微管道中Cu-水纳米流体的流动特性(英文)

采用数值模拟和实验相结合的方法,对压力驱动下质量分数为1%的Cu-水纳米流体在直径分别为25μm和50μm且长度不同的微管道中的流动特性进行研究.实验过程中采用两步法制得稳定的纳米流体.研究结果表明,纳米流体的流量-压力特性基本呈线性关系,且流量随驱动压力的增大而增大,其流动特性符合单相流体的假设.但模拟结果与实验结果之间存在一定的差异,主要是由于基液中颗粒的团聚结构、纳米流体黏度的变化、尺度效应和边界滑移等因素造成的.     

封闭腔内MWCNT纳米流体自然对流传热的数值模拟

采用Fluent软件对封闭腔内纳米流体层流自然对流换热进行了数值模拟研究.重点分析了Ra数和纳米颗粒的体积分数对自然对流换热特性的影响.数值模拟结果表明:在机油中添加多壁碳纳米管(MWCNT)粒子并没有提高基液的自然对流传热特性;对于给定的Ra数下,随着纳米颗粒体积分数的增大,纳米流体的传热特性也随之减弱;对于给定的体积分数,随着Ra数的增大,纳米流体的传热特性显著增强,但纳米流体的传热性能比机油的要弱,且在同一体积分数下随着Ra数的增大,传热性能减弱的程度要减小.     

环形液池内耦合热-溶质毛细对流转变过程的二维数值模拟

为了解环形液池内耦合热-溶质毛细对流的转变特征,建立了环形液池内的耦合热-溶质毛细对流的物理数学模型,采用有限容积法进行二维数值模拟,得到了环形液池内耦合热-溶质毛细对流失稳的临界条件,并对耦合热-溶质毛细对流失稳机理进行了分析。结果表明:环形液池内流态从稳态到非稳态的转变为霍普夫分岔;随着深宽比、半径比和普朗特数的增加,流动更容易失稳;当刘易斯数大于1时,临界毛细雷诺数随着刘易斯数的增大而减小,流动失稳是由于溶质Marangoni效应的主导作用和流动的惯性共同作用的结果;而当刘易斯数小于1时,随着刘易斯数的增大,临界毛细雷诺数增大,流动失稳则是由于热Marangoni效应的主导作用和流动的惯性共同作用的结果。     

封闭腔内纳米流体自然对流换热的数值模拟

采用数值模拟方式研究充满了纳米流体的封闭腔内的稳态自然对流。重点分析了纳米颗粒的体积分数,Ra数以及不同类型纳米颗粒对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;对于给定的Ra数下,随着纳米流体的体积分数增大,纳米流体换热效果显著增强;对于给定的体积分数下,随着Ra数增大,纳米流体的换热强度也随之增大,并且换热机理由热传导为主变为热对流为主;通过Ag,Cu,CuO和Al2O3四种纳米颗粒的对流换热效果比较分析得出,金属Ag和Cu纳米颗粒比金属氧化物CuO和Al2O3的纳米颗粒制备的纳米流体的对流换热效果更好。     

氧化石墨烯纳米流体分散性及过冷特性研究

以质量分数为0.05%的氧化石墨烯纳米流体为实验对象,测量了不同超声分散时间下氧化石墨烯纳米流体的粒度和Zeta电位分布。同时测定了降温过程中氧化石墨烯纳米流体的过冷度和相变时间,探讨了超声时间对氧化石墨烯纳米流体分散性和过冷特性的影响。实验结果表明,超声分散时间越长,分散性能越好,但在150min后,粒径和Zeta电位大小趋于稳定;且超声分散时间为150min时,过冷度较小,相变时间较短,分别为5.2℃和4870s。     

低温气液两相流中压力波传播特性研究

以竖直管路中的液氧-气氧两相流体为研究对象,构建了液氧流动冷凝与压力波传输数学模型,并通过实验数据验证了数学模型的正确性。数值模拟了不同流速下液氧-气氧的流动冷凝过程,得到了流速对压力波传播情况的影响规律。结果表明:过热气氧在液氧中发生流动冷凝的过程中,沿流动方向截面含气率逐渐减小,且随着入口流速的增加,气氧在管内冷凝的长度逐渐增加;在恒定扰动频率下,管路内流速越大,压力波的传播速度越慢,衰减幅度越大。     

狭缝宽度及坩埚半径对分离结晶法制备CdZnTe晶体的影响

借助有限元法,在常重力条件下对分离结晶过程进行全局数值模拟,研究了狭缝宽度及坩埚半径对CdZnTe晶体生长过程中整体传热与流动特性的影响。模拟结果表明系统内传热特性、熔体流型与狭缝宽度及坩埚半径密切相关:(1)狭缝宽度对分离结晶有决定性的作用,当狭缝宽度较小时,气-液弯界面两端的温差很小,导致增大晶体重新粘附于坩埚壁面的风险;随着狭缝宽度的增大,流动不稳定性增加,很难保持稳定的气-液弯界面形状,增加了实现晶体稳定生长的难度;(2)随着坩埚半径增大,Marangoni对流对熔体流动影响逐渐增大,结晶界面附近的熔体流动不稳定性增加,这不利于晶体的稳定生长。     

圆环腔内纳米流体自然对流的数值研究

采用Fluent软件对圆环封闭腔内的Ag-水纳米流体自然对流传热进行数值模拟,着重分析在不同瑞利数下Ag纳米颗粒的添加量和圆环内外壁半径比对圆环传热性能的影响.研究结果表明,随着瑞利数的增加,圆环间的换热强度不断加剧,换热由热传导逐渐向对流转变.添加纳米颗粒降低了换热性能,且随着颗粒浓度的增加换热效果不断恶化;同时,圆环半径比对换热有很大的影响,对一定的瑞利数而言随着半径比的减小,换热性能逐渐增强,且增大的趋势越来越显著.     

搅拌摩擦焊焊缝塑性流动规律的数值模拟

使用FLUENT流体工程仿真软件对搅拌摩擦焊缝金属的塑性流动进行了数值模拟;初步得出了搅拌摩擦焊焊缝塑性流体流动规律.实验结果表明:随着距轴肩和搅拌针距离的增大,速度场开始减弱,焊缝金属由顶面向底面、由搅拌区向旋转区的流动也随之减弱.     

倾斜方腔内纳米流体自然对流的数值研究

对充满Cu-水纳米流体的二维倾斜方腔内的自然对流换热进行了数值研究,研究了纳米颗粒体积份额φ、Ra数和腔体倾角对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;在一定的腔体倾角φ下,增大Ra均可以强化腔体内的自然对流换热,而且随Ra数的增大,强化效果越强;当Ra=104时,对不同的腔体倾角,纳米流体对换热强度提高的比例大致相当。     

Computer simulations of surfactants and surfactant/polymer assemblies

Applications of computer simulation methods, such as atomistic simulation, coarse-grain simulation and mesoscopic simulation, on surfactant assemblies at the interface, surfactant aggregates, and the surfactant/polymer assemblies were summarized based on our works. And the development and prospect of applying computer simulation to study self-assembling surfactant systems were also referred to.     

Integrated simulation tool for quality support in the low-volume high-complexity electronics manufacturing domain

Low-volume high-complexity printed circuit board manufacturing is a highly dynamic domain because of prevailing global pressures. In such an evolving environment, quality issues caused by manufacturing defects are the major concern. The generation, detection and elimination of those defects further impact customer requirements and demands. Current practices in terms of identification and solution of quality issues have three major drawbacks: (i) the metrics used are not meaningful; (ii) several manual operations are involved; and (iii) there is no significant decision support. A novel integrated simulation tool for quality support in low-volume electronics manufacturing that overcomes these weaknesses is presented in this paper. The simulation tool supports current needs in the domain, i.e. knowledge capitalisation, waste reduction, right-first-time performance and agility, as well as the domain customer requirements, i.e. lead time, cost, quality and reliability. Quantitative results from a case study are presented as evidence of the usefulness of the tool in a real context. The results show that the approximately 80% non-value-added cost for the product studied is due to just two types of manufacturing defects. This outcome is key for root cause analysis based not only on defect quantity.     

矿物颗粒的随机分形仿真算法

具有复杂形状的真实矿物颗粒仿真已成为影响分选理论研究一个重要瓶颈.为实现对矿物颗粒的真实模拟,提出了一种随机仿射分形仿真的计算机图形学算法,利用VC和OpenGL编程实现,并已应用于煤炭颗粒的振动筛分过程的虚拟实验仿真系统中.应用表明该算法能真实地模拟实际颗粒,增加了仿真的真实感和准确性,并具有较高的运行效率.     

Computer simulation for quality and reliability engineering

Computer simulation has been used widely in many industries for many applications. A simulation model mimics a real world system, enabling an investigation of its operation. More recently simulation models have incorporated a visual display and interactive features to aid understanding and enhance the investigation. Computer simulation has many potential uses in quality and reliability engineering, for instance, modelling equipment failures, quality control strategies, maintenance requirements and operational logistics. A case study shows how simulation has been used to study the throughput, flexibility and robustness of a manufacturing plant design. Alternative simulation software packages are briefly discussed.     

乙烯在不同结构PE/分子筛膜中的吸附蒙特卡洛模拟

目的利用蒙特卡洛法模拟分析基体PE的结构变化对其吸附乙烯的影响,从微观角度展现新型活性包装材料PE/分子筛膜对乙烯的吸收过程,揭示微观吸收机理。方法通过MaterialsStudio软件分别构建不同聚合度和分子链数目的 PE/分子筛高分子模型,采用蒙特卡洛法模拟PE/分子筛体系对乙烯的吸附过程,并绘制吸附等温线来分析吸附效果。结果 PE/分子筛体系对乙烯的吸附量随聚合度的增加而减小,随分子链数目的增加而增加;达到吸附平衡后,吸附量在一定范围内存在明显的波动。结论基体结构对活性包装材料PE/分子筛膜的吸收效果有较大的影响。在相同条件下,以低聚合度和多分子链数目结构形成的PE/分子筛包装体系更有利于对乙烯的吸附,且该吸附平衡是一个吸附与脱吸同时发生的动态平衡。     

舰船辐射噪声模拟产生技术方法综合研究

本文总结了各种舰船辐射噪声特性及其模拟产生原理技术方法 ,重点分析研究了常用的水声换能器模拟方法的各种模拟技术原理、技术实现及其应用特点 ,对相关设备的研究有一定的参考价值。     

室内气流组织数值模拟及仿真软件

不同的气流组织形式对室内空气品质会产生影响,用CFD技术模拟气流组织具体影响,将室内空气品质的研究体现在工程设计上是必要的。本文就数值方法和相关的气流组织模拟软件作了分析和介绍,并说明了在应用过程中的步骤。     

印刷机仿真平台的研究与设计

为了满足印刷机原理教学和培训的要求,解决实物教学面临的资金及设备数量的不足,选用基于模型的虚拟环境建立方法,采用Solidworks、3DsMax、director等三维设计及多媒体制作软件,探索了功能分组的机械建模方法和虚拟驱动的动态仿真,构建了虚拟印刷机使用平台,获得了比实物印刷机教学更好的效果.     

仿真技术发展及应用

从仿真技术的发展、成熟、再发展的观点论述了它的发展过程。介绍了仿真技术在国民经济各个领域中的应用。分析了国内外仿真技术水平及现状，展望了仿真技术的发展趋势。     

Evaluating small failure probabilities of multiple limit states by parallel subset simulation

A novel subset simulation algorithm, called the parallel subset simulation, is proposed to estimate small failure probabilities of multiple limit states with only a single subset simulation analysis. As well known, crude Monte Carlo simulation is inefficient in estimating small probabilities but is applicable to multiple limit states, while the ordinary subset simulation is efficient in estimating small probabilities but can only handle a single limit state. The proposed novel stochastic simulation approach combines the advantages of the two simulation methods: it is not only efficient in estimating small probabilities but also applicable to multiple limit states. The key idea is to introduce a “principal variable” which is correlated with all performance functions. The failure probabilities of all limit states therefore could be evaluated simultaneously when subset simulation algorithm generates the principal variable samples. The statistical properties of the failure probability estimators are also derived. Two examples are presented to demonstrate the effectiveness of the new approach and to compare with crude Monte Carlo and ordinary subset simulation methods.