单晶硅磨削过程分子动力学仿真并行算法

建立单晶硅超精密磨削过程的三维分子动力学仿真模型,分析分子动力学仿真串行程序特点和并行仿真的可行性,提出基于区域二次划分的分子动力学仿真并行算法.编制并行仿真程序,进行分子动力学仿真,从瞬间原子位置图方面分析单晶硅超精密磨削过程的加工机理.将并行仿真结果与串行程序仿真结果进行对比分析,从瞬间原子位置图和系统能量方面验证并行程序结果的正确性,在仿真规模和计算时间方面并行程序有很大优势,从而说明并行仿真程序是有效的,可以应用在不同原子规模的分子动力学仿真计算中.     

基于辛算法的纳米加工过程的分子动力学仿真研究

近年来,从统计物理学中衍生出来的分子动力学仿真技术(Moleculardynamicssimulation,MDS)做为一种描述微观现象的有效方法,得到人们越来越广泛的重视,并成功应用于包括纳米加工技术在内的许多微观研究领域。随着分子动力学仿真技术的日益成熟,作为提高其计算精度及效率基础的仿真算法的研究也日益引起人们的关注。在运算周期很长的分子动力学仿真研究中,实践证明辛算法(Symplecticalgorithm)是一种高精度的收敛算法。以一维谐振摆为例,分析比较了几种辛算法和非辛算法的优劣,并进行了纳米加工的分子动力学仿真,从中可以看出辛算法有效地控制了动力学计算的误差积累,保证了计算精度。     

单晶铜纳米机械加工的分子动力学模拟与实验的间接对比

以单晶铜微探针纳米刻划加工为例,提出了一种分子动力学模拟与实验的间接对比方法,依次开展了工件材料的弹性常量的定量对比、工件材料机械性能的纳米压痕测量的定量对比、已加工表面形貌的定性对比。单晶铜工件压缩、剪切、拉伸和纳米压痕的分子动力学模拟显示,分子动力学模拟体系的弹性模量与实验测得值相同,压痕后工件表面材料堆积的对称特性与实验结果相符。研究结果表明,所使用的嵌入原子势能函数可以精确地描述单晶铜工件中铜原子之间的相互作用,纳米机械加工的分子动力学模拟具有较高的精度,并且可以很好地预测纳米机械加工的实验结果。     

单晶铜薄膜纳米压痕过程的分子动力学模拟

使用三维分子动力学方法模拟了单晶铜薄膜的纳米压痕过程,研究了压头半径对纳米压痕过程的影响;采用Morse势函数计算试样原子与压头原子之间、试样原子之间的相互作用关系.结果表明:单晶铜薄膜纳米压痕的力学机理是非晶态产生的变形;纳米压痕过程具有尺寸效应,压头大小对单晶铜薄膜纳米压痕的分子动力学模拟结果有显著的影响.     

基于分子动力学的单晶硅压痕过程计算机仿真研究

对单晶Si的压痕过程进行了分子动力学模拟.采用Morse势函数描述原子间的相互作用,以牛顿方程建立力学运动方程,使用改进后的Verlet算法解原子运动轨迹,通过对MD仿真结果的分析研究,将压痕过程分为三个特征阶段,即初期弹性变形阶段、中期塑性变形阶段及非晶层形成阶段.并从原子角度分析了压痕过程中原子间势能、磨削力的变化、应力状态、磨削温度等特征,解释了微观材料的去除和表面形成机理.     

基于单晶铜的纳米压痕的机理分析

为了进一步深入研究纳米压痕的机理，提高纳米压痕的测量精度和应用范围，对单晶铜纳米压痕的机理展开详细分析与研究。从纳米压痕的理论方法入手，建立单晶铜的分子动力学模型，利用该模型对压力和势能进行仿真分析，并得到相应的曲线。在单晶铜的纳米压痕过程中，压力先增加后下降，其中，曲线的波动主要受表面粗糙度、表面化学反应膜、表面力、表面加工硬化等因素的影响；原子势能一直上升，最后趋于稳定，推断出纳米压痕没有出现位错的现象。最后，对纳米压痕的局限性进行总结，并针对不同的问题，提出行之有效的措施，为纳米压痕的精度提高奠定良好的基础。     

光学石英玻璃纳米级加工性能

提出了一种石英玻璃仿真模型的构建方法,并应用分子动力学(MD)仿真结合纳米压痕实验对石英玻璃进行了纳米级加工性能的研究。通过计算石英玻璃模型的密度和纳米硬度,验证了模型的准确性。对石英玻璃进行了纳米压痕实验,得到了压痕曲线并观察了纳米压痕形貌。最后,对纳米级压痕过程进行了仿真,通过计算配位数研究了损伤层的形成及扩展机理。计算得到的石英玻璃模型的纳米硬度约为9.7~10.7GPa,密度约为2.28g/cm3,与实际测量结果基本一致。仿真结果表明:石英玻璃有着稳定的塑性变形和少量的弹性变形,且存在压痕的尺寸效应。当压头压下时会形成大量的原子稠密区,失去原来共价键的强度,形成损伤层;而表面形貌主要是由于压头向两侧挤压原子和压头的黏附作用形成的。仿真和实验结果都表明石英玻璃比较适合超精密加工。     

各向同性热解石墨的纳米压痕试验与有限元仿真研究

通过对各向同性热解石墨进行了纳米压痕试验,得到了其材料的载荷-位移曲线.并根据Olive和Pharr理论算出了其硬度与弹性模量值,得到了主要的材料性能.在纳米压痕试验的基础上,通过有限元单元法建立了纳米压痕试验的数值模型,通过比较有限元所拟合的载荷一位移曲线和实际纳米压痕试验所得到的曲线,进行相应的修正,最后得到了该材料的塑性性能,也证明了有限元仿真的可行性.     

MEMS粘附问题研究

针对MEMS粘附现象,论述了有关粘附问题的研究现状,揭示了粘附的本质和研究范围,介绍了目前研究粘附问题所用的分子动力学、连续介质法、准连续介质法、蒙特卡罗法及纳米压痕法和悬臂梁法等各种计算和实验的前沿方法,并对粘附研究的发展提出了初步展望.     

CGMD运算方法在纳米压痕上的应用

分子动力学是用来描述原子尺度行为的一种重要方法,但是如果尺度上升到巨宽尺度,分子动力学所需要的计算量非常庞大,其运算时间也需要很长。针对上述问题,研究了将CGMD运算方法运用到纳米压痕上,并将得到的结果与分子动力学进行比较,结果表明,CGMD与分子动力学这2种运算方法在纳米压痕的变形机制与物理行为是很接近的,但由CGMD模拟得到的载荷-位移曲线所估算的薄膜基板材料性质略高于分子动力学的模拟结果。     

单晶铜纳米压印亚表层晶体结构演变机理

为研究纳米压印中单晶铜亚表层晶体结构演变机理,采用分子动力学方法构建纳米压印仿真模型并模拟单晶铜纳米压印过程。采用改进的中心对称参数法分析单晶铜试件位错形核过程及缺陷演化机理,发现纳米压印时位错缺陷在压头下方形核并沿{1 1 1}滑移系向试件内部扩展形成堆垛层错,试件表面有原子台阶残留,试件亚表面损伤层存在V形位错等典型缺陷。针对位错形核区域及位错扩展区域材料晶体结构状态的识别,采用球谐函数法对模拟结果进行分析。由分析结果可知:位错形核区域材料晶体结构由FCC转变为排列更为紧密的HCP和ICO结构;位错扩展区域材料主要转变为DFCC结构。     

Stabilized multi-domain simulation algorithms and their application in simulation platform for forging manipulator

Most researches focused on the analytical stabilized algorithm for the modular simulation of single domain, e.g., pure mechanical systems. Only little work has been performed on the problem of multi-domain simulation stability influenced by algebraic loops. In this paper, the algebraic loop problem is studied by a composite simulation method to reveal the internal relationship between simulation stability and system topologies and simulation unit models. A stability criterion of multi-domain composite simulation is established, and two algebraic loop compensation algorithms are proposed using numerical iteration and approximate function in multi-domain simulation. The numerical stabilized algorithm is the Newton method for the solution of the set of nonlinear equations, and it is used here in simulation of the system composed of mechanical system and hydraulic system. The approximate stabilized algorithm is the construction of response surface for inputs and outputs of unknown unit model, and it is utilized here in simulation of the system composed of forging system, mechanical and hydraulic system. The effectiveness of the algorithms is verified by a case study of multi-domain simulation for forging system composed of thermoplastic deformation of workpieces, mechanical system and hydraulic system of a manipulator. The system dynamics simulation results show that curves of motion and force are continuous and convergent. This paper presents two algorithms, which are applied to virtual reality simulation of forging process in a simulation platform for a manipulator, and play a key role in simulation efficiency and stability.     

求解模糊作业车间调度问题的混合优化算法

针对模糊作业车间调度问题(Fuzzy job-shop scheduling problem, FJSSP),提出一种结合化学反应优化和禁忌搜索的混合算法(Chemical-reaction optimization and tabu search, CROTS),优化的目标是最小化最大模糊完工时间。算法采用基于工序的编码,通过扩展壁面碰撞、分子碰撞、合成、分解等操作算子,改进了基本化学反应优化(Chemical-reaction optimization, CRO)的四类基元反应。给出一种有效的交叉算子,并应用到分子碰撞、合成、分解三种基元反应中。对最好解进行禁忌搜索,进一步提高种群的搜索能力。结合16个经典算例试验分析,并与三种典型算法比较,验证算法具有较强的全局和局部搜索能力。通过18个随机算例的测试,验证算法具备求解较大规模问题的能力。     

A Local Region Molecular Dynamics Simulation Method for Nanoscale Sliding Contacts

Computational efficiency and accuracy always conflict with each other in molecular dynamics (MD) simulations. How to enhance the computational efficiency and keep accuracy at the same time is concerned by each corresponding researcher. However, most of the current studies focus on MD algorithms, and if the scale of MD model could be reduced, the algorithms would be more meaningful. A local region molecular dynamics (LRMD) simulation method which can meet these two factors concurrently in nanoscale sliding contacts is developed in this paper. Full MD simulation is used to simulate indentation process before sliding. A criterion called contribution of displacement is presented, which is used to determine the effective local region in the MD model after indentation. By using the local region, nanoscale sliding contact between a rigid cylindrical tip and an elastic substrate is investigated. Two two-dimensional MD models are presented, and the friction forces from LRMD simulations agree well with that from full MD simulations, which testifies the effectiveness of the LRMD simulation method for two-dimensional cases. A three-dimensional MD model for sliding contacts is developed then to show the validity of the LRMD simulation method further. Finally, a discussion is carried out by the principles of tribology. In the discussion, two two-dimensional full MD models are used to simulate the nanoscale sliding contact problems. The results indicate that original smaller model will induce higher equivalent scratching depth, and then results in higher friction forces, which will help to explain the mechanism how the LRMD simulation method works. This method can be used to reduce the scale of MD model in large scale simulations, and it will enhance the computational efficiency without losing accuracy during the simulation of nanoscale sliding contacts.     

A Local Region Molecular Dynamics Simulation Method for Nanoscale Sliding Contacts

Computational e ciency and accuracy always conflict with each other in molecular dynamics(MD) simulations. How to enhance the computational e ciency and keep accuracy at the same time is concerned by each corresponding researcher. However, most of the current studies focus on MD algorithms, and if the scale of MD model could be reduced, the algorithms would be more meaningful. A local region molecular dynamics(LRMD) simulation method which can meet these two factors concurrently in nanoscale sliding contacts is developed in this paper. Full MD simulation is used to simulate indentation process before sliding. A criterion called contribution of displacement is presented, which is used to determine the e ective local region in the MD model after indentation. By using the local region, nanoscale sliding contact between a rigid cylindrical tip and an elastic substrate is investigated. Two two?dimensional MD models are presented, and the friction forces from LRMD simulations agree well with that from full MD simulations, which testifies the e ectiveness of the LRMD simulation method for two?dimensional cases. A three?dimensional MD model for sliding contacts is developed then to show the validity of the LRMD simulation method further. Finally, a discussion is carried out by the principles of tribology. In the discussion, two two?dimensional full MD models are used to simulate the nanoscale sliding contact problems. The results indicate that original smaller model will induce higher equivalent scratching depth, and then results in higher friction forces, which will help to explain the mechanism how the LRMD simulation method works. This method can be used to reduce the scale of MD model in large scale simulations, and it will enhance the computational e ciency without losing accuracy during the simula?tion of nanoscale sliding contacts.     

大规模生产调度问题的研究现状与展望

为解决大多数已有调度算法无法直接应用于大规模生产调度的问题，以典型生产调度问题为背景，综述了现阶段已有大规模生产调度问题的算法。分析了大规模生产调度问题规模增长的因素，重点介绍了基于问题分解的各类方法、拉格朗日松弛／分解法及智能优化算法。在此基础上，展望了大规模生产调度问题的研究发展趋势。     

基于十字链叉的NURBS曲面插补算法及仿真分析

针对目前曲面插补算法存在的实时性不强,插补算法需要大量的额外空间,算法步骤繁琐以及对插补过程产生的大量数据点的数据处理问题,为了保证作为数控技术核心模块的曲面插补算法的高速、高精度性能,基于德布尔递推算法思想,重新推导出了适合于曲面插补的新的NURBS曲面表达式,在此基础上重新设计了曲面插补快速算法,并着重研究了新算法的实时性.另外,为验证新算法的正确性和有效性,提出并实现了十字链叉数据表达结构,对NURBS曲面插补点微细步长及插补质量进行了分析.建立了以VC6.0/MFC为平台的、集弓高误差、速度、加速度等功能分析于一体的算法仿真验证系统,并以汽轮机叶片为例进行了验证.研究结果表明,该算法可以满足曲面插补高速、高精度的性能要求.     

基于匈牙利算法的路由排队研究及仿真

输入排队调度算法就是通过获得路由器输入输出端口的最大匹配从而达到提高吞吐量的目的。在调度算法理论研究中可以采用二部图最大匹配的MSM和MWM算法作为各种调度算法性能的评价标准。匈牙利算法是二部图匹配的经典算法,将匈牙利算法应用到输入排队调度算法中,得出了典型算法MSM和MWM的性能仿真曲线,为未来高性能路由器的设计提供了依据。     

汽车传动系相关NVH问题的动力学研究论述

总结汽车传动系相关NVH问题的难点,典型振动、噪声现象的特征及产生机理和国内外研究进展,介绍传动系噪声、振动与声振粗糙度(Noise, vibration and harshness, NVH)动力学问题的主要研究内容及路线。从仿真和试验的角度展开论述：在仿真研究中,详细分析系统动力学、多体动力学、结构动力学模型及系统、结构动力学混合模型的四种传动系力学模型及其各自的特点,总结建模所使用的坐标与坐标系,并针对传动系NVH问题的动力学研究,从定量与定性两个方面总结主要的仿真研究方法;在试验研究中,介绍试验研究的主要内容、数据处理的方法及试验的主、客观评价方法。