CN118392065A - Sensitization component based on fiber bragg grating sensor and pipeline pressure monitoring method - Google Patents
Sensitization component based on fiber bragg grating sensor and pipeline pressure monitoring method Download PDFInfo
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Abstract
The invention provides a sensitization component based on a fiber bragg grating sensor and a pipeline pressure monitoring method, and relates to the technical field of fiber bragg grating sensors, wherein the sensitization component comprises: pipe clamp and double triangle fiber grating sensor; the pipe clamp is annular and provided with an opening, the double-triangle fiber bragg grating sensor is connected to two ends of the opening, and the sensitization component is sleeved on the wall of the pipe to be detected; the double-triangle fiber bragg grating sensor is composed of four connecting arms and an arch bridge-shaped strain beam, the four connecting arms and the arch bridge-shaped strain beam are integrally formed, the four connecting arms form an isosceles triangle with two opposite vertexes, one end of each of the four connecting arms is fixed on the double-triangle fiber bragg grating sensor, the other ends of every two connecting arms intersect at one point to form the vertex of the isosceles triangle, the arch bridge-shaped strain beam is connected with the two vertexes, and the FBG sensor is packaged on the arch bridge-shaped strain beam. The technical scheme of the invention solves the problems that the monitoring sensitivity of the pipeline is low and the sensor is difficult to be arranged on the surface of the pipeline in the prior art.
Description
Technical Field
The invention relates to the technical field of fiber bragg grating sensors, in particular to a sensitization component based on a fiber bragg grating sensor and a pipeline pressure monitoring method.
Background
Pipeline monitoring is a critical component in oil and gas pipeline transportation. Because the surrounding environment of the pipeline is complex, the emergency is more, false alarm and even failure are extremely easy to be caused, and the pipeline has extremely large potential safety hazard. The domestic pipeline industry starts later, the detection technology for the pipeline is relatively backward, and fewer sensors which can be directly applied to nondestructive detection of the pipeline are provided. In the current pipeline pressure monitoring, the following defects exist in a mode of measuring the pipe wall strain caused by the pipeline pressure change by using a bare fiber bragg grating: (1) The tube wall strain measurement is poor and the strain sensitivity is typically only 1.2 pm/. Mu.epsilon. (2) In engineering applications, bare fiber gratings are extremely fragile and subject to damage. (3) it is difficult to directly install on the surface of the pipe. (4) The measurement accuracy is susceptible to environmental and fixing effects.
Therefore, there is a need for a sensitization component based on fiber bragg grating sensors and a method for monitoring pipeline pressure that can perform nondestructive testing on pipelines with high sensitivity.
Disclosure of Invention
The invention mainly aims to provide a sensitization component based on a fiber bragg grating sensor and a pipeline pressure monitoring method, so as to solve the problems that the pipeline monitoring sensitivity is low and the sensor is difficult to be arranged on the surface of a pipeline in the prior art.
In order to achieve the above object, the present invention provides a sensitization component based on a fiber bragg grating sensor, comprising: pipe clamp and double triangle fiber grating sensor; the pipe clamp is annular and provided with an opening, the double-triangle fiber bragg grating sensor is connected to two ends of the opening, and the sensitization component is sleeved on the wall of the pipe to be detected; the double-triangle fiber bragg grating sensor is composed of four connecting arms and an arch bridge-shaped strain beam, the four connecting arms and the arch bridge-shaped strain beam are integrally formed, the four connecting arms form an isosceles triangle with two opposite vertexes, one end of each of the four connecting arms is fixed on the double-triangle fiber bragg grating sensor, the other ends of every two connecting arms intersect at one point to form the vertex of the isosceles triangle, the arch bridge-shaped strain beam is connected with the two vertexes, and the FBG sensor is packaged on the arch bridge-shaped strain beam.
Further, the inner wall of the pipe clamp, which is contacted with the wall of the pipeline to be tested, is round, and the outer wall of the pipe clamp is octagonal.
Further, the thickness of the arch bridge-shaped strain beam gradually becomes thinner from the connection part with the connecting arm to the middle, and the width of the arch bridge-shaped strain beam gradually becomes smaller from two ends to the middle.
Further, the end points of the connecting arms fixed on the pipe clamp areThe other end of the connecting arm is the vertex of an isosceles triangle, namelyThe thickness of the connecting arm is defined byPointing toThe dots become thinner.
Further, the pipe clamp is made of steel, and the double-triangle fiber bragg grating sensor is made of aluminum alloy.
Further, the outer diameter of the arch bridge shaped strain beamThe value range is 11 mm-20 mm.
The included angle formed by the two connecting arms, namely the vertex angle of an isosceles triangle formed by the two connecting arms is，The range of the values is as follows=90°=150°。
Further, the thickness of the thinnest part of the middle of the arch bridge-shaped strain beamThe range of the values is as follows: =0.25 mm to =1.5mm。
Minimum value of middle width of arch bridge-shaped strain beamThe range of the values is as follows: =0.4 mm to =2mm。
The invention also provides a pipeline pressure monitoring method, which utilizes the sensitization component based on the fiber bragg grating sensor provided by the invention, and specifically comprises the following steps:
s1, taking a micro-element body on the surface of the pipeline, and when the pipeline bears the internal pressure When the pipe clamp generates circumferential forceHoop stressCircumferential forceIs decomposed into horizontal forceAnd vertical tensionWherein the horizontal forceCalculated according to formula (1):
（1）；
Wherein the connecting arm is fixed on the pipe clamp through the pins, theta is the included angle between the two pins and the geometrical center connecting line of the pipe clamp, Is the inner diameter of the pipeline,Connecting line for micro element and pipe centerAn included angle of the shaft; the microelements are points on the surface of the pipeline.
S2, introducing coefficientsAndHorizontal forceAt a certain connecting armUpper pointGenerates a force atThe following steps are:
（2）；
Wherein, AndIs a coefficient.
S3，、Respectively connecting armsUpper partAxial and vertical tension of the point:
（3）；
（4）；
Wherein, Is the length of the connecting arm; Is a moment.
According to the principle of graph multiplicationNormalized to 1, reduced to equation (5) and equation (6):
（5）；
（6）；
Wherein, 、AndNormalized forces are respectively、And。
Further, the method also comprises the following steps:
s4, calculating vertical displacement of the connecting arm by using the Karsch second theorem in material mechanics The calculation process is shown in formula (7):
（7）；
Wherein, For connecting armsThe moment of inertia of the cross-section,；For connecting armsIs defined by the cross-sectional area of (a),，Is the internal pressure of the pipeline.
Is thatThe amount of vertical displacement of the point,The calculation formula of (2) is as follows:
（8）；
Wherein, Is Young's modulus.
S5, considering the length of the arch bridge-shaped strain beam to beFinal strain value of arch bridge shaped strain beamAs shown by formula (9):
（9）。
Further, the method also comprises the following steps:
S6, assuming that a coefficient exists between the wavelength drift amount of the FBG and the internal pressure of the pipeline The following steps are:
（10）；
Wherein, Is the center wavelength drift amount of the fiber bragg grating.
Substitution of equation (9) into equationThe FBG wavelength drift value is calculated from equation (11):
（11）。
Wherein, Is that，Is the effective grating refractive index; representing the period of the reflection of the grating, Is the coefficient of thermal expansion of the optical fiber,Is the thermo-optic coefficient of the optical fiber,Is an effective elasto-optical coefficient; Is the fiber temperature; Is the amount of change in the temperature of the optical fiber.
S7, performing temperature compensation or assuming constant temperature, i.eZero, obtain:
（12）。
Coefficients of Calculated from equation (13):
（13）。
The invention has the following beneficial effects:
In the sensitization component provided by the invention, the processability of the sensitization component of the sensor is considered, and the gradual change arch bridge shape strain beam is provided. In finite element calculation software, the sensitization component can amplify the strain of the pipe wall surface by 61.10 times under the condition of applying 1MPa to the inner wall of the pipe. A pipeline pressure monitoring experiment is established, and experiments prove that when the pipeline pressure is 1MPa, the pipe wall strain can be amplified by 20.53 times by the sensitization component provided by the invention. Compared with the traditional sensor sensitization component, the strain of the pipe wall can be amplified by 5.07 times, and the strain of the pipe wall is obviously improved.
Compared with the prior art that the sensor needs to be fixed on the outer wall of the pipeline in a threaded connection or welding mode and the like at the opening of the pipeline, the sensitization component provided by the invention can avoid the following defects: (1) The invention starts from a non-invasive structure, completely isolates the medium inside the pipeline, and monitors the pressure inside the pipeline through the strain of the outer wall. The tightness of the pipeline is ensured, the mechanical property of the pipeline is not changed, and the service cycle of the pipeline is not influenced; (2) When the measuring medium is corrosive, the sensor is ensured not to be damaged without selecting materials compatible with the measuring medium or carrying out special process treatment. (3) In the aspect of convenience, the monitoring can be completed by fixing the sensitization component on the upper part of the pipeline, and the sensitization component can be installed at a later stage according to the requirement and can be disassembled at any time. (4) The invention can realize distributed measurement, one optical fiber can measure the pipeline along multiple points, and is very suitable for long-distance large-range monitoring of oil and gas long-distance pipelines and suitable for various actual engineering operation environments. (5) In terms of cost, the sample processing mode adopted in the experiment is linear cutting processing preliminary processing, a few parts are further processed by adopting a processing center, the processing mode and the process are mature, and the cost is well controlled. (6) The bare optical fiber is packaged at the upper part of the sensitization component to protect the fragile bare optical fiber, so that the sensitization component is applicable to field severe environments and has reliability compared with a method for directly monitoring the bare optical fiber.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art. In the drawings:
FIG. 1 shows an overall block diagram of a fiber grating sensor-based sensitization component of the present invention.
Fig. 2 shows a block diagram of a double triangle fiber grating sensor of the present invention.
Fig. 3 shows a left side view of fig. 2.
Fig. 4 shows an overall assembly of the sensitization component provided by the present invention to a pipeline.
Fig. 5 shows a front view of fig. 1.
Fig. 6 shows a stress-strain state diagram of the pipe wall under the action of internal pressure.
FIG. 7 shows a force analysis diagram of a double triangle fiber grating sensor.
Fig. 8 shows an enlarged detail view at C of fig. 7.
Fig. 9 shows different arch bridge strain Liang WaijingA graph of the change in strain value at the midpoint of the lower arch bridge shaped strain beam.
FIG. 10 shows different anglesA graph of the change in strain value at the midpoint of the lower arch bridge shaped strain beam.
FIG. 11 shows the minimum thickness of different arch bridge shaped strain beamsA graph of the change in strain value at the midpoint of the lower arch bridge shaped strain beam.
FIG. 12 shows the minimum width of a different arch bridge shaped strain beamA graph of the change in strain value at the midpoint of the lower arch bridge shaped strain beam.
Fig. 13 shows a graph of the center wavelength variation of the #3FBG due to temperature.
Fig. 14 shows a center wavelength variation diagram of the #1 FBG.
FIG. 15 shows a center wavelength variation diagram of the #2 FBG.
The reference numerals in the above figures are:
10. A pipe clamp; 20. a double triangle fiber grating sensor; 21. a connecting arm; 22. arch bridge shaped strain beam; 30. a conduit wall; 40. and (5) a pin.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
A fiber grating sensor-based sensitization component as shown in fig. 1, comprising: a pipe clamp 10 and a double triangle fiber bragg grating sensor 20; the pipe clamp is annular and provided with an opening, the double-triangle fiber bragg grating sensor is connected to two ends of the opening, and the sensitization component is sleeved on the wall 30 of the pipe to be detected; the double-triangle fiber bragg grating sensor is composed of four connecting arms 21 and an arch bridge-shaped strain beam 22, the four connecting arms and the arch bridge-shaped strain beam are integrally formed, the four connecting arms form an isosceles triangle with two opposite vertexes, one end of each of the four connecting arms is fixed on the double-triangle fiber bragg grating sensor, the other ends of every two connecting arms intersect at one point to form the vertex of the isosceles triangle, the arch bridge-shaped strain beam is connected with the two vertexes, and the FBG sensor is packaged on the arch bridge-shaped strain beam.
Specifically, the inner wall of the pipe clamp, which is contacted with the wall of the pipeline to be tested, is round, and the outer wall of the pipe clamp is octagonal.
In particular, the thickness of the arch bridge shaped strain beam gradually thins from the connection with the connecting arm to the middle, i.e. the thickness is gradually reduced fromGradually decrease toThe width of the arch bridge-shaped strain beam gradually decreases from two ends to the middle, i.e. the width is fromGradually decrease to。Is the thickness of the connecting arm at the end point.
Specifically, the end point of the connecting arm fixed on the pipe clamp isThe other end of the connecting arm is the vertex of an isosceles triangle, namelyThe thickness of the connecting arm is defined byPointing toThe dots become thinner.
Specifically, the pipe clamp is made of steel, and the double-triangle fiber bragg grating sensor is made of aluminum alloy.
In particular, arch bridge strain Liang WaijingThe value range is 11 mm-20 mm; the included angle formed by the two connecting arms, namely the vertex angle of an isosceles triangle formed by the two connecting arms is，The range of the values is as follows=90°=150°. By changingThe value may change the strain sensitivity of the structure.
In particular, the thickness of the thinnest part of the arch bridge shaped strain beamThe range of the values is as follows: =0.25 mm to =1.5 Mm; minimum value of middle width of arch bridge-shaped strain beamThe range of the values is as follows: =0.4 mm to =2mm。
The length, the minimum width and the minimum thickness of the arch bridge-shaped strain beam are respectively used、AndThe outer contour of the pipe clamp is octagonal, the inner contour is circular, and the tangent circle radius of the outer contour is recorded asThe radius of the internal contour circle is recorded. Will beAnd (3) withThe difference between them is called the thickness of the pipe clamp, and is recorded as（）。
The two ends of the double-triangle fiber bragg grating sensor are symmetrical triangle strain beams (namely triangle strain beams formed by four connecting arms), the design of the arch bridge strain beams considers that the arch bridge has the advantages of good mechanical transmission performance, firm and stable structure and difficult deformation, and is inspired by the structure of the arch bridge type bridge, and the triangle strain beams at the two ends are connected by the arch bridge strain beams with the middle part which are flat up and flat down. In order to better transfer the strain on the pipe wall of the target pipeline to the arch bridge-shaped strain beam and reduce the energy loss in the transfer process, the double-triangle fiber bragg grating sensor needs to have excellent mechanical transfer performance to play a role in strain amplification, so that the design thought of gradual change in thickness is adopted in the design of the connecting arm or the arch bridge-shaped strain beam. Triangle strain beam thickness at both endsBy thickness of boltGradually reduced to the thickness at two ends of arch bridge-shaped strain beamThe cut-away view from the pin to the arch bridge shaped strain beam connection in fig. 3 is isosceles trapezoid instead of rectangle in conventional designs. Furthermore, it is clearly observed from fig. 2 and 3 that the arch bridge-shaped strain beam has a width from both ends to the midpoint in the present inventionGradually decrease toFrom the two ends to the middle pointGradually decrease to. The arch bridge shape and the thickness gradient structural design are designed in consideration of improving the sensitization effect of the double-triangle fiber grating sensor and enabling the structure to have reasonable stress distribution, so that the durability of the structure is improved. As shown in fig. 4, the double-triangle fiber bragg grating sensor is fixed on the pipe clamp through a pin, the outer wall of the pipe clamp structure is regular octagon, the inner wall of the pipe clamp structure is round with the radius being matched with the outer diameter of the pipe, the pipe clamp which is bilaterally symmetrical is fixed on the target pipe through a bolt, the FBG sensor is packaged on the arch bridge-shaped strain beam, and the strain value can be measured by the central wavelength of the FBG. Thus, the FBG sensor can monitor the pipeline pressure, and the total assembly structure is shown in fig. 4.
The strain transmission path of the sensitization component provided by the invention is analyzed by combining the actual stress condition of the pipe wall, a pipe wall mechanical model is established by utilizing a static equilibrium equation and a physical equation, the amplification principle is analyzed, and the strain amplification factor is quantized. The stress on the pipe wall generated under the action of internal pressure is firstly transferred to the pipe clamp and then transferred to the triangular strain beam, and the final strain value of the pipe wall is measured by the FBG sensor after multistage amplification in the transfer process.
The invention also provides a pipeline pressure monitoring method, which utilizes the sensitization component based on the fiber bragg grating sensor provided by the invention, and specifically comprises the following steps:
s1, taking a micro-element body on the surface of the pipeline under the action of internal pressure, wherein the stress-strain state of the pipeline wall is shown in figure 6, and when the pipeline bears the internal pressure When the pipe clamp generates circumferential forceHoop stressAs can be seen from fig. 6Is related to the pipe clamp included angle theta, and the circumferential force is appliedIs decomposed into horizontal forceAnd vertical tensionWherein the horizontal forceCalculated according to formula (1):
（1）；
Wherein the connecting arm is fixed to the pipe clamp by the pins 40, as shown in fig. 5, θ is the included angle between the two pins and the geometrical center line of the pipe clamp, Is the inner diameter of the pipeline,Connecting line for micro element and pipe centerAn included angle of the shaft; the microelements are points on the surface of the pipeline.
S2, the pin on the pipe clamp pulls horizontallyTransmitting to two ends of the double triangle fiber grating sensor. Because friction exists among the connecting parts of the pipe wall, the pipe clamp and the double-triangle fiber bragg grating sensor, certain energy loss can be generated in the force transmission process. Horizontal forceAnd cannot be completely transmitted to the double-triangle fiber bragg grating sensor. Thus, the coefficient is introducedAndHorizontal forceAt a certain connecting armUpper pointGenerates a force atThe following steps are:
（2）；
Wherein, AndIs a coefficient.
S3, under forceUnder the action of the (2), the double-triangle fiber bragg grating sensor is arranged onSome horizontal and vertical displacement occurs on the beam, as shown in figures 7 and 8,Horizontal displacement of points andFor vertical displacement of pointsAndAnd (3) representing. In practice, horizontal displacementAnd vertical displacementThere is an amplifying relationship between them. Because of the symmetry of the double-triangle fiber bragg grating sensor structure, the mechanical analysis of the double-triangle strain gauge can be completed only by marking 1/4 of the amplified part. Then, a force balance equation and a bending moment balance equation are established based on the generalized diagram multiplication (GDMM), and the relationship thereof can be expressed as formula (3) and formula (4).、Respectively connecting armsUpper partAxial and vertical tension of the point:
（3）；
（4）；
Wherein, Is the length of the connecting arm; Is a moment.
According to the principle of graph multiplicationNormalized to 1, reduced to equation (5) and equation (6):
（5）；
（6）；
Wherein, 、AndNormalized forces are respectively、And。
Specifically, the method further comprises the following steps:
s4, calculating vertical displacement of the connecting arm by using the Karsch second theorem in material mechanics The calculation process is shown in formula (7):
（7）；
Wherein, For connecting armsThe moment of inertia of the cross-section,；For connecting armsIs defined by the cross-sectional area of (a),，The internal pressure of the pipeline is set;
Is that The vertical displacement of the point is easy to obtain due to the symmetry of the double-triangle fiber grating sensor structure on the left side and the right sideIs thatTwice as many as, therefore,The calculation formula of (2) is as follows:
（8）；
Wherein, Is Young's modulus.
S5, as the double-triangle fiber bragg grating sensor is also of an up-down symmetrical structure, the vertical total deformation isIs 2 times as large as the above. Consider the length of the arch bridge shaped strain beam to beFinal strain value of arch bridge shaped strain beamAs shown by formula (9):
（9）。
specifically, the method further comprises the following steps:
S6, calculating the strain value of the arch bridge-shaped strain beam The pressure inside the pipe can be measured indirectly. But due to friction coefficientAndIs uncertain and therefore the strain value cannot be calculated accurately by equation (9). The accurate value of the strain value can be obtained through finite element numerical simulation, and the magnification of the structure can be determined by comparing the strain value with the strain value of the pipe wall. At the same time, it is assumed that there is a coefficient between the wavelength drift amount of the FBG and the internal pressure of the pipelineThe following steps are:
（10）；
Wherein, Is the center wavelength drift amount of the fiber bragg grating.
Substitution of equation (9) into equationThe FBG wavelength drift value is calculated from equation (11):
（11）；
Wherein, Is that，Is the effective grating refractive index; representing the period of the reflection of the grating, Is the coefficient of thermal expansion of the optical fiber,Is the thermo-optic coefficient of the optical fiber,Is an effective elasto-optical coefficient; Is the fiber temperature; Is the amount of change in the temperature of the optical fiber.
S7, performing temperature compensation or assuming constant temperature, i.eZero, obtain:
（12）。
from equation (12), it can be seen that the FBG wavelength drift amount is determined in the case of determining the specific size parameter of the sensitization component And has a certain relation with the pipeline pressure. Coefficients ofCalculated from equation (13):
（13）。
from the above analysis, it can be seen that the pressure in the pipeline The central wavelength drift amount of the fiber bragg grating is read through a demodulator in a certain number relation with the strain value epsilon on the sensitization componentThe pressure in the pipeline is indirectly monitored.
The strain amplification effect of the sensitization component is related to the double triangle fiber bragg grating sensor. Therefore, in order to obtain more accurate strain magnification, an Ansys workbench finite element analysis software is adopted in the section to establish a finite element model of the pipeline and the sensitization component. The length, thickness and inner diameter of the pipe were set to 500.0mm, 3.0mm and 83.0mm, respectively. The initial dimensions of the sensitized components are shown in table 1.
TABLE 1 initial parameter size of sensitization components
。
The pipe and tube clamp materials were set to 304 steel and 45 steel, and the double triangular strain gauge material was set to 6061 aluminum alloy. The summary of the properties of the materials involved in the finite element model is shown in table 2.
TABLE 2 Material Properties of finite element model
。
And applying a constant pressure of 1.0MPa to the inner wall of the pipeline, and setting constraint conditions on the boundary of the model according to actual working conditions. Firstly, two ends of a pipeline are restrained by fixed ends, the joint of the outer wall surface of the pipeline and a rotating hinge of a pipe clamp and a rotating hinge of the pipe clamp and a double-triangle fiber bragg grating sensor are set to be sliding friction, and then solving is carried out.
The strain amplifying effect of the sensitization component provided by the invention is related to the structural size thereof. Therefore, key parameters of the sensitization component are optimized through the establishment of a finite element analysis environment. The parameter optimization only selects main parameters which have obvious influence on the strain amplification effect, wherein the selected optimization parameters are as follows、、And. The initial values of the selected parameters are set as shown in table 1. Then, a pressure of 1.0MPa was applied to the inner surface of the pipe. In order to obtain the variation trend of the strain sensitivity of the design structure along with the selected parameters, each parameter is simulated five times and the average value is taken as a result, so that the reliability of the result is ensured.
(1) Parameters (parameters)And (3) optimizing and analyzing:
arch bridge shape strain Liang Waijing for changing sensitization components in finite element analysis software By comparing differentThe amplification effect of the lower sensitization component is used for determining the optimal value, and other structural parameters of the sensitization component in the simulation set are kept unchanged in table 1 in order to ensure the accuracy of the test result. The amplification effect of the sensitization sensor is represented by the ratio of the strain at the middle point of the arc-shaped strain beam of the sensor to the strain of the outer wall of the circular tube, which is calculated by software, and the larger the ratio is, the better the amplification effect of the sensitization component is.
By comparing differentThe amplification effect of the lower sensitization sensor is used to determine the optimal value, and in the simulation of the groupTaking 120 °, the other parameters all remain unchanged from the values in table 1. In consideration of the durability of the sensor and the feasibility of actual processing, the radian of the arch bridge-shaped strain beam cannot be too large, and as the two ends of the arch bridge-shaped strain beam are fixed, the arc can be only realized by changing the circle center and the radius of the circular arc when the radian is adjusted, and the smaller the radius is, the larger the radian of the arch bridge-shaped strain beam is. Simulating the slave=11 Mm toThe amplification of the strain of the sensitization sensor under the strains Liang Waijing R of 10 groups of different arch bridges is carried out by taking one group every 1mm, and in addition, the strain value of the outer wall of the pipelineStrain value at midpoint of arch bridge-shaped strain beamMagnification factorAre all recorded in table 3.
TABLE 3 differentLower strain measurement
。
Drawing simulation results into different arch bridge shape strains Liang WaijingThe change curve of the strain value at the midpoint of the lower arch bridge shaped strain beam, as shown in fig. 9, changes Liang Waijing with arch bridge shape strainThe magnification of the sensitization component increases from 11.01 to 30.33. This means that within a certain range,The larger the value of (c), the larger the magnification of the sensitized component, considering the difficulty of processing, and the too thin arch bridge shaped strain beam is too easily damaged during the actual installation,Set to 11mm, the arch bridge-shaped strain beam is designed into a bridge-shaped structure with a horizontal upper part and a curved lower part.
(2) Parameters (parameters)And (3) optimizing and analyzing:
Other structural parameters of the sensor in the simulation set all keep the values in table 1 unchanged, and the angle is too large or too small to be in line with the practical engineering application, so that the common slave in the engineering is selected in the software =90°A total of 5 groups of differences were taken every 15 ° for =150°Strain amplification of lower sensitization component, and strain value of outer wall of circular tubeStrain value at midpoint of arch bridge-shaped strain beamMagnification factorAre all recorded in table 4.
TABLE 4 variation ofLower strain measurement
。
As shown in fig. 10, withThe magnification of the sensitized component increases from 41.31 to 60.57 and then decreases to 56.87. This means that within a certain range,At 120 °, the magnification of the sensitization component is maximized, and thereforeThe value of (2) is set to 120.
(3) Parameters (parameters)And (3) optimizing and analyzing:
in the simulation of this group =120°, The other parameters all kept unchanged from the values in table 1, the slave was simulated in software=0.25 Mm toTake a total of 6 minimum thickness of different arch bridge shaped strain beams every 0.25mm =1.5 mmThe lower sensitization sensor amplifies the strain, and in addition, the strain value of the outer wall of the pipelineStrain value at midpoint of arch bridge-shaped strain beamMagnification factorAre all recorded in table 5.
TABLE 5 variation ofLower strain measurement
。
As shown in fig. 11, the beam is strained with the minimum thickness of the arch bridgeThe magnification of the sensitization component is reduced from 60.57 to 12.96. This means that the minimum thickness of the arch bridge shaped strain beam is within a certain rangeThe larger the magnification of the sensitization component, the smaller. Considering smallerThe value would result in an excessively thin overall strain beam structure, thus setting the minimum thickness of the arched bridge-shaped strain beam to 0.25mm.
(4) Parameters (parameters)And (3) optimizing and analyzing:
In this set of simulations β=120°, =0.25 Mm, the other parameters all kept the values in table 1 unchanged. Simulating a slave in software=0.4 Mm toTaking the minimum width of 6 groups of different arch bridge shape strain beams in total =2 mmThe strain of the lower sensitization component is amplified, and in addition, the strain value of the outer wall of the pipelineStrain value at midpoint of arch bridge-shaped strain beamMagnification factorAre all recorded in table 6.
TABLE 6 differentLower strain measurement
。
As shown in fig. 12, withThe magnification of the sensitization component is reduced from 84.70 to 42.80. This means that within a certain range,The larger the value of (2), the smaller the magnification of the sensitized component. Considering smallerValues may result in inadequate structural strength of the arch bridge shaped strain beam, thus setting the minimum width of the strain beam to 1mm.
The sensitivity of the sensitization component provided by the invention is verified as follows:
based on the parameters of the sensitization component determined by the process, a pipeline pressure monitoring experiment platform is built, and the actual effect of the designed strain sensitization component is verified. The whole set of test system comprises an FBG demodulator, a pressure pump, a pipeline, a designed strain sensitization component, a notebook computer, a plurality of connecting wires and the like.
The pipe used in the test system was 304 steel with a length, an inner diameter and a wall thickness of 500.0mm, 83.0mm and 3.0mm, respectively. The two ends of the pipeline are fixed by adopting flange plates, one end is completely sealed, and the other end is connected with a hose to be used as an input and output port (with a pressure release valve) of the pressure pump. The maximum sampling frequency of the pressure pump and the FBG demodulator is 1000.0Hz, and the maximum resolution is 1.0pm.
The FBG on the sensitized component is labeled #1FBG, parallel to the pipe axis. The FBG on the pipe wall is marked #2FBG, perpendicular to the pipe axis. The temperature of the experimental room was kept around 25.0 ℃. In order to reduce the influence of temperature, the #3FBG for temperature compensation is fixed to the pipe with only one end fixed and one end free. Three FBGs were respectively attached to the corresponding positions with 353ND special glue, and specific parameters of the FBGs used are shown in table 7.
Table 7 FBG detailed parameters
。
The pipeline pressure is pressurized from 0MPa to 1.0MPa by a pressure pump, the sampling interval is 0.1MPa each time, 10 sample points are taken for evaluation, and the central wavelength change conditions of the #1FBG and the #2FBG are recorded. To verify the accuracy and reliability of the sensitized component, two sets of sample tests were performed and each sample was subjected to two cycles of pressurization and depressurization, respectively. The changes in the center wavelengths of the #1FBG and the #2FBG were converted to strain values of the pipes, and recorded as shown in table 8.
Table 8 test data and relative error
。
As known from the FBG operating principle, both strain and temperature changes can shift the center wavelength of the fiber. Thus, to exclude the effect of temperature on the experimental test results, the center wavelength variation of the #3FBG within 5 minutes was recorded simultaneously during the experiment, as shown in fig. 13. The black lines are original signals, and the red lines are signals after wavelet transformation and noise reduction. As can be seen from fig. 13, the center wavelength of the #3FBG is almost constant, which means that the temperature remains substantially unchanged during the test, i.e. Δt=0. Therefore, the effect of temperature on the test results during the test can be ignored.
In order to more visually show the actual strain magnification of the sensitized component. The center wavelength data of the test resulting #1FBG and #2FBG were linear fitted. Fig. 14 shows the measurement results obtained by #1FBG bonded on the sensitized component. It can be seen that the center wavelength shift of the #1FBG is in a linear relationship with the pressure change in the pipeline, the sensitivity of the sensitization component measured in the test is about 1475.8pm/MPa, the fitting coefficient F c = 0.9744, and the fitting curve is y=1475.8x+14.006; from the results reflected by the #2FBG, the center wavelength shift and the pressure in the pipeline also show a significant linear relationship, as shown in fig. 15, the sensitivity of the outer surface of the pipeline is 71.9pm/MPa, the fitting coefficient F c = 0.9737, and the fitting curve is: y=71.901x+0.4867, it can be seen that the sensitization effectively amplifies the strain value of the pipe surface caused by pressure changes by about 20.53 (1475.8/71.9=20.53) compared to the pipe strain.
The experimental results show that: the sensitization component provided by the invention can release the strain of the surface of the pipeline by 20.53 times, and a plurality of groups of repeated tests are carried out to verify the effectiveness and the reliability of the sensitization component.
It should be understood that the above description is not intended to limit the invention to the particular embodiments disclosed, but to limit the invention to the particular embodiments disclosed, and that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the invention.
Claims (10)
1. A fiber grating sensor-based sensitization component, comprising: pipe clamp and double triangle fiber grating sensor; the pipe clamp is annular and provided with an opening, the double-triangle fiber bragg grating sensor is connected to two ends of the opening, and the sensitization component is sleeved on the wall of the pipe to be detected; the double-triangle fiber bragg grating sensor is composed of four connecting arms and arched bridge-shaped strain beams, the four connecting arms and the arched bridge-shaped strain beams are integrally formed, the four connecting arms form isosceles triangles with two opposite vertexes, one ends of the four connecting arms are fixed on the double-triangle fiber bragg grating sensor, the other ends of every two connecting arms intersect at one point to form the vertexes of the isosceles triangles, the arched bridge-shaped strain beams are connected with the two vertexes, and the arched bridge-shaped strain beams are provided with FBG sensors in an encapsulation mode.
2. The sensitization component based on the fiber bragg grating sensor according to claim 1, wherein the inner wall of the pipe clamp, which is in contact with the wall of the pipe to be detected, is circular, and the outer wall of the pipe clamp is octagonal.
3. A fiber grating sensor-based sensitization component as recited in claim 1, wherein said arch bridge shaped strain beam has a thickness that tapers from a junction with said connecting arm toward the middle, and a width that tapers from both ends toward the middle.
4. A fiber grating sensor-based sensitization component as recited in claim 1, wherein said attachment arms are secured to said tube clamp at end points that areThe other end of the connecting arm is the vertex of an isosceles triangle, namelyA point, the thickness of the connecting arm is defined byPointing toThe dots become thinner.
5. The fiber grating sensor-based sensitization component of claim 4, wherein said tube clamp is made of steel and said double triangular fiber grating sensor is made of aluminum alloy.
6. A fiber grating sensor-based sensitization component as recited in claim 5, wherein said arch bridge strain Liang WaijingThe value range is 11 mm-20 mm; the included angle formed by the two connecting arms, namely the vertex angle of an isosceles triangle formed by the two connecting arms is，The range of the values is as follows=90°=150°。
7. A fiber grating sensor-based sensitization component as recited in claim 3, wherein said arch bridge-shaped strain beam has a thickness at a thinnest intermediate portion thereofThe range of the values is as follows: =0.25 mm to =1.5 Mm; the minimum value of the middle width of the arch bridge-shaped strain beamThe range of the values is as follows: =0.4 mm to =2mm。
8. A method for monitoring pipeline pressure by using the sensitization component based on the fiber bragg grating sensor as claimed in any one of claims 1-7, which is characterized by comprising the following steps:
s1, taking a micro-element body on the surface of the pipeline, and when the pipeline bears the internal pressure When the pipe clamp generates circumferential forceHoop stressCircumferential forceIs decomposed into horizontal forceAnd vertical tensionWherein the horizontal forceCalculated according to formula (1):
（1）；
Wherein the connecting arm is fixed on the pipe clamp through the pins, theta is the included angle between the two pins and the geometrical center connecting line of the pipe clamp, Is the inner diameter of the pipeline,Connecting line for micro element and pipe centerAn included angle of the shaft; the micro-element body is a point on the surface of the pipeline;
s2, introducing coefficients AndHorizontal forceAt a certain connecting armUpper pointGenerates a force atThe following steps are:
（2）；
Wherein, AndIs a coefficient;
S3，、 Respectively connecting arms Upper partAxial and vertical tension of the point:
（3）；
（4）；
Wherein, Is the length of the connecting arm; is a moment;
According to the principle of graph multiplication Normalized to 1, reduced to equation (5) and equation (6):
（5）；
（6）；
Wherein, 、AndNormalized forces are respectively、And。
9. The method of monitoring pipeline pressure according to claim 8, further comprising the steps of:
s4, calculating vertical displacement of the connecting arm by using the Karsch second theorem in material mechanics The calculation process is shown in formula (7):
（7）；
Wherein, For connecting armsThe moment of inertia of the cross-section,；For connecting armsIs defined by the cross-sectional area of (a),，The internal pressure of the pipeline is set;
Is that The amount of vertical displacement of the point,The calculation formula of (2) is as follows:
（8）；
Wherein, Is Young's modulus;
s5, considering the length of the arch bridge-shaped strain beam to be Final strain value of arch bridge shaped strain beamAs shown by formula (9):
（9）。
10. A method of monitoring pipeline pressure as claimed in claim 9, further comprising the steps of:
S6, assuming that a coefficient exists between the wavelength drift amount of the FBG and the internal pressure of the pipeline The following steps are:
（10）；
Wherein, The center wavelength drift amount of the fiber bragg grating;
Substitution of equation (9) into equation The FBG wavelength drift value is calculated from equation (11):
（11）；
Wherein, Is that，Is the effective grating refractive index; representing the period of the reflection of the grating, Is the coefficient of thermal expansion of the optical fiber,Is the thermo-optic coefficient of the optical fiber,Is an effective elasto-optical coefficient; Is the fiber temperature; Is the temperature variation of the optical fiber;
s7, performing temperature compensation or assuming constant temperature, i.e Zero, obtain:
（12）；
Coefficients of Calculated from equation (13):
（13）。
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