Pre-sheath formation in an oblique magnetic field: fluid model and PIC simulation

We present some results of a one-dimensional fluid model with a floating electrode immersed in plasma with magnetic field applied at an oblique angle. The model equations are integrated numerically in order to find the space profiles of the ion velocities and electrostatic potential for various strenghts and angles of the magnetic field. We assume a collisionless magnetized pre-sheath with isothermal ions. The results are then compared with the spatial profiles obtained by a computer simulation. We use a BIT1 particle-in-cell code. The simulations input parameters are chosen in the way, that they resemble the fluid model as much as possible. Because the results of the simulation are given in the absolute SI units, they have to be normalized correctly. We evaluate the model results and compare them with the computer simulation results. Special attention is brought on formation of the pre-sheath with magnetic field applied at intermediate angles. The results of the simulation are in good qualitative agreement with the model.     

Models,predictions, and experimental measurements of far-infrared NH3-laser dynamics and comparisons with the Lorenz-Haken model

Dynamics of the intensity and optical field amplitude of a coherently pumped far-infrared NH₃-laser are measured and characterized. The experimental findings in certain parameter ranges closely follow the dynamics of the Lorenz model and its generalization for laser systems. Similarities and some specific differences are found in geometrical or statistical characterizations of the attractors. The experimental results are also consistent with the results of a model of optically pumped three-level lasers which takes into account the presence of a multiplicity of velocity groups as well as three-level coherence effects. For a certain region in parameter space, this far more complex model with a much larger phase space produces results similar to the dynamics of the Lorenz model. The model also provides explanations of differences between the experimental results and results from the Lorenz model.     

两种气液两相流模型的应用和比较

本文应用MUSIG模型[1]和均一直径模型对某溶液堆台架模型堆芯内气液流动传热进行了数值模拟.在MUSIG模型中堆芯内离散相气泡被分为5组不同直径的气泡,用于分析堆芯内气泡的流动变化和大小分布,采用Luo and Svendsen[2]和Prince and Blanch[3]模型描述不同直径气泡组间的破裂和聚合.在均一直径模型中,堆芯内的气体被考虑为同一直径的组分,并且不考虑其破裂与聚合现象.计算得到采用两个模型的模拟结果并且对其进行了对比研究.结果显示应用MUSIG模型的计算结果与台架实验结果吻合更好.     

Model for spatial microtubule oscillations

Under particular in vitro conditions, oscillating spatial and temporal waves of assembled microtubules can be observed. A reaction-diffusion model is presented to reproduce these results. This model is based on a set of chemical reaction equations and extended to include spatial dependence and diffusion. The basic properties of the model are presented and the results are demonstrated to connect the observable waves with turbidimetric measurements. The results of the model are consistent with experimental findings.     

Determination of equivalent salt deposit density using wind velocity for a contaminated insulator

This paper illustrates a new analytical model for determining equivalent salt deposit density (ESDD) on contaminated insulators using wind velocity. The analytical model is derived using the dimensional analysis technique. The values of ESDD from the analytical model are calculated using different values of wind velocity. These results are compared with the experimental results obtained from sites. The analytical results are also compared with the polynomial model output obtained via least-squares analysis of experimental data. It is found that the results obtained by the analytical model are quite consistent with the experimental results for different range of wind velocity.     

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor(HEMT) with an artificial neural network(ANN).The AlGaN/GaN HEMT device structure and its fabrication process are described.The circuit-based Neuro-space mapping(neuro-SM) technique is studied in detail.The EEHEMT model is implemented according to the measurement results of the designed device,which serves as a coarse model.An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model.Its optimization is performed.The simulation results from the model are compared with the measurement results.It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model.     

基于速度势侵彻模型的应用研究

 研究了Rubin等人提出的基于Rankine卵形体速度势函数分析的侵彻模型。根据该侵彻模型的基本方法编制了计算程序,计算头部形状为锥形、卵形和球形的长杆弹体垂直碰撞靶板时的侵彻深度和穿透靶板后的剩余速度,分析侵彻模型对不同头部形状的长杆弹体的适用性。另外,利用该分析方法计算并分析了卵形头部长杆弹体对铝靶侵彻和穿透的缩比模型问题,用分析方法验证了无量纲侵彻深度和剩余速度相等的侵彻几何相似规律,同时得到了弹体减加速度与几何尺寸成反比的重要结论。最后对混凝土靶板的侵彻与穿透问题进行了尝试计算,得到了同实验基本一致的计算结果并对其进行了深入分析。     

频率对热声制冷机影响的研究

分析和研究了频率对热声制冷机声压、温差和声功的影响 ;使用网络模型计算的结果与实验结果相吻合 ;该研究也是对网络模拟和声功测量方法的验证。     

A lattice Bhatnagar--Gross--Krook model for a class of the generalized Burgers equations

A new lattice Bhatnagar--Gross--Krook (LBGK) model for a class of the generalized Burgers equations is proposed. It is a general LBGK model for nonlinear Burgers equations with source term in arbitrary dimensional space. The linear stability of the model is also studied. The model is numerically tested for three problems in different dimensional space, and the numerical results are compared with either analytic solutions or numerical results obtained by other methods. Satisfactory results are obtained by the numerical simulations.     

旋流对煤粉燃烧NO排放影响的数值模拟

本文用基于HCN释放的简化Solomon模型的NO生成湍流反应的统一二阶矩代数模型(AUSM)和煤粉燃烧的双流体模型,对不同旋流数下煤粉燃烧器内两相流动,煤粉燃烧和NO生成进行了数值模拟。模拟结果和文献中实验结果符合很好。模拟结果指出,随着旋流数的增加,NO的排放先减少后增加,燃尽率先增加后减小,和气体燃烧中得到的规律类似。     

基于二阶矩燃烧模型的液雾燃烧大涡模拟

采用亚网格动能(k方程)应力模型、二阶矩(SOM)燃烧模型和欧拉拉氏两相流模型,对乙醇-空气液雾燃烧进行了大涡模拟(LES)。瞬态结果显示:在火焰的高温区域,旋涡强度较大;在高温区边缘附近存在的拟序结构有脱落的趋势。在燃烧装置的燃料进口附近,近喷嘴中心区域,大量液滴聚集在条状湍流拟序结构的周围。LES模拟的统计结果给出的温度分布与实验结果吻合较好。说明SOM燃烧模型适用于液雾两相湍流燃烧研究,计算结果经过和实验数据对比发现,LES-SOM燃烧模型优于RANS-PDF及LES-FA计算结果。数值计算结果与实验结果的误差主要是由于采用统观一步反应机理引起的,表明燃烧模型还有待进一步改进。     

水力旋流器湍流流动的数值模拟

本文采用雷诺应力模型计算了水力旋流器的水相湍流流场,计算结果与实验数据吻合很好。与相关文献中采用修正的κ-ε模型的计算结果比较,本文采用雷诺应力模型的计算结果更接近于实验结果。计算得到了水力旋流器内的流线图、等压线以及零速包络面。     

电离能下降对于硅等离子体辐射不透明度影响的研究

电离能下降的现象与等离子体的成分、电离分布、热力学、输运性质息息相关,其精确测量值对于整个实验的模型检验和方案设计都至关重要.本文考虑粒子数的涨落,对经典的Stewart和Pyatt的模型进行修正,并耦合进先前发展的等离子体模型.利用修正的模型对熊刚等人的实验进行了解释,发现当前模型所得结果要优于其他理论结果,与实验更加一致.     

气泡成核过程的格子Boltzmann方法模拟

利用精确差分格子Boltzmann模型探讨水在特定温度下的亚稳态及不稳定平衡态, 获得等温相变过程中形成气泡和液滴的条件, 模型预测结果与理论解符合良好. 在该等温模型的基础上耦合能量方程, 通过调节流体-壁面相互作用力获得不同的气泡与固壁间接触角, 从而建立了一种新的描述气液相变的格子Boltzmann理论模型. 利用该新模型模拟不同流体-壁面相互作用力下凹坑气泡成核过程, 再现了气泡成核过程中的三阶段特性; 探讨了接触角、曲率半径及气泡体积随气泡成核过程的变化关系, 获得了与文献结果定性符合的曲率-气泡体积关系曲线. 关键词： 格子Boltzmann方法 气泡成核过程 气液相变 接触角     

旋流燃烧NO生成的USM湍流反应模型

用统一二阶矩(USM)湍流反应模型对不同旋流数下甲烷-空气旋流燃烧NO生成进行了数值模拟,并和EBU-Arrhenius(E-A)燃烧模型对燃烧的模拟结果和简化PDF湍流反应模型对NO生成的模拟结果以及相应的实验结果进行对比。结果表明,USM模型显著地优于E-A模型和简化PDF模型。E-A模型不能合理地模拟有限反应动力学,而简化PDF模型用两个单变量PDF的乘积代替联合PDF,大大地低估了NO湍流反应率。USM模型预报结果和实验结果符合最好。     

Treatment of metal for the FDTD analysis of terahertz devices

A terahertz stop band filter and a resonator consisting of metal gratings are analyzed using the finite-difference time-domain (FDTD) method, with special attention to the treatment of metal. Numerical results based on a perfect electric conductor (PEC) approximation are compared to those with a metal dispersion being taken into account by the Drude model. It is shown that the results of the resonator for the PEC model are favorably compared with those for the Drude model at frequencies of less than 1 THz. However, care must be taken at higher frequencies, since not only the transmittance at the resonance remarkably reduces for the Drude model, but also its resonance frequency deviates, in comparison with those for the PEC model. Metal mesh structures are also investigated using the periodic FDTD. The differences are found to be relatively small, due to the weak confinement of THz waves in metal mesh structures. The results can serve as a guideline for the FDTD analysis of THz devices consisting of metal.     

Ground State Properties of Superheavy Nuclei in Macroscopic-Microscopic Model

The ground state properties of superheavy nuclei are systematically calculated by the macroscopic-microscopic (MM) model with the Nilsson potential. The calculations well produced the ground state binding energies, α-decay energies, and half lives of superheavy nuclei. The calculated results are systematically compared with available experimental data. The calculated results are also compared with theoretical results from other MM models and from relativistic mean-field model. The calculations and comparisons show that the MM model is reliable in superheavy region and that the MM model results are not very sensitive to the choice of microscopic single-particle potential.     

The Non—local Thermodynamical Equilibrium Effects on Opacity

Based on the detailed configuration accounting(DCA) model,a method is developed to include the resonant photoionization and the excitation-autoionization in the non-local thermodynamical equilibrium (NLTE) average atom (AA) model.Using this new model,the mean charge states and the opacity are calculated for NLTE high-Z plasmas and compared with other results.The agreement with AA model is poor at low electron density.The present results agree well with those of DCA model within 10%.The calculations show that the NLTE effects on opacity are strong.     

On the Computations of Gas-Solid Mixture Two-Phase Flow

This paper presents high-resolution computations of a two-phase gas-solid mixture using a well-defined mathematical model. The HLL Riemann solver is applied to solve the Riemann problem for the model equations. This solution is then employed in the construction of upwind Godunov methods to solve the general initial-boundary value problem for the two-phase gas-solid mixture. Several representative test cases have been carried out and numerical solutions are provided in comparison with existing numerical results. To demonstrate the robustness, effectiveness and capability of these methods, the model results are compared with reference solutions. In addition to that, these results are compared with the results of other simulations carried out for the same set of test cases using other numerical methods available in the literature. The diverse comparisons demonstrate that both the model equations and the numerical methods are clear in mathematical and physical concepts for two-phase fluid flow problems.     

基于前向散射核函数拟合冰雪反射光谱各向异性

对地表反射光谱的各向异性进行建模和拟合,是遥感对地观测的重要研究内容。传统的线性核驱动模型拟合方法使用的核函数是基于植被覆盖地表辐射传输模型导出的,因此难以准确地描述冰雪覆盖地表前向散射强的特征。提出一种在线性核驱动模型中增加前向散射核函数的拟合方法,并采用地面多角度观测架测量的冰雪反射光谱对该方法的有效性进行了验证。验证结果表明该方法能够较好地拟合冰雪反射光谱的各向异性(R2=0.997 5, RMSE=0.022 6),准确地反映冰雪前向散射较强的特征。通过对提出的方法与经验函数法、传统线性核驱动模型拟合方进行比较,可以发现线性核驱动模型方法明显优于经验函数拟合法,其中增加前向散射核函数能够显著提高对冰雪覆盖地表二向反射因子的拟合精度,并在各波段都有稳定的拟合效果。