CN116026419A - Buried pipeline deflection and stress direction prediction method based on distributed optical fibers - Google Patents
Buried pipeline deflection and stress direction prediction method based on distributed optical fibers Download PDFInfo
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Abstract
The invention provides a deflection and stress direction prediction method of a buried pipeline based on distributed optical fibers, and belongs to the technical field of deflection and stress direction prediction of long-distance buried oil and gas pipelines. According to the invention, distributed strain sensing optical fibers and temperature sensing optical fibers are axially distributed on the surface of a pipeline, and are connected with a distributed optical fiber demodulation instrument in sequence through a wireless network and are connected with a server, a cloud end and a PC end for data analysis. According to the method, the temperature influence of the strain optical fiber is considered, the temperature compensation is carried out on corresponding data, the follow-up prediction result is more accurate and reliable, then the bending strain values of the vertical direction and the transverse direction of the pipeline are calculated based on the strain data after the temperature compensation, and finally the deflection of the pipeline, the external force and the included angle between the vertical direction of the pipeline are calculated. The invention is realized based on the distributed optical fiber sensing technology, has lower layout difficulty and convenient and quick construction, can comprehensively grasp the strain and deformation state of the pipeline under the ground, and provides scientific basis for the safety early warning of the pipeline in high-risk areas.
Description
Technical Field
The invention belongs to the technical field of deflection and stress direction prediction of long-distance buried oil and gas pipelines, and particularly relates to a deflection and stress direction prediction method of a buried pipeline based on distributed optical fibers.
Background
The safe and stable supply of energy is the first requirement of the development of the oil and gas industry in China. In recent years, with the increase of oil gas consumption and import in China, the scale of oil gas pipe networks is continuously enlarged. The long-distance buried pipeline passes through various complex geological units, and geological disasters such as landslide, debris flow and the like frequently occur under severe natural conditions; and engineering activities such as foundation pit excavation, drilling construction, pumping and draining groundwater and the like form serious threats to long-term stable operation of pipelines. Therefore, the safe state of the long-distance pipeline under the action of geological disasters is monitored in real time by adopting a reliable and efficient technical means, the deformation scale and the deformation direction of the long-distance pipeline are predicted in a data analysis and calculation mode, theoretical guidance can be provided for pipeline deformation damage risk evaluation and safety forecasting and early warning, and the method has a very strong technical value in the technical field of long-distance buried oil and gas pipeline engineering safety.
The current pipeline monitoring technology mainly comprises a closed circuit television image monitoring technology, an ultrasonic technology, a magnetic leakage detection technology, a resistance type sensing technology, a vibrating wire type sensing technology and the like. The closed-circuit television image monitoring technology has the advantages that real-time, first-hand and visual image information acquired by a mobile camera is provided, visual judgment is facilitated for technicians, the application of the technology is limited by picture quality, the accuracy of defect identification can be affected due to lack of experience and insufficient attention of the technicians, and the technology needs in-pipe oil gas outage to ensure movement of a robot crawler. The types of defects detected by ultrasonic technology include internal and external metal loss, cracks, wall thickness variation and the like, but the defects require liquid coupling, so the defects are not suitable for natural gas pipelines, and the external environmental noise has a large influence on the measured quality. The magnetic leakage detection technology has the advantages of higher detection speed, low cost and convenient operation, however, excessive use of the magnetic leakage method can lead to permanent magnetization of the steel pipe, thereby restricting the flow of internal fluid and bringing about the problems of incapability of welding and the like. Therefore, closed-circuit television image monitoring technology, ultrasonic technology and magnetic flux leakage detection technology can detect pipeline defects as pipeline quality detection technology, but still have some problems, and also lack effective means for acquiring pipeline strain parameters and describing pipeline deformation characteristics.
The resistance type and vibrating string type sensing technology is a mature structure strain and deformation monitoring technology, is widely applied to large-scale structural engineering such as various bridges and dams, can obtain strain change states on sensing points by applying the two technologies, but has two main limitations when applied to buried long oil and gas pipeline engineering: leak detection and electrostatic sparks are liable to occur. Moreover, the resistance strain gauge and the vibrating wire sensor are both monitored at a single point, linear coverage of a long distance and a large range cannot be realized, and undetected parts between measuring points are difficult to predict if abnormality occurs. In addition, the two technologies adopt a power supply and a magnetic source, static electricity is accumulated when the technology is distributed on petrochemical storage and transportation facilities, the risk of generating electric sparks exists, and the technology belongs to a dangerous source in safety management.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a buried pipeline deflection and stress direction prediction method based on distributed optical fibers, which solves the problems of missed detection, easiness in generating electrostatic spark, incapability of realizing long-distance large-range linear coverage and the like in the traditional pipeline monitoring.
The present invention achieves the above technical object by the following means.
A buried pipeline deflection and stress direction prediction method based on distributed optical fibers comprises the following steps:
step 1: distributing distributed strain sensing optical fibers and distributed temperature sensing optical fibers on the surface of the pipeline along the axial direction;
step 2: the method comprises the steps that a distributed strain sensing optical fiber and a distributed temperature sensing optical fiber are respectively connected with a corresponding distributed optical fiber demodulation instrument, the distributed optical fiber demodulation instrument is connected with a server through a wireless network, the server is connected to a cloud end, and the cloud end is connected with a PC end;
step 4: the server receives strain data and temperature data detected by the distributed strain sensing optical fiber and the distributed temperature sensing optical fiber, simplifies the pipeline into a simply supported beam model, takes one end of the pipeline as an origin, and takes the pipeline along the axial direction
In the axial direction, carrying out temperature compensation on the corresponding data, respectively calculating the vertical and transverse bending strain values of the pipeline based on the strain data after the temperature compensation, and calculating to obtain the deflection of the pipeline, the included angle between the external force and the vertical direction of the pipeline based on the vertical and transverse bending strain values;
step 5: the server stores the calculation result in the cloud end, forms a corresponding graph based on the calculation result, and displays the graph on the PC end for relevant personnel to check and analyze.
Further, four distributed strain sensing optical fibers and one distributed temperature sensing optical fiber are distributed on the surface of the pipeline, the four distributed strain sensing optical fibers are respectively located on the upper surface, the lower surface and the front side and the rear side of the pipeline, and connecting lines among the distributed strain sensing optical fibers with opposite positions are in a cross shape.
Further, in the step 4, temperature compensation is performed using the following formula corresponding to the variable data:
in the method, in the process of the invention,
、/>
、/>
、/>
respectively representing strain data acquired by the distributed strain sensing optical fibers at the lower surface, the upper surface, the front side and the rear side of the pipeline; />
Representing strain data acquired by the distributed temperature sensing optical fiber; />
、/>
、/>
、/>
Respectively representing strain data corresponding to the temperature compensated lower surface, the upper surface, the front side and the rear side of the pipeline distributed strain sensing optical fiber.
Further, in the step 4, based on the strain data after temperature compensation, bending strain values in the vertical direction and the transverse direction of the pipeline are calculated respectively by using the following methods
And->
：
In the method, in the process of the invention,
、/>
、/>
、/>
respectively representing strain data corresponding to the temperature compensated lower surface, the upper surface, the front side and the rear side of the pipeline distributed strain sensing optical fiber.
Further, in the step 4, the pipeline deflection calculation process is as follows:
substituting the vertical and transverse bending strain values of the pipeline into the following formula to obtain the transverse deflection of the pipeline
And vertical deflection->
：/>
The pipe is deflected
The method comprises the following steps: />
；
In the method, in the process of the invention,
is a deflection distribution function along the axial direction of the pipeline; />
As a function of bending strain along the axial direction of the pipe,
distance parameter of distributed strain sensing optical fiber in axial direction of pipeline, < >>
Is the distance between the distributed strain sensing optical fiber and the neutral surface of the pipeline; />
、/>
Is constant.
Further, in the step 4, an included angle between the external force and the vertical direction of the pipeline is
，/>
，
Represents the transverse bending strain value of the pipeline, +.>
Representing the vertical bending strain value of the pipeline.
The invention has the following beneficial effects:
1. the invention predicts the deflection and the stress direction of the pipeline based on the distributed optical fiber sensing technology, and the distributed optical fiber has the characteristics of light weight, small volume, flexibility, electromagnetic interference resistance, distributed, long distance, large-scale sensing and the like, and is not only a sensing element but also a transmission medium after being distributed on the surface of a pipeline, and can sense thousands of measuring points, so that the problems of few monitoring points and easy detection omission of the traditional point type sensor are not easy to occur; the distributed optical fiber has the characteristics of slender flexibility and softness, so that the difficulty in arrangement can be reduced, and the construction efficiency can be improved; the distributed optical fiber has the characteristics of light source transmission and intrinsic safety, and can solve the risk problem of electric spark generated by electrostatic accumulation of point type and magnetic type sensors on the metal surface.
2. According to the invention, the temperature influence of the strain optical fiber is considered, the temperature compensation optical cable is synchronously laid, the accuracy of the strain monitoring result can be improved, and the guarantee is provided for accurate calculation of the deflection and the stress direction of the pipeline.
3. According to the invention, the distributed optical fibers are distributed on the buried pipeline, and the deflection and the stress direction of the pipeline are obtained by combining calculation, so that the strain and deformation state of the pipeline in the ground can be comprehensively mastered under the condition that the oil and gas pipeline is not stopped and is not excavated for inspection, the nerve perception of the buried pipeline is realized, and a scientific basis is provided for the safety forecasting and early warning of the pipeline in high-risk areas.
4. According to the characteristic that the temperature difference is generated between the pipeline and the surrounding environment when the pipeline leaks, the position of the pipeline where the pipeline leaks can be monitored simultaneously by using the laid temperature sensing optical cable, so that the multi-parameter and three-dimensional monitoring functions of the buried pipeline such as strain, temperature, deformation deflection, stress direction, leakage and the like can be realized, and the safe and continuous operation of the pipeline is ensured.
Drawings
FIG. 1 is a schematic diagram of a distributed strain sensing optical fiber and a distributed temperature sensing optical fiber arrangement;
FIG. 2 is a schematic cross-sectional view of a distributed strain sensing optical fiber and a distributed temperature sensing optical fiber arrangement;
FIG. 3 is a schematic diagram of a test apparatus;
FIG. 4 is a graph of pipeline deflection test results;
FIG. 5 is a schematic view of the neutral plane of the pipeline;
FIG. 6 is a graph of angle estimates for a 0 loading angle;
FIG. 7 is a graph of angle estimates for a 30 loading angle;
FIG. 8 is a graph of angle estimates for a 45 loading angle;
fig. 9 is a graph of angle estimates for a 60 deg. loading angle.
In the figure: 1-a pipeline; 2-distributed strain sensing optical fiber; 3-distributed temperature sensing fiber; 4-distributed optical fiber demodulation instrument; 5-a server; 6-cloud end; 7-PC end; 8-fiber grating demodulator; 9-resistance strain gauge.
Detailed Description
The invention will be further described with reference to the drawings and the specific embodiments, but the scope of the invention is not limited thereto. In the embodiment, a PVC pipe (hereinafter referred to as a pipeline 1) with the length of 4m and the diameter of 75mm is selected as a measuring object, the loading of weights is combined to simulate the underground stress condition of a buried pipeline, the pipeline deflection and the stress direction are predicted and analyzed, and an optical fiber grating string and a resistance strain gauge are introduced in the process to perform comparative analysis so as to prove the superiority of the distributed optical fiber sensing technology.
The invention relates to a method for predicting deflection and stress direction of a buried pipeline based on distributed optical fibers, which comprises the following steps:
step 1: laying optical fibers;
as shown in fig. 1 and 2, distributed strain sensing optical fibers 2 are distributed on the surface of a pipeline 1 and are used for acquiring strain change data of the surface of the pipeline 1; in this embodiment, the distributed strain sensing optical fibers 2 are distributed back and forth on the surface of the pipeline 1 in a loop-shaped manner, four sections of main body parts parallel to the axis of the pipeline 1 are formed on the surface of the pipeline 1 (i.e., the distributed strain sensing optical fibers 2 1, 2, 3 and 4 shown in fig. 2), the distributed strain sensing optical fibers 2 1 and 4 are respectively positioned on the lower surface and the upper surface of the pipeline 1, the distributed strain sensing optical fibers 2 and 3 are respectively positioned on two sides of the pipeline 1, and the connection line between the distributed strain sensing optical fibers 2 1 and 4 and the connection line between the distributed strain sensing optical fibers 2 and 3 are in a cross shape;
then, a distributed temperature sensing optical fiber 3 is arranged on the surface of the pipeline 1 and used for acquiring temperature change data in the axial direction of the pipeline 1, so that temperature compensation is carried out on the distributed strain sensing optical fiber 2; the distribution position of the distributed temperature sensing optical fiber 3 has no specific requirement, and the distributed temperature sensing optical fiber 3 is axially and straightly arranged along the pipeline 1 in the embodiment;
in the embodiment, the distributed strain sensing optical fiber adopts a 0.9mm tight sleeve polyurethane optical fiber, and the distributed strain sensing optical fiber 2 and the distributed temperature sensing optical fiber 3 are adhered and fixed with the pipeline 1 through epoxy resin.
Step 2: a plurality of groups of fiber bragg grating strings and resistance strain gauges are stuck on the upper surface and the lower surface of the pipeline 1, which are close to the distributed strain sensing optical fibers 2, for subsequent data comparison analysis;
step 3: setting up a test device;
as shown in fig. 1 and 3, two ends of a pipeline 1 are fixed on a support frame body by using a clamp, and a plurality of dial indicators (preferably five in the embodiment) are uniformly distributed on the upper surface of the pipeline 1 at intervals and used for measuring the actual deflection value of the pipeline 1;
then the distributed strain sensing optical fiber 2 and the distributed temperature sensing optical fiber 3 are respectively connected with the corresponding distributed optical fiber demodulation instrument 4, the fiber grating string is connected with the fiber grating demodulation instrument 8, the resistance strain gauge is connected with the resistance strain gauge 9, the distributed optical fiber demodulation instrument 4, the fiber grating demodulation instrument 8 and the resistance strain gauge 9 are connected with the server 5 in a 4G/5G mode, the server 5 is connected to the cloud end 6, the cloud end 6 is connected with the PC end 7, and further data recording, storage, calculation, analysis and processing are achieved;
then, a plurality of weights with weights of 2kg and 1kg are prepared for loading the pipeline 1; after the whole test device is built and stabilized, starting the test.
Step 4: predicting deflection of the pipeline 1:
step 4.1: when the pipeline 1 is in an empty state, the values of the dial indicators are recorded and input into a PC end, the values are transmitted to a server through the PC end, and meanwhile, output data of the distributed optical fiber demodulation instrument 4, the optical fiber grating demodulation instrument 8 and the resistance strain gauge 9 are also transmitted to the server;
step 4.2: suspending a 2kg weight at the midpoint position of the pipeline 1, continuously recording the values of the dial indicators after the weight is stabilized, inputting the values into a PC end, and simultaneously transmitting output data of the distributed optical fiber demodulation instrument 4, the optical fiber grating demodulation instrument 8 and the resistance strain gauge 9 to a server;
step 4.3: continuously and sequentially loading weights of 2kg, 2kg and 1kg, recording the current dial indicator value after each stabilization, inputting the current dial indicator value into a PC end, and simultaneously transmitting output data of the distributed optical fiber demodulation instrument 4, the optical fiber grating demodulation instrument 8 and the resistance strain gauge 9 to a server;
step 4.4: the server 5 receives all acquired data and analyzes and calculates the deflection of the pipeline 1;
the distributed optical fiber demodulation apparatus 4 is based on the BOTDA technology, the temperature and the strain can cause the brillouin scattering light frequency in the distributed strain sensing optical fiber 2 to drift, and the linear relation between the drift amount (frequency shift amount) of the brillouin scattering light frequency and the strain and the temperature is as follows:
in the method, in the process of the invention,
the method comprises the steps of testing the frequency drift amount of brillouin scattering light in a front-back distributed strain sensing optical fiber 2; />
、/>
The axial strain values of the distributed strain sensing optical fiber 2 before and after the test are respectively +.>
、/>
The temperature values of the distributed strain sensing optical fibers 2 before and after the test are respectively; />
、/>
Strain influence coefficient and temperature influence coefficient respectively; based on the above relation, the distributed optical fiber demodulation instrument 4 can realize the distributed strain after automatically measuring the shift amount of the brillouin scattering light frequency along the length direction of the distributed strain sensing optical fiber 2Distributed measurement of axial temperature and strain of the sensing fiber 2;
step 4.4.1: temperature compensation is carried out on strain data acquired by the distributed strain sensing optical fiber 2;
the pipeline 1 with two fixed ends is simplified into a simply supported beam model, the left end of the pipeline 1 is taken as an origin, and the pipeline 1 is axially taken as
In the axial direction, strain data +.f corresponding to the distributed strain sensing optical fiber No. 1, no. 2, no. 3 and No. 4 after temperature compensation are calculated by the following formula>
、/>
、/>
、/>
：
In the method, in the process of the invention,
、/>
、/>
、/>
respectively representing strain data acquired by the distributed strain sensing optical fibers No. 1, no. 2, no. 3 and No. 4; />
Representing temperature compensation data, namely strain data acquired by the distributed temperature sensing optical fiber 3;
step 4.4.2: based on the strain data after temperature compensation, bending strain values of the pipeline 1 in the vertical direction (namely the direction of the distributed strain sensing optical fiber connecting line of No. 1 and No. 4) and the transverse direction (namely the direction of the distributed strain sensing optical fiber connecting line of No. 2 and No. 3) are calculated respectively
And->
：
Step 4.4.3: based on
And->
The lateral deflection of the pipe 1 is calculated using the following formula>
And vertical deflection->
：/>
In the method, in the process of the invention,
is a deflection distribution function along the axial direction of the pipeline 1; />
As a function of bending strain along the axial direction of the pipe 1 +.>
Distance parameter of the distributed strain sensing fiber in the axial direction of the pipe 1, e.g./>
Represents the bending strain value at 2.58 meters from the left end of the pipe 1,/o>
Representing the deflection value at 3.65 meters from the left end of the pipe 1; />
The distance between the distributed strain sensing optical fiber and the neutral surface of the pipeline is distributed; in the case of a known length and diameter of the pipe 1
Lower parameters
、/>
According to boundary conditions: length of->
The deflection of both ends of the pipe 1 is 0 (i.e. +.>
，
) Obtaining;
the pipe 1 is deflected
The method comprises the following steps: />
；
Step 4.4.4: and the server 5 stores the calculated deflection data of the pipeline 1 in the cloud.
Step 5: and (3) carrying out statistics on deflection test results of the pipeline 1:
the server 5 calculates a plurality of different deflection values obtained by three sensors (namely the distributed strain sensing optical fiber 2, the fiber bragg grating string and the resistance strain gauge) under four-level loading, and forms a corresponding pipeline deflection test result graph which is displayed at a PC end for relevant personnel to check and analyze;
in the embodiment, five deflection values are calculated based on each sensor, and a pipeline deflection test result graph is shown in fig. 4;
in fig. 4, the abscissa represents the horizontal axial distance (in meters) of the pipe 1, and the ordinate represents the deflection value (in millimeters); the three curves are deflection curves corresponding to the three sensors respectively, the solid line is a deflection curve of the distributed strain sensing optical fiber, the long dashed line is a deflection curve corresponding to the fiber bragg grating string, the short dashed line is a deflection curve corresponding to the resistance strain gauge, and the square points are data measured by a dial indicator, wherein the data measured by the dial indicator are used as real deflection values for analysis; because the fiber grating strings and the resistance strain gauges are point-type measurement, in order to see the deflection curve forms of the fiber grating strings and the resistance strain gauges, two adjacent point deflection values are connected into a straight line to be displayed in the graph in the embodiment;
as can be seen from FIG. 4, the deflection curves corresponding to the distributed strain sensing optical fiber 2, the fiber grating string and the resistance strain gauge have stronger correlation, the presented forms are very similar, and the coincidence degree of the measured data of the dial indicator is higher, wherein the deflection curve obtained by the distributed strain sensing optical fiber 2 is smooth and continuous, and is more in line with the actual form of the deflection deformation of the pipeline 1, the error of the monitoring result based on the distributed strain sensing optical fiber 2 is very small and between 2% and 3%, the requirement of the monitoring of the pipeline 1 can be met, the technology can fully monitor the distribution of the deformation of the pipeline 1 in a distributed manner, and the monitoring advantage of the pipeline 1 is very obvious.
Step 6: a pipeline 1 is prepared again, distributed strain sensing optical fibers 2 are only distributed on the pipeline 1 according to the step 1, and then a test device is built according to the step 3.
Step 7: predicting the stress direction of the pipeline 1:
step 7.1: in the initial state, the rotation angle (loading angle) of the pipeline 1 is 0 degrees, and various data in the initial state are recorded according to the step 4.1;
step 7.2: suspending a 1kg weight at the position of the middle point of the pipeline 1, and continuously recording various data at the moment in the step 4.1 after the weight is stabilized;
step 7.3: continuously and sequentially loading weights of 1kg, 1kg and 1kg, and recording all data at the moment according to the step 4.1 after each stabilization;
step 7.4: removing the weights and the clamps at the two ends of the pipeline 1, continuously fixing the pipeline 1 by the clamps after rotating the pipeline 1 integrally for 30 degrees, repeating the steps 7.1 to 7.3, and recording various data under the loading angle of 30 degrees;
step 7.5: repeating the step 7.4, and recording various data under loading angles of 45 degrees and 60 degrees;
step 7.6: the server 5 receives all the acquired data, and firstly calculates and obtains the vertical bending strain value of the pipeline 1 according to the method in the step 4.4
And transverse bending strain value->
Then the angle between the external force F (i.e. the stress direction) and the vertical direction of the pipeline 1 is determined to be +.>
；
In the method, in the process of the invention,
represents the modulus of elasticity>
A representation of moment of inertia; as shown in fig. 5, ->
Represents the distance between the distributed strain sensing optical fiber No. 1 or No. 4 and the central surface of the pipeline, and is +.>
Representing the distance between the No. 2 or No. 3 distributed strain sensing optical fiber and the central surface of the pipeline; />
Representing a bending moment function in the axial direction of the pipe 1, e.g +.>
Representing a bending moment at 2.56 meters from the left end of the pipe 1;
calculated out
Is an angle estimated value; finally, the server 5 stores the calculated angle calculation value data in the cloud end 6.
Step 8: calculating the prediction result of the stress direction of the pipeline 1;
the server 5 calculates corresponding angle calculation value data of the five-stage weight loading under each loading angle according to the method in the step 7, forms a corresponding angle calculation value graph, displays the angle calculation value graph at the PC end 7, and allows related personnel to check and analyze the angle calculation value graph;
the angle estimated value graphs are shown in fig. 6 to 9, wherein the abscissa represents the loading times, the ordinate represents the angle estimated value, and the broken lines in the graphs represent the actual angle value; the error of the calculated angle value and the actual angle value is counted, the relative error is between 10% and 20%, and the angle value deduced from the test value of the distributed strain sensing optical fiber 2 is more consistent with the actual angle value, so that the distributed strain sensing optical fiber 2 is suitable for predicting the deformation direction of the pipeline 1.
In the embodiment, the deflection value is calculated based on the fiber bragg grating string and the resistance strain gauge detection in the prior art, and the invention is not repeated. The examples are preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments, and any obvious modifications, substitutions or variations that can be made by one skilled in the art without departing from the spirit of the present invention are within the scope of the present invention.
Claims (6)
1. A method for predicting deflection and stress direction of buried pipeline based on distributed optical fiber is characterized by comprising the following steps:
step 1: a distributed strain sensing optical fiber (2) and a distributed temperature sensing optical fiber (3) are arranged on the surface of the pipeline (1) along the axial direction;
step 2: the distributed strain sensing optical fiber (2) and the distributed temperature sensing optical fiber (3) are respectively connected with a corresponding distributed optical fiber demodulation instrument (4), the distributed optical fiber demodulation instrument (4) is connected with a server (5) through a wireless network, the server (5) is connected to a cloud end (6), and the cloud end (6) is connected with a PC end (7);
step 4: the server (5) receives strain data and temperature data detected by the distributed strain sensing optical fiber (2) and the distributed temperature sensing optical fiber (3), simplifies the pipeline (1) into a simply supported beam model, takes one end of the pipeline (1) as an origin point and takes the pipeline (1) as an axial direction
Carrying out temperature compensation on the corresponding data in the axial direction, respectively calculating the vertical and transverse bending strain values of the pipeline (1) based on the strain data after the temperature compensation, and calculating to obtain the deflection of the pipeline (1) and the included angle between the external force and the vertical direction of the pipeline (1) based on the vertical and transverse bending strain values;
step 5: the server (5) stores the calculation result in the cloud end, forms a corresponding graph based on the calculation result, and displays the graph on the PC end for relevant personnel to check and analyze.
2. The method for predicting the deflection and stress direction of the buried pipeline based on the distributed optical fibers according to claim 1, wherein four distributed strain sensing optical fibers (2) and one distributed temperature sensing optical fiber (3) are distributed on the surface of the pipeline (1), the four distributed strain sensing optical fibers (2) are respectively positioned on the upper surface, the lower surface and the front side and the rear side of the pipeline (1), and connecting lines between the distributed strain sensing optical fibers (2) with opposite positions are in a cross shape.
3. The method for predicting the deflection and stress direction of a buried pipeline based on a distributed optical fiber according to claim 1, wherein in the step 4, temperature compensation is performed by using the following corresponding data:
in the method, in the process of the invention,
、/>
、/>
、/>
respectively show the lower surface and the upper surface of the pipelineStrain data acquired by the surface, front side and rear side distributed strain sensing optical fibers (2); />
Representing strain data acquired by the distributed temperature sensing optical fiber (3); />
、/>
、/>
、/>
Respectively representing the strain data corresponding to the temperature compensated lower surface, the upper surface, the front side and the rear side of the pipeline distributed strain sensing optical fiber (2).
4. The method for predicting deflection and stress direction of buried pipeline based on distributed optical fiber according to claim 1, wherein in the step 4, based on the strain data after temperature compensation, bending strain values of the pipeline (1) in vertical and horizontal directions are calculated respectively by using the following formula
And->
：
In the method, in the process of the invention,
、/>
、/>
、/>
respectively representing the strain data corresponding to the temperature compensated lower surface, the upper surface, the front side and the rear side of the pipeline distributed strain sensing optical fiber (2).
5. The method for predicting the deflection and the stress direction of the buried pipeline based on the distributed optical fiber according to claim 1, wherein in the step 4, the deflection calculation process of the pipeline (1) is as follows:
substituting the values of the vertical and transverse bending strain of the pipeline (1) into the following formula to obtain the transverse deflection of the pipeline (1)
And vertical deflection->
：
The deflection of the pipeline (1)
The method comprises the following steps:
in the method, in the process of the invention,
for along the pipeline (1)An axial deflection distribution function; />
As a function of bending strain along the axial direction of the pipe (1)>
Is a distance parameter of the distributed strain sensing optical fiber (2) in the axial direction of the pipeline (1), and is +.>
Is the distance between the distributed strain sensing optical fiber (2) and the neutral surface of the pipeline; />
、/>
Is constant.
6. The method for predicting deflection and stress direction of buried pipeline based on distributed optical fiber according to claim 1, wherein in step 4, the included angle between the external force and the vertical direction of the pipeline (1) is
，/>
，
Represents the transverse bending strain value of the pipeline (1), & lt->
Represents the vertical bending strain value of the pipeline (1). />
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