CN104101648A - Ultrasonic guided-wave defect locating method based on Liapunov index - Google Patents

Ultrasonic guided-wave defect locating method based on Liapunov index Download PDF

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CN104101648A
CN104101648A CN201410142371.3A CN201410142371A CN104101648A CN 104101648 A CN104101648 A CN 104101648A CN 201410142371 A CN201410142371 A CN 201410142371A CN 104101648 A CN104101648 A CN 104101648A
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signal
lyapunov exponent
detection
defect
intercept
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张伟伟
武静
马宏伟
杨飞
林金保
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Jinan University
University of Jinan
Taiyuan University of Science and Technology
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Jinan University
Taiyuan University of Science and Technology
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Abstract

The invention discloses an ultrasonic guided-wave defect locating method based on Liapunov index, and the method is as follows: constructing a duffing oscillator signal detection system on the basis of duffing equation, calculating the Liapunov index variable with driving force F change; exciting ultrasonic guided wave signals on a to-be-tested material through an emitter, traversing all positions of the to-be-tested material with the ultrasonic guided wave signals, and obtaining an actually measured signal by a receiver; constructing a window function, intercepting, from the actually measured signal, interception signals with length corresponding to different window length, inputting each interception signal into theinterception signal, calculating the Liapunov index with driving force F change after the interception signals are inputted; determining the interception signal corresponding to the window length of greatest driving force F change amount, moving the window function to scan the interception signal for defect locating of the to-be-tested material. The ultrasonic guided-wave defect locating method can be used for ultrasonic guided wave signal identification, locating of defects in different degrees of injury, and improvement of the sensitivity of ultrasonic guided wave identification of small defects.

Description

The method of the supersonic guide-wave location defect based on Lyapunov exponent
Technical field
The present invention relates to ultrasonic guided wave detection technology field, particularly a kind of method of the supersonic guide-wave location defect based on Lyapunov exponent.
Background technology
Pipeline transportation is widely used in industry-by-industry in recent years, is one of important component part of national economy multi-transportation, is also the outstanding feature whether national energy of measurement and forwarding business be flourishing.But the pipeline accident causing due to the factor such as environmental impact and artificial destruction takes place frequently, cause serious national economy loss and casualties.Therefore, pipeline is carried out to health detection very necessary.Utilize ultrasonic guided wave detecting method to become the important method that long distance line detects, compared with conventional ultrasonic wave Non-Destructive Testing, it is fast that supersonic guide-wave has detection speed, and sensing range is wide and without removing the advantages such as overlayer.At present, accuracy of detection and detection distance and defect parameters identification problem have become the difficulties of ultrasonic guided wave detection technology.
In order to improve the detection sensitivity of supersonic guide-wave, Chinese scholars is mainly optimized from following three aspects: one, the Propagation Characteristics of ultrasound wave pipeline configuration; Two, exciting with receiving trap of supersonic guide-wave studied; Three, signal analysis and defect characteristic extract.At present, researcher more and more payes attention to analysis and the research to ultrasonic guided wave signals both at home and abroad, and has developed many methods effectively.But these methods are the basis such as characteristic and the signal to noise ratio (S/N ratio) research from signal itself mostly, mostly adopt noise reduction and improve the method for signal to noise ratio (S/N ratio), there is certain difficulty.Find new Weak Signal Detection Method and become a large hot issue urgently to be resolved hurrily.And chaos system is owing to having initial value susceptibility, noise signal is had to certain immunocompetence simultaneously, become the frontier of Testing of Feeble Signals under very noisy.But utilizing the Testing of Feeble Signals of chaos system is master mainly with detection sine, cosine signal; Be new application in recent years to the identification of ultrasonic guided wave signals, still in the theory study stage, concerning staff in the industry, Major Difficulties is setting parameter and the defect parameters identification of smart detector system.
Summary of the invention
In order to address the above problem, the invention provides a kind of method of the supersonic guide-wave location defect based on Lyapunov exponent, so that ultrasonic guided wave signals is identified, and the defect of Injured level is positioned, raising supersonic guide-wave is identified the sensitivity of little defect.
A kind of method that the invention provides supersonic guide-wave location defect based on Lyapunov exponent, comprises the following steps:
S1, based on duffing equation structure Du Fen oscillator signal detection system, and calculate the Lyapunov exponent changing with driving force F;
S2, encourage ultrasonic guided wave signals by transmitter detecting on thing, make all positions of ultrasonic guided wave signals traversal detection thing, then obtain measured signal by receiver;
S3, tectonic window function intercept intercept signal corresponding to different window length from described measured signal, by described each intercept signal input Du Fen oscillator signal detection system, and calculate respectively the Lyapunov exponent changing with driving force F after input intercept signal;
S4, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it, thereby the defect detecting on thing is positioned.
Preferably, in described step S1, further comprise based on duffing equation structure Du Fen oscillator signal detection system:
S11, choose duffing equation, and be provided with detection signal, its formula is as follows:
x · · + k x · - x 3 + x 5 = F cos ωt + s ‾ ( t ) - - - ( 1 )
Wherein, k is damping ratio, and ω is driving force angular frequency, (x 3+ x 5) be nonlinear resilience item, for detection signal, Fcos ω t is driving force item, and F is driving force, and described F meets when and if only if ultrasonic guided wave signals input duffing equation, and described Du Fen oscillator signal detection system changes;
S12, choose displacement x and speed v formula (1) rewritten as follows:
x · = v v · = - kv + x 3 - x 5 + F cos ( ωt ) + s ‾ ( t ) - - - ( 2 )
Complete the structure of Du Fen oscillator signal detection system.
Preferably, in described formula (1), k gets 0.5, F, and to get 0.8105, ω identical with the frequency of intercept signal to be measured.
Preferably, in described step S1, the Lyapunov exponent of Du Fen oscillator signal detection system is calculated as follows:
The Du Fen oscillator signal detection system that formula (2) is represented forms the three dimension system taking displacement x, speed v and time t as state variable, in the t=0 moment, and centered by x0, || δ x (x 0, 0) || for radius does a three-dimensional sphere, along with the evolution of time, be deformed into three-dimensional ellipsoid at this sphere of t moment, half axial length of establishing i change in coordinate axis direction of this ellipsoid is || δ x i(x 0, 0) ||, i Lyapunov exponent of described three dimension system is:
L i = lim t → ∞ 1 t ln | | δ x i ( x 0 , t ) | | | | δ x i ( x 0 , 0 ) | | - - - ( 3 )
Through type (3) calculates the Lyapunov exponent of Du Fen oscillator signal detection system.
Preferably, described in described step S2, the expression formula of ultrasonic guided wave signals is:
s ( t ) = [ 1 2 ( 1 - cos 2 π f c t n ) ] sin ( 2 π f c t )
(4)
Wherein, n is the single audio frequency number of selecting, f cfor the centre frequency of signal.
The window function of preferably, constructing in described step S3 is:
S*=g(t-τ)S,
Wherein, S represents the measured signal of recording, and S* represents intercept signal.
Preferably, described step S4 further comprises:
S41, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it;
S42, in the moving process of described window function, draw the curve that Lyapunov exponent changed with center moment of described window function;
S43, sudden change location defect guided wave signals according to described Lyapunov exponent on described curve, and lead velocity of wave propagation according to defect, the defect on described detection thing is positioned.
Preferably, described step S43 is further:
Work as L 1when > 0, corresponding intercept signal does not have flaw indication, detects thing excellent; Work as L 1when < 0, corresponding intercept signal contains flaw indication, detects in thing containing defectiveness.
Preferably, described method further comprises:
S5, the corresponding intercept signal of window length of described Lyapunov exponent change amount maximum is carried out to spectrum analysis, defect location result in described result of spectrum analysis and described step S4 is compared, further the sensitivity of the defect location in described step S4 is assessed.
Preferably, described step S5 intermediate frequency spectrum analytical formula is:
F S ( j&omega; ) = lim t &RightArrow; &infin; 1 T | &Integral; 0 T s ( t ) e - j&omega;t dt | 2
(6)。
The beneficial effect of the embodiment of the present invention is: the method for a kind of supersonic guide-wave location defect based on Lyapunov exponent provided by the invention, utilize the center moment location defect guided wave signals of time shift window function, and according to guided wave velocity of propagation location defect, utilize the present invention can orient the position of less defect, it is simple to operate, accurate, economical, there is innovative significance, have a wide range of applications.
Brief description of the drawings
Fig. 1 is the process flow diagram of the method for a kind of supersonic guide-wave location defect based on Liapunov Lyapunov index of one embodiment of the invention;
Fig. 2 is the intercept signal corresponding to different window length of one embodiment of the invention;
Fig. 3 is the rule figure of the change amount of the caused Lyapunov exponent of different window length of one embodiment of the invention;
Fig. 4 is the schematic diagram that utilizes pipeline experiment;
Fig. 5 is the displacement time-history curves of corresponding measured signal under two kinds of operating modes;
Fig. 6 is the spectrum analysis curve map of corresponding intercept signal under two kinds of operating modes;
Fig. 7 is the Lyapunov exponent analytic curve figure of corresponding intercept signal under two kinds of operating modes;
Fig. 8 is two kinds of intercept signal curve maps under operating mode and corresponding defect location curve map.
Embodiment
For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, embodiment of the present invention is described further in detail.
As shown in Figure 1, the invention provides a kind of method of the supersonic guide-wave location defect based on Liapunov Lyapunov index, comprise the following steps:
S1, based on duffing equation structure Du Fen oscillator signal detection system, and calculate the Lyapunov exponent changing with driving force F;
S2, encourage ultrasonic guided wave signals by transmitter detecting on thing, make all positions of ultrasonic guided wave signals traversal detection thing, then obtain measured signal by receiver;
S3, tectonic window function intercept intercept signal corresponding to different window length from described measured signal, by described each intercept signal input Du Fen oscillator signal detection system, and calculate respectively the Lyapunov exponent changing with driving force F after input intercept signal;
S4, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it, thereby the defect detecting on thing is positioned.
In described step S1, further comprise based on duffing equation structure Du Fen oscillator signal detection system:
S11, choose duffing equation, and be provided with detection signal, its formula is as follows:
x &CenterDot; &CenterDot; + k x &CenterDot; - x 3 + x 5 = F cos &omega;t + s &OverBar; ( t ) - - - ( 1 )
Wherein, k is damping ratio, and ω is driving force angular frequency, (x 3+ x 5) be nonlinear resilience item, for detection signal, Fcos ω t is driving force item, and F is driving force, and described F meets when and if only if ultrasonic guided wave signals input duffing equation, and described Du Fen oscillator signal detection system changes;
S12, choose displacement x and speed v formula (1) rewritten as follows:
x &CenterDot; = v v &CenterDot; = - kv + x 3 - x 5 + F cos ( &omega;t ) + s &OverBar; ( t ) - - - ( 2 )
Complete the structure of Du Fen oscillator signal detection system.
Preferably, in described formula (1), k gets 0.5, F, and to get 0.8105, ω identical with the frequency of intercept signal to be measured.
Preferably, in described step S1, the Lyapunov exponent of Du Fen oscillator signal detection system is calculated as follows:
The Du Fen oscillator signal detection system that formula (2) is represented forms the three dimension system taking displacement x, speed v and time t as state variable, in the t=0 moment, and centered by x0, || δ x (x 0, 0) || for radius does a three-dimensional sphere, along with the evolution of time, be deformed into three-dimensional ellipsoid at this sphere of t moment, half axial length of establishing i change in coordinate axis direction of this ellipsoid is || δ x i(x 0, 0) ||, i Lyapunov exponent of described three dimension system is:
L i = lim t &RightArrow; &infin; 1 t ln | | &delta; x i ( x 0 , t ) | | | | &delta; x i ( x 0 , 0 ) | | - - - ( 3 )
Through type (3) calculates the Lyapunov exponent of Du Fen oscillator signal detection system.
Foregoing is explained: in the time that duffing equation is applied to identification supersonic guide-wave, need suitable adjustment System parameter, establish z=t, duffing equation (1) is converted into third-order self-governing system:
x &CenterDot; = y
y &CenterDot; = - ky + x 3 - x 5 + F cos &omega;z
z &CenterDot; = 1
Described duffing equation is found out to the sphere of one 3 dimension, along with the evolution of time becomes the ellipsoid of 3 dimensions, calculated the value of the different Lyapunov exponent in above-mentioned three directions of Duffing system under different F, use respectively L 1, L 2, L 3represent.Wherein, L 1corresponding to parameter x, L 2corresponding to parameter z, L 3corresponding to parameter y.In the time that driving force F changes, along with the evolution of time, L 2be constantly equal to 0, it represents neither to increase also and do not dwindle along track tangential direction.In fact,, in non-autonomous system, the value that at least has a Lyapunov index is 0, corresponding to the direction of time variable t; L 1can with driving force be greater than 0 and be less than 0 between change, L 3perseverance is less than 0; Visible, L 1can be used to judgement system state, will utilize L herein 1judge and in detection signal, whether contain flaw echo.
Utilize the method for the above-mentioned Lyapunov of solving index, solve respectively Du Fen oscillator signal detection system and add before and after guided wave signals, the Lyapunov index L of Du Fen oscillator signal detection system self 1with the Changing Pattern of driving force amplitude F, find in the time of F=0.8105 Lyapunov index L 1in the time not adding guided wave signals for being greater than 0, and in the time of input guided wave signals, Lyapunov index obviously changes into and is less than 0, the chaos state of this illustrative system when inputting without guided wave changes periodic motion into, the identification of supersonic guide-wave a little less than utilizing this character to realize, to improve the detection sensitivity of supersonic guide-wave.Therefore, we set the duffing equation detection system that F=0.8105 place is guided wave.
Preferably, for the ultrasonic guided wave signals that makes excitation is concentrated in a narrower frequency band, selecting centre frequency is the ultrasonic guided wave signals of 65~75kHz, preferred, its centre frequency is 70kHz, and described in described step S2, the expression formula of ultrasonic guided wave signals is:
s ( t ) = [ 1 2 ( 1 - cos 2 &pi; f c t n ) ] sin ( 2 &pi; f c t )
(4)
Wherein, n is the single audio frequency number of selecting, f cfor the centre frequency of signal.
The window function of preferably, constructing in described step S3 is:
S*=g(t-τ)S,
Wherein, S represents the measured signal of recording, and S* represents intercept signal; Fig. 2 is intercept signal corresponding to different window length.
Preferably, described step S4 further comprises:
S41, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it; Fig. 3 shows the change amount of the caused Lyapunov exponent of different window length;
As seen in Figure 3, select the change amount of the different caused Lyapunov exponents of window length.Within the specific limits, the change amount of Lyapunov exponent is along with window length is dull trend, in the time selecting window length to be an incident wave wavelength, change amount to Lyapunov exponent is the most obvious, effect is best, and can find also may make Lyapunov exponent still for being greater than 0 in the time that the signal of inputting is long, cannot judge the existence of incident wave.Therefore, select the signal of suitable length to detect extremely important.According to Fig. 3, the length of selecting intercept signal length to equal the wavelength of an incident wave is damaged Position Research.
S42, in the moving process of described window function, draw the curve that Lyapunov exponent changed with center moment of described window function;
S43, sudden change location defect guided wave signals according to described Lyapunov exponent on described curve, and lead velocity of wave propagation according to defect, the defect on described detection thing is positioned.Known in conjunction with above-mentioned elaboration, work as L 1when > 0, corresponding intercept signal does not have flaw indication, detects thing excellent; Work as L 1when < 0, corresponding intercept signal contains flaw indication, detects in thing containing defectiveness.
Preferably, described method further comprises:
S5, the corresponding intercept signal of window length of described Lyapunov exponent change amount maximum is carried out to spectrum analysis, defect location result in described result of spectrum analysis and described step S4 is compared, further the sensitivity of the defect location in described step S4 is assessed.Described spectrum analysis formula is:
F S ( j&omega; ) = lim t &RightArrow; &infin; 1 T | &Integral; 0 T s ( t ) e - j&omega;t dt | 2
(6)。
Test as detecting thing using pipeline below:
A) as shown in Figure 4, choosing the two long 3m of being, radiuses is that two steel pipes that 50.75mm and wall thickness are 2.32mm are tested, the uniform pipeline parallel piezoelectric sheet 3 of a week of 2 and 16 length concertina types of piezoelectric ring is set in one end of pipeline 1, encourage ultrasonic guided wave signals by piezoelectric ring 2, make all positions of ultrasonic guided wave signals traversal pipeline 1, and obtain measured signal by piezoelectric patches 3; Wherein, piezoelectric patches 3 is of a size of 15.4mm × 3.2.mm × 0.9mm;
B) the artificial different operating mode of defect of manufacturing at the middle part of two pipelines 1 respectively:
Operating mode one: select crackle hoop size θ to be taken as π/8.Crack depth a is taken as 1mm, and cross section slip is 3%;
Operating mode two: select crackle hoop size θ to be taken as pi/2, crack depth a is taken as 2mm, and cross section slip is 24%.
C) according to formula (4), the guided wave signals editting is input to waveform generator by USB device, after power amplifier amplifies, puts on piezoelectric ring 2, utilize the inverse piezoelectric effect of piezoelectric ceramics ring 2, in pipeline 1, produce longitudinal ultrasonic guided wave.Echo is received by piezoelectric patches 3, and utilizes oscillograph to gather measured signal;
D) as shown in Figure 5, be the displacement time-history curves of corresponding measured signal under two kinds of operating modes, Fig. 5 (a) is the displacement time-history curves of operating mode one, Fig. 5 (b) is the displacement time-history curves of operating mode two; Therefrom can find out, for flaw echo, only in the situation that defect is larger, just can observe flaw echo, as shown in figure Fig. 5 (b), between incident wave and end face echo, can significantly observe the existence of flaw echo, and for the operating mode one as shown in Fig. 5 (a), because defect of pipeline is less, detection signal almost obtains identical signal with intact pipeline, is difficult to judge pipeline and whether has defect.
E), in order to improve flaw echo detection sensitivity, we,, by the detection signal intercepting between incident wave and flaw echo, do respectively spectrum analysis and are input in Du Fen oscillator signal detection system, do Lyapunov exponent analysis; As shown in Figures 6 and 7:
Fig. 6 (a) is the spectrum analysis curve map of operating mode one intercept signal; Fig. 6 (b) is the spectrum analysis curve map of operating mode two intercept signals.
Fig. 7 (a) is the Lyapunov exponent analytic curve figure of operating mode one intercept signal; Fig. 7 (b) is the Lyapunov analysis curve map of operating mode two intercept signals.
F) signal of each section intercepting is input to respectively in said detecting system, carries out the calculating of Lyapunov index, further determine damage position, due to the change of the state of system only and L 1relevant, therefore, only draw L 1with the variation of intercept signal time, as shown in Figure 8, wherein, Fig. 8 (a) is the intercept signal curve map of operating mode one and corresponding defect location curve map, and Fig. 8 (b) is the intercept signal curve map of operating mode two and corresponding defect location curve map;
As can be seen from the figure, for operating mode one, in conjunction with Fig. 5, Fig. 6, Fig. 8 can find out, utilize displacement time-history curves and spectrum analysis, all cannot judge and in echoed signal, whether contain guided wave signals, can judge the general location of flaw echo by calculating Lyapunov exponent, as shown in Figure 8 (a), show as only at approximately centre position and 0.9ms place, largest Lyapunov exponent L1 is less than 0, the former is the weak guided wave signals that causes reflection due to the existence of defect, thereby illustrate that defectiveness exists herein, the latter is the existence of the mode of flexural vibration slow due to velocity of propagation.Due to L(0 in communication process, 2) velocity of propagation is the fastest, mode of flexural vibration velocity of propagation is slow, therefore ripple to the moment more a little later, also illustrate that Lyapunov exponent not only can identify L(0,2) guided wave of mode, the mode of flexural vibration slow to velocity of propagation also can detect well, be not subject to the impact of guided wave modal, be applicable to being very much applied to detection and the location of defect.And for operating mode two, because defect is larger, from displacement time-history curves and spectrogram, can find out obvious flaw echoes, this measured signal is input to Du Fen oscillator signal detection system, can obtain same conclusion, verify the correctness that detects the detection of the Lyapunov exponent that utilizes Du Fen oscillator signal detection system.
Further utilize following formula to calculate respectively the ducted defective locations of operating mode one and operating mode two correspondences:
2x p=C*t????(7)
Wherein, represent velocity of wave, be generally group velocity, can estimate by Young speed, t represents the mistiming of incident wave and reflection wave process measuring point, x prepresent defective locations in pipe.Utilize said method, obtain experimental result as shown in table 1.
? Ripple is to moment (s) Defective locations (m) Experimental error
Operating mode one L (0,2) 5.8697×10 -4-6.0897×10 -4 1.44 4%
Table 1 experimental result
? ? ? ?
Operating mode two L (0,2) 5.697×10 -4-5.8097×10 -4 1.39 7%
The beneficial effect of the embodiment of the present invention is: the method for a kind of supersonic guide-wave location defect based on Lyapunov exponent provided by the invention, utilize the center moment location defect guided wave signals of time shift window function, and according to guided wave velocity of propagation location defect, utilize the present invention can orient the position of less defect, it is simple to operate, accurate, economical, there is innovative significance, have a wide range of applications.
The foregoing is only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.All any amendments of doing within the spirit and principles in the present invention, be equal to replacement, improvement etc., be all included in protection scope of the present invention.

Claims (10)

1. a method for the supersonic guide-wave location defect based on Lyapunov exponent, is characterized in that, comprises the following steps:
S1, based on duffing equation structure Du Fen oscillator signal detection system, and calculate the Lyapunov exponent changing with driving force F;
S2, encourage ultrasonic guided wave signals by transmitter detecting on thing, make all positions of ultrasonic guided wave signals traversal detection thing, then obtain measured signal by receiver;
S3, tectonic window function intercept intercept signal corresponding to different window length from described measured signal, by described each intercept signal input Du Fen oscillator signal detection system, and calculate respectively the Lyapunov exponent changing with driving force F after input intercept signal;
S4, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it, thereby the defect detecting on thing is positioned.
2. the method for claim 1, is characterized in that, in described step S1, further comprises based on duffing equation structure Du Fen oscillator signal detection system:
S11, choose duffing equation, and be provided with detection signal, its formula is as follows:
x &CenterDot; &CenterDot; + k x &CenterDot; - x 3 + x 5 = F cos &omega;t + s &OverBar; ( t ) - - - ( 1 )
Wherein, k is damping ratio, and ω is driving force angular frequency, (x 3+ x 5) be nonlinear resilience item, for detection signal, Fcos ω t is driving force item, and F is driving force, and described F meets when and if only if ultrasonic guided wave signals input duffing equation, and described Du Fen oscillator signal detection system changes;
S12, choose displacement x and speed v formula (1) rewritten as follows:
x &CenterDot; = v v &CenterDot; = - kv + x 3 - x 5 + F cos ( &omega;t ) + s &OverBar; ( t ) - - - ( 2 )
Complete the structure of Du Fen oscillator signal detection system.
3. method as claimed in claim 2, is characterized in that, in described formula (1), k gets 0.5, F, and to get 0.8105, ω identical with the frequency of intercept signal to be measured.
4. method as claimed in claim 2, is characterized in that, in described step S1, the Lyapunov exponent of Du Fen oscillator signal detection system is calculated as follows:
The Du Fen oscillator signal detection system that formula (2) is represented forms the three dimension system taking displacement x, speed v and time t as state variable, in the t=0 moment, and centered by x0, || δ x (x 0, 0) || for radius does a three-dimensional sphere, along with the evolution of time, be deformed into three-dimensional ellipsoid at this sphere of t moment, half axial length of establishing i change in coordinate axis direction of this ellipsoid is || δ x i(x 0, 0) ||, i Lyapunov exponent of described three dimension system is:
L i = lim t &RightArrow; &infin; 1 t ln | | &delta; x i ( x 0 , t ) | | | | &delta; x i ( x 0 , 0 ) | | - - - ( 3 )
Through type (3) calculates the Lyapunov exponent of Du Fen oscillator signal detection system.
5. method as claimed in claim 3, is characterized in that, described in described step S2, the expression formula of ultrasonic guided wave signals is:
s ( t ) = [ 1 2 ( 1 - cos 2 &pi; f c t n ) ] sin ( 2 &pi; f c t ) - - - ( 4 )
Wherein, n is the single audio frequency number of selecting, f cfor the centre frequency of signal.
6. method as claimed in claim 4, is characterized in that, the window function of constructing in described step S3 is:
S*=g(t-τ)S,
Wherein, S represents the measured signal of recording, and S* represents intercept signal.
7. method as claimed in claim 6, is characterized in that, described step S4 further comprises:
S41, determine that Lyapunov exponent change measures the maximum corresponding intercept signal of window length, mobile described window function scans it;
S42, in the moving process of described window function, draw the curve that Lyapunov exponent changed with center moment of described window function;
S43, sudden change location defect guided wave signals according to described Lyapunov exponent on described curve, and lead velocity of wave propagation according to defect, the defect on described detection thing is positioned.
8. method as claimed in claim 7, is characterized in that, described step S43 is further:
Work as L 1when > 0, corresponding intercept signal does not have flaw indication, detects thing excellent; Work as L 1when < 0, corresponding intercept signal contains flaw indication, detects in thing containing defectiveness.
9. method as claimed in claim 8, is characterized in that, described method further comprises:
S5, the corresponding intercept signal of window length of described Lyapunov exponent change amount maximum is carried out to spectrum analysis, defect location result in described result of spectrum analysis and described step S4 is compared, further the sensitivity of the defect location in described step S4 is assessed.
10. method as claimed in claim 9, is characterized in that, described step S5 intermediate frequency spectrum analytical formula is:
F S ( j&omega; ) = lim t &RightArrow; &infin; 1 T | &Integral; 0 T s ( t ) e - j&omega;t dt | 2 - - - ( 6 ) .
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