Underwater structure crack in-situ monitoring system based on distributed alternating current electric field

Abstract

The present application belongs to the field of nondestructive testing of underwater structure, and particularly relates to an underwater structure crack in-situ monitoring system based on distributed alternating current field. The monitoring system realizes high-sensitivity monitoring of underwater structure cracks, and realizes full-coverage monitoring of multiple scattered cracks of underwater structure pipe nodes, thereby providing technical support for safe service of underwater structure. The monitoring system comprises a detection probe, an underwater signal cabin and a land integrated machine. The detection probe further comprises a probe main body, a front-end signal processing circuit and a front-end signal processing circuit shell; the underwater signal cabin further comprises an excitation signal generation module, a signal processing module and a signal acquisition module; and the land integrated machine further comprises an operation display module, a Wi-Fi module, a lithium battery and a power conversion module.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing of underwater structures, and particularly relates to an in-situ monitoring system for underwater structural cracks based on a distributed alternating electric field. Background Technology

[0002] As a fundamental connecting component in offshore drilling platforms, underwater (pipe joint) structures are exposed to the complex marine environment for extended periods during service, continuously subjected to the loads of wind, waves, and ocean currents. Combined with the alternating stress generated by the immense weight of the underwater structure itself, this makes it highly susceptible to the initiation of multiple dispersed fatigue cracks in high-stress areas such as welds and heat-affected zones. These cracks, under the combined effects of seawater corrosion and stress concentration, continue to propagate, severely impacting the overall load-bearing capacity of the offshore drilling platform. Sudden fractures could not only cause significant economic losses but also lead to severe marine environmental pollution and even endanger the lives of personnel.

[0003] Alternating Current Field In-situ Monitoring (ACIM) is a novel non-destructive testing technique for real-time dynamic monitoring of various physical quantities (such as electric fields, temperature fields, stress fields, and flow fields). Specifically, it utilizes a flat-panel design for the excitation module of the detection probe to generate a uniformly distributed alternating current field on the surface of a conductive material. When the measured area is defect-free, this alternating current field exhibits a regular distribution; however, when discontinuous defects such as cracks are present, the current is forced to bypass the crack tip and bottom, causing local current path distortion and thus generating corresponding magnetic field disturbances in space. By acquiring the corresponding electromagnetic field distortion signals, key information such as the location, orientation, and size of the crack can be deduced.

[0004] However, further research revealed that the underwater structure operates in a complex environment, facing a series of challenges such as strong electromagnetic interference, high dielectric conductivity, and severe signal attenuation. This results in extremely weak characteristic signals generated by cracks. Existing in-situ AC electric field monitoring equipment is limited by its insufficient sensitivity and anti-interference capabilities, making it difficult to effectively extract such weak signals. Furthermore, the complex geometry of underwater structures means that cracks often exhibit multi-point, dispersed, and non-directional distribution characteristics. Existing in-situ AC electric field monitoring equipment can only cover a single monitoring point, limiting the monitoring coverage and creating blind spots, thus failing to meet the need for comprehensive and continuous monitoring of the underwater structural areas of offshore drilling platforms.

[0005] Therefore, it is urgent for those skilled in the art to develop a distributed AC electric field underwater structural crack in-situ monitoring system with high sensitivity, strong anti-interference capability and wide coverage capability, so as to realize real-time and accurate perception and early warning of multiple and dispersed cracks in underwater pipe node structures, and provide reliable technical support for the safe operation and maintenance and life assessment of marine drilling and production platforms. Summary of the Invention

[0006] This invention provides an in-situ monitoring system for underwater structural cracks based on a distributed AC electric field. This system combines energy coupling principles, resonant circuits, and AC electromagnetic field detection principles to achieve highly sensitive monitoring of underwater structural cracks. Furthermore, by using multiplexed control of multiple monitoring probes, it achieves full-coverage monitoring of scattered cracks at multiple locations in underwater structural pipe nodes, providing technical support for the safe operation of underwater structures.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The underwater structural crack in-situ monitoring system based on distributed AC electric field includes the following structure: detection probe, underwater signal cabin and land-based integrated unit; The detection probe includes a probe body, a front-end signal processing circuit, and a housing for the front-end signal processing circuit. The probe body is composed of a flexible coil unit and a resonant capacitor bank. The flexible coil unit consists of an excitation coil, a coupling coil, and an array detection coil. The excitation coil comprises two semi-circular excitation coil units, through which sinusoidal alternating currents in opposite directions are passed to generate a uniform induced current field on the surface of the underwater structure to be monitored. The array detection coil is positioned below the excitation coil and is used to collect induced magnetic field signals perpendicular to the surface of the underwater structure to be monitored. The coupling coil is positioned between the excitation coil and the array detection coil and is composed of multiple layers of series-connected absolute coils. Adjacent layers of absolute coils are connected in series through through-holes in an insulating substrate to couple and enhance the transmitted signals between the excitation coil and the array detection coil. The resonant capacitor group consists of three parts: the excitation coil resonant capacitor, the coupling coil resonant capacitor, and the array detection coil resonant capacitor; wherein, the excitation coil resonant capacitor and the excitation coil, the coupling coil resonant capacitor and the coupling coil, and the array detection coil resonant capacitor and the array detection coil respectively cooperate to form an LC resonant circuit. The front-end signal processing circuit consists of a multiplexing circuit and an amplification and filtering circuit. The multiplexing circuit is connected to the flexible coil unit via pin headers and sockets to convert multiple detection signals into differential signals. The amplification and filtering circuit is used to filter low-frequency noise in the differential signal and then amplify the filtered differential signal. The underwater signal cabin includes an excitation signal generation module, a signal processing module, and a signal acquisition module; wherein, the excitation signal generation module includes a signal generator and a power amplifier; the signal generator is used to output two sinusoidal AC signals with the same amplitude, which are amplified by the power amplifier, one of which is used as the excitation signal and the other as the reference signal; The signal processing module consists of a distributed probe control circuit, a bandpass filter circuit, and a lock-in amplifier circuit. The distributed probe control circuit receives control signals and selects one of the multiple detection signals for acquisition. The bandpass filter circuit filters out high-frequency noise and coupling interference signals from the signals acquired by the distributed probe control circuit. The lock-in amplifier circuit amplifies the bandpass-filtered AC signal into a DC signal. The signal acquisition module aggregates and processes the DC signal processed by the signal processing module with the induced magnetic field signal acquired by the array detection coil.

[0008] Preferably, the land-based integrated unit includes a computing and display module, a Wi-Fi module, a lithium battery, and a power conversion module; wherein, the computing and display module is used to display, process, and store the monitoring signals of the underwater structure to be monitored.

[0009] Preferably, the housing of the front-end signal processing circuit is provided with a cable hole for connecting a multi-core Remo cable for transmitting signals; The front-end signal processing circuit housing also has screw mounting holes for fixing.

[0010] Preferably, the underwater signal cabin and the land-based integrated unit communicate with each other via a power line carrier module and a twisted-pair power line.

[0011] This invention provides an in-situ monitoring system for underwater structural cracks based on a distributed alternating current electric field. The monitoring system includes a detection probe, an underwater signal housing, and a land-based integrated unit. The detection probe further includes a probe body, a front-end signal processing circuit, and a housing for the front-end signal processing circuit. The underwater signal housing further includes an excitation signal generation module, a signal processing module, and a signal acquisition module. The land-based integrated unit further includes a computing and display module, a Wi-Fi module, a lithium battery, and a power conversion module.

[0012] The underwater structural crack in-situ monitoring system based on a distributed AC electric field, possessing the aforementioned structural features, has at least the following technical advantages compared to existing technologies: (1) The underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention adopts a "relay focusing" design for its coupling coil, which is nested between the excitation coil and the array detection coil. Compared with the existing design without coupling structure, it can effectively constrain the diffusion path of the magnetic field, so that the magnetic field energy is concentrated on the detection area of ​​the underwater structure to be monitored, significantly improving the eddy current density of the specimen and the signal-to-noise ratio of the detection signal. In addition, the excitation coil, coupling coil and array detection coil are all matched with external resonant capacitors. By adjusting the resonant capacitor group, the resonant frequency of each coil of the excitation coil, coupling coil and array detection coil is kept consistent with the excitation frequency.

[0013] (2) The underwater structure crack in-situ monitoring system based on distributed AC electric field provided by the present invention sets up a distributed probe control circuit, a bandpass filter circuit, and a phase-locked amplifier circuit in the signal processing module, and uses time-division multiplexing technology to construct a selection mechanism for multi-channel detection signals. Combined with the distributed deployment of detection probes, a working mode of "multi-probe coverage + time-sequence acquisition" is formed, which realizes full-area blind-zone monitoring of distributed cracks on the surface of the underwater structure to be monitored, and avoids the risk of missed detection and crosstalk.

[0014] (3) The underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention realizes the communication connection between the underwater signal cabin and the land-based integrated machine through the power line carrier module and twisted-pair power line, supports reverse transmission, and ensures long-distance anti-interference communication. In addition, the underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention constructs a remote data transmission link for detection signals through bidirectional interaction between the local and cloud, and forms a working mode of "data cloud storage + remote access" in combination with multi-terminal scenarios. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the following drawings: Figure 1 A schematic diagram of the underwater structural crack in-situ monitoring system based on a distributed AC electric field provided by the present invention; Figure 2a This is a schematic diagram of the probe body. Figure 2b for Figure 2a A schematic diagram of the actual structure of the probe body shown; Figure 3 This is a schematic diagram of the structure of the excitation coil, coupling coil, and array detection coil in a flexible coil unit; Figure 4This is a schematic diagram of the structure of the resonant capacitors of the excitation coil, the coupling coil, and the array detection coil in the resonant capacitor group. Figure 5a A schematic diagram of the reference circuit structure for the resonant circuit of the excitation coil; Figure 5b This is a schematic diagram of the reference circuit structure for the resonant circuit of the coupled coil; Figure 5c This is a schematic diagram of the reference circuit structure for the resonant circuit of the array detection coil; Figure 6a A schematic diagram of the crack magnetic field image of a detection probe with coupled resonance; Figure 6b A schematic diagram of the crack magnetic field image of a detection probe without coupling resonance; Figure 7 A comparison chart of the detection signal sensitivity with and without coupled resonance; Figure 8 This is a comparison chart of the detection signal sensitivity with coupled resonance and the signal-to-noise ratio of the monitoring signal without coupled resonance. Figure 9a This is a schematic diagram of the magnetic field image obtained by detecting the signal when there is coupled resonance. Figure 9b This is a schematic diagram of the magnetic field image obtained by detecting the signal under uncoupled resonance. Figure 10a This is a schematic diagram of the lower housing structure of the signal processing circuit board; Figure 10b This is a schematic diagram of the outer casing structure on the signal processing circuit board; Figure 11 This is a schematic diagram of the structure of a distributed probe control circuit; Figure 12 To utilize Figure 11 The diagram shows multiple crack signals of different lengths monitored by the distributed probe control circuit. Figure 13 This is a schematic diagram illustrating the data transmission process of a power line carrier module. Figure 14 This is a schematic diagram of the encapsulated probe body. Figure 15 This is a schematic diagram of a bandpass filter circuit. Figure 16 This is a schematic diagram of a bandpass filter circuit. Figure 17 This is a physical schematic diagram of the PCB board for the distributed probe control circuit.

[0016] Figure label: 1. Probe body; 1.1 Excitation coil; 1.2 Coupler coil; 1.3 Array detection coil; 1.2.1 Excitation coil resonant capacitor; 1.2.2 Coupler coil resonant capacitor; 1.2.3 Array detection coil resonant capacitor; 2. Front-end signal processing circuit; 3. Front-end signal processing circuit housing; 3.1 Upper housing of signal processing circuit board; 3.1.1 Screw mounting holes; 3.1.2 Screw connection part; 3.2 Lower housing of signal processing circuit board; 3.2.1 Cable hole; 3.2.2 Outer edge of lower housing of signal processing circuit board. Detailed Implementation

[0017] This invention provides an in-situ monitoring system for underwater structural cracks based on a distributed AC electric field. This system combines energy coupling principles, resonant circuits, and AC electromagnetic field detection principles to achieve highly sensitive monitoring of underwater structural cracks. Furthermore, by using multiplexed control of multiple monitoring probes, it achieves full-coverage monitoring of scattered cracks at multiple locations in underwater structural pipe nodes, providing technical support for the safe operation of underwater structures.

[0018] like Figure 1 As shown, the underwater structural crack in-situ monitoring system based on a distributed AC electric field provided by the present invention includes the following structure: a detection probe, an underwater signal cabin, and a land-based integrated unit.

[0019] The detection probe further includes a probe body 1, a front-end signal processing circuit 2, and a front-end signal processing circuit housing 3. Specifically, as shown... Figure 2a , Figure 2b As shown, the probe body 1 is composed of a flexible coil unit and a resonant capacitor group. The flexible coil unit consists of three parts: an excitation coil 1.1, a coupling coil 1.2, and an array detection coil 1.3. In a preferred embodiment, the excitation coil 1.1, coupling coil 1.2, and array detection coil 1.3 are bonded together via positioning lines on a flexible circuit board silkscreen layer. The fabricated detection probe is then subjected to a vulcanization treatment to make it water-resistant and corrosion-resistant, ultimately forming the probe body structure.

[0020] For reference Figure 3As shown, the excitation coil 1.1 consists of two semi-circular excitation coil units. Sinusoidal alternating currents with opposite directions are passed through these two units to generate a uniform induced current field on the surface of the underwater structure to be monitored. The array detection coil 1.3 is positioned below the excitation coil 1.1 and is used to acquire the induced magnetic field signal perpendicular to the surface of the underwater structure. The coupling coil 1.2 is positioned between the excitation coil 1.1 and the array detection coil 1.3. It consists of multiple layers of absolute coils connected in series. Adjacent layers of absolute coils are connected in series through through-holes in the insulating substrate to couple and enhance the transmitted signal between the excitation coil 1.1 and the array detection coil 1.3.

[0021] It is worth noting that the reason for placing the coupling coil 1.2 between the excitation coil 1.1 and the array detection coil 1.3 is that this "relay coupling" mechanism can optimize the magnetic field energy transfer path. By "focusing" the originally easily divergent magnetic field on the detection area, the leakage magnetic loss to the surrounding environment is greatly reduced, the induced current is concentrated at the crack tip, and the initial leakage magnetic signal response through the crack is stronger, thereby enhancing the monitoring sensitivity of the AC electromagnetic field and leakage magnetic response signal during the crack propagation process.

[0022] In addition, such as Figure 4 As shown, the resonant capacitor bank consists of three parts: the excitation coil resonant capacitor 1.2.1, the coupling coil resonant capacitor 1.2.2, and the array detection coil resonant capacitor 1.2.3. Specifically, the excitation coil resonant capacitor 1.2.1, the coupling coil resonant capacitor 1.2.2, and the array detection coil resonant capacitor 1.2.3, in conjunction with the array detection coil 1.3, form LC resonant circuits.

[0023] As a preferred embodiment of the present invention, the resonant capacitances of the excitation coil 1.1, coupling coil 1.2, array detection coil 1.3 and their matching are further calculated (the purpose is to enable each coil of the excitation coil 1.1, coupling coil 1.2, and array detection coil 1.3 to generate a resonant circuit at an excitation frequency of 40kHz, see reference...). Figure 5a , Figure 5b , Figure 5c (As shown). The inductance values ​​of the excitation coil 1.1, coupling coil 1.2, and array detection coil 1.3 are referenced to be 170.9 μH, 63.2 μH, and 27.7 μH, respectively. The resonant frequency is calculated using the formula: The capacitance values ​​corresponding to the resonance of each coil at the excitation frequency of 40kHz were found to be 93nF, 250nF, and 571nF, respectively.

[0024] It should be added that the array detection coil resonant capacitor 1.2.3 can be directly soldered to the pin header of the front-end signal processing circuit, while the excitation coil resonant capacitor 1.2.1 and the coupling coil resonant capacitor 1.2.2 can be soldered to the corresponding capacitor pads of the coils. Figure 14 As shown, Figure 14 A schematic diagram of the encapsulated probe body is provided. The fixed probe body undergoes vulcanization treatment using Hasuncast 713 flexible polyurethane adhesive. This adhesive not only has strong flame retardancy and good insulation properties, but also achieves IP68 waterproof protection. Furthermore, when the material ratio is 1:8, the cured hardness is 40A, exhibiting good flexibility, making it ideal for protecting underwater flexible monitoring probes.

[0025] Furthermore, when the excitation coil 1.1 resonates in series, the current driven by the voltage source is at its maximum, which significantly enhances the alternating magnetic field and thus increases the eddy current density of the underwater structure being monitored. When the coupling coil 1.2 resonates in parallel, the maximum impedance maximizes the voltage across the coupling coil, thereby improving the efficiency of magnetic field energy transfer to the detection coil and increasing the induced current intensity. Additionally, when the array detection coil 1.3 resonates in parallel, the impedance of the detection coil is at its maximum, and its induced voltage amplitude is at its highest. Minor eddy current disturbances caused by defects in the underwater structure significantly alter the voltage signal of the detection coil. At this point, using a detection probe with coupled resonance and a conventional detection probe without coupled resonance to measure the same carbon steel surface crack (10mm long, 0.5mm wide, 4mm deep), the crack magnetic field images are as follows: Figure 6a , Figure 6b As shown.

[0026] Furthermore, the relative change between the defect-free region and the defective region is used as the sensitivity S at the crack. The sensitivity S satisfies: . The response voltage when there is a defect. The response voltage when there are no defects is referenced as follows: Figure 7 As shown, the coupled resonance detection probe provided by this invention has approximately 30% higher monitoring sensitivity compared to existing non-coupled resonance detection probes. The signal-to-noise ratio (SNR) is used as the ratio between signal strength and noise intensity when evaluating the system's ability to monitor defects (where a high SNR means the system can more accurately distinguish between signal and noise). .in, The voltage difference between the maximum and minimum values. To calculate the average voltage after removing the absolute values ​​of the maximum and minimum values, refer to the following: Figure 8As shown, the coupled resonant detection probe provided by this invention has a signal-to-noise ratio approximately 1.5 times higher than that of existing probes without resonance. Using the same probe to monitor a surface crack in carbon steel (5mm long, 0.5mm wide, 2mm deep), the existing probe without resonance, limited by its lower signal-to-noise ratio and sensitivity, struggles to effectively capture the magnetic field signal corresponding to the crack and cannot generate a clear crack magnetic field image. In contrast, the coupled resonant detection probe provided by this invention, with its superior signal-to-noise ratio and sensitivity, can accurately capture the crack-related magnetic field characteristics and successfully output a clearly identifiable crack magnetic field image. This provides reliable data support for the accurate location and assessment of cracks of this size in underwater structures. (See reference...) Figure 9a , Figure 9b As shown. At this point, the magnetic field image is input into the previously trained quantization regression network, and the average quantization error is further reduced to 0.3 mm, which can achieve high-precision quantization of crack propagation.

[0027] The front-end signal processing circuit consists of a multiplexing circuit and an amplification and filtering circuit. The multiplexing circuit, connected to the flexible coil unit via pin headers and sockets, converts multiple detection signals into differential signals (preferably converting 64 detection signals into 4 differential signals). The amplification and filtering circuit filters low-frequency noise from the differential signals and then amplifies the filtered differential signals (e.g., by a factor of 500). This "multiplexing and reduction, then integration" design logic aims to reduce the original 64 parallel transmission paths to 4, significantly reducing noise coupling opportunities. Furthermore, this integrated design simplifies the hardware structure, adapts to the limited installation space of the detection probes, and allows for the convergence of multi-area monitoring signals from underwater structures within the same monitoring system through a distributed centralized management architecture. This ensures high-quality transmission and processing of weak signals while reducing deployment costs and maintenance complexity.

[0028] As a preferred embodiment of the present invention, refer to, Figure 10a and Figure 10bAs shown, the front-end signal processing circuit housing 3 preferably consists of two parts: an upper housing 3.1 and a lower housing 3.2 of the signal processing circuit board. The front-end signal processing circuit housing 3 has screw mounting holes 3.1.1 and screw connecting parts 3.1.2. These screw mounting holes 3.1.1 and screw connecting parts 3.1.2 connect the upper housing 3.1 and the lower housing 3.2 of the signal processing circuit board into a single structure, simultaneously sealing the front-end signal processing circuit within the housing (i.e., within the space between the outer edge 3.2.2 of the lower housing of the signal processing circuit board and the upper housing 3.1). Furthermore, the front-end signal processing circuit housing also has a cable hole 3.2.1 for connecting a multi-core Remo cable for signal transmission. Here, a 16-core Remo cable with a length of 50 meters is selected. The detection probe is connected to the computing and display module of the land-based integrated machine via a Remo connector. After the front-end signal processing circuit housing and signal processing circuit board are assembled and wired, sealant is poured into the underwater signal chamber to achieve a waterproof effect.

[0029] In addition, such as Figure 1 As shown, the underwater signal chamber includes an excitation signal generation module, a signal processing module, and a signal acquisition module. The excitation signal generation module comprises a signal generator and a power amplifier. The signal generator outputs two sinusoidal AC signals of the same amplitude (e.g., a 2V, 40kHz sinusoidal AC signal). After amplification by the power amplifier, one signal is used as the excitation signal (amplified approximately 10 times), and the other as the reference signal (amplified approximately 2 times), while avoiding circuit interference caused by an excessively strong reference signal.

[0030] The signal processing module consists of a distributed probe control circuit, a bandpass filter circuit, and a lock-in amplifier circuit. The distributed probe control circuit receives control signals and selects one of the multiple detection signals for acquisition. (See reference...) Figure 11 As shown, the distributed probe control circuit is constructed using four ADG1608 chips. When the control digital signal is 000, the probe signal at the first crack monitoring point on the underwater structure is output; when the control digital signal is 001, the probe signal at the second crack monitoring point on the underwater structure is output, and so on. Up to eight distributed detection probes can be connected simultaneously, enabling accurate monitoring of up to eight cracks at different locations on the same underwater structure. A schematic diagram of the distributed probe control circuit PCB board can be found in [reference needed]. Figure 17 As shown. Further as... Figure 12As shown, assuming there are three cracks in the heat-affected zone of a weld on the same underwater structure, each 0.5mm wide and 3mm deep, differing only in length, three detection probes are attached to the surface of each crack. Using the digital signal output function of this distributed probe control circuit, the three induced magnetic field signals can be selected and switched in a time-division manner. The selected target signals are then acquired and saved, ultimately resulting in a clear magnetic field image of each crack characteristic displayed remotely on a land-based integrated device. This approach achieves efficient utilization of hardware resources through time-division multiplexing, reducing signal crosstalk caused by multiple probes operating simultaneously and significantly improving the data accuracy of underwater structure crack monitoring. It also offers advantages such as flexible control, convenient expansion, and integrated intelligence, allowing the number of probes to be increased or decreased according to the crack distribution characteristics of the underwater structure, perfectly adapting to the efficient, accurate, and scalable requirements of distributed monitoring of multiple cracks in underwater structures on a single platform.

[0031] like Figure 15 As shown, Figure 15 A schematic diagram of a bandpass filter circuit is provided. This bandpass filter circuit is used to filter out high-frequency noise and coupling interference signals in the signals acquired by the distributed probe control circuit. A second-order active bandpass filter is designed using an NE5532 operational amplifier. The schematic diagram of the bandpass filter circuit is shown below. Figure 16 As shown. C5 and C6 are decoupling capacitors at the power input. In the schematic diagram of the bandpass filter circuit, capacitors C1 and C2 in the first half, together with resistors R1 and R2, form a second-order active low-pass filter. Its cutoff frequency can be calculated as follows. In the schematic diagram of the bandpass filter circuit, capacitors C3 and C4, along with resistors R3 and R4, form a second-order active high-pass filter. Its cutoff frequency can be calculated as follows: Through the cascading of high-pass and low-pass filtering stages, the circuit ultimately achieves a passband width of approximately 10kHz. The lock-in amplifier circuit is used to amplify the bandpass-filtered AC signal into a DC signal (with an amplification factor of at least 2x).

[0032] The signal acquisition module is used to aggregate and process the DC signal processed by the signal processing module and the induced magnetic field signal acquired by the array detection coil. (See reference...) Figure 13 As shown, the signal acquisition module collects and summarizes up to eight channels of signals output by the lock-in amplifier circuit and uploads them to the location of the land-based integrated machine. At the same time, it can transmit the control signals output by the land-based integrated machine to the location of the distributed probe control circuit or the location of the array detection coil, so as to realize the use and control of the multiplexing circuit in the front-end signal processing circuit.

[0033] In a preferred embodiment of the present invention, the underwater signal cabin and the land-based integrated unit are connected for communication via a power line carrier module and a twisted-pair power line, as shown in the reference... Figure 13As shown, the underwater power line carrier module converts Ethernet signals into power line carrier signals and transmits them to the water surface via twisted-pair power lines; then, the power line carrier module on the water surface converts them back into Ethernet signals and transmits them to the land-based integrated unit. The power line carrier signals can be transmitted using high-frequency signals, enabling not only long-distance signal transmission but also strong anti-interference capabilities.

[0034] Furthermore, in a preferred embodiment of the present invention, the land-based integrated unit includes a computing and display module, a Wi-Fi module, a lithium battery, and a power conversion module. The computing and display module is used to display, process, and store monitoring signals from the underwater structure being monitored. The Wi-Fi module transmits the raw and processed signals from the computing and display module to a cloud server. This breaks the local limitations of data storage and processing, enabling centralized management and sharing of large-scale data with the help of cloud resources, facilitating simultaneous data acquisition and collaborative analysis across multiple terminals. It also supports remote processing, allowing personnel to perform in-depth data analysis via the cloud without needing to be physically present at the monitoring site. The power conversion module converts the 24V output of the lithium battery or charger, ultimately powering each module.

[0035] This invention provides an in-situ monitoring system for underwater structural cracks based on a distributed alternating current electric field. The monitoring system includes a detection probe, an underwater signal housing, and a land-based integrated unit. The detection probe further includes a probe body, a front-end signal processing circuit, and a housing for the front-end signal processing circuit. The underwater signal housing further includes an excitation signal generation module, a signal processing module, and a signal acquisition module. The land-based integrated unit further includes a computing and display module, a Wi-Fi module, a lithium battery, and a power conversion module.

[0036] The underwater structural crack in-situ monitoring system based on a distributed AC electric field, possessing the aforementioned structural features, has at least the following technical advantages compared to existing technologies: (1) The underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention adopts a "relay focusing" design for its coupling coil, which is nested between the excitation coil and the array detection coil. Compared with the existing design without coupling structure, it can effectively constrain the diffusion path of the magnetic field, so that the magnetic field energy is concentrated on the detection area of ​​the underwater structure to be monitored, significantly improving the eddy current density of the specimen and the signal-to-noise ratio of the detection signal. In addition, the excitation coil, coupling coil and array detection coil are all matched with external resonant capacitors. By adjusting the resonant capacitor group, the resonant frequency of each coil of the excitation coil, coupling coil and array detection coil is kept consistent with the excitation frequency.

[0037] (2) The underwater structure crack in-situ monitoring system based on distributed AC electric field provided by the present invention sets up a distributed probe control circuit, a bandpass filter circuit, and a phase-locked amplifier circuit in the signal processing module, and uses time-division multiplexing technology to construct a selection mechanism for multi-channel detection signals. Combined with the distributed deployment of detection probes, a working mode of "multi-probe coverage + time-sequence acquisition" is formed, which realizes full-area blind-zone monitoring of distributed cracks on the surface of the underwater structure to be monitored, and avoids the risk of missed detection and crosstalk.

[0038] (3) The underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention realizes the communication connection between the underwater signal cabin and the land-based integrated machine through the power line carrier module and twisted-pair power line, supports reverse transmission, and ensures long-distance anti-interference communication. In addition, the underwater structural crack in-situ monitoring system based on distributed AC electric field provided by this invention constructs a remote data transmission link for detection signals through bidirectional interaction between the local and cloud, and forms a working mode of "data cloud storage + remote access" in combination with multi-terminal scenarios.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An in-situ monitoring system for underwater structural cracks based on a distributed alternating current electric field, characterized in that, It includes the following structure: detection probe, underwater signal cabin and land-based integrated unit; The detection probe includes a probe body, a front-end signal processing circuit, and a housing for the front-end signal processing circuit. The probe body is composed of a flexible coil unit and a resonant capacitor bank. The flexible coil unit consists of an excitation coil, a coupling coil, and an array detection coil. The excitation coil comprises two semi-circular excitation coil units, through which sinusoidal alternating currents in opposite directions are passed to generate a uniform induced current field on the surface of the underwater structure to be monitored. The array detection coil is positioned below the excitation coil and is used to collect induced magnetic field signals perpendicular to the surface of the underwater structure to be monitored. The coupling coil is positioned between the excitation coil and the array detection coil and is composed of multiple layers of series-connected absolute coils. Adjacent layers of absolute coils are connected in series through through-holes in an insulating substrate to couple and enhance the transmitted signals between the excitation coil and the array detection coil. The resonant capacitor group consists of three parts: the excitation coil resonant capacitor, the coupling coil resonant capacitor, and the array detection coil resonant capacitor; wherein, the excitation coil resonant capacitor and the excitation coil, the coupling coil resonant capacitor and the coupling coil, and the array detection coil resonant capacitor and the array detection coil respectively cooperate to form an LC resonant circuit. The front-end signal processing circuit consists of a multiplexing circuit and an amplification and filtering circuit. The multiplexing circuit is connected to the flexible coil unit via pin headers and sockets to convert multiple detection signals into differential signals. The amplification and filtering circuit is used to filter low-frequency noise in the differential signal and then amplify the filtered differential signal. The underwater signal cabin includes an excitation signal generation module, a signal processing module, and a signal acquisition module; wherein, the excitation signal generation module includes a signal generator and a power amplifier; the signal generator is used to output two sinusoidal AC signals with the same amplitude, which are amplified by the power amplifier, one of which is used as the excitation signal and the other as the reference signal; The signal processing module consists of a distributed probe control circuit, a bandpass filter circuit, and a lock-in amplifier circuit. The distributed probe control circuit receives control signals and selects one of the multiple detection signals for acquisition. The bandpass filter circuit filters out high-frequency noise and coupling interference signals in the signals acquired by the distributed probe control circuit. The lock-in amplifier circuit amplifies the bandpass-filtered AC signal into a DC signal. The signal acquisition module is used to collect and process the DC signal processed by the signal processing module and the induced magnetic field signal acquired by the array detection coil.

2. The underwater structural crack in-situ monitoring system based on a distributed AC electric field according to claim 1, characterized in that, The land-based integrated unit includes a computing and display module, a Wi-Fi module, a lithium battery, and a power conversion module. The computing and display module is used to display, process, and store monitoring signals from the underwater structure being monitored.

3. The underwater structural crack in-situ monitoring system based on a distributed AC electric field according to claim 1, characterized in that, The front-end signal processing circuit housing is provided with a cable hole, which is used to connect a multi-core Remo cable for transmitting signals. The front-end signal processing circuit housing also has screw mounting holes for fixing.

4. The underwater structural crack in-situ monitoring system based on a distributed AC electric field according to claim 1, characterized in that, The underwater signal cabin and the land-based integrated unit communicate with each other via a power line carrier module and twisted-pair power lines.

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