A Method for Analyzing the Influencing Factors of Island-Induced Wake Electromagnetic Field

Abstract

This application relates to the field of marine geophysical exploration technology and provides a method for analyzing the influencing factors of island-induced wake induced electromagnetic fields. The method includes: setting up a three-dimensional island wake hydrodynamic model; constructing an index system of influencing factors for island-induced wake induced electromagnetic fields, including eddy current, ocean current velocity, and Coriolis force parameters; obtaining the mechanism by which eddy current, ocean current velocity, and Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating wake dynamics; identifying the main influencing factors; and determining the layout of monitoring points and the range of influence of island-induced wakes on the induced electromagnetic field in actual island-induced wake induced electromagnetic field monitoring based on the identified main influencing factors. This application clearly distinguishes the differentiated response mechanisms of induced electric and induced magnetic fields, providing a clear physical basis for the interpretation of marine electromagnetic signals and wake identification.

Description

Technical Field

[0001] This application relates to the field of marine geophysical exploration technology, specifically to a method for analyzing the influencing factors of island-induced wake electromagnetic fields. Background Technology

[0002] When island-induced wake fluids encounter obstacles such as islands during their movement, complex flow structures are formed on their leeward or downstream sides due to topographic obstruction and boundary layer friction. These structures manifest as vortex shedding, wave generation, and flow field disturbances. When ocean currents circumnavigate islands, the wake structure becomes even more complex due to the combined effects of Earth's rotation (Coriolis force), stratification, and bottom friction. When conductive seawater is in a geomagnetic environment and moves, it induces an electromagnetic field. In the interdisciplinary field of marine and earth sciences, the induced electromagnetic field of island wakes falls under the category of the interaction between the ocean and the Earth's magnetic field, representing a crucial dynamic process in the study of coupling between different spheres. Since Faraday proposed the hypothesis that seawater movement cutting through geomagnetic field lines can generate induced electromotive force, the research paradigm in this field has continuously evolved. With the improvement of computing power and the continuous advancement of numerical algorithms, wake electromagnetic field research is increasingly focusing on high-precision numerical simulation and multi-factor analysis.

[0003] The generation and evolution of the induced electromagnetic field in island-induced wakes are influenced by a synergistic effect of multiple factors, which can be categorized into four main types: First, topographic factors: the geometric dimensions of the island (length, width, height), coastline slope, and water depth distribution directly determine the blocking strength of ocean currents around the island and the morphology of flow field disturbances, thus affecting the shedding patterns of wake vortices and ultimately altering the excitation intensity and spatial distribution of the induced electromagnetic field, influencing the characteristics and identification difficulty of the electromagnetic signal in the wake region. Second, flow field dynamic factors: the velocity, direction, and incident angle of the background ocean current, as well as seawater stratification and turbulence intensity, regulate the evolution period, vortex intensity, and flow field shear force of the wake. The velocity of the flow field is the core driving force for the generation of the induced electromagnetic field. Changes in the number of electromagnetic disturbances directly lead to significant fluctuations in the amplitude of electromagnetic disturbances, thus affecting the accuracy of quantitative analysis of electromagnetic signals in the wake region. Thirdly, geographical environmental factors, such as the intensity, inclination, and direction of the background geomagnetic field, directly affect the efficiency of seawater movement in cutting magnetic field lines, determining the potential for induced electromotive force generation, which is a fundamental prerequisite for the excitation of induced electromagnetic fields. This also affects the difficulty of distinguishing wake region electromagnetic signals from background noise. Furthermore, latitude also affects the magnitude of the Coriolis force parameter, which is also an important factor in regulating wake morphology. Fourthly, seawater physical properties, such as the conductivity of seawater, affect its conductivity, thereby regulating the propagation efficiency and attenuation rate of electromagnetic energy, significantly impacting the capture and quantitative analysis of electromagnetic signals in the wake region.

[0004] The study and analysis of factors influencing the electromagnetic field induced by island-induced wakes is a gap in the research on the electromagnetic effects of topographically forced flow fields at small and medium scales. Wake vortices induced by topographic obstacles such as islands are a common dynamic event in areas with a high concentration of islands. From a theoretical perspective of electromagnetic induction, such flow field disturbances can induce magnetic field strengths at the sea surface in the nanotesla (nT) range. These magnetic field fluctuations not only introduce errors into the interpretation of marine magnetotelluric data but may also introduce noise interference in relevant frequency bands to various electromagnetic observations. Current mainstream marine electromagnetic models have significant limitations: model construction often focuses on the electromagnetic induction process itself, and the input flow fields used are often oversimplified, failing to fully reflect the complexity of the real marine environment. Crucially, many factors influence the electromagnetic field induced by island wakes, and existing methods lack specific design for these aspects, resulting in models that cannot accurately characterize the multi-scale coupling mechanism between topography, flow field, and electromagnetic field.

[0005] The aforementioned problems have resulted in a significant gap in the research on the influencing factors of island wake-induced electromagnetic fields. How to systematically analyze the mechanism of each influencing factor, quantify its degree of influence, achieve accurate identification and reliable quantitative analysis of electromagnetic signals in the wake region, and then design relevant marine observation points are key technologies that urgently need further improvement in the analytical methods of related fields. Summary of the Invention

[0006] To address the problems existing in the prior art, this application proposes an analysis method for the influencing factors of island-induced wake electromagnetic fields, in order to solve the problems existing in the prior art.

[0007] This application provides a method for analyzing the influencing factors of island-induced wake electromagnetic fields, including: Step S1: Set up a three-dimensional island wake hydrodynamic model; Step S2: Construct an index system of influencing factors of the electromagnetic field induced by island wake, the index system of influencing factors including eddy current, ocean current velocity and Coriolis force parameters; Step S3: Set up multiple monitoring points on the seabed below the island wake region of the island geometric structure model, set the same parameters and boundary conditions, and perform forward modeling of the island wake electromagnetic induction model to obtain the induced electromagnetic field of the island wake at each monitoring point. Step S4: Compare and analyze the induced electromagnetic field of the island wake at each monitoring point, and synchronously correlate the wake vortex shedding frequency with the electromagnetic disturbance frequency to obtain the mechanism by which the vortex indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics. Step S5: Set different ocean current velocity parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point. Step S6: Analyze the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point, and synchronously correlate the wake vortex shedding frequency and electromagnetic disturbance frequency to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of induced electromagnetic field by regulating wake dynamics. Step S7: Set different Coriolis force parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point, as well as the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile line. Step S8: Analyze the induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point and the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile line, and synchronously correlate the wake vortex shedding frequency and electromagnetic disturbance frequency to obtain the mechanism by which the Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating the wake dynamic characteristics. Step S9: By comprehensively comparing the analysis results of Steps S4, S6 and S8, rank the sensitivity of the three influencing factors, namely eddy current, ocean current velocity and Coriolis force parameter, and identify the main influencing factors. Step S10: Based on the main influencing factors identified in step S9, determine the layout of monitoring points and the range of influence of island-induced wake on the induced electromagnetic field in actual island-induced wake monitoring.

[0008] Further, step S4 includes: Spectral analysis was performed on the induced electromagnetic field to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components By analyzing the spectral characteristics of the time series components and synchronously correlating the wake vortex shedding frequency with the electromagnetic disturbance frequency, the mechanism by which eddies indirectly influence the spectral characteristics of the induced electromagnetic field by modulating the wake dynamics was obtained.

[0009] Furthermore, the mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency allows us to obtain the mechanism by which the vortex indirectly affects the spectral characteristics of the induced electromagnetic field through the regulation of the wake dynamics includes: analyzing the changes in the amplitude of the induced electromagnetic field along the downstream direction from the island center; analyzing the changes in the amplitude of the induced electromagnetic field away from the downstream direction from the island center; obtaining the relationship between the time-domain signal period of the induced electromagnetic field and the vortex shedding period; and obtaining the relationship between the peak value of the induced electromagnetic field spectrum and the range of the vortex shedding frequency.

[0010] Further, step S6 includes: Spectral analysis was performed on the induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components The spectral characteristics of the time series components were analyzed, and the wake vortex shedding frequency and electromagnetic disturbance frequency were synchronously correlated to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0011] Furthermore, the mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency, and the control of ocean current velocity by regulating wake dynamic characteristics, indirectly affects the spectral characteristics of the induced electromagnetic field, includes: analyzing the influence of ocean current velocity on the dynamic structure, induced electric field strength, spatial coupling characteristics, and induced magnetic field of the wake region.

[0012] Further, step S8 includes: Spatiotemporal variation data of induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were extracted and transformed to the frequency-wavenumber domain using a two-dimensional Fourier transform. The frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were obtained. The frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were analyzed. The wake vortex shedding frequency and electromagnetic disturbance frequency were simultaneously correlated to obtain the mechanism by which the Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0013] Furthermore, the mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency, and the acquisition of Coriolis force parameters, indirectly influences the spectral characteristics of the induced electromagnetic field through the regulation of wake dynamics includes: analyzing the relationship between Coriolis force parameters, vortex structure scale and spatial evolution process, and the distribution morphology and response range of electric and magnetic fields.

[0014] Further, step S10 includes: based on the main influencing factor types identified in step S9, adopting a differentiated monitoring point deployment scheme, using a cross-shaped monitoring array or a matrix-shaped monitoring array to complete the full-area deployment at once, and selecting corresponding points in the array to achieve targeted monitoring for different influencing factors, thereby determining the influence range of island-induced wake on the induced electromagnetic field.

[0015] Furthermore, the cross-shaped monitoring array includes: a cross-shaped observation framework formed along the longitudinal direction of the flow and the transverse direction perpendicular to the flow, with the core area of ​​the island wake as the center, to quickly capture key changes in the electromagnetic field along the flow direction and transverse direction; The matrix monitoring array includes: multiple profile lines arranged parallel to each other along the wake direction behind the island, with multiple monitoring points set at equal intervals on each profile line; the lateral influence range of the wake behind the island is identified based on the monitoring points on the same profile line; and the attenuation range of the wake behind the island along the axial direction is identified based on the monitoring points on different profile lines perpendicular to the wake direction, thereby achieving full coverage detection of the wake influence.

[0016] Furthermore, when monitoring different influencing factors, longitudinal flow profile points are selected to capture changes in electromagnetic field intensity driven by flow velocity, transverse deflection section points are selected to capture the spatial shift and expansion characteristics of electromagnetic field caused by the Coriolis effect, and core vortex shedding zone, transition zone, and far-field zone points are selected to capture the electromagnetic signal characteristics corresponding to vortex shedding.

[0017] Based on the above-described invention, compared to the prior art, this application achieves the following technical effects: (1) Through multi-monitoring point and multi-parameter comparative forward modeling, the regulation law of the three key factors of eddy structure, ocean current velocity and Coriolis force on the induced electromagnetic field of island wake was revealed for the first time. The intrinsic relationship between the time domain period of the induced electromagnetic field and the eddy shedding period and the spectral peak corresponding to the characteristic frequency of the eddy was clarified, filling the gap in the study of electromagnetic response mechanism of small and medium scale terrain wake.

[0018] (2) Clearly distinguish the different response mechanisms of induced electric field and induced magnetic field: induced electric field is highly sensitive to local velocity gradient, while induced magnetic field is dominated by the spatial integral effect of flow field. The response characteristics of the two can be mutually verified, providing a clear physical basis for the interpretation of marine electromagnetic signals and wake identification.

[0019] (3) This application forms a complete and repeatable analysis process for the influencing factors of island wake induced electromagnetic fields, which can be directly applied to actual marine electromagnetic exploration and seabed environmental monitoring. It is highly practical and has a wide range of applications, improving the accuracy and reliability of electromagnetic data interpretation in marine geophysical exploration. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating a method for analyzing the influencing factors of an island-induced wake electromagnetic field according to an embodiment of this application. Figure 2 This is a schematic diagram of the island geometry model and computational domain provided in the embodiments of this application; Figure 3 The induced magnetic fields of monitoring points P1, P2, and P3 provided in the embodiments of this application are The components of the signal and their spectrum; Figure 4 The induced electric fields at monitoring points P1, P2, and P3 provided in the embodiments of this application are The components of the signal and their spectrum; Figure 5 These are the velocity field and induced electromagnetic field of the island wake at monitoring point P1 under three ocean current velocities provided in the embodiments of this application; Figure 6 The induced electric field at monitoring point P1 under three ocean current velocities provided in the embodiments of this application. Component time-frequency characteristics; Figure 7 The induced magnetic field at monitoring point P1 under the three ocean current velocities provided in the embodiments of this application is... Component time-frequency characteristics; Figure 8 These are the velocity field and induced electromagnetic field of the island wake at monitoring point P1 under three Coriolis force parameters provided in the embodiments of this application. Figure 9 The frequency-wavenumber spectrum and phase velocity of the induced electromagnetic field of profile line L1 under the three Coriolis force parameters provided in the embodiments of this application; Figure 10 This is an overview diagram of the actual work area provided in the embodiments of this application; Figure 11 This is a comparison diagram of the power spectrum of induced magnetic fields under the same ocean current velocity time period with different flow directions, provided in the embodiments of this application; Figure 12 This is a comparison chart of the power spectrum of induced magnetic fields at different ocean current velocities in the same direction during different time periods, provided in an embodiment of this application. Detailed Implementation

[0022] To better understand the technical solution of this invention, the embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are merely some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a," "the," and "the" as used in the embodiments of this application are also intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0025] See Figure 1 This is a flowchart illustrating a method for analyzing the influencing factors of an island-induced wake electromagnetic field, provided in an embodiment of this application. Figure 1 As shown, it mainly includes the following steps.

[0026] Step S1: Set up a three-dimensional island wake hydrodynamic model.

[0027] The three-dimensional island wake hydrodynamic model includes an island geometry model, a vertically stratified seawater velocity profile, and background geomagnetic field parameters.

[0028] Figure 2 This is a schematic diagram of the island's geometric structure model and computational domain, as shown below. Figure 2 As shown, the expression for the island's geometric structure model is: ,in, Representing the island's topography in the corresponding Altitude at coordinate location, height of mountain peak Width at the center of the mountain The terrain is submerged in water to a depth of 500m. The characteristic scale of the island's terrain is defined as the ratio of its longitudinal profile area to its submerged height; the calculated characteristic scale D is 450m. To calculate the horizontal coordinates within the computational domain, the origin of the domain is used as the reference point, with the direction of the current flowing along the coast as the positive direction. The unit is meters (m). The horizontal coordinate corresponding to the geometric center of the mountain is 2500m. When x = 2500m, h = H = 600m, meaning the main peak of the island is located at x = 2500m, which is the highest point on the island. The 2500m value here is a reference point used in this example and can also be considered as a parameter that can be adjusted according to specific circumstances.

[0029] like Figure 2 As shown, the entire computation domain is set to one. A cuboid, with its entrance boundary located 2.5 km upstream of the island's center, with Coriolis force parameters... Using constant velocity inlet conditions, ,in, They are respectively Velocity field in the direction; This represents the initial scalar flow rate at the inlet.

[0030] The outlet boundary is located 7.5 km downstream of the island's center, and pressure outlet boundary conditions are used. The lateral boundary is 2.5 km from the island. Both the lateral and upper boundaries use slip wall boundary conditions. The island topographic boundary and bottom boundary are the main sources of vorticity and use no-slip wall boundary conditions, meaning all ocean current velocity components on the wall are zero. All fluid domain boundaries are simultaneously set as external magnetic vector potential boundary conditions to simulate an open electromagnetic field environment. The fluid domain boundaries include the inlet boundary, outlet boundary, lateral boundary, bottom boundary, and upper boundary. The bottom boundary refers to the seabed, and the upper boundary refers to the water surface.

[0031] The vertical stratified velocity profile of seawater is described by a continuous function that varies with water depth, and the expression for the vertical stratified velocity profile of seawater is: (1) in, This is a vertical stratified velocity profile of seawater. For reference depth, A function to describe the stratification characteristics of seawater. This refers to the depth of the seawater.

[0032] In this application, all seawater depths are based on the sea surface, with downwards as the positive direction, and the unit is meters (m).

[0033] The reference depth is 10 m below the sea surface. This depth is less affected by sea surface wave disturbances and the current velocity data is highly stable.

[0034] Functions describing seawater stratification characteristics The expression is: (2) or (3) in, , For undetermined coefficients, For reference depth, Seawater depth is the Kármán constant.

[0035] KAMAN constant The value of varies in different regions, with an average value of 0.4.

[0036] Step S2: Construct an index system of influencing factors of the electromagnetic field induced by island wake, which includes eddy current, ocean current velocity, and Coriolis force parameters.

[0037] Step S3: Set up multiple monitoring points on the seabed below the island wake region of the island geometric structure model, set the same parameters and boundary conditions, and perform forward modeling of the island wake electromagnetic induction model to obtain the induced electromagnetic field of the island wake at each monitoring point.

[0038] The distance of different monitoring points from the island determines the size of the eddy current. Therefore, the induced electromagnetic field of the island wake at each monitoring point can reflect the influence of the eddy current on the induced electromagnetic field of the island wake.

[0039] The forward modeling of this application can be performed using a magnetohydrodynamic method for simulating the electromagnetic field induced by island wakes, as detailed in patent document CN121981016A.

[0040] like Figure 2 As shown, three monitoring points, P1, P2, and P3, were set up on the seabed below the island wake region in the island's geometric model to obtain the induced electromagnetic field of the island wake at monitoring points P1, P2, and P3. Among them, monitoring point P1 is 1.5 km downstream from the center of the island, and monitoring points P2 and P3 are 1 km away from point P1 along the x and y directions, respectively.

[0041] Step S4: Compare and analyze the induced electromagnetic fields of the island wake at each monitoring point, and synchronously correlate the wake vortex shedding frequency with the electromagnetic disturbance frequency to obtain the mechanism by which the vortex indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0042] Spectral analysis was performed on the induced electromagnetic field to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components By analyzing the spectral characteristics of the time series components and synchronously correlating the wake vortex shedding frequency with the electromagnetic disturbance frequency, the mechanism by which eddies indirectly influence the spectral characteristics of the induced electromagnetic field by modulating the wake dynamics was obtained.

[0043] Figure 3 The induced magnetic fields at monitoring points P1, P2, and P3 The components of the signal and their spectrum; Figure 3 (a) represents the induced magnetic field. The time-domain signal waveform of the component. Figure 3 (b) is Figure 3 The spectrum of the time-domain signal in (a) is shown. Figure 4 The induced electric fields at monitoring points P1, P2, and P3 The components of the signal and their spectrum, Figure 4 In the middle (a), the induced electric field is... The time-domain signal waveform of the component. Figure 4 (b) is Figure 4 The spectrum of the time-domain signal in (a) is shown. Analysis of these data reveals the characteristics of electromagnetic field changes during wake evolution and the underlying physical mechanisms.

[0044] The mechanism by which the wake vortex shedding frequency and electromagnetic disturbance frequency are correlated to obtain the effect of vortex on the spectral characteristics of induced electromagnetic field indirectly by regulating wake dynamics includes: analyzing the change in amplitude of induced electromagnetic field along the downstream direction of the island center; analyzing the change in amplitude of induced electromagnetic field away from the downstream direction of the island center; obtaining the relationship between the time domain signal period of induced electromagnetic field and vortex shedding period; and obtaining the relationship between the peak value of induced electromagnetic field spectrum and vortex shedding frequency range.

[0045] Depend on Figure 3 (a) and Figure 4 As can be seen in (a), the amplitude of the induced electromagnetic field at point P2 is smaller than that at point P1, but it remains at a high level, indicating that it is still affected by the large-scale eddies in the wake region, but the intensity has weakened. The amplitude of the induced electromagnetic field at point P3 has significantly decreased because it has deviated towards the Y-axis and is far away from the core region of the wake, and is therefore less affected by the eddies.

[0046] Induced magnetic field at monitoring point P1 in the core area The time-domain component signal exhibits typical amplitude modulation, with an envelope period of 50 s, precisely corresponding to the vortex shedding period. The induced magnetic field at monitoring point P1 in the core area... The time-domain component signal exhibits typical amplitude modulation, with an envelope period of 50 s, precisely corresponding to the vortex shedding period. Figure 3Spectral analysis in (b) shows that the 0.02Hz dominant frequency component accounts for 62% of the magnetic field energy spectral density, indicating that large-scale vortex structures dominate the electromagnetic signal. Induced magnetic field at the monitoring point. Component spectrum in A peak appears around 0.02 Hz, a frequency that coincides with the vortex shedding frequency, indicating that the wake region is mainly controlled by large-scale vortices, and also influenced by smaller-scale vortices generated by the dissipation of large-scale vortices. Figure 4 As shown in (b), the spectra of the three measuring points all exhibit a certain broadband distribution characteristic. Within the locally magnified frequency range, the spectral amplitude of P1 is generally higher, P2 is in the middle, and P3 is relatively lower. This indicates that the intensity of the electric field signal received at different measuring points varies, with P1 showing a more pronounced response to electric field fluctuations.

[0047] In summary, the eddy structure in the wake significantly influences the changes in the electromagnetic field, and the location of the monitoring point directly affects the measurement results. Monitoring points closer to the core region of the wake (such as monitoring point P1) exhibit stronger oscillations and more complex spectral characteristics. The amplitude and spectral characteristics of the induced electromagnetic field reflect the eddy structure and energy dissipation process in the wake region. Monitoring point P1, located in the core region of the wake, is dominated by large-scale eddies, resulting in the largest electromagnetic field amplitude, continuous energy distribution in the spectrum, and multiple secondary peaks. Monitoring point P2, located in the transition region of the wake, is influenced by both large-scale and smaller-scale eddies, resulting in a reduced electromagnetic field amplitude and a multi-band superposition characteristic in the spectrum. Monitoring point P3, far from the wake region, is mainly influenced by large-scale eddies, resulting in the smallest electromagnetic field amplitude and concentrated spectral energy.

[0048] Step S5: Set different ocean current velocity parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point.

[0049] Currently, ocean current velocities around 0.3 m / s are generally considered weak currents, while those above 0.7 m / s are considered strong currents. Under the same conditions of other parameters and boundary conditions, forward modeling of the electromagnetic induction model of an island wake was performed with ocean current velocities of 0.3 m / s, 0.5 m / s, and 0.7 m / s to obtain the induced electromagnetic field of the island wake at the same monitoring point under different ocean current velocity parameters.

[0050] Step S6: Analyze the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point, and synchronously correlate the wake vortex shedding frequency with the electromagnetic disturbance frequency to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0051] Figure 5 The velocity field and induced electromagnetic field of the island wake at monitoring point P1 under three ocean current velocities are shown. Figure 5 In the figure, 'a' represents the velocity field U when the inlet flow velocity is 0.3 m / s. Figure 5 In the figure, d represents the induced electric field E when the inlet flow velocity is 0.3 m / s. Figure 5 In the middle, g represents the induced magnetic field at an inlet flow velocity of 0.3 m / s. Quantity, Figure 5 In the diagram, b represents the velocity field U when the inlet flow velocity is 0.5 m / s. Figure 5 In this context, e represents the induced electric field E when the inlet flow velocity is 0.5 m / s. Figure 5 In the middle, h represents the induced magnetic field when the inlet flow velocity is 0.5 m / s. Quantity, Figure 5 In the figure, c represents the velocity field U when the inlet flow velocity is 0.7 m / s. Figure 5 In the equation f, E represents the induced electric field when the inlet flow velocity is 0.7 m / s. Figure 5 In this context, i represents the induced magnetic field at an inlet flow velocity of 0.7 m / s. Quantity.

[0052] Depend on Figure 5 middle a It can be seen that when the inlet velocity is 0.3 m / s, the wake exhibits periodic oscillating characteristics, and the vortex shedding frequency is approximately 10. -3 The vortex core structure is intact and its migration velocity is low. The velocity field indicates that after forming in the initial region of the wake, the vortex core breaks up at approximately one scale of the island topography (450 m), producing a stable and symmetrical shedding vortex phenomenon. Figure 5 middle d It can be seen that the induced electric field strength is relatively weak, but its distribution closely matches the periodicity of eddy shedding, with extreme values ​​appearing in the wake eddy core region. This region forms a low-pressure area due to drastic changes in ocean current velocity gradient, verifying the sensitivity of the induced electric field to local velocity gradients. Figure 5 middle g It can be seen that the induced magnetic field exhibits a spatially gentle gradient distribution, with low intensity in the vortex core region and no significant local enhancement, indicating that the magnetic field response at low flow velocities is dominated by the spatial integral effect.

[0053] Depend on Figure 5 middle b It can be seen that when the flow velocity increases to 0.5 m / s, the vortex shedding frequency increases to 0.01 Hz, the wake symmetry weakens, and the shedding vortices gradually break down into complex turbulent structures downstream. The vortex core breakup distance does not change significantly, but the increased inertial force leads to faster kinetic energy dissipation. Figure 5 middle e It can be seen that the peak intensity of the induced electric field reaches 2.3 times that under low-speed conditions, and the strong electric field region extends 23° along the core region of the wake. Figure 5In the intervals d, e, and f, this angle is 23°; only one instance is indicated here. Furthermore, it forms a banded reinforcement feature within the separated shear layer, reflecting the enhancing effect of the vortex shedding frequency on the local response of the electric field. (From...) Figure 5 middle h It can be seen that the intensity of the induced magnetic field is slightly increased, with local enhancement in the vortex core fragmentation zone, but the overall distribution remains smooth, indicating that although the increase in the velocity gradient affects the magnetic field, its response is still constrained by the global integral effect.

[0054] Depend on Figure 5 middle c It can be seen that when the flow velocity reaches 0.7 m / s, the vortex shedding frequency rises to 0.02 Hz, the wake exhibits highly asymmetric characteristics, the initial region of the vortex core rapidly destabilizes and breaks up, and kinetic energy dissipation accelerates significantly. Figure 5 middle f It can be seen that the peak intensity of the induced electric field increases to 3.8 times that under low-speed conditions, and its spatial distribution is highly coupled with the transient vortex structure, with an electric field extremum induced by shedding vortices appearing in the downstream far field. Figure 5 middle i It can be seen that although the induced magnetic field exhibits local extrema in the vortex core fragmentation region, it maintains a smooth overall characteristic and does not show vortex fragmentation features. This indicates that the magnetic field is less sensitive to local velocity gradients, and its distribution reflects more the average response of the wake vortex structure, which contrasts sharply with the high-frequency dynamic characteristics of the electric field.

[0055] Spectral analysis was performed on the induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components The spectral characteristics of the time series components were analyzed, and the wake vortex shedding frequency and electromagnetic disturbance frequency were synchronously correlated to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0056] The mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency allows us to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field through the regulation of wake dynamics includes: analyzing the influence of ocean current velocity on the dynamic structure, induced electric field strength, spatial coupling characteristics, and induced magnetic field of the wake region.

[0057] Figure 6 The induced electric field at monitoring point P1 under three ocean current velocities The components of the signal and their spectrum, Figure 7 Induced magnetic field at monitoring point P1 under three ocean current velocities The components of the signal and their spectrum. Figure 6(a) shows the induced electric field at monitoring point P1 under three ocean current velocities. The time-domain signal waveform of the component. Figure 6 (b) is Figure 6 The spectrum diagram of the time-domain signal in (a); Figure 7 (a) shows the induced magnetic field at monitoring point P1 under three ocean current velocities. The time-domain signal waveform of the component. Figure 7 (b) is Figure 7 The spectrum of the time-domain signal in (a) is shown.

[0058] Depend on Figure 6 As can be seen in (a), the amplitude of the induced electric field increases to some extent with the increase of ocean current velocity. From Figure 6 As can be seen from (b), The spectrum diagram shows a low-frequency, high-energy phenomenon, with all three flow velocity conditions approaching 10. -2 There is a peak value in the Hz range. The increase in ocean current velocity causes the peak value to shift to higher frequencies. This corresponds to the frequency of vortex shedding in the wake region: as the ocean current velocity increases, the vortex shedding frequency increases, thereby increasing the peak frequency of its induced electric field.

[0059] Depend on Figure 7 (a) and Figure 7 As can be seen in (b), the amplitude and frequency of the induced magnetic field exhibit the same characteristics as the induced electric field, both showing a positive correlation with the increase in ocean current velocity.

[0060] Comparative analysis of the distribution characteristics of the velocity field, induced electric field, and induced magnetic field, as well as the video characteristics of the induced electromagnetic field, reveals that the increase in ocean current velocity significantly alters the dynamic structure and electromagnetic field characteristics of the wake region. The induced electric field is highly sensitive to local ocean current velocity gradients, and the increase in ocean current velocity significantly enhances its intensity and spatial coupling characteristics. The changes in the induced magnetic field are more dominated by the spatial integral effect of the flow field, maintaining a smooth distribution but exhibiting small amplitude responses in local regions. Furthermore, there is a correlation between the induced electromagnetic field signal of the wake and the vortex shedding frequency in the wake. These characteristics indicate that changes in ocean current velocity play a crucial role in regulating the electromagnetic properties of the wake, which is of great significance for wake monitoring and identification based on electromagnetic signals.

[0061] Step S7: Set different Coriolis force parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point, as well as the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile.

[0062] The Coriolis force parameter varies significantly with latitude, directly affecting the volume forces acting on fluid motion, and potentially influencing the dynamic structure and induced electromagnetic field characteristics of the wake. Under the same parameters and boundary conditions, Coriolis force parameters were set for three typical latitudes: 10°, 20°, and 38°. , and Forward modeling was performed on the electromagnetic induction model of the island wake to obtain the velocity field and induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point.

[0063] Step S8: Analyze the induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point and the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile line, and synchronously correlate the wake vortex shedding frequency and electromagnetic disturbance frequency to obtain the mechanism by which the Coriolis force parameter indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamic characteristics.

[0064] Figure 8 The velocity field and induced electromagnetic field of the island wake at monitoring point P1 under three Coriolis force parameters are given. Figure 8 In the middle, 'a' represents the Coriolis force parameter. The velocity field U at that time Figure 8 In the middle, d is the Coriolis force parameter. The induced electric field E at that time Figure 8 In the middle, g is the Coriolis force parameter. Induced magnetic field at time Quantity, Figure 8 In the middle, b represents the Coriolis force parameter. The velocity field U at that time Figure 8 In the middle, e represents the Coriolis force parameter. The induced electric field E at that time Figure 8 In the middle, h is the Coriolis force parameter. Induced magnetic field at time Quantity, Figure 8 In the middle, c represents the Coriolis force parameter. The velocity field U at that time Figure 8 f is the Coriolis force parameter. The induced electric field E at that time Figure 8 In the middle, i represents the Coriolis force parameter. Induced magnetic field at time Quantity.

[0065] Depend on Figure 8 middle a It can be seen that under weak Coriolis force conditions, the wake exhibits high symmetry, with a complete vortex core structure and low migration velocity. The velocity field shows that the vortex core breaks up approximately 2 km behind the island, but still maintains stability within a certain distance. Figure 8 middle dIt can be seen that the induced electric field distribution is highly correlated with the velocity field. The vortex core region generates significant electric field extrema due to the drastic velocity gradient, with its influence area within 13°, which is relatively narrow. The red dashed line indicates that the electric field is concentrated near the vortex core. Figure 8 middle g It can be seen that the induced magnetic field exhibits a gentle gradient distribution in the initial region of the wake, while a large-scale weak magnetic field response appears in the far field region, corresponding to the spatial integral effect of the wake vortex structure.

[0066] Depend on Figure 8 middle b It can be seen that as the Coriolis force increases, the wake deflection effect becomes significant, the vortex core breaking distance shortens to 1.5 km, and the symmetry gradually weakens and evolves into a complex turbulent structure. Figure 8 middle e It can be seen that the influence range of the induced electric field extends to 22°, and the red dashed circle shows its distribution coupled with the transient vortex structure, but the peak intensity is not significantly increased. Figure 8 middle h It can be seen that the induced magnetic field distribution in the near field region still maintains its smooth characteristics, while the far field response range is significantly reduced. The area marked by the red dashed line shows that the far field magnetic field gradient disappears, reflecting the enhanced turbulent energy dissipation caused by the intensification of vortex breaking.

[0067] Depend on Figure 8 middle c It can be seen that under the influence of strong Coriolis force, the vortex core in the initial region of the wake rapidly becomes unstable and breaks up, with the breaking distance shortened by about 1 km compared to the weaker Coriolis force, and the flow exhibits a highly turbulent mixing state. Figure 8 middle f It can be seen that the influence range of the induced electric field further extends to 34°, and its distribution is highly synchronized with the transient structure of the wake, but the peak intensity remains stable. Figure 8 middle i It can be seen that the magnetic field maintains a smooth distribution in the near field region, and the response in the far field is further weakened. The red dashed circle shows that the magnetic field extrema only exist in the local broken region, indicating that the strong Coriolis force weakens the spatial integral effect of the magnetic field by enhancing turbulent energy dissipation, and the overall distribution is more dependent on the average response characteristics of the flow field.

[0068] Because the Coriolis force is a non-conservative force, traditional spectral analysis methods based on single-point time series are insufficient to effectively capture its physical effects—these methods obscure spatial distribution information during integration. The dispersion effect caused by the Coriolis force is essentially a redistribution of wave energy with spatial location and frequency components. To further explore the mechanism of the Coriolis force in the generation of wake electromagnetic fields, spatiotemporal variation data of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were extracted. These data were then transformed to the frequency-wavenumber domain using a two-dimensional Fourier transform to obtain the frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile. The frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were analyzed. Simultaneously, the wake vortex shedding frequency and electromagnetic disturbance frequency were correlated to obtain the mechanism by which the Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

[0069] like Figure 2 As shown, a representative profile line L1 is selected in the island wake region, and Coriolis force parameters are set for three typical latitudes of 10°, 20° and 38°. , and Forward modeling was performed on the electromagnetic induction model of the island wake to obtain the induced electromagnetic field of the island wake under different Coriolis force parameters at profile line L1. The spatiotemporal variation data of the induced electric and magnetic fields of the island wake under different Coriolis force parameters at profile line L1 were extracted and transformed to the frequency-wavenumber domain using a two-dimensional Fourier transform, as shown below. Figure 9 The frequency-wavenumber spectrum and phase velocity of the induced electromagnetic field of profile line L1 under the three Coriolis force parameters are shown. Figure 9 In the middle (a), the frequency-wavenumber spectrum of the induced electric field of profile line L1 is shown under three Coriolis force parameters. Figure 9 (b) shows the frequency-wavenumber spectrum of the induced magnetic field of profile line L1 under three Coriolis force parameters. Figure 9 In the middle (c), the phase velocity of the induced electromagnetic field of profile line L1 is shown under three Coriolis force parameters.

[0070] The frequency-wavenumber spectrum further reveals the differential modulation effect of different Coriolis forces on the induced electromagnetic field in the wake region.

[0071] Depend on Figure 9 As can be seen from (a), in terms of electric field, Under weak Coriolis force conditions, the peak frequency of the induced electric field energy spectrum appears Nearby, the dominant mode corresponding to the small-scale vortex structure, characterized by the response of the main conductive field of the small-scale vortex structure, has a phase velocity of approximately 0.00083 m / s. This corresponds to the low migration rate of the vortex core, which is beneficial for maintaining the integrity of the structure. Under moderate Coriolis force conditions, the peak frequency of the electric field energy spectrum shifts to Nearby, the phase velocity increases to 0.00147 m / s, reflecting energy transfer to a larger scale, and the electric field distribution expands accordingly. Under strong Coriolis force conditions, the dispersion relation is further adjusted, and the peak frequency remains at [value missing]. Near the vicinity, the phase velocity increases to 0.0029 m / s, indicating that the rotation effect plays an important role in the wave propagation characteristics, promotes the conversion of energy into large-scale structures, and the induced electric field response region expands synchronously.

[0072] Depend on Figure 9 As can be seen in (b), the induced magnetic field response exhibits different dispersion characteristics than the induced electric field. Under weak Coriolis force conditions, the peak frequency of the magnetic field energy spectrum is The frequency is less than the peak frequency of the electric field, and the phase velocity is approximately 0.00429 m / s. As the Coriolis force increases, the peak frequency of the magnetic field energy spectrum is at [values ​​missing] under medium and strong Coriolis force conditions. and Near the vicinity, the phase velocity increases to approximately 0.0088 m / s, indicating that energy spreads more widely in the spatial domain, further highlighting its sensitivity to large-scale vortex structure responses.

[0073] Depend on Figure 9 As can be seen in (c), the phase velocity of the induced magnetic field not only far exceeds that of the electric field by nearly an order of magnitude, but its changing trend is also different: as the Coriolis force changes from... Increase to The phase velocity of the induced magnetic field decreased slightly from 0.00882 m / s to 0.00832 m / s, showing nonlinear saturation characteristics.

[0074] Under weak Coriolis force conditions, the wake is mainly influenced by local ocean current velocity gradients and turbulent mixing, and its flow pattern and induced electromagnetic field distribution are dominated by local characteristics. However, under strong Coriolis force conditions, the deflection and separation phenomena of the wake will be significantly enhanced, and the kinetic energy distribution and eddy shedding behavior in the wake will change significantly, which may lead to a more complex spatial distribution of the induced electromagnetic field.

[0075] The above analysis shows that ocean current velocity primarily controls the absolute intensity of the induced electromagnetic field, while the Coriolis force influences the scale and spatial evolution of the vortex structure through dispersion relations, thus determining the distribution and response range of the electric and magnetic fields. The differentiated modulation effect of the Coriolis force on the electric and magnetic fields demonstrates the complexity and importance of the rotational effect in the multi-physics coupled system of the island wake induced electromagnetic field.

[0076] Step S9: By comprehensively comparing the analysis results of Steps S4, S6 and S8, rank the sensitivity of the three influencing factors, namely eddy current, ocean current velocity and Coriolis force parameter, and identify the main influencing factors.

[0077] Specifically, this includes: comprehensively comparing the analysis results of steps S4, S6, and S8; quantitatively ranking the sensitivity of three influencing factors—eddy structure, ocean current velocity, and Coriolis force parameters—based on the changes in induced electromagnetic field amplitude, spectral energy proportion, spatial influence range, and dispersion characteristics; identifying the main controlling influencing factors based on the changes and contribution of dispersion characteristics; and clarifying the influence of each factor on the induced electromagnetic field of the island-induced wake.

[0078] Step S10: Based on the main influencing factors identified in step S9, determine the layout of monitoring points and the range of influence of island-induced wake on the induced electromagnetic field in actual island-induced wake monitoring.

[0079] Based on the main influencing factor types identified in step S9, a differentiated monitoring point deployment scheme is adopted. The entire area is deployed at once using a cross-shaped monitoring array or a matrix-shaped monitoring array. By selecting corresponding points in the array, targeted monitoring is achieved for different influencing factors, and the influence range of island-induced wake on the induced electromagnetic field is determined.

[0080] The cross-shaped monitoring array includes: a cross-shaped observation framework centered on the core area of ​​the island wake, forming a cross along the longitudinal direction of the flow and the transverse direction perpendicular to the flow, to quickly capture key changes in the electromagnetic field along the flow direction and transverse direction; The matrix monitoring array includes: multiple profile lines set parallel to the wake direction behind the island, with multiple monitoring points set at equal intervals on each profile line; the lateral influence range of the wake behind the island is identified based on the monitoring points on the same profile line; and the attenuation range of the wake behind the island along the axial direction is identified based on the monitoring points on different profile lines perpendicular to the wake direction, thus achieving full coverage detection of the wake influence.

[0081] When monitoring different influencing factors, longitudinal flow profile points are selected to capture changes in electromagnetic field intensity driven by flow velocity, transverse deflection section points are selected to capture the spatial shift and expansion characteristics of electromagnetic field caused by Coriolis force effect, and core vortex shedding zone, transition zone, and far field zone points are selected to capture the electromagnetic signal characteristics corresponding to vortex shedding.

[0082] Multiple influencing factors can be monitored by selecting sub-points as needed using the same array, eliminating the need for repeated deployment and effectively improving the efficiency of actual marine observation.

[0083] The following specific example illustrates the application effect of the method in this application.

[0084] Data on induced electromagnetic fields were collected at point A in the northern sea area of ​​Weihai City. For example... Figure 10 As shown, there are two collection directions: flow direction 1 and flow direction 2.

[0085] Data from two time periods were selected for comparison: the period from 11:40 to 12:10 when the current speed of direction 1 was approximately 0.2 m / s, and the period from 13:10 to 13:40 when the current speed of direction 2 was approximately 0.2 m / s.

[0086] Power spectrum analysis was performed on the induced magnetic field at monitoring point A. Figure 11 Comparison of the power spectrum of induced magnetic fields over time for the same ocean current velocity with different flow directions. Figure 11 (a) is a comparison of the power spectra of the Hx component of the induced magnetic field over time with the same ocean current velocity but different flow directions. Figure 11 (b) is a comparison of the power spectra of the Hy component of the induced magnetic field over time periods with the same ocean current velocity but different flow directions. Figure 11 It can be seen that, under the condition of equal ocean current velocity but opposite flow direction, the induced magnetic field power spectral density of monitoring point A shows a significant enhancement in flow direction 1, with its low-frequency energy increasing by approximately 2.3 times compared to flow direction 2, and the full width at half maximum (FWHM) of the dominant frequency peak decreasing by 38%. The power spectral characteristics indicate that the magnetic field energy in flow direction 1 is concentrated in... Frequency band, corresponding to the characteristic frequency of vortex shedding.

[0087] Based on the above analysis, it is preliminarily determined that the flow direction 1 is behind the island, and point A is the wake region.

[0088] In the direction of flow 1, the induced magnetic field data were analyzed for two time periods: between 9:30 and 10:30, when the ocean current velocity was approximately 0.45 m / s; and between 11:30 and 12:30, when the ocean current velocity was approximately 0.2 m / s. Figure 12 This is a comparison of the power spectra of induced magnetic fields at different ocean current velocities within the same current direction over time periods. Figure 12 (a) is a comparison of the power spectra of the Hx component of the induced magnetic field over time periods with different ocean current velocities in the same direction. Figure 12 (b) shows a comparison of the power spectra of the Hy component of the induced magnetic field over time periods with different ocean current velocities in the same direction. Figure 12 It can be seen that the magnetic field power spectral density is significantly enhanced under the higher ocean current velocity of 0.45 m / s, with its dominant frequency peak amplitude being approximately 2.1 times that of the lower ocean current velocity period of 0.2 m / s, and the spectral energy is above 10. -2 The distribution is more concentrated near the Hz frequency band.

[0089] This further indicates that direction 1 is towards the rear of the island. It was later confirmed that, along direction 1, point A is located behind Chu Island in Weihai, as shown below. Figure 10 As shown.

[0090] This application proposes a method for analyzing the influencing factors of the induced electromagnetic field in island-induced wakes. This method involves forward modeling a three-dimensional island wake hydrodynamic model by varying the monitoring point location, setting different ocean current velocities, and different Coriolis force parameters to obtain the induced electromagnetic field and velocity field of the island wake. Through spectral analysis and two-dimensional Fourier transform analysis of the induced electromagnetic field, the influence control mechanism of different influencing factors on the induced electromagnetic field of the island wake is obtained. The results show that the time-domain signal period of the induced electromagnetic field is equal to the vortex shedding period; the spectral peak of the induced electromagnetic field is located within the vortex shedding frequency range; the ocean current velocity mainly affects the overall energy level of the induced electromagnetic field by changing the fluid kinetic energy; the Coriolis force affects the vortex structure scale and spatial evolution process through dispersion relations, thereby determining the distribution and response range of the electric and magnetic fields. Comprehensive analysis shows that islands, as flow field obstacles, significantly enhance the electromagnetic field intensity and signal characteristic identifiability of the wake region by changing the local flow field structure and energy dissipation path, providing a physical basis for wake identification in marine environmental electromagnetic monitoring.

[0091] Based on the above-described invention, compared to the prior art, this application achieves the following technical effects: (1) Through multi-monitoring point and multi-parameter comparative forward modeling, the regulation law of the three key factors of eddy structure, ocean current velocity and Coriolis force on the induced electromagnetic field of island wake was revealed for the first time. The intrinsic relationship between the time domain period of the induced electromagnetic field and the eddy shedding period and the spectral peak corresponding to the characteristic frequency of the eddy was clarified, filling the gap in the study of electromagnetic response mechanism of small and medium scale terrain wake.

[0092] (2) Clearly distinguish the different response mechanisms of induced electric field and induced magnetic field: induced electric field is highly sensitive to local velocity gradient, while induced magnetic field is dominated by the spatial integral effect of flow field. The response characteristics of the two can be mutually verified, providing a clear physical basis for the interpretation of marine electromagnetic signals and wake identification.

[0093] (3) This application forms a complete and repeatable analysis process for the influencing factors of island wake induced electromagnetic fields, which can be directly applied to actual marine electromagnetic exploration and seabed environmental monitoring. It is highly practical and has a wide range of applications, improving the accuracy and reliability of electromagnetic data interpretation in marine geophysical exploration.

[0094] In this embodiment of the invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, the simultaneous existence of A and B, or the existence of B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, and c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0095] The above description is merely a specific embodiment of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for analyzing the influencing factors of island-induced wake electromagnetic fields, characterized in that, include: Step S1: Set up a three-dimensional island wake hydrodynamic model; Step S2: Construct an index system of influencing factors of the electromagnetic field induced by island wake, the index system of influencing factors including eddy current, ocean current velocity and Coriolis force parameters; Step S3: Set up multiple monitoring points on the seabed below the island wake region of the island geometric structure model, set the same parameters and boundary conditions, and perform forward modeling of the island wake electromagnetic induction model to obtain the induced electromagnetic field of the island wake at each monitoring point. Step S4: Compare and analyze the induced electromagnetic field of the island wake at each monitoring point, and synchronously correlate the wake vortex shedding frequency with the electromagnetic disturbance frequency to obtain the mechanism by which the vortex indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics. Step S5: Set different ocean current velocity parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point. Step S6: Analyze the velocity field and induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point, and synchronously correlate the wake vortex shedding frequency and electromagnetic disturbance frequency to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of induced electromagnetic field by regulating wake dynamics. Step S7: Set different Coriolis force parameters, and perform forward modeling of the island wake electromagnetic induction model under the same other parameters and boundary conditions to obtain the velocity field and induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point, as well as the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile line. Step S8: Analyze the induced electromagnetic field of the island wake under different Coriolis force parameters at the same monitoring point and the induced electromagnetic field of the island wake under different Coriolis force parameters at the same profile line, and synchronously correlate the wake vortex shedding frequency and electromagnetic disturbance frequency to obtain the mechanism by which the Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating the wake dynamic characteristics. Step S9: By comprehensively comparing the analysis results of Steps S4, S6 and S8, rank the sensitivity of the three influencing factors, namely eddy current, ocean current velocity and Coriolis force parameter, and identify the main influencing factors. Step S10: Based on the main influencing factors identified in step S9, determine the layout of monitoring points and the range of influence of island-induced wake on the induced electromagnetic field in actual island-induced wake monitoring.

2. The method according to claim 1, characterized in that, Step S4 includes: Spectral analysis was performed on the induced electromagnetic field to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components By analyzing the spectral characteristics of the time series components and synchronously correlating the wake vortex shedding frequency with the electromagnetic disturbance frequency, the mechanism by which eddies indirectly influence the spectral characteristics of the induced electromagnetic field by modulating the wake dynamics was obtained.

3. The method according to claim 2, characterized in that, The mechanism by which the wake vortex shedding frequency and electromagnetic disturbance frequency are correlated to obtain the effect of vortex on the spectral characteristics of induced electromagnetic field indirectly by regulating wake dynamics includes: analyzing the change in amplitude of induced electromagnetic field along the downstream direction of the island center; analyzing the change in amplitude of induced electromagnetic field away from the downstream direction of the island center; obtaining the relationship between the time domain signal period of induced electromagnetic field and vortex shedding period; and obtaining the relationship between the peak value of induced electromagnetic field spectrum and vortex shedding frequency range.

4. The method according to claim 1, characterized in that, Step S6 includes: Spectral analysis was performed on the induced electromagnetic field of the island wake under different ocean current velocity parameters at the same monitoring point to extract the induced electric field. Components and induced magnetic fields Spectral characteristics of the time series of the components; analysis of the induced electric field. Spectral characteristics and induced magnetic field of the time series of components The spectral characteristics of the time series components were analyzed, and the wake vortex shedding frequency and electromagnetic disturbance frequency were synchronously correlated to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

5. The method according to claim 4, characterized in that, The mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency allows us to obtain the mechanism by which ocean current velocity indirectly affects the spectral characteristics of the induced electromagnetic field through the regulation of wake dynamics includes: analyzing the influence of ocean current velocity on the dynamic structure, induced electric field strength, spatial coupling characteristics, and induced magnetic field of the wake region.

6. The method according to claim 1, characterized in that, Step S8 includes: Spatiotemporal variation data of induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were extracted and transformed to the frequency-wavenumber domain using a two-dimensional Fourier transform. The frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were obtained. The frequency-wavenumber spectra and phase velocities of the induced electric and magnetic fields of island wakes under different Coriolis force parameters at the same profile were analyzed. The wake vortex shedding frequency and electromagnetic disturbance frequency were simultaneously correlated to obtain the mechanism by which the Coriolis force parameters indirectly affect the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics.

7. The method according to claim 6, characterized in that, The mechanism by which the synchronous correlation between the wake vortex shedding frequency and the electromagnetic disturbance frequency, and the Coriolis force parameters are obtained, indirectly affects the spectral characteristics of the induced electromagnetic field by regulating the wake dynamics features, includes: analyzing the relationship between the Coriolis force parameters, the scale and spatial evolution of the vortex structure, and the distribution and response range of the electric and magnetic fields.

8. The method according to claim 7, characterized in that, Step S10 includes: based on the main influencing factor types identified in step S9, adopting a differentiated monitoring point deployment scheme, using a cross-shaped monitoring array or a matrix-shaped monitoring array to complete the full-area deployment at once, and selecting corresponding points in the array to achieve targeted monitoring for different influencing factors, thereby determining the influence range of island-induced wake on the induced electromagnetic field.

9. The method according to claim 8, characterized in that, The cross-shaped monitoring array includes: a cross-shaped observation framework formed along the longitudinal direction of the flow and the transverse direction perpendicular to the flow, with the core area of ​​the island wake as the center, to quickly capture key changes in the electromagnetic field along the flow direction and transverse direction. The matrix monitoring array includes: multiple profile lines arranged parallel to each other along the wake direction behind the island, with multiple monitoring points set at equal intervals on each profile line; the lateral influence range of the wake behind the island is identified based on the monitoring points on the same profile line; and the attenuation range of the wake behind the island along the axial direction is identified based on the monitoring points on different profile lines perpendicular to the wake direction, thereby achieving full coverage detection of the wake influence.

10. The method according to claim 9, characterized in that, When monitoring different influencing factors, longitudinal flow profile points are selected to capture changes in electromagnetic field intensity driven by flow velocity, transverse deflection section points are selected to capture the spatial shift and expansion characteristics of electromagnetic field caused by Coriolis force effect, and core vortex shedding zone, transition zone, and far field zone points are selected to capture the electromagnetic signal characteristics corresponding to vortex shedding.

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