KR20080016140A - Inspection device, method for thickness and material properties of structure and monitoring method for thickness thinning of the same - Google Patents

Abstract

A device and a method for inspecting thickness and properties of a structure, and a method for monitoring thinning are provided to measure thickness of the structure quickly and accurately by attaching two sensors to the structure and measuring delay time of vibration wave between the sensors. A device for inspecting thickness and properties of a structure(210) comprises an exciting unit(110), two measuring sensors(132,134), and a collecting and analyzing unit(150). The exciting unit applies impact to the structure to generate vibration wave. The measuring sensors are attached to the structure to measure the vibration wave between the two points. The collecting and analyzing unit calculates group velocity based on wave delay time in the measured vibration wave and estimates the thickness of the structure between the two points.

Description

Inspection Device, Method for Thickness and Material Properties of Structure and Monitoring Method for Thickness Thinning of the Same}

1 is a block diagram showing a thickness inspection process of a conventional structure;

2 is a perspective view of a typical three dimensional shell element;

3 is a graph showing the theoretical value of the group speed for each frequency according to the thickness of the plate;

Figure 4 is a schematic view showing a thickness inspection apparatus of the structure according to the present invention;

5 is a block diagram showing a process of inspecting the thickness of the plate by the thickness inspection apparatus of the structure according to the present invention;

FIG. 6 is a graph showing an analysis result by Wigner-Ville distribution of vibration wave signals measured by two measurement sensors of FIG. 5; FIG.

FIG. 7 is a graph showing the maximum value curve of the vibration wave signal shown in FIG. 6 and the group speed calculated accordingly; FIG.

8 is a graph comparing the theoretical value of the group speed and the experimental value predicted by the thickness inspection apparatus of the present invention on a plate having a thickness of 2 mm;

9 is a perspective view showing a process of inspecting the thickness of the pipe used in the nuclear power plant by the thickness inspection apparatus of the structure according to the present invention;

10 is a cross-sectional view showing the dimensions of the pipe of Figure 9 and the installation state of the measurement sensor;

FIG. 11 is a graph showing an analysis result based on Wigner-Ville distribution of a vibration wave signal measured by any one of the measuring sensors of FIG. 10;

12 is a graph showing the maximum value curve of the vibration wave signal shown in FIG. 11 and the group speed calculated accordingly;

FIG. 13 is a graph showing experimental values of group speed predicted by the thickness inspection apparatus of the present invention in the pipe of FIG. 9; FIG.

<Explanation of Signs of Major Parts of Drawings>

110: excitation unit 130: measuring sensor

132: first measuring sensor 134: second measuring sensor

150: analysis unit 210: the target structure

220: flat plate 230: piping

The present invention relates to a thickness inspection apparatus of a structure and a thickness inspection method of a structure, and more particularly, to a thickness inspection apparatus and a thickness inspection method of a structure capable of quickly and accurately predicting the thickness of the structure.

Inside the piping used in nuclear power plants, especially in the turbine generator system (secondary side) of the nuclear power plant, fluid flows at a very high speed with high pressure and temperature. Therefore, the phenomenon of corrosion or wear caused by the flow of the fluid causes the pipe thickness to become thin. This phenomenon is prominent in curved pipes having a predetermined curvature. As a result of the thinning of the pipe in this manner, the pipe cannot overcome the high pressure and temperature inside and leaks.

In fact, in 2004, a case was reported in which a rupture caused by thinning of the turbine-side piping of a nuclear power plant caused water leakage and killed several people.

It is very important to monitor the pipe thinning because the damage caused by the thinning of the pipe can cause a big problem that can damage not only money and time, but also human life.

As a method of checking the thickness of a pipe, a method through mode analysis, a method using a filter, a method using ultrasonic waves, and the like have been proposed. Among these, the method using ultrasonic waves is the most commonly used method to date.

Referring to FIG. 1, a thickness inspection apparatus using ultrasonic waves generally used is as follows.

As shown in FIG. 1, the thickness inspection apparatus using ultrasonic waves includes an ultrasonic sensor 11 and an analyzer 13 receiving and analyzing a signal from the ultrasonic sensor 11.

Here, the ultrasonic sensor 11 is a sensor generally used for non-destructive inspection, is installed in the pipe 21, generates an ultrasonic signal and detects the ultrasonic signal reflected by the change of the medium.

And the analyzer 13 measures the thickness of the object by the time difference between the generated signal and the detection signal measured by the ultrasonic sensor.

On the other hand, the thickness measurement by the ultrasonic wave is performed on a grid point formed at regular intervals after removing the thermal insulation material 23 surrounding the outside in the pipe 21 having a constant curvature of the ultrasonic sensor 11. Then, the thickness of the pipe 21 is predicted through the thickness information of each grid point.

However, the above-described thickness inspection apparatus and inspection method of the conventional structure has the following problems.

First, in the case of measuring the thickness of the pipe by ultrasonic, there is a problem that it takes a long time to check the thickness because the thickness must be measured for each point after dividing the grid finely horizontally and vertically.

Second, the conventional inspection device has a problem that it is difficult to measure the thickness during operation. This is because the signal to noise ratio of the ultrasonic sensor is significantly lowered when the fluid flows inside the nuclear power plant, which significantly reduces the accuracy of the thickness inspection. In addition, due to the vibration generated by the flow of the fluid, not only accurate measurement is difficult, but also a problem that it is difficult to firmly attach the ultrasonic sensor.

Third, as can be seen in Figure 1 there is a problem in that to remove the thermal insulation material in a relatively large area in order to measure the thickness.

Fourth, since the conventional ultrasonic method uses a high frequency bending wave signal, the attenuation of the signal is large so that the thickness can be measured only near the generation point of the ultrasonic wave.

In addition to the method using ultrasonic wave, the method through mode analysis and the method using filter have many difficulties in practical application because the system itself is complicated.

The present invention is to solve the above-mentioned conventional problems, an object of the present invention is to provide a thickness inspection apparatus and inspection method of the structure that can accurately measure the thickness of the target structure by a simple method in a short time.

Another object of the present invention is to provide a thickness inspection apparatus and inspection method of the structure capable of accurate thickness prediction even if the fluid flows inside.

Still another object of the present invention is to provide a method for measuring physical properties of a structure when the thickness of the structure is known.

In order to achieve the above object, the present invention, the excitation unit for generating a vibration wave by applying a shock to the target structure, the installation point is provided at a predetermined interval along the direction of travel of the vibration wave on the surface of the target structure, In order to calculate the group velocity based on the vibration wave delay time between the two points by receiving a pair of measurement sensors for measuring the signal of the vibration wave and the vibration wave signal measured at each of the measurement sensor, It provides a thickness inspection apparatus of the structure comprising a collection analysis unit for predicting the thickness of the target structure between the unit.

And the measuring sensor is generally an accelerometer for measuring the acceleration at the installed point.

Meanwhile, the target structure may be a plate, a pipe, or other structures having various shapes. As an example, the target structure may be a pipe in which a fluid flow path is formed, and the pipe may be a pipe used in a turbine generator system of a nuclear power plant.

In the collection analysis unit, the vibration wave delay time between the two points is preferably calculated in the time-frequency domain. When measuring the time delay between two points in the time domain, since the medium has dispersion characteristics, the shock signal is deformed according to the distance and thus cannot accurately find the time delay. Moreover, since background noise or operating noise are measured together when measuring signals, it is easy to see that there are many errors when measuring time delay in the time domain. Therefore, in the present invention, the group speed is predicted by measuring the time delay between two sensors using a time-frequency technique, which is a multidimensional analysis.

Here, the maximum value for each frequency is more preferably calculated after removing a signal due to resonance of the target structure. Wigner-Ville distribution may be used for the time-frequency analysis technique. In addition, the thickness of the structure is preferably predicted by the group speed in the frequency band with a high signal to noise ratio.

On the other hand, in the physical property inspection apparatus of the structure according to the present invention, the collection and analysis unit receives the signal of the vibration wave measured by each of the measuring sensor to calculate the group velocity (group velocity) based on the vibration wave delay time between the two points And predicting the physical properties of the target structure based on the calculated group speed and the thickness of the structure.

In the thickness inspection method of the structure according to the present invention by applying an impact to the target structure generating a vibration wave, the vibration wave signal at two points at a predetermined interval along the direction of travel of the vibration wave on the surface of the target structure Measuring, receiving a signal of the measured vibration wave, calculating a group velocity based on the vibration wave delay time between the two points, and predicting the thickness of the target structure between the two points based on the calculated group velocity It includes a step.

In the step of calculating the group speed, the vibration wave delay time between two points is obtained by the maximum value for each frequency according to the time-frequency analysis technique, and the maximum value for each frequency is calculated after removing the signal due to the resonance of the target structure. It is preferable.

In particular, the Wigner-Ville distribution may be used for the time-frequency analysis technique.

And the thickness of the structure is preferably predicted by the group speed in the frequency band with a good signal to noise ratio (signal to noise ratio).

In addition, the property value inspection method of the structure according to the present invention measures the thickness of the structure, and predicts the property value of the target structure based on the measured thickness of the structure and the calculated group speed.

On the other hand, the thickness reduction monitoring method of the structure according to the present invention, the step of generating a vibration wave by applying a shock to the target structure, at the two points having a predetermined interval along the direction of the vibration wave on the surface of the target structure Measuring a signal of a vibration wave, calculating a group velocity based on a vibration wave delay time between two points by receiving the measured signal of the vibration wave, and comparing the calculated group speed with a preset reference group speed Monitoring the reduction in thickness of the target structure between the two points.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of this embodiment, the same name and the same reference numerals are used for the same configuration and additional description thereof will be omitted.

First, referring to FIG. 2, a theoretical formula for calculating a group speed of a general shell structure is as follows.

방향은 굽힘파의 변위방향,

및

는 각 좌표 방향의 곡률반경,

는 쉘의 두께를 나타낸다. 그리고,

와

는 각각 쉘의 밀도와 탄성계수를 나타낸다.2 illustrates a shell structure with any curvature. here,

Direction is the displacement direction of the bending wave,

And

Is the radius of curvature of each coordinate direction,

Represents the thickness of the shell. And,

Wow

Represents the density and modulus of elasticity of the shell, respectively.

)이고 균일한 재질이라고 가정할 때, 회전 관성 및 전단 변형에 의한 영향을 모두 고려한 파(wave)의 군속도는 다음과 같다:The shell structure as shown in Figure 2 is a thin shell in the low frequency region (

Assuming a uniform material, the group velocity of the wave taking into account both the effects of rotational inertia and shear deformation is:

.

.

는 각속도,

,

이고,

는 포아송 비,

를 나타낸다.here,

Is the angular velocity,

,

ego,

Poisson Rain,

Indicates.

이므로

, 실린더 쉘의 경우에는 , 구형 쉘인 경우에는

라는 조건에 의해 상기 수학식 1을 보다 단순화시킬 수 있다.Equation 1 can be used to calculate the group speed in the shell of the general form. Especially in the case of flat plates, there is no curvature.

Because of

In the case of a cylinder shell , For older shells

Equation 1 can be further simplified by the condition of.

이고

이므로,If the structure is a flat plate,

ego

Because of,

It can be simplified as

As can be seen in Equations 1 and 2, it can be seen that the group speed in a general shell and plate is a function of the thickness h. In particular, in the case of a flat plate it can be seen that the larger the thickness (h) of the flat plate in proportion to the faster the group speed of the plate.

Figure 3 shows the result of calculating the group speed according to the thickness in accordance with the equation (2) when the plate is made of SUS304 material, the length and width of each length 600mm.

As shown in FIG. 3, the group speed in the plate increases as the thickness increases, and tends to increase as it increases in frequency.

As in the above results, since the group speed of the structure changes according to the thickness of the structure, conversely, if the group speed in the general shell-type structure is known, the thickness of the structure can be predicted.

By measuring the thickness of the structure and calculating the group speed, it is also possible to predict the material properties of the structure. Here, the physical properties of the structure may be an elastic modulus or density.

The present invention relates to an apparatus and method for inspecting the thickness of a structure using the correlation between the group speed and the thickness of the structure.

Referring to Figure 4, when explaining the basic configuration and thickness prediction principle of the thickness inspection apparatus of the structure according to the present invention.

The thickness inspection apparatus of the structure according to the present invention includes an excitation unit 110, a measurement sensor 130, and a collection analysis unit 150.

The excitation unit 110, by applying an impact to the target structure 210 to excite the target structure 210, serves to generate a vibration wave. There is no limitation on the type of excitation unit 110, this embodiment, as shown in Figure 4, illustrates that the excitation unit 110 is made in the form of a hammer (hammer).

The measuring sensor 130 is composed of a pair of sensors (132, 134), is installed at a predetermined interval on the surface of the target structure 210 to measure the signal of the vibration wave. On the other hand, in order to obtain a delay time of the vibration wave by the measurement sensor 130, the measurement sensor 130 is preferably installed along the traveling direction of the vibration wave.

On the other hand, there is no limitation on the type of measurement sensor, this embodiment used an accelerometer as the measurement sensor 130.

The collection analysis unit 150 receives the signal of the vibration wave measured by the measurement sensor 130 and calculates a group velocity based on the vibration wave delay time of two points.

The principle of calculating the group speed by the vibration wave delay time is as follows.

인 경우, 두 지점에서의 진동파 지연시간이

로 산출되면, 대상 구조물에서 군속도는,As shown in Figure 4 the distance between the two measuring sensors (132, 134)

If the vibration wave delay time at two points

If calculated, the military speed in the target structure,

It can be represented as. That is, when the delay time of the two vibration waves is obtained, the group speed between the two points can be calculated accordingly.

5 to 8, when the target structure is a flat plate, a process of actually measuring the group speed will be described.

First, the installation state of the apparatus for measuring the thickness of the actual flat plate will be described with reference to FIG. 5.

The target structure 220 is made of SUS304 material, and is a flat plate having a length and width of 600 mm and a thickness of 2 mm, respectively. The distance between the two measuring sensors 132 and 134 is set to 100 mm, and each measuring sensor 132 and 134 is connected to the collection analyzing unit 150 to transmit a signal of the measured vibration wave.

On the other hand, although not shown, the excitation unit generates a vibration wave by impacting the plate at a point in line with the two measuring sensors.

The vibration wave generated by the excitation unit propagates along the structure, and when the vibration wave signal from the measurement sensor 130 is installed along the traveling direction of the vibration wave, the delay time of the vibration wave can be obtained at two point perspectives.

However, in the shell and plate structures, since the propagation speed of energy varies according to frequencies, the entire waveform changes with time and travel distance. Moreover, the presence of any noise makes it very difficult to measure group speed in the time domain.

Therefore, it is preferable to analyze the vibration wave by the time-frequency analysis technique of the signal which can be determined for each frequency.

Typical time-frequency analysis techniques include short time fourier transforms (STFTs), wavelet transforms, and Wigner-Ville distributions.

Here, STFT is a technique that is performed by sequentially executing Fourier transform while moving the window according to time by using the appropriate window function suitable for the purpose. It is a spectrum analysis method that can observe the occurrence of. However, STFT has low time and frequency resolution, which makes it difficult to accurately analyze the transient signal.

Wavelet transform is an analysis technique that provides various time-frequency resolutions according to frequency bands, and is particularly excellent in analyzing signals having rapid changes in a short time.

On the other hand, as described above, the Fourier transform uses an infinite time window, while the STFT and wavelet transforms use a given short window. However, if the shock wave signal is buried in white noise, it is difficult to clearly find the frequency component included in the signal of the shock wave through the Fourier transform.

The most commonly used method in this case is the Wigner-Ville distribution which is defined as the Fourier transform for the time delay of the autocorrelation function.

Among the above-described time-frequency analysis techniques, the Wigner-Ville distribution method has an excellent advantage in analyzing transient abnormal signals with high time-frequency resolution. In this example, the Wigner-Ville distribution, which is particularly suitable for group velocity prediction, was analyzed.

The Wigner-Ville distribution is a way to improve time and frequency resolution independently, a kind of bilinear Time Frequency Representation (TFR), whose definition is:

.

.

는 시간종속 자기상관함수 (time dependent autocorrelation function),

는 신호의 해석함수,

는

의 퓨리에 변환이다. 한편, 상기 위그너-빌(Wigner-Ville) 분포는 물리적으로는 각 시간별 신호의 에너지에 대한 주파수 분포를 나타낸다.here,

Is a time dependent autocorrelation function,

Is the interpretation function of the signal,

Is

Is the Fourier transform. On the other hand, the Wigner-Ville distribution physically represents the frequency distribution of the energy of each time signal.

Figure 6 shows the results of analyzing the vibration wave signals obtained from the two measurement sensors by the Wigner-Ville distribution. Here, (a) of Figure 6 is a vibration wave signal of the measurement sensor installed at a point close to the excitation unit, Figure 6 (b) is an analysis result of the vibration wave signal of the measurement sensor provided at a point far from the excitation unit.

In each of (a) and (b) of FIG. 6, the graph located at the center shows a vibration wave signal in which the horizontal axis represents time and the vertical axis represents frequency. The graph located on the lower side shows the vibration wave signal in the time domain, and the graph located on the left side shows the vibration wave signal in the frequency domain.

First, in (a) and (b) of FIG. 6, it can be seen that the amplitude of the vibration wave signal decreases with time and the time is delayed.

Next, referring to FIG. 7, the method of calculating the group speed by the Wigner-Ville analysis will be described.

FIG. 7 (a) shows a line connecting the maximum value at each frequency in the analysis results of FIGS. 6 (a) and 6 (b), where the left line is a point close to the excitation unit. This is the vibration wave signal of the measuring sensor installed at, and the right line shows the vibration wave signal of the measuring sensor installed at a point far from the excitation unit.

On the other hand, the delay time at each frequency can be obtained by the two lines that are connected to the maximum value for each frequency in this way. FIG. 7B shows the group speed calculated based on the delay time obtained through the upper result. Through (b) of Figure 7, it can be seen that the group speed on the plate tends to increase as the frequency increases.

8 is a graph comparing experimental values and theoretical values of group velocities calculated through a series of processes described above when the thickness of the plate is 2 mm. As shown in Figure 8, it can be seen that the experimental value tends to be very similar to the theoretical value.

The group speed measurement process of the flat plate mentioned above is applicable also in the case of piping.

The pipe may be in various forms used in a nuclear power plant, a hydro power plant, a thermal power plant, or a general plant.

9 to 13, a process of measuring a group speed will be described as an example of a pipe used in a turbine generator system (secondary side) of a nuclear power plant.

As described above, the pipe 230 used in the nuclear power plant has a high temperature and high pressure fluid flows at a very high speed and has a predetermined curvature so that the thickness of the pipe 230 becomes corroded and worn by the fluid flow. do.

In order to predict the thickness of the pipe 230 to monitor the pipe thinning, as shown in FIG. 9, the excitation unit 110 is prepared, and along the traveling direction of the vibration wave generated by the excitation unit 110. The measuring sensor 130 is installed at two points.

And each of the measuring sensors is connected to the collection analysis unit 150, it is configured to transmit a signal of the vibration wave.

)는 50 mm가 되도록 설치하였다.10 is a cross-sectional view showing the dimensions of the pipe of FIG. 9 and the installation state of the sideline sensor. In this embodiment, the height H of the pipe is 650 mm, the width L between the ends of the pipe is 400 mm. The inner diameter d _i is 35 mm. And the distance between a pair of measuring sensors

) Was installed to be 50 mm.

The thickness h of the pipe was measured by dividing it into 2 mm and 4 mm cases, respectively. Therefore, the outer diameter d _o of the pipe is 39 mm when the thickness h is 2 mm, and 43 mm when the thickness h is 4 mm.

FIG. 11 (a) shows the result of analyzing the vibration wave signal obtained from the measuring unit at the point closest to the excitation unit of the two measuring sensors by the Wigner-Ville distribution as described above.

As can be seen in (a) of FIG. 11, the vibration wave signal obtained from the measuring sensor includes not only a signal due to impact but also a signal due to resonance due to the sensor and the sensor attachment effect. Since the signal required for group speed measurement is a shock signal by the excitation unit, it is possible to calculate the group speed more precisely by removing the resonance component.

FIG. 11B shows the result of the time-frequency domain from which signal components due to resonance are removed in FIG.

As described above, the signal of the measuring sensor may include not only a signal caused by the impact of the excitation unit but also various signals such as a component caused by resonance or noise of a high frequency component. Thus, a high pass filter or a band pass filter may be included. It is preferable to go through the process of extracting only the signal caused by the impact of the excitation unit by using an appropriate filter such as a filter.

FIG. 12 (a) shows a line connecting the maximum value for each frequency after the shock signal extraction process, in which the left line is close to the excitation unit and the right line is installed at a point far from the excitation unit. The vibration wave signal of the sensor is shown.

Fig. 12B shows the group speeds calculated by calculating the delay time at each frequency from the two lines obtained in Fig. 12A.

FIG. 13 finally shows the group speed distribution for each frequency in the case of 2 mm in thickness, and the group speed distribution for each frequency in the case of 4 mm in thickness obtained by the above-described process.

As shown in FIG. 13, the group speed of the pipe shows a characteristic that varies with frequency, but shows a substantially constant value in a region where the signal to noise ratio (SNR) is high.

Therefore, the representative value of the group speed is preferably predicted by the group speed in the frequency band with a good signal-to-noise ratio. In this embodiment, the average value of the group speed in the frequency band where the signal-to-noise ratio is 30 dB or more is determined to determine the representative value of the group speed.

In the frequency band, the group speed of the pipe is about 1100 m / sec when the thickness is 2 mm, about 1600 m / sec when the thickness is 4 mm, and the group speed of the pipe increases as the thickness of the pipe increases. .

However, instead of averaging the group speed in a frequency band of a certain section, it is also possible to calculate the group speed using a value at a certain frequency value as a representative value.

As in the above results, the thickness of the pipe can be estimated by finding the group speed in the pipe. In particular, when applied to the monitoring of the thinning of pipes used in nuclear power plants, the group speed without thinning is defined as the reference group speed. You can set the time.

Alternatively, the thickness of the pipe can be monitored by determining the thickness as the safety standard, measuring the group speed, and determining the group speed as a reference group speed, and then determining the case where the measured group speed is smaller than the pipe life limit.

Until now, the thickness inspection apparatus and inspection method for the structure mainly in the form of a flat plate and a pipe was described as an example.

In addition, when the group velocity is calculated and the thickness of the target structure is actually measured through the above-described Equations 1 and 2, the physical property value of the structure can be predicted based on this.

Accordingly, those skilled in the art can make modifications without departing from the spirit of the present invention and such modifications are within the scope of the present invention.

Thickness inspection apparatus and inspection method of the structure according to the present invention having the above configuration has the following effects.

First, by calculating the group speed of the structure by a simple inspection device and accordingly configured to predict the thickness of the structure, there is an advantage that can quickly and accurately predict the thickness of the structure.

In particular, by applying the thinning of the pipe used in the nuclear power plant, there is an advantage that can determine the degree of thinning accurately to eliminate the risk due to the source.

In addition, compared with the conventional method using ultrasonic waves, the thickness of the structure between the two measuring sensors can be predicted without the need to measure the thickness of the lattice points one by one, thereby significantly reducing the time required to estimate the thickness.

Second, in the case of measuring the thickness of the pipe in which the fluid flows inside, even if the fluid is flowing because the device is in operation, the interference between the vibration wave due to the fluid flow and the vibration wave due to the shock wave is very small, so that the thickness of the structure There is an advantage that can be accurately predicted.

Third, because the group speed is a function of the thickness of the structure, the physical properties, etc., if the thickness of the structure is known, there is an advantage that the physical properties of the structure, for example, the elastic modulus of the material, can be obtained by obtaining the group speed.

Claims (16)

An excitation unit for generating an oscillation wave by applying an impact to a target structure; A pair of measuring sensors installed at predetermined intervals along a traveling direction of the vibration wave on the surface of the target structure to measure a signal of the vibration wave at the installed point; And A collection and analysis unit which receives a signal of the vibration wave measured by each of the measurement sensors, calculates a group velocity based on the vibration wave delay time between two points, and estimates a thickness of the target structure between the measurement units; Thickness inspection device of the structure comprising a. The method of claim 1, The measuring sensor, Thickness tester of the structure, characterized in that the accelerometer for measuring the acceleration at the installed point. The method of claim 1, The target structure, Thickness inspection apparatus of the structure, characterized in that the pipe is formed with a flow path through which the fluid flows. The method of claim 3, The pipe is a thickness tester for the structure, characterized in that the pipe used in the turbine generator system of the nuclear power plant. The method of claim 1, In the collection analysis unit, The vibration wave delay time between two points is calculated by the maximum value for each frequency according to the time-frequency analysis technique. The method of claim 5, The maximum value for each frequency is calculated after removing the signal caused by the resonance of the target structure thickness measuring apparatus. The method of claim 5, Wigner-Ville distribution is used for the time-frequency analysis technique. The method of claim 1, The thickness of the structure, Thickness to noise ratio (signal to noise ratio) is a structure thickness inspection apparatus characterized in that predicted by the group speed in the high frequency band. An excitation unit for generating an oscillation wave by applying an impact to a target structure; A pair of measuring sensors installed at predetermined intervals along a traveling direction of the vibration wave on the surface of the target structure to measure a signal of the vibration wave at the installed point; And Receive the signals of the vibration wave measured by each of the measuring sensors to calculate the group velocity based on the vibration wave delay time between the two points, the physical properties of the target structure based on the calculated group velocity and the thickness of the target structure Collection analysis unit for predicting; Physical property inspection device of the structure comprising a. Impacting the target structure to generate a vibration wave; Measuring the vibration wave signals at two points at regular intervals along a traveling direction of the vibration wave on the surface of the target structure; Receiving a signal of the measured vibration wave and calculating a group velocity based on the vibration wave delay time between two points; And Predicting a thickness of the target structure between the two points by the calculated group speed; Thickness inspection method of the structure comprising a. The method of claim 10, In calculating the military speed, The vibration wave delay time between two points is determined by the maximum value for each frequency according to the time-frequency analysis technique. The method of claim 11, The maximum value for each frequency is calculated after removing the signal caused by the resonance of the target structure thickness measurement method of the structure. The method of claim 11, The Wigner-Ville distribution method is used for the time-frequency analysis technique. The method of claim 10, The thickness of the structure, A method for testing the thickness of a structure, characterized by predicting the group speed in a frequency band with a good signal to noise ratio. Impacting the target structure to generate a vibration wave; Measuring a signal of the vibration wave at two points at a predetermined interval along the traveling direction of the vibration wave on the surface of the target structure; Calculating a group velocity based on the vibration wave delay time between the two points by receiving the measured vibration wave signal; And Monitoring the thickness reduction of the target structure between the two points by comparing the calculated group speed with a preset reference group speed; Monitoring method for reducing the thickness of a structure comprising a. Measuring a thickness of the target structure; Impacting the target structure to generate a vibration wave; Measuring a signal of the vibration wave at two points at a predetermined interval along the traveling direction of the vibration wave on the surface of the target structure; Calculating a group velocity based on the vibration wave delay time between the two points by receiving the measured vibration wave signal; And And predicting a property value of the target structure based on the calculated group speed and the measured thickness of the target structure.

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