A three-axis FBG acceleration measuring device and a measuring method

Abstract

The application relates to the field of vibration acceleration measurement, and discloses a three-axis FBG acceleration measurement device and a measurement method. The measurement device comprises an isosceles right triangle structure solid shell, three edges of the solid shell are respectively provided with cavities, FBG measurement units are arranged in the cavities, the FBG measurement unit comprises a cantilever beam, a mass block and an optical fiber, the middle part of the optical fiber is engraved with an FBG; one end of the cantilever beam is fixed to the cavity side surface of the solid shell, and the other end is connected to the mass block; a groove is arranged at the bottom of the cavity, the mass block is embedded in the groove and can slide in the groove along the length direction of the cantilever beam; the optical fiber is integrally pasted on the surface of the cantilever beam, and two ends are respectively fixed to the mass block and the cavity side surface of the solid shell. The device disclosed by the application can realize accurate measurement of three-component acceleration, is stable in structure, and can reduce the influence of environmental factors such as wind resistance and water erosion.

Description

Technical Field

[0001] This invention relates to the field of vibration acceleration measurement, and in particular to a triaxial FBG acceleration measuring device and method. Background Technology

[0002] Oil and gas pipelines are primarily used for the efficient and safe transportation of oil and natural gas resources, reducing transportation costs and environmental impact. Internal factors affecting pipeline vibration include fluid flow characteristics (such as pressure fluctuations and velocity changes) and vibrations from machinery and equipment; external factors mainly involve changes in the natural environment (such as earthquakes, wind, and water flow loads) and improper human operation and maintenance. These unstable factors can trigger pipeline vibration problems, causing fatigue damage, pipe bundle collisions, and wear, thus affecting their service life. Influenced by internal fluid excitation, support structure problems, external disturbances, and inherent pipeline defects, oil and gas pipeline vibrations may occur simultaneously in multiple directions. Therefore, monitoring vibration in only one direction of an oil and gas pipeline cannot comprehensively reflect its vibration state, leading to biased or incomplete monitoring results.

[0003] The triaxial accelerometer can monitor the vibration of oil and gas pipelines in three dimensions, capturing vibration information in different directions to provide more comprehensive and accurate monitoring data. Compared to traditional electrical accelerometers, fiber optic grating (FBG) accelerometers do not require an external power supply, are resistant to electromagnetic interference, have a long lifespan, can monitor over long distances, and feature multiple sensor arrays and unique wavelength division multiplexing capabilities.

[0004] Most current triaxial sensors have a design feature where height and length are similar, resulting in low space utilization and drawbacks such as poor stability, limited applicability, and difficult assembly. In particular, under harsh environmental conditions, the sensors are susceptible to wind resistance and water erosion. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a triaxial FBG acceleration measurement device and method, which aims to achieve accurate measurement of the three-part acceleration and ensure structural stability, thereby reducing environmental impacts such as wind resistance and water erosion.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A triaxial FBG acceleration measurement device includes a solid shell with an isosceles right-angled triangular structure. Cavities are formed along the three sides of the solid shell, and each cavity contains an FBG measurement unit. Each FBG measurement unit includes a cantilever beam, a mass block, and an optical fiber. FBG is etched in the middle of the optical fiber. One end of the cantilever beam is fixed to the side of a cavity in the solid shell, and the other end is connected to the mass block. A groove is formed at the bottom of the cavity, and the mass block is embedded in the groove and can slide along the length of the cantilever beam within the groove. The optical fiber is entirely attached to the surface of the cantilever beam, with both ends fixed to the mass block and the side of the cavity in the solid shell, respectively.

[0008] In the above scheme, mounting holes are provided at the three corner positions and the center of gravity position of the solid shell.

[0009] In the above scheme, the solid shell, cantilever beam, and mass block are all made of stainless steel.

[0010] In the above scheme, one end of the cantilever beam is fixed to the side of the cavity of the solid shell by welding, and the other end is inserted into the center of the mass block and fixed by laser welding.

[0011] In the above scheme, the optical fiber is pre-stretched and then pasted onto the surface of the cantilever beam.

[0012] In the above scheme, a temperature compensation optical fiber is attached near the center of the solid shell, and a temperature compensation FBG is engraved in the middle of the temperature compensation optical fiber.

[0013] A method for measuring triaxial FBG acceleration, using a triaxial FBG acceleration measuring device as described above, includes the following process:

[0014] A triaxial FBG accelerometer is installed on the outer wall of the pipe under test. During installation, ensure that one right-angled side of the solid shell is aligned with the pipe. When installed at the tee position, ensure that the other two right-angled sides of the solid shell are aligned with the two pipe sections respectively. When the pipe vibrates, due to inertial forces, the mass block will displace relative to the cantilever beam within the groove, causing the cantilever beam to bend and deform. This, in turn, causes the optical fiber attached to the cantilever beam to be stretched or compressed. The FBG on the optical fiber has strain-sensitive characteristics; when subjected to stretching or compression, its center wavelength will change. By measuring the center wavelength shift of the FBG... The measurement yielded the acceleration near the outer side of the pipe. Size.

[0015] In a further technical solution, the effect of temperature is ignored, and the center wavelength shift is... With acceleration The relationship is:

[0016]

[0017] In the formula, Let be the elastic modulus of the cantilever beam. The width of the fixed end of the cantilever beam and the solid shell. For the thickness of the cantilever beam, The mass of the mass block. For the effective elastic coefficient, The center wavelength of FBG This is the length of the cantilever beam.

[0018] Through the above technical solution, the triaxial FBG acceleration measuring device and method provided by the present invention have the following beneficial effects:

[0019] 1. The measuring device of the present invention adopts an isosceles right triangle structure, which is a stable geometric shape with two sides of equal length and equal included angle. It has the advantages of good structural support, small size, light weight, compact structure and shell that is not easily deformed. It can reduce deformation caused by external vibration or impact and improve the measurement accuracy and long-term stability of the sensor.

[0020] 2. This invention uses an isosceles right triangle structure with three sides fixed to a cantilever beam, enabling the measuring device to directly correspond to and sensitively capture acceleration changes in these three directions. This simplifies the internal structural layout of the measuring device and makes efficient use of limited space. It also effectively reduces cross-interference between the three component measurements, improving the accuracy and reliability of the measurement.

[0021] 3. This invention utilizes the FBG strain sensing principle. Taking the X-component sensing unit as an example, the FBG is encapsulated on the upper surface of a cantilever beam. The mass block is affected by acceleration, causing the cantilever beam to deform. The FBG receives the acceleration signal by sensing the deformation of the cantilever beam. By measuring the center wavelength drift of the vibration sensing fiber optic grating, the magnitude of the acceleration near the detection point is obtained.

[0022] 4. This invention uses FBG as the sensing unit, which has the advantages of being resistant to electromagnetic interference, being passive underwater, safe, capable of remote measurement, small size, low cost, and able to work stably for a long time in environments with electromagnetic interference and underwater. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0024] Figure 1 This is a schematic diagram of a triaxial FBG acceleration measurement device disclosed in an embodiment of the present invention;

[0025] Figure 2 This is a structural diagram of the solid shell disclosed in the embodiments of the present invention;

[0026] Figure 3 This is a structural diagram of the FBG measurement unit disclosed in the embodiments of the present invention;

[0027] Figure 4 This is a schematic diagram of the installation position of the three-axis FBG acceleration measurement device according to an embodiment of the present invention.

[0028] In the diagram, 1. Solid shell; 2. Cantilever beam; 3. Mass block; 4. Optical fiber; 5. FBG; 6. Mounting hole; 7. Pipe; 8. Triaxial FBG acceleration measuring device; 9. Groove. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0030] This invention provides a triaxial FBG acceleration measurement device, such as... Figure 1 and Figure 2 As shown, a solid shell 1 with an isosceles right-angled triangular structure is included. Cavities are formed on three sides of the solid shell 1, and FBG measurement units are installed in each cavity. The FBG measurement units on the two right-angled sides are the X-direction FBG measurement units and the Y-direction FBG measurement units, respectively, and the FBG measurement unit on the hypotenuse is the Z-direction FBG measurement unit.

[0031] like Figure 3 As shown, the FBG measurement unit includes a cantilever beam 2, a mass block 3, and an optical fiber 4. An FBG 5 is engraved in the center of the optical fiber 4. One end of the cantilever beam 2 is fixed to the side of the cavity of the solid shell 1 by welding, and the other end is inserted into the center of the mass block 3 and fixed by laser welding. A groove 9 is formed at the bottom of the cavity, and the mass block 3 is embedded in the groove 9 and can slide along the length of the cantilever beam 2 within the groove 9. After pre-stretching, the optical fiber 4 is adhered to the surface of the cantilever beam 2, with both ends fixed to the mass block 3 and the side of the cavity of the solid shell 1, respectively. The depth of the groove 9 is much smaller than the height of the mass block 3 to facilitate the connection between the mass block 3 and the cantilever beam 2. The groove 9 provides a "track" or "limit" for the movement of the mass block 3, effectively restricting its lateral movement range. This restriction ensures that when the mass block 3 is subjected to acceleration, it mainly moves along a predetermined direction (such as the sensitive axis of the sensor).

[0032] In this embodiment, the solid shell 1, the cantilever beam 2, and the mass block 3 are all made of stainless steel.

[0033] Mounting holes 6 are provided at the three corners and the center of gravity of the solid shell 1 to facilitate the stable mounting of the device onto the object to be measured. In physics, the center of gravity of an object is the point where all its mass is concentrated, and the equilibrium state of the measuring device depends on the position of this center of gravity. By fixing the mounting holes 6 at the center of gravity of the solid shell 1, the weakest point of the solid shell 1 is near the three corners; by fixing the mounting holes 6 at the three corners of the solid shell 1, the weakest point of the solid shell 1 is near its center of gravity; by fixing the mounting holes 6 at the center of gravity and the three corners of the solid shell 1, the solid shell 1 is more stable under force, thus making the structure more stable.

[0034] In a preferred embodiment, a temperature-compensating optical fiber is attached near the center of the solid housing 1, and a temperature-compensating FBG is etched in the middle of the optical fiber. Through the temperature-compensating optical fiber, temperature compensation is provided to the three-component sensing unit while simultaneously measuring the temperature near the device.

[0035] A method for measuring triaxial FBG acceleration, employing the triaxial FBG acceleration measuring device described above, includes the following steps:

[0036] like Figure 4 As shown, the triaxial FBG acceleration measuring device 8 is installed on the outer wall of the pipe 7 to be measured. During installation, one right-angled side of the solid shell 1 is aligned with the pipe 7. When installed at the tee position of the pipe 7, the two right-angled sides of the solid shell 1 are aligned with the two pipes 7 respectively. When the pipe 7 vibrates, due to the inertial force, the mass block 3 will be displaced relative to the cantilever beam 2 in the groove 9, causing the cantilever beam 2 to bend and deform. This, in turn, causes the optical fiber 4 attached to the cantilever beam 2 to be stretched or compressed. The FBG 5 on the optical fiber 4 has strain-sensitive characteristics. When subjected to stretching or compression, its center wavelength will change. By measuring the center wavelength drift of the FBG... The measurement yielded the acceleration near the outer side of pipe 7. The magnitude of the acceleration can be determined by combining the different sensitive directions of the three FBG measurement units, thereby enabling the measurement of the X, Y, and Z components of acceleration.

[0037] Ignoring the effect of temperature, center wavelength shift With acceleration The relationship is:

[0038]

[0039] In the formula, Let be the elastic modulus of the cantilever beam. The width of the fixed end of the cantilever beam and the solid shell. For the thickness of the cantilever beam, The mass of the mass block. For the effective elastic coefficient, The center wavelength of FBG This is the length of the cantilever beam.

[0040] In this invention, three FBG measurement units are positioned on the same horizontal plane. Lateral interference in the Z direction is related to interference in the X and Y directions. By analyzing the signals in the X and Y directions, the influence of lateral interference in the Z direction can be eliminated. Similarly, lateral interference in the X and Z directions can also be eliminated. (For example, the signal measured in the X direction may be affected by 10% interference in the Y direction and 5% interference in the Z direction, but since all three components are on the same horizontal plane and the signal data of all three components are collected simultaneously, this influence can be eliminated through post-processing.)

[0041] The natural frequency and sensitivity of the measuring device are determined by three sensing units. These can be altered by adjusting the dimensions and size of the cantilever beam 2 and the mass block 3. A thinner and longer cantilever beam 2, and a heavier mass block 3, result in a lower natural frequency and higher sensitivity, and vice versa. Through adjustment, the measuring device can reach frequencies exceeding 1000 Hz, with the natural frequencies of the three sensing units being close; the highest sensitivity can reach over 500 pm / g.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring triaxial FBG acceleration, employing a triaxial FBG acceleration measuring device, characterized in that, The device includes a solid shell with an isosceles right-angled triangular structure. Cavities are formed along the three sides of the solid shell, and each cavity houses an FBG measurement unit. Each FBG measurement unit includes a cantilever beam, a mass block, and an optical fiber. FBG is etched in the middle of the optical fiber. One end of the cantilever beam is fixed to the side of a cavity in the solid shell, and the other end is connected to the mass block. A groove is formed at the bottom of the cavity, and the mass block is embedded in the groove and can slide along the length of the cantilever beam within the groove. The optical fiber is entirely adhered to the surface of the cantilever beam, with both ends fixed to the mass block and the side of the cavity in the solid shell, respectively. The measurement method includes the following process: A triaxial FBG accelerometer is installed on the outer wall of the pipe under test. During installation, ensure that one right-angled side of the solid shell is aligned with the pipe. When installed at the tee position, ensure that the other two right-angled sides of the solid shell are aligned with the two pipe sections respectively. When the pipe vibrates, due to inertial forces, the mass block will displace relative to the cantilever beam within the groove, causing the cantilever beam to bend and deform. This, in turn, causes the optical fiber attached to the cantilever beam to be stretched or compressed. The FBG on the optical fiber has strain-sensitive characteristics; when subjected to stretching or compression, its center wavelength will change. By measuring the center wavelength shift of the FBG... The measurement yielded the acceleration near the outer side of the pipe. Size; Ignoring the effect of temperature, center wavelength shift With acceleration The relationship is: ； In the formula, Let be the elastic modulus of the cantilever beam. The width of the fixed end of the cantilever beam and the solid shell. For the thickness of the cantilever beam, For the mass of the mass block, For the effective elastic coefficient, The center wavelength of FBG This is the length of the cantilever beam.

2. The triaxial FBG acceleration measurement method according to claim 1, characterized in that, Mounting holes are provided at the three corners and the center of gravity of the solid shell.

3. The triaxial FBG acceleration measurement method according to claim 1, characterized in that, The solid shell, cantilever beam, and mass block are all made of stainless steel.

4. A triaxial FBG acceleration measurement method according to claim 1 or 3, characterized in that, One end of the cantilever beam is fixed to the side of the cavity of the solid shell by welding, and the other end is inserted into the center of the mass block and fixed by laser welding.

5. A triaxial FBG acceleration measurement method according to claim 1 or 3, characterized in that, The optical fiber is pre-stretched and then bonded to the surface of the cantilever beam.

6. The triaxial FBG acceleration measurement method according to claim 1, characterized in that, A temperature-compensating optical fiber is attached near the center of the solid shell, and a temperature-compensating FBG is engraved in the middle of the temperature-compensating optical fiber.

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