Method for detecting cavity in structure by using elastic wave

Abstract

The present invention relates to a method for detecting a cavity in a structure using an elastic wave, the method comprising the steps of: installing a plurality of acceleration sensors capable of measuring accelerations in three axial directions in the structure; applying a plurality of three-dimensional loads having elastic waves in the vicinity of the acceleration sensor, and measuring a three-dimensional acceleration by the acceleration sensor; generating two-dimensional distributed load data by superimposing the three-dimensional load applied to each of the plurality of acceleration sensors; calculating superimposed acceleration data by superimposing the measured three-dimensional acceleration; and applying the two-dimensional distribution load data and the superimposed acceleration data to a two-dimensional elastic wave inversion analysis algorithm.

Description

Technical Field

[0001] The present disclosure relates to a method of detecting cavities within a structure using elastic wave analysis. Background Art

[0002] Although effective nondestructive testing techniques such as impact echo method, electromagnetic wave testing method and ultrasonic method have been developed to analyze defects in concrete walls of nuclear power plants, there is still no standardized method specifically for nondestructive evaluation of nuclear power plant structures.

[0003] Existing nondestructive assessment methods are primarily targeted at assessing top-layer damage in bridge decks and road surfaces. These methods have had limited success in verifying the integrity of nuclear power plant containment vessels, which are typically more than one meter thick.

[0004] Current elastic wave-based nondestructive testing methods, including shock echo, shock response, and surface wave spectroscopy, primarily use travel-time tomography to estimate internal structural conditions based on wave arrival times. Such methods provide only limited information about the continuous material properties within the target structure.

[0005] In order to ensure the safety and efficient operation of nuclear power plant structures, reliable diagnostic technologies that can accurately detect cavities within the containment walls are urgently needed. Summary of the Invention

[0006] Technical issues

[0007] Therefore, the present disclosure is directed to providing an improved method for accurately detecting cavities within structures using elastic wave analysis.

[0008] Technical Solution

[0009] The present disclosure proposes a method for detecting cavities in a structure using elastic waves, comprising the following steps: installing a plurality of acceleration sensors capable of measuring accelerations along three orthogonal axes within the structure; applying a plurality of three-dimensional loads that generate elastic waves near the acceleration sensors, and measuring the three-dimensional accelerations generated thereby; generating two-dimensional distributed load data by superimposing the three-dimensional loads applied near each acceleration sensor; calculating combined acceleration data by superimposing the measured three-dimensional accelerations; and applying the two-dimensional distributed load data and the combined acceleration data to a two-dimensional elastic wave inversion analysis algorithm.

[0010] In particular, the structure being inspected may include the containment vessel of a nuclear power plant.

[0011] A plurality of acceleration sensors may be arranged at vertical intervals along the height of the containment vessel, with loads applied adjacent to both sides of each sensor.

[0012] The load can be applied using an impact hammer. The i-th distributed load L iIt can be calculated by the following formula:

[0013]

[0014] In this equation, A represents the cross-sectional area subjected to the load and is determined by multiplying the diameter of the hammer head by the length of the load distribution. ij Represents the load data of the i-th acceleration sensor row (1ine) and the j-th impact position, N L is the number of loads for the ith sensor row.

[0015] The superimposed acceleration mk at the kth measurement position can be calculated as follows:

[0016]

[0017] In the above formula, a ij k N represents the response measured from the kth acceleration sensor when a load is applied to the i-th sensor row and the j-th impact location. S Indicates the total number of acceleration sensor rows, N L Represents the total number of loads for the i-th sensor row.

[0018] Beneficial effects

[0019] Embodiments of the present disclosure provide an improved method for reliably detecting cavities in structures, significantly improving the accuracy and reliability of non-destructive structural assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart illustrating a method for detecting a cavity according to an embodiment of the present disclosure.

[0021] Figure 2 The arrangement of load and acceleration sensors in the method for detecting a cavity according to an embodiment of the present disclosure is shown.

[0022] Figure 3 The application of simulated distributed load in the method for detecting a cavity according to an embodiment of the present disclosure is shown.

[0023] Figure 4 FIG. 4 shows a distributed load vertically acting on an analysis domain in a method for detecting a cavity according to an embodiment of the present disclosure.

[0024] Figure 5 Superposition acceleration data in a method for detecting a cavity according to an embodiment of the present disclosure is shown.

[0025] Figure 6 is a diagram showing elastic wave measurement and data superposition.

[0026] Figure 7 This is a conceptual diagram showing elastic full waveform inversion analysis. DETAILED DESCRIPTION

[0027] Hereinafter, the present disclosure will be described in more detail with reference to the accompanying drawings.

[0028] The accompanying drawings are merely examples for illustrating the technical concept of the present disclosure in more detail, and therefore, the concept of the present disclosure is not limited to the accompanying drawings. In addition, the sizes and intervals in the accompanying drawings may be exaggerated to more clearly illustrate the relationship between components.

[0029] According to an embodiment, elastic waves are generated on the surface of the structure being evaluated and the transmitted, reflected and refracted acceleration responses are measured. Using the load time history and acceleration waveforms, elastic full waveform inversion is performed to detect cavities within the structure.

[0030] In the following description, reference is primarily made to nuclear power plant containment vessels, but the disclosed method is applicable to conventional building structures including reinforced concrete structures.

[0031] The sensor and load arrangements shown herein can be adjusted as required by specific assessment needs.

[0032] Will refer to Figures 1 to 5 A method of detecting a cavity according to an embodiment of the present disclosure is described.

[0033] First, a plurality of acceleration sensors capable of measuring acceleration in three orthogonal directions are mounted on the structure ( S100 ).

[0034] like Figure 2 As shown, 15 acceleration sensors can be attached to the wall at fixed intervals in the vertical direction.

[0035] An accelerometer outputs an electrical signal proportional to acceleration within a specific frequency range. Attached to the surface of the containment vessel wall, the accelerometer measures the instantaneous acceleration response in three directions. For example, the 356A16 accelerometer from PCB Corporation can be used.

[0036] Next, a plurality of three-dimensional elastic wave loads are applied near the sensor, and the resulting three-dimensional accelerations are measured ( S200 ).

[0037] like Figure 2 As shown, for each acceleration sensor, three impact loads can be applied to both sides, for a total of six times. The spacing between the loads can be constant.

[0038] Thus, there were six shock loads in total, three shock loads on each side along the corresponding row of each accelerometer, and the shock loads were applied repeatedly to all accelerometer rows, for a total of 90 shock loads.

[0039] The loads may be applied sequentially, one at a time, a few at a time, or all at once.

[0040] The load can be applied using an impact hammer. The impact hammer is capable of generating elastic waves over a wide frequency range and can be used in a variety of directions and positions. Although not limited to this, the impact hammer can use the 086D20 from PCB Company.

[0041] Next, to apply the 3D load data applied to the surface of the nuclear power plant's containment wall and the measured acceleration response to the 2D elastic wave inversion algorithm, the load time histories and acceleration time histories are superimposed. The order in which the load and acceleration time histories are superimposed is not restricted.

[0042] This will be described in detail below.

[0043] Two-dimensional distributed load data is generated by superimposing three-dimensional loads applied to the respective acceleration sensors ( S300 ). This stage is configured to superimpose surface loads.

[0044] like Figure 3 and Figure 4 As shown, a two-dimensional analysis domain with a constant elastic modulus and a line load in the direction normal to the surface is assumed.

[0045] Data on the load applied by the impact hammer is extracted by a data collection device.

[0046] The six loads applied in the sensor row are added together and then divided by the cross-sectional area A to which the loads are applied to obtain the superimposed distributed load Li for each sensor row.

[0047]

[0048] In the above formula, A is the cross-sectional area where the load is applied. A is calculated by multiplying the diameter of the hammer head by the length of the load applied. ij is the load data of the i-th accelerometer row and the j-th impact position, N L is the number of loads for the ith sensor row.

[0049] Examples of superimposed surface loads are as follows:

[0050]

[0051] By applying 6 shock loads (N L ) and dividing the sum by the cross-sectional area over which the load is applied to calculate the superimposed line load L1 applied to sensor row 1.

[0052] A total of 15 superimposed line loads were applied in the direction perpendicular to the surface of the finite element analysis model, with each line load corresponding to one accelerometer row.

[0053] Next, the measured three-dimensional accelerations are superimposed to obtain combined acceleration data ( S400 ).

[0054] In order to utilize the three-dimensional response of field measurements in the two-dimensional elastic wave inversion algorithm, the measured acceleration response needs to be superimposed. The superimposed acceleration response m at the kth measurement position is k The calculation is as follows.

[0055]

[0056] Here, a ij k N represents the acceleration measured by the kth acceleration sensor when a load is applied to the ith sensor row at the jth impact position. s is the total number of accelerometers, N L is the number of loads for the ith sensor row.

[0057] An example of the superposition process showing the measured responses is provided below.

[0058]

[0059] A total of 90 impact loads were applied on the studied wall surface, involving 15 sensor rows (N S ), each sensor row has 6 impact locations (N L ). The combined response m1 at sensor location 1 is obtained by adding the 90 responses recorded by sensor 1 under all applied shock loads.

[0060] The process of superimposing shock load and acceleration data is described in further detail below.

[0061] Figure 6 is a diagram showing the measurement and superposition of elastic waves and acceleration data.

[0062] Figure 6 The superposition of impact load and acceleration data for the examples presented can be summarized in Table 1 below.

[0063]

[0064]

[0065] -Superposition of loads

[0066] Although the experiments were performed on a 3D structure, the inverse analysis algorithm assumes 2D plane strain conditions; therefore, the 3D loading data needs to be converted into 2D data.

[0067] In the inverse analysis algorithm, loads are applied simultaneously at multiple locations on the surface of the analysis domain. Since it is impractical to apply multiple loads simultaneously during an experiment, the loads are applied individually and their effects are subsequently summed.

[0068] The experimentally measured three-dimensional impact loads were converted into equivalent two-dimensional distributed loads using the above procedure.

[0069] Superimposed distributed loads act as two-dimensional uniformly distributed loads applied in the direction normal to the surface of the analysis domain.

[0070] -Superposition of acceleration response

[0071] As shown in Item A of Table 2, the acceleration response generated by a single impact load was obtained through experiments.

[0072] In the analysis domain, an equivalent two-dimensional distributed load derived from the experimental impact load is applied simultaneously.

[0073] As shown in Item B of Table 2, in order to perform the inverse analysis, the acceleration response generated at each sensor location due to the simultaneously distributed load is required.

[0074] When distributed loads are applied simultaneously, the response calculated at a given sensor location is equal to the sum of all individual acceleration responses measured at that sensor location during the experiment.

[0075] The superimposed acceleration time history is compared with the acceleration response obtained by elastic wave propagation analysis for inverse analysis.

[0076]

[0077]

[0078] Finally, the processed distributed load data and superimposed acceleration data are applied to a two-dimensional elastic wave inversion analysis algorithm (S500). This can determine the distribution of material properties within the structure and identify cavities.

[0079] Elastic full waveform inversion is a technique that uses the complete measured waveform (including the transmitted wave, reflected wave and refracted wave within the structure) to determine the unknown system parameters through inversion analysis.

[0080] In order to detect cavities in the containment wall of a nuclear power plant using elastic wave response, the wall is approximated as a two-dimensional elastic domain, and elastic full waveform inversion is performed.

[0081] Inverse analysis involves generating elastic waves on the surface of the containment wall; measuring these waves as they propagate and reflect inside; and estimating the distribution of material properties by minimizing the difference between the measured and calculated response waveforms.

[0082] Diagnosing cavities within the containment wall of a nuclear power plant requires: 1. performing elastic wave analysis in the time domain based on the geometry of the containment wall; and 2. exciting elastic waves in the containment wall and measuring the response.

[0083] The embodiments of the present disclosure specifically relate to a method for measuring elastic wave excitation and response of a nuclear power plant containment wall (2) and applying the measured data to an inversion analysis algorithm.

[0084] Algorithms for elastic full waveform inversion techniques

[0085] Reference Figure 7 ,The process of inversion analysis is described as follows.

[0086] ① Configure a two-dimensional finite element model for elastic wave analysis based on the geometry of the containment wall to be diagnosed.

[0087] ② The analysis is restricted to a finite domain, and perfectly matched layers are implemented at the boundaries to absorb outward propagating waves and prevent artificial reflections.

[0088] ③ Assign initial estimates of the spatial distribution of mechanical properties within the finite element model.

[0089] ④ Use an impact hammer to excite elastic waves on the surface of the containment wall, and use appropriate data acquisition equipment to record the input load time history and the corresponding acceleration response.

[0090] ⑤ Apply the recorded surface load time history to the finite element model to simulate the propagation of elastic waves, including the transmission, reflection and refraction components within the structure.

[0091] ⑥ Update the material property distribution of the finite computational domain by incorporating the difference between the calculated response and the experimentally measured response into the inverse analysis algorithm.

[0092] ⑦ Repeat iterative steps ⑤ and ⑥ to minimize the objective function representing the mismatch between the calculated response and the measured response, thereby obtaining the optimal distribution of material properties within the containment wall.

[0093] The process of cavity detection using elastic full waveform inversion is described as follows.

[0094] The inverse analysis procedure can be used to determine the optimal distribution of material properties (especially the Lamé constant) within the containment wall of a nuclear power plant.

[0095] If the estimated material properties within specific areas differ significantly from the known properties of the concrete used in the containment and are assessed to be significantly lower than the properties of the surrounding areas, then these areas can be identified as potential cavities.

[0096] A B-scan image of the containment wall can be generated based on the reconstructed material property distribution. The resulting single-layer image can identify the location and geometry of cavities, as indicated by areas exhibiting abnormally low material property values.

[0097] An embodiment of the present disclosure provides a data processing method that utilizes elastic wave data obtained from experiments to perform two-dimensional inversion analysis under a plane strain assumption.

[0098] By applying 3D experimental measurements to 2D full waveform inversion, cavity detection can be performed on specific parts of concrete walls.

[0099] To assess the internal condition of thick concrete walls in nuclear power plant containment vessels, elastic waves, which can transmit more energy than ultrasonic or electromagnetic waves, can be used to improve diagnostic reliability.

[0100] The foregoing embodiments are provided as examples to illustrate the present disclosure, and the present disclosure is not limited thereto. Since ordinary technicians in the technical field of the present disclosure will be able to implement the present disclosure by making various modifications to the present disclosure, the technical protection scope of the present disclosure should be defined by the appended claims.

Claims

1. A method for detecting a cavity in a structure using elastic waves, the method comprising: mounting a plurality of acceleration sensors in the structure, each of the plurality of acceleration sensors being capable of measuring acceleration along three orthogonal axes; applying a plurality of three-dimensional loads that generate elastic waves near the acceleration sensor, and measuring the resulting three-dimensional acceleration response using the sensor; generating two-dimensional distributed load data by superimposing the three-dimensional load applied at each of the plurality of acceleration sensors; calculating superimposed acceleration data by summing the measured three-dimensional acceleration responses; as well as The two-dimensional distributed load data and the superimposed acceleration data are applied to a two-dimensional elastic wave inversion analysis algorithm.

2. The method according to claim 1, wherein The structure comprises the containment vessel of a nuclear power plant.

3. The method according to claim 2, wherein: The plurality of acceleration sensors are spaced apart along a height direction of the containment shell; and The load is applied to both side surfaces of each of the acceleration sensors.

4. The method according to claim 3, wherein: applying the load using an impact hammer; and The i-th distributed load L is obtained from the distributed load data using the following formula: i : Where A is the cross-sectional area to which the load is applied and is calculated by multiplying the diameter of the hammer tip by the length of the applied load distribution, I ij is the load data corresponding to the i-th accelerometer row and the j-th impact position, N L is the amount of load applied at the ith position of the acceleration sensor.

5. The method according to claim 4, wherein According to the superposition acceleration data, the superposition acceleration mk at the kth response measurement position is obtained using the following formula: Among them, a ij k is the acceleration response measured at the kth acceleration sensor when a load is applied to the i-th acceleration sensor row and the j-th impact location, N s is the number of acceleration sensors, N L is the amount of load applied at the i-th position of the acceleration sensor.

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