Fatigue analysis method for bolts of wind power gear box

Abstract

The invention relates to the technical field of wind power gear box structure design, in particular to a wind power gear box bolt fatigue analysis method which comprises the following steps: establishing a bolt connection analysis model; analyzing finite element analysis model calculation under a unit working condition, and obtaining an internal force curve of the bolt under different loads; based on a stress calculation formula, the stress time sequence of the multiple point positions of the bolt is calculated according to the internal force curve; a rain flow counting algorithm is used for counting stress amplitudes and cycle times of a plurality of point positions of the bolt; an SN curve is established, and accumulated damage is calculated based on the stress amplitude and the number of cycles; the maximum cumulative damage is evaluated. According to the scheme, the fatigue damage conditions of the bolt under various different loads can be comprehensively analyzed, the part, most prone to fatigue damage, of the bolt and the service life of the bolt are evaluated more accurately and comprehensively, the structural design strength of the bolt set of the wind power gear box is improved, and stable operation of a wind turbine generator is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of wind turbine gear box structure design, and in particular to a fatigue analysis method for bolts of a wind turbine gear box. Background Art

[0002] As one of the key components of large wind turbines, wind turbine gearboxes play the role of torque conversion and speed increase in terms of function, and play the role of connecting the wind wheel and the generator in terms of mechanical structure. Since wind turbines are in harsh outdoor environments for a long time, the unpredictable wind force directly leads to complex and changeable load conditions on the gearbox. Therefore, the strength of the gearbox is crucial to the normal operation of the entire wind turbine, which also puts higher requirements on the reliability of the gearbox structure design.

[0003] As the most important connecting element of the gearbox, high-strength bolts play the role of connection, positioning and sealing, and have an important impact on the safety and reliability of the gearbox. In wind farms, the entire wind turbine stops operating due to the fracture and failure of the gearbox connection bolt group, causing huge losses. Therefore, analyzing the different loading conditions of the box connection bolt group that is subjected to complex and random loads will help improve the structural strength of the gearbox to ensure the stable operation of the wind turbine in complex and changeable field environments.

[0004] Conventional bolt fatigue analysis methods usually analyze the reaction force after the bolt is subjected to load. For example, the prior art "A planetary gearbox bolt analysis method" (publication number: CN111046512B) analyzes the reaction force of the bolt when the gears inside the gearbox are in different meshing states, thereby calculating the fatigue damage of the bolt.

[0005] The existing technology only analyzes the support reaction force of the bolt. The support reaction force is the reaction force generated by the bolt when it is subjected to an external force. It is the force generated on the contact boundary between the bolt and the gear box body. However, since the loads on the wind power gearbox during operation are very complex, the internal stress of the bolt will also be complex and changeable under different working conditions. This will make the bolts that are most prone to fatigue damage in the gearbox during operation not necessarily located at the position with the strongest support reaction force. If only the influence of the support reaction force is considered, the overall strength of the bolt group cannot be accurately evaluated. The evaluation result may cause the bolts to be insufficiently strong during structural design and processing, resulting in the bolt group breaking and failure during the operation of the gearbox after actual installation, thereby causing the wind turbine to stop operating. Summary of the invention

[0006] The present invention provides a fatigue analysis method for wind turbine gearbox bolts, which can solve the problem that the gearbox bolt analysis method in the prior art cannot accurately evaluate the bolt strength, resulting in insufficient strength of the bolts during structural design and processing, causing the bolts to break and fail in actual work, and further causing the wind turbine to shut down.

[0007] The present application provides the following technical solution: a fatigue analysis method for bolts of a wind turbine gearbox, comprising the following steps:

[0008] Establish a bolt connection analysis model; analyze the finite element analysis model calculation under unit working conditions to obtain the internal force curve of the bolt under different loads; calculate the stress time series of multiple points on the bolt according to the internal force curve based on the stress calculation formula; use the rain flow counting algorithm to count the stress amplitude and number of cycles at multiple points on the bolt; establish the SN curve, and calculate the cumulative damage based on the stress amplitude and number of cycles; evaluate the maximum cumulative damage.

[0009] Invention concept:

[0010] The conventional method for fatigue analysis of bolts of wind power gearboxes is as described in the above background technology, but the inventors conducted simulation detection and analysis with the above scheme. During the simulation analysis, it was found that the bolts were prone to fracture failure, and the fracture locations of the bolts in various parts of the gearbox were different. Therefore, the inventors re-verified the calculation data and found that the data and formula calculations were normal, so they conducted simulation detection again, but the problem of bolt fracture failure still occurred, and the location of the bolt failure was random, while the bolts themselves were standard parts and this phenomenon should not occur. The inventors continued to think that the applied load first acted on the gearbox, and then the gearbox transferred the load to the bolts. Therefore, the inventors suspected that the gearbox might cause this effect, and the structure of the gearbox was extremely complex, the shape was extremely irregular, and its stiffness was uneven, so that the deformation of each part was different when subjected to load. Therefore, when the load was transferred to the bolts through the gearbox, the load size and direction distribution of the bolts were uneven. Therefore, it was difficult to lock the reaction force of the bolts when they were subjected to load using the analysis method in the prior art, resulting in natural inaccuracy in fatigue damage analysis. Therefore, the inventors considered that the support reaction force was manifested on the outer surface of the bolt and could not accurately evaluate the bolt strength, so they took the internal force of the bolt as the entry point and established a complete geometric analysis model, thereby completing the present invention.

[0011] Beneficial effects: This solution uses finite element analysis software to obtain the internal force curves corresponding to the bolts under multiple different working conditions. The internal force curves reflect the changes in the internal forces inside the bolts when the bolts are subjected to different loads, including size and direction, so as to calculate the stress time series of each bolt on the gearbox, and can feedback the stress changes inside the bolts in different time periods, so that the loads on the screws can be obtained more comprehensively. Then, the rain flow counting algorithm is used to simplify the complex variable loads into multiple groups of cyclic loads of different sizes, and the parts of the bolts that are subjected to the most and strongest forces under different loads can be obtained. Combined with the SN curve, the fatigue damage of the bolts under various loads can be comprehensively analyzed. Compared with the existing technology, it can more accurately and comprehensively evaluate the parts and life of the bolts that are most prone to fatigue damage, improve the structural design strength of the bolt group of the wind power gearbox, and ensure the stable operation of the wind turbine.

[0012] Furthermore, the steps for obtaining the internal force curve are as follows: extract the axial force load and two bending moment loads that the bolt is subjected to under different working conditions, perform load step calculations in the finite element analysis, output the results of each step, and finally form the internal force curve under the corresponding working condition.

[0013] Beneficial effects: Dividing the total load into steps and outputting the results of each step can better capture the internal force of the bolt during the loading process. Since the actual loads under different working conditions are different, this solution uses the interpolation method to match the loads under different working conditions to the unit load, which is conducive to a clearer feedback of the distribution relationship between the load and the internal force, thereby improving the accuracy of the analysis.

[0014] Furthermore, the stress time series calculation formula is as follows:

[0015] Stress calculation of bolt under axial force: σaxis = SForce / S equivalent area

[0016] Stress calculation of bolts under bending moment: σbend = (Mtorque / Iz)*X, σbend = (Mtorque / Iz)*Y, IZ = πD4 / 32

[0017] Where SForce is the axial force on the bolt, M_torque is the bending moment on the bolt, S equivalent area is the effective cross-sectional area of ​​the bolt, and Iz is the moment of inertia on the equivalent area of ​​the bolt.

[0018] X and Y are the distances between the force-bearing position and the center axis of the bolt. X and Y can take 8 values ​​respectively: -0, -R*sin(45°), -R, -R*sin(135°), 0, R sin(45°), R, -R*sin(135°).

[0019] Beneficial effect: The stress time series is calculated based on the internal force curve, which can provide feedback on the stress changes inside the bolt under different loads, so as to facilitate the subsequent evaluation of the fatigue strength of the bolt as a whole.

[0020] Furthermore, in the stress time series calculation, eight evaluation points are evenly selected for the cross section of the bolt, and the stress calculation formula is used to sequentially calculate the stress at each evaluation point under each working condition to obtain the stress time series of the eight evaluation points.

[0021] Beneficial effect: As a connecting part, the stress distribution on the cross section of the bolt may not be uniform when it is subjected to load. By selecting multiple evaluation points, the stress changes at different positions can be captured, so as to more accurately understand the overall stress state of the bolt.

[0022] Furthermore, before calculating the cumulative damage, the SN curve of the bolt needs to be calculated based on the DNVGL-ST-0361 standard, and the stress range ΔσR of the inflection point of the SN curve needs to be calculated. The calculation formula is as follows:

[0023]

[0024] Δσ D The stress cycle number is 5×10 6 The fatigue limit value, that is, the fatigue limit at the turning point of the curve, is expressed as:

[0025]

[0026] Calculate the infinite life cutoff point Δσ L , whose value is:

[0027]

[0028] Δσ c The number of stress cycles is 2×10 6 The fatigue limit value, Δσ c The calculation expression is as follows:

[0029] When the bolt size is less than or equal to M30:

[0030] Δσ c =DC / γ m

[0031] When the bolt size is larger than M30:

[0032] Δσ c =DC / γ m κ s

[0033] In the formula, DC represents the design fatigue safety level. According to the clear provisions of the offshore wind turbine certification specifications on the fatigue level of bolts, the design fatigue level is DC≥50.

[0034] γ m represents the material safety factor; κ s It represents the reduction factor considering the bolt size effect, which is calculated as follows:

[0035] κ s =(30 / D) 0.25

[0036] Where D is the bolt diameter. Beneficial Effect: By calculating the SN curve and its inflection point stress range, the fatigue life and safety of the bolt can be evaluated more accurately. This helps to take fatigue factors into account at the design stage, thereby avoiding safety accidents caused by fatigue fracture in actual use.

[0037] Furthermore, when calculating the cumulative damage, the stress amplitudes obtained in sequence using the rainflow counting algorithm are Δσ,

[0038] If Δσ is greater than ΔσR, use the following formula to calculate: N = N D (ΔσR / Δσ) 3

[0039] If Δσ is less than ΔσR, use the following formula: N = N D (ΔσR / Δσ) 5

[0040] Among them, N D =5*10 6

[0041] Then, the damage factor is obtained by dividing the number of cycles corresponding to the stress amplitude by N. The damage factors of the eight evaluation points are calculated and added up in the above manner to obtain the cumulative damage of the eight evaluation points on the bolt under one load.

[0042] Beneficial effects: This solution is based on the SN curve fitted by experimental data. It takes into account the nonlinear effect of stress amplitude on fatigue life through an accurate formula, thereby improving the accuracy of fatigue life prediction. It also uses the rain flow counting algorithm to effectively handle complex loads and decompose them into simple stress cycles, making the calculation process more reasonable and in line with actual working conditions. At the same time, the solution linearly adds the damage factors under different stress amplitudes, simplifying the calculation process of cumulative damage. It not only improves the reliability of the design, but also analyzes the fatigue problem of bolts more fully and accurately, ensuring that the gearbox structure can still maintain sufficient fatigue life under complex load conditions, and improving the overall safety and service life of the gearbox.

[0043] Furthermore, when evaluating the maximum cumulative damage, the cumulative damage of the bolt is calculated under each load and the maximum cumulative damage is accumulated.

[0044] Beneficial effect: Under all load conditions, finding one or several load combinations that cause the greatest cumulative damage to the bolts will help to more comprehensively analyze the potential fatigue risk points of the bolts, making it easier to take appropriate measures in the structural design stage to reduce or eliminate these risks, thereby improving the overall safety and reliability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a logic block diagram of the present invention.

[0046] Figure 2 It is the SN curve diagram of the present invention. DETAILED DESCRIPTION

[0047] The following is further described in detail through specific implementation methods:

[0048] Embodiment 1

[0049] A fatigue analysis method for bolts of a wind turbine gearbox comprises the following steps:

[0050] 1. Establish a bolt connection analysis model. Use finite element analysis software ANSYS or ABAQUS to establish a three-dimensional analysis model of the bolt connection.

[0051] 2. Analyze the finite element analysis model calculation under unit working conditions to obtain the internal force curve of the bolt under different loads. The steps for obtaining the internal force curve are as follows: extract the axial force load and two bending moment loads that the bolt is subjected to under different working conditions, perform load step calculation in the finite element analysis, divided into 10 steps, output the three internal force components of the bolt under each load step, and then match all the internal force components with the unit load, use the interpolation method to obtain the internal force size under the unit load, and fit it into the internal force curve.

[0052] 3. Based on the stress calculation formula, calculate the stress time series of multiple points of the bolt according to the internal force curve; in the stress time series calculation, select eight evaluation points evenly for the cross section of the bolt, and use the stress calculation formula to calculate the stress at each evaluation point under each working condition in turn, and obtain the stress time series of the eight evaluation points. The stress time series calculation formula is as follows:

[0053] Stress calculation of bolt under axial force: σaxis = SForce / S equivalent area

[0054] Stress calculation of bolts under bending moment: σbend = (Mtorque / Iz)*X, σbend = (Mtorque / Iz)*Y, IZ = πD4 / 32

[0055] Where SForce is the axial force on the bolt, M_torque is the bending moment on the bolt, S equivalent area is the effective cross-sectional area of ​​the bolt, and Iz is the moment of inertia on the equivalent area of ​​the bolt.

[0056] X and Y are the distances between the force-bearing position and the center axis of the bolt. X and Y can take 8 values ​​respectively: 0, -R*sin(45°), -R, -R*sin(135°), 0, R sin(45°), R, -R*sin(135°).

[0057] 4. Use the rain flow counting algorithm to count the stress amplitude and cycle times at multiple points of the bolt;

[0058] 5. Establish the SN curve and calculate the cumulative damage based on the stress amplitude and the number of cycles. Before calculating the cumulative damage, the SN curve of the bolt needs to be calculated based on the VDI2230 standard, and the stress range ΔσR of the inflection point of the SN curve needs to be calculated:

[0059]

[0060] Δσ D The stress cycle number is 5×10 6 The fatigue limit value, that is, the fatigue limit at the turning point of the curve, is expressed as:

[0061]

[0062] Calculate the infinite life cutoff point Δσ L , whose value is:

[0063]

[0064] Δσ c The number of stress cycles is 2×10 6 The fatigue limit value, Δσ c The calculation expression is as follows:

[0065] When the bolt size is less than or equal to M30:

[0066] Δσ c =DC / γ m When the bolt size is larger than M30:

[0067] Δσ c =DC / γ m κ s

[0068] In the formula, DC represents the design fatigue safety level. According to the clear provisions of the offshore wind turbine certification specifications on the fatigue level of bolts, the design fatigue level is DC≥50.

[0069] γ mrepresents the material safety factor; κ s It represents the reduction factor considering the bolt size effect, which is calculated as follows:

[0070] κ s =(30 / D) 0.25

[0071] Where D represents the bolt diameter.

[0072] When calculating the cumulative damage, the stress amplitudes obtained in sequence using the rainflow counting algorithm are Δσ.

[0073] If Δσ is greater than ΔσR, use the following formula to calculate: N = N D (ΔσR / Δσ) 3

[0074] If Δσ is less than ΔσR, use the following formula: N = N D (ΔσR / Δσ) 5

[0075] Among them, N D =5*10 6

[0076] Then, the damage factor is obtained by dividing the number of cycles corresponding to the stress amplitude by N. The damage factors of the eight evaluation points are calculated and added up in the above manner to obtain the cumulative damage of the eight evaluation points on the bolt under one load.

[0077] 6. Evaluate the maximum cumulative damage. Add up the cumulative damage of the eight evaluation points calculated under all load conditions to obtain the cumulative damage of the eight points on the bolt.

[0078] This solution uses finite element analysis software to obtain the internal force curves corresponding to the bolts under multiple different working conditions. The internal force curves reflect the changes in the internal forces inside the bolts when the bolts are subjected to different loads, including the size and direction. The stress time series of multiple points of the bolts are calculated based on this, and the stress changes at various points inside the bolts in different time periods can be fed back, so that the loads on the screws can be obtained more comprehensively. The rain flow counting algorithm is then used to simplify the complex variable loads into multiple groups of cyclic loads of different sizes, and the parts of the bolts that are subjected to the most and strongest forces under different loads can be obtained. Combined with the SN curve, the fatigue damage of the bolts under various loads can be comprehensively analyzed. Compared with the existing technology, it can more accurately and comprehensively evaluate the parts and life of the bolts that are most prone to fatigue damage, improve the structural design strength of the bolt group of the wind turbine gearbox, and ensure the stable operation of the wind turbine.

[0079] The above are only embodiments of the present invention. The invention is not limited to the fields involved in this implementation case. The common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A fatigue analysis method for bolts of wind turbine gearbox, characterized in that: The steps include: Establish a bolt connection analysis model; analyze the finite element analysis model calculation under unit working conditions to obtain the internal force curve of the bolt under different loads; calculate the stress time series of multiple points of the bolt according to the internal force curve based on the stress calculation formula; use the rain flow counting algorithm to count the stress amplitude and cycle number at multiple points of the bolt; establish the SN curve, and calculate the cumulative damage based on the stress amplitude and cycle number; Evaluate the maximum cumulative damage.

2. The fatigue analysis method for bolts of a wind turbine gearbox according to claim 1, characterized in that: The steps for obtaining the internal force curve are as follows: extract the axial force load and two bending moment loads that the bolt is subjected to under different working conditions, perform load step calculations in the finite element analysis, output the results of each step, and finally form the internal force curve under the corresponding working condition.

3. The fatigue analysis method for bolts of a wind turbine gearbox according to claim 2, characterized in that: The stress time series calculation formula is as follows: Stress calculation of bolt under axial force: σaxis = SForce / S equivalent area Stress calculation of bolts under bending moment:σbend=(Mtorque / Iz)*X,σbend=(Mtorque / Iz)*Y,IZ=πD4 / 32 Where SForce is the axial force on the bolt, M_torque is the bending moment on the bolt, S equivalent area is the effective cross-sectional area of ​​the bolt, and Iz is the moment of inertia on the equivalent area of ​​the bolt; X and Y are the distances between the force-bearing position and the center axis of the bolt. X and Y can take 8 values ​​respectively: -0, -R*sin(45°), -R, -R*sin(135°), 0, R sin(45°), R, -R*sin(135°).

4. The fatigue analysis method for bolts of a wind turbine gearbox according to claim 3 is characterized in that: In the stress time series calculation, eight evaluation points are evenly selected on the cross section of the bolt, and the stress calculation formula is used to calculate the stress at each evaluation point under each working condition in turn to obtain the stress time series of the eight evaluation points.

5. The fatigue analysis method for bolts of a wind turbine gearbox according to claim 4, characterized in that: Before calculating the cumulative damage, the SN curve of the bolt needs to be calculated based on the DNVGL-ST-0361 standard, and the stress range ΔσR of the inflection point of the SN curve needs to be calculated. The calculation formula is as follows: Δσ D The stress cycle number is 5×10 6 The fatigue limit value, that is, the fatigue limit at the turning point of the curve, is expressed as: Calculate the infinite life cutoff point Δσ L , whose value is: Δσ c The number of stress cycles is 2×10 6 The fatigue limit value, Δσ c The calculation expression is as follows: When the bolt size is less than or equal to M30: Board c =DC / γ m When the bolt size is larger than M30: Board c =DC / γ m ·k s In the formula, DC represents the design fatigue safety level. According to the clear provisions of the offshore wind turbine certification specifications on the fatigue level of bolts, the design fatigue level is DC≥50. γ m represents the material safety factor; κ s It represents the reduction factor considering the bolt size effect, which is calculated as follows: k s =(30 / D) 0.25 Where D represents the bolt diameter.

6. The fatigue analysis method for bolts of a wind turbine gearbox according to claim 5, characterized in that: When calculating the cumulative damage, the stress amplitude is obtained in sequence using the rain flow counting algorithm. The stress amplitude is Δσ. If Δσ is greater than ΔσR, use the following formula to calculate: N = N D (ΔσD / Δσ) 3 If Δσ is less than ΔσR, use the following formula: N = N D (ΔσD / Δσ) 5 Among them, N D =5*10 6 Then, the damage factor is obtained by dividing the number of cycles corresponding to the stress amplitude by N. The damage factors of the eight evaluation points are calculated and added up in the above manner to obtain the cumulative damage of the eight evaluation points on the bolt under one load.

7. A fatigue analysis method for bolts of a wind turbine gearbox according to claim 6, characterized in that: When evaluating the maximum cumulative damage, the cumulative damage of the bolt is calculated under each load and the maximum cumulative damage is accumulated.

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