JPH0546504B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for measuring the kinetic energy of an object when the object collides with a structure, and particularly relates to a method for measuring the kinetic energy of an object when it collides with a structure, and in particular, when a foreign metal object collides with the inner wall of a nuclear reactor pressure vessel. This invention relates to a method for measuring the impact energy of.

[Background of the invention]

Conventionally, the kinetic energy E of an object that collided with a structure was determined by installing an acoustic detector (such as an acceleration detector using a piezoelectric element) at an appropriate location on the structure to detect the impact sound, and measuring the amplitude value of the output signal. a and the distance r from the collision position to the detector position, E=k・a ²・r _u2.J ...(1). Here, k is a constant determined by the detector sensitivity, etc., and J is an attenuation constant due to acoustic propagation. However, when the shape of the structure becomes complex, the attenuation constant J differs depending on the propagation path of the impact sound. Therefore, assuming a constant J, Equation (1)
There will be a large error when calculating. In addition, in a cylindrical structure such as a reactor pressure vessel, the sound waves rotating clockwise and counterclockwise on the side wall of the vessel interfere with each other, making it difficult to obtain accurate wave height values, which makes it difficult to measure the energy E. This is a major cause of error.

[Purpose of the invention]

The purpose of the present invention is to determine the detector to be used for energy estimation for each region of the target structure,
Further, it provides a method for accurately determining the kinetic energy of a foreign object when it collides with a structure by referring to the peak value of the detector signal when a shock of known energy is applied to each region. It is.

[Summary of the invention]

In the present invention, when an impact is applied to a structure with a constant kinetic energy, even if the distance from the impact point to the detector is constant, if the positional relationship between the impact point and the detection point changes, the peak value of the detection signal will change. It was experimentally confirmed that the main cause of this change is due to the interference of sound waves, and that there is a risk of an error of more than one digit when determining the energy using equation (1). In order to eliminate errors caused by interference, the energy of the unknown impact is determined by referring to the peak value of the detector output when an impact of known energy is applied to the structure in advance.

[Embodiments of the invention]

Below, based on experimental data, we will explain the detection signal peak value when impact sound on a structure is detected by an acoustic detector, and the positional relationship between the sound source and the detector.
Furthermore, the impact energy measuring method according to the present invention will be explained.

FIG. 1 shows a developed view of the side wall of a cylindrical tank used for impact sound detection. This cylindrical tank has a height of 5 m and a diameter of 2 m, so the cylinder is approximately
It is 6m long. As shown in Figure 1, nine detectors were attached to the side wall of this cylindrical tank to detect impact sounds. Further, as shown in FIG. 1, an impact was applied to each part of the side wall of the cylindrical tank using a steel ball pendulum. The kinetic energy of the steel ball pendulum upon impact is always 1.5mJ.

FIG. 2 shows the relationship between the peak value of the impact sound signal and the distance from the sound source position to the detector position, that is, the propagation distance of the sound wave. In Figure 2, the data of all the detectors in Figure 1 are plotted.
There are many impact sound sources not only in the area circled in Figure 1, but also all over the side wall of the tank. These data plot the average value of the wave height when three impacts are applied to the same sound source position.
The reproducibility of wave height values is within ±10% when impact is applied to the same point with the same energy. As is clear from FIG. 2, even if the impact energy is the same and the propagation distance is the same, the wave height values vary by about one order of magnitude. This variation is much larger than the variation in peak values (within ±10%) when impact sounds at the same point are detected by the same detector. From this fact, when energy E is calculated from the peak value based on equation (1), there will be a variation of about two orders of magnitude, and the energy estimation will include an extremely large error. There are several reasons why the wave height varies greatly even when the impact energy is constant and the propagation distance is the same, but the main cause in the case of the cylindrical tank 7 is considered to be the interference of sound waves. That is, some sound waves from the sound source travel clockwise around the tank and reach the detector, while others travel counterclockwise and reach the detector, and these sound waves cause interference with each other. A slight difference in phase between a clockwise sound wave and a counterclockwise sound wave causes a large change in the wave height value. Therefore, in order to avoid variations in the wave height value, the wave height must be measured with a detector located at a position that does not cause interference as much as possible. Figure 3 shows the impact when a constant energy is applied to the area surrounded by the circle in Figure 1.
It shows the relationship between the signal peak value detected by the detector 2 and the propagation distance. FIG. 4 shows the signal peak value of the detector 5, and FIG. 5 shows the signal peak value of the detector 7. If we consider these figures 3 to 5, we will find the following. In FIG. 3, based on the positional relationship between the sound source area and the detector 2 in FIG. Since the sound waves that reach the are considerably attenuated, there is almost no interference. Therefore, the variation in wave height is becoming smaller. Furthermore, since the difference between a small propagation distance and a large propagation distance is about twice, the smaller the propagation distance, the larger the wave height, and the data has a downward slope to the right. In the case of FIG. 4, the sound wave reaches the detector 5 while going around the tank side wall in the right direction in FIG. In this case as well, in order to go around the cylinder in the opposite direction and reach the detector 5, the signal must go around the cylinder almost once, so interference with the direct wave is considered to be small, and data variation is small. Furthermore, since the maximum and minimum propagation distances differ by only about 1.4 times, the dependence on distance does not appear significantly. It can be seen that the variations in peak values in the cases of FIGS. 3 and 4 are within ±15%. Fifth
In the case of the figure, the maximum and minimum data variations are approximately five times as large. As is clear from the positional relationship between the sound source region and the detector 7 in FIG. 1, FIG. It is considered that there is almost no difference in the propagation distance between the sound waves reaching the detector 7 and the clockwise and counterclockwise sound waves interfering with each other. For this reason, the peak values vary by about five times.
The following is understood from the above experimental facts. Firstly,
Even if the impact energy is the same and the propagation distance of the sound wave is the same, the detected wave height values vary by about one order of magnitude. Second, by limiting the impact sound source position within a certain area and limiting the detection position to a specific position, the variation in wave height values can be kept within ±15%. Based on the above knowledge, the error in impact energy measurement can be reduced by the following method.

(1) Place multiple acoustic detectors on the structure.

(2) Divide the structure into appropriate regions and apply a shock to each region with known energy. In this case, the impact is applied to several positions within the same area at intervals of approximately 1/2 the wavelength of the sound wave.

(3) Record the data of the peak value a _ij of the signal detected by each detector j when an impact is applied with kinetic energy E ₀ to each region i.

(4) Select a detector with the least variation in wave height data for multiple impact sounds in each region i.
In this case, if there are two or more detectors whose data variation is within an allowable range, those detectors are selected.

(5) When an unknown impact sound is detected, first locate the sound source and determine which region i the sound source belongs to.

(6) Once region i has been determined, find the wave height value A _j for the unknown sound of a predetermined detector j, which will be used to measure the impact energy in that region.

(7) Determine the impact energy E using the following formula.

E=E ₀・(A _j /a _ij ) ² ...(2) The impact energy E can be determined from the above, but as shown in the graph in Figure 3, even within the same area, the sound source and The peak value may change depending on the distance to the detector. In such a case, the attenuation constant J with respect to distance is determined in advance from the data, and the impact energy E is determined using the following equation.

E= _E0・( _Aj /( _aij ) ₀ ) ²・( _r0j / _Rj ) _2J ...(3) where, _Rj : Distance from unknown sound source to detector j _r0j : Identification of area i Distance from the position to detector j (a _ij ) ₀ : Peak value of detector j when an impact of known energy E is applied to a specific position in area i Now, to measure the impact energy applied to the structure is based on knowing the distance r _0j from the detector to the impact point or the area i to which the impact point belongs, that is, locating the impact sound source position.
There are various methods for locating impact sound sources, but methods that apply pattern recognition are effective for structures with complex shapes.

Hereinafter, an example in which the method of the present invention is applied to a pressure vessel impact energy measurement device will be described in detail.

A preferred embodiment is shown in FIGS. 6 and 7.

As shown in FIG. 6, J detectors S ₁ , S ₂ ...S _J are attached to the pressure vessel 1, and the signals detected by them are input to the pressure vessel impact energy measuring device 100. ing. This pressure vessel impact energy measuring device is constructed as shown in FIG. In FIG. 7, the detector S ₁ ,
Signals from _S2 ... _SJ are input to the signal waveform storage device 120 via amplifiers 111,...11J. The signal waveform storage device stores the number of times before and after the impact sound occurs.
The signal waveform of each detector for a period of about 10 ms can be stored. The stored waveform is used in the sound source position location and impact energy measurement calculator 13.
0 and extracts the information necessary for position location and energy estimation. The reference sound source data library storage device 140 stores each part of the pressure vessel in advance.
The signal arrival time difference and peak value of acoustic signals output from each detector when struck by a hammer or the like are recorded as standard pattern data in association with the striking position, that is, the known sound source position. Additionally, information on kinetic energy at the time of impact is also recorded. In other words, the pressure vessel is
The peak value a _ij of the output signal of the j-th detector S _j corresponding to the sound source position of the representative point i of each region, the signal arrival time difference τ _ij and the kinetic energy E ₁ at the time of impact are recorded. has been done. Furthermore, the detector number j ₀ used for energy measurement in the i region is also recorded.

Further, in the computer 130, when a signal from an unknown sound source is input to the signal waveform storage device 120, the peak value A _j of each detector j is calculated from the waveform of this unknown sound source.
and the signal arrival time difference τ _j . These unknown sound source information A _j , τ _j (j=1, 2,...J) and the reference pattern data a _ij , τ _ij (i=1, 2,...I, j) in the reference acoustic data library storage device 140 =1,
2,...J), first, the sound source position is determined to which region the sound source belongs using the following equation.

D ^T _i = {V ^a _jr (τ _ij −τ _j )} ^1/2 …(5) D ^c _i = (1−α)D ^A _i +αD ^T _i …(6) With these equations, V ^a _jr (X _j ) represents the variance of X _j . D ^A _i is the pattern distance between the wave height information A _j of the unknown sound source and the reference wave height information a _ij of the reference point i, and the smaller the value of D ^A _i is, the closer the reference sound source and unknown sound source are. D ^T _i is a pattern distance similarly defined for the signal arrival time difference. D ^C _i is a pattern distance obtained by combining D ^A _i and D ^T _i , and the constant α when calculating D ^C _i from equation (6) is determined to be an appropriate value between 0 and 1. As described above, the pattern distance D ^C _i is calculated for each i (i=1, 2, . . . I), and i with the minimum D ^C _i value is determined from among them. The unknown sound source belongs to the region i determined in this way. Once i is determined here, the reference wave height data a _ij0 corresponding to the i area and the kinetic energy data E ₁ when hitting the reference point i are read out from the reference data library, and the equation (2) is used. The energy E of the unknown sound source is determined using equation (7) based on the equation (7).

E=E _i・(A _j0 /a _ij ) ² ...(7) The area i to which the sound source belongs and the impact energy E calculated in this way are
By displaying it on the GRT150, it is possible to know which part of the pressure vessel the energy impact has occurred at.

The above methods are summarized in the form of a flowchart,
This can be shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the energy measurement of impact sound inside a pressure vessel, which had an error of one digit or more, can now be measured with an error of ±30%, dramatically reducing the error. There is an effect that can be done.

[Brief explanation of the drawing]

Figure 1 is a developed view of the side wall of a cylindrical tank used in experiments supporting the present invention, and Figures 2 to 5 show the acoustic signals detected when a certain amount of impact energy is applied to the tank side wall. A diagram showing the relationship between wave height value and acoustic propagation distance, FIGS. 6 and 7 are diagrams showing an embodiment of the present invention, and FIG. 8 is a flowchart explaining the operation of the embodiment of FIGS. 6 and 7. It's a chat. DESCRIPTION OF SYMBOLS 1... Pressure vessel, 100... Pressure vessel impact energy measuring device, 120... Signal waveform storage device, 130
...Calculator for sound source position location and impact energy measurement, 140...Storage device for reference sound source data library, 150...CRT with keyboard.

Claims (1)

[Claims] 1. A plurality of detectors for detecting sound are installed at appropriate locations on a structure, and the impact sound generated when an object collides with the structure is extracted in the form of an electrical signal, and the signal is In the method of measuring the kinetic energy of an object when the object collides by processing, the structure is divided into regions as appropriate, and each of the detections is performed when an object collides with each region with a known kinetic energy. A detector that records the peak value of the impact sound signal of the device along with the area number and detector number, and that exhibits the least variation in the peak value when multiple impacts are applied to each of the areas with constant energy. is determined in advance as the detector to be used to measure impact energy in that area, and when an impact sound with unknown energy is detected, the area where the impact sound is generated is first determined and used to measure the energy in that area. A method of measuring the kinetic energy of an impacting object based on the ratio of the signal peak value for an impact sound with known kinetic energy of the detector to the signal peak value for an impact sound with unknown energy.