Speed estimation device, evaluation system, and speed estimation method

Abstract

To provide a speed estimation device, an evaluation system, and a speed estimation method that can improve the accuracy of estimating elastic wave velocity.SOLUTION: A speed estimation device of an embodiment has a spectrum information extraction unit, a peak frequency extraction unit, a range determination unit, a specification unit, and an elastic wave velocity estimation unit. The spectrum information extraction unit extracts, for each of different measurement points, spectrum information of one or more elastic waves generated from impact on the measurement points in a target member. The peak frequency extraction unit extracts one or more peak frequencies in every spectrum information extracted for each of the measurement points. The range determination unit determines a frequency range of the elastic wave on the basis of the one or more peak frequencies obtained for each of the measurement points. The specification unit specifies the peak frequency at each measurement point on the basis of the spectrum information and the frequency range. The elastic wave velocity estimation unit estimates the elastic wave velocity at each measurement point on the basis of the peak frequency and thickness information of the target member.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] Embodiments of the present invention relate to a speed estimation device, an evaluation system, and a speed estimation method.

Background Art

[0002] In recent years, problems associated with the aging of industrial equipment and structures have become apparent. Since the damage caused by an accident in industrial equipment or structures is incalculable, technologies for monitoring the state of industrial equipment and structures have been developed conventionally. For example, a method for diagnosing soundness by combining an elastic wave source density distribution representing each source of a plurality of elastic waves generated from damage in terms of density distribution and a velocity distribution representing the velocity of each of the plurality of elastic waves in terms of distribution has been proposed.

[0003] Patent Document 1 discloses a method for quantitatively evaluating soundness using an elastic wave velocity distribution and an elastic wave source density distribution. Patent Document 2 discloses elastic wave tomography that generates elastic waves in a structure and performs elastic wave tomography analysis based on the arrival time difference that occurs when the elastic waves penetrate the material to obtain a velocity field distribution. Patent Document 3 discloses a method in which sounds emitted from a measurement object are received by a plurality of installed elastic wave waveform measurement sensors, and calculations are performed using a mathematical formula for estimating the transmission time and transmission position based on the received time and received position thus specified to obtain the estimated transmission time and estimated transmission position of the emitted sound, and then tomographic analysis is performed using the obtained values of the estimated transmission time and estimated transmission position. Non-Patent Document 1 uses a method for calculating the elastic wave velocity based on the spectral peak of the elastic waves that are multiply reflected between the application surface and the bottom surface when impact elastic waves are applied and the known plate thickness.

[0004] Tomographic methods that perform inverse analysis have problems such as high computational load, time-consuming to obtain results, and the need to change conditions and re-analyze when convergence does not occur in the case of non-uniform structures, resulting in high computational costs. In addition, there is a problem that the determination error of the arrival time leads to an error in the speed, making it difficult to accurately obtain the speed. On the other hand, the method using multiple reflections of impact elastic waves can obtain the speed by simple forward analysis for uniform materials, but there is a problem that it is difficult to identify the spectral peak corresponding to the known plate thickness for non-uniform materials. Especially in actual road slabs, when there are multiple locations where reflections occur, such as at the interface between internal steel bars and pavement, it is particularly difficult to identify the desired spectrum. Therefore, sufficient speed estimation accuracy may not be obtained in some cases.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem to be solved by the present invention is to provide a speed estimation device, an evaluation system, and a speed estimation method capable of improving the estimation accuracy of elastic wave speed.

Means for Solving the Problems

[0008] The velocity estimation device of the embodiment includes a spectrum information extraction unit, a peak frequency extraction unit, a range determination unit, an identification unit, and an elastic wave velocity estimation unit. The spectrum information extraction unit extracts, for each measurement point, the spectrum information of one or more elastic waves generated by impacts on different measurement points of the target member. The peak frequency extraction unit extracts one or more peak frequencies from each of the spectrum information extracted for each measurement point. The range determination unit determines the frequency range of the elastic wave based on the one or more peak frequencies obtained for each measurement point. The identification unit identifies the peak frequency at each measurement point based on the spectrum information extracted for each measurement point and the frequency range. The elastic wave velocity estimation unit estimates the elastic wave velocity at each measurement point based on the peak frequency identified for each measurement point by the identification unit and the thickness information of the target member.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 8

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0010] Hereinafter, a velocity estimation device, an evaluation system, and a velocity estimation method according to embodiments will be described with reference to the drawings.

[0011] (Principle of Elastic Wave Velocity Estimation Using Multiple Reflections) First, before explaining the content in the embodiment, the principle of elastic wave velocity estimation using multiple reflections will be explained. Conventionally, as a method for measuring the elastic wave velocity, a method of obtaining the velocity based on the arrival time difference of elastic waves detected by two sensors with known distances is generally used. However, this method has problems such as depending on the arrival time determination accuracy and the detected velocity being the surface wave velocity and not reflecting the characteristics inside the structure. Therefore, a velocity estimation method using multiple reflections of elastic waves as shown in the following Reference 1 has been proposed.

[0012] (Reference 1: Nicholas J. CARINO, “Impact Echo: The Fundamentals”, International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE), 15 - 17 Sep 2015, Berlin, Germany.)

[0013] In the method shown in Reference 1, an elastic wave is generated inside the structure by applying a sufficiently wideband and high-intensity impact to the structure. The elastic wave generated inside undergoes multiple reflections at the interfaces between the internal voids of the structure and the air. Let the velocity of the elastic wave propagating inside the structure (elastic wave velocity) be C p Then, in the vibration waveform detected by the sensor installed on the surface of the structure, the distance twice the plate thickness T of the structure is the elastic wave velocity Cp Peaks appear at the travel time Δt period propagated therein. Therefore, the frequency f of the observed vibration is expressed as in the following formula (1).

[0014]

Equation

[0015] That is, when the plate thickness T is known and the peak frequency of the elastic wave corresponding to the plate thickness mode in the vibration waveform observed by the sensor is f, the elastic wave velocity C p is expressed as in the following formula (2). Here, the plate thickness mode means being reflected on the surface opposite to the surface where the impact is applied. That is, the elastic wave corresponding to the plate thickness mode means the elastic wave reflected on the surface opposite to the surface where the impact is applied.

[0016]

Equation

[0017] The frequency f in Equation (2) can be obtained by performing a fast Fourier transform (FFT) on the vibration waveform observed by the sensor. Other methods such as the maximum entropy method (MEM) may be used to calculate the frequency f. However, as shown in FIG. 1, the frequency spectrum of the vibration waveform measured in an actual structure generally has multiple peaks. FIG. 1 is a diagram showing an example of the frequency spectrum of the vibration waveform. As shown in FIG. 1, when multiple peaks appear, it is unclear which peak frequency corresponds to the peak frequency of the plate thickness mode. Also, the peak amplitude corresponding to the plate thickness mode is not necessarily large. Further, when there are voids or damages in a shallow location, the portion sandwiched between the surface of the structure and the voids etc. may vibrate at a frequency lower than the frequency f obtained from the relationship of Equation (2), and the vibration mode at this time is called the bending mode. In the bending mode, since the low-frequency vibration appears more prominently, the lowest frequency peak is not necessarily the plate thickness mode. Thus, conventionally, when multiple peaks appear, the peak frequency corresponding to the plate thickness mode cannot be specified, and sufficient speed estimation accuracy cannot be obtained. Therefore, in the embodiments shown below, a method for specifying the peak frequency corresponding to the plate thickness mode and improving the accuracy of speed estimation will be described.

[0018] (Estimation method for plate thickness mode frequency range) A method for specifying the peak frequency corresponding to the plate thickness mode in the embodiment will be described. In an actual structure, the elastic wave velocity C p has dispersion due to the influence of the inhomogeneity of the structure, internal voids, damages, etc. Here, consider the case where there are voids (shown as void in FIG. 2) inside the structure as shown in FIG. 2. As shown in FIG. 2, the thickness of the structure is T. At measurement point A, there is a void at a depth d. At measurement point B, there is no void. At measurement point A, multiple reflections due to the void (frequency f void ) and multiple reflections with the opposite surface bypassing the void (frequency f T´) occurs. At this time, the propagation distance increases by an additional distance ΔT due to detouring. At measurement point B, only multiple reflections with the opposite surface (frequency f T ) occur. The peak frequency f T of multiple reflections with the opposite surface, the peak frequency f void of multiple reflections due to the gap, and the peak frequency f T´ of multiple reflections with the opposite surface detouring around the gap are expressed as in the following equations (3) to (5).

[0019]

Equation

[0020]

Equation

[0021]

Equation

[0022] Here, if we set the ratio of the increased distance due to detouring as ΔT / T = α (>0), the peak frequency f T´ of multiple reflections with the opposite surface detouring around the gap is expressed as in the following equation (6).

[0023]

Equation

[0024] In the plate thickness mode, it appears as if the speed has decreased from C p to C p / ((1 + α)). As a result, the frequency spectra at measurement points A and B are as shown in Fig. 3. Fig. 3 is a diagram showing an example of the frequency spectra at measurement points A and B. (A) in Fig. 3 represents the frequency spectrum at measurement point A, and (B) in Fig. 3 represents the frequency spectrum at measurement point B.

[0025] When the frequency spectrum at measurement point A shown in Fig. 3(A) and the frequency spectrum at measurement point B shown in Fig. 3(B) are superimposed, it becomes as shown in Fig. 4(A). Fig. 4(B) shows an image obtained by superimposing the frequency spectra observed at more measurement points.

[0026] As shown in Fig. 4, as a result, for the frequency spectrum of the plate thickness mode, the peak position of the frequency spectrum fluctuates due to the influence of internal voids and the like. For the multiple reflection spectrum caused by internal voids, since there is no detour, the speed change is small and the fluctuation of the peak position is also small. From this difference in distribution, it becomes possible to specify the frequency range of the plate thickness mode. First, in the speed estimation device according to the embodiment, a frequency spectrum is obtained based on the observed vibration waveform at one measurement point, and one or more peak frequencies are extracted from the obtained frequency spectrum. Further, the speed estimation device calculates a peak frequency frequency distribution based on the results of extracting peak frequencies in the same manner at a plurality of measurement points, and specifies a plate thickness mode frequency range representing the frequency range corresponding to the plate thickness mode. The following shows a specific procedure for specifying the plate thickness mode frequency range.

[0027] Here, for the sake of explanation, when the thickness is 0.4 m and there is an internal void at a position of 0.2 m, the results of performing a Monte Carlo simulation of 50 samples with the average speed of 4000 m / s and randomly changing the speed and the detour coefficient α are shown. The peak frequency frequency distribution in this case is as shown in Fig. 5. Fig. 5 is a diagram showing an example of the peak frequency frequency distribution obtained by a simulation simulating the speed reduction due to internal voids. It can be seen that the frequency spectrum due to internal voids is concentrated around approximately 10 kHz, and the frequency spectrum due to the plate thickness mode is distributed from 2500 to 6000 Hz. The frequency spectrum due to the plate thickness mode is affected by the speed change due to detour and has a more dispersed distribution than the frequency spectrum due to internal voids. Based on the above points, it is conceivable that the speed estimation device obtains the frequency distribution of the peak frequencies and, when a multi-peak distribution with a plurality of peaks is obtained, estimates that the set with a lower frequency is the plate thickness mode.

[0028] On the other hand, when there are voids in a shallower location (such as "lifting" of concrete), as shown in Fig. 6, there may be a case where a lower-frequency peak occurs (this is called the bending mode). In Fig. 6, the peak occurring at a position below 2500 Hz is the bending mode. In such a case, the lowest set may not be the plate thickness mode, and there is a possibility of incorrect estimation. Therefore, the velocity estimation device can determine that the plate thickness mode frequency range is 2500 - 6000 Hz by determining that the set with the largest variance among the sets of multiple distributions is the plate thickness mode. In this way, it becomes possible to accurately identify the frequency range of the plate thickness mode even when internal voids and bending vibrations coexist.

[0029] (Elastic wave velocity calculation at each measurement point) Here, a case of specifying the frequency of the plate thickness mode at each measurement point based on the frequency range of the plate thickness mode will be described. Here, the velocity estimation device is at a certain measurement point M i (where i is an identifier such that when the number of measurement points is N, i = 0, 1, …, (N - 1)), the peak frequency with the largest amplitude existing in the frequency range of the plate thickness mode obtained by the method described above (for example, 2500 - 6000 Hz) is taken as the frequency f i of the plate thickness mode at the measurement point M Ti and determined. Here, when there is no peak frequency within the determined frequency range of the plate thickness mode, the velocity estimation device may take the peak closest to the lower limit of the frequency range of the plate thickness mode as the plate thickness mode frequency f Ti . At this time, since the plate thickness T is known, from the relationship of the above formula (1), the elastic wave velocity C i at the measurement point M pi can be calculated.

[0030] As an example, Fig. 7 will be used to explain with reference to the frequency spectrum obtained at a certain measurement point shown in Fig. 1. Fig. 7 is a diagram for explaining the method of determining the peak frequency in the frequency range of the plate thickness mode. As shown in Fig. 7, the velocity estimation device, in the frequency spectrum obtained at a certain measurement point, takes the peak frequency f with the largest amplitude existing in the frequency range of the plate thickness mode (for example, 2500 - 6000 Hz)P is determined as the frequency f of the plate thickness mode at a certain measurement point. The velocity estimation device performs the same processing on the frequency spectrum obtained at each measurement point. Note that the frequency range of the plate thickness mode is the same at any measurement point. T

[0031] (Elastic wave velocity distribution) As described above, the elastic wave velocities in the plate thickness direction at a plurality of measurement points M can be calculated. Since the positions of the measurement points are known, it is possible to draw a two-dimensional map (elastic wave velocity distribution) using the elastic wave velocities in the plate thickness direction at each measurement point as representative values. At this time, by appropriately approximating between the measurement points, a spatially continuous velocity distribution can also be drawn.

[0032] The above is the processing flow of the velocity estimation method in the embodiment. Hereinafter, a specific configuration for realizing the above processing will be described.

[0033] FIG. 8 is a diagram showing the configuration of the structure evaluation system 100 in the embodiment. The structure evaluation system 100 is used for evaluating the soundness of the structure 50. In the following description, "evaluation" means determining the degree of soundness of the structure 50, that is, the deterioration state of the structure 50, based on a certain criterion.

[0034] In the following description, the case where the structure 50 is a bridge will be described as an example, but the structure 50 does not necessarily have to be limited to a bridge. The structure 50 may be any structure in which elastic waves are generated due to the occurrence or progress of cracks, or external impacts (such as rain, artificial rain, etc.). Note that a bridge is not limited to a structure erected over a river, valley, etc., but also includes various structures provided above the ground (such as an elevated expressway bridge). The structure may be a plate-like member.

[0035] As damage that affects the evaluation of the deterioration state of the structure 50, there is, for example, damage inside the structure that obstructs the propagation of elastic waves such as cracks, cavities, and soil liquefaction. Here, cracks include vertical cracks, horizontal cracks, and diagonal cracks. A vertical crack is a crack that occurs in a direction perpendicular to the road surface. A horizontal crack is a crack that occurs in a direction horizontal to the road surface. A diagonal crack is a crack that occurs in a direction other than horizontal and vertical with respect to the road surface. Soil liquefaction is deterioration in which concrete changes into a soil-like state mainly at the boundary between asphalt and the concrete slab.

[0036] The structure evaluation system 100 includes an impact application unit 10, a plurality of sensors 20-1 to 20-n (n is an integer of 2 or more), a signal processing unit 30, and a structure evaluation device 40. Each of the plurality of sensors 20-1 to 20-n and the signal processing unit 30 are communicably connected by wire. The signal processing unit 30 and the structure evaluation device 40 are communicably connected by wire or wirelessly. In the following description, when the sensors 20-1 to 20-n are not distinguished, they are described as sensors 20.

[0037] The impact application unit 10 is installed, for example, on the same surface as the surface on which the sensor 20 is installed, and applies an impact to the structure 50. The impact application unit 10 applies an impact to the structure 50, for example, by hitting the structure 50. Note that the method by which the impact application unit 10 applies an impact to the structure 50 is not limited to this method, and any other method may be used as long as it can apply an impact to the structure 50. The impact application unit 10 may be installed on a surface different from the surface on which the sensor 20 is installed. A surface different from the surface on which the sensor 20 is installed is, for example, the opposite surface to the surface on which the sensor 20 is installed, the side surface of the structure 50, or the like.

[0038] Since the impact application unit 10 applies impacts at a plurality of locations, it is desirable that it be movable by the user. Each of the plurality of locations where the impact application unit 10 applies an impact is the above-described measurement point. Since the plurality of locations where the impact application unit 10 applies an impact can be freely set, the positions of the measurement points are known.

[0039] The sensor 20 has a piezoelectric element and detects elastic waves reflected inside or on the end face of the structure 50. The sensor 20 is installed at a position where it can detect elastic waves on the surface of the structure 50. For example, the sensors 20-1 to 20-n are installed at different intervals, either the same or different, in the vehicle traveling axis direction and the direction perpendicular to the vehicle traveling axis on any one of the road surface, side surface, and bottom surface. The vehicle traveling axis direction represents the direction in which the vehicle travels on the road surface. The direction perpendicular to the vehicle traveling axis represents the direction perpendicular to the vehicle traveling axis direction. The sensor 20 converts the detected elastic waves into electrical signals. In the following description, the case where the sensor 20 is installed on the bottom surface of the structure 50 will be described as an example.

[0040] For the sensor 20, a piezoelectric element having sensitivity in the range of, for example, 10 kHz to 1 MHz is used. The sensor 20 has types such as a resonance type having a resonance peak within the frequency range and a broadband type with suppressed resonance, but any type of the sensor 20 may be used. The method by which the sensor 20 detects elastic waves includes a voltage output type, a resistance change type, a capacitance type, etc., but any detection method may be used.

[0041] An acceleration sensor may be used instead of the sensor 20. In this case, the acceleration sensor detects elastic waves generated inside the structure 50. Then, the acceleration sensor converts the detected elastic waves into electrical signals by performing the same processing as the sensor 20.

[0042] The signal processing unit 30 is an example of the above-described velocity estimation device. The signal processing unit 30 takes as input the electrical signal output from the sensor 20. The signal processing unit 30 performs signal processing on the input electrical signal. The signal processing performed by the signal processing unit 30 includes, for example, spectrum extraction, peak frequency extraction, determination of the frequency range in the plate thickness mode, identification of the peak frequency at each measurement point, estimation of the elastic wave velocity, etc. Note that the signal processing unit 30 may perform noise removal, extraction of feature quantities of elastic waves, etc. The signal processing unit 30 generates transmission data including the position information of each measurement point obtained by signal processing and the information on the elastic wave velocity at each measurement point. It is assumed that the position information of each measurement point has been input to the signal processing unit 30 before measurement starts at each measurement point. Therefore, the position information of each measurement point is known.

[0043] The signal processing unit 30 outputs the generated transmission data to the structure evaluation device 40. Note that each time the signal processing unit 30 estimates the elastic wave velocity at one measurement point, it may transmit the transmission data including the information on the elastic wave velocity at the estimated measurement point to the structure evaluation device 40, or when the elastic wave velocities at a predetermined number of measurement points are estimated, it may transmit the transmission data including the information on the plurality of elastic wave velocities at the estimated predetermined number of measurement points to the structure evaluation device 40.

[0044] The signal processing unit 30 is configured using a digital circuit. The digital circuit is realized, for example, by an FPGA (Field Programmable Gate Array) or a microcomputer. The digital circuit may also be realized by a dedicated LSI (Large-Scale Integration). Further, the signal processing unit 30 may be equipped with a non-volatile memory such as a flash memory or a removable memory. In the following description, the case where the signal processing unit 30 is configured using a digital circuit will be described.

[0045] The structure evaluation device 40 evaluates the deterioration state of the structure 50 based on the information on the elastic wave velocity at each of a plurality of measurement points included in the transmission data transmitted from the signal processing unit 30. For example, the structure evaluation device 40 generates an elastic wave propagation velocity distribution based on the information on the elastic wave velocity at each of the plurality of measurement points, and evaluates the deterioration state of the structure 50 based on the generated elastic wave propagation velocity distribution. The elastic wave propagation velocity distribution represents a distribution showing the propagation velocity of the elastic waves generated in the structure 50. For example, the elastic wave propagation velocity distribution may be represented by a contour diagram. The structure evaluation device 40 is configured using an information processing device such as a personal computer.

[0046] FIG. 9 is a diagram showing a configuration example of the signal processing unit 30 in the embodiment. The signal processing unit 30 includes a waveform acquisition unit 31, a spectrum information extraction unit 32, a peak frequency extraction unit 33, a frequency range determination unit 34, a specification unit 35, an elastic wave velocity estimation unit 36, and an output unit 37.

[0047] The waveform acquisition unit 31 is configured using an amplifier, an analog filter, and an analog-to-digital converter. The amplifier amplifies the electrical signal (analog signal) output from the sensor 20 to such an extent that it can be processed by the analog-to-digital converter. The amplifier outputs the amplified electrical signal to the analog filter. The analog filter removes noise components outside a predetermined frequency band. The analog filter is, for example, a band-pass filter (BPF: Band Pass Filter). It is desirable to use a filter with a sufficiently wide passband width so as not to distort the shape of the elastic wave (AE signal) for the band-pass filter used here. The electrical signal from which noise has been removed by the analog filter is input to the analog-to-digital converter. The analog-to-digital converter quantizes the electrical signal from which noise has been removed and converts it into a digital signal. The analog-to-digital converter outputs waveform data, which is a digital signal, to the spectrum information extraction unit 32.

[0048] The spectrum information extraction unit 32 converts the waveform data output from the waveform acquisition unit 31 into data in the frequency domain by performing FFT on the waveform data. Thereby, the information on the frequency spectrum included in the waveform data can be extracted. In this way, the spectrum information extraction unit 32 extracts the spectrum information of one or more elastic waves generated by impacts on different measurement points in the structure 50 for each measurement point. Hereinafter, the information on the frequency spectrum extracted by the spectrum information extraction unit 32 is referred to as frequency spectrum information.

[0049] The peak frequency extraction unit 33 extracts a plurality of frequencies (peak frequencies) having relatively prominent peaks from the frequency spectrum information extracted by the spectrum information extraction unit 32. There are various algorithms for extracting the peak frequency, but it is not particularly limited. For example, as a simple method, an algorithm of searching for a point where the difference in intensity at adjacent frequencies in the frequency spectrum information becomes 0 can be applied. The peak frequency extraction unit 33 performs this process on the waveform data based on the elastic waves obtained at a plurality of measurement points. Thereby, the peak frequency extraction unit 33 can extract a plurality of peak frequencies in each of the spectrum information extracted for each measurement point. The peak frequency extraction unit 33 creates a peak frequency list integrating all the peak frequencies. The peak frequency list is a list in which information on the frequency (number of times) extracted as the peak frequency is registered in association with the frequency.

[0050] The frequency range determination unit 34 calculates the frequency distribution of the peak frequencies based on the peak frequency list created by the peak frequency extraction unit 33. The frequency range determination unit 34 identifies the plate thickness mode frequency range corresponding to the plate thickness mode based on the calculated frequency distribution of the peak frequencies. The frequency range determination unit 34 may, for example, use the frequency range where the set with lower frequencies is located as the plate thickness mode frequency range, or use the frequency range where the set with the largest dispersion is located as the plate thickness mode frequency range. Note that the frequency range for one set may be set in advance, or may be up to the point where the count of the peak frequency adjacent to the peak frequency included in one set is less than the threshold value. The frequency range determination unit 34 is one aspect of the range determination unit.

[0051] The identification unit 35 identifies the plate thickness mode frequency at each measurement point based on the frequency spectrum information at each measurement point extracted by the spectrum information extraction unit 32 and the plate thickness mode frequency range determined by the frequency range determination unit 34. Specifically, the identification unit 35, in the frequency spectrum information based on the elastic wave obtained at a certain measurement point M i determines the peak with the largest amplitude existing in the plate thickness mode frequency range determined by the frequency range determination unit 34 as the plate thickness mode frequency f Ti . Note that when there is no peak frequency in the plate thickness mode frequency range, the identification unit 35 may determine the peak closest to the lower limit of the plate thickness mode frequency range as the plate thickness mode frequency f Ti . The identification unit 35 determines the plate thickness mode frequency f T at all measurement points M.

[0052] The elastic wave velocity estimation unit 36 estimates the elastic wave velocity C i at the measurement point M Ti identified by the identification unit 35 using the plate thickness mode frequency f i at the measurement point M and the known plate thickness T based on the above formula (1). The elastic wave velocity estimation unit 36 estimates the elastic wave velocity C pi at all measurement points by executing this process at all measurement points. p

[0053] The output unit 37 generates transmission data including the elastic wave velocity C at a plurality of measurement points estimated by the elastic wave velocity estimation unit 36. The output unit 37 transmits the generated transmission data to the structure evaluation device 40 by wire or wirelessly. p Returning to FIG. 8, the description will be continued. The structure evaluation device 40 includes a communication unit 41, a control unit 42, a storage unit 43, and a display unit 44.

[0054]

[0055] The communication unit 41 receives one or more pieces of transmission data transmitted from the signal processing unit 30.

[0056] The control unit 42 controls the entire structure evaluation device 40. The control unit 42 is configured using a processor such as a CPU (Central Processing Unit) and a memory. By executing a program, the control unit 42 functions as an acquisition unit 421, a distribution generation unit 422, and an evaluation unit 423.

[0057] Some or all of the functional units of the acquisition unit 421, the distribution generation unit 422, and the evaluation unit 423 may be realized by hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA, or may be realized by cooperation between software and hardware. The program may be recorded on a computer-readable recording medium. A computer-readable recording medium is a non-temporary storage medium such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a portable medium such as a CD-ROM, or a storage device such as a hard disk built into a computer system. The program may be transmitted via an electric communication line.

[0058] ​Some of the functions of the acquisition unit 421, the distribution generation unit 422, and the evaluation unit 423 do not necessarily need to be pre-installed in the structure evaluation device 40, and may be realized by installing an additional application program in the structure evaluation device 40.

[0059] The acquisition unit 421 acquires various information. The acquisition unit 421 acquires, for example, one or more pieces of transmission data received by the communication unit 41. The acquisition unit 421 stores the acquired one or more pieces of transmission data in the storage unit 43.

[0060] The distribution generation unit 422 generates an elastic wave propagation velocity distribution based on the one or more pieces of transmission data stored in the storage unit 43. Specifically, the distribution generation unit 422 generates an elastic wave propagation velocity distribution by recording the elastic wave velocity at a known measurement point as the elastic wave velocity at the measurement point coordinates. When the two-dimensional coordinates at a certain measurement point are (x, y), the elastic wave velocity at the position (x, y) can be recorded as z and represented as matrix data of (x, y, z). The distribution generation unit 422 may output the matrix data as a numerical value, or may also represent it as a figure such as a contour line or a heat map. When displaying as a figure, estimated values at coordinates other than the measurement points can be obtained by complementing the velocities at coordinates other than the measurement points using various complementation techniques such as linear complementation, polynomial complementation, and spline complementation, which is useful.

[0061] The evaluation unit 423 evaluates the deterioration state of the structure 50 based on the elastic wave propagation velocity distribution generated by the distribution generation unit 422. For example, the evaluation unit 423 evaluates a region where the elastic wave velocity is less than a predetermined threshold value in the elastic wave propagation velocity distribution as a deteriorated region. The evaluation unit 423 evaluates a region where the elastic wave velocity is equal to or greater than a predetermined threshold value in the elastic wave propagation velocity distribution as a sound region. The sound region represents a region where no damage has occurred inside the structure 50, or a region where, even if damage has occurred, the damage is relatively small.

[0062] The evaluation unit 423 may evaluate the structure 50 as follows. For example, the evaluation unit 423 divides the elastic wave propagation velocity distribution into two regions: a region with a high propagation velocity and a region with a low propagation velocity based on a reference value regarding the propagation velocity of elastic waves (hereinafter referred to as the "propagation velocity reference value"). Specifically, the evaluation unit 423 divides the regions by binarizing the elastic wave propagation velocity distribution based on the propagation velocity reference value. In this embodiment, as an example, the propagation velocity reference value is set to 3800 m / s. The evaluation unit 423 binarizes the regions in the elastic wave propagation velocity distribution, considering the region with a propagation velocity equal to or higher than the propagation velocity reference value (3800 m / s) as the region with a high propagation velocity and the region with a propagation velocity lower than the propagation velocity reference value (3800 m / s) as the region with a low propagation velocity. Note that the propagation velocity reference value does not necessarily have to be limited to the above value and may be changed as appropriate. Then, the evaluation unit 423 may evaluate the region with a high propagation velocity as a sound region and the region with a low propagation velocity as a region where deterioration has occurred.

[0063] The storage unit 43 stores one or more pieces of transmission data acquired by the acquisition unit 421. The storage unit 43 is configured using a storage device such as a magnetic hard disk drive or a semiconductor storage device. Note that the evaluation results obtained by the evaluation unit 423 may also be stored in the storage unit 43.

[0064] The display unit 44 displays the evaluation results according to the control of the evaluation unit 423. For example, the display unit 44 may display, as the evaluation result, whether deterioration has occurred inside the structure 50, or may display the region where deterioration has occurred on the elastic wave propagation velocity distribution. The display unit 44 is an image display device such as a liquid crystal display or an organic EL (Electro Luminescence) display. The display unit 44 may also be an interface for connecting the image display device to the structure evaluation device 40. In this case, the display unit 44 generates a video signal for displaying the evaluation results and outputs the video signal to the image display device connected to itself.

[0065] FIG. 10 is a flowchart showing the flow of the speed estimation process performed by the signal processing unit 30 in the embodiment. The process of FIG. 10 is executed when an impact is applied at a certain measurement point and elastic waves are detected by the sensor 20.

[0066] The waveform acquisition unit 31 acquires an electrical signal based on the elastic wave generated by the impact applied at a certain measurement point from the output of the sensor 20. The waveform acquisition unit 31 acquires waveform data at a certain measurement point by performing signal amplification, filtering, and analog-to-digital conversion on the acquired electrical signal (step S101). The waveform acquisition unit 31 outputs the acquired waveform data to the spectrum information extraction unit 32.

[0067] The spectrum information extraction unit 32 extracts frequency spectrum information by performing an FFT on the waveform data at a certain measurement point output from the waveform acquisition unit 31 (step S102). Thereby, the spectrum information extraction unit 32 extracts frequency spectrum information as shown in, for example, FIG. 1. The spectrum information extraction unit 32 outputs the extracted frequency spectrum information at a certain measurement point to the peak frequency extraction unit 33 and the specifying unit 35. The peak frequency extraction unit 33 extracts one or more peak frequencies based on the frequency spectrum information output from the spectrum information extraction unit 32 (step S103). The peak frequency extraction unit 33 registers the information of the one or more extracted peak frequencies in the peak frequency list. For example, when the extracted peak frequencies are f t1 and f t2 , the peak frequency extraction unit 33 adds 1 to the frequency values associated with the frequencies f t1 and f t2 in the peak frequency list.

[0068] The signal processing unit 30 determines whether the velocity estimation condition is satisfied (step S104). The velocity estimation condition is a condition for starting the estimation of the propagation velocity of elastic waves. For example, it may be that frequency spectrum information for a predetermined number of measurement points (at least two or more measurement points) has been obtained. When the signal processing unit 30 determines that the velocity estimation condition is not satisfied (step S104 - NO), the signal processing unit 30 repeatedly executes the processing after step S101. In this case, the user moves the impact applying unit 10 to other measurement points and applies an impact at the other measurement points. Thereby, elastic waves are generated at the other measurement points. By repeatedly executing the processing from step S101 to step S103, frequency spectrum information at a plurality of measurement points is obtained.

[0069] When the signal processing unit 30 determines that the velocity estimation condition is satisfied (step S104 - YES), the frequency range determination unit 34 calculates a peak frequency frequency distribution with reference to the peak frequency list (step S105). The frequency range determination unit 34 specifies a plate thickness mode frequency range corresponding to the plate thickness mode based on the calculated peak frequency frequency distribution (step S106). The frequency range determination unit 34 outputs information indicating the specified plate thickness mode frequency range to the specifying unit 35. The specifying unit 35 specifies the plate thickness mode frequency at each measurement point based on the spectrum information of each measurement point output from the spectrum information extraction unit 32 and the information indicating the plate thickness mode frequency range output from the frequency range determination unit 34 (step S107).

[0070] Specifically, the specifying unit 35 determines the peak frequency with the largest amplitude within the plate thickness mode frequency range in each of the spectrum information of each measurement point output from the spectrum information extraction unit 32. Thereby, the specifying unit 35 determines the peak frequency with the largest amplitude within the plate thickness mode frequency range for each measurement point. The specifying unit 35 specifies the peak frequency determined for each measurement point as the plate thickness mode frequency at each measurement point. The specifying unit 35 outputs information indicating the plate thickness mode frequency at each specified measurement point to the elastic wave velocity estimation unit 36.

[0071] The elastic wave velocity estimation unit 36 uses the information indicating the plate thickness mode frequency at each measurement point output from the specifying unit 35 and the known plate thickness T to estimate the elastic wave velocity C at each measurement point based on the above formula (1). p (Step S108). The elastic wave velocity estimation unit 36 outputs information indicating the estimated elastic wave velocity C at each measurement point to the output unit 37 in association with the information indicating the position of each measurement point. The output unit 37 generates transmission data including the information output from the elastic wave velocity estimation unit 36 and outputs it to the structure evaluation device 40. p

[0072] According to the structure evaluation system 100 configured as described above, the signal processing unit 30 includes a spectrum information extraction unit 32 that extracts spectrum information of one or more elastic waves generated by impacts on different measurement points in the structure 50 for each measurement point, a peak frequency extraction unit 33 that extracts one or more peak frequencies in each of the spectrum information extracted for each measurement point, a frequency range determination unit 34 that determines the frequency range (plate thickness mode frequency range) of the elastic wave reflected from the surface opposite to the surface where the impact was applied based on the one or more peak frequencies obtained for each measurement point, a specifying unit 35 that specifies the peak frequency at each measurement point based on the spectrum information extracted for each measurement point and the frequency range, and an elastic wave velocity estimation unit 36 that estimates the elastic wave velocity at each measurement point based on the peak frequency specified for each measurement point by the specifying unit 35 and the thickness information of the target member.

[0073] As described above, by determining the frequency range of the plate thickness mode based on the one or more peak frequencies obtained for each measurement point, it is possible to exclude the frequencies of the elastic waves reflected by internal damages of the structure 50 such as voids. Thereby, it is possible to specify the peak frequency of the elastic wave corresponding to the known plate thickness. Therefore, it is possible to accurately estimate the propagation velocity based on the specified peak frequency of the elastic wave corresponding to the known plate thickness. Therefore, it is possible to improve the estimation accuracy of the elastic wave velocity.

[0074] Furthermore, the frequency range determination unit 34 calculates a peak frequency frequency distribution representing the frequency of peak frequencies by summing up one or more peak frequencies obtained for each measurement point, and determines the frequency range of the plate thickness mode based on the calculated peak frequency frequency distribution. Thereby, the frequency range of the plate thickness mode can be determined based on the peak frequency frequency.

[0075] Furthermore, the frequency range determination unit 34 determines, in the peak frequency frequency distribution, the set with the largest dispersion as the frequency range of the plate thickness mode. As described above, the frequency spectrum of the elastic wave in the plate thickness mode has detours due to the influence of internal voids or the like, so the peak position of the frequency spectrum fluctuates. On the other hand, the frequency spectrum of the elastic wave reflected by the internal voids has little velocity change and little fluctuation in the peak position because there are no detours. Taking this point into account, it becomes possible to easily identify the frequency range of the plate thickness mode by determining the set with the largest dispersion as the frequency range of the plate thickness mode. In particular, such a determination method can easily determine the frequency range of the plate thickness mode even when a peak at a lower frequency called the bending mode occurs.

[0076] Furthermore, the frequency range determination unit 34 determines, in the peak frequency frequency distribution, the set with the lowest frequency as the frequency range of the plate thickness mode. As described above, the frequency spectrum due to internal voids often appears at a higher position than the frequency spectrum due to the plate thickness mode. Therefore, it becomes possible to easily identify the frequency range of the plate thickness mode by determining the set with a lower frequency as the frequency range of the plate thickness mode.

[0077] (Modification 1) In each of the above embodiments, a configuration is shown in which a plurality of sensors 20-1 to 20-n are connected to one signal processing unit 30. The structure evaluation system 100 may include a plurality of signal processing units 30, and each sensor 20 may be connected to a different signal processing unit 30. In this case, each of the plurality of signal processing units 30 estimates the elastic wave velocity based on the elastic wave detected by the sensor 20 to which it is connected.

[0078] (Modification Example 2) Some or all of the functional units included in the structure evaluation device 40 may be included in other devices. For example, the display unit 44 included in the structure evaluation device 40 may be included in other devices. When configured in this way, the structure evaluation device 40 transmits the evaluation result to another device including the display unit 44. The other device including the display unit 44 displays the received evaluation result.

[0079] (Modification Example 3) The signal processing unit 30 may include a conversion unit that converts the frequency axis in the frequency spectrum obtained at each measurement point into information in the depth direction (the thickness direction of the structure) based on the estimated result of the elastic wave velocity. When configured in this way, the conversion unit uses the elastic wave velocity C i at the measurement point M pi to convert the frequency axis f in the spectrum of the measurement point M pi into the thickness direction distance d based on the relationship of f = C i / 2d, thereby converting the frequency axis in the frequency spectrum obtained at each measurement point into information in the depth direction (the thickness direction of the structure). The result of converting the frequency axis in the frequency spectrum obtained at a certain measurement point into information in the depth direction (the thickness direction of the structure) is shown in FIG. 11. (A) in FIG. 11 represents the frequency spectrum obtained at a certain measurement point, and (B) in FIG. 11 represents the result of converting the frequency axis into information in the depth direction (the thickness direction of the structure).

[0080] The conversion unit converts the elastic wave velocity C p obtained at all measurement points into information in the depth direction (the thickness direction of the structure). The output unit 37 generates transmission data including information in the depth direction at a plurality of measurement points converted by the conversion unit. The output unit 37 transmits the generated transmission data to the structure evaluation device 40 by wire or wirelessly.

[0081] The distribution generation unit 422 of the structure evaluation device 40 generates a depth-direction reflection intensity distribution in which the information on the reflection intensity in the depth direction is shown by recording the information in the depth direction at known measurement points as the depth direction at the measurement point coordinates. Thereby, the distribution generation unit 422 can obtain the reflection distribution in the thickness direction for each measurement point. The evaluation unit 423 evaluates the deterioration state of the structure 50 based on the depth-direction reflection intensity distribution generated by the distribution generation unit 422. For example, the evaluation unit 423 can estimate the depth at which internal voids occur. Further, for example, when internal voids occur, the evaluation unit 423 can also evaluate that deterioration has occurred.

[0082] Note that the evaluation unit 423 can also estimate the depth at which internal voids occur based on the frequency axis shown in Fig. 11(B) based on the information in the depth direction (the thickness direction of the structure). In the example shown in Fig. 11(B), it can be estimated that internal voids occur at a depth of 0.2 m.

[0083] (Modification Example 4) The structure evaluation device 40 may evaluate the deterioration state of the structure 50 by combining the elastic wave propagation velocity distribution obtained by the method described above and the elastic wave source density distribution. The elastic wave source density distribution represents a distribution in which the value of the density obtained according to the number of elastic wave sources included in each region is shown for each predetermined region in the distribution in which the generation sources of the elastic waves generated in the structure 50 are shown. Existing methods are used to derive the elastic wave source density distribution. For example, the method for deriving the AE source density distribution described in Patent Document 1 may be used.

[0084] Furthermore, the evaluation unit 423 evaluates the deterioration state of the structure 50 by combining the elastic wave propagation velocity distribution and the elastic wave source density distribution according to the method described in Patent Document 1. Specifically, the evaluation unit 423 divides the elastic wave propagation velocity distribution into two regions, a region with a high propagation velocity and a region with a low propagation velocity, based on the propagation velocity reference value, and divides the elastic wave source density distribution into two regions, a region with a sparse source and a region with a dense source, based on a reference value regarding the density of the source (hereinafter referred to as the "density reference value"). Then, the evaluation unit 423 overlaps the elastic wave propagation velocity distribution (binary elastic wave propagation velocity distribution) divided into two regions and the elastic wave source density distribution (binary elastic wave source density distribution) divided into two regions, and evaluates the soundness of the structure in at least four levels according to the classification result of the overlapped regions. Here, specific examples of the four-level evaluation include soundness I, soundness II, soundness III, and soundness IV.

[0085] In the order of soundness I, soundness II, soundness III, and soundness IV, it indicates that the deterioration of the structure is progressing. That is, soundness I indicates that the deterioration of the structure has progressed the least, and as it approaches soundness IV, it indicates that the deterioration of the structure is progressing. The evaluation unit 423 evaluates which of soundness I, soundness II, soundness III, and soundness IV each region (each overlapped region) of the structure corresponds to based on the evaluation conditions described in Patent Document 1 below. Soundness I corresponds to soundness as described in Patent Document 1, soundness II corresponds to intermediate deterioration I as described in Patent Document 1, soundness III corresponds to intermediate deterioration II as described in Patent Document 1, and soundness IV corresponds to limit deterioration as described in Patent Document 1. It has been found that this evaluation method can be a correct evaluation index compared to simply combining the two conventional evaluation methods. In the embodiment, it is possible to use elastic wave measurement and sensors, and by having a function of switching any one or a plurality of the filter frequency characteristics, measurement sample length, and preamplifier gain of the measurement device, the elastic wave propagation velocity distribution and the elastic wave source density distribution can be simultaneously acquired in one measurement. Therefore, it is suitable for use in the structure evaluation system 100 that evaluates the high and low of such elastic wave propagation velocity and the sparseness and density of the elastic wave source density as two-dimensional evaluation axes respectively.

[0086] According to at least one embodiment described above, the signal processing unit 30 includes a spectrum information extraction unit 32 that extracts spectrum information of one or more elastic waves generated by impacts on different measurement points in the structure 50 for each measurement point, a peak frequency extraction unit 33 that extracts one or more peak frequencies in each of the spectrum information extracted for each measurement point, a frequency range determination unit 34 that determines the frequency range of the elastic waves reflected from the surface opposite to the surface where the impact was applied based on the one or more peak frequencies obtained for each measurement point, an identification unit 35 that identifies the peak frequency at each measurement point based on the spectrum information extracted for each measurement point and the frequency range, and an elastic wave velocity estimation unit 36 that estimates the elastic wave velocity at each measurement point based on the peak frequency identified for each measurement point by the identification unit 35 and the thickness information of the target member. Thereby, the estimation accuracy of the elastic wave velocity can be improved.

[0087] Some of the processes performed by the signal processing unit 30 in the above-described embodiments may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Note that the "computer system" referred to here includes hardware such as an OS and peripheral devices. Further, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or the like, and a storage device such as a hard disk incorporated in a computer system. Furthermore, the "computer-readable recording medium" also includes, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, a medium that dynamically holds a program for a short period of time, and also includes a volatile memory inside a computer system that serves as a server or a client in that case and holds a program for a certain period of time. Also, the above program may be for realizing a part of the above-described functions, and may further be realized in combination with a program already recorded in a computer system for realizing the above-described functions, or may be realized using a programmable logic device such as an FPGA.

[0088] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0089] 10... Impact application unit, 20, 20-1 to 20-n... Sensors, 30... Signal processing unit, 31... Waveform acquisition unit, 32... Spectrum information extraction unit, 33... Peak frequency extraction unit, 34... Frequency range determination unit, 35... Identification unit, 36... Elastic wave velocity estimation unit, 37... Output unit, 40... Structure evaluation device, 41... Communication unit, 42... Control unit, 43... Memory unit, 44... Display unit, 100... Structure evaluation system

Claims

1. A spectrum information extraction unit that extracts spectrum information of one or more elastic waves generated by impacts on different measurement points on a target member for each measurement point; A peak frequency extraction unit that extracts one or more peak frequencies from each of the spectrum information extracted for each measurement point; A range determination unit that determines the frequency range of the elastic wave based on the one or more peak frequencies obtained for each measurement point; A specification unit that specifies the peak frequency at each measurement point based on the spectrum information extracted for each measurement point and the frequency range; An elastic wave velocity estimation unit that estimates the elastic wave velocity at each measurement point based on the peak frequency specified for each measurement point by the specification unit and the thickness information of the target member; A velocity estimation device comprising the above.

2. The range determination unit calculates a peak frequency frequency distribution representing the frequency of peak frequencies by summing the one or more peak frequencies obtained for each measurement point, and determines the frequency range of the elastic wave based on the calculated peak frequency frequency distribution. The velocity estimation device according to Claim 1.

3. The range determination unit determines, in the peak frequency frequency distribution, the set with the largest dispersion as the frequency range of the elastic wave. The velocity estimation device according to Claim 2.

4. The range determination unit determines, in the peak frequency frequency distribution, the set with the lowest frequency as the frequency range of the elastic wave. The velocity estimation device according to Claim 2.

5. An impact application unit that applies impacts to different measurement points on a target member; One or more sensors that are installed on the target member and detect elastic waves generated by the impacts applied by the impact application unit; The velocity estimation device according to any one of Claims 1 to 4 that estimates the elastic wave velocity propagating within the target member based on the elastic waves detected by the one or more sensors; An evaluation device that evaluates the deterioration state of the target member based on the elastic wave velocity; An evaluation system comprising the above.

6. The velocity estimation device further comprises a conversion unit that converts the spectrum information of the one or more elastic waves into information in the thickness direction of the target member based on the estimated elastic wave velocity at each measurement point; The evaluation device evaluates the deterioration state of the target member based on the information in the thickness direction of the target member converted by the conversion unit. The evaluation system according to Claim 5.

7. Extract the spectral information of one or more elastic waves generated by impacts on different measurement points on the target member for each measurement point, Extract one or more peak frequencies in each of the spectral information extracted for each measurement point, Determine the frequency range of the elastic wave based on the one or more peak frequencies obtained for each measurement point, Specify the peak frequency at each measurement point based on the spectral information extracted for each measurement point and the frequency range, A velocity estimation method for estimating the elastic wave velocity at each measurement point based on the peak frequency specified for each measurement point and the thickness information of the target member.

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