Macro-micro cross-scale analysis method for tribological performance of wind turbine main shaft sliding bearing

Abstract

The sliding main bearing of the wind driven generator is insufficient to form a complete fluid lubrication film in the heavy load working condition in the starting stage, that is, the friction surface forms a boundary lubrication state, and the friction in this stage seriously affects the service life of the bearing. In view of this, the macro model and the micro model are coupled, and the multi-scale model is verified by experiment. The macro model is established based on the actual structure of the wind power main shaft sliding bearing, and is equivalent to a three-layer structure of rigid bearing base-elastic surface support layer-main shaft; the micro model faces the boundary lubrication state of the friction pair, and a three-layer micro molecular model representing the "main shaft-lubricating oil-elastic support layer" is established. The macro model changes the thickness of the support layer, the micro model changes the component of the support layer material, the friction coefficient of the tribological interface under different support layer thickness and material component is analyzed through the macro-micro cross-scale analysis model, and the best thickness and the best material component ratio suitable for the service condition of the wind power main shaft sliding bearing are obtained.

Description

Technical fields:

[0001] This invention relates to a macro- and micro-tribological analysis method for sliding bearings in wind turbine main shafts, belonging to the field of tribology. Background technology:

[0002] In practical engineering applications, wind turbines require friction reduction under boundary lubrication. Under heavy load conditions, during startup and low-speed operation, the lubricating oil film is insufficient to form a complete fluid lubrication film, resulting in boundary lubrication. However, the friction during this stage can significantly impact the durability and reliability of the wind turbine's sliding main bearing, making it an urgent issue for optimizing the structure and materials of the wind turbine's main bearing.

[0003] Currently, tribological performance analysis methods for wind turbine main shaft sliding bearings typically focus on single-scale (macro or micro) studies, making it difficult to comprehensively reflect the bearing's behavior under actual operating conditions. For example, macroscopic analysis methods can assess the overall frictional performance of sliding bearings under different loads and speeds, but often neglect the influence of surface microstructure and material microstructure on friction and wear behavior. While microscopic analysis methods can delve into the effects of surface morphology and material microstructure on tribological behavior, they are difficult to directly apply to the evaluation and prediction of macroscopic operating conditions.

[0004] To gain a more comprehensive understanding and optimize the tribological performance of wind turbine main shaft sliding bearings, a cross-scale analysis method that combines macroscopic performance with microscopic mechanisms is urgently needed. This cross-scale analysis method can establish a multi-scale model of the tribological performance of sliding bearings, linking macroscopic operating conditions with microscopic structures. This allows for a more accurate simulation of the actual operating conditions of wind turbine main shaft sliding bearings and the prediction and optimization of their tribological performance. This is of great significance for improving the operating efficiency of wind turbine units, extending their service life, and reducing maintenance costs. Summary of the Invention:

[0005] To address the aforementioned problems in existing technologies, this invention provides a macro- and micro-scale cross-scale analysis method for the tribological properties of wind turbine main shaft sliding bearings. The aim is to accurately simulate the actual working conditions of wind turbine sliding main bearings and simultaneously optimize the bearing structure and materials. The main approach is as follows:

[0006] 1. In order to accurately simulate the friction characteristics of wind turbine main bearings under boundary lubrication conditions, this invention couples macroscopic models and molecular dynamics models to establish a new multi-scale model for the tribological study of wind turbine sliding main bearings under boundary lubrication. The interface friction coefficient is calculated by summing, and the correctness of the new multi-scale model is verified by experiments on a friction and wear testing machine.

[0007] 2. The macroscopic model is based on the actual structure of the sliding bearing of the wind turbine main shaft, equivalent to a three-layer structure: rigid bearing base—elastic surface support layer—main shaft. Under the load and speed of the wind turbine main unit, the elastic surface support layer undergoes elastic deformation, generating stress and friction at the tribological interface.

[0008] 3. The microscopic model is oriented towards the boundary lubrication state of the friction pair. The thickness of the lubricating oil is only a few nanometers. In the molecular simulation software, a three-layer microscopic molecular model representing "main axis-lubricating oil-elastic support layer" is defined and established based on its main elemental composition. Through geometric optimization, dynamic optimization, annealing and other means, the energy of the molecular structure of the friction pair is made to converge to a suitable value, and the model is fully relaxed.

[0009] Finally, a parametric study was conducted on the thickness design of the macrostructure and the selection of the component ratio of PEEK-type composite materials in the microstructure. Specific friction reduction schemes were obtained from the data. Through coupled calculations of multi-scale models, the simultaneous optimization of the main bearing structure and materials was achieved, and the optimal thickness and optimal material composition ratio suitable for the service conditions of the wind turbine main shaft sliding bearing were obtained.

[0010] Specifically, the macroscopic model of this invention is based on the actual structure of the sliding bearing of the wind turbine main shaft, that is, the bearing bush and the main shaft are coaxially connected, and the bearing is supplied with lubricating oil to provide support when it is operating normally. That is, a three-layer structure of rigid bearing base - elastic surface support layer - main shaft. However, the lubricating oil layer in the wind turbine main shaft is too thin and can be ignored in the macroscopic model.

[0011] In response, this invention models the structure of the bearing bush and the main shaft in 3D software. Considering that the commonly used PEEK material for bearing bushes is elastic and that changes in thickness will affect the pressure distribution, a parametric analysis of the thickness of the PEEK material for bearing bushes is performed.

[0012] After completing the 3D modeling, based on the actual operating conditions of wind power, the friction coefficient calculated in the microscopic model is applied to the contact area of ​​the macroscopic model, along with boundary conditions such as fixed supports, loads, and rotational speeds. This ultimately simulates the pressure and velocity distribution of the main shaft sliding bearing under actual wind power operating conditions.

[0013] In the specific case of this invention, considering the wind power operating conditions and the structure of the wind turbine main bearing, the macroscopic model is subsequently treated as a disk friction structure, and the model is simplified for analysis. A circular segmentation method is used to divide the area into regions i, and the friction coefficient within each region i is calculated separately, followed by summation to calculate the interface friction coefficient.

[0014] Specifically, the microscopic model described in this invention is oriented towards the lubrication state of the friction pair boundary. The thickness of the lubricating oil is only a few nanometers. In molecular simulation software, a three-layer microscopic molecular model representing "main axis-lubricating oil-elastic support layer" is defined and established based on its main elemental composition. In the microscopic model, the molecular unit structure of the main axis boundary layer, the lubricating oil layer, and the elastic support boundary layer is defined based on their main elemental composition, and the molecular layer structure is further established.

[0015] In molecular dynamics (MD) simulations, a three-layer structure was further established as a friction pair, and geometric optimization, dynamic optimization, and annealing were performed successively to ensure that the energy of the molecular structure of the friction pair converged to a suitable value, allowing the model to fully relax. Furthermore, since the amount of lubricating oil applied during experiments affects the oil film thickness, the molecular thickness of the lubricating oil layer was also parametrically analyzed in the MD simulations. This simulated the friction process with different amounts of lubricating oil, explaining the friction reduction mechanism of the lubricating oil on the friction pair at the microscopic scale.

[0016] In the microscopic model, the input boundary conditions are the load distribution P calculated in the macroscopic model. i and velocity distribution V i (where V) i =ωR i ω is the radius of rotation, R i Substituting the load P and sliding velocity V into the microscopic model (where V is the average radius of each annular region), the average atomic force F in the X direction is obtained through Confined Shear simulation. x and the average atomic force F in the Z direction Z Finally, the friction coefficient within the region is obtained. Finally obtained The obtained μ i It can also be substituted into the macroscopic model, becoming the contact input condition for the macroscopic model, thus achieving coupled calculation. Then, the friction coefficient, pressure, and area of ​​the 3-5 divided annular regions i are calculated separately, and the friction interface is calculated using the summation method. To ensure the accuracy of the calculation, the convergence condition of the iterative calculation is defined as the rate of change between two adjacent iterations of the friction coefficient of the interface not exceeding 10%. Furthermore, the macro-micro cross-scale model is verified through end-face friction experiments under corresponding wind power conditions. If the relative difference between the experimental friction coefficient and the friction coefficient calculated by the multi-scale model does not exceed 20%, the verification of the multi-scale model is completed.

[0017] In summary, this invention considers the influence of the elastic structure of the PEEK layer on pressure distribution and constructs a macro- and micro-scale model of the wind turbine sliding main bearing. This model accurately simulates the friction state under different wind power operating conditions, calculates the friction coefficient, and simultaneously provides optimization schemes for bearing structure thickness and material composition. Since the calculated values ​​are theoretical simulation results, to verify their authenticity and rationality, this invention also conducts end-face friction experiments under the same wind power operating conditions to validate the macro- and micro-scale friction calculation model. Attached image description:

[0018] 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.

[0019] Figure 1 This is a flowchart of the macro-micro cross-scale analysis method for the tribological properties of the sliding bearing of the wind turbine main shaft according to the present invention;

[0020] Figure 2 This is the physical and macroscopic model used in the tribological study of the sliding bearing of the wind turbine main shaft in this invention;

[0021] Figure 3 This invention provides a method for dividing the annular region of the macroscopic model in the tribological performance study.

[0022] Figure 4 The process of establishing a microscopic model in the tribological study of the sliding bearing of the wind turbine main shaft of the present invention;

[0023] Figure 5 This is a schematic diagram of the end face friction in the friction test experiment of the sliding bearing of the wind turbine main shaft in this invention;

[0024] Figure 6 This invention provides a comparison between the friction coefficient calculated by the model and the experimental friction coefficient. Detailed implementation method:

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] Figure 1 This is a flowchart of the macro-micro cross-scale analysis method for the tribological properties of the sliding bearing of the wind turbine main shaft according to the present invention.

[0027] Figure 2This invention presents the physical and macroscopic models for the tribological study of the wind turbine main shaft sliding bearing. The physical model represents the actual structure of the wind turbine main shaft sliding bearing; the macroscopic model is built upon the physical model, specifically consisting of the "rigid bearing base—elastic surface support layer—wind turbine lubricating oil—main shaft" shown in the dashed box. The lubricating oil layer is too thin to be considered in the macroscopic model. Therefore, this invention models the rigid bearing base, elastic surface support layer, and main shaft structure in 3D software. The main shaft has a fixed thickness of 10mm and a diameter of 20mm. The two symmetrically placed through holes are for placement on a friction and wear testing machine. The PEEK elastic layer has a diameter of 20mm and thicknesses of 4mm, 6mm, and 8mm, respectively, allowing for parametric studies of the PEEK layer thickness.

[0028] After completing the 3D modeling, mesh generation is performed in Ansys software. Based on the actual working conditions of wind power, the friction coefficient, fixed support, load, rotation speed, etc. calculated in the micro-model are applied in the finite element analysis to finally simulate the pressure distribution and velocity distribution of the main shaft sliding bearing under the actual working conditions of wind power.

[0029] Considering the macroscopic model is a disk structure, a ring-shaped segmentation method is used to divide the region, and the interface friction coefficient is subsequently calculated by summing the results. Figure 3 As shown. Because the rotational angular velocity applied to the model is fixed, the linear velocity in the region is linearly distributed. The load distribution is obtained from the Ansys simulation results and substituted into the microscopic model to further solve for the friction coefficient in the distribution surface i region.

[0030] Figure 3 This invention presents a method for dividing the macroscopic model into annular regions in the tribological performance study. Considering that the simulated wind turbine main shaft and bearings in the experiment are all disc structures, annular division is used to divide the friction region. The pressure distribution and linear velocity V of each annular region i are calculated. μ1p1A1, μ2p2A2, and μ3p3A3 are obtained for each of the three annular regions. Then, based on… Figure 1 The calculation method of the macro-micro model and the coupled calculation method described in the paper are used to calculate the friction coefficient of the friction interface.

[0031] Figure 4 In the tribological study of the sliding bearing of the wind turbine main shaft of this invention, the microscopic model establishment process is described. Under boundary lubrication conditions, the thickness of the lubricating oil is only about 3-5 nm. Therefore, a three-layer model of "PEEK elastic layer - lubricating oil - main shaft" can be established in molecular simulation software. In the microscopic model, the main elemental components are defined as PEEK, PAO base oil, and iron atom layer, respectively. In the molecular dynamics simulation software Materials Studios, the three-layer structure is established as a friction pair, and the lattice lengths of this friction pair in the X and Y directions are both... The thickness of the PEEK and iron atom layers in the Z direction is The wind turbine sliding bearing is oil-lubricated, meaning the thickness of the PAO base oil in the Z-direction is designed according to the oil supply volume during the experiment. Perform parametric analysis as well.

[0032] To prepare for further simulations, the iron atom layer was fixed, and geometric optimization, kinetic optimization, and annealing were performed in the molecular simulation to bring the energy of the friction pair molecular structure to a suitable value and allow the model to fully relax. To obtain the friction coefficient within the distribution region, the annealed model underwent a Forcite Confined Shear treatment—the iron atom layer was removed, allowing the PEEK layer molecules to move along the X-axis. The average atomic force F in the X-direction was then obtained through Confined Shear simulation. x and the average atomic force F in the Z direction Z The input boundary conditions are the load distribution P calculated in the macroscopic model. i and velocity distribution V i (where V) i =ωR i ω is the radius of rotation, R i The average radius of each annular region is given, which ultimately yields... After completing the calculations for the macroscopic and microscopic models, according to... Figure 3 The method involves dividing the friction region, calculating the friction coefficient, pressure, and area of ​​3-5 divided regions i, and then... Figure 1 The coupling approach to calculate the friction interface To ensure the accuracy of the calculation, the convergence condition for the iterative calculation is defined as the rate of change of the friction coefficient between two adjacent iterations of the interface not exceeding 10%.

[0033] Figure 5 This diagram illustrates the end-face friction test of the sliding bearing of the wind turbine main shaft in this invention. Under boundary lubrication conditions, the thickness of the lubricating oil film is typically very thin, generally only a few nanometers to tens of nanometers. Therefore, a thin layer of lubricating oil is coated on the surface of the main shaft sample. The amount of lubricating oil is controlled by a micro-injector. After squeezing out a certain amount of oil, a small brush is used to spread the lubricating oil evenly, ensuring that the thickness of the lubricating oil layer matches that of the boundary lubrication condition.

[0034] After placing the spindle sample and applying lubricating oil, the PEEK workpiece, i.e., the bearing portion of the simulated wind turbine spindle, was fastened to the upper end of the friction and wear testing machine. The height was adjusted to ensure contact between the spindle and the bearing. The friction state, applied force, applied rotational speed, and friction time of the end-face friction pair were then set, and the interfacial friction coefficient, friction torque, and temperature changes under specific parameter conditions were recorded. Through end-face friction experiments under corresponding wind power operating conditions, the macro-micro cross-scale model was verified. Figure 2 , Figure 4 After simulation, in Figure 1 If the relative difference between the experimental friction coefficient and the friction coefficient calculated by the multi-scale model does not exceed 10%, then the verification of the multi-scale model is complete.

[0035] Figure 6 In this invention, when the PEEK material is subjected to working conditions of 30rpm-100N and 30rpm-150N, the friction coefficient calculated by the model is compared with the experimental friction coefficient. It is found that the relative difference between the experimental friction coefficient and the friction coefficient calculated by the multi-scale model does not exceed 20% under both working conditions, thus completing the experimental verification of the multi-scale model.

[0036] 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; and these 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.

Claims

1. A macro-micro cross-scale analysis method for the tribological properties of sliding bearings for wind turbine main shafts, characterized in that: A macroscopic force analysis model of the friction pair of the sliding bearing of the wind turbine main shaft is established using the finite element method (FEM). A microscopic analysis model of the tribological interface performance is established using a molecular dynamics model. The stress and velocity distributions of the friction pair surface obtained from the macroscopic analysis model are input into the microscopic molecular dynamics model, and the interface friction coefficient obtained from the microscopic molecular dynamics model is input into the macroscopic finite element model. The tribological performance of the friction pair under different material compositions and the thickness of the elastic surface support layer of the sliding bearing is obtained through iterative calculation. This enables the integrated structure-material optimization design of the elastic surface support layer thickness and material composition of the wind turbine main shaft sliding bearing. The pressure and velocity distributions of the tribological interface are obtained from the macroscopic analysis model, with the interface friction coefficient obtained from the microscopic analysis model as the input boundary condition. Specifically, the materials of the three-layer structure—rigid bearing base, elastic surface support layer, and main shaft—are set separately, and the friction coefficient is set at the contact surface. A tetrahedral mesh with a side length of 0.2 mm is used for meshing. Concentrated loads, rotational speeds, and fixed supports are applied, and the pressure distribution and elastic deformation are calculated. The interface friction coefficient is obtained from the microscopic analysis model, with the load distribution P calculated in the macroscopic analysis model as the input boundary condition. i and velocity distribution V i V i =ωR i ω is the radius of rotation, R i The average radius of each annular region is given by the following process: The load P and sliding velocity V are substituted into the microscopic analysis model, and the average atomic force F in the X direction is obtained through Confined Shear simulation. x and the average atomic force F in the Z direction Z Finally, the friction coefficient within the region is obtained. Based on the friction coefficient, pressure, and area in each region, the friction coefficient of the friction interface is calculated using the summation method. The integrated structure-material optimization design involves changing the thickness of the support layer through a macroscopic analysis model, changing the composition of the support layer material through a microscopic analysis model, and analyzing the friction coefficient of the tribological interface under different support layer thicknesses and material compositions through a macro-micro cross-scale analysis model to obtain the optimal thickness and optimal material composition ratio suitable for the service conditions of the sliding bearing of the wind turbine main shaft.

2. According to the method described in claim 1, the macroscopic analysis model is established based on the actual structure of the wind turbine main shaft sliding bearing, which is equivalent to a three-layer structure of rigid bearing base, elastic surface support layer, and main shaft. Under the action of wind turbine main load and speed, the elastic surface support layer undergoes elastic deformation, and stress and friction are generated in the tribological interface. Under the friction coefficient conditions given in the initial / microscopic analysis model, the pressure distribution and velocity distribution of the tribological interface of the wind turbine main shaft sliding bearing under actual working conditions are obtained through finite element analysis.

3. According to the method described in claim 1, the microscopic analysis model is oriented towards the boundary lubrication state of the friction pair, and the thickness of the lubricating oil is only a few nanometers. In the molecular simulation software, a three-layer microscopic molecular model representing "main axis-lubricating oil-elastic support layer" is defined and established based on its main elemental composition. Through geometric optimization, dynamic optimization, and annealing, the energy of the molecular structure of the friction pair is made to converge to a suitable value, and the model is fully relaxed.

4. The method according to claim 1, wherein the convergence condition of the iterative calculation is that the rate of change of the friction coefficient between two adjacent iterations of the interface does not exceed 10%.

5. The method according to any one of claims 1 to 4, through end-face friction experiments under corresponding wind power conditions, verifies the macro-micro cross-scale model. If the relative difference between the experimental friction coefficient and the friction coefficient calculated by the multi-scale model does not exceed 20%, the verification of the multi-scale model is completed.

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