A method for simulating three-dimensional electromagnetic fields induced by oceanic movements

Abstract

The application discloses a marine motion-induced three-dimensional electromagnetic field simulation method, comprising the following steps: obtaining a marine velocity field, a background geomagnetic field and conductive structure parameters, establishing a seawater layer grid and interpolating the velocity field; calculating distributed external current density (determined by coupling of conductivity, velocity and geomagnetic field) in each grid unit; constructing a three-dimensional conductive model containing a seawater layer, a sediment layer, a crust and land, mapping the current to the model to solve electromagnetic response; finally, extracting electric field, magnetic field, motion impedance and tipper type response at land-based, seabed or sea surface observation points to complete simulation. The method solves the problems of oversimplified marine motion source expression, insufficient coupling of land-sea three-dimensional conductive structure and single type of observation response extraction in the prior art electromagnetic field simulation technology. The method can directly construct a distributed external current from a marine motion velocity field, and uniformly coupled with land-sea three-dimensional conductive structure for solving, and supports multiple types of observation response extraction.

Description

Technical Field

[0001] This invention specifically relates to a method for simulating three-dimensional electromagnetic fields induced by ocean motion based on distributed external current construction, which is applicable to the simulation and response analysis of induced electromagnetic fields generated by ocean motion processes such as tsunamis, tides, and ocean currents. Background Technology

[0002] When conductive seawater moves within the background geomagnetic field, it generates observable electric and magnetic field anomalies due to electromagnetic induction. Existing research has shown that the electromagnetic fields induced by seawater movement can be observed not only on the seabed but also recorded at observation points on land and islands. Therefore, accurate simulation of the electromagnetic response induced by ocean movement is of great significance for the analysis of ocean dynamic processes, the study of conductive seabed structures, and related monitoring applications.

[0003] Existing methods fall into two categories. One approach involves a simplified source representation of ocean motion-induced magnetic fields (OMPs), such as considering only local equivalent sources or retaining source components in only certain directions. Another approach, while employing 3D modeling, often fails to integrate the ocean motion field, land-sea conductive structure, and extraction of various observation responses into a unified process. Current research on tsunami-induced magnetic fields clearly indicates that some past works have failed to achieve accurate 3D simulations of tsunami-induced magnetic fields using rigorous Maxwell equations, especially in the case of seabed observations where precise 3D calculations are crucial. For example, while the published paper CN121981016A(D1) calculates the induced current based on the generalized Ohm's law, its construction of the ocean motion source remains relatively macroscopic, failing to truly achieve discretized source construction based on grid cells. Furthermore, it lacks sufficient modeling of abrupt changes in conductivity at the land-sea interface, and particularly lacks explicit construction of an integrated 3D conductive structure model encompassing both land areas and coastlines.

[0004] On the other hand, existing materials provide the physical basis for the construction of external currents: for a seawater conductor moving in a background geomagnetic field, the external current Jext can be determined by the coupling relationship between seawater conductivity, flow velocity field, and background magnetic field; in practical implementation, heterogeneous source terms can be loaded into a three-dimensional electromagnetic induction code for solution in a three-dimensional Cartesian coordinate system. Existing research has also given the definition and application of motion impedance and tipper-type response, indicating that ocean motion-induced electromagnetic response can not only output electric and magnetic fields, but also further extract higher-level response functions.

[0005] However, existing solutions still have the following shortcomings: First, the spatial non-uniformity of ocean motion sources is not adequately represented. Existing related technologies often simplify the sources into uniform layers or analytical functions, which makes it difficult to truly reflect the spatial distribution characteristics of motion fields such as tsunamis, tides, or ocean currents. Second, conductive structural factors such as land-sea boundaries, seabed sediment layers, and changes in seawater layer thickness are not fully incorporated into a unified simulation framework. In particular, the step changes in conductivity at the coastline are often ignored or oversimplified. Third, there is a lack of a unified extraction process among electric field, magnetic field, motion impedance type responses, and tipper type responses. Summary of the Invention

[0006] The purpose of this invention is to provide a method for simulating three-dimensional electromagnetic fields induced by ocean motion based on the construction of distributed external currents, in order to solve the problems of overly simplified representation of ocean motion sources, insufficient coupling of land and sea three-dimensional conductive structures, and limited types of observation response extraction in existing related technologies. This method can directly construct distributed external currents from the ocean motion velocity field and solve them in a unified coupled manner with the land and sea three-dimensional conductive structures, while also supporting the extraction of multiple types of observation responses.

[0007] The technical solution of this invention is as follows: like Figure 1 As shown, the present invention provides a method for simulating three-dimensional electromagnetic fields induced by ocean motion based on distributed external current construction, comprising: S1, Data Acquisition and Mesh Construction: Acquire ocean velocity field data, background geomagnetic field data, and conductive structure parameters of the study area, and establish a seawater layer mesh specifically for electromagnetic simulation.

[0008] S2, Distributed External Current Construction: The ocean velocity field data is mapped onto the seawater layer grid using a spatial interpolation method. Then, based on electromagnetic principles, the seawater conductivity is utilized... σ w Interpolated ocean velocity field v With background geomagnetic field B Coupling relationship between 0: In each seawater layer grid cell, the distributed external current density is independently and discretized and constructed. This process can accurately characterize the source distribution generated by spatially non-uniform ocean motion.

[0009] S3, Construction of a three-dimensional conductive structure model: A multi-dimensional three-dimensional conductive structure model is established. This model not only includes the seawater layer and the seabed sediment layer, but also integrates the deeper crustal medium and land area. The land-sea boundary at the coastline is explicitly defined to accurately simulate the step change in conductivity at the land-sea boundary and its impact on the electromagnetic field distribution.

[0010] S4, Solving the three-dimensional electromagnetic response: The distributed external currents calculated in step S2 and distributed in each seawater layer grid cell are accurately loaded onto the corresponding seawater layer grid cells in the three-dimensional conductive structure model constructed in step S3 through spatial mapping technology, serving as the excitation source of Maxwell's equations, and then solving the three-dimensional electromagnetic response induced by ocean motion in the entire model region.

[0011] S5, Multi-type observation response extraction: Based on the simulation requirements, extract electric field response and magnetic field response from preset land observation points, seabed observation points or sea surface observation points as the final analysis results.

[0012] Preferably, the ocean velocity field data can come from tsunami numerical simulations, tidal models, ocean current numerical models, or observational inversion results.

[0013] Preferably, in step S3, the three-dimensional conductive structure model explicitly defines a conductivity step boundary between the seawater layer and the land area at the coastline location during model construction. (During model construction, the coastline is explicitly modeled as an independent boundary, and different conductivity values ​​are set on both sides, rather than approximating it through smooth transition or ignoring the boundary.) Preferably, the response solution in step S4 is obtained using a frequency domain solution method; for general ocean motion velocity fields, it can be solved directly in the time domain; preferably, when the ocean motion velocity field is time-varying data, the velocity field can be first converted to the frequency domain according to the time series, and then each frequency component can be solved and combined separately. (S4 describes a general solution method and does not limit whether the motion field is time-varying. Time-varying cases are a further preferred frequency domain processing method.) In step S4, the distributed external current is loaded into the corresponding grid cell of the seawater layer through a one-to-one mapping or interpolation mapping between the ocean motion field grid and the electromagnetic simulation grid.

[0014] Preferably, in step S5, in addition to directly extracting the electric field and magnetic field, motion impedance response and tipper response are also extracted to characterize the coupling relationship between the ocean motion-induced magnetic field and the underground conductive structure at different observation points.

[0015] The beneficial effects of this invention are as follows: 1. High-fidelity source simulation: By constructing distributed external source currents by grid cell, it overcomes the errors caused by the simplification of traditional point sources, line sources or uniform sources. It can realistically reflect the spatial non-uniformity of ocean movement processes such as tsunamis and tides, and significantly improve the physical realism of the simulation. It is fundamentally different from existing related technologies (such as the macroscopic source representation used in D1). 2. Complex land-sea coupling capability: Through the "three-dimensional conductive structure model that explicitly includes the abrupt change in conductivity at the land-sea boundary", the electrical boundaries of the seawater layer, sedimentary layer, crust, land area and coastline are unified into a simulation framework for the first time. It can accurately simulate the propagation and distortion effect of electromagnetic field in complex land-sea transition zone, and is especially suitable for nearshore and island environments. 3. Supports the extraction of multiple response results from different observation locations such as land, seabed, and sea surface, facilitating unified analysis of multiple types of observations; It can simultaneously output electric field, magnetic field, motion impedance type response and tipper type response, which is convenient for analyzing the characteristics of marine motion sources and the influence of underground conductive structures. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the overall process of a three-dimensional electromagnetic field simulation method for ocean motion-induced motion based on distributed external current construction, as described in this invention. Figure 2 This is a schematic diagram of the marine sports field and distributed external current structure of the present invention; Figure 3 This is a schematic diagram of the three-dimensional conductive structure model for land and sea of ​​the present invention; Figure 4 This is a schematic diagram of the distributed external current loading and three-dimensional electromagnetic response solution of the present invention; Figure 5 This is a schematic diagram of the multi-type observation response extraction of the present invention.

[0017] 2—Oceanic sports field and distributed external current structure; 21—Oceanic sports field; 22—Background geomagnetic field; 23—Seawater layer grid; 24—Seawater layer grid cell; 25—Distributed external current; 26—Direction of external current density; 3—Three-dimensional conductive structure model of land and sea; 31—Seawater layer; 32—Seafloor sedimentary layer; 33—Crustal medium; 34—Land region; 35—Land-sea boundary; 36—Observation point; 37—External current loading area; 4—External current loading and response solution structure; 41—Distributed external current mapping module; 42—Seawater layer loading unit; 43—Three-dimensional electromagnetic response solution module; 44—Electric field response; 45—Magnetic field response; 46—Frequency component or frequency domain solution results; 5—Multi-type observation response extraction structure; 51—Land observation point; 52—Seabed observation point; 53—Sea surface observation point; 54—Electric field response; 55—Magnetic field response; 56—Motion impedance type response; 57—Tipper type response. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] Step S1: Acquisition of marine sports field data like Figure 1 As shown, in step S1, ocean motion velocity field data, background geomagnetic field data, and conductive structure parameters of the study area are acquired.

[0020] The ocean velocity field data can be two-dimensional or three-dimensional velocity field data, and can come from tsunami propagation numerical simulations, tidal model calculations, ocean current model outputs, or other ocean dynamics results; preferably, the ocean velocity field includes at least a horizontal velocity component. The background geomagnetic field data includes the intensity and direction information of the background magnetic field, which is used for subsequent external current construction.

[0021] Step S2: Construction of Distributed External Current Source like Figure 2 As shown, the marine sports field and distributed external current structure 2 includes a marine sports field 21, a background geomagnetic field 22, a seawater layer grid 23, and a distributed external current 25. The seawater layer grid 23 includes each seawater layer grid cell 24, and the distributed external current 25 includes the direction of external current density 26.

[0022] In this embodiment, a seawater layer grid 23 is first established based on the ocean motion field 21 and the background geomagnetic field 22, and the ocean motion velocity field is interpolated into each seawater layer grid cell 24. Subsequently, a distributed external current 25 is constructed cell by cell according to the grid cell, and its current density direction is represented by the external current density direction 26.

[0023] Preferably, the distributed external current density is determined by the seawater conductivity. σ w Ocean motion velocity field v and background geomagnetic field B The coupling relationship of 0 is determined. In existing research, the external current... J ext It has been clearly defined as the external current term obtained by coupling the seawater conductivity with the ocean velocity field and the background geomagnetic field.

[0024] Compared with existing related technologies that simplify the source to a single point, a single line, or a uniform source, this embodiment constructs a distributed external source current 25 unit by unit through seawater layer grid cells 24. This can accurately characterize the complex and spatially varied source distribution generated by non-uniform flow fields such as tsunami wavefronts and tidal eddies. This is one of the key innovations of this invention.

[0025] Step S3: Establishment of a three-dimensional conductive structure model for land and sea like Figure 3 As shown, the three-dimensional conductive structure model 3 of land and sea includes a seawater layer 31, a seabed sedimentary layer 32, a crustal medium 33, a land region 34, a land-sea boundary 35, an observation point 36, and an external current loading region 37. Among them, the seawater layer 31 is located at the top of the model, below which are the seabed sedimentary layer 32 and the crustal medium 33 in sequence; the land region 34 is adjacent to the seawater layer 31, the seabed sedimentary layer 32, and the crustal medium 33 on the same horizontal plane, and its boundary line is the land-sea boundary 35.

[0026] In this embodiment, the seawater layer 31 represents the spatial distribution of seawater and the variation in water layer thickness; the seafloor sedimentary layer 32 represents the high-conductivity or relatively high-conductivity sediments in the upper part of the seafloor; the crustal medium 33 represents the crust below the seafloor sedimentary layer or deeper conductive structures; the land region 34 represents the land portion above sea level; at the land-sea boundary 35 (coastline and land-sea boundary), the conductivity of the seawater layer 31 and the land region 34 is set to have at least an order of magnitude difference to simulate real electrical abrupt changes. The core feature of this model is that at the coastline location, the model simultaneously includes the land region 34 and the seawater layer 31, and explicitly sets a large conductivity difference between the two to simulate real boundary effects. Observation points 36 can be located on land, seabed, or sea surface. The external current loading region 37 is located within the seawater layer 31 and is used to carry the distributed external current constructed in step S2.

[0027] Preferably, during model construction, the grid is refined for coastal areas, shallow sea areas (i.e., areas with a water depth of less than 200 meters), seafloor sedimentary layers, and areas near preset observation points to improve the simulation accuracy of land-sea coupled response. In existing studies, seawater layers, seafloor sedimentary layers, and crustal and subsurface conductive structures have been uniformly incorporated into three-dimensional models and used to simulate land, island, and seafloor observations.

[0028] Step S4: External Current Loading and Three-Dimensional Electromagnetic Response Solution like Figure 4 As shown, the external current loading and response solution structure 4 includes a distributed external current mapping module 41, a seawater layer loading unit 42, and a three-dimensional electromagnetic response solution module 43.

[0029] In this embodiment, the distributed external current 25 constructed in step S2 is mapped to the seawater layer loading unit 42 by the distributed external current mapping module 41. The seawater layer loading unit 42 calculates the electromagnetic response source term of each grid cell based on the loaded distributed external current 25, and inputs the source term to the three-dimensional electromagnetic response solving module 43. The three-dimensional electromagnetic response solving module 43 then solves the three-dimensional electromagnetic response induced by ocean motion. The solution results include at least the electric field response 44 and the magnetic field response 45; at the same time, frequency components or frequency domain solution results 46 can also be obtained.

[0030] Preferably, the solution is implemented using a three-dimensional electromagnetic integral equation forward modeling framework, and heterogeneous source terms are handled in a three-dimensional Cartesian coordinate system. Existing English literature has already explained that relevant three-dimensional electromagnetic induction code uses heterogeneous source terms, three-dimensional Cartesian coordinates, and the MIDM framework for solution. Existing program materials also indicate that complete three-dimensional electromagnetic forward modeling modules, wavenumber domain modules, Green's function modules, and response output modules are available and can serve as the software implementation basis for this method.

[0031] For time-varying ocean motion processes, it is preferable to first convert the ocean motion velocity field to the frequency domain according to the time series, solve for each frequency component separately, and then recover or combine them to obtain the target response. Existing research on tsunami-induced electromagnetism uses the conversion of the velocity field time series to the frequency domain, followed by three-dimensional solution.

[0032] Step S5: Extraction of Multi-type Observation Responses like Figure 5 As shown, the multi-type observation response extraction structure 5 includes land observation point 51, seabed observation point 52, and sea surface observation point 53.

[0033] In this embodiment, simulation results can be extracted from land observation point 51, seabed observation point 52, and sea surface observation point 53, respectively. The extracted results include one or more of the following: electric field response 54, magnetic field response 55, motion impedance response 56, and tipper response 57.

[0034] Specifically, the motion impedance response 56 is preferably obtained by combining the ratios of the horizontal electric field component and the horizontal magnetic field component; the tipper response 57 is preferably obtained by the conversion relationship between the vertical magnetic field and the horizontal magnetic field. By simultaneously providing these different types of responses, this method provides rich information for subsequent analysis and inversion, which is another important innovation of this invention.

[0035] Application scenarios This invention can be widely applied to electromagnetic signal simulation in tsunami warning systems, electromagnetic interference assessment in submarine cable routing planning, background field correction in controlled-source electromagnetic methods (CSEM), and seabed structure imaging using natural source (ocean current, tide) signals. Any simulation method employing the technical approach of "constructing distributed external currents in the ocean's dynamic field unit by unit + coupling solution of a three-dimensional conductive structure model explicitly including the land-sea boundary + extraction of multiple types of observation responses" should be considered to fall within the scope of protection of this invention.

[0036] The above-described embodiments are merely one implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for simulating three-dimensional electromagnetic fields induced by ocean motion, characterized in that, include: S1, Data Acquisition and Mesh Construction: Acquire ocean velocity field data, background geomagnetic field data, and conductive structure parameters of the study area, and establish a seawater layer mesh specifically for electromagnetic simulation; S2, Distributed External Current Construction: The ocean velocity field data is mapped onto the seawater layer grid using a spatial interpolation method; then, based on electromagnetic principles, the seawater conductivity is utilized... σ w Interpolated ocean velocity field v With background geomagnetic field B Coupling relationship between 0: In each seawater layer grid cell, the distributed external current density is independently and discretized to characterize the source distribution generated by the non-uniform ocean motion in space. S3, Construction of a three-dimensional conductive structure model: A multi-dimensional three-dimensional conductive structure model is established. This three-dimensional conductive structure model not only includes the seawater layer and the seabed sediment layer, but also integrates the deeper crustal medium and land area, and explicitly defines the land-sea boundary at the coastline to accurately simulate the step change of conductivity at the land-sea boundary and its influence on the electromagnetic field distribution. S4, Three-dimensional electromagnetic response solution: The distributed external currents calculated in step S2 and distributed in each seawater layer grid cell are accurately loaded onto the corresponding seawater layer grid cells in the three-dimensional conductive structure model constructed in step S3 through spatial mapping technology, as the excitation source of Maxwell's equations, and then the ocean motion-induced three-dimensional electromagnetic response in the entire model area is solved. The response solution adopts the frequency domain solution method. S5, Multi-type observation response extraction: Based on the simulation requirements, extract electric field response and magnetic field response from preset land observation points, seabed observation points or sea surface observation points as the final analysis results.

2. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, The ocean velocity field data can come from tsunami numerical simulations, tidal models, ocean current numerical models, or observational inversion results.

3. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, In step S3, the three-dimensional conductive structure model is constructed by explicitly defining the conductivity step boundary between the seawater layer and the land area at the coastline location.

4. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, The response solution in step S4 is as follows: For a general ocean velocity field, it is solved directly in the time domain; when the ocean velocity field is time-varying data, the velocity field is first converted to the frequency domain according to the time series, and then each frequency component is solved and combined.

5. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, In step S4, the distributed external current is loaded into the corresponding grid cell of the seawater layer through a one-to-one mapping or interpolation mapping between the ocean motion field grid and the electromagnetic simulation grid.

6. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, Step S5 further includes extracting motion impedance-type responses and tipper-type responses to characterize the coupling relationship between the ocean motion-induced electromagnetism and the underground conductive structure at different observation points.

7. The method for simulating three-dimensional electromagnetic fields induced by ocean motion according to claim 1, characterized in that, Specifically, it includes: Step S1: Obtaining data for marine sports fields In step S1, data on ocean motion velocity field, background geomagnetic field, and conductive structure parameters of the study area are acquired. The ocean motion velocity field data includes two-dimensional or three-dimensional velocity field data, and the sources include tsunami propagation numerical simulation, tidal model calculation, ocean current model output, or other ocean dynamics results; the ocean motion velocity field includes at least a horizontal velocity component; the background geomagnetic field data includes the intensity and direction information of the background magnetic field, which is used for subsequent external current construction. Step S2: Construction of Distributed External Current Source The structure of the ocean sports field and distributed external current includes the ocean sports field, background geomagnetic field, seawater layer grid and distributed external current, wherein the seawater layer grid includes each seawater layer grid cell and the distributed external current includes the direction of external current density; First, a seawater layer grid is established based on the ocean motion field and the background geomagnetic field, and the ocean motion velocity field is interpolated into each seawater layer grid cell; then, a distributed external current is constructed cell by cell according to the grid cell, and the direction of its current density is represented by the direction of the external current density. Distributed external current density is determined by seawater conductivity σ w Ocean motion velocity field v and background geomagnetic field B The coupling relationship of 0 is determined; Step S3: Establishment of a three-dimensional conductive structure model for land and sea The three-dimensional conductive structure model of land and sea includes a seawater layer, a seabed sedimentary layer, a crustal medium, a land area, a land-sea boundary, observation points, and an external current loading area. Among them, the seawater layer is located at the top of the model, followed by the seabed sedimentary layer and the crustal medium. The land area is adjacent to the seawater layer, seabed sedimentary layer, and crustal medium on the same horizontal plane, and the boundary line is the land-sea boundary. The seawater layer represents the spatial distribution of seawater and the variation in water layer thickness; the seafloor sedimentary layer represents the high-conductivity or relatively high-conductivity sediments in the upper part of the seafloor; the crustal medium represents the crust below the seafloor sedimentary layer or deeper conductive structures; the land area represents the land portion above sea level; at the land-sea boundary, the conductivity of the seawater layer and the land area is set to have at least one order of magnitude difference to simulate real electrical abrupt changes; at the coastline location, the model simultaneously includes the land area and the seawater layer, and explicitly sets a large conductivity difference between the two to simulate real boundary effects; the observation points are located on land, on the seabed, or at the sea surface; the external current loading area is located within the seawater layer and is used to carry the distributed external current constructed in step S2; During model construction, the grid is refined for coastal areas, shallow sea areas, seabed sedimentary layers, and areas near preset observation points to improve the simulation accuracy of land-sea coupled response. Step S4: External Current Loading and Three-Dimensional Electromagnetic Response Solution The structure for solving the external current loading and response includes a distributed external current mapping module, a seawater layer loading unit, and a three-dimensional electromagnetic response solving module. The distributed external current constructed in step S2 is mapped to the seawater layer loading unit through the distributed external current mapping module. The seawater layer loading unit calculates the electromagnetic response source term of each grid cell based on the loaded distributed external current, and inputs the source term to the three-dimensional electromagnetic response solving module. The three-dimensional electromagnetic response solving module then solves the three-dimensional electromagnetic response induced by ocean motion. The solution results include electric field response and magnetic field response, as well as frequency components or frequency domain solution results. The solution is achieved using a forward modeling framework of three-dimensional electromagnetic integral equations, and heterogeneous source terms are handled in a three-dimensional Cartesian coordinate system. For time-varying ocean motion processes, the ocean motion velocity field is first converted to the frequency domain according to the time series, and each frequency component is solved separately. Then, the target response is recovered or combined. Step S5: Extraction of Multi-type Observation Responses The multi-type observation response extraction structure includes land observation points, seabed observation points, and sea surface observation points; Simulation results were extracted from land observation points, seabed observation points, and sea surface observation points; the extracted results included one or more of the following: electric field response, magnetic field response, kinematic impedance response, and tipper response; Among them, the motion impedance type response is obtained by combining the ratio of the horizontal electric field component to the horizontal magnetic field component; the tipper type response is obtained by the conversion relationship between the vertical magnetic field and the horizontal magnetic field.

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