System and method for detecting stress concentrations in a structure

Abstract

To enable detection of stress concentration on structures.SOLUTION: Disclosed herein is a system comprising an optical fiber that can be installed on a structure, a light sensing unit for acquiring light scattering properties of the optical fiber, and an arithmetic processing unit configured to compute a stress distribution on the structure using the light scattering properties obtained by the light sensing unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fiber optic sensing technology. [Background technology]

[0002] A technology has been proposed in which an optical fiber is attached along the shape of a structure such as a building, and the strain applied to the structure is estimated by measuring the strain distribution of the optical fiber (see, for example, Non-Patent Document 1). In Non-Patent Document 1, the type of force applied to the structure is estimated from the strain distribution applied to the optical fiber. For this reason, in Non-Patent Document 1, it was necessary to firmly fix the optical fiber to the structure and wire it so that the state of the structure would be reflected in the state of the optical fiber.

[0003] However, due to Saint-Venant's theorem, it is difficult to estimate the distribution of force from parameters such as strain, which are the "result of the application of force." Furthermore, when sensing structures, the most important parameters are not indirect parameters such as strain, but parameters that directly correspond to the shape of the structure, such as stress concentration and deformation, but in fact these cannot be directly obtained from parameters such as strain, which are the "result of the application of force." [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] “Development of a distributed sensing technique using brillouin scattering”, Journal of Lightwave Technology, Vol.13, No.7, pp.1296-1302 [Non-patent document 2] “Shape sensing using multi-core fiber optic cable and parametric curve solution”, Optics Express, Vol.20, No.3, pp.2967-2973 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, an object of the present disclosure is to make it possible to detect stress concentrations in a structure. [Means for solving the problem]

[0006] The system of the present disclosure includes an optical fiber that can be attached to a structure, an optical sensing unit, and a processing unit that functions as the device of the present disclosure. The stress detection method of the present disclosure includes the optical sensing unit acquiring light scattering characteristics of the optical fiber that is attached to the structure without twisting, and the processing unit calculating the stress distribution in the structure using the light scattering characteristics acquired by the optical sensing unit.

[0007] The arithmetic processing unit Calculating the shape of the optical fiber; calculating a deformation of the structure based on the shape of the optical fiber; A stress distribution in the structure may be calculated based on the deformation of the structure.

[0008] The arithmetic processing unit Calculating the overall deformation of the structure; The stress distribution of the structure may be calculated using the finite element method in which the calculated global deformation is given as a forced displacement.

[0009] The optical fiber may be an optical cable that can be attached to a structure without twisting, or may be a multi-core fiber.

[0010] The above disclosures can be combined as much as possible. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to make it possible to detect stress concentrations in a structure. [Brief explanation of the drawings]

[0012] [Figure 1] 1 illustrates an example system configuration of the present disclosure. [Figure 2] 1 shows an overview of the stress detection method of the present disclosure. [Figure 3] 1 shows an example of the state of an optical fiber attached to a structure. [Figure 4] An example of the measurement results of the shape of an optical fiber is shown. [Figure 5] An example of stress distribution is shown below. [Figure 6] 1 illustrates an example system configuration of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0014] (First embodiment) An example system configuration of the present disclosure is shown in Figure 1. The system of the present disclosure includes an optical fiber 91 for measuring the shape of a structure 90, an optical sensing unit 92 for acquiring the light scattering characteristics of the optical fiber 91, and an arithmetic processing unit 93 for calculating the stress distribution of the structure 90 using the light scattering characteristics of the optical fiber 91. The arithmetic processing unit 93 functions as the device of the present disclosure.

[0015] Normally, the only physical quantity that can be measured with optical fiber is the expansion and contraction of the optical fiber. Conventional technology has utilized this to measure the strain of a structure. When using this principle, the optical fiber must be wired in close contact with the structure, and when strain occurs in the structure, that is, when expansion and contraction occurs on the surface, the optical fiber also expands and contracts by the same amount, so it must be attached so that the expansion and contraction of the glass of the optical fiber and the expansion and contraction of the structure are integrated. How it is attached depends on the surface condition of the structure, so it requires trial and error on a case-by-case basis, but at the very least, it is necessary to firmly attach everything so that neither the cable nor the glass of the optical fiber inside moves.

[0016] An overview of the stress detection method of the present disclosure is shown in Figure 2. As shown in Figure 3, the present disclosure measures the shape of an optical fiber 91 attached along the shape of a structure 90 (S11), calculates the deformation of the structure 90 using the shape of the optical fiber 91 (S12), and calculates the stress distribution in the structure 90 based on the deformation of the structure 90 (S13). In this way, the present disclosure can detect stress concentration in the structure 90 and further identify the locations of stress concentration in the structure 90 (S14).

[0017] As shown in FIG. 3 , in the present disclosure, it is sufficient that the optical fiber 91 moves in the same manner when the structure 90 is bent or distorted. That is, in the present disclosure, in step S11, the optical fiber 91 is loosely attached to the surface of the structure 90. For example, if the optical fiber 91 is tightly attached to the structure 90, the optical fiber 91 will stretch when the structure 90 is bent. However, in the present disclosure, when the structure 90 is bent, the optical fiber 91 simply becomes longer (or shorter if on the inside of the bend) by that amount, and at that time, the optical fiber 91 does not stretch, but the optical fiber 91 moves and the bent portion becomes longer (or shorter). That is, in the present disclosure, it is sufficient that the optical fiber 91 moves in the axial direction and deforms in response to the bend. Specifically, for example, it is sufficient to stretch the optical fiber 91 in a way that allows it to move in the axial direction without twisting.

[0018] Therefore, in the present disclosure, in step S11, when the optical fiber 91 is arranged along the structure 90 as a shape sensor, it is arranged under the following conditions. The optical fiber 91 is not constrained in the longitudinal direction. · Twisting of the optical fiber 91 is suppressed by reducing friction with the structure 90. However, twisting of the structure 90 itself can be measured.

[0019] In the shape sensing in step S11, the optical sensing unit 92 inputs light into the optical fiber 91 and receives scattered light in the optical fiber 91, thereby acquiring the light scattering characteristics at each position in the longitudinal direction of the optical fiber 91. The calculation processing unit 93 performs shape sensing of the optical fiber 91 using the light scattering characteristics obtained by the optical sensing unit 92. In the present disclosure, in this shape sensing, the overall deformation of the structure 90 is measured.

[0020] Any shape sensing method using the optical fiber 91 can be used, but an example is a method using a multicore fiber as disclosed in Non-Patent Document 2. By comparing the degree of distortion of each core in the cross section of the multicore fiber, it is possible to determine that the fiber is bent in the direction of greater distortion by the amount of greater distortion. The shape of the optical fiber 91 can also be measured in a similar manner using a plurality of single-core fibers. Below, an example in which the optical fiber 91 is a multicore fiber will be described.

[0021] The optical sensing unit 92 is any device capable of measuring the strain of each core. For example, as shown in Fig. 1, it can be a Brillouin Optical Time Domain Reflectometer (BOTDR) or an Optical Frequency Domain Reflectometer (OFDR), which is connected to one side of the optical fiber 91 and receives light reflected or scattered by each core. Alternatively, it can be a Brillouin Optical Time Domain Analysis (BOTDA), which is connected to both sides of the optical fiber 91 and receives continuous light that has passed through each core.

[0022] Here, to correspond the position in the optical fiber 91 to the position of the structure 90, it is made possible to identify the longitudinal position on the optical fiber 91 during measurement and the position on the structure 90. For example, one of the ends of the optical fiber 91 is set as a reference, and the temperature is changed at a predetermined position on the structure 90, or a local bend is applied to the optical fiber 91 at a predetermined position on the structure 90.

[0023] FIG. 4 shows an example of the measurement results of the shape of the optical fiber 91. The x-axis direction indicates the length direction of the optical fiber 91, and the y-axis direction indicates the direction perpendicular to the length direction of the optical fiber 91. The shape of the optical fiber 91 includes a three-dimensional direction in the z-direction. In the present disclosure, it is assumed that the surface of the structure 90 is deformed in accordance with the shape of the optical fiber 91, and the deformation of the structure 90 is calculated. Whether or not the deformation is a total deformation of the structure 90 can be calculated by attaching the optical fiber 91 to the entire structure 90. For example, if the optical fiber 91 is bent, it can be determined that that part of the structure 90 is also bent with the same curvature.

[0024] The trajectory of the curve in three-dimensional space (each position in the length direction of the optical fiber 91) can be analytically defined by determining κ (curvature: how much it is bent in which direction) and τ (torsion: how much the initial coordinates (absolute coordinates based on the top and bottom of the earth) that serve as the basis for the bending direction have rotated) using the Frenet-Serret formula.

[0025] The desired optical fiber trajectory vector r(s) is expressed by the following equation:

number

[0026] Here, the position vector T(s) is expressed by the following equation:

number

[0027] An example of stress distribution is shown in Figure 5. The calculation of stress distribution in step S13 can use, for example, the finite element method (FEM). By applying the overall deformation of the structure 90 to the finite element method as a forced displacement, the stress acting on the structure 90 can be calculated for each position on the structure 90, thereby making it possible to evaluate stress concentration (S14).

[0028] In the present disclosure, in step S11, the temperature is changed at a predetermined position on the structure 90, or a local bend is applied to the optical fiber 91 at a predetermined position on the structure 90. Therefore, in step S14, it is possible to identify the position in the x-axis direction where strain due to temperature or bending is detected, and thereby it is possible to identify the position on the structure 90 where stress concentration occurs.

[0029] (Second embodiment) 6 shows an example of a system configuration of this embodiment. In this embodiment, the side of an optical fiber 91 is covered with a bendable pipe 81. The pipe 81 is any cylindrical body in which one or more optical fibers 91 can be arranged in a hollow portion and which can be bent while maintaining the hollow portion. Any configuration can be used to make the pipe 81 bendable, and examples include making part of the material of the pipe 81 flexible or making it bellows-shaped.

[0030] In this embodiment, the optical fiber 91 is disposed in a bendable pipe 81, and the optical fiber 91 is allowed to rotate freely within the pipe 81. This makes it possible for the present disclosure to prevent the optical fiber 91 from twisting.

[0031] The pipe 81 may be filled with a liquid 82. The liquid 82 may be a gel. This prevents the space inside the pipe 81 from narrowing, reduces friction between the inner wall of the pipe 81 and the optical fiber 91, and further mechanically suppresses twisting of the optical fiber 91. Note that any configuration may be used to prevent the liquid 82 from leaking out from the end of the pipe 81. Furthermore, a liquid, gel, or other anti-friction layer may be formed on the inner wall surface of the pipe 81 to reduce friction with the optical fiber 91.

[0032] In this embodiment, even if the pipe 81 is twisted, the optical fiber 91 is not twisted. Therefore, the present disclosure can sense the twist of the structure 90 without twisting the optical fiber 91.

[0033] The arithmetic processing unit 93 of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of the present disclosure is a program for realizing a computer as each functional unit of the arithmetic processing unit 93 of the present disclosure, and is a program for causing a computer to execute each step of the stress detection method executed by the arithmetic processing unit 93 of the present disclosure. [Explanation of symbols]

[0034] 81: Pipe 82:Liquid 90: Structure 91: Optical fiber 92: Optical sensing unit 93: Processing unit

Claims

1. An optical fiber is attached to a structure without twisting and a temperature change or local bending is applied to the optical fiber at a predetermined position on the structure, and the longitudinal position on the optical fiber and the position on the structure are identified using the light scattering characteristics of the optical fiber, and each longitudinal position of the optical fiber in three-dimensional space is calculated using the curvature and torsion at each position along the length of the optical fiber, and the overall deformation of the structure is calculated based on each longitudinal position of the optical fiber; Calculating the stress distribution in the structure using a finite element method in which the calculated global deformation is given as a forced displacement. Device.

2. The device of claim 1; the optical fiber attachable to the structure; a light sensing unit for acquiring light scattering characteristics in the optical fiber; A system that includes:

3. The optical fiber is an optical cable that can be attached to the structure without twisting. The system of claim 2 .

4. The optical fiber is a multi-core fiber. The system of claim 3.

5. an optical sensing unit acquires light scattering characteristics of the optical fiber attached to a structure without twisting and to which a temperature change or a local bend is applied at a predetermined position on the structure; The calculation processing unit using the light scattering characteristics obtained by the light sensing unit to identify a longitudinal position on the optical fiber and a position on the structure, to calculate each longitudinal position of the optical fiber in three-dimensional space using the curvature and torsion at each position in the longitudinal direction of the optical fiber, and to calculate the overall deformation of the structure based on each position in the longitudinal direction of the optical fiber; Calculating the stress distribution in the structure using a finite element method in which the calculated global deformation is given as a forced displacement. Stress detection method.

6. A program for causing a computer to implement the device according to claim 1.

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