Method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visual model

Abstract

The invention discloses a method for extracting characteristic parameters of an electromagnetic field in a plume propagation path based on a visual model, and the method comprises the steps: employing SPIS simulation software according to the working state of a Hall thruster, introducing macro particles based on a PIC algorithm, and obtaining a plume distribution model diagram through calculation; extracting the plume density of each grid in the plume distribution model graph, converting a color image of the plume distribution model into a gray level image, and drawing an isodensity line for the color image by distinguishing the gray level of the image to obtain the density of the plume in different transmission paths; on the basis of collision in plume, a Dyde model is adopted to represent a relative dielectric constant; the same relative dielectric constants are divided into one layer, a layered structure is adopted to build a transmission model of electromagnetic waves in plume, electromagnetic solving is carried out, and electromagnetic wave transmission characteristic parameters are obtained. According to the invention, the characteristic parameters of the electromagnetic waves in the plume propagation path can be efficiently and accurately obtained, so that the related research and application effects of the Hall thruster can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave transmission characteristics in a Hall thruster plume, and in particular relates to a method for extracting characteristic parameters of an electromagnetic field in a plume propagation path based on a visualization model. Background Art

[0002] Plume is a term used in fluid mechanics and also refers to a Taoist priest. There are four elements to a plume: 1. It is a fluid Flow 1 that contains momentum; 2. It is a fluid medium Flow 2 that does not contain momentum; 3. The density difference between Flow 1 and Flow 2 cannot be too large, but at the same time, the two cannot be homogeneous so that the boundary between them cannot be clearly distinguished; 4. F1 is not obstructed by anything outside F2 - that is, Flow 1 flows completely in Flow 2.

[0003] Hall thruster, also known as Hall effect thruster, is a thruster in which the propellant is accelerated by an electric field. The Hall thruster confines electrons in a magnetic field and uses electrons to ionize the propellant, accelerate the ions to generate thrust, and neutralize the ions in the plume.

[0004] Hall thruster is an advanced electric propulsion device, which is widely used in the field of satellite position keeping and attitude control. 3 With advantages such as speed on the order of s) and high efficiency (up to over 60%), it has become one of the preferred propulsion devices for future space vehicles.

[0005] There are currently two main methods for studying the transmission characteristics of electromagnetic waves in the plume of a Hall thruster, namely experimental measurement and numerical simulation. The experimental measurement method requires simulating the plume environment of a Hall thruster on the ground and transmitting and receiving electromagnetic waves to measure the characteristics of the electromagnetic waves passing through the plume. However, the experimental measurement method not only costs a lot of money and time, but also in some cases it is difficult to achieve an accurate simulation of the real environment. In contrast, the numerical simulation method uses a combination of mathematical methods and physical models to calculate the amplitude and phase changes of electromagnetic waves in the plume, which has the advantages of low cost and fast calculation speed.

[0006] In terms of numerical simulation, the methods commonly used by researchers at home and abroad include the finite difference method (FDTD), the finite element method (FEM), the geometric optics method, etc. (references: He Wusheng, N. de Mejanes, Yu Bo). Although these methods can simulate the propagation characteristics of electromagnetic waves in plumes to a certain extent, they still have problems such as large amount of calculation and slow operation speed. For example, performing dynamic particle calculations on all particles in the plume separately is not only computationally intensive but also time-consuming. In order to overcome these shortcomings, simplifying the plume model to obtain more accurate simulation results has become an inevitable trend.

[0007] The existing technology lacks an efficient and accurate simulation method when dealing with the electromagnetic wave transmission characteristics in plumes. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the prior art and propose a method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on a visualization model.

[0009] In order to achieve the above object, the present invention proposes a method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model, comprising:

[0010] Step 1) According to the working state of the Hall thruster, SPIS simulation software is used, based on the PIC algorithm, macro particles are introduced, and a plume distribution model diagram is obtained through calculation;

[0011] Step 2) extracting the plume density of each grid in the plume distribution model diagram, converting the color image of the plume distribution model into a grayscale image, and drawing iso-density lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths;

[0012] Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant;

[0013] Step 4) Divide the same relative dielectric constant into a layer, use the layered structure to build an electromagnetic wave transmission model in the plume, perform electromagnetic solution, and obtain the electromagnetic wave transmission characteristic parameters.

[0014] Preferably, the working state of the Hall thruster in step 1) includes: divergence angle, ionization rate, thrust and mass flow.

[0015] Preferably, in step 1), based on the PIC algorithm, macro particles are introduced to establish a plume distribution model; comprising:

[0016] Introducing macro particles, using the movement of macro particles to replace the actual movement of charged particles, and using the volume of each macro particle falling in the grid as the weight assigned to the grid to establish a plume distribution model. The weight is used to represent the density and frequency of macro particles.

[0017] The grid of the macro particles is a cone of different sizes.

[0018] Preferably, in step 2), the color image of the plume distribution model is converted into a grayscale image, and iso-density lines are drawn on the color image by distinguishing the grayscale levels of the image, including:

[0019] The color image of the plume distribution model is converted into a 256-level grayscale image, the maximum and minimum pixel values ​​are identified, and the pixel values ​​within the maximum and minimum pixel value range are divided into several levels. The positions of the same pixel value are smoothly connected to obtain the equal density lines.

[0020] Preferably, the relative dielectric constant ε in step 3) is r (ω) is:

[0021]

[0022] in, is the plume plasma frequency, ω is the electromagnetic wave frequency, v c is the plume collision frequency, j represents the imaginary part, n e is the plasma electron density, e is the unit charge, e = 1.6 × 10 -19 C, ε 0 is the vacuum dielectric constant, ε 0 =8.85×10 -12 F / m,m e is the mass of the electron, m e =9.11×10 -31 kg.

[0023] Preferably, performing electromagnetic solution to obtain characteristic parameters of electromagnetic wave transmission includes:

[0024] The CST electromagnetic calculation tool is introduced, and the FIT algorithm is used to numerically solve the Maxwell equations. By discretizing space and time, the time-varying behavior of the electromagnetic field is calculated to obtain the characteristic parameters of electromagnetic wave transmission, including transmission coefficient and reflection coefficient.

[0025] Preferably, performing electromagnetic solution to obtain characteristic parameters of electromagnetic wave transmission includes: introducing a finite difference method, a finite element method or a geometric optics method to calculate the time-varying behavior of the electromagnetic field to obtain characteristic parameters of electromagnetic wave transmission, including: a transmission coefficient and a reflection coefficient.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] The present invention effectively solves the problems of large amount of calculation, slow operation speed and insufficient simulation accuracy in the prior art research on the electromagnetic wave transmission characteristics of the Hall thruster plume by introducing a visual model extraction method. The present invention processes the plume distribution image obtained by SPIS software simulation, thereby reducing the calculation cost while improving the calculation speed and ensuring the accuracy of the simulation results. Through the method of the present invention, the characteristic parameters of the electromagnetic wave in the plume propagation path can be obtained efficiently and accurately, thereby improving the effect of the research and application related to the Hall thruster. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the plume distribution model obtained by SPIS simulation;

[0029] Figure 2 is a schematic diagram of the SPIS macroparticle grid;

[0030] Figure 3 It is a schematic diagram of the plume density of each grid extracted from SPIS simulation;

[0031] Figure 4 It is a schematic diagram of the plume isodensity lines;

[0032] Figure 5 It is a schematic diagram of the electromagnetic wave transmission model;

[0033] Figure 6 It is a flow chart of the method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model of the present invention. DETAILED DESCRIPTION

[0034] The present invention proposes a method for extracting characteristic parameters of the electromagnetic field in the plume propagation path based on a visualization model. By processing the plume distribution image obtained by software simulation, accurate simulation results can be obtained at a lower computing cost and faster speed, effectively making up for the shortcomings of the existing technology.

[0035] The purpose of the present invention is to provide a method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model, so as to solve the problems of large amount of calculation, slow operation speed and insufficient simulation accuracy in the prior art in the study of electromagnetic wave transmission characteristics in the plume of Hall thrusters. The present invention processes the plume distribution image obtained by SPIS software simulation, thereby reducing the calculation cost while improving the calculation speed and ensuring the accuracy of the simulation results. Through the method of the present invention, the characteristic parameters of electromagnetic waves in the plume propagation path, such as transmission coefficient S21 and reflection coefficient S22, can be obtained efficiently and accurately, thereby improving the effect of related research and application of Hall thrusters.

[0036] 1. The plume model is calculated using SPIS (Spacecraft Plasma Interaction Software) developed by the European Space Agency. By setting the divergence angle, ionization rate, thrust, mass flow and other parameters of the Hall thruster, the PIC (Particle-In-Cell) algorithm is used to introduce the concept of macro particles, which represent all the physical properties of all particles in a volume, including density and frequency. The volume of each macro particle falling in the grid is used as the weight assigned to the grid to represent the density and frequency of the macro particles. The plume distribution model is obtained by replacing the actual movement of charged particles with the movement of a part of the macro particles. Figure 1 shown.

[0037] 2. If Figure 2 As shown in the figure, the meshes of the macroparticles are all cones of different sizes. There are many meshes and there is no clear relationship between the meshes, which makes it difficult to build a plume model. In addition, the plume density of each mesh obtained by SPIS simulation is extracted as follows: Figure 3 As shown, there is no accurate position information given to each grid, and the manual extraction of the density of each grid is a lot of work. Therefore, the SPIS simulation results cannot be directly converted into characteristic parameters of the electromagnetic field in the plume propagation path.

[0038] 3. Based on Figure 1 Visualization model, extract density information from plume, Figure 1 The color image is converted into a grayscale image, and the isodensity lines are drawn on the color image by distinguishing the grayscale levels of the image. Specifically, the color image is converted into a 256-level grayscale image, and the pixel values ​​in the range are evenly divided into 6 levels by identifying the maximum and minimum pixel values, and the positions of the same pixel value are smoothly connected. The lines of these systems are used as isodensity lines. For different antenna and Hall thruster layouts, the propagation paths of electromagnetic waves in their plumes are different. Taking the electromagnetic waves penetrating the plume 10 cm away from the thruster outlet as an example, the system parameter settings in its transmission path are represented by the values ​​of the isodensity line layer traversed at this position, and the values ​​of the corresponding isodensity line layers are taken as the average value of each level.

[0039] like Figure 4 As shown, the density parameters of the plume in different transmission paths are obtained.

[0040] 4. In the plume, the most common type of collision is elastic collision. Since the mass of Xe (xenon) atoms is much greater than the mass of electrons, the speed of Xe atoms is much lower than that of electrons and can be almost regarded as stationary. Therefore, in the plume, the collision between electrons and Xe atoms meets the conditions of the Drude model. In order to simplify the description of the plume model, we can use the Drude model to represent its relative dielectric constant:

[0041]

[0042] in, is the plume plasma frequency, ω is the electromagnetic wave frequency, v c is the plume collision frequency. n e is the plasma electron density, e is the unit charge, which is e = 1.6×10 -19 C, ε 0 is the vacuum dielectric constant, and ε 0 =8.85×10 -12 F / m,m e is the mass of the electron, m e =9.11×10 -31kg, in the above formula, except for the plasma electron density, the other values ​​are constants. It can be seen that the plasma frequency is determined by its electron density. The Drude model follows the classical collision model and classical electromagnetic field theory. Compared with other models, the mathematical expression of the Drude model is relatively simple, so it has the advantage of high computational efficiency.

[0043] 5. Combination Figure 4 , the same relative dielectric constant is divided into a layer, and a layered structure is used to build a transmission model of electromagnetic waves in the plume, such as Figure 5 As shown. The electromagnetic wave transmission model is then introduced into different electromagnetic calculation tools to obtain the corresponding electromagnetic wave transmission characteristics. Here, the CST electromagnetic calculation tool is introduced, and the FIT algorithm is used to calculate the time-varying behavior of the electromagnetic field by discretizing space and time based on the numerical solution of the Maxwell equations.

[0044] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0045] Example

[0046] like Figure 6 As shown, an embodiment of the present invention proposes a method for extracting characteristic parameters of an electromagnetic field in a plume propagation path based on a visualization model, comprising:

[0047] Step 1) According to the working state of the Hall thruster, SPIS simulation software is used, based on the PIC algorithm, macro particles are introduced, and a plume distribution model diagram is obtained through calculation;

[0048] Step 2) extracting the plume density of each grid in the plume distribution model diagram, converting the color image of the plume distribution model into a grayscale image, and drawing iso-density lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths;

[0049] Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant;

[0050] Step 4) Divide the same relative dielectric constant into a layer, use the layered structure to build an electromagnetic wave transmission model in the plume, perform electromagnetic solution, and obtain the electromagnetic wave transmission characteristic parameters.

[0051] The innovation of the present invention is that by introducing a visual model extraction method, the problems of large amount of calculation, slow operation speed and insufficient simulation accuracy in the prior art research on the electromagnetic wave transmission characteristics of the Hall thruster plume are effectively solved. The specific innovations are as follows:

[0052] 1. Using SPIS to simulate plume model:

[0053] The present invention adopts SPIS software, sets the divergence angle, ionization rate, thrust, mass flow and other parameters of the Hall thruster, uses the PIC algorithm, introduces the concept of macro particles, replaces the actual movement of charged particles with the movement of a part of macro particles, and represents the actual situation of macro particles in a weighted manner, thereby obtaining an accurate plume distribution model.

[0054] 2. Simplify the complexity of the plume model:

[0055] Traditional plume models are difficult to build because there are many macroparticle grids and no clear relationship between grids, which makes model building difficult. By extracting the plume density of each grid obtained by SPIS simulation and converting it into an easy-to-process grayscale image, the complexity of the plume model is effectively simplified and the efficiency of model building is improved.

[0056] 3. Density extraction method based on visualization model:

[0057] The present invention processes the plume distribution image obtained by simulation, converts the color image into a grayscale image, and draws iso-density lines by distinguishing the grayscale levels of the image, thereby obtaining the density parameters of the plume on different transmission paths. Compared with manually extracting the density of each grid, this method greatly reduces the workload and improves accuracy and efficiency.

[0058] 4. Conversion from simulation results to characteristic parameters:

[0059] The present invention proposes a new method, which can convert the plume distribution image in the SPIS simulation result into the characteristic parameters of the electromagnetic field on the plume propagation path, and overcomes the problem in the prior art that the simulation result cannot be directly converted into the actual application parameter.

[0060] Alternative solution:

[0061] Traditional numerical simulation methods such as finite difference method (FDTD), finite element method (FEM), geometric optics method, etc. can be used as an alternative to step 4), and the Drude model is introduced into these algorithms to calculate the electromagnetic characteristics. In this way, the corresponding electromagnetic wave transmission characteristics can be obtained using different electromagnetic calculation tools, thereby verifying and optimizing the method of the present invention.

[0062] Step 1: Input the working state parameters of the thruster such as divergence angle, ionization rate, thrust, mass flow, etc. into the SPIS software to obtain the density distribution model of each particle in the plume;

[0063] Step 2: Input the collision frequency of the plume and the electron density obtained by SPIS into the Drude model to simplify the plume model;

[0064] Step 3: Input the discretized plume model and electromagnetic wave frequency band into the electromagnetic solver, and obtain the transmission characteristics of the electromagnetic wave: the closer the propagation path of the electromagnetic wave is to the thruster outlet, the greater its attenuation degree; and the attenuation degree of the electromagnetic wave has no obvious connection with the angle of the incident plume, and is more affected by the area with higher particle density in the plume.

[0065] The present invention adopts a density extraction method based on a visualization model, which brings significant beneficial effects by converting the plume distribution image obtained by simulation into a grayscale image and drawing isodensity lines by distinguishing the grayscale levels of the image. Specifically, this method simplifies the complexity of the plume model and improves the efficiency and accuracy of model construction. In addition, by introducing a hierarchical structure to build a transmission model of electromagnetic waves in the plume, the simulation accuracy of the electromagnetic wave transmission characteristics is further improved. Combined with different electromagnetic calculation tools, the characteristic parameters of electromagnetic waves in the plume propagation path can be obtained efficiently and accurately, which significantly reduces the calculation cost and time and improves the reliability and practicality of the simulation results.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A method for extracting characteristic parameters of electromagnetic fields in plume propagation paths based on a visualization model, comprising: Step 1) According to the working state of the Hall thruster, SPIS simulation software is used, based on the PIC algorithm, macro particles are introduced, and a plume distribution model diagram is obtained through calculation; Step 2) extracting the plume density of each grid in the plume distribution model diagram, converting the color image of the plume distribution model into a grayscale image, and drawing iso-density lines on the color image by distinguishing the grayscale levels of the image to obtain the density of the plume in different transmission paths; Step 3) Based on the collision in the plume, the Drude model is used to represent the relative dielectric constant; Step 4) Divide the same relative dielectric constant into a layer, use the layered structure to build an electromagnetic wave transmission model in the plume, perform electromagnetic solution, and obtain the electromagnetic wave transmission characteristic parameters.

2. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1 is characterized in that: The working state of the Hall thruster in step 1) includes: divergence angle, ionization rate, thrust and mass flow.

3. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1 is characterized in that: In the step 1), macro particles are introduced based on the PIC algorithm to establish a plume distribution model; including: Introducing macro particles, using the movement of macro particles to replace the actual movement of charged particles, and establishing a plume distribution model according to the volume of each macro particle falling in the grid as the weight assigned to the grid. The weight is used to represent the density and frequency of macro particles. The grid of the macro particles is a cone of different sizes.

4. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1 is characterized in that: In the step 2), the color image of the plume distribution model is converted into a grayscale image, and iso-density lines are drawn on the color image by distinguishing the grayscale levels of the image, including: The color image of the plume distribution model is converted into a 256-level grayscale image, the maximum and minimum pixel values ​​are identified, and the pixel values ​​within the maximum and minimum pixel value range are divided into several levels. The positions of the same pixel value are smoothly connected to obtain the equal density lines.

5. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1, characterized in that: In the step 3), the relative dielectric constant ε r (ω) is: in, is the plume plasma frequency, ω is the electromagnetic wave frequency, v c is the plume collision frequency, j represents the imaginary part, n e is the plasma electron density, e is the unit charge, e = 1.6 × 10 -19 C, ε0 is the dielectric constant of vacuum, ε0=8.85×10 -12 F / m,m e is the mass of the electron, m e =9.11×10 -31 kg.

6. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1, characterized in that: The electromagnetic solution is performed to obtain the electromagnetic wave transmission characteristic parameters, including: The CST electromagnetic calculation tool is introduced, and the FIT algorithm is used to numerically solve the Maxwell equations. By discretizing space and time, the time-varying behavior of the electromagnetic field is calculated to obtain the characteristic parameters of electromagnetic wave transmission, including transmission coefficient and reflection coefficient.

7. The method for extracting characteristic parameters of electromagnetic field in plume propagation path based on visualization model according to claim 1, characterized in that: The electromagnetic solution is performed to obtain the characteristic parameters of electromagnetic wave transmission, including: introducing a finite difference method, a finite element method or a geometric optics method to calculate the time-varying behavior of the electromagnetic field to obtain the characteristic parameters of electromagnetic wave transmission, including: a transmission coefficient and a reflection coefficient.

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