负径向电场对荷电粒子运动的影响及其数值模拟

从负径向电场产生的电漂移改变荷电粒子运动的极向运动速度着手，推导出在负径向电场存在时安全因子的表达式，分析了安全因子对荷电粒子漂移位移和运动轨迹的影响。建立了在负径向电场条件下，荷电粒子在梯度磁场和曲率磁场中运动数学模型。通过数值模拟，获得了通行粒子、香蕉粒子的漂移位移和运动轨迹所呈现出的新特点和规律:负径向电场改变了荷电粒子的最大漂移位移。当荷电粒子的极向运动速度增加时，最大漂移位移减小，反之增大；改变了荷电粒子的运动轨迹，通行粒子的轨亦可能变为香蕉粒子的轨迹，香蕉粒子的轨迹可能变为通行粒子的轨迹，当电场达到足够的强度时，均成为在极向上顺时针运动的通行粒子轨迹。     

等离子体合成射流对超声速混合层的混合增强

采用实验加仿真方法研究了等离子体合成射流对超声速混合层的影响.使用基于纳米粒子的平面激光散射技术(nanoparticle-based planar laser scattering,NPLS)、粒子图像测速技术(particle image velocimetry,PIV)以及纹影手段获取了单次脉冲对混合层的影响.采用二维数值仿真对布置在不同位置的高频激励器的混合效果以及激励器的性能进行了研究.通过对比有扰动和无扰动的NPLS、PIV以及纹影实验结果,发现等离子体合成射流对超声速混合层有明显的扰动,射流喷出时会产生较强的斜激波.对数值仿真结果的分析表明,等离子体合成射流可以有效地增强混合层的厚度.对比激励器布置在不同位置工况下的混合层厚度,可以看出在激励器隔板末端对混合层的扰动效果最好,混合层对在隔板末端的激励器扰动响应也是最快的.对等离子体合成射流激励器的性能分析表明,在隔板末端的激励器输出的能量最多.通过分析等离子体合成射流的作用过程,可以看出激励器在隔板上下表面布置的作用形式是通过作用来流进而影响混合层,在隔板尾端布置的等离子体合成射流激励器直接作用在混合层上,实现混合增强.     

正交电磁场中粒子束的质量聚焦及粒子轨迹

<正>交电磁场中粒子的运动轨迹在拐点处按指数规律变化,使不同质量离子的轨迹有明显区别,由此可创建新的电磁核素分离法。从牛顿运动方程出发,基于单粒子轨道法阐述被分离核素在正交电磁场中的运动规律,重点找出轨迹的拐点。给出了多质量粒子束在正交电磁场中的质量聚焦特性,以Li离子为例,应用MATLAB模拟粒子束的运动轨迹,结果表明正交电磁场中可实现多质量束流的质量分离。总结出粒子轨迹方程的特点,为多质量束流分离结构的工程化实现提供参数。研究成果可应用到质量分离器、质谱分析仪及材料提纯等装置的研制中,同时对于特殊位形电磁场控制多质量束流等相关领域的研究亦有一定的参考价值。     

带电粒子在正交电磁场中运动状态的计算机模拟

利用MATLAB软件模拟处在正交电磁场中的具有不同方向初速度的带电粒子的运动状态,粒子会呈现三种不同类型的运动轨迹,即长轴旋轮线状态、普通旋轮线状态和短轴旋轮线运动轨迹,对所得的三种状态进行分析。     

磁场中圆周轨迹确定法

求解带电粒子在匀强磁场中做匀速圆周运动题目时，画出粒子的运动轨迹是相当关键的一步．下面就圆周轨迹的画法做一下总结．     

层流入口段中单个固体粒子的径向迁移

一、引言 许多实验表明悬浮粒子在圆管层流中出现径向迁移。这是因为粒子在入口段剪切场中受到一个垂直于粒子运动方向的升力作用,该升力是由粒子与流体之间的速度差和剪切层共同作用而产生的,因此建立了基于惯性-涡量诱导作用的粒子穿越流线迁移的流体动力模型。本文首先计算分析圆管入口段的速度场分布,然后采用该模型分别研究粒子在入口段核心区速度变化情况和在剪切区的运动轨迹,并用自行研制的CCD粒子轨迹记录系统记录了粒子在层流入口段中的运动轨迹。     

基于离焦成像的粒子轨迹测速

提出将离焦成像与粒子轨迹测速相结合,分别针对直线型和曲线型粒子轨迹,构建了离焦特征参数σ的识别算法,形成了用于三维速度测量的离焦粒子轨迹测速(DPSV)方法.该方法基于粒子图像离焦特征参数σ沿运动轨迹线的线性变化假设,通过拟合粒子图像的灰度分布来识别σ,从而获得粒子深度信息.在直线轨迹拟合的基础上,进一步采用圆弧拟合处理湍流实验中常见的弯曲轨迹图像.形成了相应的图像处理流程,并采用仿真图像验证了参数识别的准确性,在本文实验装置的噪声水平下相对误差为9.4％左右.采用LED光源和5μm孔径光阑组成的发光点进行模拟实验,验证了深度位置z与σ的线性关系.最后,将DPSV技术应用于射流流场,得到了三维速度分布.     

用"符号判断法"解磁场中原子衰变问题

一个静止原子核在磁场中发生天然衰变，衰变出粒子和反冲核在磁场中的运动轨迹如图1所示．它们的轨迹半径之比为44，求发生衰变的原子核的原子序数．     

封面说明

封面图为利用热敏液晶技术在对流槽不同高度拍摄到的俯视图.图中颜色由红到绿再到蓝,代表了温度由低到高,通过选用较长的曝光时间(0.77s),拍摄到的图片可以记录下热敏液晶粒子的运动轨迹,由这些轨迹我们可以得到流场的分布.左图为距离对流槽上底板2mm处拍摄到的图片.图中粒子的     

基于三角波瓣混合器的超声速流场精细结构和掺混特性

在超声速吸气式混合层风洞中,采用基于纳米粒子的平面激光散射(NPLS)技术对平板混合层和三角波瓣混合器诱导的混合层流场精细结构进行了对比实验研究.上下两层来流的实测马赫数分别为1.98和2.84,对流马赫数为0.2.NPLS图像清晰地展示了Kelvin-Helmholtz涡、流向涡、波系结构以及大尺度涡结构的配对合并过程.通过对比分析时间相关的NPLS流场图像,发现了大尺度拟序结构随时间发展演化的非定常特性.基于流动显示结果,采用分形维数和间歇因子指标对流场结构和混合特性进行了定量分析.实验研究表明,三角波瓣混合器诱导的流向涡结构显著提高了上下两层来流的掺混效率,其流动远场的分形维数突破了平板混合层中完全湍流区的分形维数值,达到了1.88,流场结构表现出明显的破碎性,有利于流动在标量层面的扩散和掺混.流动间歇性分析表明,流向涡与展向涡的相互剪切作用主导着混合层的掺混特性,同时由于流向涡的卷吸作用,三角波瓣混合器诱导的混合层混合区域更大,更多的流质被卷入混合区完成混合.     

The effect of sawtooth oscillations on the alpha particle distribution and energy balance in the ITER plasma

The mixing of toroidal plasma under the conditions of sawtooth oscillations is considered using the Kadomtsev model. A new mixing formula for the averaged distribution function of fast transit and trapped particles is proposed in the methodology of a kinetic equation averaged over drift trajectories. The proposed formula generalizes the known results for the case of non-circular magnetic surfaces, an arbitrary aspect ratio, and charged particle drift trajectories significantly deviating from the magnetic surfaces. The formula is applicable for a sufficiently wide class of instabilities. The 3D kinetic equation is numerically solved using the FPP- 3D computation code for parameters close to the ITER inductive scenario. The alpha particle distribution function and the power introduced by alpha particles in plasma when sawtooth oscillations occur are calculated. It is shown that such oscillations may change the energy input of a thermonuclear reaction in certain areas by several times.     

Lagrangian investigation of local extinction,re-ignition and auto-ignition in turbulent flames

Lagrangian PDF investigations are performed of the Sandia piloted flame E and the Cabra H₂/N₂ lifted flame to help develop a deeper understanding of local extinction, re-ignition and auto-ignition in these flames, and of the PDF models' abilities to represent these phenomena. Lagrangian particle time series are extracted from the PDF model calculations and are analyzed. In the analysis of the results for flame E, the particle trajectories are divided into two groups: continuous burning and local extinction. For each group, the trajectories are further sub-divided based on the particles' origin: the fuel stream, the oxidizer stream, the pilot stream, and the intermediate region. The PDF calculations are performed using each of three commonly used models of molecular mixing, namely the EMST, IEM and modified Curl mixing models. The calculations with different mixing models reproduce the local extinction and re-ignition processes observed in flame E reasonably well. The particle behavior produced by the IEM and modified Curl models is different from that produced by the EMST model, i.e., the temperature drops prior to (and sometimes during) re-ignition. Two different re-ignition mechanisms are identified for flame E: auto-ignition and mixing-reaction. In the Cabra H₂/N₂ lifted flame, the particle trajectories are divided into different categories based on the particles' origin: the fuel stream, the oxidizer stream, and the intermediate region. The calculations reproduce the whole auto-ignition process reasonably well for the Cabra flame. Four stages of combustion in the Cabra flame are identified in the calculations by the different mixing models, i.e., pure mixing, auto-ignition, mixing-ignition, and fully burnt, although the individual particle behavior by the IEM and modified Curl models is different from that by the EMST model. The relative importance of mixing and reaction during re-ignition and auto-ignition are quantified for the IEM model.     

等单元长度多间隙加速结构的束流动力学特性

等单元长度多间隙加速结构是一种非同步加速结构,当粒子在加速结构中的速度变化很明显时,粒子在每个间隙的相位是不相同的,薄透镜近似下的束流纵向运动方程没有考虑粒子在加速结构中的速度变化,这在单腔的能量增益相对于粒子能量很小的情况下是合理的,但是当粒子在加速结构中的速度有明显变化时,这种处理方式是不够的。本文从带电粒子在电磁场中的运动方程出发,通过目前普遍采用的理论建立了束流在这种加速结构中的纵向运动方程,通过数值方法得到了粒子在这种结构的相运动,计算了不同初始能量的粒子在不同的电场梯度及单元数的加速腔中运动的能量变化情况。结果显示:粒子相运动与不考虑粒子速度变化的薄透镜近似下的相运动轨迹有明显差异,当粒子速度变化超过一定值后,薄透镜近似下束流纵向运动方程在计算束流能量增益时与同步相位之间满足的余弦关系不再成立,并给出了能量增益变化曲线相对余弦曲线的偏离情况与电场梯度、间隙数、初始能量等参数的关系。     

Position measurements in the de Broglie–Bohm interpretation of quantum mechanics

The de Broglie–Bohm interpretation of quantum mechanics assigns positions and trajectories to particles. We analyze the validity of a formula for the velocities of Bohmian particles which makes the analysis of these trajectories particularly simple. We apply it to particle detectors of four different types and show that the detectors of three of these types lead to “surrealistic trajectories”, i.e., leave a trace where the Bohmian particle was not present.     

旋转间断过渡层中的粒子轨道

用一维粒子Code研究了旋转间断过渡层中的粒子轨道。发现绝大多数粒子都能穿过过渡层到达下游区;但是,有少量的粒子被捕获在过渡层内;也有一定数量的粒子被反射回上游区。捕获粒子数和反射粒子数与过渡层厚度D有关。在稳定旋转间断中,反射粒子数和捕获粒子数分别为2％和3％左右。对于不稳定的旋转间断,这两个比值可上升2-4倍。反射粒子和捕获粒子的动力学效应可以很好地解释旋转间断,中间激波和多重激波模拟的一些重要结果.     

Observation of quantum particles on a large space-time scale

A quantum particle observed on a sufficiently large space-time scale can be described by means of classical particle trajectories. The joint distribution for large-scale multiple-time position and momentum measurements on a nonrelativistic quantum particle moving freely inR ^v is given by straight-line trajectories with probabilities determined by the initial momentum-space wavefunction. For large-scale toroidal and rectangular regions the trajectories are geodesics. In a uniform gravitational field the trajectories are parabolas. A quantum counting process on free particles is also considered and shown to converge in the large-space-time limit to a classical counting process for particles with straight-line trajectories. If the quantum particle interacts weakly with its environment, the classical particle trajectories may undergo random jumps. In the random potential model considered here, the quantum particle evolves according to a reversible unitary one-parameter group describing elastic scattering off static randomly distributed impurities (a quantum Lorentz gas). In the large-space-time weak-coupling limit a classical stochastic process is obtained with probability one and describes a classical particle moving with constant speed in straight lines between random jumps in direction. The process depends only on the ensemble value of the covariance of the random field and not on the sample field. The probability density in phase space associated with the classical stochastic process satisfies the linear Boltzmann equation for the classical Lorentz gas, which, in the limith0, goes over to the linear Landau equation. Our study of the quantum Lorentz gas is based on a perturbative expansion and, as in other studies of this system, the series can be controlled only for small values of the rescaled time and for Gaussian random fields. The discussion of classical particle trajectories for nonrelativistic particles on a macroscopic spacetime scale applies also to relativistic particles. The problem of the spatial localization of a relativistic particle is avoided by observing the particle on a sufficiently large space-time scale.     

高速流动PIV示踪粒子跟随性分析

通过理论推导提出了一种评价高速流动PIV示踪粒子随流能力的松弛特性分析模型,在法向Mach数大于1.4时具有良好的适用性.将新模型应用于试验测量,发展了高速流动PIV系统和示踪粒子布撒技术,验证了高速流动PIV的定量化测量能力.针对空间发展的二维超声速气固两相混合层,数值模拟了不同Stokes数和对流Mach数（M_c）下的粒子跟随性以及弥散和迁徙运动,结果表明:相同对流Mach数,粒径越小的示踪粒子跟随性越好,Stokes数在[1, 10]范围内的粒子有最大扩散距离.示踪粒子的直径大小决定其在超声速混合层大涡拟序结构中的分布特征,且粒径越小,气体与粒子的掺混越剧烈.相同粒径的粒子,对流Mach数越大跟随性越差.      

椭球颗粒搅拌运动及混合特性的数值模拟研究

为探讨在强制搅拌下同属性颗粒由分层到分布均匀状态的运动特征及规律, 本研究利用三维离散单元法模拟不同转速下U形罐体内等粒径椭球颗粒的混合过程. 从单颗粒随机运动轨迹、宏观颗粒流运动矢量图的角度分析颗粒混合过程的宏观混合规律及局部混合特征, 定量描述混合度与搅拌叶片旋转圈数的数学关系. 结果表明, 强制搅拌下同属性分层颗粒的混合是在对流混合及四个局部混合共同作用下实现的; 分层颗粒的混合度与搅拌轴的转速无关, 而与搅拌轴旋转圈数直接相关; 混合度与圈数的关系符合指数增长模型. 研究结果可为散体物料增混行业的设备改进及操作控制提供依据和参考.     

宽筛分煤粉颗粒间相互作用的数值研究

本文采用颗粒轨道模型,对不同直径的细小煤粉颗粒绕流单个球形大颗粒后的运动轨迹进行了数值模拟,研究了宽筛分条件下大颗粒的尾涡作用对小颗粒运动情况的影响．同时将计算结果同激光全息的实验结果进行了对照,二者符合得较好．结果表明,只有当煤粉颗粒的尺寸小到一定程度时,大颗粒的尾涡才对其运动轨迹产生显著影响．