Deformation detection method based on soft optical waveguide mechanism

Abstract

The invention provides a deformation detection method based on a soft optical waveguide mechanism, and relates to the technical field of computer processing, and the method comprises the following steps: S01, flexible optical waveguide sensors which are distributed at intervals are arranged in a to-be-detected area, and each flexible optical waveguide sensor at least comprises an elastic cladding and satisfies a Mooney-Rivlin hyperelastic model; the curvature of the bent section of the flexible optical waveguide sensor is dynamically associated with pipeline deformation, and the inclination angle # imgabs0 # of the flexible optical waveguide sensor is determined according to the relation between the deformation height # imgabs1 # and the straight section length # imgabs2 #. Through multi-physics field coupling modeling, material optimization design and a high-precision photoelectric conversion mechanism, and through high-sensitivity detection, strong environmental adaptability and long-term stability of deformation of the flexible optical waveguide sensor, the device has the advantages of low cost and easy deployment, and provides reliable technical support for pipeline safety monitoring.

Description

Technical Field

[0001] The present invention relates to the field of computer processing technologies, and particularly to a deformation detection method based on the mechanism of soft optical waveguides. Background Art

[0002] With the wide application of industrial pipeline systems, pipeline safety monitoring has become an important link in ensuring energy transportation and industrial production. During long-term operation, pipelines are prone to local deformations, depressions, or cracks due to factors such as external environmental corrosion, mechanical stress, and geological settlement. If these defects are not detected and processed in a timely manner, they may lead to pipeline leakage, rupture, or even explosion, causing serious economic losses and environmental pollution. Therefore, developing efficient and accurate pipeline deformation detection technologies has important practical significance.

[0003] Traditional pipeline detection technologies, such as ultrasonic detection (refer to Chinese published patent, publication number CN119246680A, a pipeline ultrasonic guided wave detection system disclosed), magnetic flux leakage detection (refer to Chinese authorized patent, publication number CN117849164B, a pipeline magnetic flux leakage detection system disclosed), and ray detection (refer to Chinese published patent, publication number CN116879322A, a pipeline ray detection device disclosed), although they can identify pipeline defects to a certain extent, have limitations such as high detection costs, complex operations, and strict requirements for pipeline materials and structures. In addition, these technologies usually require external equipment support and are difficult to achieve real-time and continuous monitoring.

[0004] In recent years, optical fiber sensing technology has gradually become a research hotspot in the field of pipeline detection due to its advantages such as anti-electromagnetic interference, high sensitivity, and small size. However, traditional optical fiber sensors have poor adaptability in complex pipeline environments, especially in internal pipeline deformation detection, where their flexibility and shock resistance are insufficient, limiting their practical applications. Summary of the Invention

[0005] In view of the above technical problems, the technical solution adopted by the present invention is a deformation detection method based on the mechanism of soft optical waveguides, and the method includes the following steps:

[0006] S01. Arrange flexible optical waveguide sensors distributed at intervals in the area to be measured, where:

[0007] The flexible optical waveguide sensor includes at least an elastic cladding and satisfies the Mooney-Rivlin hyperelastic model

[0008] The curvature of the bending section of the flexible optical waveguide sensor is dynamically correlated with the pipeline deformation, and its tilt angle Through the deformation height And the straight section length The relationship is determined as:

[0009] ;

[0010] The flexible optical waveguide sensor can obtain the relationship between the probe curvature and the deformation height h inside the pipeline :

[0011] ;

[0012] wherein, is the length from the semi-circular arc vertex of the flexible optical waveguide to the inclined connection, is the angle between the probe and the detection plane under the initial condition;

[0013] S02. Inject an original optical signal with a working wavelength of 940 nm into the flexible optical waveguide sensor through a photoelectric emission diode, and detect the output optical signal in real time through a photoelectric receiving diode, where:

[0014] The output optical power of the photoelectric emission diode satisfies: , where: is the electro-optical conversion efficiency of the photoelectric emission diode, is the drive current, (unit: C) is the electron charge, (unit: m / s) is the speed of light in vacuum, is the light source wavelength (unit: nm), (unit: J) is the Planck constant;

[0015] S03. Detect the light intensity of the output optical signal in real time through a photoelectric receiving diode, and calculate the pipeline deformation parameters based on the optical loss model, and the optical loss model includes:

[0016] S31. Macro-bending loss:

[0017] ;

[0018] ;

[0019] wherein, is the baseline light intensity without deformation, is the material constant, L is the length of the bending section, is the curvature of the bending section of the flexible optical waveguide sensor, is the measured baseline light intensity, is the light intensity loss;

[0020] S32. Radial extrusion loss: Describe the relationship between the normal stress and strain through the Neo-Hookean model:

[0021] ;

[0022] wherein, is the radial stress, is the draw ratio, is the material constant;

[0023] S33, temperature-loss coupling effect: eliminating the influence of ambient temperature on light intensity through a temperature compensation model, the temperature compensation model including the temperature drift of LED optical power and the dark current correction of the photoelectric receiving diode :

[0024] ;

[0025] wherein, is the optical responsivity of the photoelectric receiving diode, is the LED temperature coefficient, is the dark current, is the temperature change value (unit: K), is the optical output power at temperature ;

[0026] S34, generating a pipeline deformation detection result according to the deformation parameters, the deformation parameters including the bending radius, the depression depth and the local curvature, and their mapping relationship with the light intensity attenuation is pre-established through experimental calibration or numerical simulation.

[0027] Preferably, the curvature of the macro-bending loss in the optical loss model in the step S03 is dynamically corrected by the geometric parameter dynamic correction formula of the flexible optical waveguide sensor as follows:

[0028] ;

[0029] wherein, R is the bending radius, is the central angle of the bending section of the flexible optical waveguide sensor, L is the length of the bending section, and the material constant is calibrated through experiments, .

[0030] Preferably, the attenuation coefficient of the macro-bending loss in the 31 further satisfies:

[0031] ;

[0032] wherein, is the refractive index of the waveguide core layer, is the refractive index of the cladding, is the core layer radius, is a constant related to the material, is the curvature of the bending section of the flexible optical waveguide sensor.

[0033] Preferably, in the Neo-Hookean model of the radial extrusion loss described in 32, the material constant has a value range of , and the stretch ratio and the compressive strain coefficient are related as: , where .

[0034] Preferably, the radial extrusion loss includes the light intensity attenuation satisfies: , where (unit: dB / ℃) is the bending sensitivity coefficient, is the temperature change value (unit: k).

[0035] Preferably, in the temperature compensation model:

[0036] The temperature correction formula for the output power is: , where is the optical output power under the reference temperature i.e., the standard test conditions, (unit: ℃) is the LED temperature coefficient, is the temperature change value (unit: k), is the optical output power at the temperature ;

[0037] The temperature dependence of the dark current of the photoelectric receiving diode satisfies: , in the formula, is the bandgap energy of the photoelectric receiving / emitting diode material, is the Boltzmann constant, is the temperature value (unit: k), is the initial value of the dark current.

[0038] Preferably, in step S33, the temperature-loss coupling effect includes the temperature drift correction of the waveguide refractive index : , in the formula, is the temperature change value (unit: k), (unit: ℃) is the temperature coefficient of the material refractive index.

[0039] Preferably, in step S02:

[0040] The temperature drift of the emission wavelength of the photoelectric emission diode satisfies: (unit: nm / ℃), and the electro - optical conversion efficiency of the optoelectronic receiving diode value , is the temperature drift value of the emission wavelength, is the temperature change value (unit: K);

[0041] The optical responsivity of the optoelectronic receiving diode satisfies: , where is the quantum efficiency of the optoelectronic receiving diode (representing the ratio of photons converted into effective carriers), is the optical frequency, (unit: J) is the Planck constant.

[0042] Preferably, the Mooney - Rivlin hyperelastic model parameters in the step S01 are: (unit is Mpa), (unit is Mpa), and the strain energy density expression is: , where is the strain invariant, is the material constant, and the flexible optical waveguide sensor includes a core layer, an elastic cladding, and a filling layer;

[0043] The flexible optical waveguide sensor includes a core layer, an elastic cladding, and a filling layer.

[0044] Preferably, the optical loss model in the step S03 further includes Rayleigh scattering loss:

[0045] ;

[0046] In the formula, , where is the refractive index of the waveguide core layer, represents the Boltzmann constant, is the temperature value (unit: K), is the volume expansion coefficient, representing the volume change caused by temperature change.

[0047] The present invention has at least the following beneficial effects:

[0048] 1. By constructing a multi - physical - field optical loss model including macro - bending loss, radial extrusion loss, and temperature - loss coupling effect, it can accurately quantify the influence of different deformation types on optical signals, significantly improving the detection sensitivity of pipeline deformation.

[0049] 2. The flexible optical waveguide sensor adopts an integrated casting design of an elastic cladding and a filling layer, with hyperelasticity, which can closely fit the pipeline deformation and avoid performance degradation caused by mechanical fatigue.

[0050] 3. The electro-emitting diode uses a light source with a wavelength of 940 nm, matches the high transmittance of the glycerol core layer, and combines with the quantum efficiency of the photoelectric receiving diode After optimization, the optical power output is increased to 50 nW, and the transmission loss is reduced.

[0051] 4. Rayleigh scattering loss modeling and micro-bending loss suppression design reduce the total scattering loss to 0.04 dB / m, enhancing the long-distance transmission performance. And the dynamic correction of macro-bending loss and the radial extrusion strain correlation model can distinguish the deformation types and reduce the misjudgment rate.

[0052] 5. The flexible sensor based on the flexible optical waveguide has a simple structure, does not require external complex circuits, reduces the manufacturing cost by more than 40%, and can be directly embedded in the pig detector probe for integrated installation, suitable for rapid deployment and large-scale application in various scenarios such as oil and gas pipelines and urban pipe networks. Brief Description of the Drawings

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0054] Figure 1 It is a schematic diagram of macro-bending loss provided by the embodiment of the present invention.

[0055] Figure 2 It is a schematic diagram of the normal extrusion deformation loss provided by the embodiment of the present invention.

[0056] Figure 3 It is a schematic diagram of the geometric structure of the flexible optical waveguide sensor provided by the embodiment of the present invention.

[0057] Figure 4 Provided by the embodiment of the present invention Figure 3 Schematic diagram of the implementation structure of the flexible optical waveguide sensor under force deformation in Detailed Embodiments

[0058] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0059] It should be noted that the terms "first", "second", etc. in the specification, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or server comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0060] This embodiment provides a deformation detection method based on the mechanism of soft optical waveguide. The method includes the following steps, as Figures 1-4 shown:

[0061] S01. Arrange flexible optical waveguide sensors distributed at intervals in the area to be measured, where:

[0062] The flexible optical waveguide sensor at least includes a core layer, an elastic cladding layer and a filling layer (and the flexible optical waveguide sensor satisfies the Mooney-Rivlin hyperelastic model).

[0063] The curvature of the bending section of the flexible optical waveguide sensor is dynamically correlated with the pipeline deformation, and its inclination angle is determined by the relationship between the deformation height and the straight section length :

[0064] ;

[0065] The curvature of the bending section of the flexible optical waveguide sensor is dynamically correlated with the pipeline deformation, and the relationship between the probe curvature and the deformation height h inside the pipeline can be obtained (combined with Figure 4 it can be known):

[0066] ;

[0067] Among them, is the length from the vertex of the semi-circular arc of the flexible optical waveguide to the inclined connection, is the angle between the probe and the detection plane in the initial situation.

[0068] The Mooney-Rivlin hyperelastic model parameters in the above S01 are (unit is Mpa), (unit is Mpa), and the strain energy density expression is: Among them, is a strain invariant, and is a material constant.

[0069] The above-mentioned Figure 4 shows that when the flexible optical waveguide sensor encounters a protrusion on the optical surface and deforms, while the initial state is the normal state of the flexible optical waveguide sensor. When encountering a protrusion, it bends as shown in the deformation. At this time, the flexible optical waveguide sensor bends, which changes the conduction of the optical path, that is, the parameters for deformation detection are obtained. Based on the particularity of the flexible optical waveguide sensor, the above-mentioned area to be measured can be used for the detection of rigid pipes, flexible pipes, and narrow areas, including the detection of boxes, tanks, walls, and collapses, including the detection of seawall subsidence, river embankment collapse, and landslides.

[0070] Moreover, when detecting sealed areas such as pipes or boxes, the flexible optical waveguide sensor needs to be bent into a U shape, and then the two ends of the U shape are attached to the side wall, and then it is pushed for detection. Preferably, in this application, it is arranged in a spaced manner, the flexible optical waveguide sensor is bent into a U shape and arranged at intervals, and then the deformation during use is detected. When detecting collapses, it does not need to be bent into a U shape.

[0071] The flexible optical waveguide sensor includes a core layer, an elastic cladding layer, and a filling layer, where:

[0072] The above-mentioned filling layer can be glycerol, an optical path filling layer, a flexible colloid, or other well-known filling materials in the art. However, in actual applications, when the filling layer is glycerol or an optical path filling layer, the volatility needs to be calculated to obtain the optical loss. The calculation formula is as follows: The vapor pressure of the filling layer is calculated by the Antoine equation:

[0073] ,

[0074] And at when, the vapor pressure (the unit is Pa).

[0075] In the above technology, the core layer uses high refractive index glycerol. In addition, glycerol also has the characteristics of high transparency and low volatility; the cladding layer uses a rubber tube. Rubber is a flexible material with a low modulus (the Young's modulus is about 1 MPa), allowing large curvature bending. A 940 nm photoelectric emission diode is used as the LED light source in the optoelectronic system.

[0076] When the filling layer is a flexible colloid, there is no need to consider the problem of optical loss caused by volatility.

[0077] Furthermore, in the state without deformation, the optical loss of the optical waveguide is mainly composed of material absorption, Rayleigh scattering, mode decoupling, and port coupling, etc. The optical signal will undergo a constant attenuation, and its attenuation formula is as follows:

[0078] ;

[0079] Among them, is the material absorption loss, is the Rayleigh scattering loss (decreases with decreasing), is the energy loss caused by mode decoupling, is the port coupling loss (depending on the waveguide end face quality, incident angle, etc.).

[0080] In the deformed state, due to the deformation of the optical waveguide, the equivalent refractive index of the high-order mode decreases. The equivalent refractive index of the m-th order mode is: ;

[0081] Among them, is the equivalent refractive index (dimensionless) of the -th order mode, is the propagation constant (unit: ) of the -th order mode, is the free space wave vector, and the calculation formula is . When , the high-order mode leaks into the cladding, forming a mode leakage loss, and its loss coefficient is calculated as follows:

[0082] ;

[0083] Among them, is the working wavelength (unit: nm), a is the core radius, R is the bending radius, is the refractive index of the waveguide core layer, is the refractive index of the cladding. When the deformation curvature radius R becomes smaller, the mode leakage increases significantly, and the optical signal attenuation intensifies. It can be seen that when the flexible optical waveguide is not deformed, the high-order mode loss is restricted by total internal reflection, and the optical loss is low. When it is deformed, the high-order mode leakage causes the optical loss to decrease.

[0084] (2) Reversibility of light intensity response

[0085] The reversibility of the light intensity response is mainly determined by the elastic recovery mechanism of the rubber material and the long-term stability of glycerol. The rubber cladding has superelastic characteristics (Mooney-Rivlin superelastic model):

[0086] ;

[0087] Among them, W is the strain energy density of the rubber material, that is, the elastic energy stored in the material per unit volume, (the unit is Mpa), (unit is MPa) is the material constant, is the strain invariant, is the material constant.

[0088] The vapor equation for glycerol, based on the Antoine equation:

[0089] ;

[0090] P is the equilibrium vapor pressure of the liquid (unit: Pa), T is the temperature (unit: k), A and B are empirical constants of specific substances. For glycerol, there are experimental data giving the corresponding constants A=18.3 (dimensionless) and B=5200 (unit: k), then: ;

[0091] Therefore, the evaporation of glycerol meets the light intensity reversibility requirement.

[0092] S02, injecting an original optical signal with a working wavelength of 940 nm into the flexible optical waveguide sensor through a photoelectric emitting diode, and detecting the output optical signal in real time through a photoelectric receiving diode, wherein:

[0093] The output optical power of the photo-emitting diode satisfy: , where: is the electro-optical conversion efficiency of the photo-emitting diode, is the driving current, (unit is C) is the electron charge, (Unit: m / s) is the speed of light in vacuum, is the wavelength of the light source (unit: nm), (Unit: J) is Planck's constant.

[0094] In the above technology, the photoelectric receiving / emitting diode is the core component of the optical waveguide sensor system, which is responsible for converting the optical signal into an electrical signal. This application uses 940nm emission as the light source of the photoelectric emitting diode, and performs photocurrent detection through the photoelectric receiving diode. A stable constant current source is used for power supply at the transmitting end, and a stable voltage is used at the receiving end to reverse bias the photoelectric receiving diode to ensure the stability and high sensitivity of the sensing system.

[0095] Furthermore, a photoluminescent diode is a light source based on the electroluminescent effect. When the LED is in forward bias, the electrons in the N region and the holes in the P region recombine in the depletion layer, releasing energy and generating photons. The LED light-emitting mechanism can be described by the following equation:

[0096] ;

[0097] in, is the energy of the photon (unit: ), (unit: J), (unit: m / s) is the speed of light in vacuum. is the wavelength of the light source (unit: nm). As the optimal selection = 940 nm. As the emission wavelength of the photoelectric emission diode, it can effectively improve the transmittance of the glycerol core layer, reduce the light consumption during transmission, and the light wave with a wavelength of 940 nm can improve the quantum efficiency of the photoelectric receiving diode , enhance the signal conversion efficiency. In addition, it improves the environmental anti-interference ability, avoids visible light interference, and reduces the influence of ambient light on the sensing system.

[0098] Among them, the light output power of the LED depends on its injection current and photoelectric conversion efficiency, and can be deduced through the carrier recombination process:

[0099]

[0100] Among them, (unit is C) is the electron charge. The light power expression is as follows:

[0101] ;

[0102] Among them, is the electro-optical conversion efficiency of the photoelectric receiving and emitting diode (typical value 15%), (unit is C) is the electron charge, is the drive current of the LED (unit: A), is the wavelength of the light source (unit: ), (unit: J) is the Planck constant, (unit: m / s) is the speed of light in vacuum. Increasing the LED drive current can increase the light power output. Optimizing the electro-optical conversion efficiency of the photoelectric receiving and emitting diode can improve the light emission intensity of the system.

[0103] Further more, the above-mentioned photoelectric receiving diode operates in the photocurrent mode with a reverse bias of 3.3 V. In the reverse bias state: incident photons excite electron-hole pairs, and a photocurrent is formed under the action of an electric field. The calculation of the photocurrent involves photon flux, quantum efficiency, and electro-optical conversion efficiency. The incident optical power corresponding photon number rate:

[0104] ;

[0105] Among them, is the photon flux per unit time, (Unit: J) is the Planck constant, representing the frequency of light.

[0106] The quantum efficiency of the photodetector diode is the ratio of photons converted into effective carriers (typical value 80%). The number rate of effective carriers:

[0107] ;

[0108] where, is the quantum efficiency of the photodetector diode, dimensionless, the photon flux per unit time, is the incident optical power, (Unit: J) is the Planck constant, representing the frequency of light.

[0109] The photocurrent expression: The electric charge passing through the device per unit time is the current:

[0110] ;

[0111] where, is the effective carrier efficiency, (unit is C) is the electron charge, (Unit: J) is the Planck constant, representing the frequency of light.

[0112] Further define the responsivity:

[0113] ;

[0114] where, (unit is C) is the electron charge, (Unit: J) is the Planck constant, representing the frequency of light.

[0115] Obtain the final photocurrent model:

[0116] ;

[0117] Since is a constant related only to device parameters (such as quantum efficiency, electron charge, photon energy), so is linearly related to the incident optical power line that is, it is in a proportional relationship.

[0118] The emission wavelength and output power of the above LED are affected by temperature. When the temperature rises, the bandgap energy of the LED decreases, resulting in the temperature drift of the emission wavelength of the photodiode satisfying: (unit: nm / ℃), and the electro - optical conversion efficiency of its optoelectronic receiving and emitting diode value , is the temperature drift value of the emission wavelength, is the temperature change value (unit: K).

[0119] An increase in temperature will affect the transmission efficiency of the optical waveguide, and the output power of the LED will decrease. Therefore, the temperature correction formula for the output power of the LED is: , where is the optical output power at the reference temperature i.e., under standard test conditions, (unit: ℃) is the temperature coefficient of the LED, is the temperature change value (unit: K), is the optical output power at the temperature ;

[0120] The temperature dependence of the dark current of the optoelectronic receiving diode satisfies: , in the formula, is the band - gap energy of the optoelectronic receiving / emitting diode material, is the Boltzmann constant, is the temperature value (unit: K), is the initial value of the dark current.

[0121] The temperature drift formula of the photocurrent is , where is the photocurrent at the temperature , is the photocurrent at the reference temperature , is the sensitivity coefficient of the photocurrent to temperature change, is the temperature change value (unit: K).

[0122] S03. Real - time detect the light intensity of the output optical signal through the optoelectronic receiving diode, and calculate the pipeline deformation parameters based on the optical loss model.

[0123] The curvature of the macro - bending loss in the optical loss model in the above steps is dynamically corrected by the geometric parameter formula of the flexible optical waveguide sensor as follows:

[0124] ;

[0125] Among them, R is the bending radius, is the central angle of the bending section of the flexible optical waveguide sensor, L is the length of the bending section, and the material constant is calibrated through experiments, .

[0126] The above optical loss model also includes Rayleigh scattering loss:

[0127] ;

[0128] In the formula, , where, is the refractive index of the waveguide core layer, represents the Boltzmann constant, is the temperature value (unit: K), is the volume expansion coefficient, representing the volume change caused by temperature change.

[0129] Rayleigh scattering loss is caused by microscopic defects, impurities or inhomogeneities inside the optical waveguide. Rayleigh scattering has a more significant impact on short-wavelength optical signals, and it causes energy loss by changing the propagation direction of light. For long-wavelength light, the impact of Rayleigh scattering is smaller.

[0130] The above optical loss model includes:

[0131] S31. Macro-bending loss:

[0132] ;

[0133] ;

[0134] In the formula, is the baseline light intensity without deformation, is the material constant, L is the length of the bending section, is the curvature of the bending section of the flexible optical waveguide sensor, is the measured baseline light intensity, is the light intensity loss;

[0135] The attenuation coefficient of the above macro-bending loss further satisfies:

[0136] ;

[0137] In the formula, is the refractive index of the waveguide core layer, is the refractive index of the cladding, is the core radius, is a constant related to the material, is the curvature of the bending section of the flexible optical waveguide sensor.

[0138] S32. Radial extrusion loss: The relationship between normal stress and strain is described by the Neo-Hookean model:

[0139] ;

[0140] In the formula, is the radial stress, is the draw ratio, is the material constant, and in combination with Figure 2 as shown, is the circumferential diameter of the original core layer, while is the circumferential diameter of the core layer under bending deformation, and the draw ratio is the ratio of the two, that is .

[0141] In the above Neo-Hookean model of radial extrusion loss, the value range of the material constant is , and the relationship between the draw ratio and the compressive strain coefficient is: , where .

[0142] And the light intensity attenuation amount of the radial extrusion loss satisfies: , where (unit: dB / ℃) is the bending sensitivity coefficient, is the temperature change value (unit: k).

[0143] S33, temperature-loss coupling effect: Eliminate the influence of ambient temperature on light intensity through the temperature compensation model, and the temperature compensation model includes the temperature drift of the LED light power and the dark current correction of the photoelectric receiving diode :

[0144] ;

[0145] Among them, is the light responsivity of the photoelectric receiving diode, (unit: ℃) is the LED temperature coefficient, is the dark current, is the temperature change value (unit: k), is the light output power at temperature ;

[0146] In the above temperature compensation model:

[0147] In the temperature compensation model:

[0148] The temperature correction formula for the LED output power is: , where is the light output power at the reference temperature i.e., under standard test conditions, (unit: ℃) is the LED temperature coefficient, is the temperature change value (unit: K), at temperature the optical output power is;

[0149] The temperature dependence of the dark current of the photoelectric receiving diode satisfies: , where is the bandgap energy of the photoelectric receiving / emitting diode material, is the Boltzmann constant, is the temperature value (unit: K), is the initial value of the dark current.

[0150] Furthermore, the temperature-loss coupling effect includes the temperature drift correction of the waveguide refractive index : , where is the temperature change value (unit: K), (unit: °C) is the temperature coefficient of the material refractive index.

[0151] Even further, the optical loss model in step S03 also includes Rayleigh scattering loss:

[0152] ;

[0153] where , where is the refractive index of the waveguide core layer, represents the Boltzmann constant, is the temperature value (unit: K), is the volume expansion coefficient, indicating the volume change caused by temperature change. In the above technology, macro-bending loss refers to the reduction of the transmitted optical power due to the leakage of optical modes when the optical waveguide is bent on a large scale. When the optical waveguide undergoes a large-angle bend, the propagation path of light changes with the curvature, and some light rays may not be able to maintain total internal reflection, thus penetrating the cladding and leaking into the external environment. This loss mainly occurs in the higher-order modes because these modes have larger propagation angles and are more susceptible to bending and refraction leakage. As the bending radius decreases, the mode leakage effect increases, resulting in an increase in the overall loss of the optical waveguide. The magnitude of the macro-bending loss is affected by factors such as the structure of the waveguide, the refractive index distribution, and the operating wavelength.

[0154] When only considering the effect of macro-bending, the optical intensity loss (in units) is defined as:

[0155] ;

[0156] is the measured baseline optical intensity, is the baseline intensity without deformation.

[0157] When the cross-sectional area of ​​the optical waveguide is considered as a circle, In a bent fiber, the attenuation coefficient per unit length is can be written as:

[0158] ;

[0159] In the formula, is the refractive index of the waveguide core, is the cladding refractive index, is the core radius, is a constant related to the material, is the curvature of the curved section of the flexible optical waveguide sensor.

[0160] Using Beer's law, the total power around a curve of length L can be found to be:

[0161] .

[0162] Combining the above three equations, we can derive the relationship between the measured strength of the flexible optical waveguide with a bending curvature of k and the initial strength without deformation as follows:

[0163] ;

[0164] L is the length of the bending section, is the curvature of the bending section of the flexible optical waveguide sensor, is the measured baseline light intensity, is the light intensity loss. Figure 3 It can be seen that the so-called bending section length refers to the tilt angle of the flexible optical waveguide sensor. The length of the part, i.e. .

[0165] It can be seen that when other variables are constant, the ratio of the measured strength to the initial strength has an exponential relationship with the bending radius.

[0166] (like Figure 2 Normal compression deformation loss refers to the radial compression of the flexible optical waveguide sensor caused by external force, which in turn affects the light propagation characteristics in the optical waveguide. Normal compression is usually caused by external physical force acting on the waveguide cladding, resulting in deformation of the waveguide core and cladding. This deformation not only affects the geometric structure of the waveguide, but may also cause local small bends, resulting in light loss.

[0167] When modeling the loss of radial extrusion deformation, the Neo-Hookean material model is used. This material model is widely used to describe soft materials such as rubber with large deformation. The stress-strain relationship of this model can be expressed by the following formula:

[0168] ;

[0169] wherein, is the radial stress, is the draw ratio. This model is applicable to describe the compression behavior under large deformation and can reasonably reflect the influence of the deformation caused by normal extrusion on the optical waveguide transmission.

[0170] Under the condition of normal compression, the optical signal in the waveguide will undergo two main changes: First, the size of the waveguide changes, especially the local bending between the core layer and the cladding; Second, small deformations may be caused on both sides of the indenter, and this deformation will further affect the transmission characteristics of the optical waveguide. According to the existing research and experimental data, the small bending caused by normal compression is the main source of light intensity loss, and the leakage of high-order modes is not the main loss mechanism in such relatively large-sized optical waveguides. The optical loss caused by extrusion can be estimated through the local bending caused by the indenter. Since the size of the waveguide is relatively large (for example, the core diameter of the waveguide is 3 mm), at this size, the optical modes in the optical waveguide will not undergo significant decoupling, and the loss is mainly caused by small bending. Based on this, the relationship between the loss and the radial compressive strain can be approximately expressed by the following formula:

[0171] ;

[0172] wherein, is the light intensity loss (light intensity attenuation amount) caused by compression, is the sensitivity coefficient related to bending, is the temperature change (or direct compressive strain change) caused by the normal compressive strain, that is, the temperature change value (unit: K).

[0173] The loss of normal extrusion deformation mainly stems from the geometric deformation of the waveguide caused by external pressure, especially the compression of the waveguide cladding and core. Although the influence of mode decoupling on the loss is small, due to the local bending effect, the optical signal will attenuate, especially when the indenter applies pressure.

[0174] Under the influence of temperature change, the transmission loss of the optical waveguide shows two main mechanisms: one is the optical loss caused by geometric deformation, and the other is the light intensity attenuation caused by the change of the material refractive index. Temperature change will cause the length change of the optical waveguide, thereby affecting the light propagation path and mode matching. Through the comprehensive analysis of geometric deformation and material property changes, a temperature-loss coupling model can be constructed. The temperature change causes the change of the waveguide length, and the specific temperature effect can be expressed as:

[0175] ;

[0176] wherein, is the original length, is the linear expansion coefficient of the material, is the temperature change value (unit: K).

[0177] The temperature change will also cause a change in the refractive index of the waveguide material. Therefore, the above temperature-loss coupling effect includes the temperature drift correction of the waveguide refractive index : , where is the temperature change value (unit: K), (unit: °C) is the temperature coefficient of the refractive index of the core material.

[0178] The change in refractive index will directly affect the propagation mode of the optical waveguide, especially the propagation efficiency of the high-order mode. In the optical waveguide, the propagation of the high-order mode is greatly affected by the change in the refractive index of the material. Therefore, the temperature change will cause leakage or propagation loss of these modes, thereby affecting the light intensity. The change in light intensity caused by the temperature change can be calculated by the comprehensive influence of temperature on the waveguide length and refractive index. Usually, the change rate of light intensity is determined by various factors such as the change in the geometric shape of the optical waveguide (length change, bending, etc.), the mode loss caused by the change in refractive index, and the propagation loss of the optical mode in the optical waveguide. The final expression of the light intensity change can be expressed as:

[0179] ;

[0180] where and are the temperature sensitivity coefficients caused by waveguide bending and normal compression respectively.

[0181] In the case of no deformation, the temperature change mainly affects the change in the refractive index of the material, and the change in light intensity is usually relatively gentle. The relationship between the temperature change and the light intensity change may show linear or weak non-linear changes. When deformation occurs, especially when the optical waveguide is bent, the influence of temperature on the light intensity shows a more significant change. This is because the propagation of the high-order mode is restricted, and the leakage of the high-order mode caused by bending makes the propagation performance of the optical waveguide greatly affected. Specifically, in the case of a small bending radius, the change in refractive index caused by temperature may lead to a greater degree of leakage of the high-order mode, resulting in a change in light intensity. The flexible optical waveguide sensor in this paper is embedded in the probe of the pigging device and is cast integrally. When the external working temperature is constant, the friction generated during operation has a limited impact on the temperature of the internal flexible optical waveguide sensor.

[0182] S04. Generate the pipeline deformation detection result according to the deformation parameters. The deformation parameters include the bending radius, the depression depth, and the local curvature, and their mapping relationship with the light intensity attenuation is established in advance through experimental calibration or numerical simulation.

[0183] As described above, the geometric structure of the flexible optical waveguide sensor determines its optical transmission characteristics in practical applications. Based on the general dimensions of the pigging probe on the market, the structure of the flexible optical waveguide sensor is designed in this embodiment. Figure 4 As shown, it presents the basic shape and related geometric parameters of the flexible optical waveguide sensor. The tilt angle of the flexible optical waveguide sensor:

[0184] ;

[0185] Where: is the height of the probe deformation, and the length is the bent section where the flexible optical waveguide sensor is bent into a U shape, and the radius and the curvature The relationship between them defines the bending characteristics of the optical waveguide. This geometric feature affects the propagation path of light. Especially in the bent section of the flexible optical waveguide sensor, the propagation of light is greatly affected by the curvature.

[0186] Pipeline deformations usually manifest as bending, denting, ovalization, etc. Especially in the structure of the U-shaped optical waveguide, the changes in the bending radius and angle have a particularly significant impact on the optical waveguide. The propagation path of light changes with the curvature. Especially the higher-order modes are more vulnerable to being affected. Therefore, the increase in optical mode leakage will lead to the attenuation of light intensity. In the U-shaped optical waveguide, the change in the curvature of the waveguide directly affects the propagation of optical modes. Especially the higher-order modes are more likely to leak. The reduction of the curvature radius leads to more serious leakage of the higher-order modes, thus increasing the overall loss of the optical waveguide.

[0187] In summary, by constructing a multi-physical-field optical loss model that includes macro-bending loss, radial extrusion loss, and temperature-loss coupling effect, it is possible to accurately quantify the influence of different deformation types on the optical signal and significantly improve the detection sensitivity of pipeline deformation. Further, the flexible optical waveguide sensor adopts an integrated casting design of an elastic cladding and a filling layer, which has super elasticity and can closely fit the pipeline deformation to avoid performance degradation caused by mechanical fatigue. Secondly, the light-emitting diode uses a 940-nm wavelength light source, which matches the high transmittance of the glycerol core layer, combined with the quantum efficiency of the photoelectric receiving diode. Optimization: The optical power output is increased to 50 wM, reducing the transmission loss. Moreover, the Rayleigh scattering loss modeling and the micro-bending loss suppression design reduce the total scattering loss to 0.04 dB / m, enhancing the long-distance transmission performance. Also, the macro-bending loss dynamic correction and the radial extrusion strain correlation model can distinguish the deformation types and reduce the misjudgment rate. Furthermore, the flexible sensor based on the flexible optical waveguide has a simple structure, does not require an external complex circuit, reduces the manufacturing cost by more than 40%, and can be directly embedded in the pig detector probe for integrated installation, being suitable for rapid deployment and large-scale applications in various scenarios such as oil and gas pipelines and urban pipe networks.

[0188] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or decorations to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as the content does not depart from the technical solution of the present invention, any simple modification, equivalent change, and decoration made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A deformation detection method based on the mechanism of soft optical waveguide, characterized in that, The method includes the following steps: S01. Deploy flexible optical waveguide sensors distributed at intervals in the area to be measured, where: The flexible optical waveguide sensor includes at least an elastic cladding and satisfies the Mooney-Rivlin hyperelastic model; The curvature of the bending section of the flexible optical waveguide sensor is dynamically correlated with the pipeline deformation, and its tilt angle is determined by the relationship between the deformation height and the straight section length : ； The flexible optical waveguide sensor can obtain the relationship between the probe curvature and the deformation height h inside the pipeline : ； Among them, is the length from the semi-circular arc vertex of the flexible optical waveguide to the inclined connection, is the angle between the probe and the detection plane under the initial condition; S02. Inject an original optical signal with a working wavelength of 940 nm into the flexible optical waveguide sensor through a photoelectric emission diode, and detect the output optical signal in real time through a photoelectric receiving diode, where: The output optical power of the photoemissive diode satisfies: , where: is the electro-optical conversion efficiency of the photoemissive diode, is the drive current, is the electron charge, is the speed of light in vacuum, is the wavelength of the light source, is the Planck constant; S03. Detect the light intensity of the output optical signal in real time through a photoelectric receiving diode, and calculate the pipeline deformation parameter based on the optical loss model, and the optical loss model includes: S31. Macro-bending loss: ； ； In the formula, is the baseline light intensity without deformation, is the material constant, L is the length of the bending section, is the curvature of the bending section of the flexible optical waveguide sensor, is the measured baseline light intensity, is the light intensity loss; S32. Radial extrusion loss: Describe the relationship between normal stress and strain through the Neo-Hookean model: ； In the formula, is the radial stress, is the draw ratio, is the material constant; S33. Temperature-loss coupling effect: eliminating the influence of ambient temperature on light intensity through a temperature compensation model, where the temperature compensation model includes the temperature drift of LED optical power and the dark current correction of a photoelectric receiving diode : ； Among them, is the optical responsivity of the photodetector diode, is the LED temperature coefficient, is the dark current, is the temperature change value, is at temperature of the optical output power; S34. Generate a pipeline deformation detection result based on the deformation parameters, where the deformation parameters include the bending radius, the depression depth, and the local curvature, and their mapping relationship with the light intensity attenuation is pre-established through experimental calibration or numerical simulation.

2. The deformation detection method based on the soft optical waveguide mechanism according to claim 1, characterized in that The curvature of the macro-bending loss in the optical loss model described in step S03 The dynamic correction formula for the geometric parameters of the flexible optical waveguide sensor is as follows: ； Among them, R is the bending radius, is the central angle of the bending section of the flexible optical waveguide sensor, L is the length of the bending section, and the material constant is calibrated through experiments, .

3. A deformation detection method based on the mechanism of soft optical waveguide according to claim 1, characterized in that, The attenuation coefficient of the macro-bending loss described in S31 further satisfies: ； In the formula, is the refractive index of the waveguide core layer, is the refractive index of the cladding, is the core radius, is a constant related to the material, is the curvature of the bent section of the flexible optical waveguide sensor.

4. The deformation detection method based on the soft optical waveguide mechanism according to claim 1, characterized in that In the Neo-Hookean model of the radial extrusion loss described in step S32, the material constant has a value range of , and the relationship between the draw ratio and the compressive strain coefficient is: , where .

5. A deformation detection method based on the mechanism of soft optical waveguide according to claim 4, characterized in that The radial extrusion loss includes the light intensity attenuation amount Satisfy: , where is the bending sensitivity coefficient, is the temperature change value.

6. The deformation detection method based on the soft optical waveguide mechanism according to claim 1, characterized in that, In the temperature compensation model in step S33: The temperature correction formula for the output power is as follows: , where is the optical output power at the reference temperature , that is, under the standard test conditions, is the LED temperature coefficient, is the temperature change value, is the optical output power at the temperature ; The temperature dependence of the dark current of the photodetector diode satisfies: , where is the bandgap energy of the photodetector / emitter diode material, is the Boltzmann constant, is the temperature value, is the initial value of the dark current.

7. A deformation detection method based on the mechanism of soft optical waveguide according to claim 1, characterized in that The temperature-loss coupling effect in the step S33 includes temperature drift correction of the waveguide refractive index : , where is the temperature change value, is the temperature coefficient of the material refractive index.

8. A deformation detection method based on the mechanism of soft optical waveguide according to claim 1, characterized in that In step S02: The temperature drift of the emission wavelength of the photoelectric emission diode satisfies: , and the electro-optical conversion efficiency of the photoelectric emission diode value , is the temperature drift value of the emission wavelength, is the temperature change value; The optical responsivity of the photodetector diode satisfies: , where is the quantum efficiency of the photodetector diode, is the optical frequency, is the Planck constant.

9. The deformation detection method based on the soft optical waveguide mechanism according to claim 1, wherein The Mooney-Rivlin hyperelastic model parameters in the step S01 are as follows: , , and the strain energy density expression is: , where is the strain invariant, is the material constant, and the flexible optical waveguide sensor includes a core layer, an elastic cladding layer, and a filling layer.

10. A deformation detection method based on the mechanism of soft optical waveguide according to claim 1, characterized in that, The optical loss model in step S03 further includes Rayleigh scattering loss: ； In the formula, , where is the refractive index of the waveguide core layer, represents the Boltzmann constant, is the temperature value, is the volume expansion coefficient.

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