Externally-attached fiber bragg grating strain sensor based on winding coupling and application structure of externally-attached fiber bragg grating strain sensor

Abstract

The invention discloses an externally-attached fiber bragg grating strain sensor based on winding coupling and an application structure thereof, and relates to the technical field of fiber bragg grating sensors, the sensor comprises a substrate and an optical fiber, the top surface of the substrate is provided with a wiring groove and at least two system columns, and the optical fiber is wound on the system columns to form an effective strain sensing area. The winding coupling mode replaces traditional gluing fixation, the problem of measurement misalignment caused by adhesive aging and creep deformation is fundamentally avoided, and the long-term stability and reliability of the sensor are remarkably improved. The sensor is installed on the surface of a tested structure in a bonding or mechanical connection mode, and precise monitoring of the surface strain of the structure is achieved. By means of the externally-attached design, the inherent defects that an embedded sensor cannot be replaced and maintained are overcome, the sensor has the advantages of being replaceable and easy to maintain, and reliable technical support is provided for safety monitoring of key facilities in long-term service and service life prolonging operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber grating sensor, more particularly to an externally attached fiber grating strain sensor based on winding coupling and an application structure thereof. BACKGROUND

[0002] Nuclear power, as a kind of efficient and clean energy, plays an important role in the global energy structure. However, its safety has always been the focus of the public, government and industry. The containment, as the ultimate safety barrier of the nuclear power plant, is one of the most important structures of the nuclear power plant. In order to ensure its structural integrity and functionality during the entire service period (including extended operation), the service performance of the containment must be monitored effectively and for a long time. Among them, the structural strain is a key parameter for evaluating its mechanical state.

[0003] Currently, the strain monitoring of the containment structure generally uses internal embedded sensors, that is, the sensors (such as steel chord strain gauges, fiber grating strain gauges, etc.) are pre-embedded in the structure during the construction of the containment concrete pouring. The advantage of this method is that the sensor is directly coupled with the concrete, which can initially obtain the internal strain. However, this method has the following inherent and difficult to overcome defects:

[0004] 1. High failure rate and non-maintainability: According to the International Atomic Energy Agency (IAEA) “International Generic Ageing Lessons Learned Report for Nuclear Power Plant Structures, Systems and Components (IGALL)”, the average failure rate of sensors such as steel beam strain gauges, strain gauges and thermometers pre-embedded in the containment of French nuclear power plants is as high as about 2% per year. The sensors will gradually age and fail under the harsh service environment (high humidity, alkalinity, radiation, long-term load) for decades. Once damaged, due to being tightly wrapped by concrete, it cannot be repaired, calibrated or replaced, resulting in interruption of monitoring data and forming a “data black hole”.

[0005] 2. Restriction on extended operation: As the design life of a large number of nuclear power units around the world approaches, the demand for extended operation is increasingly urgent. However, the internal embedded sensors fail on a large scale as the operation time increases, resulting in a lack of effective data to support the evaluation of the service performance of the containment structure in the most critical post-service stage of the unit, which brings great uncertainty to the safety evaluation of the extended operation and seriously restricts the decision and safe operation of the extended operation of the unit.

[0006] 3. Limitations of traditional alternative technologies: In order to solve the monitoring problem after the failure of the internal embedded sensors, the industry has tried to use traditional technologies such as externally attached strain gauges. However, the strain gauges have poor long-term stability, are easily affected by electromagnetic interference, have short signal transmission distance, and have large data fluctuations (such as the report Figures 2-6It is difficult to meet the requirements of high reliability and long-term on-line monitoring of nuclear power plants due to the disadvantages such as the above-mentioned. In addition, the traditional fiber grating sensor is packaged and fixed by adhesive, and the adhesive itself has problems such as aging and creep, which affects the accuracy and stability of long-term measurement.

[0007] In summary, the current containment structure monitoring field of nuclear power plants faces a serious technical contradiction: on the one hand, the inevitable loss of the embedded sensor leads to unreliable monitoring data or even missing; on the other hand, the existing external monitoring technology cannot meet the requirements of long-term, stable and high-precision. Therefore, developing a new type of external monitoring technology that can replace the embedded sensor, has long-term stability, high precision, replaceability and easy maintenance, has become a key technical problem to be solved in the field of nuclear safety, which has great significance for ensuring the safe operation of active units and promoting the life extension of units. SUMMARY

[0008] Therefore, the application provides an external fiber grating strain sensor based on winding coupling and an application structure thereof, aiming at solving the above technical problems.

[0009] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0010] An external fiber grating strain sensor based on winding coupling comprises:

[0011] A substrate, the top surface of the substrate is provided with a wiring slot, and at least two cable fixing piles are fixed on the top surface of the substrate along the direction of the wiring slot;

[0012] An optical fiber is introduced from one end of the wiring slot, wound on a plurality of cable fixing piles in turn, and led out from the other end of the wiring slot, so that the optical fiber between two adjacent cable fixing piles forms an effective strain sensing area.

[0013] Through the above technical solutions, the optical fiber is fixed by winding coupling, which avoids the long-term stability problem caused by the aging and creep of the adhesive in the traditional adhesive method, improves the measurement accuracy and reliability of the sensor; at the same time, the structure is simple and compact, easy to manufacture and maintain, effectively reduces the failure rate, and is suitable for long-term strain monitoring in harsh environment.

[0014] Preferably, in the above-mentioned external fiber grating strain sensor based on winding coupling, the wiring slot is a straight line through the top surface of the substrate at both ends, the number of cable fixing piles is two, and they are arranged alternately on both sides of the wiring slot.

[0015] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, the wiring groove comprises a fiber groove in the middle, and fiber sleeve grooves and jumper grooves symmetrically and sequentially connected to both ends of the fiber groove, the jumper grooves at both ends being used for embedding fiber jumpers and meeting the introduction and extraction of the fiber, the fiber sleeve grooves being used for embedding fiber sleeves and protecting the fiber, and the fiber groove being used for embedding the fiber.

[0016] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, the tethering post has a threaded groove for the fiber wrapping.

[0017] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, the base is provided with a first connecting hole for connection.

[0018] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, it further comprises a packaging cover covering the top surface of the wiring groove and the tethering post.

[0019] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, the base is provided with a second connecting hole for connection with the packaging cover, and the packaging cover is provided with a third connecting hole corresponding to the second connecting hole.

[0020] Preferably, in the above-mentioned wrapping-coupling-based externally attached fiber grating strain sensor, the packaging cover has a break joint, and the break joint is cross-arranged with the fiber pulled between the two tethering posts.

[0021] The application further provides an application structure of the wrapping-coupling-based externally attached fiber grating strain sensor, wherein the base is connected to a structure to be tested by bonding or mechanical connection, thereby realizing the surface strain measurement of the structure to be tested.

[0022] Through the above technical solution, the sensor can be flexibly installed on the surface of the structure to be tested by bonding or mechanical connection, direct and reliable monitoring of the structure strain is realized, and the application is particularly suitable for key facilities such as the containment of nuclear power plants; the externally attached design overcomes the defects of the non-replaceable and difficult-to-maintain internal embedded sensor, provides a reusable and easy-to-maintain monitoring solution, and guarantees the continuity and accuracy of the structure safety evaluation.

[0023] Preferably, in the application structure of the wrapping-coupling-based externally attached fiber grating strain sensor, the structure to be tested is a containment structure of a nuclear power plant.

[0024] Compared with the prior art, the application provides an externally attached fiber grating strain sensor based on winding coupling and an application structure thereof, and has the following beneficial effects:

[0025] 1. Long-term stability and reliability are improved: winding coupling is used to replace the traditional adhesive method, which fundamentally eliminates the measurement drift and failure problems caused by the aging and creep of the adhesive, so that the sensor can work stably in harsh environments for a long time.

[0026] 2. Maintenance and replacement are realized: the externally attached design solves the data black hole problem that the internal embedded sensor cannot be replaced once damaged, greatly improving the maintainability of the monitoring system and the data continuity in the whole life cycle.

[0027] 3. The structure is optimized and protective: the unique wiring groove, system column and packaging cover design not only ensures accurate positioning of the optical fiber and efficient strain transmission, but also provides strong physical protection for the fragile sensing optical fiber.

[0028] 4. The installation is flexible and widely applicable: the sensor can be fixed on the surface of the structure by adhesion or mechanical means, which is simple and convenient to install, and is not only particularly suitable for major projects such as nuclear power plant containment, but also suitable for various occasions requiring surface strain monitoring.

[0029] 5. Anti-interference and accurate measurement: based on fiber grating technology, it is essentially resistant to electromagnetic interference; at the same time, the design of the packaging cover gap isolates external mechanical interference, ensuring that the substrate deformation can be accurately transmitted to the optical fiber, thereby realizing high-precision measurement. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only embodiments of the application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0031] Figure 1 The accompanying drawings are structural schematic diagrams of the externally attached fiber grating strain sensor based on winding coupling provided by the application;

[0032] Figure 2 The accompanying drawings are structural exploded schematic diagrams of the externally attached fiber grating strain sensor based on winding coupling provided by the application;

[0033] Figure 3 The accompanying drawings are structural schematic diagrams of the base provided by the application;

[0034] Figure 4 The accompanying drawings are structural schematic diagrams of the wiring groove of the base provided by the application;

[0035] Figure 5 Figure is a half cutaway schematic view of the substrate provided by the present application;

[0036] Figure 6 Figure is an enlarged view of part A of the substrate provided by the present application; Figure 5

[0037] Figure 7 Figure is a schematic view of the structure of the encapsulation cover provided by the present application;

[0038] Figure 8 Figure is a schematic view of the force analysis of the sensor structure provided by the present application;

[0039] Figure 9 Figure is a wavelength variation curve provided by the present application;

[0040] Figure 10 Figure is a schematic view of the integrity test of the containment shell provided by the present application;

[0041] Figure 11 Figure is a comparison of the monitoring curves of the conventional strain gauge and the sensor of Example 1 provided by the present application;

[0042] Figure 12 Figure is a tangential strain test verification of the sensor provided by the present application;

[0043] Figure 13 Figure is a schematic view of the measurement point position provided by the present application;

[0044] Figure 14 Figure is a monitoring initial debugging display interface provided by the present application;

[0045] Figure 15 Figure is a 16m paint surface strain monitoring curve provided by the present application;

[0046] Figure 16 Figure is a 24m paint surface strain monitoring curve provided by the present application;

[0047] Figure 17 Figure is a 32m paint surface strain monitoring curve provided by the present application;

[0048] Figure 18 Figure is an inter-shell temperature variation curve provided by the present application.

[0049] wherein:

[0050] 1 - substrate;

[0051] ​11-Cable tray; 111-Fiber optic groove; 112-Fiber optic sleeve groove; 113-Patch cord groove; 12-Cable bollard; 121-Threaded groove; 13-Fiber optic patch cord; 14-Fiber optic sleeve; 15-First connection hole; 16-Second connection hole;

[0052] 2-Fiber optic cable;

[0053] 3-Encapsulation cover;

[0054] 31 - Third connecting hole; 32 - Break. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Example 1:

[0057] See appendix Figure 1 To be continued Figure 4 This invention discloses an externally mounted fiber optic strain sensor based on wound coupling, comprising:

[0058] The base 1 has a cable tray 11 on its top surface, and at least two mooring posts 12 are fixed on the top surface of the base 1 along the direction of the cable tray 11.

[0059] Fiber 2 is introduced from one end of the cable tray 11 and wound around multiple mooring bollards 12 in sequence, and led out from the other end of the cable tray 11, so that the fiber 2 between two adjacent mooring bollards 12 forms an effective strain sensing area.

[0060] To further optimize the above technical solution, the cable tray 11 runs straight through both ends of the top surface of the base 1, and there are two mooring bollards 12, which are arranged alternately on both sides of the cable tray 11.

[0061] See appendix Figure 4 To be continued Figure 6 The cable tray 11 includes a central fiber optic groove 111, and symmetrical fiber optic sleeve grooves 112 and patch cord grooves 113 connected sequentially to both ends of the fiber optic groove 111. The patch cord grooves 113 at both ends are used to embed fiber optic patch cords 13 and to facilitate the introduction and exit of fiber optic 2. The fiber optic sleeve groove 112 is used to embed fiber optic sleeves 14 and to protect fiber optic 2. The fiber optic groove 111 is used to embed fiber optic 2.

[0062] In the embodiment, the jumper groove 113 has a diameter of 3 mm, the fiber sleeve groove 112 has a diameter of 1 mm, and the fiber groove 111 has a diameter of 0.25 mm.

[0063] To further optimize the above technical solution, the tethering post 12 has a threaded groove 121 for winding the optical fiber 2. The threaded groove 121 can make the wound fiber grating at the same spatial height and avoid the interference of the wound optical fiber. In the embodiment, the threaded groove 121 has 5 layers, which can make the optical fiber wind 5 times on the tethering post, and the pitch between adjacent threads is 0.9 mm.

[0064] To further optimize the above technical solution, the base 1 is provided with a first connecting hole 15 for connection.

[0065] To further optimize the above technical solution, the base 1 is provided with a first connecting hole 15 for connection.

[0066] To further optimize the above technical solution, the base 1 is provided with a second connecting hole 16 for connecting with the packaging cover 3, and the packaging cover 3 is provided with a third connecting hole 31 corresponding to the second connecting hole 16. The packaging cover 3 and the base 1 are assembled by bolts to protect the fragile fiber grating.

[0067] Referring to FIG. 1, Figure 7 The packaging cover 3 has a slit 32, and the slit 32 is arranged to cross the optical fiber 2 pulled between the two tethering posts 12.

[0068] In the embodiment, the slit 32 is a millimeter slit with a width of 1 mm. Since the base 1 is the main deformation component in structural monitoring, it is necessary to not only satisfy the protection function of the packaging cover 3 but also isolate the influence of the packaging cover 3 on the deformation of the base 1. Therefore, the slit 32 can protect the grating to the greatest extent without affecting the deformation of the base.

[0069] In the embodiment, the sensor base structure and the packaging cover 3 are processed by a 3D printing process, and the processing material is black resin.

[0070] Embodiment 2:

[0071] For the packaging mode of embodiment 1, the effective strain sensing area of the fiber grating is coupled with the base structure by winding, not by gluing. Therefore, the stress mode of the structure is as shown in FIG. 2. Figure 8

[0072] When the wound fiber grating sensor of embodiment 1 is pasted on the building structure to be measured by an adhesive, the deformation of the building structure itself will be transmitted to the base 1 of the sensor, and the base 1 will generate an internal force T a ​; and the optical fiber 2 fixed on the cable 12 by winding forms an internal force T1; according to Hooke's law, the optical fiber 2 will produce a displacement X due to the influence of T1, which in turn causes the center wavelength λ of the fiber grating to change; thus the change of the wavelength can be read by the fiber grating demodulator, and the strain of the building structure can be calculated through the strain sensitivity coefficient.

[0073] In order to realize the preparation and measurement of the structure strain data of the whole integrity test process of the containment structure, the related parameters of the test winding sensor need to be calibrated, mainly including temperature sensitivity and strain sensitivity.

[0074] Temperature sensitivity calibration:

[0075] The fiber grating is a temperature and strain dual-sensitive optical sensor, and the relationship between its center wavelength and temperature and strain can be expressed as:

[0076]

[0077] In formula (1), Δλ is the change of the center wavelength of the fiber grating strain sensor, λ is the original center wavelength, α f is the thermal expansion coefficient of the optical fiber, ξ is the thermal-optic coefficient of the optical fiber core, P e is the strain-optic coefficient, and ΔT is the temperature change.

[0078] According to formula (1), if the sensor is to monitor the strain parameter alone, the influence of temperature on the sensor needs to be excluded, so temperature sensitivity calibration is needed.

[0079] The temperature sensitivity calibration test selects a sensor with:

[0080] the fiber grating strain sensor of Example 1;

[0081] BRX-SFA8 fiber grating demodulator;

[0082] constant temperature drying box.

[0083] Before the test, the sensor to be tested is placed in the constant temperature drying box, and the grating is connected to the demodulation system. The temperature of the drying box is gradually increased from the initial 25.1℃ to 39.4℃, and the grating reflection spectrum waveform data during the temperature increasing process are automatically collected. The collected data at each temperature are peak searched by the half-peak average method to obtain the wavelength values of the grating at different temperatures.

[0084] The wavelength scanning range is mainly determined according to the measured grating center wavelength, and the wavelength scanning range is ensured to cover the wavelength variation range of the grating in the whole experiment. The wavelength resolution refers to the ability to separate two spectral lines with close wavelengths, that is, the minimum wavelength difference that can be distinguished. Before the test, it is tested and shown that the wavelength resolution of 0.2 nm is suitable for detecting the fiber grating reflection spectrum in the present test. If the wavelength resolution value is too large, the positions of the two inclined edges of the fiber Bragg grating reflection spectrum will be inaccurate, causing demodulation errors. If the wavelength resolution value is too small, the fiber Bragg grating reflection peak will be low, causing large noise interference.

[0085] According to the initial temperature and the terminal temperature of the constant temperature drying box, the temperature sensitivity of the fiber grating strain sensor is obtained by fitting the temperature difference and the wavelength variation. The wavelength variation curve measured in the test is shown in FIG. 6. Figure 9

[0086] After the test calibration, the temperature sensitivity coefficient of the fiber grating strain sensor obtained is 47.986 pm / ℃.

[0087] Strain laboratory test verification:

[0088] Considering that the fiber grating strain sensor will be applied to the concrete surface strain measurement of the containment integrity test, as shown in FIG. 7, the tangential strain sensitivity calibration is performed. Figure 10

[0089] The test is divided into four groups, and the accuracy of the fiber grating strain sensor of embodiment 1 in testing strain is mainly explored. In the test process, the fiber grating strain sensor of embodiment 1 and the conventional strain gauge are used to test the strain of the test object under the load.

[0090] The I-shaped tensile plate and the fiber grating strain sensor of embodiment 1 are coupled together by gluing. Compared with the axial tensile calibration, this time, the uniform load with equal steps is applied to the center position of the plate, so that the plate is bent. The fiber grating strain sensor coupled with the plate is also bent synchronously. The bending strain of the plate and the wavelength change of the fiber grating strain sensor in the bending process are fitted to obtain the strain sensitivity of the sensor, that is, the tangential strain sensitivity. The maximum tensile side strain of the plate when bent is measured by the resistance strain gauge.

[0091] The reflection spectrum of the grating is collected by the corresponding demodulation system at each load step, and the grating wavelength information is extracted by the half-peak average method. In order to eliminate the influence of the temperature change in the laboratory on the grating wavelength, a temperature compensation grating is used in the test.

[0092] The tangential strain sensitivity calibration selects the test white resin plate with:

[0093] (1) white resin plate; ​​

[0094] (2) Fiber Bragg Grating strain sensor of Example 1;

[0095] (3) Strain gauge;

[0096] (4) Steel ruler;

[0097] (5) Weights;

[0098] (6) BRX-SFA8 fiber Bragg grating demodulator;

[0099] (7) DH3802 strain acquisition instrument;

[0100] (8) Mechanical displacement table.

[0101] The test process first fixes the strain gauge and the fiber Bragg grating strain sensor of Example 1 at the center of the plate, then turns over and fixes the whole on the mechanical displacement table, then places the steel ruler in the middle of the plate and applies the same step weight to simulate the uniform load borne by the containment structure during the integrity test process.

[0102] During the calibration process, it can be obviously observed that the monitoring data curve of the strain gauge fluctuates more greatly than the fiber Bragg grating, and the data is not stable, as shown in FIG. 2, which reflects the monitoring advantage of the fiber Bragg grating compared with the strain gauge. Figure 11

[0103] Four groups of fiber Bragg grating strain sensor tangential strain sensitivity verification are carried out, as shown in FIG. 3, the fitting curve relationship between the wavelength and strain measured by the test is shown in Table 1, the correlation coefficient of the fitting curve and the test data is greater than 0.99, indicating the accuracy of the test verification result. Figure 12

[0104] Table 1 Test verification data

[0105]

[0106]

[0107] After taking the average value of the four groups of test calibration results, the tangential strain sensitivity of the fiber Bragg grating strain sensor is 2.73 pm / με.

[0108] Example 3:

[0109] In this embodiment, strain field test verification is carried out:

[0110] ​​Measurement point arrangement: Before laying the sensor, the basic environmental state of the shell needs to be surveyed first. After the survey, the laying angle of about 281° is selected. Since this angle is located between the buttress column and the equipment gate, the strain change of the concrete inner shell at this angle may be more special during the pressure test. Therefore, this angle is selected as the sensor laying direction. Since this test is mainly for the verification test of the fiber Bragg grating strain sensor of Example 1, the determination of the measurement point height mainly depends on the height position of the ring corridor walkway and the steel platform to facilitate the laying of the sensor. The laying height is selected at 8m, 16m, 24m, and 32m. Among them, a temperature sensor is set at 8m to compensate for the temperature field in the shell. The remaining elevations are laid with wrapped fiber Bragg grating strain sensors, as shown in Figure 13 .

[0111] Before laying the sensor, the temperature field at different elevations in the shell was also measured. The measurement shows that the temperature difference in the entire shell is not large. Although there is a fireproof door between different heights, they are basically in the same temperature field. Therefore, only one temperature sensor at 8m can meet the temperature monitoring requirements. It needs to be noted that the temperature sensor needs to be laid on the inner surface of the containment shell to avoid the influence of structural strain on temperature compensation. The temperature table measurement results show that the shell temperature is about 26.8℃.

[0112] After determining the measurement point position, the sensor laying stage is entered. Since the nature of this test is to verify the effect of the sensor, the paint surface of the concrete inner shell is not polished. The sensor is mainly coupled with the paint surface of the containment shell through epoxy resin, and the sensor jumper is fixed with insulating tape.

[0113] After the sensor is laid, the fiber jumper is laid. There are 4 bundles of jumpers, each 120m long. The FC-APC heads at both ends of the jumper are connected to the sensor and the demodulator channel respectively. After the wiring is completed, the computer is turned on and the monitoring equipment is debugged, as shown in Figure 14 . After debugging, all equipment is placed at the 16m ring corridor walkway and all materials are wrapped with fireproof cloth.

[0114] Test results:

[0115] (1) The acquisition equipment started collecting at 16:00 on November 20, 2024, and stopped collecting at 20:44 on November 23, 2024, with a duration of 76h 44min, about 88440 wavelength data per measurement point. The reason for stopping collection may be related to the computer performance or monitoring software bugs. The initial collection frequency of the computer is 1Hz, but according to the post-processing of the data, it is found that as the number of measurement points increases and the computer working time increases, the collection frequency will gradually decrease, and the computer load will gradually increase. By 20:40 on November 23, the collection frequency decreased to 0.25Hz.

[0116] (2) When the computer stopped collecting, the containment seal test was just at the highest pressure platform, but due to the inability to enter the shell during the test to debug the equipment to handle accidental conditions, the paint surface strain change during the containment pressure relief process was not monitored, so the "strain-data volume" curve shown in the subsequent analysis is only the monitoring content before the highest pressure platform, and the strain collected by the sensor is the paint surface strain of the concrete inner shell, not the strain of the concrete.

[0117] (3) Note that: because the paint surface and the concrete are completely different materials, their physical properties also differ greatly, and the painting of the paint surface has some cracks due to the long time elapsed; all of the above will cause the strain generated by the concrete during the seal test to be reduced when transmitted to the sensor on the paint surface.

[0118] (4) This time the containment pressure test process overview:

[0119] 2024.11.22 1:00 negative pressure;

[0120] 2024.11.22 7:25 start to increase pressure;

[0121] 2024.11.22 9:00 34m human gate leakage occurred, so the pressure increase was temporarily suspended;

[0122] 2024.11.23 6:30 restart to increase pressure;

[0123] 2024.11.23 20:14 reached the highest pressure platform;

[0124] 2024.11.25 00:00 start to relieve pressure;

[0125] 2024.11.25 16:00 containment pressure test is completed.

[0126] Monitoring data analysis:

[0127] From 0-3w on the abscissa, the paint surface strain overall showed a downward trend and the degree of decline gradually slowed down and stabilized; this is because the sensor undergoes a certain degree of pre-tension when it is pasted to the paint surface. With the passage of time, the fiber Bragg grating will shrink by a small amount (about 30pm) and eventually stabilize.

[0128] From 3w-3.9w on the abscissa, the fiber Bragg grating basically completes the shrinkage and stabilizes, at which time the monitored strain change is the 16m strain change during the daily operation of the containment inner shell, such as Figure 15The horizontal, 45°, and vertical directions all have a sudden increase in strain. This is likely due to some condition at 16m, such as equipment impact or collision when passing through the measurement point.

[0129] From 3.9w to 5.5w, the strain of the paint surface decreases significantly. This is due to the negative pressure process from 1:00 to 7:00 on November 22, 2024, causing the inner shell to contract and produce compressive strain.

[0130] From 5.5w to 6.7w, the sensor clearly monitors a "rise-stable-fall" process. This is the entire process of "pressure rise-detection-pressure relief" due to the human gate leak at 34m.

[0131] From 7.6w to 8.8w, the sensor clearly monitors the process of re-pressurizing to the highest pressure platform after the accident repair is completed.

[0132] In addition, comparing the monitoring curves of the "horizontal, 45°, and vertical" directions, it is clear that the horizontal direction data is the most clear, indicating that the horizontal deformation of the containment vessel at 16m is more prominent, and the 45° and vertical deformations are less clear compared to the horizontal direction.

[0133] From 0 to 3w, similar to 16m, the strain decreases, which is due to the shrinkage of the fiber Bragg grating (30pm) causing the wavelength to gradually decrease and eventually stabilize.

[0134] From 3w to 3.9w, the fiber Bragg grating completes the shrinkage and stabilizes. At this time, the monitored strain change is the 24m strain change during the daily operation of the inner shell of the containment vessel, as shown in Figure 16 .

[0135] From 3.9w to 5.5w, the strain decreases significantly. Analysis shows that this is the compressive strain caused by the inner shell contraction during the negative pressure phase.

[0136] From 5.5w to 6.7w, the complete "rise-stable-fall" process is also monitored, which is the strain change caused by the pressure rise and fall in the containment vessel due to the human gate leak.

[0137] From 7.6w to 8.8w, the sensor monitors the complete pressure rise process after the repair of the leak is completed.

[0138] In addition, unlike 16m, the strain monitoring curve of the "24m-45°" direction has a clear demarcation point for each stage, but the overall trend is downward (under pressure), and the tensile strain growth trend is weak when the pressure is increased. This is because the paint surface between the "24m-45°" and "24m-vertical" sensors has a relatively obvious fine crack after the compression test is completed. When the paint surface cracks, the coupling effect of the paint surface and the concrete surface will be greatly affected, and it is difficult to ensure the coordinated deformation and good strain transmission of the two. Therefore, the strain monitoring curve of the sensor at 24m-45° is quite different from that of the horizontal and vertical directions. By comparing the strain curves of the horizontal and vertical directions, it is found that the horizontal direction strain curve is clearer than the vertical direction, indicating that the horizontal deformation is still the dominant deformation at 24m.

[0139] From 0-3w of the abscissa, the strain shows a downward trend, which is due to the shrinkage of the fiber grating (30pm) causing the wavelength to gradually decrease and eventually stabilize.

[0140] From 3w-3.9w of the abscissa, the fiber grating basically completes the shrinkage and tends to be stable, and the strain change monitored at this time is the 32m strain change of the inner shell during daily operation of the safety shell, as shown in Figure 17

[0141] From 3.9w-5.5w of the abscissa, the strain shows a downward trend with a large amplitude, and analysis shows that this is the compression strain caused by the inward shrinkage of the inner shell during the negative pressure stage.

[0142] From 5.5w-6.7w of the abscissa, the complete process of "rise-stable-fall" is monitored, which is the strain change caused by the pressure rise and fall in the shell when the human gate leaks.

[0143] From 7.6w-8.8w of the abscissa, the sensor monitors the complete pressure rise process after the repair leak is completed.

[0144] In addition, the strain curve of the "32m-vertical direction" shows obvious damage, and it can be seen that the strain fluctuates obviously up and down. The reason may be that the monitoring software failed to bind the sensor successfully, which is caused by the vulnerability of the monitoring software. The strain curves of the horizontal and 45° positions are very clear, and the stages occurring during the printing process of the safety shell can be clearly monitored. The reason why the curve at 32m is clearer than that at 16m and 24m is that the 32m position is located near the middle of the safety shell cylinder, and its stress characteristics during the compression test are more typical than the rest of the elevations. Therefore, the deformation at 32m is the largest, the strain peak is the highest, and the strain change trend is the most obvious. Similarly, the horizontal direction is still clearer than the 45°, that is, the horizontal deformation is still dominant at 32m.

[0145] As shown in Figure 18 ​As shown, according to the temperature change curve, the temperature change between the shells is very small, and the maximum temperature difference is 0.6℃, which shows that the temperature between the shells is basically a constant temperature field, and the temperature environment between the shells is good for the sensor with the temperature and strain dual-sensitive characteristics of the fiber grating, which is helpful for strain monitoring of the sensor.

[0146] In summary, the sensor of the embodiment can effectively monitor the strain change of the inner surface of the inner shell of the containment vessel and the outer surface of the outer shell in the "daily operation", "pressure test" or other scenarios by the surface mounting method, and the deformation of the inner shell and the special conditions between the shells can be observed obviously through the strain curve. Compared with the embedded strain gauge, the sensor has the advantages of replaceability and easy replacement, which is helpful for the intelligent operation and maintenance of the containment vessel structure.

[0147] As for the problems such as "decrease in collection frequency" and "stop collecting due to uncontrollable factors" that occur during the monitoring process, the subsequent monitoring optimization can be carried out by using a computer with higher performance, using a remote screen to operate the monitoring software to avoid the problem of stopping collection caused by accidental factors, and the like, which does not affect the verification effect of the embodiment.

[0148] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0149] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An externally mounted fiber optic strain sensor based on wound coupling, characterized in that, include: The base (1) has a cable tray (11) on its top surface and at least two mooring posts (12) are fixed on the top surface of the base (1) along the direction of the cable tray (11). An optical fiber (2) is introduced from one end of the cable tray (11) and wound around a plurality of mooring bollards (12) in sequence, and led out from the other end of the cable tray (11) so that the optical fiber (2) between two adjacent mooring bollards (12) forms an effective strain sensing zone.

2. The externally mounted fiber optic strain sensor based on wound coupling according to claim 1, characterized in that, The cable tray (11) runs straight through both ends of the top surface of the base (1), and there are two mooring bollards (12), which are arranged alternately on both sides of the cable tray (11).

3. The externally mounted fiber optic strain sensor based on wound coupling according to claim 1, characterized in that, The cable tray (11) includes a central fiber optic groove (111), and symmetrical fiber optic sleeve grooves (112) and patch cord grooves (113) connected sequentially to both ends of the fiber optic groove (111). The patch cord grooves (113) at both ends are used to embed fiber optic patch cords (13) and to facilitate the introduction and exit of the fiber optic cable (2). The fiber optic sleeve groove (112) is used to embed fiber optic sleeves (14) and to protect the fiber optic cable (2). The fiber optic groove (111) is used to embed the fiber optic cable (2).

4. The externally mounted fiber optic strain sensor based on wound coupling according to claim 1, characterized in that, The mooring bollard (12) has a threaded groove (121) for winding the optical fiber (2).

5. The externally mounted fiber optic strain sensor based on wound coupling according to claim 1, characterized in that, The base (1) has a first connection hole (15) for connection.

6. An externally mounted fiber optic strain sensor based on wound coupling according to any one of claims 1-5, characterized in that, It also includes an encapsulation cover (3) covering the top surface of the base (1), the encapsulation cover (3) covering the top surface of the cable tray (11) and the mooring post (12).

7. The externally mounted fiber optic strain sensor based on wound coupling according to claim 6, characterized in that, The substrate (1) has a second connection hole (16) for connecting with the encapsulation cover (3), and the encapsulation cover (3) has a third connection hole (31) corresponding to the second connection hole (16).

8. The externally mounted fiber optic strain sensor based on wound coupling according to claim 6, characterized in that, The encapsulation cover (3) has a slit (32) that is intersected with the optical fibers (2) that are pulled between the two mooring posts (12).

9. An application structure for an externally attached fiber optic strain sensor based on wound coupling as described in any one of claims 1-8, characterized in that, The substrate (1) is attached to the structure under test by bonding or mechanical connection, thereby realizing the surface strain measurement of the structure under test.

10. The application structure of an externally attached fiber optic strain sensor based on wound coupling according to claim 9, characterized in that, The structure under test is the containment structure of a nuclear power plant.

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