A method for calculating the climbing rate of a wind power variable pitch bearing

Abstract

The application belongs to the technical field of bearings, and particularly relates to a method for calculating the climbing rate of a wind power variable-pitch bearing. The method comprises the following steps: S1, establishing and solving a wind power variable-pitch bearing overall model to obtain the displacement of the rollers of the variable-pitch bearing in each coordinate axis direction; the rollers of the variable-pitch bearing are constrained in the form of spring elements, rod elements or beam elements to simulate the Hertz contact between the rollers and the raceways; S2, cutting out the variable-pitch bearing part from the wind power variable-pitch bearing overall model and densifying the grid to obtain a sub-model with the displacement of the rollers of the variable-pitch bearing in each coordinate axis direction as the boundary condition, and solving the sub-model to obtain the contact stress distribution between the rollers and the raceways of the variable-pitch bearing; and S3, determining the contact ellipse between the rollers and the raceways according to the contact stress distribution, and taking the truncation rate of the contact ellipse as the climbing rate of the variable-pitch bearing. The application solves the technical problem of large calculation error of the climbing rate in the existing variable-pitch bearing checking calculation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bearings, and particularly relates to a method for calculating the climbing rate of a wind power variable-pitch bearing. BACKGROUND

[0002] The bearing is a key load-bearing and supporting component in a fan and is one of the core components for realizing the function of the fan. Bearing failure not only affects the normal operation of the fan, but also has a high maintenance cost. The four-point ball variable-pitch bearing applied to the variable-pitch system of a wind turbine mainly adjusts the angle of the blades of the wind turbine to adapt to different wind speed conditions, so as to keep the power output of the wind turbine stable. Existing researches show that in the structural design of the bearing, the contact angle is an important structural parameter of the bearing, and the change of the contact angle has a significant effect on improving the load-carrying capacity of the bearing and prolonging the service life of the bearing. However, an excessively large designed contact angle may cause an excessively high climbing rate of the contact shoulder, resulting in the climbing problem of the bearing, and thus causing the risk of early failure of the bearing at the shoulder position. Therefore, a reasonable initial designed contact angle is selected to avoid the climbing problem of the bearing under the action of the limit load.

[0003] For the checking calculation of the variable-pitch bearing, there are generally two methods, i.e., engineering checking calculation and finite element simulation analysis. The engineering checking calculation is based on the Hertz contact theory and assumes that the inner and outer rings are rigid bodies, so that only the local contact deformation of the rollers and the average contact stress between the rollers and the raceway can be calculated, and the overall deformation of the bearing and the stress condition of the bearing under flexible support cannot be analyzed.

[0004] In the finite element simulation analysis, the bearing is generally simplified, and a super element composed of spring elements and rigid beams is used to simulate the contact problem between the rollers and the raceway. This method avoids the convergence difficulty of the contact analysis, but the calculation accuracy is difficult to guarantee. Since the tangential and normal friction between the rollers and the raceway cannot be considered, the contact behavior between the rollers and the raceway cannot be accurately simulated, and there is a large error in the calculation of the climbing rate compared with the real model. SUMMARY

[0005] The purpose of the application is to provide a method for calculating the climbing rate of a wind power variable-pitch bearing, so as to solve the technical problem of large calculation error of the climbing rate in the existing checking calculation of the variable-pitch bearing.

[0006] To solve the above technical problems, the technical scheme of the method for calculating the climbing rate of the wind power variable-pitch bearing provided by the application is as follows: a method for calculating the climbing rate of a wind power variable-pitch bearing, which comprises the following steps:

[0007] S1, establishing a whole model of the wind power variable-pitch bearing and solving the whole model of the wind power variable-pitch bearing to obtain the displacement of the rollers of the variable-pitch bearing in each coordinate axis direction;

[0008] The wind power variable pitch bearing overall model comprises a variable pitch bearing, a blade and a hub; in the wind power variable pitch bearing overall model, a constraint is applied to a roller of the variable pitch bearing in the form of a spring unit, a rod unit or a beam unit, so that Hertz contact between the roller and a raceway of the variable pitch bearing can be simulated;

[0009] S2, a variable pitch bearing part is cut from the wind power variable pitch bearing overall model and a grid is encrypted to obtain a sub-model, with displacement of the roller of the variable pitch bearing in each coordinate axis direction as a boundary condition, and a contact stress distribution between the roller and the raceway of the variable pitch bearing is solved by solving the sub-model;

[0010] S3, a contact ellipse between the roller and the raceway is determined according to the contact stress distribution, and a truncation rate of the contact ellipse is taken as a climbing rate of the variable pitch bearing.

[0011] The beneficial effects of the above technical solution are: the technical solution of the wind power variable pitch bearing climbing rate calculation method belongs to an improved invention. The roller modeled as a flexible body is constrained in the form of a spring unit, a rod unit or a beam unit, so that the contact between the roller and the raceway is more realistically simulated. The invention can more realistically simulate the contact behavior of the roller and the raceway, consider the tangential and normal friction of the roller and the raceway, and realize the infinite approach of the roller and the raceway elastic approach amount to the Hertz classic contact theory by adjusting the contact stiffness of the roller and the raceway, so that the data when calculating the climbing rate is more close to the actual situation, and the calculation accuracy is greatly improved. The invention solves the technical problem of large calculation error of the climbing rate in the existing variable pitch bearing checking calculation.

[0012] Further, the truncation rate of the contact ellipse is obtained in the following manner: the ratio of the truncation amount of the contact ellipse in the major axis direction to the major axis of the ellipse is taken as the truncation rate of the contact ellipse.

[0013] Further, the truncation amount Δ x According to the following formula:

[0014]

[0015] Wherein, a is the major semi-axis of the contact ellipse; X 1 is the distance between the center point of the contact ellipse and the outer shoulder of the raceway in the chord direction; X 2 is the distance between the center point of the contact ellipse and the inner shoulder of the raceway in the chord direction.

[0016] Further, the X 1 and X 2 are obtained in the following manner:

[0017] extract the spatial coordinates of the contact points between the rollers and the raceway in the sub-model, and fit the spatial coordinates of the contact points to obtain a raceway profile curve; mark the center and boundary of the contact ellipse on the raceway profile curve, and measure in AutoCAD to obtain the contact ellipse parameters X 1 and X 2.

[0018] Further, the spatial coordinates of the contact points are fitted by a parabolic curve to obtain a raceway profile curve.

[0019] Further, the blade prosthesis of the blade is a nonlinear material; the components other than the blade prosthesis of the blade are set as linear elastic materials.

[0020] Further, the process of solving the overall model of the wind power variable pitch bearing includes: applying maximum pretightening force to the bolts for connecting the variable pitch bearing and the hub and the bolts for connecting the variable pitch bearing and the blade; based on the maximum pretightening force, applying a limit load to the variable pitch bearing to obtain the displacement of the rollers of the variable pitch bearing in each coordinate axis direction of the finite element model of the variable pitch bearing under the limit load.

[0021] Further, the bolts for connecting the variable pitch bearing and the hub and the bolts for connecting the variable pitch bearing and the blade are modeled by a beam element beam188, and the cross-section properties of the beam element beam188 are defined to simulate the thread and the light pole part of the bolt.

[0022] Further, in the overall model of the wind power variable pitch bearing, the grid size of the hub is lower than the grid size of the variable pitch bearing and the blade.

[0023] Further, the limit load is a limit load at a main node; the main node is arranged at the center of the root of each blade, and a beam element beam188 is used to connect the main node and the upper end surface node of the root, so that the load at the main node can be transmitted to the entire blade. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The method flowchart of the embodiment of the present application is shown in the figure;

[0025] Figure 2 The schematic diagram of the constraint loading of the overall analysis model in the embodiment of the present application is shown in the figure;

[0026] Figure 3 The schematic diagram of the local grid of the variable pitch bearing in the embodiment of the present application is shown in the figure;

[0027] Figure 4 The schematic diagram of the bolt connection in the embodiment of the present application is shown in the figure;

[0028] Figure 5 The schematic diagram of the roller constraint in the embodiment of the present application is shown in the figure;

[0029] Figure 6 A variable pitch bearing roller contact stress cloud diagram in the embodiment of the application;

[0030] Figure 7 A submodel schematic diagram in the embodiment of the application;

[0031] Figure 8 A submodel contact stress cloud diagram in the embodiment of the application;

[0032] Figure 9 A bearing climbing rate calculation schematic diagram in the embodiment of the application.

[0033] 1, blade prosthesis; 2, inner ring bolt; 3, blade flange; 4, roller; 5, bearing outer ring; 6, outer ring bolt; 7, hub; 8, gear; 9, bearing inner ring. DETAILED DESCRIPTION

[0034] The application applies constraints to the roller modeled as a flexible body in the form of a spring unit, a rod unit or a beam unit to more realistically simulate the contact between the roller and the raceway. The application can more realistically simulate the contact behavior of the roller and the raceway, consider the tangential and normal friction of the roller and the raceway, and realize the infinite approximation of the roller and the raceway to the classic contact theory of Hertz by adjusting the contact stiffness of the roller and the raceway, so that the data when finally calculating the climbing rate is closer to the actual value, and the calculation accuracy is greatly improved. The application solves the technical problem of large calculation error of the climbing rate in the existing variable pitch bearing checking calculation.

[0035] Embodiment of a wind power variable pitch bearing climbing rate calculation method:

[0036] As shown in Figure 1 A wind power variable pitch bearing climbing rate calculation method, the method comprises:

[0037] S1, establishing a wind power variable pitch bearing overall model and solving the wind power variable pitch bearing overall model to obtain the displacement of the roller of the variable pitch bearing in each coordinate axis direction;

[0038] The wind power variable pitch bearing overall model comprises a variable pitch bearing, a blade and a hub; constraints are applied to the roller of the variable pitch bearing in the form of a spring unit, a rod unit or a beam unit in the wind power variable pitch bearing overall model to simulate the Hertz contact between the roller of the variable pitch bearing and the raceway;

[0039] S2, taking the displacement of the roller of the variable pitch bearing in each coordinate axis direction as a boundary condition, cutting out the variable pitch bearing part from the wind power variable pitch bearing overall model and encrypting the grid to obtain a submodel, and solving the submodel to obtain the contact stress distribution between the roller of the variable pitch bearing and the raceway;

[0040] S3. Determine the contact ellipse between the roller and the raceway based on the contact stress distribution, and use the cutoff rate of the contact ellipse as the ramp rate of the pitch bearing.

[0041] Specifically, the method for calculating the gradeability of the wind turbine pitch bearing in this embodiment includes the following steps:

[0042] (1) The overall model of the wind turbine pitch bearing (i.e., the multi-blade overall finite element model, which is a three-blade model in this embodiment) is as follows: Figure 3 As shown, taking the blade as an example, the model consists of components such as inner ring bolts 2, outer ring bolts 6, gears 8, pitch bearings, hubs 7, and blades. The pitch bearing includes rollers 4, an inner ring 9, and an outer ring 5. The inner ring 9 and outer ring 5 form a four-point contact area with the rollers 4, respectively forming the inner and outer contact raceways of the bearing. The blade includes a blade spur 1 and a blade flange 3. The pitch bearing is connected to the hub 7 by outer ring bolts 6, and the pitch bearing is connected to the blade by inner ring bolts 2. First, the model is constructed and assembled using the 3D software SolidWorks.

[0043] (2) Material creation: Perform HyperMesh and ANSYS joint simulation analysis. Preprocessing is completed in HYPERMESH software. Import the 3D model created in SolidWorks and create material properties in the materials module of HYPERMESH.

[0044] 1) Right-click in the blank area under the Model tree and select Create→Material, then name it “STEEL-BEARING”. Click “STEEL-BEARING”, change Young’s modulus to “205000”, and set the principal Poisson’s ratio to “0.3”. Keep other options at their default values. This material corresponds to bearings and bolt components.

[0045] 2) Right-click in the blank area under the Model tree and select Create→Material, then name it “STEEL-BLADE”. Click “STEEL-BLADE” and set the material parameters for the nonlinear material: radial Young's modulus “13500”, circumferential Young's modulus “11000”, axial Young's modulus “29000”, radial / circumferential Poisson's ratio “0.3”, axial / radial Poisson's ratio “0.3”, axial / circumferential Poisson's ratio “0.47”, radial / circumferential shear modulus “4000”, axial / radial shear modulus “4000”, axial / circumferential shear modulus “6600”. Keep other options at their default values. This material corresponds to the blade component.

[0046] 3) Right click on the blank space under the Model tree and select Create→Material, and name it "STEEL-HUB". Click on "STEEL-HUB", change the Young's modulus to "169000"; set the main Poisson's ratio to "0.3". Other options remain default, which corresponds to the hub component.

[0047] 4) Right click on the blank space under the Model tree and select Create→Material, and name it "STEEL-FLANGE". Click on "STEEL-FLANGE", change the Young's modulus to "206000"; set the main Poisson's ratio to "0.3". Other options remain default, which corresponds to the flange component.

[0048] (3) The three-dimensional geometric model is meshed by using a finite element pre-processing software: wherein, the hub is meshed by using a ten-node tetrahedral element solid187; the remaining components (such as gears, bearing inner rings, bearing outer rings, rollers, blade flanges, blade prostheses, etc.) are simulated by using a regular twenty-node hexahedral element solid186.

[0049] (4) The finite element model is established by using a finite element pre-processing software according to the actual contact relationship between adjacent components. The bearing outer ring 5 and the hub 7, the blade flange 3 and the blade blade root part, and the blade flange 3 and the bearing inner ring 9 are set as frictional contact, and the contact relationship between the remaining components is set as binding contact.

[0050] The TARGE170 unit is used to simulate the target surface, and the 174 unit is used to simulate the contact surface in the surface-to-surface contact. The specific operation of establishing the contact relationship in the HYPERMESH software is as follows:

[0051] 1) Right click on the blank space under the Model tree and select→Sensor, and rename it conta174. Because the solid186 element is used in the front entity element, the contact element and the target element are selected as conta174 and targe170 respectively.

[0052] 2) Right click on the blank space under the Model tree and select→Property, and name it conta174p and targe170p respectively, and set the Card Image to conta174p and targe170p respectively. Two element types are established respectively, which are the contact element and the target element.

[0053] 3) Right click on the blank area under the Model tree, select → contact, a Group will be added and an automatic contact pair will be added, left click on the contact pair to set the various items displayed below. MASTER is the information related to the contact, SLAVE is the information related to the target, which are the contact surface set and element type, the target surface set and target element type, and the contact characteristics.

[0054] 4) Switch to the Contact bar, and switch the contact type under the contact pair to Standard, which is equivalent to the friction contact type, and set the friction coefficient to 0.2. All other contact settings are set to default.

[0055] 5) Set the face-to-face contact between the roller and the raceway, the blade flange and the bearing inner ring, and the bearing outer ring and the hub.

[0056] (5) The beam element beam188 is used to model the connection bolt between the pitch bearing and the hub 7 (i.e. the inner ring bolt 2), and the pitch bearing and the blade connection bolt (i.e. the outer ring bolt 6), and the threaded part and the light pole part of the inner ring bolt 2 and the outer ring bolt 6 are simulated by defining the cross-section properties of the beam element beam188; the engagement between the thread and the screw is realized by rigidly coupling the beam element with the surrounding nodes.

[0057] The steps for building the bolt connection are as follows: right click on the blank area under the Model tree, select Create → component, and name it "beam" to build the beam element under this component. Right click on the blank area under the Model tree, select Create → component, and name it "rigid" to build the rigid coupling element under this component.

[0058] 1) The establishment of the beam element is operated according to the following steps: establish the beam element under the 1D panel, and ensure that there are at least three nodes to define the beam element. Enter the creation page, select one of the nodes a and another node b, and note that the orientation below needs to be selected in a different direction from the two nodes.

[0059] 2) The establishment of the beam element (beam188) cross-section, right click on the blank area of the model tree, beamsection, the default parameter is to generate a circular interface for the beam element cross-section, the beam element cross-section diameter is 10, and the beam element cross-section needs to be modified according to the needs.

[0060] 3) The establishment of the beam element (beam188) element, right click on the blank area of the model tree, sensors, elementtype to create beam188 element.

[0061] 4) Beam element (beam 188) unit properties are established, right-click on the blank area of the model tree properties, select SECTYPE in the Card Image of the card, and select the cross-section beam established in the previous step under hyperbeam section. Make it associate with the cross-section properties of the beam element.

[0062] 5) Assign beam components materials, elements, and properties, respectively select the beam elements, materials, and properties established in the previous steps under the beam component.

[0063] 6) Set the rigid component to the current group, and place the rigid coupling constraint generated by the beam element end point and bolt hole in the next operation in this group.

[0064] As a preferred embodiment, a beam element at the bolt hole position can be constructed, and the beam elements at other positions are realized through a circular array of coordinate systems.

[0065] 7) The beam element end points are coupled with the bolt hole, one end of the bolt is coupled with the multiple nodes of the bolt hole through the main node formed by connecting one end point of the beam element to form an umbrella structure, and the other end of the bolt is also coupled with the multiple nodes of the bolt hole through the main node formed by connecting one end point of the beam element to form an umbrella structure.

[0066] 8) As a preferred embodiment, the circular array in the circumferential direction can be realized by using the TCL script language of HYPERMESH, which not only reduces the mistakes of manual operation, but also improves the work efficiency.

[0067] 9) Application of bolt pretension force, the pretension force of the pitch bearing bolt is usually inserted at the intermediate node of the 1D element (BEAM188) (i.e. PRETS179 element).

[0068] 10) The 1D beam element is realized in the pretention type under the tool, pretention bolt menu of HYPERMESH, the bolt pretension element is automatically added by manually picking up the common nodes of the two beam elements, and the final bolt connection structure is formed as shown in Figure 4 The bolt pretension force is added in the SLOAD card under the CARDS card of HYPERMESH.

[0069] The bolt connection is simplified to a spider-shaped rigid connection structure, the core idea of which is to use two sections of beam elements connected head to tail for each mounting bolt (i.e. Figure 4Two beam188 beam elements in the middle of the two segments) are simulated, and the parameters (area, bending section modulus, elastic modulus, etc.) of the beam element are determined according to the actual bolt calculation. The pre-tightening force load is applied at the center node of the beam188 beam element, and the direction is loaded in two steps along the bolt axis: the first step applies the pre-tightening force, and the second step locks the displacement. The beam188 beam element head and tail nodes are respectively coupled with the bearing end face screw hole node and the bolt hole node of the connecting piece to simulate the nut and threaded hole.

[0070] (6) Weak spring constraint is applied to the roller to limit the rigid body displacement, so as to simulate the Hertz contact between the roller and the raceway of the pitch bearing. It is realized by respectively constructing X, Y and Z three direction grounding springs (combine14). Taking the establishment of the X direction weak spring as an example, the establishment steps are as follows:

[0071] 1) The establishment method of the combine14 spring element. The spring element is established under the 1D panel, and it is necessary to ensure that there are two nodes, and the two nodes are I and J.

[0072] 2) The establishment of the spring element (combine14) unit. Right click on the sensors in the blank area of the model tree, create a combine14 unit under element type, and set the X direction stiffness in the Keyopt2 option 1. Y and Z directions are set with different parameters in the option,

[0073] 3) The establishment of the spring element (combine14) unit constant. Right click on the properties in the blank area of the model tree, select combine14 in the Card Image of the card, and associate it with the X direction spring element attribute. The roller constraint is as Figure 5 shown.

[0074] In other embodiments, a relatively weak unit such as a rod element or a beam element can also be used as a constraint applied to the roller.

[0075] (7) All degrees of freedom of the main shaft prosthesis part rear end surface node are fully constrained, and a main node is arranged at the center of each blade root part, and the three blade root parts are connected by a rigid beam element beam188, and the limit load of the three blade root parts is transmitted to the three blades. The limit load is the limit load at the center of the three blade root parts. The bearing constraint and loading are as shown in Figure 2 .

[0076] (8) The displacement of the roller in X, Y and Z directions is obtained by solving, and the result is viewed by post-processing software. The contact effect of the roller and the raceway is as shown in Figure 6The contact patch gradually decreases from the bearing load zone to the non-load zone, which is consistent with the test law.

[0077] (9) Submodel analysis, the operation steps are as follows.

[0078] Step 1: On the basis of the foregoing operation, generate and analyze a relatively rough model, and use ANSYS to perform overall analysis, generally divide relatively sparse grids. After calculation, generate fullmodel.db and fullmodel.rst files.

[0079] Step 2: Create a relatively fine grid submodel (i.e. the finite element model of the pitch bearing) and save the submodel database. The submodel is a local area model cut from the overall model, and a finer grid is re-divided. The submodel only includes the pitch bearing part, i.e. the roller 4, the bearing inner ring 9 and the bearing outer ring 5, ignoring the blades, flanges and hub and other components, and the bearing inner ring 9 and the bearing outer ring 5 and the roller 4 form a four-point contact area, respectively forming the inner and outer contact raceways of the bearing.

[0080] The created submodel is shown in Figure 7 The boundary conditions of the submodel are the displacements of the roller in X, Y and Z directions obtained by solving the overall model, and the nodes on the cutting boundary of the submodel are written into the node file (model.node). The specific implementation method is:

[0081] Main Menu→Preprocessor→Create→Nodes→Write Node File

[0082] Step 3: According to the calculation results of the overall model, and the cutting boundary node file, generate the displacement interpolation load definition file (model.cbdo) on the cutting boundary nodes of the submodel.

[0083] Step 4: Perform submodel analysis calculation, which needs to read the displacement interpolation load definition file (model.cbdo) on the cutting boundary nodes of the submodel, define the analysis calculation load step setting, and solve to obtain the roller and raceway contact stress distribution near the shoulder of the pitch bearing raceway. The result is shown in Figure 8

[0084] (10) Calculation method of roller and raceway climbing rate.

[0085] The contact ellipse truncation amount near the shoulder of the raceway is defined as the percentage of the total ellipse length (i.e. the major axis of the ellipse), and the calculation method is as follows:

[0086] ​1) Extract the contact stress of the contact point space coordinates and, through secondary development in AutoCAD, develop a macro program to construct the raceway arc profile by multiple point regression.

[0087] Specifically, the contact point space coordinates are fitted by a parabolic curve to obtain the raceway arc profile.

[0088] 2) Determine the center and boundary of the contact ellipse through the contact stress, and mark the curve of the constructed arc (i.e., the parabolic curve obtained by fitting).

[0089] 3) According to the raceway arc profile obtained in 1), measure the Figure 9 , a , X 1 and 2 in AutoCAD; calculate the elliptical truncation rate (i.e., the bearing climb rate) according to the following formula: X

[0090]

[0091] wherein, f is the bearing climb rate; a is the semi-major axis of the contact ellipse; X 1 is the distance between the contact ellipse center point and the raceway outer shoulder in the chord length direction; X 2 is the distance between the contact ellipse center point and the raceway inner shoulder in the chord length direction; and x is the elliptical truncation amount.

[0092] When the ellipse overlaps the raceway edge (Δ x > 0), the truncation is positive, and the positive value of the truncation indicates that the truncation occurs.

[0093] When the ellipse falls within the raceway edge (Δ x ≤ 0), the truncation is negative, and the negative value of the truncation indicates that there is no truncation.

[0094] The present application has the following features:

[0095] The present application applies constraints to the rollers in the form of spring units to more realistically simulate the contact between the rollers and the raceway. The present application can more realistically simulate the contact behavior of the rollers and the raceway, consider the tangential and normal friction of the rollers and the raceway, and achieve the infinite approximation of the Hertz classical contact theory of the rollers and the raceway by adjusting the contact stiffness of the rollers and the raceway, so that the data in the final calculation of the climb rate is closer to the actual value, and the calculation accuracy is greatly improved.

[0096] ​Finally, it should be noted that the above description is only the preferred embodiments of the present application, and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that modifications can be made to the technical solutions described in the foregoing embodiments without departing from the spirit and principle of the present application, or some technical features thereof can be replaced by equivalent features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating the gradeability of a wind turbine pitch bearing, characterized in that, The method includes: S1. Establish an overall model of the wind turbine pitch bearing, including the pitch bearing, blades, and hub, and apply the maximum preload to the bolts used to connect the pitch bearing to the hub and the bolts used to connect the pitch bearing to the blades; apply the ultimate load to the pitch bearing based on the maximum preload to obtain the displacement of the rollers of the pitch bearing in each coordinate axis direction of the finite element model of the pitch bearing under the ultimate load. In the overall model of wind turbine pitch bearing, constraints are applied to the rollers of the pitch bearing in the form of spring elements, rod elements or beam elements to simulate the Hertzian contact between the rollers and raceways of the pitch bearing. S2. Using the displacement of the rollers of the pitch bearing in each coordinate axis direction as boundary conditions, cut out the pitch bearing part from the overall model of the wind power pitch bearing and refine the mesh to obtain a sub-model, and solve the sub-model to obtain the contact stress distribution between the rollers and raceway of the pitch bearing. S3. Determine the contact ellipse between the roller and the raceway based on the contact stress distribution; Extract the spatial coordinates of the contact points between the roller and the raceway in the sub-model, and fit these spatial coordinates to obtain the raceway profile curve; mark the center and boundary of the contact ellipse on the raceway profile curve to obtain the distance X1 between the center point of the contact ellipse and the outer shoulder of the raceway in the chord direction, and the distance X2 between the center point of the contact ellipse and the inner shoulder of the raceway in the chord direction; then calculate the bearing ramp rate f: Δx = a - min(X1, X2) 'a' represents the semi-major axis of the contact ellipse.

2. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, The process of obtaining X1 and X2 includes: After marking the center and boundary of the contact ellipse on the raceway profile curve, X1 and X2 are measured in AutoCAD.

3. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, The raceway profile curve is obtained by fitting the spatial coordinates of the contact point with a parabolic curve.

4. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, The blade prosthesis of the blade is made of a nonlinear material; the components other than the blade prosthesis of the blade are made of a linear elastic material.

5. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, Bolts used to connect the pitch bearing to the hub and bolts used to connect the pitch bearing to the blades are modeled using beam188 elements, and the cross-sectional properties of the beam188 elements are defined to simulate the threaded and smooth parts of the bolts.

6. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, In the overall model of the wind turbine pitch bearing, the mesh size of the hub is smaller than that of the pitch bearing and the blade.

7. The method for calculating the gradeability of wind turbine pitch bearings according to claim 1, characterized in that, The ultimate load is the ultimate load at the main node; the main node is located at the center of the blade root of each blade, and is connected to the upper end face node of the blade root by a beam element beam188, so that the load at the main node can be transferred to the entire blade.

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