Optical fiber measuring device for bolt axial force monitoring and optical fiber measuring system for bolt axial force monitoring

Abstract

This optical fiber measurement device (100) for monitoring the axial force of a bolt is provided with: an optical fiber (23) for measuring the strain of an object to be measured; an optical fiber attachment fixing body (25) having an optical fiber attachment nut (21S) to which an optical fiber (23) is attached by changing the shape of the outer peripheral portion of the nut (21) related to at least one combination of the plurality of sets of bolts (20) and nuts (21); and an optical fiber strain distribution measurement unit (24) that measures the circumferential strain distribution of the optical fiber attachment nut (21S) generated by the bolt axial force along the optical fiber (23) attached to the outer peripheral surface of the optical fiber attachment nut (21S), and that measures the circumferential strain and the circumferential strain distribution of the optical fiber attachment nut (21S) in advance by means of the optical fiber strain distribution measurement unit (24). An optical fiber (23) is installed at a specified axial position corresponding to the circumferential strain value or the circumferential strain distribution measured in advance, and the bolt axial force is monitored.

Description

Technical Field

[0001] This disclosure relates to an optical fiber measuring device and an optical fiber measuring system for monitoring bolt axial force. Background Technology

[0002] As usage records of wind turbines used in wind power generation accumulate, problems arising from long-term use are gradually being identified. For example, during the operation of wind turbine facilities, blades (winglets) may fall off or break, with 20% to 30% of turbines experiencing damage over a 10-year period. Analysis of the causes of this damage revealed that a significant proportion of the problems stemmed from loose bolts at the joints between the blades and the nacelle (the blade mounting structure) and between the nacelle and the tower (the nacelle support structure), which are used to secure the turbine's components. Furthermore, the decrease in axial force on the bolts due to loose bolts was a particular concern in the analysis of the damage causes (see, for example, non-patent literature 1 and 2).

[0003] Therefore, it is necessary to measure bolt axial force and other parameters through spot checks or inspections to confirm the installation status of bolts at the joints, in order to prevent bolt loosening (decreased axial force), breakage, etc., and to detect such occurrences as early as possible. In addition, to improve the situation of bolt loosening, regular spot checks are also required in addition to the initial spot checks of wind power generation equipment.

[0004] Therefore, in view of this situation, in recent years, guidelines for periodic inspection of wind power generation equipment have also been developed (see Non-Patent Literature 3).

[0005] On the other hand, inspecting and confirming whether these bolts are loose or broken is very costly, which has become a major issue affecting the profitability of wind power generation. The total number of bolts used in the joints of the aforementioned wind turbines can sometimes exceed 50 per joint. Therefore, it is currently difficult to conduct a full inspection of the bolt installation status, including axial force, at joints during regular inspections. Especially for offshore equipment, how to integrate wind power generation equipment has become an urgent issue to be addressed from both safety and economic perspectives.

[0006] While wireless methods exist for measuring bolt axial force (e.g., see Non-Patent Document 4), they utilize nuts with special mechanisms and dynamically deformable shapes, making them unsuitable for ordinary nuts. Furthermore, conventional methods for managing the axial torque of bolts used in wind power equipment are not applicable to the entire equipment, but only to individual inspections (see Non-Patent Document 5).

[0007] Existing technical documents

[0008] Non-patent literature

[0009] [Non-Patent Document 1] "Investigation Report on Bolt Damage of Unit 1 and Unit 3 of Taikoyama Wind Power Station, Kyoto Prefecture", May 29, 2014. [online], [Searched on September 25, Reiwa 5], Internet <URL:https: / / www.meti.go.jp / shingikai / sankoshin / hoan_shohi / denryoku_anzen / newenergy_hatsuden_wg / pdf / 003_01_01.pdf>.

[0010] [Non-Patent Document 2] "Fragmentation of Blade Mounting Bolts at No. 3 Wind Turbine, Chubu Electric Power Co., Ltd. Omaezaki Wind Power Plant (Final Report)", July 30, 2015. [online], [Searched on September 25, Reiwa 5], Internet <URL:https: / / www.meti.go.jp / shingikai / sankoshin / hoan_shohi / denryoku_anzen / newenergy_hatsuden_wg / pdf / 007_04_00.pdf>.

[0011] [Non-Patent Document 3] Japan Electric Power Association, Power Generation and Transformation Division, "Guidelines for Periodic Inspection of Wind Power Generation Equipment", JEAG 5005-2017, pp. 11, 15, 16, 20, 22, 24, 27, 31, April 1, 2019 (First Edition)

[0012] [Non-Patent Document 4] NRJ_LST Product Catalog, [online], [searched on September 25, 2006], Internet <URL:https: / / www.nord-lock.com / globalassets / mediavalet / web-assets / downloads / brochure / 00297_sb_lst_4-pager-jp-web.pdf>.

[0013] [Non-Patent Document 5] NejiLaw Catalog, [online], [searched on September 25, 2006], Internet <URL:https: / / www.nejilaw.com / special_smartNeji.html>.

[0014] [Non-Patent Document 6] Technical Report "Definition of the IEA Wind 15-Megawatt Offshore Reference Wind Turbine", IEA Wind TCP Task 37, pp. 25-28, March 2020.

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Application Publication No. 2010-216877 Summary of the Invention

[0017] The technical problem that the invention aims to solve

[0018] As explained above, in the past, each blade in wind power equipment used 80 to 300 bolts. Therefore, in the case of three blades, the number of bolts used reached 200 to 900.

[0019] Regarding bolt axial force, from a technical perspective, it is necessary to conduct a full inspection of all bolts in use every six months. However, the regulations for wind power generation equipment used on land only require an annual inspection of 20% of the total number of bolts.

[0020] In addition, offshore wind power equipment faces increased operating costs and more stringent conditions (reduced inspection frequency) during severe weather.

[0021] Furthermore, regarding the inspection accuracy in quantitative checks, there has been a previous issue of insufficient accuracy in detecting bolt loosening. For example, there is a method using ultrasonic waves to measure the axial force of bolts, but this method has a measurement error of more than 10%.

[0022] Furthermore, in qualitative inspections, the primary method for checking loose bolts is currently visual inspection. Additionally, drones can be used for offshore operations, but even with drones, the fundamental nature of the measurement remains visual inspection; this point remains unchanged.

[0023] The purpose of this disclosure is to provide a technology related to the inspection and maintenance of wind power generation equipment for solving the above-mentioned problems. The bolt axial force and other measuring systems used in this inspection are capable of self-maintenance and can automatically inspect the installation status of all bolts used in the constituent equipment of the wind power generation equipment, including the axial force, even at a distance.

[0024] Technical means for solving technical problems

[0025] In the fiber optic measurement system for monitoring bolt axial force disclosed herein, The object is fixed by a fastener consisting of multiple sets of bolts and nuts, and the axial force generated in the bolts is monitored using optical fibers, including... Optical fiber, used to measure the strain of the object being measured; An optical fiber mounting fixture that modifies the shape of the nut involved in at least one combination of a plurality of standard bolts and nuts, such that the optical fiber is mounted on the outer periphery of the nut, thereby having an optical fiber mounting nut with the optical fiber mounted; and The fiber optic strain distribution measurement unit measures the circumferential strain distribution of the fiber optic mounting nut along the fiber optic cable mounted on the outer peripheral surface of the fiber optic mounting nut, caused by the axial force of the bolt. The circumferential strain and circumferential strain distribution of the optical fiber mounting nut are pre-measured by the optical fiber strain distribution measurement unit, and the optical fiber is installed at a specified axial position corresponding to the pre-measured circumferential strain value or the circumferential strain distribution, thereby monitoring the axial force of the bolt.

[0026] Invention Effects

[0027] According to the fiber optic measurement system for monitoring bolt axial force disclosed herein, the measurement system is capable of self-monitoring and can automatically check the installation status, including axial force, of all bolts used in the constituent parts of a wind power generation device, even at long distances. Attached Figure Description

[0028] Figure 1 This is a block diagram illustrating an application example of the fiber optic measurement system for monitoring bolt axial force according to Embodiment 1.

[0029] Figure 2A It is used for explanation Figure 1 A diagram of the equipment structure of a windmill.

[0030] Figure 2B It is used for explanation Figure 2A A diagram showing the detailed connection between the blades and the hub inside section C.

[0031] Figure 3 This is a diagram illustrating an example of the fiber optic measuring device for monitoring bolt axial force according to Embodiment 1.

[0032] Figure 4A This is a diagram showing an example of a nut used as a fiber optic mounting fixture for a fiber optic measuring device for monitoring bolt axial force according to Embodiment 1.

[0033] Figure 4BThis is a diagram showing another example of a nut used as a fiber optic mounting fixture for a fiber optic measuring device for monitoring bolt axial force according to Embodiment 1.

[0034] Figure 4C This is a diagram showing another example of a nut used as a fiber optic mounting fixture for a fiber optic measuring device for monitoring bolt axial force according to Embodiment 1.

[0035] Figure 4D This is a diagram illustrating an example of the fiber optic mounting nut used in the fiber optic measuring device for monitoring bolt axial force according to Embodiment 1.

[0036] Figure 5 This is a block diagram illustrating a structural example of the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0037] Figure 6A This is a cross-sectional view illustrating an example of the structure of the cable used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0038] Figure 6B It means Figure 6A The diagram shows the components of a cable, i.e., an optical fiber bus.

[0039] Figure 7A This is a conceptual diagram of the dual-port module used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0040] Figure 7B This is a diagram illustrating an example of a dual-port module used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0041] Figure 7C This is a diagram illustrating another example of the dual-port module used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0042] Figure 8A This is a diagram illustrating the connection method of the dual-port module and optical fiber used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0043] Figure 8B This is a diagram illustrating an example of the connection between the dual-port module and the optical fiber used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0044] Figure 9 This is a diagram illustrating the relationship between the dual-port module used in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2 and the measurement data corresponding to the setting position of the fiber optic bus.

[0045] Figure 10This is a diagram illustrating the installation state of the optical fiber when the bolt axial force is measured simultaneously in the optical fiber measurement system for monitoring bolt axial force according to Embodiment 2.

[0046] Figure 11 This is a diagram illustrating the data management method in the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0047] Figure 12 This is a diagram illustrating a test apparatus used to measure the circumferential strain distribution generated on a nut to evaluate the axial force of a bolt.

[0048] Figure 13 It means through Figure 12 The graph shows the relationship between the fiber length (distance from the reference point) of the optical fiber wound on the nut of the test apparatus and the circumferential strain under the condition of changing the bolt axial force.

[0049] Figure 14 It is used to transfer by Figure 12 A diagram illustrating the common coordinate system used to compare the circumferential strain values ​​measured by the experimental setup with the analytical values ​​obtained using the FEM analysis model.

[0050] Figure 15 It is for use Figure 12 The graph compares the circumferential strain values ​​measured by the experimental setup with the circumferential strain values ​​obtained from the analytical model.

[0051] Figure 16 It is shown by Figure 12 The graph shows the measurement results of the relationship between bolt axial force and strain when the axial position of the nut is changed, measured by the test device.

[0052] Figure 17 It is shown by Figure 12 A figure illustrating an example of the measurement of strain change as bolt axial force increases using a test setup.

[0053] Figure 18 It is shown by Figure 12 A figure illustrating an example of the measurement of strain change when bolt axial force decreases using a test setup.

[0054] Figure 19 It is shown by Figure 12 The figure shows another example of the measurement of the strain change when the axial force of a bolt decreases, measured by the test apparatus.

[0055] Figure 20 This is a diagram illustrating an example of the structure of the fiber optic measurement system for monitoring bolt axial force according to Embodiment 3. Detailed Implementation

[0056] This disclosure relates to a measurement system for monitoring bolt axial force using optical fiber for the maintenance and inspection of wind turbines (including those for offshore wind power generation). Hereinafter, the content of this application will be described using the accompanying drawings, with examples of representative embodiments.

[0057] Implementation method 1.

[0058] use Figures 1-3 An application example of the fiber optic measuring device 100 for monitoring bolt axial force according to Embodiment 1 will be described.

[0059] Figure 1 This is a block diagram showing the overall structure of a wind power generation device, specifically an application example of the fiber optic measuring device 100 for monitoring bolt axial force according to Embodiment 1, namely, its use in offshore wind power generation.

[0060] exist Figure 1 The aforementioned wind power generation equipment includes: multiple wind turbines 1 serving as a floating offshore wind farm; a fixed body 2 consisting of a combination of bolts and nuts (not shown) used to fix the blades (wings) of the wind turbines 1 to the hub; a measuring optical fiber (not shown, to be described in detail below) wound around the nuts for dynamically (more than once per second) measuring the axial force change of the bolts; and a dynamic cable 5 (see reference) several hundred meters long, mostly located in the sea, for transmitting the measurement signals measured by the optical fiber to a measuring instrument station 9 set on land via a floating body connection 3 and a buoy 4. Figure 1 (The curve shown by the dashed line), etc.

[0061] The measurement signal transmitted from the floating substation 7 via the dynamic cable 5 is transmitted to the measurement instrument station 9 via the connection part 6 between the static cable and the dynamic cable located on the seabed, which is included in the wind power generation equipment, and the static cable 8 located on the seabed (approximately 30 km in length).

[0062] In addition, the ocean water depths where windmills 1 and floating substations 7 are installed are usually in the range of 50m to 200m, but it is expected that they will be set up in the deep sea at 3000m in the future.

[0063] As detailed below, the measuring instrument station 9 has a measurement signal analysis system that measures the Brillouin and Rayleigh backscattered light caused by the strain generated in the bolt, based on the bolt axial force measurement signal measured by optical fiber.

[0064] Therefore, a measuring device equipped with Brillouin and Rayleigh methods can measure the changes in temperature and strain in a distributed manner along the optical fiber by determining the frequency shift of the optical fiber measurement signal caused by the strain generated in the bolt, even when temperature and strain change simultaneously (see, for example, Patent Document 1).

[0065] Furthermore, while the above explanation uses the scenario of multiple wind turbines as an example, it is not limited to this; it could also be a single wind turbine. Additionally, the aforementioned optical fiber could be embedded in a power transmission line that provides electricity from the wind power generation equipment.

[0066] Furthermore, the power generation-related signals generated by the wind turbine 1 of the aforementioned wind power generation equipment are transmitted to the substation 10 via the aforementioned floating body connection 3, dynamic cable 5, buoy 4, cable connection 6, floating substation 7, and static cable 8, and then transmitted to the system 13, represented by iron towers, via the underground transmission cable 11 (tens of kilometers in length) and switch station 12. Therefore, the aforementioned dynamic cable 5 and static cable 8 are sometimes collectively referred to as transmission lines below. In this case, the transmission line incorporates optical fibers that combine bolt axial force measurement and communication functions.

[0067] Next, use Figure 2A , Figure 2B The main equipment structure of the wind turbine 1 of the wind power generation equipment using the fiber optic measurement device for bolt axial force monitoring according to Embodiment 1 will be described here. Figure 2A It is used for explanation Figure 1 A diagram of the windmill's equipment structure. Figure 2B It is used for explanation Figure 2A A diagram showing the detailed connection between the blades and the hub inside section C.

[0068] like Figure 2A As shown, generally speaking, a wind turbine 1 mainly consists of four devices: blades 15 that rotate in the wind, a hub 16 that connects the blades to the rotating shaft, a nacelle 17 that houses the speed increaser and generator connected from the hub 16 through the rotating shaft, and a tower 18 that supports the nacelle 17.

[0069] And, as Figure 2B As shown, the joint 22 between the blade 15 and the hub 16 ( Figure 2A The fiber optic cable is fixed inside section C using a combination of bolts 20 and a nut 21S (described in detail below) for mounting the fiber optic cable.

[0070] Here, in the fiber optic measuring device for monitoring bolt axial force in Embodiment 1... Figure 2BMore specifically, the joint 22 between the blade 15 and the hub 16, shown as two donut-shaped discs in black and white, is secured using multiple sets of bolts 20 and fiber optic mounting nuts 21S, which combine bolts 20 and fiber optic mounting nuts 21S to which strain sensing fibers are mounted. In this case, the fixing body for securing the joint 22 is the fiber optic mounting fixing body 25. Furthermore, the joint 22 will also be referred to as the fixed body 22 below. Moreover, the joint between the blade and the hub is not limited to the blade-hub joint; the joint between the nacelle and the tower is also referred to as the joint 22 (or the fixed body 22).

[0071] Next, use Figure 3 The conceptual diagram illustrates the main structure of the fiber optic measuring device 100 for monitoring bolt axial force according to Embodiment 1.

[0072] exist Figure 3 In this configuration, the fixed body 22 is secured by the aforementioned fiber optic mounting fixture 25. In this case, the fixed body 22 is secured by applying an axial load, i.e., axial force (also called bolt axial force), through a combination of bolts 20 (the bolt shaft is indicated by the dashed line) constituting the fiber optic mounting fixture 25 and fiber optic mounting nuts 21S. The fiber optic mounting nut 21S has an outer diameter that is approximately the same as, but slightly smaller than, the outer diameter of the nut, the diameter of the axial central portion of the outer circumference of the fiber optic mounting diameter (the diameter of the fiber winding portion). Furthermore, in addition to including the standard-specification bolts 20 and fiber optic mounting nuts 21S, the aforementioned fiber optic mounting fixture 25 sometimes also partially includes a combination of standard-specification bolts 20 and standard-specification nuts 21. Additionally, for reference, a top view of the bolt 20 is shown above it, and a bottom view of the fiber optic mounting nut 21S is shown below it. The circle indicated by the dashed line in this bottom view represents the aforementioned fiber optic mounting diameter.

[0073] Furthermore, on the outer periphery of the aforementioned fiber mounting nut 21S, in order to measure the circumferential strain generated on the nut by the bolt axial force, multiple turns of optical fiber 23 (see the following description) are wound around it. Figure 4D Furthermore, the signal measured by the wound optical fiber 23 is processed by the fiber strain distribution measurement unit 24 of the Rayleigh and Brillouin methods (the fiber strain distribution measurement unit 24 has a processor for calculation and a memory for data storage, the details of which will be described below), and the strain distribution of the nut with the wound optical fiber 23 at a specified position is obtained, thereby monitoring the axial force applied to the bolt.

[0074] Next, the following will use Figures 4A to 4D This section describes the nut structure used in the fiber optic mounting fixture 25 for installing the fiber optic nut 21S.

[0075] first, Figure 4AThis diagram illustrates the structure of nut 21a, which has a shape equivalent to a standard specification (e.g., an M30 nut) but with some shape modifications (a new groove, described below), to accommodate optical fibers. The top view is its plan view, and the bottom view is its front view. In the front view, the portion indicated by reference numeral E represents the nut body, and the portion indicated by reference numeral G represents the groove formed on the nut body for mounting the optical fiber. Only this groove differs from the structure of a standard specification nut. Furthermore, the groove is formed axially on the upper surface of the nut (the surface B that contacts the fixed body 22, see reference 21a). Figure 3 (of the "B").

[0076] Additionally, the dashed line shown in the top view represents the bottom surface of the aforementioned groove G. The bottom surface of groove G has a circular shape (outer periphery) with a diameter Dg, as shown in the figure. Furthermore, as shown in the front view, this groove is formed near the upper surface of the nut, with a width of Lg and a depth of (De - Dg) / 2. Here, De represents the size of the nut, Dr represents the nominal diameter of the nut, and Lw represents the thickness of the nut.

[0077] Next, we will use Figures 4B to 4D This section describes another nut structure used as a fiber optic mounting nut. First, regarding... Figure 4B , Figure 4C The nut shown is explained below.

[0078] Figure 4B , Figure 4C The nuts shown all have the same Figure 4A The nut 21a shown has the same thickness (Lw) and is the same as... Figure 4A A groove of the same or similar shape is formed on the surface B that contacts the fixed body 22, and a flange portion (flange portion) F (Da, Db > De) with an outer circumferential dimension larger than that of a nut of the same shape as the standard specification is formed on the upper surface side. In addition, the thickness dimension of this flange portion is Lf, which is thinner than the thickness dimension of a nut of the same shape as the standard specification is formed (Lf < Lw).

[0079] also, Figure 4B The nut 21b shown is identical in shape to the standard nut, except that the thickness of its lower portion is smaller. Additionally, Figure 4C In the nut 21c shown, the lower part has a frustum-shaped cone.

[0080] These nuts 21b and 21c, having flange portions (protruding flange portions), are expected to suppress bolt shaft breakage and other issues caused by circumferential strain in these portions.

[0081] Next, use Figure 4D For those with Figure 4A The optical fiber mounting nut 21Sa, on which the optical fiber is wound, is described.

[0082] Figure 4D This is a conceptual diagram of an optical fiber mounting nut 21Sa, which has a spiral groove with a width of 1 mm and a depth of about 0.3 mm formed on the cylindrical outer circumference of the nut. The optical fiber is wound in the groove along almost the entire length of the nut axis in a single turn or multiple turns. In addition, a waterproof membrane is applied to the surface of the optical fiber.

[0083] By using this type of fiber optic mounting nut as the fiber optic mounting fixture, the positive and negative crossover positions of the circumferential strain values ​​when the bolt axial force is relaxed can be accurately detected (details will be explained below). Furthermore, the fiber used for this application should be selected with high bending resistance and low connection loss.

[0084] Implementation method 2.

[0085] Next, use Figure 5 The block diagram illustrates a structural example of the measurement system of the fiber optic measurement system 101 for monitoring bolt axial force according to embodiment 2. In this diagram, dashed arrows represent electrical signal lines, and solid arrows represent optical signal lines. First, the relationships between the components indicated by arrow label a will be explained.

[0086] The fiber optic measurement system for monitoring bolt axial force disclosed herein includes: a monitoring, control, and management system 30, which is a computer with a processor and memory for monitoring, controlling, and maintaining wind power generation equipment; a fiber optic strain distribution measurement unit 24, which receives command signals from the monitoring, control, and management system 30 and issues signals to begin measuring the axial force of bolts, which are components of the wind turbine fixing body 2 (the signals include command signals to measure the circumferential strain distribution generated by a specified nut among the nuts set to the aforementioned special shape); an optical switch 31, which designates the measurement location of the axial force of the wind turbine fixing body 2 and, together with the signal from the fiber optic strain distribution measurement unit 24, switches and outputs a command signal for selection control when monitoring multiple wind turbines separately; a transmission line embedded fiber optic cable 32, which receives signals from the optical switch 31 and has fibers embedded in the aforementioned transmission line; and a monitoring fiber optic cable, which receives signals from the transmission line embedded fiber optic cable 32, and all these components are configured in a single-path continuous connection manner for measuring the designated measurement location. The signal from the monitoring fiber optic cable 33 of this single-path continuous connection method uses a flexible fiber optic cable 34 for optical communication between the tower and blades of the wind turbine, for example, via the platform nacelle 35 (also called the base nacelle 35), a device in the wind turbine's constituent equipment that connects the fixed and rotating equipment, extending to the rotary joint 36 for connection with the rotating blades, and then connected to the axial force monitoring fiber optic cable 23 via the blade monitoring fiber optic cable 37. Here, the aforementioned platform nacelle 35 is a nacelle with a unique shape for improving the power generation efficiency of the wind turbine.

[0087] Next, the relationship between the constituent elements indicated by arrow b will be explained, taking into account the structural example of the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2.

[0088] The signal of the circumferential strain of the nut, generated by the axial force applied to the bolt, which is a component of the wind turbine fixing body 2, is detected by the aforementioned axial force monitoring optical fiber 23 and transmitted sequentially to the blade monitoring optical fiber 37, rotary joint 36, platform nacelle 35, flexible optical fiber cable 34, monitoring optical fiber 33 in a single continuous connection mode, and transmission line built-in optical fiber 32. Finally, via optical switch 31, it is sent to the optical fiber strain distribution measurement unit 24. The optical fiber strain distribution measurement unit 24, which receives the signal of the circumferential strain of the nut, includes a processor and a memory. Using the Brillouin method or Rayleigh method, it calculates the circumferential strain of the fixing part (fixed body), the object to be monitored, and corresponds it to the required measurement points, stores the result in the memory, and sends the necessary data signals to the monitoring control and management system 30 according to the instructions of the monitoring control and management system 30. Furthermore, the monitoring control and management system 30 also stores the data transmitted from the aforementioned optical fiber strain distribution measurement unit and monitors the axial force of the bolt based on the stored data.

[0089] In addition, an example of the monitoring fiber optic cable 33 for the above-mentioned single-path continuous connection method will be specifically described below with accompanying drawings. As mentioned above, in wind power generation equipment, each blade uses dozens or more bolts, and it is difficult to consider the inspection of such a large number of bolts as sufficient.

[0090] Therefore, to improve this situation, it is necessary to improve the inspection method. To achieve this goal, the following will use... Figures 6A to 11 A fiber optic measurement system for simultaneously measuring bolt axial force is described. By implementing such a system, bolt inspection time can be reduced, allowing for the inspection of a larger number of bolts even during routine inspections.

[0091] First, regarding an example of the hardware for implementing the fiber optic measurement system for monitoring bolt axial force as described in Embodiment 2 above, using... Figures 6A to 8B Please provide an explanation. Figure 6A , Figure 6B This is a diagram illustrating the fiber optic bus, which is the first component among the main components of the hardware for implementing the fiber optic measurement system for monitoring bolt axial force according to Embodiment 2. Figure 7A , Figure 7B , Figure 7C This is a diagram illustrating the dual-port module, which is the second component among the main components of the aforementioned hardware. Figure 8A , Figure 8B This is a diagram illustrating the connection methods of the two main components mentioned above, along with representative connection examples.

[0092] First, regarding the fiber optic bus 53, which is the first constituent element, using Figure 6A , Figure 6B Please provide an explanation. Figure 6A This is a cross-sectional view of a cable 50 (also called a transmission line 50) with a transmission cable 51 disposed in the center. Additionally, Figure 6B This will be explained in detail below. Figure 6A An enlarged perspective view of the detailed structure of the fiber optic bus 53 shown.

[0093] In Figure 6A In this cable 50, multiple fiber optic buses 53, each containing multiple internal optical fibers 23, are arranged around its outer periphery. These fiber optic buses 53 are configured to be sandwiched between multiple armored wires 52. Additionally, as... Figure 6B As shown, multiple optical fibers 23 (optical fibers F1 and F2 shown in the figure) are arranged on the outermost periphery of the optical fiber bus 53.

[0094] Next, regarding the two-port module, which is the second component, we will use... Figure 7A , Figure 7B , Figure 7C Please provide an explanation.

[0095] first, Figure 7A This is a conceptual diagram of a dual-port module. Figure 7A The two ports Pa and Pb are individually connected to the monitored objects such as nuts, blades, and cables, and have the following characteristics: they can be identified by connection ID (also simply called ID; here, ID is an abbreviation for identifier); both ports Pa and Pb are optical fibers of sufficient length for fusion splicing and can be identified by color, length, etc.; and the Brillouin and Rayleigh measurements performed in the factory are used as initial values ​​after the optical fiber is installed.

[0096] Next, Figure 7B A circumferential strain measurement module using a nut is shown as an example of a dual-port module, also having two different ports Pa and Pb.

[0097] also, Figure 7C Another example of a dual-port module is a blade deformation measurement module that uses the pressure side (PS side) and suction side (SS side) of the wind turbine blade as separate ports. These two ports are referred to as port Pp and port Ps, respectively.

[0098] exist Figure 5 In the fiber optic measurement system for monitoring bolt axial force shown, the aforementioned fiber optic bus and dual-port module will be referred to below as... Figure 8A Connected to each other in the manner shown, and in Figure 8B The method shown combines the fiber optic bus with modules, enabling monitoring on a module-by-module basis.

[0099] Figure 8A This diagram illustrates the connection method between the monitoring objects and the optical fibers when modularizing multiple monitoring objects such as nuts, blades, and cables, and using optical fibers as a monitoring means to measure and monitor the modular monitoring objects.

[0100] exist Figure 8A In the process, the optical fiber 23, located on the outer periphery of the optical fiber bus and extending outward from the optical fiber bus, connects to the two ports of the monitored object (e.g., port Pa and port Pb) at connection point C. P and C Q Combined at the same time.

[0101] Next, according to Figure 8B Provide a specific connection example. Figure 8B In the middle, an optical fiber is led out from the outer periphery of the optical fiber bus 53 (refer to...) Figure 6B The fiber optic cable F2 shown is used, for example, in a circumferential strain measurement module (module M1) such as a fiber optic mounting nut. (Refer to...) Figure 7B One port of ) through the above Figure 8AConnect and combine using the connection methods described in the document (refer to...). Figure 8B Connection point C shown FM ).

[0102] Furthermore, module M1 is connected to another point on fiber F2 via another port of module M1. Additionally, module M2 is connected to another point on fiber F2 that differs from both of the aforementioned points.

[0103] Next, connect the other port of module M2 to one port of module M3 (see reference). Figure 8B Connection point C shown MM Similarly, connect module M3 and module M4, and connect module M4 to fiber optic F2 at another point.

[0104] Thus, as Figure 8B As shown by the thick solid line, the optical path becomes a "single-path continuous connection". Using this single-path continuous connection, multiple modules that are the objects of monitoring can be monitored using a single optical fiber.

[0105] Figure 9 This diagram illustrates an example of monitoring multiple modules connected by a single, continuous optical fiber using the aforementioned combination method, showing the measured signals in each module in relation to their respective positions. In this diagram, the measured value of the Brillouin frequency, represented by the dashed curve, is compared with the measured values ​​of the modules labeled M1 to M4 and the optical fiber bus (in this...). Figure 9 In the diagram, the location of the fiber optic bus (abbreviated as "bus") is shown accordingly (indicated by a thick solid line).

[0106] As mentioned above Figure 9 As shown, the measured Brillouin frequencies exhibit step differences at each connection point. Furthermore, based on the characteristics of the curves in each module, correlation analysis can identify each module.

[0107] Furthermore, by using the methods described above, and by storing and analyzing the measured values ​​of the Brillouin frequency of the time series, it is possible to monitor the time-varying changes of multiple monitoring objects using a single optical fiber.

[0108] Figure 10 This diagram illustrates a specific example of mounting a single, continuously connected optical fiber onto multiple circumferential strain measurement modules, i.e., nuts. Figure 10 In the rectangular frame D surrounded by dotted lines, the elliptical group connected by straight lines and the straight lines protruding from the left and right ends are monitoring optical fibers 33 (refer to the above-mentioned single-path continuous connection method) constructed using optical fibers 23. Figure 5 An example of ).

[0109] Furthermore, for ease of explanation, an example is shown here in which the monitoring optical fiber 33 is constructed in a single continuous connection manner on only a number of nuts within the aforementioned elliptical group. However, this example is not limited to, and the monitoring optical fiber 33 in the single continuous connection manner can also be constructed on almost all of the nuts.

[0110] In addition, in Figure 10 The diagram shows a case where only the fiber optic mounting fixture 25, indicated by the dashed rectangle, is designated as the measurement object. That is, fixtures other than those shown by the dashed lines are not designated as measurement objects; therefore, in this case, only the appropriate portion needs to be selected from the measured signal.

[0111] Next, we will use Figure 11 A data management method is described for monitoring modules using the aforementioned single-path continuous connection method.

[0112] Figure 11 This example illustrates how physical quantities (e.g., circumferential strain) of multiple modules (M1 to M4) that are being managed are managed by the amount of change relative to their initial values, and how the magnitude of this change determines whether the modules being managed are normal or abnormal.

[0113] In Figure 11 In the table, the leftmost column represents fiber optic coordinates, such as the axial distance of the nut, which are assumed to be equally spaced coordinates. The top row represents the segment name, elapsed time, and other management item names. Here, Monitoring 1 represents elapsed time 1, Monitoring 2 represents elapsed time 2, and Monitoring 3 represents elapsed time 3; the larger the number, the longer the elapsed time.

[0114] Should Figure 11 It shows that, except for module 2 (M2), all other modules are normal regardless of the time elapsed, but module 2 shows an anomaly during monitoring phase 2 (e.g., the bolt axial force becomes loose).

[0115] Therefore, for module 2, it is shown that maintenance work (e.g., increasing the axial force of the fixing body and tightening it) was performed after time 2 of monitoring 2, and the result was that it returned to normal at time 3 of monitoring 3 (time 3). In addition, regarding module 2, since the maintenance work is expected to involve the replacement of bolts, nuts and other components, it is determined that the measurement position needs to be reset, that is, the coordinate distance of the fiber optic coordinates needs to be reset.

[0116] Next, use Figure 12 This describes the structure of a test apparatus used to measure the circumferential strain distribution generated by a nut. This apparatus is used to evaluate the axial force of the bolt, a component of the fixing body 2, in order to determine the aforementioned... Figure 3 , Figure 4DThe location where the groove of the fiber optic mounting nut is formed is shown.

[0117] Figure 12 This is a diagram showing the structure of a test apparatus in the fiber optic measuring device for monitoring bolt axial force according to Embodiment 1, which measures the circumferential strain distribution generated on the nut by the bolt axial force in order to evaluate the bolt axial force when fixing an object (also called the fixed body).

[0118] like Figure 12 As shown, this experimental setup includes a fiber optic strain distribution measuring instrument 40 capable of performing measurements using both the Brillouin and Rayleigh methods. By using this type of fiber optic strain distribution measuring instrument, even when the temperature and strain of the measured object change simultaneously, the changes in temperature and strain can be measured simultaneously (see, for example, Patent Document 1). Furthermore, the fiber optic strain distribution measuring instrument 40 includes a processor for computation and a memory for storing measurement signals.

[0119] The reason for using fiber optic distribution measurement instruments that employ both the Brillouin and Rayleigh methods is as described above. Figure 1 When laying static cables underground at the water depth shown, from the perspective of measurement accuracy, it may be necessary to consider not only the cable deformation caused by strain, but also the influence of cable deformation caused by temperature changes on the measurement signal.

[0120] As a method to confirm the corresponding location, temperature, deformation, or vibration signals are applied to that location, and the strain signal generated by the optical fiber strain distribution measuring instrument 40 is measured to confirm the location. In other words, after the optical fiber mounting fixture is installed on the fixed body, the position of that location can be confirmed at any time.

[0121] Here, as Figure 12 As shown, this test apparatus includes: an ultrasonic axial force meter 41 for confirming and verifying the axial force of the bolt; an ultrasonic transducer 42 for transmitting the ultrasonic signal from the ultrasonic axial force meter 41 with minimal attenuation; a bolt tensioner 43 capable of generating a high axial force in the bolt with high precision; a nut 44 with a fiber optic sensor (the fiber optic cable used here is approximately 10m long); and a temperature-compensated nut 45 (similar to the aforementioned nut 44 with a fiber optic sensor, it has a fiber optic cable wound around its outer circumference for temperature compensation). Furthermore, during the test, bolts 20 with the same nominal diameter as those used in actual windmill operation and standard-shaped nuts 21 are used as components of the fixing body 2. At this time, with... Figure 3 Similarly, in Figure 12 In this context, the surface that contacts the fixed object 22 is designated as surface B (refer to...). Figure 3 The "B" of the nut refers to the side of the nut opposite to surface B, which is called surface A.

[0122] Next, the measurement results obtained by this experimental setup will be used in sequence below. Figure 13 , Figures 15-19 An explanation will be provided here. Figure 13 This graph uses the bolt axial force as a parameter to represent the circumferential strain distribution detected by the optical fiber wound on the nut of this test apparatus. The horizontal axis represents the distance along the fiber-to-fiber plane (unit: m), and the vertical axis represents the circumferential strain value (unit: με). In this experiment, the bolt axial force varied from 0 to 300 kN (at... Figure 13 (The parameters are shown as experimental condition parameters).

[0123] like Figure 13 As shown, under the same axial force condition, the strain value on surface B is greater than that on surface A. Furthermore, there is a trend that the larger the axial force, the smaller the strain change. In other words, the strain generated on the nut is not linearly related to the axial force. It is also evident that even if the axial force changes, the position where the positive and negative strain values ​​cross (equivalent to a fiber length of approximately 10m) remains unchanged.

[0124] In addition, in this test setup, a total of 72 turns of optical fiber were wound on the nut 44 with the optical fiber sensor (each turn is about 141 mm long, and the resolution of the measuring instrument is set to less than half of one turn).

[0125] Next, the circumferential strain values ​​measured by this experimental setup will be compared with the analytical values ​​from the three-dimensional FEM analysis model. First, using... Figure 14 Explain the coordinate system used by both.

[0126] exist Figure 14 In this context, the axial distance of the nuts is represented by the coordinate Z (unit: mm). Here, the range of Z for comparison is 0 mm (equivalent to...). Figure 3 (B-side position) to 20mm (equivalent to) Figure 3 (The position of face A). Additionally, a circumferential coordinate θ is defined for comparing the two regarding the circumferential angle of the nut. In this comparison, θ = 0° is specifically compared (see below). Figure 15 (Data represented by black dots) and θ = 180° (see below) Figure 15 The value at the location indicated by the white dot in the text.

[0127] Next, use Figure 15 The circumferential strain values ​​measured by this experimental setup are compared with those obtained from the 3D model analyzed by FEM. The horizontal axis represents the axial distance (Z above, unit: mm). The vertical axis represents the circumferential strain value (unit: με).

[0128] In Figure 15The diagram shows the results of comparing two cases: setting the axial force to 300kN and the circumferential angle of the nut as described above, θ = 0° (measured value as solid line) and θ = 180° (measured value as dashed line).

[0129] Here, because the fiber diameter used in the experiment is 0.25 mm, it is possible for the first time to obtain the strain distribution of the nut's circumferential strain with a spatial resolution of 0.25 mm. Its characteristics are: regardless of the axial force, the circumferential strain at the nut contact end is positive (the nut undergoes expansion deformation), the circumferential strain at the nut free end is negative (the nut undergoes contraction deformation), and there is a zero-strain position at the midpoint (…). Figure 15 In the middle, the axial position (approximately 14mm) remains unchanged.

[0130] In this disclosure, a method for monitoring bolt axial force is developed using the characteristics of the aforementioned positive and negative circumferential strain distribution or the location of zero strain. The characteristics of the circumferential strain distribution of a nut vary depending on the nut size or specification, but if the nut size or shape is the same, its characteristics (positive and negative distribution of circumferential strain, location of zero strain) are considered constant. If the values ​​at each measuring point are actually measured when installing the bolt axial force strain distribution measuring device, it can be monitored as a management object.

[0131] In addition, as follows Figure 18 As described in the explanation, when the bolt axial force decreases, i.e., the bolt tightening force loosens, the aforementioned circumferential strain distribution will change significantly, and the position of the zero point where the positive and negative crossovers occur will change markedly compared to the previous situation. The reason for this is not yet clear, but it can be considered to be caused by a change in the friction state.

[0132] Here, to estimate the strain at a specified location, the result of spline interpolation of measurement data for every 50 mm is presented as the Z-value. The numerical analysis results are presented based on the FEM three-dimensional model. For example... Figure 15 As shown, it can be said that the two are of the same order of magnitude.

[0133] Based on the above explanation Figure 13 , Figure 15 The results show that, when using such Figure 4A When standard-sized or standard-shaped nuts are used to construct a fixed object, the strain magnitude will deviate depending on the axial position of the nut. This may result in portions of the bolt or nut bearing more than the rated load at specific axial positions, located on the side where the nut contacts the object being fixed during installation. Furthermore, this deviation in strain magnitude can sometimes cause cracks on the bolt shaft, thus requiring confirmation through inspection.

[0134] In other words, since the above-described issues are presumed to be the cause of bolt loosening and breakage, a solution is proposed to improve this situation by using a nut with a specially shaped outer perimeter as a component of the fixing body in the windmill. Specifically, the first suggestion is to use... Figure 4B and Figure 4C The nut shown is of a special shape.

[0135] Furthermore, the purpose of this disclosure is to monitor the loosening of bolt axial force in wind turbine equipment, etc., by measuring circumferential strain. Therefore, in order to determine the relationship between bolt axial force and circumferential strain, the measurement results obtained by changing the measurement position (in this case, the axial position of the nut) are presented below. Figure 16 .

[0136] Figure 16 In this study, the relationship between bolt axial force and circumferential strain was determined, particularly at the initial circumferential angular position (0°). Here, to estimate the circumferential strain at a specified location, the results of spline interpolation of measurement data for every 50 mm are shown. Furthermore, the same value as at the 0° position was also measured at the 180° angular position.

[0137] First, from this Figure 16 This also shows that regardless of the bolt axial force, the resulting circumferential strain value varies significantly depending on the axial position of the nut. Furthermore, it is evident that the circumferential strain value is greater at locations closer to the object being fixed on the nut's surface, i.e., where the axial force of the nut is smaller. In other words, measurements taken at these locations exhibit better sensitivity.

[0138] Furthermore, it is known that the strain generated in the nut is not linearly related to the bolt axial force, and the larger the axial force, the smaller the change in circumferential strain. In addition, as mentioned above, the difference in measured values ​​due to different circumferential measurement positions is almost imperceptible.

[0139] Furthermore, a positive circumferential strain value (measured at 2.02m, 6.96m, and 11.90m along the axial direction in this figure) indicates that the outer periphery of the nut has undergone expansion deformation, while a negative circumferential strain value (measured at 18.92m along the axial direction in this figure) indicates that the outer periphery of the nut has undergone contraction deformation.

[0140] Next, the relationship between the change in bolt axial force and the change in strain was investigated. First, for an increase in bolt axial force, the change in fiber length (measurement location) and circumferential strain were measured when the change in bolt axial force was set to 50 kN. Furthermore, since the detection of bolt loosening has been found to be crucial, to confirm the extent to which a change in bolt axial force would produce strain, the change in fiber length (measurement location) and circumferential strain were measured when the change in bolt axial force was set to 10 kN and 5 kN. The following uses... Figures 17-19 Explain these results.

[0141] first, Figure 17 The figure shows the measurement results of the change in circumferential strain when the bolt axial force increases. In this case, the change in bolt axial force is set as the range of bolt axial force changes when the bolt axial force decreases by a fixed value of 50 kN, and the range of the above axial force change parameter is set to 6 stages from 0 to 50 kN to 250 to 300 kN.

[0142] It can be determined that the strain change at position B is greater than the strain change at position A. Furthermore, it can be determined that the point where the positive and negative strain values ​​cross is at a fiber length of approximately 10m.

[0143] Next, use Figure 18 , Figure 19 The measurement results of strain change when bolt axial force decreases are explained.

[0144] Figure 18 In this experiment, the distribution of circumferential strain changes detected by the optical fiber wound on the nut of the nut was shown, using the range of bolt axial force variation when the reduction in bolt axial force was set to a fixed value of 10 kN as a parameter. In this experiment, the range of the aforementioned axial force variation parameter was 290–300 kN to 250–260 kN (within this...). Figure 18 (This is also shown as a parameter for axial force variation). Here, the strain variation along the longitudinal axis ranges from -40 με to 40 με. Furthermore, this... Figure 18 Setting the horizontal axis and Figure 13 The situation is the same, so the explanation is omitted here.

[0145] in addition, Figure 19 This is another example of a measurement showing the change in strain when the bolt axial force decreases, as measured by this test apparatus.

[0146] exist Figure 19 In this experiment, the range of bolt axial force variation when the reduction in bolt axial force is set to a fixed value of 5 kN is used as a parameter to show the distribution of circumferential strain variation detected by the optical fiber wound on the nut of this test apparatus.

[0147] In this experiment, the range of the parameters for the aforementioned axial force variation was from 245–250 kN to 225–230 kN (within this range). Figure 19 (This is also shown as a parameter for the variation of axial force).

[0148] In addition, Figure 19 The setting of the horizontal and vertical axes in the text and Figure 18 The situation is the same, so the explanation is omitted here.

[0149] like Figure 18 , Figure 19 As shown, it can be seen that the axial force decreases at position B (refer to...). Figure 12 The circumferential strain change at point B is less than that at point A (reference point). Figure 12 The value at point A).

[0150] In addition, from Figure 18 It can be seen that the intersection of positive and negative strain is independent of the parameters of axial force variation, and is located around 14m in length of the optical fiber. Furthermore, this location is significantly different from the location when the axial force increases. This indicates that there is a difference in the frictional force generated between the nut and the bolt relative to the axial force.

[0151] In addition, from Figures 18-19 It can be seen that the change in circumferential strain during axial force variation seems to correspond to the range (magnitude) of axial force variation. Based on the above, the detection accuracy of axial force variation is estimated to be around 5kN to 10kN.

[0152] Implementation method 3.

[0153] In embodiments 1 and 2, a system was proposed to improve bolt loosening by using an optical fiber mounting nut as a component of the fixing body. In the optical fiber measurement system 102 for monitoring bolt axial force in this embodiment 3, compared with existing maintenance checks, it is possible to achieve more accurate and reliable monitoring and maintenance of bolt axial force. The following uses... Figure 20 The system will be described.

[0154] exist Figure 20 In the process, the fixed body 22 is connected to the above-mentioned bolts 20 and... Figure 3 The fiber optic mounting nut 21S shown is used for fixing. An optical fiber 23 for measuring circumferential strain is wound around the outer circumference of the nut 21S. The signal generated by the strain occurring in the nut is detected by the optical fiber 23 and analyzed by the optical fiber strain distribution measurement unit 24 to determine the strain distribution, etc.

[0155] At this time, during the initial setting of fixing the fixed body by bolt 20 and fiber optic mounting nut 21S, the strain distribution and other data detected by the fiber optic 23 and analyzed by the fiber optic strain distribution measurement unit 24 are transmitted to a computer 26 that has a processor and memory and performs calculations on the input data and outputs the data. As needed, after calculations, the data is stored as the initial data of the strain distribution and other data in the first database (hereinafter referred to as the first DB).

[0156] Here, various axial forces of different magnitudes, as instructed by computer 26, are applied to bolt 20 via bolt tensioners or the like (not shown). The data when the axial force changes as a parameter are organized as a function of the bolt axial force and stored in the first database.

[0157] In addition, every few fixed periods after the initial setting by the computer 26, the circumferential strain values ​​of the fiber optic mounting nut 21S at various axial positions measured by the fiber optic strain distribution measurement unit 24 are separately stored and saved in the second database (hereinafter referred to as the second DB).

[0158] At this time, the aforementioned fixed periods are set to be shorter than the periodic inspection periods specified in the existing maintenance standards, and are stored and saved in the second database. Data related to these fixed periods are retrieved from the computer when measuring the circumferential strain at various axial positions of the aforementioned nuts, and are used when performing strain measurements.

[0159] Then, based on the circumferential strain data of each nut at each axial position measured after multiple fixed periods stored in the second database, the data is divided into independent circumferential strain data according to the nut shape during periodic inspections as specified by existing maintenance standards. The computer 26 calculates the estimated value for periodic inspections, stores it as maintenance data in the second database, and uses it as reference data during periodic inspections.

[0160] Furthermore, at predetermined intervals, the circumferential strain generated in the fiber optic mounting nut 21S is measured by the fiber optic strain distribution measurement unit, and this measured data is stored as time-related data in the measurement unit and the computer. Then, the computer compares the stored measured data with the initial data stored in the first database or the maintenance data stored in the second database, thereby enabling the development of a maintenance plan for the fixture.

[0161] This disclosure describes various exemplary embodiments and examples, but the various features, forms and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can be applied to the embodiment alone or in various combinations.

[0162] Therefore, numerous variations not illustrated can be conceived within the scope of the technology disclosed in this specification. For example, this could include variations, additions, or omissions of at least one component, or the extraction of at least one component and its combination with components of other embodiments. For instance, the above description assumes the optical fiber core is a single fiber, but it is not limited to this; the same effect can be achieved even with two or more cores.

[0163] Label Explanation

[0164] 1 Windmill, 2 Fixed body, 3 Floating body connection, 4 Buoy, 5 Dynamic cable, 6 Cable connection, 7 Floating body substation, 8 Static cable, 9 Measuring instrument station, 15 Blade, 16 Hub, 17 Nacelle, 18 Tower, 20 Bolt, 21, 21a, 21b, 21c Nuts, 21S, 21Sa Fiber optic mounting nuts, 22 Fixed body (joint), 23 Fiber optic (axial force monitoring fiber optic), 24 Fiber optic strain distribution measurement unit, 25 Fiber optic mounting and fixing body, 30 Monitoring, control and management system, 31 Optical switch, 32 Transmission line built-in fiber optic, 33 Monitoring fiber optic in single-channel continuous connection mode, 34 Flexible fiber optic cable, 35 Platform nacelle, 36 Rotary joint, 37 Blade monitoring fiber optic, 40 Fiber optic strain distribution measuring instrument, 41 Ultrasonic axial force gauge, 42 Ultrasonic transducer, 43 Bolt tensioner, 44 Nuts with fiber optic sensors, 45 Nuts for temperature compensation, 50 Cables, 51 Power transmission cables, 52 Armored wires, 53 Fiber optic buses, 100 Fiber optic measuring devices for monitoring bolt axial force, 101 and 102 Fiber optic measuring systems for monitoring bolt axial force, and M1, M2, M3, and M4 modules.

Claims

1. A fiber optic measuring device for monitoring bolt axial force, comprising fixing a fixed body composed of multiple sets of bolts and nuts, and using optical fibers to monitor the bolt axial force generated in the bolts, characterized in that, The fiber optic measuring device for monitoring bolt axial force includes: Optical fiber, used to measure the strain of the object being measured; An optical fiber mounting fixture that modifies the shape of the nut involved in at least one combination of the plurality of bolts and nuts, such that the optical fiber is mounted on the outer periphery of the nut, thereby having an optical fiber mounting nut with the optical fiber mounted; and An optical fiber strain distribution measurement unit measures the circumferential strain distribution of the optical fiber mounting nut caused by the axial force of the bolt along the optical fiber mounted on the outer peripheral surface of the optical fiber mounting nut. The circumferential strain and circumferential strain distribution of the optical fiber mounting nut are measured in advance by the optical fiber strain distribution measurement unit. Based on the pre-measured circumferential strain value or circumferential strain distribution, the optical fiber is installed at a specified axial position of the optical fiber mounting nut, thereby monitoring the axial force of the bolt.

2. The fiber optic measuring device for monitoring bolt axial force as described in claim 1, characterized in that, Based on the pre-measured circumferential strain distribution, the optical fiber is installed at a specified axial position on the optical fiber mounting nut. The circumferential strain distribution is measured by the optical fiber strain distribution measuring unit, and the position where the positive and negative strain values ​​of the circumferential strain distribution intersect is determined. Based on the change in the position where the positive and negative strain values ​​intersect, the axial force of the bolt is monitored.

3. The fiber optic measuring device for monitoring bolt axial force as described in claim 1 or 2, characterized in that, The nut in which the optical fiber is installed is cylindrical in shape, and the axial predetermined position of the optical fiber installed in the optical fiber mounting nut is set on the side of the fixed body on the upper and lower axial surfaces of the optical fiber mounting nut.

4. The fiber optic measuring device for monitoring bolt axial force as described in any one of claims 1 to 3, characterized in that, The optical fiber is configured and mounted on the fixing body in such a way that the axial force generated in the bolts of the fixing body, which is secured by multiple sets of bolts and the optical fiber mounting nut, is measured together.

5. A fiber optic measurement system for monitoring bolt axial force, comprising fixing a fixed body composed of multiple sets of bolts and nuts, and using optical fibers to monitor the bolt axial force generated in the bolts, characterized in that, The fiber optic measurement system for monitoring bolt axial force includes: Optical fiber, used to measure the strain of the object being measured; An optical fiber mounting fixture that alters the shape of the nut involved in at least one combination of the plurality of bolts and nuts, such that the optical fiber is mounted on the outer periphery of the nut, thereby having an optical fiber mounting nut with the optical fiber mounted. An optical fiber strain distribution measurement unit measures the circumferential strain distribution of the optical fiber mounting nut along the optical fiber mounted on the outer peripheral surface of the optical fiber mounting nut, which is generated by the axial force of the bolt. An optical fiber bus, disposed on the outer peripheral surface portion within a power transmission cable, having two or more of the aforementioned optical fibers internally; and A dual-port module that can be identified by an ID and can store physical quantities measured using the Rayleigh and Brillouin methods via an optical fiber located in the optical fiber bus. The optical fiber of the optical fiber bus is led out to the outside and connected to two different parts of the dual-port module. The circumferential strain and circumferential strain distribution of the optical fiber mounting nut are measured in advance by the optical fiber strain distribution measurement unit, and the measured data is stored in the dual-port module. The optical fiber is installed at a specified axial position on the optical fiber mounting nut based on the value of the circumferential strain or the circumferential strain distribution stored in the dual-port module, thereby monitoring the axial force of the bolt.

6. The fiber optic measurement system for monitoring bolt axial force as described in claim 5, characterized in that, include: A structural module for monitoring bolt axial force, which combines the fiber optic mounting nut with all the bolts of the fixing body composed of multiple sets of bolts and nuts, and fastens the fixed body by applying bolt axial force; A computer, which has a processor and memory, processes input data and outputs it; The first database includes a bolt tensioner that can set the bolt axial force of the bolt axial force monitoring structure module to a specified value when the fixed body is initially set, and measures the circumferential strain of each fiber optic mounting nut at each position in the axial direction relative to the bolt axial force when the bolt axial force is used as a parameter and changed within a specified range by the fiber optic strain distribution measurement unit, and stores the measured data as initial data. as well as A second database stores the circumferential strain values ​​of the fiber optic mounting nut at various axial positions after a fixed period from the initial setting, for maintenance purposes. This fixed period is shorter than the periodic inspection period specified by existing maintenance standards. At predetermined intervals, the circumferential strain generated in the nut is measured by the fiber optic strain distribution measurement unit, and the measured data associated with the elapsed time is stored in the fiber optic strain distribution measurement unit and the computer. The maximum axial force of each fiber optic mounting nut, calculated from the measured data stored in the computer, is compared with the maximum axial force of each fiber optic mounting nut corresponding to the initial data stored in the first database, or the maximum axial force of each fiber optic mounting nut corresponding to the maintenance data after the fixing period stored in the second database, thereby monitoring the fixing body.

7. The fiber optic measurement system for monitoring bolt axial force as described in claim 5 or 6, characterized in that, The fixed body is a component of a floating offshore wind farm, and the fiber optic strain distribution measurement unit is located at a distance of about 10 km or more from the floating offshore wind farm.

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