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

Abstract

When a sliding main bearing of a wind driven generator is under a heavy-load working condition, a lubricating oil film in a starting stage is not enough to form a complete fluid lubricating film, namely, a friction surface forms a boundary lubrication state, and friction in the stage seriously affects the service life of the bearing. In this way, a macroscopic model and a microscopic model are coupled, and a multi-scale model is verified through experiments. The macroscopic model is established based on an actual structure of a wind power main shaft sliding bearing, and is equivalent to a three-layer structure of a rigid bearing base, an elastic surface supporting layer and a main shaft; a three-layer microcosmic molecular model representing'main shaft-lubricating oil-elastic supporting layer 'is established by the microcosmic model facing the boundary lubrication state of a friction pair. Wherein the thickness of the supporting layer is changed by the macroscopic model, the components of the supporting layer material are changed by the microscopic model, the friction coefficient of the tribological interface under different supporting layer thicknesses and material components is analyzed through the macro-micro cross-scale analysis model, and the optimal thickness and the optimal material component proportion suitable for the service condition of the wind power main shaft sliding bearing are obtained.

Description

Technical field:

[0001] The invention relates to a macro-micro tribology analysis method in a wind turbine main shaft sliding bearing, and belongs to the field of tribology. Background technology:

[0002] Wind turbines in actual engineering have the need to reduce friction under boundary lubrication. Under heavy load conditions, during startup and low-speed operation, the lubricating oil film is not enough to form a complete fluid lubrication film, forming a boundary lubrication state. However, the friction at this stage will have a great impact on the durability and reliability of the wind turbine sliding main bearing, which has become an urgent problem for the optimization of the wind turbine main bearing structure and materials.

[0003] At present, the tribological performance analysis methods of wind turbine main shaft sliding bearings are usually focused on the study of a single scale (macro or micro), which is difficult to fully reflect the behavior of bearings under actual working conditions. For example, the macroscopic analysis method can evaluate the overall friction performance of sliding bearings under different loads and speeds, but often ignores the effects of surface microstructure, material microstructure, etc. on friction and wear behavior. Although the microscopic analysis method can deeply study the effects of surface morphology, material microstructure, etc. on tribological behavior, it is difficult to directly apply it to the evaluation and prediction of macroscopic working conditions.

[0004] In order to more comprehensively understand and optimize the tribological performance of wind turbine main shaft sliding bearings, a cross-scale analysis method that can combine macroscopic performance with microscopic mechanisms is urgently needed. Through the macro-micro cross-scale analysis method, a multi-scale model of the tribological performance of sliding bearings can be established, and the macroscopic working conditions can be linked to the microstructure, so as to more accurately simulate the actual working conditions of wind turbine sliding main bearings, and predict and optimize the tribological performance of sliding bearings. This is of great significance for improving the operating efficiency of wind turbines, extending their service life, and reducing maintenance costs. Summary of the invention:

[0005] In view of the above problems existing in the prior art, the present invention provides a macro-micro cross-scale analysis method for the tribological performance of wind turbine main shaft sliding bearings. It strives to accurately simulate the actual working conditions of wind turbine sliding main bearings and achieve simultaneous optimization in the main bearing structure and materials. The main ideas are as follows:

[0006] 1. In order to accurately simulate the friction characteristics of wind turbine main bearings under boundary lubrication conditions, the present invention couples the macroscopic model and the molecular dynamics model, establishes a new multi-scale model for tribological research of wind turbine sliding main bearings under boundary lubrication, cumulatively calculates the interface friction coefficient, and conducts experiments on a friction and wear testing machine to verify the correctness of the new multi-scale model.

[0007] 2. The macro model is 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-main shaft. Under the action of the wind turbine main engine load and speed, the elastic surface support layer produces elastic deformation, and stress and friction are generated in 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 the "spindle-lubricating oil-elastic support layer" is defined and established according to its main elemental components. Through geometric optimization, dynamic optimization, annealing treatment and other means, the energy of the molecular structure of the friction pair converges to an appropriate 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 composite materials in the microstructure. A specific friction reduction scheme was obtained from the data. Through the coupling calculation of the multi-scale model, the main bearing structure and material were optimized simultaneously, and the optimal thickness and optimal material component ratio suitable for the service conditions of the wind turbine main shaft sliding bearing were obtained.

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

[0011] To this end, the present invention models the structure of the bearing and the main shaft in three-dimensional software, and considering that the PEEK material commonly used in the bearing has elasticity and thickness changes will affect the distribution of pressure, a parametric analysis is performed on the thickness of the PEEK material of the bearing.

[0012] After completing the 3D modeling, based on the actual working conditions of wind power, the friction coefficient calculated in the micro model is applied to the contact area of ​​the macro model, as well as boundary conditions such as fixed support, load, and rotation speed. Finally, the pressure distribution and velocity distribution of the main shaft sliding bearing under the actual working conditions of wind power are simulated.

[0013] In the specific case of the present invention, combined with the wind power working conditions and the wind power main bearing structure, the macro model is subsequently regarded as a disc friction structure, and the model is simplified for analysis. The ring segmentation method is used to divide the region i, and the friction coefficient in each i region is calculated separately, and then the interface friction coefficient is calculated by summing.

[0014] Specifically, the microscopic model described in the present invention 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 characterizing the "spindle-lubricating oil-elastic support layer" is defined and established according to its main elemental components. In the microscopic model, the molecular unit structures of the spindle boundary layer, the lubricating oil layer, and the elastic support boundary layer are defined according to their main elemental components, and the molecular layer structure is further established.

[0015] In the molecular dynamics (MD) simulation, the three-layer structure was further established as a friction pair, and geometric optimization, dynamic optimization, and annealing treatment were successively performed to make the energy of the molecular structure of the friction pair converge to an appropriate value and the model fully relax. Because the amount of lubricant brushing during the experiment will affect the thickness of the oil film, the molecular thickness of the lubricant layer was also parameterized in the MD simulation, simulating the friction process of different lubricant amounts, and explaining the wear reduction mechanism of lubricants on friction pairs at the microscopic scale.

[0016] In the microscopic model, the input boundary condition is the load distribution P calculated in the macroscopic model. i and the velocity distribution V i (Where V i =ωR i , ω is the radius of rotation, R i is the average radius of each annular region), the load P and the sliding velocity V are substituted into the microscopic 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 in the area is obtained Finally get The obtained μ i It can also be substituted into the macro model to become the contact input condition of the macro model, thus realizing the coupled calculation. Then the friction coefficient, pressure and area in the 3-5 divided circular areas i are calculated separately, and the friction interface is calculated according to the accumulation 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 iterative friction coefficients of the interface does not exceed 10%, and the macro-micro cross-scale model is verified by the end face friction experiment under the corresponding wind power working 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, the present invention takes into account the influence of the elastic structure of the elastic support layer - PEEK layer on the pressure distribution, and constructs a macro-micro model of the wind power sliding main bearing, accurately simulates the friction state under different wind power working conditions, calculates the friction coefficient, and can simultaneously provide an optimization solution in terms of bearing structure thickness and material component composition. Because the calculated value is a theoretical simulation result, in order to verify its authenticity and rationality, the present invention also conducts end face friction experiments under the same wind power working conditions to verify the macro-micro friction calculation model. Description of the drawings:

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. 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 according to the actual scale.

[0019] Figure 1 This is a flow chart of the macro-micro cross-scale analysis method of the tribological performance of the wind turbine main shaft sliding bearing of the present invention;

[0020] Figure 2 It is the physical and macroscopic model in the tribology research of the wind turbine main shaft sliding bearing of the present invention;

[0021] Figure 3 It is a method for dividing the annular region of the macro model in the tribological performance research of the present invention;

[0022] Figure 4 The microscopic model establishment process in the tribology research of the wind turbine main shaft sliding bearing of the present invention;

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

[0024] Figure 6 The friction coefficient calculated by the model in the present invention is compared with the experimental friction coefficient; Specific implementation method:

[0025] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Figure 1 This is a flow chart of the macro-micro cross-scale analysis method for tribological performance of wind turbine main shaft sliding bearings of the present invention

[0027] Figure 2This is the physical and macroscopic model in the tribological research of the wind turbine main shaft sliding bearing of the present invention. The physical model is the actual structure of the wind turbine main shaft sliding bearing; the macroscopic model is established based on the physical model, specifically the "rigid bearing base-elastic surface support layer-wind turbine lubricating oil-spindle" shown in the dotted box, where the lubricating oil layer is too thin and can be ignored in the macroscopic model. Therefore, the present invention models the structure of the rigid bearing base, elastic surface support layer and spindle in three-dimensional software, where the thickness of the spindle is fixed to 10mm and the diameter is 20mm, and the two symmetrical through holes are for placement on a friction and wear testing machine. The diameter of the PEEK elastic layer is 20mm, and the thickness is 4mm, 6mm, and 8mm respectively, so as to perform a parametric study on the thickness of the PEEK layer.

[0028] After completing the 3D modeling, meshing was performed in the 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 were 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 that the macro model is a disk structure, the ring segmentation method is used to divide the area, and then the interface friction coefficient is calculated by summing up, as shown in Figure 3 As shown in the figure, since the rotational angular velocity applied to the model is fixed, the linear velocity in the area is distributed linearly, and the load distribution is obtained through the simulation results of Ansys, and is substituted into the microscopic model to further solve the friction coefficient in the distribution surface i area.

[0030] Figure 3 This is the annular area division method of the macro model in the tribological performance research of the present invention. Considering that the wind turbine main shaft simulated in the experiment has a disc structure, the bearing bushing is divided into a circular ring. Therefore, the circular ring division method is used to divide the friction area, and the pressure distribution and linear velocity V of each circular ring area i are calculated. The μ1p1A1, μ2p2A2, and μ3p3A3 are obtained in the three circular areas respectively. Figure 1 The friction coefficient of the friction interface is calculated using the calculation method of the macro-micro model and the coupling calculation method described in.

[0031] Figure 4 The microscopic model establishment process in the tribological research of the wind turbine main shaft sliding bearing of the present invention is that under the boundary lubrication state, the thickness of the lubricating oil is only about 3-5nm, so a three-layer model of "PEEK elastic layer-lubricating oil-main shaft" can be established in the molecular simulation software. In the microscopic model, PEEK, PAO base oil, and iron atomic layer are defined according to their main elemental components. The three-layer structure is established as a friction pair in the molecular dynamics simulation software Materials Studios, and the lattice lengths of the friction pair in the X and Y directions are both The thickness of the PEEK and iron atomic layers in the Z direction is Wind turbine sliding bearings are oil lubricated, that is, the thickness of the PAO base oil in the Z direction is designed according to the oil supply during the experiment. Parametric analysis was also performed.

[0032] In preparation for further simulation, the iron atomic layer is fixed, and geometric optimization, dynamic optimization, and annealing are performed in molecular simulation to converge the energy of the friction pair molecular structure to an appropriate value and fully relax the model. In order to obtain the friction coefficient in the distribution area, the annealed model is processed by Forcite Confined Shear - the iron atomic layer is unfixed, and the PEEK layer molecules are moved along the X-axis direction. After Confined Shear simulation, the average atomic force F in the X direction is obtained. x , and the average atomic force F in the Z direction Z The input boundary condition is the load distribution P calculated in the macro model. i and the velocity distribution V i (Where V i =ωR i , ω is the radius of rotation, R i is the average radius of each ring area, and finally we get ). After completing the calculation of the macro model and the micro model, according to Figure 3 The friction area is divided into 3-5 divided areas, and the friction coefficient, pressure and area in each area i are calculated respectively, and then the friction coefficient, pressure and area in each divided area i are calculated according to the friction coefficient, pressure and area in each divided area i. Figure 1 The coupling idea of ​​​​the friction interface is calculated In order to ensure the accuracy of calculation, the convergence condition of the iterative calculation is defined as the change rate between two adjacent iterative friction coefficients of the interface does not exceed 10%.

[0033] Figure 5 The end face friction diagram of the wind turbine main shaft sliding bearing friction test experiment in the present invention. Under the boundary lubrication state, the thickness of the lubricating oil film is usually 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, wherein the amount of lubricating oil is controlled by a micro-injector. After squeezing out a certain amount of oil, the lubricating oil is evenly applied with a small brush to make the thickness of the lubricating oil layer consistent with the boundary lubrication state.

[0034] After the spindle sample is placed and lubricated, the PEEK workpiece, i.e. the bearing part of the simulated wind turbine main shaft, is fastened to the upper end of the friction and wear tester. After adjusting the height to make the spindle and the bearing contact, the friction state, loading force, applied speed and friction time of the end face friction pair are set respectively, and the interface friction coefficient, friction torque and temperature change under certain parameter conditions are recorded. The macro-micro cross-scale model is verified through the end face friction experiment under the corresponding wind power working condition, i.e. Figure 2 , Figure 4 After simulation, 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%, the verification of the multi-scale model is completed.

[0035] Figure 6 When the PEEK material is subjected to working conditions of 30rpm-100N and 30rpm-150N in the present invention, the friction coefficient calculated by the model is compared with the experimental friction coefficient. It is found that under the two working conditions, the relative difference between the experimental friction coefficient and the friction coefficient calculated by the multi-scale model does not exceed 20%, 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, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 tribological performance of wind turbine main shaft sliding bearings, characterized by: A macroscopic force analysis model of the friction pair of the wind turbine main shaft sliding bearing is established by finite element analysis, and a microscopic analysis model of the tribological interface performance is established by molecular dynamics model. The surface stress distribution and velocity distribution of the friction pair obtained by the macroscopic model are input into the microscopic molecular dynamics model, and the interface friction coefficient obtained by the microscopic molecular dynamics model is input into the macroscopic finite element model. The tribological performance of the friction pair under different material components and thicknesses of the elastic surface support layer of the sliding bearing is obtained by iterative calculation, thereby realizing the structural-material integrated optimization design of the thickness of the elastic surface support layer and material components of the wind turbine main shaft sliding bearing.

2. According to claim 1, the macro 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-main shaft. Under the action of the wind turbine main engine load and speed, the elastic surface support layer produces elastic deformation, and stress and friction are generated in the tribological interface. Under the conditions of the friction coefficient initially given / obtained by the micro 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 claim 1, the microscopic model is oriented to the boundary lubrication state of the friction pair, the thickness of the lubricating oil is only a few nanometers, and a three-layer microscopic molecular model characterizing "spindle-lubricating oil-elastic support layer" is defined and established in the molecular simulation software according to its main elemental components. Through geometric optimization, dynamic optimization, annealing treatment and other means, the energy of the molecular structure of the friction pair converges to an appropriate value and the model is fully relaxed.

4. According to claim 1, the pressure distribution and velocity distribution of the tribological interface are obtained according to the macroscopic model, and the input boundary condition is the interface friction coefficient obtained in the microscopic model. The specific process is: set the materials for the three-layer structure of rigid bearing substrate-elastic surface support layer-spindle respectively, set the friction coefficient on the contact surface, divide the grid into 0.2mm, apply concentrated load, rotation speed and fixed support, and calculate the pressure distribution and elastic deformation.

5. According to claim 1, the interface friction coefficient is obtained by a microscopic model, and its input boundary condition is the load distribution P calculated in the macroscopic model. i and the velocity distribution V i (Where V i =ωR i , ω is the radius of rotation, R i is the average radius of each circular ring area). The specific process is: Substitute the load P and the sliding velocity V into the microscopic model, and obtain the average atomic force F in the X direction through Confinedshear simulation. x , and the average atomic force F in the Z direction Z Finally, the friction coefficient in the area is obtained According to the friction coefficient, pressure and area in each area, the friction interface is calculated by the accumulation method.

6. According to claim 1, the convergence condition of the iterative calculation is that the change rate between two adjacent iterative friction coefficients of the interface does not exceed 10%.

7. According to the model shown in claims 1 to 5, the macro-micro cross-scale model is verified by performing 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.

8. According to claim 1, the structure-material integrated optimization design is to change the thickness of the support layer through a macro model, change the composition of the support layer material through a micro model, and analyze 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 wind turbine main shaft sliding bearing.

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