CN1712950A - Audio-frequency detection of concrete fault - Google Patents

Abstract

A method for detecting defect of concrete by audio includes using spring and exciting hammer to knock detecting point on known - custom concrete plate and using Fourier transform to convert these sound signals to be standard reference data corresponding to detecting point on known - custom concrete plate; utilizing the same method as above to obtain signal process data corresponding to abovementioned plate for detected concrete plate; confirming defect condition of detected point on detected concrete plate by comparing two data groups .

Description

Audio-frequency detection of concrete fault

Technical field

The present invention relates to detection technique, particularly relate to a kind of audio detection technology that is used to detect concrete defect.

Background technology

In the engineering detecting field; relate to the defective that detects concrete slab through regular meeting; because this life-span and sustainable use to structure has important effect; if detect the position and the size of defective; so just can in time safeguard reinforcing; thereby improve the serviceable life of buildings, save the engineering cost social resources.Varied in the method that detects concrete defect at present, mainly contain several: ultrasonic pulse method, acoustic-emission, shock reflection method, reflection of radar wave method, method of direct observation (hammering method).

The application of ultrasonic pulse method aspect Non-Destructive Testing is more, use detecting structure inherent vice (hollowing, peel ply, weaker zone, crack etc.) morely, but what this method adopted at present is to penetrate test, need two relative test surfaces, just limited its range of application, using such as structural often being difficult to such as road surface, runway, body of wall, negative, bank protection, large-scale concrete slab, the lining cutting of tunnel, ultrasonic pulse method also has problems aspect signal Processing in addition; Acoustic-emission is meant and utilizes detecting instrument to be subjected to external force or endogenetic process to produce distortion or fracture to material and produce the stress wave that discharges with the elastic wave form and write down, analyze acoustic emission signal and utilization sound generation signal and infer acoustic emission source judging the technology of defective, but this method is received in use that environmental impact is very big and can't carry out overall time to large scale structure and detected; The shock reflection method is to have realized the single face test well, has remedied the defective of ultrasonic pulse method in broad aspect very, and convenient test, quick, directly perceived.But this method can only be surveyed a bit and judge a bit, and not only consuming time but also economical inadequately when detecting large scale structure, can't realize the effect of whole fast detecting; The reflection of radar wave method, be that Tongji University adopts it to survey underground utilities, old building concrete stake, paleo-streams, dark creek etc. at home the earliest, obtained good effect, recently, beginning is used for the structure detection aspect on a large scale, but this method can not realize real-time monitored, difficult analysis of data.Method of direct observation (hammering method) is because the subjective influence of observer makes very out of true of its conclusion.

Defectives such as the hollowing in the concrete component, honeycomb can have a strong impact on intensity, the quality of concrete component, are the comparison difficulties yet want the concrete defective of Non-Destructive Testing in detecting in engineering, also have the ultrasound wave of employing, impact echo method to detect at present.But above-mentioned detection method trace routine complexity, operation inconvenience is difficult for promoting.

Summary of the invention

At the defective of above-mentioned existing building structure Dynamic Non-Destruction Measurement, technical matters to be solved by this invention provides a kind of concrete component that do not damage, and is simple to operate, testing result reliable audio-frequency detection of concrete fault.

In order to solve the problems of the technologies described above, a kind of audio-frequency detection of concrete fault provided by the present invention, its step is as follows:

One) set for comparison usefulness with reference to information:

1) knocks the concrete slab check point of various known customizations with spring energized hammer, the concrete slab of described various known customizations comprises no hollowing (bubble), the concrete slab of the various known customizations of different big or small hollowings (bubble) is arranged, and with stationary installation voice signal is sampled, described stationary installation is meant that the distance of the concrete slab check point of the audio sensor that is used to sample and various known customizations is a fixed value; It is fixed value that spring hammer knocks energy;

2) voice signal that sampling is obtained carries out fast Fourier transform (FFT), convert the standard reference information corresponding with the concrete slab check point of various known customizations to, described standard reference information comprises the power spectrum chart of sound, the envelope diagram of spectrogram and the shape index ξ of envelope diagram;

Two) tested concrete slab is sampled:

1) use step 1) same method and same device carry out the sampling of voice signal to tested concrete slab check point, promptly knock intensity and knock tested concrete slab check point, detect with same audio sensor (or the identical audio sensor of sensitivity) and with tested concrete slab and order the same apart from voice signal is sampled with the same energy of same quantitative spring energized hammer;

2) voice signal that sampling is obtained is handled, at first carry out filtering and eliminating noise, Fourier transform (FFT) then, convert the signal Processing information corresponding with the concrete slab check point of various known customizations to, described signal Processing information comprises the power spectrum chart of sound, envelope diagram and the shape index λ of envelope diagram and the hydridization coefficient ξ of power spectrum chart of spectrogram;

Three) will detect information and standard reference information is compared, determine the defect situation of the tested measuring point of tested concrete slab, the tested measuring point of promptly determining tested concrete slab is identical or close with the known customization concrete slab check point of known any defect level; Described comparison is similar information comparison, i.e. the power spectrum chart of power spectrum chart of Jian Ceing and reference comparison, the envelope diagram of detection and the comparison of the envelope diagram of reference, the shape index λ of detection and the shape index λ of standard reference ₀, and spectrogram hydridization coefficient ξ and canonical reference hydridization coefficient ξ ₀

Preferably, described comparison mode is the computing machine comparison.

Preferably, described comparison mode is artificial comparison.

Utilize audio-frequency detection of concrete fault provided by the invention, owing to utilized voice signal in different objects, to propagate, can produce different power densities, can form different power spectrum charts, different envelope diagram and different shape index and hydridization coefficients through fast fourier transform, and then detect concrete defect situation according to standard reference information; So can neither damage concrete component, can obtain reliable result again, and also simple to operate.

Description of drawings

Fig. 1 is the schematic block diagram of concrete defect audio detection device of the present invention;

Fig. 2 is the power spectrum chart of sound;

Fig. 3 A is the spectrogram of intact plate;

Fig. 3 B is the spectrogram that there are free clappers at the 10mm place;

Fig. 4 is the normal section synoptic diagram of the test beam of the embodiment of the invention;

Fig. 5 is that the check point of the test beam of the embodiment of the invention is arranged synoptic diagram;

Fig. 6 A, B are the test findings charts of the main check point of embodiment of the invention test beam;

Fig. 7 is the check point plane of arrangement figure of another embodiment of the present invention;

Fig. 8 is the test findings chart of another embodiment of the present invention.

Embodiment

Below in conjunction with description of drawings embodiments of the invention are described in further detail, but present embodiment is not limited to the present invention, every employing similarity method of the present invention and similar variation thereof all should be listed protection scope of the present invention in.

The principle that sound spectrum is analyzed among the present invention:

Sound and vibration is closely to link to each other, and mechanical vibration usually cause sound radiation.During object vibration, encourage its ambient air particle vibration, because air has compressibility, under the interaction of particle, the vibrating object ambient air just alternately produces compression and expands, and outside gradually the propagation forms sound wave.Acoustic pressure acts on the transducer, and transducer is converted into certain electric signal, can measure, analyze this electric signal.

The analysis of acoustical signal, its fundamental measurement is spectrum analysis, that is to say, requires to obtain the relation of energy in the signal or distribute power.

To this simulating signal of sound, Fourier transform is used in its analysis and processing widely, the disposal route that changes into digital audio signal is being used discrete Fourier transform (DFT), but calculating discrete Fourier transform (DFT), what adopt is high efficiency fast Fourier transform (FFT), the definition of discrete Fourier transform (DFT):

$R\left(\mathrm{\τ}\right)=\underset{T\→\∞}{\lim }\frac{1}{T}\underset{-T/2}{\overset{T/2}{\∫}}p\left(t\right)p(t+\mathrm{\τ})\mathrm{dt}$

A _n--n coefficient of-discrete Fourier transform (DFT)

X _kK sampled value in N sampling time sequence of---have

n，k＝0，1，......，N-1

The ultimate principle of fast fourier transform is to utilize W ^N=1 character is calculating the required multiplying of doing of discrete Fourier transform (DFT) coefficient from N ²Be compressed to 0.5Nlog ₂N time, (a for positive integer) arbitrarily.

Finally try to achieve power spectrum density:

W(f)＝4πS(f)

And

$S\left(f\right)=\frac{1}{2\mathrm{\π}}\underset{-\∞}{\overset{\∞}{\∫}}R\left(\mathrm{\τ}\right)e^{-2\mathrm{\π}/\mathrm{\τ}}\mathrm{d\τ}$

Wherein autocorrelation function is: $R\left(\mathrm{\τ}\right)=\underset{T\→\∞}{\lim }\frac{1}{T}\underset{-T/2}{\overset{T/2}{\∫}}p\left(t\right)p(t+\mathrm{\τ})\mathrm{dt}$

The principle of sound intermediate frequency detection technique of the present invention:

Cause that with spring energized hammer the material vibration produces sound when detection faces is knocked, its physical mechanism is:

1) if an intact concrete slab, the moment excitation causes the plate surface vibration, and sound is propagated by the vibration of air molecule continuity sound source.Bump before and after the air molecule spreads the energy vibration from sound source.The propagation of sound is with this locality vibration process to one by one regional spread.The change in location of local air molecule is to carry out along the direction of vibration propagation, so sound is longitudinal propagation.An audio frequency sensing receiver (as the microphone vibrating membrane) that is placed in the sound field can vibrate according to the pressure that acts on above it, and medium density is big more, has propagated easily and has finished.But the process of successively decreasing gradually that the process of this sound transmission is an energy, power spectrum presents overall attenuation trend.

2) but the power spectrum approximate reverse of gathering is answered the dynamic response of plate under certain marginal condition, if the intact then power spectrum of plate is remarkable in low frequency part, and if tangible convex-concave appears in the shape of defectiveness power spectrum, and spectrogram hydridization phenomenon is outstanding, and higher vibration shape vibration energy consumption significantly increases.The spectrogram of intact plate as shown in Figure 3A, there is the spectrogram of free clappers at the 10mm place shown in Fig. 3 B.

The power spectrum of acoustical signal will be drawn in actual applications after the acoustical signal process fast Fourier transform (FFT) signal transformation that be collected, as shown in Figure 2.

Referring to shown in Figure 1, audio-frequency detection of concrete fault provided by the present invention, its step is as follows:

One) set for comparison usefulness with reference to information:

1) knocks the concrete slab check point of various known customizations with spring energized hammer 1, the concrete slab 3 of described various known customizations comprises no hollowing (bubble), the concrete slab of the various known customizations of different big or small hollowings (bubble) is arranged, and with stationary installation voice signal is sampled, described stationary installation is meant that the microphone 2 that is used to sample and the distance of concrete slab 3 check points of various known customizations are fixed value; It is fixed value that spring hammer 1 knocks energy;

2) voice signal that sampling is obtained carries out fast Fourier transform (FFT), convert the standard reference information corresponding with the concrete slab check point of various known customizations to, described standard reference information comprises the power spectrum chart of sound, the envelope diagram of spectrogram and the shape index ξ of envelope diagram;

Two) tested concrete slab is sampled:

1) use step 1) same method and same device carry out the sampling of voice signal to tested concrete slab check point 3, promptly knock intensity and knock tested concrete slab 3 check points, detect with same audio sensor 2 (or the identical audio sensor of sensitivity) and with tested concrete slab and order the same apart from voice signal is sampled with same quantitative spring energized hammer 1 same energy;

2) voice signal that sampling is obtained is handled, at first carry out filtering and eliminating noise, then in acoustic analysis device 5, carry out Fourier transform (FFT), convert the signal Processing information corresponding with the concrete slab check point of various known customizations to and import plotting apparatus 6 into, described signal Processing information comprises the power spectrum chart of sound, envelope diagram and the shape index λ of envelope diagram and the hydridization coefficient ξ of power spectrum chart of spectrogram; 4 is flaw among Fig. 1;

Three) will detect information and standard reference information is compared, determine the defect situation of the tested measuring point of tested concrete slab, the tested measuring point of promptly determining tested concrete slab is identical or close with the known customization concrete slab check point of known any defect level; Described comparison is similar information comparison, i.e. the power spectrum chart of power spectrum chart of Jian Ceing and reference comparison, the envelope diagram of detection and the comparison of the envelope diagram of reference, the shape index λ of detection and the shape index λ of standard reference ₀, and spectrogram hydridization coefficient ξ and canonical reference hydridization coefficient ξ ₀The comparison mode is the computing machine comparison; Also available in other embodiments of the invention artificial comparison.

Embodiment one

Be beforehand with three groups of (A, B, C) test beams in testing laboratory, seen shown in Figure 4;

The size of three groups of test beams is the rectangular beam of 3400 * 200 * 400mm, and normal section is of a size of 200 * 400mm.

In A group and B group beam, respectively buried a foam in advance, investigate as hollowing, the position is 55mm in the central authorities of beam apart from the soffit, but size is differentiated, foam size in the A group beam is than 140 * 140 * 150mm more greatly of the size in the B group beam, size 100 * 100 * 120mm in the B group beam.There is not pre-buried any impurity in the C group beam, as the intact beam of defective reference.

Test method and check point are arranged

1) test method

In the laboratory, will be placed on respectively on the cushion block than big spacing (2 meters), same position is selected check point in three groups of beams respectively, to instrument same position being tested respectively in three groups of beams, compares its result.In process of the test, keep the peace and quiet of testing laboratory as far as possible, as often as possible avoid the influence of noise.

2) measuring point is arranged

The measuring point arrangenent diagram of three beams as shown in Figure 5, totally 2 groups of measuring points, three every group correspondence position points, the 1st group three some A1, B1, C1 are located at 1/4 place of three groups of beams respectively, the 2nd group three some A2, B2, C2 are located at 1/2 place of three groups of beams respectively.

Shown in Fig. 6 A, B, by chart as can be known, in main result, the 1st group of three some A1, B1, C1 are intact falling into, and the 2nd group A2 has big hollowing defective, and the 2nd group B2 has the hollowing defective, and the 2nd group C2 is intact falling into;

The comparison standard

Envelope diagram among above Fig. 6 A, the B is to draw at the low frequency part of the signal of being gathered, because the frequency of reflect structure performance is generally at the low frequency position.Behind the envelope diagram of spectrum power figure in drawing above-mentioned Fig. 6 A, B, whether defectiveness is crucial how to evaluate check point, has introduced the level and smooth and steep prominent index of evaluation envelope diagram: a shape index λ here ₀, and the hydridization coefficient ξ of expression spectrogram hydridization phenomenon ₀, the numerical value of each sampled point of envelope diagram (being response spectrum) is carried out numerical analysis calculating, calculate the shape index λ of its fitted figure ₀With hydridization coefficient ξ.

As ξ 〉=ξ ₀The time, figure occurs than great fluctuation process, especially in low frequency part.Explanation is at this check point place defectiveness.

As ξ＜ξ ₀The time, figure is comparatively level and smooth.This structure detection point place zero defect is described.

Embodiment two

To the B1 concrete cast-in-situ floor of certain engineering (gross building area: 62,458m ²) defects detection the time used the equipment of preliminary form of the present invention, mainly be that detection is judged in hollowing, the crack of concrete cast-in-situ intralamellar part.

Point position and demarcation

The B1 part floor that needs detection, and the about square meter more than 10,000 of area (total building sides: 62,458m ²), utilize the software instrument of the inventive method to detect to surveying district's reinforced concrete frame cast-in-situ floor (planimetric map is seen Fig. 7) inherent vice, because survey area is very big, detects and chosen 9 check points (seeing planimetric map Fig. 7);

Signal that instrument is gathered and analysis

Repeat to have surveyed three times at each check point, obtain three groups of frequency spectrums, total 9 measuring points obtain 27 power spectrum charts altogether, and respectively the defect situation at this 9 measuring point place is detected with additive method, so that with compare by Acoustic detection instrument measured result of the present invention, check the degree of accuracy of the accuracy of detection of this instrument.Analyze and realize that the degree of accuracy of instrument of the present invention aspect detecting defects form and defect size is very high.Chosen the representative power spectrum chart of defective separately, analyzed.The results list such as Fig. 8.

For introducing the present invention better, be explained as follows with regard to relevant knowledge:

1. sound and acoustical signal

1.1 the essential characteristic of sound wave and parameter

Sound is the physical phenomenon of outwardness, and its existence must have two pacing itemss:

1) vibrating object as sound source is arranged;

2) medium that can propagate vibration is arranged.Be the mechanical vibration of the sound source propagation phenomenon in the medium around so sound can be sketched, this propagation phenomenon sound wave occurs being called with the form of ripple.All continuous elasticity things can be as the medium of acoustic propagation.

1.2 describe the physical parameter of sound wave

1.2.1 frequency, wavelength, the velocity of sound

Relation between frequency, wavelength, the velocity of sound three:

λ＝c/f

The c---velocity of sound (m/s)

λ---wavelength (m)

F---frequency (Hz)

1.2.2 acoustic pressure

Instantaneous sound pressure P:

$P=\mathrm{\&gamma;}\frac{{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A20051002748100172.png"\; state="\{\{state\}\}">P</figure-callout>}}_0}{{\mathrm{\&rho;}}_0}{\mathrm{\&rho;}}^{\&prime;}={\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2{\mathrm{\&rho;}}^{\&prime;}$

γ---equipressure and the specific heat ratio that waits appearance

The medium density increment that ρ '---sound wave causes

ρ ₀--the density during-static balancing

ρ ₀--the static pressure during-static balancing

And time effective sound pressure commonly used: the root-mean-square value of certain section interior instantaneous sound pressure of time is called effective sound pressure P _e:

$p_e=\sqrt{\frac{1}{T}}{\&Integral;}_0^T{p}^2\left(t\right)\mathrm{dt}$

1.2.3 frequency spectrum

The sound of being gathered all is that multiple frequency is formed, the frequency content that is comprised in a certain signal, press its amplitude (or its decibel value) or phase place as the function of frequency as distribution plan, be called this signal spectrogram.

Major part is a continuous spectrum in the voice signal of being gathered.

1.2.4 sound interval

For continuous signal, the amplitude of obtaining each frequency content can not also be unnecessary, sometimes can become some little frequency bands to the frequency partition of a certain scope, each section is representative with its centre frequency, obtain the amplitude of acoustical signal on the centre frequency of each frequency band then, as a kind of frequency spectrum, be called sound interval with dividing the frequency band that comes out like this.

1.3 the energy problem in the sound field

Be the communication process of vibrational energy on the sound wave process nature, the mode of sonic propagation kinetic energy is by the propagation of energy rather than the propagation of material.

1.3.1 acoustic energy

The deformation potential that medium has in acoustic energy=particle vibration energy+propagation.

Acoustic energy in the unit volume is called energy density ε and average acoustic energy density ${\stackrel{\&OverBar;}{\mathrm{\&epsiv;}}}_0:=\frac{{\mathrm{<figure-callout\; id="2"\; label="p\; e"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">p</figure-callout>}}_e^{}}{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}$

${\stackrel{\&OverBar;}{\mathrm{\&epsiv;}}}_0=0.5{\mathrm{\&rho;}}_0({\mathrm{\&mu;}}^2+\frac{{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">p</figure-callout>}}^2}{{\mathrm{\&rho;}}_0^2{c}^2})=\frac{{\mathrm{<figure-callout\; id="2"\; label="p\; e"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">p</figure-callout>}}_e^{}}{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}$

The vibration coefficient of μ---volume element

1.3.2 acoustical power

Acoustical power is the acoustic energy of sound source radiation in the unit interval, represents with w, and unit is watt, is called average acoustical power w by the average acoustic energy stream perpendicular to the area S of acoustic propagation direction in the unit interval.

$\stackrel{\&OverBar;}{w}={\stackrel{\&OverBar;}{\mathrm{\&epsiv;}}}_0\mathrm{cS}$

1.3.3 the sound intensity

By being called the average acoustic energy current density perpendicular to the average acoustical power on the unit area of acoustic propagation direction or claiming sound intensity I

1.3.4 the relation of the sound intensity and acoustic pressure

$I={\mathrm{\&rho;}}_{0}c{\mathrm{\&mu;}}_e^2=\frac{{\mathrm{<figure-callout\; id="2"\; label="p\; e"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">p</figure-callout>}}_e^{}}{{\mathrm{\&rho;}}_{0}c}$

1.4 sound intensity level sound pressure level sound power level

The definition of the level of a physical quantity is some and the logarithm of the ratio of datum quantity (or claiming reference quantity) in acoustics.

1.4.1 sound intensity level

The sound intensity level Li of a sound is that the common logarithm of the sound intensity and the ratio of reference sound intensity of this sound multiply by 101, with decibel (dB) metering, that is: and 10 ²w

I ₀---reference sound intensity is 10 at air ^-12W/m ²

14.2 sound pressure level

The common logarithm of certain acoustic pressure p and reference acoustic pressure p0 multiply by 20 sound pressure levels that are called sound, in decibel (dB), that is:

$L_p=20\mathrm{<figure-callout\; id="0"\; label="lg\; p\; p"\; filenames="A20051002748100172.png"\; state="\{\{state\}\}">lg</figure-callout>}\frac{p}{p_{}}\frac{{}_0}{}$

p ₀---reference acoustic pressure in air is: 2 * 10 ^-5Pa

1.4.3 sound power level

Certain acoustical power w and reference sound power w ₀The common logarithm of ratio multiply by 10 sound power levels that are called this sound, come in decibel, that is:

$L_w=10\mathrm{<figure-callout\; id="0"\; label="lg\; w\; w"\; filenames="A20051002748100172.png"\; state="\{\{state\}\}">lg</figure-callout>}\frac{w}{w_{}}\frac{{}_0}{}$

w ₀---reference sound power level is 10 in air ²W.4) relation of sound intensity level, sound pressure level

Reference sound intensity takes 10 by force ^-12W/m ², reference acoustic pressure corresponding with it is 2 * 10 ^-5Pa, the condition that obtains these values is that the characteristic impedance of getting air is 400Pas/m.Draw sound pressure level and sound intensity level approximately equal thus.

$L_I=10\lg \frac{I}{I_0}10\lg (\frac{{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">p</figure-callout>}}^2}{{\mathrm{\&rho;}}_{0}c}\&CenterDot;\frac{400}{{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="A20051002748100172.png"\; state="\{\{state\}\}">p</figure-callout>}}_0^2})=10\lg \frac{p^2}{{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="A20051002748100172.png"\; state="\{\{state\}\}">p</figure-callout>}}_0^2}+10\mathrm{<figure-callout\; id="400"\; label="lg"\; filenames="A20051002748100173.png,A20051002748100174.png"\; state="\{\{state\}\}">lg</figure-callout>}\frac{400}{{\mathrm{\&rho;}}_{0}c}=L_p+10\mathrm{<figure-callout\; id="400"\; label="lg"\; filenames="A20051002748100173.png,A20051002748100174.png"\; state="\{\{state\}\}">lg</figure-callout>}\frac{400}{{\mathrm{\&rho;}}_{0}c}$

We have analyzed the fundamental characteristics of sound, and what we were concerned about as can be seen is frequency, sound intensity level, sound pressure level, the acoustical power of sound.And all parameters are finally summed up in the point that the frequency (velocity of sound) of sound.The audio parameter that has also promptly drawn the most critical relevant with defective is: sound frequency (velocity of sound).

2 elastomeric vibrations

2.1 the vibration of string

2.1.1 the vibration equation of string

If ${\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2=\frac{T}{\mathrm{\&delta;}},$ The vibration equation of string is:

$\frac{{\&PartialD;}^2\mathrm{\&eta;}}{\&PartialD;x^2}=\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}\frac{{\&PartialD;}^2\mathrm{\&eta;}}{{\&PartialD;\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}$

In the formula: the transverse vibration displacement of η-string

The line density of δ-string

The tension force of T---string

2.1.2 the vibration universal law of string

Having separated of full scale equation if the two ends of string are fixing:

Wherein the natural frequency of string is:

$f_i=\frac{\mathrm{ic}}{2l}=\frac{n}{2l}\sqrt{\frac{T}{\mathrm{\&delta;}}},i=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,N$

2.2 the extensional vibration of rod

2.2.1 the equation of longitudinal of rod

Order $c=\sqrt{\frac{E}{\mathrm{\&rho;}}}$ The compressional vibration velocity of propagation of-rod then

$\frac{{\&PartialD;}^2\mathrm{\&xi;}}{\&PartialD;x^2}=\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}\frac{{\&PartialD;}^2\mathrm{\&xi;}}{\&PartialD;{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}$

2.2.2 the extensional vibration universal law of rod

1) the fixing rod in two ends

ξ _i(x，t)＝A _isin?k _ixcos(2πf _it- _i)

Wherein Bang vibration natural frequency is: $f_i=\frac{\mathrm{ic}}{2l},$ I=1 wherein, 2 ..., N.

2) excellent two ends freedom

ξ _i(x，t)＝B _isin?k _ixcos(2πf _it- _i)

Wherein Bang vibration natural frequency is: $f_i=\frac{\mathrm{ic}}{2l},$ I=1 wherein, 2 ..., N.

3) the free end of an end of rod is fixed

Can draw normal frequency by the difference of boundary condition is:

$f_i=(2i-1)\frac{c}{4l},(i=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,N).$

Symbolic significance in the following formula: the extensional vibration displacement of ξ-rod

The fundamental frequency of the rod that the free end of one end is fixing is at half than preceding two kinds of situations when same length l, and its general frequency is also different with the rule of preceding two kinds of situations, only there is the general frequency of odd number in it to this a kind of border, hence one can see that, if we get the rod of same length and different in addition borders, give same excitation then, then the fundamental frequency that excites of two rods is all different with general frequency, so that people feel that acoustic tones and tone color that they send are also inequality.

2.3 the vibration of plate

2.3.1 the vibration equation of plate

$\frac{{\mathrm{<figure-callout\; id="2"\; label="EK"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">EK</figure-callout>}}^2}{\mathrm{\&rho;}(1-{\mathrm{\&sigma;}}^2)}{\&dtri;}^4\mathrm{\&eta;}+\frac{{\&PartialD;}^2\mathrm{\&eta;}}{\&PartialD;{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20051002748100171.png,A20051002748100182.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}=0$

Wherein: radius of gyration $K=\frac{h}{\sqrt{12}},$ H is the thickness of plate

${\&dtri;}^4={(\frac{{\&PartialD;}^2}{\&PartialD;x^2}+\frac{{\&PartialD;}^2}{{\&PartialD;y}^2})}^2$

The ratio of the horizontal compression of σ-unit length and longitudinal tensile strain, i.e. Poisson ratio

2.3.2 the universal law of affixed symmetric vibration around the circular slab

The normal frequency of panel vibration is:

$\begin{array}{c}{f}_i=\frac{{\mathrm{\&mu;}}_i^{2}h}{4\mathrm{\&pi;}{a}^2}\sqrt{\frac{\mathrm{<figure-callout\; id="3"\; label="E"\; filenames="A20051002748100171.png"\; state="\{\{state\}\}">E</figure-callout>}}{3\mathrm{\&rho;}(1-{\mathrm{\&sigma;}}^2)}},i=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,N\\ i>3,{\mathrm{\&mu;}}_i=\mathrm{i\&pi;}\end{array}$

Claims (3)

1, a kind of audio-frequency detection of concrete fault is characterized in that, method step is as follows:

One) set for comparison usefulness with reference to information:

1) knocks the concrete slab check point of various known customizations with spring energized hammer, and voice signal is sampled with stationary installation;

2) voice signal that sampling is obtained carries out fast fourier transform, convert the standard reference information corresponding with the concrete slab check point of various known customizations to, described standard reference information comprises the power spectrum chart of sound, the envelope diagram of spectrogram and the shape index ξ of envelope diagram;

Two) tested concrete slab is sampled:

1) use step 1) same method and same device carry out the sampling of voice signal to tested concrete slab check point;

2) the described voice signal that sampling is obtained is handled, at first carry out filtering and eliminating noise, Fourier transform then, convert the signal Processing information corresponding with the concrete slab check point of various known customizations to, described signal Processing information comprises the power spectrum chart of sound, envelope diagram and the shape index λ of envelope diagram and the hydridization coefficient ξ of power spectrum chart of spectrogram;

Three) will detect information and standard reference information is compared, determine the defect situation of the tested measuring point of tested concrete slab; Described comparison is similar information comparison, i.e. the power spectrum chart of power spectrum chart of Jian Ceing and reference comparison, the envelope diagram of detection and the comparison of the envelope diagram of reference, the shape index λ of detection and the shape index λ of standard reference ₀, and spectrogram hydridization coefficient ξ and canonical reference hydridization coefficient ξ ₀

2, audio-frequency detection of concrete fault according to claim 1 is characterized in that, in step 3) in, described comparison mode is the computing machine comparison.

3, audio-frequency detection of concrete fault according to claim 1 is characterized in that, in step 3) in, described comparison mode is artificial comparison.

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