A cable based on optical fiber technology and a method for measuring its cable force

Abstract

The present invention discloses a cable based on optical fiber technology and a method for measuring the cable force thereof, including obtaining the monitoring data and status data of the cable, performing temperature compensation on the monitoring data to obtain a temperature-compensated wavelength, correcting the temperature-compensated wavelength to obtain a first corrected wavelength, correcting the first corrected wavelength to obtain a second corrected wavelength, determining the first cable force according to the second corrected wavelength, constructing a cable force measurement model, optimizing the cable force measurement model according to the cable force error, and inputting the monitoring data and status data of the cable to be measured into the optimized cable force measurement model to obtain a cable force measurement result. The present invention obtains an optical wave signal by installing the cable based on optical fiber technology on a structure, processes the optical signal and calculates the cable force, and measures the cable force during the use of the cable based on optical fiber technology.

Description

Technical Field

[0001] The present invention relates to the field of non-destructive testing, and particularly to a cable and a method for measuring the cable force based on optical fiber technology. Background Art

[0002] As a key load-bearing component in large bridges and high-rise structures, the accurate measurement of the cable force of a cable is crucial for the safety monitoring and assessment of the structure. Traditional methods for measuring the cable force of a cable have problems such as large influence of the environment on the measurement accuracy and complex installation and maintenance. As an emerging sensing technology, optical fiber technology has the characteristics of small size, light weight, and strong anti-electromagnetic interference ability. These excellent characteristics have promoted the development of the cable force measurement technology based on optical fiber technology, which is of great significance for the health monitoring of major structures.

[0003] As a monitoring element that is cross-sensitive to strain and temperature, Fiber Bragg Grating (FBG) sensors still have problems such as fragility and easy breakage and low monitoring range in practical applications. It is necessary to innovate the protection method and layout form of FBG. In addition, the accurate FBG wavelength-cable force relationship is the key to effective cable force measurement. However, the cable force measurement of a cable is affected not only by temperature changes, but also by various factors such as environmental noise, wind speed, structural deformation, and cable scale. The above influencing factors have difficulties such as complex data types, large data volume, and complex calculation processes in the data post-processing process. Combining machine learning technology to capture the complex relationship between monitoring data, status data and the true cable force can accurately predict the cable force of the cable. Therefore, designing a cable and a method for measuring the cable force based on optical fiber technology to overcome the deficiencies of the existing cable force measurement devices and methods in detection accuracy, so as to improve the accuracy and efficiency of cable force measurement and provide strong support for the structural health monitoring of large bridges and high-rise structures. Summary of the Invention

[0004] The purpose of the present invention is to provide a cable and a method for measuring the cable force based on optical fiber technology.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The present invention includes the following steps:

[0007] Obtain the monitoring data and status data of the cable, and preprocess the monitoring data and the status data; the status data includes environmental status data and structural status data;

[0008] Perform temperature compensation on the monitoring data to obtain a temperature-compensated wavelength, obtain an environmental influence factor according to the environmental status data, and correct the temperature-compensated wavelength to obtain a first corrected wavelength;

[0009] Determine the scale influence coefficient, determine the scale influence factor according to the structural state data and the scale influence coefficient, and correct the first corrected wavelength to obtain the second corrected wavelength;

[0010] Determine the first cable force according to the second corrected wavelength, and construct a cable force measurement model according to the first cable force, the environmental influence factor and the scale influence factor;

[0011] Optimize the cable force measurement model according to the cable force error, and input the monitoring data and state data of the cable to be measured into the optimized cable force measurement model to obtain the cable force measurement result.

[0012] Furthermore, the method for obtaining the temperature compensation wavelength by performing temperature compensation on the monitoring data includes:

[0013] Perform a calibration experiment on the single-bar force measuring element, control the stress and temperature changes of the main single-bar force measuring element, control the temperature change of the auxiliary single-bar force measuring element to obtain test calibration data, and solve the binary surface fitting equation of strain and temperature according to the test calibration data. The expression is:

[0014]

[0015] b=(H T +H) -1 ·H T ·T

[0016] where ε ij is the binary surface fitting equation of strain, T ij is the binary surface fitting equation of temperature. When the corresponding state is ε ij or T ij takes the calibration value, the wavelength change of the main single-bar force measuring element is the wavelength change of the auxiliary single-bar force measuring element i is the set stress state, j is the set temperature state, a=[a0,a1,a2,a3,a4,a5] T 、b=[b0,b1,b2,b3,b4,b5] T are the constant coefficients of the binary surface fitting equation, is the calibration point data matrix, k ε is the strain sensitivity coefficient, k T is the temperature sensitivity coefficient;

[0017] The main single-bar force measuring element is used to make the stressed cable, and the auxiliary single-bar force measuring element is used to make the temperature compensation element. Calculate the strain and temperature values according to the binary surface fitting equation of strain and temperature and the monitored wavelength change value, and perform fitting reconstruction on the strain and temperature data according to the fiber optic sensing principle to obtain the temperature compensation wavelength.

[0018] Further, the method for obtaining the first corrected wavelength includes:

[0019] Inputting the status data into the environmental impact function to obtain the environmental impact factor, and correcting the temperature compensation wavelength with the environmental impact factor to obtain the first corrected wavelength. The expression is:

[0020]

[0021] where Effect1 is the environmental impact factor, w1, w2, and w3 are the weights of the environmental impact factor, N0 is the environmental noise limit, N1 is the current environmental noise, a is the bridge vibration acceleration, v is the bridge vibration velocity, w is the wind speed, is the angle between the wind direction and the longitudinal direction of the bridge, λ1 is the first corrected wavelength, λ0 is the initial wavelength of the optical fiber, λ w is the temperature compensation wavelength.

[0022] Further, the method for obtaining the scale influence coefficient includes:

[0023] The scale influence coefficient includes the spiral angle influence coefficient and the stress level influence coefficient;

[0024] Respectively conducting the static tensile test and the finite element simulation test on the single-reinforcement force-measuring element, adjusting the stress level and the optical fiber spiral winding angle of the single-reinforcement force-measuring element to obtain the tensile test data and the simulation data, and fitting the tensile test data and the simulation data to obtain the spiral angle influence coefficient and the stress level influence coefficient. The expression is:

[0025]

[0026] where δ θ is the spiral angle influence coefficient, c1, c2, c3, and c4 are constant coefficients obtained by data fitting, θ is the optical fiber winding spiral angle, δ σ is the stress level influence coefficient, is the optical fiber stress, E g is the elastic modulus of the optical fiber, K εg is the strain sensitivity of the optical fiber, c5 is the proportionality coefficient, and c6 is the nonlinear index.

[0027] Further, the method for obtaining the second corrected wavelength includes:

[0028] Calculating the user utilization coefficient and the size coefficient respectively according to the structural status data, and determining the usage scale influence factor according to the scale influence coefficient, the user utilization coefficient, and the size coefficient. The expression is:

[0029]

[0030] Effect2 = [h1(δ θ + δ σ ) + h2δ use cos(2πδ size )

[0031] where δ use is the user usage coefficient, δ size is the size coefficient, Effect2 is the usage scale influence factor, d1, d2 are the weights of the user usage coefficient, d3 is the weight of the size coefficient, h1, h2 are the weights of the usage scale influence factor, M 1use is the number of channels used by the fiber optic demodulator, M 1max is the maximum number of channels of the fiber optic demodulator, M 2use is the number of sensor connections within a single channel, M 2max is the maximum number of sensor connections within a single channel, L max is the length of the access fiber, L use is the length of the monitored section of the fiber, r g is the radius of the fiber, r a is the radius of the groove, r m is the radius of the matrix rib;

[0032] The second corrected wavelength is obtained by correcting the first corrected wavelength according to the usage scale influence factor, and the expression is;

[0033]

[0034] where λ2 is the second corrected wavelength, λ1 is the first corrected wavelength, and λ0 is the initial wavelength.

[0035] Furthermore, the method for determining the first cable force according to the second corrected wavelength includes:

[0036] Determine the proportional relationship between the strain of the optical fiber at the non-glued and fixed part in the spiral groove of the matrix rib and the strain on the surface of the rib, and the expression is:

[0037]

[0038] a = 1 + L2 / 2L1

[0039]

[0040] where β is the strain transfer rate, representing the proportional relationship between the strain of the unfixed optical fiber in the middle and the strain on the surface of the rib, a is the gauge ratio coefficient, L2 is the length of the optical fiber in the middle gauge section, L1 is the length of the optical fiber at the fixed end, k is the material coefficient, G j is the shear modulus of the adhesive at the fixed end, r j is the radius of the adhesive;

[0041] Determine the cable force of the first cable according to the strain transfer rate, the output wavelength of the optical fiber, the material and size parameters of the cable. The expression is as follows:

[0042]

[0043] where F1 is the cable force of the first cable, E m is the elastic modulus of the reinforcement, A c is the cross-sectional area of the cable, n is the number of single-reinforcement force-measuring elements in the cable, λ 2i is the second corrected wavelength of the i-th single-reinforcement force-measuring element in the cable, λ 0i is the initial wavelength of the i-th single-reinforcement force-measuring element in the cable, μ is the cable structure coefficient, d i is the distance from the center of the i-th single-reinforcement force-measuring element in the cable to the center of the cable, R is the radius of the cable, A c is the cross-sectional area of the cable, A m is the cross-sectional area of the single-reinforcement force-measuring element.

[0044] Furthermore, the method for constructing the cable force measurement model includes:

[0045] Calculate the cable force deviation according to the measured cable force and the cable force of the first cable. Combine the cable force deviation, the measured cable force, the cable force of the first cable, the scale influence factor, and the environmental influence factor to form a comprehensive data set. Use the random forest algorithm to divide the comprehensive data set into a training set and a test set at a ratio of 7:3;

[0046] Construct a cable force measurement model according to the comprehensive data set. The cable force measurement model includes an input layer, a base model layer, a strategy layer, and an output layer;

[0047] The base model layer is used to predict the cable force according to the data law of the comprehensive data set. The base models include a linear regression model, a decision tree model, and a BP neural network model;

[0048] The linear regression model is responsible for capturing the linear relationship between the input data features and the measured cable force, and ensuring the model stability by standardizing the input features;

[0049] The decision tree model is responsible for capturing the non-linear relationship between the input data features and the measured cable force, preventing overfitting by setting the maximum depth, and determining the optimal depth by cross-validation;

[0050] The BP neural network model is responsible for capturing the complex non-linear relationship between the input data features and the measured cable force, using the ReLU activation function, using dropout to prevent overfitting, and determining the number of training rounds by the early stopping method;

[0051] The strategy layer is used to integrate the output of the base model layer, perform feature engineering and model fusion, and output the cable force prediction result;

[0052] The particle swarm optimization algorithm is used to optimize the hyperparameters of the cable force measurement model according to the error between the predicted cable force of the test data and the measured cable force.

[0053] Furthermore, the method for optimizing the cable force measurement model according to the cable force error includes:

[0054] Initialize the population size N and the maximum number of iterations T, and perform chaotic mapping on the search sub-population. The expression is:

[0055]

[0056] where x t is the position of the particle after chaotic mapping, x t0 is the position of the particle before chaotic mapping, q is a chaotic random number in [0, 1], and p is taken as 0.4;

[0057] Calculate the fitness of the position where the particle is located, set the fitness threshold γ, and calculate the contraction-expansion coefficient according to the fitness value difference. The expression is:

[0058]

[0059] where is the contraction-expansion coefficient, is the maximum contraction-expansion coefficient, is the minimum contraction-expansion coefficient, T is the maximum number of iterations, t is the current iteration number, rand(·) is a random perturbation, Fitness i,t is the fitness of the position corresponding to particle i at the t-th iteration, Fitness g is the fitness of the position where the global optimal particle is located;

[0060] Update the individual optimal position p i,t+1 of the particle, the global optimal position g t+1 and the average optimal position m best , and update the particle position. The expression is:

[0061]

[0062] where x i,t+1 is the position update of particle i at the (t + 1)-th iteration, x i,t is the position of particle i at the t-th iteration, ζ and z are random numbers in [0, 1], and v is a regulation parameter in [0, 1];

[0063] Judge whether the particle is out of bounds. When the particle is out of bounds, perform chaotic boundary mutation. The expression is:

[0064]

[0065] where x‘ i,t+1 is the position of the i-particle after chaotic boundary mutation when the position exceeds the boundary at the (t + 1)-th iteration, maxx t+1 is the upper boundary of the particle swarm in the (t + 1)-th iteration, min x t+1 is the lower boundary of the particle swarm in the (t + 1)-th iteration, is the chaotic mapping random number in the (t + 1)-th iteration, is the chaotic mapping random number in the t-th iteration, s = 0.2;

[0066] Calculate the cable force error of the search particle, and the expression is:

[0067]

[0068] where Error i,t+1 is the error of the i-particle at the (t + 1)-th iteration, o is a random number within [0, 1], F i ′ ,t+1 is the predicted cable force result of the i-particle at the (t + 1)-th iteration, F i is the measured cable force of the i-particle, χ is the flight coefficient, τ is the attenuation factor, is the inertia weight, w is the modulation constant, is the standard deviation of the first normal distribution random number k, is the standard deviation of the second normal distribution random number l, is the flight parameter;

[0069] Iterate continuously until the cable force error is minimized or the maximum number of iterations is reached and then stop the iteration;

[0070] Input the monitoring data and status data of the cable to be measured into the optimized cable force measurement model to obtain the cable force measurement result.

[0071] On the other hand, a cable based on optical fiber technology includes: ordinary reinforcement, single-reinforcement force-measuring element, and HDPE protective glue; the HDPE protective glue is wrapped outside the ordinary reinforcement and the single-reinforcement force-measuring element; the single-reinforcement force-measuring element includes an optical fiber, a paste-fixed end, and a matrix reinforcement; a spiral groove is provided on the matrix reinforcement; the optical fiber is wound and arranged inside the spiral groove; the optical fiber is fixed inside the spiral groove in the form of a long gauge through the paste-fixed end; grating areas are inscribed on the optical fiber between the paste-fixed ends; there are multiple grating areas on the optical fiber of the single-reinforcement force-measuring element; the grating areas are connected in series; the port of the optical fiber is connected to an external optical fiber grating demodulator.

[0072] The beneficial effects of the present invention are:

[0073] The present invention relates to a cable and a cable force measurement method based on optical fiber technology. Compared with the prior art, the present invention has the following technical effects:

[0074] A cable force measurement method based on optical fiber technology provided by the present invention can improve the efficiency and accuracy of cable force measurement based on optical fiber technology through steps such as temperature compensation, constructing environmental impact factors, using scale impact factors, correcting wavelengths, calculating cable forces, constructing models, and optimizing models. It can make the cable force measurement intelligent, greatly save resources, and can realize the measurement of the cable force of the cable to be measured, quickly and real-time measure the cable force of the cable to be measured with high precision, provide strong technical support for the cable force measurement, and is of great significance to the development of structural health monitoring and safety assessment in the field of civil engineering.

[0075] A cable based on optical fiber technology provided by the present invention sets spiral grooves on the matrix reinforcement when manufacturing a single-reinforcement force-measuring element, arranges the optical fiber inside the spiral grooves, effectively protects the optical fiber, and improves the survival rate of the optical fiber in the single-reinforcement force-measuring element; the optical fiber is spirally wound and arranged with a long gauge length, reducing the strain sensitivity of the optical fiber and increasing the monitoring range of the single-reinforcement force-measuring element, contributing to the development of structural monitoring of cables for long-span and high-stress bridges. Description of the Drawings

[0076] Figure 1 It is a flowchart of the steps of a cable force measurement method based on optical fiber technology of the present invention;

[0077] Figure 2 It is a schematic cross-sectional view of a cable based on optical fiber technology provided by the present invention;

[0078] Figure 3 It is a schematic diagram of a single-reinforcement force-measuring element of a cable based on optical fiber technology provided by the present invention;

[0079] Figure 4 It is a schematic diagram of the unfolded optical fiber of a single-reinforcement force-measuring element of a cable based on optical fiber technology provided by the present invention;

[0080] Figure 5 It is a schematic cross-sectional view of a single-reinforcement force-measuring element of a cable based on optical fiber technology provided by the present invention;

[0081] In the figure: 1 - ordinary reinforcement; 2 - single-reinforcement force-measuring element; 3 - paste adhesive fixed end; 4 - spiral groove; 5 - optical fiber; 6 - matrix reinforcement; 7 - HDPE protective glue; 8 - grid area. Detailed Embodiments

[0082] The present invention will be further described below through specific embodiments. The illustrative embodiments and explanations of this invention are used to explain the present invention, but do not limit the present invention.

[0083] A cable and a cable force measurement method based on optical fiber technology according to the present invention include the following steps:

[0084] As Figure 1 shown, in this embodiment, a cable force measurement method based on optical fiber technology includes:

[0085] Obtain the monitoring data and status data of the cable, and preprocess the monitoring data and the status data; the status data includes environmental status data and structural status data;

[0086] Perform temperature compensation on the monitoring data to obtain a temperature-compensated wavelength, obtain an environmental influence factor according to the environmental status data, and correct the temperature-compensated wavelength to obtain a first corrected wavelength;

[0087] Determine the scale influence coefficient, determine the scale influence factor according to the structural status data and the scale influence coefficient, and correct the first corrected wavelength to obtain a second corrected wavelength;

[0088] Determine the first cable force according to the second corrected wavelength, and construct a cable force measurement model according to the first cable force, the environmental influence factor, and the scale influence factor;

[0089] Optimize the cable force measurement model according to the cable force error, and input the monitoring data and status data of the cable to be measured into the optimized cable force measurement model to obtain the cable force measurement result.

[0090] In this embodiment, the method for performing temperature compensation on the monitoring data to obtain a temperature-compensated wavelength includes:

[0091] Perform a calibration experiment on the single-bar force-measuring element, control the stress and temperature changes of the main single-bar force-measuring element, control the temperature change of the auxiliary single-bar force-measuring element to obtain test calibration data, and solve the binary surface fitting equation of strain and temperature according to the test calibration data. The expression is:

[0092]

[0093] b = (H T +H) -1 ·H T ·T

[0094] where ε ij is the binary surface fitting equation of strain, T ij is the binary surface fitting equation of temperature, and when the corresponding state is ε ij or T ij takes the calibration value, the wavelength change of the main single-bar force-measuring element is the wavelength change of the auxiliary single-bar force-measuring element i is the set stress state, j is the set temperature state, a = [a0, a1, a2, a3, a4, a5] T and b = [b0, b1, b2, b3, b4, b5] T are the constant coefficients of the binary surface fitting equation is the calibration point data matrix, k ε is the strain sensitivity coefficient, k T is the temperature sensitivity coefficient;

[0095] The main single-rebar force-measuring element is used to make the stressed cable, and the auxiliary single-rebar force-measuring element is used to make the temperature compensation element. According to the binary surface fitting equation of strain and temperature and the monitored wavelength change value, the strain and temperature values are calculated, and according to the optical fiber sensing principle, the strain and temperature data are fitted and reconstructed to obtain the temperature compensation wavelength;

[0096] In the actual evaluation, the monitoring data of the single-rebar force-measuring elements in two cables at different positions of a certain bridge are collected (for the main single-rebar force-measuring element, the data of one sensor is taken): Cable A: main single-rebar force-measuring element (initial wavelength 1545.1110 nm, output wavelength 1549.8258 nm), auxiliary single-rebar force-measuring element (initial wavelength 1545.0154 nm, output wavelength 1545.0043 nm); Cable B: main single-rebar force-measuring element (initial wavelength 1544.9399 nm, output wavelength 1548.7103 nm), auxiliary single-rebar force-measuring element (initial wavelength 1545.1024 nm, output wavelength 1545.1018 nm);

[0097] According to the calibration experiment, in the binary surface fitting equation, the temperature compensation wavelengths of the main single-rebar force-measuring element of Cable A are obtained as 1549.8298 nm and that of the main single-rebar force-measuring element of Cable B are obtained as 1548.7389 nm through fitting and reconstruction of the monitoring data.

[0098] In this embodiment, the method for obtaining the first corrected wavelength includes:

[0099] Inputting the state data into the environmental impact function to obtain the environmental impact factor, and correcting the temperature compensation wavelength by the environmental impact factor to obtain the first corrected wavelength. The expression is:

[0100]

[0101] where Effect1 is the environmental impact factor, w1, w2, w3 are the weights of the environmental impact factor, N0 is the environmental noise limit, N1 is the current environmental noise, a is the bridge vibration acceleration, v is the bridge vibration speed, w is the wind speed, is the angle between the wind direction and the longitudinal direction of the bridge, λ1 is the first corrected wavelength, λ0 is the initial wavelength of the optical fiber, λw is the temperature-compensated wavelength;

[0102] In the actual evaluation, the environmental data of a certain bridge is obtained: the noise limit of the machine working environment is 55 dB, the current environmental noise is 68 dB, the bridge vibration acceleration is 0.5 m / s 2 , the bridge vibration velocity is 6 mm / s, the wind speed is 10 m / s, and the angle between the wind direction and the longitudinal direction of the bridge is 45°;

[0103] Taking w1 = 2, w2 = 0.8, w3 = 0.8, the environmental impact factor Effect1 = 0.6351 is calculated, and the first corrected wavelengths of stay cables A and B are calculated to be 1549.7052 nm and 1548.6386 nm respectively.

[0104] In this embodiment, the method for obtaining the scale influence coefficient includes:

[0105] The scale influence coefficient includes a helix angle influence coefficient and a stress level influence coefficient;

[0106] The static tensile test and finite element simulation test of the single-reinforcement force measuring element are carried out respectively. The stress level of the single-reinforcement force measuring element and the fiber optic helix winding angle are adjusted to obtain the tensile test data and simulation data. The helix angle influence coefficient and the stress level influence coefficient are obtained by fitting the tensile test data and simulation data. The expressions are:

[0107]

[0108] where δ θ is the helix angle influence coefficient, c1, c2, c3, c4 are constant coefficients obtained by data fitting, θ is the fiber optic winding helix angle, δ σ is the stress level influence coefficient, is the fiber optic stress, E g is the elastic modulus of the fiber optic, K εg is the strain sensitivity of the fiber optic, c5 is a proportionality coefficient, and c6 is a non-linear exponent;

[0109] In the actual evaluation, the helix angle of the fiber optic in the single-reinforcement force measuring element 1 of stay cables A and B is 15°, c1 = 0.01, c2 = 0.05, c3 = 0.1, c4 = 0.1. According to the above formula, the helix angle influence coefficient is calculated to be 3.1; c5 = 0.5, c6 = 1.2, the elastic modulus of the fiber optic is taken as 72 GPa, and the strain sensitivity coefficient is taken as 1.2025 pm / με. According to the above formula, the stress level influence coefficient is calculated to be -1.4673.

[0110] In this embodiment, the method for obtaining the second corrected wavelength includes:

[0111] Calculate the user utilization coefficient and size coefficient respectively according to the structural state data, and determine the usage scale influence factor based on the scale influence coefficient, user utilization coefficient, and size coefficient. The expression is as follows:

[0112]

[0113] Effect2 = [h1(δ θ +δ σ ) + h2δ use cos(2πδ size )

[0114] where δ use is the user utilization coefficient, δ size is the size coefficient, Effect2 is the usage scale influence factor, d1, d2 are the weights of the user utilization coefficient, d3 is the weight of the size coefficient, h1, h2 are the weights of the usage scale influence factor, M 1use is the number of channels used by the fiber optic demodulator, M 1max is the maximum number of channels of the fiber optic demodulator, M 2use is the number of sensor connections within a single channel, M 2max is the maximum number of sensor connections within a single channel, L max is the length of the access fiber, L use is the length of the monitored fiber segment, r g is the radius of the optical fiber, r a is the radius of the groove, r m is the radius of the matrix rib;

[0115] Modify the first corrected wavelength according to the usage scale influence factor to obtain the second corrected wavelength. The expression is as follows;

[0116]

[0117] where λ2 is the second corrected wavelength, λ1 is the first corrected wavelength, and λ0 is the initial wavelength;

[0118] In actual evaluation, the maximum number of channels of the fiber grating demodulator is 16, the current number of used channels is 16, the maximum number of sensor connections within a single channel is 30, the current number of sensor connections within a single channel is 10, the length of the monitored fiber segment is 20.70 m, the length of the access fiber is 25 m, d1 = d2 = 0.1. Calculate the user utilization coefficient to be 0.3522 according to the above formula; d3 = 5, the radius of the optical fiber is 62.5 μm, the radius of the groove is 1 mm, and the radius of the matrix rib is 3.5 mm. Calculate the size coefficient to be 0.9845 according to the above formula;

[0119] Take h1 = h2 = 0.5, and calculate the scale influence factor to be 0.9877 according to the above formula. Substitute the scale influence coefficient, user usage coefficient, and size coefficient into the formula to calculate the second corrected wavelengths of cable A and cable B to be 1549.6386 nm and 1548.6331 nm respectively.

[0120] In this embodiment, the method for determining the first cable force according to the second corrected wavelength includes:

[0121] Determine the proportional relationship between the strain of the optical fiber at the unfixed and glued part in the spiral groove of the matrix reinforcement and the strain on the surface of the reinforcement. The expression is:

[0122]

[0123] a = 1 + L2 / 2L1

[0124]

[0125] Where β is the strain transfer rate, representing the proportional relationship between the strain of the unfixed optical fiber in the middle and the strain on the surface of the reinforcement. a is the gauge ratio coefficient, L2 is the length of the optical fiber in the middle gauge section, L1 is the length of the optical fiber at the fixed end, k is the material coefficient, G j is the shear modulus of the adhesive at the fixed end, r j is the radius of the adhesive;

[0126] Determine the first cable force according to the strain transfer rate, the output wavelength of the optical fiber, the material and size parameters of the cable. The expression is:

[0127]

[0128] Where F1 is the first cable force, E m is the elastic modulus of the reinforcement, A c is the cross-sectional area of the cable, n is the number of single-reinforcement force-measuring elements in the cable, λ 2i is the second corrected wavelength of the i-th single-reinforcement force-measuring element in the cable, λ 0i is the initial wavelength of the i-th single-reinforcement force-measuring element in the cable, μ is the cable structure coefficient, d i is the distance from the center of the i-th single-reinforcement force-measuring element in the cable to the center of the cable, R is the radius of the cable, A c is the cross-sectional area of the cable, A m is the cross-sectional area of the single-reinforcement force-measuring element;

[0129] In the actual evaluation, the optical fiber length of the middle gauge section of the single-rebar force-measuring element of Cable A is 60 mm, and the optical fiber length of the fixed end with adhesive is 40 mm. The optical fiber length of the middle gauge section of the single-rebar force-measuring element of Cable B is 120 mm, and the optical fiber length of the fixed end with adhesive is 40 mm. The shear modulus of the adhesive is 1296 MPa, and the radius of the adhesive layer is 500 μm. The strain transfer rates of the single-rebar force-measuring elements on Cable A and Cable B are calculated to be 78.54% and 72.10% respectively;

[0130] The elastic modulus of the rebar is 155.56 GPa, and the cross-sectional area of the cable is 1423.93 mm 2 , and 3 single-rebar force-measuring elements are set in the cable. 10 FBG sensors are set on each optical fiber. Combining the FBG sensor data on the other single-rebar force-measuring elements on Cable A and Cable B, the first cable forces of Cable A and Cable B are calculated to be 1075.91 kN and 943.56 kN respectively.

[0131] In this embodiment, the method for constructing the cable force measurement model includes:

[0132] Calculate the cable force deviation according to the measured cable force and the first cable force. Combine the cable force deviation, the measured cable force, the first cable force, the scale influence factor, and the environmental influence factor into a comprehensive data set. Use the random forest algorithm to divide the comprehensive data set into a training set and a test set at a ratio of 7:3;

[0133] Construct a cable force measurement model according to the comprehensive data set. The cable force measurement model includes an input layer, a base model layer, a strategy layer, and an output layer;

[0134] The base model layer is used to predict the cable force according to the data law of the comprehensive data set. The base models include a linear regression model, a decision tree model, and a BP neural network model;

[0135] The linear regression model is responsible for capturing the linear relationship between the input data features and the measured cable force, and ensuring the model stability by standardizing the input features;

[0136] The decision tree model is responsible for capturing the non-linear relationship between the input data features and the measured cable force, preventing overfitting by setting the maximum depth, and determining the optimal depth by cross-validation;

[0137] The BP neural network model is responsible for capturing the complex non-linear relationship between the input data features and the measured cable force, using the ReLU activation function, using dropout to prevent overfitting, and determining the number of training rounds by the early stopping method;

[0138] The strategy layer is used to integrate the outputs of the base model layer, perform feature engineering and model fusion, and output the prediction results of the cable forces; polynomial feature expansion and PCA are adopted in feature engineering to improve the non-linear expression ability and generalization ability of the model. The Stacking integration method is used to input the new features into the meta-learner for prediction, and the logistic regression algorithm is adopted for the meta-learner;

[0139] The particle swarm optimization algorithm is used to optimize the hyperparameters of the cable force measurement model according to the error between the predicted cable force results of the test data and the measured cable forces.

[0140] In this embodiment, the method for optimizing the cable force measurement model according to the cable force error includes:

[0141] Initialize the population size N and the maximum number of iterations T, and perform chaotic mapping on the search sub-population. The expression is:

[0142]

[0143] where x t is the position of the particle after chaotic mapping, x t0 is the position of the particle before chaotic mapping, q is a chaotic random number in [0,1], and p is taken as 0.4;

[0144] Calculate the fitness of the position where the particle is located, set the fitness threshold γ, and calculate the contraction-expansion coefficient according to the difference in fitness values. The expression is:

[0145]

[0146] where is the contraction-expansion coefficient, is the maximum contraction-expansion coefficient, is the minimum contraction-expansion coefficient, T is the maximum number of iterations, t is the current number of iterations, rand(·) is a random perturbation, Fitness i,t is the fitness of the position of particle i at the t-th iteration, Fitness g is the fitness of the position of the global optimal particle;

[0147] Update the individual optimal position p i,t+1 of the particle, the global optimal position g t+1 and the average optimal position m best , and update the particle position. The expression is:

[0148]

[0149] where x i,t+1 is the position update of particle i at the (t + 1)-th iteration, x i,t$x_i(t)$ is the position of particle $i$ at the $t$-th iteration, $\zeta$ and $z$ are random numbers within $[0, 1]$, and $v$ is an adjustment parameter within $[0, 1]$;

[0150] Judge whether the particle is out of bounds. When the particle is out of bounds, chaotic boundary mutation is performed, and the expression is:

[0151]

[0152] where $x'$ i,t+1 is the position of particle $i$ after chaotic boundary mutation when it is out of bounds at the $(t + 1)$-th iteration, $maxx$ t+1 is the upper boundary of the particle swarm in the $(t + 1)$-th iteration, $minx$ t+1 is the lower boundary of the particle swarm in the $(t + 1)$-th iteration, is the chaotic mapping random number in the $(t + 1)$-th iteration, is the chaotic mapping random number in the $t$-th iteration, $s = 0.2$;

[0153] Calculate the cable force error of the search particle, and the expression is:

[0154]

[0155] where $Error$ i,t+1 is the error of particle $i$ at the $(t + 1)$-th iteration, $o$ is a random number within $[0, 1]$, $F$ i ′ ,t+1 is the predicted result of the cable force of particle $i$ at the $(t + 1)$-th iteration, $F$ i is the measured cable force of particle $i$, $\chi$ is the flight coefficient, $\tau$ is the attenuation factor, is the inertia weight, $w$ is the modulation constant, is the standard deviation of the first normal distribution random number $k$, is the standard deviation of the second normal distribution random number $l$, is the flight parameter;

[0156] Iterate continuously until the cable force error is minimized or the maximum number of iterations is reached, then stop the iteration;

[0157] Input the monitoring data and status data of the cable to be measured into the optimized cable force measurement model to obtain the cable force measurement result;

[0158] In the actual evaluation, the measured cable forces of Cable A and Cable B are 960 kN and 890 kN respectively. The cable force errors calculated in combination with the first cable force are 12.07% and 6.02% respectively. The cable force measurement model of the cable is optimized according to the cable force error and iterated continuously until the iteration stops when the cable force error is less than 3%. The monitoring data and status data of the cable to be measured are input into the optimized cable force measurement model, and the cable force measurement results of Cable A and Cable B are 988.32 kN and 914.65 kN respectively.

[0159] As Figures 2 to 5 shown, in this embodiment, a cable based on optical fiber technology includes: ordinary reinforcement 1, single-reinforcement force measuring element 2, and HDPE protective glue 7; the HDPE protective glue 7 is wrapped outside the ordinary reinforcement 1 and the single-reinforcement force measuring element 2; the single-reinforcement force measuring element 2 includes an optical fiber 5, an adhesive fixed end 3, and a matrix reinforcement 6; a spiral groove 4 is provided on the matrix reinforcement 6; the optical fiber 5 is wound and arranged inside the spiral groove 4; the optical fiber 5 is fixed inside the spiral groove 4 in the form of a long gauge through the adhesive fixed end 3; grating regions 8 are inscribed on the optical fiber 5 between the adhesive fixed ends 3; multiple grating regions 8 are inscribed on the optical fiber 5 of the single-reinforcement force measuring element 2; the grating regions 8 are connected in series; the ports of the optical fiber 5 are connected to an external optical fiber grating demodulator.

[0160] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the cable force of a stay cable based on optical fiber technology, characterized in that, It includes the following steps: S1. Obtain the monitoring data and status data of the cable, and preprocess the monitoring data and the status data; the status data includes environmental status data and structural status data; S2. Perform temperature compensation on the monitoring data to obtain a temperature-compensated wavelength, obtain an environmental impact factor according to the environmental status data, and correct the temperature-compensated wavelength to obtain a first corrected wavelength; S3. Determine a scale impact coefficient, determine a scale impact factor according to the structural status data and the scale impact coefficient, and correct the first corrected wavelength to obtain a second corrected wavelength; S4. Determine a first cable tension according to the second corrected wavelength, and construct a cable tension measurement model according to the first cable tension, the environmental impact factor, and the scale impact factor; S5. Optimize the cable tension measurement model according to the cable tension error, and input the monitoring data and status data of the cable to be measured into the optimized cable tension measurement model to obtain a cable tension measurement result; The method for obtaining the first corrected wavelength includes: Input the status data into an environmental impact function to obtain an environmental impact factor, and correct the temperature-compensated wavelength with the environmental impact factor to obtain a first corrected wavelength. The expression is: wherein is the environmental impact factor, , , are the weights of the environmental impact factors, is the environmental noise limit, is the current environmental noise, is the bridge vibration acceleration, is the bridge vibration velocity, is the wind speed, is the angle between the wind direction and the longitudinal direction of the bridge, is the first correction wavelength, is the initial wavelength of the optical fiber, is the temperature compensation wavelength; The method for obtaining the second corrected wavelength includes: Calculate a user utilization coefficient and a size coefficient respectively according to the structural status data, and determine a use-scale impact factor according to the scale impact coefficient, the user utilization coefficient, and the size coefficient. The expression is: Among them is the user usage coefficient is the size coefficient is the usage scale influence factor 、 are the weights of the user usage coefficient is the weight of the size coefficient 、 are the weights of the usage scale influence factor is the number of channels used by the fiber optic demodulator is the maximum number of channels of the fiber optic demodulator is the number of sensor connections within a single channel is the maximum number of sensor connections within a single channel is the access fiber length is the fiber length of the monitoring section is the fiber radius is the groove radius is the matrix rib radius; Correct the first corrected wavelength with the use-scale impact factor to obtain a second corrected wavelength. The expression is: wherein is the second correction wavelength, is the first correction wavelength, is the initial wavelength.

2. The method for measuring the cable force of a stay cable based on optical fiber technology according to claim 1, wherein The method for performing temperature compensation on the monitoring data to obtain a temperature-compensated wavelength includes: Perform a calibration experiment on a single-bar force-measuring element, control the stress and temperature changes of the main single-bar force-measuring element, control the temperature change of the auxiliary single-bar force-measuring element to obtain test calibration data, and solve a binary surface fitting equation of strain and temperature according to the test calibration data. The expression is: where is the binary surface fitting equation for strain, is the binary surface fitting equation for temperature, and the corresponding state is or When taking the calibration value, the wavelength change of the main single-rebar force measuring element is , the wavelength change of the auxiliary single-rebar force measuring element , is the set stress state, is the set temperature state, , are the constant coefficients of the binary surface fitting equation, is the calibration point data matrix, is the strain sensitivity coefficient, is the temperature sensitivity coefficient, is the calibrated strain, is the calibrated stress, is the single-rebar calibrated elastic modulus, is the calibration temperature; The main single-bar force-measuring element is used to make a stressed cable, and the auxiliary single-bar force-measuring element is used to make a temperature compensation element. Calculate the strain and temperature values according to the binary surface fitting equation of strain and temperature and the wavelength change monitoring value, and perform fitting reconstruction on the strain and temperature data according to the fiber optic sensing principle to obtain a temperature-compensated wavelength.

3. The method for measuring the cable force of a stay cable based on optical fiber technology according to claim 1, wherein The method for obtaining the scale impact coefficient includes: The scale impact coefficient includes a helix angle impact coefficient and a stress level impact coefficient; Perform a static tensile test and a finite element simulation test on the single-bar force-measuring element respectively, adjust the stress level and the fiber optic helix winding angle of the single-bar force-measuring element to obtain tensile test data and simulation data, and fit the tensile test data and the simulation data to obtain the helix angle impact coefficient and the stress level impact coefficient. The expression is: Among them is the spiral angle influence coefficient, , , , are constant coefficients obtained by data fitting, is the spiral angle of fiber winding, is the stress level influence coefficient, is the fiber stress, is the elastic modulus of the fiber, is the strain sensitivity of the fiber, is the proportionality coefficient, is the nonlinear index.

4. The method for measuring the cable force of a stay cable based on optical fiber technology according to claim 1, characterized in that The method for determining a first cable tension according to the second corrected wavelength includes: Determine the proportional relationship between the fiber optic strain at the unfixed and unglued part in the spiral groove of the matrix reinforcement and the surface strain of the reinforcement. The expression is: Among them is the strain transfer rate, representing the proportional relationship between the strain of the unfixed optical fiber in the middle and the strain on the surface of the reinforcing material is the gauge length ratio coefficient is the optical fiber length of the middle gauge section is the optical fiber length of the fixed end is the material coefficient is the shear modulus of the adhesive at the fixed end is the elastic modulus of the optical fiber is the radius of the adhesive Determine a first cable tension according to the strain transfer rate, the fiber optic output wavelength, and the material and size parameters of the cable. The expression is: Among them is the cable force of the first cable is the elastic modulus of the reinforcing material is the cross-sectional area of the cable is the strain sensitivity of the optical fiber is the number of single-reinforcement force-measuring elements in the cable is the second corrected wavelength of the th single-reinforcement force-measuring element in the cable is the initial wavelength of the th single-reinforcement force-measuring element in the cable is the cable structure coefficient is the distance from the center of the th single-reinforcement force-measuring element in the cable to the center of the cable is the cable radius is the cross-sectional area of the cable is the cross-sectional area of the single-reinforcement force-measuring element 5. The method for measuring the cable force of a stay cable based on optical fiber technology according to claim 1, characterized in that, The method for constructing the cable tension measurement model includes: Calculate the cable force deviation based on the measured cable force and the cable force of the first stay cable. Combine the cable force deviation, the measured cable force, the cable force of the first stay cable, the scale influence factor, and the environmental influence factor to form a comprehensive data set. Use the random forest algorithm to divide the comprehensive data set into a training set and a test set at a ratio of 7:3; Construct a cable force measurement model based on the comprehensive data set. The cable force measurement model includes an input layer, a base model layer, a strategy layer, and an output layer; The base model layer is used to predict the cable force according to the data law of the comprehensive data set. The base models include a linear regression model, a decision tree model, and a BP neural network model; The linear regression model is responsible for capturing the linear relationship between the input data features and the measured cable force, and ensuring the model stability by standardizing the input features; The decision tree model is responsible for capturing the non-linear relationship between the input data features and the measured cable force, preventing overfitting by setting the maximum depth, and determining the optimal depth by cross-validation; The BP neural network model is responsible for capturing the complex non-linear relationship between the input data features and the measured cable force, using the ReLU activation function, using dropout to prevent overfitting, and determining the number of training epochs by the early stopping method; The strategy layer is used to integrate the output of the base model layer, perform feature engineering and model fusion, and output the cable force prediction result; Use the particle swarm optimization algorithm to optimize the hyperparameters of the cable force measurement model according to the error between the cable force prediction result of the test data and the measured cable force.

6. The method for measuring the cable force of a stay cable based on optical fiber technology according to claim 1, wherein, The method for optimizing the cable force measurement model according to the cable force error includes: Initialize the population size and the maximum number of iterations , and perform a chaotic mapping on the search sub-population. The expression is as follows: wherein is the particle position after chaotic mapping, is the particle position before chaotic mapping, is the chaotic random number of take 0.4; Calculate the fitness of the particle's position and set the fitness threshold , calculate the contraction-expansion coefficient according to the difference in fitness values, and the expression is: wherein is the contraction-expansion coefficient, is the maximum contraction-expansion coefficient, is the minimum contraction-expansion coefficient, is the maximum number of iterations, is the current number of iterations, is the random perturbation, is the particle at the th iteration corresponding to the fitness at the corresponding position, is the fitness of the position where the globally optimal particle is located; Update the individual optimal position of the particle , the global optimal position and the average optimal position , and update the particle position. The expression is as follows: wherein is the position update of the particle at the -th iteration, is the position of the particle at the -th iteration, , is a random number within is a regulation parameter within; Judge whether the particle is out of bounds. When the particle is out of bounds, perform chaotic boundary mutation, and the expression is: where is the position of the particle after chaotic boundary mutation when its position exceeds the boundary in the th iteration, is the upper boundary of the particle swarm in the th iteration, is the lower boundary of the particle swarm in the th iteration, is the chaotic mapping random number in the th iteration, is the chaotic mapping random number in the th iteration, ; Calculate the cable force error of the search particle, and the expression is: where is the error of the particle at the -th iteration, is a random number within is the predicted cable force of the particle at the -th iteration, is the measured cable force of the particle, is the flight coefficient, is the attenuation factor, is the inertia weight, is the modulation constant, is the standard deviation of the first normal distribution random number and is the standard deviation of the second normal distribution random number and is the flight parameter; Iterate continuously until the cable force error is minimized or the maximum number of iterations is reached, and then stop the iteration; Input the monitoring data and status data of the cable to be measured into the optimized cable force measurement model to obtain the cable force measurement result.

7. A cable based on optical fiber technology for performing the method according to any one of claims 1-6, characterized in that, Including: Plain reinforcement, single-reinforcement force measuring element, and HDPE protective glue; the HDPE protective glue is wrapped outside the plain reinforcement and the single-reinforcement force measuring element; the single-reinforcement force measuring element includes an optical fiber, a paste-fixed end, and a matrix reinforcement; spiral grooves are provided on the matrix reinforcement; the optical fiber is wound and arranged inside the spiral grooves; the optical fiber is fixed inside the spiral grooves in the form of a long gauge through the paste-fixed end; grating areas are inscribed on the optical fiber between the paste-fixed ends; there are multiple grating areas on the optical fiber of the single-reinforcement force measuring element; the grating areas are connected in series; the port of the optical fiber is connected to an external fiber Bragg grating demodulator.

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