Wind driven generator thread structure monitoring device and method based on optical fiber sensing

Abstract

The invention provides a wind driven generator thread structure monitoring device and method based on optical fiber sensing, and the device comprises a thread structure, sensing optical fibers, a first spring, a second spring and a third spring, the structures and initial states of the first spring, the second spring and the third spring are the same, and each spring is uniformly provided with a sensing optical fiber segment along the coiling direction. The three sensing optical fiber sections are connected in series and then connected with the strain measurement system, the first spring and the second spring are symmetrically arranged on the upper side and the lower side of the tower, the first spring is arranged between the top end of a nut of the bolt and the nut side of the tower, the second spring is arranged between the bottom end of the nut and the nut side of the tower, and the third spring is arranged between the bottom end of the nut and a connecting plate at the bottom end of the bolt; and the strain measurement system determines the loosening condition of the thread structure and the temperature of the wind driven generator according to the measured dependent variable of each sensing optical fiber section. The loosening condition of the thread structure and the temperature of the wind driven generator can be accurately and simultaneously monitored through the sensing optical fiber, and the structure is simple.

Description

Technical Field

[0001] The invention belongs to the field of thread structure loosening monitoring, and in particular relates to a wind turbine thread structure monitoring device and method based on optical fiber sensing. Background Art

[0002] Threaded connections are widely used in the mechanical field due to their advantages such as reliable connection and easy installation and disassembly. However, in actual use, threaded connection structures may become loose due to factors such as vibration, impact, and corrosion, which will bring huge safety hazards to the mechanical structure. Therefore, it is very important to identify the degree of loose damage to the threaded structure. For the threaded structure used to fix the tower on the wind turbine, since the tower has a certain temperature, the temperature will affect the monitoring of the sensing optical fiber, and the temperature may change. Therefore, when using the existing threaded structure loosening monitoring device based on optical fiber sensing for monitoring, the monitoring accuracy of the loose threaded structure on the wind turbine is very low. Although there are optical fiber sensing devices that can detect temperature and strain at the same time, the structure is relatively complex and is not suitable for loose detection of threaded structures on wind turbines. Summary of the invention

[0003] The present invention provides a wind turbine thread structure monitoring device and method based on optical fiber sensing, so as to solve the problems that the existing thread structure loosening monitoring device based on optical fiber sensing has low monitoring accuracy due to the influence of wind turbine temperature, and the existing optical fiber sensing device that can simultaneously detect temperature and strain has a relatively complex structure and is not suitable for thread structure loosening detection.

[0004] According to a first aspect of an embodiment of the present invention, there is provided a wind turbine thread structure monitoring device based on optical fiber sensing, comprising a thread structure, a sensing optical fiber, and a first spring, a second spring, and a third spring having the same structure as that in an initial state, wherein the thread structure uses bolts and nuts thereof to fix a tower, sensing optical fiber segments are evenly distributed on each spring along its winding direction, and the three sensing optical fiber segments are connected in series and connected to a strain measurement system, wherein the first spring and the second spring are symmetrically arranged on the upper and lower sides of the tower, wherein the two ends of the first spring are respectively connected to the top of the nut of the bolt and the nut side of the tower, and the two ends of the second spring are respectively connected to the bottom end of the nut and the nut side of the tower, and a connecting plate is provided at the bottom end of the bolt, and the two ends of the third spring are respectively connected to the bottom end of the nut and the connecting plate; as the bolt loosens and rotates upward, the first spring stretches, and as the nut loosens and rotates downward, the second spring stretches, and the third spring contracts first and then stretches;

[0005] The strain measurement system measures the strain magnitude of each sensing optical fiber segment, and determines the looseness of the thread structure and the temperature of the wind turbine generator according to the measured strain magnitude of each sensing optical fiber segment.

[0006] In an optional implementation, a fourth spring is further included, on which a sensing optical fiber segment is arranged along its winding direction. The fourth spring has the same structure and initial state as the first spring, and is symmetrical with respect to the bolt. The two ends of the fourth spring are respectively connected to the top of the nut of the bolt and the side of the tower nut.

[0007] According to a second aspect of the present invention, a monitoring method for the above-mentioned wind turbine thread structure monitoring device is provided, and the strain measurement system performs the following steps:

[0008] Step S100, assuming that the magnitude of the strain of the sensing optical fiber segment under the influence of the monitorable wind turbine temperature range is a first magnitude, the magnitude of the strain caused by the loosening of the bolt and the loosening of the nut is a second magnitude, and the first magnitude is smaller than the second magnitude;

[0009] Step S200, for a vertically arranged threaded structure, determine whether only the temperature of the wind turbine generator has changed according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring, if so, execute step S300; otherwise, execute step S400;

[0010] Step S300, determining the wind turbine temperature of the thread structure in the circumferential direction of the wind turbine according to the strain of the sensing optical fiber segment on the first spring or the second spring, and executing step S500;

[0011] Step S400, determining the looseness of the thread structure and the wind turbine temperature of the thread structure in the circumferential direction of the wind turbine according to the strain of the sensing optical fiber segment on the first spring, the second spring and the third spring corresponding to the thread structure, and executing step S500;

[0012] Step S500: for the thread structure inclined in the circumferential direction on the wind turbine, determine the looseness of the thread structure according to the strain amounts of the sensing optical fiber segments on the first spring, the second spring and the third spring corresponding to the thread structure.

[0013] In an optional implementation, the step S200 specifically includes:

[0014] If the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the first magnitude, it means that only the temperature of the wind turbine generator has changed, and step S300 is executed;

[0015] If the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the second magnitude, it means that only the thread structure is loose, or the thread structure is loose and the temperature of the wind turbine also changes.

[0016] In another optional implementation, the strain amount in steps S200 and S300 is: the change of the strain measured this time compared with the strain measured last time of the corresponding sensing optical fiber segment; step S300 specifically includes:

[0017] The temperature difference of the wind turbine between this measurement and the last measurement is determined according to the strain of the sensing optical fiber segment on the first spring or the second spring; the temperature of the wind turbine determined last is added to the temperature difference of the wind turbine to obtain the circumferential temperature of the wind turbine where the threaded structure is located on the wind turbine.

[0018] In another optional implementation, the step S400 specifically includes:

[0019] Step S410: For a vertically arranged threaded structure, setting the bolt not to be tilted;

[0020] The strain ε of the sensing optical fiber segment on the first spring 1 is: 1 =ε 11 +ε 12 (1)

[0021] ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε 12 Indicates the strain of the sensing optical fiber segment on the first spring caused by the loosening and upward rotation of the bolt;

[0022] The strain ε of the sensing fiber on the second spring 2 is: 2 =ε 21 +ε 22 (2)

[0023] ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε 22 Indicates the strain of the sensing optical fiber segment on the second spring caused by the nut loosening and rotating downward;

[0024] The strain ε of the sensing optical fiber on the third spring 3 is: 3 =ε 21 -k 1 *ε 22 (3)

[0025] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0026] Step S420: Determine the conversion coefficient k between the strain of the sensing optical fiber segment on the first spring and the strain of the sensing optical fiber segment on the second spring under the influence of the temperature of the wind turbine according to the thickness of the tower and the thermal conductivity of the tower. 2 , so that ε 11 =k 2 *ε 21 (4);

[0027] Step S430: Solve the above formulas (1) to (4) to obtain ε 11 , ε 12 , ε 21 and ε 22 ;

[0028] Step S440, determine the total strain caused by the loosening of the thread structure: ε 12 +ε 22 , and the circumferential temperature ε of the thread structure on the wind turbine 11 and ε 21 .

[0029] In another optional implementation, the step S500 specifically includes: step S510, for the threaded structure of the wind turbine located in the circumferential direction, the bolt will be tilted, and it is assumed that the strain of the sensing optical fiber segment of the first spring and the second spring caused by the inclination of the bolt is the same, at this time, the strain of the sensing optical fiber segment of the first spring ε′ 1 for:

[0030] ε′ 1 =ε 11 +ε′ 12 +ε 13 (5)

[0031] where ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 Indicates the strain amount of the sensing optical fiber segment on the first spring caused by the inclination of the bolt;

[0032] The strain ε′ of the sensing optical fiber segment on the second spring 2 for:

[0033] ε′ 2 =ε 21 +ε′ 22 -ε 13 (6)

[0034] Where ε21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 represents the strain of the sensing optical fiber segment on the second spring caused by the loosening and downward rotation of the nut, -ε 13 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt;

[0035] The strain ε′ of the sensing optical fiber segment on the third spring 3 for:

[0036] ε′ 3 =ε 21 -k 1 *ε′ 22 (7);

[0037] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0038] Step S520: Solve the above formulas (5) to (7) to obtain ε′ 12 , ε′ 22 and ε 13 ;

[0039] Step S530: determine the total strain caused by the loosening of the bolts and nuts: ε′ 12 +ε′ 22 .

[0040] In another optional implementation, the step S500 also includes: for the threaded structure on the wind turbine that is inclined in the circumferential direction, determining the looseness of the bolts and nuts in the threaded structure and the inclination of the bolts according to the strain of the sensing optical fiber segment on the first spring, the second spring, the third spring and the fourth spring corresponding to the threaded structure.

[0041] In another optional implementation, the step S500 specifically includes:

[0042] Step S540: For the threaded structure inclined in the circumferential direction on the wind turbine, the bolts thereof will be inclined. Assuming that the strains of the sensing optical fiber segments of the first spring and the second spring caused by the inclination of the bolts are different, the strain ε′ of the sensing optical fiber segment of the first spring is 1 for:

[0043] ε′ 1 =ε 11 +ε′ 12 +ε 13 (8)

[0044] where ε11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 The strain of the sensing optical fiber section on the first spring caused by the inclination of the bolt;

[0045] The strain ε′ of the sensing optical fiber segment on the second spring 2 for:

[0046] ε′ 2 =ε 21 +ε′ 22 -ε 23 (9)

[0047] where ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 represents the strain of the sensing optical fiber segment on the second spring caused by the loosening and downward rotation of the nut, -ε 23 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt;

[0048] The strain ε′ of the sensing optical fiber segment on the third spring 3 for:

[0049] ε′ 3 =ε 21 -k 1 *ε′ 22 (10)

[0050] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0051] The strain ε′ of the sensing optical fiber segment on the fourth spring 4 for:

[0052] ε′ 4 =ε 11 +ε′ 12 -ε 13 (11)

[0053] Step S550: Solve the above formulas (8) to (11) to obtain ε′ 12 , ε′ 22 , ε 13 and ε 23 ;

[0054] Step S560: determine the total strain caused by the loosening of the bolts and nuts: ε′12 +ε′ 22 .

[0055] In another optional implementation, the strain amount in steps S400 and S500 is: the change of the strain measured this time compared with the strain measured for the first time of the corresponding sensing optical fiber segment.

[0056] The beneficial effects of the present invention are:

[0057] 1. The present invention arranges the sensing optical fiber segment on the bent spring, which can greatly increase the strain caused by the inclination of the bolts and the loosening of the bolts and nuts, so that the strain caused by the temperature and the strain caused by the loosening of the threaded structure are in completely different magnitudes. In this way, it can be determined whether the strain is only caused by the temperature change according to the magnitude of the strain detected by the sensing optical fiber segment; for a vertically arranged threaded structure, in addition to the first spring and the second spring for directly monitoring the loosening of the bolts and nuts, the present invention also arranges a third spring. By making the first spring and the second spring symmetrical with respect to the tower, the strain of the sensing optical fiber segment on the first spring under the influence of the temperature of the wind turbine can be There is a certain corresponding relationship between the variable and the strain of the sensing optical fiber segment on the second spring; by making the second spring and the third spring have the same structure and initial state, and making both of them connected to the top of the nut, and stretching or expanding as the nut loosens, it can be made that during the process of the nut loosening and rotating downward, there is a certain corresponding relationship between the strain of the sensing optical fiber segment on the second spring and the strain transformation of the sensing optical fiber segment on the third spring, and both of these corresponding relationships can be obtained through simulation. On this basis, the total strain caused by the loosening of the threaded structure and the circumferential temperature of the threaded structure on the wind turbine can be determined according to the strain on the three springs; it can be seen that the present invention can simultaneously monitor the loosening of the threaded structure and the temperature of the wind turbine, with high accuracy and simple structure;

[0058] 2. The present invention sets a fourth spring so that the fourth spring has the same structure and initial state as the first spring and is symmetrical with respect to the bolt. In this way, the strain of the sensing optical fiber segments on the first spring and the fourth spring caused by the temperature of the wind turbine is the same, the strain of the sensing optical fiber segments on the first spring and the fourth spring caused by the inclination of the bolt is the same in value but in opposite directions, and the strain of the sensing optical fiber segments on the first spring and the fourth spring caused by the loosening and rotation of the bolt is the same. Therefore, according to the strain of the sensing optical fiber segments on the first spring, the second spring, the third spring and the fourth spring, the loosening of the bolts and nuts in the threaded structure and the inclination of the bolts can be determined, so as to realize detailed monitoring of the loosening of the threaded structure and improve the accuracy of monitoring the loosening of the threaded structure;

[0059] 3. Since the probability of the screw being tilted in a vertically arranged threaded structure is very small, the present invention first determines whether the strain is only caused by the temperature change of the wind turbine generator according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring corresponding to the threaded structure. If so, the wind turbine generator temperature in the circumference of the threaded structure on the wind turbine generator is determined according to the strain. Otherwise, the looseness of the threaded structure and the wind turbine generator temperature in the circumference of the wind turbine generator are determined according to the strain of the sensing optical fiber segment on the first spring, the second spring and the third spring. Thereafter, for the threaded structure arranged obliquely in the circumference, its looseness is determined according to the strain of the sensing optical fiber segment on the second spring, the second spring and the third spring of the threaded structure. It can be seen that the present invention has the advantages of monitoring the looseness of the threaded structure. When the looseness of the thread structure and the temperature of the wind turbine are detected, the strain of the sensing optical fiber segment corresponding to the thread structure is not detected alone, but the strain of the sensing optical fiber segment corresponding to the vertical thread structure and the inclined thread structure located in the same circumferential direction of the wind turbine is combined, so that the looseness of the thread structure and the temperature of the wind turbine can be monitored simultaneously, and the monitoring method and structure are very simple; in addition, when determining the temperature of the wind turbine, the present invention is aimed at the vertically arranged thread structure, and according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring, it is judged whether the strain is only caused by the temperature change of the wind turbine. When it is determined that it is only caused by the temperature of the wind turbine, the temperature of the wind turbine is determined according to the strain on the sensing optical fiber segment, so that the strain caused by the temperature of the wind turbine can be distinguished more accurately;

[0060] 4. For a vertically arranged thread structure, the present invention determines that the strain obtained by this measurement is only caused by the temperature change of the wind turbine generator. When determining the wind turbine generator temperature in the circumferential direction of the thread structure on the wind turbine generator according to the strain, the strain measured this time is compared with the strain measured last time to obtain the strain. After obtaining the wind turbine generator temperature difference between this measurement and the last measurement according to the strain, the wind turbine generator temperature determined last time is added to the wind turbine generator temperature difference. In this way, the thread structure can be prevented from loosening before this measurement, which may affect the determination of the wind turbine generator temperature, thereby ensuring the accuracy of the wind turbine generator temperature determination.

[0061] 5. When judging whether the strain is caused only by the temperature change of the wind turbine, the present invention compares the strain measured this time with the strain measured last time to obtain the strain. Thus, when the strain measured this time is of the second order of magnitude compared with the initially measured strain, but the strain measured this time is of the first order of magnitude compared with the last measured strain, that is, compared with the last time, only the strain caused by the temperature change of the wind turbine occurs this time, it is possible to avoid the need to integrate the strains of the sensing optical fiber segments on the three springs to determine the looseness of the threaded structure, thereby improving the execution efficiency of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a schematic structural diagram of an embodiment of a wind turbine thread structure monitoring device based on optical fiber sensing of the present invention;

[0063] Figure 2 It is a schematic diagram of the arrangement of the sensing optical fiber segment on the spring of the present invention;

[0064] Figure 3 It is a schematic structural diagram of another embodiment of a wind turbine thread structure monitoring device based on optical fiber sensing according to the present invention;

[0065] Figure 4 It is a flow chart of an embodiment of a method for monitoring the thread structure of a wind turbine based on optical fiber sensing of the present invention. DETAILED DESCRIPTION

[0066] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0067] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0068] See also Figure 1 , is a schematic diagram of an embodiment of a wind turbine thread structure monitoring device based on optical fiber sensing according to the present invention. Figure 2As shown, the wind turbine thread structure monitoring device based on optical fiber sensing may include a thread structure, a sensing optical fiber 1, and a first spring 2, a second spring 3, and a third spring 4 with the same structure and initial state. The thread structure uses its bolts 11 and nuts 12 to fix the tower 5. Each spring is evenly provided with sensing optical fiber segments along its winding direction. The three sensing optical fiber segments are connected in series and connected to the strain measurement system. The first spring 2 and the second spring 3 are symmetrically arranged on the upper and lower sides of the tower 5. The two ends of the first spring 2 are respectively connected to the top of the nut 13 of the bolt 11 and the tower nut side 5. The two ends of the second spring 3 are respectively connected to the bottom end of the nut 12 and the tower nut side 5, the bottom end of the bolt 11 is provided with a connecting plate 14, and the two ends of the third spring 4 are respectively connected to the bottom end of the nut 12 and the connecting plate 14; as the bolt 11 loosens and rotates upward, the first spring 2 stretches, as the nut 12 loosens and rotates downward, the second spring 3 stretches, and the third spring 4 contracts first and then stretches; the strain measurement system measures the strain size of each sensing optical fiber segment, and determines the looseness of the threaded structure and the temperature of the wind turbine generator according to the measured strain amount of each sensing optical fiber segment.

[0069] In this embodiment, the first spring 2, the second spring 3 and the third spring 4 are all arranged obliquely relative to the tower, and buckles can be provided on the two free ends of the spring wire in the first spring 2, and slots can be provided at the corresponding positions on the side of the nut 13 of the tower 5 and at the outer edge of the top of the nut 13. During installation, the buckles on the two free ends of the first spring 2 can be respectively snapped into the slots on the side of the nut 13 of the tower 5 and the slots at the outer edge of the top of the nut 13. Similarly, buckles can be provided on the two free ends of the spring wire in the second spring 3, and slots can be provided at the corresponding positions on the side of the nut 12 of the tower 5 and at the outer edge of the bottom of the nut 12. During installation, the buckles on the two free ends of the second spring 3 can be respectively snapped into the slots on the side of the nut 12 of the tower 5 and the slots at the outer edge of the bottom of the nut 12. A vertical through hole 6 may be provided on the tower, and the sensing optical fiber segment on the first spring 2 may be connected to one end of the middle optical fiber segment, and the other end of the middle optical fiber segment may be connected to the sensing optical fiber segment on the second spring 3 after passing through the vertical through hole. The fixing position of the first spring 2 on the nut 13 side of the tower 5 and the fixing position of the second spring 3 on the nut 12 side of the tower 5 may be symmetrical with respect to the tower 5; the heights of the nut 13 and the nut 12 are equal, and the fixing position of the first spring 2 on the nut 13 and the fixing position of the second spring 3 on the nut 12 may be symmetrical with respect to the tower 5; the angles of the first spring 2, the second spring 3 and the third spring 4 relative to the tower 5 may be the same.

[0070] The two free ends of the spring wire in the third spring 4 may also be provided with buckles, and the connecting plate 14 may also be provided with a slot. During installation, the buckles on the two free ends of the third spring 4 may be respectively connected to the slots on the connecting plate and the slots at the outer edge of the bottom end of the nut 12. The slots at the outer edge of the bottom end of the nut 12 are used to connect the second spring 3 and the third spring 4. After the bolt passes through the bolt through hole, its bottom end may be fixedly connected to the connecting plate by a screw. The first spring 2, the second spring 3 and the third spring 4 may be on the same plane, and the second spring 3 and the third spring 4 may be located on the same inclined line.

[0071] It can be seen from the above embodiments that the present invention arranges the sensing optical fiber segment on the bent spring, which can greatly increase the strain caused by the inclination of the bolt and the loosening of the bolt and nut, so that the strain caused by the temperature and the strain caused by the loosening of the threaded structure are at completely different orders of magnitude. In this way, it can be determined whether the strain is only caused by the temperature change based on the order of magnitude of the strain detected by the sensing optical fiber segment. For a vertically arranged threaded structure, when determining the strain caused by the loosening of the threaded structure and the strain caused by the temperature change of the wind turbine, in addition to the first spring and the second spring for directly monitoring the loosening of the bolt and the nut, a third spring is also provided. By making the first spring and the second spring symmetrical with respect to the tower, the sensing optical fiber on the first spring can be made symmetrical under the influence of the temperature of the wind turbine. There is a certain corresponding relationship between the strain of the sensing optical fiber segment on the second spring and the strain of the sensing optical fiber segment on the second spring; by making the second and third springs have the same structure and initial state, and making both of them connected to the top of the nut, and both of them stretch or contract as the nut loosens, it can be made that during the process of the nut loosening and rotating downward, there is a certain corresponding relationship between the strain of the sensing optical fiber segment on the second spring and the strain transformation of the sensing optical fiber segment on the third spring, and both of these corresponding relationships can be obtained through simulation. On this basis, the total strain caused by the loosening of the threaded structure and the circumferential temperature of the threaded structure on the wind turbine can be determined according to the strain on the three springs; it can be seen that the present invention can simultaneously monitor the loosening of the threaded structure and the temperature of the wind turbine, with high accuracy and simple structure.

[0072] See also Figure 3 , is a schematic structural diagram of another embodiment of a wind turbine thread structure monitoring device based on optical fiber sensing according to the present invention. Figure 3 and Figure 1The difference between the illustrated embodiment is that the device may further include a fourth spring 7, on which a sensing optical fiber segment is arranged along the winding direction thereof, the fourth spring 7 has the same structure and initial state as the first spring 2, and is bilaterally symmetrical with respect to the bolt 11, and the two ends of the fourth spring 7 are respectively connected to the top of the nut 13 of the bolt 11 and the side of the nut 13 of the tower 5. Buckles may also be provided on the two free ends of the spring wire in the fourth spring 7, another clamping groove may also be provided on the tower nut side 5, and another clamping groove may be provided on the outer edge of the top of the nut 13. During installation, the buckles on the two free ends of the fourth spring 7 may be respectively clamped into the clamping groove on the tower nut side 5 and the clamping groove at the outer edge of the top of the nut 13. The sensing optical fiber segments on the first to fourth springs belong to the same sensing optical fiber.

[0073] It can be seen from the above embodiments that the present invention arranges the sensing optical fiber segment on the bent spring, which can greatly increase the strain caused by the inclination of the bolts and the loosening of the bolts and nuts, so that the strain caused by the temperature and the strain caused by the loosening of the threaded structure are at completely different orders of magnitude. In this way, it is possible to determine whether the strain is only caused by temperature changes based on the order of magnitude of the strain detected by the sensing optical fiber segment. For a vertically arranged threaded structure, when determining the strain caused by the loosening of the threaded structure and the strain caused by the temperature change of the wind turbine, in addition to the first spring and the second spring for directly monitoring the loosening of the bolts and nuts, the third spring is also provided. By making the first spring and the second spring symmetrical with respect to the tower, the sensing optical fiber segment on the first spring can be made symmetrical under the influence of the temperature of the wind turbine. There is a certain corresponding relationship between the strain amount and the strain amount of the sensing optical fiber segment on the second spring; by making the second spring and the third spring the same in structure, initial state and tilt direction, and making both of them connected to the top of the nut, and stretching or contracting as the nut loosens, it can be made that during the process of the nut loosening and rotating downward, there is a certain corresponding relationship between the strain amount of the sensing optical fiber segment on the second spring and the strain transformation of the sensing optical fiber segment on the third spring, and both of these corresponding relationships can be obtained through simulation. On this basis, the total strain amount caused by the loosening of the threaded structure and the circumferential temperature of the threaded structure on the wind turbine can be determined according to the strain amounts on the three springs; it can be seen that the present invention can simultaneously monitor the loosening of the threaded structure and the temperature of the wind turbine, with high accuracy and simple structure.

[0074] In addition, the present invention arranges a fourth spring so that the fourth spring has the same structure and initial state as the first spring and is symmetrical with respect to the bolt, so that the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the temperature of the wind turbine are the same, the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the inclination of the bolt are the same in value but opposite in direction, and the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the loosening and rotation upward of the bolt are the same. Therefore, according to the strain amounts of the sensing optical fiber segments on the first spring, the second spring, the third spring and the fourth spring, the loosening conditions of the bolts and nuts in the threaded structure and the inclination conditions of the bolts can be determined respectively, so as to realize the detailed monitoring of the loosening of the threaded structure and improve the accuracy of monitoring the loosening of the thread.

[0075] See also Figure 4 As shown, a flow chart of an embodiment of a method for monitoring the thread structure of a wind turbine based on optical fiber sensing of the present invention. The method may include a strain measurement system performing the following steps:

[0076] Step S100, assuming that the strain magnitude of the sensing optical fiber segment under the influence of the monitorable wind turbine temperature range is a first magnitude, the strain magnitude caused by the loosening and rotating upward of the bolt and the loosening and rotating downward of the nut to the sensing optical fiber segment is a second magnitude, and the first magnitude is smaller than the second magnitude.

[0077] For the threaded structure used to fix the tower, the factors causing strain detected by the optical fiber sensor are mainly four aspects: the strain caused by temperature change, the strain caused by the bolt tilting under gravity or external force after the threaded structure is loosened, the strain caused by the bolt rotating upward due to loosening, and the strain caused by the nut rotating downward due to loosening. Simply setting up sensing optical fiber segments for bolts and nuts separately cannot distinguish the factors causing the strain. To this end, the present invention designs springs so that each spring is arranged with a sensing optical fiber along its winding direction, and the first spring is arranged between the nut of the bolt and the nut side of the tower, so that the strain detected by the sensing optical fiber on the first spring includes the strain caused by temperature change, bolt tilt and bolt loosening; the second spring is arranged between the nut and the nut side of the tower, so that the strain detected by the sensing optical fiber on the second spring includes the strain caused by temperature change, bolt tilt and nut loosening; the present invention arranges the sensing optical fiber segment on the bent spring, which can greatly increase the strain caused by bolt tilt, bolt and nut loosening (that is, the strain caused by thread structure loosening), so that the strain caused by temperature and the strain caused by thread structure loosening are in completely different magnitudes, so that according to the magnitude of the strain detected by the sensing optical fiber segment, it can be determined whether the strain is only caused by temperature change.

[0078] Step S200: For a vertically arranged threaded structure, determine whether only the temperature of the wind turbine has changed according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring. If so, execute step S300; otherwise, it means that only the threaded structure has become loose, or the threaded structure has become loose and the temperature of the wind turbine has also changed, and execute step S400.

[0079] Since the bolts of a vertically arranged threaded structure rarely tilt, the present invention first determines whether the strain is only caused by the temperature change of the wind turbine according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring of the vertically arranged threaded structure. When it is determined that it is only caused by the temperature of the wind turbine, the temperature of the wind turbine is determined according to the strain on the sensing optical fiber. In this way, the strain caused by the temperature of the wind turbine can be distinguished more accurately.

[0080] Wherein, the step S200 may specifically include: if the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the first magnitude, it means that only the temperature of the wind turbine generator has changed, and step S300 is executed; if the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the second magnitude, it means that only the thread structure has loosened, or the thread structure has loosened and the temperature of the wind turbine generator has changed. The strain in step S200 may be: the change of the strain measured by the corresponding sensing optical fiber segment this time compared with the strain measured last time. When judging whether the strain is caused only by the temperature change of the wind turbine, the present invention compares the strain measured this time with the strain measured last time to obtain the strain. Thus, when the strain measured this time is of the second order of magnitude compared with the first time, but the strain measured this time is of the first order of magnitude compared with the last time, that is, compared with the last time, only the strain caused by the temperature change of the wind turbine occurs this time, it can be avoided that the strain of the sensing optical fiber segments on the three springs needs to be integrated to determine the looseness of the threaded structure, thereby improving the execution efficiency of the method.

[0081] Step S300, determining the wind turbine temperature of the threaded structure in the circumferential direction of the wind turbine according to the strain of the sensing optical fiber segment on the first spring or the second spring, and executing step S500.

[0082] The temperature of the wind turbine in the same circumferential direction is the same. Therefore, after determining the temperature of the wind turbine in the circumferential direction of the vertically arranged thread structure on the wind turbine, the temperature of the wind turbine corresponding to all the inclined thread structures in the circumferential direction can be determined.

[0083] Among them, the strain amount in the step S300 can be: the change of the strain measured this time by the corresponding sensing optical fiber segment compared with the strain measured last time; the step S300 can specifically include: determining the temperature difference of the wind turbine measured this time and last time according to the strain amount of the sensing optical fiber segment on the first spring or the second spring; adding the wind turbine temperature determined last time to the wind turbine temperature difference to obtain the circumferential wind turbine temperature of the threaded structure on the wind turbine. According to the present invention, for a vertically arranged threaded structure, after determining that the strain amount obtained in this measurement is only caused by the temperature change of the wind turbine, when determining the wind turbine temperature of the threaded structure in the circumferential direction of the wind turbine based on the strain amount, the strain measured this time is compared with the strain measured last time to obtain the strain amount, and after obtaining the temperature difference of the wind turbine between this measurement and the last measurement based on the strain amount, the wind turbine temperature determined last is added to the wind turbine temperature difference, so as to avoid loosening of the threaded structure before this measurement, which would affect the determination of the wind turbine temperature, thereby ensuring the accuracy of the wind turbine temperature determination.

[0084] Step S400, determine the looseness of the thread structure and the circumferential temperature of the wind turbine where the thread structure is located on the wind turbine according to the strain of the sensing optical fiber segment on the first spring, the second spring and the third spring corresponding to the thread structure, and execute step S500.

[0085] In this step, for a vertically arranged threaded structure, when it is determined that the strain obtained by this measurement is not caused only by the temperature change of the wind turbine, in order to distinguish the strain caused by the loosening of the threaded structure from the strain caused by the temperature change of the wind turbine, the present invention can set the bolt not to tilt. Therefore, the step S400 can specifically include:

[0086] Step S410: For a vertically arranged threaded structure, setting the bolt not to be tilted;

[0087] The strain ε of the sensing optical fiber segment on the first spring 1 It can be: 1 =ε 11 +ε 12 (1)

[0088] ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε 12 Indicates the strain of the sensing optical fiber segment on the first spring caused by the loosening and upward rotation of the bolt;

[0089] The strain ε of the sensing fiber on the second spring 2 It can be: 2 =ε21 +ε 22 (2)

[0090] ε21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε 22 Indicates the strain of the sensing optical fiber segment on the second spring caused by the nut loosening and rotating downward;

[0091] Since the second spring and the third spring have the same structure, initial state and tilt direction, both are connected to the top of the nut and stretch or contract as the nut loosens, it can be determined that during the process of the nut loosening and rotating downward, there is a certain correspondence between the strain of the sensing optical fiber segment on the second spring and the strain transformation of the sensing optical fiber segment on the third spring. Therefore, in the contraction stage of the third spring, the strain of the sensing optical fiber ε 3 It can be: 3 =ε 21 -k 1 *ε 22 (3)

[0092] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0093] Step S420: Determine the conversion coefficient k between the strain of the sensing optical fiber segment on the first spring and the strain of the sensing optical fiber segment on the second spring under the influence of the temperature of the wind turbine according to the thickness of the tower and the thermal conductivity of the tower. 2 , so that ε 11 =k 2 *ε 21 (4);

[0094] Step S430: Solve the above formulas (1) to (4) to obtain ε 11 , ε 12 , ε 21 and ε 22 ;

[0095] Step S440, determine the total strain caused by the loosening of the thread structure: ε 12 +ε 22 , and the circumferential temperature ε of the thread structure on the wind turbine 11 and ε 21 The strain amount in step S400 is: the change of the strain measured this time compared with the strain measured for the first time for the corresponding sensing optical fiber segment. The strain measured for the first time may be 0.

[0096] When determining the strain caused by the loosening of the threaded structure and the strain caused by the temperature change of the wind turbine for a vertically arranged threaded structure, the present invention provides a third spring in addition to the first spring and the second spring for directly monitoring the loosening of the bolts and nuts. By making the first spring and the second spring symmetrical with respect to the tower, a certain corresponding relationship can be established between the strain of the sensing optical fiber segment on the first spring and the strain of the sensing optical fiber segment on the second spring under the influence of the temperature of the wind turbine. By making the second spring and the third spring have the same structure, initial state and tilt direction, and making both connected to the top of the nut, and stretching or contracting as the nut loosens, a certain corresponding relationship can be established between the strain of the sensing optical fiber segment on the second spring and the strain transformation of the sensing optical fiber segment on the third spring during the process of the nut loosening and rotating downward. Both of these corresponding relationships can be obtained through simulation. On this basis, the total strain caused by the loosening of the threaded structure and the circumferential temperature of the threaded structure on the wind turbine can be determined according to the strain on the three springs.

[0097] Step S500: for the thread structure inclined in the circumferential direction on the wind turbine, determine the looseness of the thread structure according to the strain amounts of the sensing optical fiber segments on the first spring, the second spring and the third spring corresponding to the thread structure.

[0098] The step S500 specifically includes: step S510, for the threaded structure of the wind turbine located in the circumferential direction, the bolt will be inclined, and the strain of the sensing optical fiber segment on the first spring and the second spring caused by the inclination of the bolt is the same, at this time, the strain ε′ of the sensing optical fiber segment on the first spring 1 for:

[0099] ε′ 1 =ε 11 +ε′ 12 +ε 13 (5)

[0100] where ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 Indicates the strain amount of the sensing optical fiber segment on the first spring caused by the inclination of the bolt;

[0101] The strain ε′ of the sensing optical fiber segment on the second spring 2 for:

[0102] ε′ 2 =ε 21 +ε′ 22 -ε 13 (6)

[0103] where ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 represents the strain of the sensing optical fiber segment on the second spring caused by the loosening and downward rotation of the nut, -ε 13 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt;

[0104] The strain ε′ of the sensing optical fiber segment on the third spring 3 for:

[0105] ε′ 3 =ε 21 -k 1 *ε′ 22 (7);

[0106] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0107] Step S520: Solve the above formulas (5) to (7) to obtain ε′ 12 , ε′ 22 and ε 13 ;

[0108] Step S530: determine the total strain caused by the loosening of the bolts and nuts: ε′ 12 +ε′ 22 .

[0109] In the above steps, when determining the looseness of the inclined threaded structure, the strain of the sensing optical fiber segments on the first spring and the second spring caused by the inclination of the bolt is considered to be the same, but in fact the two are not the same, so the monitoring accuracy of the looseness of the threaded structure obtained in the above steps is low. In order to improve the monitoring accuracy, the present invention introduces a fourth spring, and the step S500 also includes: for the inclined threaded structure on the wind turbine located in the circumferential direction, according to the strain of the sensing optical fiber segments on the first spring, the second spring, the third spring and the fourth spring corresponding to the threaded structure, determine the looseness of the bolts and nuts in the threaded structure and the inclination of the bolts. At this time, the step S500 may specifically include:

[0110] Step S540: For the threaded structure inclined in the circumferential direction on the wind turbine, the bolts thereof will be inclined. Assuming that the strains of the sensing optical fiber segments of the first spring and the second spring caused by the inclination of the bolts are different, the strain ε′ of the sensing optical fiber segment of the first spring is 1 for:

[0111] ε′ 1 =ε 11 +ε′ 12 +ε 13 (8)

[0112] where ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 The strain of the sensing optical fiber section on the first spring caused by the inclination of the bolt;

[0113] The strain ε′ of the sensing optical fiber segment on the second spring 2 for:

[0114] ε′ 2 =ε 21 +ε′ 22 -ε 23 (9)

[0115] where ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 Indicates the strain of the sensing optical fiber segment on the second spring caused by the loosening and downward rotation of the nut, --ε 23 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt;

[0116] The strain ε′ of the sensing optical fiber segment on the third spring 3 for:

[0117] ε′ 3 =ε 21 -k 1 *ε′ 22 (10)

[0118] where k 1 Indicates the conversion coefficient between the strain of the sensing optical fiber section on the third spring and the strain of the sensing optical fiber section on the second spring caused by the loosening and upward rotation of the nut;

[0119] The strain ε′ of the sensing optical fiber segment on the fourth spring 4 for:

[0120] ε′ 4 =ε 11 +ε′ 12 -ε 13 (11)

[0121] Step S550: Solve the above formulas (8) to (11) to obtain ε′ 12 , ε′22 , ε 13 and ε 23 ;

[0122] Step S560: determine the total strain caused by the loosening of the bolts and nuts: ε′ 12 +ε′ 22 The strain amount in step S500 is: the change of the strain measured this time compared with the strain measured for the first time for the corresponding sensing optical fiber segment.

[0123] The present invention arranges a fourth spring so that the fourth spring has the same structure and initial state as the first spring and is symmetrical with respect to the bolt, so that the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the temperature of the wind turbine are the same, the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the inclination of the bolt are the same in value but opposite in direction, and the strain amounts of the sensing optical fiber segments on the first spring and the fourth spring caused by the loosening and rotation upward of the bolt are the same. Therefore, according to the strain amounts of the sensing optical fiber segments on the first spring, the second spring, the third spring and the fourth spring, the loosening conditions of the bolts and nuts in the threaded structure and the inclination conditions of the bolts can be determined, thereby improving the accuracy of monitoring the loosening of the threaded structure.

[0124] It can be seen from the above embodiments that since the probability of the screw being tilted in the vertically arranged threaded structure is very small, the present invention first determines whether the strain is only caused by the temperature change of the wind turbine generator according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring corresponding to the threaded structure. If so, the wind turbine generator temperature in the circumferential direction of the threaded structure on the wind turbine generator is determined according to the strain. Otherwise, the looseness of the threaded structure and the wind turbine generator temperature in the circumferential direction of the threaded structure on the wind turbine generator are determined according to the strain of the sensing optical fiber segment on the first spring, the second spring and the third spring. Thereafter, for the inclined thread structure located in the circumferential direction, its looseness is determined according to the strain of the sensing optical fiber segment on the second spring, the third spring and the third spring of the thread structure. It can be seen that when monitoring the looseness of the thread structure and the temperature of the wind turbine, the present invention is not based solely on the strain of the sensing optical fiber segment corresponding to the thread structure, but combines the strain of the sensing optical fiber segment corresponding to the vertical thread structure and the inclined thread structure located in the same circumferential direction of the wind turbine. In this way, the looseness of the thread structure and the temperature of the wind turbine can be monitored simultaneously, and the monitoring method and structure are very simple.

[0125] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0126] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A wind turbine thread structure monitoring device based on optical fiber sensing, characterized in that: It comprises a threaded structure, a sensing optical fiber, and a first spring, a second spring and a third spring with the same structure as the initial state. The threaded structure uses bolts and nuts to fix the wind turbine tower. Each spring is evenly provided with sensing optical fiber segments along its winding direction. The three sensing optical fiber segments are connected in series and connected to a strain measurement system. The first spring and the second spring are symmetrically arranged on the upper and lower sides of the tower. The two ends of the first spring are respectively connected to the top of the nut of the bolt and the nut side of the tower. The two ends of the second spring are respectively connected to the bottom end of the nut and the nut side of the tower. A connecting plate is provided at the bottom end of the bolt. The two ends of the third spring are respectively connected to the bottom end of the nut and the connecting plate. As the bolt is loosened and rotated upward, the first spring stretches. As the nut is loosened and rotated downward, the second spring stretches. The third spring contracts first and then stretches. The strain measurement system measures the strain magnitude of each sensing optical fiber segment, and determines the looseness of the thread structure and the temperature of the wind turbine generator according to the measured strain magnitude of each sensing optical fiber segment.

2. The device according to claim 1, characterized in that It also includes a fourth spring, on which a sensing optical fiber segment is arranged along the winding direction of the fourth spring. The fourth spring has the same structure and initial state as the first spring, and is symmetrical with respect to the bolt. The two ends of the fourth spring are respectively connected to the top of the nut of the bolt and the side of the tower nut.

3. A monitoring method for a wind turbine thread structure monitoring device based on optical fiber sensing according to claim 1 or 2, characterized in that: The strain measurement system performs the following steps: Step S100, assuming that the magnitude of the strain of the sensing optical fiber segment under the influence of the monitorable wind turbine temperature range is a first magnitude, the magnitude of the strain caused by the loosening of the bolt and the loosening of the nut is a second magnitude, and the first magnitude is smaller than the second magnitude; Step S200, for a vertically arranged threaded structure, determine whether only the temperature of the wind turbine generator has changed according to the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring, if so, execute step S300; otherwise, execute step S400; Step S300, determining the wind turbine temperature of the thread structure in the circumferential direction of the wind turbine according to the strain of the sensing optical fiber segment on the first spring or the second spring, and executing step S500; Step S400, determining the looseness of the thread structure and the wind turbine temperature of the thread structure in the circumferential direction of the wind turbine generator according to the strain of the sensing optical fiber segment on the first spring, the second spring and the third spring corresponding to the thread structure, and executing step S500; Step S500: for the thread structure inclined in the circumferential direction on the wind turbine, determine the looseness of the thread structure according to the strain amounts of the sensing optical fiber segments on the first spring, the second spring and the third spring corresponding to the thread structure.

4. The method according to claim 3, characterized in that The step S200 specifically includes: If the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the first magnitude, it means that only the temperature of the wind turbine generator has changed, and step S300 is executed; If the magnitude of the strain of the sensing optical fiber segment on the first spring or the second spring is the second magnitude, it means that only the thread structure is loose, or the thread structure is loose and the temperature of the wind turbine also changes.

5. The method according to claim 3 or 4, characterized in that: The strain amount in steps S200 and S300 is: the change of the strain measured this time compared with the strain measured last time of the corresponding sensing optical fiber segment; step S300 specifically includes: The temperature difference of the wind turbine between this measurement and the last measurement is determined according to the strain of the sensing optical fiber segment on the first spring or the second spring; the temperature of the wind turbine determined last is added to the temperature difference of the wind turbine to obtain the circumferential temperature of the wind turbine where the threaded structure is located on the wind turbine.

6. The method according to claim 3, characterized in that: The step S400 specifically includes: Step S410: For a vertically arranged threaded structure, setting the bolt not to be tilted; The strain ε1 of the sensing optical fiber segment of the first spring is: ε1 = ε 11 +ε 12 (1) ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε 12 Indicates the strain of the sensing optical fiber segment on the first spring caused by the loosening and upward rotation of the bolt; The strain ε2 of the second spring sensing optical fiber is: ε2 = ε 21 +ε 22 (2) ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε 22 Indicates the strain of the sensing optical fiber segment on the second spring caused by the nut loosening and rotating downward; The strain ε3 of the sensing optical fiber on the third spring is: ε3 = ε 21 -k1*ε 22 (3) Where k1 represents the conversion coefficient between the strain of the sensing optical fiber segment on the third spring and the strain of the sensing optical fiber segment on the second spring caused by the loosening and upward rotation of the nut; Step S420: Determine the conversion coefficient k2 between the strain of the sensing optical fiber segment on the first spring and the strain of the sensing optical fiber segment on the second spring under the influence of the wind turbine temperature according to the thickness of the two wind turbine towers and the thermal conductivity of the towers, so that: e 11 =k2*e 21 (4); Step S430: Solve the above formulas (1) to (4) to obtain ε 11 , ε 12 , ε 21 and ε 22 ; Step S440, determine the total strain caused by the loosening of the thread structure: ε 12 +ε 22 , and the circumferential temperature ε of the thread structure on the wind turbine 11 and ε 21 .

7. The method according to claim 3 or 6, characterized in that: The step S500 specifically includes: step S510, for the threaded structure of the wind turbine that is inclined in the circumferential direction, the bolt will be inclined, and it is assumed that the strain of the sensing optical fiber segment of the first spring and the second spring caused by the inclination of the bolt is the same. At this time, the strain ε′1 of the sensing optical fiber segment of the first spring is: e′1=e 11 +e′ 12 +e 13 (5) where ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 Indicates the strain amount of the sensing optical fiber segment on the first spring caused by the inclination of the bolt; The strain ε′2 of the second spring sensing fiber segment is: e′2=e 21 +e′ 22 -e 13 (6) where ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 represents the strain of the sensing optical fiber segment on the second spring caused by the loosening and downward rotation of the nut, -ε 13 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt; The strain ε′3 of the sensing optical fiber segment on the third spring is: e′3=e 21 -k1*e′ 22 (7); Where k1 represents the conversion coefficient between the strain of the sensing optical fiber segment on the third spring and the strain of the sensing optical fiber segment on the second spring caused by the loosening and upward rotation of the nut; Step S520: Solve the above formulas (5) to (7) to obtain ε′ 12 , ε′ 22 and ε 13 ; Step S530: determine the total strain caused by the loosening of the bolts and nuts: ε′ 12 +ε′ 22 .

8. The method according to claim 3, characterized in that The step S500 also includes: for the thread structure inclined in the circumferential direction on the wind turbine, according to the strain of the sensing optical fiber segment on the first spring, the second spring, the third spring and the fourth spring corresponding to the thread structure, determining the looseness of the bolts and nuts in the thread structure and the inclination of the bolts.

9. The method according to claim 8, characterized in that The step S500 specifically includes: Step S540: For the threaded structure inclined in the circumferential direction on the wind turbine, the bolts thereof will be inclined. Assuming that the strains of the sensing optical fiber segments of the first spring and the second spring caused by the inclination of the bolts are different, the strain ε′1 of the sensing optical fiber segment of the first spring is: e′1=e 11 +e′ 12 +e 13 (8) where ε 11 represents the strain of the sensing optical fiber section on the first spring on the nut side under the influence of the wind turbine temperature, ε′ 12 represents the strain of the sensing fiber section on the first spring caused by the loosening and upward rotation of the bolt, ε 13 The strain of the sensing optical fiber section on the first spring caused by the inclination of the bolt; The strain ε′2 of the second spring sensing fiber segment is: e′2=e 21 +e′ 22 -e 23 (9) where ε 21 represents the strain of the sensing optical fiber section on the second spring on the nut side under the influence of the wind turbine temperature, ε′ 22 represents the strain of the sensing fiber section on the second spring caused by the loosening and downward rotation of the nut, -ε 23 The strain of the sensing optical fiber section on the second spring caused by the inclination of the bolt; The strain ε′3 of the sensing optical fiber segment on the third spring is: e′3=e 21 -k1*e′ 22 (10) Where k1 represents the conversion coefficient between the strain of the sensing optical fiber segment on the third spring and the strain of the sensing optical fiber segment on the second spring caused by the loosening and upward rotation of the nut; The strain ε′4 of the sensing optical fiber segment on the fourth spring is: e′4=e 11 +e′ 12 -e 13 (11) Step S550: Solve the above formulas (8) to (11) to obtain ε′ 12 , ε′ 22 , ε 13 and ε 23 ; Step S560: determine the total strain caused by the loosening of the bolts and nuts: ε′ 12 +ε′ 22 .

10. The method according to claim 3, characterized in that The strain amount in steps S400 and S500 is: the change of the strain measured this time compared with the strain measured for the first time of the corresponding sensing optical fiber segment.

Images