CN109946384A - A Signal Acquisition Process Optimization Method Based on RAPID Tomography - Google Patents

Abstract

The present invention is being a kind of based on Lamb wave progress structural damage detection, signal collection is carried out using new model, and the optimization and processing on algorithm are carried out to signal, it is divided with useful signal section from extraction algorithm, damage field and the method for time frequency analysis combines, emphatically using the mode of segmentation truncation related coefficient algorithm, signal is analyzed and is adjusted, with RAPID imaging algorithm, comprehensive diagnos is carried out to damage location, positioning accuracy is improved, achievees the purpose that carry out damage check with less sensor.

Description

A Signal Acquisition Process Optimization Method Based on RAPID Tomography

technical field

The invention relates to mechanical damage diagnosis technology, in particular to a damage diagnosis and positioning technology

Background technique

At present, ultrasound is often used for mechanical damage diagnosis and damage location is based on the propagation time of damage scattered signals. Lamb wave is a kind of ultrasonic guided wave, which has the characteristics of long propagation distance, multi-mode, and dispersion. When it propagates to the damage, scattering and energy attenuation will occur, and the signal amplitude will change significantly. The energy spectrum analysis can determine the variation of the amplitude, and then judge whether there is damage to the structure in the path. The RAPID algorithm mainly uses the signal feature SDC (signal difference coefficient, signal difference coefficient), and compares the statistics of the reference signal and the damaged signal, and then obtains the position of the damaged part. However, most of the existing technologies and achievements can only be carried out at a specific time and under certain circumstances, which have certain limitations and cannot achieve accurate detection;

The above algorithms and methods have many deficiencies: 1) the number of sensors is too large, the cost is too high, and the difficulty is too high; 2) accurate data analysis and positioning cannot be performed, and multiple damaged areas cannot be accurately positioned; 3) follow-up structural health The detection does not work effectively;

SUMMARY OF THE INVENTION

The problem solved by the present invention is to provide a signal acquisition process optimization method based on RAPID tomography technology. The signal segments before and after the damage are intercepted in sections and the correlation coefficients are compared. Then, the RAPID localization algorithm is used to construct an ellipse probability map and image it, thereby improving the efficiency of signal processing and the accuracy of damage localization. This method reduces the number of sensors and improves damage. The positioning accuracy greatly simplifies the difficulty and cost of sensor array layout, and provides greater convenience for subsequent structural health monitoring.

The present invention is achieved through the following technical solutions:

A signal acquisition process optimization method based on RAPID tomography technology includes the following steps:

1) Install piezoelectric sensors on the mechanical structure to be detected, and reduce the number of sensors to 4, and use piezoelectric sensors as the excitation end of the signal or the receiving end of the signal for device detection;

2) Under the initial condition of the mechanical structure, one of the piezoelectric sensors is used as the excitation end and the signal is excited, and the rest of the piezoelectric sensors are the receiving ends to receive signals. Every two piezoelectric sensors propagate on the sensing path. All signals will be collected, and the collected signals will be used as health signals;

3) When the mechanical structure is damaged, one of the piezoelectric sensors is used as the excitation terminal to excite the signal, and the other piezoelectric sensors are the receiving terminals to receive signals, and each two piezoelectric sensors transmit signals on the sensing path. are collected, and the collected signal is regarded as the damage signal;

4) Use the characteristics of Lamb waves to collect and process signals: use the effective signal segment self-extraction algorithm to obtain the time of one cycle of the receiving sensor, and extract and process the received signal in combination with the distance between the sensors. Compared with the damage signal, the appearance time of the newly excited mode due to the mode conversion can be identified, and then the damage position in the structure can be judged;

5) When the Lamb wave signal propagates to the damage, scattering and energy attenuation will occur, and the signal amplitude will change significantly. The adaptive interception algorithm is used to intercept the first wave amplitude spectrum, and the damage first wave amplitude and the healthy first wave are used. Comparing the amplitudes, the amplitude/energy coefficient ratio of the data collected by the four sensor arrays can be obtained, and the coefficient ratio threshold is set. Based on this, a six-part elliptical detection area is constructed;

6) Based on the above data, the RAPID tomography method is used to locate the damage and reconstruct the image of the damage;

7) According to the results of imaging, set appropriate thresholds to ensure clear images and accurate positioning;

The advantages of the technology of the present invention are mainly reflected in: the present invention is based on the existing damage localization principle, that is, the damage localization is performed by using the RAPID algorithm. According to the imaging algorithm, the first wave energy analysis and the segmented correlation coefficient interception method are used to further reduce the number of sensor arrays to four, which greatly simplifies the difficulty and cost of sensor array layout. In terms of signal processing and damage localization, it is divided into four parts to diagnose the damaged part by placing the sensor position, using the effective signal segment self-extraction algorithm, segmented truncation correlation coefficient algorithm, damage area division and time-frequency analysis and synthesis, thereby improving the localization. accuracy.

Description of drawings

Fig. 1 is a schematic diagram of the collected signal;

Fig. 2 is a schematic diagram of effective signal extraction;

Fig. 3 is waveform and piecewise correlation coefficient diagram after self-extraction;

Figure 4-1 is a schematic diagram of short-time Fourier transform of healthy and damaged waveforms;

Figure 4-2 is a schematic diagram of the amplitude/energy coefficient ratio;

Figure 4-3 is a schematic diagram of detection;

Fig. 5 is the damage probability distribution diagram of the ellipse region of the present invention;

FIG. 6 is a schematic diagram of damage in the detection area;

Figure 7 is a schematic diagram of damage diagnosis;

Detailed ways

The present invention will be described in detail below, which is to explain rather than limit the present invention.

The signal is received and transmitted by the sensor, and the signal is processed by means of effective signal segment extraction and segmental interception, and the damaged part is determined and the area division and time-frequency analysis are used to accurately and effectively realize the damage diagnosis, including the following steps:

1) On the mechanical structure to be tested, install four piezoelectric sensors in a rectangular manner, and set boundaries;

2) In the initial non-damaged state of the mechanical structure, one of the piezoelectric sensors is used as the excitation end to excite the signal, and the other piezoelectric sensors are used as the receiving end to receive the signal, and every two piezoelectric sensors propagate the signal. are collected, and the collected signal is used as a reference signal;

3) When the mechanical structure is damaged, one of the piezoelectric sensors is used as the excitation terminal to excite the signal, and the other piezoelectric sensors are used as the receiving terminal to receive the signal, and the transmitted signals of each two piezoelectric sensors are collected. , and take the collected signal as the damage signal;

4) Adjust the distance between the installed piezoelectric sensors, set the time when the wave S ₀ reaches the receiving sensor as T ₀ , and the time when the wave A ₀ reaches the receiving sensor as T ₁ , S ₀ starts from the excitation sensor and reaches the receiving sensor through damage or boundary The time of the sensor is later than the square of the time from the exciting sensor to the receiving sensor _;

5) Intercept the signal data: the time point obtained by dividing the straight-line distance L between the excitation end and the receiving end by the maximum propagation speed V _max of the Lamb wave in the effective frequency band is taken as the starting point t ₀ of the effective data, and the difference between the excitation end and the receiving end is used as the starting point t 0 . The straight-line distance L of the end is multiplied by the scale parameter P of the RAPID algorithm to obtain the maximum path length PL in the calculation area, which is divided by the minimum propagation velocity V _min of the Lamb wave in the effective frequency band plus the half period of the excitation signal 1/ 2T. The obtained time point is taken as the valid data termination point t ₁ ;

6) From theoretical analysis and experiments, the modal speed of Lamb wave S ₀ and A ₀ can be obtained. Combined with the distance between sensors, the arrival time t ₁ of the direct wave from the excitation end to the receiving end of S ₀ can be obtained; the direct time of A ₀ t ₂ , the width and length of the Lamb wave are recorded as Δt, in order to reduce the error, multiply by an optimization coefficient n, and perform data extraction;

7) Compare the health signal and the damage signal, use the rectangular window to intercept the sensing signal in segments, obtain the correlation coefficient between the health and damage signal after segmentation, measure its linear correlation, and use the correlation coefficient as the judgment basis to identify The time of occurrence of the damage is used to determine the damage location; the signal segments before and after the damage collected from a certain path are segmented to define the damage index DC. , through the reasonable selection of the DC value, the damage location can be judged intuitively, as shown in Figure 3;

8) The A sensor excites the signal, performs adaptive interception and segmental correlation coefficient analysis on the received signals of the B and D sensors, and marks the first data point that reaches the predetermined threshold. Since the Lamb wave propagation speed in the plate is constant Therefore, the sensor that arrives first (such as B) means that the damage is located in the area surrounded by ABC. Similarly, if sensor B excites a signal, sensors A and C receive signals. If sensor C arrives first, the detection area can be further reduced to OBC. , and the collaborative analysis with the damage area division algorithm can further reduce the detection area, as shown in Figure 5;

Specifically, in this experimental scheme, the experimental research object adopts 4 piezoelectric sensors, and adopts the installation method as shown in Figure 5. The specific steps are as follows:

1) Install sensors on the mechanical structure to be tested, and arrange them in rectangles to form a device network;

2) Adjust the distance between the installed piezoelectric sensors, set the time for wave S ₀ to reach the receiving sensor as T ₀ , and the time for wave A ₀ to reach the receiving sensor as T ₁ , S ₀ starts from the excitation sensor and reaches the receiving sensor through damage or boundary The time of the sensor is later than the square of the time from the exciting sensor to the receiving sensor _;

3) From theoretical analysis and experiments, the modal speed of Lamb wave S ₀ and A ₀ can be obtained. Combined with the distance between sensors, the arrival time t ₁ of the direct wave from the excitation end to the receiving end of S ₀ can be obtained; the direct time of A ₀ t ₂ ; record the Lamb wave width and length as Δt, in order to reduce the error, multiply by an optimization coefficient n, the formula is

4) Extract the received signal. The extraction process is as follows: set t ₁ as the starting point of the effective signal segment, and set t ₂ +Δt×n as the end point, then the effective signal segment is t ₂ +Δt×nt ₁ , as shown in Figure 1, 2 shown;

5) Using the method of segmental interception of the correlation coefficient, the rectangular window is used to intercept the sensor signal in segments, and the correlation coefficient between the health and damage signals after segmentation is obtained, and the linear correlation is measured, and the correlation coefficient is used as the judgment basis to identify the occurrence of damage. By comparing the health signal and the damage signal, the appearance time of the newly excited mode due to the mode conversion can be identified, and then the location of the damage in the structure can be judged.

When receiving signals, a shorter signal segment should be used to participate in the calculation of the damage index, because a part of the effective signal may be missing from the signal received by the receiving sensor that is far away from the excitation sensor. According to the calculation, more irrelevant signals may be added to the signal received by the receiving sensor farther away from the excitation sensor, thereby interfering with the extraction of the effective signal;

And further analysis, the signal segments before and after the damage collected by a certain path are denoted by H _i and D _i respectively after segmented interception, ρ(H _i , D _i ) represents the correlation coefficient of the signals H _i and D _i ,

For discrete signals, are the mean values of the signals _Hi and Di respectively; _Hik and _Dik are the _kth values of _Hi and _Di respectively; N is the length of the intercepted signal segment. The damage index DC is defined as

DC(H _i ,D _i )=1-|ρ(H _i ,D _i )|

6) When there is no abnormal comparison difference, the correlation coefficient of the intercepted signal of each previous section is comprehensively sorted, which is the guidance value when the next section of signal data appears, and based on the guidance value and the correlation coefficient of the next section of signal data Compare, and then conduct a comprehensive analysis according to the result value of the correlation coefficient comparison. If the difference between the intercepted health damage signal segments is larger, the correlation is smaller, that is, the larger the DC value is. Through the reasonable selection of the DC value, it can be judged intuitively. The damage location is shown in Figure 3;

7) According to the characteristics of Lamb wave, determine the change of signal amplitude, and determine the amount of change in amplitude by performing energy spectrum analysis on the waveform before and after the damage, and then determine whether there is damage to the structure in the path, and determine the health and damage waveforms. Perform short-time Fourier transform, and the obtained result is shown in Figure 4-1. Then use the adaptive interception algorithm to intercept the first wave amplitude spectrum, and compare the damaged first wave amplitude with the healthy first wave amplitude, we can get 4 The amplitude/energy coefficient ratio of the data collected by each sensor array, as shown in Figure 4-2, set the coefficient ratio threshold. The part where the energy coefficient ratio of the first wave of the damaged and healthy waveform is higher than the preset threshold is called detectable The part below the threshold is called the non-detectable area, and the detection schematic diagram is shown in Figure 4-3;

8) According to the principle of RAPID tomography, according to the above data, after comparing the damage signal and the health signal, the correlation coefficient of the signal is determined, and the ellipse is drawn according to the nature of the ellipse, and the ellipse signal decreases from the inside to the outside. Assign a value, and color it by the assignment size, and process it according to the larger the value, the darker the color. 6 ellipses can be drawn by 4 sensors for analysis, and it can be found that the area with the darkest color is the damaged area. As shown in Figure 6, it is the process of ellipse structure and whether the damage is within the detection area;

9) A damage diagnosis image can be formed to determine the damage location, as shown in Figure 7.

Claims (4)

1. a kind of signal acquisition optimization method based on RAPID chromatography imaging technique, it is characterised in that: this method include with Lower step:

1) in mechanical structure to be measured according to useful signal section from extraction algorithm, arrange piezoelectric transducer, quantity control is four；

It 2) is the excitation for motivating end and carrying out signal with one in piezoelectric transducer under mechanical structured member primary condition, with Remaining piezoelectric transducer is that receiving end receives signal, and the signal that every two piezoelectric transducer is propagated is all collected, is collected Signal be considered as health signal；

3) when carrying out data extraction, processing is extracted to signal is received, using the method for segmentation interception related coefficient, utilizes square Shape window carries out segmentation interception to transducing signal, and the related coefficient of health and damage signal after being segmented measures its linear correlation Property；

4) it according to the characteristic of Lamb wave, determines that signal amplitude changes, by carrying out energy spectrum analysis to damage front and back waveform, determines The variable quantity of amplitude, and then judge the structure in the path with the presence or absence of damage；

5) short time discrete Fourier transform is carried out to health and damage waveform, and as guidance, constructs six part-elliptical detecting areas Domain intercepts the first amplitude spectrum using adaptive interception algorithm, and carries out to damage the first amplitude and healthy the first amplitude Comparison can obtain amplitude/energy coefficient ratio of 4 sensor array acquisition data；

6) according to RAPID tomography principle, damage diagnostic image is constituted, and then determines damage location.

2. one kind according to claim 1 is for RAPID chromatography imaging technique signal acquisition optimization method, feature It is: it is described that piezoelectric transducer is installed from algorithmic approach is extracted with useful signal section in affiliated step 1, and carry out signal collection.

3. one kind according to claim 1 is for RAPID chromatography imaging technique signal acquisition optimization method, feature It is: in affiliated step 3, when the data are extracted to signal is received, using the method for segmentation interception related coefficient, signal point At subsection one by one, respectively by the healthier related coefficient with damage signal of every subsection, value analysis is successively carried out, with The mode of short message number section participates in damage criterion calculating, and then improves the accuracy of positioning.

4. it is according to claim 1 a kind of for RAPID chromatography imaging technique signal acquisition optimization method, it is special Sign is: when being imaged with RAPID algorithm, elliptic region is constructed using ellipse properties according to signal circulation way, and Randomization is carried out, is successively successively decreased from inside to outside, and gives assignment variation, the differentiation in color, value are carried out according to the size of assignment Bigger field color is deeper otherwise color is shallower, bigger for damage location assignment, darker, more clear when being allowed to be imaged It is clear, convenient for determining damage location.