CN102539539B - Cavitation erosion detection method based on acoustic emission - Google Patents
Cavitation erosion detection method based on acoustic emission Download PDFInfo
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- CN102539539B CN102539539B CN201210018026.XA CN201210018026A CN102539539B CN 102539539 B CN102539539 B CN 102539539B CN 201210018026 A CN201210018026 A CN 201210018026A CN 102539539 B CN102539539 B CN 102539539B
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Abstract
The invention discloses a cavitation erosion detection method based on acoustic emission, which comprises the following steps: utilizing an acoustic emission sensor to collect an acoustic emission signal in unit time length during cavitation erosion development; performing wavelet decomposition on the acoustic emission signal according to set layer number to obtain a wavelet coefficient and relevant degree of the cavitation erosion and frequency range where the wavelet coefficient is located, and denoising the wavelet coefficient according to the relevant degree and the set layer number; performing signal reconstruction by utilizing the wavelet coefficient after denoising, and obtaining a reconstruction signal; setting parameter estimating threshold and counting time interval of the reconstruction signal; calculating acoustic emission event number and acoustic emission even average energy of the reconstruction signal; and judging plastic deformation and mass loss condition during cavitation erosion development according to the acoustic emission even number and the acoustic emission even average energy. The cavitation erosion detection method based on the acoustic emission performs denoising according to the characteristics of the acoustic emission signal and utilizes a simple estimating parameter to represent the development condition of plastic deformation and mass loss during cavitation erosion.
Description
Technical field
The present invention relates to a kind of method of direct-detection cavitation corrosion, specifically, relate to a kind of method of the detection cavitation corrosion based on acoustic emission.
Background technology
Liquid can produce cavity when local pressure is enough low; When crumbling and fall, cavity cause the process of damage to be called cavitation corrosion to solid material surface.Cavitation corrosion is the common failure mode of fluid machinery: slight cavitation corrosion makes the material surface generation pit that tarnishes; Serious cavitation corrosion makes material become loose even to come off, affect the running status of fluid machinery.First for avoiding violent cavitation corrosion, need to monitor the situation occurred of cavitation corrosion, adjust hydraulic running status; Secondly for avoiding serious cavitation corrosion phenomenon, need before it occurs, study for a second time courses one has flunked by convection cell mechanical surface, rationally determine that the time of studying for a second time courses one has flunked is to obtain maximum economic benefit; Need to detect cavitation corrosion with monitoring cavitation level.At present, the research of cavitation corrosion status monitoring has been subjected to attention, common cavitation corrosion monitoring method is passed through noise and Monitoring of Structural Vibration cavitation phenomenon and other physical quantity indirect monitoring cavitation corrosion, what for example Chinese invention patent instructions ZL 02131333.4 " cavitation of the hydraulic turbine and the on-line monitoring method of cavitation erosion and diagnostic device " provided is a kind of by the cavitation coefficient, cavitation factor, Toma coefficient of monitoring fluid machinery, pressure fluctuation in runner, the energy response of fluid machinery, the first-class method indirect monitoring of working water cavitation corrosion, document " Cavitation in Hydraulic Machinery online monitoringand diagnose system " (source: water conservancy and hydropower technology, 2002, 33 (7): 17-20) working pressure pulsation, efficiency and cavitation noise indirect monitoring cavitation corrosion, and document " Cavitations monitoring and diagnosis of hydropower turbine online based on vibration and ultrasound acoustic " (source: Proceedings of the Sixth International Conference on Machine Learning and Cybernetics, the vibration that 2007:19-22) use cavitation causes and ultrasonic to monitoring cavitation with indirect monitoring cavitation corrosion, but the corresponding relation between physical quantity and cavitation corrosion that these are relevant to cavitation is also unclear, therefore take these physical quantitys as basic indirect monitoring mode, be difficult to accurately estimate the state of cavitation corrosion.For monitoring better cavitation corrosion, need to find a kind of technological means to cavitation erosion direct-detection.Acoustic emission is that the local source in material produces the phenomenon of Elastic wave because the material failure phenomenons such as generation distortion and Crack Extension under effect of stress release energy fast.Acoustic emission can detect with Crack Extension phenomenon acoustic emission source distortion by using sensor to gather acoustic emission signal, in partial failure context of detection, obtained widespread use at present, result confirms that it is very high to the detection sensitivity of local acoustic emission source.Cavitation corrosion is a kind of material partial failure phenomenon on generating material surface, and therefore the localized source generation Elastic wave that also can release energy fast when it occurs can be used acoustic emission to detect cavitation corrosion.Because acoustic emission is that cavitation corrosion phenomenon directly causes, so process the direct monitoring that can realize cavitation corrosion by extracting the acoustic emission signal of cavitation corrosion.
Summary of the invention
The object of the present invention is to provide a kind of signal processing method that uses acoustic emission direct-detection cavitation corrosion, by the method, set up the correlationship between acoustic emission parameter and cavitation corrosion state, and judge cavitation corrosion development.
Technology contents of the present invention is as follows:
Based on a cavitation erosion detection method for acoustic emission, comprise the following steps: use calibrate AE sensor to gather the acoustic emission signal of unit interval length in cavitation corrosion evolution; The described acoustic emission signal gathering is carried out wavelet decomposition and is obtained wavelet coefficient according to setting the number of plies, and obtain the frequency range at described wavelet coefficient place and the degree of correlation of cavitation corrosion, according to described degree of correlation and the setting number of plies to described wavelet coefficient denoising; Use the described wavelet coefficient after denoising to carry out signal reconstruction, obtain reconstruction signal; Set parameter estimation threshold value and the gate time interval of described reconstruction signal; Calculate acoustie emission event number and the acoustie emission event average energy of described reconstruction signal; According to described acoustie emission event number and described acoustie emission event average energy, judge plastic yield and mass loss situation in cavitation corrosion evolution.
Further, described cavitation erosion detection method also comprises: judge whether described wavelet coefficient is disposed, to use described wavelet coefficient after treatment to carry out signal reconstruction, otherwise wavelet coefficient described in the lower one deck of selection, and judge the frequency range at this layer of described wavelet coefficient place and the degree of correlation of cavitation corrosion.
Further: the degree of correlation that estimates described cavitation corrosion according to the spectrum of the described acoustic emission signal collecting in cavitation corrosion situation.
Further: the mode that judges the degree of correlation of described cavitation corrosion is that the power spectrum of observing the described acoustic emission signal in cavitation corrosion situation changes situation about changing with cavitation corrosion; According to the obvious degree of the situation of change of the power spectrum of described acoustic emission signal, judge the degree of correlation of described cavitation corrosion.
Further: the denoising method of described wavelet coefficient is Soft-threshold Denoising Method.
Further: described setup parameter estimates that the method for threshold value is that the amplitude of described reconstruction signal is divided into ratio by the size of the absolute value of described amplitude is the value of 2: 8.
Further: the event count time interval of described setting is 50 μ s.
Further: described acoustie emission event average energy E
a=E
t/ C, wherein,
E
t＝∑E
i，
C is described acoustie emission event number, x
irepresent the amplitude of described acoustic emission signal, j represents the starting point of a described acoustie emission event, and k represents the end point of a described described acoustie emission event.
Further: described plastic yield active state judges according to cavitation generation medium and described acoustie emission event numerical value, described mass loss activity judges according to described cavitation generation medium and described acoustie emission event the average energy value.
Technique effect of the present invention is as follows:
Use calibrate AE sensor to gather the signal of the acoustic emission information causing because of cavitation corrosion, for the feature of acoustic emission signal, carry out denoising, and used simple estimated parameter to characterize respectively plastic yield in Surface During Cavitation Erosion and the development of mass loss.
Accompanying drawing explanation
Fig. 1 is the processing flow chart of the cavitation erosion detection method based on acoustic emission of the present invention;
Fig. 2 is the schematic diagram of the cavitation corrosion acoustic emission detection experimental provision of the preferred embodiments of the present invention;
Fig. 3 is the spectrum drawing for estimate of the acoustic emission signal that gathers in different cavitation corrosion situation of the present invention;
Fig. 4 is the denoising schematic diagram of the preferred embodiments of the present invention;
Fig. 5 is the trend map of event count of the present invention;
Fig. 6 is the trend map of event average energy of the present invention.
Embodiment
Below in conjunction with drawings and Examples, the present invention is further described.
As shown in Figure 1, be the processing flow chart of the cavitation erosion detection method based on acoustic emission of the present invention.
In the preferred embodiment of the invention, in cavitation corrosion testing process, first need to utilize calibrate AE sensor to measure the acoustic emission signal producing in Surface During Cavitation Erosion, obtain the signal that includes the acoustic emission being caused by cavitation corrosion.Acquisition includes after the signal of the acoustic emission being caused by cavitation corrosion, adopts the cavitation erosion detection method based on acoustic emission of the present invention to detect cavitation corrosion.
Step 101: use calibrate AE sensor to gather the acoustic emission signal of unit interval length in cavitation corrosion evolution, detailed process is as follows:
1) as shown in Figure 2, be the schematic diagram of the cavitation corrosion acoustic emission detection experimental provision of the preferred embodiments of the present invention.Select tap water 4 for cavitation generation medium, in the container 5 that is 5L at volume, contain the tap water 4 of 4.5L left and right; The degree of depth that regulates ultrasonic output terminal 1 to enter in water is 10-15mm; Calibrate AE sensor 3 is arranged on to sample 2 times, every 5 minutes, gathers 131070 signals, gather 6 hours.Through observing, find, specimen surface has experienced incubation period, accelerated period, maximum eroding rate phase, the stationary phase of cavitation corrosion successively.The principal feature of each phase is: incubation period, material plasticity distortion was fast, and also very fast in quality of materials loss in early stage incubation period, but later stage mass loss is slow; Accelerated period material plasticity distortion is slowed down, and mass loss speeds; Maximum eroding rate phase material plasticity distortion is slow, and mass loss is fast; Stationary phase, material plasticity distortion was larger, and mass loss is less.
2) signal while taking out 225min, 265min, 295min, 360min, represents respectively the cavitation corrosion signal in later stage incubation period, accelerated period, maximum eroding rate phase and stationary phase; To signal, use maximum entropy spectrum modelling (AR method) to compose estimation, obtain power spectrum chart.As shown in Figure 3, be the spectrum drawing for estimate of the acoustic emission signal that gathers in different cavitation corrosion situation of the present invention.Therefrom can see that the frequency range high with cavitation corrosion correlativity is more than 100kHz.
Step 102: acoustic emission signal is carried out to wavelet decomposition.
Step 103: select one deck wavelet coefficient, detailed process is as follows:
As shown in Figure 4, be the denoising schematic diagram of the preferred embodiments of the present invention.Select a signal S, it is carried out to 4 layers of wavelet decomposition.First signal S is decomposed into cA1 and cD1, then cA1 is decomposed into cA2 and cD2, then cA2 is decomposed into cA3 and cD3, finally cA3 is decomposed into cA4 and cD4.Signal S is divided into 5 frequency ranges the most at last, by frequency range, is respectively cA4, cD4, cD3, cD2 and cD1 from low to high, and its frequency range is about respectively 0-63kHz, 63-125kHz, 125-250kHz, 250-500kHz, 500-1000kHz.
Step 104: the degree of correlation that judges each layer of wavelet coefficient place frequency range and cavitation corrosion.Basis for estimation in the preferred embodiment of the invention is: according to the power spectrum of the acoustic emission signal in different cavitation corrosion situations, with cavitation corrosion, change situation about changing, if the situation of change of power spectrum is more obvious, the degree of correlation of this frequency range is higher.
Step 105: cA4 low cavitation corrosion correlativity and cD4 wavelet coefficient are made zero.
Step 106: cD3 high cavitation corrosion correlativity, cD2 and cD1 wavelet coefficient are carried out to denoising.In the preferred embodiment of the invention, wavelet coefficient high cavitation corrosion correlativity is carried out to soft-threshold denoising processing by default threshold, wherein, default threshold is
, σ is that signal standards is poor, N is this layer of wavelet coefficient length; Obtain cD3 ', cD2 ' and cD1 ' wavelet coefficient after denoising.
Step 107: judge whether all wavelet coefficients are disposed, and are to enter step 109, select lower one deck wavelet coefficient otherwise proceed to step 108, and enter step 104.
Step 109: use each layer of wavelet coefficient reconstruction signal after denoising, obtain reconstruction signal S '.
Step 110: the threshold value that setup parameter is estimated, the amplitude that is about to all reconstruction signal S ' is divided into the value of 2: 8 by the size of the absolute value of its amplitude; Setting the event count time interval is 50 μ s.
Step 111: obtain event count.Event number adopts conventional acoustic emission signal method for parameter estimation to obtain.
Step 112: obtain event average energy.
Event average energy E
aaccount form as follows,
E
A＝E
t/C
E
t＝∑E
i
Wherein, C is event count, E
tfor described acoustie emission event gross energy,
Wherein, E
irepresent the energy of an acoustie emission event i, x
ithe amplitude that represents acoustic emission signal, j represents the starting point of an acoustie emission event, k represents the end point of an acoustie emission event.
Step 113: the cavitation corrosion testing process based on acoustic emission finishes.
As shown in Figure 5, be the trend map of event count of the present invention, wherein take the time as horizontal ordinate, the event count obtaining after processing take each time place's parameter estimation is as ordinate.As can see from Figure 5, event counter value continues slight increase in incubation period (0-230min), in accelerated period (230-280min), continue sharply to reduce, in the maximum eroding rate phase (280min-325min), remain very little, and get back to a larger numerical value in stationary phase (330-360min).
As shown in Figure 6, be the trend map of event average energy of the present invention, wherein take the time as horizontal ordinate, the event average energy obtaining take each time place's parameter estimation is as ordinate.As can see from Figure 6, event average energy is larger in early stage incubation period (0-100min), in later stage incubation period (100-230min) event average energy, reduce gradually, lasting increase of accelerated period event average energy, at maximum eroding rate phase event the average energy value, reach maximum and maintain high level, stationary phase event the average energy value reduce to a lower level.
Plastic yield active state judges according to cavitation generation medium harmony transmit events numerical value, and mass loss activity judges according to cavitation generation medium and acoustie emission event the average energy value.With reference to figure 5, Fig. 6 and in conjunction with the phenomenon observed, can find in the preferred embodiment of the invention, event number is more active in 220 activities of plastic yield when above, as occurs in the cavitation corrosion phenomenon of incubation period and degradation period; Event average energy illustrates that mass loss activity is more active 200 when above, as occurs in the cavitation corrosion phenomenon of accelerated period and maximum eroding rate phase; Event number below 150 and event average energy illustrate below 120 time plastic yield and mass loss activity all inactive, as occur in the cavitation corrosion phenomenon of stationary phase.
Claims (9)
1. the cavitation erosion detection method based on acoustic emission, comprises the following steps:
Use calibrate AE sensor to gather the acoustic emission signal of unit interval length in cavitation corrosion evolution;
The described acoustic emission signal gathering is carried out wavelet decomposition and is obtained wavelet coefficient according to setting the number of plies, and obtain the frequency range at described wavelet coefficient place and the degree of correlation of cavitation corrosion, according to described degree of correlation and the setting number of plies to described wavelet coefficient denoising;
Use the described wavelet coefficient after denoising to carry out signal reconstruction, obtain reconstruction signal;
Set parameter estimation threshold value and the event count time interval of described reconstruction signal;
Calculate acoustie emission event number and the acoustie emission event average energy of described reconstruction signal;
According to described acoustie emission event number and described acoustie emission event average energy, judge plastic yield and mass loss situation in cavitation corrosion evolution.
2. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, it is characterized in that, described cavitation erosion detection method also comprises: described the described acoustic emission signal gathering is carried out wavelet decomposition and obtained wavelet coefficient according to setting the number of plies, and obtain the frequency range at described wavelet coefficient place and the degree of correlation of cavitation corrosion, according to described degree of correlation and set the number of plies to after the step of described wavelet coefficient denoising, judge whether described wavelet coefficient is disposed, to use described wavelet coefficient after treatment to carry out signal reconstruction, otherwise wavelet coefficient described in one deck under selecting, and judge the frequency range at this layer of described wavelet coefficient place and the degree of correlation of cavitation corrosion.
3. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, is characterized in that: the degree of correlation that estimates described cavitation corrosion according to the spectrum of the described acoustic emission signal collecting in cavitation corrosion situation.
4. the cavitation erosion detection method based on acoustic emission as claimed in claim 3, is characterized in that: the mode that judges the degree of correlation of described cavitation corrosion is that the power spectrum of observing the described acoustic emission signal in cavitation corrosion situation changes situation about changing with cavitation corrosion; According to the obvious degree of the situation of change of the power spectrum of described acoustic emission signal, judge the degree of correlation of described cavitation corrosion.
5. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, is characterized in that: the denoising method of described wavelet coefficient is Soft-threshold Denoising Method.
6. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, is characterized in that: described setup parameter estimates that the method for threshold value is that the amplitude of described reconstruction signal is divided into the value that ratio is 2:8 by the size of the absolute value of described amplitude.
7. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, is characterized in that: the event count time interval of described setting is 50 μ s.
8. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, is characterized in that: described acoustie emission event average energy E
a=E
t/ C, wherein,
E
t＝ΣE
i，
C is described acoustie emission event number, E
tfor described acoustie emission event gross energy, E
irepresent the energy of a described acoustie emission event, x
irepresent the amplitude of described acoustic emission signal, j represents the starting point of a described acoustie emission event, and k represents the end point of a described described acoustie emission event.
9. the cavitation erosion detection method based on acoustic emission as claimed in claim 1, it is characterized in that: described plastic yield active state judges according to cavitation generation medium and described acoustie emission event numerical value, described mass loss activity judges according to described cavitation generation medium and described acoustie emission event the average energy value.
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| DE202012009675U1 (en) * | 2012-10-10 | 2014-01-13 | Ulrich Seuthe | Apparatus for detecting cracking of a component due to induction hardening of the component |
| CN103854658B (en) * | 2012-11-29 | 2019-01-11 | 沈阳工业大学 | Steel plate corrosion Research on Denoising in Acoustic Emission Signals based on Short Time Fractal Numbers enhancing method |
| CN105510210B (en) * | 2015-11-25 | 2018-08-21 | 江苏大学 | A kind of test-type metallic solution cavitation damage device |
| CN106814136A (en) * | 2015-11-27 | 2017-06-09 | 北京声华兴业科技有限公司 | A kind of on-line fault monitoring method for high pressure apparatus top hammer |
| JP6639013B2 (en) * | 2016-03-14 | 2020-02-05 | 株式会社神戸製鋼所 | Resin pelletizer device and cavitation monitoring method |
| CN110222650A (en) * | 2019-06-10 | 2019-09-10 | 华北水利水电大学 | A kind of acoustie emission event classification method based on sound emission all band acquisition parameter |
| CN110458976B (en) * | 2019-07-18 | 2020-06-30 | 浙江大学 | Propeller cavitation state detection method based on wavelet and principal component analysis |
| CN111610143B (en) * | 2020-06-17 | 2021-07-06 | 武汉理工大学 | Ship material cavitation erosion test real-time detection system and method based on ultrasonic detection technology |
| CN113624848A (en) * | 2021-08-10 | 2021-11-09 | 北京理工大学 | Cutting state identification method and system based on acoustic emission |
| CN114235966A (en) * | 2021-12-22 | 2022-03-25 | 广西大学 | Ultrasonic cavitation device for monitoring metal cavitation erosion process in real time by adopting acoustic emission |
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