Method for calculating structural strength of attachment in offshore tower

Abstract

The invention relates to a method for calculating the strength of an attachment structure in an offshore tower. The method comprises the steps that S10, a geometric model of the attachment structure in the offshore tower is simplified and segmented; s20, establishing a finite element model of the attachment structure in the offshore tower; s30, design of an inner accessory structure of the offshore tower, wherein the design of the inner accessory structure of the offshore tower comprises the steps of S31, finite element simulation of an inner accessory platform main and auxiliary beam structure of the offshore tower; s32, finite element simulation of an attachment welding structure in the offshore tower; s33, calculating the ultimate strength of the attachment structure in the offshore tower; and S34, calculating the fatigue strength of the attachment structure in the offshore tower. According to the technical scheme, the problems that in the prior art, design accuracy of accessories in an offshore tower is not high, and more materials are wasted are effectively solved.

Description

Technical Field

[0001] The present application relates to the technical field of offshore tower design, and in particular to a method for calculating the strength of an accessory structure within an offshore tower. Background Art

[0002] The tower is one of the key mechanical structural parts of a wind turbine. It has to withstand complex alternating inertial loads during the operation of the wind turbine. Therefore, it must have sufficient strength and rigidity to ensure the stability and reliability of the wind turbine operation. The tower itself has a simple structure, but due to the complex structure of the internal accessories, the engineering algorithm in the existing technology has low calculation accuracy for this complex structure. In order to ensure high calculation accuracy, the finite element method is usually used for strength calculation. This method not only shortens the R&D design cycle, improves product reliability, but also reduces design costs. However, when using the finite element method for strength analysis, the correctness of the boundary loading of the analysis model will directly determine the accuracy of the analysis results. At present, the calculation force state and boundary description of the internal accessories of the tower are unclear, the load boundary is unreasonable, and the stiffness design evaluation method of the internal accessory platform and its impact on the reliability of wind turbine operation are not considered.

[0003] The shape of the accessory structure inside the offshore tower is complex and irregular, and traditional engineering algorithms are not applicable. According to the requirements of GL specifications, the finite element method is used for analysis. The accessories inside the tower are welded to the tower and connected to the tower platforms by bolts. They bear the load from the wind turbine tower and the weight of the platform and electrical equipment, and the force situation is complex. In order to ensure the normal operation of the wind turbine generator set, it is necessary to perform a strength analysis on the accessory structure inside the tower. Since the accessories and platforms inside the tower are connected to multiple complex components by bolts, the strength analysis of their structures is complex and difficult. Many of them use a large amount of excess materials, resulting in a lot of material waste. Summary of the invention

[0004] The present application provides a method for calculating the structural strength of an internal accessory of an offshore tower, so as to solve the problems of low design accuracy and high material waste of internal accessories of an offshore tower in the prior art.

[0005] A method for calculating the strength of an accessory structure of an offshore tower provided in this application includes: S10 Simplification and segmentation of the geometric model of the internal accessory structure of the offshore tower; S20 Establish the finite element model of the internal accessory structure of the offshore tower; S30 Design of accessories inside offshore towers. The design of accessories inside offshore towers includes: S31 Finite element simulation of main and auxiliary beam structure of the accessory platform inside the offshore tower; S32 Finite element simulation of welding structure of internal accessories of offshore tower; S33 Calculation of ultimate strength of accessory structures inside offshore towers; S34 Calculation of fatigue strength of accessory structures within offshore towers.

[0006] Furthermore, step S31 includes: S311 Ultimate strength assessment of the main and auxiliary beam structures of the internal accessory platform; S312 The ultimate strength calculation of internal accessory welded structure considers the following working conditions: Using the tower bottom limit load, platform deadweight, and deadweight of electrical equipment on the platform, apply the Mxy value and Fxy value in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state; The tower bottom maintenance load, platform deadweight, deadweight of electrical equipment on the platform and uniformly distributed load are adopted, and Mxy and Fxy are used in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state.

[0007] Furthermore, the welding between the accessory welding bracket and the tower in the offshore tower is a T-joint type, and the weld toe stress is a singular point. In the established finite element model, the relevant loads are applied for calculation, and the welding bracket is allowed to have plastic deformation but the total strain is less than 1%, and the maximum area is 1 / 2 of the tower wall thickness at the corresponding position.

[0008] Furthermore, step S32 includes: Calculate the stress concentration factor at the weld of the welded bracket, apply a bending moment of unit My, calculate the stress concentration factor at the weld of the welded bracket, and apply it in the y direction to ensure that the load is parallel to the weld of the welded bracket; The nominal stress calculation formula at the weld is as follows:

[0009] Where: ——Unit bending moment, in kN.m or Nm; ——Bending section coefficient of the tower section corresponding to the welded bracket, in m 3 or mm 3 . Furthermore, the stress at the weld of the welded bracket is obtained by extrapolation based on IIW:

[0010] Where: ——Stress at the hot spot of the weld, in MPa or Pa; ——The stress at 0.4t from the weld toe on the interpolation path. The stress type is the principal stress: the first principal stress S1 and the third principal stress S3, in MPa or Pa; ——The stress on the interpolation path 1t away from the weld toe. The stress type is principal stress: the first principal stress S1 and the third principal stress S3, in MPa or Pa.

[0011] Furthermore, the SCF calculation at the weld of the welded bracket is shown in the formula: .

[0012] Furthermore, the nominal stress method is used to calculate the fatigue of the weld of the welded bracket, and the stress amplitude under load is calculated as shown in the formula:

[0013] Where: ——Markov matrix projection angle The corresponding load range is in Nm; Wxy——Bending section modulus of the tower corresponding to the welded bracket, in units of m3 or mm3.

[0014] Furthermore, the cumulative fatigue damage of the weld of the welded bracket is calculated according to the formula:

[0015] Where: —— The number of cycles; ——The number of cycles corresponding to the inflection point of the material SN curve, ND=5E6; ——material safety factor; ——actual stress range value, in MPa or Pa; ——The stress range value corresponding to the inflection point of the SN curve, in MPa or Pa, calculated as shown in formula (14); ——the slope of the SN curve, , k=3, otherwise k=5,

[0016] Where: nA——The number of cycles corresponding to Δσc, nA=2E6; nD——The number of cycles corresponding to ΔσD, nD=5E6; Δσc——fatigue design level.

[0017] Furthermore, the constraints imposed by the finite element model of the accessory structure in the offshore tower are: load application of the tower accessory platform welding bracket, tower bottom limit load, platform and equipment deadweight, live load displacement constraints specified by the standard, and constraints imposed on the lower end face of the tower body.

[0018] Furthermore, the finite element modeling of the internal accessory structure of the offshore tower includes the tower body, the internal accessory welding structure and the main and auxiliary beam structure of the internal accessory platform; the main and auxiliary beams of the internal accessory platform are evaluated using solid units, and the finite element model includes the platform and the welded bracket. The platform and the welded bracket are mechanically simplified, and the bolt holes and process holes that have little impact on the calculation results are deleted. The internal bolt connection structure of the platform is not considered in the platform evaluation, and it is assumed to be a common node. The finite element model of the tower accessory platform welded bracket is established using solid units. The welding bracket and the remaining tower welding areas in this model require refined meshes. The finite element model mainly includes: the tower body, the welded bracket and the accessory platform. The tower and the accessory platform welding bracket are established using solid units. The main and auxiliary beams of the accessory platform can be simulated using solid units, and / or Beam188 units or rigid connection units MPC184 units, which can efficiently and accurately consider the influence of the stiffness of the main and auxiliary beams of the platform.

[0019] By applying the technical solution of the present application, the geometric model of the accessory structure inside the offshore tower is first simplified and segmented, which is convenient for subsequent simulation, verification and calculation. The overall finite element model can obtain the weak points that can withstand the force, and then simulate the easily damaged parts such as the main and auxiliary beam structures and welding structures, thereby further improving the design of the easily damaged positions. By calculating the ultimate strength and fatigue strength, the ultimate strength and fatigue strength of the accessory structure inside the offshore tower are further guaranteed, that is, the design is carried out from both static and dynamic perspectives. The technical solution of the present application effectively solves the problems of low design accuracy and high material waste in the accessories inside the offshore tower in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0021] In order to more clearly illustrate the embodiments of the present application 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 A schematic diagram showing a flow chart of a method for calculating the strength of an accessory structure in an offshore tower according to an embodiment of the present application; Figure 2 Shows Figure 1 Schematic diagram of finite element simulation of the strength calculation method of the internal accessory structure of the offshore tower; Figure 3 Shows Figure 1 Another structural finite element simulation diagram of the strength calculation method of the internal attachment structure of the offshore tower; Figure 4 Shows Figure 1 Schematic diagram of boundary conditions for the strength calculation method of the internal attachment structure of the offshore tower; Figure 5 Shows Figure 1 Schematic diagram of stress cycle and stress range of the strength calculation method of the internal accessory structure of the offshore tower; Figure 6 Shows Figure 1 Schematic diagram of stress distribution of main and auxiliary beams without platform deadweight load in the calculation method of the structural strength of the internal accessories of the offshore tower; Figure 7 Shows Figure 1 Schematic diagram of stress distribution of main and auxiliary beams under platform deadweight load based on the calculation method of structural strength of accessories inside offshore tower. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0025] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways, rotated 90 degrees or in other orientations, and the spatially relative descriptions used herein are interpreted accordingly.

[0026] The evaluation of the tower's internal accessory structure is mainly divided into two parts, namely the internal accessories and the internal accessory platform beam structure. The tower's accessory platform is generally composed of a main beam, an auxiliary beam and a panel. The main beam and the auxiliary beam are load-bearing structures. The impact of the panel is generally not considered when evaluating the internal accessory platform beam structure. The internal accessory structure evaluation includes the static strength evaluation of the weld between the welded bracket and the cylinder; the static strength evaluation of the welded bracket itself; and the fatigue strength evaluation of the weld between the welded bracket and the cylinder.

[0027] 1. Geometric model processing In order to reduce the calculation scale of the calculation model, the non-critical areas of the tower frame's internal accessory structure can be appropriately simplified, such as removing small transition arcs, circular holes, chamfers, etc.; removing some structural details (such as chamfers, chamfers, circular holes, etc.). In order to improve the calculation accuracy of key areas, it is necessary to perform necessary and appropriate geometric segmentation on some parts of the tower frame's internal accessories, such as the topological structure of the critical welding area, to meet the meshing requirements of special areas (such as hexahedral meshes for bodies and mapped meshes for faces).

[0028] 2. Establishment of finite element model.

[0029] The finite element modeling of the tower's internal accessory structure includes the tower body, the internal accessory welding structure, the main and auxiliary beam structure of the internal accessory platform, etc. The main and auxiliary beams of the internal accessory platform are evaluated using solid units, and the finite element model includes the platform and welded bracket. The platform and welded bracket are mechanically simplified, and the bolt holes, process holes and other structures that have little impact on the calculation results are deleted. The internal bolt connection structure of the platform is not considered in the platform evaluation, and it is assumed to be a common node. The finite element model of the tower accessory platform welded bracket is established using solid units. The welded bracket and the remaining tower welding area in this model need to be refined. The finite element model mainly includes: the tower body, the welded bracket, and the accessory platform. The tower and the accessory platform welding bracket are established using solid units. The main and auxiliary beams of the accessory platform can be evaluated using solid units. If the time is tight and the task is heavy and a quick evaluation is required, the Beam188 unit or the rigid connection unit MPC184 unit can be considered for simulation, which can efficiently and accurately consider the influence of the stiffness of the main and auxiliary beams of the platform.

[0030] 3. Boundary conditions are applied.

[0031] The constraints imposed by the finite element model of the tower's internal accessory structure are: Tower accessory platform welding bracket load application: tower bottom limit load, platform and equipment deadweight (including load safety factor), standard live load (including load safety factor) Displacement constraint: The constraint is imposed on the lower end face of the tower body.

[0032] 4. Extreme working conditions 1) Ultimate strength assessment of the main and auxiliary beam structures of the internal accessory platform The solid unit modeling is used to extract the stress of the platform beam structure and evaluate it using the fourth strength theory. If the stress is less than the allowable stress, a safety factor is required; if the stress exceeds the yield strength, the total strain is evaluated to be less than 1% and the plastic area is limited to a local position.

[0033] a) According to DNVGL-ST-0126, the disturbance of the platform beam structure shall be evaluated and shall meet the standard requirements, see formula (1).

[0034] (1) Where: ——The maximum vertical downward movement distance of the beam relative to its original position, in m or mm; ——The span of the beam. For a cantilever beam, L can be taken as twice the cantilever length, in m or mm.

[0035] 2) The working conditions considered in the calculation of the ultimate strength of the internal accessory welding structure are: a) Using the ultimate load at the bottom of the tower, the deadweight of the platform, and the deadweight of the electrical equipment on the platform, apply the Mxy value and Fxy value in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state; b) Use the tower bottom maintenance load, platform deadweight, deadweight of electrical equipment on the platform and uniformly distributed load (if the equivalent platform model is used, the uniformly distributed load is equivalent to a concentrated force), and use Mxy and Fxy in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state; The welding between the internal accessory welding bracket and the tower is a T-joint type, and the weld toe stress is a singular point. In the established finite element model, the relevant loads are applied for calculation. The welding bracket is allowed to have plastic deformation but the total strain is less than 1%, and the maximum area is 1 / 2 of the tower wall thickness at the corresponding position.

[0036] 5. Fatigue strength of welds in welded structures of accessories inside offshore towers.

[0037] Calculate the stress concentration factor at the weld of the welded bracket, establish a local coordinate system, apply the unit My bending moment (My=1000kN.m) to calculate the stress concentration factor at the weld of the welded bracket, and apply it in the y direction to ensure that the load is parallel to the weld of the welded bracket.

[0038] The calculation of nominal stress at the weld is shown in formula (9).

[0039] (9) Where: ——Unit bending moment, in kN.m or Nm.

[0040] ——Bending section coefficient of the tower section corresponding to the welded bracket, in m3 or mm3.

[0041] The stress at the weld of the welded bracket is obtained by extrapolation based on IIW, see formula (10).

[0042] (10) Where: ——Stress at the hot spot of the weld, in MPa or Pa; ——The stress at 0.4t from the weld toe on the interpolation path, the stress type is the principal stress (the first principal stress S1 and the third principal stress S3), the unit is MPa or Pa; ——The stress on the interpolation path 1t away from the weld toe. The stress type is the principal stress (S1 and S3), and the unit is MPa or Pa.

[0043] The SCF calculation at the weld of the welded bracket is shown in formula (11).

[0044] (11) The nominal stress method is used to calculate the fatigue of the weld seam of the welded bracket. The stress amplitude under load is calculated as shown in formula (12): (12) Where: ——Markov matrix projection angle The corresponding load range is in Nm; Wxy——Bending section modulus of the tower corresponding to the welded bracket, in units of m3 or mm3.

[0045] According to EN1993-1-9, the fatigue grade of weld seam of welded bracket is DC100, and according to Markov matrix and SN curve (see Figure 5 ) Calculate the cumulative fatigue damage of the weld of the welded bracket. See formula (13) for calculation.

[0046] (13) Where: —— The number of cycles; ——The number of cycles corresponding to the inflection point of the material SN curve, ND=5E6; ——material safety factor; ——actual stress range value, in MPa or Pa, calculated as shown in formula (12); ——The stress range value corresponding to the inflection point of the SN curve, in MPa or Pa, calculated as shown in formula (14); ——the slope of the SN curve, , k=3, otherwise k=5.

[0047] (14) Where: nA——The number of cycles corresponding to Δσc, nA=2E6; nD——The number of cycles corresponding to ΔσD, nD=5E6; Δσc——fatigue design level.

[0048] like Figures 1 to 5 As shown, the strength calculation method of the accessory structure of the offshore tower in this embodiment includes: S10 simplification and segmentation of the geometric model of the accessory structure of the offshore tower; S20 establishment of a finite element model of the accessory structure of the offshore tower; S30 design of the accessory structure of the offshore tower, the accessory structure design of the offshore tower includes: S31 finite element simulation of the main and auxiliary beam structure of the accessory platform of the offshore tower; S32 finite element simulation of the welding structure of the accessory of the offshore tower; S33 ultimate strength calculation of the accessory structure of the offshore tower; S34 fatigue strength calculation of the accessory structure of the offshore tower.

[0049] By applying the technical solution of this embodiment, the geometric model of the accessory structure inside the offshore tower is first simplified and segmented, which is convenient for subsequent simulation, verification and calculation. The overall finite element model can obtain the weak points that can withstand the force, and then simulate the easily damaged parts such as the main and auxiliary beam structures and welding structures, thereby further improving the design of the easily damaged positions. By calculating the ultimate strength and fatigue strength, the ultimate strength and fatigue strength of the accessory structure inside the offshore tower are further guaranteed, that is, the design is carried out from both static and dynamic aspects. The technical solution of this embodiment effectively solves the problems of low design accuracy and high material waste in the accessories inside the offshore tower in the prior art.

[0050] Step S31 includes: S311 Ultimate strength assessment of the main and auxiliary beam structures of the internal accessory platform; S312 The ultimate strength calculation of internal accessory welded structure considers the following working conditions: Using the tower bottom limit load, platform deadweight, and deadweight of electrical equipment on the platform, apply the Mxy value and Fxy value in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state; The tower bottom maintenance load, platform deadweight, deadweight of electrical equipment on the platform and uniformly distributed load are adopted, and Mxy and Fxy are used in the y direction and x direction respectively to ensure that the welding bracket is in the worst compression state; for the tower limit load Mxy, all possible dangerous working conditions need to be considered, and the load directions are parallel to the welding bracket, perpendicular to the welding bracket, and parallel and perpendicular to the center line of the two welding brackets.

[0051] The welding between the accessory welding bracket and the tower in the offshore tower is a T-joint type, and the weld toe stress is a singular point. In the established finite element model, the relevant loads are applied for calculation. The welding bracket is allowed to have plastic deformation but the total strain is less than 1%, and the maximum area is 1 / 2 of the tower wall thickness at the corresponding position.

[0052] In step S32, it includes: Calculate the stress concentration factor at the weld of the welded bracket, apply a bending moment of unit My, calculate the stress concentration factor at the weld of the welded bracket, and apply it in the y direction to ensure that the load is parallel to the weld of the welded bracket; The nominal stress calculation formula at the weld is as follows:

[0053] Where: ——Unit bending moment, in kN.m or Nm; ——Bending section coefficient of the tower section corresponding to the welded bracket, in m 3 or mm 3 . The stress at the weld of the welded bracket is obtained by extrapolation based on IIW:

[0054] Where: ——Stress at the hot spot of the weld, in MPa or Pa; ——The stress at 0.4t from the weld toe on the interpolation path, the stress type is the principal stress (S1 and S3), the unit is MPa or Pa; ——The stress on the interpolation path 1t away from the weld toe. The stress type is the principal stress (S1 and S3), and the unit is MPa or Pa.

[0055] The SCF calculation formula for the weld seam of the welded bracket is as follows:

[0056] The nominal stress method is used to calculate the fatigue of the weld seam of the welded bracket. The stress amplitude under load is calculated as shown in the formula:

[0057] Where: ——Markov matrix projection angle The corresponding load range is in Nm; Wxy——Bending section modulus of the tower corresponding to the welded bracket, in units of m3 or mm3.

[0058] Calculate the cumulative fatigue damage of the weld of the welded bracket. The calculation formula is as follows:

[0059] Where: —— The number of cycles; ——The number of cycles corresponding to the inflection point of the material SN curve, ND=5E6; ——material safety factor; ——actual stress range value, in MPa or Pa; ——The stress range value corresponding to the inflection point of the SN curve, in MPa or Pa, calculated as shown in formula (14); ——the slope of the SN curve, , k=3, otherwise k=5,

[0060] Where: nA——The number of cycles corresponding to Δσc, nA=2E6; nD——The number of cycles corresponding to ΔσD, nD=5E6; Δσc——fatigue design level.

[0061] The constraints imposed by the finite element model of the internal accessory structure of the offshore tower are: the load application of the welding bracket of the tower accessory platform, the ultimate load of the tower bottom, the deadweight of the platform and equipment, the live load displacement constraints specified by the standard, and the constraints imposed on the lower end face of the tower body.

[0062] The finite element modeling of the internal accessory structure of the offshore tower includes the tower body, the internal accessory welding structure and the main and auxiliary beam structure of the internal accessory platform; the main and auxiliary beams of the internal accessory platform are evaluated using solid units. The finite element model includes the platform and the welded bracket. The platform and the welded bracket are mechanically simplified, and the bolt holes and process holes that have little impact on the calculation results are deleted. The internal bolt connection structure of the platform is not considered in the platform evaluation, and it is assumed to be a common node. The finite element model of the tower accessory platform welded bracket is established using solid units. The welding bracket and the remaining tower welding area in this model need to be refined. The finite element model mainly includes: the tower body, the welded bracket and the accessory platform. The tower and the accessory platform welding bracket are established using solid units. The main and auxiliary beams of the accessory platform can be simulated using solid units, and / or Beam188 units or rigid connection units MPC184 units, which can efficiently and accurately consider the influence of the stiffness of the main and auxiliary beams of the platform. When the solid unit establishes the finite element model of the tower accessories, it is necessary to refine the mesh of the welding bracket and the surrounding area of ​​the tower. The principle of geometric model segmentation is as follows: regular mesh in the transverse weld area, ensuring a regular mesh at a distance of 5 times the tower wall thickness in the weld direction, and regular mesh in the longitudinal weld area, and there is no need to extend the regular mesh in the weld direction.

[0063] There are many contents that need to be evaluated in the accessory structures of offshore towers, including the main and auxiliary beam structures of the platform, the welding structures of the internal accessories, etc. The form is complex. It is necessary to establish a reasonable and accurate model and consider the structural connections of each part to ensure the reliability of the evaluation results.

[0064] In the finite element model of the internal accessory structure of the offshore tower, the tower and the accessory platform welding bracket are modeled with solid units, and the main and auxiliary beams of the accessory platform and other structures are modeled with solid units or Beam188 units or rigid connection units MPC184 units; when the rigid connection unit MPC184 unit is used to simulate the influence of the stiffness of the main and auxiliary beams, it is necessary to select the contact area between the internal accessories and the main and auxiliary beams for stiffness coupling connection to ensure the accuracy of the force transmission route. Different coupling areas have a great influence on the final result, and some may have a stress difference of hundreds of MPa.

[0065] This method considers the influence of the stiffness of the main and auxiliary beams of the internal accessory platform on the strength calculation of the internal accessory structure of the offshore tower, and the calculation method is comprehensive.

[0066] In the calculation of the internal accessory structure of the offshore tower, the main and auxiliary beams of the platform are complex and the modeling is very time-consuming. In order to accurately and efficiently evaluate the internal accessory welding structure, the rigid connection unit is used to simulate the influence of the main and auxiliary beams on its stiffness, which is efficient and reliable.

[0067] Through the study of the strength calculation method of the accessory structure in the offshore tower, a refined finite element modeling method is adopted, and reasonable unit types, material models, contact relationships and grid sizes are selected to accurately reflect the working performance of the accessory structure in the offshore tower. The mechanical properties of the structure can be calculated more accurately through the refined finite element model. The established finite element model can better simulate the failure mode of the structure under all design conditions.

[0068] This method can be used to calculate and verify the stress analysis of the accessory structure inside the offshore tower, and can be directly applied to actual engineering projects in the future. According to the actual situation of the project, structural modeling, calculation and simulation analysis can be realized, and a calculation and analysis method can be provided for the design of the accessory structure inside the offshore tower to ensure the safe and reliable operation of the structure.

[0069] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0070] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0071] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating the strength of an accessory structure of an offshore tower, characterized in that: include: S10 Simplification and segmentation of the geometric model of the internal accessory structure of the offshore tower; S20 Establish the finite element model of the internal accessory structure of the offshore tower; S30 Design of internal accessory structures of offshore towers, including: S31 Finite element simulation of main and auxiliary beam structure of the accessory platform inside the offshore tower; S32 Finite element simulation of welding structure of internal accessories of offshore tower; S33 Calculation of ultimate strength of accessory structures inside offshore towers; S34 Calculation of fatigue strength of accessory structures within offshore towers.

2. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 1, characterized in that: Step S31 includes: S311 Ultimate strength assessment of the main and auxiliary beam structures of the internal accessory platform; S312 The ultimate strength calculation of internal accessory welded structure considers the following working conditions: Using the tower bottom limit load, platform deadweight, and deadweight of electrical equipment on the platform, apply the Mxy value and Fxy value in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state; The tower bottom maintenance load, platform deadweight, deadweight of electrical equipment on the platform and uniformly distributed load are adopted, and Mxy and Fxy are used in the y direction and x direction respectively to ensure that the welded bracket is in the worst compression state.

3. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 2, characterized in that: The welding between the accessory welding bracket and the tower inside the offshore tower is a T-joint type, and the weld toe stress is a singular point. In the established finite element model, relevant loads are applied for calculation. Plastic deformation is allowed for the welding bracket, but the total strain is less than 1%. At the same time, the maximum area is 1 / 2 of the tower wall thickness at the corresponding position.

4. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 2, characterized in that: In step S32, it includes: Calculate the stress concentration factor at the weld of the welded bracket, apply a bending moment of unit My, calculate the stress concentration factor at the weld of the welded bracket, and apply it in the y direction to ensure that the load is parallel to the weld of the welded bracket; The nominal stress calculation formula at the weld is as follows: Where: ——Unit bending moment, in kN.m or Nm; ——Bending section coefficient of the tower section corresponding to the welded bracket, in m 3 or mm 3 .

5. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 4, characterized in that: The stress at the weld of the welded bracket is obtained by extrapolation based on IIW: Where: ——Stress at the hot spot of the weld, in MPa or Pa; ——The stress at 0.4t from the weld toe on the interpolation path. The stress type is the principal stress: the first principal stress S1 and the third principal stress S3, in MPa or Pa; ——The stress on the interpolation path 1t away from the weld toe. The stress type is principal stress: the first principal stress S1 and the third principal stress S3, in MPa or Pa.

6. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 5, characterized in that: The SCF calculation formula for the weld seam of the welded bracket is as follows: 。 7. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 6, characterized in that: The nominal stress method is used to calculate the fatigue of the weld seam of the welded bracket. The stress amplitude under load is calculated as shown in the formula: Where: ——Markov matrix projection angle The corresponding load range is in Nm; Wxy——Bending section modulus of the tower corresponding to the welded bracket, in units of m3 or mm3.

8. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 7, characterized in that: Calculate the cumulative fatigue damage of the weld of the welded bracket. The calculation formula is as follows: Where: —— The number of cycles; ——The number of cycles corresponding to the inflection point of the material SN curve, ND=5E6; ——material safety factor; ——actual stress range value, in MPa or Pa; ——The stress range value corresponding to the inflection point of the SN curve, in MPa or Pa; ——the slope of the SN curve, , k=3, otherwise k=5, Where: nA——The number of cycles corresponding to Δσc, nA=2E6; nD——The number of cycles corresponding to ΔσD, nD=5E6; Δσc——fatigue design level.

9. The method for calculating the strength of the internal accessory structure of an offshore tower according to any one of claims 1 to 8, characterized in that: The constraints imposed by the finite element model of the internal accessory structure of the offshore tower are: the load application of the welding bracket of the tower accessory platform, the ultimate load of the tower bottom, the deadweight of the platform and equipment, the live load displacement constraints specified by the standard, and the constraints imposed on the lower end face of the tower body.

10. The method for calculating the strength of the internal accessory structure of an offshore tower according to claim 9, characterized in that: The finite element modeling of the internal accessory structure of the offshore tower includes the tower body, the internal accessory welding structure and the main and auxiliary beam structure of the internal accessory platform; the main and auxiliary beams of the internal accessory platform are evaluated using solid units. The finite element model includes the platform and the welded bracket. The platform and the welded bracket are mechanically simplified, and the bolt holes and process holes that have little impact on the calculation results are deleted. The internal bolt connection structure of the platform is not considered in the platform evaluation, and it is assumed to be a common node. The finite element model of the tower accessory platform welded bracket is established using solid units. The welding bracket and the remaining tower welding area in this model need to be refined. The finite element model mainly includes: the tower body, the welded bracket and the accessory platform. The tower and the accessory platform welding bracket are established using solid units. The main and auxiliary beams of the accessory platform can be simulated using solid units, and / or Beam188 units or rigid connection units MPC184 units, which can efficiently and accurately consider the influence of the stiffness of the main and auxiliary beams of the platform.

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