Three-axis FBG acceleration measuring device and measuring method

Abstract

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

Description

Technical Field

[0001] The invention relates to the field of vibration acceleration measurement, and in particular to a three-axis FBG acceleration measurement device and a measurement method. Background Art

[0002] Oil and gas pipelines are mainly used to transport oil and natural gas resources efficiently and safely, reducing transportation costs and environmental impacts. The internal factors of pipeline vibration are affected by fluid flow characteristics (such as pressure fluctuations, flow velocity changes) and machine equipment vibration; external factors mainly involve changes in the natural environment (such as earthquakes, wind, water flow loads) and improper human operation and maintenance. These unstable factors can cause pipeline vibration problems, cause pipeline fatigue damage, pipe bundle collision, wear, and affect its service life. Affected by multiple factors such as internal fluid excitation, support structure problems, external disturbances, and pipeline defects, the vibration of oil and gas pipelines may occur in multiple directions at the same time. Therefore, only monitoring the vibration in a certain direction of the oil and gas pipeline cannot fully reflect the vibration state of the pipeline, resulting in deviations or omissions in the monitoring results.

[0003] The three-axis acceleration measurement device can monitor the vibration of oil and gas pipelines in three dimensions and capture the vibration information of pipelines in different directions, thereby providing more comprehensive and accurate monitoring data. Compared with traditional electrical acceleration sensors, fiber grating (FBG) acceleration sensors do not require external power supply, are resistant to electromagnetic interference, have a long life, can monitor over long distances, have multiple sensor arrays, and have unique wavelength division multiplexing capabilities.

[0004] Most of the current three-axis sensors have design features of similar height and length, low space utilization, poor stability, small application range, and difficult assembly. Especially under harsh environmental conditions, the sensors are easily affected by wind resistance and water erosion. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a three-axis FBG acceleration measurement device and a measurement method, so as to achieve the purpose of accurately measuring the three-component acceleration, and having a stable structure, and reducing environmental influences such as wind resistance and water erosion.

[0006] To achieve the above object, the technical solution of the present invention is as follows: A three-axis FBG acceleration measurement device comprises a solid shell of an isosceles right triangle structure, wherein three sides of the solid shell respectively have cavities, wherein FBG measurement units are arranged in the cavities, wherein the FBG measurement units comprise a cantilever beam, a mass block and an optical fiber, wherein an FBG is engraved in the middle of the optical fiber; one end of the cantilever beam is fixed to the side surface of the cavity of the solid shell, and the other end is connected to the mass block; a groove is provided at the bottom of the cavity, wherein 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 adhered to the surface of the cantilever beam, and its two ends are respectively fixed to the mass block and the side surface of the cavity of the solid shell.

[0007] In the above solution, mounting holes are provided at three corner positions and the center of gravity of the solid shell.

[0008] In the above solution, the solid shell, cantilever beam and mass block are all made of stainless steel.

[0009] In the above solution, one end of the cantilever beam is fixed to the side surface 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.

[0010] In the above scheme, the optical fiber is pre-stretched and then adhered to the surface of the cantilever beam.

[0011] In the above solution, 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.

[0012] A three-axis FBG acceleration measurement method, using a three-axis FBG acceleration measurement device as described above, includes the following process: The three-axis FBG acceleration measurement device is installed on the outer wall of the pipeline to be measured. During installation, one of the right-angled sides of the solid shell is ensured to be in the same direction as the pipeline. When installed at the tee position of the pipeline, the two right-angled sides of the solid shell are ensured to be in the same direction as the two pipelines respectively. When the pipeline vibrates, due to the action of inertial force, the mass block will be displaced in the groove relative to the cantilever beam, causing the cantilever beam to bend and deform, thereby causing the optical fiber attached to the cantilever beam to be stretched or compressed. The FBG on the optical fiber has strain-sensitive characteristics. When stretched or compressed, its central wavelength will change. By measuring the central wavelength drift of the FBG The acceleration near the outside of the pipe is measured size.

[0013] In a further technical solution, ignoring the temperature effect, the center wavelength drift is With acceleration The relationship is: In the formula, is the elastic modulus of the cantilever beam, is the width of the cantilever beam and the fixed end of the solid shell, is the cantilever beam thickness, is the mass of the mass block, is the effective elastic-optical coefficient, is the FBG center wavelength, is the cantilever beam length.

[0014] Through the above technical solution, the three-axis FBG acceleration measurement device and measurement method provided by the present invention have the following beneficial effects: 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 angles. It has the advantages of good structural support, small size, light weight, compact structure and shell that is not easy to deform. It can reduce deformation caused by external vibration or impact and improve the measurement accuracy and long-term stability of the sensor.

[0015] 2. The present invention adopts a cantilever beam with three sides fixed in an isosceles right triangle structure, so that the measuring device can directly correspond to and sensitively capture the acceleration changes in these three directions, simplifying the internal structure layout of the measuring device and efficiently utilizing the limited space; effectively reducing the cross-interference between the three component measurements and improving the accuracy and reliability of the measurement.

[0016] 3. The present 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 the cantilever beam. The mass block is affected by the acceleration, causing the cantilever beam to deform. The FBG receives the acceleration signal by sensing the deformation of the cantilever beam. By measuring the central wavelength drift of the vibration sensing fiber Bragg grating, the magnitude of the acceleration near the detection point is obtained.

[0017] 4. The present invention adopts FBG as the sensing unit, which has the advantages of being resistant to electromagnetic interference, passive underwater, safe, remotely measurable, small in size, low in cost, and able to work stably for a long time in electromagnetic interference and underwater environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0019] Figure 1 A schematic diagram of a three-axis FBG acceleration measurement device disclosed in an embodiment of the present invention; Figure 2 This is a structural diagram of a solid shell disclosed in an embodiment of the present invention; Figure 3 This is a structural diagram of the FBG measurement unit disclosed in an embodiment of the present invention; Figure 4This is a schematic diagram of the installation position of the three-axis FBG acceleration measurement device according to an embodiment of the present invention.

[0020] In the figure, 1. solid shell; 2. cantilever beam; 3. mass block; 4. optical fiber; 5. FBG; 6. mounting hole; 7. pipeline; 8. three-axis FBG acceleration measurement device; 9. groove. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] The present invention provides a three-axis FBG acceleration measurement device, such as Figure 1 and Figure 2 As shown, it includes a solid shell 1 of an isosceles right triangle structure, and cavities are respectively formed on the three sides of the solid shell 1, and FBG measurement units are arranged in the cavities. The two right-angled sides are respectively the X-direction FBG measurement unit and the Y-direction FBG measurement unit, and the hypotenuse is the Z-direction FBG measurement unit.

[0023] like Figure 3 As shown in FIG. 1 , the FBG measurement unit includes a cantilever beam 2, a mass block 3 and an optical fiber 4, and an FBG 5 is engraved in the middle 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 provided at the bottom of the cavity, and the mass block 3 is embedded in the groove 9 and can slide in the groove 9 along the length direction of the cantilever beam 2; after being pre-stretched, the optical fiber 4 is adhered to the surface of the cantilever beam 2 as a whole, and the two ends are respectively fixed to the side of the cavity of the mass block 3 and the solid shell 1. The depth of the groove 9 is much smaller than the height of the mass block 3, so as 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 limiting the range of its lateral movement. This limitation ensures that the mass block 3 moves mainly along a predetermined direction (such as the sensitive axis of the sensor) when subjected to acceleration.

[0024] In this embodiment, the materials of the solid shell 1, the cantilever beam 2 and the mass block 3 are all stainless steel.

[0025] The solid shell 1 has mounting holes 6 at three corner positions and the center of gravity, so that the device can be stably mounted on 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 weak points of the solid shell 1 are near the three corner positions; by fixing the mounting holes 6 at the three corner positions of the solid shell 1, the weak points of the solid shell 1 are near its center of gravity; by fixing the mounting holes 6 at the center of gravity of the solid shell 1 and the mounting holes 6 at the three corner positions, the force on the solid shell 1 is stable, so the structure is more stable.

[0026] In a preferred embodiment, a temperature compensation optical fiber is attached near the center of the solid housing 1, and a temperature compensation FBG is engraved in the middle of the temperature compensation optical fiber. The temperature compensation optical fiber can provide temperature compensation to the three-component sensing unit while measuring the temperature near the device.

[0027] A three-axis FBG acceleration measurement method, using a three-axis FBG acceleration measurement device as above, includes the following process: like Figure 4 As shown, the three-axis FBG acceleration measurement device 8 is installed on the outer wall of the pipeline 7 to be measured. During installation, one of the right-angled sides of the solid shell 1 is ensured to be in the same direction as the pipeline 7. When installed at the three-way position of the pipeline 7, the two right-angled sides of the solid shell 1 are ensured to be in the same direction as the two pipelines 7 respectively. When the pipeline 7 vibrates, due to the action of the inertial force, the mass block 3 will be displaced relative to the cantilever beam 2 in the groove 9, thereby causing the cantilever beam 2 to bend and deform, thereby causing 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 stretched or compressed, its central wavelength will change. By measuring the central wavelength drift of the FBG The acceleration near the outside of pipe 7 is measured. By combining the different sensitive directions of the three FBG measurement units, the measurement of the three components of X, Y, and Z acceleration can be achieved.

[0028] Ignoring the temperature effect, the center wavelength drift With acceleration The relationship is: In the formula, is the elastic modulus of the cantilever beam, is the width of the cantilever beam and the fixed end of the solid shell, is the cantilever beam thickness, is the mass of the mass block, is the effective elastic-optical coefficient, is the FBG center wavelength, is the cantilever beam length.

[0029] In the present invention, the three FBG measurement units are arranged on the same horizontal plane. The lateral interference in the Z direction is related to the interference in the X and Y directions. By analyzing the signals in the X and Y directions, the influence of the lateral interference in the Z direction can be eliminated. Similarly, the lateral interference in the X and Z directions can also be eliminated. (For example, the signal measured in the X direction is interfered by 10% in the Y direction and 5% in the Z direction. However, since the three components are on the same horizontal plane, the signal data of the three components are collected at the same time, and this influence can be eliminated through post-processing.)

[0030] The natural frequency and sensitivity of the measuring device are determined by the three sensing units, and their natural frequency and sensitivity can be changed by adjusting the size and size of the cantilever beam 2 and the mass block 3 structure. The thinner the cantilever beam 2, the longer the length, and the heavier the mass block 3, the lower the natural frequency of the measuring device and the higher the sensitivity, and vice versa. Through adjustment, the highest frequency of the measuring device can reach more than 1000Hz, and the natural frequencies of the three-component sensing units are close; the highest sensitivity can reach more than 500pm / g.

[0031] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-axis FBG acceleration measurement device, characterized in that: The invention comprises a solid shell with an isosceles right triangle structure, wherein three sides of the solid shell respectively have cavities, wherein FBG measurement units are arranged in the cavities, wherein the FBG measurement units comprise a cantilever beam, a mass block and an optical fiber, wherein an FBG is engraved in the middle of the optical fiber; one end of the cantilever beam is fixed to the side surface of the cavity of the solid shell, and the other end is connected to the mass block; a groove is arranged at the bottom of the cavity, wherein 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 adhered to the surface of the cantilever beam, and the two ends of the optical fiber are respectively fixed to the mass block and the side surface of the cavity of the solid shell.

2. A three-axis FBG acceleration measurement device according to claim 1, characterized in that: The three corner positions and the center of gravity position of the solid shell are provided with mounting holes.

3. A three-axis FBG acceleration measurement device according to claim 1, characterized in that: The solid shell, cantilever beam and mass block are all made of stainless steel.

4. A three-axis FBG acceleration measurement device according to claim 1 or 3, characterized in that: One end of the cantilever beam is fixed to the side surface 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 three-axis FBG acceleration measurement device according to claim 1 or 3, characterized in that: The optical fiber is pre-stretched and pasted on the surface of the cantilever beam.

6. A three-axis FBG acceleration measurement device according to claim 1, characterized in that: A temperature compensation optical fiber is pasted near the center of the solid shell, and a temperature compensation FBG is engraved in the middle of the temperature compensation optical fiber.

7. A three-axis FBG acceleration measurement method, using a three-axis FBG acceleration measurement device as described in any one of claims 1 to 6, characterized in that: The process includes the following: The three-axis FBG acceleration measurement device is installed on the outer wall of the pipeline to be measured. During installation, one of the right-angled sides of the solid shell is ensured to be in the same direction as the pipeline. When installed at the tee position of the pipeline, the two right-angled sides of the solid shell are ensured to be in the same direction as the two pipelines respectively. When the pipeline vibrates, due to the action of inertial force, the mass block will be displaced in the groove relative to the cantilever beam, causing the cantilever beam to bend and deform, thereby causing the optical fiber attached to the cantilever beam to be stretched or compressed. The FBG on the optical fiber has strain-sensitive characteristics. When stretched or compressed, its central wavelength will change. By measuring the central wavelength drift of the FBG The acceleration near the outside of the pipe is measured size.

8. A three-axis FBG acceleration measurement method according to claim 7, characterized in that: Ignoring the temperature effect, the center wavelength drift With acceleration The relationship is: In the formula, is the elastic modulus of the cantilever beam, is the width of the cantilever beam and the fixed end of the solid shell, is the cantilever beam thickness, is the mass of the mass block, is the effective elastic-optical coefficient, is the FBG center wavelength, is the cantilever beam length.

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