高超声速流中碳材料烧蚀的分子动力学模拟
发布时间：2018-11-09 08:17
【摘要】：高超声速环境下材料的烧蚀破坏问题是发展高超声速飞行器技术的关键问题。本文主要应用分子动力学方法对石墨受到高超声速氧分子流烧蚀过程进行了模拟研究。本文的主要工作有以下几个方面:(1)运用基于Reax FF力场势的分子动力学方法模拟了双层以及三层石墨与高超声速氧分子流的相互作用过程。石墨在高超声速氧分子流的持续冲击作用下,氧原子与表层石墨原子结合;可以观察到部分结合了氧原子的碳原子以CO2的形式从表层石墨解离,石墨出现缺陷,逐渐破坏。另外发现三层石墨的情况下表层石墨温度上升速度较慢。(2)运用基于REBO势的分子动力学方法对多层石墨受高超声速氧分子流的烧蚀过程进行了模拟。对LAMMPS中只包含碳、氢原子的REBO势函数进行修改,加入氧原子。分析了石墨氧化对其等效面内刚度的影响。研究发现,多层石墨在受到高超声速氧分子流冲击烧蚀过程中出现逐层破坏的现象,且模拟随着层数的增多,石墨破坏的时间相对延后。研究了缺陷对双层石墨受高超声速氧分子流冲击烧蚀过程的影响,发现双空位缺陷加速了表层石墨升温破坏的过程,单空位缺陷的影响次之,而Stone-Wales型缺陷对烧蚀过程的影响可以忽略。氧原子以吸附的方式与石墨结合对其等效面内刚度基本没有影响,而在缺陷处与碳原子结合则降低了石墨的等效面内刚度。(3)对研究石墨烧蚀问题时,分子动力学方法的可计算规模进行了探讨。运用基于REBO势的分子动力学方法采用单核计算对包含33516个碳原子,12000个氧原子的系统进行300ps的模拟,时间步长为1fs。总的计算机时约为10个小时,这相对于采用Reax FF力场势所能计算的规模有了很大的提高。另外详细描述了表层石墨在受高超声速氧分子流冲击作用过程中从缺陷产生、缺陷扩展到破坏解体的阶段性现象,分析了模拟过程中表层石墨的温度和系统势能的变化。
[Abstract]:The problem of material ablation in hypersonic environment is a key problem in the development of hypersonic vehicle technology. In this paper, the molecular dynamics method is used to simulate the process of supersonic oxygen molecular ablation of graphite. The main work of this paper is as follows: (1) the interaction process of two-layer and three-layer graphite with hypersonic oxygen flow is simulated by using the molecular dynamics method based on Reax FF force field potential. Under the continuous impact of hypersonic oxygen molecule flow, the oxygen atom binds to the surface graphite atom, and it can be observed that the carbon atom which binds oxygen atom dissociates from the surface graphite in the form of CO2, and the graphite appears defects and gradually destroys. In addition, it is found that the temperature of surface graphite rises slowly in the case of three layers of graphite. (2) the ablation process of multilayer graphite subjected to hypersonic oxygen flow is simulated by molecular dynamics method based on REBO potential. The REBO potential function containing only carbon and hydrogen atoms in LAMMPS is modified and oxygen atoms are added. The effect of graphite oxidation on the equivalent in-plane stiffness was analyzed. It is found that the multi-layer graphite is destroyed layer by layer in the process of supersonic oxygen molecular flow impact ablation, and the time of graphite destruction is relatively delayed with the increase of the number of layers. The effect of defects on the ablation process of double layer graphite by hypersonic oxygen molecular flow is studied. It is found that the double vacancy defect accelerates the process of surface graphite heating destruction, and the effect of single vacancy defect is the second. However, the effect of Stone-Wales defects on the ablation process can be neglected. The adsorption of oxygen atoms with graphite has little effect on the in-plane equivalent stiffness of graphite, but it decreases the equivalent in-plane stiffness of graphite by bonding with carbon atom at defects. (3) when studying the problem of graphite ablation, The computational scale of molecular dynamics method is discussed. The molecular dynamics method based on REBO potential was used to simulate the 300ps of a system containing 33516 carbon atoms and 12,000 oxygen atoms with a time step of 1fs. The total computer time is about 10 hours, which is much higher than that calculated by using the Reax FF force field potential. In addition, the phase phenomenon of surface graphite produced from defect to destruction and disintegration during the process of hypersonic oxygen molecular flow impact is described in detail. The temperature and system potential energy of surface graphite in the simulation process are analyzed.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：V219
[Abstract]:The problem of material ablation in hypersonic environment is a key problem in the development of hypersonic vehicle technology. In this paper, the molecular dynamics method is used to simulate the process of supersonic oxygen molecular ablation of graphite. The main work of this paper is as follows: (1) the interaction process of two-layer and three-layer graphite with hypersonic oxygen flow is simulated by using the molecular dynamics method based on Reax FF force field potential. Under the continuous impact of hypersonic oxygen molecule flow, the oxygen atom binds to the surface graphite atom, and it can be observed that the carbon atom which binds oxygen atom dissociates from the surface graphite in the form of CO2, and the graphite appears defects and gradually destroys. In addition, it is found that the temperature of surface graphite rises slowly in the case of three layers of graphite. (2) the ablation process of multilayer graphite subjected to hypersonic oxygen flow is simulated by molecular dynamics method based on REBO potential. The REBO potential function containing only carbon and hydrogen atoms in LAMMPS is modified and oxygen atoms are added. The effect of graphite oxidation on the equivalent in-plane stiffness was analyzed. It is found that the multi-layer graphite is destroyed layer by layer in the process of supersonic oxygen molecular flow impact ablation, and the time of graphite destruction is relatively delayed with the increase of the number of layers. The effect of defects on the ablation process of double layer graphite by hypersonic oxygen molecular flow is studied. It is found that the double vacancy defect accelerates the process of surface graphite heating destruction, and the effect of single vacancy defect is the second. However, the effect of Stone-Wales defects on the ablation process can be neglected. The adsorption of oxygen atoms with graphite has little effect on the in-plane equivalent stiffness of graphite, but it decreases the equivalent in-plane stiffness of graphite by bonding with carbon atom at defects. (3) when studying the problem of graphite ablation, The computational scale of molecular dynamics method is discussed. The molecular dynamics method based on REBO potential was used to simulate the 300ps of a system containing 33516 carbon atoms and 12,000 oxygen atoms with a time step of 1fs. The total computer time is about 10 hours, which is much higher than that calculated by using the Reax FF force field potential. In addition, the phase phenomenon of surface graphite produced from defect to destruction and disintegration during the process of hypersonic oxygen molecular flow impact is described in detail. The temperature and system potential energy of surface graphite in the simulation process are analyzed.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：V219
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