本文關(guān)鍵詞：基于能量轉(zhuǎn)換速度修正的分子動力學方法及靜止微納顆粒的受力特性研究　出處：《浙江大學》2017年碩士論文　論文類型：學位論文

  更多相關(guān)文章： 分子動力學 速度修正方法 ECBC 微納顆粒 布朗力

【摘要】：分子動力學(moleculardynamics,MD)模擬已成為研究微米或納米尺度動力學、流體及固體統(tǒng)計特性的重要工具。目前,分子動力學主要分為兩大類:平衡分子動力學(equilibrium molecular dynamics,EMD)和非平衡分子動力學(non-equilibrium molecular dynamics,NEMD)。本文針對 MD 模擬提出一 種新的基于能量轉(zhuǎn)換的速度修正法(energy conversion based correction,ECBC)。不同于傳統(tǒng)的依賴于宏觀參數(shù)的系統(tǒng)性速度修正方法,ECBC方法基于分子或原子對間的相互作用物理過程中的能量守恒與轉(zhuǎn)換特性發(fā)展而來。采用ECBC修正方法進行MD模擬時,由于不用施加額外勢能或引入溫度等宏觀參數(shù),因此毋需針對NEMD采用特殊的處理方法即可直接用于EMD和NEMD模擬,特別是非保守(開放)系統(tǒng)的MD模擬。該方法突破了現(xiàn)有MD計算方法基于保守平衡系統(tǒng)思想引起的許多應(yīng)用限制,可以極大的拓展MD應(yīng)用范圍。微納顆粒在流體中的布朗運動主要取決于流體分子對顆粒的作用力。由于顆粒尺寸極小,并且流體分子與其碰撞頻率極高,因此難以通過實驗手段測得顆粒所受布朗力。本文采用MD方法研究作用于顆粒的布朗力,發(fā)現(xiàn)一些很有意義的新現(xiàn)象:(1)對于不同的1/Kn數(shù),布朗力的概率分布都符合高斯分布且具有自相似性;(2)與常用于郎之萬模型不同,布朗力的頻譜圖并非白噪聲,而是具有優(yōu)先頻率的類似對數(shù)正態(tài)分布的噪聲;(3)隨著微納顆粒的尺寸變化,作用于顆粒的布朗力呈現(xiàn)出非單調(diào)性。當1/Kn數(shù)由小變大時,作用于顆粒的布朗力首先增加并且在1/Kn≈250達到最大值,之后隨著1/Kn數(shù)繼續(xù)增大,布朗力逐漸減小。本文發(fā)現(xiàn)的布朗力的變化規(guī)律對于顆粒的布朗運動的動力學特性研究將起到很好的促進作用。
[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，

本文編號：1385011