Charged lunar dust motion simulation method based on plume lunar dust and lunar surface electric field coupling

Abstract

The invention provides a charged lunar dust motion simulation method based on plume lunar dust and lunar surface electric field coupling, which takes charged lunar dust particles, solar wind electrons, solar wind ions and photoelectrons as particle objects, a computational domain plane is perpendicular to the lunar surface, the bottom takes the lunar surface as a solid wall surface, and a solar wind-lunar surface sheath layer is obtained through PIC numerical simulation. The electrification quantity of lunar dust particles is solved by a charging balance equation, the interaction of the electrified lunar dust and the lunar surface sheath is realized through an electrified lunar dust and solar wind-lunar surface sheath bidirectional coupling model, the electrification of the lunar dust is combined with plume dust raising, and the real-time updating and characteristic analysis of the movement of the electrified lunar dust are realized.

Description

Technical Field

[0001] The invention relates to the fields of dust plasma and lunar exploration, and in particular to a method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and the lunar surface electric field.

[0002] The PIC (Particle-In-Cell) method simulates the behavior of plasma from a microscopic perspective and depicts the overall behavior of plasma by directly examining the movement of a large number of particles. The PIC method realizes the interaction between particles through physical fields: the physical quantities carried by the particles are counted in the computational domain grid to obtain various physical fields, and then the field values ​​at the location of the particles are interpolated, so that the particles are processed accordingly. In this way, the collisions between particles and the interactions between charges are solved. The four main links of physical quantity statistics and interpolation, electromagnetic field solution, particle promotion and collision between particles are continuously iterated until a stable result is calculated. Background Art

[0003] Moon dust and lunar soil mainly refer to lunar surface weathering materials. The entire lunar surface is almost covered by moon dust and lunar soil. Moon dust particles stationary on the lunar surface are similar to dust immersed in a plasma environment. They will be charged due to the deposition of plasma on the surface of the particles. At the same time, due to the ultraviolet rays of sunlight on the lunar surface, the moon dust particles themselves can also be excited to produce photoelectrons. Under the combined effect of these two factors, the surface of the moon dust particles can carry a certain amount of charge. In addition, the lunar surface is in a vacuum state. Under the bombardment of solar wind plasma and solar radiation, a sheath is formed to generate a lunar surface electric field. During the soft landing of the lander on the lunar surface, the engine plume impacts the lunar surface, stirring up a large amount of moon dust. These charged moon dust are subjected to Coulomb force in the sheath electric field and change their motion state. Charged moon dust is easy to adhere to and contaminate the space suit and the surface of the spacecraft. Severe adhesion can cause the mechanical structure to get stuck and the sealing mechanism to fail. Therefore, the study of the moon dust environment on the lunar surface is particularly important. In the 1960s and 1970s, astronauts in the United States conducted lunar exploration missions and found that the difficulties caused by lunar dust were beyond imagination. In severe cases, it would cause the lunar exploration system to malfunction and even affect the safety of astronauts. Therefore, the dust prevention and removal of the lunar exploration system and space suits are particularly important. With the proposal of lunar exploration plans by major space powers in the world, the problem of lunar dust on the lunar surface has gradually become a very important and urgent problem in lunar exploration activities. Establishing a computational model to simulate the movement of charged lunar dust is of great significance for correctly predicting the movement of plumes impacting lunar dust, and has important application value for further proposing corresponding dust prevention and removal plans, ensuring manned lunar landings, and establishing a major strategic task of lunar space research stations.

[0004] For the study of the movement of charged lunar dust, the current research at home and abroad is mainly divided into three methods: ground experiments, landing image analysis and simulation research. The high vacuum and low gravity environment on the lunar surface are the main difficulties in conducting ground experiments, and the information obtained from the lander image analysis is relatively limited. Simulation research does not have the above limitations. By establishing a computational model of plume dust and lunar dust charging, the movement characteristics of charged lunar dust under the impact of plumes are analyzed, which is the main way to study the movement of charged lunar dust. Zhang et al. studied the surface erosion process and erosion characteristics of the low-thrust plume of "Chang'e 5"; Li et al. combined the dynamic method of simulating particle motion with the direct simulation Monte Carlo method of simulating the rarefied plume field, and established a macroscopic gas-particle bidirectional coupling method to simulate the interaction between plumes and lunar dust; Morris et al. used DSMC to study the plume characteristics in the engine nozzle and the plume diffusion characteristics in the vacuum environment of the lunar surface; these studies only considered the forces on lunar dust under the condition of neutral charge, while in reality, charged lunar dust is also subject to Coulomb force when moving in the electric field of the lunar sheath. Wang et al. used the full particle method to establish a numerical simulation program for the illuminated area near the lunar surface terminator, and used the program to study the effect of changes in the solar angle on the suspension of lunar dust; Sternovsky et al. studied the effect of changes in solar radiation on the generation rate of photoelectrons and found that higher photoelectron density would increase the potential on the lunar surface; Poppe et al. conducted a one-dimensional PIC modeling of the photoelectron sheath to study the dust suspension on the lunar surface and explored the effect of solar illumination intensity on the sheath structure under different photoelectron velocity distribution functions; Andrew et al. established a three-dimensional PIC simulation program, focusing on the effect of the lunar surface morphology on the lunar photoelectron sheath and the electrostatic migration of lunar dust; these studies only analyzed the motion characteristics of the lunar surface sheath and charged lunar dust under natural conditions, but during the lunar landing process, the large amount of lunar dust raised by the impact of the engine plume was the main source of lunar dust movement. In summary, the simulation of lunar dust movement at home and abroad lacks a simulation method that combines lunar dust charging and plume dust raising and updates the motion state of charged lunar dust in real time. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and the lunar surface electric field.

[0006] Specifically, a gas-solid two-phase flow model of the lander engine plume impacting the lunar dust is established, a solar wind-lunar sheath calculation model is established, a lunar dust particle charge calculation model is established, and a two-way coupling model of charged lunar dust and solar wind-lunar sheath is established, and the motion state of charged lunar dust is updated in real time. Among them, the solar wind-lunar sheath calculation model: the lunar surface is in a vacuum state, the solar wind directly impacts the lunar surface, forming the solar wind-lunar sheath, and at the same time, the lunar dust particles on the lunar surface are irradiated by the sun to produce a photoelectric effect, and the existence of photoelectrons also affects the potential distribution of the solar wind-lunar sheath. Using the PIC method, solar wind electrons, solar wind ions, and photoelectrons are used as particle objects, and the lunar surface is used as a solid wall to simulate the formation of the solar wind-lunar sheath. The lunar dust particle charge calculation model: lunar dust particles are charged under the action of the solar wind plasma environment and solar radiation. The charge of lunar dust particles of different particle sizes is calculated by establishing and solving the charge balance equation of lunar dust particles. The charge balance equation includes electron current, ion current, and photoelectron current. Bidirectional coupling model of charged lunar dust and solar wind-lunar sheath: During the landing process, the plume of the lander engine impacts the lunar surface, blowing up a large amount of lunar dust. These lunar dust are charged and have a large spatial number density. During the movement, they are affected by the electric field force from the solar wind-lunar sheath, which also changes the charge distribution in the sheath, resulting in changes in the sheath. This interaction mechanism between charged lunar dust and the solar wind-lunar sheath is realized by establishing a lunar dust particle-sheath bidirectional coupling model based on PIC.

[0007] The steps of this simulation method are:

[0008] Step 1: Establish a gas-solid two-phase flow model of the lander engine plume impacting lunar dust;

[0009] Step 2: Establish a model for calculating the charge of lunar dust particles;

[0010] Step 3: Establish a solar wind-lunar sheath calculation model;

[0011] Step 4: Establish the coupling relationship between the two models in step 1 and step 3.

[0012] Among them, the fourth step in the simulation method is the core part of the present invention, and the method of establishing the coupling relationship is as follows:

[0013] The charge and position coordinates of all the lunar dust particles in the calculation domain are input into the PIC program of sheath simulation. The implementation method is as follows: the PIC program reads the lunar dust particle information matrix, and the charge and position coordinates of all the lunar dust particles in the calculation domain are included in the statistics of charge density distribution. As the fourth type of charged particles besides solar wind electrons, solar wind ions, and lunar surface photoelectrons, the Poisson equation is solved after the statistics of charge density distribution is completed to obtain the sheath potential distribution, thus realizing the effect of charged lunar dust on the sheath. After solving the sheath potential distribution, the electric field intensity at the position coordinates of each lunar dust particle is calculated by electric field interpolation. The Coulomb force on the lunar dust particle can be calculated by multiplying the electric field intensity by the charge of the lunar dust particle, thus realizing the effect of the sheath electric field on the charged lunar dust. The velocity vectors and position coordinates of all the lunar dust particles in the calculation domain are input into the CFD program of plume simulation. The implementation method is as follows: the CFD program reads the lunar dust particle information matrix, and the density and velocity of the flow field at the position coordinates of each lunar dust particle are calculated by interpolation. The drag force on the lunar dust particle can be calculated by the drag formula. By adding the drag force on the lunar dust particles from the engine plume and the Coulomb force vector from the electric field of the lunar sheath, we can get the resultant force on the lunar dust particles at this moment. The motion state of the lunar dust particles is updated according to Newton's second law. At the next time step, the PIC program and CFD program respectively read the new lunar dust particle information matrix. In this way, iterative calculation realizes the physical process of interaction between the charged lunar dust and the lunar sheath under the impact of the plume, and establishes the coupling relationship between the plume lunar dust model and the lunar surface electric field model. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1a is the computational domain of the method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and lunar surface electric field of the present invention;

[0015] Figure 1b is the calculation domain of the solar wind-lunar sheath calculation model in the simulation method of the present invention;

[0016] Figure 2 It is a flow chart of the charged lunar dust motion simulation method based on PIC according to the present invention. DETAILED DESCRIPTION

[0017] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] Reference Figure 1a , is the computational domain of the invented method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and lunar surface electric field. The plume of the lander engine blows up the charged lunar dust. Under the influence of solar wind plasma bombardment and solar radiation, there is a solar wind-lunar sheath on the lunar surface. When the charged lunar dust moves over the lunar surface, it will be affected by the Coulomb force from the electric field of the lunar sheath. At the same time, the distribution of charged lunar dust in the sheath will also affect the electric potential distribution of the sheath. Figure 1b, is the computational domain of the solar wind-lunar sheath computational model. The computational domain plane is perpendicular to the lunar surface, with lunar soil at the bottom. The corresponding particle boundary condition is an insulating wall. When charges hit this boundary, they will be deposited on it. The electric field boundary condition is a Neumann boundary condition. The particle boundary conditions on the left and right boundaries are periodic boundary conditions. After leaving one boundary, the particles will re-enter the computational domain symmetrically from the other boundary. The upper boundary is the particle entrance boundary. The solar wind plasma enters the computational domain from this boundary. The electric field boundary condition is a Drichlet boundary condition.

[0019] Reference Figure 2 , is the calculation flow chart of the present invention. A method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and lunar surface electric field, the specific implementation method is as follows:

[0020] Step 1: Establish a gas-solid two-phase flow model of the lander engine plume impacting lunar dust;

[0021] Fluid control equations:

[0022]

[0023] The drag equation of the plume acting on the lunar dust particles is:

[0024]

[0025] Step 2: Establish a model for calculating the charge of lunar dust particles;

[0026] The surface charge of lunar dust particles is: Q d =C d ·φ d , assuming that the moon dust particles are spherical, their capacitance is: C d =4πε0r d , the charge balance equation of lunar dust particles is:

[0027] in:

[0028] Electron current (φ d <0) and (φ d >0) are:

[0029]

[0030] Ion current (φ d <0) and (φ d >0) are:

[0031]

[0032] Photoelectron current (φ d <0) and (φ d >0) are:

[0033]

[0034] Photoelectric effect current (φ d >0) and (φ d ≤0) are:

[0035]

[0036] Step 3: Establish a solar wind-lunar sheath calculation model;

[0037] Specific steps:

[0038] (1) Establishing a grid, setting the time step, setting the boundary conditions, setting the plasma parameters, and setting the macro-particle weight coefficient;

[0039] (2) Generate a corresponding number of simulated particles within a time step at the entrance boundary of the computational region;

[0040] (3) The charge of the simulated particles in each grid is distributed to the corresponding grid nodes using the volume weight method to obtain the charge density distribution of the particles in the calculation area;

[0041] (4) Solving the Poisson equation Get the electric potential of each grid node, and then get the corresponding electric field;

[0042] (5) After obtaining the corresponding electric field distribution, the electric field force on each simulated particle is obtained by interpolation method;

[0043] (6) According to Newton's second law, solve the acceleration and velocity of the simulated particle, and then obtain the corresponding velocity and position;

[0044] (7) Repeat steps 2-7 and iterate to the set number of time steps.

[0045] Step 4: Establish the coupling relationship between the two models in step 1 and step 3.

[0046] Specific steps:

[0047] (1) Based on the established solar wind-lunar sheath model and lunar dust charging model, the charge and position coordinates of all lunar dust particles in the calculation domain are input into the PIC program of sheath simulation. The specific implementation method is that the PIC program reads the lunar dust particle information matrix, where the lunar dust particle information matrix is ​​in the form of: x, y, z are the spatial coordinates of the lunar dust particles, u, v, w are the velocity components of the lunar dust particles in the x, y, z directions, q is the charge of the lunar dust particles, which is calculated by the charge calculation model in the second step above, F is the drag force on the lunar dust particles from the flow field, which is calculated by the gas-solid two-phase flow model of the lander engine plume impacting the lunar dust in the first step above, and the subscripts 1 to n are the indexes of the lunar dust particles in the program, and n corresponds to the number of lunar dust particles in the entire calculation domain.

[0048] (2) The charge and position coordinates of all lunar dust particles in the computational domain are included in the statistics of the charge density distribution as the fourth type of charged particles in addition to solar wind electrons, solar wind ions, and lunar surface photoelectrons. The specific implementation method is to interpolate the charge of each lunar dust particle to the grid node of PIC, where q is the charge of the lunar dust particle and V is the volume of the four adjacent grids. The interpolation method is as follows:

[0049]

[0050] (3) Solve the Poisson equation after completing the statistics of charge density distribution The sheath potential distribution is obtained, thus realizing the effect of charged lunar dust on the sheath;

[0051] (4) After solving the sheath potential distribution, the electric field strength at the coordinates of each lunar dust particle is calculated by electric field interpolation. The electric field strength multiplied by the charge of the lunar dust particle can be used to calculate the electric field force on the lunar dust particle. In this way, the effect of the sheath electric field on the charged lunar dust is realized.

[0052] (5) Update the motion state of lunar dust particles according to Newton's second law At the next time step, the PIC program reads the new lunar dust particle information matrix, so that the iterative calculation realizes the bidirectional coupling between lunar dust particles and sheath.

[0053] At this point, the method for simulating the motion of charged lunar dust based on the coupling of plume lunar dust and the electric field on the lunar surface invented in this article has been completed. In addition, the above only describes some embodiments, which can be changed, modified, added or varied without departing from the scope and essence of the disclosed embodiments. The embodiments are illustrative rather than restrictive. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for simulating the motion of charged lunar dust based on the coupling of lunar dust plumes with the lunar surface electric field, characterized in that: The gas-solid two-phase flow model of the lander engine plume impacting the lunar dust, the solar wind-lunar regolith calculation model, the lunar dust particle charge calculation model, and the bidirectional coupling model of charged lunar dust and the solar wind-lunar regolith are integrated into a multi-model coupled method for simulating the motion of charged lunar dust.

2. The solar wind-lunar sheath calculation model according to claim 1, characterized in that: The charges of charged lunar dust particles and the charges of simulated particles in each grid are distributed to the corresponding grid nodes using the volume weight method. Compared with traditional PIC, the charge density statistics of lunar dust particles are added, and the charge density distribution of the grid is determined together with other simulated particles.

3. The charged lunar dust and solar wind-lunar sheath bidirectional coupling model as claimed in claim 1, characterized in that: The PIC program reads the lunar dust particle information matrix, incorporates the charge and position coordinates of all lunar dust particles in the calculation domain into the statistics of the charge density distribution, and solves the Poisson equation as the fourth type of charged particles in addition to solar wind electrons, solar wind ions, and lunar surface photoelectrons to obtain the sheath potential distribution. The electric field strength at the position coordinates of each lunar dust particle is calculated by electric field interpolation, the Coulomb force on the lunar dust particles is calculated, and the motion state of the lunar dust particles is updated according to Newton's second law. At the next time step, the PIC program reads the new lunar dust particle information matrix and repeats the above steps for iterative calculation.

4. The method for reading the lunar dust particle information matrix by a PIC program as claimed in claim 2, characterized in that: The form characteristics of the lunar dust particle information matrix are: x, y, z are the spatial coordinates of the lunar dust particles, u, v, w are the velocity components of the lunar dust particles in the x, y, z directions, q is the charge of the lunar dust particles, which is calculated by the charge calculation model described in claim 1, F is the drag force from the flow field on the lunar dust particles, which is calculated by the gas-solid two-phase flow model of the lander engine plume impacting the lunar dust described in claim 1, and the subscripts 1 to n are the indexes of the lunar dust particles in the program, and n corresponds to the number of lunar dust particles in the entire calculation domain.

Images