A method and system for monitoring offshore wind power sea cable based on distributed optical sensing

Abstract

The application discloses a kind of offshore wind power submarine cable monitoring method and system based on distributed optical sensing, it is related to submarine cable monitoring technical field, the method includes: narrowband light source is emitted to transmission optical fiber, the narrowband light source is carried out Rayleigh scattering in the transmission optical fiber to form backscattering light signal, the transmission optical fiber is arranged along the axial direction of submarine cable and is closely fixed with submarine cable, to make transmission optical fiber synchronous vibration and deformation with submarine cable;The backscattering light signal is received, and the intensity information and phase information are calculated according to the backscattering light signal;The intensity information and phase information are received, and the vibration information, strain information and spatial position information of the submarine cable are extracted according to the intensity information and phase information.The application can realize the online monitoring, positioning and early warning of the vibration, disturbance, deformation and fault condition of submarine cable.

Description

Technical Field

[0001] This invention relates to the field of submarine cable monitoring technology, and in particular to a method and system for monitoring offshore wind power submarine cables based on distributed optical sensing. Background Technology

[0002] Currently, submarine cables have become a crucial link for long-distance transoceanic energy transmission and large-scale offshore new energy development, and their strategic importance is increasingly prominent against the backdrop of global energy structure transformation. In recent years, with the rapid development of the offshore wind power industry, the scale of laying large-capacity, high-reliability submarine cables has continued to expand. However, submarine cables face complex and ever-changing challenges in actual operating environments, including human-caused damage and natural disasters, leading to frequent cable safety issues and seriously affecting the stability of power transmission.

[0003] In actual operation, submarine cables are exposed to the complex and ever-changing marine environment for extended periods, frequently subjected to external forces such as tides, waves, and ocean currents, leading to fatigue damage under continuous dynamic loads. Fatigue damage is a significant cause of cable failure, often manifesting as progressive damage accumulation in the cable material, ultimately potentially leading to structural failure or even fracture. Particularly in harsh marine environments, cables are subjected to prolonged cyclic loads, making them prone to microcrack propagation and internal material damage accumulation. Therefore, fatigue analysis and life prediction research for submarine cables are of paramount importance.

[0004] To address the aforementioned issues, establishing a comprehensive submarine cable safety monitoring system, especially one capable of high-precision real-time monitoring and risk early warning, is crucial. However, due to the complex seabed environment and the difficulty in deploying detection equipment, traditional monitoring technologies are insufficient to meet the high-precision real-time monitoring requirements for submarine cable operational safety under the new circumstances. Therefore, researching and developing a reliable, real-time, and intelligent monitoring technology and system has become an important task for ensuring the safe operation of submarine cables and reducing maintenance costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for monitoring submarine wind power cables based on distributed optical sensing, which can realize distributed dynamic sensing of the status of submarine cables.

[0006] To address the aforementioned technical problems, this invention provides a method for monitoring submarine wind power cables based on distributed optical sensing, comprising: transmitting a narrowband light source into a transmission optical fiber, wherein the narrowband light source performs Rayleigh scattering within the transmission optical fiber to form a backscattered light signal; the transmission optical fiber is axially laid along the submarine cable and tightly fixed to the submarine cable so that the transmission optical fiber vibrates and deforms synchronously with the submarine cable; receiving the backscattered light signal and calculating light intensity information and phase information based on the backscattered light signal; receiving the light intensity information and phase information and extracting vibration information, strain information, and spatial position information of the submarine cable based on the light intensity information and phase information.

[0007] As an improvement to the above scheme, the step of transmitting a narrowband light source into the transmission optical fiber includes: outputting a narrowband light source; performing beam splitting processing on the narrowband light source to generate a probe light and a reference light; performing modulation processing on the probe light according to a modulation command to generate a probe pulse; performing amplification processing on the probe pulse; and injecting the amplified probe pulse into the transmission optical fiber so that the probe pulse undergoes Rayleigh scattering within the transmission optical fiber to form a backscattered light signal.

[0008] As an improvement to the above scheme, the step of calculating phase information based on the backscattered light signal includes: interfering the backscattered light signal with a reference light to generate a photocurrent signal; converting the photocurrent signal into an electrical signal; converting the electrical signal into a digital signal; and demodulating the digital signal to generate phase information.

[0009] As an improvement to the above scheme, the photocurrent signal is:

[0010]

[0011]

[0012]

[0013]

[0014] in, It is a photocurrent signal. To detect the light field, As a reference light field, To detect the amplitude of light, To detect the frequency of light, The phase change caused by the disturbance. For reference light amplitude, As the reference optical frequency, This represents the frequency difference between the reference light and the probe light.

[0015] As an improvement to the above scheme, the step of demodulating the digital signal to generate phase information includes: mixing the digital signal with a preset reference quadrature signal respectively; performing low-pass filtering on the mixed digital signal; and calculating the quadrature components based on the low-pass filtered digital signal to generate phase information.

[0016] As an improvement to the above scheme, the step of extracting the strain information of the submarine cable includes: according to the formula Calculate the strain information of the submarine cable; among which, For strain information, The wavelength of light The difference in phase information. For the fiber refractive index, The Pockels coefficient is the value of the single-mode fiber glass. This is the gauge length.

[0017] As an improvement to the above scheme, the step of extracting the vibration information of the submarine cable includes: according to the formula To calculate the vibration information of submarine cables; among which, For vibration information, To detect the amplitude of light, The reference light amplitude.

[0018] Accordingly, the present invention also provides a monitoring system for offshore wind power cables based on distributed optical sensing, including a transmission optical fiber, an optical fiber demodulation device, and a monitoring host computer; the transmission optical fiber is axially laid along the submarine cable and vibrates and deforms synchronously with the submarine cable; the optical fiber demodulation device is connected to the transmission optical fiber and is used to emit a narrowband light source into the transmission optical fiber, the narrowband light source undergoes Rayleigh scattering within the transmission optical fiber to form a backscattered light signal; the optical fiber demodulation device is also used to receive the backscattered light signal and calculate light intensity information and phase information based on the backscattered light signal; the monitoring host computer is connected to the optical fiber demodulation device and is used to receive the light intensity information and phase information, and extract the vibration information, strain information, and spatial position information of the submarine cable based on the light intensity information and phase information.

[0019] As an improvement to the above solution, the fiber demodulation device includes a narrowband laser, an acousto-optic modulator, an erbium-doped amplifier, a circulator, a first optical coupler, a balanced detector, a second optical coupler, an arbitrary waveform generator, a demodulation module, and a high-speed data acquisition module. The narrowband laser outputs a narrowband light source to the first optical coupler. The first optical coupler splits the narrowband light source to generate a probe light and a reference light, outputting the probe light to the acousto-optic modulator and the reference light to the second optical coupler. The acousto-optic modulator modulates the probe light according to the modulation command of the arbitrary waveform generator to generate a probe pulse, outputting the probe pulse to the erbium-doped amplifier. The erbium-doped amplifier amplifies the probe pulse and outputs the amplified probe pulse to the second optical coupler. The circulator is configured to inject the amplified probe pulse into the transmission optical fiber, causing the probe pulse to undergo Rayleigh scattering within the transmission optical fiber to form a backscattered light signal; the circulator is also configured to receive the backscattered light signal and output the backscattered light signal to the second optical coupler; the second optical coupler is configured to interfere the backscattered light signal with the reference light to generate a photocurrent signal, and output the photocurrent signal to the balanced detector; the balanced detector is configured to convert the photocurrent signal into an electrical signal and output the electrical signal to the high-speed data acquisition module; the high-speed data acquisition module is configured to convert the electrical signal into a digital signal and output the digital signal to the demodulation module; the demodulation module is configured to demodulate the digital signal to generate phase information.

[0020] As an improvement to the above scheme, the offshore wind power cable monitoring system based on distributed optical sensing also includes a flexible carrier, in which the transmission optical fiber is embedded and laid together with the functional optical fiber in the submarine cable.

[0021] Implementing this invention has the following beneficial effects:

[0022] This invention achieves distributed dynamic sensing of the submarine cable's status by transmitting a narrowband light source with a specific frequency and pulse width into the transmission optical fiber and receiving backscattered light signals generated by events such as changes in the submarine cable's shape, ocean current impact, or anchoring. Simultaneously, by analyzing the intensity and phase changes in the backscattered light signals, monitoring information such as vibration (vibration state), strain (stress-strain), and spatial location (spatial curve) of the submarine cable can be extracted in real time, thereby enabling online monitoring, location, and early warning of vibration, disturbance, deformation, and fault conditions of the submarine cable.

[0023] Furthermore, the transmission optical fiber in this invention adopts redundant optical fiber pre-embedded inside the submarine cable. This redundant optical fiber is laid in the same cable as the power optical fiber or communication optical fiber of the submarine cable, but does not carry power or communication services. It is only used for monitoring purposes, thereby ensuring that the monitoring system is physically isolated from the power or communication system and does not interfere with each other. Attached Figure Description

[0024] Figure 1 This is a flowchart of an embodiment of the offshore wind power submarine cable monitoring method based on distributed optical sensing of the present invention;

[0025] Figure 2 This is a schematic diagram of an embodiment of the offshore wind power submarine cable monitoring system based on distributed optical sensing of the present invention;

[0026] Figure 3 This is a schematic diagram of an embodiment of the fiber optic demodulation device in this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It is hereby declared that the directional terms such as up, down, left, right, front, back, inside, and outside used in this text are based solely on the accompanying drawings and are not intended to specifically limit the invention.

[0028] See Figure 1 , Figure 1 The flowchart illustrates an embodiment of the offshore wind power submarine cable monitoring method based on distributed optical sensing of the present invention, which includes:

[0029] S101, emits a narrowband light source into the transmission optical fiber;

[0030] In this invention, the transmission optical fiber is axially laid along the submarine cable and tightly fixed to the submarine cable so that the transmission optical fiber vibrates and deforms synchronously with the submarine cable.

[0031] Furthermore, the transmission optical fiber is embedded inside the flexible carrier, and it is laid in the same cable as the functional optical fiber inside the submarine cable. In this invention, the transmission optical fiber can be a redundant optical fiber pre-embedded inside the submarine cable. This redundant optical fiber is laid in the same cable as the power optical fiber or communication optical fiber of the submarine cable, but it does not carry power or communication services and is only used for monitoring purposes, thereby ensuring physical isolation and non-interference between the monitoring system and the power or communication system.

[0032] It should be noted that when a submarine cable is subjected to external force or structural changes, the transmission optical fiber vibrates and deforms synchronously with the submarine cable. The narrowband light source incident on the transmission optical fiber undergoes Rayleigh scattering under the action of the vibration or deformation of the transmission optical fiber, resulting in a change in the local optical path difference, thus forming a special backscattered light signal.

[0033] Accordingly, the steps of transmitting a narrowband light source into the transmission optical fiber include:

[0034] (1) Output narrowband light source;

[0035] (2) The narrowband light source is split to generate probe light and reference light;

[0036] (3) Modulate the probe light according to the modulation command to generate a probe pulse;

[0037] (4) Amplify the detection pulse;

[0038] (5) Inject the amplified probe pulse into the transmission fiber so that the probe pulse undergoes Rayleigh scattering in the transmission fiber to form a backscattered light signal.

[0039] During operation, the stable narrowband light source (e.g., a single-frequency continuous wave) emitted by the narrowband laser 21 is first split by the first optical coupler 25 at a ratio of 10:90. 90% of the probe light enters the acousto-optic modulator 22, and 10% of the reference light enters the second optical coupler 27. The frequency difference between the probe light and the reference light is [missing information]. f The probe light enters the acousto-optic modulator 22 and is modulated into a probe pulse by the arbitrary waveform generator 28. It is then amplified by the erbium-doped amplifier 23 and injected into the transmission optical fiber via the circulator 24. As the probe pulse propagates in the transmission optical fiber, it interacts with the weak vibrations or strain caused by disturbances in the submarine cable, generating a backscattered light signal that carries disturbance information (see [link]). Figure 3 ).

[0040] S102 receives the backscattered light signal and calculates the light intensity and phase information based on the backscattered light signal;

[0041] Accordingly, the steps for calculating phase information based on the backscattered light signal include:

[0042] (1) Interference processing is performed between the backscattered light signal and the reference light to generate a photocurrent signal;

[0043] The specific photocurrent signal is:

[0044]

[0045]

[0046]

[0047]

[0048] in:

[0049] It is a photocurrent signal;

[0050] To detect the light field (i.e., backscattered light);

[0051] As a reference light field;

[0052] To detect the amplitude of light;

[0053] To detect the frequency of light;

[0054] The phase change caused by the disturbance;

[0055] For reference light amplitude;

[0056] The reference optical frequency;

[0057] This represents the frequency difference between the reference light and the probe light.

[0058] It should be noted that, and It is a DC component, which can be removed by filtering; As a useful signal carrying disturbance information, the phase demodulation algorithm can accurately measure the location and intensity of disturbance events on the submarine cable, enabling real-time monitoring and early warning of offshore wind power submarine cables.

[0059] (2) Convert the photocurrent signal into an electrical signal;

[0060] (3) Convert electrical signals into digital signals;

[0061] (4) Demodulate the digital signal to generate phase information.

[0062] To obtain phase information, IQ demodulation can be used to process the digital signal. That is, the detected intermediate frequency signal (it should be noted that the electrical signal from the balanced detector is a mixed signal with a high-frequency carrier (near the LO frequency), the most critical part of which is the fixed difference frequency) is processed. The corresponding voltage waveform (which this invention refers to as the "intermediate frequency signal") is mixed with locally preset reference quadrature signals (cosine and sine) and high-frequency terms are eliminated by low-pass filtering. Finally, the distributed phase information in the transmission optical fiber is obtained by calculating the quadrature components, thereby enabling real-time and accurate monitoring and location of disturbance events on wind power submarine cables. Further, the step of demodulating the digital signal to generate phase information includes:

[0063] (4.1) Mix the digital signal with the preset reference quadrature signal respectively;

[0064] The detected intermediate frequency signal is mixed with locally preset reference quadrature signals (cosine and sine) respectively, where:

[0065] The mixing signal for the in-phase branch (I-path) is:

[0066]

[0067] The mixing signal for the quadrature branch (Q-path) is:

[0068]

[0069] (4.2) Perform low-pass filtering on the digital signal after mixing;

[0070] After low-pass filtering to remove high-frequency terms, both I / O paths are retained, including:

[0071] After low-pass filtering, the output of the in-phase branch (I-path) is:

[0072]

[0073] After low-pass filtering, the output of the quadrature branch (Q-path) is:

[0074]

[0075] (4.3) Calculate the quadrature components based on the digital signal after low-pass filtering to generate phase information.

[0076] The final phase information obtained through the I / Q outputs is:

[0077]

[0078] in:

[0079] For optical phase information;

[0080] The in-phase component after passing through the low-pass filter (LPF) reflects the correlation between the signal and the local carrier cosine component, and is the extraction of the real part of the signal in demodulation.

[0081] The quadrature component, after passing through the low-pass filter, reflects the correlation between the signal and the local carrier sinusoidal component and is the extraction of the imaginary part of the signal.

[0082] In addition, the steps for calculating light intensity information based on backscattered light signals include:

[0083] (1) Interference processing is performed between the backscattered light signal and the reference light to generate a photocurrent signal;

[0084] (2) Convert the photocurrent signal into an electrical signal;

[0085] (3) Amplify and filter the electrical signal;

[0086] (4) The amplified and filtered electrical signal is used as light intensity information.

[0087] Accordingly, through the I / Q outputs, the final light intensity information of the signal under test is obtained as follows:

[0088]

[0089] in:

[0090] For light intensity information;

[0091] The in-phase component after passing through a low-pass filter;

[0092] These are the quadrature components after passing through the low-pass filter.

[0093] S103 receives light intensity and phase information, and extracts vibration, strain and spatial location information of the submarine cable based on the light intensity and phase information.

[0094] In this invention, strain information is directly calculated from the optical phase using a standard linear method. Accordingly, the strain information of the submarine cable can be calculated according to the following formula:

[0095]

[0096] in:

[0097] This is strain information, in m / m;

[0098] The wavelength of light is typically taken as 1550.12e-9m;

[0099] This represents the difference in phase information, expressed in rad.

[0100] This is the fiber refractive index (i.e., the effective refractive index of the optical fiber), which is typically taken as 1.46.

[0101] is the Pockel coefficient of single-mode fiber glass, typically taken as 0.79;

[0102] This is the gauge length, typically taken as 4.8m.

[0103] Furthermore, this invention utilizes the principle of optical time-domain reflectometry (OTDR) to determine the spatial location of the event. Specifically, by transmitting an optical pulse into the transmission fiber and measuring the return time of the backscattered light signal, and since the propagation speed of the optical pulse in the transmission fiber is known, the location of the scattering event can be calculated using the following formula:

[0104]

[0105] in:

[0106] This refers to spatial location information, specifically the location where the scattering event occurred.

[0107] The speed of light;

[0108] This is the time difference between the emission and return of the light pulse;

[0109] is the fiber refractive index.

[0110] In addition, the present invention can also extract the vibration information of the submarine cable based on the light intensity information and phase information.

[0111] It should be noted that the magnitude of the vibration information (i.e., vibration amplitude) comes from the amplitude response envelope of the light intensity information, that is, the mode length after the amplitude of the I and Q baseband signals is synthesized.

[0112] because:

[0113]

[0114]

[0115]

[0116] available:

[0117]

[0118] For the beat frequency intensity (interference term after removing the DC term), i.e., the vibration amplitude, the envelope is:

[0119]

[0120] in:

[0121] For vibration information;

[0122] To detect the amplitude of light;

[0123] The reference light amplitude.

[0124] Therefore, this invention achieves distributed dynamic sensing of the submarine cable's status by transmitting a narrowband light source of specific frequency and pulse width into redundant optical fibers and receiving backscattered light signals generated by events such as changes in submarine cable morphology, ocean current impact, or anchoring. Simultaneously, by analyzing the intensity and phase changes in the backscattered light signals, monitoring information such as vibration (vibration state), strain (stress-strain), and spatial location (spatial curve) of the submarine cable can be extracted in real time, enabling online monitoring, location, and early warning of submarine cable vibration, disturbances, deformation, and fault conditions. Furthermore, this invention is unaffected by electromagnetic interference and can adapt to complex seabed environments, making it of significant practical importance for improving the safety monitoring level of submarine cables and reducing risks caused by human and natural damage.

[0125] See Figure 2 , Figure 2 The specific structure of the offshore wind power submarine cable monitoring system based on distributed optical sensing of the present invention is shown, which includes a transmission optical fiber 1, an optical fiber demodulation device 2, and a monitoring host computer 3, specifically:

[0126] The transmission optical fiber 1 is laid axially along the submarine cable and is tightly fixed to the submarine cable so that the transmission optical fiber 1 vibrates and deforms synchronously with the submarine cable.

[0127] The fiber demodulation device 2 is connected to the transmission fiber 1 and is used to emit a narrowband light source into the transmission fiber 1. The narrowband light source performs Rayleigh scattering in the transmission fiber 1 to form a backscattered light signal.

[0128] The fiber optic demodulation device 2 is also used to receive backscattered light signals and calculate light intensity and phase information based on the backscattered light signals;

[0129] The monitoring host computer 3 is set on the shore and connected to the fiber optic demodulation device 2 via the Internet. It is used to receive light intensity information and phase information, and extract vibration information, strain information and spatial location information of the submarine cable based on the light intensity information and phase information.

[0130] It should be noted that when a submarine cable is subjected to external forces or structural changes, the transmission optical fiber 1 vibrates and deforms synchronously with the submarine cable. Narrowband light incident on the transmission optical fiber 1 undergoes Rayleigh scattering under the influence of the vibration or deformation of the fiber, resulting in a localized change in optical path difference, thus forming a unique backscattered light signal. Therefore, by analyzing the intensity and phase changes in the backscattered light signal, monitoring information such as vibration (vibration state), strain (stress-strain), and spatial location (spatial curve) of the submarine cable can be extracted in real time. This enables online monitoring, location, and early warning of vibration, disturbance, deformation, and fault conditions of the submarine cable.

[0131] Therefore, this invention can overcome the technical problems in the prior art, such as the difficulty in achieving high-precision real-time monitoring of offshore wind power cables, fatigue damage early warning and positioning, and ensure the safety and reliability of submarine cable operation.

[0132] Furthermore, the offshore wind power cable monitoring system based on distributed optical sensing also includes a flexible carrier. The transmission optical fiber 1 is laid along the axial direction of the submarine cable and embedded inside the flexible carrier. At the same time, the transmission optical fiber 1 and the functional optical fiber in the submarine cable are laid together.

[0133] It should be noted that the transmission fiber 1 can be a redundant fiber optic cable pre-embedded inside the submarine cable. This redundant fiber optic cable is laid in the same cable as the power fiber optic cable or communication fiber optic cable of the submarine cable, but it does not carry power or communication services. It is only used for monitoring purposes, thereby ensuring that the monitoring system is physically isolated from the power or communication system and does not interfere with each other.

[0134] Therefore, this invention transmits a narrowband light source with a specific frequency and pulse width to redundant optical fibers and receives backscattered light signals generated in the optical fibers due to events such as changes in the shape of submarine cables, ocean current impacts, or anchor strikes, thereby achieving distributed dynamic sensing of the status of submarine cables. At the same time, the backscattered light signals are analyzed by the optical fiber demodulation device 2 and the monitoring host computer 3 to obtain real-time monitoring information of the submarine cables, enabling high-sensitivity, long-distance real-time monitoring of submarine cables, effectively improving the operational stability, safety, and fault early warning capabilities of wind power submarine cables.

[0135] like Figure 3 As shown, the fiber optic demodulation device 2 includes a narrowband laser 21, an acousto-optic modulator 22, an erbium-doped amplifier 23, a circulator 24, a first optical coupler 25, a balanced detector 26, a second optical coupler 27, an arbitrary waveform generator 28, a demodulation module 29, and a high-speed data acquisition module 30. Specifically:

[0136] Narrowband laser 21 is used to output a narrowband light source to the first optical coupler 25;

[0137] The first optical coupler 25 is used to perform beam splitting on the narrowband light source to generate probe light and reference light, and outputs the probe light to the acousto-optic modulator 22 and the reference light to the second optical coupler 27.

[0138] The acousto-optic modulator 22 is used to modulate the probe light according to the modulation command of the arbitrary waveform generator 28 to generate a probe pulse, and output the probe pulse to the erbium-doped amplifier 23.

[0139] Erbium-doped amplifier 23 is used to amplify the detection pulse and output the amplified detection pulse to circulator 24;

[0140] The circulator 24 is used to inject the amplified probe pulse into the transmission optical fiber so that the probe pulse undergoes Rayleigh scattering in the transmission optical fiber to form a backscattered light signal. It is also used to receive the backscattered light signal and output the backscattered light signal to the second optical coupler 27.

[0141] The second optical coupler 27 is used to interfere with the backscattered light signal and the reference light to generate a photocurrent signal, and output the photocurrent signal to the balanced detector 26.

[0142] The balanced detector 26 is used to convert the photocurrent signal into an electrical signal and output the electrical signal to the high-speed data acquisition module 30;

[0143] The high-speed data acquisition module 30 is used to convert electrical signals into digital signals and output the digital signals to the demodulation module 29;

[0144] The demodulation module 29 is used to demodulate digital signals to generate phase information.

[0145] During operation, the stable narrowband light source (e.g., a single-frequency continuous wave) emitted by the narrowband laser 21 is first split by the first optical coupler 25 at a ratio of 10:90. 90% of the probe light enters the acousto-optic modulator 22, and 10% of the reference light enters the second optical coupler 27. The frequency difference between the probe light and the reference light is [missing information]. f The probe light enters the acousto-optic modulator 22 and is modulated into a probe pulse by the arbitrary waveform generator 28. After being amplified by the erbium-doped amplifier 23, it is injected into the transmission optical fiber through the circulator 24. When the probe pulse is transmitted in the transmission optical fiber, it generates a backscattered light signal with the weak vibration or strain caused by the disturbance of the submarine cable, forming a backscattered light signal carrying the disturbance information. The reflected backscattered light signal is guided by the circulator 24, interferes with the reference light through the second optical coupler 27, and is converted into an electrical signal by the balanced detector 26. Subsequently, the electrical signal is connected to the high-speed data acquisition module 30, digitized, and sent to the demodulation module 29 for modulation processing to achieve phase reconstruction.

[0146] Accordingly, the interference principle between the backscattered light signal and the reference light in the second optical coupler 27 is as follows:

[0147] Let the probe light (i.e., backscattered light) field be... for:

[0148]

[0149] in, To detect the amplitude of light, To detect the frequency of light, This refers to the phase change caused by the disturbance.

[0150] Reference light field for:

[0151]

[0152] in, For reference light amplitude, Let the reference optical frequency be , and satisfy:

[0153]

[0154] Then, the photocurrent signal after the two beams of light interfere within the second optical coupler 27 for:

[0155]

[0156] in, and It is a DC component, which can be removed by filtering; As a useful signal carrying disturbance information, the phase demodulation algorithm can accurately measure the location and intensity of disturbance events on the submarine cable, enabling real-time monitoring and early warning of offshore wind power submarine cables.

[0157] Meanwhile, to obtain phase information, demodulation module 29 can process the digital signal using IQ demodulation. Specifically, the detected intermediate frequency signal is mixed with locally preset reference orthogonal signals (cosine and sine), and high-frequency terms are eliminated through low-pass filtering. Finally, the distributed phase information in the transmission optical fiber is obtained by calculating the orthogonal components, thereby enabling real-time and accurate monitoring and location of disturbance events on the wind power submarine cable. The specific steps are as follows:

[0158] (1) The detected intermediate frequency signal is mixed with the locally preset reference quadrature signals (cosine and sine) respectively, wherein:

[0159] The mixing signal for the in-phase branch (I-path) is:

[0160]

[0161] The mixing signal for the quadrature branch (Q-path) is:

[0162]

[0163] (2) After low-pass filtering to remove high-frequency terms, the I / O channels are retained respectively, of which:

[0164] After low-pass filtering, the output of the in-phase branch (I-path) is:

[0165]

[0166] After low-pass filtering, the output of the quadrature branch (Q-path) is:

[0167]

[0168] (3) The phase information finally obtained through the I / Q outputs is:

[0169]

[0170] in:

[0171] For optical phase information;

[0172] The in-phase component after passing through the low-pass filter (LPF) reflects the correlation between the signal and the local carrier cosine component, and is the extraction of the real part of the signal in demodulation.

[0173] The quadrature component, after passing through the low-pass filter, reflects the correlation between the signal and the local carrier sinusoidal component and is the extraction of the imaginary part of the signal.

[0174] As can be seen from the above, the fiber optic demodulation device 2 in this invention adopts a heterodyne detection structure, which has significant advantages in sensitivity and noise immunity compared with traditional direct detection systems. Simultaneously, by combining the acousto-optic modulator 22 with the arbitrary waveform generator 28, this invention achieves precise modulation of the probe light, allowing minute phase perturbations in the signal to be frequency-shifted to the mid-frequency region, effectively suppressing the influence of intensity noise and improving the detection capability for low-amplitude events. Furthermore, this invention enhances the signal-to-noise ratio of the interference signal through the balanced detector 26, providing strong support for subsequent high-precision phase demodulation.

[0175] Furthermore, this invention incorporates a high-speed data acquisition module 30 and a demodulation module 29, enabling real-time acquisition and digital processing of electrical signals. Compared to traditional analog circuits, this design not only improves the system's response speed and adjustability but also facilitates the introduction of advanced digital signal processing methods (such as IQ demodulation, time-frequency conversion, or deep learning recognition). Simultaneously, the compact optical path structure utilizes two couplers to rationally allocate the reference and probe beams, improving system stability and possessing excellent integration potential, making it suitable for distributed fiber optic vibration monitoring tasks in various complex environments.

[0176] Furthermore, this invention can also calculate light intensity information based on backscattered light signals. Specifically, the backscattered light signal can be interfered with a reference light to generate a photocurrent signal, which is then converted into an electrical signal. This electrical signal is then amplified and filtered, and finally, the amplified and filtered electrical signal is used as the light intensity information. Through I / Q dual-channel output, the light intensity information of the signal under test is ultimately obtained. for:

[0177]

[0178] in, The in-phase component after passing through a low-pass filter These are the quadrature components after passing through the low-pass filter.

[0179] Furthermore, the phase information processed by the demodulation module 29 is monitored by the host computer, and the strain value is directly calculated from the optical phase using a standard linear method:

[0180] Specifically, the strain information of the submarine cable can be calculated using the following formula:

[0181]

[0182] in:

[0183] This is strain information, in m / m;

[0184] The wavelength of light is typically taken as 1550.12e-9m;

[0185] This represents the difference in phase information, expressed in rad.

[0186] The refractive index of the fiber is typically taken as 1.46.

[0187] is the Pockel coefficient of single-mode fiber glass, typically taken as 0.79;

[0188] This is the gauge length, typically taken as 4.8m.

[0189] Meanwhile, the monitoring host computer 3 also utilizes the principle of optical time domain reflectance (OTDR) to determine the spatial location of the event. Specifically, by emitting an optical pulse into the transmission fiber and measuring the return time of the backscattered light signal; since the propagation speed of the optical pulse in the transmission fiber is known, the location of the scattering event can be calculated according to the following formula. (i.e., spatial location information):

[0190]

[0191] in, At the speed of light, The time difference between the emission and return of the light pulse. is the fiber refractive index.

[0192] In addition, the monitoring host computer 3 can also extract the vibration information of the submarine cable based on the light intensity information and phase information.

[0193] It should be noted that the magnitude of the vibration information (i.e., vibration amplitude) comes from the amplitude response envelope of the light intensity information, that is, the mode length after the amplitude of the I and Q baseband signals is synthesized.

[0194] because:

[0195]

[0196]

[0197]

[0198] available:

[0199]

[0200] For the beat frequency intensity (interference term after removing the DC term), i.e., the vibration amplitude, the envelope is:

[0201]

[0202] in, For vibration information, To detect the amplitude of light, The reference light amplitude.

[0203] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0204] (1) Utilize the existing redundant optical fibers in the submarine cable as the sensing medium to make full use of existing resources, save costs and not affect the original business of the submarine cable.

[0205] (2) Real-time monitoring of submarine cables with long distance and high spatial resolution can be achieved through fiber optic sensing technology, which can accurately sense various deformations such as vibration, strain, and bending.

[0206] (3) By monitoring the host computer to display and warn of abnormal events in submarine cable operation in real time, the proactive maintenance capability for safe operation of submarine cable is improved, and the failure rate and maintenance cost are effectively reduced;

[0207] (4) This invention has the advantages of strong anti-electromagnetic interference capability, high real-time performance, high precision, strong stability and adaptability to complex marine environments. It can be widely used in the real-time safety monitoring of submarine cables in offshore wind power and other marine engineering fields.

[0208] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for offshore wind farm sea cable monitoring based on distributed optical sensing, characterized in that, include: A narrowband light source is emitted into the transmission optical fiber, and the narrowband light source performs Rayleigh scattering in the transmission optical fiber to form a backscattered light signal. The transmission optical fiber is laid axially along the submarine cable and is tightly fixed to the submarine cable so that the transmission optical fiber vibrates and deforms synchronously with the submarine cable. Receive the backscattered light signal and calculate the light intensity information and phase information based on the backscattered light signal; The system receives the light intensity information and phase information, and extracts the vibration information, strain information and spatial position information of the submarine cable based on the light intensity information and phase information. The step of transmitting a narrowband light source into the transmission optical fiber includes: outputting a narrowband light source; performing beam splitting on the narrowband light source to generate a probe light and a reference light; modulating the probe light according to a modulation command to generate a probe pulse; amplifying the probe pulse; and injecting the amplified probe pulse into the transmission optical fiber so that the probe pulse undergoes Rayleigh scattering within the transmission optical fiber to form a backscattered light signal. The steps for calculating phase information based on the backscattered light signal include: interfering the backscattered light signal with a reference light to generate a photocurrent signal; converting the photocurrent signal into an electrical signal; converting the electrical signal into a digital signal; and demodulating the digital signal to generate phase information. The photocurrent signal is: wherein is the photocurrent signal, is the probe light field, is the reference light field, is the probe light amplitude, is the probe light frequency, is the phase change induced by the perturbation, is the reference light amplitude, is the reference light frequency, is the frequency difference between the reference light and the probe light; The steps for extracting the strain information of the submarine cable include: according to the formula Calculate the strain information of the submarine cable; among which, For strain information, The wavelength of light The difference in phase information. For the fiber refractive index, The Pockels coefficient is the value of the single-mode fiber glass. This is the gauge length; The steps for extracting the vibration information of the submarine cable include: according to the formula To calculate the vibration information of submarine cables; among which, For vibration information, To detect the amplitude of light, The reference light amplitude.

2. The method for monitoring offshore wind power submarine cables based on distributed optical sensing as described in claim 1, characterized in that, The step of demodulating the digital signal to generate phase information includes: The digital signal is mixed with a preset reference quadrature signal respectively; The digital signal after mixing is subjected to low-pass filtering. Quadrature components are calculated based on the low-pass filtered digital signal to generate phase information.

3. A distributed optical sensing-based offshore wind power cable monitoring system, applied to the distributed optical sensing-based offshore wind power cable monitoring method described in claim 1 or 2, characterized in that, Includes transmission optical fiber, optical fiber demodulation device and monitoring host computer; The transmission optical fiber is laid axially along the seabed cable and vibrates and deforms synchronously with the seabed cable. The fiber demodulation device is connected to the transmission fiber and is used to emit a narrowband light source into the transmission fiber. The narrowband light source performs Rayleigh scattering in the transmission fiber to form a backscattered light signal. The fiber optic demodulation device is also used to receive the backscattered light signal and calculate the light intensity information and phase information based on the backscattered light signal; The monitoring host computer is connected to the fiber optic demodulation device to receive the light intensity information and phase information, and to extract the vibration information, strain information and spatial position information of the submarine cable based on the light intensity information and phase information. The fiber optic demodulation device includes a narrowband laser, an acousto-optic modulator, an erbium-doped amplifier, a circulator, a first optical coupler, a balanced detector, a second optical coupler, an arbitrary waveform generator, a demodulation module, and a high-speed data acquisition module. The narrowband laser is used to output a narrowband light source to the first optical coupler. The first optical coupler is used to split the narrowband light source to generate a probe light and a reference light, and outputs the probe light to the acousto-optic modulator and the reference light to the second optical coupler. The acousto-optic modulator is used to modulate the probe light according to the modulation command of the arbitrary waveform generator to generate a probe pulse, and output the probe pulse to the erbium-doped amplifier. The erbium-doped amplifier is used to amplify the detection pulse and output the amplified detection pulse to the circulator; The circulator is used to inject the amplified probe pulse into the transmission optical fiber, so that the probe pulse undergoes Rayleigh scattering in the transmission optical fiber to form a backscattered light signal. It is also used to receive the backscattered light signal and output the backscattered light signal to the second optical coupler. The second optical coupler is used to interfere the backscattered light signal with the reference light to generate a photocurrent signal and output the photocurrent signal to the balanced detector. The balanced detector is used to convert the photocurrent signal into an electrical signal and output the electrical signal to the high-speed data acquisition module; The high-speed data acquisition module is used to convert the electrical signal into a digital signal and output the digital signal to the demodulation module; the demodulation module is used to demodulate the digital signal to generate phase information.

4. The offshore wind power submarine cable monitoring system based on distributed optical sensing as described in claim 3, characterized in that, It also includes a flexible carrier, in which the transmission optical fiber is embedded and laid together with the functional optical fiber in the submarine cable.

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