焦区附近球形粒子对高斯光束的弹性散射

本文应用复源球面波理论,将高斯光束场按矢量球波函数展开,对高斯光束入射到单个球形粒子上时的弹性散射问题进行了理论分折。并对球形粒子在波束传播轴上时的远场散射光强角分布进行了数值计算,同时还与平面波散射的结果进行了比较。     

偏振比法的微小颗粒粒径反演研究

在Mie散射理论的基础上推导了偏振比法微纳颗粒检测理论.该理论避免了检测光路中气体组分对颗粒测量的影响,实现了微纳颗粒的准确测量.在检测理论的基础上建立了颗粒粒径反演模型,并引入遗传算法对偏振散射光信号进行分析.通过MATLAB仿真研究,获得偏振比法颗粒粒径测量范围为0.1~0.5μm.对服从R-R分布的均匀球形颗粒群进行模拟仿真,通过加入随机噪声模拟实际测量时的外界干扰,根据反演结果对该方法的抗噪性和精度进行了评测.     

玻璃微珠颗粒系中超声散射的数值和实验研究

利用超声在球形颗粒中的单散射理论模型, 分析了散射系数计算收敛问题, 玻璃微珠颗粒的散射声压分布和消声系数随物性参数和颗粒尺寸参数的变化关系, 进而研究了不同粒度分布颗粒群中声衰减谱的特性. 由变声程脉冲回波法测量了3种不同粒度分布玻璃微珠声散射衰减谱, 与理论计算进行了对比, 二者较好地吻合. 结果表明, 具有合适物性参数的弹性颗粒声散射模型可用于声散射衰减谱准确预测, 采用宽频超声衰减谱有利于对颗粒系进行粒度分布分析.     

矿物颗粒形状对球磨机磨矿性能的影响

为了探究矿物颗粒形状对球磨机研磨作业的影响机制,运用离散单元法,采用球体和由球形颗粒凝聚而成的正四面体、平行六面体矿物颗粒模型,数值模拟球磨机的磨矿过程,分析矿物颗粒形状对运动形式、碰撞形式以及球磨机磨矿性能的影响。结果表明,矿物颗粒形状对球磨机磨矿性能的影响很大,相同条件下,球形矿粒碰撞能最大,正四面体矿粒次之,平行六面体矿粒最小。     

文丘里粉体喷射器内部颗粒运动特性的联合仿真

采用计算流体力学-离散单元法(CFD-DEM)耦合方法,对文丘里粉体喷射器内部5种不同粒径球形颗粒组成的颗粒群的气力输送过程进行数值模拟;分析颗粒的运动轨迹,发现部分颗粒在吸收室的底部聚集,颗粒在文丘里喷射器内部的运动集中分布在输送管道的中下部位,小尺寸颗粒速度较快,颗粒尺寸越大,颗粒与颗粒碰撞次数越多,颗粒与壁面碰撞次数越少;采用离散单元法-有限单元分析(DEM-FEA)耦合方法对颗粒与壁面碰撞引起的壁面应力变化进行分析。结果表明,喷射器在喷嘴出口处附近和吸收室底部出现应力峰值。     

滚筒装备内颗粒混合与粉磨研究进展

综述滚筒装备内颗粒混合和粉磨的实验和数值模拟研究;指出已有研究中缺少对小规模滚筒内颗粒轴向混合以及工业规模滚筒装备内颗粒混合和粉磨过程的研究,并且对不规则形状颗粒、微米尺度颗粒、湿颗粒的混合和粉磨过程的研究较少;认为今后的工作中应开展滚筒内颗粒轴向或整体混合研究,并将相似原理、粗粒模型引入工业规模滚筒装备内颗粒动力学离散元模拟中,在此基础上,开展涉及非球形颗粒的流固耦合模型及数值模拟方法研究。     

颗粒团聚分布的复合材料数值模型

目的 提出颗粒团聚分布的数值模型参数化建模方法,以高效建立颗粒有序分布的复合材料微观构型。方法 以颗粒尺寸、颗粒团聚区域的半径以及团聚区域局部体积分数和整体体积分数的比值作为表征颗粒团聚结构的基本建模控制参数,首先建立了圆形/球形区域内的Voronoi多胞元结构,其次编写基于Python语言的接口程序,根据角点坐标和几何拓扑关系将多胞元结构导入有限元软件中,并对每个胞元按团聚区域局部体积分数进行缩放,形成了圆形/球形区域的颗粒团簇,最后使用随机顺序吸附算法将团聚颗粒在代表单元内周期性随机投放,生成了颗粒团聚分布的复合材料二维/三维微观构型。结果 使用不同控制参数进行数值建模测试,生成一个颗粒数目在1 000以内的二维/三维颗粒团聚微观构型仅需要数分钟,验证了本文方法的有效性。使用二维模型对单轴拉伸进行数值模拟,结果表明,材料宏观塑性随着颗粒团聚程度的增大而降低。结论 本文建模方法可以为复合材料结构设计提供有效的数值仿真支撑。     

经典Mie散射的数值计算方法改进

在光散射颗粒测量技术中,Mie散射理论的计算非常重要。本文介绍一种改进的Mie散射数值计算方法,通过对Mie散射系数进行重新构造,找到参量来控制Mie计算的收敛和计算精度。对各有关参量选用合适、稳定的递推关系进行计算。数值计算结果表明该方法具有快速、稳定的优点,可以在极大的颗粒粒径和折射率范围内得到合理结果。     

球形壳体障板声散射近场矢量特性

为了实现矢量水听器在水面或水下载体上的工程应用,研究了球形壳体障板声散射近场矢量特性。采用弹性薄壳理论结合边界条件导出了球形壳体障板声散射的声压和质点振速表达式,给出相应的声强表达式。数值计算了球形壳体障板声散射的近场特性,重点关注其近场矢量特性。理论分析和数值计算结果表明,由于球形壳体障板的散射作用,声压场和质点振速场表现为复杂的干涉结构;质点振速方向和声源方位不一致;声压和质点振速不再同相;声强方向也不再反映声源方位。本文结果为矢量水听器在球形载体和球形障板条件下的工程应用提供理论依据。     

柱状和球形颗粒在锥形布料盘表面的运动特性

采用离散元法(DEM)对柱状和球形颗粒在开槽前后正锥形布料盘表面的运动过程进行数值模拟,研究颗粒在锥形布料盘表面的运动速度、布撒轨迹,并探讨开槽前后布料盘直径、转速以及颗粒形状对运动过程的影响。结果表明:颗粒出盘的水平、竖直速率随布料盘转速和直径的增大而增大;柱状颗粒出盘的水平、竖直速率略大于球形颗粒;布料盘开槽后颗粒的过槽率随布料盘转速的增大而减小,随布料盘直径的增大而增大;柱状颗粒的过槽率大于球形颗粒;布料盘开槽后颗粒出盘的水平、竖直速率大于开槽前。     

Digital holographic particle validation via complex wave

The inability to distinguish between particle images and noise in holographic reconstruction of dense particle fields hampers the advancement of holographic particle diagnostic techniques including holographic particle image velocimetry. We developed a method to separate particles from the noise by unlocking a unique particle signature in the complex reconstructed field. This complex-wave signature is present in digital particle holograms recorded at any scattering angle. Simulations of single and multiple particle holograms, as well as preliminary laboratory particle-field experiments, not only demonstrated the existence of the particle signature but also evaluated its ability to remove noise. Regardless of particle seeding density, scattering angle of hologram recording and particle size range, the particle identification/validation routine consistently provides >50% removal of "bad" particles and <8% of good particles.     

Soot formation characteristics in a pulverized coal flame formed in a swirling flow

To understand the soot formation characteristics in a pulverized coal flame with a swirling flow, simultaneous imaging of Mie scattering of coal particles and laser induced incandescence (LII) of soot were performed in this study. The pulverized coal flame was stabilized by a hydrogen diffusion pilot flame. The characteristic structures of soot formation in the pulverized coal flame with a swirling flow were analyzed based on a comparison of the experimental results and two-dimensional numerical simulation in the mixing region of coal particles and the oxidizer. The interactions between coal particle clouds and soot formation are discussed in detail. The results clearly show that the averaged radial dispersions of scattering signals from coal particles and of the LII signals from soot are overlapped. The overlapping region appeared nearby the nozzle exit due to the turbulent mixing and the high temperature region formed by swirl-induced recirculation flow. This overlapping region radially expands with increasing the height from the burner. Additionally, the characteristic areas of soot formation were observed in the results of simultaneous imaging of Mie scattering and LII. These areas are 1) streaky soot formation areas around the particle clouds, 2) soot formation areas inside of the particle clouds and 3) soot formation areas around the large coal particles.     

Particulate flow simulations using lubrication theory solution enrichment

A technique for the numerical simulation of suspensions of particles in fluid based on the extended finite element method (X‐FEM) is developed. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The finite element basis is enriched with the Stokes flow solution for flow past a single particle and the lubrication theory solution for flow between particles. The latter enrichment allows the simulation of particles that come arbitrarily close together without refining the mesh in the gap between them. Example problems illustrating both types of enrichment are shown, along with a study of a 50% solution in channel flow. Copyright © 2003 John Wiley & Sons, Ltd.     

亚微米级扁椭球颗粒群的散射特性

采用T矩阵方法计算亚微米级扁椭球随机取向分布颗粒群的散射特性,研究消光截面、散射截面、吸光截面、单散射反照率、非对称因子以及散射矩阵元素与颗粒的大小、折射率、长短轴比之间的关系。结果表明,随颗粒粒径增大,消光截面、散射截面、吸光截面、非对称因子都单调增加,散射相函数F11的角分布曲线特征可以区分颗粒的大小;颗粒越偏离球形,颗粒对入射光的衰减效率越低,后向散射光强越强,在轴比不大时,前向50°内的F22/F11值可以区分颗粒的形状;折射率变化主要是对后向散射光的分布产生影响,实部、虚部的变化可分别通过F34/F11的角分布曲线、F12/F11的第一个峰值来体现。     

Multispectral diffuse optical tomography with absorption and scattering spectral constraints

We present a new method to simultaneously reconstruct the images of oxyhemoglobin, deoxyhemoglobin, and water concentrations, as well as the volume fraction images of the scattering particles using continuous wave multispectral diffuse optical tomography with the absorption and scattering spectral prior constraints. In this method, the nonlinear relationship between the reduced scattering coefficient and the volume fraction and the size of the particles is linearized, allowing direct reconstruction of the volume fraction of scattering particles in tissues. The method is validated by a series of numerical simulations, phantom experiments, and in vivo clinical experiments. The initial clinical results indicate that the volume fraction of scattering particles in a malignant tumor is higher than that in a benign tumor.     

A Monte Carlo program for quantitative electron-induced X-ray analysis of individual particles

A versatile Monte Carlo program for quantitative particle analysis in electron probe X-ray microanalysis is presented. The program includes routines for simulating electron-solid interactions in microparticles lying on a flat surface and calculating the generated X-ray signal. Simulation of the whole X-ray spectrum as well as phi(z) curves is possible. The most important facility of the program is the reverse Monte Carlo quantification of the chemical composition of microparticles, including low-Z elements, such as C, N, O, and F. This quantification method is based on the combination of a single scattering Monte Carlo simulation and a robust successive approximation. An iteration procedure is employed; in each iteration step, the Monte Carlo simulation program calculates characteristic X-ray intensities, and a new set of concentration values for chemical elements in the particle is determined. When the simulated X-ray intensities converge to the measured ones, the input values of elemental concentrations used for the simulation are determined as chemical compositions of the particle. This quantification procedure was evaluated by investigating various types of standard particles, and good accuracy of the methodology was demonstrated. A methodology for heterogeneity assessment of single particles is also described.     

纳米及微米磁性颗粒在长波长下的光散射特性分析

根据Mie散射理论,分析计算了纳米级、微米级磁性颗粒的光散射特性。针对目前在导航、遥控及雷达等行业广泛应用的纳米、微米磁性颗粒,在Mie散射系数中引入磁导率变量,对比分析了磁性与非磁性颗粒、吸收性与非吸收性颗粒的散射特性规律。数值计算结果表明,磁导率的变化对具有吸收性磁性颗粒的散射特性造成影响,随着磁导率的增大,颗粒的散射光强及吸收性能将逐渐增大,同时磁导率增大对颗粒散射特性的影响将会受到复折射率实部的制约。     

Fundamental Mass Flow Measurement of Solid Particles

A generic mass flow measurement device was developed as a variation on the theme of counting. In a hypothetical infinitely sparse mass flow, the number of passing particles could be counted in a time frame and multiplied by the mean mass per particle to obtain a mass flow per time unit. In a mass flow of realistic density, however, particles travel in cluster formation and direct counting of individual particles is impossible. If a method could be available that reconstructs the original number of particles in a cluster, the mass flow can be computed for realistic clustered mass flows. This reconstruction algorithm was developed in this research; it uses the measured cluster lengths to reconstruct the total number of particles in each passing cluster. The lengths of the clusters were measured with an optoelectronic device. The reconstruction algorithm was developed using simulation, augmented by clustering theory. For identical diameter particle flow, simulation results showed that the number of particles in a cluster could be reconstructed using a very simple reconstruction formula. This formula uses only the total number of clusters per time frame and the total number of individual particles measured in the same time frame. However, identical diameter flow is not realistic, since even identical particles are measured with a certain error. Reconstruction of the realistic distributed diameter particle flow was approximated using the identical particle method. The optical mass flow sensor has major advantages over traditional methods. It is virtually insensitive to vibrations, contamination, temperature drift, and misalignment and the underlying measurement concept is well understood. But most importantly, the sensor does not require calibration. The mass flow of identical particles (4.5 mm air gun pellets) was measured with an error smaller than 3% even for high density flow rates.     

Fundamental Mass Flow Measurement of Solid Particles

A generic mass flow measurement device was developed as a variation on the theme of counting. In a hypothetical infinitely sparse mass flow, the number of passing particles could be counted in a time frame and multiplied by the mean mass per particle to obtain a mass flow per time unit. In a mass flow of realistic density, however, particles travel in cluster formation and direct counting of individual particles is impossible. If a method could be available that reconstructs the original number of particles in a cluster, the mass flow can be computed for realistic clustered mass flows. This reconstruction algorithm was developed in this research; it uses the measured cluster lengths to reconstruct the total number of particles in each passing cluster. The lengths of the clusters were measured with an optoelectronic device. The reconstruction algorithm was developed using simulation, augmented by clustering theory. For identical diameter particle flow, simulation results showed that the number of particles in a cluster could be reconstructed using a very simple reconstruction formula. This formula uses only the total number of clusters per time frame and the total number of individual particles measured in the same time frame. However, identical diameter flow is not realistic, since even identical particles are measured with a certain error. Reconstruction of the realistic distributed diameter particle flow was approximated using the identical particle method. The optical mass flow sensor has major advantages over traditional methods. It is virtually insensitive to vibrations, contamination, temperature drift, and misalignment and the underlying measurement concept is well understood. But most importantly, the sensor does not require calibration. The mass flow of identical particles (4.5 mm air gun pellets) was measured with an error smaller than 3% even for high density flow rates.     

Gas thermodynamics and optics of a monodisperse supersonic jet interacting with an aerodynamic body

On the basis of the previously developed gas dynamics model of the polydisperse jet flowing over a blunt body, the optics of a compressed layer is studied under close-to-experimental conditions. The effect of scattering of monochromatic radiation by the particles on the observed picture in the ??laser sheet?? plane is numerically estimated. The study is carried out on the assumption that the cloud formed by the particles is optically thin (single scattering). The effects of absorption and scattering of the radiation by the carrying gas are neglected. The numerical studies have been carried out for wide ranges of the particle sizes and optical parameters of the matter.