A Joint Simulation Method for Magnetic Anomaly Characteristics of Underwater Targets

Abstract

The present invention discloses a joint simulation method for the magnetic anomaly characteristics of underwater targets, belonging to the technical field of underwater target detection, and comprising the following steps: Step S1: Create a geometric model of an underwater target in COMSOL Multiphysics; Step S2: Establish a computational domain to form a union with the geometric model of the underwater target; Step S3: Set the heading angle, speed, and diving depth of the geometric model of the underwater target; Step S4: Set the material and physical field properties; Step S5: Perform mesh division on the model; Step S6: Add a study and calculate and plot; Step S7: Use MATLAB to call the COMSOL model; Step S8: Input a set of parameters according to actual needs; Step S9: Solve the model and display the spatio-temporal distribution of the magnetic anomaly field; Step S10: Perform data processing and analysis according to the simulation results; In the present invention, under Windows, with MATLAB language and MATLAB APP Designer as tools, the simulation results in one-dimensional, two-dimensional, and three-dimensional views are visually presented.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater target detection, and particularly relates to a joint simulation method for magnetic anomaly characteristics of underwater targets. Background Art

[0002] The magnetization of the geomagnetic field causes many substances to exhibit magnetic characteristics and generate magnetic fields. When the magnetic field of an object is superimposed on the geomagnetic field, the geomagnetic field will change to a certain extent, forming a magnetic anomaly phenomenon.

[0003] In order to accurately evaluate the magnetic anomaly characteristics of a target in an actual situation, it is necessary to deeply model and analyze the spatio-temporal characteristics of the target magnetic anomaly field by combining a magnetic anomaly model and various changing factors, so as to be more effectively applied to fields such as assisted airborne magnetic exploration, magnetic navigation, and ship degaussing.

[0004] Currently, the mainstream magnetic field finite element analysis software includes ANSYS, FLUX3D, COMSOL, etc. The reasons for jointly using MATLAB and COMSOL for simulation are as follows:

[0005] MATLAB three-dimensional dynamic graphics have special limitations and cannot implement user-defined arbitrary three-dimensional shape models. COMSOL not only has rich CAD modeling tools but also supports the import of third-party models, meeting the requirements for establishing three-dimensional dynamic models in the simulation system;

[0006] However, MATLAB is an interpreted language, which occupies a lot of computer resources and has low code running efficiency. COMSOL, a simulation software based on finite element analysis, is a large-scale general-purpose CAE software with powerful solving and post-processing functions and is widely used in the field of finite element simulation;

[0007] However, COMSOL has weak data processing capabilities, while MATLAB has significant advantages in data processing. Moreover, MATLAB APPDesigner can easily create application programs, and users can write visual data analysis application programs according to their usage requirements. Therefore, a joint simulation method for magnetic anomaly characteristics of underwater targets is needed to solve the above problems. Summary of the Invention

[0008] The object of the present invention is to provide a joint simulation method for the magnetic anomaly characteristics of underwater targets, extract the magnetic field simulation function of COMSOL, use MATLAB APP Designer to design the simulation interface for the magnetic anomaly field characteristics of underwater targets, give full play to the advantages of MATLAB and COMSOL, realize the data transfer between COMSOL and MATLAB, avoid the complicated model establishment, reduce the actual operation threshold, and through the interaction process, obtain the spatio-temporal characteristics of the magnetic anomaly field of underwater targets under different parameters more simply and intuitively while ensuring the simulation accuracy, thereby improving the efficiency of the magnetic detector for positioning and identifying underwater targets.

[0009] To achieve the above object, the present invention provides the following technical solution: A joint simulation method for the magnetic anomaly characteristics of underwater targets, comprising the following steps:

[0010] Step S1: Create a geometric model of an underwater target in COMSOL Multiphysics;

[0011] Select three dimensions in the model wizard, and under the physics interface, select the "Magnetic field, no current" physics field in the AC / DC module; create a simplified model of an underwater target, where the stern is a frustum shell, and the sail is a solid cylinder stretched from an ellipse to simulate the asymmetric factors in the vertical direction of the target;

[0012] Step S2: Establish a computational domain to form a union with the geometric model of the underwater target;

[0013] Step S3: Set the heading angle, speed, and diving depth of the geometric model of the underwater target;

[0014] α is the target heading angle, that is, the angle of rotation of the carrier target relative to the detection coordinate system around the z-axis. The magnetic field intensity generated by a target with a magnetic moment of M at a spatial field point (x, y, z) is: where the modulus of the vector r is the distance from the calculation field point to the target center, and the direction of r is from the target center to the calculation field point. The speed is expressed as the speed at which the target moves along a certain route at a certain heading angle, and the diving depth is expressed as the vertical distance of the target relative to the sea level;

[0015] Step S4: Set the material and physical field properties;

[0016] Step S5: Mesh the model;

[0017] The middle part of the underwater target model is divided by the mapping function, and the bow, stern, and sail are divided by free triangular meshes; the computational domain is divided by free tetrahedral meshes; the mesh accuracy is selected as "user-defined", and the mesh element parameters of the maximum / minimum element size are set;

[0018] Step S6: Add research and calculate the drawing;

[0019] Set the solver. Since the magnetic anomaly field of the underwater target is a static magnetic field, the "steady state" method is selected for calculation; the background magnetic field is the geomagnetic field H b , then the expression of the magnetic field is: H = -▽V m +H b ; where V m is the scalar magnetic potential; the magnetic field constitutive relation is: B = μ 0 μ r H; the underwater target is magnetized under the action of the geomagnetic field, then the relationship between its magnetic moment M and the magnetic field is: B = μ 0 (H + M); considering the influence of the target shell thickness d, then: n.(B 1 -B 2 ) = -▽ t d(μ 0 μ r ▽ t V m );

[0020] Step S7: Use MATLAB to call the COMSOL model;

[0021] Step S8: Input a set of parameters according to actual needs;

[0022] Step S9: Solve the model and display the spatio-temporal distribution of the magnetic anomaly field;

[0023] Step S10: Perform data processing and analysis according to the simulation results.

[0024] As a preferred solution, in step S2, a calculation domain is drawn around the geometric model of the underwater target, which is divided into an upper air domain and a lower seawater domain. The model is placed inside the seawater domain, and a union will be automatically formed after all are constructed.

[0025] As a preferred solution, in step S4, the materials of the underwater target model and the calculation domain are selected from the corresponding materials in the built-in material library, and the relative magnetic permeability and the target magnetic shielding thickness are set;

[0026] The geomagnetic field intensities along the x, y, and z components can be respectively expressed as

[0027] Set the total geomagnetic field intensity B E = 50000 nT, the magnetic inclination I = 28°, and the magnetic declination D = -2°.

[0028] As a preferred solution, in step S7, MATLAB APP Designer is used to design the visualization simulation system, including a parameter setting module, a model establishment module, a result display module, and a data processing module, and then the real-time connection between COMSOL and MATLAB is realized through Livelink for MATLAB;

[0029] In step S8, the parameter setting module realizes the setting of geometric parameters, motion parameters, and detection height, and the user can input a set of parameters according to actual needs.

[0030] As a preferred solution, in step S9, the result display module can select the detection position, detection path, and detection plane. Click the "Plot" button, and the system will transfer the set input parameters to MATLAB, automatically run the solver according to the parameters input in step S8, and perform numerical solution.

[0031] As a preferred solution, in step S10, the data processing module automatically determines the detection possibility according to the magnetic detector resolution input in step S8 and the maximum value of the magnetic anomaly field calculated in step S9: if the result shows "Yes", it means the target can be detected, and if it shows "No", it means the target cannot be detected, thus completing the entire simulation process.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] In the present invention, under Windows, using MATLAB language and MATLAB APP Designer as tools, only by selecting the corresponding options and inputting key parameters, the rapid design of the method for analyzing the characteristics of the magnetic anomaly field of underwater targets can be realized, and the simulation results in one-dimensional, two-dimensional, and three-dimensional views can be visually presented;

[0034] The present invention provides a new idea for using computer simulation software, expands the application scope of electromagnetic simulation software such as COMSOL, realizes the data transfer between COMSOL and MATLAB, avoids the cumbersome model establishment, reduces the actual operation threshold, improves the analysis efficiency of the spatio-temporal characteristics of the magnetic anomaly field of underwater targets, and can be applied in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the flowchart of the joint simulation method for the magnetic anomaly characteristics of underwater targets provided by the present invention;

[0036] Figure 2 is the geometric model diagram of the underwater target provided by the present invention;

[0037] Figure 3It is the combined model diagram of the underwater target and the computational domain provided by the present invention;

[0038] Figure 4 It is the schematic diagram of the relationship between the heading of the underwater target model and the detection coordinate system provided by the present invention;

[0039] Figure 5 It is the schematic diagram of the relationship between the geomagnetic coordinate system and the detection coordinate system provided by the present invention;

[0040] Figure 6 It is the mesh division diagram of the underwater target model provided by the present invention;

[0041] Figure 7 It is the combined simulation interface diagram of MATLAB and COMSOL provided by the present invention;

[0042] Figure 8 It is the combined model diagram of the underwater target geometric model and the computational domain provided by the present invention;

[0043] Figure 9 It is the time-domain characteristic diagram of the total magnetic anomaly field at the detection position provided by the present invention;

[0044] Figure 10 It is the time-domain characteristic diagram of the longitudinal (x) magnetic anomaly field at the detection position provided by the present invention;

[0045] Figure 11 It is the time-domain characteristic diagram of the transverse (y) magnetic anomaly field at the detection position provided by the present invention;

[0046] Figure 12 It is the time-domain characteristic diagram of the vertical (z) magnetic anomaly field at the detection position provided by the present invention;

[0047] Figure 13 It is the change trend diagram of the total magnetic anomaly field on the detection path provided by the present invention;

[0048] Figure 14 It is the change trend diagram of the longitudinal (x) magnetic anomaly field on the detection path provided by the present invention;

[0049] Figure 15 It is the change trend diagram of the transverse (y) magnetic anomaly field on the detection path provided by the present invention;

[0050] Figure 16 It is the change trend diagram of the vertical (z) magnetic anomaly field on the detection path provided by the present invention;

[0051] Figure 17 It is the distribution cloud diagram of the total magnetic anomaly field on the detection plane provided by the present invention;

[0052] Figure 18It is the contour map of the longitudinal (x) magnetic anomaly field distribution on the detection plane provided by the present invention;

[0053] Figure 19 It is the contour map of the transverse (y) magnetic anomaly field distribution on the detection plane provided by the present invention;

[0054] Figure 20 It is the contour map of the vertical (z) magnetic anomaly field distribution on the detection plane provided by the present invention;

[0055] Figure 21 It is the target geometric parameter setting table provided by the present invention;

[0056] Figure 22 It is the target motion parameter setting table provided by the present invention;

[0057] Figure 23 It is the computational domain geometric parameter setting table provided by the present invention;

[0058] Figure 24 It is the grid cell parameter setting table provided by the present invention;

[0059] Figure 25 It is the input parameter setting table provided by the present invention. Detailed implementation manners

[0060] The present invention will be further described below in conjunction with embodiments.

[0061] The following embodiments are used to illustrate the present invention, but cannot be used to limit the protection scope of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention all belong to the scope required to be protected by the present invention.

[0062] Please refer to Figures 1 - 25 , the present invention provides a joint simulation method for underwater target magnetic anomaly characteristics, including the following steps: Step S1: Create an underwater target geometric model in COMSOL Multiphysics;

[0063] Open the COMSOL Multiphysics software, select the model wizard, "3D" spatial dimension, and "magnetic field, no current" physical field;

[0064] As Figure 2 shown, create a simplified model of an underwater target; the stern part is a frustum shell, and the sail is a solid cylinder stretched from an ellipse to simulate the vertical asymmetry factor of the target;

[0065] As Figure 21 shown, it is a set of geometric parameters of the underwater target model.

[0066] Step S2: Establish a computational domain and form a union with the underwater target geometric model;

[0067] As Figure 3 shown, draw the computational domain around the underwater target geometric model, divide it into the upper air domain and the lower seawater domain, place the model inside the seawater domain, and a union will be automatically formed after all are constructed;

[0068] As Figure 23 shown, it is a set of geometric parameters of the computational domain.

[0069] Step S3: Set the heading angle, speed, and diving depth of the underwater target geometric model;

[0070] As Figure 4 shown, α is the target heading angle, which is the angle of rotation of the carrier target relative to the detection coordinate system around the z-axis. The magnetic field intensity generated by a target with a magnetic moment of M at the spatial field point (x, y, z) is: where the modulus of the vector r is the distance from the calculation field point to the target center, and the direction of r is from the target center to the calculation field point. The speed is the speed at which the target moves along a certain route at a certain heading angle, and the diving depth is the vertical distance of the target relative to the sea level;

[0071] As Figure 22 shown, it is a set of motion parameters of the underwater target;

[0072] Step S4: Set the material and physical field properties;

[0073] The material of the underwater target model uses the steel material in the built-in material library, with a relative magnetic permeability of 4000, a magnetic shielding thickness of 60 mm, and the material type is selected as "solid"; the relative magnetic permeabilities of the air domain and the seawater domain are 1 and 0.99999 respectively;

[0074] As Figure 5 shown, the relationship between the direction of the geomagnetic field and the detection coordinate system: Assume that the positive direction of the x-axis of the detection coordinate system is due north geographically, the positive direction of the y-axis is due west geographically, and the z-axis is vertically upward; B E is the geomagnetic field, B Exy is the projection of B E on the xy plane; the angle between B Exy and the due north direction is the magnetic declination D, with eastward deviation being positive; the angle between B E and B E is the magnetic inclination I, with downward inclination being positive;

[0075] The geomagnetic field intensities along the x, y, and z components can be respectively expressed as

[0076] Set the total geomagnetic field intensity B E= 50000 nT, magnetic dip angle I = 28°, magnetic declination D = -2°.

[0077] Step S5: Conduct mesh generation for the model;

[0078] The middle part of the underwater target model is divided using the mapping function, and the bow, stern, and fairwater are divided using free triangular meshes; the computational domain is divided using free tetrahedral meshes; the mesh accuracy is selected as "user-defined";

[0079] As Figure 24 shown, it is a set of mesh element parameter settings;

[0080] As Figure 6 shown, the color bar on the right represents the range of the maximum angle. The closer its value is to 1, the better the mesh quality. The statistical information shows that a total of 6588323 domain elements, 95385 boundary elements, and 1811 edge elements are divided. The minimum element quality is 0.1858. Therefore, the mesh quality is good.

[0081] Step S6: Add a study and calculate and plot;

[0082] Set the solver. Since the magnetic anomaly field of the underwater target is a static magnetic field, the "steady state" method is selected for calculation. The background magnetic field is the geomagnetic field H b , then the expression of the magnetic field is: H = -▽v m + H b , where V m is the scalar magnetic potential; the magnetic field constitutive relation is: B = μ 0 μ r H;

[0083] The underwater target is magnetized under the action of the geomagnetic field, then the relationship between its magnetic moment M and the magnetic field is: B = μ 0 (H + M); Considering the influence of the target shell thickness d, then: n.(B 1 - B 2 ) = -▽ t d(μ 0 μ r ▽ t V m) ;

[0084] Define the detection position, take the point directly above the target center at 50 m above the sea surface; define the detection path, take the straight line along the x direction at the middle of the section at 50 m above the sea surface; define the detection plane, take the section perpendicular to the z axis at 50 m above the sea surface;

[0085] Add one-dimensional and two-dimensional plotting groups in the results column of the main screen bar, and generate and save the total magnetic anomaly field and various vector field distribution maps of the target at the detection position, detection path, and detection plane.

[0086] Step S7: Use MATLAB to call the COMSOL model;

[0087] As Figure 7 shown, use MATLAB APP Designer to design a visualization simulation system, including a parameter setting module, a model establishment module, a result display module, and a data processing module, and then realize the real-time connection between COMSOL and MATLAB through Livelink for MATLAB.

[0088] Step S8: Input a set of parameters according to actual needs;

[0089] The parameter setting module realizes the settings of geometric parameters, motion parameters, detection height, etc.; according to the parameter settings in Steps S1 - S6;

[0090] As Figure 25 shown, it is a set of parameters default input in the simulation interface.

[0091] As Figure 8 shown, after inputting the above parameters and clicking the "Display" button in the model establishment module, a combined model diagram of the underwater target geometric model and the calculation domain can be automatically drawn in the coordinate area.

[0092] Step S9: Solve the model and display the spatio-temporal distribution of the magnetic anomaly field;

[0093] As Figure 7 shown, the result display module can select the detection position, detection path, and detection plane. Click the "Plot" button, and the system will transfer the set input parameters to MATLAB, automatically run the solver according to the parameters input in Step S8, and perform numerical solution; each method includes a function to save pictures of the total magnetic anomaly field and distribution diagrams of each vector field for simulation operators to view;

[0094] As Figures 9 to 12 shown, it is a picture saved when selecting the detection position;

[0095] As Figures 13 to 16 shown, it is a picture saved when selecting the detection path;

[0096] As Figures 17 to 20 shown, it is a picture saved when selecting the detection plane.

[0097] Step S10: Perform data processing and analysis according to the simulation results;

[0098] The data processing module automatically determines the detection possibility according to the magnetic detector resolution input in Step S8 and the maximum value of the magnetic anomaly field calculated in Step S9: the result shows "Yes", indicating that the magnetic detector can detect the target, thus completing the entire simulation process;

[0099] Through the above joint simulation method for the magnetic anomaly characteristics of underwater targets, on the one hand, this method uses the Matlab language and MATLAB APP Designer as tools. Only by selecting the corresponding options and inputting the key parameters can it quickly design the analysis method for the magnetic anomaly field characteristics of underwater targets and visually present the simulation results in one-dimensional, two-dimensional, and three-dimensional views. On the other hand, it provides a new idea for using computer simulation software, expands the application scope of electromagnetic simulation software such as COMSOL, realizes the data transfer between COMSOL and MATLAB, improves the analysis efficiency of the spatio-temporal characteristics of the magnetic anomaly field of underwater targets, and can be applied in practical engineering.

[0100] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A joint simulation method for underwater target magnetic anomaly characteristics, characterized by: The following steps are involved: Step S1: Create an underwater target geometry model in COMSOL Multiphysics; Select 3D in the Model Wizard and select the "Magnetic Field, No Current" physics field in the AC / DC module under the Physics Interface. Create a simplified model of an underwater target, in which the stern is a truncated cone shell and the enclosure is a solid cylinder formed by stretching an ellipse to simulate the vertical asymmetry of the target. Step S2: Establish a computational domain to form a union with the underwater target geometric model; Step S3: setting the heading angle, speed and diving depth of the underwater target geometric model; α is the target heading angle, that is, the angle at which the carrier target rotates around the z-axis relative to the detection coordinate system. The magnetic field intensity generated by the target with a magnetic moment of M at the spatial field point (x, y, z) is: The magnitude of the vector r is the distance between the calculation field point and the target center, and the direction of r is from the target center to the calculation field point. The speed is expressed as the speed of the target moving along a certain route at a certain heading angle, and the diving depth is expressed as the vertical distance of the target relative to the sea level; Step S4: Setting material and physical field properties; Step S5: meshing the model; The middle part of the underwater target model is divided by the mapping function, and the bow, stern and hull are divided by free triangle mesh; the calculation domain is divided by free tetrahedral mesh; the mesh accuracy is selected as "user defined" to set the mesh unit parameters of the maximum / minimum unit size; Step S6: Add study and calculate drawing; Set up the solver. The underwater target magnetic anomaly field is a static magnetic field, so the "steady state" method is selected for calculation; the background magnetic field is the geomagnetic field H b , then the expression of the magnetic field is: Among them, V m is the scalar magnetic potential; the constitutive relation of magnetic field is: B=μ0μ r H; Underwater targets are magnetized under the action of the geomagnetic field, and the relationship between its magnetic moment M and magnetic field is: B = μ0 (H + M); Considering the influence of the target shell thickness d, then: Step S7: Using MATLAB to call the COMSOL model; Step S8: input a set of parameters according to actual needs; Step S9: solving the model to display the spatial and temporal distribution of the magnetic anomaly field; Step S10: Perform data processing and analysis according to the simulation results.

2. The method for joint simulation of underwater target magnetic anomaly characteristics according to claim 1, characterized in that: In step S2, a calculation domain is drawn outside the underwater target geometric model, which is divided into an upper air domain and a lower sea water domain. The model is placed inside the sea water domain, and a union is automatically formed after all the constructions are completed.

3. The method for joint simulation of underwater target magnetic anomaly characteristics according to claim 1, characterized in that: In step S4, the materials of the underwater target model and the calculation domain adopt the corresponding materials in the built-in material library, and the relative magnetic permeability and the target magnetic shielding thickness are set; The geomagnetic field strength along the x, y, and z components can be expressed as Set the total strength of the geomagnetic field B E =50000nT, magnetic inclination I=28°, magnetic declination D=-2°.

4. The method for joint simulation of underwater target magnetic anomaly characteristics according to claim 1, characterized in that: In step S7, MATLAB APP Designer is used to design a visual simulation system, including a parameter setting module, a model building module, a result display module and a data processing module, and then Livelink for MATLAB is used to realize the real-time connection between COMSOL and MATLAB; In step S8, the parameter setting module implements the setting of geometric parameters, motion parameters and detection height, and the user can input a set of parameters according to actual needs.

5. The method for joint simulation of underwater target magnetic anomaly characteristics according to claim 1, characterized in that: In step S9, the result display module can select the detection position, detection path, and detection plane. Click the "Draw" button, and the system will pass the set input parameters to MATLAB, and automatically run the solver according to the parameters entered in step S8 to perform numerical solution.

6. The method for joint simulation of underwater target magnetic anomaly characteristics according to claim 1, characterized in that: In step S10, the data processing module automatically determines the detection possibility based on the resolution of the magnetometer input in step S8 and the maximum value of the magnetic anomaly field calculated in step S9: if the result shows "yes", it means that the target can be detected, and if "no", it means that the target cannot be detected, thereby completing the entire simulation process.

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