JP7232520B2 - Stress estimation device, stress estimation method, and program - Google Patents

Description

The present invention relates to a stress estimating device, a stress estimating method, and a program for estimating stress generated in a tubular body.

Techniques for detecting the status of pipes such as water supply and gas pipelines are known. For example, Patent Literature 1 discloses a technique of detecting a signal (AE signal) from an AE (Acoustic Emission) sensor attached to a pipe body and detecting corrosion of an underground pipe based on the detected AE signal. ing.

JP 2005-351884 A

As described above, the technique of detecting the status of piping using an AE sensor is useful because it can non-destructively inspect the target pipe. Due to the constraints involved, it would be nice to have other non-destructive techniques.

The present invention has been made in view of the above circumstances, and aims to provide a stress estimating device, a stress estimating method, and a program capable of estimating stress generated in a tubular body by nondestructive inspection. do.

In order to achieve the above object, the stress estimation device according to the first aspect of the present invention includes:
During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. an image information acquiring means for acquiring image information indicating an image to be captured;
The image information acquired by the image information acquisition means is analyzed by an image correlation method to obtain time series information of the three-dimensional displacement of the tubular body, and based on the obtained time series information of the displacement Strain amount calculation means for calculating time-series information of the strain amount in a predetermined direction of the tubular body;
From the time-series information of the strain amount calculated by the strain amount calculation means, extracting a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount, the tubular body and a stress estimating means for calculating the estimated stress generated in the predetermined direction.

The strain amount calculation means calculates time-series information of the strain amount at a plurality of preset extraction points for the image obtained by capturing the outer peripheral surface,
The stress estimation means may calculate the estimated stress at the plurality of extraction points.

The specific amount of strain may be a maximum value of the amount of strain in the predetermined direction.

The stress estimating device further comprises pressure acquiring means for acquiring time-series information of the pressure applied to the tubular body by the fluid,
The stress estimating means, in addition to the first estimated stress as the estimated stress, based on the difference between the pressure at the time of indicating the specific strain amount and a predetermined reference pressure, the predetermined direction generated in the tubular body A second estimated stress at may be calculated.

The predetermined direction may include a direction orthogonal to the extending direction of the tubular body.

The fluid may be a liquid and the pressure waves may be caused by water hammer.

In order to achieve the above object, the stress estimation method according to the second aspect of the present invention includes:
During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. obtaining image information indicative of an image to be displayed;
Time-series information of three-dimensional displacement of the tubular body is obtained by analyzing the acquired image information by an image correlation method, and based on the time-series information of the displacement obtained, in a predetermined direction of the tubular body A step of calculating time-series information of the amount of strain;
From the time-series information of the calculated strain amount, extract a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount In the predetermined direction generated in the tubular body and calculating an estimated stress.

In order to achieve the above object, a program according to the third aspect of the present invention,
the computer,
During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. image information acquisition means for acquiring image information indicating an image to be displayed;
The image information acquired by the image information acquisition means is analyzed by an image correlation method to obtain time series information of the three-dimensional displacement of the tubular body, and based on the obtained time series information of the displacement strain amount calculation means for calculating time-series information of strain amount in a predetermined direction of the tubular body;
From the time-series information of the strain amount calculated by the strain amount calculation means, extracting a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount, the tubular body It functions as stress estimating means for calculating the estimated stress generated in the predetermined direction.

ADVANTAGE OF THE INVENTION According to this invention, the stress which generate|occur|produced in the tubular body can be estimated by the non-destructive test|inspection.

1 is a schematic configuration diagram of a stress estimation system according to one embodiment of the present invention; FIG. 6 is a flowchart showing an example of stress estimation processing; (a) is a diagram showing time-series data of strain in the direction perpendicular to the axis obtained by the image correlation method, and (b) is the data in the direction perpendicular to the axis after performing noise filtering on the data in (a) of FIG. is a diagram showing time-series data of the strain of . It is a reference diagram showing the relationship between the effective value voltage as an AE parameter obtained by experiment and the water pressure vibration. FIG. 10 is a diagram of a table showing each condition of Cases 1 to 9 as setting conditions of a tubular body at the time of experiment. (a) is a diagram showing time-series data of water pressure in Case 3, and (b) is a diagram showing time-series data of water pressure when continuous water hammer action is generated in Case 6. (a) is a diagram in which the x and y axes are defined with respect to the image analysis screen, and (b) is a developed view when the tubular body is cut open along the x axis. It is a figure for demonstrating the extraction point of the data in experiment. (a) is a diagram showing the relationship between the stress intensity factor and the stress distribution near the crack, and (b) is a conceptual diagram showing the force balance between the internal pressure of the tubular body and the stress generated in the tubular body. 3(a) to 3(c) are graphs showing changes over time in applied stress and strain in the direction perpendicular to the axis determined by experiments in Cases 1 to 3. FIG. (a) to (c) are diagrams showing changes over time in applied stress and strain in the direction perpendicular to the axis determined by experiments in Cases 4 to 6. FIG. In Cases 1 to 6, it is a diagram of a table showing the stress distribution estimated at the maximum strain observation time in the direction perpendicular to the axis. (a) is a graph showing the stress field near the slit in Case 3, and (b) is a graph showing the stress field near the slit in Case 5. FIG.

An embodiment of the present invention will be described with reference to the drawings.

A stress estimation device 40 according to the present embodiment is included in a stress estimation system 100 as shown in FIG. The stress estimation system 100 estimates the stress in the inspection target area A of the pipe 1 (pipe) constituting the piping facility using internal water pressure such as water supply and industrial water supply, and the damage state of the pipe 1 from the estimated stress. It is a system that evaluates In the tubular body 1, water shall flow from the pressure water tank 2u on the upstream side toward the downstream end water tank 2d on the downstream side. The tubular body 1 is formed in a cylindrical shape, for example.

The stress estimation system 100 includes an imaging unit 10, a pressure gauge 20, a valve 30, and a stress estimation device 40, as shown in FIG.

The photographing unit 10 includes a plurality of cameras 11 and photographs an inspection target area A of the tubular body 1 . The camera 11 is a visible light camera (digital camera or high-speed camera) that includes an imaging element such as a CCD or CMOS, a lens that forms an image of a subject on the imaging element, and the like.

The imaging unit 10 is composed of, for example, two cameras 11 . The two cameras 11 are spaced apart from each other and photograph the same subject (in the present embodiment, the inspection target area A of the tubular body 1). The two cameras 11 are calibrated using the same calibration plate. The two cameras 11 perform stereo imaging of the inspection target area A. FIG. The two cameras 11 supply the stress estimation device 40 with digital data (image data) of images of the inspection target area A captured at predetermined intervals during the imaging period.

The image data obtained by the two cameras 11 are obtained by using the digital image correlation method (DICM) (hereinafter referred to as the image correlation method) executed by the stress estimation device 40 as described later. Used to measure the strain on the outer peripheral surface (three-dimensional surface) of the In this embodiment, since the image correlation method is used, a random pattern is previously applied to the outer peripheral surface of the inspection target area A of the tubular body 1 by spraying or the like.

The pressure gauge 20 measures the water pressure in the tubular body 1 and supplies data indicating the measured water pressure to the stress estimation device 40 . The pressure gauge 20 is provided, for example, in the vicinity of the inspection target region A of the tubular body 1 .

The valve 30 is composed of, for example, an electromagnetic valve or an electric valve, and is switched between an open state in which the flow path in the pipe 1 is opened and a closed state in which the flow path in the pipe 1 is closed under the control of the stress estimation device 40. The valve 30 is provided downstream of the inspection target region A of the tubular body 1 . At least one of the pressure gauge 20 and the valve 30 may be an existing infrastructure.

The stress estimating device 40 is configured by a computer, and estimates the stress generated in the tubular body 1 based on the image data acquired from the imaging unit 10 and the water pressure acquired from the pressure gauge 20 . The stress estimation device 40 includes a control section 41 and a storage section 42 . The stress estimation device 40 may be composed of a plurality of computers that can communicate with each other.

The control unit 41 includes a CPU (Central Processing Unit), a timer, etc., and executes an operation program stored in the storage unit 42 to control operations of the imaging unit 10 , the pressure gauge 20 and the valve 30 . In addition, the control unit 41 controls the operation of each configuration of the imaging unit 10, the pressure gauge 20, and the valve 30 via an I/F (interface) or wired or wireless communication means, and various Get the data of

The storage unit 42 includes a ROM (Read Only Memory) that stores fixed data, a RAM (Random Access Memory) that temporarily stores data indicating various calculation results, and the like. In the ROM of the storage unit 42, data of various operation programs (including a program PG for executing a stress estimation process described later), data related to formulas for calculating estimated stress, and calculated estimated stress Pipe body 1 Data for judging the damage status of the device is stored in advance.

The control unit 41 functions as image information acquiring means, strain amount calculating means, stress estimating means, and pressure acquiring means, as described below.

The control unit 41, which functions as an image information acquisition means, controls the inspection target area of the tubular body 1 during the imaging period including the period in which pressure waves (water hammer pressure) are generated due to unsteady changes in the water flowing inside the tubular body 1. Image data (image information) representing an image obtained by photographing A at predetermined intervals by the photographing unit 10 (plurality of cameras 11) is acquired. The control unit 41 causes the imaging unit 10 to image the examination target area A of the tubular body 1 at a predetermined cycle during the imaging period, and acquires the image data from the imaging unit 10 . In this embodiment, the control unit 41 controls the valve 30 from the open state to the closed state to generate a pressure wave due to the water hammer action inside the tubular body 1 . Here, water hammer pressure means that when the flow of water supplied in facilities such as pressurized conduits, transmission pipes, and water pipes is suddenly obstructed and unsteady changes occur, the kinetic energy of the pipes It is an action that causes a sudden change in the pressure on the body 1, resulting in an impact.

The control unit 41 functioning as a strain amount calculation means obtains time-series information (time-series data) of the three-dimensional displacement of the tubular body 1 by analyzing the acquired image data by the image correlation method, and obtains Based on the time-series information of the displacement, the time-series information of the strain amount in the predetermined direction of the tubular body 1 is calculated.
Specifically, the control unit 41 calculates the displacement of the outer peripheral surface of the inspection target area A of the tubular body 1 using the image correlation method based on a plurality of image data within the imaging period acquired in time series from the imaging unit 10. demand. At this time, based on the image data obtained from each of the two cameras 11, the control unit 41 obtains the three-dimensional displacement of the outer peripheral surface of the inspection target area A of the tubular body 1 according to the principle of stereoscopic vision. For example, the control unit 41 obtains the post-deformation position of a predetermined subset (calculation area made up of a plurality of pixels) using the correlation of luminance value distribution or the like. The position of the deformed subset is determined by finding a region in the modified image that has the same luminance distribution as the pre-deformed subset. The control unit 41 obtains the three-dimensional displacement of the outer peripheral surface of the inspection target area A of the tubular body 1 by obtaining the movement amount of the subset from the image data acquired in time series. In addition, the control unit 41 uses the displacement-strain relational expression from the obtained three-dimensional displacement distribution to obtain the strain (amount of strain) of the outer peripheral surface (three-dimensional surface) in the inspection target area A of the tubular body 1. The method of obtaining strain from displacement is arbitrary, and there are various methods such as a method of differentiating the displacement distribution, a method of approximating the function of the displacement distribution by the method of least squares and differentiating the function, a method of using the finite element method, etc. A known method can be used.

In this embodiment, the control unit 41 obtains time-series data of the strain _eyy in the tangential direction (perpendicular direction to the axis, which will be described later) of the outer peripheral curved surface of the tubular body 1 for each of a plurality of set extraction points. FIG. 3A is a graph showing an example of time-series data of strain in the direction perpendicular to the axis obtained by the control unit 41 at predetermined extraction points. The control unit 41 performs noise processing (noise filtering) on the strain in the axis-perpendicular direction obtained in this way. Specifically, the control unit 41 performs moving average method (for example, simple moving average of moving section 10 term (0.5 s)) and high-pass filter processing (for example, 0.2 Hz or less) for the obtained strain in the direction perpendicular to the axis cut) noise processing. FIG. 3(b) is a graph showing an example of time-series data of the strain in the direction perpendicular to the axis after noise processing is performed on the strain in the direction perpendicular to the axis in FIG. 3(a). 3(a) and 3(b) are data in Case 4 described later, and WH in the figures corresponds to the timing of WH shown in FIG.

The control unit 41 functioning as a stress estimating means extracts the maximum value of the strain _eyy in the direction perpendicular to the axis from the time-series data of the amount of strain, and based on the extracted maximum value, the strain in the direction perpendicular to the axis Calculation of Estimated Stress Specifically, the control unit 41 estimates the stress generated in the tubular body 1 from the strain in the axis-perpendicular direction after performing the noise processing. Specifically, using the strain-stress relational expression, the control unit 41 multiplies the Young's modulus [N/mm ² ] of the tubular body 1 by the strain in the direction perpendicular to the axis to obtain the estimated stress [N/mm ² ]. . In this embodiment, the control unit 41 obtains the estimated stress from the maximum strain in the direction perpendicular to the axis in the time-series data of strain in the direction perpendicular to the axis after noise processing.

Further, the control unit 41 functioning as a pressure acquisition unit acquires time-series data of water pressure applied to the tubular body 1 from the pressure gauge 20 . Then, in addition to the estimated stress obtained by image analysis as described above, the control unit 41 functioning as a stress estimating means generates in the tubular body 1 based on the time-series data of the water pressure obtained from the pressure gauge 20 at a predetermined cycle. Calculate the estimated stress. A method for calculating the estimated stress based on water pressure will be described later.

The configuration of the stress estimation system 100 is as described above. Next, an example of stress estimation processing using the stress estimation device 40 and an example of a stress estimation method will be described.

For example, the control unit 41 starts the stress estimation process shown in FIG. 2 in response to receiving a predetermined operation performed on an operation unit (keyboard, touch panel, etc.) not shown. First, the control unit 41 controls the pressure gauge 20 to start measuring the water pressure inside the tubular body 1 (step S1). Subsequently, the controller 41 opens the valve 30 (step S2). Thereby, water flows in the tubular body 1 .

Subsequently, the control unit 41 determines whether or not the water pressure obtained from the pressure gauge 20 is stable (step S3), and when the water pressure is stable (step S3; Yes), the inspection of the tubular body 1 by the imaging unit 10 Imaging of the target area A is started (step S4). If the water pressure is not stable (step S3; No), the controller 41 waits until the water pressure stabilizes.

Any method can be used to determine whether the water pressure has stabilized. Whether or not the water pressure has stabilized may be determined based on whether or not the water pressure has become less than or whether or not a predetermined set period has elapsed since the valve 30 was opened. The threshold value and the set period may be stored as data in the ROM in advance.

Subsequently, the controller 41 closes the valve 30 (step S5). Thereby, a pressure wave (water hammer pressure) is generated in the tubular body 1 .

Subsequently, the control unit 41 determines whether or not the water pressure has stabilized (step S6). If the water pressure has stabilized (step S6; Yes), the photographing by the photographing unit 10 and the measurement of the water pressure by the pressure gauge 20 are terminated. (step S7). If the water pressure is not stable (step S6; No), the controller 41 waits until the water pressure stabilizes. The method of determining whether or not the water pressure has stabilized is the same as in step S3.

Subsequently, the control unit 41 estimates the stress generated in the tubular body 1 based on the image correlation method (step S8). Specifically, as described above, the control unit 41 uses the image correlation method based on a plurality of image data within the imaging period acquired in time series from the imaging unit 10 to examine the region A of the tubular body 1. Determine the three-dimensional displacement of the outer peripheral surface. In addition, the control unit 41 obtains time-series data of the strain in the direction perpendicular to the axis from the obtained three-dimensional displacement distribution for each set extraction point. As a reference for the image of the image correlation method, for example, the image at the start of imaging in step S3 may be used as a reference, and the displacement and distortion may be obtained based on the difference from the reference. The control unit 41 also performs moving average and high-pass filter processing on the strain in the direction perpendicular to the axis at each extraction point, and obtains time-series data of the strain in the direction perpendicular to the axis at each extraction point after noise processing. Then, the control unit 41 obtains an estimated stress (hereinafter referred to as a first estimated stress) from the maximum strain in the direction perpendicular to the axis in the time-series data of the strain in the direction perpendicular to the axis after the noise processing.

Subsequently, the control unit 41 estimates the stress generated in the tubular body 1 based on the time-series data of water pressure acquired from the pressure gauge 20 at predetermined intervals (step S9). The control unit 41 calculates the stress distribution at a plurality of inspection points set within the inspection target area A using equations (5), (6), and (1) described later. The control unit 41 first obtains the water pressure change amount ΔP based on the water pressure at the start of photographing in step S4, and obtains the stress in the axis-perpendicular direction using the equation (5). Next, using equation (6), the stress intensity factor K is obtained from the obtained stress in the direction perpendicular to the axis. Then, by substituting d [mm] corresponding to a plurality of inspection points using the equation (1), an estimated stress (hereinafter referred to as a second estimated stress) at each inspection point is calculated. A stress estimation method based on water pressure using these formulas will be described in detail later.

Then, the control unit 41 evaluates the damage condition of the tubular body 1 in the inspection target area A based on the first estimated stress obtained in step S8 and the second estimated stress obtained in step S9 (step S10). For example, when at least one of the first estimated stress and the second estimated stress exceeds a predetermined threshold value, the control unit 41 determines that the tubular body 1 is damaged (for example, a crack occurs). Evaluate as possible. In addition, the control unit 41 may perform the situation evaluation of the tubular body 1 based on the estimated stress calculated by a simple average or a weighted average of the first estimated stress and the second estimated stress. In addition, based on the table data in which the range of multiple stages of the estimated stress (at least one of the first estimated stress and the second estimated stress) corresponds to the multiple stages of the evaluation degree of the tubular body 1, the control unit 41 may perform an evaluation of the tube 1 . As the evaluation degree of multiple stages, "no abnormality", "possibility of breakage", "high possibility of breakage", etc. can be provided. Threshold data and table data may be determined in advance by performing experiments or the like and stored in the ROM of the storage unit 42 .

The above is the stress estimation processing. Note that the control unit 41 may display the photographed image of the inspection target area A, the image analysis screen, the evaluation result, and the like on the display unit (not shown). The display unit is composed of, for example, a liquid crystal display (LCD), an organic EL display (OELD), or the like. That is, the stress estimation device 40 or the stress estimation system 100 may be configured including such a display unit.

With the stress estimating device 40 described above, the damage condition of the tubular body 1 can be evaluated using pressure waves (water hammer waves) generated in the tubular body 1 (pipe). Specifically, the three-dimensional image measurement by the image correlation method is used to detect the pressure wave, the strain amount is calculated from the three-dimensional movement amount of the pixel group of the visible image, and the strain amount in the tubular body 1 is calculated from the calculated strain amount. Stress distribution can be estimated. In the above description, the pressure waves are artificially generated by closing the valve 30. However, pressure waves generated in existing facilities such as infrastructure can be used to generate the strain amount and stress distribution of the tubular body 1 according to the above methods. can also be estimated.

Among social infrastructure facilities, piping facilities that use internal water pressure, such as water supply and industrial water, are more difficult to restore than roads in the event of a sudden disaster such as a large-scale earthquake. Accompany. If the stress estimation method described above is used, for example, for water supply and industrial water facilities, pressure waves (water hammer pressure) generated in existing facilities can be used for non-destructive and non-contact inspection. It is possible to identify the stress situation near the damage (crack). An embodiment of the stress estimating device 40, a stress estimating process using the same, and a stress estimating method will be described below. As an example, the inventor of the present application conducted an experiment under the conditions described below.

(Example)
(Target facility)
The facility (model pipeline) to be tested is a single pipeline consisting of the pressure water tank 2u, pipe 1, valve 30, and downstream end water tank 2d. , with a tube thickness of 1.5 mm. The tubular body 1 was laid spirally and formed of SUS304 (stainless steel). The pressure wave propagation velocity of the target facility is 1,310 m/s. In the experiment, a pressure gauge 20 of piezoelectric element type provided 1.77 m upstream (L1=1.77 m in FIG. 1) from the valve 30, which is a solenoid valve, measured the water pressure fluctuation in the tubular body 1. As a reference, elastic wave measurement by the AE method was also performed at the same time.

(Image acquisition method)
The tubular body 1 between the flanges 24.28 m to 24.61 m upstream from the valve 30 (L2 = 24.28 m, L3 = 24.61 m in FIG. 1) is the inspection target area A, and the deformation of the tubular body 1 by image measurement. Measurements were taken. In addition to the photographing unit 10 composed of two CCD cameras, one high-speed camera was used for image acquisition by photographing. The image data obtained by the CCD camera was used for analysis of the strain field on the outer peripheral surface of the tubular body 1 . Data from the high speed camera were used to estimate the start time of the CCD camera. A Grasshopper 3 GS3-U-60S6M (manufactured by PointGrey Research) was used as a CCD camera, and a Xenoplan 2.0/28 (manufactured by Schneider KREUZNACH) was attached to the lens. The resolution of the CCD camera was 2736×2192 pixels, and the imaging interval was 20 Hz. In order to correct the aberration of the camera lens, calibration was performed using a calibration plate with a dot spacing of 7 mm. A USB 3.0 high-speed camera k5 (manufactured by Kato Koken Co., Ltd.) was used as a high-speed camera, and a lens M6Z1212-3S (manufactured by Computer Co., Ltd.) was attached. The resolution of the high-speed camera was 640×480 pixels, and the shooting interval was 250 Hz. A dedicated trigger switch and synchronization cable were used to capture the shooting start time of the high-speed camera into the AE measuring device.

(elastic wave measurement)
In order to measure elastic waves generated by deformation originating from pressure waves, AE measurement was also performed using an AE sensor and an AE measuring device (not shown) as a reference. A 150 kHz resonance type AE sensor was used. The AE sensors were attached using couplant and arranged in the vicinity of the slit S formed in the tubular body 1 to simulate a crack. The measurement conditions were a preamplifier amplification value of 40 dB, an AE measuring device (manufactured by SAMOS PAC) threshold of 30 dB, and a measurement interval of 1 MHz. An external synchronization cable is used to time-synchronize the AE measurement result by the AE measurement device with the measured water pressure and image measurement, and the stress estimation device 40 is loaded with the shooting start time of the high-speed camera and the water pressure measurement value. connected. The measurement interval for external synchronization was set to 10 Hz. The experiment was performed in the same procedure as the stress estimation process described above, except that the AE measurement was started before step S1 in the stress estimation process (see FIG. 2) and ended after step S9. After the valve 30, which is a solenoid valve, is closed, water pressure vibration occurs as shown in FIG. I understand. In other words, it can be inferred that the response of the tubular body 1 receiving the water hammer pressure (such as deformation of the tubular body 1) is the AE generation source.

(experimental case)
As shown in the table in FIG. 5, the inventor of the present application changed the conditions of the slit S applied to the tubular body 1 to simulate a crack and the water hammer pressure generated in the tubular body 1, a total of 9 patterns. was carried out (Cases 1 to 9).
The conditions of the slit S are as follows: in the slit S having a length of 50.0 mm and a width of 1.0 mm, the tubular body 1 (Cases 1 to 3) with a depth of 0.5 mm and a depth of 1.0 mm. Two types of tubular bodies 1 (Cases 4 to 6) were prepared. For comparison, experiments were also conducted on the tubular body 1 without the slit S (Cases 7 to 9). In addition, the length of the slit S is the length along the extension direction of the tubular body 1 .
As the water hammer pressure conditions, while maintaining the upstream end pressure at 0.25 MPa for the tubular body 1 in each case, the flow velocity at the time of water flow is 0.20 m / s, 0.35 m / s, 0.50 m / By adjusting each value of s, the maximum water hammer pressure (pressure wave maximum water pressure) is 0.52 MPa (Case 1, 4, 7), 0.67 MPa (Case 2, 5, 8) and 0.85 MPa (Case 3 , 6, 9). In addition, the flow velocity of the experimental conditions was set from the analysis results of the unsteady flow regime analysis so that the maximum water hammer pressure would be the above values. In addition, since the valve operation in the model pipeline experiment (the closing operation by the valve 30 consisting of a solenoid valve) is abrupt closing, the maximum water hammer pressure can also be calculated using the Joukowski formula.

6(a) and 6(b) show an example of pressure vibration due to the water hammer action on the tubular body 1. FIG. FIG. 6(a) is time-series data (change over time) of water pressure measured by the pressure gauge 20 in Case 3. FIG. FIG. 6B is time-series data of the measured water pressure in Case 6 when the valve 30 is not completely closed. FIG. 6(b) simulates a state in which the valve 30 is not completely closed due to the occurrence of an earthquake or the like, and shows a case where a continuous water hammer action occurs. In both figures, T1 is the opening start (water supply start) timing of the valve 30, and T2 is the closing timing of the valve 30. As shown in FIG. In both figures, it can be confirmed that immediately after the valve 30 is closed, the water pressure in the tubular body 1 rapidly rises to about 10 times the pressure before the valve 30 is closed, and water hammer pressure is generated.

(analytic focus and description method)
7(a) and 7(b) show the definition of the direction in deformation measurement of the tubular body 1. FIG. FIG. 7(a) is an image analysis screen showing the amount of displacement calculated using the image correlation method from the image captured by one CCD camera, and the analysis screen of FIG. The y-axis is set in the vertical direction and the x-axis is set in the horizontal direction in the screen of FIG. That is, the x-axis is along the extension direction of the tubular body 1 and the y-axis is along the radial direction of the tubular body 1 .
When the tubular body 1 is cut open along the x-axis, the tubular body 1 is developed as shown in FIG. 7(b) and can be regarded as a plane. Since the stress and strain acting on the tubular body 1 subjected to water pressure occur on this plane, the extension direction of the tubular body 1 is defined as the "axial direction" separately from the image analysis screen, and the direction perpendicular to this axial direction is Defined as "perpendicular to the axis". This axis-perpendicular direction corresponds to the tangential direction of the outer peripheral curved surface of the tubular body 1 .

It is expected that stress concentration will occur in the vicinity of the slit S when the pressure wave propagates through the tubular body 1 . Taking this into account, as shown in FIG. 8, as data extraction points, two extraction points P1 and P2 are set at both ends of the slit S where stress concentration is expected to occur, and the slit S is set at the side of the slit S A total of four points, one extraction point P3 set between both ends and one extraction point P4 moved from the upstream end of the slit S by 20 mm in the x direction and -5 mm in the y direction as a non-defective part. determined. In Cases 7 to 9 in which the slit S was not provided, data were also extracted at four points corresponding to the above extraction points P1 to P4.

(Experimental result)
(Estimation of stress acting on tubular body 1)
In order to evaluate the stress distribution in the vicinity of the slit S, the stress in the direction perpendicular to the axis acting on the tubular body 1 was obtained in each case. In the experiment, the stress obtained from the water pressure measured by the pressure gauge 20 was used as the load stress in the following formula (1), and the stress intensity factor K (fracture mechanics index) was estimated. where K: stress intensity factor [Pa·√m], σ _y : stress in the direction perpendicular to the axis [N/m ² ], and d: distance [m] from the end of the crack (slit S). Equation (1) can be used to estimate the stress intensity factor K when the distance d is within a predetermined range, but is not suitable for the estimation when the distance d is too large. For reference, FIG. 9(a) shows the relationship between the stress intensity factor and the stress distribution in the vicinity of the crack. Here, the distance from the upstream end of the slit S toward the upstream side is d, but the distance from the downstream end of the slit S toward the downstream side may be d.

As a calculation principle of the load stress, it is considered that when water pressure acts on the tubular body 1, stress in the direction perpendicular to the axis acts on the tubular body 1, causing deformation. On the XX' line in FIG. 9B, the following formula (2) is established from the balance of force due to internal pressure and stress. Here, r ₀ : initial inner radius [m], P ₀ : initial water pressure [Pa], t: pipe thickness [m], σ ₀ : initial stress [N/m ² ].

When the water pressure in the tubular body 1 changes from P ₀ to P ₀ +ΔP, the stress becomes σ ₀ +Δσ, the inner radius becomes r ₀ +Δr, and the following formula (3) holds. Here, Δr: amount of change in inner radius [m], ΔP: amount of change in water pressure [Pa], Δσ: stress due to change in water pressure [N/m ² ].

Since Δr is sufficiently small compared to other variations, approximating Δr=0 in equation (3) results in the following equation (4).

Further, by substituting σ ₀ in the formula (2) into the formula (4) and arranging it, the following formula (5) is obtained.

Equation (5) indicates that in the axis-perpendicular direction of the tubular body 1, a tensile stress acts when the water pressure increases, and a compressive stress acts when the water pressure decreases. Δσ acting on the XX′ line in FIG. 9(b) acts as a load stress σ used in the following formula (6), and according to the above formula (1), a crack (slit S) on the XX′ line Stress concentration occurs near the edge.

In this experiment, the load stress σ was obtained based on the water pressure measured by the pressure gauge 20 and Equation (5). Specifically, Δσ calculated by substituting the water pressure change amount ΔP with respect to the predetermined reference water pressure into the equation (5) was used as the load stress σ. The amount of change in water pressure .DELTA.P substituted into the equation (5) was obtained from the difference from the water pressure at the start of imaging by the imaging unit 10 as a reference. In the measurement of deformation of the tubular body 1 by the image correlation method, the image at the start of imaging by the imaging unit 10 was used as a reference, and analysis was performed based on the difference from the reference. In order to match the stress calculated based on the water pressure and the strain obtained by the image analysis, the above water pressure variation ΔP was used in the calculation.

In each case (Cases 1 to 6), the load stress σ calculated based on the water pressure and the measurement results of the axial strain e _yy at the end of the slit S by image analysis using the image correlation method are shown in FIG. 10(a). to (c) and FIGS. 11(a) to (c).
"e _yy-max observation time" in the figure indicates the observation time at which the amount of strain in the axis-perpendicular direction e _yy at the end of the slit S becomes maximum. "P _max observation time" indicates the observation time of the maximum water pressure measured by the pressure gauge 20 (Cases 1, 2, 5, 6). It should be noted that, if a significant peak can be confirmed in the axis-perpendicular strain e _yy during the action of the water hammer pressure, instead of the P _max observation time, the time indicating the peak was indicated as "e _yy observation time" (Case 3 , 4). These are times targeted for the evaluation of the stress distribution at the end of the slit S, which will be described later. Note that the measurement results of Cases 7 to 9 are omitted in this paper because the tubular body 1 does not have the slit S and no significant strain amount peak appears. As a result of examining the measurement results of FIGS. 10 (a) to (c) and FIGS. 11 (a) to (c), especially in Case 6, the load stress σ (about 7 [N/mm ² ]) obtained based on the water pressure and the tube deformation (e _yy ) obtained from image analysis were suggested to be closely related.

(Evaluation of stress distribution near slit S)
Subsequently, the stress estimated based on the water pressure measured by the pressure gauge 20 and the stress estimated based on the image analysis using the image correlation method were compared and evaluated.

In estimating the stress distribution based on the water pressure, the stress intensity factor K was obtained using the equation (6), and then the distribution of the stress σ _y near the slit S was calculated using the equation (1). The stress in the direction perpendicular to the axis calculated from the water pressure was used as the load stress σ in Equation (6). Specifically, as described above, the water pressure change amount ΔP from the reference water pressure was substituted into the equation (5) to calculate Δσ, which was used as the load stress σ. Then, the stress intensity factor K was obtained by substituting the load stress σ into the equation (6). Then, by substituting the obtained stress intensity factor K into the equation (1), the arbitrarily set distance d from the end of the slit S (the distance d corresponds to an arbitrary inspection point described in step S9 above) ) was _obtained . Note that the control unit 41 that executes the process of step S<b>9 described above calculates the estimated stress based on the water pressure measured by the pressure gauge 20 using a method similar to this. The distribution of the stress σ _y was calculated at intervals of 0.1 mm in the range of 0.1 mm to 10 mm (d=0.1×10 ⁻³ m to 10×10 ⁻³ m) from the edge of the slit S.
FIG. 12 shows the values of the load stress, stress intensity factor, and maximum stress calculated based on the water pressure at the maximum strain observation time in the direction perpendicular to the axis (eyy _-max observation time) specified by image analysis.

The strain-stress relational expression was used to calculate the stress distribution by image analysis. The Young's modulus of the tubular body 1 used for the calculation is 193×10 ³ [N/mm ² ]. The strain is obtained by setting extraction points at intervals of 0.2 mm in the range from the end of the slit S on the upstream side (P1 in FIG. 8) to 10 mm on the upstream side, and performing noise processing for each extraction point. _eyy was used. 13 (a) and (b) show an example of the stress distribution (in the figure, "stress obtained from tube deformation") at the maximum strain observation time in the direction perpendicular to the axis ( _eyy-max observation time) (Case 3, 5).

As shown in FIG. 12, in stress estimation based on water pressure, an increase in stress (stress concentration) near the slit S was confirmed in cases other than Case 4 (Cases 1 to 3, 5, and 6).
On the other hand, in the stress estimation by image analysis using the image correlation method, in particular, the stress on the edge of the slit S in Case 3 shown in FIG. stress obtained from deformation”) becomes 15.845 [N/mm ² ], and the stress on the edge of the slit S in Case 5 shown in FIG. (see "Stress obtained from tube deformation") was 11.847 [N/mm ² ], which was close to the calculated maximum stress (see Fig. 12). Although not shown, the stress on the edge of the slit S in Case 2 was 12.233 [N/mm ² ], which was also close to the calculated maximum stress (see FIG. 12).

By the above method, e _yy is calculated by three-dimensional image analysis, and the stress concentration at the tip of the slit S (crack) can be identified by non-destructive and non-contact inspection at the e _yy-max observation time. I understand. Based on this, if the stress e _yy in the direction perpendicular to the axis is estimated at an arbitrary extraction point in the inspection target area A of the tubular body 1 by image analysis, as described in step S10 of the stress estimation process described above, the tubular body It is also possible to evaluate the damage situation of 1.

The present invention is not limited by the above embodiments and drawings. Modifications (including deletion of constituent elements) can be added as appropriate without changing the gist of the present invention. An example of modification will be described below.

(Modification)
Although an example in which water flows through the tubular body 1 to be inspected has been described above, the tubular body 1 to be inspected may flow a liquid other than water, a mixed liquid, or a gas such as gas. In other words, the tubular body 1 to be inspected may be one that allows a fluid to flow. Since the water hammer effect occurs not only in liquid but also in gas, it is possible to estimate the stress generated in the tubular body 1 by using the stress estimating device 40 described above.

Although the tubular body 1 having a cylindrical shape has been described above, the tubular body 1 may have any shape as long as it is cylindrical, and may be, for example, a square tube. In the above, when using the image correlation method, an example was described in which a random pattern was applied to the outer peripheral surface of the inspection target area A of the tubular body 1 by spraying. If you have it, you don't have to use the spray. Furthermore, a random pattern may be given by projecting light onto the outer peripheral surface of the tubular body 1 .

Although the example in which the pressure wave due to the water hammer action is generated in the tubular body 1 by closing the valve 30 under the control of the control unit 41 has been described above, the present invention is not limited to this. A pressure wave generated independently of the control of the control unit 41 may be used in an existing piping facility. For example, the control unit 41 periodically causes the imaging unit 10 to image the inspection target area A of the tubular body 1, analyzes the data when the strain _eyy in the direction perpendicular to the axis exceeds a predetermined threshold value, and calculates the stress. can be estimated. In addition, the control unit 41 periodically causes the imaging unit 10 to image the inspection target area A of the tubular body 1, and the water pressure acquired from the existing pressure gauge 20 and the AE signal from the AE sensor provided on the tubular body 1 When the occurrence of water hammer is specified based on, the stress may be estimated from the strain e _yy in the direction perpendicular to the axis.

In the above, an example was shown in which the control unit 41 functioning as a strain amount calculation means calculates the strain e _yy in the direction perpendicular to the axis of the tubular body 1, but the strain in the direction other than the direction perpendicular to the axis is calculated and the strain is It may be used to evaluate the condition of the body 1. In addition, the noise processing performed by the control unit 41 functioning as a strain amount calculation means on the strain time-series data can be arbitrarily selected from known processing suitable for noise processing. A moving average or the like may be used.

In the above example, the control unit 41 functioning as a stress estimating means calculates the second estimated stress based on the water pressure acquired from the pressure gauge 20 in addition to the first estimated stress based on the image analysis. can't The control unit 41 functioning as stress estimating means may calculate at least the first estimated stress based on image analysis.

In the above, the control unit 41 functioning as a stress estimating means calculates the estimated stress in the axis-perpendicular direction generated in the tubular body 1 based on the maximum value of the strain _eyy in the axis-perpendicular direction extracted from the strain amount time-series data. Although an example of calculation has been shown, the present invention is not limited to this. The control unit 41 extracts a strain amount at one or a plurality of points in time that exceeds a predetermined value from the time-series data of the strain amount as a specific strain amount, and calculates the estimated stress based on the specific strain amount. good too. This specific strain amount may be a value that can be regarded as the maximum value, and may be a value in the vicinity including the maximum value, or may be a value next to the maximum value. In this way, for example, when the maximum value in the strain amount time-series data is an error value, the error value can be excluded.

The program PG for executing each process described above is pre-stored in the storage unit 42, but may be distributed/provided on a detachable recording medium. Also, the program PG may be downloaded from another device connected to the stress estimation device 40 . Moreover, the stress estimation device 40 may execute each process according to the program PG by exchanging various data with other devices via a telecommunication network or the like.

[1] The stress estimating device 40 described above includes, as functions of the control unit 41, image information obtaining means, strain amount obtaining means, and stress estimating means. The image information acquisition means detects the outer peripheral surface of the tubular body 1 with a random pattern (for example, the inspection target area Image information indicating an image obtained by photographing A) with a plurality of cameras 11 at predetermined intervals is acquired. The strain amount calculation means obtains the time series information of the three-dimensional displacement of the tubular body 1 by analyzing the image information acquired by the image information acquisition means by the image correlation method, and the time series information of the displacement obtained Based on this, the time-series information of the amount of strain in a predetermined direction of the tubular body 1 (for example, the strain e _yy in the direction perpendicular to the axis) is calculated. The stress estimation means calculates a specific strain amount (for example, the maximum strain e _yy-max in the direction perpendicular to the axis) at which the strain amount in the predetermined direction is a predetermined value or more from the time series information of the strain amount calculated by the strain amount calculation means. The estimated stress in the predetermined direction generated in the tubular body 1 is calculated based on the extracted specific strain amount.
According to this stress estimating device 40, it is only necessary to analyze the image data (image information) from the imaging unit 10, so the stress generated in the tubular body 1 can be estimated by non-destructive and non-contact inspection with a simple configuration. can do.

[2] The strain amount calculation means includes a plurality of extraction points (for example, extraction points P1 to P4 shown in FIG. 8) preset for an image of the outer peripheral surface of the tubular body 1, and arbitrary The time-series information of the amount of strain may be calculated at a point moved by a distance), and the stress estimation means may calculate the estimated stress at the plurality of extraction points.
[3] The specific strain amount may be the maximum strain amount in the predetermined direction (maximum strain e _yy-max in the direction perpendicular to the axis).

[4] The stress estimation device 40 may further include, as a function of the control unit 41 , pressure acquisition means for acquiring time-series information on the pressure applied to the tubular body 1 by the fluid. Then, the stress estimating means, in addition to the estimated stress (first estimated stress) calculated based on the image analysis, based on the difference (ΔP) between the pressure at the time of indicating the specific strain amount and the predetermined reference pressure, A second estimated stress in the predetermined direction generated in the body 1 may be calculated.
According to the configuration in which the second estimated stress is calculated in addition to the first estimated stress in this way, the situation of the tubular body 1 can be evaluated more satisfactorily.

[5] The predetermined direction may include a direction orthogonal to the extending direction of the tubular body 1 (a direction perpendicular to the axis of the tubular body 1).
[6] The fluid may be liquid and the pressure waves may be caused by water hammer.

[7] The stress estimation method using the stress estimation device 40 described above includes the step of acquiring the image information by the image information acquisition means, and the strain amount ( For example, it comprises a step of calculating time-series information of the strain e _yy in the axis-perpendicular direction, and a step of calculating the estimated stress generated in the tubular body 1 in the predetermined direction by the stress estimating means.
[8] The program PG described above causes the computer to function as the image information acquiring means, the strain amount calculating means, and the stress estimating means.
According to the stress estimation method and the program PG described above, it is only necessary to analyze the image data (image information) from the imaging unit 10. Therefore, with a simple configuration, the tubular body 1 can be inspected in a non-destructive and non-contact manner. The induced stress can be estimated.

In the above description, descriptions of well-known technical matters are omitted as appropriate in order to facilitate understanding of the present invention.

DESCRIPTION OF SYMBOLS 100... Stress estimation system 10... Imaging part, 11... Camera 20... Pressure gauge, 30... Valve 40... Stress estimation apparatus 41... Control part, 42... Storage part, PG... Program 1... Tubular body (pipe), A... Inspection Target area S... Slit 2u... Pressure water tank 2d... Downstream end water tank

Claims (8)

During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. an image information acquiring means for acquiring image information indicating an image to be captured;
The image information acquired by the image information acquisition means is analyzed by an image correlation method to obtain time series information of the three-dimensional displacement of the tubular body, and based on the obtained time series information of the displacement Strain amount calculation means for calculating time-series information of the strain amount in a predetermined direction of the tubular body;
From the time-series information of the strain amount calculated by the strain amount calculation means, extracting a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount, the tubular body a stress estimating means for calculating the estimated stress in the predetermined direction generated,
Stress estimator. The strain amount calculation means calculates time-series information of the strain amount at a plurality of preset extraction points for the image obtained by capturing the outer peripheral surface,
wherein the stress estimating means calculates the estimated stress at the plurality of extraction points;
The stress estimation device according to claim 1. The specific strain amount is the maximum value of the strain amount in the predetermined direction,
The stress estimation device according to claim 1 or 2. further comprising pressure acquisition means for acquiring time-series information of the pressure applied to the tubular body by the fluid;
The stress estimating means, in addition to the first estimated stress as the estimated stress, based on the difference between the pressure at the time of indicating the specific strain amount and a predetermined reference pressure, the predetermined direction generated in the tubular body calculating a second estimated stress at
The stress estimation device according to any one of claims 1 to 3. The predetermined direction includes a direction orthogonal to the direction in which the tubular body extends,
The stress estimating device according to any one of claims 1 to 4. wherein said fluid is a liquid and said pressure waves are caused by water hammer;
The stress estimation device according to any one of claims 1 to 5. During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. obtaining image information indicative of an image to be displayed;
Time-series information of three-dimensional displacement of the tubular body is obtained by analyzing the acquired image information by an image correlation method, and based on the time-series information of the displacement obtained, in a predetermined direction of the tubular body A step of calculating time-series information of the amount of strain;
From the time-series information of the calculated strain amount, extract a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount In the predetermined direction generated in the tubular body calculating the estimated stress;
stress estimation method. the computer,
During an imaging period including a period in which pressure waves are generated due to unsteady changes in the fluid flowing inside the tubular body, the random patterned outer peripheral surface of the tubular body is photographed at predetermined intervals by a plurality of cameras. image information acquisition means for acquiring image information indicating an image to be displayed;
The image information acquired by the image information acquisition means is analyzed by an image correlation method to obtain time series information of the three-dimensional displacement of the tubular body, and based on the obtained time series information of the displacement strain amount calculation means for calculating time-series information of strain amount in a predetermined direction of the tubular body;
From the time-series information of the strain amount calculated by the strain amount calculation means, extracting a specific strain amount in which the strain amount in the predetermined direction is a predetermined value or more, and based on the extracted specific strain amount, the tubular body Functioning as stress estimation means for calculating the estimated stress in the predetermined direction that has occurred,
program.

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