共查询到20条相似文献,搜索用时 140 毫秒
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为了计算微波器件的微放电阈值,提出了一种快速单粒子蒙特卡罗方法.该方法对二次电子出射能量、出射角度和相位等参数进行随机处理,结合四阶龙格库塔法和Furman模型模拟了电子运动和二次电子发射系数,并以多次连续碰撞的二次电子发射系数的算数平均值作为微放电效应发生的判据.以平板传输线横电磁模式为研究对象,分别采用快速单粒子蒙特卡罗方法、统计模型、传统蒙特卡罗方法以及粒子模拟方法计算其微放电阈值和敏感区域.计算结果表明,该方法不仅具有与统计模型和粒子模拟方法相当的计算精度,而且比统计模型方法的适应性更强,比传统蒙特卡罗方法的稳定性更好,比粒子模拟方法的计算效率高几十倍以上. 相似文献
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用区域分解算法结合蒙特卡罗法求坦克温度场和红外辐射出射度 总被引:3,自引:0,他引:3
本文将区域分解算法和蒙特卡罗法相结合,求坦克温度场和红外辐射出射度.采用蒙特卡罗法计算辐射传递系数,可以考虑界面的复杂辐射特性,如:镜反射、各向异性发射、各向异性反射等;可直接考虑界面的复杂几何特性,如:相互遮挡、太阳入射方向上的投影面积等.引入辐射传递系数,分离了计算的难点,使得在时间域(计算步骤)上能把整个问题分解为若干个子问题并行处理、在空间域(计算区域)上将坦克分解为若干个子区域,缩小计算规模,并可使用多个处理器并行计算;同时减轻了蒙特卡罗法编程的难度,缩短了计算时间. 相似文献
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2.1AGeVNe NaF碰撞中的粒子群关联与集体性 总被引:1,自引:0,他引:1
提出了粒子群关联概念,并以此建立了一种检测集合流的新方法,采用新方法对2.1AGeVNe+NaF碰撞的Bevalac流光室4π实验事件粒子群的关联进行了研究.通过与蒙特卡罗结果进行比较,推测该实验事件集合流的集体性约在75%-95%之间。 相似文献
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采用理想流体对称碰撞模型,分析了爆炸焊接流场中沿流线的物理变形,推导出了角变形的理论计算公式,并采用Visual C++语言对其进行了编程计算,获得了驻点近区角变形的大小及变化规律。结果表明,在驻点近区,沿来流至出流方向角变形逐步增大,其变化率在驻点附近最大;沿出流方向,给定碰撞角,角变形随来流速度的增加而增大;给定来流速度,角变形随碰撞角的增大而减小。从理论和实验方面,间接地将计算结果与前人的结论进行了对比验证,结果是一致的,以此为基础配合驻点近区的应变率场,讨论了其对爆炸焊接波状界面形成的影响。 相似文献
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Wilson F. N. Santos 《Brazilian Journal of Physics》2012,42(5-6):373-390
This work deals with a computational investigation on the small ballistic reentry Brazilian vehicle SAtélite de Reentrada Atmosférica (SARA). Hypersonic flows over the vehicle SARA at zero-degree angle of attack in chemical equilibrium and thermal nonequilibrium are modeled by the direct simulation Monte Carlo method, which has become the main technique for studying complex multidimensional rarefied flows, and which properly accounts for the nonequilibrium aspects of the flows. The emphasis of this paper is to examine the behavior of the primary properties during the high-altitude portion of SARA reentry. In this way, velocity, density, pressure, and temperature field are investigated for altitudes of 100, 95, 90, 85, and 80?km. In addition, comparisons based on geometry are made between axisymmetric and planar two-dimensional configurations. Some significant differences between these configurations were noted on the flowfield structure in the reentry trajectory. The analysis showed that the flow disturbances have different influence on velocity, density, pressure, and temperature along the stagnation streamline ahead of the capsule nose. It was found that the stagnation region is a thermally stressed zone. It was also found that the stagnation region is a zone of strong compression, high wall pressure. Wall pressure distributions are compared with those of available experimental data, and good agreement is found along the spherical nose for the altitude range investigated. 相似文献
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Particle formation in opposed-flow diffusion flames of ethylene: An experimental and numerical study
Andrea D’Anna Mario Commodo Patrizia Minutolo 《Proceedings of the Combustion Institute》2009,32(1):793-801
An experimental and numerical study on particles inception and growth is performed in opposed-flow diffusion flames of ethylene and air characterized by different sooting tendencies. Spectrally resolved UV-visible laser induced fluorescence, laser induced incandescence and laser light scattering measurements are used to characterize different classes of combustion-generated compounds. A detailed kinetic model accounting for both gas-phase and particle formation is used. Comparison between experimental results and numerical predictions gives a qualitative view of the mechanism of particle formation in opposed-flow flames.Particle inception is the result of both chemical growth and coagulation of aromatic compounds. In the region close to the flame front where the temperature is relatively high and radicals are abundant, the particle inception is due to a chemical growth mechanism by which aromatic molecules add aromatic radicals leading to the formation of biphenyl-like structures. The growth process continues as high-molecular mass aromatics are moved away from the flame zone towards the stagnation plane by the addition of acetylene and other aromatics forming particles of increasing sizes. Graphitization of these particles and thermal annealing lead to the formation of soot particles. At relatively lower temperatures, found across the stagnation plane, particles growth still occurs and it is mainly due to a process of physical coagulation of PAHs.The experimental and numerical results obtained in this work demonstrate and explain the sensibility of inception and growth of particles to radical concentration and temperature in opposed-flow flame configurations. 相似文献
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针对高超声速飞行器防热, 搭建了螺线管磁控热防护系统的物理模型. 采用低磁雷诺数磁流体数学模型, 分析了外加磁场强度及磁场形态对磁控热防护效果的影响. 对比了三种磁场类型(磁偶极子、螺线管、均布磁场)下磁控热防护效果的差异, 分析了螺线管几何参数对磁控热防护效果的影响. 研究表明, 磁场降低表面热流作用存在“饱和现象”; 三种磁场形态的磁控热防护能力从小到大依次为磁偶极子、螺线管、均布磁场; 相同驻点磁感应强度条件下, 增大螺线管半径有利于提高磁控热防护效果, 缩短螺线管与驻点距离不利于驻点和肩部防热, 螺线管长度对磁控热防护效果影响相对较小. 相似文献
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Kroupp E Osin D Starobinets A Fisher V Bernshtam V Weingarten L Maron Y Uschmann I Förster E Fisher A Cuneo ME Deeney C Giuliani JL 《Physical review letters》2011,107(10):105001
The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission. 相似文献
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T. S. Pan Y. Zhang J. Huang M. Gao Y. Lin 《Applied Physics A: Materials Science & Processing》2014,114(3):973-978
Fabricating composite thin films is an effective and economic solution to improve the thermal performance of the films. The diamond particles of different sizes were successfully embedded in AlN thin films by a chemical solution approach, which was confirmed by scanning electron microscope, x-ray diffraction analysis and x-ray photoelectron spectroscopy. The thermal properties of the films embedded with different diamond particles were studied by using a 3-omega method, which was observed to be strongly dependent on the particle size. A 19 % enhancement in thermal conductivity can be achieved by embedding diamond particles of 1-μm radius in AlN thin films. However, the thermal conductivity decreases after embedding with 10-nm radius diamond particles. The results are discussed with high volume model, which confirms that the interface thermal resistance between the embedded materials and the films plays an important role in determining the thermal conductivity of the as-grown carbon material embedded AlN films. 相似文献
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A new technique for measuring local heat transfer coefficients on complex-shaped models is described. This technique is referred to as the shroud technique and is a variation on the well-known transient method. The technique involves preheating a model inside a shroud while it is installed in a wind tunnel. The shroud is then ejected, exposing the model to ambient temperature air. The transient temperature on the surface of the model is measured using liquid crystals and recorded with a video system. Although an infinite variety of model shapes can be used, measurements on a cylinder in cross-flow are used to demonstrate this technique. The measurements are compared with earlier measurements, which used different techniques. Good agreement is found at the stagnation point and in the front laminar boundary-layer region. In the separation region, the heat transfer rate is dependent an the thermal boundary condition, which in the transient method is affected by the selection of the nondimensional liquid crystal temperature. In the wake region, it was found that the results depend on the flow development time relative to the transient measurement time. 相似文献
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针对高超声速飞行器前缘疏导式防热结构的特点,设计前缘内嵌高导热率材料结构和一体化层板热管结构两类对比实验,用于验证前缘疏导式防热结构的可行性.利用球形短弧氙灯作为辐射热源模拟气动加热,分别对钢质前缘、内嵌铜材料的钢质前缘和一体化层板式热管前缘进行加热,测量前缘驻点区域和尾部翼面区域的温度变化.实验结果表明:内嵌高导热率材料的前缘疏导结构能够降低头部驻点区的温度,提高尾部低温区的温度,实现对前缘结构的热防护;以蒸馏水作为工质一体化层板式热管前缘结构,在较低热流条件下也能够实现对前缘驻点区的疏导式热防护,但在较高热流条件下,由于水蒸气压力过大使得层板式前缘结构发生破坏,体现出热管内部工作介质对结构防热效果和应用范围都起到的关键作用. 相似文献