基于负氢离子源的全三维PIC/MCC模拟算法研究

在分析负氢离子源中等离子体物理机理基础下, 研究并优化粒子模拟算法, 设计高效的粒子存储方法. 研究并运用粒子碰撞蒙特卡罗方法, 考虑等离子体势以及带电粒子间库仑碰撞, 研制了全三维粒子模拟/蒙特卡罗算法(PIC/MCC). 采用磁荷模型, 运用时域有限差分方法计算多峰磁场, 并结合国外负氢离子源JT-60U, 考虑负氢离子源中主要反应, 对全三维PIC/MCC模拟算法模拟验证.     

三维电磁粒子模拟并行计算的研究

三维电磁粒子模拟基于时域有限差分算法（FDTD）和PIC（particle-in-cell）方法.根据FDTD和PIC方法的特点,可以将整个模拟区域分割为多个子区域,每个计算进程模拟计算一个子区域,通过消息传递交换子区域的边界数据从而实现并行计算这一基本思路,完成了并行算法的设计,并分析了并行加速比的影响因素.在三维电磁粒子模拟软件CHIPIC3D上实现了该并行算法并验证了算法的正确性,最后应用CHIPIC3D并行版本对磁绝缘线振荡器和相对论速调管两种典型的高功率微波源器件进行了模拟,证明了该并行算法能取 关键词： 电磁粒子模拟 时域有限差分 并行计算 高功率微波源     

3维电磁粒子模拟程序设计

 在3维Yee网格模型以及蛙跳模型的基础上，分析了3维电磁场离散算法及其稳定条件，讨论了3维空间网格上电磁场作用于粒子的平均场权重法和粒子作用于电磁场的Charge-conserving法，同时也讨论了3维空间网格上理想导体边界条件、自由吸收边界条件、爆炸式发射模型的模拟实现方法。以向内发射同轴二极管为例从其电流电压关系及电子束运动特性方面验证了模拟的正确性。     

坐席低谷效应的时域有限差分多项模拟

介绍了交错网格下,以声压和质点振动速度为声场参量的室内声学时域有限差分递推格式,给出了在建筑边界截断计算区域的边界条件差分格式。在水平地面房间模型下,应用时域有限差分法模拟了坐席低谷效应对于空间和时间的多种特性;此外,模拟了地面起坡时的低谷效应。     

高功率电磁脉冲对砷化镓金属半导体场效应管的影响

 采用时域有限差分方法，通过求解麦克斯韦方程、热传导方程和载流子方程，模拟了在电磁脉冲辐射下，场效应管器件温度和端口散射参数的变化过程。研究了不同幅度脉冲序列和上升沿不同的脉冲对砷化镓金属半导体场效应管的影响，对比了各种不同脉冲作用下场效应管性能的变化规律。该方法克服了传统电路模型无法模拟电磁波与器件内部活动粒子作用过程的缺点，可以直接模拟器件温度和散射参数在高功率电磁脉冲辐射下的时域变化过程。     

电各向异性色散介质电磁散射的三维递推卷积-时域有限差分方法分析

根据递推卷积原理，将磁化等离子体的频域介电系数过渡到时域，通过引入时域复数极化率张量和时域复数电位移矢量，得到了磁化等离子体的三维时域有限差分方法迭代式. 为了验证该方法，用它计算了非磁等离子体球的后向雷达散射截面，与移位算子法结果符合很好. 应用该方法计算和分析了磁化等离子体球的电磁波散射，发现其后向散射时域波形明显出现了交叉极化分量. 关键词： 递推卷积 磁化等离子体 电磁散射 时域有限差分方法     

负媒质模型的时域有限差分法分析

 负折射率媒质是一种人造媒质，在某一微波波段内其介电常数和磁导率同时为负值。对TE模电磁场满足的麦克斯韦方程组进行数值处理，解决了直接利用时域有限差分方法在Yee’s网格下计算负折射率媒质内部场分布时的数值发散问题。通过数值算例，验证了方法的可行性，模拟了负折射率媒质内部及周围的电磁场分布。     

三维时变等离子体目标的电磁散射特性研究

基于电流密度拉普拉斯变换方法改进的时域有限差分(LTJEC-FDTD)算法, 研究时变等离子体目标的电磁散射特性.由Maxwell方程和等离子体本构方程出发, 利用拉普拉斯变换和拉普拉斯逆变换, 推导出计算三维时变问题的时域有限差分(FDTD)算法的迭代式. 采用模式匹配方法验证了FDTD迭代式的正确性, 并通过计算等离子体球的雷达散射截面(RCS)验证了算法相关边界的正确性. 最后用LTJEC-FDTD算法分析了涂覆时变等离子体的战斧式巡航导弹的RCS. 关键词： 时变等离子体 雷达散射截面 模式匹配方法 时域有限差分方法     

3维并行全电磁粒子模拟软件UNIPIC-3D

介绍了自行研制的3维并行全电磁粒子模拟软件UNIPIC-3D。在该软件中,电磁场量用二阶精度的时域有限差分方法迭代,粒子用相对论牛顿-洛仑兹力方程推进。该软件拥有复杂器件的几何建模和网格自动剖分的功能,具有模拟相对论返波管、虚阴极振荡器、磁绝缘线振荡器等高功率微波器件的能力。且该软件具有强大的后处理功能,可以显示电场、磁场、电流、电压、功率、频谱、粒子相空间等。在高性能并行计算机上对软件的并行效率进行了测试。通过与2.5维UNIPIC软件的结果进行比较,验证了UNIPIC-3D软件的正确性。     

各向异性渗透率油藏数值模拟

建立三维三相各向异性油藏渗流数值模拟模型并应用于油藏开发.模型包含完全各向异性渗透率张量,采用十九点有限差分格式和全隐式迭代方法求解.可以描述不同区域不同主方向的各向异性渗透率分布,准确计算各向异性油藏内流体运动过程、剩余油分布和压力分布.     

Full-wave parallel dispersive finite-difference time-domain modeling of three-dimensional electromagnetic cloaking structures

A parallel dispersive finite-difference time-domain (FDTD) method for the modeling of three-dimensional (3-D) electromagnetic cloaking structures is presented in this paper. The permittivity and permeability of the cloak are mapped to the Drude dispersion model and taken into account in FDTD simulations using an auxiliary differential equation (ADE) method. It is shown that the correction of numerical material parameters and the slow switching-on of source are necessary to ensure stable and convergent single-frequency simulations. Numerical results from wideband simulations demonstrate that waves passing through a three-dimensional cloak experience considerable delay comparing with the free space propagations, as well as pulse broadening and blue-shift effects.     

Three-dimensional FDTD method for optical pulse propagation analysis in microstructured optical fibers

We propose a three-dimensional (3D) finite-difference time-domain (FDTD) method to analyze the pulse propagation characteristics in microstructured optical fibers (MOFs). The computation domain size is greatly reduced by adopting the technique of moving problem space. The propagating pulse is virtually held in the buffer cell of the problem space as simulation continues. This method is capable to investigate the temporal evolution of the propagating pulse. Spectral information can be obtained by Fourier analysis. As an example, the influence of the kerr nonlinearity on the optical pulse propagation in a Lorentz dispersive MOF is demonstrated. The model is also used to simulate the nonlinear interactions between the pump spectral broadening and third harmonic generations in a highly nonlinear fused silica nanowire with good agreement with the generalized nonlinear envelop equation (GNEE) model.     

混合物介质中声波尾波成因的随机过程分析

该文基于声波在混合物介质中传播时反射及散射的随机特性，把混合物介质抽象为三维各向同性的马尔科夫链，把声波在混合物介质中传播过程抽象为声波在三维马尔科夫链中以声速进行“随机游走”的随机过程。用空间内某点接收到声波的概率类比该点接收波振幅，以声波到达该点所走过的步数类比接收波时域曲线的时间。此理论模型可较好解释声波在混合物介质中传播时“峰波延后”及“尾波”等现象。     

Modeling light propagation through taper-microfiber structures integrated on substrates

<正>We use the three-dimensional finite-difference time-domain(3D-FDTD) method to model silica taper-microfiber structures integrated on substrates.The dependence of the transmission on the length of the microfiber is investigated for two different structures.Optimization of the geometric parameters is provided and two substrate materials,namely MgF_2 and fluorosilicate glass,are considered.We also investigate the case where the structure is covered with a dielectric material.     

光学材料亚表面缺陷处强激光电磁场分布的3维模拟

 利用时域有限差分法求解麦克斯韦旋度方程,研究了光学材料表面缺陷对入射激光场的调制作用,建立了亚表面缺陷的3维模型。以长方体表面缺陷为例,对缺陷附近的光场分布进行了3维数值计算,给出了电场强度3维分布图和缺陷不同尺寸时的最大电场强度。研究表明,相对于2维简化情况,3维表面缺陷对强激光电磁场的调制作用更加明显。     

多孔材料在压缩载荷作用下的屈曲失效模式分析

压缩是工程材料最基本的承载方式之一,多孔材料中的孔棱受到压缩载荷时可能产生屈曲行为.建立了各向同性三维网状高孔率多孔材料的简化结构失效模型,分析了这种材料在不同压缩载荷作用下由于孔棱发生屈曲而引起的失效模式,系统地得出了单向压缩、双向压缩和三向压缩等三种承载形式下这种多孔体受压而导致孔棱屈曲时名义主应力与孔率的数理关系.在此基础上,进一步得出了此类材料在压缩载荷作用下发生孔棱屈曲的载荷条件.     

Surface plasmon polariton coupling between nano recording marks and their effect on optical read-out signal

We use the three-dimensional finite-difference time-domain method to investigate surface plasmon polariton coupling between two nano-recording marks which are of different shapes. The different coupling characteristics and the influence of these coupling effects on the read-out reflection signal will be discussed.     

Time- and frequency-domain computations of broadband noise due to interaction between incident turbulence and rectilinear cascade of flat plates

Time-domain computational aeroacoustic (CAA) techniques are developed to investigate the broadband noise resulting from the interaction of a rectilinear cascade of flat plates with incident homogeneous, isotropic turbulence. The investigation is carried out by comparing the prediction results obtained by employing the time-domain CAA method with those using existing frequency-domain methods. A semi-analytic model (Wei & Cheong, 2010) and a full three-dimensional rectilinear cascade model (Lloyd & Peake, 2008; Lloyd, 2009) are adopted for the frequency-domain computations. By comparing these computation results, the three-dimensional characteristics of inflow turbulence noise are investigated; in particular, the effects of the wavenumber components of ingested turbulence in the spanwise direction are taken into consideration in the investigation. First, CAA results are compared with those from the semi-analytic model. The results for the acoustic modes of relatively low spanwise wavenumbers obtained using both methods show good agreement, but as the spanwise wavenumber increases, the results obtained by the two methods become increasingly different. To investigate in detail the reason for these differences, mode-decomposition analysis is performed by adopting a hybrid method as well as by employing the CAA and the semi-analytic method. The hybrid method involves the following two sequential computations: (i) the upwash velocities on the flat plate airfoils of the rectilinear cascade are first predicted using the frequency-domain method, and (ii) the acoustic wave propagation is subsequently analyzed using time-domain CAA techniques, with these upwash velocities applied as the boundary conditions on the flat plate. It is seen that the results of the time-domain CAA technique and the hybrid method show good agreement, irrespective of the wavenumber and frequency. However, comparisons of the acoustic solutions from three computations reveal that the prediction results of the semi-analytic model deviate more from the other two predictions as the spanwise wavenumber of the acoustic wave increases and the frequency decreases. On a basis of this observation, a formulation is derived for the error in the pressure jump across the flat-plate predicted by using the semi-analytic method. This formulation shows that the error is approximately inversely proportional to the sound speed in the spanwise direction of the concerned acoustic modes. This result quantitatively clarifies the limitations of applying the frequency-domain method of Wei & Cheong (2010) to the three-dimensional turbulence-cascade interaction problems. Secondly, the prediction results using the time-domain CAA method are compared with those from the full three-dimensional rectilinear model that is believed to be exact model for the cascade geometry considered in this paper. This comparison shows the good agreements between two predictions, which support the above arguments for the error and the successful application of the time-domain CAA methods. It is expected that these methods can be extended to the broadband noise problem in an annular cascade, including the nonlinear interaction of the real-airfoil cascade with the incident nonhomogeneous gust.     

支板凹腔一体化超燃冲压发动机实验研究

本文针对以凹腔支板一体化燃烧室为基本结构的超燃冲压模型发动机在自由射流风洞中的性能,主要研究了燃料在不同位置喷入时,燃烧室几何结构/气动性能/燃料混合及燃烧特性的相互耦合,以及对发动机推力性能的影响.结果表明支板与凹腔的一体化在合理配置燃料分布情况下可以获得较好的发动机性能.     

新型被动在轨非连接支撑研究现状

支撑结构是低温贮箱及飞行器杜瓦瓶的关键部件,对低温燃料液体的承装及其漏热有重要影响。文中阐述了低温绝热支撑近几年的研究进展,针对新型被动在轨非连接支撑(简称PODS),就其结构、材料及其他相关问题进行了分析。随着新型被动在轨非连接支撑研究的深入,其在空间及工业低温贮箱领域将会获得广泛应用。