CN100580445C - Engineering structure damage active monitoring Lamb wave time-reversal focusing method - Google Patents

Abstract

The invention discloses a method of focusing by time reversal for Lamb wave in actively monitoring the engineering structural damage. The method includes the following steps: step one: collecting the damage dispersion signals; step two: carrying out time reversing treatment; and step three: focusing the damage dispersion signals. By sue of the sensor/stimulator array technology, and based on the prior structural damage monitoring equipment, the invention, having no necessity of any other special equipment, adopts the convolution operation to focus the Lamb wave signals in the damage monitoring system, improves the signal to noise ratio of the damage dispersion signals, and simplifies the method of extracting the characteristic parameters, thereby enhancing the accuracy and the stability of the monitoring system.

Description

Lamb wave time-reversal focusing method in a kind of engineering structure damage active monitoring

One, technical field

The present invention relates to the initiatively method of Lamb ripple damage monitoring of a kind of plate class engineering structure, relate in particular to a kind of initiatively Lamb wave structure damage monitoring signal time counter-rotating focusing enhancing of realization under conventional common apparatus condition, thus the method for realization engineering structure damage monitoring.

Two, background technology

Along with to the improving constantly of safety of structure, reliability requirement, the on-line monitoring of structural damage and diagnosis cause people's great attention day by day, for disaster or the loss that prevents that structural damage from bringing, must effectively monitor structure.

It is relative simple with collecting device that the on-line monitoring of structural damage requires coherent signal to take place, and monitoring must have very high real-time and accuracy.The damage monitoring of plate structure generally adopts the initiatively method of Lamb ripple, promptly at the driver and the sensor of body structure surface or inner integrated some, as piezoelectric element, in addition, whole monitoring system also comprises signal generation apparatus, power amplifier, signal amplifier and counts the equipment etc. of adopting, when monitoring, at first in structure, encourage certain waveform, receive the scattering wave of response of structure and damage generation by sensor, collect in the computing machine, computer program is determined the position and the scope of damage according to information such as the due in that damages scattering wave, phase places.According to the Lamb theory of wave propagation, there is mode conversion in the communication process of Lamb ripple in plate structure, each mode signal has different sensitivitys and response to damage, monitored structure is generally all comparatively complicated simultaneously, in the transducing signal aliasing there are a large amount of scattered signals that cause by border, screw hole, reinforcement etc., these undesired signals are identical with the mechanism of production of damage scattered signal, therefore have identical time and frequency domain characteristics, also just are difficult to they are made a distinction.These problems have been brought difficulty to the characteristic parameter of correct analysis sonic propagation process and extraction damage scattered signal, especially in compound substance plate structure damage monitoring, owing to there is anisotropy, make this problem become complicated more.For example: Flight Vehicle Structure has adopted a large amount of compound substances at present, and structure is all very complicated, the online damage monitoring of exploratory flight device structure must at first overcome the extraction problem of damaging scattered signal.Therefore, must effectively amplify,, guarantee authenticity, validity and the stability of monitoring result correctly to extract and to damage relevant characteristic parameter to the damage scattered signal.

After time reversal, (being called phase conjugate in the frequency domain) focus method was meant that sensor array receives the time-domain signal of sound source emission, anti-during with its signal, launch again, arrive first promptly that the back is sent out, the back is to sending out earlier.This method can make the energy of signal obtain focusing on room and time, realizing sound-source signal reconstruct by this focusing, is that a kind of priori of medium and sensor array character and structure that do not need just can realize the method that the sound wave self-adaptation focuses on and detects.This theory is proved to be the self-adaptation focusing power of wave source and can be used for realizing in the conventional ultrasound Non-Destructive Testing signal focus of injury region is improved the energy of damage scattered signal whereby, improves the signal to noise ratio (S/N ratio) of transducing signal.But present signal time counter-rotating focus method is realizing under the complex apparatus condition comparatively that all sensor/exciter array, signal generator, data acquisition equipment etc. are all had very high requirement, does not obviously satisfy the requirement of online structure damage monitoring; Simultaneously, in the active Lamb of plate structure ripple damage monitoring, the Lamb ripple is propagated non-directional, and each sensor is when receiving damage focusing enhancing scattered signal, also receiving signal time reversal that each sensor excites, these signals will be superimposed and be difficult to distinguish.Therefore, in active Lamb wave structure health monitoring technology, adopt conventional equipment and method to be difficult to obtain and focus on the damage scattered signal that strengthens, must adopt new disposal route and technology to realize the focusing and the collection of damage scattered signal.

Three, summary of the invention

1, technical matters: technical matters of the present invention provides Lamb wave time-reversal focusing method in a kind of engineering structure damage active monitoring, this method has been used sensor/exciter array technology, on existing structure damage monitoring appointed condition basis, need not other specific installations adopts convolution algorithm to handle the focusing that realizes Lamb ripple signal in the damage monitoring system, improve the signal to noise ratio (S/N ratio) of damage scattered signal, simplify the characteristic parameter extraction method, thereby improve the accuracy and the stability of monitoring system.

2, technical scheme: in order to solve above-mentioned technical matters, method of the present invention comprises the following steps:

(1) gather the structural response signal:

Comprise the following steps:

(1.1) structurally arrange one group of piezoelectric element composition sensing/excitation array;

(1.2) Lamb ripple narrow band signal is loaded into a piezoelectric excitation element (P of piezoelectric element group in the step (1.1) by function generator and power amplifier _j) on, in structure, excite pumping signal; Another piezoelectric element (P in the selected simultaneously piezoelectric element group _j) as the sensor acquisition structural response;

(1.3) be basic signal with the structural response under the health status, the structural response under the faulted condition is subtracted each other with it, obtain damaging scattered signal;

(1.4) piezoelectric element of selected piezoelectric element group obtains the damage scattered signal (f under all excitation/sensing passages as driver successively _Ji) (i, j=1,2,3 ...);

(2) handle time reversal:

Damage scattered signal (the f that collects according to step (1) _Ji) attenuation degree of energy, carry out time reversal and handle, obtain treated damage loose thank signal (f ' _Ji); When carrying out handling time reversal, the selected identical zero hour and time span formation time window, the concentration of energy that makes response signal is reversed the signal in the time window in this time window;

(3) the damage scattered signal focuses on:

The damage scattered signal of handling through time reversal that step (2) is obtained (f ' _Ji) with step (1) in the damage scattered signal (f that handles without counter-rotating _Ji) corresponding convolution, the convolution results correspondence is added up realize each sensor (P again _i) on the damage scattered signal focus on to strengthen, be beneficial to the knowledge of debating of structural damage state, thus the implementation structure damage monitoring.

In this step, all through intercepting and the damage scattered signals after handling time reversal with handle before all damage scattered signals---damage scattering---according to acoustic wave excitation the process rule of sensing carried out corresponding convolution, with add up damage scattering focus signal on each sensor of realization of convolution results correspondence.

Debate when knowing carrying out the structural damage state, at first carry out the extraction of characteristic parameter, in the damage scattering focus signal that obtains in step (3), extract the peak value due in as damage scattered signal due in, as characteristic parameter, carry out damage check, position that obtains damaging and scope, thus analyze, judge the health condition that obtains monitored structure.Can adopt damage detecting method commonly used, method such as 4 circular arc localization methods, oval localization method for example calculates the position of damage, finishes the monitoring of structural health situation.

Ultimate principle of the present invention is: determining frequently thickly when long-pending, the propagation characteristic of Lamb ripple signal determines that thereupon parameters such as speed are also just determined.Therefore, can adopt the Signals ﹠ Systems theory, it is a system that signal excitation, propagation and sensing process are regarded as, adopts systematic analytic method, and Lamb ripple communication process is analyzed and handled.In the system that forms by exciting element, structure, sensor, exciting element can be regarded signal input part as, sensor is an output terminal, and structure can be described with transport function, and the output of system just can be regarded the convolution of pumping signal and structure transport function as.When damage takes place in structure, all comprise scattered signal in the Lamb signal that each sensor receives from same damage, and therefore each self-contained other boundary scattering signal has only damage to play the wave source effect in the communication process of whole signal from the scatterer of diverse location.Utilize the time reversal theory to the self-adaptation focusing power of wave source, by each transducing signal time-reversal focusing being strengthened the intensity of injury region signal, and then the energy of raising damage scattered signal, and the boundary scattering signal is not owing to possess the feature of wave source, to can not get focusing on and strengthen, thereby outstanding damage scattered signal, the signal to noise ratio (S/N ratio) of raising signal.Based on systematic analytic method, adopt process of convolution can in computing machine, realize this process, thereby on the basis that does not need other appointed conditions, realize the focusing enhancing and the signal to noise ratio (S/N ratio) of damage scattered signal are improved.The inventive method is according to the signal system theory method, ultimate principle according to time-reversal focusing, adopt convolution algorithm to realize the focusing enhancement process of damage scattered signal, solve the reception problem again of damage scattered signal, the signal to noise ratio (S/N ratio) that can effectively realize signal under limited appointed condition improves, and helps promoting the promotion and application of structural health monitoring technology.

Further specify this method below in conjunction with computing formula:

According to signal system theory, work as P _jDuring for driver, the signal transfer function that can set from the exciting element to the injury region is H _JD(ω), and injury region is H to the transport function of each sensor _Di(ω), (i, j=1,2,3 ...), sensor P then _iOn the damage scattered signal f that receives _JiFrequency spectrum F _Ji(ω) be:

F _ji(ω)＝S(ω)·H _jD(ω)·H _Di(ω) (3-1)

The anti-loading during with transducing signal then can obtain at injury region:

$D_i\left(\mathrm{\ω}\right)=\underset{i}{\mathrm{\Σ}}{S}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right)\·H_{D}i\left(\mathrm{\ω}\right)---(3-2)$

$=S^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}\left(\mathrm{\ω}\right)$

The enhancing that each sensor receives the damage scattered signal will change into:

$R_k\left(\mathrm{\ω}\right)=H_{\mathrm{Dk}}\left(\mathrm{\ω}\right)\·S^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}\left(\mathrm{\ω}\right)---(3-3)$

$=\underset{i}{\mathrm{\Σ}}(S^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right))\·(H_{\mathrm{Di}}\left(\mathrm{\ω}\right)\·H_{\mathrm{Dk}}\left(\mathrm{\ω}\right))$

K=1 wherein, 2,3 ...

From formula (3-3), be not difficult to find " S ^*(ω) H _JD ^*(ω) H _Di ^*(ω) " be sensor P _iReceive initial excitation element P _jSignal time reversal of the damage scattered signal during excitation, and " H _Di(ω) H _Dk(ω) " just be piezoelectric element P _iAs exciting element, piezoelectric element P _kThe transport function of the damage scattering sensing passage during as sensor.In practical operation, can ask for the transport function of monitoring channel in order to reduce computing, with convolution S (ω), then (3-3) can be write as at (3-3) formula two ends:

$R_k^{\′}\left(\mathrm{\ω}\right)=R_k\left(\mathrm{\ω}\right)\·S\left(\mathrm{\ω}\right)=H_{\mathrm{Dk}}\left(\mathrm{\ω}\right)\·S^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}\left(\mathrm{\ω}\right)\·S\left(\mathrm{\ω}\right)---(3-4)$

$=\underset{i}{\mathrm{\Σ}}(S^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{jD}}^{*}\left(\mathrm{\ω}\right)\·H_{\mathrm{Di}}^{*}\left(\mathrm{\ω}\right))\·(H_{\mathrm{Di}}\left(\mathrm{\ω}\right)\·H_{\mathrm{Dk}}\left(\mathrm{\ω}\right)\·S\left(\mathrm{\ω}\right))$

H in the following formula _Di(ω) H _Dk(ω) S (ω) is piezoelectric element P _iAs exciting element, piezoelectric element P _kDamage scattered signal during as sensor, such processing will reduce the difficulty and the operand of actual treatment greatly, can't change transport function simultaneously, and will be only relevant with the form of pumping signal, bring influence therefore can't for the damage location.

In the above-mentioned formula, formula (3-1), formula (3-2), formula (3-4) have been expressed the operating process of step (1), step (2), step (3) respectively.

3, beneficial effect: (1) method of the present invention has improved the Signal-to-Noise based on the structure damage monitoring method of active Lamb wave technology, helps the practicability of this technology.As Fig. 2, shown in Figure 4, for same device parameter situation, the amplitude that adopts the inventive method to handle the damage scattered signal that obtains obviously strengthens, ripple bag for energy maximum in the whole signal, and when adopting classic method, the ripple bag that can not guarantee energy maximum in the transducing signal is for the damage scattered signal, as the f among Fig. 2 c ₃₄, f ₄₂Deng; (2) method of the present invention need not change or increase equipment and parameter in implementation procedure, utilizes the existing hardware system just can realize; (3) implementation method of the present invention is simple, need not to know the priori of monitoring target and sensor array; (4) the present invention can simplify the temporal signatures Parameter Extraction.Reaching of damage signal constantly is to adopt maximum characteristic parameters, in classic method, since in the transducing signal aliasing a large amount of edge reflection signals, need to adopt comparatively complicated signal processing technology to draw damage signal and reach constantly, and the inventive method only need determine that the maximal peak point moment corresponding gets final product.

Four, description of drawings

Fig. 1 the inventive method principle schematic;

Among the figure: a, based on the damage sensing process of piezoelectric-array; B, the counter-rotating of damage scattered signal focus on sensing process again;

The damage scattered signal figure that obtains by classic method when Fig. 2 forms sensor/exciter array by 4 piezoelectric patches;

Among the figure: a, sensing/excitation array layout synoptic diagram and the test specimen original paper (piezoelectric patches spacing 15cm～20cm, test specimen are the carbon fibre composite plate) formed by 4 piezoelectric elements; B, excitation signal waveforms time-domain diagram; C, respectively damage scattered signal normalization waveform time-domain diagram;

Fig. 3 carries out result schematic diagram after handle time reversal to normalization damage scattered signal among Fig. 2;

The enhancing damage scattered signal envelope diagram (piezoelectric element 3 is as the initial excitation element) that Fig. 4 adopts method of the present invention to obtain;

Among the figure: the focus signal envelope line chart at a, piezoelectric patches 1 place; The focus signal envelope line chart at b, piezoelectric patches 2 places; The focus signal envelope line chart at c, piezoelectric patches 4 places;

Fig. 5 damage signal time-reversal focusing enhancement process process flow diagram.

Five, embodiment

Present embodiment adopts test specimen and the piezoelectric element layout shown in Fig. 2 (a).Wherein test specimen is the carbon fibre reinforced composite plate, be of a size of 500mm * 500mm * 3mm, piezoelectric element quantity is 4, and wherein 3 elements are arranged by symmetric position, for investigating the influence of distance to signal, last piezoelectric element skew symmetry position 50mm is a true origin with the test specimen plate lower left corner, and the coordinate of 4 piezoelectric elements is respectively 1 (175mm, 175mm), 2 (175mm, 325mm), 3 (325mm, 375mm), 4 (325mm, 175mm).Embodiment adopts the generation of the mode Simulation Damage that loads counterweight, the loading position coordinate be (250mm, 285mm), diameter 19mm.

As shown in Figure 4, present embodiment comprises the following steps:

(1) gather the structural response signal:

Shown in Fig. 2 (a), structurally form sensing/excitation array according to monitoring content and 4 piezoelectric elements of area arrangements, by function generator and power amplifier the narrow band signal of setting is loaded into selected piezoelectric excitation element P _jOn, in structure, exciting pumping signal, this signal is a sinusoidal modulation signal, centre frequency 40KHz is shown in Fig. 2 (b); Selected other piezoelectric elements P _i(i, j=1,2,3 ...) as sensor, amplify the structural response signals collecting in control computer through charge amplifier, finish one group of measurement.With the structural response under the health status is basic signal, the structural response under the faulted condition is subtracted each other the damage scattered signal f that the difference signal that obtains causes for damage with it _Ji, be parameter with the signal peak, with f _JiCarry out normalized.In turn selected piezoelectric element obtains the normalization damage scattered signal under all excitation/sensing passages, shown in Fig. 2 (c) as driver.

The employed hardware components of present embodiment method is identical with the hardware components of classic method monitoring system, generally by forming with the lower part: control computer, piezoelectric excitation/sensing network, multi-channel switch, function generator, power amplifier, charge amplifier/voltage amplifier and data collector;

(2) handle time reversal:

The attenuation degree of the structural response signal energy that collects according to step (1), the selected identical zero hour and time span formation time window, energy of the signal of window intercepting is the main part of whole response signal gross energy when making this, with the time signal counter-rotating in the window, anti-damage scattered signal f ' when obtaining _Ji, as shown in Figure 3;

(3) the damage scattered signal focuses on:

Employing formula (3-3) or the disposal route of (3-4) explaining are with all signal f ' _JiWith f _JiThe process rule of sensing is carried out corresponding convolution---to damage scattering---according to acoustic wave excitation, the convolution results correspondence added up realize damage scattering focus signal on each sensor, focus on cumulative process and result as shown in Figure 4, piezoelectric element 3 is the initial excitation element among this result, for the ease of clearly finding out the focusing process, waveform shows the envelope form that adopted;

(4) characteristic parameter extraction and structural health conditions identification:

After all signal Processing finish, respectively damage in the scattering focus signal with the peak value due in as characteristic parameter, calculate the position and the scope of damage, analyze, judge the health condition of monitored structure resulting.

Number for piezoelectric element in the sensor array, can determine according to actual condition of structure to be monitored, 3 piezoelectric elements just can be formed a monitoring means in theory, according to circumstances can form sensing network when structure is big by arranging a plurality of piezoelectric elements, adopt the mode of scanning to carry out, the monitoring concrete steps of each unit are identical in the network.

Claims (3)

1, Lamb wave time-reversal focusing method in a kind of engineering structure damage active monitoring is characterized in that, comprises the following steps:

Step 1: gather the damage scattered signal:

Comprise the following steps:

(1.1) structurally arrange one group of piezoelectric element composition sensing/excitation array;

(1.2) Lamb ripple ultrasonic signal is loaded into a piezoelectric excitation element P of piezoelectric element group in the step (1.1) by function generator and power amplifier _jOn, in structure, excite pumping signal; Another piezoelectric element P in the selected simultaneously piezoelectric element group _iAs the sensor acquisition structural response;

(1.3) be basic signal with the structural response under the health status, the structural response under the faulted condition is subtracted each other with it, obtain damaging scattered signal;

(1.4) piezoelectric element of selected piezoelectric element group obtains the damage scattered signal f under all excitation/sensing passages as driver successively _Ji, i wherein, j=1,2,3

Step 2: handle time reversal:

The damage scattered signal f that collects according to step 1 _JiThe attenuation degree of energy carries out time reversal and handles, and obtains treated damage scattered signal f ' _Ji

Step 3: the damage scattered signal focuses on:

The damage scattered signal f ' that handles through time reversal that step 2 is obtained _JiWith the damage scattered signal f that handles without counter-rotating in the step 1 _JiCorresponding convolution adds up the convolution results correspondence and realizes each sensor P _iOn the damage scattered signal focus on to strengthen.

2, Lamb wave time-reversal focusing method in a kind of engineering structure damage active monitoring as claimed in claim 1 is characterized in that, the Lamb ripple ultrasonic signal in the step 1 is an arrowband Lamb ripple signal.

3, Lamb wave time-reversal focusing method in a kind of engineering structure damage active monitoring as claimed in claim 1 or 2, it is characterized in that,---damage scattering---process rule of sensing in step 3, according to acoustic wave excitation is to the damage scattered signal f ' that handles through time reversal _JiWith the damage scattered signal f that handles without counter-rotating in the step 1 _JiCarry out corresponding convolution and add up, realize the time-reversal focusing enhancement process of damage scattered signal on each sensor.

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