基于能量转换速度修正的分子动力学方法及静止微纳颗粒的受力特性研究

发布时间：2018-01-05 22:04

  本文关键词：基于能量转换速度修正的分子动力学方法及静止微纳颗粒的受力特性研究　出处：《浙江大学》2017年硕士论文　论文类型：学位论文

  更多相关文章： 分子动力学 速度修正方法 ECBC 微纳颗粒 布朗力

【摘要】：分子动力学(moleculardynamics,MD)模拟已成为研究微米或纳米尺度动力学、流体及固体统计特性的重要工具。目前,分子动力学主要分为两大类:平衡分子动力学(equilibrium molecular dynamics,EMD)和非平衡分子动力学(non-equilibrium molecular dynamics,NEMD)。本文针对 MD 模拟提出一 种新的基于能量转换的速度修正法(energy conversion based correction,ECBC)。不同于传统的依赖于宏观参数的系统性速度修正方法,ECBC方法基于分子或原子对间的相互作用物理过程中的能量守恒与转换特性发展而来。采用ECBC修正方法进行MD模拟时,由于不用施加额外势能或引入温度等宏观参数,因此毋需针对NEMD采用特殊的处理方法即可直接用于EMD和NEMD模拟,特别是非保守(开放)系统的MD模拟。该方法突破了现有MD计算方法基于保守平衡系统思想引起的许多应用限制,可以极大的拓展MD应用范围。微纳颗粒在流体中的布朗运动主要取决于流体分子对颗粒的作用力。由于颗粒尺寸极小,并且流体分子与其碰撞频率极高,因此难以通过实验手段测得颗粒所受布朗力。本文采用MD方法研究作用于颗粒的布朗力,发现一些很有意义的新现象:(1)对于不同的1/Kn数,布朗力的概率分布都符合高斯分布且具有自相似性;(2)与常用于郎之万模型不同,布朗力的频谱图并非白噪声,而是具有优先频率的类似对数正态分布的噪声;(3)随着微纳颗粒的尺寸变化,作用于颗粒的布朗力呈现出非单调性。当1/Kn数由小变大时,作用于颗粒的布朗力首先增加并且在1/Kn≈250达到最大值,之后随着1/Kn数继续增大,布朗力逐渐减小。本文发现的布朗力的变化规律对于颗粒的布朗运动的动力学特性研究将起到很好的促进作用。
[Abstract]:Molecular dynamics molecular dynamics (MD) simulation has become an important tool for the study of dynamics, fluid and solid statistical properties in micron or nanoscale scale. Molecular dynamics can be divided into two main categories: equilibrium molecular dynamics equilibrium molecular dynamics. EMD) and non-equilibrium molecular dynamics. In this paper, a new speed correction method based on energy conversion is proposed for MD simulation. Energy conversion based correction. Different from the traditional systematic velocity correction method which depends on the macroscopic parameters, ECBCU is different from the traditional one. The ECBC method is based on the energy conservation and conversion characteristics in the physical processes of molecular or atomic interaction. The ECBC correction method is used to simulate MD. Because there is no need to apply extra potential energy or introduce macroscopical parameters such as temperature, it is not necessary to adopt special processing method for NEMD to be directly used in EMD and NEMD simulation. Especially for the MD simulation of non-conservative (open) systems, this method breaks through many application limitations caused by the existing MD calculation methods based on conservative equilibrium systems. The Brownian motion of micro and nanocrystalline particles in fluid mainly depends on the force of fluid molecules on particles. Because the particle size is very small and the collision frequency between fluid molecules and it is very high. Therefore, it is difficult to measure the Brownian force of particles by experimental means. In this paper, the Brownian force acting on particles is studied by using MD method, and it is found that some significant new phenomena: 1) for different 1 / Kn numbers. The probability distribution of Brownian force accords with Gao Si distribution and has self-similarity. (2) unlike the Langevin model, the spectrum of Brownian force is not a white noise, but a noise similar to the logarithmic normal distribution with priority frequency. (3) the Brownian force acting on the particles shows non-monotonicity with the change of the size of the micro- and nanocrystalline particles, when the number of Kn increases from small to large. The Brownian force acting on the particles first increases and reaches a maximum at 1 / Kn 鈮，

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