ReaxFF力场方法及其在含能材料中应用的研究进展

从ReaxFF分子动力学在含能材料领域的研究出发,聚焦于研究ReaxFF力场的构成和发展、力场优化方法和应用等方面。在力场开发方法方面,对局域优化方法和全局优化方法进行了重点介绍,其中多目标进化策略、增强的粒子群优化算法和基于神经网络等开发策略均有所涵盖。ReaxFF力场在含能材料模拟中的应用主要集中于探索微观结构反应性、动态演化、初始化学分解路径以及中间和稳定产物分布。根据外部条件不同而分为加热和加压、冲击加载、激光和电场等应用场景。研究主体涉及单质/共混/共晶炸药、含有缺陷炸药以及金属复合炸药。最后,针对ReaxFF的准确性和迁移性进行了展望,认为在人工智能框架下的ReaxFF反应力场训练可以大幅提高其在复杂反应中的准确性。在连续体仿真模型中,若将其局域反应度等关键指标的唯象规律替换为基于ReaxFF的反应规律,将是实现一个包含力学和化学动力学响应耦合的多尺度全流程仿真计算的重要途径。附参考文献134篇。

优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测,以正构烷烃(n-C4~C10)为训练集,通过对全原子OPLS-AA力场中非键相互作用参数(ε)的模拟优化,得到了ε与对比温度(Tr)以及正构烷烃碳原子个数(NC)的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值,预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性,并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明,采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%,显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立,对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。

CO_2在LTA型和FAU型沸石分子筛中吸附的力场研究

采用巨正则系综的蒙特卡罗法,利用几种通用力场对LTA型4A分子筛吸附CO_2进行模拟研究,基于Dreiding力场分析力场参数σ和ε对模拟结果的影响,得到适用于4A分子筛吸附CO_2的准确Dreiding力场参数。将该力场参数应用到LTA型5A分子筛吸附模拟中,得到5A分子筛吸附模拟的力场参数。最后将4A分子筛吸附CO_2的力场参数应用到FAU型13X分子筛的吸附模拟中。结果表明:模拟结果与实验数据吻合较好,分子筛阳离子的改变对吸附力场影响较大,而分子筛结构对力场的影响相对较小。与13X具有同种阳离子的4A分子筛力场参数可直接作为13X分子筛的力场,具有通用性。

Middle or low water pressure direct spiral double helix converging nozzle structure optimization and flow field analysis

In order to solve the problem of using new nozzle is proposed in fire rescue robot. middle or low water pressure to form fine water mist, a Existing water mist nozzles are basically used for high pressure and in large size, complex structure and poor low pressure atomization effect in comparison with requirement of snake-like fire rescue robots. On the basis of comprehensive typical spray noz- zles, a direct spiral double helix converging nozzle （DSDHCN） is proposed, which has the advanta- ges of small volume, light weight, simple structure, and convenient installation. To make the spray nozzle have good performance, and meet the requirements of more efficient fire extinguishing, a nu- merical study is carried out to analyze the internal and external full flow field of nozzle. A gas-liquid two-phase flow is applied to simulate the external full flow field of nozzle with VOF model in fluent software. The simulation results show the real situation of water flow out of the atomization nozzle and the water jet trajectory. Some simulations about middle or low water pressure direct spiral double he- lix converging optimized nozzle have been done in 30bar pressure. The simulation results show that the optimized nozzle structure not only makes the spray droplets have a good cone angle, but also have a sufficient axial velocity,which proves the structure rationality of the proposed optimized nozzle.

HOW to Look at the ＂Migrant Worker Shortage＂ from an Economic Perspective

The ＂migrant worker shortage＂ which occurred several）pears ago and the recent ＂labor shortage＂ were both caused by an imbalance between the supply and demand of migrant workers. It is a periodical outcome of spontaneous adjustment by the migrant labor market. As rural welfare was greatly enhanced in 2009, migrant workers＇ opportunity cost of working outside their hometowns was raised. The connotation of migrant workers＇ ＂market price＂ is changing. The new generation of migrant workers, namely, those born after 1980, are becoming the mainstay of enterprises＇ employment. Being better educated, they have different lifestyles than previous generations. ＂Leisure and entertainment＂ have become part of their opportunity cost and reduced their labor supply. ＂Labor shortage＂ is an endogenous force that helps transform China＇s growth patter, upgrade the industrial structure and promote urbanization. The seasonal ＂return of migrant workers＂ and the ＂labor shortage＂ which appears around China＇s Spring Festival each year have grown into a unique b,t effective collective bargaining mechanism that helps increase migrant workers＇ wages. Facing labor shortages, governments should regulate the labor market pricing and orientate labor-intensive enterprises towards transition, continue to enhance the social security system for migrant workers and those in rural areas, and make an accurate forecast of the population trend and adjust population policies.

Optimal short-term load dispatch strategy in wind farm

With the increasing number of wind farms in power systems, the scheduling of a single wind farm needs to be improved. For this end, this paper proposes an optimal short-term load dispatch strategy for a single wind farm. Firstly, considering the large number of wind units and the high dimensionality of the scheduling solutions, we analyze the unit load characteristics, from which we extract the unit load characteristic matrix, and then classify the wind power units with the FCM fuzzy clustering algorithm. Secondly, we define the running loss indicator and action loss indicator. Based on the prediction of wind power and the load instructions, we establish a unit commitment model in wind farm, and solve the model using a combination of the fuzzy clustering algorithm and genetic algorithm, which overcomes the difficulty of the high dimensionality of the solution in the wind farm scheduling problem, to obtain the optimal scheduling strategy. Finally, through the simulation of the scheduling strategy for a 45 MW wind farm, we demonstrate the feasibility and effectiveness of the proposed strategy.

High-efficiency magnetophoretic separation based on synergy of magnetic force field and flow field in microchannels

Magnetophoresis is one of the most important separation methods in biological and chemical engineering. In this paper,a novel impact parameter on separation efficiency,i.e.,the angle between the vectors of magnetic force and fluid velocity,was derived from the basic equation describing the motion of magnetic beads in microchannels. It is proposed that one of the most important approaches for separation efficiency enhancement is to improve the coordination of magnetic force field and fluid flow field. A T-shaped microchannel magnetophoretic separator was designed based on the angle. And then a two-dimensional dynamic model of magnetic beads moving in microchannels was established to study the separation efficiency of T-shaped microseparator by combined use of finite element method and Runge-Kutta method. The results show that the capture effi-ciency of T-shaped microseparator is much higher than that of the straight microseparator at the same conditions. For small magnetic beads at high fluid velocities,the designed T-shaped microseparator could still keep high separation efficiency whereas the conventional straight microseparator fails to separate the magnetic beads. Further analysis shows that the mechanism of separation efficiency enhancement lies in the synergy of magnetic force field and flow field,which directly leads to large deflected velocity of the magnetic beads from the main stream,and thus increasing the separation efficiency. It is anticipated that the results in this paper are theoretically helpful for the optimum design of highly efficient magnetophoretic separators.

Optimization of CHARMM force field parameters for the chalcone fragment

In this work,we developed the CHARMM all-atom force field parameters for the nonstandard biological residue chalcone,followed by the standard protocol for the CHARMM27 force field development.Target data were generated via ab initio calculations at the MP2/6-31G* and HF/6-31G* levels.The reference data included interaction energies between water and the model compound F(a fragment of chalcone).Bond,angle,and torsion parameters were derived from the ab initio calculations and renormalized to maintain compatibility with the existing CHARMM27 parameters of standard residues.The optimized CHARMM parameters perform well in reproducing the target data.We expect that the extension of the CHARMM27 force field parameters for chalcone will facilitate the molecular simulation studies of the reaction mechanism of intramolecular cyclization of chalcone catalyzed by chalcone isomerase.