On-line monitoring method and system for pre-tightening stress of blade root bolt of wind turbine generator

Abstract

An on-line monitoring method and system for pre-tightening stress of a blade root bolt of a wind turbine generator. The method comprising: step S1, on the basis of a material type of a measured bolt, calculating bolt parameters in a zero-load state; and step S2, collecting related data of the measured bolt, and calculating to obtain an axial stress of the bolt to complete monitoring. The transit time of ultrasonic longitudinal and transverse waves in the bolt is measured by using the acoustic elasticity theory, and the axial stress of the bolt is obtained by performing ratio calculation on the basis of the transit time of longitudinal and transverse waves, so that the pre-tightening force of the blade root bolt is monitored in real time. The pre-tightening force of the fastened bolt of the blade root is monitored by using a double-wave method, which reduces the complexity of measurement, and facilitates the large-scale application of engineering projects.

Description

Online monitoring method and system for pre-tightening stress of wind turbine blade root bolts Technical Field

[0001] The present invention relates to the field of bolt pre-tightening force monitoring, and in particular to an online monitoring method and system for pre-tightening stress of blade root bolts of a wind turbine generator set. Background Art

[0002] Wind turbine blades, hubs, main shafts, towers, foundations, and other major components are fastened together using high-strength bolts. Blade root bolts, in particular, are subject to complex operating conditions such as impact, vibration, alternating loads, wear, and corrosion during wind turbine operation. These bolts frequently loosen, fail, or even break, resulting in significant economic losses. Therefore, real-time online monitoring of blade root bolt preload and the analysis and identification of potential bolt connection failures are crucial for ensuring the safe operation of wind turbines and preventing major safety incidents and economic losses.

[0003] Methods for monitoring bolt preload include torque method, strain gauges, built-in fiber Bragg grating (FBG), and ultrasonic measurement. The torque method is suitable for construction and installation but not for real-time monitoring. Strain gauges and fiber Bragg grating (FBG) require structural improvements to the bolts and are not suitable for actual engineering applications. The ultrasonic method includes single-wave and dual-wave methods. The traditional single-wave method for measuring bolt preload requires loosening the installed bolts, making the measurement process complex.

[0004] Chinese patent publication CN108775984B discloses a baseline-free ultrasonic guided wave bolt preload monitoring method. This method employs a time reversal method or a modified time reversal method to generate a refocused signal from the excitation signal at different preloads. This refocused signal is then used to calculate tightening indices at different torques. While this patent document's tightening indices calculations do not require a reference signal, the present invention utilizes an ultrasonic dual-wave method, which is fundamentally different from the methods and techniques employed in this patent document. Summary of the Invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a method and system for online monitoring of the pre-tightening stress of blade root bolts of a wind turbine generator set.

[0006] According to the present invention, a method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine generator set is provided, comprising:

[0007] Step S1: Calculate the bolt parameters under zero load state according to the material type of the bolt being tested;

[0008] Step S2: Collect relevant data of the bolt under test, calculate the axial stress of the bolt, and complete the monitoring.

[0009] Preferably, the step S1 calculates the bolt parameters under zero load state through the material database; the bolt parameters include the longitudinal wave acoustic elastic constant A L , shear wave acoustic elastic constant A T , longitudinal wave speed and shear wave speed

[0010] Preferably, in step S1:

[0011] Among them, ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

[0012] Preferably, step S2 includes the following sub-steps:

[0013] Step S2.1: Measure the bolt clamping length L g and nominal diameter d, calculate the effective stress length L of the bolt e ;

[0014] Step S2.2: Collect the transit time of the bolt ultrasonic pulse longitudinal wave and shear wave transit time The axial stress σ of the bolt is calculated based on the ultrasonic longitudinal and transverse wave sound time ratio and stress relationship model;

[0015] Step S2.3: Collect the current bolt temperature T C , the longitudinal wave temperature compensation coefficient calculated by calibration and shear wave temperature compensation coefficient Calculate the ultrasonic transit time after temperature compensation and the axial stress σ after temperature compensation c .

[0016] Preferably, in step S2.1: L i =L0+L e ;

[0017] Among them, L i is the total length of the bolt, L0 is the length of the bolt without stress, L σ is the stressed length in the bolt, and E is the elastic modulus.

[0018] Preferably, the step S2.2 comprises, according to the acoustic elasticity theory:

[0019] in, are the longitudinal wave speed and the shear wave speed under the stress state of the bolt respectively;

[0020] The acoustic time of the longitudinal wave signal received by the ultrasonic probe and the acoustic time of the shear wave signal They are:

[0021] Calculate the ratio of the longitudinal wave sound time to the shear wave sound time, perform Taylor expansion, and use the first-order Taylor series to approximate the axial stress σ:

[0022] Preferably, the step S2.3 includes a linear relationship between the temperature compensation coefficient and the temperature difference:

[0023] in, is the longitudinal wave temperature compensation coefficient, is the shear wave temperature compensation coefficient, T n is the temperature value at point n, T0 is the temperature value at point 0, When the longitudinal wave is at point n, For the longitudinal wave at the calibrated 0-point sound, When the transverse wave is at point n, is the sound time of the shear wave at 0 o'clock;

[0024] The temperature compensation coefficient is obtained by calibrating the same bolt

[0025] Echo time after temperature compensation:

[0026] Where T C is the current temperature of the bolt, T r Calibrate the initial temperature of the bolt, For the longitudinal wave signal after temperature compensation, is the sound time of the shear wave signal after temperature compensation;

[0027] Calculate the acoustic time ratio of longitudinal and transverse waves after temperature compensation:

[0028] The bolt axial stress σ after temperature compensation is obtained c Among them, L i is the total length of the bolt.

[0029] According to the present invention, a wind turbine blade root bolt preload stress online monitoring system is provided, comprising:

[0030] Module M1: Calculate the bolt parameters under zero load state according to the material type of the bolt being tested;

[0031] Module M2: Collects relevant data of the bolt under test, calculates the axial stress of the bolt, and completes the monitoring.

[0032] Preferably, the module M1 calculates the bolt parameters under zero load state through the material database; the bolt parameters include the longitudinal wave acoustic elastic constant A L , shear wave acoustic elastic constant A T , longitudinal wave speed and shear wave speed

[0033] Preferably, in the module M1:

[0034] Among them, ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

[0035] Preferably, the module M2 includes the following submodules:

[0036] Module M2.1: Measuring the bolt clamping length L g and nominal diameter d, calculate the effective stress length L of the bolt e ;

[0037] Module M2.2: Collecting the transit time of the bolt ultrasonic pulse longitudinal wave and shear wave transit time The axial stress σ of the bolt is calculated based on the ultrasonic longitudinal and transverse wave sound time ratio and stress relationship model;

[0038] Module M2.3: Collect current bolt temperature T C , the longitudinal wave temperature compensation coefficient calculated by calibration and shear wave temperature compensation coefficient Calculate the ultrasonic transit time after temperature compensation and the axial stress σ after temperature compensation c .

[0039] Preferably, in the module M2.1: L i =L0+L e ;

[0040] Among them, L i is the total length of the bolt, L0 is the length of the bolt without stress, L σ is the stressed length in the bolt, and E is the elastic modulus.

[0041] Preferably, the module M2.2 comprises according to the acoustic elasticity theory:

[0042] in, are the longitudinal wave speed and the shear wave speed under the stress state of the bolt respectively;

[0043] The acoustic time of the longitudinal wave signal received by the ultrasonic probe and the acoustic time of the shear wave signal They are:

[0044] Calculate the ratio of the longitudinal wave sound time to the shear wave sound time, perform Taylor expansion, and use the first-order Taylor series to approximate the axial stress σ:

[0045] Preferably, the module M2.3 includes a temperature compensation coefficient having a linear relationship with the temperature difference:

[0046] in, is the longitudinal wave temperature compensation coefficient, is the shear wave temperature compensation coefficient, T n is the temperature value at point n, T0 is the temperature value at point 0, When the longitudinal wave is at point n, For the longitudinal wave at the calibrated 0-point sound, When the transverse wave is at point n, is the sound time of the shear wave at 0 o'clock;

[0047] The temperature compensation coefficient is obtained by calibrating the same bolt

[0048] Echo time after temperature compensation:

[0049] Where T C is the current temperature of the bolt, T r Calibrate the initial temperature of the bolt, For the longitudinal wave signal after temperature compensation, is the sound time of the shear wave signal after temperature compensation;

[0050] Calculate the acoustic time ratio of longitudinal and transverse waves after temperature compensation:

[0051] The bolt axial stress σ after temperature compensation is obtained c Among them, L i is the total length of the bolt.

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

[0053] 1. The present invention can use the acoustic elasticity theory to measure the transit time of ultrasonic longitudinal and transverse waves in the bolt, and obtain the axial stress of the bolt based on the ratio calculation of the transit time of the longitudinal wave and the transverse wave, thereby realizing real-time monitoring of the preload force of the blade root bolt.

[0054] 2. The present invention adopts a dual-wave method to monitor the pre-tightening force of the fastened bolts at the blade root, which reduces the complexity of the measurement, facilitates large-scale application in engineering, and has high practicality.

[0055] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0057] FIG1 is a block diagram of the online calculation of bolt preload in the present invention. DETAILED DESCRIPTION

[0058] The present invention is described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, without departing from the scope of the present invention, a number of variations and improvements may be made by those skilled in the art. These all fall within the scope of protection of the present invention.

[0059] 1 , a method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine generator system includes:

[0060] First, according to the material of the high-strength bolt being tested, the longitudinal and transverse wave acoustic elastic constants A of the bolt in the zero-load state are calculated through the material database. L 、A T , longitudinal and transverse wave speeds

[0061] According to the material parameters of the high-strength bolts at the blade root under test, calculate the longitudinal and transverse acoustic elastic constants A of the bolts under zero load L 、A T , and the longitudinal and shear wave speeds in,

[0062] Where ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

[0063] Then, according to the model and specifications of the high-strength bolt to be tested, such as (M64*500, M56*400, M48*200, M45*300, M36*300, etc.), measure the bolt clamping length L g , nominal diameter d, calculate the effective stress length L of the bolt e , according to the test effective stress length L e There is the following relationship: L i =L0+L e ;

[0064] Among them, L i is the total length of the bolt, L0 is the length of the bolt without stress, L e is the effective stress length of the bolt, L σ is the stressed length in the bolt.

[0065] By collecting the longitudinal and shear wave transit time of ultrasonic pulses of high-strength bolts The axial stress of the bolt is calculated based on the relationship model between the ultrasonic longitudinal and transverse wave sound time ratio and stress:

[0066] According to the acoustic elasticity theory

[0067] in, It is the speed of sound of longitudinal and transverse waves when the bolt is under stress.

[0068] The acoustic times of the longitudinal and shear wave signals received by the ultrasonic probe are:

[0069] Calculate the ratio of the longitudinal wave sound time to the shear wave sound time, perform Taylor expansion, and take the first-order Taylor series approximation as follows:

[0070] The bolt axial stress σ can be calculated according to the above formula, and this stress does not take temperature deviation into account.

[0071] Finally, the current bolt temperature T is collected by the temperature sensor C , the longitudinal and transverse wave temperature compensation coefficients calculated by calibration Calculate the ultrasonic transit time after temperature compensation, and thus calculate the compensated bolt axial stress σ c :

[0072] Since temperature has a significant impact on the acoustic time of ultrasonic pulses, the influence of temperature should be compensated. Within the positive difference range, the temperature compensation coefficient is linearly related to the temperature difference:

[0073] in, is the longitudinal wave temperature compensation coefficient, is the shear wave temperature compensation coefficient, T n is the temperature value at point n, T0 is the temperature value at point 0, When the longitudinal wave is at point n, For the longitudinal wave at the calibrated 0-point sound, When the transverse wave is at point n, It is the sound time of shear wave at 0 o'clock.

[0074] The temperature compensation coefficient can be obtained by calibrating the same bolt

[0075] Echo time after temperature compensation:

[0076] in, For the longitudinal wave signal after temperature compensation, is the shear wave signal after temperature compensation, T C is the current temperature of the bolt, T r Calibrate the initial temperature for the bolt.

[0077] Calculate the acoustic time ratio of longitudinal and transverse waves after temperature compensation:

[0078] The temperature-compensated bolt axial stress σ is obtained. c , completing the monitoring process.

[0079] The present invention can use the acoustic elasticity theory to measure the transit time of ultrasonic longitudinal and transverse waves in the bolt, and obtain the axial stress of the bolt according to the ratio calculation of the transit time of the longitudinal wave and the transverse wave, so as to realize the real-time monitoring of the pre-tightening force of the blade root bolt; the dual-wave method is used to monitor the pre-tightening force of the tightened bolts at the blade root, which reduces the complexity of the measurement, facilitates the large-scale application of the project, and has high practicality.

[0080] The present invention also provides an online monitoring system for the pre-tightening stress of blade root bolts of a wind turbine generator set. The online monitoring system for the pre-tightening stress of blade root bolts of a wind turbine generator set can be implemented by executing the process steps of the online monitoring method for the pre-tightening stress of blade root bolts of a wind turbine generator set. That is, those skilled in the art can understand the online monitoring method for the pre-tightening stress of blade root bolts of a wind turbine generator set as an optimal implementation of the online monitoring system for the pre-tightening stress of blade root bolts of a wind turbine generator set.

[0081] Specifically, an online monitoring system for pre-tightening stress of blade root bolts of a wind turbine generator system includes:

[0082] Module M1: Calculate the bolt parameters under zero load state according to the material type of the bolt being tested;

[0083] Module M2: Collects relevant data of the bolt under test, calculates the axial stress of the bolt, and completes the monitoring.

[0084] The module M1 calculates the bolt parameters under zero load state through the material database; the bolt parameters include the longitudinal wave acoustic elastic constant A L , shear wave acoustic elastic constant A T , longitudinal wave speed and shear wave speed

[0085] In the module M1:

[0086] Among them, ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

[0087] The module M2 includes the following submodules:

[0088] Module M2.1: Measuring the bolt clamping length L g and nominal diameter d, calculate the effective stress length L of the bolt e ;

[0089] Module M2.2: Collecting the transit time of the bolt ultrasonic pulse longitudinal wave and shear wave transit time The axial stress σ of the bolt is calculated based on the ultrasonic longitudinal and transverse wave sound time ratio and stress relationship model;

[0090] Module M2.3: Collect current bolt temperature T C , the longitudinal wave temperature compensation coefficient calculated by calibration and shear wave temperature compensation coefficient Calculate the ultrasonic transit time after temperature compensation and the axial stress σ after temperature compensation c .

[0091] In the module M2.1: L i =L0+L e ;

[0092] Among them, L i is the total length of the bolt, L0 is the length of the bolt without stress, L σ is the stressed length in the bolt, and E is the elastic modulus.

[0093] The module M2.2 includes, according to the acoustic elasticity theory:

[0094] in, are the longitudinal wave speed and the shear wave speed under the stress state of the bolt respectively;

[0095] The acoustic time of the longitudinal wave signal received by the ultrasonic probe and the acoustic time of the shear wave signal They are:

[0096] Calculate the ratio of the longitudinal wave sound time to the shear wave sound time, perform Taylor expansion, and use the first-order Taylor series to approximate the axial stress σ:

[0097] The module M2.3 includes a temperature compensation coefficient that is linearly related to the temperature difference:

[0098] in, is the longitudinal wave temperature compensation coefficient, is the shear wave temperature compensation coefficient, T n is the temperature value at point n, T0 is the temperature value at point 0, When the longitudinal wave is at point n, For the longitudinal wave at the calibrated 0-point sound, When the transverse wave is at point n, is the sound time of the shear wave at 0 o'clock;

[0099] The temperature compensation coefficient is obtained by calibrating the same bolt

[0100] Echo time after temperature compensation:

[0101] Where T C is the current temperature of the bolt, T r Calibrate the initial temperature of the bolt, For the longitudinal wave signal after temperature compensation, is the sound time of the shear wave signal after temperature compensation;

[0102] Calculate the acoustic time ratio of longitudinal and transverse waves after temperature compensation:

[0103] The bolt axial stress σ after temperature compensation is obtained c Among them, L i is the total length of the bolt.

[0104] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0105] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for online monitoring of pre-tightening stress of blade root bolts of wind turbine generator set, characterized in that: include: Step S1: Calculate the bolt parameters under zero load state according to the material type of the bolt to be tested; Step S2: Collect relevant data of the bolt under test, calculate the axial stress of the bolt, and complete the monitoring.

2. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 1, characterized in that: The step S1 calculates the bolt parameters under zero load state through the material database; the bolt parameters include the longitudinal wave acoustic elastic constant A L , transverse wave acoustic elastic constant A T , longitudinal wave speed and shear wave speed 3. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 2, characterized in that: In step S1: Among them, ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

4. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 1, characterized in that: The step S2 comprises the following sub-steps: Step S2.1: Measure the bolt clamping length L g and nominal diameter d, calculate the effective stress length L of the bolt e ; Step S2.2: Collect the transit time of the longitudinal wave of the bolt ultrasonic pulse and shear wave transit time The axial stress σ of the bolt is calculated based on the ultrasonic longitudinal and transverse wave sound time ratio and stress relationship model; Step S2.3: Collect the current bolt temperature T C , the longitudinal wave temperature compensation coefficient calculated by calibration and shear wave temperature compensation coefficient Calculate the ultrasonic transit time after temperature compensation and the axial stress σ after temperature compensation c .

5. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 4, characterized in that: In step S2.1: L i =L0+L e ; Among them, L i is the total length of the bolt, L0 is the length of the bolt that is not stressed, and L σ is the stressed length in the bolt and E is the elastic modulus.

6. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 5, characterized in that: The step S2.2 comprises, according to the acoustic elasticity theory: in, They are respectively the longitudinal wave speed and the transverse wave speed under the bolt stress state; The acoustic time of the longitudinal wave signal received by the ultrasonic probe and the acoustic time of the shear wave signal They are: Calculate the ratio of the longitudinal wave sound time to the transverse wave sound time, perform Taylor expansion, and take the first-order Taylor series to approximate the axial stress σ:

7. The method for online monitoring of pre-tightening stress of blade root bolts of a wind turbine according to claim 4, characterized in that: The step S2.3 includes that the temperature compensation coefficient is linearly related to the temperature difference: in, is the longitudinal wave temperature compensation coefficient, is the shear wave temperature compensation coefficient, T n is the temperature value at point n, T0 is the temperature value at the calibration point 0, When the longitudinal wave is at point n, For the longitudinal wave at the calibrated 0 point, For the transverse wave at point n, is the sound time of the transverse wave at 0 point; The temperature compensation coefficient is obtained by calibrating the same bolt According to the echo time after temperature compensation: Where T C is the current temperature of the bolt, T r Calibrate the initial temperature of the bolt, For the longitudinal wave signal sound after temperature compensation, It is the sound time of the shear wave signal after temperature compensation; Calculate the acoustic time ratio of longitudinal and transverse waves after temperature compensation: The bolt axial stress σ after temperature compensation is obtained c Among them, L i is the total length of the bolt.

8. An online monitoring system for pre-tightening stress of blade root bolts of wind turbines, characterized in that: include: Module M1: Calculate the bolt parameters under zero load state according to the material type of the bolt being tested; Module M2: Collect relevant data of the bolt under test, calculate the axial stress of the bolt, and complete the monitoring.

9. The wind turbine blade root bolt preload stress online monitoring system according to claim 8, characterized in that: The module M1 calculates the bolt parameters under zero load state through the material database; the bolt parameters include the longitudinal wave acoustic elastic constant A L , transverse wave acoustic elastic constant A T , longitudinal wave speed and shear wave speed 10. The wind turbine blade root bolt preload stress online monitoring system according to claim 9, characterized in that: In the module M1: Among them, ρ is the density of the material, λ and μ are the second-order elastic coefficients of the material, and l, m, and n are the third-order elastic coefficients of the material.

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