A non-intrusive monitoring device for the health status of prestressed steel cable group system

Abstract

The present application discloses a non-invasive monitoring device for the health status of a prestressed steel cable group system. When a monitoring operation needs to be implemented, the tension of the steel cable is converted into axial stress through a fiber grating strain sensor. The fiber grating strain sensor can detect the change in the reflected wavelength to measure the tension change of the steel cable. Generally speaking, the closer the fiber grating strain sensor is to the prestressed relaxation steel cable, the greater the wavelength drift. When the steel cable is subjected to tension, the sleeve can withstand the tension of the steel cable and transmit the strain of the steel cable. The fiber grating strain sensor is arranged at the detection point of the sleeve to detect the strain change of the sleeve. The position of the stress relaxation of the steel cable can be roughly determined by relying on the strain change of each sensor, avoiding the deficiency in the related art that the number of fiber grating strain sensors directly determines the monitoring accuracy. The monitoring device of the present application reduces the number of fiber grating strain sensors.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber sensing, and in particular to a non-invasive monitoring device for the health status of a prestressed steel cable group system. Background Art

[0002] At present, with the continuous application of prestressed structures in the engineering field, the demand for prestress monitoring of various high-strength prestressed steel cable group systems is increasing.

[0003] Traditional monitoring technologies mainly include: magnetic flux method, frequency method and detection methods based on force ring, steel string, strain gauge, etc. Compared with traditional detection technologies, fiber grating sensors have the advantages of anti-electromagnetic interference, compact size, good long-term stability, corrosion resistance, and easy to realize large-scale deployment and distributed measurement.

[0004] In order to monitor the strain of steel strands, Chinese patent document 02138980.2 arranges the optical fiber on the outside of the steel cable, which makes the optical fiber very easy to be damaged and the measurement is inaccurate. The method also mentions that the optical fiber can be arranged in the groove of the steel cable, which damages the structure of the steel cable and affects its long-term working performance and service life.

[0005] Chinese patent document CN103292721A proposes a fiber grating large-range strain sensor for monitoring the strain of prestressed steel strands. Installing this fiber grating sensor on one of the steel wires of the steel strand can accurately measure the strain of the steel strand, but this method can only be deployed before the installation of the steel cable group system, and cannot be adjusted, replaced or moved later. However, in many projects, prestressed steel cables are used in large quantities in the form of steel cable groups and play a prestressing role. For such a large number and widely distributed prestressed steel cable group system, if the prestress of each steel cable is to be monitored at the same time, a large number of sensors will need to be deployed over a large area, which will easily lead to redundant sensor lines, affecting the efficiency of later data transmission and analysis, and it is difficult to meet the large-scale monitoring needs of the prestressed health status of the prestressed steel cable group system. Summary of the invention

[0006] In view of this, the present application provides a non-invasive monitoring device for the health status of a prestressed steel cable group system, which can reduce the number of required sensors without destroying the original structure of the measured matrix.

[0007] The present application provides a non-intrusive prestressed steel cable group system health status monitoring device, comprising:

[0008] A sleeve, the inner cavity of which is used to accommodate the group of steel cables to be monitored;

[0009] A plurality of fiber grating strain sensors are arranged on the sleeve around the sleeve axis and used to collect the change of strain borne by the sleeve due to the tension of the steel cable;

[0010] The fiber grating temperature sensor is used to collect the temperature change of the steel cable group.

[0011] Optionally, the fiber Bragg grating strain sensor and the fiber Bragg grating temperature sensor are connected in series through a fiber optic fusion splicer to form a sensor network, the sensor network is connected to a demodulator, and the demodulator is connected to a host computer.

[0012] Optionally, the fiber grating strain sensor includes a first metal capillary and a first fiber grating encapsulated by the first metal capillary.

[0013] Optionally, the fiber Bragg grating temperature sensor includes a second metal capillary and a second fiber Bragg grating encapsulated by the second metal capillary.

[0014] Optionally, the sleeve is injection-molded using a potting glue as a raw material.

[0015] Optionally, the mold used for glue injection molding includes an outer template for injecting the injection glue, a steel cable clamp fixed to the inner wall of the outer template, and a glue injection nozzle is opened on the outer template.

[0016] Optionally, the mold further includes a positioning wire rope arranged at the end of the outer template.

[0017] Optionally, the mold further comprises a mounting nut for assembling and covering the two parts constituting the outer template.

[0018] The beneficial effects brought by the technical solution provided above include at least:

[0019] 1. The non-invasive prestressed steel cable group system health status monitoring device of the present application uses a quasi-distributed fiber grating sensor to form a sensor monitoring network, which can realize the simultaneous monitoring of the health status of multiple steel cable group systems.

[0020] 2. The non-invasive prestressed steel cable group system health status monitoring device of the present application can meet the monitoring needs for the health status of a large number of steel cable group systems. The number of sensors required is small, the number of channels occupied is small, and the size is compact.

[0021] 3. The non-invasive prestressed steel cable group system health status monitoring device of the present application does not destroy the original structure of the steel cable and will not cause any impact on the health status of the steel cable group system.

[0022] 4. The non-invasive prestressed steel cable group system health status monitoring device of the present application can qualitatively determine whether the steel cable group needs to be re-tightened. If only one steel cable has prestressed relaxation, its position can be determined. Furthermore, by increasing the number of strain sensors, multiple prestressed steel cables can be located. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0024] Figure 1 A schematic diagram of the mold for this application;

[0025] Figure 2 This is a schematic diagram of the overall structure of the mold in this application when it is working;

[0026] Figure 3 The working diagram of the monitoring device for this application;

[0027] Figure 4 A schematic diagram of a fiber Bragg grating strain sensor according to the present application;

[0028] Figure 5 This is a schematic diagram of the fiber Bragg grating temperature sensor of the present application.

[0029] The components in the figure are marked as follows:

[0030] 1-1, cable bayonet; 1-2, mounting nut; 1-3, glue injection nozzle; 1-4, positioning wire rope; 2-1, cable group; 2-2, fiber Bragg grating strain sensor; 2-3, fiber Bragg grating temperature sensor; 3-1, sleeve; 4-1, first metal capillary 1; 4-2, first fiber Bragg grating; 5-1, second metal capillary; 5-2, second fiber Bragg grating. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0032] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0033] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0035] refer to Figure 1-Figure 5 The present application provides a non-intrusive prestressed steel cable group system health status monitoring device, comprising:

[0036] A sleeve 3-1, whose inner cavity is used to accommodate the steel cable group 2-1 to be monitored;

[0037] A plurality of fiber grating strain sensors 2-2 are arranged on the sleeve 3-1 around the axis of the sleeve 3-1 and used to collect the change of strain borne by the sleeve 3-1 due to the tension of the steel cable;

[0038] The fiber grating temperature sensor 2-3 is used to collect the temperature change of the above-mentioned steel cable group 2-1.

[0039] The above monitoring device, when it is necessary to implement the monitoring operation, converts the tension of the steel cable into axial stress through the fiber Bragg grating strain sensor 2-2. The fiber Bragg grating strain sensor 2-2 can detect the change of the reflected wavelength to measure the tension change of the steel cable. Generally speaking, the closer the fiber Bragg grating strain sensor 2-2 is to the prestressed relaxation steel cable, the greater the wavelength drift. When the steel cable is subjected to the tension force, the sleeve 3-1 can withstand the tension of the steel cable and transmit the strain of the steel cable. The fiber Bragg grating strain sensor 2-2 is arranged at the detection point of the sleeve 3-1 to detect the strain change of the sleeve 3-1. The optical fiber strain sensors arranged on the sleeve 3-1 around the axis of the sleeve 3-1 can roughly determine the position of the stress relaxation of the steel cable based on the strain change of each sensor, thereby avoiding the deficiency of the number of fiber Bragg grating strain sensors 2-2 in the related art that directly determines the monitoring accuracy. Alternatively, the monitoring accuracy of the monitoring device of the present application does not depend on the number of fiber Bragg grating strain sensors 2-2, thereby reducing the number of fiber Bragg grating strain sensors 2-2.

[0040] In a typical implementation, the fiber Bragg grating strain sensor 2-2 and the fiber Bragg grating temperature sensor 2-3 are connected in series through a fiber optic fusion splicer to form a sensor network, and the sensor network is connected to a demodulator, which is connected to a host computer.

[0041] In this way, the fiber grating sensors all have different central wavelengths, so that after all the sensors are connected in series, a sensor network can be formed to achieve quasi-distributed measurement, and then multiple cable group 2-1 systems can be monitored simultaneously.

[0042] As a packaging method, the fiber grating strain sensor 2 - 2 includes a first metal capillary 4 - 1 and a first fiber grating 4 - 2 packaged by the first metal capillary 4 - 1 .

[0043] Here, in this packaging method, the grating is kept at the center of the metal capillary, and a packaging adhesive, preferably epoxy resin adhesive, is filled into the metal capillary using high pressure.

[0044] As a packaging method, the fiber grating temperature sensor 2 - 3 includes a second metal capillary 5 - 1 and a second fiber grating 5 - 2 packaged by the second metal capillary 5 - 1 .

[0045] Here, in this packaging method, the second optical fiber Bragg grating 5-2 is inserted into the metal capillary and the two ends are bonded. The second optical fiber Bragg grating 5-2 needs to be kept suspended in the metal capillary.

[0046] As an exemplary implementation of the sleeve 3 - 1 , the sleeve 3 - 1 is formed by injection molding using a potting glue as a raw material.

[0047] In this way, the steel cable group 2-1 is easily installed in the sleeve 3-1. Specifically, after the steel cable group 2-1 is installed in the sleeve 3-1, an outer template for injecting a potting glue is used to cover the outer surface of the steel cable group 2-1, and the positions of different steel cables of the steel cable group 2-1 are adjusted until the outer template can fit the steel cable well. At this time, the potting glue is injected into the inner cavity of the outer mold, and after the outer mold and the steel cable are demolded, it can be ensured that the molded sleeve 3-1 maintains good contact with the steel cable, thereby ensuring good contact between the fiber grating strain sensor 2-2 and the sleeve 3-1.

[0048] In order to facilitate the installation of the steel cable, a steel cable clamping opening 1-1 on the inner wall of the outer template and a glue injection nozzle 1-3 are provided on the outer template.

[0049] Therefore, it is convenient to inject the potting glue into the inner cavity of the outer template through the glue injection nozzle 1-3, and it is convenient to fix the steel cable through the steel cable clamping mouth 1-1 to prevent the steel cable from sliding when the potting glue is injected.

[0050] It is worth adding that the sensor is installed at the positioning position, and a high-pressure gas cylinder is used to inject the potting glue into the special mold through the glue injection nozzle 1-3 until the entire mold is filled. Wait for 48 hours, and remove the mold and the positioning wire rope 1-4 after the potting glue is completely cured. The potting glue can be a modified epoxy resin structural glue, which has the characteristics of strong shear resistance, aging resistance, seawater corrosion resistance, strong impact resistance, room temperature curing, good thixotropy, etc., and is preferably a potting type steel adhesive.

[0051] As for the demoulding of the outer template, it can be made of a non-stick material, preferably polytetrafluoroethylene.

[0052] In a typical embodiment, the mold further comprises positioning wire ropes 1-4 disposed at the ends of the outer template.

[0053] Thus, by positioning the steel wire rope 1-4, the fiber Bragg grating strain sensor 2-2 and the fiber Bragg grating temperature sensor 2-3 can be better positioned when installed relative to the steel cable group 2-1, preventing the fiber Bragg grating strain sensor from sliding and causing inaccurate measurement.

[0054] In a typical embodiment, the mold further comprises a mounting nut 1-2 for assembling and covering the two parts constituting the outer mold plate.

[0055] Thus, by installing the nuts 1-2, the two parts of the outer template can be disassembled, thereby improving the convenience of demoulding the outer template.

[0056] Now, the operation process of monitoring in this application is described in an application scenario of offshore wind turbine cable monitoring. It should be noted that this common implementation scheme cannot be used as a basis for understanding the essential feature identification of the technical problem claimed to be solved by this application, and it is only a demonstration.

[0057] Prestress monitoring of cable group 2-1 consisting of 31 cables with a diameter of 15.7 mm in the offshore wind turbine

[0058] S1: Encapsulate the fiber grating strain sensor 2-2. Insert the first fiber grating 4-2 into a customized metal capillary, preferably with an outer diameter-inner diameter of 3mm×0.5mm, adjust the optical fiber so that the first fiber grating 4-2 is located at the center of the first metal capillary 4-1, use a high-pressure glue injection tank to fill the first metal capillary 4-1 with epoxy resin glue, and after curing, the encapsulation is completed;

[0059] S2: Encapsulate the fiber grating temperature sensor 2-3. Extend the second fiber grating 5-2 into the customized metal capillary, adjust the position of the second fiber grating 5-2 to be in the center of the second metal capillary 5-1, keep the second fiber grating 5-2 suspended in the second metal capillary 5-1, bond the two ends, protect the part of the second fiber grating 5-2 extending out of the second metal capillary 5-1, and the encapsulation is completed.

[0060] S3: Install the mold made of polytetrafluoroethylene on the restraining section of the steel cable, clip the steel cable into the steel cable clip 1-1, and tighten the mounting nut 1-2.

[0061] S4: Use positioning wire ropes 1-4 to locate the installation position of the fiber Bragg grating sensor at the two ends of the mold, and install the fiber Bragg grating sensor.

[0062] S5: Protect the extended part of the optical fiber. Apply foam glue on the outer surface of the mold, which can seal the two ports after foaming.

[0063] S6: Use a high-pressure gas cylinder to pour the steel glue into the mold through the glue injection nozzles 1-3 until the entire cavity is filled. After 48 hours, the steel glue is solidified and the mold is removed.

[0064] S7: Use a fiber fusion splicer to weld all the optical fibers of the fiber grating sensors together, connect the sensors in series, insert a jumper at the end of the optical fiber, connect the demodulator, and connect to the host computer, and use the measurement system to monitor the sensor network.

[0065] S8: Use simulation software to simulate the stress relaxation of prestressed steel bars, and bind 31 steel cables to sleeve 3-1. The steel cables use No. 45 steel material parameters, and the sleeve 3-1 part uses Shanghai Hammer Company's HM-120 steel adhesive material parameters, with a tensile elastic modulus of 5.4G pa.

[0066] S9: According to the technical solution, the tension of the wind turbine cable is 5750KN, which is distributed to 31 cables. The force on each cable is 185.5KN, and the prestress tolerance is 8%, which is equivalent to 14.84KN. In the simulation, a load of 14.84KN is applied to the two cables respectively, and three paths are added to the model, which are the areas where the fiber grating strain sensors #FBG1, #FBG2, and #FBG3 are arranged, and the strain distribution is simulated and analyzed.

[0067] S10: The simulation results show that the strains of #FBG11, #FBG12, and #FBG13 are basically the same. The two ends are subjected to about 130 microstrains, and the middle stable area is subjected to about 13 microstrains. This is because the stressed steel bars are located in the center of sleeve 3-1, and the three FBG sensors are subjected to the same strain.

[0068] S11: The simulation results show that #FBG21 and #FBG22 have the same strain, with about 50 microstrains at both ends and about 7 microstrains in the middle stable area. #FBG23 has a larger strain, with about 980 microstrains at both ends and about 20 microstrains in the middle stable area. It can be seen that in the wind turbine cable system, the prestress relaxation of one of the cables will cause the sleeve 3-1 to produce strain, and the part close to the stressed cable has a larger strain.

[0069] S12: The results show that when the prestress of a single steel cable in the wind turbine cable system is relaxed by 8%, the strain change of the fiber Bragg grating sensor caused by it is higher than the monitoring limit of the fiber Bragg grating strain sensor 2-2. This solution can meet the monitoring and early warning needs of prestress relaxation of steel cables. In addition, the approximate location of the relaxed steel cable can be distinguished by the transmission strain measured by three fiber Bragg grating strain sensors 2-2 arranged at an angle of 120°.

[0070] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A non-intrusive prestressed steel cable group system health status monitoring device, characterized in that: include: A sleeve, the inner cavity of which is used to accommodate the steel cable group to be monitored; the sleeve is injection-molded using injection glue as a raw material; The mold for glue injection molding includes an outer mold plate for injecting the injection glue, and the outer mold plate is provided with a glue injection nozzle; A plurality of fiber grating strain sensors are arranged on the sleeve around the sleeve axis and used to collect the change of strain borne by the sleeve due to the tension of the steel cable. The plurality of fiber grating strain sensors are arranged at equal angles on the sleeve. According to the strain magnitude detected by the plurality of fiber grating strain sensors, the distance between the stressed steel bar and the plurality of fiber grating strain sensors can be determined. According to the distance between the stressed steel bar and the plurality of fiber grating strain sensors, the specific position of the stressed steel bar in the sleeve can be determined. The fiber grating temperature sensor is used to collect the temperature change of the steel cable group.

2. The monitoring device according to claim 1, characterized in that: The fiber Bragg grating strain sensor and the fiber Bragg grating temperature sensor are connected in series through a fiber optic fusion splicer to form a sensor network. The sensor network is connected to a demodulator, and the demodulator is connected to a host computer.

3. The monitoring device according to claim 1, characterized in that: The fiber grating strain sensor includes a first metal capillary and a first fiber grating encapsulated by the first metal capillary.

4. The monitoring device according to claim 1, characterized in that: The fiber Bragg grating temperature sensor includes a second metal capillary and a second fiber Bragg grating encapsulated by the second metal capillary.

5. The monitoring device according to claim 1, characterized in that: The mold used for glue injection molding comprises an outer template for injecting the injection glue, a steel cable clamp fixed on the inner wall of the outer template, and a glue injection nozzle is opened on the outer template.

6. The monitoring device according to claim 5, characterized in that: The mold also includes a positioning wire rope arranged at the end of the outer template.

7. The monitoring device according to claim 5, characterized in that: The mold also includes a mounting nut for assembling and covering the two parts constituting the outer mold plate.

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