Design method of high-strength connecting bolt of wind power transformer

Abstract

The invention belongs to the field of wind power transformer bolt connection simulation calculation, and particularly relates to a design method for a high-strength connection bolt of a wind power transformer, which comprises the following steps of: 1) establishing an integral finite element model of the wind power transformer; a bolt part needing to be checked is cut out, and a finite element local model is formed; (2) simulation is conducted through the wind power transformer finite element local model, and the axial force and the transverse force of the bolt are obtained; 3) establishing a standard component library and a bolt connection database, and evaluating and checking the bolt according to an input value calculated according to the VDI2230 standard; (4) the safety coefficients of the bolts are evaluated respectively, if all the safety coefficients are larger than or equal to 1, bolt type selection and connection meet the use requirements, and bolt type selection succeeds; on the contrary, if a certain safety coefficient is smaller than 1, the bolts are optimized and then selected again; and 5) repeating the steps until all the safety coefficients meet the requirements, and outputting a bolt calculation check report with all the parameters.

Description

Technical Field

[0001] The invention belongs to the field of wind power transformer bolt connection simulation calculation, in particular to a design method for high-strength connection bolts of a wind power transformer. Background Art

[0002] In the past decade, standard VDI2230 has been widely used in the strength research of bolted connections. Li Yana, Wu Zili and others used standard VDI2230 combined with experimental research methods to conduct relevant analysis on high-strength bolted connections. Chen Zhen, Du Jing, He Yulin and others analyzed and studied the eccentric loading model of bolted connections based on the VDI2230 standard in the verification of high-strength bolted connections of tower flanges of MW-class wind turbines, and verified the reliability of numerical calculations of the VDI2230 standard. Du Jing and others established a mathematical calculation model for the axial stiffness of bolts of horizontal-axis wind turbines, and calculated the thread force and the equivalent stress of bolts under actual working conditions. He Yulin, Wang Xiuwen and Ding Shuaiming conducted a fatigue life analysis of variable pitch bolts of MW-class wind turbines, established and modified the SN curve based on VDI2230, and finally used the Palmgren-Miner linear damage theory to obtain the damage value of the yaw gear ring bolts of wind turbines. E Qiangqiang et al. compared the stress intensity and fatigue strength obtained under different preload conditions and proposed a reference range of preload values. Liu Xianchao, Ma Siqun, Wang Dahong et al. studied the strength verification of the end support connection bolts of railway tank cars based on VDI2230. Wang Weihui, Li Yana, Wang Chunyan et al. analyzed the connection strength of EMU couplers based on the VDI2230 standard. Chen Weijin studied the comparative analysis of the bolt technology used in German and Chinese locomotives and vehicles.

[0003] Foreign research: Croccolo Dario et al. used VDI2230 and experimental research methods to conduct relevant analysis on high-strength bolt connections, and gave a calculation formula that can calculate the maximum equivalent stress of bolts. Schaumann P et al. and Dinger G et al. used VDI2230 standards and experimental methods to simulate and analyze the stiffness and compression model of bolt connections on wind turbines, and the results were relatively ideal.

[0004] According to the above research status at home and abroad, the existing technology has the following defects and shortcomings:

[0005] (1) The scope involved is relatively limited: From the perspective of papers and patents, bolt verification based on the VDI2230 standard is mainly widely used in rail transit, and is occasionally applied to automobiles and wind turbines. There is currently no research on other wind power equipment;

[0006] (2) Bolt verification items are not comprehensive: Currently, the focus is mainly on bolt strength and screw life, without comprehensive verification from the aspects of bolt connection strength, fatigue, internal pressure, slip and shear force;

[0007] (3) No optimization method is given for bolt failure: Currently, finite element models are based on simulation analysis of the design structure, extracting bolt forces or directly using finite element models for evaluation. There is no improvement on how to optimize the treatment if the bolts fail to meet the inspection requirements.

[0008] (4) There are many factors that affect bolt calibration, but there is no description or solution for these factors.

[0009] (5) The finite element overall model uses contact simulation analysis, which has a large amount of calculation and low calculation efficiency.

[0010] Therefore, it is particularly important to design a design method for connecting bolts used in other wind power equipment. Summary of the invention

[0011] The purpose of the present invention is to provide a design method for high-strength connecting bolts of wind power transformers. Parametric modeling is used for the bolts in the finite element model of the wind power transformer. A local simulation model of the bolt part is taken in the overall finite element model of the wind power transformer to improve the calculation efficiency and calculation accuracy. The axial force and lateral force of the bolt obtained by simulation are used as the input values ​​of the VDI2230 numerical calculation, and then the bolt is checked by the VDI2230 method and the database of bolt parameters. The present invention belongs to the field of wind power transformers and belongs to the forward design of simulation calculation and theoretical calculation.

[0012] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a design method for high-strength connecting bolts of a wind power transformer, comprising the following steps:

[0013] 1) Establish an overall finite element model of the wind power transformer; and cut out the bolt part that needs to be checked in the overall finite element model of the wind power transformer to form a local finite element model;

[0014] 2) The axial force and lateral force of the bolts are obtained by simulating the local finite element model of the wind power transformer as input values ​​for calculation according to the VDI2230 standard;

[0015] 3) Before bolt evaluation, a standard parts library and a bolt connection database are established respectively, and the bolts are evaluated and checked according to the input values ​​calculated according to the VDI2230 standard;

[0016] 4) Combined with the standard parts library and bolt connection database, the safety factors of the bolt's yield point, internal pressure, fatigue, slip and shear are evaluated respectively. If all safety factors are greater than or equal to 1, the bolt selection and connection meet the use requirements, and the bolt selection is successful; otherwise, if a safety factor is less than 1, the bolt is optimized and reselected;

[0017] 5) Repeat steps 1) to 4) until all safety factors meet the requirement of being greater than or equal to 1, and output a bolt calculation verification report with all parameters.

[0018] The establishment of the overall finite element model of the wind power transformer includes: wind power transformer component modeling and bolt parameterized modeling;

[0019] (1) Modeling of wind power transformer components, namely:

[0020] Obtain the geometric dimension data of wind power transformers, including the shape and size information of iron core, winding, body clamps, insulating supports, dry-type transformer cover, oil tank of oil-immersed transformer, fixed support base, radiator and other components; mesh the entire geometric model and apply boundary conditions according to actual working conditions;

[0021] (2) Parametric modeling of bolts in transformers, namely:

[0022] a. Determine the key geometric parameters of the bolt, and determine the value range and default value of each parameter according to the standard specifications and actual design requirements of the bolt;

[0023] b. In the finite element software, create a 3D geometric model of the bolt by inputting parametric expressions and geometric operation commands; associate each geometric feature of the bolt with the defined parameters to ensure that the geometric shape of the bolt is automatically updated when the parameter value changes;

[0024] c. In the overall model of the wind power transformer, determine the installation position and connection method of the bolts, and simulate the connection relationship between the bolts and the connected parts by establishing constraint conditions; for multiple bolt connections, consider the preload force distribution and loading sequence of the bolts, and use preload force units or set normal stiffness in the contact pairs to simulate the effect of preload force;

[0025] d. Set up a parametric driving mechanism to update the geometric model and overall assembly relationship of the bolt by modifying the parameter values; perform mesh quality checks and preliminary calculation verification on the models under different parameter combinations to ensure the stability and reliability of the model within the parameter variation range;

[0026] (3) Assemble the parameterized bolt model with other components of the wind power transformer to form a complete finite element model of the wind power transformer, check the assembly relationship and interference between the components, and ensure the integrity and rationality of the model.

[0027] In step 1), the bolt part that needs to be checked is cut out from the overall finite element model of the wind power transformer to form a local finite element model, specifically:

[0028] 1-1) Select the bolt area:

[0029] According to the design requirements and analysis purposes, select the corresponding bolts and the surrounding areas in the overall model using the geometric selection tool;

[0030] 1-2) Extract local geometry:

[0031] Use the cutting or extraction provided by the finite element software to extract the selected bolt and its surrounding parts from the overall model to form a new local geometric model; check the extracted local geometry to ensure its integrity and geometric accuracy to avoid loss or error of geometric information due to cutting operations;

[0032] 1-3) Grid Re-division:

[0033] For the extracted local model, according to its own characteristics and analysis requirements, re-grid the local model, refine the mesh, define the contact settings between the bolt gasket and the fastener, and improve the calculation accuracy and efficiency;

[0034] 1-4) Local boundary conditions and load adjustment:

[0035] According to the boundary conditions, loads and overall finite element simulation results of the overall model, the overall finite element simulation results are transferred to the local model as the boundary conditions and load conditions of the local finite element simulation; the setting of the boundary conditions is provided by the overall finite element model.

[0036] The step 2) is specifically:

[0037] 2-1) Conduct finite element simulation calculation

[0038] Select the solver according to the characteristics of the model and the purpose of analysis; and determine the calculation type: static structural analysis is used to solve the bolt force under steady state, and transient analysis is used to consider the change of bolt force under dynamic load;

[0039] According to the limit of the number of iterations, the solution control parameters are set, and the local finite element model of the wind power transformer is submitted for simulation calculation. The solver will calculate the displacement and stress results of each node in the model based on the established equations and the applied boundary conditions and loads;

[0040] 2-2) Extract the axial force and lateral force of the bolt

[0041] Axial force extraction: Determine the axial direction of the bolt, find the force component along this direction in the results, and obtain the axial force of the bolt by checking the force output of specific nodes or units on the bolt axis. For bolts with preload, distinguish between the axial force increment generated by the preload and the working load.

[0042] Transverse force extraction: According to the coordinate system of the bolt, the transverse direction is determined, and the force component perpendicular to the axial direction of the bolt is extracted as the transverse force; by observing the relative displacement and force distribution of the bolt between the connected parts, the magnitude and direction of the transverse force can be determined.

[0043] 2-3) The extracted bolt axial force and lateral force are used as input values ​​and substituted into the calculation formula specified in the VDI2230 standard; the simulation calculation results are used as input values.

[0044] The standard parts library includes: bolt specifications, nominal diameter, major diameter, minor diameter, thread pitch, bolt length, bolt rotation angle and bolt material;

[0045] The parameters of the bolt connection database include: installation preload torque, friction coefficient between clamping parts, friction coefficient between bolt head and clamped parts, diameter area of ​​bolt fixing parts, thickness of clamped parts, connection coefficient, thread friction coefficient, outer diameter of bolt head bearing plane, inner diameter of load-bearing plane, tightening coefficient, tightening torque coefficient, reduction coefficient, load factor and lubricant.

[0046] In step 4), the safety factor of the yield point of the bolt is evaluated, specifically:

[0047] For connections that do not exceed the bolt yield point during loading:

[0048] In working condition, the total bolt load F Smax for:

[0049]

[0050] Among them, E Mzul is the allowable preload; is the load factor of the bolt; F Amax is the maximum axial load; ΔF Vth is the change of preload;

[0051] Maximum tensile stressσ zmax ,Right now:

[0052] σ zmax =F Smax / A0

[0053] Among them, A0 is the nominal cross-sectional area of ​​the bolt;

[0054] Maximum torsional stress τ max ,Right now:

[0055] τ max =M G / W P

[0056] Among them, M G is the thread torque, in Nm; W P is the polar resistance moment of the bolt cross section;

[0057] For reduced or relative stresses associated with torsional stresses in applications, the recommended factor k is τ = 0.5, reduced to k τ Situation:

[0058]

[0059] Then the bolt yield point safety factor S F for:

[0060] S F =R P0.2min / σ red，B ≥1.0

[0061] Among them, R P0.2min is the minimum yield point of the bolt.

[0062] In step 4), the safety factor of the internal pressure of the bolt is evaluated, specifically:

[0063] The surface pressure calculated based on the expected chamfer error and the surface pressure does not exceed the surface limit pressure of the fastened material, following the following relationship:

[0064] P Mmax Assembly lower surface limit pressure:

[0065] P Mmax =E Mzul / A Pmin ≤P G

[0066] Among them, A Pmin is the bolt minor diameter cross-sectional area;

[0067] P Bmax Surface limit pressure under working condition:

[0068] P Bmax =(F Vmax +F Amax -ΔF Vth ) / AP min ≤P G

[0069] Among them, F Vmax Maximum applied preload;

[0070] Maximum surface pressure P for tightening techniques with yield or angle control G , considering the dispersion of yield points, refer to the following formula:

[0071]

[0072] Among them, E MTab Provide preload for bolt installation;

[0073] Pressure safety factor: S P =P G / P M / Bmax ≥1.0.

[0074] In step 4), the fatigue safety factor of the bolt is evaluated, specifically:

[0075] The number of alternating cycles under continuous load is N D ≥2*10 6 and stress cross section A S The fatigue limit reference values ​​of relevant high-strength bolts are as follows:

[0076] The fatigue limit of rolled SV before heat treatment is:

[0077]

[0078] Where, d is the bolt diameter;

[0079] The fatigue limit of rolled SG after heat treatment is:

[0080]

[0081] Among them, F Sm is the average bolt load, F 0.2min Bolt load at minimum yield point or at 0.2% allowable stress;

[0082] If it is greater than the fatigue strength σ AS The stress amplitude has a cycle frequency of only a few thousand times (N Z >10 4 ), the endurance limit of the connection can be established if the following dynamic strength values ​​are determined:

[0083] Rolling SV before heat treatment:

[0084]

[0085] Rolling SG after heat treatment:

[0086]

[0087] Among them, N D is the number of alternating cycles under continuous load, N Z is the number of alternating cycles of loading within the fatigue strength range.

[0088] In step 4), the fatigue safety factor of the bolt is evaluated, specifically:

[0089] If the number of joint surfaces q F and q M Inevitably involving slip and the friction coefficient μT of the joint surface, the minimum residual preload F KRmin and the preload F required to transfer the lateral load KQerf They are:

[0090]

[0091] Among them, α A is the tightening factor; F Z It is the preload loss caused by embedding during operation;

[0092]

[0093] Among them, q F is the number of internal interfaces where the bolt may slip or shear; μ μ μ Tmin is the friction coefficient at the interface; M Ymax is the maximum axial torque of the bolt; q M r is the number of internal interfaces where the bolt may slip and transmit torque; a M Ymax The friction radius of the clamped parts during action;

[0094] The safety verification to prevent slipping is:

[0095]

[0096] Safety verification of shear resistance, namely:

[0097]

[0098] Among them, τ B is the shear strength, A τ is the shear cross section under transverse load.

[0099] In step 5), the optimization of the bolts includes: changing the material of the bolts, and then checking whether the new material bolts meet the safety factor assessment requirements according to the VDI2230 standard;

[0100] Another solution is: if changing the bolt material including stainless steel, 8.8 grade carbon steel, 10.9 grade carbon steel, and 12.9 grade carbon steel still cannot meet the bolt's yield point, internal pressure, fatigue, slip and shear safety factors that are greater than or equal to 1, then change the bolt specification model through the parametric model drive and then recalculate.

[0101] The present invention has the following beneficial effects and advantages:

[0102] 1. The present invention fills the gap in bolt calibration in the field of wind power transformers. Finite element simulation is combined with VDI2230 standard to accurately calibrate the bolts of wind power transformers, providing a reliable and systematic calibration method for wind power transformer bolt calibration;

[0103] 2. The present invention is more comprehensive based on the standard VDI2230 assessment, and comprehensively checks the strength, fatigue, internal pressure, slip and shear force of the bolt connection. It is a forward design of bolt simulation calculation and theoretical calculation, which provides reliable support for selection and has the advantage of comprehensive safety factor assessment;

[0104] 3. The present invention proposes for the first time that when the yield point, internal pressure, fatigue, slip and shear safety factors are less than 1 during bolt verification, optimization calculation is performed through an adaptive optimization feedback method until all safety factors are greater than 1 and meet the design requirements. It has the advantages of high automation and advanced optimization methods.

[0105] 4. The present invention proposes for the first time to establish a standard parts database for bolts based on the calculation requirements of the VDI2230 standard, and to suggest a parameter selection database for the parameters that need to be defined in the calculation. The establishment of the bolt standard parts library increases the convenience of bolt verification and improves the efficiency of bolt verification;

[0106] 5. The present invention proposes for the first time in bolt verification to combine the overall finite element model of the structure with the local model to simulate and calculate the axial force and lateral force of the bolt. The establishment of the overall simulation model makes the simulation model closer to the actual situation, and the local simulation model makes the grid finer, the calculation more accurate and the calculation efficiency high. The establishment of the overall simulation model and the local model takes into account both accuracy and greatly improves the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] Figure 1 is a flow chart of the method of the present invention;

[0108] Figure 2 It is a finite element overall model of the wind power transformer of the present invention;

[0109] Figure 3 It is a finite element local bolt model of the wind power transformer of the present invention. DETAILED DESCRIPTION

[0110] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0111] like Figure 1 As shown, it is a flow chart of the method of the present invention. The design method of a high-strength connecting bolt of a wind power transformer of the present invention comprises the following steps:

[0112] (1) Establish an overall finite element model of the wind power transformer, in which the bolt model in the transformer is parametric modeling (solid bolts, nuts and washers), which can be driven and updated by parameters;

[0113] 1.1 Wind power transformer component modeling and bolt parametric modeling:

[0114] Modeling of wind power transformer components, such as Figure 2 As shown:

[0115] Obtain the geometric dimension data of wind power transformers, including the shape and size information of iron core, winding, body clamps, insulating supports, dry-type transformer cover, oil tank of oil-immersed transformer, fixed support base, radiator and other components; mesh the entire geometric model and apply boundary conditions according to actual working conditions;

[0116] Parametric modeling of bolts in transformers, namely:

[0117] a. Determine the key geometric parameters of the bolt, and determine the value range and default value of each parameter according to the standard specifications and actual design requirements of the bolt;

[0118] b. In the finite element software, create a 3D geometric model of the bolt by inputting parametric expressions and geometric operation commands; associate each geometric feature of the bolt with the defined parameters to ensure that the geometric shape of the bolt is automatically updated when the parameter value changes;

[0119] c. In the overall model of the wind power transformer, determine the installation position and connection method of the bolts, and simulate the connection relationship between the bolts and the connected parts by establishing constraint conditions; for multiple bolt connections, consider the preload force distribution and loading sequence of the bolts, and use preload force units or set normal stiffness in the contact pairs to simulate the effect of preload force;

[0120] d. Set up a parametric driving mechanism to update the geometric model and overall assembly relationship of the bolt by modifying the parameter values; perform mesh quality checks and preliminary calculation verification on the models under different parameter combinations to ensure the stability and reliability of the model within the parameter variation range;

[0121] Assemble the parameterized bolt model with other components of the wind power transformer to form a complete finite element model of the wind power transformer, check the assembly relationship and interference between the components, and ensure the integrity and rationality of the model.

[0122] 1.2 Forming a local finite element model:

[0123] a) Select the bolt area:

[0124] According to the design requirements and analysis purposes, select the corresponding bolts and the surrounding areas in the overall model using the geometric selection tool;

[0125] b) Extract local geometry:

[0126] Use the cutting or extraction provided by the finite element software to extract the selected bolt and its surrounding parts from the overall model to form a new local geometric model; check the extracted local geometry to ensure its integrity and geometric accuracy to avoid loss or error of geometric information due to cutting operations;

[0127] c) Grid Re-division:

[0128] For the extracted local model, according to its own characteristics and analysis requirements, re-grid the local model, refine the mesh, define the contact settings between the bolt gasket and the fastener, and improve the calculation accuracy and efficiency;

[0129] d) Local boundary conditions and load adjustments:

[0130] According to the boundary conditions, loads and overall finite element simulation results of the overall model, the overall finite element simulation results are transferred to the local model as the boundary conditions and load conditions of the local finite element simulation; the setting of the boundary conditions is provided by the overall finite element model.

[0131] (2) Cut out the bolt part that needs to be checked from the overall finite element model of the wind power transformer to form a local finite element model, such as Figure 3 As shown, the boundary condition settings are provided by the finite element overall model. The local model refines the mesh and defines the contact settings between the bolt gasket and the fastener to improve the calculation accuracy and efficiency;

[0132] (2-1) Perform finite element simulation calculation

[0133] Select the solver according to the characteristics of the model and the purpose of analysis; and determine the calculation type: static structural analysis is used to solve the bolt force under steady state, and transient analysis is used to consider the change of bolt force under dynamic load;

[0134] According to the limit of the number of iterations, the solution control parameters are set, and the local finite element model of the wind power transformer is submitted for simulation calculation. The solver will calculate the displacement and stress results of each node in the model based on the established equations and the applied boundary conditions and loads;

[0135] (2-2) Extracting bolt axial force and lateral force

[0136] Axial force extraction: Determine the axial direction of the bolt, find the force component along this direction in the results, and obtain the axial force of the bolt by checking the force output of specific nodes or units on the bolt axis. For bolts with preload, distinguish between the axial force increment generated by the preload and the working load.

[0137] Transverse force extraction: According to the coordinate system of the bolt, the transverse direction is determined, and the force component perpendicular to the axial direction of the bolt is extracted as the transverse force; by observing the relative displacement and force distribution of the bolt between the connected parts, the magnitude and direction of the transverse force can be determined.

[0138] (2-3) The extracted bolt axial force and lateral force are used as input values ​​and substituted into the calculation formula specified in the VDI2230 standard; the simulation calculation results are used as input values.

[0139] (3) The local finite element model of the wind turbine transformer is simulated to obtain the bolt axial force and lateral force, which are used as input values ​​for calculation according to the VDI2230 standard;

[0140] (4) Evaluate and verify bolts according to VDI2230 standard and establish a standard parts library: including bolt specifications, nominal diameter, major diameter, minor diameter, pitch, bolt length, bolt rotation angle and bolt material;

[0141] Establish a bolt connection database with parameters including installation preload torque, friction coefficient between clamped parts, friction coefficient between bolt head and clamped parts, diameter area of ​​bolted parts, thickness of clamped parts, connection coefficient, thread friction coefficient, outer diameter of bolt head bearing plane, inner diameter of load-bearing plane, tightening coefficient, tightening torque coefficient, reduction coefficient, load factor and lubricant, etc.

[0142] 4.1 Bolt yield point

[0143] In the event that the connection is tightened beyond the elastic limit, it is permissible to exceed the yield point. The preload will decrease during the working stress process. For connections that do not exceed the yield point of the bolt during loading:

[0144] In working condition, the total bolt load F Smax The calculation is as follows:

[0145]

[0146] In the formula, FMzul is the allowable preload force, in N; is the load factor of the bolt; F Amax is the maximum axial load, in N; ΔF Vth is the preload change, unit is N.

[0147] Maximum tensile stressσ zmax It can be calculated according to the following formula:

[0148] σ zmax =F Smax / A0......................(2)

[0149] Where A0 is the nominal cross-sectional area of ​​the bolt, in m 2 .

[0150] Maximum torsional stress τ max It can be calculated according to the following formula:

[0151] τ max =M G / W P .......................(3)

[0152] Where M G is the thread torque, in Nm; W P It is the polar resistance moment of the bolt cross section, in Nm.

[0153] For reduced or relative stresses with torsional stress in applications (recommended factor k τ =0.5) is reduced to k τ of:

[0154]

[0155] Bolt yield point safety factor S F :

[0156] S F =R P0.2min / σ red，B ≥1.0.......................(5)

[0157] In the formula, R P0.2min It is the minimum yield point of the bolt, in MPa.

[0158] 4.2 Bolt internal pressure

[0159] The surface pressure between the bolt head and the nut on the one hand and the fastened part on the other hand leads to creep associated with the reduction of the preload, which is not effective as a result of the assembly preload or the maximum load in service. The surface pressure calculated based on the expected tolerance of the chamfer should not exceed the surface limit pressure of the fastened material. The following formula must be followed:

[0160] P Mmax Assembly lower surface limit pressure:

[0161] P Mmax =F Mzul / A Pmin ≤P G ........................(6)

[0162] In the formula, A Pmin is the bolt minor diameter cross-sectional area, unit: m 2 .

[0163] P Bmax Surface limit pressure under working condition:

[0164] P Bmax =(F Vmax +F Amax -ΔF Vth ) / A Pmin ≤P G ...............(7)

[0165] In the formula, F Vmax Maximum applied preload in N.

[0166] Maximum surface pressure P for tightening techniques with yield or angle control G , to consider the yield point dispersion, refer to the following formula:

[0167]

[0168] In the formula, F MTab It is the bolt installation preload force, in N.

[0169] The pressure safety factor is:

[0170] S P =P G / P M / Bmax ≥1.0.......................(9)

[0171] 4.3 Bolt slip and shear

[0172] Transverse loads occurring in bolted connections are transmitted by friction clamping, which, in the case of overloaded or just-fitted bolts, excludes failure of the connection due to shear or exceeding the permissible bearing stress of the bolts.

[0173] If the number of joint surfaces q F and q M Inevitably involving slip and the friction coefficient μT of the joint surface, the following formula applies to the minimum residual preload F KRmin and the preload F required to transfer the lateral load KQerf :

[0174]

[0175] In the formula, α A is the tightening factor; F Z It is the preload loss caused by embedding during operation, unit is N.

[0176]

[0177] Among them, q F The number of internal interfaces where the bolt may slip or shear, μT min is the friction coefficient at the interface; M Ymax is the maximum axial torque of the bolt; q M r is the number of internal interfaces where the bolt may slip and transmit torque; a M Ymax The friction radius of the clamped parts during action;

[0178] The safety verification to prevent slipping is:

[0179]

[0180] Safety verification of shear resistance, namely:

[0181]

[0182] Among them, τ B is the shear strength, A τ is the shear cross section under transverse load.

[0183] 4.4 Bolt fatigue

[0184] The number of alternating cycles under continuous load is N D ≥2*10 6 and stress cross section A S The fatigue limit reference values ​​of relevant high-strength bolts are as follows:

[0185] The fatigue limit of rolled SV before heat treatment is:

[0186]

[0187] Where, d is the bolt diameter;

[0188] The fatigue limit of rolled SG after heat treatment is:

[0189]

[0190] Among them, F Sm is the average bolt load, F 0.2min Bolt load at minimum yield point or at 0.2% allowable stress;

[0191] If it is greater than the fatigue strength σ AS The stress amplitude has a cycle frequency of only a few thousand times (N Z >10 4 ), the endurance limit of the connection can be established if the following dynamic strength values ​​are determined:

[0192] Rolling SV before heat treatment:

[0193]

[0194] Rolling SG after heat treatment:

[0195]

[0196] Among them, N D is the number of alternating cycles under continuous load, N Z is the number of alternating cycles of loading within the fatigue strength range.

[0197] (5) The bolt's yield point, internal pressure, fatigue, slip and shear safety factors are evaluated. If the safety factor is greater than 1, the bolt selection and connection meet the use requirements and the bolt selection is successful. If the safety factor is not greater than 1, there are two optimization solutions: one is to change the bolt material and then check whether the new material bolt meets the requirements according to the VDI2230 standard; the other is to change the bolt specification model through parametric model driving and then recalculate.

[0198] (6) The optimization program and method are updated through adaptive feedback until all safety factors meet the requirements, and a bolt calculation verification report with all parameters is output.

[0199] Those skilled in the art will appreciate that the above are only preferred embodiments of the present invention, and the various embodiments of the present disclosure and / or the features described in the claims may be combined or combined in various ways, even if such combinations or combinations are not explicitly described in the present disclosure. It is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments, or perform equivalent substitutions on some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

[0200] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A design method for high-strength connecting bolts of wind power transformers, characterized in that: The following steps are involved: 1) Establish an overall finite element model of the wind power transformer; and cut out the bolt part that needs to be checked in the overall finite element model of the wind power transformer to form a local finite element model; 2) The axial force and lateral force of the bolts are obtained by simulating the local finite element model of the wind power transformer as input values ​​for calculation according to the VDI2230 standard; 3) Before bolt evaluation, a standard parts library and a bolt connection database are established respectively, and the bolts are evaluated and checked according to the input values ​​calculated according to the VDI2230 standard; 4) Combined with the standard parts library and bolt connection database, the safety factors of the bolt's yield point, internal pressure, fatigue, slip and shear are evaluated respectively. If all safety factors are greater than or equal to 1, the bolt selection and connection meet the use requirements, and the bolt selection is successful; otherwise, if a safety factor is less than 1, the bolt is optimized and reselected; 5) Repeat steps 1) to 4) until all safety factors meet the requirement of being greater than or equal to 1, and output a bolt calculation verification report with all parameters.

2. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: The establishment of the overall finite element model of the wind power transformer includes: wind power transformer component modeling and bolt parameterized modeling; (1) Modeling of wind power transformer components, namely: Obtain the geometric dimension data of wind power transformers, including the shape and size information of iron core, winding, body clamps, insulating supports, dry-type transformer cover, oil tank of oil-immersed transformer, fixed support base, radiator and other components; mesh the entire geometric model and apply boundary conditions according to actual working conditions; (2) Parametric modeling of bolts in transformers, namely: a. Determine the key geometric parameters of the bolt, and determine the value range and default value of each parameter according to the standard specifications and actual design requirements of the bolt; b. In the finite element software, create a 3D geometric model of the bolt by inputting parametric expressions and geometric operation commands; associate each geometric feature of the bolt with the defined parameters to ensure that the geometric shape of the bolt is automatically updated when the parameter value changes; c. In the overall model of the wind power transformer, determine the installation position and connection method of the bolts, and simulate the connection relationship between the bolts and the connected parts by establishing constraint conditions; for multiple bolt connections, consider the preload force distribution and loading sequence of the bolts, and use preload force units or set normal stiffness in the contact pairs to simulate the effect of preload force; d. Set up a parametric driving mechanism to update the geometric model and overall assembly relationship of the bolt by modifying the parameter values; perform mesh quality checks and preliminary calculation verification on the models under different parameter combinations to ensure the stability and reliability of the model within the parameter variation range; (3) Assemble the parameterized bolt model with other components of the wind power transformer to form a complete finite element model of the wind power transformer, check the assembly relationship and interference between the components, and ensure the integrity and rationality of the model.

3. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: In step 1), the bolt part that needs to be checked is cut out from the overall finite element model of the wind power transformer to form a local finite element model, specifically: 1-1) Select the bolt area: According to the design requirements and analysis purposes, select the corresponding bolts and the surrounding areas in the overall model using the geometric selection tool; 1-2) Extract local geometry: Use the cutting or extraction provided by the finite element software to extract the selected bolt and its surrounding parts from the overall model to form a new local geometric model; check the extracted local geometry to ensure its integrity and geometric accuracy to avoid loss or error of geometric information due to cutting operations; 1-3) Grid Re-division: For the extracted local model, according to its own characteristics and analysis requirements, re-grid the local model, refine the mesh, define the contact settings between the bolt gasket and the fastener, and improve the calculation accuracy and efficiency; 1-4) Local boundary conditions and load adjustment: According to the boundary conditions, loads and overall finite element simulation results of the overall model, the overall finite element simulation results are transferred to the local model as the boundary conditions and load conditions of the local finite element simulation; the setting of the boundary conditions is provided by the overall finite element model.

4. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: The step 2) is specifically: 2-1) Conduct finite element simulation calculation Select the solver according to the characteristics of the model and the purpose of analysis; and determine the calculation type: static structural analysis is used to solve the bolt force under steady state, and transient analysis is used to consider the change of bolt force under dynamic load; According to the limit of the number of iterations, the solution control parameters are set, and the local finite element model of the wind power transformer is submitted for simulation calculation. The solver will calculate the displacement and stress results of each node in the model based on the established equations and the applied boundary conditions and loads; 2-2) Extract the bolt axial force and lateral force Axial force extraction: Determine the axial direction of the bolt, find the force component along this direction in the results, and obtain the axial force of the bolt by checking the force output of specific nodes or units on the bolt axis. For bolts with preload, distinguish between the axial force increment generated by the preload and the working load. Transverse force extraction: According to the coordinate system of the bolt, the transverse direction is determined, and the force component perpendicular to the axial direction of the bolt is extracted as the transverse force; by observing the relative displacement and force distribution of the bolt between the connected parts, the magnitude and direction of the transverse force can be determined. 2-3) The extracted bolt axial force and lateral force are used as input values ​​and substituted into the calculation formula specified in the VDI2230 standard; the simulation calculation results are used as input values.

5. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: The standard parts library includes: bolt specifications, nominal diameter, major diameter, minor diameter, thread pitch, bolt length, bolt rotation angle and bolt material; The parameters of the bolt connection database include: installation preload torque, friction coefficient between clamping parts, friction coefficient between bolt head and clamped parts, diameter area of ​​bolt fixing parts, thickness of clamped parts, connection coefficient, thread friction coefficient, outer diameter of bolt head bearing plane, inner diameter of load-bearing plane, tightening coefficient, tightening torque coefficient, reduction coefficient, load factor and lubricant.

6. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: In step 4), the safety factor of the yield point of the bolt is evaluated, specifically: For connections that do not exceed the bolt yield point during loading: In working condition, the total bolt load F Smax for: Among them, E Mzul is the allowable preload; is the load factor of the bolt; F Amax is the maximum axial load; ΔF Vth is the change of preload; Maximum tensile stressσ zmax ,Right now: s zmax =F Smax / A0 Among them, A0 is the nominal cross-sectional area of ​​the bolt; Maximum torsional stress τ max ,Right now: t max =M G / W P Among them, M G is the thread torque, in Nm; W P is the polar resistance moment of the bolt cross section; For reduced or relative stresses associated with torsional stresses in applications, the recommended factor k is τ = 0.5, reduced to k τ Situation: Then the bolt yield point safety factor S F for: S F =R P0.2min / s red，B ≥1.0 Among them, R P0.2min is the minimum yield point of the bolt.

7. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: In step 4), the safety factor of the internal pressure of the bolt is evaluated, specifically: The surface pressure calculated based on the expected chamfer error and the surface pressure does not exceed the surface limit pressure of the fastened material, following the following relationship: P Mmax Assembly lower surface limit pressure: P Mmax =And Mzul / TO Pmin ≤P G Among them, A Pmin is the bolt minor diameter cross-sectional area; P Bmax Surface limit pressure under working condition: P Bmax =(F Vmax +F Amax -ΔF Vth ) / A Pmin ≤P G Among them, F Vmax Maximum applied preload; Maximum surface pressure P for tightening techniques with yield or angle control G , considering the dispersion of yield points, refer to the following formula: Among them, E MTab Provide preload for bolt installation; Pressure safety factor: S P =P G / P M / Bmax ≥1.

0.

8. The design method of high-strength connecting bolts for wind power transformers according to claim 1 is characterized in that: In step 4), the fatigue safety factor of the bolt is evaluated, specifically: The number of alternating cycles under continuous load is N D ≥2*10 6 and stress cross section A S The fatigue limit reference values ​​of relevant high-strength bolts are as follows: The fatigue limit of rolled SV before heat treatment is: Where, d is the bolt diameter; The fatigue limit of rolled SG after heat treatment is: Among them, F Sm is the average bolt load, F 0.2min Bolt load at minimum yield point or at 0.2% allowable stress; If it is greater than the fatigue strength σ AS The stress amplitude has a cycle frequency of only a few thousand times (N Z >10 4 ), the endurance limit of the connection can be established if the following dynamic strength values ​​are determined: Rolling SV before heat treatment: Rolling SG after heat treatment: Among them, N D is the number of alternating cycles under continuous load, N Z is the number of alternating cycles of loading within the fatigue strength range.

9. The design method of high-strength connecting bolts for wind power transformers according to claim 1, characterized in that: In step 4), the fatigue safety factor of the bolt is evaluated, specifically: If the number of joint surfaces q F and q M Inevitably involves slip and the friction coefficient μ of the joint surface T , then the minimum residual preload F KRmin and the preload F required to transfer the lateral load KQerf They are: Among them, α A is the tightening factor; F Z It is the preload loss caused by embedding during operation; Among them, q F is the number of internal interfaces where the bolt may slip or shear; μ Tmin is the friction coefficient at the interface; M Ymax is the maximum axial torque of the bolt; q M r is the number of internal interfaces where the bolt may slip and transmit torque; a M Ymax The friction radius of the clamped parts during action; The safety verification to prevent slipping is: Safety verification of shear resistance, namely: Among them, τ B is the shear strength, A τ is the shear cross section under transverse load.

10. The design method of high-strength connecting bolts for wind power transformers according to claim 1, characterized in that: In step 5), the optimization of the bolts includes: changing the material of the bolts, and then checking whether the new material bolts meet the safety factor assessment requirements according to the VDI2230 standard; Another solution is: if changing the bolt material including stainless steel, 8.8 grade carbon steel, 10.9 grade carbon steel, and 12.9 grade carbon steel still cannot meet the bolt's yield point, internal pressure, fatigue, slip and shear safety factors that are greater than or equal to 1, then change the bolt specification model through the parametric model drive and then recalculate.

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