月球表面鞘层的数值模拟

发布时间：2018-06-13 15:44

本文选题：月球表面鞘层 + 数值模拟　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：月球表面的月壤环境对登月航天器和探月设备仪器的可靠性提出了极为严峻的挑战，在月球表面电场环境下，月尘带电导致悬浮，月尘的悬浮容易引起航天器表面污染、磨损、发热等故障，因此研究月球表面电场环境具有重要意义，而月球表面电场的主要表现形式是月球表面鞘层。为了探究月球表面鞘层，本文建立了月球表面鞘层的数学模型，得到了月球表面鞘层内各粒子的密度分布函数表达式和边界条件，进而建立了基于粒子模拟（Particle In Cell）方法的三维数值模拟程序，分别对月球表面单一鞘层内和不同类型鞘层交界区域内粒子（电子、离子、光电子）的运动进行了模拟。使用两种方法分别得到了月球表面鞘层的电势分布、各粒子的密度分布和总体电荷密度分布，两种方法的研究结果非常接近，与观测数据基本吻合，并分析了鞘层内各粒子的相对数量关系。分析了影响数值模拟程序精确度的因素，对数值模拟程序进行了初步的优化。基于建立的数学模型和数值模拟仿真程序，探究了月球表面鞘层的类型、不同类型鞘层的交界区域的过渡情况和影响鞘层振荡的因素，研究了太阳风速度、光电子密度及光照角度对鞘层的影响，分析了引入电子漂移速度的必要性。研究结果表明，基于PIC方法的数值模拟仿真程序能够很好地模拟月球表面鞘层，得到的结果在观测数据范围之内；在太阳风速度较大且靠近太阳光直射点时，月球表面的鞘层处于振荡状态，不存在反鞘层，太阳风速度和光电子密度对鞘层振荡幅度有重要影响，振荡频率与等离子体频率在同一量级，且此处月球表面电势周期性变化；电子漂移速度对研究结果具有重要影响，随着光照角度的增大，影响越来越明显，，因此在研究月球表面鞘层时不可以忽略电子的漂移速度；研究发现过渡区域月球表面电势和鞘层电场能量连续变化，随着光照角度的增大，鞘层类型依次为经典鞘层、空间饱和鞘层、振荡鞘层；太阳风速度、光电子密度、光照角度对鞘层具有显著影响，对于同一类型的鞘层，随着太阳风速度的增大，鞘层厚度减小，而光电子密度对鞘层厚度几乎没有影响。
[Abstract]:The lunar soil environment on the lunar surface poses an extremely severe challenge to the reliability of lunar spacecraft and lunar exploration equipment. Under the environment of the lunar surface electric field, the lunar dust is charged to cause the suspension, and the suspension of the lunar dust is liable to cause the spacecraft surface pollution and wear. Therefore, it is very important to study the surface electric field environment of the moon, and the main form of the lunar surface electric field is the lunar surface sheath. In order to explore the sheath layer of the lunar surface, a mathematical model of the sheath layer of the lunar surface is established, and the density distribution function and boundary conditions of the particles in the sheathing layer of the lunar surface are obtained. A three-dimensional numerical simulation program based on Particle in Cell-based particle simulation method is developed to simulate the motion of particles (electrons, ions, optoelectrons) in the single sheath layer and the boundary region of different types of sheath layers on the lunar surface, respectively. The potential distribution, particle density distribution and total charge density distribution of the sheath layer on the surface of the moon are obtained by using two methods. The results of the two methods are very close to each other and are in good agreement with the observed data. The relative quantitative relationship of the particles in the sheath layer was also analyzed. The factors influencing the accuracy of numerical simulation program are analyzed, and the numerical simulation program is preliminarily optimized. Based on the established mathematical model and numerical simulation program, the types of sheaths on the surface of the moon, the transition of the boundary regions of different types of sheaths and the factors affecting the oscillation of the sheaths are investigated, and the velocity of the solar wind is studied. The influence of optoelectron density and illumination angle on the sheath is analyzed, and the necessity of introducing electron drift velocity is analyzed. The results show that the simulation program based on PIC method can simulate the lunar surface sheath well, and the results are within the range of observed data, when the solar wind velocity is large and close to the point of direct solar light, The sheath of the lunar surface is in an oscillating state and there is no anti-sheath. The solar wind velocity and optoelectron density have an important influence on the oscillation amplitude of the sheath. The oscillation frequency is in the same order of magnitude as the plasma frequency, and the potential of the lunar surface changes periodically. The electron drift velocity has an important influence on the research results, and the influence becomes more and more obvious with the increase of illumination angle. Therefore, the electron drift velocity can not be ignored in the study of the lunar surface sheath. It is found that the surface potential and sheath electric field energy change continuously in the transitional region. With the increase of illumination angle, the sheath types are the classical sheath, the spatial saturation sheath, the oscillatory sheath, the solar wind velocity, the photoelectron density, the solar wind velocity, the photoelectron density, the solar wind velocity and the photoelectron density. For the same type of sheath, the thickness of sheath decreases with the increase of solar wind velocity, but the density of photoelectron has little effect on the thickness of sheath.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P184.5

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