Method for calculating ultimate fatigue strength of hub structure of wind turbine generator

Abstract

The invention provides a wind turbine generator hub structure ultimate fatigue strength calculation method which comprises the steps that a geometric model of a hub structure is established, the hub structure comprises a hub and a variable-pitch bearing, an outer ring of the variable-pitch bearing is connected with the hub, and a bolt hole is formed in the end face of the variable-pitch bearing; establishing a strength finite element model of the hub structure; carrying out ball finite element simulation, wherein balls are located between an inner ring and an outer ring of the variable-pitch bearing; bolt finite element simulation is carried out, and bolts are matched with bolt holes; pre-tightening force is applied to the bolt; simulating and analyzing the ultimate strength of the hub structure; and calculating the fatigue strength of the hub structure. According to the technical scheme, the problem that in the fatigue strength calculation process of the wind turbine hub in the prior art, the deviation between the calculation result and the actual value is large is effectively solved.

Description

Technical Field

[0001] The present application relates to the technical field of wind power generation, and in particular to a method for calculating the ultimate fatigue strength of a hub structure of a wind turbine. Background Art

[0002] The hub is an important force transmission and structural connection component of the wind turbine. It plays the role of transmitting the blade load to the shaft and other components through the pitch bearing. The strength margin and fatigue resistance of the hub are related to the safety of the unit. Therefore, the strength and fatigue resistance analysis and evaluation of the hub are important links in the hub structure design. Since the hub is connected to multiple complex components such as the pitch bearing, blades, and shaft through bolts, the strength and fatigue analysis of the hub is complex and difficult.

[0003] Generally, in the process of calculating the ultimate fatigue strength of the hub structure, in order to reduce the time required for simulation analysis, the model structure is usually simplified, the connection structure is deleted, and the positional relationship of each component is restricted by constraints.

[0004] In the prior art, since the main force on the hub comes from the wind turbine blades, simplifying the connection structure between the two has a significant impact on fatigue calculation results, which can lead to inaccurate calculation results and affect subsequent safety assessments. Summary of the invention

[0005] A technical problem to be solved by the present application is that, in the process of calculating the fatigue strength of the wind turbine hub, there is a problem that the calculated result has a large deviation from the actual result.

[0006] In order to solve the above technical problems, the present application provides a method for calculating the ultimate fatigue strength of a wind turbine hub structure.

[0007] A method for calculating the ultimate fatigue strength of a wind turbine hub structure provided in the present application includes the following steps: establishing a geometric model of the hub structure, the hub structure including a hub and a pitch bearing, the outer ring of the pitch bearing being connected to the hub, and the end face of the pitch bearing having a bolt hole; establishing a strength finite element model of the hub structure; ball finite element simulation, the ball being located between the inner ring and the outer ring of the pitch bearing; bolt finite element simulation, the bolt matching the bolt hole; applying a preload to the bolt; simulating and analyzing the ultimate strength of the hub structure; and calculating the fatigue strength of the hub structure.

[0008] In some embodiments, establishing a geometric model of the hub structure includes the steps of: geometrically segmenting the bolt holes.

[0009] In some embodiments, establishing a strength finite element model of a hub structure includes the steps of: establishing a shaft model and a blade root model, wherein the shaft model is connected to the hub, and the blade root model is connected to the inner ring of the pitch bearing; and performing meshing to obtain a strength finite element model.

[0010] In some embodiments, the meshing meets the following conditions: the hub is divided by a mapping network; the bolt holes are divided by a prismatic grid; and the difference between the unit solution and the node solution is less than 8%.

[0011] In some embodiments, the method for calculating the ultimate fatigue strength of the hub structure of a wind turbine generator set also includes the step of: applying boundary conditions; the boundary conditions are: a circumferential constraint is applied to the arc surface connecting the first end of the rotating shaft to the rotor bracket, and a radial constraint and an axial constraint are applied to the second end surface of the rotating shaft and the fixed axis.

[0012] In some embodiments, the variable pitch bearing includes a plurality of blade root models, and the blade root models are arranged in one-to-one correspondence with the variable pitch bearings.

[0013] In some embodiments, the fatigue strength calculation of the hub includes the steps of: setting different fatigue loads to obtain corresponding hub stress; combining the hub stress with the stress amplitude-cycle number curve of the hub material to obtain the fatigue life of the hub.

[0014] In some embodiments, the fatigue strength calculation of the hub meets the following requirements: the fatigue load includes multiple groups, each group of fatigue loads is set in one-to-one correspondence with the blade root model; each group of fatigue loads includes: Mx, My, Mz, Fx, Fy and Fz;

[0015] Calculate the average stress of the corresponding hub respectively;

[0016] in,

[0017] Mx is the magnitude of the moment along the x-axis;

[0018] My is the magnitude of the moment along the y-axis;

[0019] Mz is the magnitude of the moment along the z-axis;

[0020] Fx is the magnitude of the force along the x-axis;

[0021] Fy is the magnitude of the force along the y-axis;

[0022] Fz is the magnitude of the force along the z-axis.

[0023] In some embodiments, the stress caused by the pre-tightening force of the bolts is removed from the average stress of the hub by load combination to obtain the stress of the hub.

[0024] In some embodiments, each set of fatigue loads includes: +Mx, -Mx, +My, -My, +Mz, -Mz, +Fx, -Fx, +Fy, -Fy, +Fz, and -Fz;

[0025] in,

[0026] +Mx is the magnitude of the force along the positive x-axis;

[0027] -Mx is the magnitude of the force along the negative x-axis;

[0028] -My is the magnitude of the force along the positive y-axis;

[0029] -My is the magnitude of the force along the negative y-axis;

[0030] -Mz is the magnitude of the force along the positive z-axis;

[0031] -Mz is the magnitude of the force along the negative z-axis;

[0032] Fx is the magnitude of the force along the positive x-axis;

[0033] Fx is the magnitude of the force along the negative x-axis;

[0034] Fy is the magnitude of the force along the positive y-axis;

[0035] Fy is the magnitude of the force along the negative y-axis;

[0036] Fz is the magnitude of the force along the positive z-axis;

[0037] Fz is the magnitude of the force along the negative z-axis.

[0038] Through the above technical solution, the method for calculating the ultimate fatigue strength of the hub structure of a wind turbine provided by the present application, when establishing the geometric model of the hub structure, establishes the variable pitch bearing at the connection between the hub and the blade, and reserves bolt holes for connection, uses simulation software to establish a finite element model, and performs finite element simulation on the bolts, and in order to ensure the accuracy of the calculation results, applies a pre-tightening force to the bolts, and simulates and analyzes the fatigue strength of the hub structure. The technical solution of the present application effectively solves the problem in the prior art that in the process of calculating the fatigue strength of the wind turbine hub, there is a large deviation between the calculation results and the actual results. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A schematic flow chart of a method for calculating the ultimate fatigue strength of a hub structure of a wind turbine generator system disclosed in the first embodiment of the present application is shown;

[0041] Figure 2 Shows Figure 1A schematic diagram of the hub structure in the ultimate fatigue strength calculation method of the hub structure of a wind turbine;

[0042] Figure 3 Shows Figure 1 Structural schematic diagram of finite element simulation of bolts in the ultimate fatigue strength calculation method of the wind turbine hub structure;

[0043] Figure 4 Shows Figure 1 The structural diagram of the ball finite element simulation in the ultimate fatigue strength calculation method of the wind turbine hub structure;

[0044] Figure 5 Shows Figure 1 A schematic diagram of the structure of a finite element model of a hub structure in a method for calculating the ultimate fatigue strength of a hub structure of a wind turbine;

[0045] Figure 6 Shows Figure 1 The stress distribution results of the hub structure in the ultimate fatigue strength calculation method of the wind turbine hub structure.

[0046] Description of reference numerals:

[0047] 10. Hub structure; 11. Hub; 12. Pitch bearing; 121. Bolt hole; 20. Ball; 30. Bolt; 40. Blade root. DETAILED DESCRIPTION

[0048] The following is a further detailed description of the implementation methods of the present application in conjunction with the accompanying drawings and examples. The detailed descriptions and drawings of the following examples are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application. The present application can be implemented in many different forms and is not limited to the specific embodiments of the present application, but includes all technical solutions that fall within the scope of the claims.

[0049] The present application provides these embodiments to make the present application thorough and complete, and to fully express the scope of the present application to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, and not as limiting.

[0050] It should be noted that, in the description of this application, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0051] In addition, the words "first", "second" and similar words used in this application do not indicate any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean vertical in the strict sense, but is within the tolerance range. "Parallel" does not mean parallel in the strict sense, but is within the tolerance range. "Include" or "comprising" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements.

[0052] It should also be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0053] All terms used in this application have the same meaning as those understood by those of ordinary skill in the art to which this application belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, such as general dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined herein.

[0054] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0055] like Figures 1 to 6 As shown, the method for calculating the ultimate fatigue strength of the hub structure of a wind turbine generator system disclosed in the first embodiment of the present application includes the following steps:

[0056] A geometric model of a hub structure 10 is established. The hub structure 10 includes a hub 11 and a pitch bearing 12. The outer ring of the pitch bearing 12 is connected to the hub 11. The end surface of the pitch bearing 12 has a bolt hole 121.

[0057] Establishing a strength finite element model of the hub structure 10;

[0058] Finite element simulation of the ball 20, the ball 20 is located between the inner ring and the outer ring of the pitch bearing 12;

[0059] Finite element simulation of bolt 30, bolt 30 matches with bolt hole 121;

[0060] Applying a pre-tightening force to the bolt 30;

[0061] Simulating and analyzing the ultimate strength of the hub structure 10;

[0062] The fatigue strength of the hub structure 10 is calculated.

[0063] By applying the technical solution of the first embodiment, when establishing the geometric model of the hub structure 10, the pitch bearing 12 at the connection between the hub 11 and the blade is established, and a bolt hole 121 for connection is reserved, a finite element model is established using simulation software, and a finite element simulation is performed on the bolt 30. To ensure the accuracy of the calculation result, a pre-tightening force is applied to the bolt 30, and the fatigue strength of the hub structure 10 is simulated and analyzed. The technical solution of the first embodiment effectively solves the problem in the prior art that in the process of calculating the fatigue strength of the wind turbine hub, there is a large deviation between the calculation result and the actual result.

[0064] like Figure 2 and Figure 3 As shown, in the technical solution of the first embodiment, the geometric model of the hub structure 10 is established, including the steps of:

[0065] The bolt hole 121 is geometrically segmented. The area around the bolt hole 121 is segmented using a hexagonal prism, the cross-sectional shape of which is a regular hexagon, and the center of which is on the same straight line as the axis of the bolt hole 121, so as to improve the calculation accuracy of the key area. In the process of establishing the geometric model of the hub structure 10, some non-critical areas need to be simplified, such as transition arcs, chamfers, chamfers, etc., to reduce the difficulty of subsequent meshing and calculation. The topological structure of the critical area also needs to be geometrically segmented separately to ensure that its shape meets the requirements of subsequent meshing.

[0066] like Figures 2 to 5 As shown, in the technical solution of the first embodiment, establishing a strength finite element model of the hub structure 10 includes the following steps:

[0067] A rotating shaft model and a blade root 40 model are established, wherein the rotating shaft model is connected to the hub 11, and the blade root 40 model is connected to the inner ring of the pitch bearing 12;

[0068] Perform meshing to obtain a strength finite element model. Build models of other structures connected to the hub structure 10 to simulate the actual use environment of the hub structure 10, including: a rotating shaft model, a pulley support model, a driving axle model, a tensioning axle model, a fixed axis model, and a rotor bracket model. The hub 11 is simulated using SOLID186 units, the variable pitch bearing 12 is simulated using SOLID185 units, the blade root 40 is simulated using SOLID185 units, the rotating shaft is simulated using SOLID187 units, the bolt preload unit is simulated using PRETS179 units, and the detection simulation between the various components uses CONTA174 and TARGE170 for meshing. The ball 20 is simulated using two groups of LINK180, each group of LINK180 units has eleven units, and the two groups of LINK180 units are still crossed at 45 degrees with the center of each group. The finite element model of ball 20 needs to be debugged and calculated with reference to the Roark formula to determine the cross-sectional area, initial clearance and initial strain of each LINK180 unit to simulate the stiffness of ball 20 and the contact characteristics between ball 21 and pitch bearing 12. The nut part of bolt 30 is simulated by SOLID185 unit, and the screw section of bolt 30 is simulated by BEAM189 unit. The diameter of each section can be determined according to the actual size and relevant standards; or the diameter of the threaded section can be directly used to simulate the diameter of the bolt screw section and the threaded section;

[0069]

[0070] d s Model the diameter of the bolt:

[0071] A s is the stress cross-sectional area of ​​the bolt.

[0072] The above process simulates the actual use environment of the wheel hub 11 as much as possible to ensure the accuracy of subsequent fatigue analysis results.

[0073] like Figures 3 to 5 As shown, in the technical solution of embodiment 1, the grid division meets the following conditions:

[0074] Hub 11 uses mapping network partitioning;

[0075] The bolt hole 121 is divided into prismatic grids;

[0076] The difference between the unit solution and the node solution is less than 8%. The above division method is not prone to division failure during the mesh generation process, and the difference between the unit solution and the node solution is less than 8%, which ensures the accuracy of subsequent analysis results.

[0077] like Figure 5 As shown, in the technical solution of the first embodiment, the method for calculating the ultimate fatigue strength of the hub structure of a wind turbine generator set further includes the steps of:

[0078] Apply boundary conditions;

[0079] The boundary conditions are: the arc surface connecting the first end of the rotating shaft to the rotor support applies circumferential constraints, and the second end face of the rotating shaft applies radial constraints and axial constraints to the fixed shaft. The end face of the fixed shaft has a plane bearing, and the second end face of the rotating shaft is connected to the plane bearing. Apply preload force to the bolt 30;

[0080] F PRE = k × A s ×R P0.2 ;

[0081] F PRE A preload force applied to each bolt 30;

[0082] k is the proportional factor of the bolt assembly preload, k = 0.78;

[0083] A S is the stress cross-sectional area of ​​the bolt;

[0084] R P0.2 is the yield strength of the bolt material.

[0085] That is, during the simulation process, the influence of the pre-tightening force of the bolt 30 on the strength of the hub 11 is taken into consideration, and the calculation result is more accurate.

[0086] like Figure 5 As shown, in the technical solution of the first embodiment, the variable pitch bearing 12 includes multiple blade roots 40 models and the variable pitch bearings 12 are set one by one. In the technical solution of the first embodiment, there are three blade roots 40, corresponding to three sets of variable pitch bearings 12. In other embodiments, the blade roots 40 can also be 4, 5, etc. In the simulation process, it is necessary to consider the influence of the simultaneous setting of multiple sets of blade roots 40 on the ultimate strength of the hub 11 to ensure the accuracy of the calculation results.

[0087] like Figure 5 and Figure 6 As shown, in the technical solution of the first embodiment, the fatigue strength calculation of the hub 11 includes the steps of:

[0088] Set different fatigue loads to obtain the corresponding hub stress;

[0089] The hub stress is combined with the stress amplitude-cycle number curve of the hub material to obtain the fatigue life of the hub 11. Different fatigue loads are input, and simulations are performed respectively to obtain the corresponding stress intensity, and then the stress is scaled and combined to obtain the time series stress, so as to calculate the fatigue life of the hub 11. When the calculated value is not less than the design life, it means that its fatigue resistance meets the design requirements.

[0090] like Figure 5 and Figure 6 As shown, in the technical solution of the first embodiment, the fatigue strength calculation of the hub 11 meets the following requirements:

[0091] The fatigue loads include multiple groups, and each group of fatigue loads is set in one-to-one correspondence with the blade root 40 model;

[0092] Each group of fatigue loads includes: Mx, My, Mz, Fx, Fy and Fz;

[0093] Calculate the average stress of the corresponding wheel hub 11 respectively;

[0094] in,

[0095] Mx is the magnitude of the moment along the x-axis;

[0096] My is the magnitude of the moment along the y-axis;

[0097] Mz is the magnitude of the moment along the z-axis;

[0098] Fx is the magnitude of the force along the x-axis;

[0099] Fy is the magnitude of the force along the y-axis;

[0100] Fz is the magnitude of the force along the z-axis.

[0101] Since the blade roots 40 include three in the first embodiment, the corresponding fatigue loads include:

[0102] 1Mx, 1My, 1Mz, 1Fx, 1Fy and 1Fz applied at the roots of the first set of blades;

[0103] 2Mx, 2My, 2Mz, 2Fx, 2Fy and 2Fz applied at the roots of the second set of blades;

[0104] 3Mx, 3My, 3Mz, 3Fx, 3Fy and 3Fz applied at the roots of the second set of blades.

[0105] The specific value of each fatigue load can be selected by selecting the maximum absolute value of the time series load in each fatigue load case, so as to eliminate the influence of the bolt preload on the hub stress scaling as much as possible.

[0106] like Figure 5 and Figure 6 As shown, in the technical solution of the first embodiment, the stress caused by the preload force of the bolt 30 is removed from the average stress of the hub 11 by load combination to obtain the stress of the hub 11. The preload force of the bolt 30 generates a constant stress on the hub 11, so it is necessary to calculate the stress caused by the bolt 30 on the hub 11 separately, and then remove it from the average stress to obtain the actual stress of the hub 11. In the ANSYS software, the stress caused by the preload force is removed by load combination (LOAD CASE), and the stress of the hub 11 with each load shadow is obtained, and then scaled and combined.

[0107] like Figure 5 and Figure 6 As shown, in the technical solution of embodiment 1, each group of fatigue loads includes: +Mx, -Mx, +My, -My, +Mz, -Mz, +Fx, -Fx, +Fy, -Fy, +Fz and -Fz;

[0108] in,

[0109] +Mx is the magnitude of the force along the positive x-axis;

[0110] -Mx is the magnitude of the force along the negative x-axis;

[0111] -My is the magnitude of the force along the positive y-axis;

[0112] -My is the magnitude of the force along the negative y-axis;

[0113] -Mz is the magnitude of the force along the positive z-axis;

[0114] -Mz is the magnitude of the force along the negative z-axis;

[0115] Fx is the magnitude of the force along the positive x-axis;

[0116] Fx is the magnitude of the force along the negative x-axis;

[0117] Fy is the magnitude of the force along the positive y-axis;

[0118] Fy is the magnitude of the force along the negative y-axis;

[0119] Fz is the magnitude of the force along the positive z-axis;

[0120] Fz is the magnitude of the force along the negative z-axis.

[0121] In order to further improve the calculation accuracy, considering the influence of nonlinearity on the calculation results, it is necessary to consider the direction of fatigue load. At this time, fatigue load includes:

[0122] +1Mx, -1Mx, +1My, -1My, +1Mz, -1Mz, +1Fx, -1Fx, +1Fy, -1Fy, +1Fz and -1Fz applied at the roots of the first set of blades;

[0123] +2Mx, -2Mx, +2My, -2My, +2Mz, -2Mz, +2Fx, -2Fx, +2Fy, -2Fy, +2Fz and -2Fz applied at the roots of the second set of blades;

[0124] +3Mx, -3Mx, +3My, -3My, +3Mz, -3Mz, +3Fx, -3Fx, +3Fy, -3Fy, +3Fz and -3Fz applied at the roots of the third group of blades.

[0125] For each column of 18 positive time series loads such as +1Mx, +1My, ..., +3Fz, the positive value of the original data is retained and the negative value of the original data is set to 0; for each column of negative time series loads such as -1Mx, -1My, ..., -3Fz, the negative value of the original data is retained after it becomes positive, and the positive value of the original data is set to 0; for each fatigue load condition, in addition to the above 36 time series loads, a column of time series loads with a value of 1 is added to scale the constant stress. Therefore, each fatigue load condition has a total of 37 columns of data. For each fatigue load condition, its 37 fatigue time series loads and the above 37 stress data are read into the fatigue analysis software according to the corresponding relationship, and the scaling ratio value of each fatigue specific load, the statistical number of times of the design life condition, etc. are set, that is, the scaling and combination of the wheel hub time series stress under the fatigue condition is completed. According to this method, the scaling and combination of the wheel hub time series stress under other fatigue conditions are realized in turn. After the scaling and combination of the wheel hub's time-series stress is completed, the fatigue damage or fatigue life of the wheel hub can be calculated in the fatigue analysis software.

[0126] The difference between the technical solution of the second embodiment and the technical solution of the first embodiment is that when the pre-tightening force is applied to the bolt 30,

[0127] F PRE = k × A S ×R P0.2 / α; α is the bolt tightening dispersion coefficient, generally between 1.2-1.6;

[0128] The technical solution of the second embodiment takes into account the influence of the bolt tightening coefficient on the calculation result, and further improves the calculation accuracy.

[0129] Based on the above, the method for calculating the ultimate fatigue strength of the wind turbine hub structure of the present application includes:

[0130] 1. Geometric model processing

[0131] In order to reduce the calculation scale of the calculation model, the non-critical areas of the hub 11 can be appropriately simplified, such as removing small transition arcs, circular holes, chamfers, etc.; for non-critical components such as the shaft, pulley support, and pitch bearing 12, more structural simplification can be performed, such as 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 hub 11, such as bolt holes and the topological structure of critical areas, so as to meet the meshing requirements of special areas (such as hexahedral meshes for bodies and mapped meshes for faces).

[0132] 2. Establishment of finite element model.

[0133] The strength finite element model of the hub structure 10 mainly includes the hub 11, the rotating shaft, the pitch bearing 12, the bolt 30, the blade root, the pulley support, the drive shaft, the tensioning shaft and other components. The hub 11 is simulated by SOLID186 unit, the pitch bearing 12 is simulated by SOLID185 unit, the pitch bearing spherical ball 20 is simulated by LINK180 unit, the blade root 40 is simulated by SOLID185 unit, the rotating shaft is simulated by SOLID187 unit, the bolt body is simulated by BEAM188 or BEAM189 unit, the bolt pre-tightening unit is simulated by PRETS179 unit, the bolt head or nut is simulated by SOLID18 unit, the contact simulation between the components is CONTA174 and TARGE170, the surface of the hub 11 is mapped as much as possible, the bolt hole 121 is divided into hexahedral or prism meshes as much as possible, and the meshes of these areas are subdivided, and the final meshing requirement is that the difference between the unit solution and the node solution does not exceed 8%.

[0134] 3. Finite element simulation of ball 20.

[0135] Each ball 20 is simulated by two sets of LINK180, each set of LINK180 units has eleven (empirical value), and the two sets of LINK180 units are still crossed at 45 degrees with the center of each set. The finite element model needs to be debugged and calculated with reference to the Roark formula to determine the cross-sectional area A_b, initial gap (initial strain) and other parameters of each LINK180 unit to simulate the stiffness of the ball 20, the contact characteristics between the ball 20 and the raceway, etc.

[0136] 4. Finite element simulation of bolt 30

[0137] The strength finite element model of the hub structure 10 involves modeling of bolts such as the connecting bolts 30 between the hub 11 and the pitch bearing 12 and the connecting bolts between the hub 11 and the rotating shaft.

[0138] The following takes the connecting bolt 30 between the hub 11 and the pitch bearing 12 as an example to describe the modeling method of the bolt 30 .

[0139] The nut and screw head of each bolt 30 are simulated by SOLID185 units. The screw section and thread section of each bolt 30 are simulated by BEAM189 units. The diameter of each section can be determined according to the actual size and relevant standards; or the thread section diameter can be directly used to simulate the diameter of the bolt screw section and thread section. The bolt modeling diameter can be found in the formula:

[0140]

[0141] Where:

[0142] A s ——Stress cross-sectional area of ​​the bolt.

[0143] The two ends of each bolt model are connected to the surrounding structure in an appropriate manner to transfer the bolt preload and enable the bolt connection to effectively transfer other loads.

[0144] 5. Boundary conditions are applied.

[0145] The constraints are:

[0146] a. Bearing surface where the rotating shaft and the fixed shaft are connected: radial and axial constraints are imposed;

[0147] b. Arc surface connecting the shaft and the rotor support: apply circumferential constraints;

[0148] The strength calculation of the hub 11 under the extreme working condition, the applied load is the preload of the bolts, and the load acting on the blade root 40 under each working condition. The application of the extreme load of each working condition involves two load steps (Load Step), the method is: the application is completed in the first load step; in the second load step, it is in a locked state.

[0149] The preload force F applied to each bolt PRE , execute according to the data input conditions, or refer to the formula.

[0150] F PRE = k × A S ×R P0.2 ;

[0151] Where:

[0152] k——Proportional factor of bolt assembly preload, k=0.78;

[0153] A S ——stress cross-sectional area of ​​the bolt;

[0154] R P0.2 ——Yield strength of bolt material. For bolts with strength grade 10.9, take R P0.2 =940MPa.

[0155] If fatigue calculation of bolts is required, the influence of bolt tightening coefficient α needs to be considered. For bolt preload, refer to the formula.

[0156] F PRE = k × A S ×R P0.2 / α

[0157] Where:

[0158] α——Distribution coefficient of bolt tightening, usually between 1.2 and 1.6.

[0159] The section that generates the bolt preload must have a sufficient number of uniform grids so that the preload section can cut the bolt grid as a whole to correctly apply the bolt preload.

[0160] The loads acting on the blade root under various working conditions are 1Mx, 1My, 1Mz, 1Fx, 1Fy, 1Fz, 2Mx, 2My, 2Mz, 2Fx, 2Fy, 2Fz, 3Mx, 3My, 3Mz, 3Fx, 3Fy, 3Fz, etc. Among them, there are six load components at the three blade root positions, F represents force, M represents moment, and x, y and z represent the x-axis, y-axis and z-axis of the blade root coordinate system respectively.

[0161] 6. Limit calculation method

[0162] For a hub 11 made of ductile materials such as ductile iron, its ultimate strength is evaluated based on the equivalent stress calculated under each limit condition. The strength margin n of the hub 11 under each limit condition SRF See the formula for calculation.

[0163]

[0164] Where:

[0165] R P0.2 - yield strength of the hub 11 material;

[0166] ——Calculated value of the maximum equivalent stress of the hub 11 under extreme working conditions;

[0167] γ M1 ——The material partial coefficient of hub 11 is γ according to GL2010. M1 =1.1;

[0168] If SRF ≥1.0, indicating that the wheel hub 11 has sufficient static strength.

[0169] 7 Fatigue calculation method

[0170] The fatigue calculation of the hub 11 calculates the time-series stress of the hub 11 under each fatigue condition based on the provided fatigue condition time-series load, and finally calculates the fatigue damage or fatigue life of the hub 11 structure in combination with the stress amplitude / stress range-cycle number curve (SN curve) of the hub 11 material.

[0171] The time series loads of each fatigue working condition include the values ​​of loads changing with time such as 1Mx, 1My, 1Mz, 1Fx, 1Fy, 1Fz, 2Mx, 2My, 2Mz, 2Fx, 2Fy, 2Fz, 3Mx, 3My, 3Mz, 3Fx, 3Fy, 3Fz, etc. It is necessary to scale and combine the stress finite element calculation results under the action of each load to obtain the time series stress, so as to calculate the fatigue damage or fatigue life of the hub 11.

[0172] 7.1 Fatigue load treatment

[0173] In the fatigue condition, the finite element stress calculation of various loads under specific values, the constraint application method is the same as the calculation of the ultimate strength of the hub 11; the load application and calculation are also carried out using two load steps (LOAD STEP), that is, the bolt preload is applied in the first load step, and the specific value of the fatigue load is applied in the second load step. The fatigue loads at the three blade root centers include 1Mx, 1My, 1Mz, 1Fx, 1Fy, 1Fz, 2Mx, 2My, 2Mz, 2Fx, 2Fy, 2Fz, 3Mx, 3My, 3Mz, 3Fx, 3Fy, 3Fz. Among them, the six load components at the three blade root positions, F represents force, M represents moment, and x, y and z represent the x-axis, y-axis and z-axis of the blade root coordinate system respectively. The specific value of each fatigue load can be selected by selecting the maximum absolute value of the time series load in each fatigue load condition, so as to eliminate the influence of the bolt 30 preload on the stress scaling of the hub 11 as much as possible.

[0174] In addition, in order to consider the influence of nonlinearity on fatigue calculation results, the stresses of ±1Mx, ±1My, ±1Mz, ±1Fx, ±1Fy, ±1Fz, ±2Mx, ±2My, ±2Mz, ±2Fx, ±2Fy, ±2Fz, ±3Mx, ±3My, ±3Mz, ±3Fx, ±3Fy, ±3Fz, etc. should be calculated respectively. The preload force F of the bolt 30 acting on the hub 11 is PRE , a constant stress is generated on the hub structure 10, and the constant stress is an important component of the average stress of the hub structure 10. Therefore, the stress of the hub 11 caused by the bolt preload needs to be calculated separately.

[0175] 7.2 Fatigue load stress treatment

[0176] For the stresses under various load specific values ​​such as ±1Mx, ±1My, ±1Mz, ±1Fx, ±1Fy, ±1Fz, ±2Mx, ±2My, ±2Mz, ±2Fx, ±2Fy, ±2Fz, ±3Mx, ±3My, ±3Mz, ±3Fx, ±3Fy, ±3Fz, etc., since the calculation is performed under the condition of the preload of bolt 30, the stress caused by the preload of bolt 30 needs to be removed before scaling and combination can be performed. In ANSYS software, the stress caused by the preload of bolt 30 is removed by load combination (LOAD CASE), and the stress of hub 11 under the above fatigue specific load is obtained, with a total of 36 stress data. For the constant stress under the preload of bolt 30, no stress processing is required and it is directly used. The above fatigue load generates a total of 37 stress data.

[0177] 7.3 Stress combinations

[0178] In each fatigue load condition, 18 columns of time series loads, including 1Mx, 1My, 1Mz, 1Fx, 1Fy, 1Fz, 2Mx, 2My, 2Mz, 2Fx, 2Fy, 2Fz, 3Mx, 3My, 3Mz, 3Fx, 3Fy, and 3Fz, are processed into 36 columns of time series loads, including ±1Mx, ±1My, ±1Mz, ±1Fx, ±1Fy, ±1Fz, ±2Mx, ±2My, ±2Mz, ±2Fx, ±2Fy, ±2Fz, ±3Mx, ±3My, ±3Mz, ±3Fx, ±3Fy, and ±3Fz. For each column of 18 positive time series loads such as +1Mx, +1My, ..., +3Fz, the positive value of the original data is retained and the negative value of the original data is set to 0; for each column of negative time series loads such as -1Mx, -1My, ..., -3Fz, the negative value of the original data is retained after it becomes positive, and the positive value of the original data is set to 0; for each fatigue load condition, in addition to the above 36 time series loads, a column of time series loads with a value of 1 is added to scale the constant stress. Therefore, each fatigue load condition has a total of 37 columns of data. For each fatigue load condition, its 37 fatigue time series loads and the above 37 stress data are read into the fatigue analysis software according to the corresponding relationship, and the scaling ratio value of each fatigue specific load, the statistical number of times of the design life condition, etc. are set, that is, the scaling and combination of the time series stress of the hub 11 under the fatigue condition is completed. According to this method, the scaling and combination of the time series stress of the hub 11 in other fatigue conditions are realized in turn. After the proportional scaling and combination of the time-series stress of the hub 11 are completed, the fatigue damage or fatigue life of the hub 11 can be calculated in the fatigue analysis software.

[0179] 7.4 Wheel hub fatigue calculation

[0180] The fatigue calculation of the hub 11 is performed based on the MINER cumulative damage theory, the maximum principal stress critical plane analysis method, etc. Since the workload of the fatigue calculation of the hub 11 is large, the actual calculation can be performed on 1 / 3 of the hub structure. If the fatigue damage of the hub 11 during the design life is not greater than 1.0, or the fatigue life of the hub 11 is not less than the design life, it indicates that the fatigue resistance of the hub 11 meets the design requirements.

[0181] So far, the embodiments of the present application have been described in detail. In order to avoid obscuring the concept of the present application, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution of the present application.

[0182] Although some specific embodiments of the present application have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict.

Claims

1. A method for calculating the ultimate fatigue strength of a wind turbine hub structure, characterized in that: The method for calculating the ultimate fatigue strength of the hub structure of a wind turbine generator system comprises the following steps: A geometric model of a hub structure (10) is established, wherein the hub structure (10) comprises a hub (11) and a pitch bearing (12), wherein an outer ring of the pitch bearing (12) is connected to the hub (11), and an end surface of the pitch bearing (12) has a bolt hole (121); Establishing a strength finite element model of the hub structure (10); Finite element simulation of a ball (20), wherein the ball (20) is located between the inner ring and the outer ring of the pitch bearing (12); Finite element simulation of the bolt (30), wherein the bolt (30) matches the bolt hole (121); Applying a pre-tightening force to the bolt (30); Simulating and analyzing the ultimate strength of the hub structure (10); The fatigue strength of the hub structure (10) is calculated.

2. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 1, characterized in that: Establishing a geometric model of the hub structure (10) comprises the steps of: The bolt hole (121) is geometrically segmented.

3. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 1, characterized in that: Establishing a strength finite element model of the hub structure (10) comprises the following steps: Establishing a rotating shaft model and a blade root (40) model, wherein the rotating shaft model is connected to the hub (11), and the blade root (40) model is connected to the inner ring of the pitch bearing (12); The strength finite element model is obtained by meshing.

4. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 3, characterized in that: The grid division meets the following conditions: The hub (11) is divided by a mapping network; The bolt hole (121) is divided into prismatic grids; The difference between the element solution and the nodal solution is less than 8%.

5. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 3, characterized in that: The method for calculating the ultimate fatigue strength of the hub structure of a wind turbine generator set further comprises the steps of: Apply boundary conditions; The boundary conditions are: the arc surface connecting the first end of the rotating shaft and the rotor support imposes circumferential constraints, and the second end surface of the rotating shaft and the fixed axis impose radial constraints and axial constraints.

6. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 3, characterized in that: The variable pitch bearing (12) includes a plurality of blade roots (40) and the blade roots (40) models are arranged in one-to-one correspondence with the variable pitch bearing (12).

7. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 6, characterized in that: The fatigue strength calculation of the wheel hub (11) comprises the steps of: Set different fatigue loads to obtain the corresponding hub stress; The hub stress is combined with the stress amplitude-cycle number curve of the hub material to obtain the fatigue life of the hub (11).

8. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 7, characterized in that: The fatigue strength calculation of the hub (11) meets the following requirements: The fatigue loads include a plurality of groups, and each group of fatigue loads is set in one-to-one correspondence with the blade root (40) model; Each group of fatigue loads includes: Mx, My, Mz, Fx, Fy and Fz; respectively calculating the average stress of the corresponding wheel hub (11); in, Mx is the magnitude of the moment along the x-axis; My is the magnitude of the moment along the y-axis; Mz is the magnitude of the moment along the z-axis; Fx is the magnitude of the force along the x-axis; Fy is the magnitude of the force along the y-axis; Fz is the magnitude of the force along the z-axis.

9. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 8, characterized in that: The stress caused by the pre-tightening force of the bolt (30) is removed from the average stress of the wheel hub (11) by load combination, thereby obtaining the stress of the wheel hub (11).

10. The method for calculating the ultimate fatigue strength of a wind turbine hub structure according to claim 8, characterized in that: Each group of fatigue loads includes: +Mx, -Mx, +My, -My, +Mz, -Mz, +Fx, -Fx, +Fy, -Fy, +Fz and -Fz; in, +Mx is the magnitude of the force along the positive x-axis; -Mx is the magnitude of the force along the negative x-axis; -My is the magnitude of the force along the positive y-axis; -My is the magnitude of the force along the negative y-axis; -Mz is the magnitude of the force along the positive z-axis; -Mz is the magnitude of the force along the negative z-axis; Fx is the magnitude of the force along the positive x-axis; Fx is the magnitude of the force along the negative x-axis; Fy is the magnitude of the force along the positive y-axis; Fy is the magnitude of the force along the negative y-axis; Fz is the magnitude of the force along the positive z-axis; Fz is the magnitude of the force along the negative z-axis.

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