阅读说明：本技术 一种温度变化环境下的超声结构健康监测方法 (Ultrasonic structure health monitoring method in temperature change environment ) 是由 陈榕 赵俊杰 张昶 于 2019-10-21 设计创作，主要内容包括：本发明公开了一种温度变化环境下的超声结构健康监测方法,通过对监测信号和最优基准信号进行重构处理,计算重构后的监测信号和基准信号间的相似性,根据相似性大小判断是否有损伤存在；若有损伤存在,对损伤潜在区域的传播路径求解损伤指数,结合损伤指数与结构受损情况的回归模型输出结构受损程度,本发明所提出的超声结构健康监测方法能够实现在温度变化环境下,对结构进行实时监测且信号的处理过程简单,能够快速输出结构检测结果。(The invention discloses an ultrasonic structure health monitoring method under a temperature change environment, which comprises the steps of reconstructing a monitoring signal and an optimal reference signal, calculating the similarity between the reconstructed monitoring signal and the reference signal, and judging whether damage exists according to the similarity; if the damage exists, solving a damage index for a propagation path of a damage potential region, and outputting the damage degree of the structure by combining the damage index and a regression model of the damage condition of the structure.)

1. An ultrasonic structure health monitoring method under a temperature change environment is characterized by comprising the following steps:

step 1, respectively carrying out reconstruction processing on a monitoring signal and an optimal reference signal;

step 2, calculating the similarity between the reconstructed monitoring signal and a reference signal, and judging whether damage exists according to the similarity;

and 3, if the damage exists, solving a damage index for the propagation path of the damage potential region, and outputting the damage degree of the structure by combining the damage index and a regression model of the damage condition of the structure.

2. The method for monitoring the health of an ultrasonic structure in a temperature variation environment according to claim 1, wherein the optimal reference signal is selected by: under the structural health state, collecting ultrasonic signals at equal temperature intervals, carrying out temperature marking on the ultrasonic signals, and establishing a reference signal database for all the ultrasonic signals with the temperature marks; in the monitoring process, the ultrasonic signal with the temperature closest to the temperature of the current monitoring signal in the reference signal database is screened as the optimal reference signal of the monitoring signal.

3. The method for monitoring the health of an ultrasonic structure in a temperature change environment according to claim 1, wherein the reconstruction processing method comprises:

step 1.1, filtering the monitoring signal and the reference signal respectively;

step 1.2, the filtered signals are respectively subjected to sequencing reconstruction:

u'_baseline(n)＝sort(u_baseline(n))

u'_damage(n)＝sort(u_damage(n))

wherein u is_baseline(n) and u_damage(n) filtered reference and monitor signals, respectively, and sort (x) is a ranking function, u'_baseline(n) and u'_damage(n) are respectively the base after the sequencing reconstructionQuasi-signals and monitor signals.

4. The method for monitoring the health of an ultrasonic structure in a temperature-varying environment according to claim 1, wherein the process of step 2 is as follows:

step 2.1, calculating the similarity between the monitoring signal and the reference signal:

wherein the content of the first and second substances,is the average value of the reference signal and,the mean value of the monitoring signal.

And 2.2, setting a damage judgment Threshold value Threshold, wherein if R is less than or equal to Threshold, the damage exists, and otherwise, the structure is healthy.

5. The method for monitoring the health of an ultrasonic structure in a temperature-varying environment according to claim 1, wherein the process of step 3 is as follows:

step 3.1, calculating a reconstructed reference signal u'_baseline(n) and a monitor signal u'_damage(n) the difference signal;

step 3.2, sequentially carrying out Hilbert transformation on the difference signal and the reference signal to obtain respective corresponding envelope signals;

step 3.3, obtaining a damage index according to the reconstructed reference signal, the difference signal and the corresponding envelope signal;

and 3.4, judging the region where the damage is located according to the damage index among the propagation paths.

6. The method for monitoring the health of an ultrasonic structure under the environment with temperature change according to claim 1, wherein when the structure is healthy, if Δ T is greater than or equal to Δ d, the current optimal reference signal is input into the reference signal database to update the reference signal database, wherein Δ T is the temperature difference between the acquisition temperature of the current monitoring signal and the optimal reference signal, and dT is the temperature acquisition interval.

Technical Field

The invention belongs to the technical field of nondestructive testing and structural health monitoring, and particularly relates to an ultrasonic structural health monitoring method in a temperature change environment.

Background

Nondestructive testing belongs to off-line measurement, and can be used for nondestructively judging defects on the surface and in the structure by using a handheld or large-scale device. Nondestructive testing is generally accomplished by regular on-site measurements by professionals. And sometimes for complex structures built into the equipment, time and labor consuming disassembly work is required. The ultrasonic guided wave based structural health monitoring technology (SHM) is used for installing the sensor on a monitored structure, so that the structural state can be monitored online for a long time. The structure health monitoring technology does not need the characteristic of disassembling equipment and a structure due to online monitoring, is widely applied to the fields of space flight and aviation, high-speed trains, ships and the like, and can effectively improve the safety of the structure in the operation process and reduce the maintenance cost of the equipment. In practical application, the temperature span of the working environment of the structure is often large, and the ultrasonic signals are susceptible to temperature effects in the propagation process to generate phase deviation and amplitude fluctuation, which seriously affects the stability of the monitoring system. Therefore, the development of a stable and efficient temperature insensitive damage index is very important, which can help to prevent safety accidents and avoid unnecessary economic loss.

At present, the temperature compensation method for ultrasonic guided wave nondestructive testing mainly comprises the following steps: an optimal reference method (OBS), a reference extension method (BSS), a temperature compensation method based on a finite impulse response digital filter, and a temperature compensation method based on a physical model. The optimal reference method depends on multi-reference acquisition, although the interference caused by the temperature effect can be quickly and effectively removed, the early-stage work is too complicated, the requirement on hardware equipment is high, and the cost is higher; in the reference expansion method, as long as a single reference signal is changed into an ultrasonic signal within a compensation section of temperature range, the compensation interval is too small, and when the temperature difference is large, the signal distortion phenomenon is easy to occur in the compensation process, so that the compensation is invalid; the temperature compensation scheme of the adaptive filter well reduces the acquisition amount of the reference, but the online calculation amount of the method is large, and when the signal amplitude with large temperature difference is influenced, the compensation effect is limited; the temperature compensation scheme based on the physical model is complex in early modeling, a certain difference still exists between the analog signal and the actually measured signal, and the actual utilization rate is lower at present.

The traditional ultrasonic guided wave temperature compensation scheme is suitable for nondestructive testing in an off-line state, and can realize the storage and complex calculation of a large number of reference signals by using a larger storage space and a processor with good performance so as to realize high-precision temperature compensation. However, in the field of structural health monitoring, a structure needs to be monitored in real time, data storage and signal analysis processing need to be completed in an ultrasonic acquisition analyzer, the analyzer needs to be fixed on the structure, and the size of the analyzer needs to be as small as possible, so that the configuration of internal hardware is limited. Therefore, on the premise, the quick output of the result can be realized only by needing the pre-stored reference data quantity as little as possible and simplifying the signal processing process as much as possible.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides an ultrasonic structure health monitoring method in a temperature change environment, which can monitor a structure in real time in the temperature change environment, has a simple signal processing process and can quickly output a structure detection result.

The technical scheme adopted by the invention is as follows:

step 1, respectively carrying out reconstruction processing on a monitoring signal and an optimal reference signal;

step 2, calculating the similarity between the reconstructed monitoring signal and a reference signal, and judging whether damage exists according to the similarity;

step 3, if damage exists, solving a damage index for a propagation path of the damage potential region, and outputting the damage degree of the structure by combining the damage index and a regression model of the damage condition of the structure;

further, the method for selecting the optimal reference signal comprises the following steps: under the structural health state, collecting ultrasonic signals at equal temperature intervals, carrying out temperature marking on the ultrasonic signals, and establishing a reference signal database for all the ultrasonic signals with the temperature marks; in the monitoring process, an ultrasonic signal with the temperature closest to that of a current monitoring signal in a reference signal database is screened as an optimal reference signal of the monitoring signal;

further, the reconstruction processing method comprises the following steps:

step 1.1, filtering the monitoring signal and the reference signal respectively to remove the influence of environmental noise;

step 1.2, the filtered signals are respectively subjected to sequencing reconstruction:

u'_baseline(n)＝sort(u_baseline(n))

u'_damage(n)＝sort(u_damage(n))

wherein u is_baseline(n) and u_damage(n) filtered reference and monitor signals, respectively, and sort (x) is a ranking function, u'_baseline(n) and u'_damageAnd (n) respectively sequencing the reconstructed reference signal and the reconstructed monitoring signal.

Further, the process of step 2 is as follows:

step 2.1, calculating the similarity between the monitoring signal and the reference signal:

wherein the content of the first and second substances,is the average value of the reference signal and,the mean value of the monitoring signal.

Step 2.2, setting a damage judgment Threshold, wherein if R is less than or equal to the Threshold, damage exists, and otherwise, the structure is healthy;

further, the process of step 3 is as follows:

step 3.1, calculating a reconstructed reference signal u'_baseline(n) and a monitor signal u'_damage(n) the difference signal;

step 3.2, sequentially carrying out Hilbert transformation on the difference signal and the reference signal to obtain respective corresponding envelope signals;

step 3.3, obtaining a damage index according to the reconstructed reference signal, the difference signal and the corresponding envelope signal;

and 3.4, judging the region where the damage is located according to the damage index among the propagation paths.

Further, when the structure is healthy, if delta T is larger than or equal to delta d, the current optimal reference signal is input into the reference signal database, and updating of the reference signal database is achieved, wherein delta T is the temperature difference between the collection temperature of the current monitoring signal and the optimal reference signal, and dT is the temperature collection interval.

The invention has the beneficial effects that:

firstly, the monitoring method of the invention adopts the signal sequencing reconstruction and the correlation calculation with the reference signal, can accurately judge whether the fluctuation of the signal is the influence of the interference or the damage of the temperature effect, enlarges the compensation interval of a single reference signal, establishes a reference database by combining the optimal reference method, greatly reduces the acquisition and the storage of the reference signal, and expands the applicable temperature range of the on-line monitoring system. Secondly, through a damage judgment link, the online computation amount of the CPU can be effectively reduced, and the output of a result is accelerated; and finally, calculating a corresponding damage index according to the difference between the signals, and combining a damage grade regression model to effectively output the damage degree of the structure.

Meanwhile, the monitoring method of the invention also has the function of updating the reference signal database. As the adhesive layer is influenced by the external environment to cause the performance of the adhesive layer to be attenuated along with the use time, the existing database is updated by setting the fixed temperature collection interval dT. And when the temperature difference delta T between the scanning signal and the screened optimal reference is larger than dT and the calculated signal similarity R is larger than Threshold, storing the scanning signal into a reference signal library and expanding the applicable temperature range.

Drawings

FIG. 1 is a flow chart of a method for ultrasound structural health monitoring in a temperature changing environment;

FIG. 2 is a schematic diagram of a sensor monitoring network;

FIG. 3 is a diagram of time domain signals before and after filtering;

FIG. 4 is a graph of the difference between reference signals and the difference between damage and reference signals at different temperatures;

FIG. 5 is a reconstructed reference signal and impairment signal based on rank ordering;

FIG. 6 is a graph of injury index after injury prediction;

FIG. 7 is a regression model of injury index and injury rating.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention constructs an ultrasonic signal acquisition system based on a piezoelectric ceramic sensor for acquiring the ultrasonic signal of a structure, and the ultrasonic signal acquisition system specifically comprises: the ultrasonic signal acquisition and analysis device comprises an ultrasonic acquisition analyzer, an ultrasonic sensor and a temperature sensor, wherein excitation frequency and power amplification times are input into the ultrasonic analyzer, signals are excited and received through the ultrasonic sensor, and received signals u (n) are marked through temperature information acquired by the temperature sensor, so that the ultrasonic signals with temperature marks are obtained. In this example, an ultrasonic analyzer model D110C manufactured by Broadsens is used, the ultrasonic analyzer internally comprises an integrated signal generator module, a signal power amplifier module, a CPU online computation module and 17 ultrasonic sensor channels, each channel supports 1 sending and 4 receiving, and the total number of the channels is 17 sending and 68 receiving; the sensors used were model BHU500, model BHU580 ultrasonic sensors, and model TMP210 temperature sensors (other models of data acquisition devices, piezo ceramic sensors, and temperature sensors are equally suitable) manufactured by Broadsens. The sampling frequency of the signal is 20MHz, and the number of the sampling points is 8192 (the sampling frequency of the signal can be set to other values according to a Nyquist law, and the number of the sampling points can be adjusted according to the length of a useful signal).

Before the ultrasonic signal acquisition system works, as shown in fig. 2, firstly, the distribution of ultrasonic sensors and the interaction network of the propagation paths of the ultrasonic sensors are determined on the surface of a structure, the ultrasonic sensors are arranged in an oblique symmetry manner in an area to be monitored, it is ensured that at least one intersection point of the propagation paths exists on each propagation path, a temperature sensor is arranged on the surface of the structure, the coordinates of the sensors are input into an ultrasonic sampling system, and a sensor monitoring network is established, wherein in fig. 2, an actor is an ultrasonic sensor generating signal excitation, and Rx is an ultrasonic sensor for receiving.

Before the method starts monitoring, the ultrasonic signal acquisition system acquires ultrasonic signals at equal temperature intervals as reference signals in a structural health state, and temperature marking is carried out on the ultrasonic signals to establish a reference signal database.

Referring to fig. 1, the method for monitoring the health of an ultrasonic structure in a temperature change environment provided by the invention specifically comprises the following steps:

step 1, screening an ultrasonic signal with the temperature closest to that of a current monitoring signal from a reference signal database according to the acquired monitoring signal, and respectively carrying out reconstruction processing on the monitoring signal and the corresponding reference signal, wherein the reconstruction processing specifically comprises the following steps:

step 1.1, in the detection process of a complex structure, due to the existence of environmental noise and interference of monitoring in other areas, a phenomenon of overlapping multiple frequencies may occur in an acquired signal, so that the received signal cannot be directly used for analysis; therefore, the monitoring signal and the reference signal are respectively filtered, and the influence of environmental noise is removed as shown in fig. 3;

step 1.1.1, transforming a time domain signal to a frequency domain through FFT to obtain a frequency spectrum of the signal;

wherein, x (k) is a signal spectrum, N is a signal period, and x (N) is a periodic sequence;

step 1.1.2, picking up the center frequency of a frequency spectrum according to the excitation frequency of a signal, and utilizing a Hanning window to cut off the frequency spectrum;

wherein w [ n ] is a Hanning window function;

and step 1.1.3, carrying out iFFT (inverse fast Fourier transform) on the cut frequency spectrum, and taking a real part of a transformed signal to obtain a filtered time domain signal.

Step 1.2, sequencing and reconstructing the filtered signals respectively;

step 1.2.1, reference signal u obtained after filtering_baseline(n) and a monitoring signal u_damage(n) carrying out truncation processing, intercepting n point data points after the crosstalk wave packet, and arranging the intercepted data points:

u'_baseline(n)＝sort(u_baseline(n))

u'_damage(n)＝sort(u_damage(n))

wherein u'_baseline(n) and u'_damage(n) are the reconstructed reference signal and the reconstructed monitor signal, sort (x) is a sorting function, in this example, under the condition that the same reference is used as a reference, the difference between the reference signals at a temperature interval of 3 ℃ is far greater than the difference between the damage and the reference, as shown in fig. 4, the damage judgment cannot be accurately carried out; as can be seen from fig. 5, when only the temperature effect is present, the reconstructed signals are almost completely aligned, and when the damage is present, there is a significant deviation between the damage signal and the reference signal.

Step 2, calculating the similarity between the reconstructed monitoring signal and a reference signal, and judging whether damage exists according to the similarity;

step 2.1, obtaining a reconstructed reference signal u 'by utilizing a cross-correlation function'_baseline(n) and a monitor signal u'_damage(n) similarity coefficient between R:

wherein the content of the first and second substances,is the average value of the reference signal and,is the mean value of the monitoring signal;

and 2.2, comparing the similarity coefficient R with a damage judgment Threshold value Threshold, outputting the health condition of the structure, and extracting a path with R lower than Threshold if the damage exists.

Wherein, 1 represents that the damage exists, 0 represents that the structure is healthy, and the Threshold value Threshold is selected according to the characteristics of the material and the structure.

Step 3, if there is damage, solving a damage index for the propagation path of the damage potential region, and outputting the structural damage degree by combining the damage index and a regression model of the structural damage condition as shown in fig. 7, wherein the specific process is as follows:

step 3.1, calculating a reconstructed reference signal u'_baseline(n) and a monitor signal u'_damageDifference signal of (n):

u_residual(n)＝u'_damage(n)-u'_baseline(n)

step 3.2, solving the reconstructed reference signal u 'by using Hilbert transform'_baseline(n) and a difference signal u_residual(n) envelope signal, introducing an analytic function z (n) by Hilbert transform:

the real part of the analytic signal is a reconstructed real-value signal u (n), and the imaginary part isU (n) is obtained after Hilbert transformation,a (n) is the envelope of the signal u (n), and the specific calculation formula is as follows:

respectively obtaining reconstructed reference signals u'_baseline(n) and a difference signal u_residual(n) letterNumber envelope signal A_baseline(n)，A_residual(n)。

Step 3.3, as shown in fig. 6, the method for solving the propagation path for the damage index includes: according to the reconstructed reference signal u'_baseline(n) difference signal u_residual(n) solving the damage index DI with the obtained reconstructed signal envelope:

and 3.4, inputting the combined damage index DI into the damage grade regression model to obtain the damage degree of the structure, and further alarming the damage degree of the structure, as shown in FIG. 7.

level＝f(DI)

Wherein, f (x) is a damage grade function, f (x) is a regression model of damage index and structure damage condition, and the severity of structure damage can be output after the damage index is input.

And 4, when R between the real-time acquisition signal and the optimal reference signal is greater than Threshold, namely the structure is healthy, if delta T is greater than or equal to dT, inputting the current optimal reference signal into a reference signal database to update the reference signal database, wherein delta T is the temperature difference between the acquisition temperature of the current monitoring signal and the optimal reference signal, and dT is the temperature acquisition interval. Due to the fact that the external environment can cause aging of the bonding layer, the received ultrasonic signals are further caused to have the phenomena of amplitude attenuation and slow arrival time. In order to avoid the phenomenon of damage misjudgment caused by aging of components in the long-term monitoring process, the method can avoid the phenomenon by updating the reference signal database in real time, and ensure the stability of system operation.

The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.