Fiber bragg grating ice force sensor integrated with simply supported beam structure and force measuring method of fiber bragg grating ice force sensor

Abstract

The invention discloses a fiber bragg grating ice force sensor integrated with a simply supported beam structure and a force measuring method thereof. The fiber bragg grating ice force sensor comprises a beam body, a fixed support and an optical fiber, the two ends of the beam body are installed on the fixed supports to form a simply supported beam structure. One surface, directly bearing an ice force load, of the part, located between the fixed supports, of the beam body is a stress surface, and the other surface opposite to the stress surface is an optical fiber mounting surface; and the optical fiber is mounted on the optical fiber mounting surface of the beam body. When the stressed plate is subjected to ice force, displacement and strain are generated, the beam body is driven to be bent and deformed in a simply supported beam mode, the optical fiber connecting piece fixed to the beam body generates tiny displacement accordingly, the fiber bragg grating in the optical fiber connected with the optical fiber connecting piece generates axial strain, and therefore the Bragg wavelength of the fiber bragg grating drifts; and the size and direction of the ice force can be obtained through inversion by monitoring wavelength change. According to the invention, the metal beam body and the fiber grating sensing element are highly integrated, the structure is compact, the weight is light, and installation and arrangement on a laboratory ice force experiment model are facilitated.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of sensing technology and pressure measurement technology, specifically involving an ice pressure sensor based on fiber Bragg grating technology and its force measurement method, which is particularly suitable for pressure signal acquisition and measurement scenarios under ice load, namely, a fiber Bragg grating ice force sensor with an integrated simply supported beam structure and its force measurement method. Background Technology

[0002] In cold-region marine engineering and polar shipping, structures are frequently subjected to the impact and compression of sea ice. Ice loads are characterized by their instantaneous, nonlinear, and complex spatial distribution, making them a significant factor affecting the safe operation of offshore platforms, floating bridges, and ice-proof facilities. Accurately measuring the magnitude and variation of ice forces is crucial for studying the ice-structure interaction mechanism and improving the accuracy of structural design.

[0003] Currently, methods for monitoring ice loads mainly employ resistance strain gauges, piezoelectric sensors, or mechanical measuring devices. While these sensors can reflect force changes to some extent, they are prone to signal drift and difficulties in temperature compensation under low-temperature and strong electromagnetic interference environments. Furthermore, the sensing points are relatively dispersed, making it difficult to achieve continuous measurement of the overall force. On the other hand, ice forces exhibit significant localized concentration effects and abrupt temporal changes, making it difficult for traditional measuring devices to accurately capture their dynamic processes.

[0004] Fiber Bragg grating (FBG) sensing technology has advantages such as small size, strong resistance to electromagnetic interference, and the ability to achieve multi-point distributed monitoring. In recent years, it has been widely used in bridge health monitoring and strain testing of offshore floating structures. However, existing FBG ice force measurement devices mostly use rigid structures as carriers, resulting in complex force transmission paths that differ from the actual ice load conditions of structures, thus affecting measurement accuracy.

[0005] Simply supported beams, as a classic load-bearing structure, exhibit clear mechanical response characteristics, facilitating the establishment of the correlation between ice load and strain. Combining simply supported beam structures with fiber optic grating sensing units enables real-time measurement and distribution analysis of ice forces. By deploying fiber optic grating arrays on the beam, not only can strain changes at different locations be monitored, but the magnitude and location of ice forces can also be calculated, providing a new testing method for ice-covered structural design and marine observation. Summary of the Invention

[0006] The purpose of this invention is to provide a fiber optic grating ice force sensor and its force measurement method integrated with a simply supported beam structure. This invention overcomes the shortcomings of existing technologies by indirectly measuring pressure through structural strain, thereby effectively acquiring dynamic ice load data under ice-induced vibration. This system is particularly suitable for indoor model tests of ice-induced bridge pier vibration, accurately reflecting the changing characteristics and transmission laws of ice force. Unlike traditional fiber optic grating pressure sensors with low sensitivity, this invention fully utilizes the high strain sensitivity of fiber optic gratings to convert external pressure into a measurable strain signal. Through reasonable structural design and material matching, the sensor's output signal is stable, repeatable, and unaffected by changes in external material properties. Furthermore, the proposed structural form allows for adjustments to the beam dimensions and geometric parameters according to actual needs, flexibly changing the sensor's measurement sensitivity coefficient to adapt to different types of ice load model tests. This invention not only improves the accuracy and reliability of ice force testing but also provides a new experimental method for the dynamic study of ice-structure interaction, possessing significant engineering application value for the safety design of polar and cold-region engineering structures.

[0007] The technical solution of the present invention is as follows: a fiber optic grating ice force sensor with an integrated simply supported beam structure, characterized in that it includes a beam, fixed supports, and optical fibers; the two ends of the beam are mounted on the fixed supports to form a simply supported beam structure; the side of the beam located between the fixed supports that directly bears the ice force load is the force-bearing surface, and the opposite side is the optical fiber mounting surface; the optical fibers are mounted on the optical fiber mounting surface of the beam.

[0008] The beam is made of metal.

[0009] The beam is a long strip beam structure, and a concave groove extending along the length direction is opened in the middle of its optical fiber mounting surface. Optical fibers are installed on the top wall of the concave groove.

[0010] The top wall of the concave groove is provided with a number of slots, and optical fiber connectors are fixedly installed in the slots. The optical fiber is installed through the optical fiber connectors. The number of slots is determined according to the actual working conditions.

[0011] The cross-sectional shape of the concave groove need not be limited to arc, semi-circular, rectangular, U-shaped, trapezoidal or other suitable shapes; among them, the semi-circular or arc-shaped bottom can effectively reduce stress concentration and is suitable for working conditions that bear large or repeated ice force loads.

[0012] The concave groove provides a flat top wall for opening slots and fixing fiber optic connectors, while reserving sufficient space for the fiber optic cable to pass through, thus meeting the functional requirements. This ensures the measurement accuracy and reliability of the sensor while taking into account the manufacturability and structural optimization, enhancing the implementation flexibility and protection range of the solution.

[0013] The beam's load-bearing surface is fixed with a load-bearing plate for directly bearing ice loads.

[0014] The load-bearing plate is made of metal.

[0015] Bolt holes are provided at both ends of the beam and at the corresponding positions of the fixed support. The beam and the fixed support are fixedly connected by bolts to form a simply supported beam structure.

[0016] The fixed support has fiber optic slots on its side. The optical fiber passes through the fiber optic slots of one fixed support and multiple optical fiber connectors in sequence, and then exits from the fiber optic slots of the other fixed support.

[0017] The fiber optic cable exiting the fixed support is protected by fiber optic encapsulation.

[0018] The beam and load-bearing plate can be made of stainless steel, aluminum alloy, titanium alloy, or alloy steel, depending on the experimental requirements. The materials used for the beam and load-bearing plate have sufficient strength, elasticity, low-temperature resistance, and corrosion resistance to ensure that the sensor produces reliable reversible deformation and maintains long-term stability under ice load. This ensures measurement accuracy while also taking into account cost control, ease of processing, and environmental adaptability, thus expanding the practical application range of the solution.

[0019] The fiber optic grating ice force sensor with the integrated simply supported beam structure consists of two or more sensors, which are positioned in different directions on the structure under test to sense changes in ice force from various directions.

[0020] The two or more fiber optic grating ice force sensors with integrated simply supported beam structures are arranged and installed on a fixed base on the periphery of the structure to be measured.

[0021] The force measurement method of the present invention is as follows: when the load-bearing plate is subjected to ice force, it generates displacement and strain, which causes the beam to undergo bending deformation in the form of a simply supported beam. The optical fiber connector fixed on the beam then generates a small displacement, which causes the fiber grating in the optical fiber connected to it to generate axial strain, thereby causing the Bragg wavelength of the fiber grating to drift. By monitoring the wavelength change, the magnitude and direction of the ice force can be inverted, thus realizing the accurate measurement of the ice force.

[0022] The monitoring technology works on the following principles: Firstly, based on the working principle of fiber Bragg gratings, it can be known that the wavelength change of a fiber Bragg grating... The relationship between wavelength change and strain ε is given by the following equation: = (1) In the formula: This represents the fiber optic strain sensor sensitivity coefficient. For fiber optic cables with a pure silica core, the fiber optic grating has a center wavelength around 1550 nm. It is approximately equal to 1.2 pm / με.

[0023] The bending moment at a distance x from the point where the force is applied is as follows Figure 1 As shown, at this time Bending section modulus: Therefore, the stress at point x is: (2) In the formula: h is the beam thickness; F is the applied force; B is the maximum cross-sectional width of the beam; L is the length of the simply supported beam. According to Hooke's Law, strain is defined as: (3) In the formula: For strain; E is the elastic modulus of a simply supported beam.

[0024] According to mechanics of materials, for a simply supported beam of uniform strength as shown in Figure 1, the relationship between the strain and external force at each section of the beam is as follows: (4) In the formula: L is the length of the simply supported beam; E is the modulus of elasticity; B is the maximum cross-sectional width of the beam; h is the beam thickness. Let , can be expressed as As shown in the equation, when the beam dimensions remain constant, the value of K remains constant, and the pressure at the beam's center is linearly related to the strain along the beam's axis. Therefore, the pressure can be measured using a fiber optic grating sensor to measure strain.

[0025] The beneficial effects that this invention can achieve are: 1. The integrated simply supported beam structure integrates the metal beam body with the fiber optic grating sensing element, resulting in a compact and lightweight structure that is easy to install and arrange on laboratory ice force experimental models. It is especially suitable for cylindrical or other complex structural surfaces with limited space.

[0026] 2. By setting multiple fiber optic connectors in the concave groove of the metal beam, the number and position of the fiber optic gratings can be flexibly adjusted, improving the measurement range and sensitivity of the sensor and adapting to the needs of different ice load conditions.

[0027] 3. The simply supported beam design enables the metal beam to undergo uniform bending deformation under stress, resulting in good consistency in the fiber optic grating strain response and high measurement accuracy, which can achieve precise sensing and real-time monitoring of the magnitude of ice force.

[0028] 4. Combined with a ring-shaped fixed base or other replaceable base forms, it supports the arrangement of multiple sensors along the circumference or in an array, enabling multi-directional and all-round perception of ice force changes, significantly improving the comprehensiveness and reliability of experimental data, and avoiding the limitations of single-direction measurement.

[0029] 5. Fiber Bragg grating sensing technology has advantages such as resistance to electromagnetic interference, corrosion resistance, and good long-term stability. It is particularly suitable for low-temperature and humid ice force experimental environments, has a long service life, and low maintenance costs.

[0030] 6. With its simple overall structure, mature processing technology, and controllable cost, it is easy to mass-produce and apply in engineering, providing an efficient and reliable sensing solution for comprehensive monitoring of ice force in laboratories. Attached Figure Description

[0031] Figure 1 This is the overall force diagram of a simply supported beam sensor.

[0032] Figure 2-1 This is the front view of the metal beam. Figure 2-2 This is the left view of the metal beam. Figure 2-3 This is a bottom view of the metal beam.

[0033] Figure 3-1 This is the front view of the metal beam with fiber optic connectors installed. Figure 3-2 This is a bottom view of the metal beam with fiber optic connectors installed. Figure 3-3 This is a left view of the metal beam with fiber optic connectors installed.

[0034] Figure 4-1 This is the front view of the three-view diagram of the metal beam with its support base. Figure 4-2 This is the left view of the three-view diagram of a metal beam with its support base installed. Figure 4-3 It is the bottom view of the three views of the metal beam with the support base.

[0035] Figure 5-1 This is an oblique view of a fiber optic grating ice force sensor with an integrated simply supported beam structure. Figure 5-2 This is a downward-angled view of a fiber optic grating ice force sensor with an integrated simply supported beam structure.

[0036] Figure 6-1 This is a front view of a fiber optic grating ice force sensor with an integrated simply supported beam structure installed side by side. Figure 6-2 This is a bottom view of a fiber optic grating ice force sensor with an integrated simply supported beam structure installed side by side. Figure 6-3 This is a left view of a fiber optic grating ice force sensor with an integrated simply supported beam structure installed side by side.

[0037] In the figure: 1 Metal beam plate; 2 Concave groove; 3 Slot hole; 4 Fiber optic connector; 5 Bolt hole; 6 Bolt; 7 Fixed support; 8 Fiber optic cable; 9 Fiber optic encapsulation; 10 Fiber optic slot; 11 Metal load-bearing plate; 12 Annular fixed base. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below, with relevant examples presented in the accompanying drawings. These embodiments, illustrated with reference to the accompanying drawings, are merely for illustrating the present invention and are exemplary; they should not be construed as limiting the scope of protection of the present invention.

[0039] like Figures 1 to 6-3 As shown, a fiber optic grating ice force sensor with an integrated simply supported beam structure includes a metal beam 1, a concave groove 2, a slot 3, an optical fiber connector 4, a bolt hole 5, a bolt 6, a fixing support 7, an optical fiber 8, an optical fiber encapsulation 9, an optical fiber slot 10, a metal force-bearing plate 11, and an annular fixing base 12.

[0040] First, a concave groove 2 extending along the length direction is machined at the middle position of the side of the metal beam 1 (e.g., Figure 1 and Figures 2-1 to 2-3 As shown), multiple slots 3 are formed on the top wall of the concave groove 2 (such as...). Figures 2-1 to 2-3 As shown), used for fixing and installing fiber optic connector 4 (such as...) Figures 3-1 to 3-3 As shown in the figure, the number of slots 3 can be flexibly determined according to the experimental conditions.

[0041] Subsequently, fixed supports 7 are installed at the bottom of both ends of the metal beam 1. Bolt holes 5 are drilled at corresponding positions on the metal beam 1 and the fixed supports 7, and the two are fastened together with bolts 6 to form a stable simply supported beam structure (e.g., Figures 3-1 to 3-3 As shown). A fiber optic slot 10 is provided on the side of the fixed support 7 (as shown). Figures 4-1 to 4-3 As shown), optical fiber 8 sequentially enters from the optical fiber slot 10 of the fixed support 7 on one side, passes through multiple optical fiber connectors 4 installed in the concave groove 2 of the metal beam 1, and then exits from the optical fiber slot 10 of the fixed support 7 on the other side. The exit end of optical fiber 8 is protected by optical fiber encapsulation 9 (e.g., Figures 4-1 to 4-3 (As shown).

[0042] A metal load-bearing plate 11 is welded to the upper surface of the metal beam 1 (e.g., ...). Figures 5-1 to 5-2 As shown, the metal load-bearing plate 11 directly bears the ice force load. When the metal load-bearing plate 11 is subjected to ice force, it will generate displacement and strain, which will cause the metal beam 1 to undergo bending deformation in the form of a simply supported beam. The optical fiber connector 4 fixed on the metal beam 1 will also generate a small displacement, which will cause the fiber grating in the optical fiber 8 connected to it to generate axial strain, causing Bragg wavelength drift. The magnitude of the ice force can be reflected in real time by monitoring the wavelength change.

[0043] To accommodate different experimental structures (such as cylinders or other shapes), after the simply supported beam structure is assembled, multiple simply supported beam sensors can be fixedly mounted on the annular fixed base 12 via fixed supports 7 (e.g., Figures 6-1 to 6-3(As shown), or arranged in other forms. The fixing method usually involves drilling holes in the annular fixing base 12 and fastening it with bolts, so that the sensor can sense changes in ice force from all directions, improving the comprehensiveness and reliability of experimental data.

[0044] Measurement process and specific data examples: In this embodiment, both the metal beam 1 and the metal load-bearing plate 11 are made of 304 stainless steel. This material has an elastic modulus E ≈ 193 GPa, a yield strength ≥ 205 MPa, and excellent low-temperature resistance (maintaining good toughness below -50°C), corrosion resistance, and machinability. It is suitable for the humid and low-temperature environment of laboratory ice force experiments, and is also reasonably priced and easy to mass-produce.

[0045] The metal beam 1 is a long strip structure with a length L = 100 mm, a maximum cross-sectional width B = 20 mm, and a thickness h = 5 mm.

[0046] The metal load-bearing plate 11 has dimensions of 80 mm × 50 mm × 3 mm and is fixed to the center of the load-bearing surface of the metal beam 1 by welding.

[0047] Assume that the ice force F = 500 N is acting perpendicularly to the center of the load-bearing plate in the laboratory simulation (equivalent to the center position of the beam x = L / 2).

[0048] The load-bearing plate 11 undergoes displacement and strain, causing the metal beam 1 to undergo bending deformation in the form of a simply supported beam. At this time, the maximum strain of the beam occurs at the center position. According to the formulas of mechanics of materials: Substituting the parameters, the calculation shows that ε ≈ 777.2με (micro-strain).

[0049] The fiber optic connector 4, fixed to the top wall of the concave groove 2, undergoes a slight displacement due to the deformation of the beam, causing the fiber grating in the fiber 8 to experience axial strain. The fiber grating strain sensing sensitivity coefficient K... ε ≈ 1.2 pm / με, therefore the Bragg wavelength shift is: Δλ = K ε × ε ≈ 932.6 pm.

[0050] To determine the direction of ice force, multiple sensors can be evenly arranged around the 12 circumferences of a ring-shaped fixed base. By comparing the wavelength drift amplitude and distribution of each sensor, the main direction and spatial distribution of the ice force can be determined.

[0051] The sensor has a flexible structural design. The ring-shaped fixed base 12 or other base forms can be replaced or adjusted according to specific experimental needs to adapt to different experimental conditions, thereby realizing multi-directional and comprehensive monitoring of laboratory ice force.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An integrated simply supported beam structure fiber Bragg grating ice force sensor, characterized in that It includes a beam, fixed supports, and optical fibers; the two ends of the beam are mounted on fixed supports to form a simply supported beam structure; the side of the beam located between the fixed supports that directly bears the ice force load is the load-bearing surface, and the opposite side is the optical fiber mounting surface; the optical fibers are mounted on the optical fiber mounting surface of the beam.

2. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The beam is made of metal.

3. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The beam is a long strip beam structure, and a concave groove extending along the length direction is opened in the middle of its optical fiber mounting surface. Optical fibers are installed on the top wall of the concave groove.

4. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 3, characterized in that The top wall of the concave groove is provided with several slots, and optical fiber connectors are fixedly installed in the slots. The optical fiber is installed through the optical fiber connectors.

5. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The beam's load-bearing surface is fixed with a load-bearing plate for directly bearing ice loads.

6. The fiber optic grating ice force sensor with an integrated simply supported beam structure according to claim 5, characterized in that... The load-bearing plate is made of metal.

7. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The fixed support has fiber optic slots on its side. The optical fiber passes through the fiber optic slots of one fixed support and multiple optical fiber connectors in sequence, and then exits from the fiber optic slots of the other fixed support.

8. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The fiber optic cable exiting the fixed support is protected by fiber optic encapsulation.

9. The fiber Bragg grating ice force sensor integrated with a simply supported beam structure according to claim 1, characterized in that The fiber optic grating ice force sensor with the integrated simply supported beam structure consists of two or more sensors, which are positioned in different directions on the structure under test to sense changes in ice force from various directions.

10. The method of measuring force of the fiber Bragg grating ice force sensor of the integrated simply supported beam structure according to claim 1, characterized in that It includes the following steps: When the load-bearing plate is subjected to ice force, it generates displacement and strain, causing the beam to undergo bending deformation in the form of a simply supported beam. The optical fiber connectors fixed on the beam then undergo slight displacement, resulting in axial strain in the fiber gratings in the connected optical fibers. This causes a drift in the Bragg wavelength of the fiber gratings. By monitoring the wavelength change, the magnitude and direction of the ice force can be inverted, enabling accurate measurement of the ice force.

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