Offshore wind turbine supporting structure steel plate material design and type selection method

Abstract

The invention discloses an offshore wind turbine supporting structure steel plate material design and model selection method, and relates to the field of offshore wind power construction. The design and model selection method comprises the following steps: step 1, designing an offshore wind turbine supporting structure; 2, determining a structural design material selection principle; 3, DNV standard steel plate material selection; and 4, selecting an EN material instead of a DNV material. According to the method, by determining the maximum wall thickness and the minimum impact temperature selection principle of the main structural steel plate material under different design temperature conditions, the selection principle of replacing the DNV standard steel plate material with the EN standard steel plate material is provided, and the safety of structural design and offshore service is guaranteed; the key technical problem of model selection of the main structure material of the supporting structure of the offshore wind power project is solved, the steel plate material purchasing convenience is improved, the steel plate material cost of the offshore wind power project in foreign sea areas is greatly saved, and the construction cost is saved.

Description

Technical Field

[0001] The present invention relates to the field of offshore wind power construction, and in particular to a method for designing and selecting steel plate materials for offshore wind turbine support structures. Background Art

[0002] Offshore wind power is also known as offshore wind power generation. Wind power generation is the fastest growing green energy technology in the world. While the construction of land wind farms is developing rapidly, there are problems such as large land area and noise pollution. Due to the abundant wind energy resources at sea and the feasibility of current technology, the ocean has become a rapidly developing wind power market. The support technologies for offshore wind turbines mainly include bottom fixed support and suspended support. Among them, the bottom fixed support includes three types: gravity caisson foundation, single pile foundation, and tripod foundation. The suspended support includes two types: buoy and semi-immersed, and is mainly used in water depths ranging from 75 to 500m.

[0003] Both fixed support and suspended support technologies for offshore wind turbines are based on steel plate support structures. The main body of the support structure is constructed using steel plate materials. Since the support structure is built in the sea, it is affected by marine environmental factors, which will affect the service life and strength of the support structure materials. In addition, the designed offshore wind turbine foundation structure is different for different seawater depths. The rationality of structural design and the rapid selection of materials are key technologies to ensure the safety of offshore wind turbines in service. However, the existing material selection method for offshore wind turbine support structures is not convenient for the selection of steel plate materials, which can easily cause waste of steel plate materials and increase construction costs. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for designing and selecting steel plate materials for offshore wind turbine support structures, which solves the problem that the existing method for selecting materials for offshore wind turbine support structures is not convenient for selecting steel plate materials, easily causes waste of steel plate materials, and increases construction costs.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for designing and selecting steel plate materials for offshore wind turbine support structures, comprising the following steps:

[0006] Step 1: Design of offshore wind turbine support structures to ensure acceptable structural safety and durability within the design life of the structure;

[0007] Step 2: Determine the material selection principles for structural design, classify the support structure of the offshore wind turbine and ensure the quality of the materials;

[0008] Step 3: DNV standard steel plate material selection, screen the steel plate material according to the different classifications of the supporting structure;

[0009] Step 4: EN material replaces DNV material selection. DNV steel plate material is replaced with EN steel plate material according to the needs of different classifications of supporting structures.

[0010] Preferably, the offshore wind turbine support structure design includes:

[0011] The partial safety factor method is used to calculate the safety factor of the offshore wind turbine support structure:

[0012] Through test-assisted design, the test-assisted design is used to test and inspect the safety factor method design;

[0013] Probability-based design uses probabilistic methods to design the probability of damage events occurring to offshore wind turbine support structures.

[0014] Preferably, the structural design material selection principle ensures the quality of materials and the inspection of suitable materials through structural classification, the structural design material selection principle is used to detect defects that develop into fatigue cracks during the service life, and the structural design material selection principle is used to structurally divide offshore wind turbine support structure components into special structures, main structures and secondary structures.

[0015] Preferably, the DNV standard steel plate material is selected according to the DNV standard material, and the grade classification and definition according to the DNV-OS-B101 standard are:

[0016] NV ordinary strength steel grade, with a specified minimum yield strength of 235MPa;

[0017] NV high-strength steel grades, with specified minimum yield strengths of 265MPa, 315MPa, 355MPa and 390MPa;

[0018] NV ultra-high strength steel grades have specified minimum yield strengths of 420MPa, 460MPa, 500MPa, 550MPa, 620MPa, 690MPa, 890MPa and 960MPa.

[0019] Preferably, the DNV standard steel plate material selection includes:

[0020] For special structures, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures;

[0021] For the main structure, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures;

[0022] For secondary structures, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures.

[0023] Preferably, the EN material alternative to the DNV material selection includes:

[0024] Chemical composition, CEV, sulfur value, grain refining elements;

[0025] Mechanical properties, yield strength and tensile strength, elongation, impact properties;

[0026] Relevant steel manufacturing parameters, deoxidation methods, and Z-direction performance requirements.

[0027] Preferably, the EN material alternative to the DNV material selection includes:

[0028] For special structures, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials based on different environmental service temperatures;

[0029] For the main structure, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials based on different environmental service temperatures;

[0030] For secondary structures, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected instead of DNV standard steel plate materials based on different environmental service temperatures.

[0031] Preferably, when the EN material is used to replace the DNV material as the standard material, the chemical composition and impact test requirements of the EN material steel plate should comply with the chemical composition and low-temperature impact toughness requirements of the corresponding grade material steel plate in DNV-OS-B101.

[0032] Preferably, the DNV standard steel plate material is selected according to the material brand corresponding to the DNV-OS-B101 standard, and the chemical composition and impact test requirements of the corresponding DNV material should comply with the limits and definitions specified in DNV-OS-B101.

[0033] Preferably, the structural design material selection principle is used to detect the importance of failure consequences, and the structural design material selection principle combines stress conditions at details, welding defects and fatigue cracks with brittle fracture criteria to possibly cause brittle fracture criteria.

[0034] The present invention discloses a method for designing and selecting steel plate materials for offshore wind turbine support structures, which has the following beneficial effects:

[0035] By determining the maximum wall thickness and minimum impact temperature selection principles of the main structural steel plate materials under different design temperature conditions, the principle of replacing DNV standard steel plate materials with EN standard steel plate materials is provided to ensure the safety of structural design. At the same time, it is convenient to select materials for different structural positions, solve the key technical problems in the selection of main structural materials for supporting structures of offshore wind power projects, improve the convenience of steel plate material procurement, and significantly save the steel plate material costs of offshore wind power projects in foreign waters and save construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0038] Figure 2 This is a schematic diagram of the design structure of the offshore wind turbine support structure of the present invention; DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The embodiment of the present application provides a method for designing and selecting steel plate materials for offshore wind turbine support structures, thereby solving the problem that the existing method for selecting materials for offshore wind turbine support structures is not convenient for selecting steel plate materials, easily causing waste of steel plate materials and increasing construction costs. By determining the maximum wall thickness and minimum impact temperature selection principles of the main structural steel plate materials under different design temperature conditions, a principle for selecting EN standard steel plate materials instead of DNV standard steel plate materials is provided to ensure the safety of structural design and facilitate the selection of materials for different structural positions. This solves the key technical difficulties in selecting the main structural materials for the support structure of offshore wind power projects, improves the convenience of purchasing steel plate materials, and greatly saves the steel plate material costs and construction costs of offshore wind power projects in foreign waters.

[0041] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0042] An embodiment of the present invention discloses a method for designing and selecting steel plate materials for an offshore wind turbine support structure.

[0043] According to the attached Figure 1 -2, including the following steps:

[0044] Step 1: Design of offshore wind turbine support structures to ensure acceptable structural safety and durability within the design life of the structure;

[0045] Step 2: Determine the material selection principles for structural design, classify the support structure of the offshore wind turbine and ensure the quality of the materials;

[0046] Step 3: DNV standard steel plate material selection, screen the steel plate material according to the different classifications of the supporting structure;

[0047] Step 4: EN material replaces DNV material selection. DNV steel plate material is replaced with EN steel plate material according to the needs of different classifications of supporting structures.

[0048] The design of offshore wind turbine support structure includes design using partial safety factor method, test-assisted design and probability-based design. The safety factor method is used to calculate the safety factor of the offshore wind turbine support structure. The test-assisted design is used to test and detect the safety factor method design. The probability of damage events occurring in the offshore wind turbine support structure is designed through probabilistic methods, and the loads occurring under all temporary, operating and damage conditions are maintained to ensure acceptable structural safety within the design life of the structure, maintain acceptable safety for personnel and the environment, and have sufficient durability during the design life of the structure.

[0049] The principles of material selection for structural design ensure the quality of materials and the inspection of suitable materials through structural classification. The principles of material selection for structural design are used to detect defects that develop into fatigue cracks during the service life. The principles of material selection for structural design are used to structurally divide offshore wind turbine support structure components into special structures, main structures and secondary structures. The performance of steel plate materials is tested using visual inspection and mechanical properties. Visual inspection is used to detect the appearance size and defects of steel plate materials. Visual inspection is used to detect fatigue cracks caused by defects. Sharp defects such as cracks, accumulation of hydrogen ions, high tensile stress perpendicular to the direction of plane defects and materials with low fracture toughness are detected on the materials. Mechanical property testing is used to test the temperature resistance, time and mechanical parameters of steel plate materials. The importance of structure in terms of the consequences of failure is considered. Stress conditions at the details are considered. Brittle fracture is caused by combination with welding defects or fatigue cracks. The steel type selected for structural components should be consistent with the calculated stress and the requirements for toughness performance. The requirements for toughness performance are usually based on the V-notch test of simply supported beams, depending on the operating temperature, structural category and thickness of the structure in question.

[0050] Components are divided into structural categories according to the following criteria:

[0051] The importance of the component in terms of the consequences of failure;

[0052] Considering the stress conditions in the details, combined with possible welding defects or fatigue cracks, brittle fracture may occur.

[0053]

[0054] The steel grade selected for structural components should be consistent with the calculated stresses and the requirements for toughness properties. The requirements for toughness properties are usually based on the Charpy V-type low temperature impact notch test and depend on the operating temperature, the structural category and the thickness of the component in question.

[0055] Appearance visual inspection includes the following steps:

[0056] Step S1: Collect defective pictures and non-defective pictures of offshore wind turbine support structure steel plate materials on site;

[0057] Step S2: A semi-automatic annotation model is established based on SAM, and the contour shape and size of the defect are adjusted through the interactive function to generate the required defects, and the defect type is customized to complete the semi-automatic annotation;

[0058] Step S3: The annotated industrial defect images are trained using the YOLOv5 model, and the model with the best result is used as the supervised positioning model;

[0059] Step S4: The defect-free images are trained using the semi-supervised MemSeg model, and the model with the best result is used as the semi-supervised positioning model.

[0060] Step S5: Enlarge the labeled defect image by 1 times, cut out the outline, and classify it according to categories. Use the ViT classification model for training, and take the model with the best result as the classification model;

[0061] Step S6: The defect image data that has not been semi-automatically annotated is transferred to the fully automatic annotation tool. The defect image is located and duplicated through the trained YOLOv5 supervised model and MemSeg semi-supervised model. The coordinates of the defect center point are calculated and transmitted to the SAM model. The contour and size are adjusted through the SAM model. Finally, the defect contour is enlarged by 1 times and classified through the ViT classification model to generate annotated defects.

[0062] The SAM algorithm uses data enhancement techniques such as random rotation, scaling, cropping, flipping, color space transformation, and noise addition to improve the generalization ability of the model. The SAM model uses a pre-trained image classification model as the initial weight of the encoder to extract high-quality features of defects. The backbone network of SAM is based on the ViT algorithm, which contains a multi-head attention mechanism to calculate the similarity between each element in the input sequence and other elements, and then calculates the weight of each element based on the similarity, and finally outputs the weighted sum of the elements.

[0063] In addition, SAM also contains another layer in Transformer, called feedforward network, which is mainly used for nonlinear transformation of output sequences. SAM can accurately segment defect contours in automatic labeling tasks, interact with the annotator in real time, and has strong generalization capabilities in different tasks.

[0064] The YOLOv5 network is a single-stage detection algorithm, which mainly consists of the input end, backbone network, neck network and head network;

[0065] The input of the YOLOv5 model uses Mosaic data enhancement, adaptive anchor box calculation, and adaptive image scaling. These operations can enrich the number of features and improve the accuracy of detection.

[0066] The backbone network mainly includes the Focus structure. The main function of the Focus structure is to slice the image, which is similar to neighboring downsampling, and finally outputs a high-quality feature map with no information loss. The backbone network also includes the CSP structure. The CSP structure mainly splits the feature map into two parts. One part uses the convolution layer for feature extraction, and the other part is fused with the result of the previous part by superimposing the number of channels. CSP can reduce the amount of calculation while enhancing the learning ability of the model and improving the accuracy of model detection.

[0067] The neck network in YOLOv5 adopts the structure of FPN and PAN. The FPN layer conveys strong semantic information from top to bottom, while PAN conveys positioning features from bottom to top.

[0068] Mechanical property testing includes material aging test, material heat resistance test, material stress test, material tensile test and material deformation test. Material aging test is used to collect aging time parameters of steel plate materials. By conducting oxidation tests on offshore wind turbine support structure steel plate materials, material aging test is used to detect the influence of material aging time on material mechanical properties, which is convenient for testing the service life of steel plate materials. Material heat resistance test is used to obtain high temperature and low temperature resistance parameters of steel plate materials. Material heat resistance test is used to detect the influence of material temperature on material mechanical properties. By testing the heat resistance of steel plate materials, the service temperature of steel plate materials in different environments can be determined to facilitate the selection and use of steel plate materials. Material stress test is used to obtain Poisson's ratio parameters of steel plate materials. Material stress test is passed Poisson's ratio generates stress-strain parameters of steel plate materials. Combined with the Poisson's ratio of steel plate materials, the volume change factor of the material can be combined with the true stress-strain curve. The generated true stress-strain curve accurately reflects the material properties of the candidate materials. The material tensile test is used to collect the tensile strength and overall mechanical properties of the steel plate materials. The material tensile test reflects the tensile strength and overall mechanical properties of the candidate materials. By monitoring the cross-sectional area and displacement of the test specimens during the test, a more accurate true stress-strain curve can be generated to reflect the mechanical properties of the candidate materials. The material deformation test is used to obtain the mechanical characteristic parameters of the steel plate material during elastic deformation. The elastic deformation and plastic deformation ability of the material are tested through the material deformation test, which is convenient for reference to the deformation of the material.

[0069] DNV standard steel plate material selection is based on DNV standard materials, and the grade classification and definition according to DNV-OS-B101 standard are:

[0070] NV ordinary strength steel grade, with a specified minimum yield strength of 235MPa;

[0071] NV high-strength steel grades, with specified minimum yield strengths of 265MPa, 315MPa, 355MPa and 390MPa;

[0072] NV ultra-high strength steel grades have specified minimum yield strengths of 420MPa, 460MPa, 500MPa, 550MPa, 620MPa, 690MPa, 890MPa and 960MPa.

[0073] The selection of DNV standard steel plate materials includes: for special structures, to ensure the safety of offshore wind power structures, based on different environmental service temperatures, select the strength level of DNV standard steel plate materials; for main structures, to ensure the safety of offshore wind power structures, based on different environmental service temperatures, select the strength level of DNV standard steel plate materials; for secondary structures, to ensure the safety of offshore wind power structures, based on different environmental service temperatures, select the strength level of DNV standard steel plate materials; through the analysis of different positions of offshore wind turbine support structures, select DNV standard steel plate materials of different strengths to ensure the safety of offshore wind power structures in different use environments; the selection of DNV standard steel plate materials is based on the material brand corresponding to the DNV-OS-B101 standard; the chemical composition and impact test requirements of the corresponding DNV materials shall comply with the limits and definitions specified in DNV-OS-B101.

[0074] For special structures, in order to ensure the safety of offshore wind power structures, based on different environmental service temperatures, the strength level and maximum wall thickness principles of DNV standard steel plate materials are selected as shown in Table 1:

[0075] Table 1 Special structure - DNV standard steel plate material design and selection requirements

[0076]

[0077] For the primary structure, in order to ensure the safety of offshore wind power structures, the strength level and maximum wall thickness principle requirements of DNV standard steel plate materials are selected based on different environmental service temperatures as shown in Table 2:

[0078] Table 2 Primary structure - DNV standard steel plate material design and selection requirements

[0079]

[0080]

[0081] For the secondary structure, in order to ensure the safety of offshore wind power structures, the strength level and maximum wall thickness principle requirements of DNV standard steel plate materials are selected based on different environmental service temperatures as shown in Table 3:

[0082] Table 3 Secondary structure - DNV standard steel plate material design and selection requirements

[0083]

[0084] EN material replaces DNV material selection including chemical composition, CEV, sulfur value, grain refining elements, mechanical properties, yield strength and tensile strength, elongation, impact performance, relevant steel manufacturing parameters, deoxidation method, Z-direction performance requirements, EN material replaces DNV material selection including for special structures, to ensure the safety of offshore wind power structure, based on different environmental service temperatures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials, for main structures, to ensure the safety of offshore wind power structure, based on different environmental service temperatures, EN standard steel plate materials can be selected to replace DNV standard steel Plate materials, for secondary structures, in order to ensure the safety of offshore wind power structures, based on different environmental service temperatures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials. Through the analysis of different positions of offshore wind turbine support structures, EN standard steel plate materials with different strengths are selected to replace DNV standard steel plate materials to ensure the safety of offshore wind power structures in different use environments. When EN materials replace DNV materials and standard materials are selected, the chemical composition and impact test requirements of EN material steel plates should comply with the chemical composition and low-temperature impact toughness requirements of corresponding grade material steel plates in DNV-OS-B101.

[0085] For special structures, in order to ensure the safety of offshore wind power structures, based on different environmental service temperatures, the principle requirements for selecting EN standard steel plate materials to replace DNV standard steel plate materials are as shown in Table 4:

[0086] Table 4 Special structure - Selection requirements for EN materials to replace DNV materials

[0087]

[0088]

[0089]

[0090] For the primary structure, in order to ensure the safety of offshore wind power structures, based on different environmental service temperatures, the principle requirements for selecting EN standard steel plate materials to replace DNV standard steel plate materials are as shown in Table 5:

[0091] Table 5 Primary structure - Selection requirements for EN materials to replace DNV materials

[0092]

[0093]

[0094]

[0095]

[0096] For the secondary structure, in order to ensure the safety of offshore wind power structures, based on different environmental service temperatures, the principle requirements for selecting EN standard steel plate materials to replace DNV standard steel plate materials are as shown in Table 6:

[0097] Table 6 Secondary structure - Selection requirements for EN materials to replace DNV materials

[0098]

[0099]

[0100]

[0101]

[0102] EN material structural steel plates should comply with EN10025 standards. The steel grades corresponding to EN10025 and DNV-OS-B101 standards are as follows:

[0103] S355NL / ML(EN)—NV E36(DNV)

[0104] S355N / M(EN)—NV D36(DNV)

[0105] S355K2+N(EN)—NV D36(DNV)

[0106] S355J2+N(EN)—NV D36(DNV)

[0107] The chemical composition of EN steel plates based on smelting analysis should comply with the requirements of DNV-OS-B 101 standard. The chemical composition of the steel should meet the following table:

[0108]

[0109] 1)Given value is maximum content(by weight)unless shown as a range or as a minimum.

[0110] 2)Minimum 0.70% for thicknesses up to and including 12.5mm.

[0111] 3)Minimum limits are specified in DNV-OS-B101[1.4.7].The steel shall contain grain refining elements Al,Nb,V or Ti,either singly or in any combination,see also DNV-OS-B101[1.4.7].The total content of Nb+V+Ti shall not exceed0.12%.

[0112] 4)Maximum 0.05% Ti for TM steels subjected to agreement.

[0113] The carbon equivalent calculated based on the results of the smelting analysis should meet the requirements of standard DNV-OS-B101. The maximum carbon equivalent is 0.43%.

[0114] The calculation formula of carbon equivalent is as follows:

[0115]

[0116] The calculation formula of welding cold crack sensitivity coefficient Pcm is as follows:

[0117]

[0118] The carbon content of steel supplied in M ​​state should not be greater than 0.14%. When the carbon content is less than or equal to 0.12%, the welding cold crack sensitivity Pcm can be used instead of the carbon equivalent Ceq.

[0119] Mechanical properties: yield strength and tensile strength, elongation, impact properties (Charpy impact value, test temperature, position and direction of impact specimen);

[0120] The tensile properties of EN standard steel should meet the requirements of standard EN10025, and the tensile test should be carried out in accordance with the requirements of EN10025 and should meet the requirements of the following table:

[0121]

[0122] The impact test of EN standard material steel plates shall be carried out according to the requirements of DNV-OS-B101, using the Charpy V-notch impact test.

[0123] A single Charpy V-notch impact value may be less than the required value, but shall not be less than 70% of the required value.

[0124]

[0125] Other relevant steel manufacturing parameters: deoxidation method, Z-direction performance requirements (in accordance with DNV-OS-B101).

[0126] The steel should be killed steel and have been treated with refined grains.

[0127] EN steel delivery status is as follows:

[0128]

[0129]

[0130] For Z-direction performance steel plates, the steel should be killed steel and fine-grained.

[0131] The Z-direction performance steel plate shall comply with the requirements of standard EN10164. The thickness direction test and acceptance standard requires that the average value of the three specimens of the section shrinkage rate should not be less than 35%, and only one of the specimens is allowed to have a single value lower than the average value, but not less than 25%.

[0132] Unless there are other approved methods to enhance the properties in the thickness direction, the sulfur content based on the smelting analysis shall be less than or equal to 0.008%. When the sulfur content is less than or equal to 0.005%, the test specifications can be reduced. The section shrinkage shall meet the requirements of the following table.

[0133] Quality class Z25 Z35 Minimum average 25％ 35％ Minimum individual minimum single value 15％ 25％

[0134] A simulation model is established to form a unified data fusion layer with the three-dimensional model and the acquired data on the size, temperature resistance, time and mechanical parameters of the steel plate material, and the unified data fusion layer is dynamically visualized in real time. The model data is rendered by integrating two-dimensional and three-dimensional base map resources, point clouds, and oblique photography modeling methods. A three-dimensional model is established for the offshore wind turbine support structure, and the acquired size, temperature resistance, time and mechanical parameters of the steel plate material are combined with the three-dimensional model to form a three-dimensional data model diagram of the offshore wind turbine support structure, which facilitates the observation of the offshore wind turbine support structure and the selection of materials for different structural positions, thereby improving the convenience of steel plate material selection and procurement.

[0135] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for designing and selecting steel plate materials for offshore wind turbine support structures, characterized in that: The following steps are involved: Step 1: Design of offshore wind turbine support structures to ensure acceptable structural safety and durability within the design life of the structure; Step 2: Determine the material selection principles for structural design, classify the support structure of the offshore wind turbine and ensure the quality of the materials; Step 3: DNV standard steel plate material selection, screen the steel plate material according to the different classifications of the supporting structure; Step 4: EN material replaces DNV material selection. Replace DNV steel plate material with EN steel plate material according to the needs of different classifications of supporting structures.

2. The method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 1, characterized in that: The offshore wind turbine support structure design includes: The partial safety factor method is used to calculate the safety factor of the offshore wind turbine support structure: Through test-assisted design, the test-assisted design is used to test and inspect the safety factor method design; Probability-based design uses probabilistic methods to design the probability of damage events occurring to offshore wind turbine support structures.

3. A method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 2, characterized in that: The structural design material selection principle ensures the quality of materials and the inspection of suitable materials through structural classification. The structural design material selection principle is used to detect defects that develop into fatigue cracks during the service life. The structural design material selection principle is used to structurally divide offshore wind turbine support structure components into special structures, main structures and secondary structures.

4. A method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 3, characterized in that: The DNV standard steel plate material selection is based on the DNV standard material, and the grade classification and definition according to the DNV-OS-B101 standard are: NV ordinary strength steel grade, with a specified minimum yield strength of 235MPa; NV high-strength steel grades, with specified minimum yield strengths of 265MPa, 315MPa, 355MPa and 390MPa; NV ultra-high strength steel grades have specified minimum yield strengths of 420MPa, 460MPa, 500MPa, 550MPa, 620MPa, 690MPa, 890MPa and 960MPa.

5. A method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 4, characterized in that: The DNV standard steel plate material selection includes: For special structures, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures; For the main structure, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures; For secondary structures, in order to ensure the safety of offshore wind power structures, the strength level of DNV standard steel plate materials is selected based on different environmental service temperatures.

6. The method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 3, characterized in that: The EN material alternatives to DNV material options include: Chemical composition, CEV, sulfur value, grain refining elements; Mechanical properties, yield strength and tensile strength, elongation, impact properties; Relevant steel manufacturing parameters, deoxidation methods, and Z-direction performance requirements.

7. A method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 6, characterized in that: The EN material alternatives to DNV material options include: For special structures, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials based on different environmental service temperatures; For the main structure, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected to replace DNV standard steel plate materials based on different environmental service temperatures; For secondary structures, in order to ensure the safety of offshore wind power structures, EN standard steel plate materials can be selected instead of DNV standard steel plate materials based on different environmental service temperatures.

8. The method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 1, characterized in that: When the EN material is used to replace the DNV material and select the standard material, the chemical composition and impact test requirements of the EN material steel plate shall comply with the chemical composition and low-temperature impact toughness requirements of the corresponding grade of material steel plate in DNV-OS-B101.

9. The method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 1, characterized in that: The DNV standard steel plate material is selected according to the material brand corresponding to the DNV-OS-B101 standard, and the chemical composition and impact test requirements of the corresponding DNV material should comply with the limits and definitions specified in DNV-OS-B101.

10. The method for designing and selecting steel plate materials for offshore wind turbine support structures according to claim 1, characterized in that: The structural design material selection principle is used to detect the importance of failure consequences. The structural design material selection principle combines the stress conditions at the details, welding defects and fatigue cracks with the brittle fracture criteria that may cause brittle fracture criteria.

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