Wind power tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance

Abstract

The invention discloses a wind power tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance. The method comprises the following steps: arranging piezoelectric patches for acquiring response signals and piezoelectric patches in a reference state on the outer surface of a wind power tower; the method comprises the following steps: setting a triggering threshold value for monitoring an acoustic emission signal and the size of a data buffer area, preprocessing the collected original signal, constructing a time-frequency characteristic matrix, calculating a damage factor and judging cracks; when crack signals are detected, preprocessing of the signals under acoustic emission monitoring is stopped, and broadband excitation signals are applied to the piezoelectric patches; and acquiring response signals of the piezoelectric patches, extracting low-frequency components of the signals, comparing the currently measured impedance spectrum with a reference state, selecting an RMSD index to perform damage evaluation on the wind power tower, identifying the change degree of the structural performance, and quantifying the influence of damage on the structural safety of the wind power tower. According to the invention, high-precision identification of the crack signal is realized, and the monitoring accuracy and the detection efficiency are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine tower structure health monitoring, and in particular to a wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance. Background Art

[0002] In the wind turbine tower structure, due to its heavy weight, it has been subjected to wind loads for a long time during service. At the same time, its working environment is harsh and it is affected by natural weather for a long time, which makes it easy to produce cracks inside, causing structural instability, leading to serious accidents, and then causing serious danger to people's lives, and at the same time causing great economic losses; in addition, regular maintenance of wind turbine towers requires a lot of human and financial resources. Therefore, real-time monitoring of cracks in wind turbine towers and regular safety assessments are particularly important.

[0003] At present, the monitoring of wind turbine towers is mainly based on non-destructive testing. Traditional non-destructive testing methods mainly include ultrasonic, magnetic powder, and X-ray. Non-destructive testing can promptly detect potential defects in wind turbine towers, such as poor welding, material fatigue, and corrosion, thereby preventing structural failure, and timely conducting safety assessments on the degree of damage to wind turbine towers to ensure the safety of maintenance personnel and equipment. However, due to the harsh environment and material structural characteristics, traditional methods cannot monitor impending cracks, and rely on expensive equipment and instruments, which are inefficient and impractical, and are not suitable for on-site testing.

[0004] Due to its high sensitivity to dynamic defects, acoustic emission technology can effectively capture elastic wave signals during crack propagation and has the advantage of real-time monitoring, which is especially suitable for rapid detection of large structures. Electromechanical impedance technology, as a non-parametric nondestructive testing method, is based on the electromechanical coupling effect of piezoelectric materials and realizes health status assessment by analyzing the characteristic shift of the electrical impedance spectrum caused by structural damage. The existing technology has not effectively integrated the synergistic advantages of the two technologies: acoustic emission technology focuses on dynamic damage capture, and electromechanical impedance technology is good at quantitative assessment of structural status. The use of either technology alone has the defect of single function, and the traditional multi-sensor deployment scheme increases the complexity of the system. How to achieve dual-mode signal acquisition through the sensor multiplexing mechanism to improve equipment utilization while ensuring monitoring accuracy has become a technical bottleneck that needs to be solved urgently. In addition, the excessive reliance of existing monitoring systems on special instruments has led to high on-site deployment costs, which restricts the large-scale application of this technology in wind power tower operation and maintenance. Summary of the invention

[0005] The present invention provides a wind power tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance, which solves the problems of insufficient signal recognition accuracy and low detection efficiency of instruments and equipment.

[0006] To achieve the above object, the present invention provides the following technical solution: a wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance, comprising the following steps:

[0007] S1. First, a piezoelectric sheet for collecting a response signal and a piezoelectric sheet in a reference state are arranged on the outer surface of a wind turbine tower, wherein one response piezoelectric sheet corresponds to one reference piezoelectric sheet;

[0008] S2, then set the trigger threshold and data buffer size of the acoustic emission signal monitoring, pre-process the collected original signal and construct the time-frequency feature matrix, extract the main feature mode of the feature matrix, calculate the damage factor and judge the crack;

[0009] S3, triggering the measurement of electromechanical impedance according to the acoustic emission detection result, stopping the preprocessing of the signal under the acoustic emission monitoring when a crack signal is detected, and applying a broadband excitation signal to the piezoelectric piece;

[0010] S4, collect the response signal of the piezoelectric piece and extract the low-frequency component of the signal, calculate the impedance at different frequencies and draw the impedance spectrum, and use the impedance characteristics to make a preliminary assessment of the damage;

[0011] S5. By comparing the currently measured impedance spectrum with the reference state, the RMSD indicator is selected to conduct damage assessment on the wind turbine tower, identify the degree of change in structural performance, and quantify the impact of damage on the structural safety of the wind turbine tower.

[0012] Preferably, in step S1, the piezoelectric sheet arrangement rule includes arranging piezoelectric sheets at the weld and outer surface of the wind turbine tower, respectively, and the piezoelectric sheets located at the weld of the wind turbine tower are used for switching between acoustic emission and electromechanical impedance dual modes, and the piezoelectric sheets at the outer surface are used as the reference state for electromechanical impedance evaluation.

[0013] Preferably, step S2 specifically includes acoustic emission monitoring, first determining the trigger threshold and data buffer of the signal to ensure the integrity of the acoustic emission signal; then converting the signal from the time domain to the time-frequency domain through short-time Fourier transform to construct a time-frequency feature matrix, then performing singular value decomposition on the feature matrix to extract the main feature mode, calculating the damage factor and judging whether it exceeds the threshold under the healthy state.

[0014] Preferably, the damage factor is constructed by the ratio of the main eigenvalue obtained by singular value decomposition of the time-frequency matrix to the sum of the total eigenvalues, reflecting the proportion of the main eigenmode in the overall eigenenergy, where the damage factor D s It is expressed by the following formula:

[0015]

[0016] In the above formula, λ 1is the main eigenvalue of the singular value decomposition, r is the number of eigenvalues ​​of the matrix, and i indicates that the summed variables are 1, 2, 3, ..., r in sequence.

[0017] Preferably, the signal data in the normal state is used to statistically calculate the distribution of the damage factor, and a threshold is set according to the distribution law, wherein the threshold T is expressed by the following formula:

[0018] T=μ+kσ

[0019] In the above formula, μ and σ are the damage factors D s The mean and standard deviation of the statistical distribution, k is the coefficient for adjusting the threshold, which is used to control the sensitivity of the detection.

[0020] Preferably, in step S3, the trigger mechanism specifically includes the following:

[0021] Under normal working conditions, the piezoelectric film is preferentially used for passive monitoring of acoustic emission signals, and the real-time monitoring results of the acoustic emission signals are transmitted to the electromechanical impedance module. When the acoustic emission classification result is a crack signal, the broadband excitation in the electromechanical impedance mode is triggered, and the electromechanical impedance measurement mode is quickly switched. After an electromechanical impedance measurement is completed, the piezoelectric film switches back to the acoustic emission monitoring mode.

[0022] Preferably, in step S4, the low-frequency component signal is an electromechanical impedance response signal extracted in a low-frequency band by fast Fourier transform, avoiding interference from high-frequency acoustic emission signals; the electromechanical impedance at different frequencies is measured by a voltage-current method, and the resonant frequency shift and amplitude change characteristics of the impedance spectrum are used to perform a preliminary assessment of the damage, specifically including:

[0023] A resistor with a known resistance value is connected in series with the piezoelectric piece, and a sinusoidal excitation signal is transmitted at both ends. According to Ohm's law, the electrical impedance of the sensor is calculated by measuring the voltage signal at both ends of the sensor. The calculation formula is as follows:

[0024]

[0025] In the above formula, and are the excitation signal voltage and the voltage across the sensor respectively; R represents the electrical impedance The real part represents the resistance value; j is the imaginary unit; X is the electrical impedance The imaginary part represents the reactance; R m Represents a resistor of known resistance connected in series in a circuit.

[0026] Preferably, the impedance is measured by obtaining the amplitude and phase of the measurement signal through Fourier transform, calculating the amplitude ratio and phase difference between the excitation signal and the measurement signal, and then calculating the real impedance, and finally drawing the impedance spectrum by measuring at multiple frequency points. The process is represented by the following formula:

[0027]

[0028] In the above formula, R is the real part of the impedance, θ is the phase difference between the measured signal and the excitation signal, and U * =U A / U B .

[0029] Preferably, in step S5, the wind turbine tower damage assessment quantifies the impedance difference between the piezoelectric sheet at the wind turbine tower weld and the piezoelectric sheet at the outer surface of the wind turbine tower by RMSD, and sets different RMSD thresholds to represent different degrees of damage, thereby assessing the degree of damage to the wind turbine tower. The calculation process is expressed by the following formula:

[0030]

[0031] In the above formula, N is the total number of frequency points, f i is the index of the frequency point.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The method of the present invention combines time-frequency analysis and singular value decomposition in acoustic emission monitoring, realizes high-precision identification of early crack signals, and effectively improves the accuracy of monitoring;

[0034] 2. The present invention combines electromechanical impedance technology to quantitatively evaluate the damage degree of wind turbine towers, and constructs a damage assessment model based on impedance spectrum, which can accurately determine the degree of change in tower structure performance and the impact of damage;

[0035] 3. The present invention adopts a multifunctional integrated piezoelectric sheet and event trigger mechanism, which not only reduces the hardware complexity but also improves the monitoring efficiency. In addition, the method is suitable for complex operating environments and can realize early diagnosis and real-time monitoring of wind turbine tower structures, providing a scientific basis and decision-making support for subsequent maintenance and safety assurance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0037] In the attached picture:

[0038] Figure 1It is a flow chart of the wind power tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance of the present invention;

[0039] Figure 2 is a schematic diagram of the time-frequency characteristic matrix of background noise in an embodiment of the present invention;

[0040] Figure 3 is a schematic diagram of a time-frequency characteristic matrix when a crack occurs in an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of impedance spectra measured at the weld and the outer surface in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0043] Example: Figure 1 As shown, the wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance includes the following steps:

[0044] Step 1: Arrange piezoelectric sheets for collecting response signals and reference state piezoelectric sheets on the outer surface of the wind turbine tower, with one response piezoelectric sheet corresponding to one reference piezoelectric sheet.

[0045] The test structure used in the implementation of the present invention is Q355E steel, which is widely used in the tower field. When conducting the test, the two tower pieces are first welded together, and a piezoelectric sheet is arranged at the welding point as a response piezoelectric sheet, and a piezoelectric sheet is arranged on the other side of the tower as a reference piezoelectric sheet, which serves as a control group for damage degree assessment.

[0046] Step 2: Set the trigger threshold and data buffer size for acoustic emission signal monitoring, obtain the time-frequency feature matrix of the original signal and construct the damage factor.

[0047] By sampling the acoustic emission signal multiple times, it is ensured that the monitoring trigger threshold and data buffer can capture all sampling points. The time-frequency characteristic matrix of the signal is obtained by fast Fourier transform on the host computer, and then the main eigenvalue obtained by singular value decomposition is used to construct the damage factor. The formula is as follows:

[0048]

[0049] In the above formula, λ 1 is the main eigenvalue of the singular value decomposition, r is the number of eigenvalues ​​of the matrix, and i indicates that the summed variables are 1, 2, 3, ..., r in sequence.

[0050] Then, the damage factor threshold is determined and judged, and the acoustic emission signals under normal conditions are collected multiple times to calculate the distribution of the damage factor. Figure 2 As shown in the figure, due to the influence of background noise, the energy distribution is relatively uniform and the main eigenvalue energy is relatively small. Assuming that its distribution law follows the normal distribution, the threshold can be expressed by the following formula:

[0051] T=μ+kσ

[0052] In the above formula, μ and σ are the damage factors D s The mean and standard deviation of the statistical distribution, k is the coefficient for adjusting the threshold, which is used to control the sensitivity of the detection. Figure 3 As shown in the figure, energy fluctuation occurs. When the calculated damage factor is greater than the threshold, it is considered that the damage feature is enhanced and crack damage occurs in the tower.

[0053] Step 3: When a crack signal is detected, the preprocessing of the signal under acoustic emission monitoring is stopped, and a broadband excitation signal is applied to the piezoelectric piece.

[0054] When a crack signal is detected, the working mode of the piezoelectric piece is automatically switched, and the signal data of the acoustic emission is no longer processed. The frequency range of the broadband excitation signal is set to 20kHz to 30kHz, covering the main modal response frequency band of the structure.

[0055] Step 4: Collect the low-frequency response signal of the piezoelectric piece and calculate the impedance at different frequencies.

[0056] The electromechanical impedance response signal extracted in the low frequency band by fast Fourier transform is recorded, including the changes of complex impedance (amplitude and phase) at different frequencies to form an impedance spectrum, such as Figure 4 As shown in Figure 1, key characteristic parameters such as resonant frequency shift and impedance amplitude change are obtained.

[0057] A resistor with a known resistance value is connected in series with the piezoelectric piece, and a sinusoidal excitation signal is transmitted at both ends. According to Ohm's law, the electrical impedance of the sensor can be calculated by measuring the voltage signal at both ends of the sensor. The calculation formula is as follows:

[0058]

[0059] In the above formula and are the excitation signal voltage and the voltage across the sensor respectively; R represents the electrical impedance The real part represents the resistance value; j is the imaginary unit; X is the electrical impedance The imaginary part represents the reactance; R m Represents a resistor of known resistance connected in series in a circuit.

[0060] Since the real part of the impedance is more sensitive to damage changes, the electrical impedance can be The formula is simplified to the following expression

[0061] Mode:

[0062]

[0063] In the above formula, R is the real part of the impedance, θ is the phase difference between the measured signal and the excitation signal, and U * =U A / U B .

[0064] Step 5: By comparing the currently measured impedance spectrum with the reference state, the RMSD characteristic index is introduced to quantify the degree of structural damage of the wind turbine tower.

[0065] The impedance spectrum difference between the working piezoelectric sheet and the reference piezoelectric sheet is calculated by RMSD. This characteristic index can provide intuitive and quantitative damage assessment for structural health monitoring. The RMSD calculation formula is as follows:

[0066]

[0067] In the above formula, N is the total number of frequency points, f i is the index of the frequency point; different RMSD thresholds can be set to represent different degrees of damage, thereby completing the assessment of the damage degree of the wind turbine tower.

[0068] The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance provided by the present invention uses piezoelectric sheets for both high-frequency acoustic emission monitoring and low-frequency electromechanical impedance measurement, and uses event triggering to achieve dynamic switching between the two modes; combines time-frequency analysis with singular value decomposition to reduce the noise impact during monitoring and highlight the key features of the signal; performs impedance spectrum analysis on the electromechanical impedance signal and establishes a damage assessment model to provide quantitative damage indicators. The integrated hardware and intelligent monitoring mode improves operating efficiency and provides early diagnosis and intuitive damage degree judgment for personnel performing health inspections on tower structures.

[0069] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance, characterized by: The following steps are involved: S1. First, a piezoelectric sheet for collecting a response signal and a piezoelectric sheet in a reference state are arranged on the outer surface of a wind turbine tower, wherein one response piezoelectric sheet corresponds to one reference piezoelectric sheet; S2, then set the trigger threshold and data buffer size of the acoustic emission signal monitoring, pre-process the collected original signal and construct the time-frequency feature matrix, extract the main feature mode of the feature matrix, calculate the damage factor and judge the crack; S3, triggering the measurement of electromechanical impedance according to the acoustic emission detection result, stopping the preprocessing of the signal under the acoustic emission monitoring when a crack signal is detected, and applying a broadband excitation signal to the piezoelectric piece; S4, collect the response signal of the piezoelectric piece and extract the low-frequency component of the signal, calculate the impedance at different frequencies and draw the impedance spectrum, and use the impedance characteristics to make a preliminary assessment of the damage; S5. By comparing the currently measured impedance spectrum with the reference state, the RMSD indicator is selected to conduct damage assessment on the wind turbine tower, identify the degree of change in structural performance, and quantify the impact of damage on the structural safety of the wind turbine tower.

2. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 1 is characterized in that: In step S1, the piezoelectric sheet arrangement rule includes arranging piezoelectric sheets at the weld and outer surface of the wind turbine tower, respectively, and the piezoelectric sheets at the weld of the wind turbine tower are used for switching between acoustic emission and electromechanical impedance dual modes, and the piezoelectric sheets at the outer surface are used as the reference state for electromechanical impedance evaluation.

3. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 1 is characterized in that: In step S2, the acoustic emission monitoring specifically includes first determining the trigger threshold and data buffer of the signal to ensure the integrity of the acoustic emission signal; then converting the signal from the time domain to the time-frequency domain through short-time Fourier transform to construct a time-frequency feature matrix, and then performing singular value decomposition on the feature matrix to extract the main feature mode, calculate the damage factor and determine whether it exceeds the threshold under the healthy state.

4. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 3 is characterized in that: The damage factor is constructed by the ratio of the main eigenvalue obtained by singular value decomposition of the time-frequency matrix to the sum of the total eigenvalues, reflecting the proportion of the main eigenmode in the overall eigenenergy, where the damage factor D s It is expressed by the following formula: In the above formula, λ1 is the main eigenvalue of the singular value decomposition, r is the number of eigenvalues ​​of the matrix, and i represents the summed variables, which are 1, 2, 3, ..., r in sequence.

5. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 4 is characterized in that: Using the signal data under normal conditions, the distribution of the damage factor is statistically analyzed, and the threshold is set according to the distribution law, where the threshold T is expressed by the following formula: T=μ+kσ In the above formula, μ and σ are the damage factors D s The mean and standard deviation of the statistical distribution, k is the coefficient for adjusting the threshold, which is used to control the sensitivity of the detection.

6. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 1 is characterized in that: In step S3, the trigger mechanism specifically includes the following: Under normal working conditions, the piezoelectric film is preferentially used for passive monitoring of acoustic emission signals, and the real-time monitoring results of the acoustic emission signals are transmitted to the electromechanical impedance module. When the acoustic emission classification result is a crack signal, the broadband excitation in the electromechanical impedance mode is triggered and switched to the electromechanical impedance measurement mode. After an electromechanical impedance measurement is completed, the piezoelectric film switches back to the acoustic emission monitoring mode.

7. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 1 is characterized in that: In step S4, the low-frequency component signal is an electromechanical impedance response signal extracted in the low-frequency band by fast Fourier transform; the electromechanical impedance at different frequencies is measured by the voltage-current method, and the resonant frequency shift and amplitude change characteristics of the impedance spectrum are used to perform a preliminary assessment of the damage, specifically including: A resistor with a known resistance value is connected in series with the piezoelectric piece, and a sinusoidal excitation signal is transmitted at both ends. According to Ohm's law, the electrical impedance of the sensor is calculated by measuring the voltage signal at both ends of the sensor. The calculation formula is as follows: In the above formula, are the excitation signal voltage and the voltage across the sensor respectively; R represents the electrical impedance The real part represents the resistance value; j is the imaginary unit; X is the electrical impedance The imaginary part represents the reactance; R m Represents a resistor of known resistance connected in series in a circuit.

8. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 7 is characterized in that: The impedance measurement obtains the amplitude and phase of the measurement signal through Fourier transform, calculates the amplitude ratio and phase difference between the excitation signal and the measurement signal, and then calculates the real impedance. The impedance spectrum is finally drawn by measuring at multiple frequency points. The process is expressed by the following formula: In the above formula, R is the real part of the impedance, θ is the phase difference between the measured signal and the excitation signal, and U * =U A / U B .

9. The wind turbine tower monitoring and safety assessment method based on acoustic emission and electromechanical impedance according to claim 1 is characterized in that: In step S5, the wind turbine tower damage assessment quantifies the impedance difference between the piezoelectric sheet at the wind turbine tower weld and the piezoelectric sheet at the outer surface of the wind turbine tower through RMSD, and sets different RMSD thresholds to represent different degrees of damage, thereby assessing the degree of damage to the wind turbine tower. The calculation process is expressed by the following formula: In the above formula, N is the total number of frequency points, f i is the index of the frequency point.

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