A method and system for identifying and reconstructing the span of a submarine pipeline based on distributed fiber optic strain sensing

Abstract

This invention discloses a method and system for identifying and reconstructing suspended spans of subsea pipelines based on distributed fiber optic strain sensing, belonging to the field of subsea pipeline integrity management and structural health monitoring technology. The invention deploys distributed fiber optic strain sensors longitudinally along the monitored pipeline segment, dispersing them circumferentially to form measurement positions, thereby separating strain and determining the principal bending plane and curvature. The curvature energy ratio extrapolation is used as the convergence criterion to determine the boundary of the suspended span influence region. A simply supported conjugate beam model is established within the suspended span influence region to obtain the foundation displacement field and rotation field reflecting the elastic deformation of the suspended span. Addressing the limitation of the conjugate beam method in reconstructing the rigid body displacement effect generated by pipe-soil interaction, a zero-curvature rigid body follow-up displacement correction method is proposed. This method compensates for the missing rigid body displacement components in the real displacement field by constructing a piecewise linear correction term. This invention overcomes the difficulty of conventional numerical reconstruction relying on ideal boundaries and improves the computational accuracy of spatial displacement field reconstruction.

Description

Technical Field

[0001] This invention belongs to the field of submarine pipeline engineering technology, specifically relating to a method and system for identifying and reconstructing submarine pipeline spans based on distributed optical fiber strain sensing. Specifically, it is a method and system for acquiring longitudinal strain of multiple measuring lines using distributed optical fiber strain sensors and realizing the identification of submarine pipeline spans and the reconstruction of three-dimensional spatial displacement. It belongs to the field of submarine pipeline integrity management and structural health monitoring technology. Background Technology

[0002] Submarine pipelines are prone to localized bottom suspensions, forming spans, during seabed scouring, uneven settlement, and the evolution of pipe-soil interaction. The displacement response state of the span area and the transition zone between the pipe and soil on both sides is a fundamental input parameter for pipeline ultimate strength verification and vortex-induced vibration fatigue life assessment. Distributed fiber optic strain sensing technology can acquire continuous strain field information along the pipeline's longitudinal direction, providing real-time data for span identification and displacement reconstruction.

[0003] Submarine pipelines, when suspended, exhibit three-dimensional spatial deformation under the influence of their own weight, internal fluids, wave and current loads, and boundary constraints. Existing fiber optic strain-based displacement reconstruction techniques for these suspended sections have the following limitations: First, insufficient stability in spatial curvature decoupling. Single-line strain data struggles to accurately separate bending strain components under axial deformation coupling conditions, leading to errors in the orientation of the principal bending plane and the calculation of spatial curvature. Second, defining the suspended section boundary is challenging. A pipe-soil interaction transition zone exists between the suspended section and the seabed. Determining the boundary using fixed thresholds or manual truncation methods easily causes truncation position drift, resulting in integration calculation errors. Third, the dependence of conventional numerical reconstruction methods on ideal boundary conditions limits computational accuracy. The true boundary of a submarine pipeline's suspended section is the result of pipe-soil interaction, manifested as the natural attenuation of displacement, rotation, and curvature in the soil support zone, eventually reaching zero. This attenuated boundary formed by interaction cannot be fully equivalently described by classical simply supported or fixed-end constraints. Existing deformation reconstruction models, such as the conjugate beam method, can only adapt to ideal simply supported or fixed boundaries. If the soil-tube boundary is assumed to be simply supported in displacement reconstruction, it only solves the problem of reconstructing the foundation displacement field and rotation field reflecting the elastic deformation of the cantilever under a given observed curvature. It cannot guarantee the correct reconstruction of the real displacement field and rotation field generated by the soil-tube interaction, because the real displacement field and rotation field include not only the component reflecting the elastic deformation of the cantilever but also the rigid body displacement effect caused by the soil-tube interaction. If polynomial interpolation is directly used to force smoothing of these end errors, it will change the second derivative of the displacement function and introduce spurious distributed bending moments, causing the reconstruction results to lose mechanical authenticity. Therefore, overcoming the theoretical difficulty that conventional models such as conjugate beams cannot be applied to special boundary conditions of cantilever spans is the key to achieving high-precision cantilever span identification and spatial displacement reconstruction. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for identifying and reconstructing suspended subsea pipelines based on distributed optical fiber strain sensing, in order to solve problems such as strain separation error, unstable boundary determination, and the inability of conventional conjugate beam reconstruction to be applied to special boundary conditions of suspended subsea pipelines. This invention is of great significance for the management of suspended subsea pipelines and the maintenance of structural integrity.

[0005] To solve the above problems, the present invention adopts the following technical solution, including steps S1 to S7.

[0006] S1. Distributed fiber optic strain sensors are deployed along the longitudinal direction of the subsea pipeline to be monitored to continuously acquire longitudinal strain data, and at least three independent longitudinal strain measurement positions are dispersed in the circumferential direction at any cross section to be analyzed. S2, Based on arbitrary position of the pipeline The longitudinal strain observations are used to establish the strain distribution relationship of the cross section, separate the axial strain component and the bending strain component of the cross section, and obtain the curvature components corresponding to the vertical reference direction and the horizontal reference direction. and This allows for the determination of the pipeline's neutral plane, principal bending plane, and principal curvature. ; S3, Based on the principal curvature Construct indicators for identifying the impact area of ​​suspended bridges and determine continuous abnormal intervals covering the response of suspended bridges; S4. Set left and right boundary neighborhoods on both sides of the continuous abnormal interval, and sample within each neighborhood according to the longitudinal sampling interval. Construct a set of discrete candidate boundaries; for each candidate boundary combination Calculate bending energy based on curvature data And the curvature energy after candidate boundary expansion accounts for the proportion of the external expansion. As a candidate boundary force school core indicator; S5. In the candidate boundary combinations covering the continuous abnormal intervals, the external amplification amount is calculated based on the curvature energy ratio. The final affected area of ​​the suspension span is determined by the criterion that the area is not greater than a preset threshold and the change after expansion does not exceed a preset threshold. ; and make the bending strain and curvature at the final boundary return to zero, satisfying the interval cumulative curvature The regression should not exceed a preset threshold to indicate that the regressions at both ends of the corner are consistent. S6, in the area affected by the suspension Within this model, the boundary conditions are simplified to simply supported, and a simply supported conjugate beam model is established on the principal bending plane, with curvature... As a distributed load on the conjugate beam, the deformation is reconstructed by utilizing the dual relationship between the shear force and bending moment of the conjugate beam and the rotation and displacement of the real beam, thus obtaining the foundation rotation field that reflects the elastic deformation of the cantilever span. and basic displacement field To address the limitation of the conjugate beam method in not being able to include the rigid body displacement effect caused by the interaction between the pipe and the soil, a zero-curvature rigid body follow-up displacement correction term is constructed. The displacement field is then subjected to rigid body translation and rotation corrections to obtain the corrected displacement. ; wherein, the For in the interval A piecewise linear function that is continuous within the inflection point and satisfies the second derivative in all regions outside the inflection point. The The actual cantilever boundary constraint formed by the interaction between the soil and the pipe is determined by setting the rotation angles of the left and right segments of the broken line to be equal to the opposite values ​​of the rotation angles at both ends of the foundation rotation field, in order to compensate for the missing rigid body displacement effect in the actual displacement field and rotation field, so that the corrected left end satisfies and The right end satisfies and And combined with the endpoint regression condition in step S5, the curvature is made and ; S7. Based on the angle between the main bending plane and the horizontal reference plane. The suspended displacement within the main bending plane Projection yields the three-dimensional spatial distribution of vertical and horizontal cantilever displacements.

[0007] Furthermore, in step S1, the strain observations at any longitudinal position of the pipeline are no fewer than three and mutually independent on the cross section; the mutual independence means that the measurement positions do not coincide in pairs on the circumferential direction of the cross section and are distributed circumferentially, so that the axial strain established based on step S2 is... Vertical curvature and horizontal curvature The system of linear equations has a unique solution; where, when the number of measurement locations... When the value equals 3, it is obtained by directly solving the system of linear equations. , and When the number of measurement locations When the value is greater than 3, the least squares method is used to obtain the solution. , and .

[0008] Furthermore, the measurement positions are preferably four positions distributed approximately evenly along the circumference of the pipe cross-section, located at 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock clockwise, respectively. When the outer diameter of the pipe is... At that time, the longitudinal strain observations at the four locations were denoted as follows: , , and Then we have: axial strain components Vertical curvature component Horizontal curvature component .

[0009] Furthermore, in step S3, the continuous abnormal interval is determined by threshold discrimination: firstly, a statistic for threshold discrimination is constructed based on the median and absolute median difference of the global curvature data, and then the continuous abnormal interval is identified according to the statistic threshold of a preset multiple.

[0010] Further, in steps S4 and S5, the calculation and discrimination criteria for the curvature energy ratio of the external amplification are as follows: the curvature energy External expansion amount is defined as ,when Not greater than the preset threshold When the curvature energy increment change after the candidate window is expanded satisfies the convergence condition, its boundary is determined as the final boundary of the suspended influence area.

[0011] Furthermore, in step S6, the executable calculation method for the deformation reconstruction of the simply supported conjugate beam is as follows: in the cantilever influence area... Establish a simply supported conjugate beam model in the principal bending plane, and use curvature As a distributed load, the shear force field and bending moment field of the conjugate beam are calculated using static equilibrium conditions to obtain the foundation rotation field reflecting the elastic deformation of the cantilever span. With the basic displacement field The elastic deformation rotation angles at the left and right ends of the affected area are respectively and .

[0012] Furthermore, in step S6, the zero-curvature rigid body follower displacement correction term The construction and correction method is as follows: the suspended influence area Assuming the form of a piecewise polygonal line, the location of the inflection point is determined by making the rotation angles of the left and right segments of the polygonal line equal to the negatives of the corresponding boundary rotation angles of the simply supported conjugate beam. Based on the position coordinates of the left and right ends of the affected area of ​​the cantilever span and the location of the inflection point Determine the rigid body follower displacement correction term represented by the polygonal line. Combine it with the basic displacement field By superposition, the suspended displacement field in the principal bending plane can be determined. This ensures that the actual boundary conditions of the natural decay of the displacement, rotation angle, and curvature of the suspended influence area are all satisfied.

[0013] A subsea pipeline suspension identification and reconstruction system for implementing the above method includes: a distributed optical fiber strain acquisition unit for continuously acquiring longitudinal strain data along the longitudinal direction of the pipeline section to be monitored, and forming at least three independent longitudinal strain measurement positions in the circumferential direction of any section to be analyzed; a data processing unit for performing axial and bending strain separation, determination of the main bending plane, determination of the suspension influence area, reconstruction of conjugate beam deformation, and correction of rigid body follow-up displacement; and a result output unit for outputting the three-dimensional suspension displacement components in the vertical and horizontal directions.

[0014] The beneficial effects of this invention are as follows: (1) Based on the longitudinal strain observations that are independent of each other in the circumferential direction of the cross section, the axial strain and bending strain are separated by constructing a linear equation system, which reduces the multiple interferences caused by temperature, internal pressure and axial force, and provides a physical basis for determining curvature and main bending plane.

[0015] (2) The influence of the support section boundary on the bending deformation energy of the system is evaluated by calculating the ratio of the curvature energy increase before and after the candidate window is expanded. The boundary position containing the pipe-soil interaction zone is determined by using the ratio of the increase not greater than the preset threshold as the convergence criterion, which reduces the randomness of the boundary interval cutoff.

[0016] (3) This invention overcomes the difficulty of applying conjugate beam reconstruction to special boundary conditions of suspended subsea pipelines and proposes a zero-curvature rigid body follow-up displacement correction method. Conventional conjugate beam methods are limited by the assumption of ideal simply supported boundaries. When applied to pipe-soil interaction sections, they can only reconstruct the components reflecting the elastic deformation of the suspended span, and cannot truly restore the displacement field and rotation field containing rigid body displacement effects. Under the premise of calculating the basic displacement field and rotation field reflecting the elastic deformation of the suspended span using a simply supported conjugate beam model, this invention equates the local transition elastic deformation to inflection points and uses piecewise linear polygons to construct rigid body follow-up displacement correction terms. Since the second derivative of the piecewise linear function is always equal to zero in the region outside the inflection point, this method can satisfy the true boundary constraints of natural decay of pipe-soil interaction in the entire section without generating additional curvature by only compensating for the missing rigid body displacement effect, thus solving the theoretical limitation of numerical reconstruction relying on ideal boundary conditions.

[0017] (4) Combining the main plane projection method, the displacement distribution in the main bending plane is converted into spatial vertical and horizontal components to obtain the three-dimensional displacement curve of the submarine pipeline, providing quantitative data parameters for pipeline engineering integrity management. Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the layout of the circumferential measurement positions of the pipe cross-section in an embodiment of the present invention.

[0019] Figure 2This is a schematic diagram illustrating the principle of zero-curvature rigid body displacement correction in an embodiment of the present invention.

[0020] The attached figures are labeled as follows: 1. Submarine pipeline, 2. Distributed fiber optic strain sensor, 3. Reconstructed displacement field of simply supported conjugate beam, 4. Rigid body follow-up displacement compensation displacement field, 5. Reconstructed displacement field of suspended span, 6. Seabed. Detailed Implementation

[0021] Example 1: Sensor Configuration and Longitudinal Strain Data Acquisition like Figure 1 As shown, distributed fiber optic strain sensors 2 are deployed longitudinally along the pipeline section to be monitored in the subsea pipeline 1. Independent longitudinal strain measurement positions are formed by dispersing these sensors circumferentially at any cross-section to be analyzed. Preferably, this embodiment uses four distributed fiber optic measurement lines parallel to the pipeline's longitudinal direction, corresponding to four circumferential measurement positions at 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock clockwise on the cross-section. The distributed fiber optic strain sensors 2 at the four positions continuously output the longitudinal position of the pipeline. The strain observation data at the location are denoted as follows: , , and .

[0022] The measurement position can be formed by a single distributed optical fiber strain sensor 2 arranged in a folding manner through coordinate mapping, or it can be formed by multiple distributed optical fiber strain sensors 2 respectively. The present invention does not limit the specific number of distributed optical fiber strain sensors 2, the connection method, or the demodulation method.

[0023] Example 2: Strain Separation of Sections and Determination of Principal Bending Plane In the longitudinal position of the pipeline Establish a local reference coordinate system on the cross section. ,in The origin of the cross-section reference coordinate system is... The axis is in the vertical direction. The axis is horizontal. The outer diameter of the pipe is... By using the plane section assumption to decouple axial strain from longitudinal strain, the pipe's... The axial strain at is Based on the axial strain, the horizontal and vertical curvature components on the cross section can be further calculated as follows: and The neutral plane trace of the pipe bend satisfies The plane orthogonal to the neutral plane is the principal bending plane of the pipe. The angle between this principal bending plane and the horizontal curvature component is determined by the vertical curvature component. The curvature of the pipe in the principal bending plane is... .

[0024] Example 3: Algorithm for Identifying the Affected Area of ​​Suspended Bridges Curvature obtained based on Example 2 A search is conducted across the boundary of the affected area. First, anomaly zones are initially screened, based on all curvature data along the monitored pipe section. According to curvature data The median and absolute median difference are used for evaluation, and the segment covering the suspended response is selected as the continuous anomaly interval. Next, energy candidate verification is performed, i.e., boundary neighborhoods are established outside the left and right ends of the continuous anomaly interval, according to the sampling interval of the distributed fiber strain measurement. Generate candidate boundary combinations Next, perform an energy increment assessment, i.e., define the interval bending energy. Calculate the energy increment ratio after expanding the candidate window by one step. ,like ( If a preset threshold is used, the outward expansion area is determined to be in a stable supported state by the seabed soil. Finally, auxiliary regression verification is performed at the suspended boundary, i.e., to examine the boundary. and and the absolute value of cumulative curvature Whether the threshold condition is met, the shortest window that meets the condition is determined as the overhanging influence area. .

[0025] Example 4: Reconstruction of conjugate beam with suspended displacement and correction of rigid body dynamic displacement like Figure 2 As shown, this step uses a zero-curvature rigid body follower displacement correction algorithm to solve the problem that conventional mechanical models such as conjugate beams cannot be directly applied to the natural attenuation boundary of the pipe-soil system.

[0026] Step 1: Using a simply supported conjugate beam model, obtain the foundation displacement field and rotation field of the simply supported conjugate beam that reflect the elastic deformation of the suspended span. In the area of ​​influence Within the principal bending plane, a simply supported conjugate beam model is established. The measured curvature is used as the reference. As distributed loads on a simply supported conjugate beam, the shear force and bending moment fields of the conjugate beam are calculated using static equilibrium conditions. Utilizing the duality between the shear force and bending moment of the conjugate beam and the rotation and displacement of the actual beam, the rotation field of the simply supported conjugate beam foundation, reflecting the elastic deformation of the cantilever span, is obtained. Reconstructing the foundation displacement field with a simply supported conjugate beam 3 Due to the assumption of simply supported boundaries, although the reconstructed foundation displacement field 3 of the simply supported conjugate beam is zero at the ends, it only reflects the component of the elastic deformation of the cantilever span and fails to reconstruct the rigid body displacement effect generated by the interaction between the pipe and the soil. Therefore, residual elastic deformation rotation exists at the ends. and Moreover, the reconstructed foundation displacement field 3 of the simply supported conjugate beam is not the actual reconstructed displacement field 5 of the suspended span.

[0027] Step 2: Correction of zero-curvature rigid body displacement The actual boundary of the suspended span is the naturally decaying state formed by the interaction between pipe 1 and seabed 6, requiring displacement, rotation, and curvature to be zero simultaneously. The actual displacement and rotation fields include not only components reflecting the elastic deformation of the suspended span but also rigid body displacement effects caused by pipe-soil boundary settlement. Addressing the limitation of the simply supported conjugate beam method in lacking rigid body displacement effects, this invention considers the affected area of ​​the suspended span... Set it to a piecewise polyline format, and use the piecewise single-line correction term. The displacement field 4, which compensates for the actual rigid body motion displacement, determines the inflection point by making the rotation angles of the left and right segments of the polygonal line equal to the negatives of the corresponding boundary rotation angles of the simply supported conjugate beam. : Left section straight line: Right section straight line: Based on the position coordinates of the left and right ends of the affected area of ​​the suspension and In addition to the continuity condition within the broken line, calculate the x-coordinate of the inflection point where the straight lines of the left and right segments intersect. , making Then you can get .

[0028] Based on the determined inflection point position Determine the rigid body displacement compensation displacement field represented by the broken line 4 Segmented one-time line correction term The second derivative is always satisfied outside the inflection point. That is, the rigid body's displacement compensation displacement field 4 does not change the curvature field of the suspended influence region. With the basic displacement field By superposition, the true suspended reconstructed displacement field within the principal bending plane can be determined. and corner Furthermore, the corrected left side satisfies... The right end satisfies .

[0029] This process overcomes the limitation of the classical conjugate beam method, which can only handle ideal boundary conditions. It enables the reconstructed displacement field 5 of the suspended span to simultaneously satisfy the real boundary conditions of zero natural decay of boundary displacement, rotation angle and curvature formed by the interaction between the pipe and the soil, while retaining the measured curvature field.

[0030] Example 5: Three-dimensional spatial projection and output of suspension displacement Extracting the spatial azimuth of the principal bending plane The reconstructed displacement field 5 within the main bending plane is projected onto horizontal and vertical displacement components. After calculation by the data processing unit, the result output unit comprehensively outputs the three-dimensional spatial displacement data for subsequent pipeline ultimate strength verification and fatigue life assessment.

[0031] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for identifying and reconstructing the suspension span of a subsea pipeline based on distributed optical fiber strain sensing, characterized in that, Includes the following steps: S1. Distributed fiber optic strain sensors are deployed along the longitudinal direction of the subsea pipeline to be monitored to continuously acquire longitudinal strain data, and at least three independent longitudinal strain measurement positions are dispersed in the circumferential direction at any cross section to be analyzed. S2, Based on arbitrary position of the pipeline The longitudinal strain observations are used to establish the strain distribution relationship of the cross section, separate the axial strain component and the bending strain component of the cross section, and obtain the curvature components corresponding to the vertical reference direction and the horizontal reference direction. and This allows for the determination of the pipeline's neutral plane, principal bending plane, and principal curvature. ; S3, Based on the principal curvature Construct indicators for identifying the impact area of ​​suspended bridges and determine continuous abnormal intervals covering the response of suspended bridges; S4. Set left and right boundary neighborhoods on both sides of the continuous abnormal interval, and sample within each neighborhood according to the longitudinal sampling interval. Construct a set of discrete candidate boundaries; for each candidate boundary combination Calculate curvature energy based on curvature data And the curvature energy after candidate boundary expansion accounts for the proportion of the external expansion. As a candidate boundary force school core indicator; S5. In the candidate boundary combinations covering the continuous abnormal intervals, the external amplification amount is calculated based on the curvature energy ratio. The final affected area of ​​the suspension span is determined by the criterion that the area is not greater than a preset threshold and the change after expansion does not exceed a preset threshold. ; and make the bending strain and curvature at the final boundary return to zero, satisfying the interval cumulative curvature The regression should not exceed a preset threshold to indicate that the regressions at both ends of the corner are consistent. S6, in the area affected by the suspension Within this model, the boundary conditions are simplified to simply supported, and a simply supported conjugate beam model is established on the principal bending plane, with curvature... As a distributed load on the conjugate beam, the deformation is reconstructed by utilizing the dual relationship between the shear force and bending moment of the conjugate beam and the rotation and displacement of the real beam, thus obtaining the foundation rotation field that reflects the elastic deformation of the cantilever span. and basic displacement field To address the limitation of the conjugate beam method in not being able to include the rigid body displacement effect caused by the interaction between the pipe and the soil, a zero-curvature rigid body follow-up displacement correction term is constructed. The displacement field is then subjected to rigid body translation and rotation corrections to obtain the corrected displacement. ; wherein, the In the interval A piecewise linear function that is continuous within the inflection point and satisfies the second derivative in all regions outside the inflection point. The The actual cantilever boundary constraint formed by the interaction between the soil and the pipe is determined by setting the rotation angles of the left and right segments of the broken line to be equal to the opposite values ​​of the rotation angles at both ends of the foundation rotation field, in order to compensate for the missing rigid body displacement effect in the actual displacement field and rotation field, so that the corrected left end satisfies and The right end satisfies and And combined with the endpoint regression condition in step S5, the curvature is made and ; S7. Based on the angle between the main bending plane and the horizontal reference plane. The suspended displacement within the main bending plane Projection yields the three-dimensional spatial distribution of vertical and horizontal cantilever displacements.

2. The method for identifying and reconstructing the suspension span of a subsea pipeline based on distributed optical fiber strain sensing according to claim 1, characterized in that, In step S1, the strain observations at any longitudinal position of the pipeline are no fewer than three and mutually independent on the cross section; mutual independence means that the measurement positions do not coincide in pairs on the circumferential direction of the cross section and are distributed circumferentially, so that the axial strain established based on step S2 is obtained. Vertical curvature and horizontal curvature The system of linear equations has a unique solution; where, when the number of measurement locations... When the value equals 3, it is obtained by directly solving the system of linear equations. , and When the number of measurement locations When the value is greater than 3, the least squares method is used to obtain the solution. , and .

3. The method for identifying and reconstructing the suspension span of a subsea pipeline based on distributed optical fiber strain sensing according to claim 2, characterized in that, The preferred measurement locations are four positions distributed approximately evenly along the circumference of the pipe cross-section, located at 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock clockwise, respectively. When the pipe outer diameter is... At that time, the longitudinal strain observations at the four locations were denoted as follows: , , and Then we have: axial strain components Vertical curvature component Horizontal curvature component .

4. The method for identifying and reconstructing submarine pipeline suspensions based on distributed optical fiber strain sensing according to claim 1, characterized in that, In step S3, the continuous abnormal interval is determined by threshold discrimination: first, a statistic for threshold discrimination is constructed based on the median and absolute median difference of the global curvature data, and then the continuous abnormal interval is identified according to the statistic threshold of a preset multiple.

5. The method for identifying and reconstructing the suspension span of a subsea pipeline based on distributed optical fiber strain sensing according to claim 1, characterized in that, In steps S4 and S5, the calculation and discrimination criteria for the curvature energy ratio of the external amplification are as follows: the curvature energy External expansion amount is defined as ,when Not greater than the preset threshold When the curvature energy increment change after the candidate window is expanded satisfies the convergence condition, its boundary is determined as the final boundary of the suspended influence area.

6. The method for identifying and reconstructing the suspension span of a subsea pipeline based on distributed optical fiber strain sensing according to claim 1, characterized in that, In step S6, the executable calculation method for the deformation reconstruction of the simply supported conjugate beam is as follows: in the cantilever influence area... Establish a simply supported conjugate beam model in the principal bending plane, and use curvature As a distributed load, the shear force field and bending moment field of the conjugate beam are calculated using static equilibrium conditions to obtain the foundation rotation field reflecting the elastic deformation of the cantilever span. With the basic displacement field The elastic deformation rotation angles at the left and right ends of the affected area are respectively and .

7. The method for identifying and reconstructing submarine pipeline suspensions based on distributed optical fiber strain sensing according to claim 1, characterized in that, In step S6, the zero-curvature rigid body follower displacement correction term The construction and correction method is as follows: the suspended influence area Assuming the form of a piecewise polygonal line, the location of the inflection point is determined by making the rotation angles of the left and right segments of the polygonal line equal to the negatives of the corresponding boundary rotation angles of the simply supported conjugate beam. Based on the position coordinates of the left and right ends of the affected area of ​​the cantilever span and the location of the inflection point Determine the rigid body follower displacement correction term represented by the polygonal line. Combine it with the basic displacement field By superposition, the suspended displacement field in the principal bending plane can be determined. This ensures that the actual boundary conditions of the natural decay of the displacement, rotation angle, and curvature of the suspended influence area are all satisfied.

8. A subsea pipeline suspension identification and reconstruction system for implementing the method according to any one of claims 1 to 7, characterized in that, include: Distributed fiber optic strain acquisition unit: used to continuously acquire longitudinal strain data along the longitudinal direction of the pipeline section to be monitored on the subsea pipeline, and to form at least three independent longitudinal strain measurement positions in the circumferential direction of any section to be analyzed; Data processing unit: used to perform axial and bending strain separation, determination of the main bending plane, determination of the cantilever influence area, reconstruction of conjugate beam deformation, and correction of rigid body follow-up displacement; Result output unit: used to output the three-dimensional cantilever displacement components in the vertical and horizontal directions.

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