Fan unit blade root ultrasonic pretightening force monitoring method

Abstract

The invention discloses a fan unit blade root ultrasonic pretightening force monitoring method, and relates to the technical field of fan units, and the method comprises the following specific steps: carrying out ultrasonic fastening stress coefficient calibration on a fan unit blade root bolt material, applying axial tension to a plurality of sample bolts made of the same material, and determining the blade root ultrasonic pretightening force of the fan unit under each tension value; according to the method for monitoring the ultrasonic pretightening force of the blade root of the fan unit, the transmission speeds of ultrasonic waves in the sample bolt in different stress states are measured by utilizing ultrasonic detection equipment, and the accuracy of monitoring data can be remarkably improved; according to the method, the ultrasonic fastening stress coefficient of a bolt material is calibrated, high-precision real-time monitoring of the pretightening force of the bolt is realized by utilizing the linear relation between the ultrasonic wave spreading in the bolt and the stress, the influence of friction force on torque measurement is eliminated, and the misjudgment of pretightening force attenuation caused by temperature and vibration factors is also avoided.

Description

Technical Field

[0001] The invention relates to the technical field of fan units, and in particular to a method for monitoring ultrasonic preload force of blade roots of fan units. Background Art

[0002] In the modern energy field, wind turbine units are an important power generation equipment, and their stable and reliable operation is of vital importance to energy supply. The blades of wind turbine units are the key components for converting wind energy into mechanical energy, and the blade roots are the key parts connecting the blades and the hub. The blade roots are fastened by bolts, and the preload state of the blade root bolts is directly related to the reliability and stability of the connection between the blades and the hub. During the operation of the wind turbine unit, the blades are subjected to complex and changeable loads, including wind loads, inertia forces, etc. These loads will be transmitted to the bolts through the blade roots. When the preload of the blade root bolts is insufficient or abnormal changes occur, the blades will become loose and the vibration will intensify, causing serious accidents of blade shedding.

[0003] However, the traditional method of monitoring the preload force of blade root bolts is mainly based on torque measurement, that is, the preload force is indirectly estimated by controlling the torque value through a torque wrench when installing the bolts. On the one hand, the friction between the bolt and the nut will affect the torque measurement, and different lubrication conditions, surface roughness and tightening speed factors will cause changes in friction, resulting in large errors in the preload force results based on torque measurement; on the other hand, the traditional method cannot monitor the changes in preload force in real time. During the long-term operation of the wind turbine unit, the preload force of the blade root bolt will gradually change due to temperature changes and vibration factors, but the torque measurement method cannot obtain these change information in time during operation, and it is difficult to detect potential safety hazards in time.

[0004] In summary, the existing blade root bolt preload monitoring technology has obvious deficiencies in accuracy and real-time performance, and cannot meet the requirements of modern wind turbine units for high safety and stable operation. Therefore, a new, more accurate and real-time monitoring method of the blade root bolt preload is needed to overcome these problems and ensure the safe and stable operation of the wind turbine unit. Summary of the invention

[0005] The purpose of the present invention is to make up for the shortcomings of the prior art and provide a method for monitoring the ultrasonic preload force of the blade root of a fan unit. The method can accurately calibrate the ultrasonic tightening stress coefficient of the bolt material, fully considering the influence of material properties on the relationship between ultrasonic propagation and preload force. During the measurement process, the ultrasonic critical reflection and acoustic elasticity principles are used, combined with an adaptive compensation relationship, to effectively overcome the interference of complex working conditions such as temperature and vibration, ensure the accuracy of the ultrasonic propagation velocity calculation, and thereby improve the preload force measurement accuracy.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for monitoring the ultrasonic preload force of the blade root of a fan unit, the specific steps of the method are:

[0007] S1, ultrasonic tightening stress coefficient calibration of wind turbine blade root bolt material is carried out by applying axial tensile force F on multiple sample bolts of the same material. s At each tensile force value, the ultrasonic testing equipment is used to measure the propagation velocity V of the ultrasonic wave in different stress states in the sample bolt. s , using the initial propagation velocity V0 of the bolt in the stress-free state, according to multiple groups (F s ,V s ) data, and the ultrasonic fastening stress coefficient C is determined by linear regression analysis, which satisfies: where σ s The tensile force F of the specimen bolt s The stress generated by the action of A s is the cross-sectional area of ​​the sample bolt;

[0008] Install ultrasonic sensors at the head position A and the root position B of the blade root bolt, and the installation direction is consistent with the axial direction of the bolt, so that the sensor is in close contact with the bolt surface without air gap;

[0009] S2, the sensor at the head position A transmits an ultrasonic signal to the blade root bolt, with a transmission frequency of f and a transmission pulse width of T w , set the repetition frequency f according to the influence of the blade root bolt length and material on ultrasonic attenuation r , using the critical reflection characteristics of ultrasonic waves at different medium interfaces between bolts and nuts, bolts and blade roots, by adjusting the sensor's transmitting angle θ and receiving angle φ, the incident angle is close to the critical angle, so as to accurately identify the reflection conditions of different interfaces;

[0010] S3, receiving the reflected ultrasonic signal, amplifying the received signal, filtering out low-frequency noise and high-frequency interference components using bandpass filtering technology, retaining the effective signal frequency band related to the transmission frequency f, converting the analog signal into a digital signal through a high-speed analog-to-digital converter with a sampling frequency greater than f, and storing it;

[0011] S4, calculate the propagation speed V of the ultrasonic wave in the blade root bolt according to the time delay information of the received reflected signal, that is, the time interval from the emission to the reception of the reflected signal of different interfaces is t, the distance between the sensor and each interface is d, and the Calculate the propagation velocity of different parts, combine the ultrasonic tightening stress coefficient C, the coefficient k of the bolt geometry, and the propagation velocity V0 in the stress-free state. Calculate the preload force of the blade root bolt, where k is related to the diameter D and length L of the bolt, and k = k(D, L). Statistical analysis is performed on the propagation velocity data measured multiple times to remove abnormal values ​​and take the average value as V, and F is the preload force of the blade root bolt.

[0012] S5, install a temperature sensor on the blade root bolt to monitor the working temperature T, and establish a temperature compensation relationship based on the material thermal expansion coefficient and the relationship between ultrasonic propagation velocity and temperature, that is, the propagation velocity after temperature compensation is V t , the propagation velocity at the reference temperature T0 is V(T0), the temperature coefficients are α and β, and the compensation relationship formula is satisfied: By measuring the temperature T in real time, the ultrasonic wave propagation velocity V is corrected using the formula, thereby reducing the influence of temperature changes on the preload force calculated based on ultrasonic measurement;

[0013] Vibration sensors are installed on the blade root bolts to monitor vibration parameters, including frequency f v , amplitude A v and acceleration a. Since vibration will change the propagation path and characteristics of ultrasonic waves in the bolt, a vibration compensation relationship is established based on the influence mechanism of vibration on ultrasonic propagation. That is, the ultrasonic propagation velocity before vibration compensation is V, and the propagation velocity after vibration compensation is V v , vibration frequency f v Vibration coefficient α v To reflect its influence weight on the final compensation speed, the amplitude A v The degree of influence is determined by the vibration coefficient β v Quantified, the acceleration a is given by the vibration coefficient γ v To determine its contribution to the compensation speed, the vibration compensation relationship is: V v =V×(1-α v ×f v -βv×Av-γv×a, the measured ultrasonic propagation data is corrected by this relationship, so that when calculating the preload, the propagation velocity V after temperature and vibration compensation is considered t and V v , thereby reducing the errors caused by temperature and vibration factors in actual working conditions when calculating the preload.

[0014] Furthermore, in the process of determining the ultrasonic tightening stress coefficient C by linear regression, the experimental data points of n sample bolts are (F s1 ,V s1 ),(F s2 ,V s2 ),…,(F sn ,V sn ),according to Calculate each tension F si The corresponding stress σsi , where A s is the cross-sectional area of ​​the specimen bolt, V sn is the propagation velocity, V0 is the initial propagation velocity in the stress-free state, which is the same constant for all specimen bolts. si ,V si ), construct a linear regression equation, the linear regression equation is y=mx+b, in which y corresponds to x corresponds to σ si , m corresponds to the ultrasonic tightening stress coefficient C, b is the intercept, which is The intercept is 0, and by calculating and The corresponding σ s i and The average value of use According to the least squares method, the ultrasonic fastening stress coefficient C, that is, m is

[0015]

[0016] Furthermore, when S2 transmits an ultrasonic signal, the energy of the transmitted signal is E, which is related to the transmitting voltage U and the transmitting pulse width T. w It is related to the sensor coefficient m, satisfying E=m×U×T w , by adjusting U and T w To control the energy of the transmitted signal so that the ultrasonic wave can propagate effectively in the blade root bolt, where m is the internal circuit coefficient of the sensor.

[0017] Furthermore, the S2 for the repetition frequency f r The setting is that the effective propagation time of the ultrasonic wave in the blade root bolt is t eff , in order to avoid mutual interference between signals, satisfy where t eff The bolt length L and the propagation speed V of ultrasonic waves in the bolt material s And the correction factor n of the internal structure of the bolt is related to

[0018] Furthermore, when the critical reflection characteristic is used in S2, the critical angle of the ultrasonic wave from the bolt material medium 1 to the blade root contact surface material medium 2 is θ c , which is related to the sound speed V1 and V2 of the two media and satisfies When adjusting the transmission angle θ and the receiving angle φ, |θ-θ c |≤Δθ and |φ-θ c|≤Δφ, where Δθ and Δφ are angle deviation values, i.e., Δθ=p×r, Δφ=p×r, where r and p are the angle resolution and precision coefficient of the sensor, respectively. By controlling the angle deviation, the incident angle is made close to the critical angle to accurately identify the reflection conditions of different interfaces. At the same time, the interface conditions are further analyzed by monitoring the changes in the intensity of the reflected signal, i.e. Among them I r is the reflected signal intensity, θ is the incident angle, I0 is the original ultrasonic emission intensity, Z 1、 Z2 is the acoustic impedance of the two media.

[0019] Furthermore, the amplification process of the received signal in S3 has a signal strength of I a , the original received signal strength is I r , the amplifier gain is G, that is, I a =G×I r , in the bandpass filtering technique, the frequency of the filtered signal is f f , the original received signal frequency is f r , the lower cutoff frequency of the bandpass filter is f l , the upper cut-off frequency is f u , satisfying: when f l <f r <f u When f f =f r , filter out frequencies less than f l The low frequency noise and the noise greater than f u High frequency interference, retaining the effective signal frequency band range related to the transmission frequency f [f l ,f u ].

[0020] Furthermore, in the analog-to-digital conversion process, the sampled digital signal value is defined as D, and the analog signal voltage value V is defined as a , the resolution of the analog-to-digital converter q, the reference voltage V ref , and get the digital signal D, that is Where n is the number of bits of the analog-to-digital converter, and R is the equivalent resistance of the receiving circuit, I a is the signal strength after amplification, k v The voltage-intensity conversion coefficient is used to convert the analog signal into a digital signal through a high-speed analog-to-digital converter to accurately capture the detailed information of the signal and store it.

[0021] Furthermore, when performing statistical analysis on the propagation velocity data measured multiple times to remove abnormal values, the ultrasonic propagation velocity data set obtained by the multiple measurements is defined as V = {v1, v2, ..., v n}, where n is the number of measurements, calculate the mean of the propagation speed data and standard deviation σ, that is Set the outlier judgment threshold coefficient to k, then the outlier judgment threshold T = k × σ, for each data v in the data set V i ,when When v i The outliers are determined and removed from the data set V, the remaining data are used to calculate the preload force of the blade root bolts, and the average value of the remaining data is taken as the propagation velocity V for calculation.

[0022] Compared with the prior art, this method for monitoring the blade root ultrasonic preload of a fan unit has the following beneficial effects:

[0023] 1. The ultrasonic preload force monitoring method for the blade root of a fan unit of the present invention can significantly improve the accuracy of the monitoring data. By combining the critical reflection characteristics of ultrasound and the principle of acoustic elasticity, the ultrasonic tightening stress coefficient of the bolt material is calibrated, and the linear relationship between the ultrasonic wave propagating in the bolt and the stress is utilized to achieve high-precision real-time monitoring of the bolt preload force. This not only eliminates the influence of friction on torque measurement, but also avoids the misjudgment of preload force attenuation caused by temperature and vibration factors.

[0024] 2. The present invention realizes real-time monitoring of the preload force of the blade root bolts, greatly improving the safety of the operation and maintenance efficiency of the wind turbine unit. By real-time monitoring of the preload force of the blade root bolts, the operation and maintenance personnel can obtain the changes in the preload force of the bolts in time, thereby effectively ensuring the safe and stable operation of the wind turbine unit. At the same time, the real-time monitoring data can be used to analyze the performance change trends of the blade root bolts under different working conditions, providing a strong basis for optimizing the maintenance plan of the wind turbine unit. Through long-term data accumulation, the fatigue life of the bolts can be predicted, the maintenance cycle can be reasonably arranged, the maintenance cost can be reduced, and the availability and economic benefits of the wind turbine unit can be improved.

[0025] Other advantages, objectives and features of the present invention will be set forth in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0027] Figure 1 It is a flow chart of a method for monitoring the ultrasonic preload force of blade roots of a fan unit;

[0028] Figure 2 The present invention is a flow chart of S5 in a method for monitoring ultrasonic preload force of blade roots of a fan unit. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Embodiment 1

[0031] This embodiment describes in detail how to use the ultrasonic preload force monitoring method for the blade root of a fan unit of the present invention to accurately monitor the preload force of the blade root bolts in a low temperature environment. It fully demonstrates the application process of this method to ensure the safe operation of the fan unit under low temperature conditions, and focuses on the key role of the temperature compensation mechanism in improving monitoring accuracy.

[0032] In the specific implementation, firstly, a wind turbine unit in a large wind farm located in a cold region is selected as the test object. The average winter temperature in this region is as low as T min , extremely low temperature to T extreme The low temperature environment will shrink the blade root bolt material, thereby affecting the propagation speed of the ultrasonic wave in it and interfering with the preload monitoring. Therefore, the necessity of the temperature compensation function of the present invention is highlighted. The blade root bolts of the fan unit are made of the same material as the sample bolts used in the calibration experiment. The diameter is D and the length is L. A plurality of sample bolts of the same material and specification as the blade root bolts are prepared. In a laboratory environment, a high-precision tensile testing machine is used to apply an axial tensile force F. s The tensile loading range covers the preload range of the blade root bolt under actual working conditions. The calibration is carried out within the actual force range. The obtained ultrasonic tightening stress coefficient C is suitable for the calculation of preload under actual working conditions. The loading step is ΔF s At each tension value, a high-precision ultrasonic testing device is used to measure the propagation velocity V of the ultrasonic wave in the sample bolt. s , the number of measurements is n s , take the average value to reduce the measurement error, and assume that the initial propagation velocity of the bolt in the stress-free state is V0. According to multiple groups (F s ,V s ) data, calculate each tension F s The stress corresponding to i (A sis the cross-sectional area of ​​the sample bolt), and the relationship between tension and stress is established to prepare for the subsequent determination of the ultrasonic tightening stress coefficient.

[0033] Then, for all data points Construct the linear regression equation y=mx+b (where y corresponds to x corresponds to σ si , m corresponds to the ultrasonic tightening stress coefficient C, b is the intercept, which is The intercept is 0, and by calculating the σ corresponding to x and y s i and The average value of use According to the least squares method, the ultrasonic fastening stress coefficient C, that is, m is The purpose of using linear regression analysis and least squares method is to find the straight line that best fits the data points, so as to accurately determine the ultrasonic tightening stress coefficient C, which reflects the quantitative relationship between the change in ultrasonic propagation velocity and the stress on the bolt. At the same time, ultrasonic sensors are installed at the head position A and the root position B of the blade root bolt. The operating frequency of the sensor is f, and the installation direction is consistent with the axial direction of the bolt. It is fixed by bonding material to ensure that the sensor is in close contact with the bolt surface and there is no air gap. The fixture material is compatible with the bolt and the sensor. The bonding material has high strength, high bonding force, temperature resistance and vibration resistance. The installation of the sensor in this way ensures that the ultrasonic signal can be accurately propagated and reflected in the bolt, avoiding signal loss and distortion caused by improper sensor installation, thereby ensuring the accuracy of subsequent measurement data. Ultrasonic signals are emitted from the sensor at the head position A, the emission frequency is set to f, and the emission pulse width is T w , the transmitted signal energy E = m × U × T w (m is the internal circuit coefficient of the sensor), by adjusting the transmitting voltage U and T w Control the energy so that the ultrasonic wave can propagate effectively in the blade root bolt. In a low temperature environment, the material properties change. Adjusting the transmission energy can ensure that the ultrasonic signal can propagate a sufficient distance in the bolt and generate a detectable reflection signal. Set the repetition frequency f according to the blade root bolt length L and the effect of the material on ultrasonic attenuation. r , assuming that the effective propagation time of the ultrasonic wave in the blade root bolt is (n is the correction factor of the internal structure of the bolt, V s is the propagation speed of ultrasonic waves in the bolt material), in order to avoid mutual interference between signals, By setting the repetition frequency, it can be ensured that the reflected signal can be accurately received under different working conditions, while avoiding signal overlap interference and ensuring measurement accuracy.

[0034] Then, the reflected ultrasonic signal is received and amplified. The signal strength I a =G×I r (G is the amplifier gain, I r is the original received signal strength), using bandpass filtering technology, assuming the lower cutoff frequency of the bandpass filter is f l , the upper cut-off frequency is f u , when f l <f r <f u When the signal frequency after filtering is f f =f r , filter out low-frequency noise and high-frequency interference components, and retain the effective signal frequency band related to the transmission frequency f. In a low-temperature environment, external interference increases. Through amplification and filtering, the signal-to-noise ratio of the signal can be improved, making the subsequent processed data more reliable. Through a high-speed analog-to-digital converter (sampling frequency f s >k f ×f,k f is the multiple coefficient) to convert the analog signal into a digital signal. The sampled digital signal value is (n is the number of bits of the analog-to-digital converter, R is the equivalent resistance of the receiving circuit, k v The high-speed sampling and precise analog-to-digital conversion can accurately capture the signal details and provide a high-precision data basis for the subsequent calculation of propagation speed and preload.

[0035] Next, a temperature sensor is installed near the blade root bolt to monitor the operating temperature T. A temperature compensation equation is established based on the material thermal expansion coefficient and the ultrasonic propagation velocity and temperature relationship. The propagation velocity after temperature compensation is (V is the uncompensated ultrasonic propagation velocity, T0 is the reference temperature, α, β, etc. are temperature coefficients). In a low-temperature environment, temperature has a significant effect on the ultrasonic propagation velocity. The purpose of using this relationship is to correct the ultrasonic propagation velocity V according to the real-time measured temperature T. As the temperature decreases, the material shrinks and the ultrasonic propagation velocity changes. Through temperature compensation, the calculated propagation velocity is closer to the true value, thereby improving the accuracy of the preload calculation. At the same time, the preload calculation calculates the ultrasonic propagation velocity V in the blade root bolt based on the time delay information of the received reflected signal. Assume that the time interval from the emission to the reception of the reflected signal from different interfaces is t, and the distance between the sensor and each interface is d. Calculate the propagation velocity at different locations, and calculate the velocity by measuring time and distance as the basic data for subsequent calculation of preload. Combined with the ultrasonic tightening stress coefficient C, the coefficient k=k(D,L) related to the geometric dimensions of the bolt, and the propagation velocity V0 in the stress-free state, The preload force of the blade root bolt is calculated. The ultrasonic tightening stress coefficient C reflects the influence of material properties on the relationship between ultrasonic propagation and stress. The coefficient k related to the bolt geometry takes into account the influence of the bolt size on the preload force calculation. The propagation velocity V0 in the stress-free state is used as the reference value to accurately calculate the preload force. The propagation velocity data measured multiple times are statistically analyzed to eliminate abnormal values. The ultrasonic propagation velocity data set obtained by multiple measurements is defined as V = {v1, v2, …, v n}(n is the number of measurements), calculate the mean of the propagation speed data and Standards Set the outlier judgment threshold coefficient to k, then the outlier judgment threshold T = k × σ, according to each data v in the set V i ,when When v i The outliers are determined and removed from the data set V, and the abnormal data caused by measurement errors, environmental interference and other factors are removed to improve the accuracy and reliability of the propagation velocity data used to calculate the preload force, so that the final calculated preload force can better reflect the actual state of the bolt. The remaining data are used to calculate the preload force of the blade root bolt, and the average value of the remaining data is taken as the propagation velocity V used for calculation.

[0036] Finally, during the operation of the wind turbine unit, the above monitoring process is continuously performed to obtain the preload force data of the blade root bolts in real time, and the preload force data obtained by real-time monitoring is compared with the preset safety threshold (the upper limit threshold value F max and the lower threshold F min ), when the monitored preload exceeds the safety threshold, the system immediately triggers an alarm signal, prompting the operation and maintenance personnel to take corresponding measures, such as re-tightening or replacing the bolts, to ensure the safe operation of the wind turbine unit, and to ensure that the wind turbine unit can promptly detect abnormal changes in the preload of the blade root bolts in a low temperature environment, effectively prevent safety accidents caused by loose bolts and other problems, and improve the reliability and safety of the wind turbine unit operation.

[0037] To sum up, this embodiment applies the blade root bolt preload monitoring method of the present invention to a wind turbine unit in a low temperature environment, and demonstrates in detail the complete process from coefficient calibration to actual monitoring. In a low temperature environment, the temperature compensation mechanism accurately corrects the ultrasonic propagation velocity according to material properties and temperature changes, and then accurately calculates the blade root bolt preload. The whole process provides a comprehensive and feasible implementation plan for blade root bolt preload monitoring of wind turbine units in cold areas, effectively ensuring the safe and stable operation of the wind turbine unit in a low temperature and harsh environment, and at the same time provides solid data support for maintenance decisions based on monitoring data, which is of great significance to improving the operation and maintenance level of the wind turbine unit.

[0038] Embodiment 2

[0039] This embodiment mainly describes how the monitoring method of the present invention can effectively monitor the preload force of blade root bolts in the operating environment of wind turbine units in coastal areas, focuses on the application of vibration compensation mechanism, and elaborates on the ability of this method to ensure the safe operation of wind turbine units when dealing with complex vibration conditions.

[0040] In the specific implementation, a wind turbine unit in a wind farm located in a coastal area is selected as the test object. The sea breeze in the area is strong and unstable, and the waves hit frequently, causing obvious vibrations in the wind turbine tower and blades. This vibration will seriously affect the monitoring accuracy of the preload force of the blade root bolts. Therefore, the vibration compensation function of the present invention is urgently needed. The blade root bolts of the wind turbine unit are made of a certain material, with a diameter of D and a length of L. e Prepare several sample bolts with the same material and specifications as the blade root bolts, and apply axial tensile force F using a high-precision tensile testing machine in a laboratory environment. s The tensile loading range covers the preload range of the blade root bolt under actual working conditions. The calibration is carried out within the actual force range. The obtained ultrasonic tightening stress coefficient C is suitable for the calculation of preload under actual working conditions. The loading step is ΔF s At each tension value, a high-precision ultrasonic testing device is used to measure the propagation velocity V of the ultrasonic wave in the sample bolt. s , the number of measurements is n s Take the average value to reduce the measurement error. Assume that the initial propagation velocity of the bolt in the stress-free state is V0. According to multiple groups (F s ,V s ) data, calculate each tension F s The stress corresponding to i (A s is the cross-sectional area of ​​the specimen bolt), for all data points Construct the linear regression equation y=mx+b (where y corresponds to x corresponds to σ si , m corresponds to the ultrasonic tightening stress coefficient C, b is the intercept, b = 0 when there is no stress), by calculating and as well as Determination of ultrasonic fastening stress coefficient based on the least squares method This coefficient is a key parameter for the subsequent calculation of preload force, and its calibration accuracy directly affects the reliability of the preload force calculation results.

[0041] Ultrasonic sensors are installed at the head position A and the root position B of the blade root bolt. The sensor operating frequency is set to f. The installation direction is consistent with the bolt axis. A special clamp is used to ensure that the sensor is in close contact with the bolt surface without air gap. The clamp material is compatible with the bolt and the sensor. During installation, the sensor position is ensured to be accurate to avoid abnormal ultrasonic propagation path due to installation deviation. The close contact between the sensor and the bolt surface ensures the effective transmission of ultrasonic signals and reduces signal loss. Ultrasonic signals are emitted from the sensor at the head position A. The emission frequency is set to f and the emission pulse width is T. w , the transmitted signal energy E = m × U × T w (m is the internal circuit coefficient of the sensor), by adjusting the transmitting voltage U and T w Control the energy so that the ultrasonic wave can be effectively propagated in the blade root bolt. In coastal areas, environmental factors may affect the ultrasonic wave propagation. Adjust the transmission energy to ensure that the signal can penetrate the bolt and generate a reflection signal of sufficient strength. Set the repetition frequency f according to the length L of the blade root bolt and the influence of the material on the ultrasonic wave attenuation. r , the effective propagation time of the ultrasonic wave in the blade root bolt is (n is the correction factor of the internal structure of the bolt, V s is the propagation speed of ultrasonic waves in the bolt material), in order to avoid mutual interference between signals, The repetition frequency setting can ensure that the reflected signal can still be accurately obtained in a vibration environment, while avoiding signal overlap and improving measurement accuracy. The reflected ultrasonic signal is received and amplified. The signal strength I a =G×I r (G is the amplifier gain, I r is the original received signal strength), using bandpass filtering technology, assuming the lower cutoff frequency of the bandpass filter is f l , the upper cut-off frequency is f u , when f l <f r <f u When the signal frequency after filtering is f f =f r , filter out low-frequency noise and high-frequency interference components, and retain the effective signal frequency band related to the transmission frequency f. In the coastal vibration environment, there is a lot of external interference. Amplification and filtering can significantly improve the signal-to-noise ratio of the signal, making the subsequent processed data more reliable. Through the high-speed analog-to-digital converter (sampling frequency f s >k f ×f,k f is the multiple coefficient) to convert the analog signal into a digital signal, and set the sampled digital signal value (n is the number of bits of the analog-to-digital converter, R is the equivalent resistance of the receiving circuit, k v The high-speed sampling and precise analog-to-digital conversion can accurately capture the signal details and provide a high-precision data basis for the subsequent calculation of propagation speed and preload.

[0042] Vibration sensors are installed on the blade root bolts to monitor vibration parameters, including frequency f v , amplitude A v and acceleration a to accurately reflect the position of the blade root bolt vibration state. The installation direction is consistent with the vibration direction sensitive axis to ensure that the vibration state of the blade root bolt in actual operation can be accurately measured. The measurement range and accuracy are selected according to the vibration characteristics of the wind turbine unit in the coastal environment. The frequency measurement range is f vmin to f vmax Covers the vibration frequency and amplitude measurement range A vmin To A vmax and acceleration measurement range a min to a max To meet the monitoring needs of vibration conditions, the vibration sensor needs to be calibrated after installation to ensure the accuracy of the measurement data. During the calibration process, a standard vibration source can be used to excite the sensor, compare the measured value with the standard value, adjust the sensor parameters until the measurement error is within the allowable range, and calculate the vibration compensation and preload force. The vibration sensor monitors the vibration parameters of the blade root bolt in real time, and establishes the vibration compensation relationship V according to the influence mechanism of vibration on ultrasonic propagation. v =V×(1-α v ×f v -β v ×A v -γ v ×a), in the operation of wind turbine units in coastal areas, vibrations are frequent and complex. The purpose of applying this relationship is to accurately correct the influence of vibration on the ultrasonic propagation velocity V, where the vibration frequency f v Vibration coefficient α v Affects the compensation speed, because vibrations of different frequencies interfere with ultrasonic propagation to different degrees. High-frequency vibrations will cause the ultrasonic wavelength to change, thereby affecting the propagation speed; Amplitude A v From the vibration coefficient β v To quantify its impact, a larger amplitude will make the ultrasonic propagation path change more significantly, resulting in a change in propagation time; the acceleration a is measured through the vibration coefficient γ v Determine the contribution to the compensation speed. The change in acceleration reflects the change in the vibration state. The greater the acceleration, the greater the impact on the ultrasonic propagation speed. Collect the change data of the ultrasonic propagation speed under different vibration parameters, and obtain the coefficient value through data analysis and fitting. Calculate the propagation speed V after vibration compensation through this relationship v, so that the speed after vibration compensation is taken into account when calculating the preload, reducing the error caused by vibration factors.

[0043] Calculate the propagation velocity V of the ultrasonic wave in the blade root bolt (based on the time delay t of the reflected signal and the distance d between the sensor and the interface, ), using the speed V after vibration compensation v , combined with the ultrasonic tightening stress coefficient C, the bolt geometry correlation coefficient k = k (D, L) and the propagation velocity V0 in the stress-free state, Calculate the preload force of the blade root bolts. The calculated preload force can more accurately reflect the actual stress state of the blade root bolts in the coastal vibration environment. Similarly, statistical analysis is performed on the propagation velocity data measured multiple times to eliminate abnormal values ​​(calculate the mean Standard deviation σ, set threshold coefficient k v Determine the threshold T = k v ×σ, remove outliers and take the average value as V v ), further improve the data accuracy. When calculating the mean and standard deviation, it is necessary to ensure the randomness and independence of the data, avoid errors introduced by improper data collection methods, and ensure that the excluded abnormal values ​​are indeed abnormal data, rather than misjudgments. Continuously monitor during the operation of the wind turbine unit, and compare the real-time preload data with the preset safety threshold (F max and F min ) comparison to ensure that the threshold value can not only ensure the safe operation of the fan unit but also avoid unnecessary maintenance operations due to excessively strict threshold values. When the preload force exceeds the threshold value, the system triggers an alarm. The alarm method can be in various forms such as sound and light alarm, remote notification, etc., to ensure that the operation and maintenance personnel can obtain the alarm information in time. The operation and maintenance personnel will handle the bolts accordingly according to the alarm information. At the same time, each alarm and handling situation will be recorded to facilitate subsequent analysis of the operating status of the fan unit and optimization of maintenance strategies to ensure safe and stable operation of the fan unit.

[0044] To sum up, this embodiment targets the complex vibration environment faced by wind turbine units in coastal areas, and demonstrates in detail the application process of the monitoring method of the present invention. Through precise vibration monitoring and compensation, the interference of vibration on the preload force monitoring of blade root bolts is effectively overcome, and the preload force is accurately calculated. This implementation process provides a reliable solution for the preload force monitoring of blade root bolts of wind turbine units in coastal areas, ensuring the safe operation of wind turbine units under severe vibration conditions. It also provides a scientific basis for maintenance decisions, which helps to improve the overall operation and maintenance level of wind turbine units.

[0045] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for monitoring the ultrasonic preload force of a fan blade root, characterized in that: The specific steps of this method are: S1, ultrasonic tightening stress coefficient calibration of fan blade root bolt material is carried out by applying axial tensile force F on multiple sample bolts of the same material. s At each tensile force value, the ultrasonic testing equipment is used to measure the propagation velocity V of the ultrasonic wave in the sample bolt under different stress states. s , using the initial propagation velocity V0 of the bolt in the stress-free state, according to multiple groups (F s , V s ) data, and the ultrasonic fastening stress coefficient C is determined by linear regression analysis, which satisfies: where σ s The tensile force F of the specimen bolt s The stress generated by the action of A s is the cross-sectional area of ​​the sample bolt; Install ultrasonic sensors at the head position A and the root position B of the blade root bolt, and the installation direction is consistent with the axial direction of the bolt, so that the sensor is in close contact with the bolt surface without air gap; S2, the sensor at the head position A transmits an ultrasonic signal to the blade root bolt, with a transmission frequency of f and a transmission pulse width of T w , set the repetition frequency f according to the influence of the blade root bolt length and material on ultrasonic attenuation r , using the critical reflection characteristics of ultrasonic waves at different medium interfaces between bolts and nuts, bolts and blade roots, by adjusting the sensor's transmitting angle θ and receiving angle φ, the incident angle is close to the critical angle, so as to accurately identify the reflection conditions of different interfaces; S3, receiving the reflected ultrasonic signal, amplifying the received signal, filtering out low-frequency noise and high-frequency interference components using bandpass filtering technology, retaining the effective signal frequency band related to the transmission frequency f, converting the analog signal into a digital signal through a high-speed analog-to-digital converter with a sampling frequency greater than f, and storing it; S4, calculate the propagation speed V of the ultrasonic wave in the blade root bolt according to the time delay information of the received reflected signal, that is, the time interval from the emission to the reception of the reflected signal of different interfaces is t, the distance between the sensor and each interface is d, and the Calculate the propagation velocity of different parts, combine the ultrasonic tightening stress coefficient C, the coefficient k of the bolt geometry, and the propagation velocity V0 in the stress-free state. Calculate the preload force of the blade root bolt, where k is related to the diameter D and length L of the bolt, and k = k (D, L). Statistical analysis is performed on the propagation velocity data measured multiple times to remove abnormal values ​​and take the average value as V, and F is the preload force of the blade root bolt; S5, install a temperature sensor on the blade root bolt to monitor the working temperature T, and establish a temperature compensation relationship based on the material thermal expansion coefficient and the relationship between ultrasonic propagation velocity and temperature, that is, the propagation velocity after temperature compensation is V t , the propagation velocity at the reference temperature T0 is V(T0), the temperature coefficients are α and β, and the compensation relationship formula is satisfied: By measuring the temperature T in real time, the ultrasonic wave propagation velocity V is corrected using the formula, thereby reducing the influence of temperature changes on the preload force calculated based on ultrasonic measurement; Vibration sensors are installed on the blade root bolts to monitor vibration parameters, including frequency f v , amplitude A v and acceleration a. Since vibration will change the propagation path and characteristics of ultrasonic waves in the bolt, a vibration compensation relationship is established based on the influence mechanism of vibration on ultrasonic propagation. That is, the ultrasonic propagation velocity before vibration compensation is V, and the propagation velocity after vibration compensation is V v , vibration frequency f v Vibration coefficient α v To reflect its influence weight on the final compensation speed, the amplitude A v The degree of influence is determined by the vibration coefficient β v Quantified, the acceleration a is given by the vibration coefficient γ v To determine its contribution to the compensation speed, the vibration compensation relationship is: V v =V×(1-α v ×f v -βv×Av-γv×a, the measured ultrasonic propagation data is corrected by this relationship, so that when calculating the preload, the propagation velocity V after temperature and vibration compensation is considered t and V v , thereby reducing the errors caused by temperature and vibration factors in actual working conditions when calculating the preload.

2. According to claim 1, a method for monitoring the ultrasonic preload force of a fan blade root, characterized in that: In the process of determining the ultrasonic tightening stress coefficient C by linear regression, the experimental data points of n sample bolts are (F s1 ,V s1 ),(F s2 ,V s2 ),…,(F sn ,V sn ),according to Calculate each tension F si The corresponding stress σ si , where A s is the cross-sectional area of ​​the specimen bolt, V sn is the propagation velocity, V0 is the initial propagation velocity in the stress-free state, which is the same constant for all specimen bolts. si , V si ), construct a linear regression equation, the linear regression equation is y=mx+b, in which y corresponds to x corresponds to σ si , m corresponds to the ultrasonic tightening stress coefficient C, b is the intercept, which is The intercept is 0, and by calculating the σ corresponding to x and y s i and The average value of use According to the least squares method, the ultrasonic fastening stress coefficient C, that is, m is 3. The method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: When S2 transmits an ultrasonic signal, the energy of the transmitted signal is E, which is related to the transmitting voltage U and the transmitting pulse width T. w It is related to the sensor coefficient m, satisfying E=m×U×T w , by adjusting U and T w To control the energy of the transmitted signal so that the ultrasonic wave can propagate effectively in the blade root bolt, where m is the internal circuit coefficient of the sensor.

4. The method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: The S2 for the repetition frequency f r The setting is that the effective propagation time of the ultrasonic wave in the blade root bolt is t eff , in order to avoid mutual interference between signals, satisfy where t eff The bolt length L and the propagation speed V of ultrasonic waves in the bolt material s And the correction factor n of the internal structure of the bolt is related to 5. The method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: When S2 uses the critical reflection feature, the critical angle of the ultrasonic wave from the bolt material medium 1 to the blade root contact surface material medium 2 is θ c , which is related to the sound speed V1 and V2 of the two media and satisfies When adjusting the transmission angle θ and the receiving angle φ, |θ-θ c |≤Δθ and |φ-θ c |≤Δφ, where Δθ and Δφ are angle deviation values, i.e., Δθ=p×r, Δφ=p×r, where r and p are the angle resolution and precision coefficient of the sensor, respectively. By controlling the angle deviation, the incident angle is made close to the critical angle to accurately identify the reflection conditions of different interfaces. At the same time, the interface conditions are further analyzed by monitoring the changes in the intensity of the reflected signal, i.e. Among them I r is the reflected signal intensity, θ is the incident angle, I0 is the original ultrasonic emission intensity, and Z1 and Z2 are the acoustic impedances of the two media.

6. A method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: The S3 amplifies the received signal, and the signal strength after amplification is I a , the original received signal strength is I r , the amplifier gain is G, that is, I a =G×I r , in the bandpass filtering technique, the frequency of the filtered signal is f f , the original received signal frequency is f r , the lower cutoff frequency of the bandpass filter is f l , the upper cut-off frequency is f u , satisfying: when f l <f r <f u When f f =f r , filter out frequencies less than f l The low frequency noise and the noise greater than f u High frequency interference, retaining the effective signal frequency band range related to the transmission frequency f [f l , f u ].

7. A method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: In the analog-to-digital conversion process, the sampled digital signal value is defined as D, and the analog signal voltage value V a , the resolution of the analog-to-digital converter q, the reference voltage V ref , and get the digital signal D, that is Where n is the number of bits of the analog-to-digital converter, and R is the equivalent resistance of the receiving circuit, I a is the signal strength after amplification, k v The voltage-intensity conversion coefficient is used to convert the analog signal into a digital signal through a high-speed analog-to-digital converter to accurately capture the detailed information of the signal and store it.

8. The method for monitoring the ultrasonic preload force of a fan blade root according to claim 1, characterized in that: When performing statistical analysis on the propagation velocity data measured multiple times to remove abnormal values, the ultrasonic propagation velocity data set obtained by the multiple measurements is defined as V = {v1, v2, ..., v n }, where n is the number of measurements, calculate the mean of the propagation speed data and standard deviation σ, that is Set the outlier judgment threshold coefficient to k, then the outlier judgment threshold T = k × σ, for each data v in the data set V i ,when When v i The outliers are determined and removed from the data set V, the remaining data are used to calculate the preload force of the blade root bolts, and the average value of the remaining data is taken as the propagation velocity V for calculation.

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