A Finite Element Computational Modeling Method for Wind Turbine Hubs

Abstract

This invention provides a finite element method for modeling wind turbine hubs, comprising the following steps: acquiring a 3D model and importing it into finite element software for preprocessing to establish a finite element model; coupling the bearing mounting surface nodes of the main shaft to the geometric center through a rigid domain and applying constraints to the coupled nodes; establishing bolted connections between the pitch bearing and the hub, and between the blade root and the pitch bearing, and applying preload to the bolts; establishing a rigid connection between the blade root center and the blade root end face, and applying a load to the blade root center; using a simplified slice model to simulate the stiffness, clearance, and profile of the rollers within the finite contact length of the rolling elements; and numerically compensating for the clearance and profile of the slice springs using stiffness curves. This method overcomes the limitations of existing hub finite element models, such as inaccurate pitch bearing contact angle capture, unclear pitch gear meshing load transmission, and the influence of boundary conditions and bolted connections on the hub stress distribution, resulting in a more accurate stress distribution for the hub.

Description

Technical Field

[0001] This invention relates to the field of wind power generation technology, and more specifically to a finite element calculation modeling method for wind turbine hubs. Background Technology

[0002] The hub is one of the most important components of a wind turbine generator set. The stress level of the hub directly affects the safety of the wind turbine system, and the calculation of hub stress is based on the finite element method. The finite element model of the hub includes the hub, main shaft, pitch bearing, blade root, and pitch drive. Establishing correct boundary conditions and reasonable contact relationships directly affects the accuracy of the hub calculation results. Only a correct finite element modeling method can reflect the correct load transfer path.

[0003] In existing finite element models of wheel hubs, the contact angle of the pitch bearing is not accurately captured, the transmission of meshing load of the pitch gear is unclear, and boundary conditions and bolt connections affect the stress distribution of the wheel hub, making it impossible to accurately obtain the gravitational force distribution of the wheel hub. Summary of the Invention

[0004] In view of this, the problem to be solved by the present invention is to provide a finite element calculation modeling method for wind turbine hubs, which overcomes the problems of inaccurate capture of pitch bearing contact angle, unclear transmission of pitch gear meshing load, and the influence of boundary conditions and bolt connections on the stress distribution of the hub in existing hub finite element models. The present invention finds the correct way of load transmission in the wind turbine system and obtains a more accurate stress distribution of the hub.

[0005] This invention solves the above-mentioned technical problems through the following technical means: This invention provides a finite element calculation modeling method for wind turbine hubs, comprising the following steps:

[0006] Obtain a 3D model for wheel hub calculations;

[0007] The acquired 3D model is imported into finite element software for preprocessing to establish a finite element model;

[0008] The bearing mounting surface node of the spindle is coupled to the geometric center through a rigid domain, and constraints are applied to the coupled node;

[0009] Establish bolted connections between the pitch bearing and the hub, and between the blade root and the pitch bearing, and apply preload to the bolts;

[0010] A rigid connection is established between the center of the blade root and the end face of the blade root, and a load is applied to the center of the blade root.

[0011] Create solid models of the inner and outer rings of the pitch bearing;

[0012] A simplified slice model is used to simulate the stiffness, clearance, and profile of the roller within the limited contact length of the rolling element;

[0013] Numerical compensation for the gap and shape modification of the slice spring is performed using stiffness curves.

[0014] Then submit the calculation.

[0015] Furthermore, the acquisition of the three-dimensional model for hub calculation includes three-dimensional models of the hub, main shaft, pitch bearing, pitch drive, blade root, and connecting bolts.

[0016] Furthermore, the step of importing the acquired 3D model into finite element software for preprocessing to establish a finite element model also includes preserving the main geometric contour lines and keeping the mesh consistent with the geometric contours when establishing the finite element model.

[0017] Furthermore, during the modeling process, for solid unit meshes, at least three layers are ensured in the structural thickness direction. Symmetrical structures use symmetrical meshes. Refinement is carried out at locations with large structural changes, large surface curvature changes, large load changes, and connections between different materials. Sufficient units are retained between coarse and fine meshes for transition.

[0018] Furthermore, in the meshing modeling of the pitch bearing internal gear ring and the pitch motor gear, the gear pressure angle is considered, and Combin39 is used for simulation.

[0019] Furthermore, the establishment of bolted connections between the pitch bearing-hub and the blade root-pitch bearing includes modeling the bolts using Beam188 elements, establishing contact between the bolts and the nut and threaded hole engagement section using MPC constraint equations, and applying bolt preload according to the bolt specifications, wherein the contact surfaces are set to standard contact.

[0020] Furthermore, the simulation of roller stiffness, clearance, and profile within the limited contact length of the rolling element also includes using Combin39 elements to simulate roller stiffness, clearance, and profile.

[0021] Furthermore, the numerical compensation for the clearance and shaping of the slice spring using the stiffness curve is calculated using the following formula:

[0022] δ j，k，FEM =δ j，k -δ k，offset

[0023] δ k，offest =2P(x k )+δ0-ΔD we，T

[0024]

[0025]

[0026] ΔD we，T =Dwe α th erm ΔT

[0027] δ j，k，FEM Consider the roller profile for modification, temperature, and initial clearance;

[0028] δ k，offest Offset of slice K;

[0029] P(x k ): Roller profile function;

[0030] x k : Distance between slice K and the center slice;

[0031] δ0: Gap in the unassembled state;

[0032] ΔD WE，T Changes in roller diameter due to temperature differences;

[0033] D WE Roller diameter;

[0034] α: Initial contact angle;

[0035] C 0axial Initial axial bearing clearance in unassembled state;

[0036] α th erm Coefficient of thermal expansion.

[0037] Furthermore, the application of load includes two steps: the first step is to apply bolt preload, and the second step is to apply the load on the hub.

[0038] Furthermore, the step of submitting the calculation further includes subtracting the stress result of the first step from the stress result of the second step during the calculation process to eliminate the influence of the bolt preload and obtain the hub stress result under the ultimate load.

[0039] As can be seen from the above technical solution, the beneficial effects of the present invention are as follows: The present invention provides a finite element calculation modeling method for wind turbine hubs, including the following steps: obtaining a three-dimensional model for hub calculation; importing the obtained three-dimensional model into finite element software for preprocessing to establish a finite element model; coupling the bearing mounting surface node of the main shaft to the geometric center through a rigid domain, and applying constraints to the coupled nodes; establishing bolted connections between the pitch bearing-hub and the blade root-pitch bearing, and applying preload to the bolts; establishing a rigid connection between the blade root center and the blade root end face, and loading a load at the blade root center; establishing solid models of the inner and outer rings of the pitch bearing; using a simplified slice model to simulate the stiffness, clearance, and profile of the rollers within the finite contact length of the rolling elements; numerically compensating for the clearance and profile of the slice springs through the stiffness curve; and then submitting the calculation. This overcomes the inaccurate capture of the pitch bearing contact angle, unclear transmission of the pitch gear meshing load, and the influence of boundary conditions and bolted connections on the stress distribution of the hub in existing hub finite element models, finding the correct load transmission method in the wind turbine system, and obtaining a more accurate stress distribution in the hub. Attached Figure Description

[0040] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0041] Figure 1 A three-dimensional model diagram of the finite element calculation modeling method for wind turbine hubs provided by the present invention;

[0042] Figure 2 Refer to the grid for key areas;

[0043] Figure 3 and Figure 4 A schematic diagram of the bolt connection and stiffness curve of the leaf root;

[0044] Figure 5 and Figure 6 This is a schematic diagram of the bolt connection and stiffness curve of the pitch bearing;

[0045] Figure 7 For calculation procedures;

[0046] Figure 8 and Figure 9 Model and stiffness curves for the meshing of the pitch bearing internal gear ring and the pitch motor gear;

[0047] Figure 10 The flowchart shows the finite element calculation modeling method for wind turbine hubs provided by this invention. Detailed Implementation

[0048] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0049] Please see Figures 1-10 As shown, this invention provides a finite element method for modeling wind turbine hubs, comprising the following steps:

[0050] S1. Obtain the 3D model for wheel hub calculation;

[0051] Obtain a 3D model for hub calculations. The model includes the hub, main shaft, pitch bearing, pitch drive, blade roots, and connecting bolts, etc. Figure 1 As shown, a detailed finite element calculation model of the hub was established based on the characteristics of the wind turbine structural components and the wind turbine system.

[0052] S2. Import the acquired 3D model into finite element software for preprocessing to establish a finite element model;

[0053] Import the finite element method (FEM) software for preprocessing to establish a finite element model, preserving the main geometric contours, and ensuring the mesh is basically consistent with the geometric contours; for solid element meshes, ensure at least three layers in the structural thickness direction; use symmetrical meshes for symmetrical structures; refine the mesh for parts with large structural changes, large surface curvature changes, large load changes, or connections between different materials; ensure smooth transitions in element size, with sufficient elements between coarse and fine meshes to avoid large density differences between adjacent elements; use swept meshing for the main shaft and pitch bearings, with the main shaft sweep count greater than 50, and the number of sweep fractions for the pitch bearings determined by the number of rollers, and the sweep fractions being an integer multiple of the number of rollers; the overall mesh size for the wheel hub is less than 50mm; the mesh size for high-stress areas such as process holes and heat dissipation holes is less than 20mm; the mesh size for key areas is referenced as follows: Figure 2 As shown.

[0054] In the meshing modeling of the pitch bearing internal gear ring and the pitch motor gear, considering the gear pressure angle, Combin39 simulation is used. The model and stiffness curves are as follows: Figure 8 and Figure 9 As shown.

[0055] S3. Couple the bearing mounting surface node of the spindle to the geometric center through a rigid domain, and apply constraints to the coupled node to avoid the additional bending moment generated by the constraint surface node from affecting the calculation results.

[0056] S4. Establish bolted connections between the pitch bearing and the hub, and between the blade root and the pitch bearing, and apply preload to the bolts;

[0057] Establish bolted connections between the pitch bearing and hub, and between the blade root and pitch bearing. The bolts utilize Beam188 elements, and MPC constraint equations are used to establish contact between the bolts, nuts, and threaded hole engagement sections. Bolt preload is applied according to bolt specifications. The contact surfaces are set to standard contact, and the friction coefficient is determined based on design parameters. Figures 3-6 As shown.

[0058] S5. Establish a rigid connection between the blade root center and the blade root end face, and apply a load to the blade root center; the load is applied in two steps, the first step being the bolt preload, and the second step being the load on the hub.

[0059] S6. Create solid models for the inner and outer rings of the pitch bearing; the inner and outer rings of the pitch bearing are modeled as solid parts.

[0060] S7. A simplified slice model is used to simulate the stiffness, clearance, and profile of the roller within the limited contact length of the rolling element.

[0061] A simplified slice model is adopted, considering the nonlinearity of the roller stiffness of the pitch bearing and the variation of the rolling element profile. Combin39 elements are used to simulate the roller stiffness, clearance, and profile within a finite contact length range. The model and stiffness curves are shown below. Figures 3-6 As shown.

[0062] S8. Numerical compensation is performed on the clearance and shape modification of the slice spring using the stiffness curve;

[0063] The calculation is performed using the following formula:

[0064] δ j，k，FEM =δ j，k -δ k，offset

[0065] δ k，offest =2P(x k )+δ0-ΔD we，T

[0066]

[0067]

[0068] ΔD we，T =D we α th erm ΔT

[0069] δ j，k，FEM Consider the roller profile for modification, temperature, and initial clearance;

[0070] δ k，offest Offset of slice K;

[0071] P(xk ): Roller profile function;

[0072] x k : Distance between slice K and the center slice;

[0073] δ0: Gap in the unassembled state;

[0074] ΔD WE，T Changes in roller diameter due to temperature differences;

[0075] D WE Roller diameter;

[0076] α: Initial contact angle;

[0077] C 0axial Initial axial bearing clearance in unassembled state;

[0078] α th erm : Coefficient of thermal expansion; calculations show that the spring can only deform in the longitudinal direction, the rolling element slides on the raceway, and the bearing has no internal torque and can rotate freely.

[0079] The pitch bearing model takes into account the bearing clearance, temperature and roller stiffness changes caused by roller modification and performs numerical compensation, which can better reflect the effect of the pitch bearing on the hub stress distribution when under stress.

[0080] Since the rollers of the pitch bearing cage are simulated using Combin39 elements, they can be ignored in the finite element model.

[0081] S9. Submit the calculation;

[0082] use Figure 7 The procedure shown subtracts the stress result from the first step from the stress result of the second step to eliminate the influence of bolt preload and obtain the hub stress result under ultimate load.

[0083] This invention addresses the issues of accuracy and precision in finite element method (FEM) modeling of wind turbine hubs by employing a method for this purpose. It establishes a bolted connection, which better reflects the stress distribution in the hub under the pre-connection of blade root bolts and pitch bearing bolts. Furthermore, the influence of bolt preload on the hub stress distribution is subtracted through programmatic subtraction, demonstrating that bolts significantly impact the stress distribution. The pitch bearing model considers the initial clearance of the rollers, roller trimming, and thermal expansion, better reflecting the influence of the nonlinearity of roller stiffness on the hub stress distribution under load. Calculation results show that the accuracy of the pitch bearing model significantly affects the hub stress distribution.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A finite element calculation modeling method for a wind turbine hub, characterized in that: Includes the following steps: Obtain a 3D model for wheel hub calculations; The acquired 3D model is imported into finite element software for preprocessing to establish a finite element model; The bearing mounting surface node of the spindle is coupled to the geometric center through a rigid domain, and constraints are applied to the coupled node; Establish bolted connections between the pitch bearing and the hub, and between the blade root and the pitch bearing, and apply preload to the bolts; A rigid connection is established between the blade root center and the blade root end face, and a load is applied to the blade root center. The application of the load includes two steps: the first step is to apply bolt preload, and the second step is to apply the load on the hub. Create solid models of the inner and outer rings of the pitch bearing; A simplified slice model is used to simulate the stiffness, clearance, and profile of the roller within the limited contact length of the rolling element. Combin39 elements are used to simulate the stiffness, clearance, and profile of the roller. Numerical compensation for the clearance and profile of the slice spring is performed using the stiffness curve, calculated using the following formula: ; ; ; ; ; Consider the roller profile for modification, temperature, and initial clearance; Offset of slice K; Roller profile function; : Distance between slice K and the center slice; : Gap in the unassembled state; Changes in roller diameter due to temperature differences; Roller diameter; Initial contact angle; Initial axial bearing clearance in unassembled state; Coefficient of thermal expansion; Then, the calculation is submitted. During the calculation process, the stress result of the first step is subtracted from the stress result of the second step to eliminate the influence of the bolt preload, and the hub stress result under the ultimate load is obtained.

2. The finite element calculation modeling method for wind turbine hubs according to claim 1, characterized in that, The process of obtaining a three-dimensional model for hub calculation includes three-dimensional models of the hub, main shaft, pitch bearing, pitch drive, blade root, and connecting bolts.

3. The finite element calculation modeling method for wind turbine hubs according to claim 2, characterized in that, The step of importing the acquired 3D model into finite element software for preprocessing to establish a finite element model also includes preserving the main geometric contour lines and keeping the mesh consistent with the geometric contours when establishing the finite element model.

4. The finite element calculation modeling method for wind turbine hubs according to claim 3, characterized in that, During the modeling process, for solid unit meshes, at least three layers are ensured in the structural thickness direction. Symmetrical structures use symmetrical meshes. Refinement is performed at locations with large structural changes, large surface curvature changes, large load changes, and connections between different materials. Sufficient units are retained between coarse and fine meshes for transition.

5. The finite element calculation modeling method for wind turbine hubs according to claim 4, characterized in that, In the meshing modeling of the pitch bearing internal gear ring and the pitch motor gear, the gear pressure angle is considered, and Combin39 is used for simulation.

6. The finite element calculation modeling method for wind turbine hubs according to claim 1, characterized in that, The establishment of bolted connections between the pitch bearing-hub and the blade root-pitch bearing includes modeling the bolts using Beam188 elements, establishing contact between the bolts and the nut and threaded hole engagement section using MPC constraint equations, and applying bolt preload according to the bolt specifications, wherein the contact surfaces are set to standard contact.

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