微喷管内流动和换热的数值模拟与分析

发展了直接模拟Monte Carlo方法的压力边界条件处理方法,并使用这种方法对微型拉法尔喷管内的气体流动特性进行了数值模拟与分析.研究了两种构型的拉法尔喷管,对比了相同出口压力不同入口压力下的流场特性,以及在相同入口压力时真空压力条件和给定低压边界条件对流场的影响.     

微喷管内流动和换热的数值模拟与分析

发展了直接模拟Monte Carlo方法的压力边界条件处理方法，并使用这种方法对微型拉法尔喷管内的气体流动特性进行了数值模拟与分析。研究了两种构型的拉法尔喷管，对比了相同出口压力不同入口压力下的流场特性，以及在相同入口压力时真空压力条件和给定低压边界条件对流场的影响。     

微气体流量计的模拟与优化

温差法测流量是一种新型气体流量计的基本原理 ,温度传感器的布置对流量计的性能影响很大。本文使用基于分子运动理论的直接模拟MonteCarlo法对这种微气体流量计通道内的气体流动进行了数值模拟 ,对比了有无传感器时速度场和温度场的分布 ,指出传感器的布置对温度场的影响很小 ,并根据温差分布规律提出了传感器布置的优化方案。     

微气体流量计的模拟与优化

温差法测流量是一种新型气体流量计的基本原理,温度传感器的布置对流量计的性能影响很大.本文使用基于分子运动理论的直接模拟Monte Carlo法对这种微气体流量计通道内的气体流动进行了数值模拟,对比了有无传感器时速度场和温度场的分布,指出传感器的布置对温度场的影响很小,并根据温差分布规律提出了传感器布置的优化方案.     

拉伐尔型微喷管流场的三维模拟

微喷管设计的优劣将直接影响到微型推进系统的设计及其性能好坏.运用DSMC(direct simulation Monte-Carlo)方法对三维微喷管进行管内气体流动模拟,并对不同蚀刻深度及不同雷诺数喷管进行了模拟分析,仿真中采用与实际分子碰撞过程更为接近的内能松弛模型及CLL物面反射模型.结果表明,三维微喷管推力性能随雷诺数的增加而增大,推力及推力效率随着喷管蚀刻深度的减少而降低,由于三维喷管侧壁附面层的影响,蚀刻深度大于3倍喉部尺寸,才能避免对喷管性能的影响.     

矩形微通道流动换热特性的数值分析

对矩形微通道的传热和流动特性进行了三维数值模拟,结果表明:在所讨论的矩形微通道的转捩雷诺数提前到1000～1100之间,当Re>2500时,微通道内达到旺盛湍流;当量直径的变化对层流区换热Nu数影响不大,对湍流区换热Nu数有较大影响;对层流区的阻力系数影响很小,对湍流区的阻力系数影响明显,可为设计和分析微通道的性能提供理论参考.     

美国防洪减灾的风险分析与Monte Carlo计算机数值模拟技术研究

近年来,由于全球气候变暖以及我国快速城镇化进程等因素,引起我国洪灾频发,造成国家生命财产巨大损失,因此,加强防洪风险分析技术迫在眉睫。文章通过对美国陆军工程兵团防洪减灾的风险分析系统的因素分析、自然变量与不确定性模型以及Monte Carlo计算机数值模拟洪水不确定性风险分析系统等研究,提出了一种将洪水流量与水位评估中的不确定性与不同程度的洪水固有风险结合起来的技巧,这一方法值得在我国洪水管理区广泛地借鉴与采纳。     

薄膜生长过程的分子尺度模拟

概述了薄膜生长过程分子尺度模拟的原理及方法,并对不同模拟方法的国内外研究现状进行了分析综述.     

DF/HF化学激光器喷管设计和数值模拟

简述了喷管作用和单个喷管型面设计中存在的问题 ,根据气动理论提出了一种喷管设计新方法 ;介绍了DF HF激光器喷管流动数值模拟的控制方程、初边值条件和CS方法。     

小功率LED光源封装光学结构的Monte Carlo模拟及实验分析

采用Monte Carlo方法对不同光学封装结构的LED进行模拟,建立了小功率LED的仿真模型,应用空间二次曲面方程描述LED的封装结构,对其光强分布进行模拟和统计.通过测量实际样品,并与模拟结果进行比较和分析,表明计算机模拟值与实验测量值比较吻合.     

连续波DF/HF化学激光器环形喷管与线形喷管的对比

环形喷管阵列主要用于环柱型化学激光器,它可以分为两种构型:直喉道型和圆喉道型。二者都可以由线性喷管阵列变换得到。在变换前后保持相同的增益区体积的前提下,环形喷管阵列的横向尺寸将减小为线性喷管阵列的1/π倍,这将更有利于激光器的紧凑化设计。由于圆喉道型环形喷管阵列相对直喉道型更具实用价值,通过三维的数值模拟,比较了圆喉道型环形喷管单元和线形喷管单元的流场特性。结果表明:在相同截面尺寸及喉道面积的条件下,环形喷管出口气流马赫数、气流速度分别比线形喷管高4.03%,0.356%,静温、静压分别比线形喷管低6.08%,19.7%。在喷管的收缩段,两种喷管的边界层发展规律及厚度值基本相同,而环形喷管的气流速度要快于线形喷管,因此环形喷管的氟原子复合比例要略低于线形喷管。     

DSMC方法在微小喷管流场模拟中的应用

利用DSMC方法对不同扩张比及喉部尺寸的轴对称拉伐尔喷管流动现象进行了模拟分析,模拟中采用与实际分子碰撞过程更为接近的内能松弛模型及CLL物面反射模型。研究结果表明不同的扩张比及喉部尺寸对喷管内的流场分布有较大影响,在同等条件下,喉部尺寸较大的微喷管性能要优于喉部尺寸小的喷管,扩张比为5的微喷管流场马赫数更高而壁面承受压力更低,有更好的性能。     

Flow and heat transfer in porous micro heat sink for thermal management of high power LEDs

A novel porous micro heat sink system is presented for thermal management of high power LEDs, which has high heat transport capability. The operational principle and heat transfer characteristics of porous micro heat sink are analyzed. Numerical model for the micro heat sink is developed to describe liquid flow and heat transfer based on the local thermal equilibrium of porous media, and it is solved with SIMPLE algorithm. The numerical results show that the heated surface temperature of porous micro heat sink is low at high heat fluxes and is much less than the bearable temperature level of LED chips. The heat transfer coefficient of heat sink is very high, and increasing the liquid velocity can enhance the average heat transfer coefficient. The overall pressure loss of heat sink system increases with the increasing the inlet velocity, but the overall pressure drop is much less than the pumping pressure provided by micro pump. The micro heat sink has good performance for thermal management of high power LEDs, and it can improve the reliability and life of LEDs.     

Mesoscopic-level Simulation of Dynamics and Interactions of Biological Molecules Using Monte Carlo Simulation

A mesoscopic-level method for clarifying living cell dynamics is described that uses Monte Carlo simulation of biological molecule interactions. The molecules are described as particles that take a random walk in 3-dimensional discrete space. Many kinds of molecules (including complex forms) are supported, so complex reactions with enzymes can be simulated. Also described is an field programmable gate array system with reconfigurable hardware that that will support complete modeling of an entire cell. Two-phase processing (migration and reaction) is used to simulate the complex reactions, so the method can be implemented in a limited amount of hardware. The migration and reaction circuits are deeply pipelined, resulting in high performance. Estimated performance is 30 times faster than with a 3.2-GHz Pentium 4 computer. This approach should make it possible to eventually simulate cell interactions involving one billion particles.

皮肤三层模型的Monte Carlo法模拟激光多普勒血流测量

本文提出了用Monte Carlo法模拟光子流在表皮、真皮及皮下组织中的传播。经过对模拟结果的分析,提出通过改变环状探测器与入射光束的距离来探测不同深度血流层的血流速度;发现频谱的指数下降规律;指出在血球浓度较小时,平均频移反映红血球的平均速率,在浓度较高时反映红血球的均方根速率;本文还给出了不同血球浓度下光子的穿透深度。     

用蒙特卡罗法研究面光源在血液中的传播

用蒙特卡罗法模拟了光斑半径为0.1cm的633nm激光光源的玻璃-血液=玻璃3层样品结构中的传播，详细地讨论了漫反射率和总透过率与血液厚度的关系以及不同厚度血液其漫反射和总透过的径向强度分布。结果表明：血液的漫反射率很小且厚度达到0.08cm后，漫反射率就基本稳定；总透过率随血液厚度的增大而减小，当血液厚度达到0.10cm后，血液就基本不透光了；漫反射和总透过的径向强度主要分布的高斯光斑范围内。     

Analysis and Simulation of Light Extraction of Light-Emitting Diodes:Simulation Efficiency

Two foundational factors (escape cone and transmissivity) about light extraction of light emitting diodes (LEDs) are discussed.According to these factors,a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided.The improved method is to deal with the reflection and refraction of light (beam of light) at the interface between two mediums approximately.In addition,light extraction of traditional LEDs is simulated by different processes with the same structure and parameters.The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure.This method saves much time and improves efficiency in the simulation of light extraction of LEDs.     

Analysis and Simulation of Light Extraction of Light-Emitting Diodes: Simulation Efficiency

Two foundational factors (escape cone and transmissivity) about light extraction of light emitting diodes (LEDs) are discussed. According to these factors, a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided. The improved method is to deal with the reflection and refraction of light (beam of light) at the interface between two mediums approximately. In addition, light extraction of traditional LEDs is simulated by different processes with the same structure and parameters. The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure. This method saves much time and improves efficiency in the simulation of light extraction of LEDs.