CN-122021088-A - Method for establishing relation between submarine cable anchor state and optical fiber vibration signal

CN122021088ACN 122021088 ACN122021088 ACN 122021088ACN-122021088-A

Abstract

The invention belongs to the field of submarine cable operation and maintenance, and particularly relates to a method for establishing a relationship between a submarine cable anchor state and an optical fiber vibration signal; the method comprises the steps of establishing a model of disturbance of the submarine cable at different anchor weights, bottoming speeds and anchor smashing positions by utilizing finite element simulation software, solving and extracting vibration data of the submarine cable composite optical fiber by utilizing the model, processing simulation results by adopting an energy analysis method, respectively establishing a unitary nonlinear fitting formula of the anchor weights, bottoming speeds and anchor smashing positions to the submarine cable optical fiber vibration energy peak value, and establishing a small scale model test to verify the accuracy of a relation equation.

Inventors

LV ANQIANG
ZHOU ZIXUAN
HUANG YOUCONG
LIN ZIQI

Assignees

华北电力大学（保定）
国网福建省电力有限公司电力科学研究院

Dates

Publication Date: 20260512
Application Date: 20241111

Claims (6)

1. The method for establishing the relation between the anchor state of the submarine cable and the optical fiber vibration signal is characterized by comprising the following steps: Step 1, obtaining vibration signals of the submarine cable composite optical fiber under the conditions of different anchoring weights, bottoming speeds and anchoring position disturbance, wherein the specific method comprises the following steps: (1) And selecting finite element simulation software, establishing a geometric model according to the structures, shapes and sizes of submarine cables and ship anchors and the burial depth of engineering site soil, setting corresponding material parameters for different structures, and meshing the model by adopting a plurality of methods such as a sweeping method, a multi-region method, a surface body grid and the like. (2) The method comprises the steps of fully restraining the bottom of soil, restraining the normal direction of the soil and the side surface of a submarine cable, allowing the tangential direction of freedom, setting the soil and the submarine cable to be in non-Separation contact (No Separation), allowing gaps and relative sliding between models, setting all structural layers of the submarine cable to be in binding contact (bonded), connecting contact areas together and not sliding relatively, and setting a ship anchor to be a rigid body. (3) The method comprises the steps of setting quality grade samples M 1 ,M 2 ,…,M n meeting the national standard of ship anchors of different weights according to the maximum anchor weight M n possibly encountered by an engineering site for disturbance of the ship anchors to submarine cables, setting initial bottoming speed ranges of 0-v of the anchors according to the maximum bottoming speeds v of the ship anchors possibly encountered by the engineering site, taking samples every 2M/s for disturbance of the submarine cables at different anchor smashing positions, and taking samples every 0.5M according to the distance x 1 between the possible anchor sinking positions of the engineering site and the submarine cables until the optical fibers cannot sense signals. (4) And calculating vibration signals of the submarine cable by using a solving tool, arranging and combining discrete samples of the anchoring weight, the bottoming speed and the anchoring position to obtain a plurality of groups of data, respectively solving finite element models under different load conditions, and extracting and deriving the vibration signals of the optical fibers. Step 2, respectively establishing a unitary nonlinear fitting formula of the anchor weight, bottoming speed and anchor smashing position to the fiber vibration energy peak value of the submarine cable, wherein the concrete method comprises the following steps: (1) And (3) carrying out continuous wavelet transformation on the vibration signal obtained in the step (1), calculating the energy sum of all frequencies at each time point, and finding out normalized peak energy. (2) The method comprises the steps of obtaining an exponential function fitting equation of the light unit vibration energy peak value along with the change of the anchor weight on the premise that a decision coefficient R 2 is as close as possible to 1 by taking the anchor weight as an independent variable and taking the optical fiber vibration energy peak value as a dependent variable, obtaining a quadratic polynomial fitting equation of the light unit vibration energy value along with the bottom-to-bottom speed of the ship anchor by the same method, and obtaining a Gaussian function fitting equation of the light unit vibration energy value along with the change of the anchor breaking position. And 3, building a small scale model test to verify the accuracy of a relation equation, wherein the method comprises the following steps of: (1) The anchor length L and the density rho are used as basic dimensions, meanwhile, the energy similarity of the model and the prototype is ensured, and the scaling factor lambda L is determined on the premise of ensuring the feasibility of the test. (2) According to the step (3) and the step (1) of the step (3), preparing a model anchor and a model cable for test, connecting one optical fiber of the model cable with the distributed optical fiber vibration monitoring equipment through an optical fiber jumper of about 1000m, and knotting the tail optical fiber of the model cable to prevent the occurrence of the tail Fresnel reflection. And (5) enabling the model anchor to freely fall down respectively until the model anchor is crashed into soil, stopping moving, and carrying out 10 groups of tests on each working condition. (3) And (3) respectively calculating the energy peak value of the vibration signal monitored by each working condition, averaging, carrying out reduction according to the similarity relation, if the error between the test result and the finite element modeling fitting equation is not more than 10%, considering that the error is within a reasonable error range, if the error is more than 10%, revising the finite element model again, and repeating the steps (1) and (2) until the error is not more than 10%.
2. The method for establishing a relationship between a submarine cable anchor state and an optical fiber vibration signal according to claim 1, wherein in the step 1, for establishing a ship anchor model, the weight and the bottom area of the anchor are main factors influencing the result, the anchor is not deformed, and for reducing the calculation time, only the bottom size and the prototype are kept consistent, and the model is simplified into a quadrangular frustum.
3. The method for establishing the relationship between the anchor damage state of the submarine cable and the vibration signal of the optical fiber according to claim 1, wherein the equation for different bottoming speeds of the ship anchor in the step 3 is verified, and the equation is converted into different falling heights for test, and the conversion relationship is as follows: Wherein v represents the bottom-contacting speed of the ship anchor, h represents the falling height of the ship anchor, and g represents the gravitational acceleration.
4. The method for establishing a relationship between an anchor state of a submarine cable and an optical fiber vibration signal according to claim 1, wherein when a disturbance condition of the submarine cable changes, the above steps are repeated to correct coefficients in the formula.
5. The method for establishing a relationship between an anchor state of a submarine cable and an optical fiber vibration signal according to claim 1, wherein the fitting equation mentioned in the step 2 may be any other equation according to circumstances, but the fitting determination coefficient R 2 is not less than 0.9 and is as close to 1 as possible.
6. The method for establishing the relationship between the anchor state of the submarine cable and the optical fiber vibration signal according to claim 1, wherein the distributed optical fiber can be a submarine cable built-in optical fiber or an optical cable laid on the surface of the submarine cable, and the distributed optical fiber vibration monitoring device can be all equipment or instruments based on optical fiber backward Rayleigh scattering.

Description

Method for establishing relation between submarine cable anchor state and optical fiber vibration signal Technical Field The invention belongs to the field of submarine cable operation and maintenance monitoring, and particularly relates to a method for establishing a submarine cable anchor state and optical fiber vibration signal relationship. Background The submarine cable is widely applied to occasions such as offshore island power supply, offshore wind farm power transmission, offshore platform power utilization and the like, and is extremely easy to damage by external force in the operation process. According to the recent statistics of domestic and foreign fault data, the number of the external damage accidents of the submarine cable caused by anchoring is the largest, and exceeds 80% of the total number of the accidents, so that the safe operation of the submarine cable faces a great challenge. Under the general condition, the submarine cable is buried under the seabed for 1-2 m, but is eroded by seawater and ocean current for a long time, so that the buried depth of the cable body becomes shallow or even exposed, and serious anchor damage can directly lead to the breakage of the submarine cable, thereby causing huge economic loss and causing great environmental damage to the surrounding sea area. Therefore, it is necessary to pre-warn the anchoring disturbance of the submarine cable in advance. At present, research results in the field of anchoring disturbance of submarine cables have discrete type, disturbance of different influencing factors cannot be early warned, and a formula is not explicitly given in the engineering community. Under the background, a method for establishing a relation equation between a submarine cable disturbance signal and different influencing factors is needed, early warning is carried out on anchoring disturbance in advance, and operation and maintenance efficiency is improved. Aiming at the problems, the invention provides a method for establishing the relation between the anchor state of the submarine cable and the optical fiber vibration signal, which can rapidly predict the disturbance influence of a ship anchor on the submarine cable and provide theory and data reference for submarine cable operation and maintenance monitoring. Disclosure of Invention The invention aims to provide a method for establishing the relation between the anchor state of a submarine cable and an optical fiber vibration signal, which is used for solving the problems that the prior theory cannot early warn disturbance of different influencing factors of the submarine cable. In order to achieve the above purpose, the technical scheme provided by the invention is that a method for establishing the relation between the anchor state of a submarine cable and the vibration signal of an optical fiber is characterized by comprising the following steps: Step 1, obtaining vibration signals of the submarine cable composite optical fiber under the conditions of different anchoring weights, bottoming speeds and anchoring position disturbance, wherein the specific method comprises the following steps: (1) And selecting finite element simulation software, establishing a geometric model according to the structures, shapes and sizes of submarine cables and ship anchors and the burial depth of engineering site soil, setting corresponding material parameters for different structures, and meshing the model by adopting a plurality of methods such as a sweeping method, a multi-region method, a surface body grid and the like. (2) The method comprises the steps of fully restraining the bottom of soil, restraining the normal direction of the soil and the side surface of a submarine cable, allowing the tangential direction of freedom, setting the soil and the submarine cable to be in non-Separation contact (No Separation), allowing gaps and relative sliding between models, setting all structural layers of the submarine cable to be in binding contact (bonded), connecting contact areas together and not sliding relatively, and setting a ship anchor to be a rigid body. (3) The method comprises the steps of setting quality grade samples M 1,M2,…,Mn meeting the national standard of ship anchors of different weights according to the maximum anchor weight M n possibly encountered by an engineering site for disturbance of the ship anchors to submarine cables, setting initial bottoming speed ranges of 0-v of the anchors according to the maximum bottoming speeds v of the ship anchors possibly encountered by the engineering site, taking samples every 2M/s for disturbance of the submarine cables at different anchor smashing positions, and taking samples every 0.5M according to the distance x 1 between the possible anchor sinking positions of the engineering site and the submarine cables until the optical fibers cannot sense signals. (4) And calculating vibration signals of the submarine cable by using a solving tool, arranging and