Ship winding degaussing current solving method based on gradient tensor

Abstract

The invention belongs to the technical field of degaussing, and relates to a ship winding degaussing current solving method based on a gradient tensor, which comprises the following steps: acquiring the magnetic gradient tensor of a plane ship when coils are not electrified; respectively performing simulation electrification on the winding coils to obtain the magnetic gradient tensor of the electrified measurement plane; and calculating an efficiency matrix of the magnetic gradient tensor excited by the unit current. The gradient of the geomagnetic field is extremely small, direct detection of the magnetic gradient tensor of the ship and the electrified coil can better reflect the magnetic characteristics of the ship and the coil compared with detection of a magnetic vector, and better resolution is achieved for magnetic field changes caused by magnetic anomalies; under the motion platform, the magnetic gradient tensor is insensitive to the attitude angle error, and more accurate detection data can be obtained; in addition, the gradient tensor is weak in response to time-varying geomagnetic disturbance, and has higher anti-interference capability. Therefore, according to the method, the accuracy of ship magnetic field modeling and degaussing current calculation is improved, and the magnetic stealth performance of a ship facing high-sensitivity magnetic gradient detection equipment is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of demagnetization technology, specifically relating to a method for solving the demagnetization current of ship windings based on gradient tensors. Background Technology

[0002] In modern naval warfare, ships are typically made of magnetic materials such as steel. These materials possess residual magnetic fields and can be magnetized by the Earth's magnetic field, generating induced magnetic fields. To prevent enemy forces from detecting ships using magnetic detection technology, demagnetization can be performed to eliminate or weaken the ship's own magnetic field, thereby reducing the likelihood of detection by magnetic detection equipment and magnetic mines, and improving the ship's survivability and stealth in combat.

[0003] Traditional ship degaussing methods include two energizing approaches: direct-flow degaussing and winding degaussing. Winding degaussing is the more commonly used method, achieved by winding degaussing coils around the ship's external structure. These coils are typically wound around the main structure, forming loops or spirals in the X, Y, and Z directions to generate opposing magnetic fields that counteract the ship's magnetic field. This method allows for adjustments to the coil layout and number to optimize degaussing effectiveness in different environments. Winding degaussing can specifically compensate for magnetic fields in the X, Y, and Z directions and can be customized for different types of ships, such as small frigates and supply ships, demonstrating excellent adaptability.

[0004] In recent years, winding-type degaussing systems have commonly adopted methods for calculating compensation current based on magnetic vector measurement results. However, this method suffers from the following problems during magnetic measurements: First, the measurement data includes background geomagnetic field components, making it difficult to accurately characterize the ship's own magnetic properties. Second, magnetic vector measurements on moving platforms are easily affected by instrument attitude angles; magnetic vector measurements are also susceptible to time-varying geomagnetic fields, resulting in poor anti-interference capabilities. Currently, mines and torpedoes increasingly use magnetic gradient sensors to capture even minute magnetic field changes. Therefore, there is an urgent need to develop a method for calculating ship winding degaussing current based on gradient tensors to address the problems associated with the aforementioned magnetic vector methods. Summary of the Invention

[0005] The purpose of this invention is to provide a method for solving the demagnetizing current of ship windings based on the gradient tensor. This method uses the magnetic gradient tensor value of the measurement plane to solve the demagnetizing current, thereby solving the problem of providing a better magnetic gradient tensor demagnetizing effect while reducing the number of measurement planes.

[0006] This invention is achieved through the following technical solution:

[0007] A method for solving the demagnetizing current of ship windings based on gradient tensors includes the following steps:

[0008] A. When all the winding coils on the ship are not energized, a measuring plane is set above the ship to obtain the magnetic gradient tensor data of all measuring points on the measuring plane and their corresponding position information.

[0009] B. Simulate energizing the winding coils on the ship to obtain the magnetic gradient tensor values ​​of all measuring points on the measuring plane after each energization.

[0010] C. Calculate the efficiency matrix K of the magnetic gradient tensor excited by unit current;

[0011] D. Calculate the final demagnetizing current value using the efficiency matrix K.

[0012] Further, in step A, the magnetic gradient tensor data and their corresponding position information of all measuring points on the planar ship are measured, denoted as... The magnetic gradient tensor G is defined as the gradient of the three components of the magnetic field along the three coordinate axes of a rectangular coordinate system, and has nine components. , expressed as formula (1):

[0013]

[0014] In a source-free space, the divergence and curl of the magnetic field are both zero, that is:

[0015]

[0016] The magnetic gradient tensor G is represented by five independent components:

[0017]

[0018] Measured values Let be a column vector of 5n rows and 1 column. Assuming there are n measurement points in the measurement plane, then... It is composed of n column vectors concatenated; where each column vector is a 5x1 column matrix converted from the magnetic gradient tensor invariant of each point; the measured value It includes the following components:

[0019]

[0020] in, This refers to the induced magnetic gradient tensor of a ship excited by the Earth's magnetic field. Let be the ship's residual magnetic gradient tensor. The Earth's magnetic field can be approximated as a uniform field. The magnetic gradient tensor of a uniform field is approximately zero, therefore the measured value... It can be used alone to describe the magnetic characteristics of a ship.

[0021] Further, in step B, the simulated energizing process is as follows: a unit current is sequentially applied to each of the nine winding coils. Each time a simulated power-on is performed, the magnetic gradient tensor data and corresponding position information of all measuring points on the measuring plane are acquired. The position information is the same as that obtained in the first step. Assuming the coil number is denoted as m, the magnetic gradient tensor value of the measuring plane after each power-on is denoted as... The measured value at this time It includes the following components:

[0022]

[0023] in, This refers to the induced magnetic gradient tensor of a ship excited by the Earth's magnetic field. This refers to the induced magnetic gradient tensor of the ship caused by the magnetic field of the coil. For the ship's residual magnetic gradient tensor, Let be the magnetic gradient tensor excited by the coil; subtracting equation (4) from equation (5) yields:

[0024]

[0025] Further, in step C, the efficiency matrix K of the magnetic gradient tensor excited by unit current is calculated by formula (7); in the following formula, matrix K describes the magnitude of the five independent components of the magnetic gradient tensor excited by each coil when unit current is passed through the nine wires in the model respectively.

[0026]

[0027] The right side of formula (7) Equation (6) represents this, therefore, equation (7) can be simplified to:

[0028]

[0029] Further, step D specifically includes:

[0030] The left side of formula (9) represents the total magnetic gradient tensor excited by the coil in the model, and the right side represents the total magnetic gradient tensor generated by the ship being excited by the Earth's magnetic field and the coil's magnetic field. Formula (9) is as follows:

[0031] In the modeling, the ship is a linear magnetization model, and the induced magnetization model is selected as follows: Where H is the background field intensity, It is the vacuum permeability. It is the magnetic permeability of the ship material; formula (9) can be simplified to:

[0032]

[0033] In the formula, , All values ​​are measured values. The demagnetizing current obtained based on the magnetic gradient tensor is: .

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. The demagnetization effect of the five independent components of the ship after demagnetization is better than that of the magnetic vector-based demagnetization method. Furthermore, the three components of the magnetic field after demagnetization are close to those of the demagnetization method based on the three components of the magnetic field, and can also have a good elimination effect on the three components of the magnetic field.

[0036] 2. Previous winding-type demagnetization methods only use the magnetic vector to be eliminated as the measurement value and the object to be eliminated. This invention uses the magnetic gradient tensor as the measurement value and the object to be eliminated, which can obtain a better magnetic gradient tensor demagnetization effect while reducing the number of measurement planes. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the ship and winding coil viewed from an oblique angle, illustrating the demagnetizing current solution method for ship windings based on gradient tensors according to the present invention.

[0039] Figure 2 This is a schematic diagram of the ship and winding coil viewed from below, representing a method for solving the demagnetizing current of ship windings based on gradient tensors according to the present invention.

[0040] Figure 3 This is a schematic diagram of the winding coil energizing direction in a method for solving the demagnetizing current of ship windings based on gradient tensor according to the present invention.

[0041] Figure 4 This is a simplified demagnetization model and experimental implementation diagram of a method for solving the demagnetization current of ship windings based on gradient tensor according to the present invention.

[0042] Figure 5 This is a digital prototype of a simulation model of a method for solving the demagnetizing current of ship windings based on gradient tensor according to the present invention.

[0043] Figure 6 This is a flowchart illustrating the steps of a method for solving the demagnetizing current of ship windings based on gradient tensor according to the present invention.

[0044] In the diagram: 1. Deck 2. Engine 3. Stern 4. Keel I 5. Keel II 6. Keel III 7. Keel IV 8. Keel V 9. Bow 10. Sideplate 11. Bottom 12. Transverse Winding Coil I 13. Transverse Winding Coil II 14. Transverse Winding Coil III 15. Transverse Winding Coil IV 16. Transverse Winding Coil V 17. Longitudinal Winding Coil I 18. Longitudinal Winding Coil II 19. Vertical Winding Coil I 20. Vertical Winding Coil II 21. Measurement Plane 22. Ship 24. Horizontal Plane 25. Airspace 26. Water Area 27. Projection of Measurement Plane onto the Water Surface Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments:

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0047] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0048] This invention provides a method for solving the demagnetizing current of ship windings based on gradient tensors. Since the gradient of the Earth's magnetic field is extremely small, directly detecting the magnetic gradient tensor of the ship and its energized coils better reflects the magnetic characteristics of the ship and coils than detecting the magnetic vector, and has better resolution of magnetic field changes caused by magnetic anomalies. Under moving platforms, the magnetic gradient tensor is insensitive to attitude angle errors, allowing for more accurate detection data. Furthermore, the gradient tensor has a weak response to time-varying geomagnetic disturbances, exhibiting stronger anti-interference capabilities. Therefore, this method not only improves the accuracy of ship magnetic field modeling and demagnetizing current calculation, but also enhances the ship's magnetic stealth performance when facing highly sensitive magnetic gradient detection equipment. Figure 6 As shown, this method specifically includes the following steps:

[0049] The first step is to set up a measurement plane above the ship when all the winding coils on the ship are de-energized, and then acquire the magnetic gradient tensor data and corresponding position information of all measurement points on the measurement plane, denoted as . The magnetic gradient tensor G is defined as the gradient of the three components of the magnetic field along the three coordinate axes of a Cartesian coordinate system, and has nine components. It can be expressed as formula (1):

[0050]

[0051] In a source-free space, the divergence and curl of the magnetic field are both zero, that is:

[0052]

[0053] Therefore, the magnetic gradient tensor G can be represented by five independent components:

[0054]

[0055] Measured values Let the vector be a column vector (5n rows and 1 column). Assuming there are n measurement points in the measurement plane, then... It is composed of n column vectors concatenated. Each column vector represents the magnetic gradient tensor invariant at each point, transformed into a column matrix (5 rows, 1 column). The measured values ​​at this point... It includes the following components:

[0056]

[0057] in, This refers to the induced magnetic gradient tensor of a ship excited by the Earth's magnetic field. Let be the remanent magnetic gradient tensor of the ship. Since the Earth's magnetic field can be approximated as a uniform field, and the magnetic gradient tensor of a uniform field is approximately zero, the measured value... It can be used alone to describe the magnetic characteristics of a ship.

[0058] The second step involves simulating energizing the winding coils on the ship to obtain the magnetic gradient tensor values ​​at all measuring points on the measurement plane after each energization. For example... Figure 1 As shown, this is an embodiment of the invention showing a demagnetized ship and a winding coil installed on the ship. The magnitude of the direct current flowing through the winding coil can be adjusted to generate a magnetic field in space to compensate for the induced magnetic field and residual magnetic field of the ship. Figure 2 As shown, this embodiment includes nine winding coils: transverse winding coils I12, II13, III14, IV15, and V16; longitudinal winding coils I17 and II18; and vertical winding coils I19 and II20. The direction of direct current flowing through each coil is indicated by the arrows in the diagram.

[0059] The simulated energizing process is as follows: a unit current is sequentially applied to the nine winding coils. Each time a simulated power-on is applied, the magnetic gradient tensor data and corresponding position information of all measuring points on the measuring plane are acquired. This position information is the same as the position information obtained in the first step. Assuming the coil number is denoted as m, and the magnetic gradient tensor value of the measuring plane after each power-on is denoted as... The measured value at this time It includes the following components:

[0060]

[0061] in, This refers to the induced magnetic gradient tensor of a ship excited by the Earth's magnetic field. This refers to the induced magnetic gradient tensor of the ship caused by the magnetic field of the coil. For the ship's residual magnetic gradient tensor, Let be the magnetic gradient tensor excited by the coil. Subtracting equation (4) from equation (5) yields:

[0062]

[0063] The third step is to calculate the efficiency matrix K of the magnetic gradient tensor excited by unit current using formula (7). In the following formula, matrix K describes the magnitude of the five independent components of the magnetic gradient tensor excited by each coil when a unit current is passed through each of the nine wires in the model.

[0064]

[0065] The right side of formula (7) This can be expressed by formula (6), therefore, formula (7) can be simplified to:

[0066]

[0067] The fourth step is to calculate the final demagnetizing current value using the efficiency matrix K.

[0068] The left side of formula (9) represents the total magnetic gradient tensor excited by the coil in the model, and the right side represents the total magnetic gradient tensor generated by the ship being excited by the Earth's magnetic field and the coil's magnetic field. Formula (9) is as follows:

[0069]

[0070] In this invention, the background field size is insufficient to excite a nonlinear response in the magnetic material; therefore, the ship is modeled as a linear magnetization model, and the induced magnetization model is selected as follows: Where H is the background field intensity, It is the vacuum permeability. It is the magnetic permeability of the ship's material. Finally, formula (9) can be simplified to:

[0071]

[0072] In the formula, , All values ​​are measured. Finally, the demagnetizing current based on the magnetic gradient tensor is obtained as follows:

[0073] Similarly, the method for solving the demagnetizing current based on the three components of the magnetic field includes the following steps:

[0074] First, when none of the coils are energized, acquire the three components of the magnetic field and the corresponding position information on the same measuring plane as this invention, denoted as... (3n rows, 1 column), assuming there are n measurement points in the measurement plane, then It is composed of n column vectors. Each column vector represents the three components of the magnetic field at each point, converted into a column matrix (3 rows and 1 column). It contains the following components:

[0075]

[0076] in, It is the Earth's magnetic field. The induced magnetic field generated by the Earth's magnetic field on a ship. The remaining magnetic field of the ship.

[0077] Next, a unit current is sequentially applied to each of the nine winding coils. Each time a simulation is applied, the magnetic field three-component data and their corresponding position information of all measuring points on the measuring plane are acquired. This position information is the same as the position information obtained in the first step. Assuming the coil number is denoted as m, and the magnetic field three-component values ​​of the measuring plane after each application of power are denoted as... The measured value at this time It includes the following components:

[0078]

[0079] in, The induced magnetic field generated by the magnetic field of the coil on the ship. The magnetic field generated by the coil. Subtracting formula (11) from formula (12) yields:

[0080]

[0081] Next, similar to the method of this invention, the expression (15) for the final demagnetizing current value is obtained by combining formulas (13) and (14):

[0082]

[0083]

[0084]

[0085] However, unlike the demagnetizing current solution based on the magnetic gradient tensor, the right side of the equation... Unable to pass , To obtain the measurement value, it is necessary to measure the three-component matrix of the background field plane magnetic field. And it is calculated using the following formula (16):

[0086]

[0087] Example 1

[0088] The correctness of this invention can be demonstrated through simulation experiments. The specific model parameters and simulation results are as follows:

[0089] A, Figure 2 In the middle, the ship's five keels (keel I 4, keel II 5, keel III 6, keel IV 7, keel V 8), stern 3, bow 9, and engine 2 are configured with a relative magnetic permeability of 1000 and an electrical conductivity of The steel is made of steel with a relative permittivity of 7.8. The deck 1, bottom 11, and hull plating 10 of ship 22 are configured with a relative magnetic permeability of 4000 and an electrical conductivity of... Made of iron with a relative permittivity of 1. Nine winding coils, set with a relative permeability of 1 and a conductivity of [missing value]. Copper material with a relative permittivity of 1.

[0090] The simplified demagnetization model and experimental implementation diagram of this method are shown below. Figure 4 To clearly and intuitively show the measuring plane above the ship, only the horizontal winding coil was drawn, and the vertical and longitudinal winding coils were not drawn.

[0091] Figure 5 In the digital prototype, the x, y, and z axes correspond to the north and east directions in the geographic coordinate system, perpendicular to the downward direction of the earth. The ship's induction magnetic field is set with a magnetic declination of 50 degrees and a magnetic inclination of -10 degrees. An air domain of 25 is set above the ship, with an area of ​​900 square kilometers. The height is 10 The area beneath the ship is designated as waterway 26, with a surface area of ​​900 square kilometers. The height is 10 The plane is measured at a height of 6.5 meters. Within the square survey area, 1681 measurement points were taken at 0.5m intervals, and the projection of the measurement plane onto the water surface was 27. Figure 3 The rectangular region is shown in this embodiment. The demagnetization effects after simulation are shown in Tables 1 and 2, with five tensor invariants.

[0092] Table 1

[0093]

[0094] Table 2

[0095]

[0096] Experiment 1 in the table is based on the three components of the magnetic field. The calculated demagnetizing current value in Experiment 2 was based on five tensor invariants. The calculated demagnetizing current values ​​and the maximum error values ​​of the magnetic vector and magnetic gradient tensor components after demagnetization are shown in Table 2. The demagnetizing effect of this invention on the five independent components of the ship's external appearance is superior to the magnetic vector-based demagnetizing method. Furthermore, the demagnetizing effect of this invention on the three magnetic field components is close to that of the demagnetizing method based on the three magnetic field components, and it also has a good elimination effect on the three magnetic field components.

[0097] Table 2 compares the demagnetization effects of the current calculated by the methods based on the magnetic gradient tensor and the three-factor magnetic field in the model. It can be seen that the proposed method reduces the number of measurement planes without sacrificing demagnetization accuracy, and has great application value.

[0098] Note that the design of the digital prototype model, the parameter settings for each material, and the selection of the measuring plane described above are merely preferred embodiments and technical principles of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for solving degaussing current of ship winding based on gradient tensor, characterized in that, The method comprises the following steps: A. When all winding coils on the ship are not electrified, a measurement plane is set above the ship, and magnetic gradient tensor data of all measurement points of the ship on the measurement plane and corresponding position information are obtained; B. The winding coils on the ship are respectively simulated to be electrified, and the magnetic gradient tensor values of all measurement points on the measurement plane after each electrification are obtained; C. An efficiency matrix K of the magnetic gradient tensor excited by a unit current is calculated; D. A final demagnetization current value is calculated through the efficiency matrix K.

2. The method of claim 1, wherein the method is characterized in that: Step A, measure the magnetic gradient tensor data of all measuring points of the surface ship and the corresponding position information, denoted as ; the magnetic gradient tensor G is defined as the gradient of the three components of the magnetic field along the three coordinate axes of the orthogonal coordinate system, with 9 components , expressed as formula (1): ； In a passive space, the divergence and the curl of the magnetic field are both 0, that is: ； The magnetic gradient tensor G is represented by five independent components: ； measurement values is a column vector of 5n rows and 1 column, assuming there are n measurement points in the measurement plane, then is spliced from n column vectors; wherein each column vector is the magnetic gradient tensor invariant of each point converted into a column matrix of 5 rows and 1 column; measurement values comprises the following components: ； wherein, is the induced magnetic gradient tensor of the ship excited by the geomagnetic field, is the residual magnetic gradient tensor of the ship, the geomagnetic field can be approximated as a uniform field, the magnetic gradient tensor of the uniform field is approximately 0, so the measured value can be used alone to describe the magnetic characteristics of the ship.

3. The method of claim 1, wherein, Step B: simulate the process of energizing the 9 winding coils in sequence with unit current and obtain the magnetic gradient tensor data of all measuring points on the measuring plane and the corresponding position information each time. The position information is the same as that in the first step. Assume that the coil number is denoted as m, and the magnetic gradient tensor value of the measuring plane after each energization is denoted as The measurement value at this time is which contains the following components: ； where, is the induced magnetic gradient tensor of the ship excited by the geomagnetic field, is the induced magnetic gradient tensor of the ship excited by the coil magnetic field, is the residual magnetic gradient tensor of the ship, is the magnetic gradient tensor excited by the coil; formula (5) minus formula (4) 。 4. The method of claim 1, wherein the method is characterized by: In step C, the efficiency matrix K of the magnetic gradient tensor excited by a unit current is calculated through formula (7); in the formula, the matrix K describes the size of the five independent components of the magnetic gradient tensor excited by each coil when the nine wires in the model are respectively electrified with a unit current; ； The right side of Equation (7) is Equation (7) can be reduced to Equation (8) by Equation (6). 。 5. The method of claim 1, wherein, In step D, the specific operation is as follows: The left side of formula (9) is the total magnetic gradient tensor excited by the coils in the model, and the right side is the total magnetic gradient tensor generated by the ship excited by the geomagnetic field and the coil magnetic field, and formula (9) is as follows: ； The ship is a linear magnetization model in the modeling, and the induced magnetization model is selected as: where H is the background field intensity, is the vacuum permeability, is the permeability of the ship material; formula (9) can be transformed into: ； In the formula, , are measured values, and the demagnetizing current based on the magnetic gradient tensor is solved as: .

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