Gerber diagrams to achieve a reasonable correction of the average stress in the weld area.

[0088] This application directly relies on the measured properties of weld materials, effectively reflecting the impact of defects and residual stress introduced during the welding process, and significantly improving the accuracy of fatigue life prediction. Furthermore, this invention combines finite element analysis with stress concentration factors specified in industry standards, employing a simplified finite element model without weld details for preliminary fatigue damage prediction. Through mean stress correction based on measured ultimate strength, a relatively reasonable preliminary assessment of fatigue damage can be obtained without relying on detailed modeling of weld micro-defects. This invention significantly reduces computation time and resource consumption, making it suitable for rapid analysis and optimization in the initial design phase of offshore wind turbines.

[0089] Specifically, in one embodiment of this application, such as Figure 1 As shown, this invention provides a method for correcting the average stress of offshore wind turbines based on the ultimate tensile performance test of butt welds. In this embodiment, based on the established average stress correction method, the ultimate tensile performance test of butt welds of a single-pile foundation offshore wind turbine is carried out, along with average stress correction and fatigue damage prediction.

[0090] The case study describes a single-pile offshore wind turbine foundation steel plate connection using a full-penetration butt weld, achieved through submerged arc welding. According to GB / T 25774.2-2016 standard, for 18mm thick steel plates, the butt weld should have a double-sided V-groove, with dimensions and weld bead distribution as follows. Figure 3 As shown, the specific dimensional parameters are listed in Table 1. According to GB / T 5293-2018 standard, the welding process parameters are shown in Table 2. Before welding, the steel plate base material needs to be surface-treated to remove surface oil, oxide film, and impurities. Based on the above welding process parameters, butt welding was performed on the steel plates. To meet the requirements for preparing test pieces, the steel plates were welded along both the long and short sides, resulting in two different welded steel plates.

[0091] according to Figure 2 The technical solution described in this invention designs specimen size parameters for testing the ultimate tensile properties of welded joints, which are divided into transverse plate-shaped tensile specimens and longitudinal full-weld round bar-shaped tensile specimens. Specific size parameters are as follows: Figure 4 As shown in the figure. Four plate-shaped tensile specimens and four full-weld round bar tensile specimens were prepared. Based on the ultimate tensile performance testing method provided by this invention, the ultimate tensile strength in the direction perpendicular to the weld and along the weld direction under the tested welding condition was determined. The measured ultimate tensile strengths in different weld directions and the conventional ultimate tensile strengths of the base material Q355D steel are shown in Table 3.

[0092] A finite element model of a monopile foundation for an offshore wind turbine was established, and its nodal stress time history was analyzed. The foundation plate thickness is the same as the thickness of the transverse plate tensile specimen in the ultimate tensile performance test, which is 18 mm. Fixed constraints were set at the bottom of the foundation, and a concentrated load along the horizontal direction was applied to the top of the tower. The linear relationship between the applied load and the first principal stress of the tested node was obtained, thereby converting the given external load time history curve into a stress time history curve. The actual non-parallelism δ of the butt joint plates was calculated at the welding position using the stress concentration factor (SCF) calculation formula provided in this invention. m Taking 0.01t as the constant, the calculated SCF at the butt weld position is 1.15. Multiplying the stress amplitude of the stress-time history curve by the SCF yields the following result: Figure 5 The stress-time history of the welded joint under test is shown.

[0093] The stress time history of the tested nodes in a monopile foundation is statistically processed using the rainflow counting method to convert it into usable stress cycles, including stress amplitude and cycle number. Based on the weld ultimate tensile performance test results and the average stress correction method provided in this invention, the stress cycle amplitude statistically obtained by the rainflow counting method is corrected using Goodman curves and Gerber. Combining the obtained corrected stress cycle amplitude and cycle count, fatigue damage prediction is performed on the tested nodes of the offshore wind turbine monopile foundation based on the Palmgren-Miner rule. The fatigue damage D is calculated using the Palmgren-Miner rule as follows:

[0094]

[0095] Where n i N represents the number of stress cycles in the i-th group. i The constant amplitude stress amplitude δ i The number of cycles required for fatigue failure under load is calculated using the SN curve. The SN curve used in this example is the root curve for butt welds and pipe ring welds specified in the DNV-OS-J101 standard, and its expression is:

[0096] log 10 N = 11.378 - 3log 10 (1.8423σ)

[0097] Where σ is the stress cycle amplitude σ modified by the present invention. Goodman With σ Gerber .

[0098] Table 4 shows the fatigue damage results of the tested welded joints of the offshore wind turbine monopile foundation obtained based on the above implementation method along different weld directions. In addition, Table 4 also lists the fatigue damage results of the tested welded joints predicted by the traditional analysis method that only considers the ultimate tensile strength of the base material Q355D steel. From Table 4, it can be seen that the fatigue damage of the welded joint shown in this example, under the given load time history, should be 1.25 × 10⁻⁶ when the weld direction is perpendicular to the load direction. -5 Up to 3.66×10 -5 Between 9.15 × 10⁻⁶, and for the case where the weld direction is along the load direction, the fatigue damage should be between 9.15 × 10⁻⁶. -6 Up to 1.96×10 -5 However, if the traditional prediction method based on the strength of the parent material is used, the calculated fatigue damage is between 1.19 × 10⁻⁶. -5 Up to 3.34×10 -5 The result is lower than the fatigue damage calculated using the method of this invention when the weld direction is perpendicular to the load direction, but higher in the other direction. It can be seen that traditional fatigue damage analysis based on the strength of the base material cannot effectively account for changes in material properties caused by welding, and cannot truly reflect the fatigue performance of the weld. This may lead to conservative or overly optimistic predictions due to differences in welding processes, thus adversely affecting the design of welded joints in engineering design. The method of this invention can effectively solve this problem.

[0099] It should be noted that although the above example only demonstrates the ultimate tensile performance test and mean stress correction of the butt weld of a monopile offshore wind turbine for a specific welding process, in actual implementation, this step can also consider the influence of various different welding processes on the ultimate tensile performance. This step can also be used for mean stress correction and subsequent fatigue analysis of offshore wind turbines with different foundation types. Furthermore, those skilled in the art will understand that the above equipment may only include the factors necessary to implement the embodiments of this specification, and not necessarily all the factors shown in the specification.

[0100] Table 1 Main Dimensions of V-groove for Butt Welded Steel Plates

[0101] Dimensions Value α 70° w 1mm <![CDATA[h1]]> 3mm <![CDATA[h2]]> 11mm

[0102] Table 2 Welding process parameters for butt welding

[0103] Welding parameters Value Base pass welding wire grade THQ-50C diameter of the root pass welding wire 1.6mm Interlayer temperature control 150-300℃ Fill speed 11mm / s Welding current 600-900A Arc voltage 28-33V

[0104] Table 3 Ultimate Tensile Strength of Q355 Steel Materials and Welds

[0105] Material / Weld Direction Ultimate tensile strength Base material: Q355D steel 579.55MPa Perpendicular to the weld direction (lateral) 543.15MPa Along the weld direction (longitudinal) 932.39MPa

[0106] Table 4 Fatigue damage of offshore wind turbine welds

[0107]

[0108] In the technical solution of this application, the geometric form of the specimen used for the ultimate tensile performance test of the weld can be replaced. For example, for a longitudinal round bar specimen, it can be replaced by a square cross-section specimen or a plate.

[0109] The average stress correction method in this invention can be replaced, such as by using other average stress correction methods related to ultimate tensile strength.

[0110] In summary, this invention aims to solve the problem in the prior art where traditional methods, based on the strength of the base material, neglect the differences in weld performance. This invention directly obtains the ultimate tensile strength of the weld region through tensile tests on transverse plate-shaped specimens and longitudinal full-weld round bar specimens, and embeds it as a core parameter into the Goodman and Gerber formulas, replacing the traditional base material strength parameter.

[0111] To address the issue of high computational costs caused by existing technologies relying on complex finite element models, this invention employs a simplified model that does not include weld details. Combined with the stress concentration factor (SCF) specified in the standard, stress is corrected through measured strength, thus solving the problem of modeling complexity and making it suitable for efficient analysis in the preliminary design stage.

[0112] To address the problem that existing technologies struggle to effectively correlate measured weld data with dynamic loads, this invention combines Goodman and Gerber curves to correct stress, rapidly predicting the upper and lower limits of fatigue damage in the welded area of ​​offshore wind turbine support structures. This solves the efficiency problem of fatigue prediction under complex working conditions and provides support for selecting offshore wind turbine design schemes.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines, characterized in that, Includes the following steps: Step 1: Determine the welding process parameters and prepare the specimens for the tensile test; Step 2: Quantify the ultimate tensile properties of the weld through tensile testing to eliminate biases in the assumptions about the base material. Step 3: Establish multi-scale data correlation from macroscopic structural analysis to local stress statistics; Step 4: Correct the mean stress based on the measured ultimate tensile properties of the weld to generate an equivalent zero mean stress amplitude. Step 5: Output the fatigue damage range for preliminary design optimization of the welding area of ​​the offshore wind turbine support structure.

2. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, In step one, the welding process parameters include steel type, welding method, bevel type and size, welding wire grade, welding wire diameter, interpass temperature, filling speed, welding current, and arc voltage.

3. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, In step one, butt welding of steel plates is carried out according to the determined welding parameters, and specimens for axial tensile testing of welded joints are prepared along the transverse and longitudinal positions of the weld.

4. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, In step one, the transverse specimen is a plate-shaped tensile specimen, and the longitudinal tensile specimen is a full-weld round bar tensile specimen; for transverse plates with a thickness of less than 20mm, a full-thickness specimen should be used; the longitudinal round bar tensile specimen is a full-weld material specimen, and the diameter of the working section of the round bar is determined according to the actual weld shape, and its diameter ensures that the working section of the specimen is entirely composed of weld material.

5. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, In step two, the ultimate tensile strength of the weld is determined: the ultimate tensile strength σ is finally measured for the transverse and longitudinal specimens. u Take the average value.

6. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, Step two involves performing a tensile test on an electronic universal testing machine, including the following steps: Step 501: Select the test specimen, measure the characteristic geometric dimensions of the test section of the specimen with a vernier caliper and calculate the initial cross-sectional area S0 of the test section, and clamp the specimen; Step 502: After moving the crossbeam of the testing machine to a suitable position via the control terminal on the gatepost, place the specimen into the fixture and then clamp the upper and lower clamps. Step 503: Clear the existing test data records and set the corresponding loading speed to start this loading; Step 504: After the specimen fractures, record the maximum load F applied during the tensile process. m The loading speed was kept constant during the test. Step 505: Repeat steps 501-504 to complete the test of the next specimen, until all required test specimens have been tested. After compiling the experimental data, calculate the ultimate tensile strength σ for each specimen. u During each test, the loading rate and test parameter settings should be kept consistent. Step 506, the ultimate tensile strength σ u The calculation formula is as follows: Step 507: The ultimate tensile strength σ of each transverse and longitudinal specimen is finally measured. u Take the average value to obtain the ultimate tensile strength of the weld representing the welding type.

7. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, Step three, establishing multi-scale data associations, includes the following steps: Step 301: Based on the analyzed support geometry and main dimensions of the offshore wind turbine, establish its structural finite element model and perform finite element analysis to obtain the stress response time history at the nodes to be analyzed of the offshore wind turbine. Step 302: Calculate the stress concentration factor SCF at the welding position, and multiply the stress response time history obtained from the finite element analysis by the stress concentration factor SCF to obtain the stress response time history representing the weld area. Step 303, the stress concentration factor SCF is calculated as follows: In the formula δ0=0.05t Where, δ m δ0 represents the actual non-parallelism of the butt plates, δ0 represents the inherent misalignment deviation of the butt weld, and t represents the plate thickness.

8. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, Step four involves correcting the mean stress, including the following steps: Step 401: Statistically process the processed stress time history based on the rainflow counting method to transform it into a stress cycle that can be used for fatigue analysis, including the actual stress amplitude δ. a The number of cycles n corresponding to each stress amplitude; Step 402, based on the experimentally obtained ultimate tensile strength σ of the weld. u The obtained stress amplitudes are corrected by averaging the Goodman and Gerber curves so that the subsequent SN curves can be directly used for fatigue life prediction. The Goodman curve formula is as follows: Where σ Goodman σ represents the stress cycle amplitude under the equivalent zero mean stress, corrected based on the Goodman curve. m The average stress; The formula for the Gerber curve is as follows: Where σ Gerber The stress cycle amplitude is the equivalent zero average stress value based on the Gerber curve correction.

9. The method for correcting the average stress of the ultimate strength of butt welds in offshore wind turbines as described in claim 1, characterized in that, In step five, σ Goodman With σ Gerber The corresponding number of cycles is used for fatigue analysis, where σ is the basis. Goodman The calculated fatigue damage is the upper limit of the fatigue damage value at the weld position, based on σ. Gerber The calculated fatigue damage is the lower limit of the fatigue damage value at the welding position.

10. The method for correcting the average stress of the ultimate strength of the butt weld of an offshore wind turbine as described in claim 9, characterized in that, In step five, fatigue analysis is performed using the stress cycle amplitude after mean stress correction to determine the range of fatigue damage values ​​for the offshore wind turbine support structure, which is then used for design scheme selection in the preliminary design phase.

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