用MATLAB动态模拟并分析傅科摆的运动

用MATLAB对傅科摆的运动进行分析和计算，得出其在不同初始条件下运动轨迹并画出相应的图形．     

一种单相机测量三维运动轨迹的方法

论文提出了一种基于交汇式双目视觉模型的单个CCD相机三维立体测量方法.在CCD相机前放置两面成一定夹角的平面镜,通过一次拍摄,得到两幅存在视差的图像,该图像相当于相机在平面镜中两个虚拟相机对目标从不同角度拍摄所得到图像,根据双目视觉原理可实现三维立体测量.详细介绍了实验系统的布置方法,建立了三维坐标计算的数学模型,对系统的内外参数进行了标定.测量了静态物体的形态和尺寸,验证了系统的可行性与可靠性.并对运动物体进行了动态测量,通过视频记录物体两个虚像的平面运动图像序列,计算还原了物体空间的三维运动轨迹,并应用误差理论对实验误差进行了分析.     

利用格子Boltzmann方法模拟单个气泡在复杂流道内的运动特性

利用格子Boltzmann方法模拟了单个气泡在具有三个半圆形喉部的复杂流道内的上升过程.通过分析气泡运动过程中的形态、运动轨迹及运动速度的变化,研究复杂流道对气泡运动特性的影响.研究结果表明,在上升过程中,由于壁面的影响,气泡的形状发生严重的变形,运动轨迹也发生相应的偏转.通过实验结果的对比,验证了模拟结果的正确性.结果表明格子Boltzmann方法可以用于模拟具有复杂边界的两相流问题.     

亚微米级颗粒物在气体动压轴承内运动与沉积分析

气体轴承中的多余颗粒物是导致陀螺电机不起动的主要原因。研究颗粒物的吸入、运动沉降以及排出规律,对解决陀螺电机不启动问题具有重要意义。以螺旋槽气体动压止推轴承为研究对象,将气体流场作为连续相,颗粒物作为离散相,通过联立求解气体N-S方程和颗粒物力平衡方程,得到了亚微米级颗粒物在轴承中的运动与沉积规律。分析发现气膜中速度场分布与颗粒物沉积之间的相关性,且与实验结果有较好的一致性;同时,发现槽数为12或13、螺旋角为α=20°左右时颗粒物最容易从轴承中排除,增加槽深和较小槽长也有相同效果。为在生产实践中优化陀螺电机轴承结构参数,降低不启动率提供了理论依据。     

杆状弯曲行波型超声电机运动机理研究

为了深入研究杆状弯曲行波型超声电机的运动机理，本文分析了定子表面质点椭圆运动轨迹的形成，并将椭圆运动分解为产生驱动力的有效椭圆运动与使定、转子产生径向滑动的径向直线运动；然后基于有效椭圆运动变化情况，分析了在两相振幅不平衡和任意相位差情况下对转子运动平稳性的影响，为这类电机的设计和性能控制提供理论依据。     

Y型分支管内气固两相流动的数值模拟

本文采用Euler-Lagrange两相流研究方法,固相采用离散相(DPM)模型,对三种不同夹角的Y型分支管内气固两相流动进行了数值模拟.气相湍流采用Realizable k-ε模型,固相的湍流耗散采用随机轨道模型.模拟结果较好地预估了颗粒在分叉处的流动形态、颗粒在分支管内的运动轨迹,以及重新实现颗粒相流场均匀分布所需的距离.同时发现,随机轨道模型较适于评估分支与主管夹角较大情况下,固体颗粒在分叉处的运动.将分支管内固体颗粒质量分配的数值模拟结果与试验结果比较,发现两者较吻合,相对误差较小.     

基于MEMS传感器的手臂运动测量和识别方法

针对传统人体运动识别方法的局限,研究了一种新的基于MEMS陀螺仪、加速度计和磁强计的人体手臂运动状态测量和识别方法。通过惯性测量单元测量人体手臂运动信息,利用卡尔曼滤波算法对手臂运动的姿态角进行精确估计,可计算出手部运动轨迹。手部运动轨迹特征值和传感器测量信号的时域特征值结合起来,使用BP神经网络和SVM算法对画横线、竖线、斜线和封闭线等四种典型手臂运动状态进行识别,识别率较传统方法得到提高,分别达到97.14%和100%,表明基于MEMS传感器的人体手臂运动测量和识别方法不仅使用简单、安装方便,而且识别率高,该法具有可行性和有效性。     

高超声速火星进入环境中颗粒运动特性研究

火星大气中会发生不同规模的沙尘暴,大气中蕴含的尘埃颗粒会对高速进入的火星探测器表面造成侵蚀并导致壁面热流增加,给探测器的热防护系统设计带来巨大挑战.文章针对高超声速火星进入环境两相流动问题,基于Euler-Lagrange框架建立非平衡流场与颗粒的单向耦合计算方法,采用模态半径为0.35μm的火星大气颗粒分布模型,研究不同尺寸颗粒在流场中的运动轨迹,获得高温相变模型对颗粒运动的影响以及不同粒径颗粒的撞击能量分布.结果表明,颗粒在高温流场中运动会吸热融化甚至蒸发,高温相变模型导致的颗粒直径减小对小尺寸颗粒运动轨迹有较大影响;当前计算状态下,直径3μm以上的颗粒具有较大的Stokes数且颗粒半径在运动过程中基本保持不变,其运动轨迹受流场影响较小,该尺寸颗粒的撞击分数均达95%以上,是造成壁面撞击的主要颗粒尺寸;撞击能量分数结果表明,直径3～10μm之间的颗粒是撞击能量的主要来源,约占总撞击能量的80%.     

考虑两相流内弹道的自行火炮发射动力学计算

为了更加准确地计算火炮弹丸的起始扰动,将两相流内弹道应用于发射动力学研究。建立了完整的自行火炮系统发射动力学方程组,包括火炮系统的体动力学方程组、弹丸在膛内运动的动力学方程以及两相流内弹道方程。编制了计算程序,实现了对某自行火炮发射过程的数值模拟,在准确计算内弹道过程的同时,获得了火炮的动力响应、弹丸膛内运动和起始扰动。部分模拟结果与实验实测结果吻合较好。计算表明,采用两相流内弹道模型将提高发射动力学计算精度。     

两相流场粒子成像测速技术(PTV-PIV)初探

在单相ＰＴＶ－ＰＩＶ研究基础上，研究液固两相流场粒子成像图像数字测速技术．首次用ＰＴＶ技术得到直槽道中液固两相流场二维瞬时全场两相流速分布．初步探讨了两相ＰＴＶ－ＰＩＶ技术中与单相ＰＴＶ－ＰＩＶ测速技术的关键不同之处，提出两相ＰＴＶ－ＰＩＶ测速采样的两相相容性准则．为深入研究两相流场粒子成像测速技术奠定了基础．     

INFLUENCE OF AIR HUMIDITY ON THE SUPPRESSION OF FUGITIVE DUST BY USING A WATER-SPRAYING SYSTEM

One of the main origins of fugitive dust emission arises from bulk handling in quarries or mines, in particular, from bulk materials falling from a hopper or a conveyor belt. Water-spraying systems, using two-phase nozzles, are one of the methods to suppress such dust emission. In this work we tried to develop a mathematical model to correlate air humidity, water flux through the nozzle and the dust （in particular PM10） emission, in order to improve the application and efficiency of these systems. Sand from the Yellow River in China was dropped from a conveyor belt into a dust chamber at 1 kg·min^-1, wherefrom the emitted dust was sucked off and quantified via a cascade impactor. A two-phase nozzle was installed in the dust chamber with a water flux through the nozzle of 1.2 to 3 L·h^-1, whereas the relative air humidity changed between 55 and 73%. Dust emission was found to be linearly dependent on relative air humidity. Furthermore model equations were developed to describe the dependence of PM10 emission on water flux and relative air humidity.     

Flow and migration of nanoparticle in a single channel

A numerical simulation based on a combined Euler and Lagrange method is investigated in this work to simulate the flow and migration of nanoparticles in a single channel. The motion of discrete nanoparticles is determined by the Lagrangian trajectory method based on the Newton’s second law that includes the influence of the body force, various hydrodynamic forces, the Brownian motion and the thermophoresis force. The coupling of discrete particles with continuous flow is realized through the modification of the source term of the continuous equation. The results reveal the two-phase flow nature of nanoparticle suspensions and their implications to the convective heat transfer of nanofluids.     

大速差射流燃烧室中烟煤与贫煤燃烧的数值模拟

本文基于颗粒相的轨道模型,对大速差射流燃烧室中烟煤粉与贫煤粉的二维流动,混合及燃烧进行了数值模拟,模拟结果从两相耦合的角度,阐明了煤粉颗粒在燃烧室中运动的规律,煤粉与大速差射流诱导的中心气体逆流之间的混合及其对煤粉火焰稳定的影响,指出此种燃烧室中煤粉火焰稳定的回流区燃烧机理,气相流场及回流区的预报结果与实验符合良好。     

Shock-induced Near-wall Two-phase Flow Structure Over a Micron-sized Particles Bed

The present paper studies numerical modelling of near-wall two-phase flows induced by a normal shock wave moving at a constant speed, over a micron-sized particles bed. In this two-fluid model, the possibility of particle trajectory intersection is considered and a full Lagrangian formulation of the dispersed phase is introduced. The finiteness of the Reynolds and Mach numbers of the flow around a particle as well as the fineness of the particle sizes are taken into account in describing the interactions between the carrier- and dispersed-phases. For the small mass-loading ratio case, the numerical simulation of flow structure of the two phases is implemented and the profiles of the particle number density are obtained under the constant-flux condition on the wall. The effects of the shock Mach number and the particle size and material density on particle entrainment motion are discussed in detail. The obtained results indicate that interphase non-equilibrium in the velocity and temperature is a common feature for this type of flows and a local particle accumulation zone may form near the envelope of the particle trajectory family.     

ANALYSIS OF PARTICULATE MASS CONCENTRATION, AEROSOL NUMBER CONCENTRATION AND VISIBILITY IN BEIJING

1.IntroductionAtmosphericaerosolsplayanimportantroleinatmos-phericvisibility,irradiationbalanceandclimate.Thenum-berconcentrationofsmallparticulatesisusuallyveryhigh,butitsmassconcentrationisrelativelylow.Buzoriusetal.(1999)andPetersetal.(1997)havereportedthatparticu-latehealtheffectsmaybemoresensitivetothenumberthantothemassconcentration.Thispaperstudiestheaverageddiurnalvariationsofparticulatemassconcentra-tion,numberconcentration,atmosphericvisibility,andtheaerosolsizedistribution,n(r),und…     

冲击载荷作用下颗粒材料动态力学响应的近场动力学模拟

颗粒材料在冲击载荷作用下的动态力学行为是学术界关注的热点问题. 新近问世的近场动力学(peridynamics)理论将材料视为由大量有限体积和有限质量的物质点组成,基于非连续性和非局部作用假定建模,建立空间积分形式的运动方程,自然适应于颗粒材料动态力学行为的描述与分析. 发展了描述颗粒间接触作用的物质点尺度的排斥力模型,考虑近场动力学方法中非局部长程力特征,改进了近场动力学中的初始微观弹脆性(prototype microelastic brittle, PMB) 模型的本构力函数,并消除了原PMB 模型中存在的“边界效应” 问题. 计算分析了冲击载荷作用下碳化钨陶瓷颗粒体系的动态力学响应,得到了不同冲击速度下颗粒体系的冲击波速,PD计算结果与试验结果高度一致;通过颗粒物质点尺度作用描述单颗粒尺度的接触作用,很好地再现了颗粒的转动与平动、颗粒挤压变形以及颗粒破碎等现象;刚性冲击板附近同时存在严重的颗粒破碎与轻微的颗粒损伤,远离冲击板的部分颗粒出现破损,且颗粒破碎主要是由颗粒间挤压、碰撞以及相对滑动剪切作用造成的. 研究结果表明,所发展的计算模型和分析方法能很好地反映颗粒材料动态力学行为,具有广泛的应用价值.      

Modeling the evolution of droplet size distribution in two-phase flows

A theoretical model is developed in the present study to simulate droplet motion and the evolution of droplet size distribution (DSD) in two-phase air/dispersed water spray flows. The model takes into account several processes which influence DSD and droplet trajectory: droplet collision and coalescence, evaporation and cooling, gravitational settling, and turbulent dispersion of dispersed phase. The DSDs determined by the model at different locations in a two-phase flow are evaluated by comparing them to experimental observations obtained in an icing wind tunnel. The satisfactory coincidence between simulation and experimental results proves that the model is reliable when modeling two-phase flows under icing conditions. The model is applied for two particular examples in which the modification of DSD is calculated in two-phase flows under conditions describing in-cloud icing and freezing drizzle.     

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN PEARL RIVER DELTA REGION, CHINA

Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particie diameter smaller than 2.5 um) and PM10 (particie diameter smaller than 10 um) samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5and PM10 Ievel were 60.1 and 93.1 μg·m-3, respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations in PM2.5 were 12.0 and 5.1 μg·m-3, respectively, while those in PM10 were 16.0 and 6.5 μg·m-3, respectively. The carbo-naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC were observed at Guangzhou city in both vvinter and summer seasons. The average OC/EC ratios were 2.     

Numerical calculations for two-phase jet flow of a mixture of pulverized-coal and gas

In this paper, Euler-Lagrange type equations are used to describe the jet flow of a mixture of pulverized-coal and gas, which is an unsteady axisymmetric two-phase flow. By means of the finite-difference method, the coal particle's distribution, velocity and trajectory in the flow field are obtained. The coal particles are represented by a finite number of computational particles. Each particle's diameter is randomly assigned according to a given distribution. The states of the computational particles are different from each other. Turbulence is accounted for in a stochastic model. Explicit time-splitting scheme is used to calculate the strongly coupling interphase term. The numerical results are reasonable. The comparison between the numerical results and the experiment data for the case of the oil droplet injection shows good agreement. This numerical technique can be extended to the calculation of other two-phase flows of dilute particles or a droplet system. Mr. Mei Renwei also participated in the work of this paper.     

基于偏转距离近似模型的动能撞击小行星防御任务脉冲轨道优化研究

小行星撞击对地球上的生命存在重大潜在威胁,动能撞击是目前最易实现且成熟度最高的防御方案.动能撞击任务的一种轨道优化指标为最大化偏转距离(即小行星被偏转前后近地距的改变量),若用数值积分的方法精确计算偏转距离, 会导致优化效率较低.在动能撞击任务的设计初期, 可以对动力学模型及偏转距离的计算方法进行简化,以提升优化效率. 本文首先将高精度模型简化为二体模型,分析了两种经典偏转距离解析模型的适用条件,同时提出一种基于近地点时刻预估的偏转距离近似模型; 考虑运载约束,将化学推进变轨简化为脉冲推力变轨,建立了直接转移(两脉冲及三脉冲)和行星借力飞行转移(单次及两次借力)的动能撞击轨道优化模型,利用遗传算法求解了优化问题. 以偏转小行星Apophis为例, 相比于解析模型,验证了本文提出的近似模型可以同时提升最优性、降低求解复杂性. 优化结果表明,三脉冲直接转移方案与两脉冲直接转移方案的最优偏转效果基本一致,借力飞行转移方案相比于直接转移方案对偏转距离的提升效果并不明显.在动能撞击任务的前期设计中, 可以基于二体模型进行防御效果的快速评估,虽然对计算偏转距离存在一定误差, 但对防御窗口的优化结果影响不大. 进一步,数值求解偏转距离时, 可通过引入主要引力摄动项(金星、地球、木星)修正二体模型,使其与高精度模型之间的求解误差在1%以下.