A reliability evaluation method for oil film lubrication of sliding bearings

Abstract

The present invention provides a method for evaluating the reliability of oil film lubrication of a sliding bearing, which relates to the field of oil film lubrication reliability diagnosis. The method comprises: establishing a minimum film thickness limit state function and determining a reliable domain according to a calculation equation for the minimum oil film thickness of the bearing and a preset minimum oil film thickness threshold, solving the minimum oil film thickness by iteratively solving the elastohydrodynamic lubrication equation, and solving the non-probabilistic reliability index and design verification point by a numerical optimization algorithm; judging the joint focal element that needs extreme value analysis according to the non-probabilistic reliability index, the design verification point and the relationship between the uncertainty domain and the reliable domain, and using an intelligent genetic method to inherit its maximum and minimum values ​​to obtain the credibility and plausibility under this threshold; obtaining the credibility and plausibility under each minimum oil film thickness threshold according to the above steps, and determining a cumulative credibility function curve and a cumulative plausibility function curve for evaluating the reliability degree. In this way, the focal element that needs to be analyzed for extreme value is reduced, and the efficiency of evaluating the reliability of the sliding bearing oil film lubrication is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of oil film lubrication reliability diagnosis, and in particular to a method for evaluating the reliability of oil film lubrication of a sliding bearing. Background Art

[0002] As one of the core components of wind turbines, the performance and reliability of wind turbine gearboxes directly affect the power generation efficiency and service life of wind turbines. In order to achieve the sustainable development of the wind power industry, improving the reliability and stability of wind turbine gearboxes has become an urgent problem to be solved. Sliding bearings are gradually being used to replace rolling bearings due to their large load capacity, long service life, and low manufacturing cost. They have become the most promising support design solution for the transmission shaft system of high-power wind turbine gearboxes. However, sliding bearings face many challenges when subjected to complex load conditions, especially under strong sudden change and heavy load conditions, which puts strict requirements on their lubrication status and operational reliability.

[0003] The minimum oil film thickness is an important indicator for evaluating the lubrication status of sliding bearings, which is directly related to the reliability and service life of bearings. In practical applications, due to the influence of factors such as yaw moment, wind wheel weight and unbalanced load, sliding bearings may be subjected to frequent start-stop impacts and strong sudden changes in overload. These factors may cause the journal to tilt and the bearing to deform, which in turn causes the oil film to rupture, increase friction resistance, cause a sharp rise in temperature, change the viscosity of the lubricant, and ultimately cause lubrication failure or even surface melting. In the use of sliding bearings, there are also many uncertain factors, such as speed fluctuations, changes in lubricating oil parameters, differences in bearing surface quality, and changes in external loads. The existence of these uncertainties makes it difficult to accurately predict the lubrication performance of sliding bearings based on the reliability theory based on traditional probability distribution.

[0004] As an effective tool for processing uncertain information, evidence theory can describe the uncertainty of variables through discrete basic credibility distribution functions, and use probability intervals to jointly describe the trust of analysis results. However, in the specific implementation process, it still faces the problem of computational efficiency. Since it is necessary to perform extreme value analysis of the limit state function on each focal element to determine whether to include credibility or plausibility, such a solution process will become extremely complicated as the problem dimension and the number of focal elements increase. Especially when conducting reliability analysis of elastohydrodynamic lubrication of heavily loaded inclined journal bearings with strong mutations, calling time-consuming numerical analysis models will make the whole process more cumbersome, greatly affecting the real-time and practical nature of the analysis. In summary, how to improve computational efficiency while ensuring analysis accuracy has become a major challenge in the current research on the reliability of elastohydrodynamic lubrication of sliding bearings. Summary of the invention

[0005] The present invention provides a method for evaluating the reliability of oil film lubrication of sliding bearings, aiming to solve the problems of low computational efficiency, difficulty in handling multi-source uncertainties, and difficulty in adapting traditional reliability theories in reliability analysis of elastohydrodynamic lubrication of inclined journal bearings under strong sudden change and heavy load conditions.

[0006] According to a first aspect of the present disclosure, a method for evaluating the reliability of oil film lubrication of a sliding bearing is provided, comprising:

[0007] Step S1: According to the input multidimensional uncertain variable parameters, a joint identification framework, a joint focal element and a joint basic credibility allocation function of the multidimensional uncertain variables are constructed, and the center point of the uncertainty domain is determined;

[0008] Step S2: establishing a minimum film thickness limit state function according to the minimum oil film thickness equation of the sliding bearing and a preset minimum oil film thickness threshold, calculating a function value of the center point of the uncertainty domain according to the minimum film thickness limit state function, and determining a reliable domain of oil film lubrication safety in combination with lubrication performance requirements;

[0009] Step S3: iteratively calculating the minimum oil film thickness of the sliding bearing by the line contact elastohydrodynamic lubrication equation, and solving the design verification point and non-probabilistic reliability index under the preset minimum oil film thickness threshold by a numerical optimization algorithm based on the minimum film thickness limit state function;

[0010] Step S4: determining the joint focal element that does not require extreme value analysis and its credibility and plausibility, and determining the joint focal element that requires extreme value analysis, according to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain;

[0011] Step S5: inheriting the maximum and minimum values ​​of the joint focal element requiring extreme value analysis based on an intelligent genetic method, and determining the credibility and plausibility under the minimum oil film thickness threshold according to the credibility and plausibility of the maximum and minimum values ​​and the joint focal element not requiring extreme value analysis;

[0012] Step S6: changing the preset minimum oil film thickness threshold, cyclically executing the above steps S3 to S5 until the cycle reaches a preset number of times, and obtaining the credibility and plausibility under each minimum oil film thickness threshold;

[0013] Step S7: according to the credibility and likelihood under each minimum oil film thickness threshold, a cumulative credibility function curve and a cumulative likelihood function curve are obtained, and the reliability of the elastohydrodynamic lubrication is evaluated according to the curves.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the joint identification framework, joint focal element and joint basic credibility allocation function of the multidimensional uncertain variables are constructed according to the input multidimensional uncertain variable parameters, including:

[0015] According to the input multi-dimensional uncertain variable parameters, an identification framework and a basic credibility distribution function of a single uncertain variable parameter are constructed, wherein the multi-dimensional uncertain variable parameters include load, elastic modulus, rheological parameter and rotation speed;

[0016] Based on the identification framework and basic credibility allocation function of single uncertain variable parameters, the joint identification framework, joint focal element and joint basic credibility allocation function of multi-dimensional uncertain variables are determined.

[0017] According to the above aspects and any possible implementation, an implementation is further provided, which iteratively calculates the minimum oil film thickness of the sliding bearing through the line contact elastohydrodynamic lubrication equation, including:

[0018] Preprocess the input multi-dimensional uncertain variable parameters;

[0019] Calculate the node film thickness, density, viscosity and node elastic deformation value based on the preprocessed data;

[0020] The Reynolds equation is iteratively solved according to the node film thickness, density, viscosity and node elastic deformation value until the pressure value converges, and the minimum oil film thickness of the sliding bearing is output.

[0021] According to the above aspects and any possible implementation, an implementation is further provided, wherein the minimum film thickness limit state function is:

[0022] ;

[0023] in, is the preset minimum oil film thickness threshold; It is the minimum oil film thickness calculated for the sliding bearing under a certain state; is represented as a multidimensional uncertain variable.

[0024] According to the above aspects and any possible implementation, a further implementation is provided, wherein the oil film lubrication safety and reliability domain determined according to the minimum film thickness limit state function combined with the lubrication performance requirements is .

[0025] According to the above aspects and any possible implementation, an implementation is further provided, which solves the design verification point and the non-probabilistic reliability index corresponding to the minimum film thickness limit state function based on the following formula:

[0026] ;

[0027] in, , , , are the loads in all focal elements respectively , elastic modulus , rheological parameters ,speed Projected to The standardized evidence variables generated by the standard space, is the minimum film thickness limit state function The normalized function is transformed to the standard space.

[0028] According to the above aspects and any possible implementation, an implementation is further provided, which determines the joint focal element that needs to be subjected to extreme value analysis according to the relationship between the non-probabilistic reliability index and the limit state function value of the center point of the uncertainty domain and the reliability domain, including:

[0029] like , then no extreme value analysis is needed. ;

[0030] like , then we need to perform extreme value analysis to obtain and ;

[0031] like , then we need to perform extreme value analysis to obtain and ;

[0032] like , then no extreme value analysis is needed. ,

[0033] in, is a non-probabilistic reliability index, is the center point of the uncertainty domain, is the limit state function value at the center of the uncertainty domain, For credibility, For the degree of authenticity.

[0034] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein the method further includes:

[0035] when or When the design verification points are used, auxiliary areas are made;

[0036] If the joint focal element falls completely within the auxiliary region, there is no need to perform extreme value analysis, and its basic credibility allocation is directly included in the credibility and plausibility under the current minimum oil film thickness threshold;

[0037] If the joint focal element does not completely fall within the auxiliary area, an extreme value analysis of the joint focal element is required.

[0038] According to the above aspects and any possible implementation, an implementation is further provided, wherein if the joint focal element does not completely fall within the auxiliary region, an extreme value analysis needs to be performed on the joint focal element, including:

[0039] If the joint focal element does not completely fall within the auxiliary area, first determine whether the joint focal element has been subjected to extreme value analysis. If so, inherit its maximum and minimum values. Otherwise, calculate the maximum and minimum values ​​of the minimum film thickness of the focal element according to the minimum film thickness limit state function, and use the intelligent genetic method to inherit its maximum and minimum values.

[0040] According to the above aspects and any possible implementation, an implementation is further provided, wherein the step of evaluating the reliability of elastohydrodynamic lubrication according to the curve comprises:

[0041] The reliability of EHL is evaluated based on the distance between the cumulative credibility function curve and the cumulative likelihood function curve.

[0042] According to a second aspect of the present disclosure, there is provided a sliding bearing oil film lubrication reliability assessment device, comprising:

[0043] A joint basic credibility allocation function construction module is used to execute step S1: to construct a joint identification framework, a joint focal element and a joint basic credibility allocation function of a multidimensional uncertain variable according to the input multidimensional uncertain variable parameters, and to determine the center point of the uncertainty domain;

[0044] A minimum film thickness limit state function construction module is used to execute step S2: establish a minimum film thickness limit state function according to a minimum oil film thickness equation of a sliding bearing and a preset minimum oil film thickness threshold, calculate a function value of a center point of an uncertainty domain according to the minimum film thickness limit state function, and determine a reliable domain of oil film lubrication safety in combination with lubrication performance requirements;

[0045] An index acquisition module is used to execute step S3: iteratively calculate the minimum oil film thickness of the sliding bearing through the line contact elastohydrodynamic lubrication equation, and solve the design verification point and non-probabilistic reliability index under the preset minimum oil film thickness threshold through a numerical optimization algorithm based on the minimum film thickness limit state function;

[0046] A judgment module is used to execute step S4: determine the joint focal element that does not require extreme value analysis and its credibility and plausibility, and determine the joint focal element that requires extreme value analysis according to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain;

[0047] The credibility and plausibility acquisition module is further used to execute step S5: inherit the maximum and minimum values ​​of the joint focal element requiring extreme value analysis based on the intelligent genetic method, and determine the credibility and plausibility under the minimum oil film thickness threshold according to the maximum and minimum values ​​and the credibility and plausibility of the joint focal element not requiring extreme value analysis;

[0048] The credibility and plausibility acquisition module is further used to execute step S6: changing the preset minimum oil film thickness threshold, cyclically executing the above steps S3 to S5 until the cycle reaches a preset number of times, and obtaining the credibility and plausibility under each minimum oil film thickness threshold;

[0049] The lubrication reliability evaluation module is used to execute step S7: according to the credibility and likelihood under each minimum oil film thickness threshold, obtain the cumulative credibility function curve and the cumulative likelihood function curve, and evaluate the reliability of elastohydrodynamic lubrication according to the curves.

[0050] According to a third aspect of the present disclosure, an electronic device is provided, which includes a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, the method described above is implemented.

[0051] According to a fourth aspect of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the method described above is implemented.

[0052] Compared with the prior art, the present invention achieves the following beneficial effects:

[0053] The present invention uses the focal element reduction technology to construct the auxiliary region, and excludes the focal elements that do not need to be subjected to the minimum film thickness extreme value analysis according to the relationship between the uncertainty domain and the reliable domain, thereby greatly reducing the computational cost of the wind power sliding bearing lubrication reliability analysis. In addition, the intelligent genetic method is used to perform extreme value analysis on the focal elements that fall outside the auxiliary region, further reducing the number of calculations of the elastohydrodynamic lubrication limit state function of the inclined journal bearing, and improving the efficiency of solving the plausibility and credibility.

[0054] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, among which:

[0056] Figure 1 A flow chart of a method for evaluating the reliability of oil film lubrication of a sliding bearing according to an embodiment of the present disclosure is shown;

[0057] Figure 2 A schematic diagram of an extreme value analysis of a minimum film thickness limit state function on each joint focal element according to an embodiment of the present disclosure is shown;

[0058] Figure 3 The standardized evidence variables according to the embodiment of the present disclosure are shown. Schematic diagram of standard space;

[0059] Figure 4 A schematic diagram of constructing an auxiliary area according to an embodiment of the present disclosure is shown;

[0060] Figure 5 A flow chart of elastohydrodynamic lubrication reliability analysis based on focal element reduction technology and intelligent genetic method according to an embodiment of the present disclosure is shown;

[0061] Figure 6 A schematic diagram showing the influence of various uncertain variables on the minimum oil film thickness according to an embodiment of the present disclosure is shown;

[0062] Figure 7 A schematic diagram of credibility and plausibility under a 4-segment BPA structure for uncertain variables according to an embodiment of the present disclosure is shown;

[0063] Figure 8 A schematic diagram showing the effect of the reliability index on the reduction of the focal element according to an embodiment of the present disclosure is shown;

[0064] Fig. 9 A focus element number analysis statistical diagram without extreme value analysis according to an embodiment of the present disclosure is shown;

[0065] Fig.10 A block diagram of a sliding bearing oil film lubrication reliability assessment device according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0067] In addition, the term "and / or" in this article is only a description of the association relationship between the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0068] The specific implementation of a sliding bearing oil film lubrication reliability assessment method provided by the present disclosure is described below in conjunction with the accompanying drawings.

[0069] Embodiment 1: Figure 1 The figure is a flow chart of a method for evaluating the reliability of oil film lubrication of a sliding bearing disclosed in the present invention, the method comprising:

[0070] Step S1: According to the input multidimensional uncertain variable parameters, a joint identification framework, a joint focal element and a joint basic credibility allocation function of the multidimensional uncertain variables are constructed, and the center point of the uncertainty domain is determined.

[0071] In some embodiments, in the evidence theory model, the multi-source uncertain variable X is described by a basic credibility distribution of a series of discrete intervals (focal elements), and the credibility Bel and the plausibility Pl are the upper and lower probability boundaries of the focal element, which jointly describe the lubrication reliability. For multidimensional uncertain variables, the identification framework and basic credibility distribution function of a single uncertain variable parameter can be constructed first, and then based on the identification framework and basic credibility distribution function of a single uncertain variable parameter, the joint identification framework, joint focal element and joint basic credibility distribution function of the multidimensional uncertain variables can be determined using the Dempster and other evidence synthesis rules.

[0072] In this embodiment, statistical methods or probability distribution models are used to describe uncertainty, such as normal distribution, uniform distribution or other applicable probability density functions, to determine multidimensional uncertain variable parameters including load, elastic modulus, rheological parameters, rotation speed and other parameters.

[0073] In some embodiments, the mean or expected value of the probability distribution of each uncertain variable is used as the center point of the uncertainty domain. .

[0074] In the existing calculation method, it is necessary to perform extreme value analysis on each joint focal element to obtain the maximum and minimum values ​​of the minimum film thickness, such as Figure 2 As shown, whether the joint focal element is included in the credibility and plausibility is determined according to the relationship between the obtained maximum and minimum values ​​and the given minimum oil film thickness threshold. The present disclosure will use focal element reduction technology to construct an auxiliary area. According to the relationship between the uncertainty domain and the reliable domain, the focal element that completely falls in the auxiliary area does not need to be analyzed for the minimum film thickness extreme value, thereby greatly reducing the computational cost of the elastohydrodynamic lubrication reliability analysis of wind power sliding bearings.

[0075] Step S2: Establish a minimum film thickness limit state function according to the minimum oil film thickness equation of the sliding bearing and a preset minimum oil film thickness threshold, calculate the function value of the center point of the uncertainty domain according to the minimum film thickness limit state function, and determine the reliable domain of oil film lubrication safety in combination with the lubrication performance requirements.

[0076] In some embodiments, the minimum film thickness limit state function is:

[0077] (1)

[0078] in, is the preset minimum oil film thickness threshold; It is the minimum oil film thickness calculated for the sliding bearing under a certain state; To express it as a multidimensional uncertain variable, the oil film lubrication safety and reliability domain is determined according to the lubrication performance requirements as .

[0079] In some embodiments, the mean or expected value of the probability distribution of each uncertain variable is used as the center point of the uncertainty domain. If the domain center is not determined The origin is 0, and the limit state function value of the center point of the uncertainty domain can be calculated based on the minimum film thickness limit state function. .

[0080] Step S3: Iteratively calculate the minimum oil film thickness of the sliding bearing through the line contact elastohydrodynamic lubrication equation, and based on the minimum film thickness limit state function, solve the design verification points and non-probabilistic reliability indicators under the preset minimum oil film thickness threshold through a numerical optimization algorithm.

[0081] In some embodiments, the minimum oil film thickness can be used to determine the lubrication state of the sliding bearing, and is the basis for evaluating the lubrication reliability. The minimum thickness of the sliding bearing oil film is affected by many factors, including bearing material, hardness, operating temperature, working load, etc., and nowadays, synthetic lubricants are widely used, which often exhibit significant non-Newtonian characteristics, making the rheological behavior of lubricants an important factor in lubrication design and research. The lubricant selected in the present disclosure is based on the constitutive equation of the Ostwald model, and the main parameter affecting the lubrication characteristics of the lubricant is the rheological index. When considering multiple factors, the minimum oil film thickness formula is Has the following form:

[0082] (2)

[0083] In the formula, is a constant; is the shear elastic modulus of the material, is the pressure coefficient in the viscosity-pressure formula, is the comprehensive elastic modulus of the material, ,in , is the elastic modulus of the corresponding surface material, , is the Poisson’s ratio of the surface material; is the entrainment velocity of the two contact surfaces, is the average surface velocity, is the comprehensive curvature radius of the surface, the apparent viscosity of the lubricant ,in is the consistency index, is the shear rate, is the rheological parameter; is the load parameter, is the load; is the empirical formula index.

[0084] When the wind turbine gearbox sliding bearing is subjected to a sudden increase in heavy load, the centerline of the journal is no longer parallel to the centerline of the bearing due to the weight of the journal itself, the deformation of the bearing seat and the assembly error, resulting in a certain degree of inclination. The oil film pressure on both sides of the axial center plane is asymmetrically distributed, and the maximum oil film pressure gradually moves toward the axial end face. The greater the inclination angle, the more serious the deviation. The oil film thickness is not only related to the circumferential angle, but also to the circumferential angle. It is also a function of the shaft length z. The oil film thickness on each section of the bearing axial direction is not the same, and the oil film thickness on the far end face is much greater than that on the near end face. The oil film thickness of heavy-duty wind turbine sliding bearings is more sensitive to the influence of inclination, causing contact or even wear of the bearing edges, a significant reduction in the contact area, a sharp decrease in the lubricating film thickness, and a significant increase in contact pressure and shear stress, which causes the lubrication mechanism to change from full film lubrication to mixed lubrication or boundary lubrication, similar to a curvature radius of The lubricated contact between the elastic cylinder and the semi-infinite rigid plane is shown in Figure 1. In this process, the basic characteristics of elastohydrodynamic lubrication under strong sudden change heavy load inclined journal, such as the load-bearing capacity of the lubricating film, pressure distribution and film thickness ratio, all show similar characteristics to those of line contact elastohydrodynamic lubrication. Therefore, the minimum film thickness of elastohydrodynamic lubrication under strong sudden change heavy load inclined journal can be calculated based on the theory of line contact elastohydrodynamic lubrication.

[0085] The basic equations of line contact elastohydrodynamic lubrication include: Reynolds equation, film thickness equation, deformation equation, viscosity-pressure equation, density-pressure equation and load balance equation:

[0086] ; (3)

[0087] in, represents the coordinate along the center line of the contact area, Indicates the density of lubricating oil, Indicates the oil film thickness, Indicates the dynamic viscosity of lubricating oil, Indicates the oil film pressure, It represents the entrainment velocity of the two contact surfaces; represents the minimum oil film thickness, , are the starting and ending position coordinates of the contact area, is the integration variable, is the integration constant, is the load per unit width.

[0088] like Figure 5 As shown in the figure, the elastic deformation in the viscosity-pressure equation and the film thickness equation varies with pressure. Therefore, the general practice is to first give an initial pressure distribution (Hertz contact pressure) to calculate the film thickness and viscosity values, and then substitute it into the Reynolds equation to solve the new pressure distribution, and continuously iterate and correct the previous pressure distribution, calculate the elastic deformation, and change the film thickness. The pressure obtained must meet the load balance condition until the pressure difference obtained by the two iterations is very close, and the iteration ends. In this way, the final pressure distribution and the minimum oil film thickness including elastic deformation are obtained.

[0089] In some embodiments, based on the minimum film thickness limit state function, the design verification point and the non-probabilistic reliability index under the preset minimum oil film thickness threshold are solved by a numerical optimization algorithm, which can be solved by the optimization problem shown in formula (4):

[0090] (4)

[0091] in, , , , For all the multi-source uncertain variable loads in the focal element , elastic modulus , rheological parameters ,speed Projected to Standardized evidence variables generated in standard space. is the original minimum film thickness limit state function The normalized function is transformed to the standard space.

[0092] During the solution process, you can select an algorithm suitable for constrained optimization problems, such as sequential quadratic programming (SQP) or Lagrange multiplier method, run the optimization algorithm, and iterate until the termination condition is met. In this process, find the problem that satisfies Design verification points of conditions , the design verification point Corresponding It is a non-probabilistic reliability index.

[0093] Step S4: According to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain, determine the joint focal element that does not require extreme value analysis and its credibility and plausibility, and determine the joint focal element that requires extreme value analysis.

[0094] like Figure 3 As shown in the figure, according to the relationship between the uncertainty domain and the reliability domain, four situations are used to judge whether the joint focal element needs to be analyzed for the minimum film thickness extreme value. When it is greater than 1, it indicates that the uncertainty domain and the minimum film thickness limit state surface are completely separated, and The entire uncertainty domain It is completely within the reliable domain, so the focal element in this area does not need to be analyzed for the minimum film thickness extreme value. All focal elements in the and plausibility ,Right now When non-probabilistic reliability indicators When it is greater than 1, it indicates that the uncertainty domain and the minimum film thickness limit state surface are completely separated, and The entire uncertainty domain falls completely within the failure domain, so all uncertainty domains All focal elements in the and plausibility ,Right now . This significantly reduces the number of joint focal elements that require minimum film thickness extreme value analysis. This greatly reduces the computational cost of elastohydrodynamic lubrication reliability analysis. Specifically, it includes the following four cases:

[0095] (a) If , then no extreme value analysis is needed. ;

[0096] (b) If , then we need to perform extreme value analysis to obtain and ;

[0097] (c) If , then we need to perform extreme value analysis to obtain and ;

[0098] (d) If , then no extreme value analysis is needed. .

[0099] in, is a non-probabilistic reliability index, is the limit state function value at the center of the uncertainty domain, For credibility, is the plausibility. is a non-probabilistic reliability index, is the limit state function value at the center of the uncertainty domain, For credibility, For the degree of authenticity.

[0100] In addition, when or When , it means that the uncertainty domain intersects with the minimum film thickness limit state surface, which can be expressed as Figure 4 Design verification points shown An auxiliary region H is constructed to reduce the number of focal elements that need to be analyzed for extreme values. The focal elements that fall completely in the auxiliary region H do not need to be analyzed for extreme values, and their basic credibility allocation BPA is directly included in the credibility and plausibility, which can further effectively reduce the computational cost of lubrication reliability analysis. However, extreme value analysis is required for some focal elements that do not fall completely in the auxiliary region.

[0101] Step S5: Generate the maximum and minimum values ​​of the joint focal element requiring extreme value analysis based on the intelligent genetic method, and determine the credibility and plausibility under the minimum oil film thickness threshold according to the credibility and plausibility of the maximum and minimum values ​​and the joint focal element not requiring extreme value analysis.

[0102] When performing extreme value analysis on this part of the focal element, repeated extreme value analysis will occur on the same focal element under different oil film thickness thresholds. Calling a large number of time-consuming extreme value analysis to calculate the minimum film thickness of elastohydrodynamic lubrication under strong mutation and heavy load inclined journals is computationally expensive for actual engineering. When the present invention requires extreme value analysis for some focal elements that do not completely fall in the auxiliary area, an intelligent genetic method is introduced to first store the maximum and minimum values ​​of the focal elements that have undergone extreme value analysis. When performing reliability analysis on the next minimum oil film thickness threshold, focal element search is first performed on some focal elements that do not completely fall in the auxiliary area. If there are identical focal elements, their maximum and minimum values ​​are inherited to avoid repeated extreme value analysis on the same focal element, thereby further reducing the number of calculations of the extreme value analysis of the minimum film thickness of the elastohydrodynamic lubrication of the inclined journal bearing, and improving the efficiency of solving the similarity and credibility.

[0103] In some embodiments, according to the maximum and minimum values ​​and the credibility and plausibility of the joint focal element without extreme value analysis, the credibility and plausibility under the minimum oil film thickness threshold are determined, specifically including:

[0104] a) For joint focal elements that do not require extreme value analysis, their known credibility can be directly used and plausibility ,Right now or ;

[0105] b) For the joint focal element that does not require extreme value analysis, the credibility is updated according to the maximum and minimum values ​​of the joint focal element obtained. and plausibility , specifically:

[0106] If the minimum value of the joint focal element is within the reliable domain, the joint focal element is completely within the reliable domain, and the basic credibility distribution of the joint focal element is calculated according to the joint basic credibility distribution function, and the credibility is updated according to the basic credibility distribution of the joint focal element. and plausibility .

[0107] If the minimum value of the joint focal element is not in the reliable domain but the maximum value is in the reliable domain, the basic credibility distribution of the joint focal element is calculated according to the joint basic credibility distribution function, and only the plausibility is updated according to the basic credibility distribution of the joint focal element. ;

[0108] If the maximum value of the joint focal element is not within the reliable domain, the credibility is not updated. and plausibility .

[0109] Step S6: changing the preset minimum oil film thickness threshold, and cyclically executing the above steps S3 to S5 until the cycle reaches a preset number of times, and obtaining the credibility and likelihood under each minimum oil film thickness threshold.

[0110] In some embodiments, when the evidence theory measures uncertainty, it is necessary to perform reliability analysis on a large number of minimum oil film thickness thresholds. Therefore, it is necessary to execute the above steps S3-S5 cyclically to obtain the credibility and plausibility under each minimum oil film thickness threshold until the cycle reaches a preset number of times.

[0111] Step S7: according to the credibility and likelihood under each minimum oil film thickness threshold, a cumulative credibility function curve and a cumulative likelihood function curve are obtained, and the reliability of the elastohydrodynamic lubrication is evaluated according to the curves.

[0112] In some embodiments, the credibility and plausibility at each minimum oil film thickness threshold are connected to obtain a cumulative credibility function curve and a cumulative plausibility function curve for evaluating the reliability of elastohydrodynamic lubrication. At the same time, the distance between the cumulative credibility function curve and the cumulative plausibility function curve reflects the uncertainty of the reliability of elastohydrodynamic lubrication. If the distance is less than the preset distance, it proves that the reliability is high, otherwise, it proves that the reliability is low.

[0113] According to the embodiments of the present disclosure, the following technical effects are achieved:

[0114] (1) The auxiliary area is constructed by applying the focal element reduction technology. The focal elements that fall completely in the auxiliary area do not need to be subjected to the minimum film thickness extreme value analysis, thereby greatly reducing the computational cost of the elastohydrodynamic lubrication reliability analysis of wind turbine sliding bearings.

[0115] (2) An intelligent genetic method is used to perform extreme value analysis on the focal elements that fall outside the auxiliary area to avoid repeated extreme value analysis on the same focal element, further reducing the number of calculations for the extreme value analysis of the minimum film thickness of the elastohydrodynamic lubrication of the inclined journal bearing.

[0116] Example 2: In this example, it is assumed that the diameter of the sliding bearing and the shaft is 20.5 mm, the roller radius generated by the deformation of the bearing is 1.5 mm, the rolling-slip ratio is 0.67, and the initial viscosity is 0.0256. The iteration coefficient C1 is 0.5. The sensitivity analysis of each uncertain variable is carried out according to the calculation method of the minimum film thickness of the elastohydrodynamic lubrication under the strong sudden change and heavy load inclined journal. Figure 6 It can be seen that the load, comprehensive elastic modulus, rheological parameters and rotation speed have a significant impact on the minimum oil film thickness of the sliding bearing, showing a nonlinear effect.

[0117] According to the sensitivity analysis, the intervals of four uncertain variables are set, the load interval is [100,350]N, the comprehensive elastic modulus interval is [100,250]GPa, the rheological parameter interval is [0.5,0.9], and the tangential velocity is [0.35,0.95]m / s. It is assumed that the uncertain variables all obey the normal distribution and the coefficient of variation is 0.1. The BPA of each variable is obtained by using the probability distribution integral on the corresponding interval. Table 1 shows the BPA structure of each variable taking 4 sub-intervals.

[0118] Table 1 BPA structure with 4 subintervals for each variable

[0119]

[0120] By changing the minimum oil film thickness threshold from 0.001um to 0.6um, a series of credibility Bel and plausibility pl of elastohydrodynamic lubrication reliability can be obtained, such as Figure 7 As shown, with the minimum oil film thickness threshold As the value increases, the reliability of elastohydrodynamic lubrication of sliding bearings under strong sudden change and heavy load inclined journals gradually decreases.

[0121] The efficiency index is used to evaluate the effect of focal element reduction technology on the computational cost of elastohydrodynamic lubrication reliability analysis of sliding bearings with strong sudden changes and heavy loads on inclined journals. The efficiency index is defined as the ratio of the number of focal elements that do not require extreme value analysis to the total number of focal elements in the uncertainty domain. In this case, each variable takes a BPA structure with 4 subintervals, and the total number of focal elements in the uncertainty domain under a minimum oil film thickness threshold is 4×4×4×4=256. That is, 256 extreme value analyses must be calculated under a minimum oil film thickness threshold. In this case, 106 minimum oil film thickness thresholds were taken, and there were a total of 256×106=27136 extreme value analyses. Figure 8 It shows that the introduction of focal element reduction technology constructs auxiliary areas according to the non-probabilistic reliability index η and the design verification points to reduce the number of focal elements that need to be analyzed for extreme values ​​and the resulting efficiency. It can be seen that as the non-probabilistic reliability index increases, the number of focal elements that do not need to be analyzed for extreme values ​​at each threshold increases, and the efficiency also increases accordingly. Since the non-probabilistic reliability index in this case is relatively low, with a maximum of only 0.18, it shows that the elastic hydrodynamic lubrication of the sliding bearing is prone to failure under the strong sudden change of the heavy-loaded inclined journal. The calculation of credibility and plausibility is for cases (c) and (d). The reliability analysis of conventional evidence theory will perform extreme value analysis on all focal elements, and the computational cost is very high for this actual working condition. In this case, under this low non-probabilistic reliability index, there is also an efficiency of nearly 8%, indicating that this method can effectively reduce the computational cost for actual engineering.

[0122] The total number of focal elements that do not require extreme value analysis is statistically generated by the introduction of focal element reduction technology and intelligent genetic technology. Fig. 9 It shows that the total number of focal elements that do not need to be analyzed for extreme values ​​in this case is 1,600, and the total number of focal elements that do not need to be repeated for extreme value analysis is nearly 25,000 due to intelligent genetic technology. Nearly 92% of the repeated calculations of extreme value analysis are avoided. This shows that this method can effectively improve the reliability analysis of oil film lubrication.

[0123] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present disclosure is not limited by the described order of actions, because according to the present disclosure, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present disclosure.

[0124] The above is an introduction to the method embodiment. The following is a further explanation of the scheme disclosed in the present invention through an apparatus embodiment.

[0125] Fig.10 FIG. 1 is a block diagram of a sliding bearing oil film lubrication reliability evaluation device 110 according to an embodiment of the present disclosure. Fig.10 As shown, the device 110 includes:

[0126] The joint basic credibility allocation function construction module 111 is used to execute step S1: to construct a joint identification framework, a joint focal element and a joint basic credibility allocation function of the multidimensional uncertain variables according to the input multidimensional uncertain variable parameters, and to determine the center point of the uncertainty domain;

[0127] The minimum film thickness limit state function construction module 112 is used to execute step S2: establish a minimum film thickness limit state function according to the minimum oil film thickness equation of the sliding bearing and a preset minimum oil film thickness threshold, calculate the function value of the center point of the uncertainty domain according to the minimum film thickness limit state function, and determine the reliable domain of oil film lubrication safety in combination with the lubrication performance requirements;

[0128] The index acquisition module 113 is used to execute step S3: iteratively calculate the minimum oil film thickness of the sliding bearing through the line contact elastohydrodynamic lubrication equation, and solve the design verification point and non-probabilistic reliability index under the preset minimum oil film thickness threshold through a numerical optimization algorithm based on the minimum film thickness limit state function;

[0129] The judgment module 114 is used to execute step S4: determine the joint focal element that does not require extreme value analysis and its credibility and plausibility, and determine the joint focal element that requires extreme value analysis according to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain;

[0130] The credibility and plausibility acquisition module 115 is further used to execute step S5: inherit the maximum and minimum values ​​of the joint focal element requiring extreme value analysis based on the intelligent genetic method, and determine the credibility and plausibility under the minimum oil film thickness threshold according to the maximum and minimum values ​​and the credibility and plausibility of the joint focal element not requiring extreme value analysis;

[0131] The credibility and plausibility acquisition module 115 is further used to execute step S6: changing the preset minimum oil film thickness threshold, cyclically executing the above steps S3 to S5 until the cycle reaches a preset number of times, and obtaining the credibility and plausibility under each minimum oil film thickness threshold;

[0132] The lubrication reliability evaluation module 116 is used to execute step S7: according to the credibility and likelihood under each minimum oil film thickness threshold, obtain a cumulative credibility function curve and a cumulative likelihood function curve, and evaluate the elastohydrodynamic lubrication reliability according to the curves.

[0133] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of this disclosure can be achieved, and this document is not limited here.

[0134] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A method for evaluating the reliability of oil film lubrication of a sliding bearing, characterized in that: include: Step S1: According to the input multidimensional uncertain variable parameters, a joint identification framework, a joint focal element and a joint basic credibility allocation function of the multidimensional uncertain variables are constructed, and the center point of the uncertainty domain is determined; Step S2: establishing a minimum film thickness limit state function according to the minimum oil film thickness equation of the sliding bearing and a preset minimum oil film thickness threshold, calculating a function value of the center point of the uncertainty domain according to the minimum film thickness limit state function, and determining a reliable domain of oil film lubrication safety in combination with lubrication performance requirements; Step S3: iteratively calculating the minimum oil film thickness of the sliding bearing by the line contact elastohydrodynamic lubrication equation, and solving the design verification point and non-probabilistic reliability index under the preset minimum oil film thickness threshold by a numerical optimization algorithm based on the minimum film thickness limit state function; Step S4: determining the joint focal element that does not require extreme value analysis and its credibility and plausibility, and determining the joint focal element that requires extreme value analysis, according to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain; Step S5: inheriting the maximum and minimum values ​​of the joint focal element requiring extreme value analysis based on an intelligent genetic method, and determining the credibility and plausibility under the minimum oil film thickness threshold according to the credibility and plausibility of the maximum and minimum values ​​and the joint focal element not requiring extreme value analysis; If the joint focal element falls completely within the auxiliary region, there is no need to perform extreme value analysis, and its basic credibility allocation is directly included in the credibility and plausibility under the current minimum oil film thickness threshold; If the joint focal element does not completely fall within the auxiliary area, an extreme value analysis of the joint focal element is required, including: First, determine whether the joint focal element has been subjected to extreme value analysis. If it has been done, then inherit its maximum and minimum values. Otherwise, calculate the maximum and minimum values ​​of the minimum film thickness of the focal element according to the minimum film thickness limit state function, and use the intelligent genetic method to inherit its maximum and minimum values. The method of calculating the maximum and minimum values ​​of the minimum film thickness of the focal element according to the minimum film thickness limit state function and inheriting the maximum and minimum values ​​by the intelligent genetic method includes: When extreme value analysis must be performed on the focal elements that do not completely fall in the auxiliary area, an intelligent genetic method is introduced to first store the maximum and minimum values ​​of the focal elements that have undergone extreme value analysis. When performing reliability analysis on the next minimum oil film thickness threshold, focal element search is first performed on the focal elements that do not completely fall in the auxiliary area. If there are identical focal elements, their maximum and minimum values ​​are inherited to avoid repeated extreme value analysis on the same focal element, thereby further reducing the number of calculations for the extreme value analysis of the minimum film thickness of the elastohydrodynamic lubrication of the inclined journal bearing and improving the efficiency of solving the similarity and credibility. According to the credibility and plausibility of the maximum and minimum values ​​and the joint focal element without extreme value analysis, the credibility and plausibility under the minimum oil film thickness threshold are determined, specifically including: a) For joint focal elements that do not require extreme value analysis, their known credibility can be directly used and plausibility ,Right now or ; b) For the joint focal element that does not require extreme value analysis, the credibility is updated according to the maximum and minimum values ​​of the joint focal element obtained. and plausibility , specifically: If the minimum value of the joint focal element is within the reliable domain, the joint focal element is completely within the reliable domain, and the basic credibility distribution of the joint focal element is calculated according to the joint basic credibility distribution function, and the credibility is updated according to the basic credibility distribution of the joint focal element. and plausibility ; If the minimum value of the joint focal element is not in the reliable domain but the maximum value is in the reliable domain, the basic credibility distribution of the joint focal element is calculated according to the joint basic credibility distribution function, and only the plausibility is updated according to the basic credibility distribution of the joint focal element. ; If the maximum value of the joint focal element is not within the reliable domain, the credibility is not updated. and plausibility ; Step S6: changing the preset minimum oil film thickness threshold, cyclically executing the above steps S3 to S5 until the cycle reaches a preset number of times, and obtaining the credibility and plausibility under each minimum oil film thickness threshold; Step S7: according to the credibility and likelihood under each minimum oil film thickness threshold, a cumulative credibility function curve and a cumulative likelihood function curve are obtained, and the reliability of the elastohydrodynamic lubrication is evaluated according to the curves.

2. The method according to claim 1, characterized in that The method of constructing a joint identification framework, a joint focal element and a joint basic credibility allocation function of multidimensional uncertain variables according to the input multidimensional uncertain variable parameters includes: According to the input multi-dimensional uncertain variable parameters, an identification framework and a basic credibility distribution function of a single uncertain variable parameter are constructed, wherein the multi-dimensional uncertain variable parameters include load, elastic modulus, rheological parameter and rotation speed; Based on the identification framework and basic credibility allocation function of single uncertain variable parameters, the joint identification framework, joint focal element and joint basic credibility allocation function of multi-dimensional uncertain variables are determined.

3. The method according to claim 1, characterized in that The minimum oil film thickness of the sliding bearing is calculated iteratively through the line contact elastohydrodynamic lubrication equation, including: Preprocess the input multi-dimensional uncertain variable parameters; Calculate the node film thickness, density, viscosity and node elastic deformation value based on the preprocessed data; The Reynolds equation is iteratively solved according to the node film thickness, density, viscosity and node elastic deformation value until the pressure value converges, and the minimum oil film thickness of the sliding bearing is output.

4. The method according to claim 1, characterized in that: The minimum film thickness limit state function is: ； in, is the preset minimum oil film thickness threshold; It is the minimum oil film thickness calculated for the sliding bearing under a certain state; is represented as a multidimensional uncertain variable.

5. The method according to claim 4, characterized in that The safe and reliable domain of oil film lubrication determined according to the minimum film thickness limit state function combined with the lubrication performance requirements is: .

6. The method according to claim 1, characterized in that The design verification point and non-probabilistic reliability index under the preset minimum oil film thickness threshold are solved based on the following formula: ； in, , , , are the loads in all focal elements respectively , elastic modulus , rheological parameters ,speed Projected to The standardized evidence variables generated by the standard space, is the minimum film thickness limit state function The normalized function is transformed to the standard space.

7. The method according to claim 1, characterized in that According to the non-probabilistic reliability index, the design verification point, and the relationship between the function value of the center point of the uncertainty domain and the reliable domain, the joint focal element that does not require extreme value analysis and its credibility and plausibility are determined, and the joint focal element that requires extreme value analysis is determined, including: like , then no extreme value analysis is needed. ; like , then we need to perform extreme value analysis to obtain and ; like , then we need to perform extreme value analysis to obtain and ; like , then no extreme value analysis is needed. ; in, is a non-probabilistic reliability index, is the center point of the uncertainty domain, is the function value at the center of the uncertainty domain, For credibility, For the degree of authenticity.

8. The method according to claim 7, characterized in that The method further comprises: when or When the design verification points are used, auxiliary areas are made; If the joint focal element falls completely within the auxiliary region, there is no need to perform extreme value analysis, and its basic credibility allocation is directly included in the credibility and plausibility under the current minimum oil film thickness threshold; If the joint focal element does not completely fall within the auxiliary area, an extreme value analysis of the joint focal element is required.

9. The method according to claim 1, characterized in that: The step of evaluating the reliability of elastohydrodynamic lubrication according to the curve comprises: The reliability of EHL is evaluated based on the distance between the cumulative credibility function curve and the cumulative likelihood function curve.

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